Studyon Evaluation Methods for Lateral Stability of High-Speed Trains

Taking a high-speed train in China as an example,using computer simulation technology and comparing with the test data,the three current methods including linear stability analysis method,nonlinear stability analysis method and the field testing criterion are studied to evaluate stability of high-speed trains.A new stability evaluation method is proposed which can be used to evaluate lateral stability of high-speed vehicle based on the codes of UIC 515and UIC 518.From the viewpoint of taking the most unfavorable track conditions into account and improving the safety margin,the new method uses the root mean square of bogie lateral acceleration as a criterion to evaluate the lateral stability of high-speed trains.Numerical example shows that the proposed method not only considers the forced vibration caused by track irregularities in the actual practice,but also takes the instability self-excited vibration into account,so it can realize early warning of bogie slight unstable oscillation,meanwhile the method itself does not involve complex algorithms which has the possibility of engineering applications.

Method of measuring rotation speed of high spinning projectile based on plane magnetic induction coil

For the test of rotation speed of high spinning projectile, the general formula of the motional electromotive force （MEMF） of planar magnetic induction coil （PMIC） is derived in case of 3D rotation in a stable magnetic field. Under a reasona-ble assumption, the MEMF of PMIC is simplified after the aforementioned general formula is used to calculate high spinning PMIC in the geomagnetic field environment. The determination approach of half-cycle is discussed and the method of rotation speed test is studied, and a test is conducted in the paper. The rotation speed curve obtained by the approach in this paper is consistent with the curve by telemetry.

Sound propagation in inhomogeneous waveguides with sound-speed profiles using the multimodal admittance method

The multimodal admittance method and its improvement are presented to deal with various aspects in underwater acoustics,mostly for the sound propagation in inhomogeneous waveguides with sound-speed profiles,arbitrary-shaped liquid-like scatterers,and range-dependent environments.In all cases,the propagation problem governed by the Helmholtz equation is transformed into initial value problems of two coupled first-order evolution equations with respect to the modal components of field quantities(sound pressure and its derivative),by projecting the Helmholtz equation on a constructed orthogonal and complete local basis.The admittance matrix,which is the modal representation of Direchlet-to-Neumann operator,is introduced to compute the first-order evolution equations with no numerical instability caused by evanescent modes.The fourth-order Magnus scheme is used for the numerical integration of differential equations in the numerical implementation.The numerical experiments of sound field in underwater inhomogeneous waveguides generated by point sources are performed.Besides,the numerical results computed by simulation software COMSOL Multiphysics are given to validate the correction of the multimodal admittance method.It is shown that the multimodal admittance method is an efficient and stable numerical method to solve the wave propagation problem in inhomogeneous underwater waveguides with sound-speed profiles,liquid-like scatterers,and range-dependent environments.The extension of the method to more complicated waveguides such as horizontally stratified waveguides is available.

THE APPLICATION OF BRANCH MODE METHOD TO THE CRITICAL SPEED ANALYSIS OF COMPOUND ROTATING SYSTEMS

This paper is devoted to the application of branch mode method in the critical speed ana-lysis of compound rotating systems, in which the distributed inertia including gyroscopic effectand distributed elastic support are taken into account. Finally, the method introduced in this paper is used to calculate the critical speeds of anew-type spindle on the spinning frame. The first three critical Speeds are calculated and com-pared with the values obtained from the experimental approach and other theoretical methods.The results show that they are in good agreement with each other.

TEST METHOD OF HIGH-SPEED ON-OFF VALVE DYNAMIC CHARACTERISTICS

According to the valve port features of high speed on-off valve and its actions, the valve port can be simplified into an a-type half bridge construction. A method that tests the dynamic characteristics of the high speed on-off valve by the output pressure signal of the a-type half bridge is proposed. Having analyzed the factors related to the dynamic characteristics of an a-type half bridge, a rule for designing the outlet chamber＇s volume is worked out. According to the rule, a test stand is built to test the self-developed high-speed on-off valve. From the test results, it can be seen that with the outlet chamber＇s volume controlled by the rule the rise time of the pressure signals driven by signals with different frequencies changes very little. The test results conform to the simulation results, which nroves the correctness of the method.

Evaluation of Residual Stresses Induced by High Speed Milling Using an Indentation Method

In this work, a recently developed method based on the change of distance between collinear indents is used to evaluate different states of residual stress, which were generated in samples of AA 6082-T6 and AA 7075-T6 aluminium alloys milled at high speed. One of the advantages of this method, which needs a universal measuring machine, is not requiring neither the use of specific equipment nor highly skilled operators. Also, by integrating an indentation device to the mentioned machine, the absolute error of measurement can be reduced. In results obtained in samples subjected to different cutting conditions it is observed a correlation between the stress values and the depth of cut, showing the AA 6082-T6 alloy higher susceptibility to be stressed. Furthermore, the high sensitivity of the method allowed detecting very small differences in the values reached by different normal components in the zones corresponding to climb and conventional cutting. It is important to note that these differences were similar for both evaluated alloys. Finally, the directions associated with the principal components of residual stress, where maximum local plastic stretching occurs, were found to be strongly dependent on the rolling direction prior to machining.

A Gain Scheduled Method for Speed Control of Wind Driven Doubly Fed Induction Generator

This paper proposes a gain scheduled control method for a doubly fed induction generator driven by a wind turbine. The purpose is to design a variable speed control system so as to extract the maximum power in the region below the rated wind speed. Gain scheduled control approach is applied in order to achieve high performance over a wide range of wind speed. A double loop configuration is adopted. In the inner loop, the rotor speed is used as the scheduling parameter, while a function of wind and rotor speed is used as the scheduling parameter in the outer loop. It is verified in simulations that a high tracking performance has been achieved.

实船试航中不同浅水效应修正方法的对比分析

船舶航行时,当水深吃水比小于4或水深傅汝德数大于0.6时,会出现“浅水效应”。在实船测速试验中,需要对浅水效应进行适当修正,才能准确评估船舶的航速。目前常用的船舶浅水效应修正方法有Lackenby方法和Raven方法。本文介绍了这2种方法的基本原理和适用条件,并基于9艘船舶的实船测速试航数据,对这2种方法进行计算和比较,并分析2种方法对实船航速修正结果的影响,可为我国船舶测速试航及航速修正提供参考。

Techniques for improving computational speed in numerical simulation of casting thermal stress based on finite difference method

Finite difference method (FDM) was applied to simulate thermal stress recently, which normally needs a long computational time and big computer storage. This study presents two techniques for improving computational speed in numerical simulation of casting thermal stress based on FDM, one for handling of nonconstant material properties and the other for dealing with the various coefficients in discretization equations. The use of the two techniques has been discussed and an application in wave-guide casting is given. The results show that the computational speed is almost tripled and the computer storage needed is reduced nearly half compared with those of the original method without the new technologies. The stress results for the casting domain obtained by both methods that set the temperature steps to 0.1 ℃ and 10 ℃, respectively are nearly the same and in good agreement with actual casting situation. It can be concluded that both handling the material properties as an assumption of stepwise profile and eliminating the repeated calculation are reliable and effective to improve computational speed, and applicable in heat transfer and fluid flow simulation.

光甘草定烟酰胺纳米乳的制剂评价与透皮吸收

为提高光甘草定和烟酰胺的透皮吸收性能,利用两种高能乳化法制备了纳米乳(HPH-NE和HSSU-NE),对其形态、粒径、Zeta电位、稳定性和皮肤渗透性能进行了评价与考察.结果表明:两种纳米乳颗粒均为规则球形,未见聚集现象,平均粒径分别为51.60 nm和42.98 nm,Zeta电位分别为-50.44 mV和-68.50 mV,并且在离心、4℃和20℃以及加速试验条件下均具有较好的稳定性,两种方法制成的纳米乳相对普通乳液具有更好的皮肤渗透性能,光甘草定的平均渗透速率提高3~5倍,烟酰胺的平均渗透率提高1.6~2.6倍,为光甘草定的纳米制剂以及化妆品应用研究奠定了坚实基础.

高速列车转向架底部包覆板气动减阻效果研究

转向架的复杂机械结构及非流线化外形对高速列车气动性能产生不利影响,优化列车转向架底部流场结构,降低转向架的气动阻力占比,是进一步降低高速列车气动阻力的重要手段。为此,参考现有高速列车转向架结构设计2种转向架底部包覆板,并建立3种转向架包覆方案:方案一为带倾角包覆板+全包围裙板;方案二为平直包覆板+全包围裙板;方案三作为对照组未安装底部包覆板。基于k−ω方程湍流模型,探究不同包覆方案下高速列车气动阻力变化规律,对比分析3种方案对转向架及整车气动阻力、转向架舱内压力分布以及列车底部流动特性的影响,并通过全尺寸转向架风洞试验验证数值仿真的可靠性。研究结果表明:转向架包覆板有效减弱了气流对转向架零部件以及转向架舱后端板的冲击,使得转向架舱内压力分布更均匀,进而降低了转向架气动阻力;方案一和方案二分别使头车阻力系数降低17.3%和22.2%,整车阻力系数降低11.6%和12.9%;与方案二相比,方案一中包覆板两端的倾角能够引导气流进入转向架舱内部,加速舱内的流动循环,有利于牵引电机、轴盘等转向架零部件与外部空气的换热。研究结果可为进一步优化转向架包覆板设计方案、降低列车气动阻力提供参考。

盾构隧道下穿高铁路基变形影响规律及加固优化研究

为研究盾构隧道下穿高铁路基施工时对路基的影响规律,探究在隧道开挖过程中运用不同加固措施对既有高铁路基的影响程度。以西安市某地铁工程为依托,利用室内模型试验对比分析盾构隧道下穿高铁CFG桩复合路基过程中,无加固、超前管幕工法加固与地表袖阀管注浆加固3种隧道施工条件下,地表沉降值和沉降槽的空间分布规律;采用数值模拟分析验证超前管幕工法加固工况下盾构隧道下穿时,高铁路基、道床的位移变化规律。室内模型试验结果表明:盾构隧道施工中采用管幕工法加固后复合地基正上方的地表沉降最大值减小28.6%,采用袖阀管注浆加固后减小18.0%,并且采用两种加固措施后的CFG桩最大附加轴力均减小20%以上。因此,在隧道掘进过程中采用一定加固措施,可改善围岩稳定性,其中管幕工法加固效果更为显著。数值模拟分析表明:采取管幕工法加固施工与不采取加固措施相比,路基最大沉降量减少33.78%,道床最大沉降量减少45.08%。因此,管幕工法加固能够有效减小对既有高铁路基的影响。

药用辅料硅酸镁铝(IB型)黏度测定方法探讨

目的:确定硅酸镁铝(IB型)登记备案标准中黏度测定方法是否可行。方法:采用棒状高速搅拌器及旋转黏度计考察硅酸镁铝(IB型)黏度,采用破壁机及旋转黏度计考察硅酸镁铝(IB型)黏度。结果:采用棒状高速搅拌器及旋转黏度计考察硅酸镁铝(IB型)黏度时,样品均不符合规定,采用破壁机及旋转黏度计考察硅酸镁铝(IB型)黏度时,样品均符合规定。结论:硅酸镁铝(IB型)为触变性非牛顿流体,其黏度测定结果受高速搅拌器类型影响较大,建议药用辅料登记备案标准中明确使用的高速搅拌器类型,细化前处理方法。

基于地形特征时频变换的无人特种车辆速度自适应控制方法

为提高复杂环境下无人特种车辆安全性、自主性及作业能力,面向在崎岖地形下无人特种车辆应用需求,提出一种基于地形特征时频变换的速度自适应控制方法。通过度量地形特征崎岖度、建立崎岖度和车速数学模型,实现无人特种车辆在崎岖地形的自主、自适应车速规划。针对崎岖地形和坡度引起的点云数据失真问题,融合惯性测量单元传感器数据对点云进行补偿,获得了车辆前方地形的精准点云数据;针对可视距离与跟踪精度冲突问题,不同于传统横向曲率计算方式,采用以线到面的方式,将激光雷达纵向剖面点云数据进行时频变换后,在频域内选取次频区域的积分面积作为崎岖度量化值,实现对不同地形下的崎岖度量化;此外,基于上述获得的崎岖度,采用迭代搜索的方式建立速度与崎岖度数学模型,并采用滑动窗口的方式更新崎岖度,实现车速到崎岖度之间的连续映射。以可控震源野外勘探特种车为研究对象,采用上述方法在实际野外地形环境中进行多次实验。实验结果表明,所提出的方法在崎岖地形具有良好的安全性、自主性,可以识别地形和自适应控制车速。

考虑电池总数的锂离子电池组双层均衡方法

为了适应电池总数变化并有效提高锂离子电池组均衡速度等,设计了一种双层均衡方法。首先对电池进行分组分层,底层组内分为奇数次和偶数次均衡电路,以适应电池总数存在奇偶性不同的情况;顶层组间采用可重构电路,将满足均衡条件的电池组接进或隔离出电路;同时从电池奇偶性、均衡速度和能量转移效率等方面推论出该均衡电路的优越性。其次以电池SOC为均衡变量,采用组内和组间同时均衡的控制策略,进一步提高均衡速度。最后考虑电池总数奇偶性不同,分别选用六节、七节锂离子电池在MATLAB/Simulink平台进行实验,与传统分布式可重构双层电路相比,充电均衡时间缩短了125.44和128.92 s,放电均衡时间缩短了114.99和115.69 s;与传统集中式可重构双层电路相比,充电均衡时间缩短了57.49和59.14 s,放电均衡时间缩短了51.24和50.63 s。同时通过比较均衡完成时电池组平均SOC及SOC离散度,可以得出该均衡电路在能量转移效率和减小电池组不一致性方面的优势,验证了所设计的均衡方法的有效性。

基于Fluent案例的工程流体力学课程教学研究

工程流体力学是大多数高等学校工程类专业必修的学科基础课程,典型特点是抽象、逻辑性强。为使学生深刻理解工程流体力学关键问题,该文基于Fluent软件在理论教学中同步阐述弯管、缩放型圆管、斜三通管路流体力学问题数值模拟,在课堂教学过程中穿插数值计算结果,并让学生理解流动问题发生本质,从而激发学生学习兴趣,提高教学效果,培养学生分析问题的实践能力。

外置转向架包覆对高速列车气动阻力影响

转向架作为高速列车大面积裸露在外且外形复杂的运行部件受到列车底部气流的直接作用,区域气动外形结构对高速列车整车气动阻力具有重要影响。基于三维稳态SST k-ω双方程湍流模型,采用数值仿真方法研究了轴箱外置式转向架不同包覆方式对高速列车气动性能的影响。研究了转向架区域安装小裙板、半包裙板、全包裙板、全包裙板+小底板以及全包裙板+大底板等5种方案下的高速列车气动性能,比较了不同方案下高速列车气动阻力的变化规律,阐明了高速转向架包覆方式对整车气动阻力、车底流动特性以及列车表面压力分布的影响。研究结果表明:随着转向架裙板包覆面积的增加,转向架腔后端板受到的气流冲击逐渐减弱,后端板上的正压分布降低,列车转向架区域周围的边界层厚度逐渐减小,转向架区域内的压力分布差异性逐渐减小,从而实现了列车整车气动阻力系数的降低。与小裙板模型相比,半包裙板、全包裙板、全包裙板+小底板以及全包裙板+大底板模型的列车气动阻力系数分别降低了5.2%、8.65%、10.3%、11.1%。对于轴箱外置式转向架来说,全包裙板+大底板方案可有效改善转向架区域流场,降低整车气动阻力。研究得到的转向架包覆方式将为新一代高速列车气动减阻设计提供有利支撑,实现列车气动节能。

基于反步滑模方法的车辆纵向自适应控制

车辆纵向控制是自动驾驶研究的关键技术之一,建立了复杂的车辆纵向动力学模型,设计了合适的控制算法,并构造了控制器,提升了控制性能。首先,在考虑道路倾角、轮胎形变和车轮滑动等影响因素的基础上,建立了复杂的车辆纵向动力学模型;然后,综合运用自适应方法和反步滑模控制方法对所建模型设计控制器,并对控制系统的稳定性作了证明;最后,采用MATLAB/Simulink软件对控制系统进行仿真分析。研究结果表明:通过自适应反步滑模方法设计的控制器具有较好的稳定性,能够控制车辆以极小的误差以期望速度行驶。研究成果可为车辆自动驾驶及交通拥堵的缓解提供技术支撑。

基于分量相依性的风速随机性建模方法

由于微地形、微气象的影响,风电场风速的随机性特征复杂,为准确描述风速的随机性特征,提出基于分量相依性的风速随机性特征建模方法。首先对风速序列的随机性特征进行提取,采用变分模态分解(VMD)将风速分解为多个不同频率的模态分量,以序列自相关系数(AC)为指标,对风速成分进行划分,得到风速的波动性分量和随机性分量。然后,考虑风速随机性分量对波动性分量的相依性,以正态分布描述不同风速下的随机性特征,建立基于分量相依性的风速随机性模型。以华北张家口某风电场的运行数据为例,验证该方法的有效性。实验结果表明该文方法能更好地复现风速序列的随机性特征。

考虑路基剪切效应的高速铁路有砟轨道-车辆系统移动元分析

为在现有三层离散支撑梁有砟轨道模型中考虑路基土体间的剪切效应,在Pasternak双参数地基模型基础上对剪切层进行离散处理,采用移动单元法建立了考虑路基土体剪切效应的有砟轨道-车辆耦合动力学模型,将移动单元法与MATLAB相结合,编制计算程序,通过MATLAB数值计算,研究路基剪切效应对车-轨耦合系统的影响,以及轨道不平顺和轨枕空吊对系统动力特性的影响规律。研究结果表明,考虑路基剪切效应时,钢轨、轨枕、道砟的位移响应均有不同程度的减小,并且抑制情况从钢轨到道砟相差逐渐增大,三者的加速度响应也均有较为明显的下降,其对加速度响应的抑制效果从道砟到轨枕依次减小,但钢轨的加速度减幅大于道砟,对轮轨接触力有一定影响,但影响不明显,减幅仅为0.85%;不平顺幅值和波长特性对系统的动力响应会产生显著影响,随着幅值增大和短波成分增加,系统动力响应加剧,其中2 m左右短波不平顺和90%百分位数谱对轮轨动力特性影响显著;列车经过空吊区域时,空吊及周围区域轨道结构动力响应会发生突变,导致系统动力响应超过限值。建立的基于移动单元法的有砟轨道-车辆耦合模型及相关分析可为高速铁路的振动分析提供参考依据。