Section: New Results

Isogeometric analysis and design

Participants : Louis Blanchard, Régis Duvigneau, Bernard Mourrain [Galaad Project-Team] , Gang Xu [Galaad Project-Team] .

Design optimization stands at the crossroad of different scientific fields (and related software): Computer-Aided Design (CAD), Computational Fluid Dynamics (CFD) or Computational Structural Dynamics (CSM), parametric optimization. However, these different fields are usually not based on the same geometrical representations. CAD software relies on Splines or NURBS representations, CFD and CSM software uses grid-based geometric descriptions (structured or unstructured), optimization algorithms handle specific shape parameters. Therefore, in conventional approaches, several information transfers occur during the design phase, yielding approximations that can significantly deteriorate the overall efficiency of the design optimization procedure. Moreover, software coupling is often cumbersome in this context.

The isogeometric approach proposes to definitely overcome this difficulty by using CAD standards as a unique representation for all disciplines. The isogeometric analysis consists in developing methods that use NURBS representations for all design tasks:

• the geometry is defined by NURBS surfaces;

• the computation domain is defined by NURBS volumes instead of meshes;

• the solution fields are obtained by using a finite-element approach that uses NURBS basis functions

• the optimizer controls directly NURBS control points.

Using such a unique data structure allows to compute the solution on the exact geometry (not a discretized geometry), obtain a more accurate solution (high-order approximation), reduce spurious numerical sources of noise that deteriorate convergence, avoid data transfers between the software. Moreover, NURBS representations are naturally hierarchical and allows to define multi-level algorithms for solvers as well as optimizers.

In this context, some research axes have been developed in collaboration with GALAAD Project-Team:

• Methods for adaptive parameterization including a posteriori error estimate for elliptic problems [36] , [35] , [42] ;

• Numerical schemes based on Spline functions for 2D inviscid compressible flow simulations ;

• Optimization methods for structural elasticity, based on shape-gradient concept, and fluid-structure interactions [48] (in collaboration with Technical University of Munich).