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This book provides an overview of state-of-the-art methods in computational engineering for modeling and simulation.

This proceedings volume includes a selection of refereed papers presented at the International Conference on Advances in Computational Mechanics (ACOME) 2017, which took place on Phu Quoc Island, Vietnam on August 2-4, 2017.

The contributions highlight recent advances in and innovative applications of computational mechanics. Subjects covered include: biological systems; damage, fracture and failure; flow problems; multiscale multiphysics problems; composites and hybrid structures; optimization and inverse problems; lightweight structures; computational mechatronics; computational dynamics; numerical methods; and high-performance computing.

The book is intended for academics, including graduate students and experienced researchers interested in state-of-the-art computational methods for solving challenging problems in engineering.



Computational Fracture and Damage Mechanics


Truss Damage Detection Using Modified Differential Evolution Algorithm with Comparative Studies

In this paper, an efficient numerical algorithm is developed for the damage detection of planar and space truss structures based on the modified differential evolution algorithm (mDE) and vibration data. For this purpose, the mathematical programming of the finite element based on the force method and the singular value decomposition technique is presented. The general equilibrium equations in which unknown member forces and reaction forces are taken into account are formulated. The compatibility equations in terms of forces are explicitly presented by using the singular value decomposition method. The modified differential evolution algorithm (mDE) is used as an optimization algorithm of damage detection. The objective function for damage detection is based on vibration data such as natural frequencies and mode shapes. The feasibility and efficiency of the present method are compared with a genetic algorithm (GA) and a particle swarm optimization (PSO) for example. The numerical results show that the proposed strategy based on force method using mDE and vibration data can provide a reliable tool on determining the sites and extents of multiple damages of truss structures.

Sumin Kim, Nam Il Kim, Hyunjoo Kim, T. N. Nguyen, Q. X. Lieu, Jaehong Lee

Finite Element Simulation on Small Punch Test for an Evaluation of J-integral for TRIP Steel

The small punch test (SPT) has been recently successfully developed for the purpose of evaluating the fracture toughness in not only brittle but also ductile materials. It is considered that fracture toughness of materials can be estimated by means of the SPT based on the measurement of equivalent fracture strain in the SPT and its correlation with fracture toughness. Moreover, fracture toughness of TRIP (transformation-induced plasticity) steel was evaluated by J-integral by using pre-cracked specimen under three-point bending test in the past study. However, the value of J-integral is determined at a limited range of deformation rate in three-point bending test. Thus, fracture toughness of TRIP steel needs to be evaluated by means of the SPT, especially at a relatively high deformation rate. Additionally, since the effect of strain-induced martensitic transformation during plastic deformation of TRIP steel coupled with a high increase of temperature is quite complicated, a computational work is indispensable. In this study, finite element simulations are performed for the SPT at various deflection rates and different sizes of specimen and puncher by an application of damage model for type-304 austenitic stainless steel, a kind of TRIP steel. The rate-sensitivity of fracture-mechanical characteristics is examined for different sizes of specimen and puncher. Furthermore, a relationship between equivalent fracture strain in the SPT and J-integral obtained from three-point bending test is challenged to be correlated.

H. T. Pham, T. Iwamoto

On the Buckling Behavior of Multi-cracked FGM Plates

In this paper, a model of statically stability plate with crack-based finite element analysis will be introduced by numerical simulation computation. The simulation model was built based on phase field theory in mechanics of fracture; the case study of plate was significantly computed with the new third-order shear deformation plate theory (TSDT), which is derived from an elasticity formulation, rather by the hypothesis of displacements [1]. Importantly, to verify of reliability of the modeling computation theory, the simulation result was compared to the experiment of Seifi and Nafiseh [2] to ensure the essential reliability for the paper. After that, the authors also propose and test the effects due to the size, the declination of cracks as well as the thickness of the plate to the stability, additionally, the relation between number of cracks and buckling load involved to instability of plate will be discussed. Lastly, visual configurations about forms of instability of plate with cracks will be presented.

Nguyen Dinh Duc, Truong Duc Trinh, Thom Van Do, Duc Hong Doan

Using a Non-local Elastic Damage Model to Predict the Fatigue Life of Asphalt Pavement Structure

Asphalt concrete is a composite material comprising aggregate, sand, mineral filler and bitumen as a binder. Although good compaction is performed during the construction, there is still relatively large discontinuity inside the material, and this will favour the appearance of micro-cracks, which decreases the performance of the material. Structural cracking resulted from repeated loading, or fatigue cracking, is a common failure mode of asphalt pavement structure, reducing the serviceability of the pavement. Owing to the present of micro-cracking, the fatigue cracking of asphalt pavement is generally modelled by using damage theory. In this paper, the authors aim to illustrate the application of an isotropic non-local elastic damage model in predicting the fatigue life of a pavement structure. A scalar D, called damage variable, is used to define the damage state at a point of the material, and the evolution of this variable at a point depends on the historic damage state as well as the present strain tensor at that point. The model parameters are determined on the basis of fatigue test results—namely, 4-point bending test. Numerical examples are presented to illustrate the ability of using damage theory to predict the damage evolution of a pavement structure as well as its service life.

H. T. Tai Nguyen, N. Hung Nguyen

Failure of Building Structural Members During the Cooling Phase of a Fire

Fires in buildings are characterized by a heating phase followed by a cooling phase, but the effects of the cooling phase on structures are not well researched. This work presents an analysis of the behavior of different structural members under natural fires, with the aim to characterize their delayed failure in the cooling phase of a natural fire. Thermo-mechanical numerical simulations based on the nonlinear finite element method (SAFIR code) are conducted. Results show that, for all the studied members (column, beam) and materials (reinforced concrete, steel, steel-concrete composite), structural failure during the cooling phase of a fire is a possible event. The time structures fail can be up to 250 min later than the time maximum temperature in room reaches. The major factors that affect delayed failure time of structural members are the duration of heating phase of the fire, the applied load ratio, and the thickness of thermal insulation material (including concrete material). This work enhances the understanding of the structural behavior in the cooling phase of a fire and gives information for the safety of the fire fighters and people in a natural fire.

Q. V. Truong, T. H. Pham, T. B. Chu

Numerical Studies of Some Modified Polarization Saturation Models in 2-D Semipermeable Piezoelectric Media Using Distributed Dislocation Method

In this paper, some modified polarization saturation models are proposed and studied numerically in 2-D semipermeable piezoelectric media using distributed dislocation technique (DDT). The polarization saturation (PS) model is modified here by varying the saturated condition imposed on the electrically saturated strip, i.e. a constant saturated condition to linear, quadratic and cubic varying electric displacement saturated condition. Numerical studies for these proposed models are simulated by considering their equivalent forms based on the principle of superposition. A centre-cracked problem in 2-D semipermeable piezoelectric media under arbitrary poling direction and in-plane electromechanical loadings is considered for these analyzes. To validate the developed numerical codes and iterative numerical approach for finding the unknown saturated zone length, the obtained results for PS model are compared with the analytical results available in literature. Thereafter, the results are presented for modified PS models, they show the effect of variation in saturation condition on saturated zone length, critical applied electric displacement loading and crack opening potential (COP), whereas no significant effect has been observed on local intensity factor (LIF) and crack opening displacement (COD). Further, saturated zone length increases with respect to increase in degree of variation of saturation condition, i.e. from constant to cubic. Moreover, the variation shows the effect on implication of applied electric loading and defines the critical applied electric loading corresponding to each model. It is observed that the critical value of applied electric loading significantly decreases with the increase in degree of variation of saturation condition. Here, a significant effect of poling direction is also found in all the parameters such as saturated zone length, LIF, COD and COP.

Kuldeep Sharma, Sandeep Singh

Stress Analysis of Silicon-Based Anode in Li-Ion Battery

We analyze during charging the stress evolution in silicon-based anodes of lithium-ion batteries by using an extensive finite element simulation. Effects of charge rates and geometric parameters of the anodes are considered. Results are useful for the design of new architectures of anodes for lithium-ion batteries.

T. Nguyen-Huu, Q. Le-Minh

Modeling of 3D Inflatable Large Deformation Air Plug in Contact With Concrete Lining

Resilient tunnel plug is a recently developed technique for the block of flood in tunnel by using an inflatable cylindrical airbag with air concealed. The plug, i.e., air bag surface, itself is made of textile composite with high strength, lightweight and easily foldable. The air plug can be inflated in a short amount of time and aligns with the internal surface of the tunnel tightly so that the fluid will be stopped at the required position. The use of air plug provides new solutions to the response of emergencies and accidents in tunnel operation such as the screening of smoke from fire and flood from precipitation. Recently, the possibility of using the air plug for the rescue of accidents in tunneling construction is being explored. In this paper, the feasibility of utilizing air plug to screen the soil and water flow in case of boring face failure is investigated. Membrane element is used to model the plug, and surface-based fluid modeling based on the Uniform Pressure Method (UPM) is used to model the coupling between the deformation and the pressure of the plug. Surface-to-surface contact interaction is used to model the frictional contact between the tunnel lining and the air plug surface. It is revealed that for embedded depth up to 20 m, the air plug can provide sufficient friction to resist the flow of water and soil without inducing excessive deformation of the tunnel structure. However, the careful choice of the pressure is important to avoid excessive deformation of the tunnel lining.

Anan Liao, Hui Shang, Xiaoyong Kou, Jun Huang, Xiaoying Zhuang

Upper Bound Limit Analysis of Circular Tunnel in Cohesive-Frictional Soils Using the Node-Based Smoothed Finite Element Method

In this paper, a numerical procedure using the node-based smoothed finite element method (NS-FEM) is proposed to evaluate the stability of a plane strain circular tunnel in cohesive-frictional soils subjected to continuous loading on the ground surface. In the NS-FEM, the strain smoothing is calculated over smoothing domains associated with the nodes of the elements. The soil is described as a uniform Mohr–Coulomb material and it obeys an associated flow rule. The limit load and failure mechanisms of circular tunnel are calculated from solving the optimization problems. In this study, the influence of the soil weight (γD/c′), the ratio of tunnel diameter to its depth (H/D) on the stability numbers (σ s /c′) and collapse mechanisms are investigated. The results obtained from the present analysis are compared with the available literature for tunnels located below the horizontal ground surface.

T. Vo-Minh, T. Nguyen-Minh, A. Chau-Ngoc

Numerical Studies on Contact Problem of Inter-locking Concrete Blocks Forming Revetment Structure

The importance of revetment slope (RS) structures for protecting coastal is indisputable. RS structures not only can maintain stability of embankment, but also can reduce sea wave energy by its optimized geometric features. For years, civil engineers have developed numerous solutions of RS structures based on theoretical aspects, experiments, and numerical analysis. Due to the lack of analysis criterion, design codes, and experimental facilities, numerical analysis methods significantly become of interest. One of the most challenges is that to perform the interactions between concrete blocks, which form RS structure, and water, i.e. dynamic fluid–structure interaction (FSI). Also, interaction between RS structures and embankment or foundation slope stability must be investigated carefully. Analysis of inter-locking block interactions is one of our missions in the VLIR-OUS TEAM 2017 project that we are running. In addition, due to the limitation of existing RS structures, e.g., heavy and dense materials, optimizations of RS structure are concerned. This paper is to overview the development of RS structures and approaches for analyzing contact problems. Theoretical aspects and computational modeling procedures are mentioned. ABAQUS commercial software is adopted. Hence, novel efficient RS structures could be developed and applied in the real world.

L. Dang-Bao, P. Truong-Thi, M. A. Wahab, Hung Nguyen-Xuan

Multiscale Multiphysics Problems


Orientation-Dependent Response of Pure Zinc Grains Under Instrumented Indentation: Micromechanical Modeling

This chapter concerns the micromechanical behavior modeling of a pure zinc polycrystal. An inverse optimization strategy was developed to determine plastic deformation properties from instrumented indentation tests performed on individual grains of cold-rolled polycrystalline sheets. Nanoindentation tests have been performed on grains using a spherical–conical diamond indenter, providing load-penetration depth curves. The crystalline orientation of those grains has been determined using an EBSD analysis. Furthermore, a crystal plasticity model has been implemented in the finite element code Abaqus using a user material subroutine. To identify the constitutive model parameters, the inverse identification problem has been solved using the MOGA-II genetic algorithm coupled with a finite element analysis of the nanoindentation test. In a first approach, the identification procedure used the load-displacement curves issued from the indentation performed on a grain of given crystalline orientation. A good agreement is achieved between experimental and numerical results. This constitutive model has been validated by simulating the indentation response of grains of distinct crystalline orientations, involving different slip systems activity rates.

N. P. T. Nguyen, F. Abbès, B. Abbès, Y. Li

Atomistic Simulation of Boron Nitride Nanotubes Under Bending

We investigate the bending buckling behavior of boron nitride (BN) nanotubes through molecular dynamics finite element method with Tersoff potential. Effects of the tube length on the critical bending buckling angle and moment are examined for (5, 5) BN armchair and (9, 0) BN zigzag tubes, which exhibit approximately identical diameters. The buckling and fracture mechanisms of the tubes under bending are considered and discussed with respect to various tube length–diameter ratios L/D = 10–40. Simulation results will help to design and use BN nanotube-based nanocomposites and nanodevices.

T. Nguyen-Van, T. Nguyen-Danh, Q. Le-Minh

Optimization and Inverse Problems


A Quick Computational Method for Improving Aerodynamic Shape of UAV Wing

To obtain an optimal aerodynamic 3D shape of small-sized UAV wing at small flight speed and high lift coefficient, the optimization problem is set to minimize drag coefficient with fixed plane form and constant lift coefficient. The thickness of chordwise function is assumed to be given. The direct optimization problem must be solved by CFD methods with viscosity consideration in 3D flow that involves a great volume of computations which is feasible only to super computers [1, 6]. This chapter presents a combined direct inverse method that makes the optimization problem be feasible to ordinary PC.

D. Tran-Duy, C. Nguyen-Duc, K. Mai, T. Nguyen-Duc

Engineering Optimization Using an Improved Epsilon Differential Evolution with Directional Mutation and Nearest Neighbor Comparison

In this paper, an efficient differential evolution (DE) algorithm is presented to solve constrained optimization problem. To skip unnecessary function evaluations, a simple mechanism called nearest neighbor comparison (NNC) is applied. The NNC is a method to prejudge a solution by its nearest point in the search population, so that unpromising solution will be skipped without evaluation. The NNC has been proposed to reduce the number of function evaluations effectively in unconstrained optimization. In this study, the NNC method is proposed for constrained optimization by combining with the ε constrained method. Moreover, a simple directional mutation rule is introduced to increase the possibility of creating improved solutions. Both the NNC method and the directional mutation rule do not require additional control parameter for DE, as often found in several modified DE variants. The effectiveness of the proposed constrained DE algorithm, named as εDEdn, is illustrated by solving five benchmark engineering design problems. The results show that the NNC combined with the ε constrained method can omit up to fifty percents function evaluations. It is also shown that the direction mutation can increase the convergence rate of the optimization. Comparing with other state-of-the-art DE variants reported in the literature, the proposed DE often gives equal or better results with considerably smaller number of function calls.

A. H. Pham, C. T. Vu, D. B. Nguyen, D. T. Tran

Optimization of the Longitudinal Cooling Fin by Levenberg–Marquardt Method

The optimization of longitudinal cooling fin by using Levenberg–Marquardt method (LMM) is implemented in this paper. The fin profile is constructed by Bezier curve, and the control points of the Bezier curve are considered the optimization variables. Furthermore, a “volume updating” mechanism was introduced into LMM to obtain the minimum volume of the optimal fin. To demonstrate the proposed method, two cases with the various conditions of the longitudinal cooling fin design problems are examined and the geometry parameters of optimal fin from the proposed method will be compared with the published optimal results. From the obtained results, it can be declared that LMM can be utilized efficiently to determine the minimum volume of the longitudinal cooling fin.

Q. Nguyen, S. Nguyen-Hoai, T. Chuong-Thiet, T. Lam-Phat

An Artificial Neural Network-Based Optimization of Stiffened Composite Plate Using A New Adjusted Differential Evolution Algorithm

Stiffened composite plates have been widely used in many engineering areas including construction, shipbuilding, and aircraft. And so, the demand of optimizing the design of stiffened composite plate has also been rising. In this paper, a so-called ABDE (ANN-based differential evolution) algorithm is introduced to search for the optimal design of stiffened composite plates. The new algorithm is the combination of the artificial neural network (ANN) and an improved differential evolution (DE) algorithm in solving optimization problems. In this technique, the ANN helps to quickly compute the respond of the structure, which is used in constraint handling step or finding the value of an objective function of DE algorithm. This helps to decrease the cost and increase the speed of convergence effectively.

T. Lam-Phat, S. Nguyen-Hoai, V. Ho-Huu, Q. Nguyen, T. Nguyen-Thoi

Reinforced Concrete, Steel and Steel-Concrete Composite Structures


Theorical and Experimental Studies on Hybrid Steel-RC Walls

Hybrid RCS frames consisting of reinforced concrete (RC) column and steel (S) are used frequently in practice for mid- to high-rise buildings. RCS frames possess several advantages from structural, economical and construction view points compared to either traditional RC or steel frames. One of the key elements in RCS frames is the composite shear wall consisting of several steel sections encased in reinforced concrete. Regarding the RC walls reinforced by more than one steel profile, namely hybrid steel-RC wall, although a number of researchers have focused on its various aspects, they are currently not covered by standards because they are neither reinforced concrete structures in the sense of Eurocode 2 or ACI318, nor composite steel-concrete structures in the sense of Eurocode 4 or AISC 2010. This paper deals with theoretical and experimental study on hybrid walls with several embedded steel profiles. The first part of this paper is dedicated to present a tentative design model for hybrid elements (walls and columns) subjected to combined axial force, bending and shear. Particular attention will be paid to shear (longitudinal and transversal) resistances because preventing shear failure is one of the major concerns when designing a composite structural member. Next, an experimental study on the static behavior of hybrid walls subjected to combined shear and bending is presented. Six hybrid walls with different types of the structural steel-concrete connection and reinforcement detailing are tested. The specimens exhibited ductility behavior. The specimens with shear connectors (i.e. headed studs, stiffeners) were more ductile in terms of displacement ductility than the ones without connectors. Finally, to assess the validity of the developed design model a comparison between the experimental results and design predictions is presented.

Nguyen Quang-Huy, Hjiaj Mohammed, Tran Van Toan

Numerical Study on a New Through-Column-Type Joint for RCS Frame

Hybrid RCS frames consisting of reinforced concrete (RC) column and steel (S) are used frequently in practice for mid- to high-rise buildings. RCS frames possess several advantages from structural, economical, and constructional view points compared to either traditional RC or steel frames. One of the key elements in RCS frames is the beam–column joints. This paper deals with numerical study on static response of a new reinforce concrete-steel (RCS) exterior beam–column joint. The studied beam–column joint detail is a through-column type in which an H steel profile totally embedded inside RC column is directly welded to the steel beam. The H steel profile was covered by two supplementary plates in the joint area. This detail provides two main advantages: The column is continuous, and no stirrups in the joint area are needed. The nonlinear behavior of the new joint is studied numerically and showed that this proposed joint is suitable as a special moment connection. In addition, the parametric studies are carried out to investigate the influences of the stirrups, the encased profile length, and supplementary plate length on the behavior of the joint.

D. D. Le, X. H. Nguyen, Q. H. Nguyen

Flexural Behavior of Unbonded Post-Tensioned Concrete T-Beams Externally Bonded With CFRP Sheets Under Static Loading

This paper presents a study on flexural behavior of unbonded post-tensioned concrete T-beams (UPC) externally strengthened by CFRP sheets under static loading with or without the presence of U-strip CFRP anchorage systems. A total of nine UPC T-beams in large size including one control unstrengthened beam and eight beams externally strengthened with varied number of CFRP sheets (2, 4, and 6 plies) were tested. Two types of transverse CFRP U-strip anchorage system were also retrofitted in the shear span. The results showed that CFRP sheets significantly increased the flexural capacity (up to 37%), decreased deflection in serviceability state, improved ductility, and reduced crack width (up to 48%) of the tested beams. The maximum strain in CFRP sheets in strengthened UPC T-beams ranged from 38.7 to 69.3% of the rupture strain of the CFRP sheets and tended to decrease with a large number of CFRP sheets. Strain in tendons of strengthened beams was significantly affected by the CFRP sheets and transverse U-strip anchorage system.

Q. P. T. Truong, P. Phan-Vu, D. Tran-Thanh, T. D. Dang, L. Nguyen-Minh

Numerical Analysis of the Behaviors of End-Plate Beam-to-Column Steel Joints Subjected to Cyclic Loading

This chapter presents the implementation of the modified Richard-Abbott model for the response of the extended end-plate composite joints subjected to cyclic loading. The combination of finite element models simulated in ABAQUS and the Richard-Abbott mathematical expression is the method to construct the hysteretic moment–rotation curves of the joint. The joint’s parameters are found based upon the comparison between the analysis and the experimental results. After that, the behavior of the joint is analyzed subjected to various cyclical loads. The dissipated energy of the joint within a load cycle is estimated and discussed. Relationship between dissipated energy and stiffness degradation of a joint is found as the joint subjected to the arbitrary cyclic loading.

A. T. Le, H. Pham

Experimental and Numerical Research on the Fire Behaviour of Steel Column Protected by Gypsum Plasterboard Under Fire Condition

In Vietnam, the fire problem in steel structures is relativity much, thus the study of fire protection solutions for the load-bearing steel structures (beams, columns) is very important. One of solution is the use of gypsum plasterboard. This paper presents firstly an experimental identification of the thermal conductivity of gypsum plasterboard used in Vietnam and then a full-scale experimental investigation relative to the fire resistance of steel column protected by gypsum plasterboard. In parallel, a numerical model is also developed in order to simulate the thermal transfer and mechanical behaviour of steel column protected by gypsum plasterboard under fire conditions. This model is used to compare with the experimental results and to analyse the influence of different parameters on the fire behaviour of steel column protected by gypsum plasterboard in Vietnam conditions.

T. Nguyen-Vo, V. Nguyen-Duc, H. Tran

Composites and Hybrid Structures


Comparison Between Numerical and Experimental Results of the Hybrid Members Subjected to Bending and Shear

This paper presents experimental and numerical results of the hybrid members with several encased steel profiles subjected to bending and shear. These results are compared with each other on the load-bearing capacity, the strain distribution, the stress distribution, the slip distribution, the crack pattern, the failure modes. These steel-concrete composite structural elements belong to the so-called “hybrid” structures which are neither reinforced concrete structure in the sense of Eurocode 2, nor steel-concrete composite structures in the sense of Eurocode 4. Currently, there is no design calculation guide of the resistance for this type of structure in international standards. Therefore, the comparison between numerical and experimental results is performed to point out the mechanism of the load transfer and failure taking place within the hybrid members subjected to bending and shear. It is the basis for calibrating the proposed design method for hybrid members reinforced by several steel profiles. The six hybrid member specimens were prepared and tested at the Structures Laboratory of INSA Rennes, France. The structural response of all hybrid members specimens were simulated by a full 3D finite element model using the Abaqus software.

T. V. Tran, H. Q. Nguyen

Analytical Behavior of Rectangular Plates Under in-Plane and Lateral Dynamic Loads

Analytical behavior of rectangular plates with semi-rigid boundary conditions under in-plane and lateral dynamic loads of constant thickness resting on the Winkler foundation is analyzed using a modified Bolotin method. The presentation of the semi-rigid isotropic plate’s frequency in a form analogous to the corresponding frequency of a simply supported plate is postulated, considering the wave numbers as unknown quantities. These two equations are determined from a system of two transcendental equations, obtained from the solution of two auxiliary Levy-type problems. The method was shown to be remarkably accurate when used to determine the natural frequencies of plates with non-simply supported boundary conditions. A natural extension of this research is related to the buckling and lateral vibration of isotropic plates subjected to in-plane forces which are time invariant and constant over the area of the plate, with their principal directions parallel to the plate edges and the dynamic lateral force. It is the purpose of this paper to illustrate this extension and to demonstrate its applicability by the presentation of numerical results for a particular plate.

Sofia W. Alisjahbana, Wiratman Wangsadinata, Irene Alisjahbana

Static Analysis of FG-CNTRC Plates Using C0-HSDT

Recently, an edge-based smoothed discrete shear gap method (ES-DSG) based on the first-order shear deformation theory (FSDT) was developed to investigate static and free vibration analyses of Reissner–Mindlin plates [1]. In this paper, we extend ES-DSG to the C0-type higher-order shear deformation theory (C0-HSDT) to study static analysis of functionally graded carbon nanoreinforced composite (FG-CNTRC) plates. Four distributions of volume fractions of carbon nanotubes (CNTs) including UD, FG-V, FG-O, FG-X are considered. The governing equations are approximated according to a combination between ES-DSG and HSDT model. Hence, this does not require shear correction factors and improves the accuracy of the present method. Numerical examples are performed to show the reliability and accuracy of the present method.

T. Nguyen-Quoc, S. Nguyen-Hoai, D. Mai-Duc

Finite Element Simulation of the Strength of Corrugated Board Boxes Under Impact Dynamics

In this study, we propose a model based on the finite element method to study the behavior of corrugated cardboard boxes subjected to shocks. To reduce the preparation of the CAD model and the computational times, we have developed an elastoplastic homogenization model for the corrugated cardboard. The homogenization consists in representing a corrugated cardboard panel by a homogeneous plate. A through-thickness integration on a periodic unit cell containing a flute and two flat linerboards is proposed. Each constituent is considered as an orthotropic elastoplastic material with specific hypotheses for the corrugated medium. The model was implemented in the finite element software ABAQUS. Damage boundary curve (DBC) for corrugated cardboard boxes are defined by experimental testing and finite element simulations using the proposed model. The numerical results obtained are in good agreement with the experimental results.

V. Dung Luong, Fazilay Abbès, Boussad Abbès, P. T. Minh Duong, Jean-Baptiste Nolot, Damien Erre, Ying-Qiao Guo

Static and Free Vibration Analysis of Functionally Graded Shells Using a Cell-Based Smoothed Discrete Shear Gap Method and Triangular Elements

A cell-based smoothed discrete shear gap method (CS-DSG3) using three-node triangular element was recently proposed to improve the effectiveness of the discrete shear gap method (DSG3) for static and vibration analyses of isotropic Mindlin plates and shells. In this study, the CS-DSG3 is further extended for static and free vibration responses of functionally graded shells. In the present method, the first-order shear deformation theory is used in the formulation owing to the simplicity and computational efficiency. Several numerical examples are provided to validate high reliability of the CS-DSG3 in comparison with other numerical methods.

D. Le-Xuan, H. Pham-Quoc, V. Tran-The, N. Nguyen-Van

Optimal Volume Fraction of Functionally Graded Beams with Various Shear Deformation Theories Using Social Group Optimization

In this paper, the optimization of the volume fraction of functionally graded (FG) beams for maximizing the first natural frequency is investigated. Distribution laws using three, four and five parameters are used to describe volume fraction. Navier-type solutions based on various shear deformation theories are developed to compute the natural frequencies. A new metaheuristic algorithm called Social Group Optimization (SGO) is employed for the first time to solve the functionally graded beam optimization problem. Optimal volume fractions for beams with different material properties are then obtained. It is found that the five-parameter distributions give the highest first natural frequency for all cases. Moreover, the results show the consistency of the optimal volume fractions obtained by different shear deformation theories. It is also confirmed that SGO is an efficient tool for this complicated optimization problem.

A. H. Pham, T. V. Vu, T. M. Tran

A Node-Based MITC3 Element for Analyses of Laminated Composite Plates Using the Higher-Order Shear Deformation Theory

In this paper, the node-based smoothed finite element method is developed for three-node triangular plate elements using the mixed interpolation of tensorial components (MITC) technique to remove the shear locking. The C0-type continuous plate elements represent the higher-order shear deformation theory of laminated composite plates by adding two degree of freedoms related to derivatives of deflection. Based on the MITC3 technique for three-node triangular degenerated shell elements, an explicit formulation of gradients of the transverse shear strains is derived. The constant strain fields within the C0-type continuous plate elements are averaged over node-based domains defined by connecting the centroids and edges’ middle points of elements having common nodes. The proposed elements, namely NS-MITC3, show good accuracy and convergence as compared to other plate elements when employed to analyze laminated composite plates.

T. Chau-Dinh, T. Truong-Duc, K. Nguyen-Trung, H. Nguyen-Van

Equivalent Inclusion Approach and Approximations for Thermal Conductivity of Composites with Fibrous Fillers

Based on the polarization approximations, the expression for the thermal conductivity of composites with randomly oriented inclusions of fiber forms is firstly derived. Equivalent inclusion approach is then developed to account for possible diversions such as non-idealistic geometric forms of the inhomogeneities, or the fact that the conductivity of the fibers is unknown, using reference conductivity data. Applications involving experimental data from the literature show the usefulness of the approach.

Nguyen Trung Kien, Nguyen Thi Hai Duyen, Pham Duc Chinh

Crack Detection in a Beam on Elastic Foundation Using Differential Quadrature Method and the Bees Algorithm Optimization

In the present contribution, a practical and non-destructive method for the identification of a single crack in a beam resting on elastic foundation is presented. The beam is modelled by differential quadrature method, and the location and depth of crack are predicted by bees algorithm. The crack is assumed to be open and is simulated by torsional spring which divides all parts through cracked beam into two segments. Then, the differential quadrature method is applied to the governing differential equation of motion of each segment and the corresponding boundary and continuity conditions. An eigenvalue analysis is performed on the resulting system of algebraic equations to obtain the natural frequencies of the cracked beam on elastic foundation. Then, the location and depth of cracks are determined by bees algorithm optimization technique. The formulation of thin-walled beams theory is used for the crack detection in this research. To insure the integrity and robustness of the presented algorithm, the finite element analysis is performed on the set of cantilever beams, with different crack lengths and locations. The results show that the presented algorithm predicts location and depth of crack well and can be effectively employed for crack detection in other structures.

R. Khademi Zahedi, P. Alimouri, Hung Nguyen-Xuan, Timon Rabczuk

Nonlinear Static Bending Analysis of Functionally Graded Plates Using MISQ24 Elements with Drilling Rotations

This paper develops a computational model for nonlinear static bending analysis of functionally graded (FG) plates using a smoothed four-node quadrilateral element MISQ24 [1, 2] within the context of the first-order shear deformation theory (FSDT). In particular, the construction of the nonlinear geometric equations is based on Total Lagrangian approach in which motion at the present state compared with the initial state is considered large. Small strain–large displacement theory of von Karman will be used in nonlinear formulations of the smoothed quadrilateral element MISQ24 with drilling rotations. The drilling rotations are introduced to improve the coarse mesh accuracy of the MISQ24 element. The solution of the nonlinear equilibrium equations is obtained by the iterative method of Newton–Raphson with the appropriate convergence criteria. The present numerical results are compared with the other numerical results available in the literature in order to demonstrate the effectiveness of the developed element. These results also contribute a better knowledge and understanding of nonlinear bending behaviors of these structures.

H. Nguyen-Van, H. L. Ton-That, T. Chau-Dinh, N. D. Dao

A Pull-Out Test to Characterize the Fiber/Matrix Interfaces Aging of Hemp Fiber Reinforced Polypropylene Composites

The fiber/matrix interface of natural fibers reinforced polymer composites is the weak zone that limits their use in some applications. The existing methods of fiber/matrix interface characterization are usually expensive and complexes. Also, the ‘real’ properties of the interface have not been well taken in the Interfacial Shear Strength (IFSS) calculation. Therefore, a pull-out test has been developed recently in our laboratory to limit these shortcomings. Moreover, the interface aging by environmental factors like relative humidity (RH) is still not clearly characterized. The developed method was then applied to investigate the interface deteriorations of the hemp fibers reinforced polypropylene composites due to moisture accelerated aging. By this way, fifty single fiber micro-composite specimens were tested after one week. The pull-out test was realized using an in situ micro-tensile machine. The IFSS was then determined considering the non-regular geometry and the non-constant of the fiber cross section. The results show that the humidity exposition weakens severely the fiber–matrix adhesion, and then the fibers were pulled out effortlessly from the matrix. Furthermore, qualitative deteriorations of the fiber and the interface were noted by optical observations. The IFSS was also severely reduced to $$42.97\%$$ after one week. The qualitative deteriorations and the reduction of the mechanical properties of the interface were explicated by the occurrence of several of physicochemical phenomena during the aging.

C. Nguyen-Duy, A. Makke, G. Montay

A Modified Moving Kriging Interpolation-Based Meshfree Method with Refined Sinusoidal Shear Deformation Theory for Analysis of Functionally Graded Plates

This paper presents an efficient approach based on a modified Moving Kriging–interpolation meshfree method integrated with the refined sinusoidal shear deformation plate theory to analyze static bending and free vibration of functionally graded plates. Unlike traditional higher order shear deformation plate theories, this theory presented retains only four governing equations, accounts for a sinusoidal distribution of the transverse shear strains through the thickness of the plate, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factor. A new modified Gaussian correlation function to construct MK interpolation shape functions is presented. We first propose the formulation and then provide comparison studies via numerical examples, which are performed to confirm the accuracy and reliability of the proposed method.

V. Vu-Tan, S. Phan-Van

Bending Analysis of Laminated Composite Beams Using Hybrid Shape Functions

Bending behaviours of laminated composite beams are presented in this study. The present theory is based on a higher-order shear deformation beam theory. The governing equations are derived from Lagrange’s equations. Ritz method is applied in which new hybrid shape functions are proposed for analysis of laminated composite beams with various boundary conditions. Numerical results are presented and compared with those from earlier works to validate the accuracy of the proposed solutions and to investigate effects of the span-to-height ratio, boundary conditions, fibre orientation and material anisotropy on the displacement and stresses.

Ngoc-Duong Nguyen, Trung-Kien Nguyen, Thien-Nhan Nguyen, Thuc P. Vo

Numerical Methods and High Performance Computing


Numerical Analysis of Hybrid Members Using FEM

The paper presents the numerical study dealing with the behavior and the real load-bearing capacity of hybrid members by Abaqus software. Especially identify the behavior of the composite steel-concrete members with several fully encased steel profiles (hybrid members) while the materials were yielded until failure. Structural hybrid members, material constitutive law for steel and concrete, load schematic, element types, numerical solution controls, interactions, steel-concrete bond and mechanical contact, ...will be described in detail. It is expected that nonlinear FEM analysis can give more details on behavior as well as on shear and bending resistance mechanisms until failure of the hybrid members. The nonlinear FEM analysis will be able to predict specimen strength, maximum displacement, strains and stress distribution, crack pattern, and failure modes. The reliability of this method was evaluated by comparing the analysis results with a part of the experimental results.

T. V. Tran

Effect of Hyper-Parameters on Deep Learning Networks in Structural Engineering

Since the first journal article on structural engineering applications of neural networks (NN) was published, a large number of articles about structural engineering have been published on these fields. However, over the last decade, researchers who attempt to apply the neural network concept to structural analysis problems have reduced significantly because of a fundamental limitation. At the beginning of the new millennium, in a deep learning field, newer methods have been proposed by using new activation functions, loss functions, alleviating overfitting methods with hyper-parameters, and other effective methods. Recent advances in deep learning techniques can provide a more suitable solution to the problem. The aim of our study is to show effects and differences of newer deep learning techniques on neural networks of structural analysis topics. A well-known 10-bar truss example is presented to show condition for neural networks and role of hyper-parameters in the structures.

Seunghye Lee, Mehriniso Zokhirova, Tan Tien Nguyen, Jaehong Lee

DOF Condensation of Thick Curved Beam Element Formulated by Isogeometric Approach

The study of a thick in-plane curved beam is more complex than that of the straight beam because the structural deformations of the curved beam depend not only on the rotation and transverse displacement but also on the coupled tangential displacement caused by the curvature of the structure. The Isogeometric approach is a computational geometry based on a piecewise ratio function (Non-Uniform Rational B-Spline (NURBS)) used to represent the exact geometry. In the Isogeometric approach, the free curvature geometry of the beam element can be represented exactly. A thick two-node curved beam element can be developed by using the Isogeometric approach based on Timoshenko beam theory, which allows the transverse shear deformation and rotatory inertia effects. The natural shape of the beam curvature and the shape functions formulation of the element can be formulated by using the Isogeometric approach. However, in the Isogeometric approach, the number of equations will increase according to the number of degree of the polynomial and its control points. A novel technique is been proposed to condense the number of equations of the DOFs at control points so that it is equal to the standard two-node six DOFs beam element. This paper highlights the application of the NURBS for a curved Timoshenko beam element in the context of finite element analysis and proposes a new condensation method to eliminate the drawbacks raised from the Isogeometric approach. Examples are given to verify the effectiveness of the condensation method in static and free vibration problems.

Buntara S. Gan, Dinh-Kien Nguyen, Aylie Han, Sofia W. Alisjahbana

Optimal Airplanes’ Paths For Minimizing Airline Company’s Cost Subjected to Passengers’ Demand: Formulation and Verification

A new formulation which addresses a new/specific/practical problem facing the airline industry, such as “Optimal Airplanes’ Paths For Minimizing Airline Company’s Cost Subjected to Passengers’ Demand”, is presented in this paper. If the flying paths are explicitly used as unknown variables, then one has to deal with a very large number of unknown variables. To avoid such bottlenecks, our proposed approach consists of finding which city-pair flight legs are flown and how many times the optimum flight paths will use these flight legs. With this obtained information, the optimum flight paths can be obtained by a post-processing phase! The mentioned “Optimal Airplanes’ Paths” problem can be formulated as a nonlinear integer programming (NLIP) problem. Numerical results are also included in this paper to validate the proposed NLIP formulation.

V. H. Nguyen, M. Ehsaei, J. Creedon, G. Sanjabi, D. T. Nguyen

A New Beam Theory Considering Horizontal Shear Strain

Methods of setting up and solving problems of flexural members, considering the horizontal shear strain, have been studied since the 1970s but there has not been any complete theory. When considering the influence of horizontal shear strain, with the horizontal shear strain approaching zero (when shear elastic modulus $$G \to \infty$$ or the ratio h/l is very small), the presented solutions do not converge to the case of zero horizontal shear strain, due to the shear locking phenomenon. Many authors have conducted studies to overcome this problem. Although they have achieved acceptable solutions, theoretical mistakes are unavoidable. In this article, the author will present a new method, in which the displacement and shear force functions are considered as functions that need to be determined to set up a new Beam Theory Considering Horizontal Shear Strain. To develop beam problems based on the Method of Gauss’s Principle of Least Constraint, the author uses the calculus of variations and partial integral to establish two differential equations to determine two unknown functions and beams’ boundary conditions. The beam theory (not considering the horizontal shear strain) is a separated condition of this theory. Using this theory in calculating beams and frames does not encounter shear locking phenomenon. The author will present equations of elastic line; analytic formulas determining deflection, angle of rotation, moment and shear force of beams, with different supports and static loads. When considering horizontal shear strain, changes occur in both the displacement and internal forces of beams and frames. However, while the displacement increases considerably, the redistribution of internal forces is quite insignificant.

T. Vu-Thanh

Analytical Study on In-plane and Out-of-plane Responses of a Curved Floating Bridge

The in-plane and out-of-plane responses of a curved floating bridge that is vertically supported by pontoons and laterally held by shore abutments at two ends are studied analytically. The in-plane solution is derived based on strain compatibility. An Euler curved beam model is used to develop the solution to the out-of-plane response of the bridge. Trigonometric trial functions are adopted to approximate the vertical displacement and the torsional rotation of the curved beam. Both solutions are verified against FE analysis results and good agreement is found between the results. The studies will focus on the effect of end support stiffness on the in-plane response of the bridge and the out-of-plane response of the bridge subject to tidal variation.

B. K. Lim, J. Dai, K. K. Ang, G. C. Yap

Establishment of Artificial Accelerogram for Shaking Table Test

In order to evaluate behavior of building and other structures under seismic action, one of the methods is testing the specimen on the shaking table. This paper presents the establishment of artificial accelerogram for testing of semi-precast specimen on the shaking table by using similitude theory to convert the artificial accelerogram of the prototype building to artificial accelerogram of the small-scale specimen and compare the test result and analysis result.

T. Nguyen-Vo, T. Do-Tien, K. Nguyen-Trung

A Naturally Stabilized Nodal Integration Meshfree Formulation for Thermo-Mechanical Analysis of Functionally Graded Material Plates

This chapter presents naturally stabilized nodal integration (NSNI) meshfree formulations for thermo-mechanical analysis of functionally graded material (FGM) plates. The effective material properties of FGM plates are homogenized by a rule of mixture. Gradient strains from the present approach are directly computed at nodes, the same as the direct nodal integration (DNI). The current approach is to alleviate the instability of solutions in the DNI and to significantly decrease computational cost when compared to the high-order Gauss quadrature scheme. The enforcement of essential boundary conditions is completely similar to the finite element method (FEM) due to satisfying the Kronecker delta function property of moving Kriging integration shape functions. Numerical validations are given to show the efficiency of the present approach.

Chien H. Thai, Dung T. Tran, Hung Nguyen-Xuan

Nondestructive Vibrational Tests and Analytical Solutions to Determine the Young’s Modulus of Rammed Earth Material

Rammed earth (RE) is a construction material which is manufactured from the soil. The soil is dynamically compacted at its optimum water content, inside a formwork to build a monolithic wall. The RE wall is composed of several layers, about 10–12 cm thick. In the last decades, RE material has been the focus of numerous scientific researches because of sustainable properties of this material: low embodied energy, positive hygrothermal behavior and a particular esthetic aspect. In several situations, nondestructive methods are needed to assess the mechanical characteristics of RE material, for both old and new RE constructions. This paper presents how in situ vibrational measurements can be used to identify the dynamic behavior of RE walls and to determine the Young’s modulus of the RE walls measured. To determine Young’s modulus from the dynamic characteristics, an analytical model based on Timoshenko’s beam theory is presented, both for flexural and torsional modes. Then, the proposed analytical model is verified with measurements on several walls having different cross-sectional forms: rectangle and L-shape. The walls’ natural frequencies were identified from the dynamic measurements by using the Frequency Domain Decomposition method. In parallel, for comparison, the Young’s modulus of the RE material studied was also determined by classical static measurements (on the walls, prismatic and cylindrical specimens). The displacements were measured by using the Image Correlation technique. The comparisons showed that the results from the proposed analytical method provided high accuracies and better than that obtained by measurements on the usual specimens (prismatic and cylindrical).

Quoc-Bao Bui

Investigation of A5052 Aluminum Alloy to SS400 Steel by MIG Welding Process

This paper aims to investigate the simulation and experiment of the welding of butt joint 5052 aluminum alloy to SS400 steel by SYSWELD software and metal inert gas (MIG) welding process with AR4043 welding wire. Welding seams were evaluated by mechanical testing and metallurgical analysis, and surface morphology welding seam and other welding defects were investigated. The microstructure of intermetallic layer has been observed using microhardness testing and scanning electron microscopy (SEM). A without intermetallic layer and intermetallic layer joint between welding seam and SS400 steel at fusion area appeared after the welding process. To improve the quality of welds, the best thickness of the intermetallic (IMC) layer was from 3 µm to 7 µm. The fracture tensile inspection results of welding seam achieved at 230 MPa and the fracture occurred at the IMC layer, the average microstructure hardness of IMC layer zone is 346.3 HV and without IMC layer zone is 117.85 HV. The intermetallic layer was at the minimum to improve the quality of welds.

Quoc Manh Nguyen, Huong Thao Dang Thi, Van Thinh Nguyen, Minh Hue Pham Thi, Khac Thong Nguyen, Shyh-Chour Huang, Van Nhat Nguyen

Behaviour of Two Chamber Aluminium Profiles Under Axial Crushing: An Experimental and Numerical Study

The present study investigated experimentally and numerically the structural behaviour of two chamber extruded profiles in AA6060-T7 alloy subjected to axial crushing under quasi-static loading conditions. Experimental tests were performed (including uniaxial tests, in-plane shear test and plane strain tension tests) to characterize the elastic–plastic, anisotropy and fracture behaviour of the investigated material. The material under investigation exhibited anisotropic properties and isotropic yield models such as von-Mises were not able to predict correctly the shear and plane strain test behaviour. It depicted that the advanced material model with anisotropic Yld2004-18p yield function and ECL criterion was necessary to predict the material tests results (UT, ISS and PST) both in terms of force–displacement curves and ductile fracture. Axial crushing tests were also conducted to investigate the energy absorption capacity of two chamber profiles made of this alloy. A solid element-based numerical model of these component tests was established in the commercial finite element code LS-DYNA, and simulations were run with the calibrated material models and fracture criterion. The predicted force–displacement curves, the energy absorption and fracture were in a good agreement with the experimental results. These results demonstrate that numerical models can be used as a reliable design tool for optimizing aluminium profiles for automotive applications.

Nguyen-Hieu Hoang, Magnus Langseth, Gaute Gruben, Terence Coudert

Flow Problems


Evaluating the Saltwater Intrusion to Aquifer Upper-Middle Pleistocene (qp2–3) in Coastal Area of Tra Vinh Province Due to Groundwater Exploitation

Today, one of the most serious problems in Tra Vinh as other coastal provinces in Mekong Delta is the exploitation of groundwater for different purposes. In many cases, the aquifers are pumped or withdrawn with greater discharge to its natural ability, thus making seawater draw into the system [1]. This paper aims at evaluating the saltwater intrusion into aquifer upper-middle Pleistocene in ​​Tra Vinh province area due to groundwater extraction. The calculated area includes 2,176 nodes, 2,079 elements, and grid steps Δx = Δy = 1,000 m. The program is set up to determine the interface between freshwater and saltwater which moves from the sea into the mainland of upper-middle Pleistocene aquifer. The calculating results show that at the initial point when pumping with outflow Q = 29,987 m3/day, the toe interface in position is of 2,019 m from the sea, then with the time of exploitation t = 150,000 days, the interface moving into in the mainland is approximately 21,000–24,000 m. The calculation results enable managers and abstraction units to know the process of salt line by time in order to launch sound plan for exploitation.

Huynh Van Hiep, Nguyen The Hung, Pham Van Long

Study the Hull Form and Propeller-Rudder System of the Fishing Vessel for Vietnam

Currently, the construction of steel fishing vessels in Vietnam is extremely important. For the traditional fishing vessels were built in Vietnam, the characteristic form of the contours corresponding to low-speed running and block coefficient is increased. The transition to a new level of construction and operation of fishing vessels requires a thorough and detailed analysis of the hull form and the characteristics of propeller-rudder system, as well as their interaction in the process of fishing operations. In this paper we discuss the characteristics of the hull form and propeller-rudder system (propeller inside the nozzle) of the fishing vessel (project 70133), intended for the manufacture and operation in Vietnam by using Computational Fluid Dynamics.

Victor G. Bugaev, Dam Van Tung, Yana R. Domashevskaya

Research the Strength of the Decking Overlap of the Fishing Vessel for Vietnam

SolidWorks Simulation allows to analyze the local strength of hull construction and to determine the strength characteristics of structural elements and equipment. It is possible to assess the strength of a structure or assembly as a whole, to determine which structural elements or parts of the assembly will reduce the product’s operational reliability, and make changes to obtain an equivalent construction or assembly. The purpose of the study is to research the strength of the decking overlap of the fishing vessel by using SolidWorks Simulation.

Victor G. Bugaev, Dam Van Tung, Yana R. Domashevskaya

Analysis and Evaluation of the Ground Wave Propagation Due to Blasting Activities of the Road Construction by Numerical Models and Experiments

Blasting activities of the road construction could damage to the neighboring buildings because of the ground wave propagation. This paper focused on analyzing the numerical models of blasting in tunnel construction by using FEM software—MIDAS GTS NX and comparing to empirical measurements. From the results of analysis, we can identify the relationship of the wave propagation speed in the ground and the radius from the considering point to the source of vibration. Based on the results of this analysis assess the potential damage to neighboring buildings as well as designs the way to limit the impact of the wave propagation to neighboring buildings for similar projects.

Lan Nguyen, Huy Hung Pham, Phuong Hoa Hoang

Fluid–Structure Interaction Analysis of Revetment Structures—An Overview

The strong development of numerical models, especially, computational fluid dynamic (CFD, i.e., the using of computational software to visualize how liquid affects objects as it flows past) and fluid–structure interaction (FSI, i.e., the coupling applications of fluid and structural mechanics disciplines) brought engineers more good measures to investigate the interaction problems. Meanwhile, the understanding gap of interaction between fluid and revetment structure (RS, i.e., a special structure lean on the slope of dikes to keep the safe of slope and core from erosion due to current and wave) is one of the biggest interests. Hence, the priority aim of this study is to develop computer simulations, which will be used as the tools during the construction of RS that will better protect the coasts from flood and erosion.

T. Vu-Huu, C. Le-Thanh, Phuc Phung-Van, Hung Nguyen-Xuan, M. Abdel-Wahab

Building the Empirical Formula Defining Parameters of Blast Wave in Coral Environment

The article presents the empirical method to determine the characteristics of coral material and coral foundation serving for computation and design of defense security works on islands. The authors built the empirical formula to define the parameters of blast wave in coral medium and compared the computation results using AUTODYN software and then drew the conclusion as the basis for application in reality.

L. Vu-Dinh, T. Nguyen-Huu

A CFD Modeling of Subcooled Pool Boiling

Subcooled pool boiling is of immense importance in many industrial and engineering systems because of its great heat transfer coefficient in comparison with other heat transfer mechanisms. However it is one of the most complicated two-phase phenomena due to, for example, the simultaneous liquid/vapor motion at the same time with heat and mass transfer across the phase interfaces, distorted and deformable phase interface geometry with complicated bubble breakup/coalescence mechanisms etc. As the accuracy of the CFD simulation of two-phase flows has much improved, numerical study of subcooled pool boiling two-phase flow by using the CFD approach is desirable. To incorporate experimental and numerical studies of subcooled boiling, the objective of this study is to setup a numerical modeling of the subcooled pool boiling in a vertical pipe by using the CFD approach. The numerical setup is based on the physical experimental model developed in our previous study. For the numerical simulation of subcooled pool boiling and wall boiling, the extended RPI boiling model is exploited in the framework of the two-fluid CFD approach. Test simulations by using the numerical setup have been carried out for three cases: a single air bubble rising in still water, a vapor Taylor bubble rising in saturated still water, and a vapor bubble rising and condensing in subcooled still water. Evaluation of the model setup has been clarified. An initial simulation of subcooled pool boiling has also been demonstrated.

T. T. Nguyen, H. N. Duong, V. T. Tran, H. Kikura

Optimization of Precision Die Design on High-Pressure Die Casting of AlSi9Cu3

Precision high-pressure die casting for nonferrous casting applications is increasingly used in the foundries. This paper focuses on the following issues: filling simulation, defect analysis by computer-aided simulation, experiment with Taguchi analysis to select optimal parameters when design die for high-pressure die casting aluminum AlSi9Cu3. After analysis, the optimal parameters are as follows: cross section area of gate 40 mm2, location of gate at type 2, gate velocity 50 m/s, and liquid alloy temperature 640 °C. Based on the results of calculation parameters, we conducted design die by computer aided with the main objective is to optimize the die design parameters. The use of this integrated solution can shorten the cycle of die design and manufacture, and result in the production of high-quality die castings in the shortest time with the biggest profit.

T. A. Do, V. T. Tran

Flow and Performance Analysis of a Valveless Micropump

The flow behaviour and performance parameters of a diffuser-nozzle element of a valveless micropump have been investigated for different geometric and flow properties. When a fluctuating pressure is imposed on the inlet boundary of a diffuser-nozzle element, there is a net flow in diffuser direction due to the dynamic effect. The variation of this net flow along with rectification capacity, and diffuser efficiency has been investigated for different inlet-outlet length combination and frequencies of driving pressure. Flow behaviour and recirculation region have been studied. Pressure and velocity have been analyzed for quantitative analysis and for validation with results found in literature. 2-D geometry has been used in the present study. 3-D geometry has been modeled to justify the results obtained from 2-D analysis. Different inlet-outlet length combinations ranging from 0.2 to 1.0 mm has been investigated. Five different pressure frequencies in the range from 5 to 50 kHz have been considered to identify their effects on the performance of diffuser-nozzle element. The net flow and performance of the nozzle-diffuser element are found to be less dependent on outlet length while more dependency was found on inlet length. Further, the performance becomes weaker with the increase of frequency of inlet driving pressure pulsation.

P. K. Das, A. B. M. T. Hasan

Aeroelastic Analysis on Wing Structure Using Immersed Boundary Method

Flutter of airplane’s wing is a critical issue determining reliability of aircraft. Flutter phenomenon is the result of fluid–structure interaction and is usually involved with complicated phenomena such as shock wave–boundary layer interaction, flow separation, and nonlinear limited cycle oscillation. Accurate prediction of flutter is very challenging due to perplexing physical phenomena and requires large amount of computation. In this paper, a developed code based on immersed boundary method (IBM) was realized to predict aeroelastic response and characteristic parameters of the wing structure. There were two rectangular and two trapezoid 3D-shapes of wing; each 3D-shape of wing had NACA65A004 and supercritical airfoil, respectively. Results from IBM method were first analyzed to carry out behaviors of flow on and around airplane wings and then were compared with experimental results at low speed.

D. T. K. Hoang, S. V. Pham, K. N. Tran, C. D. Nguyen, K. P. Nguyen

Development of a 3-DOF Haptic Tele-manipulator System Using Magnetorheological Brakes

In this work, a tele-manipulator system with force feedback (Haptic tele-manipulator) is designed and manufactured. The haptic tele-manipulator system in this study consists of two main parts: slave and master manipulator. The slave manipulator is a three 3-rotary degrees of freedom (DOF) manipulator and driven by AC servo motors. At the end effector of the slave manipulator a 3D force sensor are mounted to measure impact force from the environment. The master manipulator is used to control the slave manipulator; it has a structure and shape similar to the slave manipulator. At the joints of the master manipulator, magneto-rheological brakes (MRBs) are installed. They are meants to create the variable braking torque in order to generate a required resultant force acting to the master operator. The value of required resultant force is obtained from sensors mounted on the slave manipulator. In this way, the operator of the master manipulator can feel the force at the end effector of the slave during its operation.

Nguyen Ngoc Diep, Hung Nguyen-Xuan, Nguyen Ngoc Tuyen, Nguyen Quoc Hung

Studying Convective Flow in a Vertical Solar Chimney at Low Rayleigh Number by Lattice Boltzmann Method: A Simple Method to Suppress the Reverse Flow at Outlet

Solar chimneys absorb solar radiation heat and induce natural convective airflow for natural ventilation of buildings. In this study, we simulate induced airflow in a two-dimensional vertical solar chimney by Lattice Boltzmann Method (LBM) and focus on laminar flow region at low Rayleigh (Ra) number. Standard D2Q9 and D2Q4 models with single relaxation time are used for flow and temperature fields, respectively. Airflow and air temperature distributions inside the chimney are investigated under effects of main parameters of solar chimneys: heat flux, chimney height H, and chimney width b. Typical characteristics of a solar chimney were well reproduced in our simulations. Particularly, we analyze flow reversal region near the outlet of the chimney. The flow separation regions were observed at low ratio of H/b at a given Ra number or at high Ra number at a given H/b ratio and significantly reduced the induced flowrate. To suppress the flow reversal, we propose a simple method of rearranging the heat transfer surface on the opposite side in the upper and lower halves of the chimney. The results show that this method can eliminate the separation region and increases the induced flowrate at low ratio of H/b at a given Ra number.

Y. Q. Nguyen

A Dual Approach to Modeling Solute Transport

The classic average method is usually applied to describe the solute transport equation of one-dimensional horizontal flow or two-dimensional horizontal flow. The solute transport equation is totally integrated one time from the bed to the water surface; the average values received by classic average method do not generalize by means of dual approach. So, in this paper, a dual approach is applied to solve the solute transport equation of two-dimensional horizontal flow. The equation describing the depth average concentration is obtained by two times integration: The first time integral is from the bed to the intermediate surface lays between bed and water surface, and the second time integral is from the bed to the water surface. With the dual approach, the received depth average concentration is better, particularly, in the case of stratification, mixed solute, and so on. The received governing equation based on the dual approach describes more accurately the physical characteristic of the transport phenomena in nature. Moreover, it provides flexible parameter adjustment based on the experimental data. A case study of salinity transport in Huong river is illustrated.

H. Nguyen-The

A Nonlocal Formulation for Weakly Compressible Fluid

In this paper, we propose a nonlocal formulation for both solid and weakly compressible fluid. The nonlocal fluid formulation is based on the nonlocal interaction of each material point with its neighbors, which is analogous to the peridynamic theory, a nonlocal formulation for solid. By considering the direction of the interaction, the horizon and dual-horizon are defined, and the dual property between horizon and dual-horizon is proved. The nonlocal divergence is introduced, which enables to derive the nonlocal interaction with the local formulation. The formulations allow the varying horizon size and satisfy the conservation of linear momentum, angular momentum, and energy at the same time. Two numerical examples are tested to verify the accuracy of the current method.

Huilong Ren, Xiaoying Zhuang

CFD Simulations of the Natural Cavitating Flow Around High-Speed Submerged Bodies

Cavitating flow is of considerable importance in underwater high-speed applications because of the desirable drag-reduction effect that concerns the presence of a cavity around moving objects. In many operating regimes, a proper design of high-speed underwater bodies, e.g., the slender ones, should produce not only a stable motion with a straight trajectory but also maximize the travel distance of the bodies. To this end, both physical experiment and CFD simulation can be exploited to investigate the behaviors of a body. Regarding this issue, a number of previous studies have been carried out. However, little specific data of the body design have been documented in the published literature so far. This study investigates numerically a number of varied designs of high-speed underwater slender bodies. The designs are different in some of the bodies’ typical parameters which include the cavitator shape and body length. Steady state simulations of the single/two-phase partial- and super-cavitating flows around the bodies have been carried out by using the CFD approach. A two-phase mixture formulation, turbulence k-ɛ model (for the solution of the flow field) and Zwart-Geber-Belamri (ZGB) cavitation modeling (for mass transfer modeling) are exploited. For the model validation, comparisons with the published experimental and numerical data have been performed. The behaviors of the natural cavitating flow around the different bodies investigated are obtained. The modified drag coefficient for these specific bodies and operating conditions are proposed.

T. T. Nguyen, H. N. Duong, T. Q. Nguyen, H. Kikura

Effect of Low-Frequency Flow on Cable Dry-State Galloping

Cable-stayed bridge has widely been applied for medium-to-very long span. Thanks to advanced construction technology and structural materials, its span length is being broken time by time. Due to the increase of main span, cable length becomes longer and more vulnerable to wind excitation. Common large amplitude vibration types of stay cables are rain-wind-induced vibration (RWIV) and dry-state galloping (DG). Therefore, countermeasure for DG and RWIV is one of the key design factors of cable-stayed bridges. Many studies on its mechanism and countermeasures have been conducted in which its causes and mechanism were explained to some extent. It is typically explained that an axial flow behind the cable and flow fields around the cable at the critical Reynolds number regime suppress Karman vortex shedding, and then low-frequency vortices related to latent Strouhal frequencies become stronger, which causes dry galloping at high reduced wind speeds (U/fD) [1–3], although the complete explanation for the mechanism has not been given. In this study, using a spiral protuberance cable, which was developed as an aerodynamic countermeasure stay cable [4], and a circular cable, wake flow behind the cable as well as wind-induced dynamic response were captured by wind tunnel test. Comparing power spectral densities and coherence along the cable axis of the wake flow between spiral cables and circular cables at different wind speeds, the role of low-frequency vortices/flow on dry galloping and the suppression mechanism of the spiral protuberance were clarified.

H. Vo-Duy, L. Hoang-Trong, M. Nguyen-Van, V. Nguyen-Hoang

Investigation on Turbulence Effects on Flutter Derivatives of Suspended Truss Bridge Section

This paper presents the flutter derivatives extracted from a stochastic state-space system identification method under difference turbulent flows. The aim of the study is to clarify the effects of oncoming turbulence on the flutter of suspended long-span bridges by using section model wind tunnel test. Several wind tunnel tests on a trussed deck section have been carried out with different oncoming turbulent properties involving turbulence intensities and turbulent scales. The analysis includes the transient response data from wind tunnel test which have been analyzed by the system identification technique in extracting flutter derivatives (FDs) and the difficulties involved in this method. The time-domain analysis stochastic system identification is proposed to extract simultaneously all FDs from two degree of freedom systems. Finally, the results under different condition were discussed and concluded.

L. Hoang-Trong, V. Nguyen-Hoang, H. Vo-Duy

Numerical Modelling of the Aeroelastic Response of Irregular Slender Structures

This paper presents a general framework for the evaluation of the aeroelastic response of a complex slender structure with generic cross sections. First, the Rayleigh–Ritz approach and the Lagrange equation are employed to describe the vibrations of a continuous coupled structure through a system of ordinary differential equations in common forms which are familiar to structural analysts. Then, the general framework for instability analysis will be presented. Finally, the theory is then applied to a real telecommunication pole with an irregular shape. The numerical results show different aspects from traditional findings, emphasizing the structural irregularity.

Cung H. Nguyen

Analysis of Fluid–Structures Interaction Problem of Revetment Slope Thin-Walled Structure Using Abaqus

This paper aims to analyze fluid–structure interaction (FSI) problems of revetment slope thin-walled structures using ABAQUS software. The method is based on a combination of computational fluid dynamics (CFD) for fluids and finite element method (FEM) for structures. During the simulation process, the required data are exchanged by the subsystems. Based on the co-simulation FSI, behaviors of solid structures under impact of flow are examined. The purpose of the co-simulation is to reduce costs and time consumed in manufacturing revetment slope (RS) structures. The expected results help improve geometry of blocks. Geometry dimensions of blocks of revetment slope thin-walled structure are supported by Busadco Company (Ba Ria Vung Tau Urban Sewerage and Development One Member Limited Company). In this article, an overview of computational aspect of FSI is presented. We expect to provide application of simulation technology to deal with such RS structures.

P. Truong-Thi, L. Dang-Bao, M. Abdel Wahab, H. Duong-Ngoc, T. Hoang-Duc, Hung Nguyen-Xuan

Influence of Swelling Pressure on Pore Water in Embankment Core with Swelling Clay Soil

Swelling clay soil used to fill at core of and used to waterproof for soil dam will swell and increase volume when soaked. This expansion status created the expansion pressure inside dam, increased volume of dam, and harmed the construction. It needs a cover soil to balance and keep the volume of core from expansion due to swell, make soil swelled in cover pressure condition, unchange soil volume, and reduce pore inside soil and permeability coefficient. Swelling pressure reduced pore water pressure and saturated water curve. When swelling finished, permeability coefficient reduced and saturated water curve inside dam raised up, it made pressure to the stability of dam. Changes in swelling pressure depended on type of soil, soil conditions, and density of soil. When swelling finished, friction angle and stickiness of soil increased and the stability of construction did not decrease. Recommendation applies result of this research to constructing earth dam and construction over swelling clay.

Tuong Nguyen Ke, Hung Nguyen Pham Khanh, Hung Nguyen Minh, Hung Nguyen Viet, Thi Nguyen Minh

Catastrophic Destruction Mechanics and Numerical Modelling


Concrete Mesoscopic Model and Numerical Simulation Based on Quadtree Mesh Refinement Technology

In the concrete mesoscopic model established by using the traditional background mesh method, a mesh refinement technology based on balanced quadtree is proposed to refine the elements of interfacial transition zone (ITZ). Considering the control standards of the minimum size requirement and the balancing condition, the implementation program of mesh refinement is studied. The polygonal FEM is applied to ensure the consistency of the mesh after quadtree refinement. Then, the modified concrete mesoscopic model is given, which is more reasonable for reflecting the constitutive behavior of ITZ. In the proposed concrete mesoscopic model, the correlative material parameters can directly assign to the elements of ITZ. The sawtooth defect of meshes around the aggregates in the background mesh method is also enhanced to a certain degree. Accordingly, the geometrical morphology and material property of ITZ are simulated better and more realistic. In the end, the numerical simulation is presented to preliminarily compare the differences between the background mesh method and the proposed method.

Guojian Shao, Shengyong Ding

A Coupling of Three-Dimensional Finite Element Method and Discontinuous Deformation Analysis Based on Complementary Theory

The continuous and discontinuous deformation analysis is essential for the stability analysis of the anchor bar-surrounding rock masses system. To eliminate the open-close iteration and the penalty factor of the 3D-DDA, the CDDA is proposed to extend into the three-dimensional block system. Then a novel simulation approach, the coupling method of 3D CDDA-FEM, is demonstrated, which combines the specific benefits of two numerical methods: the contacts between blocks are described by 3D-CDDA, while the displacement field inside block is described by FEM. Two numerical examples verify that the new coupling method is feasible and the displacement solution is more accurate. Taking different initial stress conditions of anchor bars into account, the stability analysis of anchor bar-surrounding rock masses system demonstrates that the appropriate installation and the optimal initial stress of anchor bar efficiently improve the stability of surrounding rock masses system of underground chamber.

C. Su, Z. M. Ren, V. H. Dao, Y. J. Dong

Computational Mechatronics


Analysis and Summarization of a Mechanism Featuring Variable Stiffness

This study presents the analysis of a novel mechanism based on the summarization of conventional models and gyroscope. The theoretical mechanism employs a nonlinear spring and a cantilever beam. This system has only one fixed support for the spring, and one non-contacted support to prevent the impact of friction in operation for cantilever beam. Exciting forces apply to the structure, including vertical and horizontal forces, and a moment. The cantilever beam is symbolized as an Euler–Bernoulli beam which has nonlinear property. After formulating, detections along the 2D coordinate are pointed out by using a nonlinear approximate method as Adomian decomposition method. The results of this method are compared with the numerical method. It is shown that the values of analysis and the numerical simulation are consistent with small errors. In addition, vibrations of the tip mass which is attached at the end of the beam are derived and simulated. The results of the tip mass vibrations are harmonic responses which prove that vibrations of any system always remain under harmonic conditions. This finding and the mentioned results are the base for the development of the new mechanism for both sensors and energy-harvesting devices.

Do Xuan Phu, Nguyen Quoc Hung, Ta Duc Huy

Dynamic Analysis of Hydraulic–Mechanical System Using Proportional Valve

Power hydraulic systems are used very often in industry. Usually, the stroke of piston—a hydraulic actuator is controlled in on–off manner using traditional valves and start/stop switches on the moving way. Another characteristic of traditional hydraulic system is suitable with static load. For applying dynamic load, the behavior of system is not properly good. Nowadays, hydraulic systems with proportional valve are used commonly. Proportional valve allows controlling for a variable stroke of piston. It also allows the system work with variable load. This paper presents the dynamic analysis of a hydraulic–mechanical system using proportional directional valve. The system dynamics is evaluated when the load changes in linear manner. A mathematical model is established to serve for determining dynamic characteristics of the system. PID control is also used in the simulation to enhance the integrity of the system.

D. T. Luan, L. Q. Ngoc, P. H. Hoang

A Tooth Profile Design for Roots Rotors of Vacuum Pump

In traditional tooth designs of the vacuum pump, the circular, cycloidal curves and their combination are usually used for generating the tooth profiles of roots rotor. However, to increase efficiency and to reduce vibration and noise for the pump, a novel tooth profile for the roots rotor of a vacuum pump is proposed, which are comprised of five different segments that are generated by the curves in order: circular arc, extended epicycloid, involute, extended hypocycloidal, and conjugated circular arc. A numeral example is presented to evaluate and compare the performance (volumetric efficiency and seal line length) for the proposed tooth profile and a traditional tooth design of the vacuum pump (cycloidal-cycloidal tooth profile) with considering to the number of rotor lobes. It reveals that the proposed tooth profile provides a much advantage than the traditional tooth profile.

V. Tran-The, T. Do-Anh

Cascade Training Multilayer Fuzzy Model for Identifying Nonlinear MIMO System

In this paper, a new cascade training Multilayer Fuzzy logic is proposed for identifying the forward model of double-coupled tank system based on experiment. The Multilayer Fuzzy model consists of multiple MISO models; for each MISO model, it consists of multiple single Fuzzy T-S models. The cascade training optimized with DE algorithm sequentially trained Multilayer Fuzzy model one by one. All parameters of the model are optimally trained with differential evolution (DE) algorithm. The experimental results show that proposed method gives better performance than the normal training. This proposed method can be used for optimal Multilayer Fuzzy logic that efficiently applied for identifying nonlinear MISO and MIMO systems. The experimental cascade training tests are presented. It proves more accuracy and takes less time to compute than the normal training method and demonstrates promisingly scalable and simple method as to successfully identify nonlinear uncertain MIMO system.

Cao Van Kien, Ho Pham Huy Anh

Enhanced Adaptive Fuzzy Sliding Mode Control for Nonlinear Uncertain Serial Pneumatic Artificial Muscle (PAM) Robot System

This chapter proposes a new enhanced adaptive fuzzy sliding mode controller (EAFSMC) with its perfect suitability for use in the control of a highly nonlinear and uncertain serial pneumatic artificial muscle (PAM) robot. The critical proof of the stability and the convergence of the overall system is presented using Lyapunov stability principle. Simulation results of the proposed EAFSMC control, applied to a two-degree-of-freedom nonlinear serial PAM robot, are implemented, and we have evaluated their efficacy in maintaining Lyapunov stability and their good performance.

Cao Van Kien, Ho Pham Huy Anh

Performance Evaluation of a 2D-Haptic Joystick Featuring Bidirectional Magneto-Rheological Actuators

In this research, a new 2D-haptic joystick featuring a 2D-gimbal mechanism and two bidirectional magneto-rheological actuators (BMRAs) is designed, manufactured, and experimentally tested. Firstly, a new configuration of proposed 2D-haptic joystick is introduced; then, the BMRAs for force feedback of the haptic joystick are proposed, optimally designed, and experimentally evaluated. The BMRA has two disks rotating in opposite directions at the same speed. The two disks are placed inside a housing which is connected to the gimbal mechanism. The BMRA has two coils placed directly on each side of the housing. A prototype of the whole haptic joystick is then manufactured, and a controller is designed to feedback a required force to the operator. Force feedback performance of the haptic joystick is then experimentally investigated and compared with simulated one.

Tri Bao Diep, Hiep Dai Le, Cuong Van Vo, Hung Quoc Nguyen

Design and Evaluation of a Shear-Mode MR Damper for Suspension System of Front-Loading Washing Machines

In this research, a low damping force shear-mode magneto-rheological (MR) damper that can replace conventional passive damper of a front-loading washing machine is designed and experimentally evaluated. In the design of the MR damper, required damping force, off-state friction force, size, and low cost of the MR damper are taken into account. Firstly, a suppression system for washing machines featuring MR dampers is proposed considering required damping force, available space, and cost of the system. Optimization of the proposed MR suspension system is then performed considering required damping force, off-state friction force, size, power consumption, and low cost of the MR damper. From the optimal results, simulated performance of the optimized MR damper is obtained and presented with discussions. A detailed design of the MR damper is then conducted, and a prototype MR damper is manufactured. In addition, experimental results on the prototype MR damper are obtained and compared with simulated ones. Finally, discussions on performance and application of the MR suspension system for front-loading washing machines are given.

D. Q. Bui, V. L. Hoang, H. D. Le, H. Q. Nguyen

Computational Dynamics


Transient Analysis of Laminated Composite Shells Using an Edge-Based Smoothed Finite Element Method

An edge-based smoothed finite element method (ES-FEM) was recently proposed to significantly improve the accuracy and convergence rate of traditional finite element method for static and force vibration analyses of plates and shells. In this paper, the ES-FEM is further extended and incorporated with mixed interpolation of tensorial components for triangular element (MITC3) [1], called ES-MITC3, for transient analysis of laminated composite shells based on the first-order shear deformation theory (FSDT). Numerical results for static analysis of isotropic and transient response of laminated composite shell with various different loadings and boundary conditions are provided. The accuracy and reliability of proposed method are verified by comparing its numerical solutions with those of other available numerical results.

D. Pham-Tien, H. Pham-Quoc, V. Tran-The, T. Vu-Khac, N. Nguyen-Van

Estimating Modal Parameters of Structures Using Arduino Platform

This paper presents the identification of the modal parameters as frequencies, damping coefficients, and mode shapes based on using Arduino platform to measure oscillation signals of structure in time domain. The use of Arduino platform aims to reduce costs in the experimental field. Experiments are carried out on a cantilever beam; the measurement process collects input/output or only output signal. MATLAB software is also used for the computing and data processing; these signals are transformed from time domain to frequency domain by fast Fourier transform (FFT). Modal parameters are estimated in the frequency domain. Comparing obtained modal parameters from experimental method with those from analysis method. Results are found to be in agreement with the theory.

Tuan Ta Duc, Tuan Le Anh, Huong Vu Dinh

Analysis of Dynamic Impact Factors of Bridge Due to Moving Vehicles Using Finite Element Method

This article presents analysis of dynamic impact factors for displacement, bending moment, and shear force of bridge under moving vehicles by finite element method. Vehicle is a dumper truck with three axles. Each axle of vehicle is idealized as two mass dynamic systems, in which a mass is supported by a spring and a dashpot. The structural bridges are simulated as bending girder elements. The finite element method is applied to establish the overall model of vehicle–bridge interaction. Galerkin method and Green theory are used to discrete the motion equation of vehicle–bridge system in space domain. Solutions of the motion equations are solved by Runge–Kutta–Mersion method (RKM) in time domain. The numerical results are in good agreement with full-scale dynamic testing under controlled traffic condition of the super T concrete girder at NguyenTriPhuong Bridge in Danang city, Vietnam. Numerical results figure out that there are significant differences between dynamic factors for displacement, bending moment, and shear force. Therefore, the common use of only one dynamic impact factor for displacements, bending moment, and shear forces of bridge structure in each limited state should add more consideration. Furthermore, current results are references for bridge engineers to have more information for safety design requirements and suitability in bridge operation.

T. Nguyen-Xuan, Y. Kuriyama, T. Nguyen-Duy

Stationary Random Vibration Analysis of Dynamic Vehicle-Bridge Interaction Due to Road Unevenness

This article presents stationary random vibration analysis of dynamic vehicle-bridge interaction due to road unevenness based on the Finite element method and Monte-Carlo simulation method. The road unevenness are described by a zero-mean stationary Gaussian random process. The vehicle is a dumper truck with three axles. Each axle of vehicle is idealised as two mass dynamic system, in which a mass is supported by a spring and a dashpot. The structural bridges are simulated as bending beam elements. The finite element method is applied to established the overall model of vehicle-bridge interaction. Galerkin method and Green theory are used to discrete the motion equation of vehicle-bridge system in space domain. Solutions of the motion equations are solved by Runge-Kutta-Mersion method (RKM) in time domain. The numerical results are in good agreement field test results of the prestressed beam-slab at Nguyen-Tri-Phuong bridge, Danang city, Vietnam. Also, the effects of road surface condition on dynamic impact factor of bridge are investigated detail. The numerical results show that dynamic impact factor of bridge has increased significantly when road unevenness have changed from Grade A-road to Grade E-road according to ISO 8608:1995 [1] “Mechanical vibration—Road surface profiles—Reporting of measured data”.

T. Nguyen-Xuan, Y. Kuriyama, T. Nguyen-Duy

Dynamic Analysis of Beams on Two-Parameter Viscoelastic Pasternak Foundation Subjected to the Moving Load and Considering Effects of Beam Roughness

In this paper, improved moving element method (IMEM) is intended to analyze the dynamic response of the beam resting on the two-parameter viscoelastic Pasternak foundation subjected to the moving load and considering effects of beam roughness. Beams are modeled by moving elements, while the load is fixed. The differential equation of motion of the structural system is established based on the principle of virtual public balance and solved by means of numerical integration based on the Newmark algorithm. The characteristic parameters of the foundation and the loads are investigated in order to analyze the dynamic response of the beam such as the second parameter of foundation, the roughness of beam, the velocity and acceleration of moving load.

T. Tran-Quoc, H. Nguyen-Trong, T. Khong-Trong

Biological Systems


The Prevention of Pressure Ulcers: Biomechanical Modelization and Simulation of Human Seat Cushion Contributions

The main cause of pressure ulcers (PUs) is high pressure on the surface of buttock-tissue and support cushion as well as the area inside the bones and muscle tissue. There are also many other factors, including shear stress, friction, temperature and moisture. So far, many studies have used numerical simulations and experiments to find the influence of the stresses and strains, the surface pressures on the formation and development of pressure ulcers. This paper presents a biomechanical modelization and simulation of the interactions between wheelchair seat cushion and human buttock-tissue (HBT) aiming to prevent ulcers. In this paper, we used three-dimensional (3D) finite element model (FEM) of a HBT in contact with a honeycomb seat cushion (HSC) in a sitting position. This cushion is made from thermoplastic polyurethane (TPU) for disabled people who use wheelchairs. Mechanical simulation was performed to find the pressure distribution, the stress and the deformation. Thermal simulation permits to identify the temperature distribution on the surface of HBT and HSC that are the factors can cause PUs. Our results showed that the highest distribution pressure, the von Mises stress, respectively, found corresponds to 175.8 and 36.45 kPa. The highest temperatures obtained in the zone of interaction between the buttock-tissue and HSC correspond to 33.74 °C after 35 min seating. Our study proposes a new methodology for the improvement and validation of FEM to identify the risk of PUs. The results will permit to improve cushion by collaboration with the manufacturer (optimization of shapes and materials) to create the own cushion model for each patient increasing his daily life.

T. H. Bui, P. Lestriez, D. Pradon, K. Debray, R. Taiar
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