A Multi-harmonic Method for Studying Effects of Mistuning on Resonant Features of Bladed Disks with Dry Friction Damping

An efficient multi-harmonic method is proposed for studying the effects of mistuning on resonant features of bladed disks with blade-to-blade dry friction damping. This method is able to predict accurately the forced response of bladed disks in frequency domain, which is validated by numerical integration method in time domain. The resonant features of both tuned and mistuned systems are investigated by using this method under various system coupling strengths, viscous dampings, and dry friction darnpings, etc. The results demonstrate that the proposed multi-harmonic method is very efficient for studying the mistuning effects on the resonant response of bladed disks with blade-to-blade dry friction damping, especially considering the combined effects of various system parameters.

A New Type of Restarted Krylov Methods

In this paper we present a new type of Restarted Krylov methods for calculating peripheral eigenvalues of symmetric matrices. The new framework avoids the Lanczos tridiagonalization process, and the use of polynomial filtering. This simplifies the restarting mechanism and allows the introduction of several modifications. Convergence is assured by a monotonicity property that pushes the eigenvalues toward their limits. The Krylov matrices that we use lead to fast rate of convergence. Numerical experiments illustrate the usefulness of the proposed approach.

Start-up phase plasma discharge design of a tokamak via control parameterization method

The tokamak start-up is a very important phase during the process to obtain a suitable equalizing plasma, and its governing model can be described as a set of nonlinear ordinary differential equations（ODEs）. In this paper, we first estimate the parameters in the original model and set up an accurate model to express how the variables change during the start-up phase, especially how the plasma current changes with respect to time and the loop voltage. Then, we apply the control parameterization method to obtain an approximate optimal parameters selection problem for the loop voltage design to achieve a desired plasma current target. Computational optimal control techniques such as the variational method and the costate method are employed to solve the problem, respectively. Finally, numerical simulations are performed and the results obtained via different methods are compared. Our numerical parameterization method and optimization procedure turn out to be effective.

A NEW METHOD TO DETERMINE THE START DEPTH IN GRAVITY ANOMALY INVERSION

The start depth in gravity anomaly inversion is discussed in this paper, and a newmethod called "test comparing method" is presented to determine the start depth when both boring dataand seismic data are not available. Anticline and synline density interface models are designed to test themethed; the calculated resall agreed well with the designed value, which Proved tha the new method canbe used to determine the start depth in the guity anomal inversion when boring data and seisndc dataare not available.

Application of Monte Carlo method in rudder control precision

After the trajectory simulation model of rudder control rocket with six degrees of freedom is established by Matlab/ Simulink, the simulated targeting of rudder control rocket with rudder angle error and starting control moment error is carried out respectively by means of Monte Carlo method and the distribution of impact points of rudder control rocket is counted from all the successful subsamples. In the case of adding interference errors associated with rudder angle error and starting time error, the simulation analysis of impact point dispersion is done and its lateral and longitudinal correction abilities at different targeting angles are simulated to identify the effects of these factors on characteristics and control precision of the rudder control rocket, which provides the relevant reference for high-precision design of rudder control system.

比较STM与START检伤分类法对地震伤的评估价值

目的探讨STM(Sacco Triage method)与传统的START(simple triage and rapid transport)检伤分类法对评估地震伤患者伤情的应用价值.方法回顾性分析四川大学华西医院地震伤员数据库中的36604例伤员报告,分别通过STM与START对患者进行分检,分别以群体死亡与创伤严重程度(ISS)为划分基准制作受试者工作曲线(ROC),计算曲线下面积并分析指标.结果总纳入危重地震伤患者34000例.以死亡为标准,STM和START检伤分类法的ROC曲线下面积分别为0.855和0.731.以ISS指数为标准,STM和START检伤分类法的ROC曲线下面积分别为0.521和0.500.结论两种指标皆提示STM较START检伤分类法在地震创伤院前检伤分类时具有更高的准确性,且以死亡为准更优.

Contribution to Development of Reliability and Optimization Methods Applied to Mechanical Structures

In order to take into account the uncertainties linked to the variables in the evaluation of the statistical properties of structural response, a reliability approach with probabilistic aspect was considered. This is called the Probabilistic Transformation Method (PTM). This method is readily applicable when the function between the input and the output of the system is explicit. However, the situation is much more involved when it is necessary to perform the evaluation of implicit function between the input and the output of the system through numerical models. In this work, we propose a technique that combines Finite Element Analysis (FEA) and Probabilistic Transformation Method (PTM) to evaluate the Probability Density Function (PDF) of response where the function between the input and the output of the system is implicit. This technique is based on the numerical simulations of the Finite Element Analysis (FEA) and the Probabilistic Transformation Method (PTM) using an interface between Finite Element software and Matlab. Some problems of structures are treated in order to prove the applicability of the proposed technique. Moreover, the obtained results are compared to those obtained by the reference method of Monte Carlo. A second aim of this work is to develop an algorithm of global optimization using the local method SQP, because of its effectiveness and its rapidity of convergence. For this reason, we have combined the method SQP with the Multi start method. This developed algorithm is tested on test functions comparing with other methods such as the method of Particle Swarm Optimization (PSO). In order to test the applicability of the proposed approach, a structure is optimized under reliability constraints.

Study of Steady-state Performances for a Novel Line-start Single-phase Permanent Magnet Synchronous Motor With Three Parallel-connected Windings

对于三相感应电动机的单相运行,学者们已经提出了多种实用的接线方式,比如Smith接法、SEMIHEX接法。然而,对于三相异步起动永磁同步电动机的单相运行,很少有合适的接法提出。将并联式接法应用于三相异步起动永磁同步电动机的单相运行,提出了一种新型三绕组并联式异步起动单相永磁同步电动机。分析了三相异步起动永磁同步电动机同步运行时以及起动瞬间的正序、负序阻抗,基于对称分量法,对该接法电机的对称运行条件进行分析,得出了电容的确定方法,并利用遗传算法对电容值进行优化。提出了该新型电机稳态性能的计算方法;设计了一台高功率因数和一台低功率因数三相异步起动永磁同步电动机作为样机,并分别将其改接为三绕组高效单相永磁同步电动机,进行实验研究。实验结果表明,低功率因数的异步起动永磁同步电动机更适合改接成新型三绕组并联式单相永磁同步电动机。由低功率因数三相永磁同步电动机改接成的单相异步起动永磁同步电动机在额定负载下运行时,具有与同容量三相永磁同步电动机相近的效率和更高的功率因数。

A New Algorithm for Black-start Zone Partitioning Based on Fuzzy Clustering Analysis

On the process of power system black start after an accident, it can help to optimize the resources allocation and accelerate the recovery process that decomposing the power system into several independent partitions for parallel recovery. On the basis of adequate consideration of fuzziness of black-start zone partitioning, a new algorithm based on fuzzy clustering analysis is presented. Characteristic indexes are extracted fully and accurately. The raw data matrix is made up of the electrical distance between every nodes and blackstart resources. Closure transfer method is utilized to get the dynamic clustering. The availability and feasibility of the proposed algorithm are verified on the New-England 39 bus system at last.

用于反应堆启动的Am-Be中子源物理特性研究

利用蒙特卡罗程序对采用合金法制备的Am-Be中子源辐照前中子源强能谱、伴生γ放射性等物理特性及其在堆内辐照过程中的变化情况进行了分析,评估了其作为压水型核电反应堆启动中子源的可行性。分析表明:合金法制作的单个Am-Be中子源(源活性区尺寸φ3.4 mm×236 mm,密度为4 g·cm^(-3))中子发射率可达3.34×10^(7)s^(-1),该源的源强虽低于核电厂反应堆常用的启动中子源,但多个Am-Be中子源叠加也可满足应用要求。Am-Be中子源在堆芯辐照过程中,由于产生的^(242)Cm等核素的影响,总中子源强高于其初始源强,保证其长期起到启动中子源作用。另外,Am-Be中子源具有较高的γ源强,在制造、运输与安装过程中需要考虑辐射防护问题。

基于动态磁网络法大型感应电机阻抗参数及起动特性计算

为提高大型感应电机动态阻抗参数及起动特性计算的准确性及计算效率,构建了考虑电机转子转速变化引起气隙磁导变化的非线性动态磁网络模型。以一台6.5 MW大型感应电机为例,分析起动电流变化对电机内各处饱和程度的影响机理,在此基础上,根据磁力线路径及电机内饱和程度确定动态磁网络模型中的非线性磁导的计算方法。将动态磁网络模型与转子趋肤效应模型相结合,提出计及漏磁并考虑转子转速变化及饱和偏移现象的电机动态阻抗参数的计算方法。推导并建立基于转子多回路法的大型感应电机的动态数学模型,根据电机瞬态过程中的电磁耦合关系,确定动态数学模型与磁网络模型的动态耦合求解方法,提出大型电机瞬态过程中考虑电流、转速、饱和及趋肤程度变化的动态阻抗参数及起动特性的计算方法。通过与有限元计算结果及实验结果对比,验证了所提出计算方法的正确性。

基于有限体积法碱金属高温热管冷态启动流动换热数值研究

为建立碱金属高温热管启动瞬态和运行稳态工作特性预测方法,本研究采用有限体积法(FVM)建立管壁导热模型、吸液芯流动传热模型和蒸气区模型。基于C语言开发并验证了碱金属高温热管的冷态启动瞬态分析程序,最大相对偏差为9.8%。仿真模拟了单根水平钠热管启动瞬态并开展敏感性分析,结果显示:对于本研究中使用的热管,在固定输入功率为1 000 W的环境条件下,启动开始后700 s热管蒸气区完全进入连续流态,到达稳态总用时为3 000 s,启动过程中工质熔化阶段吸液芯内部压力相对值逐渐增大,熔化完成后压力相对值略有降低;稳态运行下热管等温性良好,外壁面轴向温差稳定在22.5 K,吸液芯内部压降约为47 Pa;环境温度升高会延长热管到达稳态所需时间,并对稳态蒸气压力和流速分布产生一定影响;绝热段长度增加同样延长了热管启动到达稳态时间,同时对吸液芯内流体压力和速度分布存在一定影响。

表贴式永磁同步电机无位置传感器零低速起动方法的比较研究

由于运行在中高速状态下的永磁同步电机无位置传感器控制方式大多是采用反电动势来估算角度位置和转速,这在零低速往往不适用。为了实现表贴式永磁同步电机无位置传感器零低速起动和平滑切换到中高速运行,分析了恒压频比控制、恒流频比控制、脉振电压信号高频注入法三种低速起动控制方法。开环恒压频比控制采用了新的V/F曲线和电压补偿,近似补偿定子阻抗压降防止起动失败;单闭环IF控制和双闭环脉振高频电压注入控制采用加权算法切换至滑模观测器。对某一表贴式永磁同步电机应用Matlab/Simulink进行了永磁同步电机无位置传感器控制系统的仿真分析,仿真结果验证了所提出方法的有效性。

顾及起算点误差的区域参考框架约束方法研究

利用Helmert转换模型,首先对起算点先验坐标可能存在的粗差进行探测并剔除,其次依据剩余起算点坐标的相似变换构建最小约束条件,最后实现整网坐标框架的确定。选取中国境内及周边IGS站和陆态网GNSS基准站单周观测数据,采用IGS站ITRF2014坐标分别构建参数加权约束、最小约束、顾及IGS站先验坐标误差的Helmert模型约束,然后利用不同的基准约束平差方法获取整网坐标成果。实验结果表明,利用Helmert模型能有效削弱起算点坐标粗差对网形扭曲的影响,在一定程度上可提高区域参考框架的精度和可靠性。

A semi-analytical multi-harmonic balance method on full-3D contact model for dynamic analysis of dry friction systems

Dry friction damping structures are widely-used in aero-engines to mitigate vibration.The nonlinear nature of friction and the two-dimensional in-plane motion on the contact interface bring challenges to accurately and efficiently predict the forced response of frictionally damped structures.The state-of-the-art Multi-Harmonic Balance Method(MHBM)on quasi-3D contact model in engineering cannot precisely capture the kinematics on the friction interface although the efficiency is high.The full-3D contact model can describe the constitutive relationship of the interface in a more accurate manner;however,the efficiency and convergence are not guaranteed for large-scale models.In this paper,a semi-analytical MHBM on full-3D contact model is proposed.The original Trajectory Tracking Method(TTM)for evaluating the contact force is reformulated to make the calculation more concise and the derivation of the Analytical Jacobian Matrix(AJM)feasible.Based on the chain rule of derivation,the AJM which is the core to upgrade the performance is deduced.Through a shrouded blade finite element model,the accuracy and efficiency of the proposed method are compared with both the MHBM on full-3D contact model with numerical Jacobian matrix and the MHBM on quasi-3D contact model with AJM.The results show that the AJM improves significantly the efficiency of the MHBM on full-3D contact model.The time cost of the proposed method is in the same order of magnitude as that of the MHBM on quasi-3D contact model.We also confirm that the full-3D contact model is necessary for the dynamic analyses of shrouded blades.If one uses the quasi-3D model,the estimation relative error of damping can even reach 31.8%in some cases.In addition,the AJM also brings benefits for stability analysis.It is highly recommended that engineers use the MHBM on full-3D contact model for the dynamic analysis and design of shrouded blades.

考虑子单元数量与起始位置的全覆盖路径规划

移动机器人的覆盖作业任务正朝着大面积和智能化方向发展,对全覆盖路径规划的覆盖效率与环境适应性提出迫切需求。为解决传统的牛耕单元分解法在复杂地图中适应性不足的问题,并提高覆盖效率,给出一种全覆盖路径规划方法。首先,在牛耕单元分解法的基础上,提出面积降序遍历与单调多边形判断的策略对子单元进行合并,减少约一半的子单元数量。最后,通过建立子单元起始位置与终止位置的映射关系,采用遗传算法优化子单元起始位置的选择和全局访问顺序。研究结果表明:1)文中算法在处理长宽为1300像素的地图时,能够在10 s内得到计算结果,并且相较于牛耕法、神经网络法和等高线法,计算时间随地图面积的增长率更小;2)相较于牛耕法、等高线法、神经网络法和能量最优法,文中算法的机器人总作业时间减少5.4%~47.0%,无效作业时间减少5.8%~29.2%;3)文中算法在1800张测试地图的平均覆盖率达到99.91%;4)统计检验进一步验证文中算法具有显著覆盖效率优势。

异步起动永磁同步电动机齿槽转矩的削弱

由于异步起动永磁同步电动机的定转子双边开槽,增加了其齿槽转矩的特性分析及削弱措施研究的难度,现有针对该类电机齿槽转矩的削弱措施效果有限。首先,基于永磁体单独作用时的气隙磁密分布、定转子开槽引起的气隙磁导函数分布的解析模型,建立了齿槽转矩的解析分析模型;然后,研究了能有效削弱齿槽转矩的电机结构参数确定方法;最后,以一台18.5 kW样机为例,确定了能有效抑制电机齿槽转矩的定子齿宽、转子齿宽。结果显示,与现有削弱措施相比,确定的定子齿宽、转子齿宽能进一步将齿槽转矩削弱46.64%、65.98%,并且不会对电机的运行性能产生显著影响。

渐变气隙结构下单相无刷直流电机齿槽转矩解析建模

齿槽转矩的准确计算是解决单相无刷直流电机起动死点问题的基础。针对单相无刷直流电机有限元建模繁琐耗时的问题,建立渐变气隙结构下单相无刷直流电机齿槽转矩的解析模型。首先推导渐变气隙结构下气隙磁密的解析表达式,并利用能量法推导齿槽转矩的解析表达式,对其中的气隙磁密和有效气隙长度函数进行简化和傅里叶分解,最终得到齿槽转矩的解析模型。结合自适应复化梯形算法对该解析模型进行计算,避免传统模型中变量物理意义模糊,造成普适性差、预测精度低的问题。将渐变气隙结构下齿槽转矩的解析结果与有限元结果对比,并重点分析过零点偏移角度和峰值,验证所建立的齿槽转矩解析模型的正确性。该解析模型能够利用计算机编程实现快速准确地求解,且模型中各变量均与电机结构相关、物理意义清晰,便于设计人员优化齿槽转矩时寻找各变量之间的规律。

同步发电机在变频启动柴油机中的应用研究

现有的内燃机车柴油机启动方式存在设备空间占用率高、传递效率不高、故障率高等特点,在内燃机车升级换代的技术背景下,提出利用同步发电机与柴油机同轴且可以运行在电动机工况这一特点来启动柴油机,并对其电动机工况下的转速特性进行研究。通过对变频启动柴油机的工作原理及启动工况的边界条件进行分析,推导出发电机启动工况的状态方程组。为了缩短求解时间,提高求解精度,引入龙格库塔法求解上述方程组。通过编写仿真分析软件对发电机启动工况进行仿真分析,分析结果表明,同步电机启动时的机械转矩大于柴油机最大阻力转矩12000N·m,可在12s的时间内达到210r/min,满足启动工况的需求;该分析过程也可以用来校核柴油发电机组的控制策略和启动能力。

基于自适应零电压矢量三脉冲法的永磁同步电机带速重投策略

永磁同步电机运行过程中失电后,常因自身惯性或外界推动而处于高速旋转状态。若要带速重投,则需短时间内完成初始位置/转速观测。现有零电压矢量脉冲法的脉冲宽度和脉冲间隔不变,常使观测误差增大,严重时可能引起过电流。为此,研究一种自适应零电压矢量三脉冲法,可以根据零电压矢量脉冲所激励的电流矢量幅值自适应调节脉冲宽度,根据初始转速预估值自适应二次修正脉冲间隔,从而针对不同的电机参数或运行状态自动施加合理的零电压矢量脉冲。仿真结果表明,所研究的自适应零电压矢量三脉冲法脉冲宽度及脉冲间隔调节效果好,初始位置/转速观测和带速重投的可靠性高。