Characterization of vibration and acoustic noise in a gradient-coil insert

High-speed switching of current in gradient coils within high magnetic field strength magnetic resonance imaging (MRI) scanners results in high acoustic sound pressure levels (SPL) in and around these machines. To characterize the vibration properties as well as the acoustic noise properties of the gradient coil, a finite-element (FE) model was developed using the dimensional design specifications of an available gradient-coil insert and the concentration of the copper windings in the coil. This FE model was then validated using experimentally collected vibration data. A computational acoustic noise model was then developed based on the validated FE model. The validation of the finite-element analysis results was done using experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Based on the validated FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient-coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again validated through experimental vibration testing with the gradient-coil insert installed in the MRI scanner and excited using swept sinusoidal time waveforms. The simulation results from the computational acoustic noise model were also validated through experimental noise measurement from the gradient-coil insert in the MRI scanner using swept sinusoidal time waveform inputs. Comparisons show that the FE model predicts the vibration properties and the computational acoustic noise model predicts the noise characteristic properties extremely accurately.     

基于物理模型开关磁阻电机定子模态和固有频率的研究

准确计算定子模态和固有频率是降低电机噪声和振动的基础。该文基于开关磁阻电机(SR电机)物理模型，利用3维有限元软件，全面研究了定子模态和固有频率，系统分析了绕组、端盖和安装对定子模态和固有频率的影响。研究表明，对小功率SR电机，2阶模态对噪声和振动的贡献最大。定子绕组对固有频率的影响非常严重，弹性模数远低于实心铜材，绕组不宜采用质量计入磁极或铁心的方式处理。端盖、底脚安装均导致定子固有频率明显升高。最后讨论了2维有限元模型与3维有限元模型计算结果的差异。计算结果与试验结果进行了比较验证。     

Large-band reduction of magnetic vibrations of induction machineswith “breaking-of-impedance” interface

Magnetic vibration of induction machines is reduced, on a large-frequency band, with a breaking-of-impedance interface between stator core and frame. This device is designed with strong tangential stiffness and low radial stiffness. Two-dimensional finite-element (FE) dynamic response is proposed. It is based firstly on experimental determination of magnetic forces with search coils on a half polar pitch on the stator bore. Secondly, all characteristics of windings are determined versus temperature and frequency and homogenized with a linear mixing law. Thirdly, a FE modal analysis is optimized on the target function based on experimental natural frequencies, in order to identify the equivalent mechanical parameters of wound slots     

大干扰下发电机间三阶非线性相关作用

相关因子在模式分析中占有重要地位,它反映了系统中各台发电机对某一振荡模式相关程度。相关因子大,相关程度就强;相关因子小,相关就弱。目前广泛采用的线性模式分析法虽然能提供有价值的线性化系统频域信息,但却忽略了系统非线性特性和系统固有模式之间相互作用的影响,不适合大干扰的情况。基于模态级数法3阶解析解,提出了大干扰下识别系统主导低频振荡模式的方法,确定了大干扰下对系统动态特性和稳定性影响最大的主导低频振荡模式,推导了3阶情况下的非线性相关因子,确定了非线性振荡的振荡源。并用Prony方法,验证了3阶相关因子和主导模式鉴别式的正确性和有效性。     

A novel technique for generating desired vibrations in structure

A novel technique is presented for exciting desired transient vibrations in a structure. A cantilevered plate instrumented with piezoelectric sensor and actuator is used as a test-structure. Finite element model of the test-plate is developed using Hamilton's principle. Finite element model is reduced to first two modes using orthonormal modal truncation and then this reduced model is converted into a state-space model. Tracking optimal control is then employed to obtain desired transient curves simultaneously, of first two modes of vibration. Theoretical findings are verified by conducting experiments, for experimentation, Kalman observer is used to estimate first two modes and Labview software is used for interfacing. Presented strategy can be used to do dynamic vibration testing of a product by forcing the product to experience same transient vibrations that it is expected to experience in field.     

航空电反推驱动用永磁同步电机振动及强度分析

电机的模态是分析振动的基础,由固有频率、振型和阻尼比决定。当电机工作时的激振频率与某一阶的固有频率相同或者相近时,会产生共振,导致电机剧烈振动,影响其正常运转。在对应用于航空电反推系统的双通道永磁同步电机PMSM进行三维建模之后,将三维模型送入ANSYS Workbench,在ANSYS工作平台上进行电机模态、响应谱分析与冲击响应的仿真。给出了该电机的前6阶次的固有频率和振型,以及在外加响应谱下的电机等效应力与在瞬态冲击下的电机机械结构上的应力分布。     

汽车用爪极发电机的电磁建模及参数优化技术

针对现在汽车上广泛应用的爪极发电机运行效率低的问题,利用电机三维有限元分析找出其效率低的主要原因是存在严重的漏磁现象。通过优化爪极发电机的结构参数达到最小化漏磁从而间接地达到提高电机效率的目的是本文研究的出发点。爪极发电机结构参数优化需要进行大规模的迭代计算,为了降低优化计算的成本,引入了基于支持向量机非参数建模思想,非参数模型和智能优化算法的运用达到了最小化爪极发电机漏磁的目的,试验结果验证了理论分析的正确性。     

基于分解降阶模型的双馈异步发电机模态估计方法

了解双馈异步发电机的本征特性对于揭示其对电力系统稳定性影响的机理具有重要意义。传统本征特性研究方法基于双馈异步发电机详细模型分析模态,方程阶数高、计算量大,且分析结果缺乏有效验证手段。根据状态变量特征及其耦合特性,提出基于分解降阶模型的重要模态估计方法。首先基于机械传动链模型和异步发电机模型方程,分析了机械传动链和异步发电机状态变量与双馈异步发电机系统其他状态变量的多时间尺度和耦合特性。在此基础上,提出了基于分解降阶模型的轴系扭振和定转子磁链振荡模态的估计方法,并利用奇异摄动理论揭示了该降阶模态估计方法的内在本质。最后,通过对比分析分解降阶模态估计、详细模型模态分析结果,验证了分解降阶模态估计方法的正确性。     

基于时变AR模型和小波变换的时变参数识别

利用时变AR模型进行时变系统参数识别的一个关键问题就是虚假模态的剔除.针对利用p阶的时变AR模型所得到的p个频率值,提出用连续小波变换所得到的小波时频图来进行虚假模态的剔除.通过对一质量随时间变化的悬臂梁进行了有限元建模,运用计算所得到的振动响应建立了梁的时变AR模型并进行模态频率识别,利用所提方法进行了虚假模态的剔除...     

Pointing Device Usage Guidelines for People With Quadriplegia: A Simulation and Validation Study Utilizing an Integrated Pointing Device Apparatus

This study undertakes a simulation and validation experiment to provide guidelines regarding pointing device usage for quadriplegic individuals assisted by a newly developed integrated pointing device apparatus (IPDA). The simulation experiment involving 30 normal subjects whose upper limb movement was restricted by splints. Another 15 subjects with high level cervical spinal cord injury (SCI) were recruited for the validation study. All normal subjects employed six control modes for target-acquisition and drag-and-drop tasks using an IPDA to integrate common pointing devices. A previously designed software was used to evaluate the operational efficiency (OE), expressed as “able performance” (%AP), of the subjects. The experimental results indicated that the OE of normal subjects for controlling the pointing devices were dominated first by using the unilateral hand (69–100 %AP), then by using the wrist/hand (65–73 %AP), and finally by using either bilateral body parts or the combination of limb and chin (45–53 %AP). The OE for operating an orientation-rotated mouse using the dominant wrist/hand via IPDA in both tasks was equivalent to that for operating a trackball using the dominant hand. The experimental results obtained by subjects with SCI also demonstrated similar findings, although the OEs in each control mode were lower than in normal subjects. Results of this study provide valuable guidelines for selecting and integrating common pointing devices using IPDA for quadriplegic individuals. The priority for selecting which body part should control the pointing devices was as follows: unilateral hands, unilateral wrist/hands, and either bilateral body parts or a limb and chin/head/neck in combination.      

大型风力机叶片模态测试与分析

利用建成的大型风力机叶片的振动特性分析装置,用测力法和不测力法对风力机叶片进行模态试验及分析,测试了风力机叶片的模态参数（固有频率、阻尼和振型）,得到了叶片的振动特性。采用共振法将偏心电机和变频器连成一体作为激励源测试了叶片的固有频率,实验验证了单叶片的危险运行频率。对大型风力机叶片模态试验及分析提供了可靠的实验装置和试验方法,对风力机叶片动力学特性分析提供有力工具。     

行波超声波电机非参数辨识模型

超声波电机的输出特性与驱动频率呈非线性关系。同时在驱动频率切换期间,振动的初始状态对转速变化过程也会产生影响。行波超声波电机(traveling-wave ultrasonic motor, TUSM)动态过程与切换频率前后值的选取及频率变化方向有关。将TUSM频率阶跃响应过程近似线性化,利用系统辨识中的非参数建模方法,建立在特定切换频率条件下的二阶线性模型。在TUSM工作范围内,辨识若干组不同切换频率条件下的近似二阶线性模型,将这些模型的参数进行二维或三维拟合,得到了一个关于TUSM传递函数的多输入多输出模型。利用60 mm行波超声波电机作为研究实例,实验与仿真结果表明,模型计算值与实测值接近,表明建模方法可行。     

Multi-port network and 3D finite-element models for accurate transformer calculations: Single-phase load-loss test

A six-port impedance network for a three-phase transformer is obtained from a 3D time-harmonic finite-element (FE) model. The network model properly captures the eddy current effects of the transformer tank and frame. All theorems and tools of passive linear networks can be used with the multi-port model to simulate several important operating conditions without resorting anymore to computationally expensive 3D FE simulations. The results of the network model are of the same quality as those produced by the FE program. Although the passive network may seem limited by the assumption of linearity, many important transformer operating conditions imply unsaturated states. Single-phase load-loss measurements are employed to demonstrate the effectiveness of the network model and to understand phenomena that could not be explained with conventional equivalent circuits. In addition, formal deduction of novel closed-form formulae is presented for the calculation of the leakage impedance measured at the high and low voltage sides of the transformer.     

A Study of an FDTD‐Based Frequency‐Dependent Line Model for Electromagnetic Transient Simulations

Electromagnetic transient (EMT) simulations of power systems require accurate representation of models in a wide range of frequencies. This of course applies to the representation of transmission lines, and the phase‐domain frequency‐dependent line model is often used to this end. The phase‐domain line model does not require modal transformation in EMT simulations but requires modal decomposition at its model identification stage, and there are cases where it fails to fix switchovers of propagation modes with respect to frequency. Thus, a frequency‐dependent line model which essentially avoids modal decomposition is desired. This paper studies the possibility of a frequency‐dependent line model based on the FDTD (Finite Difference Time Domain) method as a candidate which satisfies the above‐mentioned requirements. First, improvements regarding computational efficiency and numerical stability are made to Kordi's FDTD‐based frequency‐dependent line model. Then, the following points are clarified using the developed model: (i) Waveform deformations due to propagation modes with different velocities can be reproduced completely without modal decomposition; (ii) As the time step size becomes larger, waveforms obtained by the developed model become less accurate due to the embedded filter for numerical stability. These points assure, if the error due to the embedded filter is reduced, that the developed model can become a useful frequency‐dependent line model without model identification problems.     

压水板式后弯管波浪能发电装置的试验研究

提出了一种带有压水板的新颖后弯管波浪能发电装置,旨在提高后弯管波浪能发电装置的俘获宽度比,拓宽装置响应频宽。建立了压水板式装置物理模型,并在波浪水槽中开展物理模型试验,通过气压测量结合流量-气压关系式计算得到装置俘获转换的气动能量。研究了喷嘴比、锚泊点位置、吃水深度对装置性能的影响,并对比了一系列波浪要素条件下压水板式装置与常规型式装置的性能。发现在测试波周期范围内压水板式装置的最大俘获宽度比常规型式的大13.8%,俘获宽度比>70.0%的频响宽度比常规型式的宽21.9%,压水板实现了增效宽频作用。     

确定AR模型解中真实模态的稳定图法

提出了利用模态稳定性图来确定AR模型解中真实模态的方法,从而避开了传统方法中的定阶难点问题。首先建立了一个悬臂梁的有限元模型,得到了其振动时域响应,建立了用于振动模态识别的AR模型。其次令AR模型的阶次在一定范围内逐渐增大并进行相应求解计算,得到模态频率的一系列值并作出稳定图。在图中出现的数条稳定竖线所对应的频率值为系统的真实模态频率。通过短时平稳假设,可将其推广应用在时变系统模态频率识别中。     

光伏电站接入对多机电力系统低频振荡的影响分析

为了研究光伏电站接入对多机电力系统低频振荡的影响,综合考虑并网光伏电站的动态模型,详细推导并建立了含光伏电站的多机系统状态方程及其线性化模型。在此基础上,选取两区四机系统作为分析案例,采用模式分析法,针对光伏电站接入后系统转动惯量改变和转动惯量保持不变两种典型分析场景,研究不同接入点及不同渗透率情况下光伏并网对于电力系统低频振荡的影响,并通过时域仿真法验证了模式分析的正确性。仿真结果表明:光伏电站不会产生新的低频振荡模式。在转动惯量改变和保持不变的两种场景下,光伏电站的接入对于系统低频振荡的影响存在显著差异,取决于其接入位置与接入容量。最后,通过特征值灵敏度分析,验证了光伏电站不同接入位置、接入容量对于区间低频振荡模式的影响。     

燃煤电厂新型静电布袋复合除尘器的开发与气流分布试验研究

提出一种新的燃煤电厂静电布袋复合除尘器，分析其技术经济特点，并提出一些需解决的技术闯题。其中静电除尘单元与布袋除尘单元之间的结合形式是一个技术难点，将影响整个除尘系统的效率和布袋的使用寿命。研究开发出一套气流分布试验台，采用一定形式的气流分布板进行冷态试验研究，分析了几个关键截面的流场，掌握了气流分布规律，确定了气流分布板的开孔分布，为进一步进行中试试验和实现工程化奠定了基础。研究表明，采用具有独创性的结合形式后，该新型静电布袋复合除尘器应用于工程后将具有非常大的经济和环保优势。     

2D finite-element determination of tank wall losses in pad-mounted transformers

This paper presents a two-dimensional (2D) finite-element (FE) analysis of losses generated in the tank wall surrounding the high-current bushings of pad-mounted transformers. Although the problem is truly three-dimensional (3D), it is shown that a 2D approach gives results that closely agree with 3D simulations and experimental results. Thus, it is possible to avoid the very demanding computational resources required for 3D modeling or the cost of experiments. Nine cases are analyzed to study the impact of inserting small plates of different geometry (located near the high-current terminals) on the reduction of tank losses. Significant reductions in stray losses on the tank wall are obtained with low-cost plate inserts. 2D and 3D time-harmonic FE models are used to determine the losses in the tank wall. Two load loss tests were carried out on experimental transformers to validate the simulations.     

脉冲涡流检测中系统冲激响应的快速计算

应用涡流无损检测中积分方程法的理想裂缝模型以及有限元-边界元耦合法,在频域中研究了平板导体中含有理想裂缝时,其上方的磁场分布.两种不同频域方法的一致结果,证明了理想裂缝模型解的正确性.结合快速傅里叶变换方法,研究了含有裂缝的导体板上方不同检测点处的磁场单位冲激响应,计算实例表明,理想裂缝模型与快速傅里叶变换相结合是一种求解磁场时域冲激响应的快速有效方法.单位冲激响应的获得,为在时域中有效提取裂缝特征参数以及用脉冲涡流检测法识别缺陷奠定了基础.