1. Validation of boundary element method for assessment of weld joints accounting for notch stress : magistrsko deloRok Skerbiš, 2022, master's thesis Abstract: Robust, automated mesh generation on arbitrary weld joint geometries, using finite element method (FEM) is a problematic task. It was previously discovered, that an arbitrary weld joint geometry can be parameterized inside a CAD environment [1], however when it comes to domain discretization and boundary conditions assignment, the parameterized approach becomes too demanding inside FEM. This results in long FEM model preparation times and sometimes in problems with the parametric model itself, which leads to a need for an additional numerical method - boundary element method (BEM), which overcomes this issue and is beneficial in this case. BEM is a numerical method, that in addition to other applications finds a use in the elasto-mechanic problems, where the only concern is the boundary of the considered geometric domain. Since notch stress calculations of weld joints fall into this category, their calculation can be carried out with it. Since there is not much available information on whether or not such calculations are a suitable alternative for the currently used FEM, this thesis had to be confirmed through a structured and step by step procedure. First, a notch mesh quality study has been made, then other entities followed. It was discovered that BEM is applicable to the problem and capable of calculating results with sufficient quality. Furthermore, the parameter driven approach and automated calculation provide for additional advantageous potentials.
Keywords: weld joint, boundary element method, finite element method, spatial discretization, notch stress
Published in DKUM: 02.11.2022; Views: 549; Downloads: 0
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2. Vpliv vrste in geometrije zvarnega spoja na koncentracijo napetosti : diplomsko deloRok Skerbiš, 2020, undergraduate thesis Abstract: Zaradi predvidene dolge obratovalne dobe tirnih vozil je trdnost in ustrezno dimenzioniranje nosilnih delov le-teh izjemnega pomena. To velja še posebej za nosilni okvir podvozja tirnega vozila, ki je v splošnem konstrukcija zvarjena iz pločevin različnih debelin in oblik. Namen diplomskega dela je določitev faktorjev koncentracij napetosti na kritičnih mestih zvarnih spojev v odvisnosti od vrste geometrije in kombinacije zvarnih spojev. Za določitev omenjenih faktorjev so bile uporabljene računalniške simulacije po metodi končnih elementov. Na podlagi dobljenih faktorjev se lahko opredeli FAT razred vsakega izmed zvarov, pri čemer velja, da zvaru z najvišjim faktorjem pripada najnižji FAT razred. Končni rezultat dela predstavlja iz standardov dobljena Wöhlerjeva krivulja za posamezen zvar, ki se lahko primerja z Wöhlerjevo krivuljo dinamičnih preizkusov. Na ta način se lahko ugotovi ali so rezultati dobljeni z računalniškimi simulacijami primerljivi z rezultati preizkusov.
Keywords: tirno vozilo, zvarni spoj, faktor koncentracije napetosti, trajna dinamična trdnost, računalniško podprto konstruiranje, metoda končnih elementov
Published in DKUM: 01.09.2020; Views: 1136; Downloads: 123
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3. Optimiranje pogonskega mehanizma stiskalnice za globoki vlekBojan Vohar, Karl Gotlih, Jože Flašker, 2002, original scientific article Abstract: V prispevku se ukvarjamo z optimiranjem večzgibnega pogona paha stiskalnice za globoki vlek pločevine. Sedanja konstrukcija ne izpolnjuje vseh postavljenih zahtev, zato jo želimo čimbolj prilagoditi idealnim zahtevam tehnološkega postopka. Osnovni namen je prilagoditi sedanjo hitrostno karakteristiko paha zahtevam delovanja v določenem območju. Zato je bilo treba izdelati analizo pogona in njegov matematični model ter izvesti optimizacijo. Uporabljena metoda za nelinearno optimizacijo je sekvenčno kvadratno programiranje. Ker je postopek časovno odvisen, optimizacijskega modela ni moč uporabiti neposredno, ampak je treba primer prevesti v časovno neodvisno obliko, ki je primerna za reševanje s standardnim optimizacijskim postopkom. Cilj optimiranja je določiti takšne izmere pogonskega mehanizma, ki bi čimbolj izpolnile zahteve. V sklepu je prikazana primerjava doseženih rezultatov optimirane konstrukcije večzgibalnega pogona z začetnim stanjem pred optimizacijo.
Published in DKUM: 10.07.2015; Views: 992; Downloads: 39
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4. Optimal kinematic design of a link-drive mechanism with prescribed velocity characteristicsBojan Vohar, Karl Gotlih, Jože Flašker, 2003, other scientific articles Abstract: The paper presents an example of a link-drive mechanism for a deep drawing mechanical press. Because of its characteristics such a drive is much more appropriate than conventional crankshaft or eccentric drive. The existing design of the drive has proved unsatisfactory and does not meet all the demands and constraints, which are ideal for deep drawing process. Optimization of the drive is therefore necessary. The intention is to achieve the required velocity characteristics in a defined area of movement. Firstly, the drive is analyzed and a mathematical model is made and prepared for optimization procedure. The process is time-dependent, so it cannot be used directly in the optimization algorithm. Mathematical model is transformed intoa form suitable for the standard non-linear optimization procedure and then optimization is carried out. The method used is sequential quadratic programming. The final objective of the optimization process is to find such dimensions of link-drive members that the given requirements are satisfied in the best possible manner.
Keywords: mechanics, dynamics of mechanical systems, closed kinematic chains, mathematical modelling, non-linear optimization, drive optimization, drive dimensioning, kinematic analysis, link-drive mechanism, deep drawing press
Published in DKUM: 01.06.2012; Views: 2506; Downloads: 151
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5. Implementation of an ANCF beam finite element for dynamic response optimization of elastic manipulatorsBojan Vohar, Marko Kegl, Zoran Ren, 2008, original scientific article Abstract: Theoretical and practical aspects of an absolute nodal coordinate formulation (ANCF) beam finite element implementation are considered in the context of dynamic transient response optimization of elastic manipulators. The proposed implementation is based on the introduction of new nodal degrees of freedom, which is achieved by an adequate nonlinear mapping between the original and new degrees of freedom. This approach preserves the mechanical properties of the ANCF beam, but converts it into a conventional finite element so that its nodal degrees of freedom are initially always equal to zero and never depend explicitly on the design variables. Consequently, the sensitivity analysis formulas can be derived in the usual manner, except that the introduced nonlinear mapping has to be taken into account. Moreover, the adjusted element can also be incorporated into general finite element analysis and optimization software in the conventional way. The introduced design variables are related to the cross-section of the beam, to the shape of the (possibly) skeletal structure of the manipulator and to the drive functions. The layered cross-section approach and the design element technique are utilized to parameterize the shape of individual elements and the whole structure. A family of implicit time integration methods is adopted for the response and sensitivity analysis. Based on this assumption, the corresponding sensitivity formulas are derived. Two numerical examples illustrate the performance of the proposed element implementation.
Keywords: ANCF beam element, dynamic response, elastic manipulator, optimization
Published in DKUM: 31.05.2012; Views: 1596; Downloads: 109
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6. Optimization of elastic systems using absolute nodal coordinate finite element formulationBojan Vohar, Marko Kegl, Zoran Ren, 2006, other scientific articles Abstract: An approach to a shape optimization of elastic dynamic multibody systems is presented. The proposed method combines an appropriate shape parameterization concept and recently introduced finite element type using absolute nodal coordinate formulation (ANCF). In ANCF, slopes and displacements are used as the nodal coordinates instead of infinitesimal or finite rotations. This way one avoids interpolation of rotational coordinates and problems with finite rotations. ANCF elements are able to describe nonlinear deformation accurately; therefore, this method is very useful for simulations of lightweight multibody structures, where large deformations have to be taken into account. The optimization problem is formulated as a nonlinear programming problem and a gradient-based optimization procedure is implemented. The introduced optimization design variables are related to the cross-sectional parameters of the element and to the shape of the whole structure. The shape parameterization is based on the design element techniqueand a rational B ezier body is used as a design element. A body-like design element makes possible to unify the shape optimization of both simple beams and beam-like (skeletal) structures.
Keywords: mechanics, dynamics of material systems, multibody systems, elastic mechanical systems, manipulators, dynamically loaded beams, optimum shape design, absolute nodal coordinate formulation, design element technique, finite element method
Published in DKUM: 31.05.2012; Views: 2227; Downloads: 122
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