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391.
392.
Jianguo Cai Meng Li Yuanyuan Li Yifan Ding Jian Feng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3343-3353
Miura-ori is a rigid origami structure utilized in the packaging of deployable solar panels for use in space or in the folding of maps. It's pattern can largely reduce the membrane stress and improve the work efficiency. Inspired by origami structures, we numerically and experimentally studied a scalable solar sail structure. As an improvement of the existing membrane simulations, a variable Poisson's ratio model considering the wrinkling effect of the membrane was introduced. We focused on a quadrant shape and studied how its geometry parameters and initial imperfections affect the membrane mechanical behavior. We also designed and fabricated a pantographic mechanism as an origami membrane actuator. In addition, design protocols of deployment applied to a scalable gossamer structure were proposed. 相似文献
393.
Ziyan Liu Yueqiang Sun Weihua Bai Junming Xia Guangyuan Tan Cheng Cheng Qifei Du Xianyi Wang Danyang Zhao Yusen Tian Xiangguang Meng Congliang Liu Yuerong Cai Dongwei Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(2):845-857
The tropopause is an important boundary in the Earth’s atmosphere, and has been the subject of close attention from atmosphere and climate researchers. To monitor the global tropopause using radio occultation (RO) data, there are two primary methods, one is the widely used temperature lapse rate method, and the other is the bending angle covariance transform method which is unique to RO data. We use FengYun3-C (FY3C) and Meteorological Operational Satellite Program (MetOp) RO data and European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis data to determine differences in RO tropopause height calculated by these two methods. We compute biases of the RO lapse rate tropopause height (LRTH) and the RO bending angle tropopause height (BATH) relative to the ECMWF LRTH. The dependences of the tropopause height biases on tropopause height (TPH) retrieval method, latitude, season and RO mission are investigated. The results indicate that BATH show a consistent 0.8–1.2 km positive bias over the tropics and high latitude regions compared with LRTH, however, over 25° to 40° latitude in both hemisphere, BATH results are less stable. Furthermore, the mean bias between BATH and LRTH displayed a different symmetrical characteristic from 2017.12 to 2018.2 (DJF) compared to 2018.6–2018.8 (JJA). However, except for some bias over Antarctica, the mean value of both LRTH and BATH show a similar tropopause variation, indicating the consistency of both methods. 相似文献
394.
气动发动机设计需要考虑多个参数间的耦合对性能优化的影响,且对理想功率、工作效率等多个性能指标难以建立客观的综合评价函数.为此以发动机进气压力和进排气机构部分控制参数为设计变量进行正交设计,利用灰色关联度分析法计算贴合期望指标组合的最优参数组合,并结合参数指标趋势图,依据计算结果对参数区间进行调整,通过有限次循环得到最优设计参数.经测试该算法快速有效,且设计参数与性能指标数量可扩展,对气动发动机的样机设计和实验具有重要的理论和工程意义. 相似文献
395.
Synthetic aperture radar(SAR)image is severely affected by multiplicative speckle noise,which greatly complicates the edge detection.In this paper,by incorporating the discontinuityadaptive Markov random feld(DAMRF)and maximum a posteriori(MAP)estimation criterion into edge detection,a Bayesian edge detector for SAR imagery is accordingly developed.In the proposed detector,the DAMRF is used as the a priori distribution of the local mean reflectivity,and a maximum a posteriori estimation of it is thus obtained by maximizing the posteriori energy using gradient-descent method.Four normalized ratios constructed in different directions are computed,based on which two edge strength maps(ESMs)are formed.The fnal edge detection result is achieved by fusing the results of two thresholded ESMs.The experimental results with synthetic and real SAR images show that the proposed detector could effciently detect edges in SAR images,and achieve better performance than two popular detectors in terms of Pratt's fgure of merit and visual evaluation in most cases. 相似文献
396.
相对于公式法,双标记法解决了焦距和焦点位移测量误差所带来的问题.但此方法在射线检测领域普及程度并不高,其中原因,首先是原理较复杂,针对性研究少,其次是测量精度没有被量化,可信度不高.本文从公式法入手,通过对原理公式的变化分析和线性化分析,明晰了双标记法缺陷深度定位原理,推导了缺陷深度定位公式,利用简化模型,对双标记法的定位精度做了进一步的分析与计算,最后针对具体被检测物,测试验证了双标记法的计算公式和测量精度,用理论和实践证明了方法和精度的可靠性. 相似文献
397.
Scale effect of fuel regression rate in hybrid rocket motor 总被引:1,自引:0,他引:1
Guobiao Cai Peng Zeng Xintian Li Hui Tian Nanjia Yu 《Aerospace Science and Technology》2013,24(1):141-146
398.
A fully flexure micro/nano transmission platform(MNTP)which has five degrees of freedom is designed on the basis of bridge type amplification mechanism.According to the kinematic theory and the elastic beam theory,the theoretical output displacement equation of the platform is derived,and then piezoelectric actuator(PZT)is calibrated.Meanwhile,a full closed-loop control strategy of the platform is established using the feedforward proportional-integral-derivative(PID)compound control algorithm based on the Preisach model.Moreover,the total transfer function of the micro positioning system is derived,and the calculation method of output signal is acquired.Finally,the theoretical output displacement is verified by finite element analysis(FEA)and positioning experiments. 相似文献
399.
求解流体力学反问题的数学方法及应用 总被引:1,自引:1,他引:0
流体力学反问题是一类重要的非线性问题,这类问题在工程中有广泛的应用,如过坝水流问题,给定流量的射流和翼型设计问题。由于这类流动求解区域不确定,导致问题的非线性特征,使数值计算十分困难,本文将以亚、跨声速翼型设计问题为例,提出了一种求解流体力学反问题的新方法。 相似文献
400.
粉末锻造钢12Cr2Ni4A和18Cr2Ni4WA的组织与性能 总被引:1,自引:0,他引:1
讨论了粉末锻造钢12Cr2Ni4A和18Cr2Ni4WA的组织与性能。氧含量低于0.2%,碳含量为0.08~0.12%的粉末锻造钢12Cr2Ni4A和碳含量为0.11~0.16%的粉末锻造钢18Cr2Ni4WA有较好的力学性能。长时间扩散退火可有效地提高粉末锻造钢的韧性。 相似文献