In 2005, the term “Isogeometric Analysis” (IGA) was introduced by Hughes et al. [1]. Since then, reams of scientific research work has been devoted to this new finite element technology, whose main idea is to use the same geometrical description during the finite element analysis (FEA) that was previously used during the design process in the computer-aided design (CAD) environment. The most widely used and best understood mathematical description in CAD is based on non-uniform rational B-splines (NURBS). Hence NURBS-based shell and solid finite elements have been developed and implemented into LS-DYNA over the last few years. Although NURBS-based solids are available, the remainder of the paper will exclusively focus on isogeometric shell element formulations in LS-DYNA.
A volatile and highly competitive market forces automotive Original Equipment Manufacturers (OEMs) to speed up their vehicle development processes. A key component in this process is structural design through Computer Aided Design (CAD) and Finite Element Analysis (FEA). Although the efficiency of this process has been significantly improved over the past years, the necessary conversion of NURBS-based CAD models into (linear) polynomial-based FEA models turned out to be a persistent challenge. Generating FEA models usually involves time- and labor-intensive clean-up, de-featuring and meshing steps leading to vehicle model generation times of several weeks. During the iterative vehicle development process, such model generations are even performed multiple times. It is furthermore current practice to apply design changes motivated by structural analysis results directly on the FEA model, which then diverges more and more from the initial CAD model. Adapting the CAD model to the modified FEA model for the next design cycle again requires a significant amount of manual work.
Isogeometric Analysis (IGA), is maturing and becoming capable to be incorporated in industrial applications. Widely used in the automotive industry for crash analysis, LS-DYNA is the first commercial solver to provide IGA features. Highest accuracy and shorter run times make IGA effective for crash analysis. Nevertheless, the complexity of the current automotive models and the maturity of the already established methods and processes require the development of the respective IGA tools and processes to reach and exceed the current levels of effectiveness. The new technical challenges offer the opportunity for new solutions and improvements in engineering simulation technology.
In contrast to the laborious and error-prone process of translating computer-aided design (CAD) into computer-aided engineering (CAE) models, isogeometric analysis (IGA) performs the finite element analysis (FEA) simulation directly on CAD geometry, using smooth spline basis functions. LS-DYNA is a leader in the industrial adoption of IGA, and has recently made a significant enhancement to broaden the possible use of IGA within LS-DYNA.
Isogeometric analysis represents a newly developed technique that offers the application of Computer Aided Design (CAD) concept of Non-uniform Rational B-Splines (NURBS) tool to describe the geometry of the computational domain. The simplified transition of CAD models into the computational domain eliminates the problems arising from the geometrical discontinuities induced by the faceted approximation of the mesh. Moreover, numerical analysis directly on NURBS objects significantly reduces the design-to-analysis time compared to traditional FEA approach. In the field of contact mechanics, when finite elements are applied to geometry with curved surfaces, the result is a non-smooth geometrical representation of interface surfaces which may lead to mesh interlocking, high jumps and spurious oscillations in contact forces. To eliminate these issues, various surface smoothening strategies are to be employed in case of FEM. Isogeometric based analysis alleviates these issues without employing any additional smoothening strategy due to inherent higher order continuity of NURBS basis functions and much more accurate results are obtained compared to conventional FE approach. In the current study, LS-DYNA is used to demonstrate the capabilities and advantage of an isogeometric analysis though an example of pendulum under gravitational load. The numerical simulation results are analytically validated and the comparison of NURBS surfaces with faceted surfaces is carried out to investigate the accuracy.
Enabling the Analysis of Topologically Connected Multi-Patch Trimmed NURBS Shells in LS-DYNA