Study on new optimum parameters in MT repeated survey

The first MT monitoring profile with initial shape both at home and abroad has been built in the northern margin of the Qinghai-Tibet Plateau. Based on MT data observed before and after the eight earthquakes of M=5-7 from 1988 to 1992,a new parameter-mean resistivity has been introduced. The results show that indicates not only the major feature of decreasing-increasing and recovering to notmal value, but also synchronism of phase or the variation in a large area, 'lead or delay' among different small areas and the amplitude decreasing with the increase of the distance from the epicenter. Two characters mentioned above might correspond to reginal field precursor of the tectonic generating earthquake and field precursor of the tectonic kinematics. This paper analyses the errors of observed data and the cause of variation. The MT profile optimum parameter system consists of parameter,apparent resistivity,twisting degree and the principal-axis azimuth which might provide quantitative criterion for the physical prooes of the great destructive earthquake and moderate and short-term earthquake prediction.

IMPROVEMENTS ON THE CONFIGURATION AND OPTIMUM PARAMETERS OF HIGH一SPEED THRUST BEARINGS

It is expounded that h2/ is the Reynolds number form of thrust bearings and effects of the centrifugal forees can be judged by its magnitude. Three methods improving the configuration of pads are given out to overcome the haimful influence of the centrifugal forees on the performance of bearings, and the optimized parameters for three kinds of high一speed thrust bearings are provi- ded by solving the varying一viscositied three一dimensional Reynolds equation.

A SEARCH TECHNIQUE FOR CHOOSING OPTIMUM PARAMETERS IN NUMERICAL WEATHER PREDICTION

The steepest descent(or ascent)search is employed for finding optimum diffusion coefficients in T42L9G model,with a view to improving the model's computational stability or prediction accuracy.The method of the steepest descent search is first described,in which the golden section search is chosen as the fundamental one- dimensional search used in the multi-dimentional steepest descent search,and then the optimization of the dif- fusion coefficients is described.

基于有限元方法的主轴轴承跨距优化

通过建立包括轴承结合面在内的主轴系统的有限元模型,利用有限元方法分析了一台龙门式数控镗铣床主轴部件的静刚度,并通过静刚度实验验证了该模型的有效性。随后在Ansuys环境下利用APDL语言实现有限元模型的参数化,并讨论了该主轴轴承跨距的优化问题。

基于ADAMS的锁紧臂机构的动力学仿真及参数化分析

在一自动对接机构设计中,为了获得符合应用要求的锁紧臂机构参数,采用系统动力学仿真软件ADAMS建立了锁紧臂机构的动力学仿真模型,利用ADAMS软件的分析工具对参数化锁紧臂机构模型进行分析研究,获得了符合应用要求的参数值,从而实现了锁紧臂机构的优化设计。

基于小生境遗传算法和RANS方程的平面叶栅气动优化设计

发展了一种将小生境遗传算法与RANS方程数值求解相结合的平面叶栅全局优化设计方法.该方法针对遗传算法的搜索原理和平面叶栅的气动外形特点,提出了与之相适应的Bezier曲线参数化表达,构造了用于优化设计的适应度函数.优化设计变量是平面叶栅的参数化Bezier曲线特征多边形控制点坐标,目标函数为极大化叶栅的升阻比,约束条件综合考虑了叶栅的进出口几何安装角及叶片强度和性能等要求,约束条件的处理采用松紧罚函数法.优化得到的叶栅升阻比比初始叶栅提高了8.3%.

基于不完全敏感性方法的低比转速离心叶轮优化研究

针对传统离心叶轮优化设计方法的不足,提出基于不完全敏感性方法的低比转速离心叶轮的优化方法。该优化方法在求设计目标函数对流道形状控制变量的梯度时,忽略流道形状的变化对流场状态变量的影响,因此在一次优化循环中,只需要进行一次流场计算,避免应用有限差分方法中计算一次梯度矢量时需要多次计算流场,也避免在伴随方法中复杂的伴随方程的推导及求解,计算量大大减少。以低比转速离心叶轮作为研究对象,采用泰勒展开法参数化控制二维叶片形状,将泰勒多项式中的系数视为控制变量,选取作用在叶片上的转矩作为优化目标函数。应用不完全敏感性方法易于计算目标函数对控制变量的梯度,沿梯度矢量的反方向不断更新叶片形状来逐步寻优,最终找到目标函数值最小时的最优设计,算例计算结果表明,提出的不完全敏感性方法应用于低比转速离心叶轮优化是可行的。

基于有限元的精密主轴多目标优化设计研究

随着切削速度的不断提高,对主轴的动静态特性要求也越来越高。经验设计已不适应新产品的研制开发需要。在对精密主轴进行参数化建模的基础上,利用有限元扫描,分析各设计变量对状态变量和目标函数的影响。在有限元软件中建立了该主轴的多目标优化模型,通过比较优化前后主轴的性能可知:通过优化不仅提高了主轴的动刚度和固有频率,而且减小了主轴的质量,使结构参数更合理,能满足工程实际应用需要。

离心泵叶轮的参数化设计

对离心泵叶轮优化设计存在的问题进行了详细的阐述,离心泵叶轮优化设计的主要困难在于复杂的内流道形状及其与泵水力性能间复杂的隐式关系,对基于NURBS的曲面设计方法、基于自由曲面变形方法及偏微分方程方法 3种离心泵叶轮参数化设计方法的研究进行了详细的介绍.为了减少计算量,采用偏微分方程方法对离心泵叶片几何形状进行参数化控制,参数化控制偏微分方程的边界条件,假定方程中的控制参数a(u,v)为常量1,采用响应面方法对泵叶轮进行优化设计,根据试验及模拟结果进行二阶多项式响应面回归,分析发现二阶多项式响应关系不能反映离心泵叶轮设计目标与控制变量间的复杂的非线性关系.为此,在此基础上提出采用偏微分方程构建设计目标的偏微分超曲面响应,数值求解多维空间上偏微分方程的边值问题,进行优化分析得到最优设计.优化设计实例计算结果表明提出的理论及方法是合理的.

主轴结构优化的有限元方法

利用有限元分析软件ANSYS计算数控镗铣钻床主轴的静态变形与一阶固有频率。在ANSYS中利用APDL语言实现主轴有限元模型的参数化,并对主轴的结构进行优化设计,求出了主轴优化后的主要结构参数。分析结果表明,采用优化的主轴参数不但降低了主轴自重而且提高了主轴的刚度和临界转速,使主轴在结构方面更加合理、安全。

液压摆臂裁断机立柱结构优化与参数化设计

对裁断机立柱的强度和刚度计算进行了详细分析 ,建立了立柱结构参数的优化设计模型 ,优化设计结果可以在GHCAD环境下 ,实现立柱零部件图形的尺寸驱动 ,完成参数化设计工作。

基于主断面参数的车身结构刚度链快速求解

在刚度链计算模型中直接利用真实主断面参数快速求解,是车身结构刚度链设计方法必须解决的关键问题.在建立和完善轿车车身弯曲静刚度链计算模型的基础上,以刚度链节点参数可控和工程化为目标,建立了刚度链节点参数与主断面截面属性参数的对应关系,研究了利用极坐标法控制真实主断面形状的参数化方法,以及由单一变量控制的复杂截面属性计算方法,实现了刚度链节点属性的参数化计算和刚度链模型计算参数的工程化,为基于真实主断面结构形状的车身静刚度优化分配研究打下了基础.最后用一个车身轻量化优化计算实例验证了研究方法的可行性.

Review on Thermocline Storage Effectiveness for Concentrating Solar Power Plant

In this paper, a literature review on thermocline storage performance for Concentrating Solar Power (CSP) plant storage systems has been conducted. The efficiency of materials to store heat depends on the storage process like sensible heat storage, latent heat storage and thermochemical one and also on their properties. This study has been focused on sensible heat storage materials especially thermocline storage system (DMT) using eco-materials which has a high potentiality (35%) to reduce CSP cost. There is a possibility to use natural rocks, industry waste and to develop also materials for a thermocline storage within a bed called packed bed using one tank. The thermal storage materials should have some optimum parameters (particle diameter less than 2 cm and good thermo-physical properties) to achieve better thermal storage performance (thermal cycle efficiency, extraction factor). However, the size and the shape of natural rocks are uncontrollable (big diameter) and can drive to thermocline degradation, catastrophic thermal ratcheting and poor thermal stratification due to the variability of the storage system porosity and the stress on the storage tank wall. Also a better thermal storage efficiency is achievable at low velocity and with good thermo-physical properties of the HTF. The ratio H/D, the height, the porosity, the shape and the position of the tank should be optimized to increase the storage efficiency.

非参数化模型的优化参数定义方法

用各种CAD软件建立分析对象的三维模型,可以很方便地利用ANSYS提供的接口导入到ANSYS中,大大节省了建模的时间,但当分析是基于模型参数时,外部导入的模型往往因采用的建模方法是非参数化建模而导致而不适用,或要花很多的时间进行处理。为了使多种建模方法得到的模型都能实现参数化分析,提出了一种非参数化模型的参数化定义方法。首先在CAD软件中对三维模型的体属性信息进行补充和添加,对需要参数化的参数按ANSYS文件名要求进行定义,然后再导入到ANSYS中,在ANSYS中模型则有了参数信息,可以实现参数化优化。以UG NX9.0为例,验证了此方法的可行性。

基于Newton-Raphson法的发电机油箱优化设计的研究

求解油箱的质量、容积与其尺寸参数间的关系是非常复杂的,而Newton-Raphson法简化了求解过程。通过参数的预置,在UG软件中建立了油箱参数化模型。借助Excel电子表格,实现了对油箱参数的目标优化搜索,最后获得理想的油箱模型。

基于NSGA-Ⅱ算法的水轮机活动导叶多目标优化设计

建立了基于NSGA-Ⅱ算法的叶片多目标水力优化设计系统,该系统以叶片的形状参数为优化变量,以能量性能和空化性能为目标函数,将NSGA-Ⅱ遗传算法引入作为优化工具以实现叶片的多目标优化设计.对某电站水轮机模型活动导叶的水力性能进行了优化设计,优化后导叶流道的进出口总压损失减小了26.97%,导叶表面上的最低静压力值上升了34.176%.结果表明,优化后的导叶不仅减小了流动损失,而且具有更好的空化性能.所提出的优化方法能以较少的变量控制叶片几何形状,且能有效分析各设计变量对目标函数的影响程度和范围,缩小优化问题的规模,得到满意的优化结果,可作为一种有效的水力机械叶片优化设计工具.

机械零件结构的参数优化设计与三维优化模型的实现

以某机床主轴设计为例,建立了零件优化设计数学模型,并设置了结构优化参数,分析了主轴轴端的变形量。利用UG软件的表达式窗口和优化模块,进行了优化计算,同时,创建了主轴结构三维参数化基础模型,并实时形成了基于基础模型的优化模型。

Application of orthogonal design in the experiment of plasma arc powder surfacing technology

In this paper, the influence of plasma arc powder surfacing technical parameters on the property of layer is defined using the orthogonal design. By the orthogonal polynomial regression, when plasma arc powder surfacing is used on the surface of the X65 steel plate with the Fe-07 alloy powder, the optimum technical parameters are the following: I=180～190 A , G=41.5 g/min , v=102 mm/min , T_0=350 ℃ , Q_l=280 L/h , Q_s=400 L/h . Further, analysis of the cracking test data showed that the cracking preheat temperature is 350 ℃ .

Improving Numerical Weather Prediction in Low Latitudes by Optimizing Diffusion Coefficients

The horizontal diffusion coefficients of the operational model (T42L9) in numerical weather prediction are optimized by the steepest descent search of multi-dimensional optimization. In order to improve prediction accuracy in low latitudes, the optimum horizontal diffusion coefficients are chosen, with changing variation of the basic diffusion coefficient with the passage of time, and later forecasts are also made better. In view of the averages of forecast verifications of 9 cases, the forecasts with optimum diffusion coefficients are an improvement on operational forecasts. It means that the forecasts are got much better with optimum values of some important parameters by optimization in numerical weather prediction.

Optimal Robust Control for Unstable Delay System

Proportional-Integral-Derivative control system has been widely used in industrial applications.For uncertain and unstable systems,tuning controller parameters to satisfy the process requirements is very challenging.In general,the whole system’s performance strongly depends on the controller’s efficiency and hence the tuning process plays a key role in the system’s response.This paper presents a robust optimal Proportional-Integral-Derivative controller design methodology for the control of unstable delay system with parametric uncertainty using a combination of Kharitonov theorem and genetic algorithm optimization based approaches.In this study,the Generalized Kharitonov Theorem(GKT)for quasi-polynomials is employed for the purpose of designing a robust controller that can simultaneously stabilize a given unstable second-order interval plant family with time delay.Using a constructive procedure based on the Hermite-Biehler theorem,we obtain all the Proportional-Integral-Derivative gains that stabilize the uncertain and unstable second-order delay system.Genetic Algorithms(GAs)are utilized to optimize the three parameters of the PID controllers and the three parameters of the system which provide the best control that makes the system robust stable under uncertainties.Specifically,the method uses genetic algorithms to determine the optimum parameters by minimizing the integral of time-weighted absolute error ITAE,the Integral-Square-Error ISE,the integral of absolute error IAE and the integral of time-weighted Square-Error ITSE.The validity and relatively effortless application of presented theoretical concepts are demonstrated through a computation and simulation example.