Papers by Author: Matej Vesenjak

Abstract: The paper presents a fluid structure interaction based numerical study of impact loading for a hemispherical structure upon water and a space capsule water landing. The study has a strong relevance in the determination of the crashworthiness of aerospace structures upon water impact loading. Finite element based numerical techniques have been used for the analysis of the underlying transient dynamic and fluid-structure interaction. Smoothed Particle Hydrodynamics (SPH) and Arbitrary Lagrange-Eulerian (ALE) methods have been used to simulate the behaviour of the fluid (water) under impact conditions. The accelerations and velocities of the impacting objects have been validated with by experimental measurements and analytical results. Numerical analyses showed a strong potential for the use of developed computational fluid structure interaction models for analyses of water impact loading related problems.

Abstract: Thermal properties of honeycomb structures with different cell shapes are investigated in this paper. The influence of cell shape, relative density and pore gases on the macroscopic honeycomb thermal properties is investigated by means of transient dynamic computational simulations. The ANSYS CFX code is used to evaluate the heat conduction trough the base material and the filler gas, as well as the convection in gas filler. The computational results clearly show a strong influence of the filler gas on heat conduction and macroscopic thermal properties of analyzed honeycomb structures, which is attributed to low relative density of the cellular structure. Additionally, the influence of considered relative densities is more prominent than the influence of cell shape. The evaluated results are valuable for further development of homogenization models of heat transfer in honeycomb structures accounting for gaseous pore fillers.

Abstract: New multiphysical computational models for simulation of regular open and closed-cell cellular structures behaviour under compressive impact loading are presented. The behaviour of cellular structures with fluid fillers under uniaxial impact loading and large deformations has been analyzed with the explicit nonlinear finite element code LS-DYNA. The behaviour of closed-cell cellular structure has been evaluated with the use of the representative volume element, where the influence of residual gas inside the closed pores has been studied. Open-cell cellular structure was modelled as a whole to properly account for considered fluid flow through the cells, which significantly influences macroscopic behaviour of cellular structure. The fluid has been modelled by applying a Smoothed Particle Hydrodynamics (SPH) method. Computational simulations showed that the base material has the highest influence on the behaviour of cellular structures under impact conditions. The increase of the relative density and strain rate results in increase of the cellular structure stiffness. Parametrical numerical simulations have also confirmed that filler influences the macroscopic behaviour of the cellular structures which depends on the loading type and the size of the cellular structure. In open-cell cellular structures with higher filler viscosity and higher relative density, increased impact energy absorption has been observed.

Abstract: The paper describes the post-impact thermal conduction of regular closed-cell cellular structure with gaseous fillers due to the dynamic compression. Two different but subsequent computational analyses have been carried out for this purpose. To define the behavior of the cellular structure under compressive dynamic loading, a unit volume element of the cellular structure has been analyzed with the explicit finite element code LS-DYNA by considering a strongly coupled interaction of the cellular structure base material with the gaseous pore filler. The resulting deformed cellular structure has then been imported in the finite volume code ANSYS CFX 10.0 for further weakly coupled thermal-structural analyses of post-impact heat conduction through the base material and filler gas. The increased temperature and pressure of the filler gas after compressive impact loading from the initial analyses have been used as initial conditions for the thermal analyses, where only the heat conduction due to the gas compression has been taken into account. This paper considers only the closed-cell cellular structure with two different relative densities and air inside the pores. Computational simulations have shown a low overall temperature increase of the cellular structure due to filler gas compression. The temperature increase of the base material is expected to be higher at lower relative densities. The presented procedure illustrates a convenient approach to solving strongly coupled fluid-structure interaction problems by considering also a weakly coupled thermal-structural solution, which can be used for a wide range of engineering applications.

Abstract: The study describes the behavior of regular closed-cell cellular structure with gaseous fillers under impact conditions and consequent post-impact thermal conduction due to the compression of filler gas. Two dependent but different analyses types have been carried out for this purpose: (i) a strongly coupled fluid-structure interaction and (ii) a weakly coupled thermalstructural analysis. This paper describes the structural analyses of the closed-cell cellular structure under impact loading. The explicit code LS-DYNA was used to computationally determine the behavior of cellular structure under compressive dynamic loading, where one unit volume element of the cellular structure has been discretised with finite elements considering a simultaneous strongly coupled interaction with the gaseous pore filler. Closed-cell cellular structures with different relative densities and initial pore pressures have been considered. Computational simulations have shown that the gaseous filler influences the mechanical behavior of cellular structure regarding the loading type, relative density and type of the base material. It was determined that the filler’s temperature significantly increases due to the compressive impact loading, which might influence the macroscopic behavior of the cellular structure.

Abstract: In this paper the behavior of hexagonal honeycombs under dynamic in-plane loading is described. Additionally, the presence and influence of the filler gas inside the honeycomb cells is considered. Such structures are subjected to very large deformation during an impact, where the filler gas might strongly affect their behavior and the capability of deformational energy absorption, especially at very low relative densities. The purpose of this research was therefore to evaluate the influence of filler gas on the macroscopic cellular structure behavior under dynamic uniaxial loading conditions by means of computational simulations. The LS-DYNA code has been used for this purpose, where a fully coupled interaction between the honeycomb structure and the filler gas was simulated. Different relative densities, initial pore pressures and strain rates have been considered. The computational results clearly show the influence of the filler gas on the macroscopic behavior of analyzed honeycomb structures. Because of very large deformation of the cellular structure, the gas inside the cells is also enormously compressed which results in very high gas temperatures and contributes to increased crash energy absorption capability. The evaluated results are valuable for further research considering also the heat transfer in honeycomb structures and for investigations of variation of the base material mechanical properties due to increased gas temperatures under impact loading conditions.