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About this book

This book consists of selected and peer-reviewed papers presented at the 13th International Conference on Vibration Problems (ICOVP 2017). The topics covered in this book include different structural vibration problems such as dynamics and stability under normal and seismic loading, and wave propagation. The book also discusses different materials such as composite, piezoelectric, and functionally graded materials for improving the stiffness and damping properties of structures. The contents of this book can be useful for beginners, researchers and professionals interested in structural vibration and other allied fields.

Table of Contents

Frontmatter

Building Structures

Frontmatter

Propagation of Viscoelastic Waves in a Single Layered Media with a Free Surface

In this work, a wave propagation formulation in a layered half space is presented. A viscoelastic layer is considered to be fixed to an elastic half space. The inhomogeneity in various reflected and refracted waves is caused due to the viscoelastic layer. In the analysis, the low-loss approximation is considered for the viscoelastic layer. Using the matrix formulation of Thomson [1] and Haskell [2], the free surface displacement functions are derived by considering boundary conditions. The effect of medium parameters and wave types on the wave propagation behavior is studied numerically and conclusions are drawn.

Pankaj Kumar, Anirvan DasGupta, Ranjan Bhattacharyya

Axial Resistance of Short Built-up Cold-Formed Steel Columns: Effect of Lacing Slenderness

Cold-formed steel (CFS) construction has become popular in the recent decades mainly due to their favorable features like higher yield strength, easy fabrication/handling, faster cost-effective construction, etc. Built-up members are often used as columns in structures with demands to resist large axial forces. Past studies have mainly stressed on evaluating the performance of battened CFS columns. Therefore, there is a need to examine the behavior of built-up laced CFS columns under the axial loading conditions. This study stresses on the numerical investigation of the influence of lacing element slenderness on the compression capacity of built-up CFS columns. Cold-formed steel columns consisting of four angle sections were connected by single lacing configuration. Test results from literature were used to calibrate the nonlinear finite element model developed. The design strengths predicted by North American Standards (AISI S-100) are calculated and compared with the test results.

M. Adil Dar, Dipti Ranjan Sahoo, Arvind K. Jain, Sunil Pulikkal

Analysis of Stepped Beam Using Reduced Order Models

Damage detection in complicated engineering systems from vibration measurements typically involves the use of algorithms that are built on the principles of bayesian dynamic state estimation. These methods invariably required the solution of the forward problem a fairly large number of times. For complex engineering systems that are numerically modeled using Finite Element (FE), this can be computationally intensive especially when a single FE run for the problem takes a large time. To alleviate this problem, there is a need for the development of Reduced Order Models (ROMs) that significantly reduce the computational cost associated with solving the forward problem, for a given measure without sacrificing the accuracy. The present study discusses three ROM methods with specific reference to a simple problem. These methods include well-known Component Mode Synthesis (CMS) and System Equivalent Reduction Expansion Process (SEREP) which are applicable only for linear systems, as well as Principal Component Analysis (PCA)—the method which is more general and can be used for nonlinear systems as well. A comparison of the performance of all these methods is carried out for a stepped beam. The FE based results obtained from the full model is treated as the benchmark.

Rahul Kumar, Sayan Gupta, Shaikh Faruque Ali

Numerical Analysis of Geosynthetic Strengthened Brick Masonry Panels

Un-reinforced masonry (URM) structure is extremely vulnerable to seismic actions. Their susceptibility to collapse has provided the concussion to develop strengthening techniques to strengthen URM buildings. The numerical analysis of the in-plane behaviour of un-reinforced and geotextile strengthened brick masonry specimen, using a 3D macro nonlinear model, is presented in this paper. All specimens are subjected to diagonal compression tests. Two different patterns viz. parallel and diagonal are strengthened. Numerical analyses are carried out to verify the efficiency of the reinforcement with geosynthetic. From the investigation, it is noticed that geosynthetic strengthening enhanced the load-bearing capability, diagonal shear strength and stiffness remarkably. It is estimated that the diagonal shear strength enhanced from 36% to 39%. Hence, masonry strengthened with geosynthetic will perform better in the seismic prone area.

Hasim Ali Khan, Radhikesh Prasad Nanda, Diptesh Das

Studies on Dynamic Characteristics of Sandwich Functionally Graded Plate Subjected to Uniform Temperature Field

The effect of uniform temperature on dynamic characteristics of a sandwich plate with functionally graded (FG) core is analyzed by finite element methods. The top and bottom of the sandwich plate are considered as metal and ceramic, and the core is considered as functionally graded. Aluminum and alumina materials are used as top and bottom face sheets, and the same materials are graded through thickness for FGM core. The material properties of FG core vary throughout the thickness direction according to the power law index. The effective material properties are calculated using the Voigt technique. The Buckling temperature of sandwich plate is analyzed for different boundary conditions and used as criteria to study the effect of temperature on natural frequencies and mode shapes.

E. Amarnath, M. C. Lenin Babu

Numerical Model and Dynamic Characteristics Analysis of Cable-Stayed Bridge

The aim of this work is to numerically model a cable-stayed bridge, study its dynamic characteristics using two engineering tools viz. MATLAB® and SAP2000® and compare the results with those from the experimental analysis. The bridge considered for the study is a two-span cable-stayed bridge over the Garigliano River along the coast road between Rome and Naples. The structural details including material or sectional properties, boundary conditions and experimental responses are adopted [2]. It is observed that the present numerical model captures the experimental data well with minor discrepancies, which can be attributed to lack of proper data in numerical modelling. The finite element model can be further improved with the access of more structural data and can be effectively used for the determination of dynamic response due to earthquake and wind.

Antara Banerjee, Atanu Kumar Dutta

Breathing Crack Detection Using Linear Components and Their Physical Insight

Identification of fatigue-breathing cracks at the time of initiation that develop in structures under repetitive loading is desirable for successful implementation of any health monitoring system. The presence of higher order harmonics and sidebands apart from the fundamental excitation harmonic in the Fourier power spectrum subjected to harmonic excitation are widely used as breathing crack damage indicators. The majority of the existing breathing crack detection and localization techniques use the amplitudes of the super harmonics/modulation components obtained spatially across the structure from the current and healthy states. In the present work, instead of using nonlinear harmonic components for breathing crack detection, we exploit the decrease in the Fourier power spectrum amplitude of the linear components due to the transfer of energy from linear components to nonlinear harmonic components in the presence of breathing crack. Two new indices quantifying the ratio of energy variations in linear and nonlinear components have been proposed to highlight the effectiveness of the proposed concept. Numerical simulation and experimental investigations established the fact that the energy variation in linear components between varied crack depths shows significantly higher sensitivity than the energy variation due to nonlinear harmonic components.

J. Prawin, A. Ramamohan Rao

Optimal Design of Structure with Specified Fundamental Natural Frequency Using Topology Optimization

Resonance occurs when the natural frequency of the system matches with the vibrating frequency. It may cause structural instabilities. To avoid this, engineers maximize the first natural frequency of the system. In many applications, the natural frequency is pre-designed. Structural engineers aim to reduce the weight of structures subject to functional and safety constraints. This motivates us to modify the frequency optimization problem to weight minimization problem, for a specified fundamental natural frequency. In this paper, we solve for weight minimization using topology optimization subject to lower bound constraint on fundamental frequency.

Kandula Eswara Sai Kumar, Sourav Rakshit

Non-linear Dynamic Analysis of Structures on Opencast Backfilled Mine Due to Blast Vibration

The structures nearby mining area are generally subjected to blast-induced ground vibration. Thus, this is imperative to understand the behaviour of such structures through numerical analysis as an experimental study would be expensive and time consuming. Hence, this paper presents a three-dimensional non-linear finite element analysis of a two-storey reinforced concrete (RC) frame structures. Global responses in terms of storey displacements, drifts as well as local responses in terms of stress and strain of concrete at each floor level are extracted and discussed. It is observed from storey drift that there is an excessive deformation of structures and it exceeds the permissible limit. Moreover, through the analysis of strain data, it is observed that the structures already reach its plastic limit zone. Therefore, the structures will collapse due to normal gravity-based design of structures. Blast-resistant design and detailing criteria should be kept in mind when designing such structures in mine regions. In future, efforts will be driven to find out the safe permissible distance of residential structures in mining areas.

S. Kumar, S. C. Dutta, S. D. Adhikary, M. A. Hussain

Seismic Response of Shear Wall–Floor Slab Assemblage

Reinforced Concrete (RC) structural walls are commonly used in tall RC frame–wall buildings in severe seismic zones for enhancing lateral strength and stiffness of the buildings. Conventionally, the structural walls in multi-storeyed buildings are designed in the same way as isolated shear walls. However, due to the presence of floor slabs at different levels, there is an increase of stiffness locally at each slab–wall junction, which may lead to a significantly different response of the assemblage as compared to the isolated shear wall. Also, the floor slabs tend to partition the slender wall into a number of smaller panels between successive floor slabs. The present study aims to investigate the seismic behaviour of such multi-storeyed slab–wall assemblage using non-linear time history analyses of three different models under ground motions recorded during a past earthquake.

Snehal Kaushik, Kaustubh Dasgupta

Comparison Between Two Modeling Aspects to Investigate Seismic Soil–Structure Interaction in a Jointless Bridge

Seismic waves propagate through a series of rock and soil layers before they interact with the foundation and superstructure. Besides the original characteristics of the earthquake motion at the instant of fault rupture, it is also essential how the soil site responds in terms of amplification or de-amplification for different frequency contents. A coupled soil–structure model is required to capture the dynamic behavior of the entire system efficiently, considering the possible nonlinear response of soil and structure. This paper focuses on the comparison of two modeling strategies for Soil–Structure Interaction (SSI) aiming to define the behavior of a jointless bridge, namely, (a) one with an explicit full-scale soil domain with bridge model and (b) another with Beam on Dynamic Winkler’s Foundation (BDWF)/nonlinear soil springs. Finally, the structural components that affect the overall behavior of superstructure are compared between these two models, and the variation of seismic response from the performance-based study is discussed.

S. Dhar, K. Dasgupta

Probabilistic Flutter Analysis of a Cantilever Wing

A probabilistic flutter analysis of geometrically coupled cantilever wing is carried out using first-order perturbation approach by considering bending and torsional rigidities as Gaussian random variables. The unsteadiness in the aerodynamic flow is modeled using Theodorsen’s thin airfoil theory. The probabilistic response of the wing is obtained in terms of mean, standard deviation, and coefficient of variation (COV) of real and imaginary parts of the eigenvalues at various free stream velocities. The perturbation results are also compared with Monte Carlo simulations. It is observed that the probabilistic response obtained from the perturbation approach is very accurate up to 7% COV in bending rigidity but in the case of torsional rigidity, it starts losing accuracy after 3%.

Sandeep Kumar, Amit K. Onkar, M. Manjuprasad

Optimum Support Layout Design for Periodically Loaded Structures Using Topology Optimization

Optimal support layout design of structures under forced vibration is determined using topology optimization method. The vibrations of a structure can be reduced by adding external supports to the structure. Linear elastic springs are used as the external supports and the objective function used is dynamic compliance of structure. Solid Isometric Material with Penalty (SIMP) method is employed to solve the topology optimization problem. The optimal support locations are determined for cantilever beam and plate structures subjected to harmonic loads.

A. T. Korade, S. Rakshit

Seismic Behaviour of RC Building Frame Considering Soil–Structure Interaction Effects

Reinforced Concrete (RC) frame buildings constitute a large fraction of the urban building stock in India. During past earthquakes, a number of these buildings have been observed to suffer extensive damages. Although conventional code-prescribed seismic design methodology does not account for consideration of soil–structure interaction, the presence of soil can cause a significant change in the seismic behaviour of the buildings. The present article investigates the seismic behaviour of an RC building frame under the influence of nonlinear Soil–Structure Interaction (SSI). Finite element analysis of a five-storeyed building frame is carried out under applied ground motions to simulate the possible effects of earthquake shaking. Analysis of various response entities reveals the mechanisms by which the influence of SSI affects the structural behaviour. Moreover, the analysis demonstrates crucial aspects of the nonlinear behaviour and energy dissipation characteristics of the building frame under the influence of SSI. The study shows that seismic soil–structure interaction cannot be ignored, contrary to the present state of practice and guidelines of the design codes of various countries.

Nishant Sharma, Kaustubh Dasgupta, Arindam Dey

Inelastic Time History Analysis of Mass Irregular Moment Resisting Steel Frame Using Force Analogy Method

In this paper, inelastic time history analysis of a six-storey moment resisting steel frame adopted from a hospital building located in Woodland Hills California (Wong and Yang, J Eng Mech 125:1190–1199 [1]) has been investigated considering both material and geometric nonlinearities, via an implemented Force Analogy Method (FAM) Matlab code. The reference steel frame has been analyzed by considering Kobe earthquake time history as the input ground motion. Storey mass has been taken as the parameter to study the effect on the structural response (e.g., displacement, etc.). Profiles of elastic, inelastic, and total displacement components of floors have been examined when irregular mass is located at different floor levels.

S. S. Ningthoukhongjam, K. D. Singh

Modification and Modeling of Experiments with Bi-directional Loading on Reinforced Concrete Columns

Capacity evaluation of bi-directionally loaded column is important not only for the performance-based seismic design of structures but also for the estimation of structural damage. In this paper, an experimental study has been carried out on full-scale columns with different axial stress ratios, followed by the development of an analytical model to predict the lateral load response of the column under bi-directional loading after taking care of the effect of the functional interactions between the two loading actuators and the column specimen. These interactions, if not taken into account, result in apparent underestimation of ultimate strength and overestimation of maximum displacement capacity of the test specimen, thereby demanding unnecessary changes in model parameters for the purpose of calibration. It is also found that the analytical model accounting for the aforementioned functional interactions leads to a more realistic and different dynamic structural response from that obtained using the analytical model ignoring the interactions.

Subhadip Naskar, Sandip Das, Hemant B. Kaushik

Fatigue Life Estimation of an Integral RC Bridge Subjected to Transient Loading Using Ansys

Integral bridges are becoming popular day by day, as they are easy to construct and require lesser maintenance efforts due to absence of bearings. There is an increasing tendency to construct long-span bridges. However, due to movement restraints, fatigue stresses build-up that leads to a reduction in the useful life. In this study, an effort has been made to estimate the fatigue life of an integral bridge subjected to transient loads. In this paper, the results of transient analysis of an integral bridge of total length 156 m having five continuous spans with a maximum span of 40 m has been done using ANSYS. The roles of deformation and von-Misses stress that occur in the bridge have been found to influence fatigue life. Further, midpoint deflection in the longest span, its variation with loading history, and its influence on fatigue life have been analyzed and found to match satisfactorily with standard results, and the same process is applied on various length of a longer span.

M. Verma, S. S. Mishra

Free Vibration of Composite Sandwich Beams with Microstretch Viscoelastic Core

In the present work, we studied a sandwich beam which is made of two thin stiff layers on top and bottom and a microstretch viscoelastic core in the middle. Here, the top and the bottom stiff layers are considered as elastic, while the inner part is taken as microstretch viscoelastic material. The free vibration of this composite beam is investigated. Differential transform method is used for the solution. The values of the frequencies obtained for microstretch case are found greater than the classical ones, as it is expected. Besides, the minimum differences between the classical frequencies and deviated classical frequencies due to the microstretch core are getting bigger for the large loss factors.

S. Aydinlik, A. Kiris, E. İnan

Seismic Response Mitigation of Structure by Negative Stiffness Devices via Mid-Story Weakening

The optimal performance of the Adaptive Negative Stiffness Device (ANSD) assisted building system has been proposed to mitigate the seismic responses of 14-story building. In the proposed implementation, the building block above the ANSD-augmented story imparts the effect of a non-conventional Tuned Mass Damper (TMD) (with large mass ratio) on the lower block and is simultaneously imparted with the isolation effect due to ANSD induced flexibility. The ANSD composed of viscous damper in addition to their negative stiffness thereby helps in dissipating the input energy and controls the large displacement in the NSD. The optimal parameters are derived based on the optimal tuning and damping ratio obtained from a state-space analysis, considering non-classical damping. To check the efficacy, non-linear time-history analysis are performed subjected to a number of ground motions (from the SAC project) representing varying degree of hazard levels. Statistical analysis reveals that the proposed system is effective in reducing seismic responses compared to its uncontrolled counterpart.

Arijit Saha, Sudib Kumar Mishra

Development of a Novel Viscoelastic Nanocomposite and Investigation of Its Damping Capacity for Large Frequency Band

Polymer-based composites work well in both low- and high-temperature range and are suitable for a wide range of excitation frequencies. The high demand for such a material having good large frequency band damping has propelled the research of polymer-based composite with nanoparticle inclusions. Even though different combinations of micro-inclusion-matrix composites are available with good damping properties, a nanoparticle-based composite has wide potential because of the extraordinary behavior of the interphase region. This study explores the possibility of using different combinations and proportions of nanoscale inclusions for vibration control through the use of nanoparticle-reinforced composite materials. The multi-scale modeling of a representative volume element of viscoelastic nanocomposite has been carried out using the representative volume element (RVE) method for unit cell analysis. The periodic force boundary condition is applied to one of the faces of the unit cell at different frequencies. The viscoelastic properties of the polymer are modeled in terms of Prony series. Subsequently, the loss factor (tan δ) is estimated using the phase lag from the stress-strain curve obtained from the FE model simulation. For a quantitative comparison between numerical and experimental results, the fabrication of a nanocomposite beam is carried out (by sonication process) using different combinations of nanoparticle-matrix material with different volume fractions of inclusions in the composite. The cantilever nanocomposite beam is given an initial excitation and the resulting transient displacement is captured by a single point laser. The loss modulus of the nanocomposite is subsequently calculated using the logarithmic decrement technique. FE simulation results and the experimental results match well and show that the damping capacity of homopolymers can successfully increase by adding nanoparticles to control the vibration.

Nitesh Shah, Bishakh Bhattacharya, Husain Kanchwala

Effect of Pulse-Type Ground Motions on the Rocking Response of Rigid Blocks on Deformable Media

This paper studies the rocking behavior of rigid blocks resting on a deformable floor under pulse-type ground motions. The deformable floor has been simulated by a concentrated spring model and the friction as analytical friction considering Coulomb’s model. The importance of the residual part and pulse part of the ground motions in the rocking response of rigid blocks has been studied by considering 40 pulse-type ground motions. The study shows that, although the pulse part dominates the failure in most cases, in some cases the non-pulse residual part of the motion may be responsible for the failure of the blocks.

V. H. Sheikh, S. Mukhopadhyay

Vibration Control of Seismically Excited Adjacent Buildings Prone to Pounding by Use of Friction Dampers

Mitigation of pounding between closely spaced building structures, subjected to earthquake excitation, by interconnecting them by friction dampers is investigated. Considering the pounding force and damper frictional force, the non-linear equations of motion of two connected single-degree-of-freedom (SDOF) structural systems subjected to recorded earthquake base motions are formulated and solved for the stick and slip phases. The pounding and damper frictional forces are represented by the Hertzian impact model and by the Coulomb friction model, respectively. Different combinations of structural time periods are considered to examine the effect of the relative flexibility of the adjacent structures on the pounding occurrence and on the performance of the damper. Results indicate that by appropriately selecting the slip force in the friction damper, it is possible to completely mitigate pounding. However, this may entail an increased displacement of the stiffer structure over that of the uncontrolled response. It is seen that a judicious choice of the damper slip force will provide substantial pounding reduction, even in case of large earthquakes, while constraining the displacements to within the uncontrolled values.

N. K. Dutta, A. D. Ghosh

Influence of BNWF Soil Modelling on Dynamic Behaviour of Pile Foundation for RC Frame with Structural Wall

Multistoried Reinforced Concrete (RC) wall-frame buildings are nowadays frequently constructed in severe seismic zones due to their large lateral stiffness and lateral strength. Conventionally, the effect of soil–structure interaction (SSI) on the dynamic behaviour of a wall-frame structure is not considered in its seismic design. As a result, the considered system is stiffer as compared to the actual condition in which the pile-soil system imparts more flexibility and can induce nonlinear behaviour of piles through large deformations. Therefore, it becomes imperative to study the nonlinear behaviour of a wall-frame-pile-soil system. In this study, two different soil domains are created for the influence of soil–structure interaction on the response of the pile foundation, namely (i) the first model incorporating soil–pile interaction effect and (ii) the second model without considering the interaction effect. The response from two different soil domains is applied on a two-dimensional RC wall-frame. The soil-pile system for the RC building frame is modelled as Beam on a Nonlinear Winkler Foundation (BNWF). It is observed that after the application of ground motion, a significant bending moment is generated near the bottom of the pile and nonlinearity extends beyond 50% of the pile length. The observations suggest the necessity for further assessment of the state of the practice for simulating seismic soil–pile interaction.

A. Sinha, N. Sharma, K. Dasgupta, A. Dey

Aerospace Structures

Frontmatter

Control and Limiting Strategies for Random Vibration Tests on Spacecraft Subsystems

Controlled vibration tests on complex spacecraft subsystem some times present several challenges to test engineers. In such cases, adopting proper control strategy becomes crucial so that the test article or subsystem undergoes a vibration test as per the test profile while safeguarding the shaker system. This paper presents different control/limiting strategies that are adopted while conducting a vibration test on spacecraft subsystems considering the safety of the subsystems and shaker systems.

A. R. Prashant, K. Sreeramulu, B. R. Nagendra, S. Ramakrishnan, M. Madheswaran, V. Rameshnaidu, P. Govindan, P. Aravindakshan

Dynamic Characterization of Large Structures and Its Application to Solid Rocket Motor Testing and Launch

Launch vehicle stages and sub-assemblies experience severe dynamic loads due to extreme launch vibration environment, thrust oscillations from solid motors, etc. Launch vehicle/spacecraft structural members and ground support structures suffer higher dynamic stress levels when the excitation frequency of vibration environment matches with its natural frequency. In addition to this, pressure oscillations inherent of large solid rocket motors tends to generate thrust oscillations with magnitude up to 1% of mean thrust. True thrust oscillation component is essential in coupled load analysis (CLA) and also in deciding the control plant requirements of launch vehicle. However, during the static test, the measured thrust suffers the structural dynamics’ interactions of the test stand. To understand the behavior of structural members under a dynamic environment, its modal parameters, viz., natural frequency, modal damping and mode shapes need to be estimated. In the present paper, dynamic characterization of large structures is discussed which has applications to launch vehicles and solid motor testing. In the first part, the dynamic characterization of a large solid rocket motor ground static test stand is studied for estimating the actual thrust oscillations generated during the ground test. The force transfer function was obtained between the motor interface to load cells using experimental modal analysis with modal shaker-based excitation. From the force transfer function, actual thrust oscillations generated by the motor are determined. In the subsequent part of the paper, dynamic characterization of the entire launch vehicle (mass of 500 tons), using the transport vibration measurements was discussed. Vibration responses of the launch vehicle at different locations were measured using servo accelerometers and its modal parameters were derived from operational modal analysis. The mode shapes are compared with that of predicted natural frequency, which match quite well. The damping ratios obtained are essential for finite element model updating to estimate the dynamic loads on the launch vehicle.

Venkata Ramakrishna Vankadari, Dileep Pasala, Jopaul Ignatius, Sankaran Sathiyavageeswaran

A New Multi-shaker System Development For Testing Launch Vehicle Subassemblies

One of the major challenges in multi (dual)-shaker vibration testing of large launch vehicle subassemblies is to maintain phase and amplitude of dual shakers in a synchronous manner. Failing to maintain synchronous nature leads to catastrophic damage to the launch vehicle subassemblies as well as shaker systems. During the qualification and acceptance vibration testing of advanced launch vehicle subassemblies which are huge in size, the prime challenge faced in attaining synchronous phase and amplitude of the dual shakers with analog multi-shaker systems has been briefly discussed. From this basis, subsequently, a new digital multi-shaker system has been realized with enhanced features, viz., defining the frequency bands for correction, automatic correction of the deviations in phase and amplitude of the dual shakers, configuring the safety threshold limits for phase and amplitude deviations to prevent asynchronous movement compared to the existing analog system.

G. Meghanath, V. Venkata Ramakrishna, A. Veerraju, Jopaul K. Ignatius

Dynamic Characterisation as a Tool for Avoiding Vibration Related Problems

In aerospace applications, mathematical models used for the dynamic analysis of launch vehicles are validated through dynamic characterization tests for better confidence in the models. The models are being used for flight critical studies; hence, the accuracy of the models in predicting the behavior of the system correctly is essential. This paper describes the dynamic characterization tests used for validating the mathematical model of the system from a dynamics point of view. In the paper, tests on three different test specimens with different requirements and different modes of testing are presented. The objective of the tests is to mainly obtain the frequency, mode shapes of the specimen, and get an estimate of the damping of the system, if required. The test methodologies are dependent on the test article configuration, which includes its material, overall layout, attachment points, etc. In the three test cases presented, the first test was an impact hammer excitation test carried out with the test specimen suspended with slings. In the second test case, the test was carried out by mounting it over the slip table of a high capacity shaker, and provided sine & random excitation through the shaker. For the third case, the specimen was fixed rigidly at the base, and excitation was carried out with small capacity shakers to estimate frequency response functions (FRFs) at various points.

Ajay Kumar Panda, Asir Nesa Dass N, R. Balaji Srinivas, Arunkumar R, M. Vasudevan Unni

A Simplified Impact Damping Model for Honeycomb Sandwich Using Discrete Element Method and Experimental Data

Honeycomb sandwich laminates with aluminum and carbon fiber reinforce polymer (CFRP) face—sheets are widely used in spacecraft structures and aerospace industries. The damping behavior of such structures is reported to improve when the granular particles, called damping particles, are inserted in the honeycomb cells. The discrete element method (DEM) has been successfully used and found to give a reasonably accurate estimate of the impact damping. In DEM formulation, Newton’s laws of motion are used to obtain the equations of motions of each damping particle considering the contact forces from immediate neighboring particles and other sources, if any. The use of DEM for the real structure where the number of particles is of order 108 or more is inefficient and impractical to perform optimization. In this paper, a damping model dissipating equivalent energy is presented for a system consisting of a small honeycomb sandwich coupon filled with damping particles and has resonance frequencies beyond the bandwidth of the model. The coupon is subjected to a range of harmonic excitations (varying frequency and amplitude). The energy dissipated by the damping particles is estimated by DEM. The normal and tangential components of contact forces are modeled using Hertz’s nonlinear dissipative and Coulomb’s laws of friction, respectively. Then the parameters of the equivalent damper are obtained which dissipates the same energy. The damping model presented incorporates the effect of fill fraction, particle size, and material, as well as the amplitude and frequency of excitation. The comparisons of the DEM model for some of the load cases are done with the experimental data showing reasonably good agreement. The model presented could be readily incorporated in the FEM model like zero-stiffness proof-mass actuator, and the effect of impact damping can be studied without actually solving the DEM governing the motions of the particles.

Nazeer Ahmad, R. Ranganath, Ashitava Ghosal

Aeroservoelastic Analysis of RLV-TD HEX01 Mission

Study of Aeroservoelastic (ASE) interactions is of prime importance in modern aircrafts employing autonomous flight control systems. The complex nature of unsteady aerodynamic forces can induce adverse ASE coupling effects leading to mission failure. This study discusses the ASE analysis of Reusable Launch Vehicle Technology Demonstrator Hypersonic Experiment (RLV-TD HEX01) of the Indian Space Research Organisation (ISRO). Pertinent modeling philosophy adopted for various subsystems, analysis methodology, validations, and simulations carried out to establish closed loop stability of RLV-TD system is discussed in detail. The results of the study clearly indicate the absence of adverse modal coupling in the presence of unsteady aerodynamic and control forces. The existence of adequate closed loop damping for critical structural modes is established through simulations to ensure adverse interaction free environment in the experimental flight.

Mahind Jayan, P. Ashok Gandhi, Sajan Daniel, R. Neetha

Time Domain Aero Control Structure Interaction Studies of Indian Reusable Launch Vehicle

Reusable Launch Vehicle Technology Demonstrator Hypersonic Experiment (RLV-TD HEX01) mission of the Indian Space Research Organisation (ISRO), was the maiden flight which employed a winged body configuration. The vehicle faces multiple excitations during its atmospheric phase of flight. In this perspective, structural vibrations on the vehicle arising out of external excitations have to be adequately stabilized to prevent adverse vibrations. A flexible vehicle response analysis package: FLXTRJ-RLV was developed to assess the aero control structure interaction characteristics of the vehicle. Results of simulation studies ensures the increase in closed-loop damping and improvement in disturbance rejection characteristics of the vehicle, thereby reducing the in-flight loads acting on the vehicle. Comprehensive post-flight analysis studies were carried out on the flight-experienced responses. The flight observed rates highlighted a benign interaction-free environment during the ascent phase of flight.

P. Ashok Gandhi, Mahind Jayan, Sajan Daniel, R. Neetha

Vehicle Dynamics

Frontmatter

Polynomial Neural Network Based Stochastic Natural Frequency Analysis of Functionally Graded Plates

The present article deals with the stochastic approach for natural frequency (NF) analysis of functionally graded (FG) plates by employing polynomial neural network (PNN) surrogate model combined with finite element (FE) method. The surrogate model for NF analysis of FG plates is validated with the original FE method. Both individual and mixed variation of material properties are taken into account. The present PNN model significantly rises the computational efficiency, and the computational cost decreased in comparison to Monte Carlo Simulation (MCS).

Pradeep Kumar Karsh, Abhijeet Kumar, Sudip Dey

Comparative Study Among Different Vehicle Models in Case of High-Speed Railways and Its Experimental Validation

A comparative study of different existing vehicle models like moving load, moving mass, discrete sprung mass and moving system are presented for addressing problems related to high-speed railways. Finite element framework is used, where the bridge deck is modelled using Bernoulli–Euler beam elements. MATLAB code has been developed for different vehicle models to obtain the bridge and vehicle responses. Such responses of bridge and vehicle, obtained for different vehicle models, show that the prediction of bridge responses can be reliably done using moving load model. On the other hand, there is a significant underestimation in the calculation of vehicle body acceleration, if one goes with the sprung mass model instead of 10 DOFs interaction model. Vehicle’s pitching effect might be the reason behind such underestimation. In addition to that, for the purpose of validation of such 10 DOFs vehicle-bridge interaction model, the response of bridge obtained through such interaction model are compared with measured response data on an existing steel girder bridge. A good matching between experimentally and theoretical evaluated data is observed, which indicates the suitability of the adopted Finite Element model in the practical field.

B. Pal, A. Dutta

Evaluation of Ride Comfort in Railway Vehicle Due to Vibration Exposure

Air spring is one of the important components in the modern railway vehicle, which affects passenger comfort. It comprises both stiffness and damping and placed between the bogie and car body. The main function of air spring is to isolate vibration, which transmits from bogie frame to car body. Deep knowledge is essential in order to study the influence of the parameters on the comfort. The vertical stiffness of air spring is calculated from force–displacement hysteresis loop, and the influences of stiffness at different frequencies are estimated for different preloada. Finally, comfort felt by the passengers is calculated by Sperling’s ride comfort for both straight and curved tracks. For better performance, optimization of preload along with the effective area of air spring is necessary.

S. Pradhan, A. K. Samantaray

Non-linear State Space Formulation Simulating Single Station Ride Dynamics of Military Vehicle

Military vehicles are generally equipped with hydro-gas suspension systems that exhibit better shock-absorbing capability over drastic dynamic environments compared to linear suspension. In order to implement suspension semi-active/active control in the future, it is required to develop the mathematical model of the vehicle using non-linear state space approach by incorporating the hydro-gas suspension trailing arm dynamics in the governing equations of motion. The present study formulates the non-linear state space approach which simulates single station ride dynamics of military vehicles. Incorporating the developed trailing arm kinematics and non-linear suspension characteristics, non-linear state space approach has been used to formulate the sprung and unsprung mass governing equations of motion. The multi-body dynamics model for the single station is established in MSC.ADAMS in order to validate the non-linear state space model. The mathematical model is solved using MATLAB and compares well with the multi-body model simulations. The entire military vehicle non-linear state space model can also be developed which would be suitable for carrying out vehicle dynamics control studies with active or semi-active suspension systems.

Saayan Banerjee, V. Balamurugan, R. Krishna Kumar

Delamination Growth Behaviour in Carbon/Epoxy Composite Road Wheel of an Armoured Fighting Vehicle Under Dynamic Load

The primary objective of this paper is to find the threshold size of delamination as well as critical delamination location for composite road wheel of the Armoured Fighting Vehicle (AFV) under severe loading condition to which an AFV is subjected to, during the operation. The composite material considered in the study is carbon/epoxy composite (AS4/3501-6). Finite element analysis was performed using Ansys Workbench 17.2 to predict the delamination location and to study the delamination growth behaviour. The delamination onset spot was predicted using the stress-based failure criteria developed by Puck. Various delamination sizes were modelled at the critical location and the Strain Energy Release Rate (SERR) with respect to the fracture modes, viz., mode I, mode II and mode III were found using Virtual Crack Closure Technique (VCCT). The 3D failure criterion which was developed based on Benzeggagh–Kenane (B-K) mixed-mode I and II failure criterion was employed to predict the delamination growth based on which the threshold delamination size was found.

Sarath Shankar, Subodh Kumar Nirala, Saayan Banerjee, Dhanalakshmi Sathishkumar, P. Sivakumar

Torsional Vibration Analysis of Crank Train and Design of Damper for High Power Diesel Engines Used in AFV

This paper analysed the torsional vibration of a 12-cylinder V-engine used for tracked vehicles and design of a suitable damper to reduce the amplitude of vibration. The entire engine crank train was modelled analytically, and mass properties are calculated using CREO software. The crank train was analysed using ABAQUS software for calculating the natural frequency of the engine. The results of the analysis were compared and validated using Holzer’s method. Suitable damper characteristics were designed using ABAQUS and MATLAB software to reduce the amplitude of vibration. Physical dimensions such as damper inertia, damper size, damping ratio and damping coefficient of the damping medium were determined to achieve the designed damper characteristics.

N. Venkateswaran, K. Balasubramaniyan, R. Murugesan, S. Ramesh

Fluid Structure Interaction

Frontmatter

Dynamic Behavior of Swaged Plates in Water-Immersed Condition

Fuel assemblies with swaged thin fuel plates are often used in high flux research reactors. In swaging operation, the fuel plates are inserted into grooves created all along the length of the plates and then the swage is rolled such that the movement of the plates is restricted. This results in a CFCF-type condition for each fuel plate. It is important to note that the boundary condition developed using swage joints is different in comparison to that of a welding joint where all the six degrees of freedom get fixed. The present work deals with the investigation of vibration characteristics of swaged plates in air as well as in water-immersed conditions for different water immersion ratios using a commercial code. This involves a realistic representation of a swage joint using a finite element model further employing coupling techniques to achieve fluid–plate interaction.

G. Verma, S. Sengupta, S. Mammen, S. Bhattacharya

Love Wave Propagation in an Anisotropic Viscoelastic Layer Over an Initially Stressed Inhomogeneous Half-Space

Love-type surface wave in a model comprising of an orthotropic viscoelastic layer supported by a half-space is investigated. The layer and half-space both are heterogeneous, and the half-space is in the state of initial stress. Employing relevant boundary conditions, frequency equation is derived, based on which numerical computations are carried out to analyze the impact of different parameters on Love wave speed. It is discovered that dissipation function and heterogeneity of the layer and initial stress and heterogeneity of the half-space has a substantial effect on phase velocity.

Bishwanath Prasad, Prakash Chandra Pal, Santimoy Kundu

Propagation of Edge Wave in Homogeneous Viscoelastic Sandy Media

The objective of this work is to investigate the propagation characteristics of edge wave in a composite structure comprised of two uniformly homogeneous viscoelastic incompressible sandy plates of finite width and infinite extent. An analytical approach is used to deduce the closed form of frequency equation concerning to phase as well as damped velocities and analyzed the various affecting parameters. The effects of influencing parameters such as viscoelastic parameter, sandy parameter of both plates and wave number on the phase as well as damped velocities of edge wave are depicted graphically with the help of numerical simulation. It has been found that all the affecting parameters have significant effects on the edge wave propagation in the composite structure.

Pulkit Kumar, Amares Chattopadhyay, Abhishek Kumar Singh

Love-Type Wave Propagation in Functionally Graded Piezomagnetic Material Resting on Piezoelectric Half-Space

The propagation of Love-type waves in functionally graded piezomagnetic layer lying on a piezoelectric half-space is studied. We have considered the interface between the Functionally Graded Piezomagnetic Material (FGPM) layer and piezoelectric half-space as imperfect and the imperfection is taken in linear form by spring model. The exponential variation is taken for the material parameters of the layer along the thickness direction. The dispersion relation in determinant form has been obtained for both magnetically open and short cases. Numerical computation and graphical demonstration have been carried out to observe the effect of gradient factor, layer’s width, and the interfacial constant on the phase velocity of Love-type waves. For validation, the present study is matched with classical Love wave result. The application of the present work may be found in designing and optimization of Surface Acoustic Wave (SAW) devices and sensors.

J. Baroi, S. A. Sahu

Fluid–Body Interactions in Fish-Like Swimming

The present study focuses on formulating a fluid–structure interaction (FSI) framework by coupling a finite element analysis (FEA) based structural solver and a lumped vortex method (LVM) based potential flow solver to study the coupled dynamics involved in the undulatory and oscillatory swimming of fishes. The caudal fin of a carangiform fish is modelled as a continuous cantilever beam with a periodic support motion. The effect of the actuation frequency on the thrust coefficient is investigated. A significant increase in the aerodynamic thrust is noticed for the support motion frequencies nearing to the structural natural frequencies of the beam. Next, the whole fish body, considering the full-body undulations, is modelled as a continuous free-free beam. This model incorporates a time-dependent actuating moment varying along the length of the body which can be attributed to the muscle moments generated by the fish. A parametric study is carried out to obtain maximum thrust output for the muscle power input in terms of the actuation moment. It is observed that the generated thrust increases significantly when the frequency of the actuation moment approaches towards the natural frequencies of the free-free beam. A comparative study of the average thrust coefficient is carried out for these two cases.

Dipanjan Majumdar, Chandan Bose, Prerna Dhareshwar, Sunetra Sarkar

Comparison of Stochastic Responses of Circular Cylinder Undergoing Vortex-Induced Vibrations with One and Two Degrees of Freedom

Vortex-induced vibration of a circular cylinder is a major research topic due to the immense applications they have in daily and industrial scenarios. Large numbers of studies have been conducted in this area in numerical and experimental domains with focus on understanding the response types, understanding the range of lock-in, the flow behavior, etc. However, most of the studies till date have been done in a deterministic environment; on the pretext that all factors about the incoming flow and input parameters are exactly known. In real-time flows, there can be a significant amount of uncertainties associated with various system parameters, which are traditionally not taken into consideration for the system. For example, randomness associated with the incoming flow might have significant effect on the associated dynamics. In this study, we do a stochastic modeling on a circular cylinder exhibiting free vibrations with one and two degrees of freedom. For this, we use Duffing Van der Pol combined system and impose fluctuations at every time step in the input flow by modeling them through a uniform distribution. The transverse oscillations of each of the cases under the presence of noise are individually studied. It is seen that noise brings in new dynamical states to the cylinder response compared to the deterministic cases. It is observed that there is a considerable difference between the responses of the single degree of freedom and two-degree of freedom cylinder. These qualitative differences are investigated in detail in the current study.

M. S. Aswathy, Sunetra Sarkar

An Exact Solution for Magnetogasdynamic Shock Wave Generated by a Moving Piston Under the Influence of Gravitational Field with Radiation Flux: Roche Model

An exact solution for the propagation of shock waves in an ideal gas with radiation heat flux and magnetic field under the impact of gravitational field is obtained. A piston in motion with time obeying power law drives out the shock wave. The unsteady Roche model is comprised of a gas dispersed with spherical symmetry around a nucleus consisting of a large mass. The density and magnetic field are presumed to vary according to power law in the undisturbed medium. The flow variables fluid velocity, pressure, density, magnetic field, and radiation flux tend to zero as the piston is approached. The effects of change in values of Alfven Mach number, gravitational parameter, and initial density variation exponent on the flow variables are worked out in detail. The increase in value of Alfven Mach number or gravitational parameter has a decaying effect on shock strength.

G. Nath, Sumeeta Singh

Isogeometric Collocation for Time-Harmonic Waves in Acoustic Problems

Isogeometric Analysis introduced by Hughes et al. [1] has gained importance in the recent times due to its ability to capture accurate solutions and exact geometry representations. In the present study, IGA-Collocation is extended for oscillatory problems in acoustics. Numerical solutions of oscillatory problems often suffer from numerical dispersion errors, which demands use of minimum of ten nodes per wavelength or higher order bases. But employing higher order bases in IGA based on Galerkin approach (IGA-G) is computationally expensive. To overcome this issue, we employed IGA based on Collocation (IGA-C) [2] which is often regarded as a rank sufficient one-point quadrature scheme and has the potential to reduce the computational cost. In the present study, IGA-C with higher order bases is employed for solving rectangular waveguide and oscillating cylinder problems with different wave numbers. The performance of IGA-C is compared with the IGA-G in terms of efficacy and computational time. From the results, the potential of IGA-C is clearly observed in solving wave problems.

M. Dinachandra, S. S. Durga Rao, R. Sethuraman

Effect of Seismic Excitation on Bubble Behavior in Liquid Between Fuel Rods of Boiling Water Reactors

Behavior of gas–liquid two-phase flow of liquid–vapor behavior is unknown under the seismic conditions. Mainly, fluctuation of void faction is an important factor for the safety operation of the nuclear reactor. In this work, the bubble behavior in between two fuel rods under seismic excitation has been investigated through numerical simulation. Initially water-sloshing problem is solved for the purpose of validation. Then, bubble behavior is analyzed with and without seismic excitation. It is found that the bubble coalescence time with free surface and pressure exert on fuel rod, which is considered as important parameters in the safety of the reactor, depends on bubble depth and seismic excitation.

S. P. Chauhan, M. Eswaran, G. R. Reddy

Experimental Study on Shallow Water Sloshing

Sloshing of liquid in a partially filled container, subjected to higher amplitude of dynamic load, is a complex phenomenon. In shallow water conditions, the natural frequency of sloshing depends on the amplitude of excitation. Sloshing frequency tends to change with increase in amplitude of excitation. The change in natural frequency is critical if we use the sloshing tank as a passive damping device, such as Tuned Liquid Damper (TLD) for offshore structures or onshore structures. A small change in sloshing frequency in TLD may affect the structural vibration control significantly. Therefore, it is essential to comprehend the natural frequency of shallow water sloshing. Experimental study is one of the best ways to understand the physical insights of change in sloshing frequency. Experimental studies are conducted to study the jump in sloshing frequency at different excitation amplitudes. Several rectangular tanks (1163, 1064, 951, and 844 mm) under different water depths (60, 50, and 40 mm) are taken for the study to generalize the results. The liquid tank is mounted on a uni-directional horizontal shake table, which is subjected to simple harmonic motion. The amplitude of excitation varied from 5 to 50 mm. A single capacitance-type wave probe is used at the end of the tank wall to measure the wave surface elevation. The wave elevation increases as the excitation frequency reaches toward the natural frequency of sloshing. The measured liquid sloshing frequency, at the resonance condition, is considered as actual sloshing frequency of liquid in tank. This sloshing frequency changes with the amplitude of excitation and shows the sudden jump in frequency from a particular amplitude of excitation. The objective of this paper is to generalize the relation between the jump frequency ratio (ratio of jump frequency to linear frequency) and the non-dimensional amplitude of excitation.

Saravanan Gurusamy, Deepak Kumar
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