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1.
Thermal post-impact behaviour of closed-cell cellular structures with fillers
Matej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, izvirni znanstveni članek

Opis: 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 thermal- structural 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.
Ključne besede: mechanics, cellular structures, closed cells, gas fillers, impact loading, fluid-structure interaction, dynamic loads, LS-DYNA, ANSYS CFX 10.0, computational simulations
Objavljeno: 31.05.2012; Ogledov: 692; Prenosov: 8
URL Celotno besedilo (0,00 KB)

2.
Evaluation of thermal and mechanical filler gas influence on honeycomb structures behaviour
Matej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, izvirni znanstveni članek

Opis: 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.
Ključne besede: mechanics, cellular materials, honeycomb structure, gas filler, thermal properties, mechanical properties, dynamic loading, LS-DYNA, computational simulations
Objavljeno: 31.05.2012; Ogledov: 742; Prenosov: 4
URL Celotno besedilo (0,00 KB)

3.
Application aspects of the meshless SPH method
Matej Vesenjak, Zoran Ren, 2007, izvirni znanstveni članek

Opis: Computational simulations have become an indispensable tool for solving complex problems in engineering and science. One of the new computational techniques are the meshless methods, covering several application fields in engineering. In this paper the Smoothed Particle Hydrodynamics (SPH) method and its implementation in the explicit finite element code LS-DYNA is discussed. Its application and efficiency is shown with two practical engineering application examples. The first example describes the modeling of fuel sloshing in a reservoir, where different formulations, using mesh-based and meshless methods, are compared and evaluated according to experimental measurements. The second example describes the impact analysis of a cellular structure, where the influence of viscous fluid pore filler flow has been studied. The SPH method proved to become a reliable and efficient tool, especially for solving large scale and advanced engineering problems.
Ključne besede: computational mechanics, smoothed particel hydrodynamics, fluid sloshing, cellular structure
Objavljeno: 31.05.2012; Ogledov: 707; Prenosov: 5
URL Celotno besedilo (0,00 KB)

4.
Behaviour of cellular materials under impact loading
Matej Vesenjak, Zoran Ren, Andreas Öchsner, 2008, izvirni znanstveni članek

Opis: The paper describes experimental and computational testing of regular open-cell cellular structures behaviour under impact loading. Open-cell cellular specimens made of aluminium alloy and polymer were experimentally tested under quasi-static and dynamic compressive loading in order to evaluate the failure conditions and the strain rate sensitivity. Additionally, specimens with viscous fillers have been tested to determine the increase of the energy absorption due to filler effects. The tests have shown that brittle behaviour of the cellular structure due to sudden rupture of intercellular walls observed in quasi-static and dynamic tests is reduced by introduction of viscous filler, while at the same time the energy absorption is increased. The influence of fluid filler on open-cell cellular material behaviour under impact loading was further investigated with parametric computational simulations, where fully coupled interaction between the base material and the pore filler was considered. The explicit nonlinear finite element code LS-DYNA was used for this purpose. Different failure criteria were evaluated to simulate the collapsing of intercellular walls and the failure mechanism of cellular structures in general. The new computational models and presented procedures enable determination of the optimal geometric and material parameters of cellular materials with viscous fillers for individual application demands. For example, the cellular structure stiffness and impact energy absorption through controlled deformation can be easily adapted to improve the efficiency of crash absorbers.
Ključne besede: mechanics, porous materials, cellular materials, impact loading, mechanical testing, fluid-structure interaction, failure mechanism
Objavljeno: 31.05.2012; Ogledov: 661; Prenosov: 7
URL Celotno besedilo (0,00 KB)

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6.
HEAT TRANSFER IN UNIPORE CELLULAR STRUCTURE
Matevž Frajnkovič, 2017, magistrsko delo

Opis: This master’s thesis deals with heat transfer in a specific cellular structure, called UniPore cellular structure. Said structure has been developed at Japan’s Kumamoto university. The structure is manufactured using the technique of explosion welding. Due to longitudinal orientation of the pores and high thermal conductivity of materials, the thermal properties of the structure as a heat exchanger have been analysed. Influence of different boundary conditions on the effectiveness of heat transfer in the structure has been analysed. The results are compared and analysed. It has been concluded, that the structure itself might be suitable when dealing with dirty liquids. Usage of the structure in such systems would enable a quick and efficient cleaning process of the waste, that deposits on the walls over time.
Ključne besede: Heat transfer, cellular structure, porous materials, CFD
Objavljeno: 24.08.2017; Ogledov: 184; Prenosov: 59
.pdf Celotno besedilo (2,59 MB)

7.
Designing the gear body structure to control vibration behaviour
Riad Ramadani, 2018, doktorska disertacija

Opis: This research presents a new approach aiming to reduce gear vibration as well as its weight by modifying the gear body structure. The primary objective was to reduce vibration and noise emission of spur gears. For this purpose, a solid gear body was replaced by a cellular lattice structure, which was expected to raise the torsional elasticity of the gear body. The cellular lattice structure was designed and optimized by FE-based topology optimization software CAESS ProTOp, which is based on strain energy control. For experimental purposes, the optimized gear was produced from Titanium alloy Ti-6Al-4V ELI by using Selective Laser Melting technique. A polymer matrix was added to increase the damping of the structure. In order to test the gears, a new test rig with closed loop was conceived, designed and produced. The test rig is equipped with two gear pairs: with the tested one and with the driving one. The gears have been run and tested at different speeds and torque. The acceleration, strain and sound pressure of a running gear pair was measured. The final processing of the signal was done by a specially developed software based on LabView. By employing the fast Fourier transformation the time signal of acceleration, strain and sound pressure has been converted to the frequency spectrum and time frequency spectrogram. The results obtained by testing the solid and cellular lattice gear body were compared. It was experimentally confirmed that the cellular lattice structure of a gear body and addition of a polymer matrix may significantly reduce the vibration.
Ključne besede: Gear vibration, cellular lattice structure, topology optimization, test rig
Objavljeno: 27.02.2018; Ogledov: 93; Prenosov: 25
.pdf Celotno besedilo (13,76 MB)

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