反应装甲与陶瓷复合装甲集成技术研究探讨

为了得到抗弹性能较好的装甲,将反应装甲与陶瓷复合装甲集成。由长杆弹侵彻复合装甲的理论和撞击反应装甲时的动量定理,得出计算模型。据此模型进行了侵彻深度的数值计算,并证明相同面密度的集成装甲的抗弹性能明显优于陶瓷复合装甲。根据此计算模型对集成装甲进行优化设计,以得到较轻和抗弹性能较好的装甲。     

Thermal performance of an open loop closed end pulsating heat pipe

This paper presents an experimental study of an open loop pulsating heat pipe (OLPHP) of 0.9 mm inner diameter. The performance characterization has been done using four working fluids at vertical and horizontal orientations. Water, Methanol, 2-Propanol and Acetone has been employed as the working fluid with 50% fill ratio. The experimental results indicate a strong influence of gravity and thermo physical properties of the working fluids on the performance of OLPHP. Considering all the working fluids used, Water has shown better thermal performance in vertical orientation while Methanol has shown better performance in horizontal orientation. All the working fluids perform better at horizontal orientation.     

Some further problems in the design of wheels and tracks

The studies reported herein attest to the need for establishing a better insight into the development of forces and moments at the terrain-vehicle interface— as a function of contact unit properties and properties of the terrain material. In turn, the reactions developed and response characteristics of the terrain can be anticipated to allow for better control for land utilization.     

Calibration of pressure transducers for small pressure differences

Two simple methods for the calibration of pressure transducers in the range 0 to 10 Pa are compared. One relies on water displaced, by known weights and the other uses helium in an inverted U-tube. The slopes of the calibration curves determined with the two methods agreed to better than 0.25% while the standard deviation of a typical calibration curve was better than 0.005 Pa.     

超高压缸的最佳化设计理论及其应用

简要分析了缩套超高压圆筒对于改善应力分布的原理,推导了双层筒体基于最佳化设计原则的缩套界面压力的计算公式及径比条件.然后针对某超高压缸所存在的问题,采用最佳化设计原则对其进行了最佳化设计,求得了最佳径比及有关尺寸.通过对最佳化设计前后的应力的比较分析,表明最佳化设计后的超高压缸的应力分布比原超高压缸有较大改善,提高了超高压缸的承载能力.     

Shock capturing viscosities for the general fluid mechanics algorithm

The performance of different shock capturing viscosities has been examined using our general fluid mechanics algorithm. Four different schemes have been tested, both for viscous and inviscid compressible flow problems. Results show that the methods based on the second gradient of pressure give better performance in all situations. For instance, the method constructed from the nodal pressure values and consistent and lumped mass matrices is an excellent choice for inviscid problems. The method based on L₂ projection is better than any other method in viscous flow computations. The residual based anisotropic method gives excellent performance in the supersonic range and gives better results in the hypersonic regime if a small amount of residual smoothing is used. © 1998 John Wiley & Sons, Ltd.     

有限元—康托洛维奇杂交法及其应用

本文将有限元法与康托洛维奇方法进行适当组合,吸收二者的主要优点,提出在单元的位移插值函数中附加康托洛维奇项。康托洛维奇方法是一种半解析法,其在解析方向具有较高的精度,在一定程度上弥补了原有限元方法中插值函数选取的盲目性,能够较好地反映微分方程的固有性质,提高其适应性。在单元的位移插值函数中附加内部无节点的位移项,无需增加新的单元与节点,使用较少的单元即可获得较高的精度。并且,这些附加项满足单元边界条件为零,故其在单元与单元的交界面上是保证协调的。本文通过算例充分说明了此方法的特点和优越性。     

L-leap-accelerating the stochastic simulation of chemically reacting systems

Presented here is an L-leap method for accelerating stochastic simulation of well-stirred chemically reacting systems,in which the number of reactions occurring in a reaction channel with the largest propensity function is calculated from the leap condition and the number of reactions occurring in the other reaction channels are generated by using binomial random variables during a leap.The L-leap method can better satisfy the leap condition.Numerical simulation results indicate that the L-leap method can obtain better performance than established methods.     

新型奥氏体不锈钢的耐磨性研究

为了解决传统奥氏体不锈钢耐磨性较差的问题,本文设计了一种新型的Fe-Mn-Si-Cr-M-C奥氏体不锈钢,并研究了其耐磨性能和耐腐蚀性能.研究表明:Fe-Mn-Si-Cr-Ni-C奥氏体不锈钢在干摩擦和油润滑条件下均具有比1Cr18Ni9Ti奥氏体不锈钢更好的耐磨性,在NaCl中耐蚀性不如1Cr18Ni9Ti不锈钢,但在NaOH中优于1Cr18Ni9Ti不锈钢.Fe-Mn-Si-Cr-Ni-C奥氏体不锈钢应力作用下发生的应力诱发γ→ε马氏体相变是其具有较高耐磨性的原因.     

FRP疲劳累积损伤理论研究进展

纤维增强树指复合材料（FRP）已成为高性能结构的先进材料。本文对FRP疲劳累积损伤理论作了详细的回顾,它们可分为剩余寿命模型、剩余刚度模型、耗散能模型、Markov链模型和其它经验公式。还用两个大样本实验数据对这些模型作了分析对比,结果表明:除Yao和Himmel的剩余强度模型略优一些,其它模型则与传统的Miner模型不相上下。      

Analytical prediction of the wave configuration size in steady flow Mach reflections

Analitycal model for predicting the size of the Mach reflection wave configuration in steady flows has been improved (Azevedo 1989; Azevedo and Liu (1993)). Predictions based on the modified analytical model were compared to available experimental results. The agreement was found to be better than that obtained by Azevedo (1989) and Azevedo and Liu (1993). The reason for the better agreement is due to the fact that, unlike Azevedo's original model, downstream effects were not neglected in the modified model which was developed in the course of this study. Received 12 May 1996 / Accepted 15 January 1997     

基于遗传算法的水轮机振动参数识别

通过对水轮机现场测试数据的频域分析，建立了测点位移响应的参数正模型。并基于遗传算法，建立了在时域内识别结构振动参数的数值方法，采用该方法对水轮机位移响应正模型的待定参数识别进行了研究。计算结果表明，所建立的基于遗传算法的参数识别方法具有良好的稳定性、抗观测噪声能力和较高的识别精度，能够反演出比较符合实际情况的位移响应振动模型。这就为荷载识别、结构优化和预报减震效果等后续工作提供了可靠的实施前提。     

低温沉积Ag-Cu薄膜的耐原子氧和摩擦学性能

采用多弧离子镀在低温(173 K)沉积了Ag-Cu薄膜,通过地面原子氧模拟试验机构考察了薄膜的耐原子氧性能,通过X射线衍射(XRD)、原子力显微镜(AFM)和球-盘摩擦试验机对薄膜结构、耐原子氧性能和摩擦学性能进行了表征,并与室温(300 K)及低温(173 K)沉积Ag薄膜进行了比较研究.结果表明:低温沉积Ag-Cu薄膜由面心立方结构的AgCu合金相和少量Ag或Cu组成,Cu元素合金和低温沉积可细化Ag薄膜的晶畴尺寸、提高其致密性,细密的薄膜结构有利于抑制原子氧对薄膜的攻击,因此低温沉积的Ag-Cu薄膜表现出较好的耐原子氧性能;磨损试验结果表明低温沉积的Ag-Cu薄膜表现出较好的耐磨性,这主要归因于其细密的薄膜结构和较高的膜-基结合强度,此外由于其耐原子氧性能的改善,低温沉积Ag-Cu薄膜在原子氧辐照前后磨损率的增加明显低于低温和室温沉积Ag薄膜.     

On the efficient application of weighted essentially nonoscillatory scheme

In this paper, the efficient application of high‐order weighted essentially nonoscillatory (WENO) reconstruction to the subsonic and transonic engineering problems is studied. On the basis of the physical considerations, two techniques are proposed to enhance the accuracy and efficiency of the WENO reconstruction. First, it is observed that the WENO scheme using characteristic variable has better accuracy and convergence speed than the scheme using primitive variable. For engineering problems with shock of moderate amplitude, on the basis of the Rankine–Hugoniot conditions, a simplified characteristic‐variable‐based WENO is developed. The simplified version significantly reduces the cost overhead without sacrificing the shock‐capturing capability. Second, in this work, it is found for viscous case that it is better to include the viscous effect. On the basis of a simple analysis, the viscous correction to the parameter ε in the WENO reconstruction is proposed. Numerical results indicate, with the proposed simplified characteristic‐variable‐based reconstruction and the viscous correction, that the nonlinear WENO interpolation is sharply activated in the region of shock jump, whereas in the shockless area, the WENO interpolation weights are tuned towards the designed optimal value for better accuracy. Compared with the original characteristic‐variable‐based WENO, the current implementation has similar accuracy and reduced cost. At the same time, compared with the primitive variable‐based WENO, better accuracy and convergence speed are obtained at marginal cost overhead. Several practical cases are calculated to demonstrate the accuracy and efficiency of the current methodology. Copyright © 2012 John Wiley & Sons, Ltd.     

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在仿真研究1/4车体二自由度液压半主动悬架的基础上,设计了一种 用于1/2车体的液压半主动悬架的参数自整定模糊PID控制器,并利用模糊控制规则对 PID参数进行在线修改. 以正弦信号路面、脉冲信号路面和C级路面3种典型路面作为输入 信号,应用MATLAB/Simulink控制系统仿真软件对该半主动悬架模型进行的计算机仿真表明, 具有模糊PID控制器的半主动悬架在提高车辆乘坐的舒适性方面要明显优于一般的模糊控制 悬架,具有更好的自适应能力.     

Dislocation dynamics

A brief summary is presented on the current status of knowledge regarding the dynamic behavior of crystalline materials in terms of athermal, thermally activated, viscous damping, and relativistic motion of dislocations. It is shown that dislocation concepts have contributed substantially to a better and more unified rationalization of the dynamic behavior of crystalline materials than heretofore possible. Particular emphasis is given to the need for a more complete theoretical understanding of dislocation mechanics. Also, the requirements for more detailed and better experiments are expressed particularly for dislocation-velocity determinations in the viscous damping and relativistic ranges of conditions.     

MEMS-IMU/GPS组合导航中的多模态Kalman滤波器设计

一般的Kalman滤波器要求有准确的动态和统计模型,而低成本的MEMS-IMU性能随着温度急剧变化,故在MEMS-IMU/GPS组合导航系统中使用一般的Kalman滤波器存在很多的局限性。针对低成本的MEMS-IMU/GPS组合导航系统,提出了多模态自适应滤波算法在MEMS-IMU/GPS组合导航系统中的应用;针对普通的多模态算法中的问题,采用修正的多模态自适应滤波算法来提高MEMS-IMU/GPS组合导航系统的性能。使用静态实时测试数据,验证了所提出的算法。测试结果表明,与普通Kalman滤波器相比,修正的多模态滤波算法提高了MEMS-IMU/GPS组合导航系统的性能;采用所提出的算法,MEMS-IMU/GPS组合导航系统的短时间静态位置精度小于5m(标准差),速度精度小于0.1m/s(标准差),姿态角精度小于0.5°(标准差)。     

MWCNTs复合物纳米流体的摩擦学性能

将油性剂油酸(OA)填充进多壁碳纳米管(MWCNTs)的空腔内制备复合物,再以复合物为添加剂制备一种纳米流体,考察了复合物的质量分数、MWCNTs的酸处理时间以及摩擦测试条件等对纳米流体摩擦学性能的影响,并分析了复合物的润滑机理. 结果表明:油酸被成功填充到经酸处理的MWCNTs管内,填充率约20%;摩擦过程中,复合物制备的纳米流体的摩擦系数有不断减小趋势,其减摩效果甚至优于同等含量的油酸乳化液;当复合物的质量分数为0.1%左右时,纳米流体可获得最佳的减摩、抗磨效果;随着酸化处理时间的增加,复合物制备的纳米流体的减摩、抗磨性能会有所提高. 摩擦过程中,复合物可释放出油酸并形成润滑膜,MWCNTs则能够在油酸形成的润滑膜上发挥“微轴承”的作用,从而使复合物获得更加优良的减摩、抗磨效果.      

Measurement and modeling of back stress at intermediate to high homologous temperatures

Unified creep-plasticity models often require a number of internal state variables to accurately capture the path dependence of rate- and temperature-dependent alloys especially at intermediate to high homologous temperatures. However, it is impossible to fully measure the internal state variables directly. Consequently, assumptions on the relative importance of the various state variables must be made when determining the material parameters and their evolution must be inferred. Any enhancements designed to better capture the evolution of the state variables are dependent on these assumptions and are generally limited. The strain transient dip test and the rapid load/unload test are two indirect experimental methods used to obtain an approximate measure of the evolutionary nature of the back stress in 60Sn–40Pb, a common rate- and temperature-dependent solder alloy. The rapid load/unload test gives a better measure of back stress because there is less time for the internal state to evolve during data acquisition. Modifications to the back stress evolution equations in the McDowell unified creep-plasticity model are proposed using these new measurements as guidance. The modified model can better capture the transients under cyclic loading and following strain-rate jumps.