Fabrication and mechanical testing of the uniaxial graded auxetic damperHasan Al-Rifaie
, Nejc Novak
, Matej Vesenjak
, Zoran Ren
, Wojciech Sumelka
, 2022, izvirni znanstveni članek
Opis: Auxetic structures can be used as protective sacrificial solutions for impact protection with lightweight and excellent energy-dissipation characteristics. A recently published and patented shock-absorbing system, namely, Uniaxial Graded Auxetic Damper (UGAD), proved its efficiency through comprehensive analytical and computational analyses. However, the authors highlighted the necessity for experimental testing of this new damper. Hence, this paper aimed to fabricate the UGAD using a cost-effective method and determine its load–deformation properties and energy-absorption potential experimentally and computationally. The geometry of the UGAD, fabrication technique, experimental setup, and computational model are presented. A series of dog-bone samples were tested to determine the exact properties of aluminium alloy (AW-5754, T-111). A simplified (elastic, plastic with strain hardening) material model was proposed and validated for use in future computational simulations. Results showed that deformation pattern, progressive collapse, and force–displacement relationships of the manufactured UGAD are in excellent agreement with the computational predictions, thus validating the proposed computational and material models.
Ključne besede: uniaxial graded auxetic damper, energy absorber, mechanical properties, finite element method, explicit solver
Objavljeno v DKUM: 28.07.2023; Ogledov: 364; Prenosov: 20
Celotno besedilo (7,31 MB)
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Solution of the problem of critical path’s finding in Excel on the basis of reducing it to ordinary transportation taskMimo Drašković
, Ludmila Malyaretz
, Oleksandr Dorokhov
, 2016, samostojni znanstveni sestavek ali poglavje v monografski publikaciji
Opis: The problem of determining the critical path for the scheduling tasks has been considered. An original technique for practical calculations using the available Solver add-on in Excel has been described. The proposed approach is based on reducing the task to solving the ordinary transportation problem, in particular to the problem of finding the longest path. Examples of solutions with the test input data and corresponding screenshots are given. The practical steps of the user’s action in the process of direct solution in Excel are consistently described. The analysis of the results of the proposed method has been performed and presented. It is established that presented method for calculating the critical path requires minimal efforts from the users, regardless of the dimension of the tasks.
Ključne besede: task scheduling, transportation tasks, calculations, critical path, Excel, Solver, software tools
Objavljeno v DKUM: 09.05.2018; Ogledov: 997; Prenosov: 84
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Computer-supported modelling of multimodal transportation networks rationalizationRatko Zelenika
, Slavomir Vukmirović
, Hilmija Mujić
, 2007, kratki znanstveni prispevek
Opis: This paper deals with issues of shaping and functioning of computer programs in the modelling and solving of multimodal transportation network problems. A methodology of an integrated use of a programming language for mathematical modelling is defined, as well as spreadsheets for the solving of complex multimodal transportation network problems. The paper contains a comparison of the partial and integral methods of solving multimodal transportation networks. The basic hypothesis set forth in this paper is that the integral method results in better multimodal transportation network rationalization effects, whereas a multimodal transportation network model based on the integral method, once built, can be used as the basis for all kinds of transportation problems within multimodal transport. As opposed to linear transport problems, multimodal transport network can assume very complex shapes. This paper contains a comparison of the partial and integral approach to transportation network solving. In the partial approach, a straight forward model of a transportation network, which can be solved through the use of the Solver computer tool within the Excel spreadsheet interface, is quite sufficient. In the solving of a multimodal transportation problem through the integral method it is necessary to apply sophisticated mathematical modelling programming languages which support the use of complex matrix functions and the processing of a vast amount of variables and limitations. The LINGO programming language is more abstract than the Excel spreadsheet, and it requires a certain programming knowledge. The definition and presentation of a problem logic within Excel, in a manner which is acceptable to computer software, is an ideal basis, for modelling in the LINGO programming language, as well as a faster and more effective implementation of the mathematical model. This paper provides proof for the fact that it is more rational to solve the problem of multimodal transportation networks by using the integral, rather than the partial method.
Ključne besede: intermodal transportation, transportation networks, spreadsheets, mathematical modelling, programming languages, Lingo, Solver
Objavljeno v DKUM: 01.06.2017; Ogledov: 1205; Prenosov: 110
Celotno besedilo (5,11 MB)
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Aerodynamic analysis of an oscillating airfoil in a power-extraction regime using the compressible Navier-Stokes equations with efficient and accurate low-speed preconditioningJernej Drofelnik
, 2012, diplomsko delo
Opis: A wing that is simultaneously heaving and pitching may extract energy from an oncoming air flow, thus acting as turbine. The purpose of this study was to analyse the relationship between the aerodynamics and the theoretical performance of this device by means of timedependent
laminar flow simulations performed with a research compressible finite volume Navier-Stokes solver COSA. In presented analyses, which confirm the findings of another
independent study, the efficiency of the power extraction of this device can be of the order of 35 %, and such an efficient operating condition is characterized due to the favourable effects of a strong dynamic stall.
This study is a part of a wider research programme of Dr. Campobasso’s group at University of Glasgow, aiming to develop a general-purpose computational framework for
unsteady aerodynamic and aeroacoustic wind energy engineering. In view of aeroacoustic applications, the developed flow solver uses the compressible formulation of the Navier-Stokes equations with carefully optimized low-speed preconditioning. To demonstrate the modeling capabilities, the accuracy and the high computational performance of the developed low-speed preconditioning technology, the unsteady aerodynamics of the energy-extracting device is simulated by using a computationally challenging freestream Mach number of 0.001. A mixed preconditioning strategy that maintains both the nominal accuracy and the computational efficiency of the solver also for time-dependent low-speed problems is presented. A fundamental element of novelty of this study is a thorough assessment of the proposed approach partly based on the challenging and realistic problem associated with the oscillating wing device.
Ključne besede: Low-speed preconditioning, compressible multigrid Navier-Stokes solver, energy-extracting oscillating wing, computational fluid dynamics.
Objavljeno v DKUM: 06.07.2012; Ogledov: 2481; Prenosov: 166
Celotno besedilo (2,40 MB)