基于矩阵摄动的随机结构动态载荷识别技术

基于矩阵摄动和正则化方法提出一种随机结构动态载荷识别的分析方法。在时域内将动态载荷表示为时间和随机参量的函数,并以结构动力响应的卷积分关系式建立随机结构动态载荷识别的正问题。在离散化卷积分的基础上,利用基于泰勒展开的矩阵一阶摄动方法将随机结构的载荷识别问题转化为两类确定性反求问题,即结构随机参量取均值时动态载荷的反求和动态载荷关于各随机参量灵敏度的反求。当测量响应中带有噪声时,利用改进的正则化及L曲线方法克服反求过程中的病态性问题,实现两类确定性问题的稳定近似反求和动态载荷统计特征的有效评估。数值算例表明,针对随机结构该方法能稳定有效地实现动态载荷的识别和评估。     

基于子结构分析的动态载荷和模型参数复合反演研究

针对结构特征参数、输入激励和输出响应等信息不完备的系统,基于子结构方法提出一种时域内动态载荷和模型参数复合反演的方法。首先,将结构划分成不同的子结构,对存在动态载荷的子结构建立有限元模型,该子结构与其他部件之间的连接关系采用等效的界面力代替。采用Green核函数法建立识别该子结构所受动态载荷的正问题模型,利用正则化方法实现时域内动态载荷的稳定识别。然后,在已识别载荷的基础上建立整体结构的有限元模型,通过非线性最小二乘法实现结构的未知模型参数的识别。数值算例表明,在响应存在测量噪声的情况下,所述的复合反演方法能够有效稳定地实现动态载荷和模型参数的复合反演。     

基于径向基网络的变速箱载荷识别研究

提出了一种基于径向基网络的识别变速箱载荷的新方法,该方法应用径向基函数网络建立了箱体表面振动响应信号与轴承激励之问的非参数映射模型。通过变速箱在随机激励下的载荷识别结果表明,这种利用径向基网络识别变速箱载荷的方法是可行的,并且具有识别精度高、运算速度快及稳定性好等优点。     

基于Green函数和正则化的动态载荷识别方法

在载荷识别过程中由于结构矩阵的病态特性以及测量噪声的影响，常规最小二乘法往往失效。针对这一问题，采用正则化方法进行载荷识别。载荷在时域内可用一系列脉冲来表示，系统的响应是载荷与单位脉冲响应函数的卷积分。通过对载荷反演模型剖析，指出该病态问题的本质，提出了相应的正则化求解方法。基于Morozov相容性原理，采用一种新的选取正则化参数的准则分别进行了单输入单输出和二输入二输出系统的载荷识别。仿真结果说明该识别方法是有效的，可以得到满足工程要求的稳定近似解。     

二维分布动载荷识别的矩量方法

运用张量理论在高维正交空间建立高维矩量基函数,利用其正交性质,将待识别的二维分布动载荷表示为待定系数的高维正交函数级数形式,根据二维结构的动力学方程在时域中建立识别模型,根据结构的稳态响应识别高维正交函数的待定系数,从而识别二维分布动载荷。将识别模型与有限元方法相结合,建立了通用的复杂结构二维分布动载荷识别模型。仿真算例验证了模型的正确性和抗干扰能力。     

船体结构冰载荷反演方法及试验验证

冰载荷是影响船舶冰区航行期间结构安全的重要环境载荷。船舶的冰压监测通常采用应变传感器,合理地布放传感器是识别冰载荷的基础。通过对比船体外板结构试验中的冲击载荷和不同测试方案下的应变信号,确定了最佳应变传感器布放方案;采用Green核函数方法建立了船体外板结构应变冲击载荷间的响应关系,并对采集信号在噪声影响下反演的不适定性进行了分析;采用Tikhonov正则化方法克服了载荷反演过程中出现的数值不稳定问题;最后将试验中的响应用到载荷识别分析中,反演的载荷可以较为准确地反映冲击载荷的时域特征并且载荷识别精度良好。     

基于时域正演法的载荷识别

针对离散系统动态载荷识别精度受测点信息和传感器布置数目限制的问题,采用逆问题正分析的方法,在时域内提出了一种基于时域正演法的载荷识别方法。具体内容包括:若已知结构的某一种响应,比如位移、速度和加速度,根据此方法,便可确定未知作用力的时间历程。同时对该反演过程中存在的病态问题进行了奇异值分解。数值算例表明,该方法能较准确地识别结果动载荷,且简便有效。     

基于稀化核函数主元分析的机械故障诊断方法研究

提出一种基于稀化核函数主元分析的机械故障诊断新方法.该方法通过核函数映射将非线性问题转换成高维的线性特征空间,引入可变权值对高维空间中的映射数据的协方差矩阵进行稀化,应用似然估计得到优化权值,再作主元分析,提取其非线性特征,对机械故障模式进行识别.提出的方法继承核函数主元分析的优良性质,同时又能保证在识别效率不降低下的情况下有效提高故障识别速度.仿真和实验结果表明,稀化核函数主元分析和核函数主元分析方法都能得到很好的识别效果.然而,稀化核函数主元分析由于减少了核矩阵的计算量,因而模式识别速度大大加快.     

基于时频域的汽车变速器试验台动态特性分析及优化

动态特性是汽车变速器动态模拟试验台最重要的性能之一。结合CATIA、ADAMS和MATLAB等工具,建立了变速器试验台多体动力学方程及动力学模型;在此基础上,提出了变速器试验台时域动态响应评价指标,以上升时间、稳定时间、超调量等评价指标建立了变速器试验台动态响应多目标优化模型,并进行了仿真分析及优化;同时,建立了变速器试验台频域动态响应模型,并在频域内进行了动态响应分析及优化。结果表明,在优化范围内转动惯量小、刚度大、阻尼比大,有利于系统动态特性;优化后较优化前超调量减小19.1%,上升时间减小5.56%,峰值时间减小17%,稳定时间减小40.7%,较大地提高了系统的动态特性。     

基于桶式原理的电机电磁-热耦合数据映射算法研究

针对电机电磁-热耦合计算问题,对耦合计算中的不同物理场载荷数据传递问题进行了研究。通过设计验证函数算例验证了径向基函数插值算法的传递精度,指出了原有算法由于涉及大规模矩阵求逆,而无法应用于耦合场计算;在径向基函数插值算法的基础上,提出了一种基于桶式原理的异构网格数据映射算法,利用分桶操作避免了大规模矩阵的求逆操作,将原有单一大规模矩阵求逆等效为若干小规模矩阵的求逆,实现了电机电磁-热耦合计算中损耗与温度在二维电磁场与三维温度场之间的相互传递;并以定子铁芯模型为算例,通过对比同构网格计算结果验证了本文所提算法的准确性。研究结果表明:该算法数据传递精度较高,能够满足电机耦合场计算需求。     

Shape reconstruction of parallelogram flaw

To reconstruct the shape of the scatterer in elastic media, the authors deduce the Born approximation solution of the two-dimensional scattering problem, which includes the shape factor that embodies all information about the shape of the scatterer. Accordingly, the change in the shape of the scatterer only necessitates the number of the corresponding new shape factors. For a parallelogram void in a long Al rod, its shape factor can be obtained. In view of the definition of a characteristic function, the shape factor has a corresponding integral representation. Obviously, the shape factor can be considered as a Fourier transform of the characteristic function, which is reconstructed from the inverse Fourier transform. The integral equation is considered as the basic equation to reconstruct the shape of the scatterer. The identification of the geometrical character of a flaw is then given by the two dimensional inverse Born approximation in a low-frequency range. For the parallelogram void, a theoretical calculating identification is performed. At the same time, the numerical results are obtained by the finite element method.     

关于摆锤式冲击弯曲试验冲击载荷精确测定的研究

提出一种考虑到应力波传播现象的比较精确测定冲击力的方法.即通过改装摆锤式冲击试验机,实现冲击载荷-时间曲线测定,然后利用叠加积分求解的原理,在通过校正实验获得传递函数之后,再运用傅里叶变换和逆变换,求得精确度比较高的冲击力.同时通过实例验证了这一方法在高、低硬度材料动载荷测定中的有效性.     

A modified conjugate gradient method based on the Tikhonov system for computerized tomography (CT)

During the past few decades, computerized tomography (CT) was widely used for non-destructive testing (NDT) and non-destructive examination (NDE) in the industrial area because of its characteristics of non-invasiveness and visibility. Recently, CT technology has been applied to multi-phase flow measurement. Using the principle of radiation attenuation measurements along different directions through the investigated object with a special reconstruction algorithm, cross-sectional information of the scanned object can be worked out. It is a typical inverse problem and has always been a challenge for its nonlinearity and ill-conditions. The Tikhonov regulation method is widely used for similar ill-posed problems. However, the conventional Tikhonov method does not provide reconstructions with qualities good enough, the relative errors between the reconstructed images and the real distribution should be further reduced. In this paper, a modified conjugate gradient (CG) method is applied to a Tikhonov system (MCGT method) for reconstructing CT images. The computational load is dominated by the number of independent measurements m, and a preconditioner is imported to lower the condition number of the Tikhonov system. Both simulation and experiment results indicate that the proposed method can reduce the computational time and improve the quality of image reconstruction.     

基于组合正弦函数的机器人轨迹规划方法

提出了一种加速度函数为组合正弦函数的轨迹规划方法,它由两种不同频率的正弦曲线组合而成,本方法不但可以降低速度和加速度的峰值,而且还可以减少运行时间,使机器人运动平稳,避免振动和过冲现象,减少机械零件的磨损,延长机器人的使用寿命,可以使机器人能够精确、稳定、快速、高效地到达预定位置,完成拾放操作.     

称重传感器非线性误差的RBFNN补偿

称重传感器的输入与输出成非线性关系,需进行非线性补偿。文中阐述了称重传感器的非线性误差,并提出了一种基于径向基函数神经网络(RBFNN)的称重传感器非线性误差补偿方法,利用RBFNN构建了称重传感器输入Fx与输出Uox的反函数,实现了称重传感器的非线性误差补偿。实验表明:采用这种方法补偿后,称重传感器大秤量段的非线性相对误差减少了一个数量级,提高了称重准确度。     

Inverse Method of Centrifugal Pump Impeller Based on Proper Orthogonal Decomposition (POD) Method

To improve the accuracy and reduce the calculation cost for the inverse problem of centrifugal pump impeller, the new inverse method based on proper orthogonal decomposition(POD) is proposed. The pump blade shape is parameterized by quartic Bezier curve, and the initial snapshots is generated by introducing the perturbation of the blade shape control parameters. The internal flow field and its hydraulic performance is predicted by CFD method.The snapshots vector includes the blade shape parameter and the distribution of blade load. The POD basis for the snapshots set are deduced by proper orthogonal decomposition.The sample vector set is expressed in terms of the linear combination of the orthogonal basis. The objective blade shape corresponding to the objective distribution of blade load is obtained by least square fit. The Iterative correction algorithm for the centrifugal pump blade inverse method based on POD is proposed. The objective blade load distributions are corrected according to the difference of the CFD result and the POD result. The two dimensional and three dimensional blade calculation cases show that the proposed centrifugal pump blade inverse method based on POD have good convergence and high accuracy, and thecalculation cost is greatly reduced. After two iterations, the deviation of the blade load and the pump hydraulic performance are limited within 4.0% and 6.0% individually for most of the flow rate range. This paper provides a promising inverse method for centrifugal pump impeller, which will benefit the hydraulic optimization of centrifugal pump.     

Inverse calculation of the friction coefficient during the warm upsetting of molybdenum

This study focused on the variation of the friction coefficient during the upsetting process and the concept of treating the solution of unknown parameters as an inverse problem. Based on the experimental measurement data, the Levenberg–Marquardt method, a numerical optimization approach was used in conjunction with the constrained function, convergence criterion and the axial symmetry thermo-elastic-plastic finite element method to solve, inversely, the variation of friction coefficient during the upsetting process.The inverse calculation steps of the warm upsetting of the molybdenum proposed in this paper was based on the load values measured in the upsetting experiment. The inverse calculation procedures were taken to solve the variation of the friction coefficient during the warm upsetting process. The results related to stress distribution, strain distribution, temperature distribution and shape variation were then compared with those reported in other studies. The comparison further confirmed the justification of using the load to solve the friction coefficient inversely. By means of the inverse algorithm presented in this paper, physical phenomena that better approximated the reality could be obtained, and the entire upsetting forming simulation could be more complete.     

WRIST FORCE SENSOR''S DYNAMIC PERFORMANCE CALIBRATION BASED ON NEGATIVE STEP RESPONSE

Negative step response experimental method is used in wrist force sensor＇s dynamic performance calibration. The exciting manner of negative step response method is the same as wrist force sensor＇s load in working. This experimental method needn＇t special experiment equipments. Experiment＇s dynamic repeatability is good. So wrist force sensor＇s dynamic performance is suitable to be calibrated by negative step response method. A new correlation wavelet transfer method is studied. By wavelet transfer method, the signal is decomposed into two dimensional spaces of time-frequency. So the problem of negative step exciting energy concentrating in the low frequency band is solved. Correlation wavelet transfer doesn＇t require that wavelet primary function be orthogonal and needn＇t wavelet reconstruction. So analyzing efficiency is high. An experimental bench is designed and manufactured to load the wrist force sensor orthogonal excitation force/moment. A piezoelectric force sensor is used to setup soft trigger and calculate the value of negative step excitation. A wrist force sensor is calibrated. The pulse response function is calculated after negative step excitation and step response have been transformed to positive step excitation and step response. The pulse response function is transferred to frequency response function. The wrist force sensor＇s dynamic characteristics are identified by the frequency response function.     

完全最小二乘下的康普顿散射图像重建

由康普顿散射能谱重建密度图像的问题是一个非线性的逆问题 ,这给重建带来很大困难。解决问题的一种方法是结合透射测量所得的衰减系数用以消除问题的非线性。但是 ,用这种方法所得到的投影矩阵却存在误差。为了减小这种误差对重建结果的影响 ,提出用完全最小二乘法来重建康普顿散射图像。数值模拟实验证明 ,这种方法极大地改善了重建图像的质量。     

Enhancing the reconstruction of acoustic source field using wavelet transformation

This paper shows the use of wavelet transformation combined with inverse acoustics to reconstruct the surface velocity of a noise source. This approach uses the boundary element analysis based on the measured sound pressure at a set of field points, the Helmholtz integral equations and wavelet transformation for reconstructing the normal surface velocity field. The reconstructed field can be diverged due to the small measurement errors in the case of nearfield acoustic holography (NAH) using an inverse boundary element method. In order to avoid this instability in the inverse problem, the reconstruction process should include some form of regularization for enhancing the resolution of source images. The usual method of regularization has been the truncation of wave vectors associated with small singular values, although the order of an optimal truncation is difficult to determine. In this paper, a wavelet transformation is applied to reduce the computation time for inverse acoustics and to enhance the reconstructed vibration field. The computational speed-up is achieved, with solution time being reduced to 14.5%.