Theoretical cross-wind speed against rail vehicle derailment considering the cross-running wind of trains and the dynamic wheel-rail effects

In this paper, a theoretical formula was proposed that predicts the derailment index due to a cross wind applied to a rail vehicle considering the cross running wind condition of two running trains as well as the dynamic wheel-rail effects. The recently developed derailment theory on a wheelset was applied to this new cross wind derailment formula. Contrary to the conventional formulas, this new derailment formula was derived considering a dynamic derailment coefficient (Q/P) under normal running, the friction coefficient between the wheel and the rail, the wheel load variation, the cross running wind effects, and the cross wind. Using this proposed formula, the derailment pattern and the critical cross wind speed of derailment could be predicted for various cross running wind conditions of two running trains. Finally, for some typical examples, the results of this proposed formula were compared and verified with those of the conventional formulas and the numerical simulation of multi-body dynamics software, Recurdyn.     

Analysis of bearing lubrication under dynamic loading considering micropolar and cavitating effects

Numerical computation of the dynamically loaded journal bearings lubricated with micropolar fluids is undertaken based on the improved Elord cavitation algorithm and over-relaxation method. The results show that the average inflow and average outflow based on the mass conservation boundary conditions are almost equal, which is in accordance with the fact. However, under the Reynolds boundary conditions, large difference is shown between the average inflow and outflow. It is also demonstrated that with the micropolar fluids lubrication, the minimum film thickness, bearing capacity and friction power loss are increased while the maximum film pressure is decreased.     

A new partitioning process for geometrical product specifications and verification

In ISO Geometrical Product Specifications and Verification Standards (GPS), Feature operations are used to obtain ideal and non-ideal features. The formalization of such operations enables to reduce ambiguity and uncertainty within the activities of design, manufacture and metrology of mechanical products, and their scientific investigation contributes to develop a sound mathematical framework and formalisms for the comprehension of engineering practices and the development of new standards. Partitioning is a fundamental operation defined in ISO GPS standard which aims at decomposing a part into independent features or surface portions for further processing and analysis. In this paper, a state-of-the-art survey of partitioning and segmentation methods and techniques reported in the literature is conducted and a comprehensive classification is proposed. Thereafter, a new partitioning process is developed for partitioning into regions and recognizing each region as one of the seven invariance classes of surfaces. It proceeds in three main steps: initial partitioning based on shape index and curvedness, refined partitioning by slippage analysis and invariance class recognition by statistical evaluation. An intuitive shape color wheel is defined to visualize the partitioned features according to their corresponding invariance classes. Experiments and results on both nominal models and measured point clouds are presented to demonstrate the effectiveness of the proposed method.     

轮对踏面擦伤检测新技术

提出一种基于结构光视觉传感的轮对踏面擦伤检测新方法。通过结构光扫描轮对踏面,产生相应的变形光,利用视觉传感及图像处理等技术提取结构光变形曲线,获取轮对踏面几何信息,实现轮对踏面擦伤的在线非接触测量。     

A method of measuring acoustic absorption coefficient of a material specimen using a dynamic microphone

This paper reports the development of a method for measuring the absorption coefficient of a material specimen mounted at one end of a planar wave tube using a dynamic microphone at the other end. In the proposed method, the dynamic microphone mounted is used as an actuator (loudspeaker) to generate sound waves and simultaneously performs as a probe to sense acoustic impedance at the same point. For the electro-mechanical acoustical system formed by the dynamic microphone and the tube, a “transduction matrix” is introduced to relate the input electrical variables (voltage and current) and the output acoustical variables (pressure and particle velocity). Once the matrix is calibrated, probing the input voltage and current to the dynamic microphone alone allows quantitative evaluation of the acoustic impedance of material specimen, from which absorption coefficient of the material is calculated. Measurements of fully-reflected end, anechoic end and a porous material specimen are carried out and compared to the results obtained by the conventional transfer function method. It is found that the results match well with each other in a frequency range depending on the length of the tube.     

考虑效率时蜗杆传动作用力的新算法

蜗杆传动因效率低,在力的大小计算时应计效率;而在考虑效率时,蜗杆副力的计算式不统一,这里推导出考虑效率时力的大小计算的两套公式。     

抓斗起升动载系数的仿真分析

运用三维建模PRO／E软件、有限元ANSYS软件以及虚拟样机ADAMS软件,对抓斗的起升过程进行仿真分析,并结合起重机设计规范,对抓斗的起升动载系数进行比较和选取,得出较合理的仿真数据。     

A new model of dynamic cell formation by a neural approach

This paper proposes a nonlinear integer model of cell formation under dynamic conditions. The cell formation (CF) problem is a portion of a cellular manufacturing strategy (CMS), in which the parts and machines are clustered with the aim of minimizing the material handling cost. In most previous research the cell formation problem has always been under static conditions in which cells are formed for a single-period planning horizon where product mix and demand are constant. In contrast, in dynamic conditions, a multi-period planning horizon is considered, where the product mix and demand in each period is different. This occurs in seasonally or monthly production. As a result, the best cell design for one period may not be efficient for subsequent periods. To verify the presented model, different problems have been solved and results are reported. Where the cell formation problem belongs to NP class, the use of a novel approach is necessary. In this research, we apply a neural approach based on mean filed theory for solving the proposed model. In this approach, the network weights are updated by an interaction procedure. The proposed model is solved by LINGO software and an optimum solution is obtained. Comparison of optimum and neural approach solutions shows the efficiency of the presented neural network approach.     

考虑转速影响的机构动平衡研究

为了对机构的内部动态性能进行改善,应该进行机构的综合动力平衡.在传统研究机构动平衡问题时,均没有考虑机构的转速对动平衡参数的影响.该文通过仿真的方法,分别研究了在采用几种不同指标为优化目标时转速对平衡的影响,其结论对实际机构动平衡的优化具有参考价值.     

A dynamic substructuring-based parametric reduced-order model considering the interpolation of free-interface substructural modes

Journal of Mechanical Science and Technology - A parametric reduced-order model (PROM) was developed by using a free-interface coupling method. For dynamic substructuring, the accuracy of the...     

考虑共因失效的新型连续时间动态 贝叶斯网络可靠性分析方法

现代系统失效行为复杂,动态性与相关性并存。首先为直观准确地刻画分析系统中的动态失效行为,提出新型连续时间动态贝叶斯网络分析方法,利用节点时序条件概率表刻画事件关系,进而提出基于节点时序条件概率表规则执行度与冲激函数抽样性质的子节点故障概率、根节点后验概率及重要度的计算方法;进一步,针对共因失效引起的系统相关性失效行为,提出考虑共因失效的新型连续时间动态贝叶斯网络分析方法,解决系统失效逻辑动态性和相关性的重叠问题。通过与贝叶斯网络、离散时间动态贝叶斯网络分析方法、Markov链、Monte Carlo法对比,验证所提方法的可行性与优越性。最后,对动态失效相关系统进行可靠性分析,结果表明,本文方法能够直观有效地刻画动态性与相关性失效行为,得到准确的系统可靠性指标,考虑共因失效相比于忽略共因失效,在任务时间为5×10~6 h时能够提高系统29%的可靠性分析精度,更加符合实际。     

可变阻抗滑动轴承的动力系数计算

本文讨论了具有两个动力缓冲器的可变阻抗滑动轴承的动力学系数及其计算方法，建立了基于Ｒｅｙｎｏｌｄｓ方程和流量连续性原理的油膜压力分布理论模型，并提出了这种轴承油膜的线性动力学系数计算的压力扰动法。理论分析结果表明这种轴承可以在运行条件下有效地改变其油膜的动力特性，为这种轴承的实际应用提供了必要的理论基础。     

A study on a new method for flexoelectric coefficient estimation of the flexoelectric unimorph sensing element

In the flexoelectric sensing element using the bending mode, the estimation of the flexoelectric coefficient was investigated using 3-D stress/strain analysis and experiments. The proposed method uses the results (deformation and strain) from the finite element analysis (FEA). The estimated flexoelectric coefficients were compared with those obtained via the conventional method (Euler’s beam theory) under the assumption of the quasi 1-D stress field. The results show that the RMS value and standard deviation of the estimated flexoelectric coefficient for the 3-D stress-field case of the sensing element are 31.51 µC/m and 0.24 %, respectively. In addition, it is found that the flexoelectric coefficient obtained from the results of the 3-D stress analysis is 1.8 % smaller than that of the quasi-1-D stress analysis. Therefore, in order to obtain a more reliable flexoelectric coefficient in the sensing element, the results of the 3-D numerical stress analysis should be used for accurate estimation of the flexoelectric coefficient.

     

塔式起重机动力系数的计算与分析

应用有限元法,以ＴＱ１－６塔式起重机为例,通过结构分析计算,掌握了塔机的动态特性,为塔机动力系数的简化计算提供了理论依据,并导出了简化计算公式。     

Study on the dynamic model and simulation of a flexible mechanical arm considering its random parameters

Randomness exists in engineering Tolerance, assemble-error, environment temperature and wear make the parameters of a mechanical system uncertain So the behavior or response of the mechanical system is uncertain In this paper, the uncertain parameters are treated as random variables So if the probability distribution of a random parameter is known, the simulation of mechanical multibody dynamics can be made by Monte-Carlo method Thus multibody dynamics simulation results can be obtained in statistics A new concept called functional reliability is put forward in this paper, which can be defined as the probability of the dynamic parameters (such as position, orientation, velocity, acceleration etc) of the key parts of a mechanical multibody system belong to their tolerance values A flexible mechanical arm with random parameters is studied in this paper The length, width, thickness and density of the flexible arm are treated as random variables and Gaussian distribution is used with given mean and variance Computer code is developed based on the dynamic model and Monte-Carlo method to simulate the dynamic behavior of the flexible arm At the same time the end effector’s locating reliability is calculated with cncular tolerance area The theory and method presented in this paper are applicable on the dynamics modeling of general multibody systems     

渐开线齿轮单齿啮合区的齿形系数

本文对范成法加工的渐开线圆柱齿轮，在单对齿啮合受载时，按轮齿危险截面形状（分平截面法和折截面法）、加工方法（分齿条刀类和插齿刀类），给出四组齿形系数的计算式。此式既可计算标准（或非标准）齿轮齿顶受载时的齿形系数，又可计算标准（或非标准）齿轮齿廓任意点受载时的齿形系数，还可计算具有非标准齿廓参数的渐开线齿轮任意点受载的齿形系数，为精确计算轮齿齿根弯曲强度提供了依据。     

A new model in rail-vehicles dynamics considering nonlinear suspension components behavior

In this paper, a complete four axle rail vehicle model is addressed with 70 degrees of freedom (DOFs) including a carbody, two bogies, and four axels. In order to include the effects of the track irregularities in vehicle dynamics behavior, a simplified track model is proposed and it is validated by some experimental data and test results. As the performance of the suspension components, especially for air springs, have significant effects on rail-vehicle dynamics and ride comfort of passengers, a complete nonlinear thermo-dynamical air spring model, which is a combination of two different models, is introduced and implemented in the complete rail-vehicle dynamics. By implementing Presthus formulation [Derivation of air spring model parameters for train simulation. Master dissertation, Department of Applied Physics and Mechanical Engineering, Division of Fluid Mechanics, LULEA University, 2002], the thermo-dynamical parameters of air spring are estimated and then they are tuned based on the experimental data. The results of the complete rail-vehicle field tests, show remarkable agreement between proposed model and test data.     

Study on stress states of a wheelset axle due to a defective wheel

High magnitude impact loads caused by a defective wheel may excite various vibration modes of the wheelset, and contribute to adversely increases in the stress states of wheelset axle in high-speed conditions. In this study, the wheelset is treated as a flexible body using the finite element method, then integrated to a multi-body dynamic model of a high-speed train coupled with a flexible track slab model. Through this model the effects of wheel defects considering wheel flats and wheel polygonalizations on the stress states of wheelset axle are evaluated in terms of bending stresses of the wheelset axle. The damage tolerances of the wheelset axle are subsequently predicted using the NASGRO algorithm. The results suggest that the impact forces caused by wheel flats and wheel polygonalizations at the wheel-rail interfaces can result in the resonance vibrations of a wheelset and give rise to severe variations in dynamic stresses of the wheelset axle. The wheel defects-induced stress load cycles considerably contribute to the propagations of the initial crack in the wheelset axle, especially for the wheel polygonalization.     

A new optical measurement system for determining the geometrical errors of rotary axis of a 5-axis miniaturized machine tool

Machine tools have greatly improved in recent decades. Among them, miniaturized machine tools (mMTs) that have advantages in terms of reduced energy consumption, space requirements, costs, and other resources are becoming more and more popular in the area of micro scale parts manufacturing. However it is exceedingly difficult to calibrate an mMT due to its small size. This paper proposes a novel method for identifying the geometrical errors of a rotary axis of miniaturized 5-axis machine tools using two position sensitive detectors (PSDs) and a laser diode. This work not only reduces the complication of the system structure and setup but also solves the problem of assembly. We propose a method to determine errors based on the geometrical position of PSDs, laser beam path, and its readout signals after each angle of rotation. The homogenous transformation approach is used to find the individual error components. A system sensitivity analysis is also presented in this paper.