四足机动平台的静步态规划研究

基于仿生学原理进行了四足机动平台的腿部结构设计,分析了负载因子、周期、步距等步态设计参数对静步态稳定性的影响,提出了平地直行条件下从起步到稳定行走的步态调整方式,并对静步态行走全过程的稳定裕度进行了求解。计算结果表明：所规划的行走步态能达到静步态运动稳定性要求。     

燃烧室压力对潜入式喷管喉衬热应力的影响

为了研究燃烧室压力对固体火箭发动机潜入式喷管热应力影响规律的问题,采用商业流体软件,基于压力求解器,求解了喷管纯气相的流场,确定了燃气温度、压力、壁面对流换热系数;采用有限元软件,依据流场计算的非均布壁面压力与非均布对流换热,求解了燃烧室压力为6 MPa下的潜入式喷管热结构问题;通过地面点火试验验证了仿真模型与数值方法的有效性与准确性;采用相同计算模型与数值方法,求解了在燃烧室压力为9 MPa、12 MPa下的喷管热结构问题,揭示了燃烧室压力对喉衬热应力的影响规律。结果表明:整个工作过程,喉衬环向应力最大值为103.9 MPa,位于内表面,且随时间增大,先增大后减小;喉衬环向拉应力也随时间先增大后减小;随压力增大,对流换热系数增大,喉衬温度升高,喉衬环向拉应力增大,喉衬环向压应力减小。     

Influences of different crossing types on dynamic response of underground cavern subjected to ground shock

An intersecting cavern is a common structural form used in underground engineering, and its safety and stability performance directly control the service performance of the whole project. The dynamic re-sponses of the three kinds of crossing type (+-shaped, T-shaped, L-shaped) caverns subjected to ground shock were studied by numerical simulation. The velocity plus force mode boundary setting method was proposed in the coupled static and dynamic analysis of a deep underground cavern. The results show that, among the three types of crossing caverns, the+-shaped cavern is the most significantly affected by the dynamic action, followed by T-shaped, and then L-shaped caverns. The vault settlement, straight wall deformation, vault peak particle velocity, effective plastic strain of surrounding rock, and maximum principal stress and strain at the bottom of the lining of the straight wall increase with the increase of cavern span. The vault settlement, straight wall deformation, effective plastic strain of surrounding rock, and the maximum principal stress and strain at the bottom of lining to the straight wall decrease with the increase of lateral pressure coefficient, and the peak particle velocity at the vault increases. The variation is small compared with the change of cavern span. The influence range of the underground cavern intersection is two cavern diameters from the intersection centre. The bottom of the straight wall at the intersection is the weak part. It is suggested to thicken the support locally to improve the stability of the cavern.     

Effect of friction stir processing on mechanical properties and heat transfer of TIG welded joint of AA6061 and AA7075

Tungsten inert gas (TIG) welding is the most commonly used joining process for aluminum alloy for AA6061 and AA7075 which are highly demanded in the aerospace engineering and the automobile sector, but there are some defects occur during TIG welding like micro-crack, coarse grain structure, and porosity. To improve these defects, the TIG welded joint is processed using friction stir processing (FSP). This paper presents the effect of friction stir processing on TIG welding with filler ER4043 and ER 5356 for dissimilar aluminum alloy AA6061 and AA7075. The mechanical characterization, finite element formulation and mathematical equations of heat transfer of TIG + FSP welded joints are investigated using ANSYS Fluent software by adjusting process parameters of FSP. The results show that the maximum compressive residual stress 73 MPa was obtained at the fusion zone (FZ) of the TIG weldment with filler ER4043, whereas minimum compressive residual stress 37 MPa was obtained at stir zone (SZ) of the TIG+FSP with filler 5356. The maximum heat flux 5.33 × 106 W/m2 and temperature 515 ℃ have observed at tool rotation 1600 rpm with a feed rate of 63 mm/min. These results give a satisfactory measure of confidence in the fidelity of the simulation     

自润滑弹带挤进过程中渗出油量的对比计算

从弹带的作用及特性出发, 通过数值计算和统计计算 2种方法计算了自润滑弹带挤进过程中的渗出油量,初步得出了渗出油量和行程之间的关系。这一问题的解决为自润滑弹带材料的选择提供了理论依据。通过对 2种算法的比较可知, 数值计算误差更小一些, 而统计计算对数学条件要求不太苛刻。     

Burgers’方程的守恒律

守恒律历来是物理学研究的中心课题之一.在数学中借助运动常数,对偏微分方程的解作出先验估计,这些估计是方程的解存在性、唯一性及稳定性的核心关键.在计算数学中较好的稳定差分格式,也用到守恒律.在Noether's定理求守恒律的基础上,利用Burgers'方程的对称群构造出相关的伴随因子得出了Burgers'方程的一类守恒律.     

两栖装备乘员可靠性影响因素分析

人的可靠性指的是人在规定的时间内、规定的条件下、完成规定任务的能力,它是整个系统可靠性一个重要的组成部分,作为装甲装备而言,乘员可靠性的高低直接影响到整个装备作战系统可靠性.针对两栖装备的使用环境和使用特点,对影响乘员可靠性的因素进行了分析,得出了结论,对于如何提高两栖装备乘员可靠性有一定的指导意义.     

大功率消磁线圈受力分析与计算

大功率消磁线圈在运行中会受到较强电磁力的作用,客观地分析和计算电磁力的大小及分布情况,是设计和建造大型消磁站的一项基础性的工作.文中从电磁场基本原理出发,应用张量理论分析、计算了大功率消磁线圈的受力情况,对于设计和建造大型消磁站具有参考作用.     

基于专家系统的防化保障预案评估研究

人工智能技术在众多领域获得广泛应用．为满足现代战争对防化指挥手段的现代化要求,针对不易量化的防化指挥决策问题的评估,提出了构建知识库并应用模糊推理机制建立专家系统,据此进行防化保障预案的评估选优方法,并对该方法的求解过程进行了探讨．     

On the median residual lifetime and its aging properties: A characterization theorem and applications

This paper is devoted to study several aspects of the median residual life function (MERLF). In reliability studies, it is well known that, although the MERLF have several advantages over the mean residual life function (MRLF), the MRLF has the good property of uniquely determine a life distribution whereas either the median residual life function (MERLF) or an α‐percentile residual life do not have such good property. We shall give a characterization result where knowledge of both the MERLF and the survival function on an interval does uniquely determine the distribution. Moreover, in order to apply this characterization in practical situations, we propose a method to estimate the necessary information of the survival function. Relationships between analytical properties of the survival function and its associated MERLF are also obtained. Bryson and Siddiqui [J Am Statist Assoc 64 (1969), 1472–1483] proved relationships among seven criteria for aging, out of which two contained the MRLF (decreasing MRLF and net decreasing MRLF). In this paper, we prove that the same pattern of relationships holds if the MRLF is replaced by the MERLF. We also examine the aging criteria corresponding to an increasing MERLF and show that there is no relation between the behavior (increasing or decreasing) of the MERLF and of the MRLF. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005