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Iso-geometry - Unified modelling for design and analysis in communicating organizations

Frontiers of knowledge and technology

Fifteen to twenty years ago high-end industries were the driving force behind the development of advanced 3D and rich-media technology. This is no longer the case. Computer games drive the evolution of 3D technology aimed at improved visual effects, but with little or no connection to the underlying physics of natural objects or human-made artefacts. Advances in both mathematical theory and computational performance now enable this gap to be closed.

Although the weaknesses of current shape representations are experienced and understood by many systems vendors and systems users, it is difficult to identify who “owns” the problem.

  • The major groups of CAD-users do not come from high-end industries[1] and the current CAD-model quality is sufficient for their daily use. Consequently, major CAD-vendors addressing the large global CAD-marked see little profit in addressing problems only encountered by high-end industries.
  • The mission of advanced manufacturing industries is to create products. Consequently, they will in general only invest in CAD-type system development when deemed necessary to solve specific well-defined challenges, in most cases related to better use of business-critical IT-systems.

Although many analysis packages are currently integrated into CAD-systems, the general problem of communication between design and analysis is not really solved. The industry experiences that what is expected to be a seamless integration typically requires manual model repair.

  • When a specific analysis package is integrated into a CAD-system, the solution is tailored to address the specific analysis package set-up. Consequently, challenges related to CAD-model quality are most often encountered  when non-standard analysis packages use CAD-models as input. As high-end industries are the most frequent users of non-standard analysis packages, high-end industries most often suffer from this.

State-of-the-art representation for sculptured surfaces in CAD is by NonUniform Rational B-Splines surfaces (NURBS-surfaces). A spline surface is a surface consisting of a mesh of polynomial patches joined with defined continuity. The (rational) B-spline representation is numerically stable.

Professor Tom Hughes[2], Institute for Computational Engineering and Sciences (ICES) at the University of Texas at Austin, has in the last years shown that iso-geometric analysis employing NURBS-based volumetric finite elements both gives more compact equation systems and more accurate analysis. Finite-element models based on NURBS can fairly simply be converted to traditional NURBS surface CAD-representation. This removes the current very severe bottleneck in feedback from analysis to CAD.

NURBS that define volumes instead of surfaces is a primary example of iso-geometric representations.

A fairly new innovation is the T-splines developed by Prof. Thomas W. Sederberg[3] from Brigham-Young University in Provo, Utah. The regular structure of piecewise polynomials in NURBS-surfaces is expanded by local refinements that do not have to be propagated to neighbouring patches contrary to traditional B-splines. This approach simplifies CAD-model repair and allows for more compact model representation, and is potentially an important component of future iso-geometric CAD-model technology.

The T-spline technology is patent protected, the patent issued in the second half of 2007.   http://www.tsplines.com/ .

To make the introduction of iso-geometric analysis feasible in industry, a bridge to current CAD has to be made. This bridge does not exist, to the best of our knowledge. STEP-type CAD-models have to be remodelled as high-quality iso-geometric CAD-models. Therefore, quality analysis and a subsequent enrichment of STEP-type CAD-models to iso-geometric models will be essential in the project. Both the analysis and enrichment (repair) much be more advanced that what is required in current standards such as:

  • AECMA-STAN LOTHAR – Long-term archiving and retrieval of digital technical product documentation such as 3D, CAD, and PDM data within aerospace industry.
  • VDA-AK CAD/CAM Scope and quality of CAD/CAM data.
  • JAMA – Japan automobile manufacturers association, PDQ guideline.
  • SASIG – Product data quality guideline for the global automotive industry.
[1] Examples of high-end industries are: automotive, aerospace, ship building, and the offshore industries

Published October 30, 2007