Author
Xiaowen Song
Other affiliations: Brigham Young University
Bio: Xiaowen Song is an academic researcher from Zhejiang University. The author has contributed to research in topics: Parasitic drag & Drag. The author has an hindex of 7, co-authored 19 publications receiving 153 citations. Previous affiliations of Xiaowen Song include Brigham Young University.
Papers
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TL;DR: The paper introduces MD-splines, which are B-spline-like curves that are comprised of polynomial segments of various degrees (MD stands for "multi-degree"), and presents formulae in terms of knot intervals for common B- Spline operations such as knot insertion, differentiation, and degree elevation.
44 citations
TL;DR: By applying displacement maps to slightly perturb two free-form surfaces, one can ensure exact agreement between the images in R3 of parameter-domain approximations to their curve of intersection, which is essential to achieving topologically consistent solid model constructions through Boolean operations.
37 citations
TL;DR: A method that serves to simultaneously determine the topological configuration of the intersection curve of two parametric surfaces and generate compatible decompositions of their parameter domains that are amenable to the application of existing perturbation schemes ensuring exact topological consistency of the trimmed surface representations is described.
Abstract: We describe a method that serves to simultaneously determine the topological configuration of the intersection curve of two parametric surfaces and generate compatible decompositions of their parameter domains, that are amenable to the application of existing perturbation schemes ensuring exact topological consistency of the trimmed surface representations. To illustrate this method, we begin with the simpler problem of topology resolution for a planar algebraic curve F(x,y)=0 in a given domain, and then extend concepts developed in this context to address the intersection of two tensor-product parametric surfaces p(s,t) and q(u,v) defined on (s,t)∈[0,1]2 and (u,v)∈[0,1]2. The algorithms assume the ability to compute, to any specified precision, the real solutions of systems of polynomial equations in at most four variables within rectangular domains, and proofs for the correctness of the algorithms under this assumption are given.
28 citations
TL;DR: In this article, the authors introduced bionic non-smooth surfaces as appendices into vehicle body design, aiming to further reduce aerodynamic drag by adapting the structure of a vehicle body from the point of boundary layer control that reduces the burst and the loss of turbulent kinetic energy.
Abstract: Inspired by the successful applications of biological non-smoothness, we introduced bionic non-smooth surfaces as appendices into vehicle body design, aiming to further reduce aerodynamic drag. The size range of the non-smooth units with pits and grooves was determined according to our analysis with the mechanisms underlying non-smooth unit mediated aerodynamic drag reduction. The bionic non-smooth units reported here were designed to adapt the structure of a given vehicle body from the point of boundary layer control that reduces the burst and the loss of turbulent kinetic energy. The engine cover lid and vehicle body cap were individually treated with the non-smooth units, and the treated vehicles were subjected to aerodynamic drag coefficient simulation tests using the computational fluid dynamics (CFD) analysis method. The simulation results showed that, in comparison with smooth surfaces, properly designed non-smooth surfaces can have greater effects on drag reduction. The mechanism underlying drag reduction mediated by non-smooth surfaces was revealed by further analyses, in which the effects of non-smooth and smooth surfaces were directly compared.
16 citations
TL;DR: In this article, a new nonsmooth surface inspired by the shape of barchan dunes has been proposed and is intended to reduce skin friction, a major cause of overall drag.
Abstract: A new type of nonsmooth surface inspired by the shape of barchan dunes has been proposed and is intended to reduce skin friction, a major cause of overall drag Simulations were carried out to obtain skin friction reduction characteristics for the nonsmooth surface using the commercial computational fluid dynamics software Fluent A realizable -e model was employed to assess the influence of the nonsmooth structure on turbulent flow and velocity fields The numerical simulation results showed that the new nonsmooth surface possesses the desired skin friction reduction effect and that the maximum skin friction reduction percentage reached 3363% at a fluid speed of 30 m/s Various aspects of the skin friction reduction mechanism were discussed, including the distribution of velocity vectors and shear stress contours and the variations in boundary layer thickness The accuracy of the flow field for the nonsmooth unit was further verified by particle image velocimetry test results The new bionic nonsmooth surface, which exceeds the limitations of existing nonsmooth bionic structures, can effectively reduce skin friction and should provide insights into engineering applications in the future
14 citations
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TL;DR: It is shown that the extraction operator and Bézier elements provide an element structure for isogeometric analysis that can be easily incorporated into existing finite element codes, without any changes to element form and assembly algorithms, and standard data processing arrays.
Abstract: We develop finite element data structures for T-splines based on Bezier extraction generalizing our previous work for NURBS. As in traditional finite element analysis, the extracted Bezier elements are defined in terms of a fixed set of polynomial basis functions, the so-called Bernstein basis. The Bezier elements may be processed in the same way as in a standard finite element computer program, utilizing exactly the same data processing arrays. In fact, only the shape function subroutine needs to be modified while all other aspects of a finite element program remain the same. A byproduct of the extraction process is the element extraction operator. This operator localizes the topological and global smoothness information to the element level, and represents a canonical treatment of T-junctions, referred to as ‘hanging nodes’ in finite element analysis and a fundamental feature of T-splines. A detailed example is presented to illustrate the ideas. Copyright © 2011 John Wiley & Sons, Ltd.
566 citations
TL;DR: A local refinement algorithm for analysis-suitable T-splines which does not produce excessive propagation of control points is developed and its use as an adaptive framework for isogeometric analysis is demonstrated.
369 citations
TL;DR: This work extends the definition of analysis-suitable T-splines to encompass unstructured control grids and develops basis functions which are smooth (rational) polynomials defined in terms of the Bezier extraction framework and which pass standard patch tests.
366 citations
TL;DR: The treatment of trimmed geometries in the context of design, data exchange, and computational simulation is reviewed.
Abstract: We review the treatment of trimmed geometries in the context of design, data exchange, and computational simulation. Such models are omnipresent in current engineering modeling and play a key role for the integration of design and analysis. The problems induced by trimming are often underestimated due to the conceptional simplicity of the procedure. In this work, several challenges and pitfalls are described.
165 citations
01 Aug 2008
TL;DR: The problem of the unavoidable gaps that arise when expressing the intersection of two NURBS surfaces using conventional trimmed-NURBS representation is addressed, and the resulting T-Spline representation can be exported without error as a collection of NurBS surfaces.
Abstract: This paper addresses the long-standing problem of the unavoidable gaps that arise when expressing the intersection of two NURBS surfaces using conventional trimmed-NURBS representation The solution converts each trimmed NURBS into an untrimmed T-Spline, and then merges the untrimmed T-Splines into a single, watertight model The solution enables watertight fillets of NURBS models, as well as arbitrary feature curves that do not have to follow iso-parameter curves The resulting T-Spline representation can be exported without error as a collection of NURBS surfaces
143 citations