Applying a Step Approach Method in Solving the Multi-Frequency Radiation From a Complex Obstacle

In this paper,a step approach method in the time domain is developed to calculate the radiated waves from an arbitrary obstacle pulsating with multiple frequencies.The computing scheme is based on the Boundary Integral Equation and derived in the time domain;thus,the time-harmonic Neumann boundary condition can be imposed.By the present method,the values of the initial conditions are set to zero,and the approach process is carried forward in a loop from the first time step to the last.At each time step,the radiated pressure on each element is updated.After several loops,the correct radiated pressures can be obtained.A sphere pulsating with a monopole frequency in an infinite acoustic domain is calculated first.This result is compared with the analytical solution,and both of them are in good agreement.Then,a complex-shaped radiator is taken as the studied case.The pulsating frequency of this case is multiple,and the waves propagate in half space.It is shown that the present method can treat multiple-frequency pulsation well,even when the radiator is a complex shape,and a robust convergence can be attained quickly.

Implementation of Time-Scale Transformation Based on Continuous Wavelet Theory

The basic objective of time-scale transformation is to compress or expand the signal in time field while keeping the same spectral properties. This paper presents two methods to derive time-scale transformation formula based on continuous wavelet transform. For an arbitrary given square-integrable function f(t),g(t) = f(t/λ) is derived by continuous wavelet transform and its inverse transform. The result shows that time-scale transformation may be obtained through the modification of the time-scale of wavelet function filter using equivalent substitution. The paper demonstrates the result by theoretic derivations and experimental simulation.

Kautz Function Based Continuous-Time Model Predictive Controller for Load Frequency Control in a Multi-Area Power System

A continuous-time Model Predictive Controller was proposed using Kautz function in order to improve the performance of Load Frequency Control(LFC).A dynamic model of an interconnected power system was used for Model Predictive Controller(MPC)design.MPC predicts the future trajectory of the dynamic model by calculating the optimal closed loop feedback gain matrix.In this paper,the optimal closed loop feedback gain matrix was calculated using Kautz function.Being an Orthonormal Basis Function(OBF),Kautz function has an advantage of solving complex pole-based nonlinear system.Genetic Algorithm(GA)was applied to optimally tune the Kautz function-based MPC.A constraint based on phase plane analysis was implemented with the cost function in order to improve the robustness of the Kautz function-based MPC.The proposed method was simulated with three area interconnected power system and the efficiency of the proposed method was measured and exhibited by comparing with conventional Proportional and Integral(PI)controller and Linear Quadratic Regulation(LQR).

基于傅里叶变换的振动切削刀具振幅测量方法

振动切削在当今时代的制造业越来越普遍,而振动切削的关键参数刀具振幅又因能量损失而无法避免,为了能保证良好的切削效果,需要知道实际切削过程中的刀具振幅。目前普遍使用激光测振仪测量振动切削的刀具振幅,但设备较为昂贵。为了实现对振动切削刀具振幅经济有效的测量,提出了一种利用加速度传感器测量振动切削刀具振幅的测量方法。利用加速度传感器获得刀具振动方向的加速度,通过傅里叶变换和频域二次积分以及傅里叶反变换,将加速度信号积分为振幅信号。根据实验结果可知,本测量系统的测量误差低于0.8%。

高速列车对综合交通枢纽中地下车站结构振动的影响

以济南遥墙综合交通枢纽为工程案例,依托CRTSⅢ型板式无砟轨道建立车辆-轨道-车站结构振动耦合模型,利用时频域分析方法,分析了不同列车通过速度下轨道与车站结构间振动传递特征、不同减振垫层刚度下车站结构顶板振动响应特征和减振效果。结果表明:列车通过速度80 km/h时,钢轨、轨道板、车站结构侧壁、车站结构顶板振动加速度绝对值依次减小,车站结构顶板振动加速度级峰值出现在100 Hz;车站结构侧壁和顶板的分频最大振级、最大Z振级均随列车通过速度增加而增大,并且最大Z振级的增幅大于分频最大振级;不同列车通过速度下车站结构侧壁的分频最大振级和最大Z振级均大于顶板;降低减振垫层刚度可有效减小车站结构顶板最大Z振级;列车以不同速度通过各股道时可通过采用不同减振垫层刚度的轨道结构达到同等减振效果。

LabWindows/CVI平台下虚拟信号分析仪的设计

针对目前传统信号分析仪功能单一、修改不易、使用不便等缺点,以Lab Windows/CVI为平台,研究开发了一种多功能虚拟信号分析仪。设计时把人机交互界面的响应处理和信号采集与显示分开成两个线程运行,大大缩短用户操作的等待时间,提高了系统运行效率。该信号分析仪具备伪随机信号产生、双通道信号采集、时域分析、频谱分析、互相关函数计算等功能。实验测试表明,该虚拟信号分析仪基本功能完全实现,信号分析结果正确,说明了推广发展虚拟仪器的可行性和必要性。

基于自适应集成学习的异常流量检测

提出了一种基于自适应集成学习的异常流量检测方法,使用离散傅里叶变换提取流量的频域特征,使得对流量特征提取过程中信息损失较小.用一种基于稳定性和准确性波动的评估指标来动态评估当前流量特征的可靠性,通过评估的特征数据块用于生成新的子分类器.同时,设计了一种集成自适应分类器,其参数和子分类器会根据当前的情况进行实时调整.实验结果表明,该方法对于解决异常流量检测中的概念漂移问题和机器学习对抗攻击问题有良好的效果.

预测规则波浪中船舶运动和载荷的频域三维计算机程序

The development of an in-house computer program for determining the motions and loads of advancing ships through sea waves in the frequency domain,is described in this paper.The code is based on the potential flow formulation and originates from a double-body code enhanced with the regular part of the velocity potential computed using the pulsing source Green function.The code is fully developed in C++language with extensive use of the object-oriented paradigm.The code is capable of estimating the excitation and inertial radiation loads or arbitrary incoming wave frequencies and incidence angles.The hydrodynamic responses such as hydrodynamic coefficients,ship motions,the vertical shear force and the vertical bending moment are estimated.A benchmark container ship and an LNG carrier are selected for testing and validating the computer code.The obtained results are compared with the available experimental data which demonstrate the acceptable compliance for the zero speed whereas there are some discrepancies over the range of frequencies for the advancing ship in different heading angles.

基于LabWindows/CVI的虚拟自控实验的设计

基于LabWindows/CVI虚拟仪器开发平台,成功设计了虚拟自控实验分析系统,主要包括:线性系统的时域分析仪、劳斯判据分析仪、根轨迹分析仪、频域分析仪及线性系统的PID校正仪等.根据实验参数给出具体示例,结果证明本实验系统能满足实验参数的精度要求.本系统对加快远程虚拟实验教学的发展具有一定意义.

小尺度封闭空间无网格Galerkin声场数值计算方法

文章将无网格法引入小尺度封闭空间声场的计算。首先推导了适用于任意形状小尺度封闭空间的无网格Galerkin声场数值计算模型。在模型中,利用Galerkin型加权残量法推导了计算节点声压的系统方程,根据移动最小二乘近似法构造了无网格形函数,并给出了积分运算方案;然后对一个矩形封闭空间的声传递函数及混响时间进行了计算,通过与理论计算结果、SYSNOISE计算结果及其文献实验结果对比,证明了模型的正确性;最后对一个实际机舱进行了建模计算,并与测量结果进行了比较,证明了模型对较复杂结构的正确性及适用性。

基于Bagging集成高斯过程回归模型的刀具寿命预测

提出了一种集成高斯过程回归(Gaussian process regression,GPR)模型的预测方法,首先将信号进行时域和频域分析,提取信号时频域特征,再结合距离相关系数(distance correlation,DC)进行特征筛选;为了提高模型的预测精度,采用Bagging算法对多个基学习器进行GPR集成,最大限度地降低噪声信号的影响;最后根据贝叶斯后验概率计算得到各子模型的权重,对子模型的输出进行融合,得到全局预测值。进行对比分析实验,验证了该方法的有效性,较之人工神经网络和支持向量机,该方法预测精度更好,具有一定的工程实用意义。

Coarse Mesh Superconvergence in Isogeometric Frequency Analysis of Mindlin–Reissner Plates with Reduced Integration and Quadratic Splines

A frequency accuracy study is presented for the isogeometric free vibration analysis of Mindlin–Reissner plates using reduced integration and quadratic splines,which reveals an interesting coarse mesh superconvergence.Firstly,the frequency error estimates for isogeometric discretization of Mindlin–Reissner plates with quadratic splines are rationally derived,where the degeneration to Timoshenko beams is discussed as well.Subsequently,in accordance with these frequency error measures,the shear locking issue corresponding to the full integration isogeometric formulation is elaborated with respect to the frequency accuracy deterioration.On the other hand,the locking-free characteristic for the isogeometric formulation with uniform reduced integration is illustrated by its superior frequency accuracy.Meanwhile,it is found that a frequency superconvergence of sixth order accuracy arises for coarse meshes when the reduced integration is employed for the isogeometric free vibration analysis of shear deformable beams and plates,in comparison with the ultimate fourth order accuracy as the meshes are progressively refined.Furthermore,the mesh size threshold for the coarse mesh superconvergence is provided as well.The proposed theoretical results are consistently proved by numerical experiments.

基于振动台试验的加速度积分位移

轨道不平顺是铁路车辆系统振动的主要激励源,车体构架运行姿态的变化会对轨道几何不平顺检测精度造成影响.理论上可通过位移传感器对车体构架的运行姿态进行测试,但多数情况下测量困难且精度较低,而采用加速度传感器测试,又存在各种噪声干扰,使积分位移中含有趋势项漂移误差.针对此类问题,提出了一种从加速度数据中获取位移时间序列的低频衰减频域积分方法.该方法从测量加速度积分开始,采用基于滑动平均的最小二乘法预处理方法,去除积分过程中的噪声产生的误差,还原实际由于轨道不平顺产生的振动响应.结合滑动平均方法、高通滤波器和频域积分,通过多次平滑、滤波和积分,得到重构位移信号,避免了信号的失真.该方法的主要优点是重构位移不存在长周期漂移.通过与振动台实测数据的对比分析,验证了该方法的准确性和可靠性.

大规模三维频率域电磁积分方程法数值模拟

地电磁学频率域电磁法在地球深部结构探测、油气勘查、环境与工程勘探等领域有着广泛的应用,其数值模拟的精度、速度直接影响资料解释结果。然而,当前频率域电磁三维数值模拟存在着求解精度差、计算时间长、计算规模受限等问题。采用积分方程法和直接解法提高求解精度,采用多层级多粒度混合并行、分布式存储等技术,大幅减少计算时间,扩大计算规模。实现了一种频点间并行、阻抗矩阵并行填充、方程组并行直接求解的快速、高精度、高可扩展性的频率域电磁三维数值模拟。首先,详细介绍了积分方程法理论和并行实现方案。然后,选取典型案例,通过与前人计算结果进行对比验证了程序的正确性。最后,针对1个16频点、16×12495个未知量、861个观测点的大规模算例进行了可扩展性测试,相比于1个节点32个进程,当计算规模达到256个节点8 192个进程时,加速比为69.69,并行效率为27.22%。此大规模并行算法适用于大地电磁和可控源音频大地电磁积分方程法。

基于六自由度振动台的车辆构架运动姿态测量

轨道几何动态检测是保障列车安全运营的重要手段,而车辆构架运动姿态测量结果的准确性直接影响到轨道几何动态检测的可靠性。为提高车辆构架运动姿态检测的准确性,提出了一种基于六自由度振动台的构架运动姿态测量方法。在模拟构架上施加不同的激励信号,利用安装测点布置位置上的4个三轴加速度计采集加速度信号,通过快速傅里叶变换的频域积分方法和基于位移数据的姿态计算算法,将加速度信号转化为模拟构架几何中心的位移及转角,并以六自由度振动台的输入信号作为标准,开展构架姿态测量方法的验证试验,结果表明构架姿态测量算法的横向位移、垂向位移、侧滚、摇头中误差分别小于0.04 mm,0.03 mm,0.05°,0.03°。

基于去斜滤波与稀疏恢复的探干一体化系统直达波抑制技术

探测干扰一体化系统通过波形一体化设计,利用无典型雷达信号特征的干扰信号进行探测,共享波形、频率、时间、孔径等资源,极大提升了系统资源的综合利用率。然而,为实现有效干扰,探测干扰一体化波形在频段上会与对方雷达信号有所重叠,一体化设备探测回波会受到由对方雷达发射信号带来的强直达波影响,造成探测性能的严重恶化。本文考虑探干一体化系统与线性调频雷达对抗的场景,提出了两种直达波抑制算法(去斜频域滤波与稀疏恢复)。在第一种算法中,通过分数阶傅里叶变换(Fractional Fourier Transform,FRFT)估计对方线性调频直达波调频斜率,构造回波去斜函数,将直达波分量变换为点频信号后通过频率滤波进行滤除。在第二种算法中,以去斜滤波方法作为预处理步骤,针对直达波功率强时去斜滤波带来的回波能量损失问题,利用稀疏恢复的方法恢复损失信号,进一步提升了探干一体化系统的探测能力。通过仿真和实测结果验证了算法可行性。

Microball lens integrated fiber probe for optical frequency domain imaging

An integrated microball lens fiber catheter probe is demonstrated, which has better lateral resolution and longer working distance than a corresponding bare fiber probe with diverging beam for Fourier domain optical coherence tomography （FDOCT）. Simulation results are shown to gain the effect of the distance between the mieroball lens and the bare fiber to the focusing plane and beam width. The freedom of modifying the working distance and lateral resolution is shown. This is achieved by changing the gap distance between the single-mode fiber and the microball lens within the packaged surgical needle catheter without using an additional beam expander having a fixed length. The probe successfully acquired crosssectional images of ocular tissues from an animal sample with the proposed miniaturized imaging probe.

通感一体化中的感知非理想因素及其消除方法

通感一体化在学术界和产业界都引起了广泛的关注和研究热潮,并被国际电信联盟ITU确定为6G的六大应用场景之一。在通信系统中引入感知功能时,由器件的非理想性引起的一些问题对于感知性能有着决定性的影响,称之为感知非理想因素。将从感知非理想因素的背景入手,进而分析四项感知非理想因素对于感知性能的影响。对于部分感知非理想因素,梳理了几种消除方法及其原理。最后,通过仿真或样机测试的方法,直观地展示了感知非理想因素的影响。特别地,在样机测试中,通过参考径方法进行感知非理想因素的消除,获取较好的效果。

风电并网系统次同步振荡传播路径频域定位方法

随着风电等新能源及电力电子设备接入比例的逐渐增大,系统动态特性更加复杂,导致系统次同步振荡风险加剧并难以定位振荡传播路径。因此,本文提出了一种风电并网系统次同步振荡传播路径的频域定位方法。首先,建立直驱风机的动态模型,包括永磁同步机及其传动系统,机侧、网侧换流器及其控制系统。然后,建立风电并网系统的状态空间模型,并推导其多输入多输出的传递函数模型,从而提出系统各节点振荡传播强度的量化方法,实现从频域的角度定量分析次同步振荡的传播特性。最后,以2台直驱风机接入4机2区系统和10机39节点系统为算例,验证所提频域分析方法对于振荡传播路径定位的有效性。

加速度频域积分中低频截止频率的优化取值

结构健康监测领域中,往往通过测试结构的加速度响应并通过积分来得到结构的位移响应。加速度积分的方法有很多种,其中频域积分方法具有计算速度快、稳定性高等优点,但由于受到低频敏感性的影响,应用受到较大限制。现有研究成果对加速度频域积分中截止频率的选择还未形成统一认识,文章就这一问题展开了深入研究。首先阐述了造成频域积分低频振荡的原因,然后通过对简谐信号的大规模数值计算,拟合出了最优截止频率的计算公式,并通过计算分析得出,最优截止频率的大小与采样频域和采样点数不存在必然关系,只与加速度信号基频线性相关。最后采用有限元仿真计算,对比了文章积分方法得出的位移与SAP2000计算位移的差异,二者平均峰值误差为1.96%,满足工程测试精度的要求。