Recent Advances in Computational Mechanics and Simulations

Instabilities in nano-sized, pressurized spherical shells are important in view of their recent applications in nanotechnology and biological systems. The mechanics in such length scale is often described by nonlocal field theory. However, analysis of buckling of a pressurized spherical shell is involved, which becomes even more complicated for nonlocal media. Such analysis is largely simplified by shallow shell representation, assuming short wavelengths of the buckling modes. In this paper, the shallow shell theory is extended for the nonlocal pressurized spherical shell. The governing equations for static instability are derived. The solution of the linearized equations is obtained in closed form, providing the critical pressure for buckling. It is observed that nonlocality reduces the critical load and the reductions become more for higher modes and increasingly thinner shell. A constricting relationship between the wavenumbers of the buckling modes also appears to be modified by the nonlocal lengths scale parameter. This results in increasing number of wavenumbers and decreasing dimension of wavelengths. The latter fact provides additional justification for the shallow shell representation adopted herein.

In this paper, newly developed single variable new first-order shear deformation nonlocal beam theory is utilized for performing flexure of shear deformable isotropic rectangular nanobeams under the action of sinusoidally distributed transverse load. This theory is applicable for flexure of linear isotropic nanobeams undergoing small deformations. Displacement functions of this theory give rise to constant transverse shear strain through the beam thickness. Hence similar to nonlocal Timoshenko beam theory, this theory requires shear correction factor. In this theory, nonlocal differential stress-strain constitutive relations of Eringen are utilized in order to take into account size-dependent effects which govern mechanical behavior of nanobeams. These nonlocal differential constitutive relations relate not only the beam axial stress with the beam axial strain but also the beam transverse shear stress with the beam transverse shear strain. Governing differential equation of this theory is obtained by utilizing beam gross equilibrium equations and it has a strong resemblance with governing differential equation of nonlocal Bernoulli-Euler beam theory. Profiles of non-dimensional beam transverse displacement for various values of nonlocal parameter of Eringen and beam thickness-to-length ratio in case of simply supported, clamped, and cantilever isotropic rectangular nanobeams under the action of sinusoidally distributed transverse load are presented. Effect of nonlocal parameter and beam thickness-to-length ratio on maximum non-dimensional beam transverse displacement for abovementioned cases of beams is presented. Obtained results are compared with corresponding results obtained by utilizing nonlocal Timoshenko beam theory so as to demonstrate the efficacy of single variable new first-order shear deformation nonlocal beam theory.

In this manuscript, we study the tribological characteristics of a carbon nanotube (CNT) moving on a graphene sheet using molecular dynamics simulations. The CNT is driven by a force acting due to a spring that itself is pulled with a constant velocity. While the interaction between the carbon-carbon atoms of both CNT and graphene are modeled using Tersoff potential, the cross-interaction between the carbon atoms of CNT and those of graphene are modeled through the Lennard-Jones potential. A dynamics based scheme is proposed in this manuscript that helps in determining the different regimes of the moving CNT. Using the proposed scheme, we show that the tribological and dynamical characteristics of the CNT-graphene system depend on the velocity with which the spring is pulled—the stick-roll motion of the CNT at low pulling velocity changes to a combination of rolling-sliding at moderate pulling velocity. Subsequently, one observes sliding motion of CNT at large pulling velocities. Further, in order to elucidate the role of thermal fluctuations we study the CNT-graphene system at very low (1K) and very high temperatures (300K). The results indicate that the tribological characteristics depend on the interaction of the CNT-graphene system with the temperature of the surrounding environment. At high temperature, thermal fluctuations are high and these fluctuations overshadow the normal dynamics of the CNT-graphene system. Our results suggest that it is possible to minimize frictional losses in the CNT-graphene system by suitably altering the driving forces.

The rising demands for high energy storage systems with greater energy and power densities than the current, commercial ones, have moved our interest toward low-weight electrode materials. Silicon, with a very high theoretical capacity of 4200 mAh/g, is the best replacement for conventionally used graphite (372 mAh/g) as the anode material for lithium-ion batteries (LiBs). The drawback associated with the usage of silicon is that, in a fully lithiated state, silicon expands volumetrically up to more than three times its original volume. The advancement in manufacturing technology has given the researchers the required impetus for exploring and exploiting the various rewards of nano-technology. The use of nanostructured Si anode particles evades few major problems satisfactorily, without compromising with the capacity of the battery. As we venture into the lower dimensions, the ratio of surface to volume increases and hence, the surface effects become more prominent. The present work caters to developing a surface stress formulation for the specific case of an annular/hollow cylindrical silicon anode particle. The formulation is validated with the pre-established results examining the effects of surface stress on diffusion-induced stresses in anodes consisting of spherical nanoparticles. It has been observed that surface stresses have a relaxing effect on bulk stresses. Here, relaxation refers to a shift in the stress trends in the negative (compressive) direction. With a decrease in the initial size (radius of curvature) of the cylindrical particles, the surface stress increases, thus increasing the extent of this relaxation. It is further affected by the rate of influx of lithium atoms. With an increase in the influx rate, surface stress increases. The surface stresses also affect the plastic stretches occurring in a particle, beyond the yield stress limit. Although the present discussion is limited to the context of lithium-ion batteries, the formulation can be generalized to assess the surface stress effects in axisymmetric nanostructured particles in any chemo-mechanical environment, undergoing finite deformation.

Single-Wall Carbon Nanotube–Aluminum (SWCNT–Al) composites are very beneficial from the structural point of view due to their considerable load-bearing capacity and high specific strength. In this study, the effect of various parameters such as length, diameter, and volume fraction of SWCNT on Young’s Modulus and stress–strain behavior of SWCNT reinforced, Al matrix composite has been investigated by molecular dynamics simulation to quantize the strength of the SWCNT–Al composites. It has been observed that Young’s modulus of SWCNT–Al composite was enhanced by 75.6 and 23.50% as compared to pure aluminum by reinforcing 11.75 volume% of zig-zag (20,0) and 8.81 volume% of armchair (10, 10) SWCNT in Al matrix, respectively. The maximum Young’s modulus of SWCNT–Al composite was found for SWCNT diameter ranging from 13–15.5 Å. The ultimate tensile strength of SWCNT–Al composite was found to decrease with an increase in the diameter of SWCNT (armchair). The maximum enhancement in the tensile strength was 14.5%, as compared to pure Al, when an armchair (2, 2) SWCNT was reinforced in Al. There was insignificant improvement in the ultimate tensile strength with an increase in the length of SWCNT. The above study would be beneficial for the design of high strength SWCNT–Al composites.

Numerous road accidents are reported every year amounting to huge loss in lives and properties. This calls for improving the crashworthiness of vehicles which can be achieved by employing lightweight materials with excellent energy absorbing capacity. Thereby, development and characterization of these materials has become need of the hour. In the present investigation, a finite element model of drop weight impact test is developed using LS-DYNA® to study the energy absorption characteristics of aluminum foam reinforced with carbon nanotubes. Herein, hammer is modeled using bilinear material model, and foam is modeled using crushable foam material model. Effect of drop height, density, and foam skin is investigated considering the energy absorption of foam used in this study. The behavior of foam is evaluated in terms of reaction force, displacement–time history, and energy absorption for all the velocities considered herein.

This study aims to determine the effect of interfacial crack on mixed-mode stress intensity factor and prediction of bone–cement interface failure of the cemented acetabular component. Three-Dimensional (3D) Finite Element (FE) model of implanted pelvic bone was developed based on the CT-scan data of the 62-year-old patient. To understand the influence of interfacial crack, edge and center crack was considered at the bone–cement interface in all four locations (superior, inferior, anterior, and posterior) of the cemented acetabular component. After seeing the possibilities, the center crack was considered in the coronal and sagittal plane; however, edge crack was considered in the sagittal plane only. 2D cracked models were developed based on the FE model and solved using the Element Free Galerkin Method (EFGM) by considering a rectangular section in the superior, inferior, anterior, and posterior locations. Interface failure was predicted in terms of mixed-mode Stress Intensity Factor (SIF). The stress values obtained from FE analysis was transferred at the cut boundary of the rectangular section and considered as mixed-mode loading condition to determine the mixed-mode SIF in the superior, inferior, anterior, and posterior location at the bone–cement interface using EFGM. The results of our study show that anterior location seems to have more chances of failure because SIF in the anterior location is found to be higher as compared to other locations (superior, inferior, and posterior). The minimum value of mixed-mode SIF was found in the superior location for a center crack; hence, the superior location has a minimum chance of failure as compared to other locations. For edge crack analysis, inferior is the safest location as compared to other locations. The chances of the sliding mode of fracture (mode-II) increase in edge crack analysis.

The Left Anterior Descending Artery (LAD) of a human arterial tree is modelled based on an analytical equation for various occlusion cases varying from 40 to 70%. The length of the lesion is also considered from 1 to 5 cm. Numerical simulation of a stenosed coronary artery for different occluded cases is carried out using 1D equations. The unknown variables, area and velocity are obtained from the characteristic variables w1 and w2 which are the solutions of a characteristic system of equations corresponding to the 1D model. A realistic pressure waveform is given at the inlet and a resistance model with zero reflection coefficient is considered at the outlet. Numerical investigations are carried out for one heart cycle comprising of systole and diastole and the 1D equations are solved using the locally conservative Galerkin method. The length of the lesion has clinical significance in the coronary artery which is graded as intermediate. The effect of occlusion percentage and lesion length on the FFR value and haemodynamic parameters is studied.

Synthetic signals that represent fatiguing contractions of biceps brachii muscle are generated in this work using a comprehensive mathematical model. These signals are the biomarkers of muscle electrical activity that could be recorded non-invasively on the skin surface using Surface Electromyography (sEMG). The important components of the adopted synthetic sEMG model are current source, volume conductor, motor unit recruitment, and firing behavior functions. For this study, the amplitude (A) and scaling factor (λ) of the current source function is selected appropriate to fatiguing conditions. Further, tunable Q-wavelet method is applied to compute the frequency range associated with fatigue in the synthetic signal. The resultant wavelet coefficients are obtained using multirate filter bank where the scaling factors α and β are chosen so as to meet the anticipated Q-factor and the ranges of frequency bands. The results show that synthetically generated signal is able to truly represent fatiguing and nonfatiguing conditions. The amplitude-based features of tunable Q-wavelet coefficients are able to identify the characteristic changes associated with varied fatiguing conditions. Model generated frequency responses in fatiguing conditions are in agreement with the experimental results reported elsewhere. As fatigue is a temporary failure of skeletal muscles to maintain a required force for the accomplishment of a particular task, the model proposed here could be used as a validation of sEMG measurements in health and disease.

Biological tissues and biopolymeric gels are considered as saturated biphasic structures. Diffusion of interstitial fluid through porous space is a key phenomenon for any biphasic system. Recent studies demonstrated deviation from ideal Fickian diffusion in various complexly structured porous media and this anomaly has been attributed to the fractal topology of the pores. In this study, an attempt has been made to reformulate the standard finite poro-elastic model for a fractal porous media. For this purpose, a fractal order Darcy’s law has been imposed and an appropriate u-p formulation is obtained. Numerical simulation schemes have been developed for two different confined compression scenarios. The results of simulations show that, with ramp and hold protocol, the transient response of the proposed model is influenced by the fractal order but the equilibrium values coincide with the response of an integer-order model. Creep compliance is observed to be inversely proportional to the fractal order of diffusion, which is a consequence of increased drainage rate with a lower order gradient of hydraulic head. A comparison with existing poro-hyperelastic model shows that the proposed fractal poro-hyperelastic model has an increased sensitivity to capture the deformation rate effects. The model has been validated against the results reported in earlier studies with the aid of appropriate model fitting techniques. The proposed model might be useful in modelling biphasic materials in various domains where a hierarchical structure of pore space is apparent, such as tissue ensembles and polymeric gels.

In neurosurgery, brain retraction technique has become popular in the field of image-guided procedures for intracranial operations such as in brain tumor, cerebral aneurysms, cerebral hematoma, etc. Brain retraction is performed for adequate exposure during surgeries as such procedures require consistent retraction. This causes several local brain contusions which limit the accuracy of the image-guided neurosurgical system. Therefore, there is a need for training in this field to enhance the efficiency of the procedure. In this study, we present a 3D finite element brain model, segmented from human head magnetic resonance images, in the visco-hyperelastic framework. The numerical model is used to predict the deformation and stress fields within the brain during brain retraction. The brain was retracted by 5 mm and retained at that position for 30 min. It was observed that during this period, the retraction pressure decreased to 30% of the maximum pressure level generated due to interhemispheric retraction. The results show that brain retraction can be performed continuously up to 30 min without any risk of local brain contusions or postoperative complications. Finally, through a combination of judicious retraction and rigorous preoperative planning, a drop in the morbidity rate due to brain retraction is expected in the future. This technique can be used for preoperative effective planning and training, especially in minimally invasive brain surgeries.

Notch stress intensity factors (NSIFs) play a critical role in the brittle fracture assessment of structures and components containing sharp V-notched. On the other hand, four-point bend (FPB) specimens with sharp V-notches are widely used experimental specimens to study the fracture of brittle materials. In the past, the accurate estimation of the mixed mode (I/II) NSIFs attained great importance for the failure analysis of the FPB specimens. In this paper, a recently developed collocation technique is used to determine the mixed mode (I/II) NSIFs of the verity of the FPB specimens. In this technique, the notch flank finite element displacements are utilized to obtain the mode I and mode II NSIFs. The NSIFs calculated using the present technique are then converted to dimensionless parameters called notch shape factors. The mixity ratio from pure mode I to pure mode II is also provided in the present analysis. The results obtained in the present investigation are compared with the results available in the literature. A good agreement has been observed between the present and the published results. Some new results have also been reported in the present work.

Non-classical beams have vast applications in NEMS/MEMS devices where scale effects are predominant, keeping these applications in mind, the present manuscript studies about the wave dispersion behavior of non-classical beam structures. Governing equations and corresponding boundary conditions for the non-classical Euler-Bernoulli & non-classical Timoshenko beam theories are derived to study the wave propagation characteristics. Time domain equations are converted into frequency domain using fast Fourier transform. Spectral finite element method (SFEM) formulation is implemented for non-classical beams to study the dynamic response of these beam structures in frequency domain. Spectrum and dispersion curves are studied with respect to scale coefficients along with the dynamic stiffness variations in the beams. Numerical experiments are conducted to identify the scale effects on dynamic wave propagation behavior of beams with the consideration of asymptotic frequencies of tera-hertz level. Exhaustive results are presented to understand the complete dynamic wave propagation behavior of these non-classical beams. The presented results are very useful in the design of NEMS/MEMS devices where the beam like elements are critical.

In this paper, finite element simulations are used to estimate the fatigue life of big turbo-generator shaft in uncontrolled and controlled system. The torque generated by the synchronous generator under loaded condition is analyzed for various types of electrical faults. The dq0 approach is used to model synchronous generator connected to an infinite bus. The torque outcome of loaded synchronous generator under various electrical faults is numerically simulated using MATLAB. The turbo-generator shaft is modeled using finite element formulation using different elements, i.e., solid cylindrical element, hollow cylindrical element and tapered element. The coupled dynamic MDOF equations are solved numerically to estimate the torque variation in shaft. The numbers of stress cycles are calculated using Rain Flow Counting method using stress at critical nodes of turbo-generator shaft. Further using piezoelectric sensor and actuator an active control system is achieved to reduce the vibrations produced in the shaft due to various faults. A closed-loop system is analyzed numerically using proportional and velocity feedback. The results of uncontrolled and controlled system are compared and vibrations in the controlled system found are to be reduced significantly using PD control law. Comparison of fatigue life generated shown that critical stress of the shaft can be reduced effectively in controlled system.

In this work, a combined methodology of continuum damage mechanics (CDM) and extended finite element method (XFEM) is used to predict the complete life of a component under creep environment. In this methodology, the life of component is predicted through CDM while XFEM facilitates the modeling of crack propagation. First, the nucleation of crack is simulated through CDM and FEM. Then, the combination of CDM and XFEM is adopted to estimate the remaining life during crack propagation. The elasto-plastic creep analysis is performed under plane strain condition. Liu–Murakami creep damage model is implemented to determine the creep strains and damage variable. The complete creep life of 316 stainless steel specimen is estimated at 550 °C. The present study establishes the effectiveness of propounded methodology in predicting the complete creep life of a component.

Hydrogen absorption can deteriorate the mechanical properties of the material at high temperature and high pressure. This deterioration phenomenon, termed as hydride-induced embrittlement, involves the simultaneous operation of diffusion of hydrogen, precipitation of hydride, mechanical deformation, and fracture in the material. In this work, hydride-induced embrittlement is modeled at the crack tip by coupling of the hydrogen diffusion and mechanical deformation in the extended finite element method (XFEM) framework. XFEM is the most suitable method to model the cracks in the coupled problems because it does not require conformal mesh and re-meshing for crack growth. The chemical potential required for hydrogen diffusion in the crack tip region depends on the hydrostatic stress gradients. The effect of hydride-induced embrittlement on the crack tip of edge crack specimen is performed in the present work. The formulation consists of two steps—first step is to determine the hydrostatic stress field from the mechanical deformation process which is used in second step to evaluate the hydrogen concentration, hydride fraction, and stress triaxiality. This is an iterative process applied at each time interval until the solution converges. The numerically obtained values of stress trace in the hydride precipitation zone are compared with the literature, and are found in good agreement.

Plastic deformation in metals and their alloys results due to the motion of large number of dislocations. Grain Boundaries (GB), by affecting various aspects of dislocation motion, add to the complexity. Classical two-dimensional (2D) Discrete Dislocation Dynamics (DDD) framework was extended to include Grain Boundaries (GB) to study the deformation in a polycrystalline metallic material and the role played by the grain boundaries therein. During plastic deformation, GBs interact with dislocations, altering their natural course, thus affecting the macroscopic mechanical response of the material. Grain boundaries are qualified as hard and soft based on whether they hinder the dislocation motion by acting as obstacles or allow the dislocations to pass through them. A polycrystalline DDD framework was developed to account for these effects in order to model the plastic deformation in the material. The study considered an annealed material with a random distribution of Frank-Read sources and no initial dislocations distributed in the sample. Dislocations were nucleated from the Frank-Read sources when the stress at the location of a source reached a critical value. Obstacles that act as pinning points were distributed randomly in the specimen. Three-dimensional effects like junction formation that account for formation of junctions, which in turn give rise to stage-II hardening were accounted for. Square and rectangular grain morphology was considered to generate mechanical response from the specimen under plane strain deformation.

In this work, effective properties of two-scale viscoelastic composite are estimated. Matrix is taken which consists of two types of inclusions: pores and a porous viscoelastic phase. Effective viscoelastic properties are obtained as a function of volume fractions of two phases dispersed in the medium. The analysis is carried out for small deformations considering the material behavior to be linear.

The goal of this study is to develop a theoretical and numerical framework to study the deformation response of shape memory polymer (SMP) composite structures. SMP materials have the ability to undergo deformation into a compact volume, which can later be recovered to transform back into its original shape. This physical phenomenon can be achieved by the application of an external stimulus in the form of mechanism driving forces induced through hygro/thermo-mechanical cycle, electromagnetism, chemical reactions, and photo-activity. This ability to undergo shape change and recovery enables it to be considered as a candidate material for morphing and self-deployable applications in aerospace structures. However, it does not possess high strength and stiffness expected from materials used in aerospace structures. This drawback can be overcome by reinforcing it by fibers. The focus in the available literature has been mostly on the development of an appropriate constitutive form to capture the deformation response of SMP materials subjected to different stimuli. Developing a modeling framework, which can aid in the design of SMP-based structures, has not received much attention. This work focuses on addressing these outstanding issues. In particular, the focus was on the development of an analytical and numerical framework to analyze the behavior of SMP sandwich structures to assess their feasibility as potential self-deployable and morphing structures. When compared to a shape memory alloy, the findings reveal that SMP composites can provide the necessary stiffness for structural applications without significantly compromising on the recovery rate.

Sandwich panels have been widely used as lightweight energy absorber for several decades now. Core materials such as woods, honeycombs, and foams, have various engineering applications from wind turbine blades to aerospace frames. The core material plays an essential role in the energy absorption capacity of a sandwich panel. This study investigates the effect of filling Aluminum honeycomb with balsa wood on energy absorption characteristics of Aluminum honeycomb. Both of the chosen materials are inexpensive, widely used, and readily available. The primary objective of the study is to compare the bare honeycomb and honeycomb filled with balsa wood based on following parameters: Peak Strength, Mean Crushing Strength, Absolute Energy Absorption (AEA), Specific Energy Absorption (SEA), and Deformation Pattern. A series of quasi-static experiments have been performed to investigate the energy absorbing characteristics of bare and filled honeycombs. Flatwise quasi-static compression tests, conducted at a constant velocity of 2 mm/min, showed that the AEA increased from 18% for Type B filled honeycomb to 32% for Type A filled honeycomb, compared to the bare honeycomb. It also showed that the honeycomb filled with balsa wood deformed more regularly than the bare honeycomb, hence absorbed higher energy. Corresponding FE simulations for bare and balsa wood filled honeycombs were performed using LS-DYNA/EXPLICIT solver. FE results of both, bare and filled honeycombs, show close correlation with the experimental results and provide deeper insights into deformation and energy absorption characteristics.

Groundwater flow and contaminant transport are complex phenomena which require partial differential equations to be solved numerically throughout the problem domain. Finite Difference method (FDM) and Finite Element method (FEM) based models are traditionally employed for these simulations. These methods suffer from certain instabilities due to the presence of mesh/grid. Stabilization techniques such as adaptive meshing/re-meshing, operator splitting and upwinding are used to counter these issues. Recently, meshless methods are being applied to a variety of groundwater flow and transport problems. In this study, a meshless method named Radial Point Collocation Method (RPCM) is demonstrated with two case studies. This method doesn’t use operator splitting for simulating decay reactions. Due to the use of local support domain, these methods are known to have better stability compared to FDM and FEM. The support domain size can be easily increased in order to enhance the model stability which is difficult to achieve in mesh/grid-based methods. A coupled reactive transport model involving single species first-order decay in an unconfined aquifer is developed for the first case study. For case study 2, a three-species decay chain-based reactive transport model is developed for an aquifer having irregular boundary. The model simulation results are compared with FDM- and FEMbased numerical models developed using well-established MODFLOW-MT3DMS and COMSOL models, respectively. The results indicate good agreement between the meshless and mesh/grid-based methods which shows the effectiveness of meshless methods.

This work proposes a novel computational model for estimating stochastic buffeting loads on an aircraft fin-like structure. Fin buffeting refers to the response of an aircraft fin to the aerodynamic excitation by separated flow from the upstream components like wing, foreplane, fuselage, etc. Depending on flight conditions and aircraft configurations, the buffeting response can be significantly large, leading to structural failure due to fatigue. Through this work, a thorough survey of the sources of fin buffeting has been performed, and each source is identified to have distinct spectral characteristics. Using available experimental data of power spectra for different buffeting sources, temporally consistent velocity fields upstream of the fin have been reconstructed using the Spectral Representation Method (SRM). In this study, we have proposed a novel implementation of the stochastic input velocity, modelled through SRM as a random process with a stipulated correlation, as an inlet boundary condition in a finite volume method-based Navier–Stokes solver. A computational study using the novel boundary condition has been performed on a symmetric NACA airfoil located in the wake of an idealised delta wing to estimate the buffeting loads. The power spectra for the lift coefficient obtained using the proposed method have been compared with Liepmann’s analytical model for buffeting.

Significant amount of research interest is focused on the development of nature-inspired Micro Areal Vehicle (MAV) due to their multifold potential in the futuristic civil and military applications over the years. Natural flyers (bird/insect) employ several flapping mechanisms to undergo complicated aerial manoeuver efficiently. The bistable “click” mechanism is one of the most popular modelling approaches for representing the muscle–wing interactions in the insect flight motor during Dipteran flight. The kinetic energy of the wing is stored as elastic energy while deforming the muscle elements in the flight motor during one stroke of flapping and gets recovered in the reverse stroke. The present work investigates the non-linear Fluid–Structure Interaction (FSI) of a Dipteran flight motor-inspired flapping system with the surrounding free stream at low Reynolds number. The FSI effects of the Dipteran wing assimilated as a forced Duffing oscillator model to gain a deep understanding of the non-linear dynamical behaviour of the system in the presence of aerodynamic loads. The aerodynamic loads on the wing are computed using a discrete forcing Immersed Boundary Method (IBM)-based in-house Navier–Stokes solver. The structural governing equation is solved using an explicit fourth-order Runge–Kutta (RK4) method and is coupled with the IBM solver through a weak coupling scheme. Dynamical time-series analysis tools have been employed to study the non-linear behaviour of the combined FSI system.

The present work focuses on investigating the underlying flow physics behind the transition from periodicity to aperiodicity in the flow past a harmonically plunging elliptic foil as the plunge amplitude is increased to a high value. Two-dimensional (2D) numerical simulations have been performed in the low Reynolds number regime using an in-house flow solver developed following the discrete forcing Immersed Boundary Method (IBM). To capture the aperiodic transition in the unsteady flow-field behind a flapping foil accurately, the boundary structures such as the leading-edge vortex and its evolution with time need to be resolved with maximum accuracy as they are the primary key to the manifestation of the aperiodic onset. Even a small discrepancy may result in a different dynamical state and lead to an erroneous prediction of the transition route. On the other hand, discrete forcing IBM is known to suffer from non-physical spurious oscillations of the velocity and pressure field near the boundary, which may affect the overall flow-field solution. In this regard, the present work investigates the efficacy of discrete forcing IBM in accurately capturing the transitional dynamics in the flow-field around a plunging elliptic foil by comparing its results with that of a well-validated body-fitted ALE solver.

The 2D flow produced by a NACA0015 airfoil pitching in still fluid (infinite Strouhal number defined as St = fA/U∞, where f is the flapping frequency, A is the peak-to-peak amplitude and U∞ is the freestream velocity) is investigated using numerical computations. Various aspects of the flow are analyzed. The jet generated by the flapping airfoil switches direction. This switching is studied at highly resolved time-steps. We devised a criterion to classify jet deflection based on the maximum resultant velocity in the jet. Using this criterion, we identified two types of jet switching patterns, namely gradual and sudden switching, which are studied in detail. We conduct parametric study by varying the amplitude and frequency of pitching and studied the flow. In all the cases, the switching is observed to be random.

Flow features at a 90-degree equal-width open-channel confluence are studied by using Computational Fluid Dynamics (CFD) software Fluent (version 17.2). Three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations supplemented with several turbulence models are solved numerically. The volume of fluid (VOF) method is used to track the water surface elevation (WSE). Three eddy viscosity turbulence models, i.e. Spalart–Allmras, Standard k-∈, SST k-ω and the Reynolds Stress Model (RSM) are chosen to model the turbulence. Simulated velocity fields and WSE match satisfactorily with the corresponding experimental results available in the literature. However, RSM shows more deviation in predicting the velocity field towards the left bank of the channel. Standard k-∈ model under-predicts the maximum width and length of the separation zone. Spalart–Allmras and SST k-ω models simulate the maximum width of the separation zone more accurately. However, these two models highly over-predict the $$L_{s}^{*} .$$ RSM model over-predicts the maximum width and length of the separation zone. Simulated WSE is more accurate using standard k-∈ model than the other turbulence models.

Modelling turbulence is essential in the chemical and bioprocess industry due to the mixing it creates. In the past, engineers have used two-equation Reynolds Averaged Navier–Stokes (RANS) k – $$\epsilon $$ model due to its economical nature; however, it lacks accuracy; whereas direct numerical simulation (DNS) is computationally expensive. Large eddy simulation (LES) turbulence model provides a bridge between the above two models as it resolves the larger scales and models the smaller universal scales of motion. The finite element method (FEM) has become popular in computational mechanics due to the ease with which it can handle unstructured meshes (as opposed to the finite difference method) and the ease in obtaining higher order accurate schemes (through the use of higher order shape functions) as compared to finite volume method. Although there is some work on the solution of LES turbulence model using FEM in the literature, there is a lack of clarity when it comes to the use of different discretisation schemes and solvers. The current work presents a detailed numerical analysis of turbulent flow over a two-dimensional backward-facing step (BFS) using a continuous Galerkin finite element method in an open-source finite element framework—Fluidity, which allows fully unstructured aniostropic adaptive mesh refinement along with the use of distributed parallelism. Fixed and adaptive mesh parallelised simulations are presented for a Reynolds number of 2000 for incompressible flow. The use of different LES models (second-order Smagorinsky and dynamic tensorial), non-linear relaxation parameters and velocity–pressure shape function pairs are thoroughly investigated. The primary reattachment length was calculated and compared against experimental data, finding a good match. Thus, it was concluded that the anisotropy of turbulence, which was captured using this method, can be modelled effectively using an adaptive mesh finite element method.

In this paper, the power-law (non-Newtonian) fluid flow in a two-dimensional square cavity is investigated in detail using an open-source finite element CFD code—Fluidity. The influence of the Reynolds number (Re) and the power-law index (n) on the vortex position and velocity distribution are extensively studied. In the numerical simulations, Reynolds number is varied from 100 to 8000, and n is ranged from 0.5 to 1.5, covering both cases of shear-thinning and shear-thickening fluids. Compared with a Newtonian fluid, numerical results show that the flow structure and number of the vortices of non-Newtonian power-law fluid are not only dependent on the Reynolds number but also related to the power-law index. Adaptive mesh refinement for the generation of highly anisotropic unstructured meshes that conform with flow solution has been utilised to demonstrate the effectiveness of Fluidity code in the solution of complex flows. Before benchmarking against Couette flow (square cavity) code verification is presented for non-Newtonian Poiseuille flow.

This study presents results obtained from a numerical simulation of a two-dimensional incompressible shear flow over a square cylinder with horizontal control plate at the downstream. Numerical simulations are performed by using HOC (Higher Order Compact) scheme for Reynolds number 100 at different values of shear parameter (K). The present results show that vortex structure behind the cylinder is strongly dependent on the shear parameter. We study the streamlines and vorticity contours, u-v velocity profiles, phase diagrams to analyse the vorticity control due to the presence of the control plate. The corresponding theoretical study of exact location and time of occurrence of the recirculation zone is done by topological aspect based structural bifurcation analysis. This analytical study confirms our computational results.

We consider two-dimensional (2-D) unsteady incompressible shear flow past an inclined square cylinder with vertical control plate. Numerical simulation is executed using stream function vorticity ( $$\psi -\omega $$ ) formulation of 2-D Navier–Stokes (N-S) equation on a uniform Cartesian grid. We used higher order compact finite difference scheme to discretise the governing equation. In this paper, simulations are presented for $$K = 0.0, 0.1$$ and 0.2 at $$Re = 100$$ . Our aim is to study the flow behaviour for distinct K values with different numerical studies. We compared our results with existing results. Results are quite interesting because it gives very accurate flow behaviour for different K values. we found in the results, vortex shedding and velocity fluctuation decrease by increasing K values. Also we present in this paper, the topological aspect based structural bifurcation analysis. Through this structural bifurcation analysis, exact location and time of occurrence of the separation point can be calculated. We consider first and second structural bifurcation in this study.

Aerodynamic force measurement is identified as one of the critical challenges in the hypersonic regime. For the specific trajectory of the hypersonic flight, structure of a vehicle and its control surfaces govern the aerodynamic forces. Henceforth, consolidation of the forces acting on the body is critically important for the design point of view. In this paper, CFD analysis have been used to quantify pressure, temperature, drag and lift forces on a blunt hemispherical shaped body placed at $$\mathbf{0} ^\circ $$ – $$\mathbf{30} ^\circ $$ with $$\mathbf{5} ^\circ $$ interval to provide the broad range of value, at sudden Mach 8 flow. Analysis of shock structure and separation of the flow at a different angle of attack were quantified. Further, pressure distribution, temperature profile, and the trend of the Lift and Drag forces were observed at Mach 8 flow. ANSYS Fluent has been used for CFD analysis for deriving pressure forces on the surface of the model. Forces derived through simulation are validated by comparing with the Newtonian and experimental Impulse Force balance technique.

In the present study acoustic analysis is performed for rigid rectangular enclosure with opening. The sound pressure level (SPL) in dB at the boundary and within the domain of the cavity has been found out. Boundary element analysis (BEA) has been used to solve the acoustic cavity problem governed by wave equation, in frequency domain. Eight-noded isoparametric serendipity elements have been used to model the geometry. A pressure–velocity formulation is adopted to model the acoustic domain. It was tried to show the variation in SPL at boundary and at domain due to the presence of different opening positions.

A numerical simulation has been performed to investigate the effect of laser on the natural convection in a cavity heated from bottom. A laser beam enters into the domain through semitransparent wall (window) situated at a non-dimensional height of 0.7 from the bottom and its power is 1000 W/m $${}^2$$ at an angle of $$45^\circ $$ . The laser feature is developed in the open source CFD software OpenFOAM framework and integrated with fluid flow and heat transfer applications of OpenFOAM. The results reveal that interaction of laser beam with natural convection changes the fluid flow and heat transfer phenomena completely. The vortices symmetric problem (without laser irradiance) breaks completely and these vortices become thicker or thinner with the nature of medium for radiative heat transfer. The participating medium increases the temperature of the bottom wall which intern reduces the maximum vertical velocity.

In current scenario, research in smart material deformations introduces a new classical continuum mechanics-based deformation approach that have enough potential to make a bold move from the conventional deformation approaches to a newer one. In line with that, the present work is concerned with the finite deformation modeling of a dielectric cylindrical actuator (DCA) with compliant electrodes. Herein, a common usage of DCA is to realize simultaneous axial and radial displacement with an electric field application across the thickness of the cylinder. Accordingly, we first presented an unified classical continuum mechanics-based approach to model the finite deformation of an incompressible isotropic electro-elastic cylindrical actuator under an applied electric field. Next, we formulate the constitutive relationships following the second law of thermodynamics with an amended form of energy function. This amended energy function successfully resolved the difficulty in the physical interpretation of Maxwell stress tensor exists in the literature under large deformations. In addition, we also propose a new energy density function for a class of an incompressible isotropic electro-elastic material. Further, we obtain a finite electro-elastic deformation model for a dielectric cylindrical actuator (DCA). Finally, we validated the obtained electro-elastic deformation model with their corresponding experimental data existing in the literature.

Numerical study is presented for the generalized modified polarization saturation (PS) model in 2-D piezoelectric media using distributed dislocation technique (DDT) and Gauss–Chebychev quadrature numerical scheme. A generalized case of modified PS model for an infinite semipermeable piezoelectric media is proposed here in the center cracked problem by varying the PS condition of the form $$f(|x/c_1 | ) D_s$$ in place of constant polarization saturation condition $$D_s$$ . Here, $$g(x) = f(|x/c_1 | )$$ is any arbitrary function of $$x/c_1$$ with x as a distance of the arbitrary point on zone length from center of the crack and $$c_1$$ is the extended crack length. But obtaining the analytical solution for this generalized model using complex variable and other mathematical techniques is difficult and hence in this paper, the DDT and Gauss–Chebychev quadrature scheme is applied to obtain the numerical solution. Applying DDT, this generalized PS problem is modeled as a continuous distribution of dislocations and by enforcing the crack-face and PS conditions reduced mathematically into simultaneous Cauchy-type singular integral equations in terms of mechanical and electrical dislocation density variables. But before solving them numerically, these developed simultaneous singular integral equations are firstly simplified into separate integral equations according to mechanical and electrical dislocation density parameters. This approach has also helped in evaluating the local stress intensity factor (LIF) obtained at the mechanical crack-tips. Moreover, the saturated zone length which is another important parameter in studying such models is an unknown quantity prior to getting any numerical solution. So, an iterative approach is implemented by varying the zone length and imposing a supplementary condition of finite electric displacement at the outer tips of the zone. Hence, a generalized numerical approach is developed here to obtain the fracture parameters such as saturated zone length and LIF for any varying PS condition of the form $$f(|x/c_1 | ) D_s$$ . To validate the numerical approach, results are obtained for particular cases, i.e., polynomial varying saturation conditions of degree up to four and compared with the analytical solutions. Excellent agreement of the numerical results has been found with analytical ones and hence showing the efficacy of the approach proposed in this paper. Additionally, the effects of loadings, crack-face conditions and poling direction have been discussed on saturated zone length and LIF.

Studying thermal conduction in low-dimensional non-integrable systems is necessary for understanding the microscopic origin of macroscopic irreversible behavior and Fourier’s law of heat conduction. Two distinct types of low-dimensional thermal conduction models have been proposed in the literature ones that display normal thermal conduction (like the $$\varPhi ^4$$ chain) and others that show anomalous thermal conduction (like the Fermi–Pasta–Ulam chain). However, in both these models nothing prevents two nearby particles from crossing each other. In this manuscript, we introduce a modification in the Hamiltonian of the traditional $$\varPhi ^4$$ chain (henceforth called $$\varPhi ^{4C}$$ model) through soft-sphere potential that prevents two particles from crossing. The proposed model is then subjected to thermal conduction by keeping its two ends at different temperatures using Nosé–Hoover thermostats. Equations of motion, derived from the Hamiltonian, are solved using fourth-order Runge–Kutta method for 1 billion time steps, where each time step is of 0.0005 time units. Averages have been computed using the last 750 million time steps. Our results indicate that the boundary effects due to contact with the thermostats is minimized in the $$\varPhi ^{4C}$$ model as compared to the traditional $$\varPhi ^4$$ chain, ensuring a smoother temperature distribution across the chain. Further, the rate of convergence of heat flux is much faster in the $$\varPhi ^{4C}$$ chain vis-á-vis the traditional $$\varPhi ^4$$ chain. However, the absolute value of heat flux is much smaller in the $$\varPhi ^{4C}$$ chain. These results suggest that collision plays an important role in quickly ensuring that a steady state is reached and diminishing the magnitude of heat flux. Interestingly enough, collision does not significantly alter the diffusive properties of the chain, irrespective of the temperature gradient within the chain.

Bubble and drops are of immense importance in multi-fluidic studies due to their certain characteristic behaviors. There are many studies for their homogeneous interactions like bubble–bubble or drop–drop dynamics and heterogeneous interactions such as interactions with solid particles. However, studies on the drop and bubble interactions are very limited, except for a few particularly targeted for micro-fluidics applications. Therefore, in the present study, the hydrodynamic behavior of bubble and drop during their interaction is studied using numerical simulations at a macroscopic scale. The open-source package ‘OpenFOAM’ is used to carry out the computations. The drop and bubble were allowed to achieve their terminal velocity before interactions in a vertical conduit. The sequence of intermediate phenomenon that occurred during the interaction of drop and bubble has been depicted with the help of phase fraction contours. The air bubble has penetrated through the core of the drop and resulted in the formation of an annular drop. However, both the bubble and drop have tended to regain their prior shape after the interaction. The vertical velocity of both the fluid particles is obtained with time for the entire sequence of interfacial dynamics.

The present paper aims to gain an understanding of the physics associated with the fluid-structure interaction behavior of a flexible filament interacting with the wake of an upstream rigid cylinder situated at a finite distance. The computational framework of the present high fidelity numerical simulations consist of an incompressible Navier-Stokes solver strongly coupled with a chord-wise flexible structural model based on a partitioned approach. The effect of body-wake interactions on the resulting vibrating modes of the chord-wise flexible foil due to its passive flapping is studied in detail. The gap between the cylinder and the flexible filament is seen to play a major role in the vortex impingements on the flexible flapper and the subsequent interactions. Insights are obtained into the dynamics through a parametric study for different values of this finite gap. Moreover, the effect of the length and thickness of the flapper on its dominant mode-shapes is also investigated. The present study shows that higher values of the gap and the length of the filament lead to the loss of periodicity in the body-wake interactions which is of current interest.

Semi-active technology offers good advantages in terms of controllability and adaptability. Magneto-rheological (MR) fluid is a class of smart fluids which display significant changes in its rheological properties under the influence of a magnetic field. Previous studies carried out using MR brake for the transfemoral prosthetic device were of multi-plate models which are complex in design and also to manufacture. Therefore, in the present study, a multi-coil rotary inverted drum brake is optimized with braking torque as the objective function. One of the advantages of the multi-coil design from multi-plate is that the former has fewer components and leads to a simpler design. The outermost geometric constraints are decided based on the knee cross-sections in anterior-posterior and mediolateral directions. Four design geometric variables are selected which are: coil depth, coil height, casing axial thickness, and casing radial thickness. A design of experiments technique is used to obtain 27 combinations of design variables. Magnetostatic analysis at each design point is performed and average flux densities in the annular and the radial gaps are determined. Regression analysis is conducted on the design data to obtain braking torque as a function of four design variables. Later, genetic algorithm is used to obtain the optimum geometric dimensions. A total maximum braking torque of 13.4 Nm is obtained using the optimum dimensions for a design current of 2 A.

In this paper, numerical results for flexure of shear-deformable isotropic square plates by utilizing recently proposed single variable new first-order shear deformation plate theory (SVNFSDT) are presented. For obtaining numerical results, fourth-order Runge-Kutta technique is used. It should be noted that the displacement functions of SVNFSDT give rise to constant transverse shear strains and hence constant transverse shear stresses through the plate thickness. Hence, similar to other first-order shear deformation plate theories reported in the literature, this theory also requires a shear correction factor. As opposed to Mindlin plate theory, SVNFSDT has only one fourth-order governing differential equation which is obtained by utilizing plate gross equilibrium equations. This theory presents physically meaningful boundary conditions. On similar lines of two-dimensional theory of elasticity approach for beam analysis, this theory also presents two different types of plate clamped edge boundary conditions. Illustrative examples presented in this paper consider Lévy-type plates with two opposite plate edges simply supported and remaining two plate edges having either simply supported, clamped, or free boundary conditions with plate under the action of uniformly distributed transverse load. Numerical results for flexure of abovementioned cases of plates are presented for different values of plate thickness-to-length ratio. In order to demonstrate the efficacy of the presented numerical solution technique, obtained results are compared with corresponding results reported in the literature.

Recently, a number of explicit time integration schemes have been proposed. They have been shown to perform better for mostly linear problems. However, there is no work to compare the performance of various explicit time integration schemes for nonlinear problems. Hence, the objective of the present work is to fill this gap. In the paper, a number of recently proposed explicit time integration schemes are analyzed for their performance when applied to nonlinear problems. In particular, a multiple degree-of-freedom nonlinear problem and a single degree-of-freedom nonlinear adhesive contact problem are solved using different schemes for different time steps. The error in energy for different time steps for each scheme is compared. The computational cost associated with each scheme is also compared. It is shown that still the classical central difference scheme performs equally well as compared to all the recently proposed explicit schemes and takes least amount of computational time.

The objective of this paper is to comparatively assess the performance of various composite implicit time integration methods. Most popular and widely used scheme—the Bathe, and some recently proposed methods like TTBDF, Wen, and NTTBDF are chosen for the purpose of comparative analysis. All the methods are unconditionally stable and show second-order accuracy. The comparison is done by integrating these schemes on a different class of nonlinear dynamic problems. It is shown that all the considered composite schemes require suitable parametric adjustment to attain the optimal performance except for Bathe as it is a parameter-free method.

It is well recognized that for proper functioning of a constitutive model selection of a computationally efficient and stable stress integration, algorithm is a key. Implementation of an advanced elastoplastic constitutive model into a finite element program requires the development of a robust and efficient numerical procedure in order to perform the local stress integration of the constitutive equations along a given loading path. Besides, as the physical domain of the problem increases, the simulation becomes time and resource consuming. Complex algorithms make the simulation even more time-consuming as accuracy and numerical complexity are strongly proportional to each other. Semi-implicit type Cutting Plane Method (CPM) and fully implicit type Closest Point Projection Method (CPPM), are the two most widely used methods for numerical integration. CPM is simple and easy to implement but less accurate and CPPM is stable and precise method, but the formulation is complex, especially for the constitutive models that contain multiple and coupled state variables, stiffness nonlinearity, multiple yielding and hardening conditions, and non-associativity. In this study, we have tried to bridge the gap by developing efficient integration schemes that provide close result to that of fully implicit method. We formulate an integration technique, namely Midpoint integration by enhancing the semi-implicit CPM framework. The algorithm is implemented for extended Mohr-Coulomb type soil constitutive model. The analysis show that the proposed integration methods gives result close to CPPM although their complexity is similar to CPM, which normally drifts away from accuracy in high plastic region.

Smoothed Particle Hydrodynamics is one of the oldest meshless methods and has undergone significant improvements in the past three decades. The method originally suffered from a few drawbacks such as tensile instability, particle inconsistency and so on. Several techniques have been proposed by researchers across the globe to overcome these difficulties. The origin of the tension instability is in the second derivative of the smoothing function. A recent formulation called Kernel Gradient Free Smoothed Particle Hydrodynamics (KGF−SPH) avoids the use of any derivatives of the smoothing function for the approximation of spatial gradients. The method is capable of handling particle inconsistency at the boundaries. In this work, a FORTRAN code based on KGF−SPH is developed to demonstrate the performance of the method, applied to $$1-$$ D and $$2-$$ D heat conduction and elastic wave propagation problems.

Ducted supersonic flows which are highly diffusive in nature are dominated by the occurrence of reflecting shock waves. Accurate numerical treatment of wall boundary conditions significantly improves the quality of solution. Improvised smoothing technique and introducing artificial viscosity to control diffusion all aid in capturing shocks crisply. In this paper, a new two-step numerical time integration scheme which implements these code development methods for Euler and Navier–Stokes solvers is discussed succinctly. Oddly enough, this solver employs state vector to smoothen the flow and to accelerate convergence, until now believed to be an improbable task and much in defiance to the conventional method of residual smoothing of flux vector in CFD codes. The new set of wall boundary conditions developed for this purpose eliminates the undesirable occurrence of Mach stem in multiple shock reflection problems. The versatility of the code is amply demonstrated through standard validation test cases of internal flows for high and low diffusion in a stepped duct and shock reflecting surfaces, respectively. The results show good agreement between theory and numerical experiments. The fact that this two-step scheme can be applied to existing viscous code with no modifications permit them to be used in gridded solvers as hybrid codes for complex flow simulation.

In the bivariate population balance model, the dispersed phase particles are represented using two internal coordinates. The direct quadrature method of moments (DQMOM) is a computationally efficient and accurate numerical technique to solve monovariate and bivariate population balance equations (PBE) [4]. In the past, bivariate PBEs have been solved using DQMOM in a few commercial and non-commercial finite-volume computational fluid dynamics (CFD) packages. However, no code contains this solution technique as a standard implementation. Moreover, all previous implementations of DQMOM have been finite volume based. Recently, DQMOM was implemented for solving monovariate PBE in a highly parallelised finite element open-source framework—Fluidity [1]. The implementation was shown to be extremely efficient in the solution of monovariate PBEs and their integration to fluid flow problems. This is particularly true due to the anisotropic adaptive unstructured meshes utilised in the Fluidity code, which significantly reduces the computational cost maintaining the solution accuracy. In the present work, DQMOM is implemented in Fluidity for solving bivariate PBE. Test cases with homogeneous aggregation and homogeneous breakage were simulated and verified against the analytical solution, showing excellent agreement. In the extension to the implementation of DQMOM for solving bivariate PBE, the potential of this finite element framework to integrate the bivariate PBE with flow problems is maintained by default.

Concrete is a composite material, which can be segmented into three major phases, namely voids, aggregates and mortar. This paper presents the digital image processing techniques based on grey value thresholding and a novel radial thresholding approach to segregate the three phases of concrete. In this context, the 8-bit images of concrete specimen obtained from X-ray microtomography (XRT) scanning of cylindrical specimen are operated. The non-local means denoising filter is used to remove the unwanted noise from the original images and enhance their clarity without losing any details. There is a clear distinction in the grey values of air voids from that of aggregates and mortar. The threshold grey value of air voids is determined by observing the variation in grey value profile near the edges of the air voids, and using this threshold grey value, air voids are segmented assuredly. However, the segmentation of phases using this thresholding technique doesn’t suffice to isolate the aggregates from mortar because of the overlap of their grey values. Hence, a radial thresholding method is proposed for the detection and determination of the phases, which works similar to our eyes. The grey value vs radius graph exhibits sudden jumps, which represent the change in contrast, that is, phase. The change in phases is evaluated by using a simple function, $$\parallel {\text{GV}}\left( {\text{n}} \right) - {\text{GV}}\left( {{\text{n}} - 1} \right)\left| { - {\text{L}}} \right| > 0$$ which is considered the radial variation for every degree rotation. The estimated air voids and aggregates content are 0.91 and 49.19%, respectively. The error in the detection of aggregates content is only 0.6%.

The study focuses on the design of an energy harvesting nonlinear dynamic vibration absorber (DVA) for possible vibration attenuation and energy generation. As an application vibration mitigation of a base-excited single degree of freedom (SDOF) system is considered. Conventional DVAs are widely used as vibration control devices that undergo large displacements in order to dissipate the energy from the primary structure. For an energy harvester higher the vibration higher is the energy generated. Therefore, if an energy harvester is attached to the DVA, the primary structure DVA interaction can be used for dual purposes. In this study, a duffing-type nonlinear DVA system with a piezo patch is proposed as energy harvesting nonlinear DVA to mitigate the vibration and to obtain electricity. The modeling of the total system is carried out considering the electromechanical interactions between the harvester-DVA and structural system. The formulation is done in time domain and a simulation study is carried out for harmonic base excitation to understand the effect of nonlinearity in voltage generation. A frequency sweep study is carried out to locate the frequency band in which the system responses are consistently higher. Further, the important design parameters are identified. A parametric study to obtain optimal design parameters is also reported. The advantages of nonlinear energy harvesting DVA over the linear ones are many. A nonlinear harvester provides power over a broad range of frequencies and, therefore would be able to dissipate energy from the primary structure over wideband excitations. Finally, the performance of the designed nonlinear DVA system with harvester is examined for vibration mitigation of SDOF primary system.

Increase in usage of small electronics and environment threat that batteries provide have accelerated the research in energy harvesting in the last decade. The main challenges in energy harvesting are to increase the operating frequency bandwidth of harvesters and to increase the amount of power harvested. Multiple tuned harvesters have gained a lot of attention in alleviating these challenges. Attaining perfect tuning is a challenge and mistuning is inherent in systems. This study looks into the effect of mistuning in a set of harvesters that are designed to be perfectly tuned. The harvester set is considered to be a set of nonlinear oscillators that represent pendulum-based energy harvester. Four different arrangements among the oscillators are considered. These are (a) series of independent harvesters, (b) series of independent but mistuned harvesters, (c) interacting harvesters, and (d) interacting but mistuned harvesters. In all these cases, base excitation is imparted to the system and physics of the system is studied. It is observed that in the mistuned cases bandwidth is larger when compared to the tuned cases.

In this manuscript, a concept flow control valve is designed, exploiting the bistable characteristics of a special class of hybrid laminates made of glass epoxy and carbon epoxy prepregs. The principal structural element of the device is a hybrid bistable laminate, having a multi-section layup laid in a symmetric configuration. The thermal curing process responsible for the inherent bistability is simulated in ABAQUS $$^{\textregistered }$$ and the equilibrium shapes hence obtained using the FEA scheme is validated against an existing semi-analytical technique based on the Rayleigh-Ritz minimization of potential functional. These multi-stable elements are then studied for their potential in controlling a flowing stream. Toward that, the snapping response of these laminates in a flow stream is analyzed using a combination of XFOIL and ABAQUS $$^{\textregistered }$$ . The pressure distribution on the laminate is estimated using XFOIL, which is an interactive program for analysis of subsonic isolated airfoils in viscous/inviscid low Reynolds number flow. The pressure distribution hence obtained is used to evaluate the load-displacement characteristics of the laminate using post-buckling regime analysis capabilities of ABAQUS $$^{\textregistered }$$ . Using these analysis tools, the design space is explored and the possibility of using the proposed bistable design elements for flow regulation is established.

Spent fuels from the nuclear power reactors (NPRs) are stored in water pools, which are provided with thick RCC walls, lined with SS plates. Seismic behavior of these submerged freestanding spent fuel trays in spent fuel storage water pool (SFSWP) is highly nonlinear due to sliding, impact of trays stack and hydrodynamic effect of sloshing water. Earlier, only uncoupled or simplified methods were implemented to consider the hydrodynamic effect of water on submerged trays stack system. Hence, numerical model accounting gap, contact, friction and sliding between trays and bottom surface accounting coupled with hydrodynamic effect on the trays is developed and validated with shake table test results. The water mass is simulated using Navier–Stokes equation. The numerical model of the two systems, that is freestanding trays stack and contained water mass are solved simultaneously using coupled Arbitrary Lagrangian–Eulerian (ALE) method to resolve high mesh deformation issues which can lead to non-convergence in the solution. Safe Shutdown Earthquake (SSE) level of site-specific design seismic ground response spectra (DGRS) of 0.2 g Peak Ground Acceleration (PGA) with compatible time history is generated and considered for the analysis. Response parameters such as convective and impulsive frequency, mode shape and slosh displacements of the system obtained from the coupled numerical analysis are compared with the shake table experiment results and are found in very close agreement. The convective frequency of sloshing water is around 0.53 Hz. No out-phase motion of freestanding trays stack system is observed in the shake table experiment and analysis.

The present work deals with the robust flutter analysis of a sweptback wing in frequency domain in the presence of various parametric uncertainties. The methodology adopted for the studies is based on the structured singular value ( $$\mu $$ ) method. $$\mu $$ method requires valid description of various uncertainties associated with the aeroelastic system and then introducing these uncertainties to the nominal aeroelastic system in the form of a feedback loop. This feedback representation of uncertainties results in the Linear Fractional Transformation (LFT) model of the uncertain aeroelastic system which is then used for robust stability studies using $$\mu $$ method. This method is implemented in MATLAB and validation studies are carried out for 3DOF airfoil system in the presence of various structural and aerodynamic uncertainties. Further, the present method is extended to study the robust flutter of AGARD 445.6 sweptback wing in the presence of structural and aerodynamic uncertainties at various Mach numbers.

Advancement in vehicle technology has explored many possibilities for improvement, keeping customer satisfaction in mind. One major criterion which a passenger always wishes to possess is ride comfort. But the suspension parameters suitable for a good ride comfort may not support another salient feature called road holding. Hence, in this work an attempt has been made to simultaneously improve the ride comfort and road holding, using a quarter car test model using MATLAB Simulink for a commercial light motor vehicle. Initially, a commercially available passive damper of light motor vehicle has been characterized using dynamic testing machine (DTM) in order to obtain its force–displacement behavior and damping nature. A design of experiment (DOE) has been conducted by taking vehicle velocity, sprung mass, spring stiffness and damping coefficient into consideration, for experimentation using quarter car model. Regression equations have been extracted for relating the problem parameters to both ride comfort and road holding. Analysis of variance (ANOVA) has been used to know the influence of each parameter toward the target response. In the later stage, response surface methodology optimization technique has been used in order to optimize the parameters for better ride comfort and road holding. Optimized parameters are substituted again in the quarter car model, to validate the results obtained during optimization. The present work concluded with an optimal ride comfort and road holding and proved the effectiveness of optimization technique in achieving so.

This study investigates the thermal characteristics of the $$3\times 8$$ Li-ion cell arrangement within the battery module numerically at different boundary conditions. Various parameters are considered in the current study, such as different ambient temperatures, inlet velocities, and duct sizes. The battery module is simulated in ANSYS Fluent 19. A three-dimensional computational model is established to analyze the thermal profile of Li-ion cells for different ambient temperatures. The forced air convection method is employed to study the effects of inlet velocities at different ambient temperatures. The thermal performance of the battery module is judged on the capability of the battery module to work within the optimal temperature range of $$0{-}40\,^\circ{\rm C}$$ . The results indicate that $$3\times 8$$ Li-ion cell arrangement at higher ambient temperature ranges works within the optimal temperature range. The thermal analysis of duct sizes shows that $$15{-}20$$ mm is the ideal inlet and outlet duct size for $$3\times 8$$ Li-ion cell arrangement. This would further give insights into the thermal profiles of $$3\times 8$$ cell arrangement, which would aid in designing efficient battery modules with cells operating within the optimal temperature ranges.

A structural dynamic problem involves extraction of eigenvalues and eigenvectors to find natural frequencies and mode shapes. $$FEAS{T}^{SMT}$$ is Finite Element (FE)-based structural analysis software developed in-house for the analysis of satellite launch vehicles structures. Solution of dynamic analysis problems is based on dynamic substructuring to achieve parallelism during computation. A bottleneck in this solution process is solving the resulting eigen system that involves nearly fully populated matrices. Lanczos method involves a series of mass matrix multiplication with factorized stiffness matrix for orthogonalization of trial vectors. FE models of launch vehicle structures are very complex and consist of large number of elements and nodes. A modified Lanczos method is developed using multifrontal-based partial factorization. Performance of the dynamic analysis in $$FEAS{T}^{SMT}$$ software is substantially improved from the existing sequential version. This paper discusses the implementation details of the modified Lanczos reduction method using multifrontal based factorization.