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151.
152.
A new algorithm for dimension variation of feature-based models is developed.The algorithm is based on B-Rep/CSG hybrid scheme and operates directly on B-Rep.Product information (including the features locating dimensions and other data for manufacture) will not lose after model variation and modification.Furthermore, the definition and solution of features constraints are also supported.The scheme of directly operating on B-Rep overcomes many drawbacks of other proposed methods, most of which need to redo all of the previous work to implement dimension variation, so the computational cost is expensive and product information will lose.What is presented in this paper makes a new way in the area of parametric design. 相似文献
153.
154.
高精度两步TVD格式的构造及数值检验 总被引:1,自引:1,他引:0
基于通量分裂的思想,利用Taylor级数理论和第二步限制器函数的控制,构造了在光滑区域空间为三阶、时间为一阶精度的高分辨率全变差递减(TVD)格式.该格式在激波过渡点降为一阶迎风格式.并从单个线形方程推广到非线性方程及方程组情形.通过几个典型算例的计算,并与二阶TVD格式作了比较,表明该方法对流场中的激波有较高的分辨率,且是无波动的. 相似文献
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156.
为更好地控制叶中尾缘分离及角区分离,优化叶片吸力面流动分离结构,本文提出了全叶高槽道加全弦长端壁抽吸的组合流动控制方案。此外,本文还设置了全叶高开槽方案与端壁抽吸方案,以探究全叶高槽道射流与端壁附面层抽吸的相互作用机理。以一大弯角扩压静子叶栅为研究对象,本文对三种流动控制方案进行了详细的性能分析及对比。结果表明:组合控制方案对于原型叶栅叶中尾缘分离及角区分离的综合控制效果最佳,能够在全攻角范围内分别将原型叶栅的总压损失、气流转折角及静压升系数平均增大-38.4%、3.1°及16.2%。相比于全叶高开槽方案,组合控制方案的端壁抽吸槽有效抑制了全叶高槽道出口前端壁二次流的发展,进一步削弱了角区分离。相比于端壁抽吸方案,组合控制方案的全叶高槽道则有效消除了尾缘分离,避免了叶中流场的恶化。总体看来,组合控制方案有利于最大程度地拓宽叶片的可用攻角范围,提高其扩压能力。 相似文献
157.
A. Gil M.V. Alania 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
We show that the amplitudes of the 27-day variations of galactic cosmic ray (GCR) intensity, solar wind and solar activity parameters have a periodicity with duration of three to four Carrington rotation periods (3–4 CRP). We assume that the general reason for this phenomenon may be related to similar cyclicity of topological structure of the solar magnetic field lines created owing to the asymmetry of turbulent solar dynamo and solar differential rotation transforming the Sun’s poloidal magnetic field to the toroidal (α–ω effect), and vice versa. 相似文献
158.
Application of hybrid regularization method for tomographic reconstruction of midlatitude ionospheric electron density 总被引:1,自引:0,他引:1
Yibin Yao Jun Tang Jian Kong Liang Zhang Shun Zhang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Reconstructing ionospheric electron density (IED) is an ill-posed inverse problem, with classical Tikhonov regularization tending to smooth IED structures. By contrast, total variation (TV) regularization effectively resists noise and preserves discontinuities of the IED. In this paper, we regularize the inverse problem by incorporating both Tikhonov and TV regularization. A specific formulation of the proposed method, called hybrid regularization, is introduced and investigated. The method is then tested using simulated data for the actual positions of the GPS satellites and ground receivers, and also applied to the analysis of real observation data under quiescent and disturbed ionospheric conditions. Experiments demonstrate the effectiveness, and illustrate the validity and reliability of the proposed method. 相似文献
159.
160.
A. Taori V. Kamalakar A. Jayaraman 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
We summarize two years of Mesosphere Lower Thermosphere Photometer (MLTP) operation of mesospheric OH and O2 emission monitoring. The deduced mesospheric OH and O2 temperatures show large variability. Nightly temperature variations over Gadanki (13.5°N, 79.2°E) are dominated by the short period wave features, while tidal amplitudes are relatively small. Our measurements are the first to report a long period seasonal variation at two upper mesospheric altitudes simultaneously over the Indian sector. Our observations reveal the presence of a dominant semi-annual oscillation (∼6 months periodicity) together with a shorter period (∼2.5 months periodicity) oscillation in both OH and O2 data. 相似文献