FORMULATION OF A SEMI-ANALYTICAL APPROACH BASEDON GURTIN VARIATIONAL PRINCIPLE FOR DYNAMICRESPONSE OF GENERAL THIN PLATES

4 semi-analytical approach for the dynamic response of general thin plates whichemployes finite element discretization in space domain and a series of representation intime demain is developed on the basis of Curtin variational principles.The formulationof time series is also investigated so that the dynamic response of plates with arbitraryshape and boundary constraints can be achieved with adequate accuracy.

THE OPTIMAL CONTROL VARIATIONAL PRINCIPLE AND FINITEELEMENTS ANALYSIS FOR VISCOPLASTIC DYNAMICS

This paper presents the optimal control variational principle for Perzyna modelwhich is one of the main constitutive relation of viscoplasticity in dynamics. And itcould also be transformed to solve the parametric quadratic programming problem.The FEM form of this problem and its implementation have also been discussed in thepaper.

Partition method and experimental validation for impact dynamics of flexible multibody system

The impact problem of a flexible multibody system is a non-smooth, high-transient, and strong-nonlinear dynamic process with variable boundary. How to model the contact/impact process accurately and efficiently is one of the main difficulties in many engineering applications. The numerical approaches being used widely in impact analysis are mainly from two fields： multibody system dynamics （MBS） and computational solid mechanics （CSM）. Approaches based on MBS provide a more efficient yet less accurate analysis of the contact/impact problems, while approaches based on CSM are well suited for particularly high accuracy needs, yet require very high computational effort. To bridge the gap between accuracy and efficiency in the dynamic simulation of a flexible multibody system with contacts/impacts, a partition method is presented considering that the contact body is divided into two parts, an impact region and a non-impact region. The impact region is modeled using the finite element method to guarantee the local accuracy, while the non-impact region is modeled using the modal reduction approach to raise the global efficiency. A three-dimensional rod-plate impact experiment is designed and performed to validate the numerical results. The principle for how to partition the contact bodies is proposed： the maximum radius of the impact region can be estimated by an analytical method, and the modal truncation orders of the non-impact region can be estimated by the highest frequency of the signal measured. The simulation results using the presented method are in good agreement with the experimental results. It shows that this method is an effec-rive formulation considering both accuracy and efficiency. Moreover, a more complicated multibody impact problem of a crank slider mechanism is investigated to strengthen this conclusion.

Electromechanical dynamics analysis and simulation on rollforming equipment with both sides variable cross-section

Electromechanical dynamics analysis and simulation on a rollforming equipment with both sides variable cross-section are discussed in this study.The system includes mechanical parts and electromagnetism parts,and it is a strongly coupled electromechanical system.Based on a virtual work principle and given power,generalized forces of this system are obtained.By using Lagrange-Maxwell equations,a model of electromechanical dynamics is established.Differential equations of two-phase winding on d-q axis are obtained by Park transformation,which comes from three-phase winding equations on the A-B-C axis.This system is solved with the 4th order Runge-Kutta's method,and discrete solutions of all variables are obtained.Finally,by using Matlab language,the system is simulated.The results show that the proposed method works very well.

Temporal Prediction of Aircraft Loss-of-Control: A Dynamic Optimization Approach

Loss of Control (LOC) is the primary factor responsible for the majority of fatal air accidents during past decade. LOC is characterized by the pilot’s inability to control the aircraft and is typically associated with unpredictable behavior, potentially leading to loss of the aircraft and life. In this work, the minimum time dynamic optimization problem to LOC is treated using Pontryagin’s Maximum Principle (PMP). The resulting two point boundary value problem is solved using stochastic shooting point methods via a differential evolution scheme (DE). The minimum time until LOC metric is computed for corresponding spatial control limits. Simulations are performed using a linearized longitudinal aircraft model to illustrate the concept.

弹性飞行器飞行动力学建模与刚柔耦合阶次分析

基于虚功率原理与混合坐标法,建立了弹性飞行器的飞行动力学模型。发现了附加在弹性结构上的部件会对飞行器姿轨运动与结构振动产生影响,从而给出了耦合系数与模态质量的修正项。定义了描述弹性变形项保留程度的刚柔耦合阶次,并以由弹性本体和刚体舵面组成的刚柔耦合多体系统为例,通过对比不同刚柔耦合阶次下动力学模型的时域响应与保守系统的动量计算结果,分析了动力学模型及动量公式中弹性变形项的保留阶次对动力学响应及动量计算精度的影响。揭示了传统模型忽略弹性变形高阶项可能导致的误差水平,为弹性飞行器动力学模型的简化与验证提供了参考。

复合驱动并联机构的动力学建模与仿真分析

针对一种PUU-2PRRS 5自由度复合驱动并联机构的刚体动力学建模问题,采用拉格朗日法结合虚功原理建立刚体动力学模型并进行仿真分析。首先,在考虑存在次闭环的情况下,采用闭环矢量法对并联机构进行运动学分析,推导出机构各构件质心的线速度和角速度;其次,采用拉格朗日法结合虚功原理建立复合驱动并联机构的刚体动力学模型,为复合驱动并联机构驱动力的求解及后续动力学仿真分析奠定了基础;最后,基于MATLAB软件和ADAMS软件对该并联机构进行动力学仿真分析,在给定相同末端轨迹的情况下,对比两种软件得到的驱动力变化曲线,仿真结果验证了所建动力学模型的正确性。文中不仅为PUU-2PRRS 5自由度复合驱动并联机构控制系统的搭建打下了基础,也为其他复合驱动并联机构的动力学建模分析提供了理论依据。

The Maximum Principle for One Kind of Stochastic Optimization Problem and Application in Dynamic Measure of Risk

The authors get a maximum principle for one kind of stochastic optimization problem motivated by dynamic measure of risk. The dynamic measure of risk to an investor in a financial market can be studied in our framework where the wealth equation may have nonlinear coefficients.

Free-Interface Dual-Compatibility Modal Synthesis Substructure Method in Large-Scale Structures

Free-interface dual-compatibility modal synthesis method(compatibility of both force and displacement on interfaces)is introduced to large-scale civil engineering structure to enhance computation efficiency. The basic equations of the method are first set up, and then the mode cut-off principle and the dividing principle are proposed. MATLAB is used for simulation in different frame structures. The simulation results demonstrate the applicability of this substructure method to civil engineering structures and the correctness of the proposed mode cut-off principle. Studies are also conducted on how to divide the whole structure for better computation efficiency while maintaining better precision. It is observed that the geometry and material properties should be considered, and the synthesis results would be more precise when the inflection points of the mode shapes are taken into consideration. Furthermore, the simulation performed on a large-scale high-rise connected structure further proves the feasibility and efficiency of this modal synthesis method compared with the traditional global method. It is also concluded from the simulation results that the fewer number of DOFs in each substructure will result in better computation efficiency, but too many substructures will be time-consuming due to the tedious synthesis procedures. Moreover, the substructures with free interface will introduce errors and reduce the precision dramatically, which should be avoided.

考虑梁端顺桥向阻力的结构竖弯等代阻尼比计算方法研究

针对梁式结构竖弯振动未考虑梁端顺桥向阻力引起阻尼比计算不准确的问题,提出桥梁结构各模态竖弯等代阻尼比计算方法。该方法通过考虑主梁竖向弯曲变形和梁端顺桥向变形之间的关系,基于能量原理,建立结构系统考虑梁端阻力的竖向弯曲振动的广义单自由度动力方程,采用RKF45预估校正法对其进行数值求解,从而确定结构各模态的竖弯等代阻尼比。应用该方法对80 m跨等截面简支梁的竖弯等代阻尼比进行计算,并分析不同的梁端阻力装置对结构竖弯等代阻尼比的影响规律。结果表明:提出的结构竖弯等代阻尼比计算方法可应用于大跨度梁式结构竖弯振动中阻尼比的计算,梁端阻力装置可有效提高结构竖弯振动的等代阻尼比,梁端阻力装置对结构竖弯等代阻尼比的影响与结构广义质量、广义竖弯刚度、竖弯振型和装置阻力本身相关。

基于模型预测控制的深海钻井立管再入井仿真分析

海洋立管在钻井作业时一旦遇到恶劣天气须将底端总成和防喷器断开,待天气好转需重新连接称为再入井作业.深海区钻井立管发生断开的概率大幅增加,为适应多变的海况需要快速完成再入井过程.提出基于模型预测控制(MPC)再入井控制系统;基于哈密顿原理建立悬挂立管分析模型,设计优化函数及约束项,构建非线性扰动观测器实现洋流力模型误差和洋流速度扰动补偿,与传统比例-积分-微分(PID)控制作业进行仿真比较.MPC系统作用下,母船迅速响应,立管能快速稳定完成再入井作业,较好处理洋流力模型误差,并在洋流速度扰动下具有良好鲁棒性.立管由于长径比大幅增加导致柔性显著增强,在母船及海洋环境力激励下,悬挂立管在快速再入井过程中高阶模态可能被激发.

直流配电系统动态相量-电磁暂态混合仿真与误差机理分析

为了高效地实现多端直流配电系统的准确动态仿真,在动态相量–电磁暂态混合仿真框架下,文章首先分析应用于直流配电系统时所涉及的子系统建模、接口机制和数据交互时序等执行要素。然后以混合仿真误差产生机理为切入点,以电磁暂态子系统为主要关注对象,详细分析简单阻感支路和复杂系统两种情况下混合仿真的误差传递过程,并推导了数值稳定的必要条件。其次,以串行时序为例,设计直流配电系统动态相量–电磁暂态混合仿真算法的主流程,并提出动态相量提取修正、直流量特征纹波添加等精度提升方法。最后,基于MATLAB/Simulink搭建多端直流配电系统同构串行混合仿真平台,通过对比全电磁暂态仿真,验证混合仿真的高效性及精度提升方法的有效性。

基于数字图像相关技术的鼓风机叶片动态应变试验

针对鼓风机叶片在共振中因大变形而引起的裂纹或断裂问题,基于双目立体视觉原理和数字图像相关法,并结合振动学理论,研究了小尺寸风机叶片在振动过程中的变形及动态应变。结果表明:叶片的最大应变位于叶根处,且整体应变随着正弦振动的激励呈现交变状态;与应变片法测得的应变和激光测振仪测得的位移相比,采用VIC-3D数字图像相关法测得叶片根部的应变和位移相对误差分别约为4.0%和3.5%,该测量方法易于操作,测量精度高。

基于小孔节流的液体动静压球轴承动态特性分析

以小孔节流方式的液体动静压球轴承为研究对象,建立球轴承的润滑数学模型,推导出层流状态下的Reynolds方程,引入流量守恒原理并结合小孔节流器的流量计算得到油腔和封油边压力分布;采用微扰法推导出扰动压力控制方程,通过有限差分法和松弛迭代法求解扰动压力控制方程得到轴承的刚度和阻尼系数。运用数值分析研究供油压力、转速及油膜间隙等参数对轴承动态特性系数的影响。结果表明,随着油膜间隙减小,供油压力的增大,刚度和阻尼系数会随之增大;随着转速增大,直接刚度变化趋势较小,直接阻尼降低趋势较明显;当油膜间隙为20μm时,轴承刚度和阻尼系数达到最大;转速的提高对于刚度影响较小,而阻尼系数则会明显降低。

大比例尺地形图动态跟踪修测工作量统计方法与应用

针对地形图动态跟踪修测工作量统计缺乏标准的问题,提出了大比例尺地形图动态跟踪修测工作量统计原则,成块区域和零星区域修测工作量的统计方法,并在杭州市基础地形图动态更新修测中得到应用,应用结果表明:采用本文提出的标准化统计方法后,各区域的工作量都按照统一的标准进行统计计算,因主观造成的差异性大大减少,很好地支撑了杭州市地理信息空间数据建设。

低固溶镁-铝和铝-镁合金高压熔点的第一性原理模拟

以往虽然针对镁(Mg)、铝(Al)单质的高压熔化曲线开展了较多研究,但是对于Mg-Al和Al-Mg合金的高压熔化却鲜有报道。本工作结合固溶无序结构建模的相似原子环境(SAE)方法,以及熔点模拟的固液共存法,实现了低固溶合金高压熔点的第一性原理分子动力学模拟。在此基础上初步研究了2种低固溶Mg-Al和Al-Mg合金的高压熔点,这2种合金分别是AZ31B和LF6Al。计算发现,高压下LF6Al的熔化温度略低于Al的熔化温度,而AZ31B的熔化温度非常接近Mg的熔化温度。为后续深入研究组分变化对Mg-Al和Al-Mg合金高压熔点的影响规律奠定了基础。

THE IMPROVED FOURIER SPLITTING METHOD AND DECAY ESTIMATES OF THE GLOBAL SOLUTIONS OF THE CAUCHY PROBLEMS FOR NONLINEAR SYSTEMS OF FLUID DYNAMICS EQUATIONS

Consider the Cauchy problems for an n-dimensional nonlinear system of fluid dynamics equations. The main purpose of this paper is to improve the Fourier splitting method to accomplish the decay estimates with sharp rates of the global weak solutions of the Cauchy problems. We will couple togeth- er the elementary uniform energy estimates of the global weak solutions and a well known Gronwall＇s inequality to improve the Fourier splitting method. This method was initiated by Maria Schonbek in the 1980＇s to study the op- timal long time asymptotic behaviours of the global weak solutions of the nonlinear system of fluid dynamics equations. As applications, the decay esti- mates with sharp rates of the global weak solutions of the Cauchy problems for n-dimensional incompressible Navier-Stokes equations, for the n-dimensional magnetohydrodynamics equations and for many other very interesting nonlin- ear evolution equations with dissipations can be established.

采油工艺措施效果经济评价方法

评价油井增产措施的经济效益的前提是正确区分和计算费用和效益,原则是以增量分析为主,兼顾总量指标,增量操作成本包含与增产措施直接相关的操作费用和增量井下作业费用。措施有效期在1a内的措施宜采用静态法,按费用处理,措施投入计入井下作业费,评价指标包括增量利润、增量净利润和利润全投入比;跨年有效的措施宜采用动态法,按投资处理,评价指标包括增量投资利润率、增量财务净现值、增量财务净现值率。用该方法评价某油田压裂、堵水、换大泵等增产措施的经济效益,评价结果与实际生产一致。

中医证候的结构化研究

基于证候理论内蕴拓扑结构的理论和方法,可以破解证候高阶多维的非线性结构,展现证候复杂多变的全貌,阐明证候动态演化过程中子集合的衍生规律,以及证候动态演化子集合主症与次症的变化规律,实现证候动态演化子集合与治则治法和方药的精准对应,揭示出证候动态演化规律的科学内涵。运用证候结构化的理论数据,通过古代名医医案和方剂证候分析的文献数据,以及临床案例证候的数据,可以实现中医理法方药知识的创新,带动养生保健和预防知识的创新,从而促进辨证论治水平的大幅度提高,促进中医学理论的发展。

偏转弹头导弹的动力学建模方法研究

偏转弹头是一种新的导弹操纵方式,动力学建模是对其研究的基础。偏转弹头导弹可以看成由弹头和弹体组成的多体系统,应用多体建模方法Schiehlen法建立系统的动力学模型。首先把弹头和弹体的运动状态用广义坐标表示,弹头的绝对运动由相对运动原理得到,根据牛顿-欧拉动力学方程分别写出弹头和弹体的质心移动方程和绕质心的转动方程,再运用达朗伯原理的理想约束性质消去方程中包含的约束力,同时方程的数目也减少到与系统的自由度数相同,从而得到维数与系统自由度数相同的二阶标量微分方程组。最后仿真验证模型,并分析得到偏转弹头导弹的一些特点,即偏转弹头导弹具有控制效率高,机动过载大,响应速度快等优点,是一种有效的快速响应控制方式。研究表明对于像偏转弹头导弹这类刚体数目少、但自由度数目较多的多体系统,其动力学建模适合使用Schiehlen法。