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Creating proper B-spline surface models is a very challenging task for designers in car-body surface design. Due to the tensor-product structure of B-spline surface, some undesirable issues of the redundant control points addition, incomplete surface definition and the difficulty of trimming boundary alteration frequently occur, when designing the car-body surface with B-spline surfaces in local-feature-lines construction, full-boundary-merging and visual surface trimming. A more efficient approach is proposed to design the car-body surface by replacing B-spline surface with classical T-spline surface. With the local refinability and multilateral definition offered by T- spline surface, those designing issues related with B-spline surface can be overcomed. Finally, modeling examples of the door, hood and rear-window are given to demonstrate the advantage of T-spline surface over B-spline surface in car-body surface design. 相似文献
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离心压气机不稳定流动的时频特征分析 总被引:1,自引:0,他引:1
离心压气机失稳过程是一个非常复杂的动态过程,提高离心压气机运行的可靠性需要准确获取失稳过程的时频特征。针对带无叶扩压器的高速离心压气机失稳过程中叶轮出口的动态压力数据,采用时空本征模态分解(STIMD)算法和经验模态分解(EMD)算法进行分解,得到了多个本征模态函数(IMF),并结合Hilbert变换对不稳定流动的动态特征进行分析。结果表明,STIMD算法得到了深喘和浅喘的时频信息,观察到了频率在150 Hz附近持续波动的失速现象,并捕捉到了浅喘先兆的频率曲线由抖动向恒定的过渡过程。STIMD算法改善了EMD的模态混叠问题,为压气机失稳分析提供了一种工具。 相似文献
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