Abstract in English:In this paper, a fully non-linear three-dimensional Numerical Wave Tank (NWT) is developed for studying propagation and scattering of non-linear random sea wave over bottom submerged bars. The simulation of fully non-linear free-surface is based on Non-Uniform Rational B-Spline formulation (NURBS) as a novel approach and Mixed Eulerian-Lagrangian method (MEL). High-order boundary integral equation is used to solve the Laplace equation in the Eulerian frame. To update the free-surface, time marching approach including material node method and fourth order Runge-Kutta time integration scheme is used. To obtain appropriate numerical solutions for wave propagation problem, damping zone is set at the downstream. Also, the NURBS approximation is employed to evaluate the velocity of the free-surface particles. Propagation of regular and irregular waves in a NWT is investigated and compared with the available experimental and numerical data. Transmission of the random sea wave over submerged bars is also compared with the experimental and prior numerical studies.
Abstract in English:In this paper we present the numerical analysis of the quasi-static behavior of an unbalance cracked shaft with straight and elliptical cracks considering an eccentric mass. The rotation of the shaft has been simulated by considering different angular positions to complete one rotation. The influence of the mass eccentricity in the opening of the crack has been studied considering different angles of eccentricity. The study of the partially opening/closing of the crack in the rotation of the shaft under the influence of the eccentric mass is analyzed. The work allows us to know the influence of the unbalance in the crack breathing mechanism and will help to predict the influence of this behavior on the values of the Stress Intensity Factor and on the propagation of cracks.
Abstract in English:In this paper, the free vibration behavior of post-buckled functionally graded (FG) Mindlin rectangular microplates are described based on the modified couple stress theory (MCST). This theory enables the consideration of the size-effect through introducing material length scale parameters. The FG microplates made of a mixture of metal and ceramic are considered whose volume fraction of components is expressed by a power law function. By means of Hamilton's principle, the nonlinear governing equations and associated boundary conditions are derived for FG micro-plates in the postbuckling domain. The governing equations and boundary conditions are then discretized by using the generalized differential quadrature (GDQ) method before solving numerically by the pseudo-arclength continuation technique. In the solution procedure, the postbuckling problem of microplates is investigated first. Afterwards, the free vibration of microplates around the buckled configuration is discussed. The effects of dimensionless length scale parameter, material gradient index and aspect ratio on the on the postbuckling path and frequency of FG microplates subject to arbitrary edge supports are thoroughly discussed.
Abstract in English:A study on the acoustic behavior of double-walled panels, with sandwiched layer of porous materials is presented within Classical Laminated Plate Theory (CLPT) for laminated composite panels. For this purpose, equations of wave propagation are firstly extracted based on Biot's theory for porous materials, then the transmission loss (TL) of the structure is estimated in a broadband frequency. Secondly, TL coefficient of the structure is determined using Statistical Energy Analysis (SEA). In the next step, accuracy of the solution is shown with comparing the data obtained from these two presented models as well as the experimental results available in literature. Finally, the effects of parameters on sound transmission loss of double porous composite panels, especially at a high frequency range, are discussed. In addition, the results show that maximum sound energy is transferred through the waves frame (structure born) due to the porous layer bonded between the two composite panels. Therefore, material parameters that are principally related to solid phase of the foam such as Poisson's ratio, bulk density and bulk Young's modulus, have the most significant effects on the transmission loss. Meanwhile, the impacts of composite material panels and composite plies arrangement on sound transmission loss structures have been addressed in this paper.
Abstract in English:This paper is concerned with the study of propagation of Stoneley waves at the interface of two dissimilar isotropic microstretch thermoelastic diffusion medium in the context of generalized theories of thermoelasticity. The dispersion equation of Stoneley waves is derived in the form of a determinant by using the boundary conditions. The dispersion curves giving the phase velocity and attenuation coefficients with wave number are computed numerically. Numerically computed results are shown graphically to depict the diffusion effect alongwith the relaxation times in microstretch thermoelastic diffusion solid half spaces for thermally insulated and impermeable boundaries, respectively. The components of displacement, stress, couple stress, microstress, and temperature change are presented graphically for two dissimilar microstretch thermoelastic diffusion half-spaces. Several cases of interest under different conditions are also deduced and discussed.
Abstract in English:This paper presents a study on the gap dependent bifurcation behavior of an electro statically-actuated nano-beam. The sizedependent behavior of the beam was taken into account by applying the couple stress theory. Two small and large gap distance regimes have been considered in which the intermolecular vdW and Casimir forces are dominant, respectively. It has been shown that changing the gap size can affect the fundamental frequency of the beam. The bifurcation diagrams for small gap distance revealed that by changing the gap size, the number and type of the fixed points can change. However, for large gap regime, where the Casimir force is the dominant intermolecular force, changing the gap size does not affect the quality of the bifurcation behavior.
Abstract in English:A damage model with different failure surface in tension and compression is formulated, implemented and validated to study reinforced concrete elements under actions which induce their collapse. The constitutive behaviour of concrete considers the softening deformation after reaching a failure surface, whereas the hardening of the reinforcing steel is represented by a plasticity von Mises surface. The developed damage model does not exhibit the problem of stress locking as the smeared cracking model does; this guaranties an adequate energy release as the material fails. Numerical examples are presented showing the validity of the developed damage model for modelling the behaviour of reinforced concrete elements up to their collapse.
Abstract in English:In the present work, the model of vibration of gold nano- beam induced by laser pulse heating is developed in the context of two-temperature generalized thermoelasticity and non-Fourier heat conduction. The analytic solution has been derived in the Laplace transform domain. The inverse Laplace transform has been calculated numerically and the numerical results have been presented graphically in two and three dimensions figures with some comparisons to stand on the effects of the two-temperature parameter and the laser pulse parameters on all the studying fields and which one of that parameters plays a vital role in the damping of the energy which has been generated inside the beam.
Abstract in English:The propagation behavior of shear wave in piezoelectric composite structure is investigated by two layer model presented in this approach. The composite structure comprises of piezoelectric layers of two different materials bonded alternatively. Dispersion equations are derived for propagation along the direction normal to the layering and in direction of layering. It has been revealed that thickness and elastic constants have significant influence on propagation behavior of shear wave. The phase velocity and wave number is numerically calculated for alternative layer of Polyvinylidene Difluoride (PVDF) and Lead Zirconate Titanate (PZT-5H) in composite layered structure. The analysis carried out in this paper evaluates the effect of volume fraction on the phase velocity of shear wave.
Abstract in English:In the present investigation, response of the stiffened sandwich foam panels with closed-cell aluminum foam cores subjected to blast load is examined. The panels have the metal foam sandwiched between two steel sheets. To improve resistance of the sandwich foam panel against blast, stiffeners are provided and their dynamic response under varying blast load is studied. Blast load is applied using blast equations available in LS-DYNA which takes into account reflection of blast from surface of the sandwich foam panel. Finite element based numerical simulations for dynamic analysis are performed employing a combination of shell and solid elements for steel sheets and metal foam, respectively. Quantitative assessment of dynamic response of the sandwich foam panels is made, primarily focusing on peak central point displacement of back-sheet (opposite to explosion) of the panel. Several analyses are carried out with an objective to understand the effects of stiffener configuration, foam thickness, foam density, and standoff distance on the blast response. Results indicate that the provision of stiffeners along with metal foam considerably increases blast resistance as compared to the unstiffened panels with the metal foam.