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排序方式: 共有218条查询结果,搜索用时 62 毫秒
91.
采用分布传递函数方法,分析任意多段分段常轴压阶梯梁的自由振动和稳定问题,得到形式统一的封闭解析解。根据梁横截面几何尺寸、梁材料和轴压沿梁轴线的变化,将梁分成多段子梁,对每一子梁采用传递函数方法得到其解析解,通过各子梁间的位移连续和力平衡条件,得到分段常轴压阶梯梁的各阶自由振动频率和失稳载荷及其相应的模态形状。通过三阶梯梁的算例验证本文方法的正确性,并以四阶梯梁为例,计算分段轴压多阶梯梁自由振动的固有频率。 相似文献
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项目型供应链管理模式能有效实现装备研制过程中行为主体间的优势互补和资源的优化配置,利于供应链整体效益的提高,但各种不确定性因素会导致主体间风险传递行为的发生。为提供风险控制有效对策,通过考虑节点位置重要度和属性重要度,构建了项目型供应链节点重要度评估模型;通过衡量行为主体风险识别和风险控制的努力程度,给出了行为主体抗风险努力程度的评价方法,最后提出了一种基于节点重要度和抗风险努力程度的项目型供应链利益分配策略,该策略能有效促使行为主体主动进行风险识别和风险控制,是一种"风险共担、利益共享"的项目型供应链合作博弈策略。 相似文献
95.
舰载捷联惯导动基座 F-QUEST 初始对准方法 总被引:2,自引:0,他引:2
针对目前基于惯性系的捷联惯导动基座对准方法信息利用率不高及矢量观测选取不确定性导致对准精度下降的问题,提出了一种新的舰载捷联惯导动基座滤波四元数估计(filter quaternion estimation,F-QUEST)对准方法。构建了捷联惯导动基座初始对准模型,并利用姿态矩阵链式法则将惯导初始对准转化为姿态确定问题,进而采用 F-QUEST 算法求取姿态矩阵以实现捷联惯导动基座对准。车载试验结果表明:相比传统方法,新方法具有更高的对准精度和更快的收敛速度,水平姿态角误差只需3 s 即可收敛到0.01°。 相似文献
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Ivonne Lockhart Smith 《African Security Review》2014,23(2):178-185
This commentary analyses the international response to the crisis that struck the Central African Republic (CAR) in early December 2013. It examines three intertwined dimensions defining the courses of action available to policymakers dealing with pre-genocidal crises: the politics and institutional manoeuvring shaping the United Nations (UN) Security Council's decision to authorise an enforcement mission without deploying ‘blue helmets’ on the ground; the operational complexities involved in launching rapid reaction forces; and the interdependent logics between peacebuilding and atrocity prevention. The author argues that there are three ways for the UN Secretariat to ensure a more effective response to CAR-type situations: generating political will to respond swiftly to deteriorating crises leading to widespread abuses of human rights by advancing the concept of Responsibility to Protect as a core component of states' national interests; developing strategic frameworks for the deployment of multi-plural missions equipped to avert the actual or potential threat of atrocities; and developing joint early warning and scenario planning between peacebuilding and atrocity prevention agencies. 相似文献
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Defence offsets are elements of defence procurement deals additional to the primary content. Offsets are usually expected to yield technological or industrial benefits to the purchasing country (e.g. countertrade, technology transfers, or additional jobs) and military buyers often require suppliers to make offsets available “cost-free.” The authors argued previously that such strategies achieve little of value to buyers that lack market power and are unnecessary otherwise, since purchasers with the market power to extract more value for money from foreign suppliers can do so anyway. This article also focuses on the supply side of offset deals. The USA is the world's largest defence offsets supplier but the US government opposes offsets demands as economically inefficient and trade distorting. Even if offsets are inefficient and trade distorting, they may still benefit a materiel-exporting country such as the USA as they may induce exports and create associated benefits for the offsets provider. 相似文献
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针对高超声速飞行器对盖板式陶瓷热防护系统的迫切需求,建立了热防护系统结构瞬态传热模型;并研究了防隔热层的物性参数,厚度尺寸,相变层的种类、位置等因素对热防护系统结构传热性能的影响。结果表明,隔热层物性参数及厚度尺寸对热防护系统结构传热性能具有决定性影响,而防热层的物性参数及厚度尺寸几乎不产生影响。相变材料的引入能够明显改善热防护系统结构的传热性能。调整和优化相变层位置是改善热防护系统结构传热性能、降低结构厚度的一个有效途径。隔热层厚度的优化结果可为热防护系统结构设计提供一定的参考和依据。 相似文献
99.
地月转移轨道设计是探月关键技术之一,微分校正法是公认的解决非线性迭代问题的有效方法。针对探月任务中地月转移轨道设计精度高、计算速度快等要求,提出一种改进的微分校正快速设计方法。该方法基于DE405/LE405星历数据下日、地、月和地球J2项摄动真实轨道动力学模型,推导了近月点和入轨点设计参数偏导数关系,在积分轨道状态量的同时积分微分校正矩阵,用积分得到的准确微分校正矩阵求逆,快速迭代得到轨道设计结果。仿真结果表明,利用该方法设计地月转移轨道收敛速度远优于同等精度动力学模型—序列二次规划算法。 相似文献
100.
《防务技术》2014,10(2):219-225
Global effects caused by the detonation of an IED near a military vehicle induce subsequent severe acceleration effects on the vehicle occupants. Two concepts to minimize these global effects were developed, with the help of a combined method based on a scaled experimental technology and numerical simulations. The first concept consists in the optimization of the vehicle shape to reduce the momentum transfer and thus the occupant loading. Three scaled V-shaped vehicles with different ground clearances were built and compared to a reference vehicle equipped with a flat floor. The second concept, called dynamic impulse compensation (DIC), is based on a momentum compensation technique. The principal possibility of this concept was demonstrated on a scaled vehicle. In addition, the numerical simulations have been performed with generic full size vehicles including dummy models, proving the capability of the DIC technology to reduce the occupant loading. 相似文献