Approximate Inertial Manifold Method andMultilevel Finite Element Approximationfor the Navier-Stokes Equations

This paper presents the Approximate Incrtial Manifold ∑ and its successive approximate incrtial manifold ∑i and ∑ij . We give the estimates of thickness of neighborhood of ∑, ∑j, Ejt respectively in which the every solution of Navier-Stokcs equation enters.Another part of this paper presents construction method for A.I.M. by multilevel finite clement method and give error estimates of the approximate solution of incrtial form.

Finite Element Approach for the Solution of First-Order Differential Equations

The finite element method has established itself as an efficient numerical procedure for the solution of arbitrary-shaped field problems in space. Basically, the finite element method transforms the underlying differential equation into a system of algebraic equations by application of the method of weighted residuals in conjunction with a finite element ansatz. However, this procedure is restricted to even-ordered differential equations and leads to symmetric system matrices as a key property of the finite element method. This paper aims in a generalization of the finite element method towards the solution of first-order differential equations. This is achieved by an approach which replaces the first-order derivative by fractional powers of operators making use of the square root of a Sturm-Liouville operator. The resulting procedure incorporates a finite element formulation and leads to a symmetric but dense system matrix. Finally, the scheme is applied to the barometric equation where the results are compared with the analytical solution and other numerical approaches. It turns out that the resulting numerical scheme shows excellent convergence properties.

A NEW APPROXIMATE INERTIAL MANIFOLD AND ASSOCIATED ALGORITHM

In this article the authors propose a new approximate inertial manifold（AIM） to the Navier-Stokes equations. The solutions are in the neighborhoods of this AIM with thickness δ=o（h^2k＋1-ε）. The article aims to investigate a two grids finite element approximation based on it and give error estimates of the approximate solution ｜｜｜（u-uh^＊·,p-ph^＊·）｜｜｜≤C（h^2k＋1-ε＋h^＊（m＋1））,where （h, h＊） and （k, m） are co^trse and fine meshes and degree of finite element subspa^es, respectively. These results are much better them Standard G^tlerkin（SG） and nonlinear Galcrkin （NG） methods. For example, for 2D NS eqs and linear element, let uh,u^h, u^＊ be the SG, NG and their approximate solutions respectively, then ｜｜u-uh｜｜1≤Ch,｜｜u-u^h｜｜i≤Ch^2,｜｜u-u^＊｜｜1≤Ch^3,and h^＊ ≈ h^2 for NG, h^＊ ≈ h^3/2 for theirs.

Fuzzy stochastic generalized reliability studies on embankment systems based on first-order approximation theorem

In order to address the complex uncertainties caused by interfacing between the fuzziness and randomness of the safety problem for embankment engineering projects, and to evaluate the safety of embankment engineering projects more scientifically and reasonably, this study presents the fuzzy logic modeling of the stochastic finite element method （SFEM） based on the harmonious finite element （HFE） technique using a first-order approximation theorem. Fuzzy mathematical models of safety repertories were introduced into the SFEM to analyze the stability of embankments and foundations in order to describe the fuzzy failure procedure for the random safety performance function. The fuzzy models were developed with membership functions with half depressed gamma distribution, half depressed normal distribution, and half depressed echelon distribution. The fuzzy stochastic mathematical algorithm was used to comprehensively study the local failure mechanism of the main embankment section near Jingnan in the Yangtze River in terms of numerical analysis for the probability integration of reliability on the random field affected by three fuzzy factors. The result shows that the middle region of the embankment is the principal zone of concentrated failure due to local fractures. There is also some local shear failure on the embankment crust. This study provides a referential method for solving complex multi-uncertainty problems in engineering safety analysis.

Meshfree First-order System Least Squares

We prove convergence for a meshfree first-order system least squares(FOSLS) partition of unity finite element method(PUFEM).Essentially,by virtue of the partition of unity,local approximation gives rise to global approximation in H(div)∩H(curl). The FOSLS formulation yields local a posteriori error estimates to guide the judicious allotment of new degrees of freedom to enrich the initial point set in a meshfree dis- cretization.Preliminary numerical results are provided and remaining challenges are discussed.

基于惯性环节的光伏组件实时热模型

提出一种基于一阶惯性环节的光伏组件温度的实时计算方法,首先,对光伏组件进行传热特性分析,基于一维非稳态导热分析解,推导基于一阶惯性环节的光伏组件温度简化计算模型;然后,使用遗传算法与拟牛顿法串行优化方法,通过数据驱动方式快速确定模型中的参数;最后,使用该文提出的模型,基于BP、LSTM的温度预测模型和传统经验公式对某光伏场站的组件温度进行分析和预测。对比结果表明:该方法表现出良好的预测精度,均方根误差<2℃,且部署模型所需的计算规模更小,运算速度可达神经网络的10倍以上,方便应用于实际控制系统中,且与神经网络方法相比更具可解释性,可作为一种实时计算光伏组件温度的有效方法。

塑料尾门耐惯性力分析及结构优化

根据GB 15086—2013的试验方法和技术要求,以塑料尾门为研究对象,建立有限元分析模型,进行了耐惯性力分析和结构优化。首先,基于塑料尾门的结构设计可行性,利用尾门结构耐惯性力仿真分析模型对塑料尾门的失效运动模式以及结构应力进行了预测和分析;其次,采用增加尾门内板载荷传力路径和局部料厚的结构优化方案,解决了塑料尾门在惯性载荷下的结构失效和开裂问题;最后,通过台架试验验证了塑料尾门优化方案的可靠性以及仿真分析模型的准确性。

基于改进粒子群算法的卸料台框架轻量化研究

针对传统经验设计的某垃圾处理流水线卸料台框架质量冗杂问题,文中采用改进粒子群算法对卸料台框架进行轻量化研究。首先,使用ANSYS有限元分析软件对卸料台框架进行静力学分析,再根据静力学分析结果对卸料台框架进行简化,最后,采用改进的粒子群算法对简化后的卸料台框架进行轻量化研究。优化后的卸料台框架在满足强度和刚度要求的前提下,较原始卸料台框架减轻了64.16%。

有限元连接方法在某无人飞行器建模中的应用

针对复杂飞行器在有限元建模中将不同结构连接的问题,对惯性释放计算方法进行验证;基于某无人飞行器的整机结构平台,分别采取1d单元、接触和共节点3种有限元连接方法实现对不同结构连接,比较每种方法的建模和计算效率以及计算结果。验证表明:在满足工程的要求下,1d单元连接方式效率最高。

移动三维扫描点云在轨道交通区间规划要素图绘制中的应用

轨道交通区间规划监督测绘翔实记录隧道区间的规划要素,核实工程建设与规划审批的一致性。文章采用集成惯导的移动三维扫描结合隧道已有CPⅢ控制点绝对定位的方式进行区间规划测量,此方法的测量精度满足验收测量要求。从融合校正后的扫描点云,提取区间点线要素,结合区间规划要素,生成规划要素图。

Application of the quadrilateral area coordinate method:a new element for laminated composite plate bending problems

Recently, some new quadrilateral finite elements were successfully developed by the Quadrilateral Area Coordinate （QAC） method. Compared with those traditional models using isoparametric coordinates, these new models are less sensitive to mesh distortion. In this paper, a new displacement-based, 4-node 20-DOF （5-DOF per node） quadrilateral bending element based on the first-order shear deformation theory for analysis of arbitrary laminated composite plates is presented. Its bending part is based on the element AC-MQ4, a recent-developed high-performance Mindlin-Reissner plate element formulated by QAC method and the generalized conforming condition method; and its in-plane displacement fields are interpolated by bilinear shape functions in isoparametric coordinates. Furthermore, the hybrid post-rocessing procedure, which was firstly proposed by the authors, is employed again to improve the stress solutions, especially for the transverse shear stresses. The resulting element, denoted as AC-MQ4-LC, exhibits excellent performance in all linear static and dynamic numerical examples. It demonstrates again that the QAC method, the generalized conforming condition method, and the hybrid post-processing procedure are efficient tools for developing simple, effective and reliable finite element models.

The Numerical Accuracy Analysis of Asymptotic Homogenization Method and Multiscale Finite Element Method for Periodic Composite Materials

In this paper,we discuss the numerical accuracy of asymptotic homogenization method(AHM)and multiscale finite element method(MsFEM)for periodic composite materials.Through numerical calculation of the model problems for four kinds of typical periodic composite materials,the main factors to determine the accuracy of first-order AHM and second-order AHM are found,and the physical interpretation of these factors is given.Furthermore,the way to recover multiscale solutions of first-order AHM and MsFEM is theoretically analyzed,and it is found that first-order AHM and MsFEM provide similar multiscale solutions under some assumptions.Finally,numerical experiments verify that MsFEM is essentially a first-order multiscale method for periodic composite materials.

基于惯性测量和卡尔曼多步观测器的船舶升沉运动测量方法

为了得到精确的船舶升沉运动信息,解决升沉加速度二次积分后的漂移和相位超前现象,基于卡尔曼滤波算法建立船舶升沉运动的多步观测模型,提出一种基于惯性测量和卡尔曼多步观测器的船舶升沉运动测量方法。首先,升沉平台模拟船舶升沉运动,使用惯性测量元件采集升沉加速度,经过滤波二次积分得到升沉位移。然后,对升沉加速度进行误差分析,运用升沉位移与升沉加速度的关系建立船舶升沉运动的状态空间模型并利用状态转移矩阵进行多步观测,消除升沉位移的漂移和延时。实验结果表明,本文所提出的测量方法可以解决不同幅值船舶运动中的偏移和相位超前问题,测量误差在0.01 m之内,体现了测量的精确性。

一种基于组合赋权法的小波去噪质量评价方法

针对传统质量评价指标在小波阈值去噪中理论依据不足的问题,提出了一种基于组合赋权法的小波去噪质量评价方法,能够为小波去噪参数的选择提供有效评价。通过分析在真值未知情况下均方根误差(RMSE)、信噪比(SNR)、平滑度等单项指标的特点,选取RMSE与平滑度作为小波去噪指标,对其进行归一化处理,采用信息熵权与变异系数的方法进行组合赋权,将归一化指标与对应权值线性组合,得到一种新的指标即为复合评价指标,其值越小,说明去噪效果越好,所选参数越优。仿真实验表明,在真值已知情况下,该评价指标具有更高的准确性,能够适用于不同的分解层数与小波基函数,具有比传统方法更好的适用性;实测数据表明,所提方法得出的小波去噪峰值域更加光滑,波形更加平稳,去噪效果更佳。

考虑转向延迟特性的自动驾驶车辆路径跟踪控制方法

自动驾驶路径跟踪系统是实现L2级以上自动驾驶的重要支撑技术。线控转向系统存在的延迟响应特性会降低路径跟踪控制器的鲁棒性和控制精度,甚至在高车速下存在失稳现象。针对以上问题本文设计了前馈加有限时域全状态反馈的误差跟踪控制架构,在此基础上将转向系统延时作为1阶惯性环节进行模型化表达,并作为状态变量增广融合到误差跟踪控制架构中。本文利用联合仿真试验对提出的跟踪控制器进行了对比验证,验证结果证明本文提出的控制器在直角弯道和高速换道场景下,最大横向误差小于0.3 m,转向盘的转角均方差分别降低1.93%和64.22%。最后的实车试验结果表明,本文提出的控制器在高速换道场景下能够有效提升横向控制精度,最大横向误差小于0.11 m。

基于有限元仿真的轿车轮胎噪声研究

为了有效研究和分析轮胎噪声,以雪地胎和四季胎为研究对象,建立振--声学仿真模型,进行轮胎噪声惯性滑行法试验,分析速度与轮胎噪声、路面的测量温度与轮胎噪声之间的关系。通过两种车胎的噪音情况进行了对比,希望可以给用户以更加直观的成果展现。结果表明:当平均车速达到70km/h以上时,噪声随着行驶速度的增大而增大;轮胎接地前端噪声小于接地后端噪声;在平整的路面且天气良好的状态下行驶时,雪地胎轮胎噪声明显高于四季胎轮胎噪声,合理选择轮胎也能有效降低轮胎噪声。

窄频差硅基环形陀螺检测闭环控制系统设计

针对窄频差硅基环形波动陀螺动态性能差的问题,提出了一种基于比例积分微分-惯性环节(proportion integral differential-inertial element,PID-IE)的串联式相位校正检测闭环系统控制器。以硅微机械陀螺仪结构运动方程为基础建立了理想的窄频差U形弹性梁硅基环形波动陀螺仪的系统模型。通过对环形陀螺开环工作状态下的系统模型及其外围电路的传递函数和波特图分析,设计了一种基于PID-IE的检测闭环系统控制器。通过对其系统模型及外围电路时域仿真,验证了该检测闭环控制系统的可行性,通过仿真发现,加入该控制器后的陀螺输出稳定时间减少了50%,陀螺检测位移输出减小了2个数量级,基本实现了该陀螺的检测位移抑制。在模拟电路中实现了该检测闭环控制系统后,通过实验测试了陀螺检测闭环控制前后的各项性能指标。通过实验测试发现,实现闭环控制后,陀螺输出稳定时间约为0.15 s,陀螺检测位移在闭环工作状态下比开环工作状态减小了97%,陀螺的标度因数比检测开环提高了10倍,零偏及零偏不稳定性与检测开环相比分别提升了3倍和8倍,且闭环控制系统的工作带宽比开环工作带宽提高了30倍。

针对电力线路弧垂测量的组合定位系统设计及应用

在紧线施工中,施工单位一般采用经纬仪对导线弧垂进行测量,但这种光学测量方法常受制于测量的时段、天气、地形等因素。采用卫星定位可规避上述因素的影响,从而实现全天候、全天气、全地形的弧垂测量,但目前常用的卫星定位方式容易出现短暂的卫星信号丢失或者卫星信号不良的情况。针对上述问题,采用连续性较强的惯性原件进行补偿和校正,设计了一种将卫星数据和惯性数据融合的组合定位系统,以提高卫星定位的适用性。系统根据测量载体的不同信号条件,设置了三种运动模式,结合卫星信号和惯性器件的不同特性,在不同条件下选取最优信号,从而提升定位精度。应用该方法进行了多次弧垂测量,结果证明该方法的定位精度能够满足紧线施工需求,同时可以满足卫星定位信号丢失条件下粗略定位的要求。

舵机用永磁同步电机的设计与温度场分析

针对舵机用大功率永磁同步电机转动惯量低、功率密度高、短时工作制的特点,对定子绕组形式和槽极数配合做了较为合理的选择,确定了电机基本尺寸。电机电磁场有限元分析结果表明,电机具有较高的电气性能。由于电机功率密度高,电磁有效部位细长,电机转速较高,电机温升问题突出。根据传热学理论,建立了永磁同步电机三维瞬态温度场求解模型,确定了表面散热系数。通过有限元分析得到了电机定子绕组铜耗、定子铁心铁耗以及永磁体和转子护套内的涡流损耗。将定子槽内和端部处导线分别等效成若干个导热体、分布排列,得到了更加符合实际情况的电机三维瞬态温度分布结果。试验结果表明设计方案合理。

方位旋转式平台惯导系统的误差分析与仿真

采用惯性平台相对惯性空间以固定角速度绕方位轴旋转的系统方法,构成方位旋转式平台惯导系统(ARGINS),通过调制惯性测量元件沿平台水平方向的输出误差,提高平台式惯导的精度。给出了ARGINS无阻尼情况下的系统误差方程,分析了静基座下的系统误差,并采用Monte-Carlo方法研究了动基座下的系统误差特性。结果表明,相对固定指北式平台惯导,由于水平方向上的惯性测量元件误差引起的随时间发散误差量被调制为常值误差,而常值误差量则被调制为可通过阻尼消除的振荡性误差,达到了抑制惯性测量元件误差的效果。