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Isogeometric analysis-suitable geometry : rebuilding CAD surface geometries via quadrilateral layouts
(2021-05) Shepherd, Kendrick Monroe, 1989-; Hughes, Thomas J. R.; Gu, Xianfeng; Rodin, Gregory J; Demkowicz, Leszek F; Beckner, William
Ironically, neither engineering design nor engineering analysis consumes the majority of the time an engineer spends in the engineering design-through-analysis process. The bottleneck—well over half of the process—involves converting a computer-aided design (CAD) object into an analysis-suitable representation: typically a mesh. This time-consuming, labor-intensive conversion step impedes the engineering workflow, limits design optimization, and costs companies (and thus their clients) handsomely. The isogeometric paradigm seeks to remove this workflow impediment by using the same smooth splines used in engineering design for engineering analysis. Under this perspective, no auxiliary (piecewise-continuous) data structure would be necessary to transform the information given in an engineering model for its subsequent use in analysis. Since their inception over a decade ago, isogeometric analysis techniques have proven to be more accurate per degree of freedom, more geometrically faithful, and more versatile than their traditional analysis counterparts. Despite these accomplishments, the fundamental goal of a streamlined design-through-analysis process has not yet been achieved. Most CAD models are built utilizing Boolean operations; these so-called “trimmed” models are not inherently suitable for use in analysis. As a result, most conforming CAD models used for isogeometric analysis are still built by hand. This is the single most limiting factor keeping isogeometric techniques from being more widely incorporated in the engineering industry. In this dissertation, I develop mathematical theory and an ensuing computational framework to automatically rebuild open CAD models into well-structured, trim-free spline representations. Beyond its automation, the methodology readily allows for user intervention, making it a viable tool for the design-through-analysis process. The techniques are validated by rebuilding the DEVCOM Generic Hull (a trimmed CAD vehicle of interest to the US Army) and portions of a 1996 Dodge Neon into spline representations with no trimming. Portions of each are input to the commercial shell solvers of LS-DYNA to show their capacity for use in engineering analysis. Ultimately, this dissertation provides missing tools necessary to enable the isogeometric framework’s adoption into the engineering workflow and to streamline the engineering design-through-analysis process.