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飞机座舱有机玻璃结构疲劳寿命估算的局部应力法 总被引:1,自引:0,他引:1
基于飞机座舱有机玻璃为脆性材料的特性,提出估算飞机座舱有机玻璃结构件疲劳寿命的局部应力法。它以缺口件韧带上距离缺口根部d处的局部应力为参数,对照光滑试验件的S-N曲线,利用线性累积损伤理论,可以较好地预测结构件的疲劳寿命。对飞机座舱有机玻璃YB3的三种结构件进行了疲劳试验和寿命分析,结果表明:寿命估算结果与试验结果吻合较好。 相似文献
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基于放松单元间连续性要求约束的广义变分原理,建立了用于几何非线性分析的非协调四边形精化杂交Mindlin板元,其非线性单元刚度矩阵可按假定应变模式分解.本文列式与现有非线性杂交混合列式的主要区别在于,它吸收了现有线性杂交元列式的所有优点,引入了非协调模式和正交化.数值结果表明,正交化法可有效地改善单元的计算精度和效率,非协调模式可克服Mindlin板的自锁问题. 相似文献
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(对数)正态未来观测的预测分布及其应用 总被引:1,自引:0,他引:1
本文用Bayes方法给出了正态、对数正态分布示来观测的预测分布。据此,给出了两分布未来观测值的预测子与预测区间及两分布可靠性的Bayes估计,而经典预测区间与无信息先验分布下的Bayes预测区间相间。 相似文献
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N. Remesh R.V. Ramanan V.R. Lalithambika 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(6):1787-1804
Two guidance schemes (i) fuel-optimal (ii) energy-optimal to realize soft landing at a desired location on the moon are developed using the optimal control laws. The optimal control laws are obtained by solving a two-point boundary value problem formulated based on Pontryagin’s principle. The guidance laws, adapted from the optimal control laws, are obtained as a function of unknown co-state variables. Differential Transformation (DT) technique is employed to determine the unknown co-states at each time instant of landing trajectory using the information on the current vehicle state, target landing site (loaded on-board apriori) and the time-to-go. The numerical integration of co-state dynamics is avoided due to the DT based approach. The time-to-go, a critical parameter for any guidance scheme, is computed and updated real time using a simple strategy which uses the current and end states. The simple strategy for time-to-go works well even when the shape of the trajectory is nonlinear. Extensive analysis is carried out to evaluate and compare the proposed guidance schemes. Further, the proposed schemes are compared with other popular guidance schemes. The DT based proposed schemes help quantify the landing masses for fuel-optimal and energy-optimal objectives. Other features of the proposed schemes are that they do not assume constant gravity field and independent of reference trajectory. 相似文献
368.
Yongliang Yan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):597-616
The increasing gap in the space capabilities of different countries has led to the need for capacity building in modern times. Space capacity building of countries without or with limited space capacity via international cooperation with advanced spacefaring nations is a good practice towards intragenerational equity among all spacefaring countries, and between spacefaring and non-spacefaring countries at the same period of time. A case study is used here to show the current situation of the Asia-Pacific Space Cooperation Organization (APSCO) and its member states that are associated with their space capacity building. The study finds that neither the satellite technology development model developed by Wood and Weigel (2011) nor the model developed by Ercan and Kale (2017) is a good fit for the development of space capability in all of the developing countries. Therefore, using the APSCO member states as a case study may offer guidelines towards the space capacity building of other developing countries. Moreover, an in-depth analysis of the merits and flaws of APSCO’s capacity building programs through comparing them with similar projects carried out by the European Space Agency (ESA), the Asia-Pacific Regional Space Agency Forum (APRSAF) and some other countries is conducive to providing some references for regional cooperation in the field of space capacity building. While international space law and the APSCO Convention can provide the general principles for capacity building activities under the framework of APSCO, they are only relevant to the development of scientific and technological capacities for space and human resources rather than organizational development and legal frameworks. Some international soft laws can likewise provide guidance for the capacity building activities of APSCO and its member states in the areas of international direct television broadcasting, remote sensing and cooperative way. To enhance its and its member states’ space capabilities, APSCO, in the context of space commercialization and maintaining the long-term sustainability of outer space activities (LTSOSA), should establish a comprehensive internal regime that addresses scientific and technological capacity building for space, human resources, organizational development and legal frameworks, a flexible regime for international cooperation with other developed spacefaring nations and international organizations with relevant technical capabilities and an internal research center for space law, and actively expand its membership by embracing other economically or technologically developed spacefaring nations in the Asia-Pacific region. 相似文献
369.
《中国航空学报》2020,33(12):3564-3574
In this paper, a novel 2-DOF rotational pointing mechanism (RPM) is designed inspired by the guidelines of the graphical approach. The mechanism integrates with a fast steering mirror (FSM) for compensating pointing errors of a laser beam. The design intends to achieve an angular travel of ±10 mrad and steers a 25 mm mirror aperture. A planar flexure with beam flexures accompanied in parallel with an axial flexure build-up mechanism configuration. Compliant mechanism-based RPM ensures high precision and compactness. Compliance characteristics are established based on the stiffness matrix method for four different planar flexure layouts. One layout with best in-plane rotational compliance is then assessed for performance sensitivity to mechanism dimension parameters and parasitic error, thus informing the design space. Rotational stiffness in both the in-plane rotational axes and stress is determined based on finite element analysis (FEA). The wire electrical discharge machining (EDM) is employed for developing the proof of concept for the RPM and is then assembled in FSM. Experiments are conducted to determine the rotational stiffness and angular travel about both in-plane rotational axes. Comparison among theoretical, numerical and experiments reveal excellent linearity of rotational stiffness along the rotational travel range. The maximum theoretical error is less than 5.5% compared with FEA while, the experimental error has a mean of 5% and 3% for both rotational axes thus satisfying the intended design requirement. 相似文献
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