Numerical analysis of thermal process in continuous drive radial friction welding

A heat source model for radial friction welding was proposed, which was determined by friction pressure, friction coefficient, material properties and extrusion speed of material. A 3D model was established to analyze the continuous drive radial friction welding temperature field of 45 steel pipe. The influences of friction pressure, friction time and rotation speed on the temperature of the friction interface were analyzed. The results showed that the temperature on the friction interface rapidly rose to a peak temperature in initial friction stage and kept constant in the stable friction stage. Welding parameters of friction pressure, friction time and rotation speed had few influences on the peak temperature, while the increase of frlctlon pressure and rotation speed could shorten the time to reach the peak temperature.

Research on Radial Friction Welding of 30 mm Shell's Band

A new radial friction welding technology of 30 mm shell's band is introduced.Bands are assembled to shell bodies without notches by using the process.The width of heat-affected zone(HAZ) is small,and the microstructure on steel side is incomplete quenching while that on cooper side is grain refining.The shear-strength of joint exceeds 200 MPa.The result of firing test indicates that radial friction welding can satisfy the assembly requirements of shell bands.

高压大排量径向柱塞泵定子运动规律分析

为改善高压大排量径向柱塞泵定子-滑靴副摩擦状况,实现泵的精确变量,提出定子圆周方向非固定安装结构。通过滑靴柱塞组件力学特性分析,建立单个滑靴滑动摩擦力矩和11个滑靴摩擦合力矩,求解得到定子角速度变化曲线。结果表明,定子在滑靴滑动摩擦力矩作用下能够运动,且排油区滑靴摩擦力矩大于吸油区滑靴摩擦力矩。径向柱塞泵正常工作后,定子角速度稳定在89.5~90.6 rad/s,呈周期变化,对定子运动起阻碍作用的滑靴个数为4、5交替变换。为高压大排量径向柱塞泵滑靴副设计、提高泵的性能提供一定参考。

径向油孔结构对环下润滑高速轴承内部流动特性的影响研究

为了研究径向油孔结构对环下润滑高速轴承内部流动特性的影响规律,根据高速轴承内部流动特征建立了数值计算方法,针对包含输油通道、径向油孔和轴承组件的物理仿真模型开展了油气两相流动计算,对比并讨论了不同径向油孔结构下轴承内部的油气分布和黏性摩擦损失。数值模拟结果表明,径向油孔孔径增大后轴承内部的平均滑油体积分数单调增加且滑油分布更均匀。径向油孔布设在周向油槽的同侧有利于提升轴承内部的平均滑油体积分数,同时滑油沿周向分布的均匀性较好。轴承组件表面扩展参数受径向油孔结构的影响,其变化趋势与平均滑油体积分数的变化相似。全部采用经验公式预测得到的黏性摩擦损失整体偏高,且不能反映径向油孔结构参数的影响,数值模拟和经验公式相结合计算得到的黏性摩擦损失与直接采用数值模拟获得的结果表现出较好的一致性。

交叉滚子轴承摩擦力矩特性研究

为研究交叉滚子轴承摩擦力矩的影响因素,建立考虑环境温度和温升影响的轴承摩擦力矩计算模型,研究工况参数、环境温度和几何参数对轴承摩擦力矩的影响规律,并进行试验验证。结果表明:交叉滚子轴承只承受轴向载荷时,摩擦力矩主要由其中一个接触对产生;只承受径向载荷或倾覆力矩时,2个接触对产生的摩擦力矩之比为1∶1;在-30~50℃内,环境温度升高,轴承的摩擦力矩先减小后增大,温度小于40℃时润滑脂黏性对总摩擦力矩起主导作用,游隙变化的影响次之,50℃时游隙变化对摩擦力矩起主导作用,润滑脂黏性的影响次之;增大径向游隙可以显著降低轴承摩擦力矩;在直母线、对数修形和全凸圆弧修形3种修形方式中,全凸圆弧修形在较宽范围的载荷条件下降低摩擦力矩的效果更显著。

圆柱滚子轴承摩擦力矩试验机

针对现阶段圆柱滚子轴承摩擦力矩试验机测量载荷较小以及大径向载荷条件下测量精度不高的问题,基于平衡法研制了圆柱滚子轴承摩擦力矩试验机,试验机主体为卧式结构,最大载荷可施加至10 k N,可以在不同转速和润滑条件下测量圆柱滚子轴承的摩擦力矩。基于试验分析了径向载荷对圆柱滚子轴承摩擦力矩的影响规律,结果表明圆柱滚子轴承摩擦力矩随径向载荷的增加逐渐增大,摩擦力矩测量值与理论计算值相差较小,验证了圆柱滚子轴承摩擦力矩试验机的实用性。

穿山甲鳞片型织构柱塞副减摩和泄漏特性分析

针对内曲线径向马达柱塞副的磨损和泄漏制约液电能量回收系统效率的问题,提出在柱塞结构表面仿穿山甲鳞片型织构以减小摩擦和泄漏的方法。采用双抛物线平移的方法表征出穿山甲鳞片型织构的数学模型,结合雷诺方程建立油膜承载力和摩擦因数仿真模型,对比分析无织构柱塞和织构柱塞的油膜压力、摩擦因数和柱塞副间隙泄漏随织构面积率的变化关系。结果表明:织构柱塞比无织构柱塞的油膜压力高出10%~35%,且具有更高的承载力和更低的摩擦因数;织构柱塞副比无织构柱塞副间隙的泄漏量减少了13.8%~27.8%,表明织构对柱塞副的密封性能有一定的提升作用。仿穿山甲鳞片型柱塞织构结构对提升液压马达液电能量回收系统的效率有显著效果。

基于ANSYS的旋转格莱圈结构改型设计与分析

针对旋转格莱圈在运转过程中存在的密封环随轴转动的问题,提出从增大O形圈预压缩率及在密封环上增加泄压槽两方面对旋转格莱圈进行结构改型设计;采用有限元分析软件ANSYS对原结构和改型结构进行仿真分析,并对比分析各结构不同部位的接触应力分布、径向力分布以及摩擦力大小。研究结果表明:增大预压缩率可以在保证旋转格莱圈密封力的前提下,使密封环与轴之间的摩擦力远小于密封环与O形圈之间的摩擦力,有效改善旋转格莱圈密封环随轴转动的问题;增加密封环泄压槽,理论上可改善旋转格莱圈密封环随轴转动的问题,但是增加泄压槽会使各个接触界面的密封力下降,增加了密封泄漏的风险,且增加泄压槽使得旋转格莱圈最大应力应变急剧增大,增加了旋转格莱圈应力失效的风险。

基于分数阶自适应神经网络的电动舵机伺服系统摩擦干扰补偿控制

摩擦干扰力矩影响电动舵机伺服系统的跟踪性能,造成位置和速度跟踪偏差,甚至可能导致伺服系统不稳定。针对摩擦力矩干扰下的电动舵机伺服系统跟踪性能差的问题,本文提出了一种分数阶自适应神经网络摩擦补偿算法(FOANN),估计并补偿摩擦干扰力矩。首先,建立基于LuGre模型的电动舵机伺服系统模型,利用径向基神经网络估计模型中的不可测状态变量。其次,设计FOANN摩擦补偿控制器,利用李雅普诺夫稳定性理论证明电动舵机闭环系统的稳定性。最后,利用仿真和实验平台,对比分析了FOANN、传统PD控制和模型自适应控制的性能。结果表明,基于本文所提出的FOANN摩擦力矩补偿控制算法,电动舵机伺服系统的位置跟踪误差和速度跟踪误差均大幅减小,FOANN算法能够有效估计并补偿摩擦力矩,降低摩擦干扰对电机舵机伺服系统的影响,提高伺服系统的动态性能。

Neural Network Based Terminal Sliding Mode Control for WMRs Affected by an Augmented Ground Friction With Slippage Effect

Wheeled mobile robots(WMRs) encounter unavoidable slippage especially on the low adhesion terrain such that the robots stability and accuracy are reduced greatly.To overcome this drawback,this article presents a neural network(NN) based terminal sliding mode control(TSMC) for WMRs where an augmented ground friction model is reported by which the uncertain friction can be estimated and compensated according to the required performance.In contrast to the existing friction models,the developed augmented ground friction model corresponds to actual fact because not only the effects associated with the mobile platform velocity but also the slippage related to the wheel slip rate are concerned simultaneously.Besides,the presented control approach can combine the merits of both TSMC and radial basis function(RBF) neural networks techniques,thereby providing numerous excellent performances for the closed-loop system,such as finite time convergence and faster friction estimation property.Simulation results validate the proposed friction model and robustness of controller;these research results will improve the autonomy and intelligence of WMRs,particularly when the mobile platform suffers from the sophisticated unstructured environment.

Effect of viscosity on material behavior in friction stir welding process

Temperature-dependent elastic viscoplastic material model was used for the numerical simulation of the friction stir welding process. The non-elastic response of the rate-dependent material in the large deformation problems was calculated by using the closest point algorithm. The numerical results show that the shape of the equivalent plastic strain looks like onion rings and the spacing of the rings is approximately equal to the forward movement of the tool in one rotation. The equivalent plastic strain is increased with the increase of viscosity coefficient due to the increase of friction stress in the pin-plate interface. The region which is influenced by the rotating tool is decreased with the decrease of viscosity coefficient. The radial and circumferential stresses in front of the pin are greater than the ones behind the pin. This difference can be reduced with the decrease of viscosity.

Tide simulation using the mild-slope equation with Coriolis force and bottom friction

Since the mild-slope equation was derived by Berkhoff （1972）,the researchers considered various mechanism to simplify and improve the equation,which has been widely used for coastal wave field calculation.Recently,some scholars applied the mild-slope equation in simulating the tidal motion,which proves that the equation is capable to calculate the tide in actual terrain.But in their studies,they made a lot of simplifications,and did not consider the effects of Coriolis force and bottom friction on tidal wave.In this paper,the first-order linear mild-slope equations are deduced from Kirby mild-slope equation including wave and current interaction.Then,referring to the method of wave equations’ modification,the Coriolis force and bottom friction term are considered,and the effects of which have been performed with the radial sand ridges topography.Finally,the results show that the modified mild-slope equation can be used to simulate tidal motion,and the calculations agree well with the measurements,thus the applicability and validity of the mild-slope equation on tidal simulation are further proved.

A New Multigrid 3D-VAR Optimization Method for Bottom Friction Using HF Radar Current Observation

This paper proposes a new method for data assimilation of the surface radial current observed by High Frequency ground wave radar and optimization of the bottom friction coefficient.In this method,the shallow water wave equation is introduced into the cost function of the multigrid three-dimensional variation data assimilation method as the weak constraint term,the surface current and the bottom friction coefficient are defined as the analytical variables,and the high spatiotemporal resolution surface radial flow observed by the high-frequency ground wave radar is used to optimize the surface current and bottom friction coefficient.This method can effectively consider the spatiotemporal correlation of radar data and extract multiscale information from surface radial flow data from long waves to short waves.Introducing the shallow water wave equation into the cost function as a weak constraint condition can adjust both the momentum and mass fields simultaneously to obtain more reasonable analysis information.The optimized bottom friction coefficient is introduced into the regional ocean numerical model to carry out numerical experiments.The test results show that the bottom friction coefficient obtained by this method can effectively improve the accuracy of the numerical simulation of sea surface height in the offshore area and reduce the simulation error.

Dufour and Soret effects on MHD flow of viscous fluid between radially stretching sheets in porous medium

The aim of this paper is two-dimensional magnetohydrodynamic viscous fluid bounded by infinite sheets to examine the Dufour and Soret effects on the （MHD） steady flow of an electrically conducting An incompressible viscous fluid fills the porous space. The mathematical analysis is performed in the presence of viscous dissipation, Joule heating, and a first-order chemical reaction. With suitable transformations, the governing partial differential equations through momentum, energy, and concentration laws are transformed into ordinary differential equations. The resulting equations are solved by the homotopy analysis method （HAM）. The convergence of the series solutions is ensured. The effects of the emerging parameters, the skin friction coefficient, the Nusselt number, and the Sherwood number are analyzed on the dimensionless velocities, temperature, and concentration fields.

横缝对高拱坝系统非线性地震响应的影响分析

对带横缝高拱坝系统非线性地震响应的影响进行了分析研究.坝体材料采用混凝土损伤塑性本构模型,采用指数型动接触本构模型模拟各个坝段之间的横缝接触作用,具体模拟了横缝张开、闭合和滑移非线性,研究了横缝条数分别为1,3,5,7,11,21,40条时高拱坝的地震响应;探讨了径向摩擦因数分别取0.0,0.2,0.4,0.6,0.8时,拱坝横缝的最大开度、径向位移响应变化规律.研究表明:7条横缝模拟时的最大开度与11、21和40条横缝模拟的结果接近;最大开度的横缝位置并非在大坝中部,而是在靠近左右两个坝肩位置的横缝处,7条横缝时最大开度出现在第1条横缝,11、21和40条横缝时最大开度均出现在第3条横缝处,且这4个最大开度横缝在大坝上的位置基本相同;缝面考虑径向摩擦的横缝开度要大于径向自由的横缝开度;径向完全自由时静荷载作用下的顺河向位移明显大于径向有摩擦的情况,且后者在地震荷载下的顺河向位移响应变幅要大于前者;摩擦因数增加到一定时,大坝的顺河向位移响应曲线基本一致.研究结果可供有关设计施工部门参考.

全金属可溶桥塞异形接触结构密封特性

全金属可溶桥塞作为一种新型压裂工具,其密封结构是影响压裂效率的关键因素。为探究不同密封环结构对密封特性的影响,建立单槽形、椭圆形、双槽形、双曲形4种金属密封环结构的数值模型,利用有限元法,对密封环径向变形特征、密封性能进行分析,以及考虑双曲形结构表面粗糙度对密封接触面积、接触应力、接触面近场应力分布的影响。研究结果表明:随着锥体轴向位移量增加,4种密封环径向变形始终与锥体轴向位移量呈正相关规律,密封环最大、最小径向变形分别位于厚度较大外圆侧、厚度较小外圆侧;复杂接触面可以强化密封环的密封性能,在同样锥体轴向位移量下,双曲形密封环结构密封性能为最好,椭圆形密封环结构性能最差;考虑切向摩擦力时,摩擦因数越大,接触面近场Mises应力沿摩擦力方向发生偏移越明显。所得结论可为井下全金属可溶桥塞密封环的结构优选提供参考。

特形微织构多油楔滑动轴承特性分析及优化

为深度挖掘微织构对提高多油楔滑动轴承多项性能的潜力,以某三油楔径向滑动轴承为研究原型,利用CFD方法对其承载压强、摩擦因数、温度进行仿真分析;依据原型轴承设计椭圆开口偏置类抛物线微织构(elliptic opening offset parabola micro texture,EOOPT)三油楔滑动轴承;采用响应面法分析EOOPT参数对轴承特性的影响规律,建立相应二次回归方程;对EOOPT进行多目标参数优化,得到最优EOOPT参数。结果表明:EOOPT参数对轴承平均承载压强和摩擦因数影响的大小顺序均为:短半轴>长半轴>深度>偏置量>织构均布角;而对平均温度影响的大小顺序为:深度>长半轴>织构均布角>偏置量>短半轴;与原型轴承相比,最优参数微织构轴承的平均承载压强提高13.7%,而摩擦因数和平均温度分别降低13.8%和8.3%。

基于不同工质进行径流式透平背叶片对推力和摩擦功耗的影响研究

径流式叶轮背部增加背叶片结构可以有效调整叶轮背部腔室的压力分布,从而调整叶轮部分的轴向推力,但同时背叶片的引入会增加叶轮背面的摩擦功耗。文章基于某一径流式叶轮,研究在两种不同工质(空气及超临界CO_(2))下背叶片对叶轮背部压力分布及摩擦功耗的影响规律,并与无背叶片结构的叶轮背部腔室进行对比,通过研究发现,带背叶片结构时,背部旋转因子随泄漏量及泄漏方向的变化有较小的改变;而无背叶片结构时,背部旋转因子随泄漏量及泄漏方向的变化非常明显。背部摩擦功耗与旋转因子有关,旋转因子较大时摩擦损失较小,旋转因子较小时摩擦损失较大。另外,带背叶片时摩擦功耗要明显大于无背叶片时的摩擦功耗。

扭矩传感器校准仪轴承摩擦力矩特性研究

为提高扭矩传感器校准仪的校准精度,建立校准仪所用深沟球轴承摩擦力矩计算模型,在上位机程序中对轴承摩擦力矩产生的误差进行补偿,利用试验机对补偿前后校准仪测量精度进行对比,研究了不同轴承结构参数对摩擦力矩的影响。结果表明,摩擦力矩补偿后轴承校准仪测量精度明显提高。轴承摩擦力矩随钢球个数增加而增大,随内外沟曲率半径系数降低而减小,随轴承径向游隙增加而减小。研究结果提出了一种提高扭矩传感器校准仪校准精度的方法,并为深沟球轴承低摩擦优化设计提供了理论依据。

石墨填料摩擦磨损与密封性能试验研究

摩擦磨损与密封性能是评价阀杆填料密封系统的重要指标。基于控制阀整机改造的新型摩擦与气密性填料综合试验系统,通过动态监测阀杆力学变化与填料函泄漏率,考察石墨填料的截面形状与组合方式对填料摩擦特性、磨损特性与密封性能的影响规律。试验研究表明:不同截面形状石墨填料的动态摩擦力水平均低于相同条件下的不同组合方式石墨填料,且阀门向下关闭的摩擦力较打开时更大;随着循环次数增加,试样的启动摩擦力呈下降趋势,而滑动摩擦力出现小幅上升,填料的磨损出现恶化,泄漏率攀升;研究的锥形、V形、菱形3种截面形状中,V形截面的启动摩擦力最小,对执行机构配置要求最低,菱形截面的滑动摩擦力最小,对控制阀位置精度影响最低;两端式和交替式2种石墨填料组合方式中,交替式石墨填料组合通过调整径向应力分布使填料摩擦力下降35%,密封特性得到改善,综合性能得到显著提高。