Numerical Analysis of Frictional Heat-Stress Coupled Field at Dynamic Contact

A new analysis method was developed to simulate the dynamic process of a frictional heatstress coupled field. The relationship between the frictional heat and the thermal stress was investigated for concave cylinder contact conditions. The results show that, as a nonlinear contact problem, the frictional heat at the contact areas changes with moving velocity in both value and distribution, and that the transient frictional heat at the dynamic condition has a peak within a cycle. The dynamic process of friction heat and thermal stresses affects diffusion of the frictional effects. The result can be helpful for dynamic simulation of diffusion lubrication of elements at elevated temperatures.     

Stability of stratified flow and slugging in horizontal gas-liquid flow

A transient one-dimensional two-fluid model is proposed to investigate numerically the interfacial instability and the onset of slugging for liquid-gas flow in a horizontal duct. In the present model, the effects of surface tension and transverse variations in dynamic pressure are taken into account. The evolution of interfacial disturbances is displayed and compared with the linear viscous Kelvin-Helmholtz stability analyses. It shows that interfacial wave is more instable due to the non-linear effect. The model predicts well the stability limit of stratified flow in comparison with the experimental data, and also automatically tracks the onset of slugging. The results show that the initiation of hydrodynamic slugging is related to local interfacial instability. Based on the cycle of slugging, a model for slug frequency is presented, which predicts the trends of slug frequencies with gas/liquid flow rate well in comparison with the available data. The effects of physical properties on slugging have been examined. It is found that with the increase in the gas viscosity and liquid density the slugging would be inhibited, whereas, with the increase in liquid viscosity and gas density, the slugging can be promoted.     

Pressure Field of Multi-pad Annular Recess Hydrostatic Thrust Bearing

In order to solve the deformation of the hydrostatic thrust bearing with multi-pad annular recess in the heavy computer numerical control(CNC)equipment,the simulation concerning pressure field of hydrostatic thrust bearing with multi-pad annular recesses was carried out.The finite volume method of computational fluid dynamics(CFD)was used to compute the three-dimensional pressure field of gap fluid between the rotary worktable and the base.The influence of the rotational speed on the bearing pressure performance was studied based on CFD and lubrication theory,and the method revealed the pressure distribution law.The results qualitatively agree well with the experimental data.The results indicate that the oil cavity pressure decreases gradually with rotational speed enhancing.The reliability of a hydrostatic thrust bearing with multi-pad annular recess can be predicted through this method,and the optimal design of such products can be achieved,and the numerical simulation method can provide reasonable data for design,lubrication,experiment,and deformation computation of hydrostatic thrust bearing in the heavy CNC equipment.     

Verification of Concurrent Assembly Programs with a Petri Net Based Safety Policy

Concurrent programs written in a machine level language are being used in many areas but verifi- cation of such programs brings new challenges to the programming language community. Most of the stud- ies in the literature on verifying the safety properties of concurrent programs are for high-level languages, specifications, or calculi. Therefore, more studies are needed on concurrency verification for machine level language programs. This paper describes a framework of a Petri net based safety policy for the verification of concurrent assembly programs, to exploit the capability of Petri nets in concurrency modeling. The con- currency safety properties can be considered separately using the net structure and by mixing Hoare logic and computational tree logic. Therefore, more useful higher-level safety properties can be specified and verified.     

A modified model for dynamic properties of visual receptive field

The extended Gabor function model for visual receptive field ( RF) was modified by substituting the term related to time with two-order integral kernel of F function to generate a new model called modified Gabor function model of RF. A set of the modified Gabor models (MGM) can present the major spatiotemporal properties of neuronal receplive fields at different levels of primary visual pathway. The transient responses, dynamic properties of RF simulated by MGM, are in good agreement with the observations in electrophysiological experiments.     

Effects of Dimensional Tolerances on the Friction Power Loss of Hydrodynamic Journal Bearing System

According to the dimensional tolerances on hydrodynamic journal bearing system, a nonlinear oil film force model was established,and the Reynolds＇ equation was solved by adopting finite difference method. In order to fulfill different dimensional tolerances in the system,adopting 2kfactor design and using the eccentricity ratio corresponding to the stability critical curve,the effects of the friction power loss brought by the dimensional tolerances of the dynamic viscosity,bearing width,bearing diameter and journal diameter were analyzed. The effect on dynamic characteristics of the hydrodynamic journal bearing system was quantitatively analyzed,and the nonlinear dynamic analysis, modeling and calculation methods were studied while considering the manufacturing tolerances. The results show that in contrast to the impacts of the tolerances in journal diameter,dynamic viscosity and bearing width,the bearing diameter tolerance would lead to the rise in the power loss, and the dimensional tolerances have different degrees of impacts on the journal bearing system. The friction power loss decreased as the eccentricity ratio increased, and when the eccentricity ratio was 0. 695 the power loss came to the minimum.The investigation would find the best solution and reduce energy consumption,then control varieties of nonlinear dynamical behavior effectively,and provide a theoretical basis for hydrodynamic journal bearing system in parameter design.     

The formation depth of coesitebearing eclogite, Dabie UHPM zone, China, modified by tectonooriginal additional hydrostatic pressure

The knowledge that hydrostatic pressure is equal to the gravity value of the overlying rocks in studying a dynamic state of certain underground site is argued. It is suggested that the stress field T in the crust is a combination or superposition of total hydrostatic pressure P with differential stress σ , and the total hydrostatic pressure P at any point in the crust comprises two parts: one is spherical stress tensor PG caused by the gravity, and the other is spherical stress tensor Ps caused by tectonic stress; therefore P could not be attributed to the gravity of overlying rocks only. The results obtained by a finite-element simulation indicate that the tectono-original additional hydrostatic pressures Ps decrease gradually from the compressive zone (Pcs) to the shear zone (PSHs) and to the tensile zone (PTs), i. e. PCS>PSHs> PTs in the same depth. On the basis of the above-mentioned research, the method of measurement and calculation of metal logenetic depth corrected by Ps is established, i.e. first tectonic additional hydrostatic pressure Ps is removed from general hydrostatic pressure P to get PG, gravity additional pressure, then accordingly the depth data are measured and calculated. The plastic deformation of garnet in coesite-bearing eclogite, quartz eclogite and garnet amphibo-lite of the ultrahigh-pressure metamorphic (UHPM) complex in the Yingshan County in Dabie Mt. is studied by the transmission electron microscope (TEM). It is shown that the garnets have ductile deformation in the metamorphic condition of eclogite and amphibolite facies. Microstructures of the garnet vary greatly among coesite-bearing eclogite, quartz eclogite and garnet amphibolite. The tectonic principal stress in three-dimensional space and the tectonic additional hydrostatic pressure are reconstructed by differential stress and strain ratio (α) of garnet in minor coesite-bearing eclogite, then the gravity and thickness of overlying rocks are determined. The formation depth of ≥ 32.09-32.106 km of the coesite-bearing eclogite in Yingshan County in the Dabie UHPM zone is obtained from difference PG which comes from P minus Ps, Ps = (σ1 + σ2 + σ3) /3. The value of P is 2.8 GPa resulting from Qz-coes geobarmeter. This result is at all different from other researchers' conclusion that the formation depth of eclogite in Dabie UHPM zone is ≥100 km by the method of weight/ special weight (W/SW). The strong tectionic action makes a great contribution to the formation of e-clogite in the Dabie UHPM zone at so shallow depth of about 32 km, therefore it is thought that attention should be paid to the tectonc-original additional hydrostatic pressure in the study on UHPM zone.     

Simulation and experimental study on lubrication characteristics of vertical hydrostatic guide rails

In order to improve the cutting stiffness,the paper studies the vertical hydrostatic bearing in the slide when a ram is in feed process.The change of the oil film thickness on hydrostatic guide rail and the curve of the oil film thickness in various cutting forces are calculated and a relation model through theoretical analysis method is derived.The pressure field of the guide rail recess is simulated based on the finite volume method and demonstrated through experiments.The study is of vital theoretical significance for the improvement of machining accuracy of numerical control machines and the entire computer numerical control （CNC） equipment and provides valuable theoretical basis for the design of hydrostatic guide rail in engineering practice.     

Dynamic Analysis of Cable Roofs Under Transient Wind:A Comparison Between Time Domain and Frequency Domain Approaches

At present, high-speed computing capabilities and advanced nonlinear dynamic finite element procedures enable detailed dynamic analysis of cable structures. Although deterministic approaches require considerable analysis time and effort in relation to modeling, running, and data processing, they seem to be the only alternative to obtain high accuracy. Detailed dynamic analysis of cable roof networks is sophisticated and requires advanced modeling expertise. This paper presents a comparison between detailed nonlinear dynamic analysis and a simplified frequency domain approach to estimate the maximum probable response of weakly nonlinear cable roofs. The approach can be considered as alternative to detailed time-domain analysis in the preliminary design phase, or can be used to validate results obtained from more elaborated numerical models. The proposed method is illustrated with two examples of cable net roofs that were also analysed in the time domain.     

Aerodynamic problems of cable stayed bridges spanning over one thousand meters

The elongating of cable-stayed bridge brings a series of aerodynamic problems. First of all,geometric nonlinear effect of extreme long cable is much more significant for cable-stayed bridge spanning over one thousand meters. Lateral static wind load will generate additional displacement of long cables,which causes the decrease of supporting rigidity of the whole bridge and the change of dynamic properties. Wind load,being the controlling load in the design of cable-stayed bridge,is a critical problem and needs to be solved. Meanwhile,research on suitable system between pylon and deck indicates fixed-fixed connection system is an effective way for improvement performance of cable-stayed bridges under longitudinal wind load. In order to obtain aerodynamic parameters of cable-stayed bridge spanning over one thousand meters,identification method for flutter derivatives of full bridge aero-elastic model is developed in this paper. Furthermore,vortex induced vibration and Reynolds number effect are detailed discussed.     

静压轴承自控系统的动态特性

为提高精密机床主轴回转精度 ,并进一步为主轴系统动态特性的改善及其优化设计提供理论依据 ,提出了带节流器的静压轴承自控系统动态品质的分析方法。通过对主轴力平衡条件和液体流量连续性方程的分析 ,推导出系统的非线性微分方程组 ,经 Taylor和 L aplace变换后 ,建立了系统的数学模型。通过对其传递函数的描述和动特性计算 ,得出了在外载荷变化情况下系统的过渡过程曲线和对数相频、幅频特性图像 (Bode图 )。利用自控系统稳定性理论对计算结果进行了综合分析 ,评定了静压轴承自控系统的动态品质     

Simulation and experiment of starting transient flow field of the hydrostatic bearing based on dynamic mesh method

A new method is developed to assess and analyze the dynamic performance of hydrostatic bear-ing oil film by using an amulets-layer dynamic mesh technique.It is implemented using C Language to compile the UDF program of a single oil film of the hydrostatic bearing.The effects of key lubrica-tion parameters of the hydrostatic bearing are evaluated and analyzed under various working condi-tions, i.e.under no-load, a load of 40t, a full load of 160t, and the rotation speed of 1r/min, 2r/min, 4r/min, 8r/min, 16r/min, 32r/min.The transient data of oil film bearing capacity under different load and rotation speed are acquired for a total of 18 working conditions during the oil film thickness changing.It allows the effective prediction of dynamic performance of large size hydrostatic bearing.Experiments on hydrostatic bearing oil film have been performed and the results were used to define the boundary conditions for the numerical simulations and validate the developed numerical model.The results showed that the oil film thickness became thinner with the increase of the operat-ing time of the hydrostatic bearing, both the oil film rigidity and the oil cavity pressure increased sig-nificantly, and the increase of the bearing capacity was inversely proportional to the cube of the change of the film thickness.Meanwhile, the effect of the load condition on carrying capacity of large size static bearing was more important than the speed condition.The error between the simula-tion value and the experimental value was 4 .25%.     

嵌入控制油腔的静压滑动轴承可控性研究

针对主动控制静压轴承转子运动的可控性和稳定性有待提高的问题,提出了一种在传统静压轴承的油腔内嵌入控制油腔的轴承结构,并采用主动单面薄膜节流器对其供油,充分利用轴承内部的二次节流,以此提高静压轴承的主动控制性能.基于雷诺润滑方程和流量守恒方程,采用有限差分法和欧拉迭代法建立了静压主轴的轴心运动计算模型,研究了不同轴承结构和进油压力下轴承的动态特性和控制特性.结果表明:当控制腔面积占比在30%,封油边宽度为5 mm时,静压轴承同时具有良好的动态特性和控制特性.通过合适的结构设计,嵌入控制油腔的轴承结构可以提高静压主轴轴心运动的可控性.      

考虑轴承热效应的转子非线性运动瞬态分析

研究了油膜热效应对滑动轴承非线性动力学特性的影响。给出了考虑油膜热效应的滑动轴承非线性油膜力的计算方法，用热量平衡法确定油膜平均温度，并把平均温度引入等温情况下的轴承非线性运动瞬态分析中，以实际轴承为例，对考虑热效应的转子－轴承系统的非线性不平衡响应进行了瞬态分析，得到了轴心运动轨迹，并与等温情况瞬态分析的计算结果进行了对比，通过一系列对比研究发现，轴承热效应对轴承的非线性动力学性能有重要影响，引入平均温度后可以减小不考虑热效应所引起的误差。     

液体静压支承动态性能表达式与应用

液体静压支承具有许多优良性能 :高运动精度 ,低摩擦功耗 ,小轴芯偏移 ,大承载能力 ,强抗震能力与长使用寿命等。但这些好的静态性能必须在优良的支承系统动态性能条件下才能充分显示出来。因此支承静态性能保证运动精度而动态性能保证工作条件。根据力学平衡与流量连续条件建立支承系统传递函数 ,导出支承系统动态性能表达式即系统稳定性、动刚度、固有频率、最大振幅与系统抗瞬态干扰能力的新表达式。通过实验验证 ,新动态性能表达式计算结果可靠 ,而且物理概念清晰 ,故可用于实际工作。     

静压支承动静特性及运动误差研究进展

目前对静压支承动静态特性的研究依赖于所采用的节流器形式和结构形式,主要集中在静压轴承(径向轴承和推力轴承)的油腔形状、轴承结构、轴承表面粗糙度、润滑介质和轴承弹性变形的影响,对于静压支承热效应的影响及静压导轨动静特性的研究涉及较少。对静压支承运动误差的研究大都是从运动件静力平衡出发,未考虑运动速度和结构变形对运动误差的影响。最后,从静压支承的标准化、模块化和产业化研究,静压支承的热效应研究,静压导轨的动静特性研究以及服役态下静压支承运动误差研究等方面提出研究展望。     

非线性动力系统周期解的反解型预测追踪算法

提出一种对非线性动力系统周期解进行预测追踪的新型算法,它利用系统周期解的稳态及瞬态信息,反解雅可比矩阵,实现对系统周期解的预测追踪。同时利用反解得出的雅可比矩阵,还可以得出系统周期解的Ｆｌｏｑｕｅｔ乘子,差别其非线性稳定性,与现有的此类算法相比,新算法在实施时,所需要的信息均可通过对系统周期解的未扰及受扰运动的观测获得,因而具有广泛的适应性。     

基于ANSYS Workbench的五自由度转向器整车模拟试验台液体静压轴承模态分析

利用ANSYS Workbench对五自由度转向器整车模拟试验台液体静压轴承进行有限元模态分析,得到液体静压轴承的前六阶固有频率及动态特性,在液体静压轴承结构设计中避免共振和辐射噪声,为五自由度转向器整车模拟试验台的研制提供参考和依据。     

滚柱轴承离合器的动力特性分析

滚柱轴承离合器是一种高性能离合器，它同时兼有离合器和轴承的功能。离合器的动态特性对整个系统有着和很大的影响。利用接触力学和振动力学理论对滚柱轴承离合器的动力特性进行了分析。给出了滚子沿接触线受力的载荷分布，通过分析表明，滚柱轴承的离合器的扭转刚度是非线性的，说明系统具有丰富的非线性动力学现象。     

滚动轴承系统摩擦振动的非线性研究

针对滚动轴承摩擦振动系统,建立了在非线性摩擦力作用下的耦合动力学方程,并运用Runge-Kutta-Felhberg算法进行求解,着重分析了摩擦润滑和结构参数对滚动轴承系统运动特性的影响.研究表明,非线性摩擦力对滚动轴承的周期运动有明显的抑制作用,可以通过调整摩擦润滑主要参数来改善系统的动态稳定性,为滚动轴承的理论设计...