大兆瓦等级中速永磁风力发电机电磁激振谐响应分析

半直驱风力发电机具有中速永磁的特点,与成熟的直驱永磁发电机相比,在转速、频率、结构、永磁固定方式、冷却方式及通风结构都存在很大不同。它兼顾了直驱的可靠、高效和双馈的低成本、小体积等优势,在近年风电整机价格的持续走低的背景下,有了较快的发展和提升。半直驱风力发电机电磁激振谐响应分析因为具有多学科耦合、建模复杂等特点,研究难度较高。本文通过对大兆瓦等级中速永磁风力发电机的设计研究,形成了电磁激励载荷的分析与提取、机电耦合分析模型的简化与建立、谐响应分析、真机试验测试对比等一整套方法,系统解决了电磁激振谐响应分析的难题。

掘进机臂架的高频激振特性研究

振动式掘进机臂架的响应频率和振幅是影响掘削效率的关键因素,由于目前机械惯性式激振系统结构复杂、响应频率及振幅较低的问题,提出一种采用转阀的臂架高频激振系统方案,并对掘进机臂架系统的激振特性进行研究。通过在ADAMS与AMESim仿真软件中分别建立臂架激振系统动力学模型和电液激振模型,仿真分析得出系统压力、激振阀阀口开度、激振频率、负载质量与臂架激振响应特性的关系;并搭建臂架激振系统试验平台,对仿真结果进行验证。研究结果表明,提高系统压力、增大激振阀阀口开度、减小负载质量可提高臂架响应振幅。随着激振频率的增大,臂架响应振幅先迅速下降,高于50Hz后,基本不再变化。为掘进机臂架系统的高频激振特性调节及控制提供依据。

煤岩体振动破坏试验及微震信号特征

通过所搭建的大型振动试验装置和微震监测系统,探究不同激励加速度和频率条件下整体煤岩试件的振动破坏特性。利用希尔伯特-黄变换(HHT)对煤岩体受迫振动过程中的监测信号进行了模态分离和信号重构,并结合振动力学知识着重阐释了共振放大效应产生的机理。研究结果表明:微震传感器监测信号具有明显的载波特征;当激励加速度峰值达到一定水平(0.5g)时,煤岩试件出现有效微震信号,首次破裂发生在煤层中,信号随传播距离的增大而衰减;随着裂隙的产生和扩展,煤岩试件自振频率降低,当激励频率等于煤体自振频率时,试件会产生共振放大效应,微震信号明显增强;激励加速度和激励频率对微震信号均有影响,激励加速度峰值越大、激励频率越接近自振频率,则微震信号越密集、幅值越大,且出现了优势频段向低频转移的趋势;理论分析解释了上述现象产生的原因。

油管内玻璃钢涂层去除机械加工的变形分析

针对油管内玻璃钢涂层的浮动切削去除工艺方法,根据其拉杆和切削头的工作状态,建立了力学模型,并进行了静态和动态计算。对其参数结果分析表明,适当减小刀具组件质量或提高弹簧刚度可以有效提高系统的切削性能,为切削工艺的改进提供了依据。

锚杆动测问题的数学物理模型及实验分析

锚杆动测问题可归结为一维波动方程在不同初始条件和边界条件下的解的问题。本文在前人研究的基础上分析了锚杆一维纵向振动模型的数学物理方程,并根据物理状态给出了定解条件,对端头自由、底端固定的锚杆锚固状态给出了基于有限差分数值模拟方法,给定3种不同瞬态激振响应模型,从解的位移、加速度响应来看,基于雷克子波激振响应的数值模拟解是稳定的,对比模型锚杆检测结果来看,数值模拟解是可靠的,以锚杆一维纵向振动模型建立的声波反射法理论体系是自洽的。

离散时间传递矩阵法在燃气轮机动力学计算中的应用

在处理时变系统,模拟激振力作用转子振动响应时,离散时间传递矩阵法有着十分明显的优势。以燃气轮机为研究对象,建立了燃气轮机低压、高压转子动力学简化模型;推导典型结构单元离散时间传递矩阵,计算转子临界特性;以流体激振和转子热变形两种故障模式为例,引入时变激振力,计算转子异常振动响应。通过实测数据验证,计算结果正确,建模方法、单元离散时间传递矩阵表达式和故障模拟方法可靠,可以直接应用到燃气轮机动力学计算中。

Noninvasive Flow Regime Identification for Wet Gas Flow Based on Flow-induced Vibration

A novel noninvasive approach, based on flow-induced vibration, to the online flow regime identification for wet gas flow in a horizontal pipeline is proposed. Research into the flow-induced vibration response for the wet gas flow was conducted under the conditions of pipe diameter 50 mm, pressure from 0.25 MPa to 0.35 MPa, Lockhart-Martinelli parameter from 0.02 to 0.6, and gas Froude Number from 0.5 to 2.7. The flow-induced vibration signals were measured by a transducer installed on outside wall of pipe, and then the normalized energy features from different frequency bands in the vibration signals were extracted through 4-scale wavelet package transform. A "binary tree" multi-class support vector machine(MCSVM) classifier, with the normalized feature vector as inputs, and Gaussian radial basis function as kernel function, was developed to identify the three typical flow regimes including stratified wavy flow, annular mist flow, and slug flow for wet gas flow. The results show that the method can identify effectively flow regimes and its identification accuracy is about 93.3%. Comparing with the other classifiers, the MCSVM classifier has higher accuracy, especially under the case of small samples. The noninvasive measurement approach has great application prospect in online flow regime identification.

Across and along-wind responses of tall building

Most modern tall buildings using lighter construction materials are more flexible, which can lead to excessive wind-induced vibrations resulting in occupant discomfort and structural unsafety. It is necessary to predict and mitigate such wind-induced vibration at the preliminary design stage. Fluctuating across and along-wind loads acting on a tall building that could not be formulated theoretically were simulated numerically in the time domain using known across and along-wind load spectra. These simulated wind loads were used to estimate the across and along-wind responses of a tall building, which are less narrow-banded processes, based on the state space variable approach. The simulated across-wind response of root-mean-square value(0.0047) and that of KAREEM's(0.0040) and the simulated along-wind response of root-mean-square value(0.021) and that of SOLARI's(0.027) were compared. It is found that these are good approximations of closed form responses. Therefore, these numerically simulated across and along-wind loads can be used for across and along-wind responses estimation for the wind-resistant design of a tall building at the preliminary design stage.

An experimental investigation of dual-resonant and non-resonant responses for vortex-induced vibration of a long slender cylinder

Experimental results of the dual-resonant and non-resonant responses are presented for vortex-induced vibrations(VIV)of a long slender cylinder.The cylinder has a diameter of 10mm and a length of 3.31 m,giving an aspect ratio of 331.The cylinder was towed by a carriage with the velocity up to 1.5 m/s,with the Reynolds number varying from 2500 to 38000.Three different weights were used to provide the initial tension.Dual resonance means that resonance occurs simultaneously in both the cross-flow(CF)and in-line(IL)directions.The experiments were conducted in two stages.At the first stage,dual-resonant dynamic features of the cylinder subjected to vortex-induced excitation were investigated.The features of CF and IL vibration amplitude,motion orbits,phase angle differences,dominant frequencies and mode order numbers are presented.At the second stage of the experiments,particular emphasis was placed on non-resonant dynamic features.The variation of multi-mode modal displacement amplitudes was investigated in detail.

Dynamic behavior of laterally loaded caisson foundations based on different cushion types: an experimental and theoretical study

Bridge foundations located in deep water are usually subjected to horizontal dynamic loads and moments which may be caused by the wind, waves, earthquake, and the possibility of boat crashing or vehicle braking. Caisson foundations based on gravel or sand cushions are a new type of deep-water foundation for bridges, suitable for meizoseismal areas. In this paper, harmonic horizontal excitation tests for the study of the lateral dynamic response of caisson foundations based on cushion layers are described. Different lateral loads and two different cushion types are considered. The results show that the lateral dynamic responses of caisson foundations based on sand and gravel cushions both show strong nonlinear characteristics, and the resonant frequency of the foundation decreases with the increase of the excitation force. The dynamic displacement of a foundation based on a sand cushion is far less than that based on a gravel cushion, and the rate of decrease of the resonant frequency of a foundation based on a gravel cushion is faster than that of a foundation based on a sand cushion under the same conditions. Under dynamic loading the gravel cushion can more effectively dissipate vibration energy and isolate the vibration, than the sand cushion can. A simplified nonlinear analysis method is proposed to simulate the lateral dynamic response of caisson foundations, and the predicted response shows a reasonable match with the results observed in laboratory tests. Scaling laws have also been applied in this small-scale vibration model test to predict the dynamic behavior of the prototype foundation.

Fiber-Optic Displacement Sensor Based on the DBR Fiber Laser

The fiber-optic displacement sensor based on the distributed Bragg reflector fiber laser is proposed, that is, the fiber laser cavity is attached to the measured object, when the measured object is stretched or contracted, and the length of the fiber laser cavity is also stretched or contracted accordingly. In view of the nonlinearity of the fiber-optic displacement sensor, the calibration based on piezoelectric ceramics is applied to improve the linearity of the displacement sensor. Experiment results show that the fiber-optic displacement sensor has a linear response with the nominal working distance of 90 um.