介电各向异性对铁电液晶光电特性的影响

提出了一种描述铁电液晶（FLC）介电各向异性的电路模型．分析了FLC介电各向异性对开关响应时间、特征时间、特征电压和极化反转电流的作用,以及铁电扭矩和介电扭矩对光透射率的影响。模拟分析显示,延迟时间随驱动电压幅度变化存在最小值,特征时间（特征电压）随二轴参量的提高而增加（减小）．随二轴参量增大,介电扭矩的贡献将超过铁电扭矩;相应的极化反转电流由双极性转变为单极性;透射率无”明态”和”暗态”的交替,且峰值逐步降低．     

平面2R机器人机构混沌运动的控制

应用混沌控制方法中的周期扰动参数方法有效地控制了平面2R机器人机构中的混沌运动．在周期扰动参数控制法中，外扰周期信号的频率和振幅是混沌控制成功与否的关键．通过计算系统的最大Lyapunov指数的符号与频率或振幅的关系，可以选取适当的频率和振幅，将系统的混沌运动转化为规则的周期运动．     

黏弹性人工边界在坞式闸室结构动力计算中的应用

应用ANSYS通用有限元软件编制黏弹性人工边界的计算程序,通过算例验证该计算方法的可行性。建立基于黏弹性人工边界的坞式闸室结构的动力计算模型,对坞式闸室结构进行固定边界和黏弹性边界下不同边界范围的动力计算分析。计算结果表明:与固定边界相比,黏弹性人工边界有更高的可靠性。在地震动力作用下,闸墙顶部的动力加速度响应最为明显,在闸墙底部拉应力响应最大;闸室底板下部受拉,最大拉应力值大于闸墙的最大应力;地基深度范围取值在2~3倍以上结构底宽时,结构响应已趋于稳定。     

两种减隔震支座性能对比研究

通过对摩擦摆支座及弹塑性钢阻尼支座两种不同类型的减隔震支座的抗震性能进行对比,选择适合项目要求的支座类型。对比结果表明:两种减隔震支座均能够有效延长桥梁结构自振周期,支座横向刚度较小的摩擦摆支座更有利于周期的延长,同时产生的墩顶剪力也较小;对于墩底截面及基顶截面的弯矩和剪力,在墩高较低时横向刚度小的摩擦摆支座减隔震性能较好,而墩高大于20 m时,横向刚度大的弹塑性钢阻尼支座更有优势。     

复合材料船体纵向极限强度可靠性分析

把船体甲板或船底板结构视为是一系列加筋板单元的组合，然后利用复合材料梁柱理论计算船体加筋板单元构件的极限承载能力，最后用Smith法计算复合材料船体的极限承载能力。由于复合材料船体纵向极限强度的极限状态方程不能简单地用船体各参数显式表达，故将近年发展起来的响应面法与JC法相结合，对复合材料船体纵向极限强度进行了可靠性分析。并讨论了影响船体纵向极限强度可靠性各变量的敏感性。     

Efficient estimation of extreme long-term stresses by considering a combination of longitudinal bending stresses

Longitudinal stresses due to combined horizontal and vertical bending moments in ships, corresponding to a return period of 20 years, are estimated by linear response analysis. In principle, the stress should be obtained by combining the stress in all sea states that can occur over a long-term period. A method to determine the desired long-term extreme stress by considering only a few short-term sea states is presented. The sea states have a certain probability of occurrence, and are each identified by a contour line in the (H _s, T _p)-plane. This approach makes it possible to estimate the extreme loads on the vessel in a practical and accurate manner. Moreover, it is shown that the long-term stress can be estimated by combining the individual long-term extreme stresses due to vertical and horizontal bending moments by using the sum-of-squares approach and accounting for the correlation between stresses. It was found that the correlation coefficient can be taken as the largest of the ones calculated along the contour line. It is shown that this correlation coefficient can even be approximated by the normalized phase angle at the wave length where the dominant response has its peak value. A comparison with the results obtained using well-known combination rules is presented. While linear analysis has been used here, it is believed that the approach can be generalized to stresses with nonlinear behavior, and hence represent a significant improvement in calculation efficiency. Received: September 18, 2001 / Accepted: December 18, 2001     

Prediction method of hydrodynamic forces acting on the hull of a blunt-body ship in the even keel condition

The mathematical modeling group (MMG) model is well known and is widely used in the field of ship maneuverability. However, the MMG model can be applied only after determination of the hydrodynamic coefficients either from comprehensive captive model tests or from general empirical data. Around the cruising speed, when a ship's drift angle is relatively small, several methods have been developed to predict hydrodynamic coefficients from the ship's principal particulars, e.g., Kijima's method. Kijima's method is efficient in predicting the ship's maneuverability at the initial design stage and is even able to assess the effect of changes in stern design. Similarly, for the low speed range when a ship's drift angle is relatively large, several methods for predicting the ship's hydrodynamic coefficients have been proposed, based on captive model tests, such as those by Kose, Kobayashi, and Yumuro. However, most of the methods developed for low speeds cannot be applied to general ship types without additional experiments being performed. In contrast, Karasuno's method uses theoretical and empirical approaches to predict the hydrodynamic forces, even for large drift motions. Although Karasuno's model utilizes the ship's principal particulars and is applicable to a general vessel, it has not been widely used. This is because the form of Karasuno's model is relatively complicated and its accuracy around the cruising speed is less than that for other methods that have been specifically developed for the cruising speed range. A practical method for predicting hydrodynamic forces for the entire operating speed range of blunt-body ships is proposed in this article. It is based on the MMG model and predicts hydrodynamic coefficients based on a ship's principal particulars. A regression model for the proposed method has also been proposed by analyzing 21 different blunt-body ships. Finally, simulations of a very large 4-m crude carrier (VLCC) model using the proposed method were carried out and the results compared with free-running experiments (both at the cruising speed and at low speeds) to validate the efficacy of the model.     

泥沙模型起动相似问题

本文根据床沙起动流速和起动拖曳力公式,分别导出了泥沙起动问题相似比尺,结果表明两者完全一致、并指出,以往所得结果之所以不一致,是因为起动流速公式中包含了阻力因素,该因素是以泥沙粒径的函数形式出现,在公式导演过程中,忽视了其阻力意义,因而导致了错误的结果.     

低速磁浮车辆导向方式及其横向动态特性

为了获得低速磁浮车辆导向设计的基本参数和设计原则,开展了磁铁模块导向性能的静态分析与动态仿真研究。对不同导向方式下磁铁模块导向力、导向刚度以及垂向和横向力耦合度的大小进行比对分析,结果表明:在被动导向方式下采用磁铁横向对中布置和在主动导向方式下采用磁铁横向错位布置可以得到良好的车辆导向性能,而且后者更优;横向位移及其速度反馈主动导向可显著增加导向力和导向刚度,极大地改善模块动态导向性能,基本实现模块垂向和横向力解耦。建议低速磁浮车辆采用磁铁横向错位布置和横向位移与速度反馈主动导向方式。     

The development of a stochastic non-linear and dynamic jack-up design and analysis method

This paper describes the development of a non-linear, dynamic jack-up analysis method in the time domain. It provides background as to why and when such analysis is required.

The theoretical background of the methods applied are discussed and the main features of the programme are described.