数字图像全息干涉法测量液相质扩散系数

为测量液相质扩散系数,首先深入研究了传统全息干涉法的实验原理.在此基础上,利用CCD传感器取代全息干板来记录全息图,优化实验装置,设计并搭建了基于数字图像全息干涉法和新的扩散槽测量液相质扩散系数的实验系统.利用该系统测定了浓度为0.33 mol·L-1KCl水溶液在298.15 K温度条件下的质扩散系数,验证了实验系统的准确性和可靠性.为测量工程上急需的新型替代工质的质扩散系数奠定了实验基础.     

基于ANSYS的有限元强度折减法求边坡安全系数

介绍了一种基于有限元的强度折减法的边坡稳定性分析方法,讨论了该方法的基本原理、安全系数的物理意义、屈服准则和流动法则的选用及边坡破坏的判据等。算例通过不断减小边坡强度参数黏聚力和内摩擦角,得到新的一组黏聚力和内摩擦角,再输入软件计算至不收敛,此时的折减系数就是边坡的安全系数。计算结果显示,用ANSYS计算边坡的安全系数有一定的实用性和可靠性。     

水下无人航行器外挂吊舱水动力试验及操纵性分析

在循环水槽开展了某带吊舱水下无人航行器的水动力试验,绘制出了航行器阻力曲线,得到了与操纵性相关的主要水动力系数,在此基础上对水下无人航行器的运动稳定性进行了分析,并与不带吊舱情况下的水下无人航行器操纵性进行了比较。试验结果可为水下无人航行器推进系统设计及运动控制与仿真提供依据。     

新规范下公路混凝土梁桥承载能力评定方法

介绍了新规范下现役公路混凝土梁桥承载能力检测评定办法。该办法主要是根据桥梁检测结果,采用引入分项检算系数修正极限状态设计表达式的方法进行承载力评定,提高了桥梁承载力评定客观性和可操作性。     

基于粗糙集理论的冲模实例特征属性权值确定方法

在简要介绍基于实例推理的冲模设计方法基础上,给出了基于粗糙集的冲模设计实例知识表达系统,然后提出了基于粗糙集理论的冲模实例特征属性约简和权值确定方法,即首先利用粗糙集理论判断实例特征属性的重要度,并将其进行规范化处理,得到各特征属性的权值.该方法可有效地克服传统权值确定方法中对主观经验的过分依赖.最后,以冲压件排料间隙的确定为例,说明了该方法有效性.     

基于多重透射改进的二维半理论及水动力系数预报

水动力系数是船舶耐波性能预报、操纵性能预报,滑行艇在静水中的运动稳定性及海豚运动预报的重要参数.探讨高效、稳定的水动力系数预报方法对准确预报上述问题具有重要的意义.该研究将地震波领域的多重透射公式应用于简单格林函数二维半理论,探讨了远方边界条件,用四阶龙阁库塔法处理自由面条件,进行详细的多重透射阶数、横剖面数、附加因子、自由面网格数量以及计算域的大小对计算结果的影响的探讨,并以Wigley船型为例计算了静水航行并做强迫振荡时的水动力系数.数值计算结果与切片方法、二维半理论复杂格林函数方法、三维频域方法及和试验结果进行了比较,比较表明多重透射公式能够有效地模拟二维半远方辐射条件,提高计算效率和稳定性,对二维半理论简单格林函数方法是一种有效的改进.     

Long-term correlation structure of wave loads using simulation

This paper proposes a new method for combining the lifetime wave-induced sectional forces and moments that are acting on the ship structure. The method is based on load simulation and can be used to determine the exceedance probabilities of any linear and nonlinear long-term load combination. It can also be used to determine the long-term correlation structure between these loads in the form of the long-term correlation coefficients. They are essential part of the load combination procedures in design and strength evaluations as well as in the fatigue and reliability analysis of ship structures.The simulation method treats the non-stationary wave elevations during the ship’s entire life (long-term) as a sequence of different stationary Gaussian stochastic processes. It uses the rejection sampling technique for the sea state generation, depending on the ship’s current position and the season. Ship’s operational profile is then determined conditional on the current sea state and the ship’s position along its route. The sampling technique significantly reduces the number of sea state-operational profile combinations required for achieving the convergence of the long-term statistical properties of the loads. This technique can even be used in combination with the existing long-term methods in order to reduce the number of required weightings of the short-term CDFs. The simulation method does, however, rely on the assumption that the ship is a linear system, but no assumptions are needed regarding the short-term CDF of the load peaks.The load time series are simulated from the load spectra in each sea state, taking into account the effects of loading condition, heading, speed, seasonality, voluntary as well as involuntary speed reduction in severe sea states and the short-crested nature of the ocean waves. During the simulation procedure, special care has been given to maintaining the correct phase relation between all the loads. Therefore, time series of various load combinations, including the nonlinear ones, can be obtained and their correlation structure examined. The simulation time can be significantly reduced (to the order of minutes rather than hours and days) by introducing the seasonal variations of the ocean waves into a single voyage simulation. The estimate of the long-term correlation coefficient, obtained by simulating only a single voyage with the correct representation of seasonality, approaches the true correlation coefficient in probability. This method can be applied to any ship and any route, or multiple routes as long as the percentage of the ship’s total lifetime spent in each of them is known.A study has been conducted to investigate the effects of ship type, route and the longitudinal position of the loads on the values of the correlation coefficients between six different sectional loads; vertical, horizontal and twisting moments, as well as shear, horizontal and axial forces. Three ocean-going ship types have been considered; bulk carrier, containership and tanker, all navigating on one of the three busy ship routes; North America-Europe, Asia-North America and Asia-Europe. Finally, the correlation coefficient estimates have been calculated for five different positions along the ship’s length to investigate the longitudinal variation of the correlation coefficient.     

双层通道中可渗透底部起伏的波浪散射(英文)

The scattering of plane surface waves by bottom undulations in channel flow consisting of two layers is investigated by assuming that the bed of the channel is composed of porous material. The upper surface of the fluid is bounded by a rigid lid and the channel is unbounded in the horizontal directions. There exists only one wave mode corresponding to an internal wave. For small undulations, a simplified perturbation analysis is used to obtain first order reflection and transmission coefficients in terms of integrals involving the shape function describing the bottom. For sinusoidal bottom undulations and exponentially decaying bottom topography, the first order coefficients are computed. In the case of sinusoidal bottom the first order transmission coefficient is found to vanish identically. The numerical results are depicted graphically in a number of figures.     

基于数值风洞的拱桥风荷载研究

计算流体动力学方法可以解决复杂拱桥的三维绕流问题。以九堡大桥主桥为工程背景,通过数值模拟得出了大桥主梁的静力三分力系数以及空间拱肋的风荷载参数,最终分析得到该桥的风荷载响应及一类稳定安全系数,为复杂桥梁结构的抗风研究提供了参考。     

运动平台磁体感应磁场建模研究

文章建立了运动平台磁体感应磁场的磁偶极子模型,通过数据拟合得到磁偶极子模型系数。将模型计算结果与数值计算结果相比较进行误差分析,验证了磁偶极子模型描述磁体远场区磁场的准确性。