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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: 894; Prenosov: 16
URL Povezava na celotno besedilo

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: 1046; Prenosov: 20
URL Povezava na celotno besedilo

Optimization of a fuel injection system for diesel and biodiesel usage
Breda Kegl, Marko Kegl, Stanislav Pehan, 2008, izvirni znanstveni članek

Opis: This paper presents an optimization procedure of a fuel injection system of a bus diesel engine. Attention is focused on the differences resulting from using two different types of fuel: diesel and biodiesel. The proposed design procedure relies on the assumption that the atomization of fuel spray influences the diesel engine performance, fuel consumption, and harmful emission significantly. As a measure of spray atomization, the Sauter mean diameter is employed and introduced into the objective function. The design problem is formulated in the form of a multiobjective optimization problem, taking into account the ESC 13 mode test for diesel engines of commercial vehicles. The design variables of the injection system are related to the shape of the cam profile, to the nozzle geometry, and to the control parameters influencing the injection quantity and timing. The geometrical properties of the cam profile and the injection parameters are kept within acceptable limits by the imposed constraints. The results of optimization using diesel and biodiesel are compared to each other to show the influence offuel type on final design and performance of the system.
Ključne besede: fuel injection system, diesel engine, biodiesel fuel, engine performance, numerical simulations
Objavljeno: 31.05.2012; Ogledov: 1266; Prenosov: 47
URL Povezava na celotno besedilo

Diesel and biodiesel fuel spray simulations
Primož Pogorevc, Breda Kegl, Leopold Škerget, 2008, izvirni znanstveni članek

Opis: This paper deals with the investigation of the influential parameters of a mathematical spray breakup model using different fuels. Beside injection system measurements, fuel physical properties and injection process characteristics were measured, because they are necessary for the spray simulation input. For validation purposes, spray was injected into motionless air at atmospheric pressure and room temperature and filmed with a high-speed camera. Spray macrocharacteristics have been determined on the recorded images. Using the simulation program, the injection processes for diesel, biodiesel, and their 50% blend B50 have been simulated. Spray mathematical model parameters were tuned based on the experimentally gained results. Primary breakup model parameters showed the biggest impact on the spray characteristics and were therefore expressed using the fuel physical properties, the injection process characteristics, and the working regime parameters. Spray simulations into the combustion chamber were made in the end. All of these results are presented and discussed in this paper.
Ključne besede: fuel spray, spray breakup, biodiesel fuel, fuels, numerical simulations, mathematical model
Objavljeno: 31.05.2012; Ogledov: 961; Prenosov: 53
URL Povezava na celotno besedilo

Coupled simulations of nozzle flow, primary fuel jet breakup, and spray formation
Eberhard von Berg, Wilfried Edelbauer, Aleš Alajbegović, Reinhard Tatschl, Martin Volmajer, Breda Kegl, Lionel C. Ganippa, 2005, izvirni znanstveni članek

Opis: Presented are two approaches for coupled simulations of the injector flow withspray formation. In the first approach the two-fluid model is used within the injector for the cavitating flow. A primary breakup model is then applied at the nozzle orifice where it is coupled with the standard discrete droplet model. In the second approach the Eulerian multi-fluid model is applied for both the nozzle and spray regions. The developed primary breakup model, used in both approaches, is based on locally resolved properties of the cavitating nozzle flow across the orifice cross section. The model provides the initial droplet size and velocity distribution for the droplet parcels released from the surface of a coherent liquid core. The major feature of the predictions obtained with the model is a remarkable asymmetry of the spray. This asymmetryis in agreement with the recent observations at Chalmers University where they performed experiments using a transparent model scaled-up injector.The described model has been implemented into AVL FIRE computational fluid dynamics code which was used to obtain all the presented results.
Ključne besede: internal combustion engines, fuel injection, simulations
Objavljeno: 01.06.2012; Ogledov: 883; Prenosov: 52
URL Povezava na celotno besedilo

Heat conduction in closed-cell cellular metals
Matej Vesenjak, Zoran Žunič, Andreas Öchsner, Matjaž Hriberšek, Zoran Ren, 2005, izvirni znanstveni članek

Opis: The purpose of this research was to describe the thermal transport properties in closed-cell cellular metals. Influence of cell size variations with different pore gases has been investigated with transient computational simulations. Heat conduction through the base material and gas in pores (cavities) was considered, while the convection and radiation were neglected in the initial stage of this research. First, parametric analysis for definingthe proper mesh density and time step were carried out. Then, two-dimensional computational models of the cellular structure, consisting of the base material and the pore gas, have been solved using ANSYS CFX software within the framework of finite volume elements. The results have confirmed theexpectations that the majority of heat is being transferred through the metallic base material with almost negligible heat conduction through the gas in pores. The heat conduction in closed-cell cellular metals is therefore extremely depended on the relative density but almost insensitive regarding tothe gas inside the pore, unless the relative density is very low.
Ključne besede: heat transfer, cellular metal materials, porous materials, closed cells, gas fillers, computational simulations
Objavljeno: 01.06.2012; Ogledov: 1325; Prenosov: 65
URL Povezava na celotno besedilo

Analytical travel time models for multi aisle automated storage and retrieval systems
Tone Lerher, Matjaž Šraml, Janez Kramberger, Iztok Potrč, Matej Borovinšek, Blaž Zmazek, 2005, izvirni znanstveni članek

Opis: Multi aisle automated storage and retrieval systems correspond to multiple picking aisles served by a single storage and retrieval machine. These systemsare used in practice when the need for pallet places is high and the throughput capacity is relatively low. Therefore, considerable savings of initial investment costs due to single aisle systems can be achieved using such systems. The objective of the presented study is to develop analytical travel time models for multi aisle automated storage and retrieval systems considering the operating characteristics of the storage and retrieval machine. With the proposed analytical travel time models, average travel time of the storage and retrieval machine, from which the performance of multi aisle automated storage and retrieval systems can be evaluated is determined. A simulation model of multi aisle automated storage and retrieval systems was developed to compare the performances of the proposed analytical travel time models. An example of multi aisle automated storage and retrieval systems withfive picking aisles was presented for the evaluation purpose. The results show that proposed analytical travel time models perform satisfactory according to the results of simulation analysis and could be very useful toolsfor designing of multi aisle automated storage and retrieval systems in real-world applications.
Ključne besede: warehousing, logistics, high rack storage, simulations, travel time models
Objavljeno: 01.06.2012; Ogledov: 1428; Prenosov: 63
URL Povezava na celotno besedilo

Mathematical model of IRIS replication mechanism for the simulation of tactical networks
Jože Mohorko, Matjaž Fras, 2009, izvirni znanstveni članek

Opis: The Multilateral Interoperability Programme (MIP) was established to promote more successful and better harmonized operational functions for international peace-keeping forces. The C2IEDM/JC3IEDM (Command and Control Information Exchange Data Model) ensures the interconnection of Command and Control Information Systems (C2ISs) throughout all levels, from the corps down to the lower ranks. The usability of C2ISs highly correlates with the capacities of data information carriers, and the need is growing for greater capacity and reliability of transmission media and cryptographic message security. Simulation of tactical networks is an important task in planning military missions. Such methodologies assure a higher probability of success during critical tactical operations. This article focuses on a new radio network modeling method for the C2IS, which is verified by the OPNET simulation environment. This modeling method can be used in tactical radio network planning and optimization processes.
Ključne besede: communications, tactical networks, tactical radio networks, traffic modelling, radio network modeling, simulations, C2IS
Objavljeno: 01.06.2012; Ogledov: 1235; Prenosov: 56
URL Povezava na celotno besedilo

Computational model for the analysis of bending fatigue in gears
Janez Kramberger, Matjaž Šraml, Srečko Glodež, Jože Flašker, Iztok Potrč, 2004, izvirni znanstveni članek

Opis: A computational model for the determination of service life of gears with regard to bending fatigue in a gear tooth root is presented. The fatigue process leading to tooth breakage is divided into crack initiation (Ni) and crack propagation (Np) periods, where the complete service life is defined as N = Ni + Np. The strain-life method in the framework of the FEM method has been used to determine the number of stress cycles Ni required for fatigue crack initiation. Gear tooth crack propagation was simulated using a FEM method based computer program which uses principles of linear elastic fracture mechanics. The Paris equation is then used for the further simulation of the fatigue crack growth. The presented model is used to determine the service life of a real spur gear made from through-hardened steel 42CrMo4.
Ključne besede: machine elements, gears, bending fatigue, service life, fatigue crack initiation, fatigue crack propagation, computational simulations, numerical modelling, fracture mechanics
Objavljeno: 01.06.2012; Ogledov: 2226; Prenosov: 60
URL Povezava na celotno besedilo

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