Search

This paper presents a quasistatic problem of an elastic body in frictional contact with a moving foundation. The model takes into account wear of the contact surface of the body caused by the friction. We recall existence and uniqueness results obtained in Sofonea et al. (2017). The main aim of this paper is to present a fully discrete scheme for numerical approximation together with an error estimation of a solution to this problem. Finally, computational simulations are performed to illustrate the mathematical model. [ABSTRACT FROM AUTHOR]

Abstract Downburst produces strong winds near the ground and causes severe damage to buildings and people. The non-stationarity of downburst is characterized by moving downdraft and pulsed jet to the ground. In practice, both characteristics have often been observed simultaneously. These characteristics significantly affect the wind loads on buildings, particularly on low-rise buildings. However, the previous experimental studies of downbursts focused on each of these characteristics separately. No study has been made of their coupled effect. Therefore, we have developed a downburst simulator, which can generate a pulsed jet and a moving downdraft either separately or simultaneously. In the present paper, we have experimentally investigated the effects of non-stationary characteristics of downbursts on the wind field and wind loads on a flat-roofed low-rise building using this downburst simulator. The results may become a useful database for validating numerical simulation models of downbursts. Highlights • Effects of movement and impinging jet on the flow field of downburst is investigated. • Non-stationary flow fields of moving and pulsed jet are experimentally reproduced. • Downburst-induced pressure on a building is measured with a downburst simulator. • Downburst-induced wind forces are different from those by turbulent boundary layers. [ABSTRACT FROM AUTHOR]

Shape-memory polymers (SMPs) represent a class of smart materials able to store a temporary shape and to recover the original shape upon an external stimulus, such as temperature. The present paper proposes a three-dimensional finite-strain phenomenological model for thermo-responsive SMPs, which distinguishes between two material phases presenting different properties and is based on a rule of mixtures. The proposed model is motivated by the earlier work of Reese et al. (2010) and it considers several significant material features that had not been addressed in previous phenomenological approaches. Specifically, the model reproduces both heating-stretching-cooling and cold drawing shape-fixing procedures and it takes into account the non-ideal behavior of realistic SMPs (i.e. imperfect shape-fixing and incomplete shape-recovery). Several numerical tests are reported to assess model performances, from simple uniaxial and biaxial tests to complex simulations of biomedical devices. Comparisons with experimental data taken from the literature are also provided to validate the model. The proposed improvements increase the model applicability over a wide range of polymer types and operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper concerns the mathematical and numerical modeling of solidification process of pure metals. Such process takes place without development of “mushy zone”, which very often occurs during solidification of alloys. The model is based on the finite element method (FEM) and takes into account the existence of a sharp solidification front which moves according to time. The paper discusses how to include the conditions of continuity on the moving interface as well as the technique of front tracking based on the level set method (LSM). The paper also presents the results of computer simulations of the solidification process of pure copper. Two in-home solvers for one- and two-dimensional problems were built. Both of them are based on FEM. The correctness of the front tracking technique was checked by comparing the results obtained from 2D simulation to 1D simulation. Furthermore, the final calculation process was done for the two-dimensional area at different temperatures on the boundaries to demonstrate the effectiveness of the solver for a complex shape of the solidification front. [Copyright &y& Elsevier]

Abstract: Stress peening forming is widely used in the aeronautics industry to induce curvatures in wing skins. Most of the investigations of stress peen forming are empirical and experimental. In this paper, a three step numerical model that can simulate this process was developed. First, an implicit Finite Element Analysis (FEA) with ANSYS where a prebending moment along the spanwise direction of the component was performed. Then, an explicit FEA with LS-DYNA simulating shot impacts on the pre-stressed component was executed in order to obtain the resulting stresses inside the component. Finally, an implicit FEA with ANSYS was performed for calculating the arc heights and the curvature radii of the component in chordwise and spanwise directions. Numerical analysis of the process shows that the prebending moments have an influence not only on the residual stress profiles but also on the curvatures of the deformed component in chordwise and spanwise directions. This model was used to establish a relationship between the prebending moment and the resulting arc heights and residual stress profiles. The numerical strategies developed in this paper supply a useful tool for studying and optimizing the stress peening process. [Copyright &y& Elsevier]

Stiffened plates are the most common structural units used in different structural applications ranging from buildings and bridges to ships and offshore structures. The present paper aiming at investigating the influence of using Y-stiffeners profile instead of conventional stiffeners on the load carrying capacity of ship deck panels under vertical hull girder bending moment. ANSYS (Release 15.0) nonlinear finite element software was used to verify the ultimate strength results obtained from applying the International Association Classification Societies-Common Structural Rules (IACS-CSR) on both conventional and novel deck panels. The developed numerical model with conventional stiffeners profile was validated in a good agreement with a benchmark study results included in the International Ship Structures Committee (ISSC). Furthermore, both analytical and numerical simulation results were in good agreement that demonstrates the capability of using IACS-CSR for designing the new stiffeners profile in practical applications. In comparison with the conventional stiffeners profile, the proposed Y-stiffeners resulted in a considerable increase in the panel safety margin to weight (area) ratio and higher ultimate strength. Moreover, the numerical simulations provided that implementing the Y-stiffeners profile can also rise the first yielding stress point of the structural response with nearly the same strain absorption in comparison with T-stiffeners profile. [ABSTRACT FROM AUTHOR]

Abstract: We revisit in this paper the theory of axisymmetric vortex rings in an ideal fluid. The boundary separating the vortex ring from the external (potential) flow is assumed of elliptic shape. For a given distribution of vorticity in the vortex core, we theoretically put into evidence the critical parameter for the existence of non-trivial solutions, thus confirming the numerical observation of Durst et al. [ZAMP 32 (1981) 156]. A sharp estimation of the critical threshold is analytically derived. Theoretical predictions are confirmed by numerical simulations using finite elements. A new numerical algorithm is presented and shown to display better performances compared to previous published algorithms using finite differences. The convergence of the iterative algorithm is proved using the theory of elliptic partial differential equations with discontinuous nonlinearities. [Copyright &y& Elsevier]

Abstract: In this paper, a three-dimensional (3D), nonisothermal, multiphysics, two-phase steady state transport model and its efficient numerical methods are systematically studied for a full proton exchange membrane fuel cell (PEMFC) in the sense of efficiency and accuracy. The conservation equations of mass, momentum, species, charge and energy are fully addressed in view of nonisothermality and multiphase characteristics. In addition, from an accurate numerical discretization’s point of view, we present some new formulations for species equations by investigating the interactions among the species. In a framework of the combined finite element-upwind finite volume method, some efficient numerical methods are developed in terms of Kirchhoff transformation for the sake of a fast and convergent numerical simulation. The 3D simulations demonstrate that the convergent solutions can be attained within 80 nonlinear iterations, in contrast to the oscillating and nonconvergent iterations conducted by commercial flow solvers or in-house code with standard finite element/volume methods. Numerical convergence tests are carried out to verify the efficiency and accuracy of our numerical algorithms and techniques. [Copyright &y& Elsevier]

Abstract: This paper presents the numerical simulations of thin-walled square hollow steel beams subjected to a uniform transverse blast load. The objectives of the numerical simulations were to gain an insight into the temporal distribution of the global and local deformation and the adiabatic temperature rise in the beams as a result of impulsive loading. Additionally, the finite element predictions using Ls-Dyna are compared to the experimentally observed global and local deformations. The full lengths of the beams were modelled using three material models based on the linear piecewise plasticity material model which incorporated strain hardening, with and without strain-rate hardening and with strain-rate hardening and temperature softening. The blast wave was simulated as a rectangular pressure pulse distributed over the top surface of the beams. Ls-Dyna and the material model used were found to predict the global and local deformation of the beams reasonably well. Incorporating strain-rate hardening was found to be important to be able to predict the global and local deformation of the beams. Thermal softening was found to play a small but not negligible role. [Copyright &y& Elsevier]