用中心管限位的椭球壳无模液压成形试验研究

理论与实践均证明,长短轴比大于2的椭球壳体在自由胀形时会在赤道附近起皱,其原因是由于存在纬向压应力。首次提出采用带中心管约束法整体无模胀形技术,对长短轴比为2的椭球壳体进行液压胀形试验研究,得到了椭球壳体胀形时应变分布及尺寸变化规律。试验结果表明：在中心管约束下的椭球壳体胀形可以较好地控制椭球轴长比。椭球状壳体在胀形过程中经历焊缝起皱凸起,后又在更高内压的作用下逐渐消皱的过程。塑性变形首先发生在赤道焊缝处,随后球瓣靠近南北极的部位也发生塑性变形,并由赤道和极板向温带区域扩展。用此方法所获得的壳体可以直接用于椭球形水塔。     

贪婪寻优算法在中继节点布局中的应用

针对目前中继节点布局算法所忽视的布局完成后网络整体能耗的问题,提出了基于最小通信网络距离因子的布局算法评价新标准,同时将中继节点布局禁区、通信路径不可逆等约束条件.解决方法上,采用了基于贪婪寻优算法的中继节点布局算法,实现了无线传感器网络中继节点的多约束容错性布局.仿真实验表明,提出的基于贪婪寻优算法的中继节点布局算法与常规中继节点布局算法相比,在降低通信网络整体能耗以及保证能耗均衡性方面具有明显的优势.     

足尺结构模型等效力控制试验研究

等效力控制试验方法是一种采用力反馈的闭环位移控制系统,本文将其先后应用于三层框支配筋砌块短肢砌体剪力墙结构和三层预制钢筋混凝土剪力墙结构足尺模型的拟动力子结构试验中,完成了试验子结构为多自由模型、计算子结构为弹性非线性复杂结构模型的拟动力子结构试验。试验结果表明,采用等效力控制进行复杂足尺结构模型的拟动力子结构试验是可行的,可以得到试验模型的下降段数据。     

前处理工艺对印刷线路板表面化学镀镍/置换镀金层性能的影响

分析了酸洗、微刻蚀及活化等前处理工艺对印刷线路板(PCB)表面化学镀镍/置换镀金层性能的影响.结果表明:备前处理工序对PCB表面性能具有较大影响,在此基础上得到了优化后的前处理工艺.     

硫酸盐三价铬电镀中铵盐的作用及影响

研究了铵盐在硫酸盐体系三价铬电镀中的作用.通过赫尔槽试验、沉积速率、极化曲线、循环伏安法等方法研究了铵盐对三价铬镀液的电沉积特性的影响.并采用Tafel曲线、电化学阻抗谱EIS测试及铜盐加速醋酸盐雾试验(CASS),对在不同浓度铵盐的镀液中得到的镀层耐蚀性进行了测试.结果表明,铵盐在镀液中不仅起导电作用而且起配位作用....     

服务质量约束下的IP组播通信可靠性评估方法

In order to estimate the reliability performance of multicast communication under multiple constraint conditions, the weight of service rate and the reliability index are defined, accompanying the calculation method. Firstly, according to the Quality of Service requirements, the appropriate routings between the central node and target nodes that meet the requirements are calculated using the iterative method in the weighted internet. Then, the disjoint set of network state and the coefficients of weighted service rate are calculated by decomposition and merge methods. Lastly, the formula for calculating the service rate is obtained based on the disjoint set of network state and the calculation of the reliability index will be completed. The simulation result shows that the reliability of multicast communication can be appropriately reflected by the weight of service rate and the calculation method, which can provide the theoretical basis for the reliability evaluation of multicast communication.     

First-principles study of point defects and Si site preference in Al3Ti

The formation energies of various point defects in Al₃Ti(D0₂₂) have been calculated by using first-principles calculation. The effects of vacancies on Si site preference were examined to better understand Si substitution behavior in Al₃Ti. The results show that, under Al-rich condition, the formation energy of antisite Al_Ti is the lowest than those of other point defects, and Ti vacancy is more preferred than Al vacancy. But Si prefers to occupy Al vacancy compared with Ti vacancy which causes a finite solubility of Si in Al₃Ti system. The calculation is instructive for the further improvements of process of Si removal.     

Promotion of L10 ordering in Pt-rich nonepitaxially grown FePt films

Multilayer Fe/Pt films with atomic ratios Fe_xPt_100-x (x = 36 ~ 58) were deposited directly onto quartz glass substrates at room temperature through magnetron sputtering. Post-annealing from 300 °C to 600 °C was carried out to investigate the effect of varied compositions on the L1₀ ordering process. The result, which is different from that of co-sputtering growth, shows an obvious promotion of the phase transformation for slightly Pt-rich off-stoichiometric compositions with x between 40 and 50. The in-plane coercivity of Fe₄₈Pt₅₂ can reach 4.1 kOe even after annealing at 300 °C. This facilitated atomic diffusion and ordering might be related to the lattice expansion due to excessive Pt content.     

附体对分层流中潜艇水动力特性的影响

为探讨密度分层流中附体对潜艇周围流场及阻力特性的影响,基于雷诺平均方程建立一种用于模拟密度分层流中水下潜体航行特征的计算流体力学模型。采用SUBOFF潜艇模型进行收敛性研究,并与实验结果进行对比验证数值模型的精确性;采用该模型模拟得到加装不同附体工况下的潜艇以不同航速航行时的水动力特性,并结合压力变化分析相关结果产生的原因。结果表明：附体对分层流中潜艇水动力特性的影响与航速高低有关;在弗劳德数为0.5附近,潜艇兴波阻力系数达到最高;附体带来的潜艇表面曲率突变会引起较大的压力变化;所建模型展示了潜艇的航行尾迹特征,并对密度分层流中水下潜体运动问题模拟方法的选取及潜艇附体的优化设计具有一定参考价值。     

无纺织物单向拉伸孔径变化试验与理论预测对比分析

无纺织物作为反滤材料,常处于单向受拉工作状态。单向拉伸引起无纺织物孔径变化,易导致反滤工程失效。通过控制织物应变的干筛试验,定量测试了无侧限单向拉应变逐级增大的过程中,两种不同厚度短纤针刺无纺织物的孔径分布曲线变化。采用干筛试验结果,对现有两种体系的单向应变下无纺织物孔径预测理论解进行验证:一类是佘巍等效孔径O95理论解,一类是Rawal孔径分布曲线理论解。通过对比两种理论解对各级拉应变下的O95值预测,归纳二者的预测误差规律,从理论假设出发分析误差原因。同时采用前人图像法测得的热粘无纺织物O95变化验证两类理论解。两种理论解均能较好地预测无侧限单向拉应变下无纺织物O95的变化规律。O95随单向拉应变呈近似线性减小的规律。对于O95变化斜率的预测,佘巍解较准确,Rawal解偏大。对于O95数值预测可结合两类理论解给出变化范围。