Wyniki wyszukiwania - Biblioteka Nauki

1

Analysis of unsteady forces acting on a slender cylinder

100%

Ziółkowski P. J. , Witkowski W. , Sobczyk B.

Transactions of the Institute of Fluid-Flow Machinery

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2018

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tom nr 140

23--38

EN

Developments in construction engineering (new materials, construction techniques) facilitate the design of very flexible, light structures with low damping which unfortunately results in higher susceptibility of these structures to wind action. It is therefore necessary to use more accurate scientific tools in the engineering phase of these structures. Analytical methods for considering wind effects on structures encounter difficulties with respect to mathematical formulations of aerodynamic forces. In this paper a 2D numerical model has been described which considers the fluid domain with respect to a cylindrical obstacle. This 2D model has been discretized using the finite volume method, and numerical simulations have been undertaken in order to describe the unsteady flow conditions within the analyzed domain. The simulations have been performed with boundary conditions characterizing the flow past a cylindrical obstacle. The results have been compared with the literature data from similar experiments. On the basis of the flow characteristics obtained, as well as the spatial distributions of the flow parameters, a model for further 3D analyses was selected. Next, a 3D numerical study of unsteady flow forces acting on a slender cylinder has been analyzed. Toward the end, a two-way fluid solid interaction approach has been utilized, which incorporates a computational fluid dynamics approach combined with computational solid dynamics.

2

Influence of the elastic cavity walls on cavity flow noise

89%

Łojek P. , Czajka I. , Gołaś A. , Suder-Dębska K.

Vibrations in Physical Systems

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2021

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tom Vol. 32, nr 1

art. no. 2021109

EN

In this study, computational fluid dynamics and computational aeroacoustics methods were used to investigate the influence of the elastic cavity walls on the noise generated by the flow over rectangular cavity. Two cases were considered and compared, one with rigid cavity walls, and one with elastic walls. In the latter case, the movement of the walls were solved by finite element modelling and coupled with CFD simulations. The noise generated by the flow over cavity was computed using Ffowcs Williams & Hawkings acoustic analogy. The increase of the sound pressure level for elastic walls case at frequency range of 1 kHz to 10 kHz is observed, compared to the rigid walls case.

3

Lattice-Boltzman Method in CFD modelling of direct acting relief valve

89%

Domagała M.

Czasopismo Techniczne. Mechanika

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2016

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tom Y. 113, iss. 4-M

101--106

EN

This paper presents the modelling of a direct acting relief valve with the use of the new approach of CFD techniques which uses the Lattice Boltzman Method (LBM). It allows for eliminating the biggest problem that occurs during the simulation of a valve operation, which is the motion of a working component. During traditional CFD modeling, a deformed mesh has to be used in such a case, which may lead to the occurrence of computational cells with negative volume and, as a consequence, remeshing of fluid domain.

PL

W artykule przedstawiono zastosowanie metody symulacji numerycznych przepływu wykorzystującą metodę siatkową Boltzmana (LBM) w modelowaniu zaworu przelewowego bezpośredniego działania. Umożliwia ona wyeliminowanie największego problemu, jaki występuje podczas symulacji pracy zaworu przelewowego tradycyjnymi metodami CFD, którą jest konieczność wykorzystywania deformującej się siatki modelu dyskretnego.

4

Modelling of direct acting relief valve using CFD-FSI simulation

75%

Domagała M.

Czasopismo Techniczne. Mechanika

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2015

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tom Y. 112, iss. 2-M

43--48

EN

This paper presents an attempt of using new capabilities of CFD tools in field of fluid-structure interaction simulation, which is called “immersed solids”. This techniques treats solids as objects immersed into fluid domain which moves along with the fluid. This paper presents comparison of selected CFD results of traditional approach and 'immersed solids' technique on example of direct acting relief valve.

PL

W artykule przedstawiono wykorzystanie nowych możliwości modelowania CFD w zakresie oddziaływania cieczy na ciała stałe przy wykorzystaniu techniki immersed solids. Na przykładzie zaworu przelewowego bezpośredniego działania przedstawiono kilka wybranych wyników symulacji CFD i porównanie z tradycyjnym podejściem w modelowaniu CFD zaworów hydraulicznych.

5

Development of a method for the analysis of mixed friction problems

75%

Albers A. , Nowicki L. , Enkler H. G.

International Journal of Applied Mechanics and Engineering

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2006

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tom Vol. 11, no 3

479-490

EN

This article deals with a holistic approach to the numerical analysis of mixed friction. By means of the finite element method, the influence of a set of selected parameters on the behaviour of the frictional contact system will be determined. For this, a three-dimensional parameterized FEM-model will be presented, which couples the equations of the structure mechanics with the Navier-Stokes-theory. To consider the roughness of machined surfaces, virtual surfaces are generated to represent the characteristics of usual manufacturing methods. At the Institute of product development, the theoretical approaches were implemented into a software code, which makes use of stochastic algorithms to obtain rough surfaces with the desired characteristics. The characterization of these virtual surfaces is done by the abbot curve and a roughness parameter. The generation of the surfaces is done by an evolutionary optimizer.

6

Model order reduction technique applied on harmonic analysis of a submerged vibrating blade

75%

Tengs E. , Charrassier F. , Holst M. , Storli P.

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tom Vol. 24, no. 1

131--142

EN

As part of an ongoing study into hydropower runner failure, a submerged, vibrating blade is investigated both experimentally and numerically. The numerical simulations performed are fully coupled acoustic-structural simulations in ANSYS Mechanical. In order to speed up the simulations, a model order reduction technique based on Krylov subspaces is implemented. This paper presents a comparison between the full ANSYS harmonic response and the reduced order model, and shows excellent agreement. The speedup factor obtained by using the reduced order model is shown to be between one and two orders of magnitude. The number of dimensions in the reduced subspace needed for accurate results is investigated, and confirms what is found in other studies on similar model order reduction applications. In addition, experimental results are available for validation, and show good match when not too far from the resonance peak.

7

Goal-oriented mesh adaptivity for fluid-structure interaction with application to heart-valve settings

71%

Wick T.

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tom Vol. LIX, nr 1

73-99

EN

We apply a fluid-structure interaction method to simulate prototypical dynamics of the aortic heart-valve. Our method of choice is based on a monolithic coupling scheme for fluid-structure interactions in which the fluid equations are rewritten in the 'arbitrary Lagrangian Eulerian' (ALE) framework. To prevent the backflow of structure waves because of their hyperbolic nature, a damped structure equation is solved on an artificial layer that is used to prolongate the computational domain. The increased computational cost in the presence of the artificial layer is resolved by using local mesh adaption. In particular, heuristic mesh refinement techniques are compared to rigorous goal-oriented mesh adaption with the dual weighted residual (DWR) method. A version of this method is developed for stationary settings. For the nonstationary test cases the indicators are obtained by a heuristic error estimator, which has a good performance for the measurement of wall stresses. The results for prototypical problems demonstrate that heart-valve dynamics can be treated with our proposed concepts and that the DWR method performs best with respect to a certain target functional.

PL

W artykule przedstawiono analizę zagadnienia oddziaływania płyn-struktura (FSI) w komputerowej symulacji pracy zastawki serca. Przedstawiono monolityczne sformułowanie tego zagadnienia, w którym równania dla struktury i płynu rozwiązywane są w pełnym sprzężeniu, przy czym do opisu ruchu płynu stosowane jest podejście typu Arbitrary Lagrangian-Euelerian (ALE). Zaproponowano metodę eliminacji zjawiska niefizycznego odbicia fal odkształceń struktury, polegającą na wprowadzeniu sztucznej dyssypacji energii tych fal w części brzegu obszaru położonej za zastawkami. W celu zwiększenia efektywności obliczeniowej wprowadzono lokalną adaptację siatki. W szczególności, porównano heurystyczne techniki adaptacji siatki z techniką opartą na wykorzystaniu ważonego residuum sprzężonego (Dual Weighted Residual, DWR). Przedstawiono wyniki obliczeń testowych demonstrujące poprawność zaproponowanego podejścia oraz skuteczność metody adaptacyjnej DWR.

8

Analysis of fluid-structure interaction of a torus subjected to wind loads

71%

Padewska A. , Szczepaniak P. , Wawrzynek A.

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tom Vol. 21, no. 2

151--167

EN

In the paper the aerodynamic forces acting on a part of a water slide or other object with curved, tubular shape, depending on the section of a torus and value of the wind velocity, were obtained. This was done by means of finite element method (FEM) and finite volume method (FVM) computer simulations, using modules: computational fluid dynamics (CFD) and fluid-structure interaction (FSI) and taking into account the Eurocode EN 1991-1-4.

9

Porównanie sił aerodynamicznych działających na połowę torusa i dwa walce o tej samej długości

71%

Padewska A. , Szczepaniak P. , Wawrzynek A.

Modelowanie Inżynierskie

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2016

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tom T. 29, nr 60

52--57

PL

W Eurokodzie PN-EN 1991-1-4 [11] brakuje wytycznych projektowych umożliwiających oszacowanie sił aerodynamicznych działających na obiekty o nietypowym kształcie. W referacie porównano zatem charakter przepływu powietrza o dużych, coraz częściej występujących na świecie prędkościach w pobliżu obiektów w kształcie połowy torusa (np. fragmentu zjeżdżalni wodnej) i dwóch walców o sumarycznej długości równej długości osi połowy torusa, ustawionych poziomo oraz odchylonych od poziomej płaszczyzny pod kątem ß = 45°. Porównano również siły aerodynamiczne działające na połowę torusa - opór aerodynamiczny i poziomą siłę prostopadłą do niego, z siłami działającymi na walce. Wyniki otrzymano na podstawie analiz numerycznych: MES i MOS, wykorzystując moduły: CFD (Computational Fluid Dynamics) i FSI (Fluid-Structure Interaction).

EN

Eurocode EN 1991-1-4 [11] does not include issues concerning wind loads acting on constructions in a non-typical shape. Therefore, in the paper the character of high-speed air flow, which increasingly occurs in the world around objects in the shape of a half - torus (eg. a fragment of a water slide) and two cylinders positioned horizontally and inclined to the horizontal plane at an angle ß = 45° were compared. Also aerodynamic forces acting on a half of the torus - an aerodynamic resistance and a horizontal force perpendicular to the direction of a wind velocity, were compared with forces acting on cylinders. Results are based on numerical analysis: FEM and FVM using the following modules: CFD (Computational Fluid Dynamics) and FSI (Fluid-Structure Interaction).

10

Patient-specific fluid-structure interaction simulation of the LAD-ITA bypass graft for moderate and severe stenosis: A doubt on the fractional flow reserve-based decision

71%

Tajeddini F. , Firoozabadi B. , Pakravan H. A. , Ahmadi Tafti S. H.

Biocybernetics and Biomedical Engineering

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2022

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tom Vol. 42, no. 1

143--157

EN

Fractional flow reserve (FFR)-based decision improves the outcomes of percutaneous coronary intervention (PCI) for some patients, while its effectiveness in improving the results of coronary artery bypass graft (CABG) is unclear, in particular for moderate stenosis. It may be due to the fact that FFR cannot take into account the impacts of competitive flow (CF), intimal hyperplasia (IH), as well as compliance mismatch (CMM). As a result, two questions arise 1) whether FFR is a sufficient factor to decide to perform the CABG for patients with moderate to severe stenosis or not and 2) whether post-operative FFR shows the effectiveness of a graft. To shed light on this matter, two patient-specific models of LAD-ITA graft, consisting of two different severities of stenosis (moderate and severe), were simulated using two-way FSI simulation. It was observed that although both pre- and postoperative FFRs for moderate stenosis were higher, CF is more intense for moderate stenosis than severe one. Also, it was seen that CM and IH are more likely to occur in the bed, toe, and heel areas of a bypass graft performed for moderate stenosis. All in all, it can be concluded that in the case of moderate stenosis, pre- and post-operative FFRs might not be a suitable index for making the decision about performing or deferring CABG and also the effectiveness of the graft. Under such circumstances, it seems rational to use CFD in a wider range to investigate patients with moderate stenosis before the operation.