Modeling and Analysis of Novel Integrated Radial Hybrid Magnetic Bearing for Magnetic Bearing Reaction Wheel

Conventional ball bearing reaction wheel used to control the attitude of spacecraft can＇t absorb the centrifugal force caused by imbalance of the wheel rotor,and there will be a torque spike at zero speed,which seriously influences the accuracy and stability of spacecraft attitude control.Compared with traditional ball-bearing wheel,noncontact and no lubrication are the remarkable features of the magnetic bearing reaction wheel,and which can solve the high precision problems of wheel.In general,two radial magnetic bearings are needed in magnetic bearing wheel,and the design results in a relatively large axial dimension and smaller momentum-to-mass ratios.In this paper,a new type of magnetic bearing reaction wheel（MBRW） is introduced for satellite attitude control,and a novel integrated radial hybrid magnetic bearing（RHMB） with permanent magnet bias is designed to reduce the mass and minimize the size of the MBRW,etc.The equivalent magnetic circuit model for the RHMB is presented and a solution is found.The stiffness model is also presented,including current stiffness,position negative stiffness,as well as tilting current stiffness,tilting angular position negative stiffness,force and moment equilibrium equations.The design parameters of the RHMB are given according to the requirement of the MBRW with angular momentum of 30 N ？ m ？ s when the rotation speed of rotor reaches to 5 kr/min.The nonlinearity of the RHMB is shown by using the characteristic curves of force-control current-position,current stiffness,position stiffness,moment-control current-angular displacement,tilting current stiffness and tilting angular position stiffness considering all the rotor position within the clearance space and the control current.The proposed research ensures the performance of the radial magnetic bearing with permanent magnet bias,and provides theory basis for design of the magnetic bearing wheel.

Real-Time Hybrid Simulation of Seismically Isolated Structures with Full-Scale Bearings and Large Computational Models

Hybrid simulation can be a cost effective approach for dynamic testing of structural components at full scale while capturing the system level response through interactions with a numerical model.The dynamic response of a seismically isolated structure depends on the combined characteristics of the ground motion,bearings,and superstructure.Therefore,dynamic full-scale system level tests of isolated structures under realistic dynamic loading conditions are desirable towards a holistic validation of this earthquake protection strategy.Moreover,bearing properties and their ultimate behavior have been shown to be highly dependent on rate-of-loading and scale size effects,especially under extreme loading conditions.Few laboratory facilities can test full-scale seismic isolation bearings under prescribed displacement and/or loading protocols.The adaptation of a full-scale bearing test machine for the implementation of real-time hybrid simulation is presented here with a focus on the challenges encountered in attaining reliable simulation results for large scale dynamic tests.These advanced real-time hybrid simulations of large and complex hybrid models with several thousands of degrees of freedom are some of the first to use high performance parallel computing to rapidly execute the numerical analyses.Challenges in the experimental setup included measured forces contaminated by delay and other systematic control errors in applying desired displacements.Friction and inertial forces generated by the large-scale loading apparatus can affect the accuracy of measured force feedbacks.Reliable results from real-time hybrid simulation requires implementation of compensation algorithms and correction of these various sources of errors.Overall,this research program confirms that real-time hybrid simulation is a viable testing method to experimentally assess the behavior of full-scale isolators while capturing interactions with the numerical models of the superstructure to evaluate system level and in-structure response.

Influence of Particles on the Loading Capacity and the Temperature Rise of Water Film in Ultra-high Speed Hybrid Bearing

Ultra-high speed machining technology enables high efficiency, high precision and high integrity of machined surface. Previous researches of hybrid bearing rarely consider influences of solid particles in lubricant and ultra-high speed of hybrid bearing, which cannot be ignored under the high speed and micro-space conditions of ultra-high speed water-lubricated hybrid bearing. Considering the impact of solid particles in lubricant, turbulence and temperature viscosity effects of lubricant, the influences of particles on pressure distribution, loading capacity and the temperature rise of the lubricant film with four-step-cavity ultra-high speed water-lubricated hybrid bearing are presented in the paper. The results show that loading capacity of the hybrid bearing can be affected by changing the viscosity of the lubricant, and large particles can improve the bearing loading capacity higher. The impact of water film temperature rise produced by solid particles in lubricant is related with particle diameter and minimum film thickness. Compared with the soft particles, hard particles cause the more increasing of water film temperature rise and loading capacity. When the speed of hybrid bearing increases, the impact of solid particles on hybrid bearing becomes increasingly apparent, especially for ultra-high speed water-lubricated hybrid bearing. This research presents influences of solid particles on the loading capacity and the temperature rise of water film in ultra-high speed hybrid bearings, the research conclusions provide a new method to evaluate the influence of solid particles in lubricant of ultra-high speed water-lubricated hybrid bearing, which is important to performance calculation of ultra-high speed hybrid bearings, design of filtration system, and safe operation of ultra-high speed hybrid bearings.

Identification of Magnetic Bearing Stiffness and Damping Based on Hybrid Genetic Algorithm

Identifying the stiffness and damping of active magnetic bearings(AMBs)is necessary since those parameters can affect the stability and performance of the high-speed rotor AMBs system.A new identification method is proposed to identify the stiffness and damping coefficients of a rotor AMB system.This method combines the global optimization capability of the genetic algorithm(GA)and the local search ability of Nelder-Mead simplex method.The supporting parameters are obtained using the hybrid GA based on the experimental unbalance response calculated through the transfer matrix method.To verify the identified results,the experimental stiffness and damping coefficients are employed to simulate the unbalance responses for the rotor AMBs system using the finite element method.The close agreement between the simulation and experimental data indicates that the proposed identified algorithm can effectively identify the AMBs supporting parameters.

Steady Characteristics of the Water-Lubricated Conical Bearings

The water-lubricated conical bearing has attracted attentions of researchers for its simple structure,easily adjusted gap ( film thickness ) , lower friction loss, and less pollution in application. A mathematic model with consideration of the effects of turbulence,two-phase flow,and temperature on the pressure field at bearing surface is proposed here. Using this model,the Reynolds' equation and energy equation are solved in which the thermo-physical properties of the water as lubricant are taken into account. The dependency of characteristics of bearing,such as load-carrying capacity,flow rate ( pumping losses ) ,and frictional losses,on angular velocity, conical angle, and radial eccentricities, is presented. The research results are beneficial to the improvement of the efficiency of conical bearing and the environmental protection.

超临界二氧化碳动静压径向可倾瓦轴承实验台设计与实验研究

针对超临界二氧化碳(S-CO_(2))动力机组在启动和停止阶段气体轴承产生非常大的摩擦磨损,以及气体轴承承载力低、刚度低、阻尼小、稳定性较差等问题,设计并改进一种新型动静压S-CO_(2)润滑径向可倾瓦轴承结构。设计并搭建S-CO_(2)润滑轴承实验台,针对于实验台转子刚启动和极低转速工况,对新型S-CO_(2)润滑动静压径向轴承在静压状态下的动态特性进行实验研究,得到轴承的动态刚度和动态阻尼,并分析静压对轴承动态性能的影响。实验结果表明,设计的S-CO_(2)动静压径向可倾瓦轴承在启停阶段,在轴瓦与轴颈之间产生了足够的静压压力,可将二者完全分隔开,从而能减少启停阶段的摩擦磨损;随着静压压力的增大,轴承X、Y方向上的整体刚度、主阻尼都增大,且2个方向的主刚度系数差别不大,而交叉刚度和交叉阻尼都接近于0。研究结果为进一步揭示S-CO_(2)润滑径向轴承动压状态特性提供参考。

钢塔-组合塔混合结构结合部承载性能试验研究

针对新型钢塔-组合塔混合结构结合部构造,开展了局部缩尺模型轴压试验,并建立了非线性有限元模型与试验结果进行比较。研究了钢塔-组合塔结合部的极限承载力以及破坏形式,探究了钢板应变分布规律和焊钉受力分布规律,并对传力路径和荷载分担比例进行了变参数分析。研究结果表明:新型钢塔-组合塔混合结构结合部的承载力符合设计要求;结合部的破坏形式表现为承压板下方钢壁板达到屈服并发生鼓曲变形;承压板为结合部的核心传力构件,增大板厚可以提高结合部承载力以及承压板所传递的荷载,其厚度宜与外壁钢板厚度相近;焊钉和开孔板连接件是保证结合部钢和混凝土共同受力的关键构造,在钢壁板屈服前以受竖向剪力为主,在钢壁板屈服后以受拉拔力为主。

基于混合式特征选择的滚动轴承故障诊断方法

为降低滚动轴承故障特征集的维数,提升诊断精度,提出一种混合式特征选择方法。该方法由两个阶段构成,首先通过费舍尔分值法对原始特征集进行预排序,根据特征的费舍尔得分按照降序排序,利用得分曲线的拐点确定预选子集的范围,去除原始特征集中的无关特征;然后将遗传算法嵌入Wrapper阶段中,利用分类器的识别精度作为评价标准,从预选子集中去除冗余特征,确定最优子集。通过实验证明,该方法可以有效地用于滚动轴承不同故障类型和不同故障程度的诊断,最优子集在仅保留了关键特征的同时,识别精度得到提升。

螺旋槽小孔节流动静压气体轴承稳态承载力分析

为研究空气轴承在动静压下的稳态承载性能,使用三维建模工具建立动静压气体轴承模型,从连续方程、可压缩流体润滑方程、气体状态方程出发,得到等温条件下稳态气体润滑Reynolds方程,并计算轴承稳态承载力。对螺旋槽小孔节流空气轴承结构建立三维模型,借助Fluent仿真软件对整个流体域进行仿真分析,探讨螺旋角、偏心率、槽宽比、槽深比、槽长比等参数对气体轴承承载性能的影响。结果表明:气源压力一定时,气膜承载力随着偏心率的增加呈现非线性上升趋势,随着槽宽比的增加呈现下降趋势,槽宽比越大,这种下降趋势更加明显;随着槽深比和槽长比的增加,气膜承载力呈现先增加后降低的趋势。对轴承结构进行优化,优化后的轴承承载性能更优。

基于粒子群-遗传混合算法的深沟球轴承优化设计

为了提高深沟球轴承的服役性能,提出一种基于粒子群-遗传混合算法的优化设计方法。其以额定动载荷和额定静载荷为目标函数,以滚动体直径、节圆直径、滚动体数目和内外圈滚道沟曲率半径系数为设计变量,基于粒子群算法,引入罚函数和遗传交叉、变异操作,解决带约束优化问题求解和局部最优问题。并以6206型轴承为算例,对优化后的轴承进行应力分析和敏感度分析。结果表明,所提出算法的收敛性能较好、优化能力较强、运算速度较快,优化后的深沟球轴承接触应力下降了31.7%,从而验证了所提出方法的有效性。

考虑边界滑移状态的液体动静压球轴承稳定性分析

液体动静压球轴承稳定性分析包括探究其动态特性及临界转速,其刚度和阻尼系数对轴承转子系统稳定性具有重要影响,而研究临界转速可有效避免轴承转子系统发生涡动失稳。考虑边界滑移条件,将小孔节流器进入油腔流量与封油边流出流量相等作为边界条件,求解出边界滑移状态下的Reynolds方程得到油腔压力和封油边压力;对边界滑移状态下瞬态Reynolds方程采用小扰动法推导出扰动压力偏微分方程,结合有限差分法和松弛迭代法求解方程得到边界滑移状态下液体动静压球轴承的刚度和阻尼系数,进而通过线性稳定性方法求解临界失稳转速,探讨滑移系数、供油压力、转子转速之于轴承动态特性的影响及临界转速之于滑移系数的变化规律。结果表明,滑移系数增大会导致4个刚度系数和交叉阻尼系数减小、直接阻尼增大;供油压力增大将导致8个动态特性系数均增大,转速增大将导致刚度增大及阻尼减小,且滑移效应的发生不影响上述规律;临界转速随滑移系数的增大而减小,系统稳定性降低。

液体动静压球轴承轴心运动轨迹研究

为研究外载荷对轴承转子系统稳定性的影响,以小孔节流的液体动静压球轴承转子系统为研究对象,建立液体动静压球轴承转子系统动力学模型。通过求解轴承润滑数学模型获得非线性油膜力,分析转子所受到的外载荷,采用欧拉算法预测出轴心下一个时刻位移、速度和加速度,并分析转子系统质量、不平衡载荷和阶跃载荷对转子回转精度的影响。结果表明:随着转子系统质量的增加,所需平衡的油膜力增加,轴心振动幅度增加,从而导致转子回转精度降低;相对于不考虑不平衡载荷,考虑不平衡载荷后其振动形态为椭圆且振动幅值增大,减小不平衡值将减小振幅并提高旋转精度;随着阶跃载荷的增加,达到平衡所需的时间也增加。

六极外转子径向混合磁轴承转子位移自检测

为了解决六极混合磁轴承位移传感器体积大、成本高的问题,提出了一种改进粒子群优化算法最小二乘支持向量机的位移估计方法.首先,介绍六极外转子径向混合磁轴承的结构和工作原理,并推导其径向悬浮力的数学模型.其次,将改进的粒子群算法的惯性权重改变,以实现更快的迭代,并建立了基于最小二乘支持向量机的预测模型,根据改进的粒子群算法优化的参数对预测模型进行了仿真和验证,并比较了改进的粒子群算法和粒子群算法的预测值.最后,进行了静态悬浮实验、动态悬浮实验、扰动实验,验证了该位移估计方法的鲁棒性和稳定性.

Seismic performance evaluation of VCFPB isolated storage tank using real-time hybrid simulation

Variable curvature friction pendulum bearings(VCFPB)effectively reduce the dynamic response of storage tanks induced by earthquakes.Shaking table testing is used to assess the seismic performance of VCFPB isolated storage tanks.However,the vertical pressure and friction coefficient of the scaled VCFPB in the shaking table tests cannot match the equivalent values of these parameters in the prototype.To avoid this drawback,a real-time hybrid simulation(RTHS)test was developed.Using RTHS testing,a 1/8 scaled tank isolated by VCFPB was tested.The experimental results showed that the displacement dynamic magnification factor of VCFPB,peak reduction factors of the acceleration,shear force,and overturning moment at bottom of the tank,were negative exponential functions of the ratio of peak ground acceleration(PGA)and friction coefficient.The peak reduction factors of displacement,acceleration,force and overturning moment,which were obtained from the experimental results,are compared with those calculated by the Housner model.It can be concluded that the Housner model is applicable in estimation of the acceleration,shear force,and overturning moment of liquid storage tank,but not for the sliding displacement of VCFPBs.

西堠门公铁两用大桥岩锚锚碇承载特性研究

甬舟铁路西堠门公铁两用大桥主桥采用主跨1488 m斜拉-悬索协作体系桥,金塘岛侧采用岩锚锚碇。为研究该桥岩锚锚碇的承载特性,基于地质概化模型、岩体力学参数,构建岩锚锚碇结构与岩体互相作用的三维数值模型,分析预应力和主缆荷载作用下围岩变形特征与塑性区分布规律及超载作用下岩锚的破坏模式与围岩稳定安全系数。结果表明:按顺序施加预应力和主缆荷载后,岩体最大变形分别为2.75 mm、1.99 mm;施加预应力有利于减小岩锚锚碇系统的变形;在承受主缆荷载时岩锚锚碇系统工作性能良好,带动了较大范围的深层岩体参与承担主缆荷载;岩锚破坏模式是从后锚室上方破坏并向上部发展;初步判断岩锚围岩稳定安全系数为7.0;建议岩锚体上方不宜大范围削坡扰动岩体,并采取增加框架锚索、锚杆防护等加固措施。

斜拉-悬索协作体系桥过渡区斜拉索和吊索布置形式研究

针对斜拉-悬索协作体系桥过渡区斜拉索和吊索共用梁上锚点的传统布置时易出现端吊索疲劳、边跨主梁恒活载弯矩大等问题,提出过渡区斜拉索和吊索纵向交错的新型布置形式。以某主跨1488 m的公铁两用斜拉-悬索协作体系桥为背景,分析过渡区斜拉索和吊索采用传统布置形式与新型布置形式时主梁竖向位移、斜拉索索力、吊索索力、刚度过渡匀顺性、主梁与桥塔活载弯矩等方面的差异。结果表明:新型布置形式对结构竖向刚度的影响较小,但显著改善了斜拉索和吊索的受力状态,提高了承载效率,且解决了端吊索的疲劳问题,改善了主梁的匀顺性,减小了主梁和桥塔的活载弯矩。

具有鸟翼轮廓仿生槽的动静压气体轴承静态特性分析

基于仿生学原理和几何重构法,在动静压气体轴承上设计具有鸟翼轮廓仿生槽,以提高其承载能力及刚度。运用变分法求解雷诺方程并使用FLUENT软件,对鸟翼轮廓仿生槽动静压气体轴承进行静态特性仿真分析,研究轴颈转速、供气压力、偏心率、槽深以及槽偏角对轴承静态特性的影响。结果表明:在偏心率相同时,随着轴颈转速的增加,轴承承载能力和刚度随之增大,随着供气压力的增加,轴承承载能力逐渐增加、刚度逐渐减小;当气膜厚度一定时,随着槽深的增加,轴承承载能力和刚度呈现先增加后减小的趋势,随着槽偏角的增加,轴承承载能力和刚度呈现先增加后减小的趋势。

复合地基褥垫层工作性能的混合试验研究

褥垫层是影响复合地基工作性能的关键影响因素。由于研究手段的欠缺,目前对复合地基褥垫层工作性能的认识还有待深入。采用开发的混合试验装置及数据交互系统开展混合试验,建立了褥垫层与上部加载的物理模型与桩土地基数值模型相结合的全组件参与的试验方法,大大缩减了模型试验工作量。利用该试验方法开展了3组不同褥褥垫层厚度的混合试验,分析了复合地基褥垫层的工作性能,揭示了桩土荷载传递规律、沉降规律及桩侧摩阻力的分布。随着褥垫层厚度的增加,桩间土承担的荷载以及桩土相对位移增加;当褥垫层厚度超过200mm时,桩土荷载分担比趋于稳定。

G3铜陵长江公铁大桥江北侧锚碇复合型地下连续墙设计

G3铜陵长江公铁大桥主桥为主跨988 m的斜拉-悬索协作体系桥。江北侧锚碇设计时对沉井基础和地下连续墙基础进行比选,综合考虑开挖范围、工程造价、施工工期等,最终采用基底深置的地下连续墙基础,以下伏基岩弱胶结泥质砂岩作为基础持力层,基础高49.5 m,地下连续墙墙底嵌入中等胶结泥质砂岩,地下连续墙高55.5 m。为减小锚碇基础的开挖量,采用大悬臂外挑锚块结构结合CFG桩复合地基加固技术的新型复合型地下连续墙基础,地下连续墙基础直径缩小至60 m,节省了工程造价。锚碇基础施工中基坑分层开挖,同时进行内衬砌施工。采用PLAIXS 3D软件对锚碇施工阶段及运营阶段进行有限元模拟分析,基坑开挖时地下连续墙结构受力安全,锚碇基础地基承载力、地基沉降结果均满足规范要求。

高强钢丝布对UHPC双向板弯曲性能的影响

为研究高强钢丝布(high strength steel wire cloth,SWC)及与混杂纤维的协同效应对超高性能混凝土(ultra-high performance concrete,UHPC)双向板抗弯性能的影响,本文进行了四边简支弯曲试验,设计变化参数为SWC层数和混杂纤维种类。结果表明:UHPC双向板的承载能力随层数的增加而提高;相比于铺设2、3层SWC的UHPC板,铺设1层SWC的板破坏时变形能力最好;从提高UHPC板承载能力和弯曲韧性的角度出发,与SWC协同效应最佳的短切纤维顺序依次为:钢纤维、聚甲醛纤维、玻璃纤维、聚乙烯醇纤维和玄武岩纤维。纤维体积掺量为1.5%时,全掺钢纤维的SWC板承载力最高,掺1.0%钢纤维和0.5%聚乙烯醇纤维的SWC板破坏时变形能力最好;玄武岩纤维相较其它纤维对UHPC板的增强效果最弱。