大规模车辆监控通信服务器的设计与实现

为了解决大规模车队同时利用短消息业务和通用分组无线业务与多个监控中心进行通信的问题,研究了基于上述两种通道的车辆监控通信模型,详细设计了其中的通信服务器的功能和结构,使其能够支持各监控中心自由选择监控车辆、信息广播、特殊信息优先等服务.为了提高服务器的运行效率,在数据结构中充分采用了以空间换时间的方法,自行设计了监控接口协议,实现时采用了多线程、消息通信和组件技术.系统完成后大量的现场实验结果表明了服务器的高效性和稳定性.      

尾流激振情况下叶片强迫响应瞬态分析方法

对叶片强迫响应问题,提出应用瞬态分析的方法,针对转子叶片在前排静子叶片尾流激振情况下的位移和应力进行预估.流场进行全场三维非定常求解,将三维非定常气动力引入转子叶片有限元结构计算中,对尾流激振情况下叶片强迫响应问题进行瞬态分析,比较了不同转速下叶片的强迫响应,得到响应位移及应力变化的分析结果.采用叶片强迫响应瞬态分析方法,从流场的求解到结构响应的求解均应用成熟的通用软件,为工程应用该方法进行尾流激振情况下叶片振动应力预估及阻尼的研究提供了一个可行的方法.      

液相环境对水泥固化土抗压强度增长的影响

对于同种土样形成的固化土,水泥掺量增加到一定程度后单位水泥量产生的固化土抗压强度增量会显著提高;物理性质相近的土样掺加等量的水泥后固化土抗压强度有显著的差异.为解释上述试验现象,测定了相应固化土孔隙液中主要离子的浓度,并进行热力学计算.结果表明:水泥掺量较少时,固化土孔隙液中Ca(OH)₂不饱和,单位水泥量水化生成的胶凝性物质量较少,故产生的固化土抗压强度增量也较小;当土样中水泥掺量达到一定程度后,固化土孔隙液中Ca(OH)₂饱和,固化土中胶凝性物质能充分生成,单位水泥量产生的固化土抗压强度增量较大.物理性质相近的土样掺加相同的水泥量,固化土孔隙液中Ca(OH)₂离子浓度不同,故而固化土抗压强度也不同.      

新淬火状态铝合金板的成形极限

论述了硬铝合金成形工艺中应变路径、固溶热处理和时效过程对成形极限的影响,由试验得到了单向拉伸预应变和固溶热处理后时效过程中的成形极限图FLD(Forming Limit Diagram),重点研究了固溶热处理后时效过程中成形极限的变化,并得到了铝合金在时效过程中的成形极限应力图FLSD(Forming Limit Stress Diagram).结果表明,原始退火状态材料的成形极限高于新淬火状态材料的成形极限,且新淬火状态材料的成形极限随时效时间增加而降低,原因主要在于固溶热处理过程中材料组织状态的变化和应变硬化指数n在时效过程中的降低;成形极限应变的降低导致成形极限应力也随时效时间增加而降低.      

轮地力学模型参数灵敏度分析与主参数估计

在星球探测过程中,星球车需要估计地面力学参数以及时调整控制策略,快速适应地形变化。针对形式复杂,参数耦合的轮地相互作用模型,采用Sobol灵敏度分析方法,分别对模型中的地面承压特性参数和剪切特性参数的灵敏度进行定量分析,筛选出沉陷指数与内摩擦角作为模型的主导参数,用于反映地面承压特性和剪切特性的变化。基于轮地相互作用力学平衡方程,通过简化应力分布公式,进一步推导出主导参数的解析表达式。通过以典型值固定非主导参数,利用系统状态参数和滤波处理完成地面力学特性主导参数的估计。结果表明,所提出的地面力学主导参数解析式及相应的估计方法能够快速反映地形的变化,沉陷指数估计的平均相对误差为2.8%,内摩擦角估计的平均相对误差小于3%。估计结果可准确预测车轮牵引力,为实现实时控制提供必要信息。     

肋片参数对辐射器散热性能的影响研究

采用蒙特卡罗法计算等截面圆管直肋式辐射器的肋片和外管壁相互间的辐射换热,数值模拟了第一类换热边界条件下散热器的散热过程。分析了辐射器的肋片数、肋片高度、肋片厚度及管壁温度对肋片散热性能的影响。结果发现,在肋片质量一定的条件下肋片数及肋片高度均存在一优值,在该值附近肋片的散热效率最高,且该值受管壁温度的影响,温度越高该值越小;在肋片外形不变的条件下,增加肋片的厚度来提高辐射器的散热性能并不是经济的途径;肋片的散热效率随管壁温度的升高而减小,壁温较高时安装肋片的必要性降低。     

Clusters of Galaxies: Setting the Stage

Clusters of galaxies are self-gravitating systems of mass ∼10¹⁴–10¹⁵ h ⁻¹ M_⊙ and size ∼1–3h ⁻¹ Mpc. Their mass budget consists of dark matter (∼80%, on average), hot diffuse intracluster plasma (≲20%) and a small fraction of stars, dust, and cold gas, mostly locked in galaxies. In most clusters, scaling relations between their properties, like mass, galaxy velocity dispersion, X-ray luminosity and temperature, testify that the cluster components are in approximate dynamical equilibrium within the cluster gravitational potential well. However, spatially inhomogeneous thermal and non-thermal emission of the intracluster medium (ICM), observed in some clusters in the X-ray and radio bands, and the kinematic and morphological segregation of galaxies are a signature of non-gravitational processes, ongoing cluster merging and interactions. Both the fraction of clusters with these features, and the correlation between the dynamical and morphological properties of irregular clusters and the surrounding large-scale structure increase with redshift. In the current bottom-up scenario for the formation of cosmic structure, where tiny fluctuations of the otherwise homogeneous primordial density field are amplified by gravity, clusters are the most massive nodes of the filamentary large-scale structure of the cosmic web and form by anisotropic and episodic accretion of mass, in agreement with most of the observational evidence. In this model of the universe dominated by cold dark matter, at the present time most baryons are expected to be in a diffuse component rather than in stars and galaxies; moreover, ∼50% of this diffuse component has temperature ∼0.01–1 keV and permeates the filamentary distribution of the dark matter. The temperature of this Warm-Hot Intergalactic Medium (WHIM) increases with the local density and its search in the outer regions of clusters and lower density regions has been the quest of much recent observational effort. Over the last thirty years, an impressive coherent picture of the formation and evolution of cosmic structures has emerged from the intense interplay between observations, theory and numerical experiments. Future efforts will continue to test whether this picture keeps being valid, needs corrections or suffers dramatic failures in its predictive power.     

基于WGA的导弹武器系统效能多目标评估

建立了导弹武器系统效能评估指标体系及评估模型,针对导弹武器系统效能的复杂性、综合性和不确定性,将层次分析法(AHP, Analytical Hierarchy Process)与加权向量法相结合,提出了一种基于加权几何平均算子的导弹武器系统效能多目标综合评估方法.将评价系统指标分为单项效能、系统效能和综合效能,利用层次分析法AHP确定各指标的权重系数,获取评价信息.通过运用加权几何平均(WGA,Weighted Geometric Average)算子和组合加权几何平均(CWGA)算子对属性值进行加权集结,得到群体综合属性值,从而确定最优方案,实现武器系统效能优劣的综合评估. 用实例进行了验证,结果表明,是导弹武器系统效能评估的有效方法.      

同一平面气动力辅助变轨的近似解及分析

采用格林函数法,给出了同一平面气动力辅助变轨飞行的3种过程约束(气动加热率、动压、升力约束)条件之间关系的近似定量描述形成的飞行包络线.由此求解了航天器同时受3种约束条件时,各种性能指标下的同一平面气动力辅助变轨轨迹的近似解及相应的最优控制规律.文中对近似解与控制规律的内部结构作了细致的分析,得到了一些有益的结论.     

Experimental investigation of rotary sinking electrochemical discharge milling with high-conductivity salt solution and non-pulsed direct current

Electrochemical milling is a modified technique of traditional electrochemical machining (ECM) that can be used to manufacture some helicopter transmission system parts. The use of rotary tools and an inner-jet electrolyte supply pattern can greatly improve the material removal rate (MRR) in a single pass. However, the feed speed is generally limited to minimize the tool wear. To increase the MRR, electrical discharge machining (EDM) is introduced into the electrochemical milling process. The tool rotation is employed to interrupt the discharge and the high-conductivity salt solution and non-pulsed direct current power supply are also adopted to increase ECM, eventually, a new machining method is proposed, which can be called rotary sinking electrochemical discharge milling (RSECD milling). The mechanism of it is explored in this study by analyzing the machined current, MRR, surface morphology, and tool wear at different applied voltages and feed speeds. Besides, the RSECD milling using the tool with a larger diameter is also conducted to further verify the effectiveness. In particular, the MRR can be increased by 742.5% when using the tool with a diameter of 20 mm at the applied voltage of 20 V.