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991.
根据传热学理论和热网络法,以某型直升机尾减速器弧齿锥齿轮传动系统为研究对象,建立了其温度场Simulink仿真计算模型。基于该模型,计算获得该传动系统正常润滑条件下的稳态温度场,并以它作为初始条件计算分析该传动系统失去润滑条件下的瞬态温度场,为预测该弧齿锥齿轮传动系统在失去润滑条件下的干运转生存能力提供理论依据。 相似文献
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Serkan Eryilmaz 《海军后勤学研究》2013,60(4):313-320
Measuring the relative importance of components in a mechanical system is useful for various purposes. In this article, we study Birnbaum and Barlow‐Proschan importance measures for two frequently studied system designs: linear consecutive k ‐out‐of‐ n and m ‐consecutive‐ k ‐out‐of‐ n systems. We obtain explicit expressions for the component importance measures for systems consisting of exchangeable components. We illustrate the results for a system whose components have a Lomax type lifetime distribution. © 2013 Wiley Periodicals, Inc. Naval Research Logistics, 2013 相似文献
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By running life tests at higher stress levels than normal operating conditions, accelerated life testing (ALT) quickly yields information on the lifetime distribution of a test unit. The lifetime at the design stress is then estimated through extrapolation using a regression model. In constant‐stress testing, a unit is tested at a fixed stress level until failure or the termination time point of test, whereas step‐stress testing allows the experimenter to gradually increase the stress levels at some prefixed time points during the test. In this work, the optimal k‐level constant‐stress and step‐stress ALTs are compared for the exponential failure data under complete sampling and Type‐I censoring. The objective is to quantify the advantage of using the step‐stress testing relative to the constant‐stress one. Assuming a log‐linear life–stress relationship with the cumulative exposure model for the effect of changing stress in step‐stress testing, the optimal design points are determined under C/D/A‐optimality criteria. The efficiency of step‐stress testing to constant‐stress one is then discussed in terms of the ratio of optimal objective functions based on the information matrix. © 2013 Wiley Periodicals, Inc. Naval Research Logistics 00: 000–000, 2013 相似文献
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We propose a nonparametric Bayesian lifetime data analysis method using the Dirichlet process mixture model with a lognormal kernel. A simulation‐based algorithm that implements the Gibbs sampling is developed to fit the Dirichlet process lognormal mixture (DPLNM) model using rightly censored failure time data. Five examples are used to illustrate the proposed method, and the DPLNM model is compared to the Dirichlet process Weibull mixture (DPWM) model. Results indicate that the DPLNM model is capable of estimating different lifetime distributions. The DPLNM model outperforms the DPWM model in all the examples, and the DPLNM model shows promising potential to be applied to analyze failure time data when an appropriate parametric model for the data cannot be specified. © 2013 Wiley Periodicals, Inc. Naval Research Logistics, 2013 相似文献
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以一种高焓高压空气加热器为研究对象,对其冷却通道的流动和传热进行了三维数值仿真,冷却剂采用液态水,燃烧室和喷管分别采用不同的壁面材料,考虑壁面材料物性随温度的变化,并通过加热器热试验证了数值仿真结果的正确性。在此基础上,对比分析了气体辐射、冷却通道结构以及冷却水的流动方式对壁面换热的影响。结果表明:气体辐射对加热器燃烧室段壁面换热影响较大,对喷管壁面换热无明显的影响。在传热计算中,忽略气体辐射会引起较大的误差;冷却通道数和宽度存在最优组合,使得壁面换热量最大。冷却水的流动方式对燃气侧壁面温度影响较小,但对冷却液侧壁面温度的影响较大。 相似文献
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Majak D’Agoôt 《Small Wars & Insurgencies》2013,24(3):679-702
ABSTRACTWhen on the wrong end of an asymmetry in the projection of hard power, weaker sides countenance the grim arithmetic of avoiding direct and massed confrontations. Invariably, insurgents have over the ages tended to employ indirect tactical methods to render their stronger opponents ineffective. Ultimately – interest asymmetry, regime type, asymmetries of strategy, and external intervention – combine in a complex interplay and pattern, to militate against a strong side. In Sudan, these factors interacted throughout the civil wars to produce regional autonomy and finally an independent South Sudan in 2011. Similar strategic logic had confronted many large African states battling insurgencies in Ethiopia, Angola, Nigeria, Zaire, and apartheid-era South Africa. Oftentimes, weakening public resolve has caused these governments to accommodate, capitulate or withdraw even if they try not to blink. Notwithstanding the regime type, it can be concluded that the majority of strong actors are prone to fail in a protracted, asymmetric conflict. Hence, the notion of linking victory in counterinsurgency to the degree of openness (democratic polyarchies); or closeness (totalitarianism) – is still valid but highly contestable in the case of Africa’s large dysfunctional states. 相似文献
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SpaceWire总线是欧洲空间局为航天应用而设计的一种高速、点对点、全双工的总线网络[1]。时延抖动是表征网络传输性能的关键参数,它度量了端到端的最大传输时延和最小传输时延的差。通过建模仿真,对于某特定应用场景下的SpaceWire总线的时延抖动进行了定量分析和研究。利用Opnet建立仿真模型,通过仿真得出最大传输时延和最小传输时延,从而统计出时延抖动。并且对时延抖动进行定性定量的分析,获得对时延抖动有影响的关键参数。跟据分析结论,提出了改善时延抖动的建议和方法。本文的研究成果对于构建低时延抖动的SpaceWire总线网络提供参考。 相似文献