Národní úložiště šedé literatury Nalezeno 38 záznamů.  1 - 10dalšíkonec  přejít na záznam: Hledání trvalo 0.01 vteřin. 
The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids
Kolman, Radek ; Berezovski, A. ; Kruisová, Alena
The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids aims to bring together scientists and engineers with interest in advanced modelling of wave propagation in solids. The Conference on Advanced Modelling of Wave Propagation in Solids will concentrate on topics related to analytical, numerical and experimental studies of linear and non-linear waves in conventional, advanced and modern materials like metamaterials and auxetic materials, to strongly dispersive wave propagation in inhomogeneous solids and to waves in materials with microstructure, etc. Attention will also be devoted to up-to-date formulations of non-linear constitutive equations in the description of material response under thermomechanical loading, dynamic fracture and damage, phase transformations, shock waves, and to dissipative effects. The recent advances and properties of analytical and numerical approaches and strategies should also be discussed. The main purpose of the Conference on Advanced Modelling of Wave Propagation in Solids is to discuss novel and recent methods of wave propagation modelling and to consider expected credibility of results especially in cases when comparison with those of experiment is not available. Theoretical, computational as well as experimental contributions on the wave propagation are welcome.
Recent progress in numerical methods for explicit finite element analysis
Kolman, Radek ; Kopačka, Ján ; Gonzalez, J. ; Gabriel, Dušan ; Cho, S.S. ; Plešek, Jiří ; Park, K.C.
In this paper, a recent progress in explicit finite element analysis is discussed. Properties and behaviour of classical explicit time integration in finite element analysis of elastic wave propagation and contact-impact problems based on penalty method in contact-impact problems are summarized. Further, stability properties of explicit time scheme and the penalty method as well as existence of spurious oscillations in transient dynamics are mentioned. The novel and recent improving and progress in explicit analysis based on a local time integration with pullback interpolation for different local stable time step sizes, bipenalty stabilization for enforcing of contact constrains with preserving of stability limit for contact-free problems and using a direct inversion of mass matrix are presented. Properties of the employed methods are shown for one-dimensional cases of wave propagation and contact-impact problems.
Computational time reversal method based on finite element method: influence of temperature
Mračko, Michal ; Kolman, Radek ; Kober, Jan ; Převorovský, Zdeněk ; Plešek, Jiří
Time reversal method is used to focus elastic waves to the location of the original source and reconstruct its source time function. The procedure consists of two steps: Frontal task and Reversal task. In the Frontal task, the medium is excited by an arbitrary source, elastic waves propagate through a body of interest and the dynamic response at few points on boundary is recorded. In the second step (say the Reversal task) the response signal is reversed in time and transmitted back into the medium resulting in focusing in the original source location. It is of practical importance to investigate a case when the medium changes its properties between the frontal and reversal wave propagation steps. An example is a problem of transferring experimentally recorded data to a computational model, where discrepancies in geometry, elastic properties and boundary conditions are expected. Our motivation is to develop a methodology for computation of time reversal problems in commercial finite element software. The results prove that this method is extremely sensitive to the change of temperature and one have to pay special attention to tuning of elastic parameters relevant to the\nexperiment.
Finite element modeling of the signal propagation in a thin tube and comparison with experimental data
Kruisová, Alena ; Kolman, Radek ; Trnka, Jan ; Mračko, Michal
In finite element modeling of wave propagation problems, both the spatial and temporal discretization lead to dispersion errors. It means that the phase velocity of propagated wave is related to its frequency. In framework of temporal-spatial dispersion analysis, the time step size for implicit time integration method based on the Newmark method is proposed for linear and quadratic serendipity plane finite elements. In this paper, we verify the theoretical dispersion analysis by elastic wave propagation in thin tube, where experimental results are known. Such time step size was used in finite element modeling of the stress wave propagating in this thin steel tube, the results of simulations were compared with experimental results.
Metodika pro modelování dynamických deju metodou konecných prvku - fáze II
Mochar, Dominik ; Mračko, Michal ; Gabriel, Dušan ; Kolman, Radek ; Kopačka, Ján
Zpráva navazuje na metodiku Z-1546/15 popisující základní metody, algoritmy a postupy pro numerické rešení MKP úloh rázové dynamiky pri vývoji komponent zbraní. V této práci byly testovány disperzní vlastnosti bilineárních ctyruzlových prvku s redukovanou integrací na úloze rázu dvou elastických válcu, pro které je k dispozici analytické rešení. Pozornost byla zamerena na zkoumání vlivu velikosti prvku a casového integracního kroku na presnost numerického rešení. Výsledky získané z MKP programu PMD, Abaqus a Ansys byly diskutovány a porovnány s analytickým rešením.
On finite element modelling in time reversal problems
Mračko, Michal ; Kober, Jan ; Kolman, Radek ; Převorovský, Zdeněk ; Plešek, Jiří ; Masák, Jan ; Kruisová, Alena
In this paper we analyse suitability and accuracy of computational techniques in time reversal applications based on finite element method (FEM) for detection and localization of defects, cracks or other acoustic emission sources in bodies and structures. As it is known, a classical explicit integration scheme - central difference is reversible. The central difference scheme as a time integrator is widely used for linear and nonlinear finite element analyses and it is also implemented in commercial and open-source finite element software. In the paper properties of the explicit FEM in time reversal problems are studied and analysed. We use the standard Galerkin FEM formulation with linear shape functions, one-point Gauss integration and lumped mass matrix. Loading by the Ricker pulse was applied for modelling of the acoustic source in an elastic square domain. A special attention is paid to the choice of boundary conditions in reverse problem which keep the reversibility of problems of interest. Finally, we show the quality of refocusing of the original acoustic source.
An explicit time scheme with local time stepping for one-dimensional wave propagation in a bimaterial bar
Kolman, Radek ; Cho, S.S. ; Gonzalez, J.G. ; Park, K.C. ; Berezovski, A.
In this paper, we test a two-time step explicit scheme with local time stepping. The standard explicit time scheme in finite element analysis is not able to keep accuracy of stress distribution through meshes with different local Courant numbers for each finite element. The used two-time step scheme with the diagonal mass matrix is based on the modification of the central difference method with pullback interpolation. We present a numerical example of one-dimensional wave propagation in a bimaterial elastic bar. Based on numerical tests, the employed time scheme with pullback interpolation and local stepping technique is able to eliminate spurious oscillations in stress distribution in numerical modelling of shock wave propagation in heterogeneous materials.
Explicit dynamic finite element analysis of a firing pin assembly
Mochar, Dominik ; Gabriel, Dušan ; Masák, Jan ; Kopačka, Ján ; Kolman, Radek ; Plešek, Jiří ; Hynek, P. ; Vtípil, J.
In this paper, explicit dynamic finite element analysis of a firing pin assembly was performed. Two different geometries of the firing pin were considered using the finite element software PMD and Abaqus. For both variants there was evaluated a stress distribution at the critical point of a tested component, that is going to be later used for a fatigue analysis of the firing pin.
Explicitní dynamická MKP analýza zápalníku zbraně
Mochar, Dominik ; Masák, Jan ; Gabriel, Dušan ; Kolman, Radek ; Kopačka, Ján ; Plešek, Jiří
Zpráva shrnuje výsledky řešení rázové úlohy zápalníku zbraně. V první části je popsán verifikační výpočet na zjednodušené úloze bez uvažování kontaktu. V druhé části zprávy jsou prezentovány výsledky získané s využitím kontaktního algoritmu.
Metodika pro modelování dynamických dějů metodou konečných prvků - fáze I
Kolman, Radek ; Gabriel, Dušan ; Červ, Jan ; Plešek, Jiří
Ve zprávě je detailně představena metoda konečných prvků (MKP) pro řešení rázových úloh šíření vln napětí v poddajných tělesech se zaměřením na explicitní integraci pohybových rovnice metodou centrálních diferencí. Je provedena dispersní analýza MKP, na jejímž základě je možné navrhnout optimální velikost prvku MKP sítě, a je taktéž sledován vliv velikosti časového kroku na dispersní hování. V závěru zprávy jsou shrnuty doporučující kritéria pro volbu velikosti prvků a časového kroku tak, aby dispersní chyby měřené rychlostmi šíření vlny nepřesáhly dovolené hodnoty.

Národní úložiště šedé literatury : Nalezeno 38 záznamů.   1 - 10dalšíkonec  přejít na záznam:
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