1. A novel particle–particle and particle–wall collision model for superellipsoidal particlesJana Wedel, Mitja Štrakl, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2023, original scientific article Keywords: multiphase flow, Lagrangian particle tracking, superellipsoid, collision, friction
Published in DKUM: 28.03.2024; Views: 171; Downloads: 9
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2. Coefficient of tangential restitution for non-spherical particlesJana Wedel, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2024, original scientific article Abstract: In various industrial and naturally occurring multiphase flows, whether dilute or dense, particle interaction plays a crucial role. In most cases, the particles are non-spherical, which poses a computational challenge in terms of particle motion and particle interaction, i.e. both particle–particle and particle–wall collisions. In this study, we present a novel frictional particle collision model to be used in general fluid flows. The model is derived for superellipsoidal particle shapes and thus allows consideration of frictional collisions of a wide variety of particle geometries. In this context, we derive an expression for the tangential coefficient of restitution applicable to arbitrarily shaped particles. Furthermore, we present the performance of the novel model by applying it to demonstrative examples ranging from two- to multi-particle systems.
Keywords: non-spherical particles, particle collision, tangential restitution coefficient, superellipsoids
Published in DKUM: 26.02.2024; Views: 293; Downloads: 40
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3. Parameter space for a dissipative Fermi-Ulam modelDiego F. M. Oliveira, Edson D. Leonel, 2011, original scientific article Abstract: The parameter space for a dissipative bouncing ball model under the effect of inelastic collisions is studied. The system is described using a two-dimensional nonlinear area-contracting map. The introduction of dissipation destroys the mixed structure of phase space of the non-dissipative case, leading to the existence of a chaotic attractor and attracting fixed points, which may coexist for certain ranges of control parameters. We have computed the average velocity for the parameter space and made a connection with the parameter space based on the maximum Lyapunov exponent. For both cases, we found an infinite family of self-similar structures of shrimp shape, which correspond to the periodic attractors embedded in a large region that corresponds to the chaotic motion.
Keywords: parameter space, Fermi-Ulam model, inelastic collision
Published in DKUM: 03.07.2017; Views: 1933; Downloads: 395
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4. Computational and experimental crash analysis of the road safety barrierZoran Ren, Matej Vesenjak, 2005, original scientific article Abstract: The paper describes the computational analysis and experimental crash tests ofa new road safety barrier. The purpose of this research was to develop and evaluate a full-scale computational model of the road safety barrier for use in crash simulations and to further compare the computational results with real crash test data. The impact severity and stiffness of the new design havebeen evaluated with the dynamic nonlinear elasto-plastic analysis of the three-dimensional road safety barrier within the framework of the finite element method with LS-DYNA code. Comparison of computational and experimentalresults proved the correctness of the computational model. The tests have also shown that the new safety barrier assures controllable crash energy absorption which in turn increases the safety of vehicle occupants.
Keywords: mechanics, collision, road restraint system, computational crash analysis, experimental crash test, impact
Published in DKUM: 01.06.2012; Views: 2150; Downloads: 115
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5. Searching for messages conforming to arbitrary sets of conditions in SHA-256Marko Hölbl, Christian Rechberger, Tatjana Welzer-Družovec, 2008, independent scientific component part or a chapter in a monograph Abstract: Recent progress in hash functions analysis has led to collisions on reduced versions of SHA-256. As in other hash functions, differential collision search methods of SHA-256 can be described by means of conditions on and between state and message bits. We describe a tool for efficient automatic searching of message pairs conforming to useful sets of conditions, i. e. stemming from (interleaved) local collisions. We not only considerably improve upon previous work [7], but also show the extendability of our approach to larger sets of conditions. Furthermore, we present the performance results of an actual implementation and pose an open problem in this context.
Keywords: hash functions analysis, messages, SHA-256, automatic searching, differential collision search
Published in DKUM: 31.05.2012; Views: 1723; Downloads: 100
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