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1

On speeding up nano- and micromechanical calculations for irregular systems with long-range potentials

Rybarska-Rusinek L., Rejwer E., Linkov A.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2020

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Vol. 68, nr 2

337--344

EN

Irregular systems with long-range interactions and multiple clusters are considered. The presence of clusters leads to excessive computational complexity of conventional fast multipole methods (FMM), used for modeling systems with large number of DOFs. To overcome the difficulty, a modification of the classical FMM is suggested. It tackles the very cause of the complication by accounting for higher intensity of fields, generated by clusters in upward and especially in downward translations. Numerical examples demonstrate that, in accordance with theoretical estimations, in typical cases the modified FMM significantly reduces the time expense without loss of the accuracy.

2

Isogeometric Fast Multipole Boundary Element Method Based on Burton-Miller Formulation for 3D Acoustic Problems

Chen Leilei, Zhao Wenchang, Liu Cheng, Chen Haibo, Marburg Steffen

Archives of Acoustics

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2019

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Vol. 44, No. 3

475--492

EN

An isogeometric boundary element method is applied to simulate wave scattering problems governed by the Helmholtz equation. The NURBS (non-uniform rational B-splines) widely used in the CAD (computer aided design) field is applied to represent the geometric model and approximate physical field variables. The Burton-Miller formulation is used to overcome the fictitious frequency problem when using a single Helmholtz boundary integral equation for exterior boundary-value problems. The singular integrals existing in Burton-Miller formulation are evaluated directly and accurately using Hadamard’s finite part integration. Fast multipole method is applied to accelerate the solution of the system of equations. It is demonstrated that the isogeometric boundary element method based on NURBS performs better than the conventional approach based on Lagrange basis functions in terms of accuracy, and the use of the fast multipole method both retains the accuracy for isogeometric boundary element method and reduces the computational cost.

3

2D Structural Acoustic Analysis Using the FEM/FMBEM with Different Coupled Element Types

Chen L., Zhao W., Liu C., Chen H.

Archives of Acoustics

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2017

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Vol. 42, No. 1

37--48

EN

A FEM-BEM coupling approach is used for acoustic fluid-structure interaction analysis. The FEM is used to model the structure and the BEM is used to model the exterior acoustic domain. The aim of this work is to improve the computational efficiency and accuracy of the conventional FEM-BEM coupling approach. The fast multipole method (FMM) is applied to accelerating the matrix-vector products in BEM. The Burton-Miller formulation is used to overcome the fictitious eigen-frequency problem when using a single Helmholtz boundary integral equation for exterior acoustic problems. The continuous higher order boundary elements and discontinuous higher order boundary elements for 2D problem are developed in this work to achieve higher accuracy in the coupling analysis. The performance for coupled element types is compared via a simple example with analytical solution, and the optimal element type is obtained. Numerical examples are presented to show the relative errors of different coupled element types.

4

Szybka wielobiegunowa metoda elementów brzegowych w homogenizacji numerycznej materiałów porowatych

Ptaszny J., Hatłas M.

Modelowanie Inżynierskie

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2015

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T. 23, nr 54

55--60

PL

W pracy przedstawiono nową wersję szybkiej wielobiegunowej metody elementów brzegowych służącą do analizy zagadnień przestrzennych liniowej teorii sprężystości, w której zastosowano elementy brzegowe o kwadratowych funkcjach kształtu oraz metodę adaptacyjnego całkowania. Metoda została zastosowana w homogenizacji materiałów porowatych zawierających pustki sferyczne. W tym celu analizowano reprezentatywne elementy objętości zawierające dużą liczbę pustek. W efekcie obliczono zastępcze stałe sprężystości materiału. Wyniki porównano z dostępnymi modelami analitycznymi otrzymanymi metodą samospójną oraz Mori-Tanaki. Porównanie wskazuje na poprawność opracowanej metody oraz wykonanych obliczeń numerycznych.

EN

In this work, a new version of the fast multipole boundary element method for three-dimensional linear elasticity problems, with boundary elements with quadratic shape functions and adaptive integration, is presented. The method was applied in the homogenization of porous materials with spherical cavities. Representative volume elements containing a high number of cavities were analysed. As a results, overall elastic constants of the porous materials were calculated. The results were compared to available analytical models obtained by the selfconsistent and Mori-Tanaka methods. The comparison confirmed vailidity of the method and computations.

5

Stress analysis of linear elastic structures by the fast multi-pole boundary element method

Ptaszny J., Fedeliński P.

Computer Assisted Mechanics and Engineering Sciences

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2009

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Vol. 16, No. 3/4

223-240

EN

In this paper a fast multipole boundary element method (FMBEM) analysis of internal stress in two-dimensional linear elastic structures is presented. The expansions of the potentials occurring in the stress integral equation are obtained by the differentiation of local series built for the displacement eąuation potentials, and application of the strain-displacement and stress-strain relations. Results of the analysis are presented. To illustrate the accuracy of the method a stress concentration problems are considered, which are a square plate with a circular hole under tension, and a gear. The application of the FMBEM can reduce the analysis time in relation to the conventional BEM case, providing similar accuracy. Presented method can be applied in the BEM analysis of non-linear structures, which requires the evaluation of internal strains or stresses.

6

Szybka wielobiegunowa metoda elementów brzegowych w analizie układów obciążonych siłami objętościowymi

Ptaszny J., Fedeliński P.

Modelowanie Inżynierskie

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2008

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T. 4, nr 35

107-114

PL

W pracy przedstawiono szybką wielobiegunową metodę elementów brzegowych (SWMEB) w analizie tarcz liniowosprężystych, obciążonych siłami objętościowymi. Opracowano program komputerowy wykorzystujący trójwęzłowe elementy brzegowe oraz sześciowęzłowe trójkątne komórki wewnętrzne. Przedstawiono przykład numeryczny analizy przemieszczeń i naprężeń w wirującym krążku. Badano czas obliczeń, pamięć oraz dokładność analizy wykonanej trzema metodami: konwencjonalną MEB, szybką metodą wielobiegunową zastosowaną tylko do obliczenia składników objętościowych oraz kompletną SWMEB.

EN

The fast multipole boundary element method (FMBEM) in analysis of linear elastic plates loaded by volume forces, is presented. A computer code, using three-node boundary element and six-node triangle internal cells, is developed. A numerical example of analysis of displacements and stresses in a rotating disc is presented. Three methods of analysis are considered, namely: the conventional BEM, the fast multipole method applied to evaluation of the volume terms only, and the complete FMBEM. Time of computations, memory and accuracy of the three methods are investigated.