Abstract

This work presents some numerical aspects of isogeometric boundary element methods (IGABEM). The behavior of hyper-singular and nearly-singular integration is first explored on the distorted NURBS surface. Several numerical treatments are proposed to enhance the quadrature in the framework of isogeometric analysis. Then a numerical implementation of IGABEM on the trimmed NURBS is detailed. Based on this idea, the surface crack problem is modeled incorporation with the phantom element method. The proposed method allows the crack to intersect with the boundary of the body while preserving the original parametrization of the NURBS-based CAD geometry.

Highlights

  • The isogeometric analysis (IGA) uses the spline-basis functions, which are adopted to describe CAD geometry, to approximate the physical fields in analysis

  • The corporation of the IGA and boundary element methods (BEM) provides a direct link between CAD and analysis since both methodologies are related to the boundary representation of the body

  • Several numerical aspects, such as the singular integration, trimmed NURBS and surface crack modeling, of the IGABEM are investigated in detail

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Summary

Introduction

The isogeometric analysis (IGA) uses the spline-basis functions, which are adopted to describe CAD geometry, to approximate the physical fields in analysis. Within the BEM community, Beer et al [5] proposed a double mapping method to perform the integration on NURBS This method relies on the establishment of the mapping area and is not able to be applied directly for a closed trimming curve, but later they proposed a stable extended B-splines scheme for IGABEM with trimmed geometry [14]. The surface crack problem has two manifolds in numerical implementation: one is the coinciding crack surfaces inside the body domain, the other is the surface discontinuity along the geometry boundary The latter can be considered as a problem of cracks in 2D plane or 3D shell conditions in the finite element method (FEM).

Trimmed NURBS Surfaces
Integration of Trimmed Elements
Applying the Prescribed Boundary Condition
Phantom Element Method for Surface Crack Modeling
Singular and Nearly Singular Integration
Singular Integration The hyper-singular integral
The Influence of Distortion Angle ψ
The Influence of Local Aspect Ratio λ
Examples of Trimmed NURBS
Patch Test
Convergence Test
Edge Crack
Conclusions
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