钢轨横向不均匀支撑刚度对钢轨波磨的影响

建立了钢轨波浪形磨损计算模型,模型中考虑车辆轨道垂向横向耦合动力学行为、轮轨三 维滚动接触力学行为和轮轨材料摩擦磨损的循环相互作用关系. 发展了相应的计算程序,并 用1: 1试验装置验证了理论模型. 详细分析了实际线路上由轨枕离散支撑导致的钢轨横向不均匀刚度和不同行车速度对曲线钢轨接触表面不均匀磨损的影响. 通过数值分析可知： (1)列车通过曲线钢轨时,轨枕离散支撑导致的钢轨横向不均匀刚度易引发曲线钢轨波磨的形 成和发展;(2)这类钢轨波磨具有与轨枕间距几乎相等的波长和28~35mm的短波长,这个短波长不均匀磨损主要是由轮轨高频接触振动引起;(3)同一个转向 架4个车轮作用下形成的钢轨波磨最大深度波谷的分布是不同的;(4) 改变过车速度不能有效地抑制轨枕离散支撑导致的钢轨波磨形成和发展速度.     

Effect of a scratch on curved rail on initiation and evolution of plastic deformation induced rail corrugation

A calculation model is put forward to analyze the effect of a scratch on the running surface of a curved rail on initiation and growth of plastic deformation induced rail corrugation when a wheelset is steadily and repeatedly curving. The numerical method considers a combination of Carter’s two-dimensional contact theory, a two-dimensional elastic–plastic finite element model and a vertical dynamics model of railway vehicle coupled with a curved track. A concept of feedback between the corrugation development and the vertical coupling dynamics of the wheelset and track is involved. The cyclic ratchetting effect of the rail material under repeated contact loadings is taken into account. The numerical results indicate that when a vehicle runs on rails with a scratch the contact vibration between the wheel and rail occurs at large amplitude, and rail corrugation due to plastic deformation initiates and develops. The corrugation has a tendency to move along the running direction and its evolution rate decays as wheelset passages increase. The passing frequencies of the plastic deformation induced corrugation depend on the natural frequencies of the track. The residual stresses stabilize after a limited number of wheelset passages. The residual strains increase at a reduced rate with increasing wheelset passages.     

Subsurface initiated rolling contact fatigue of railway wheels as generated by rail corrugation

A fracture mechanics based fatigue index for rolling contact fatigue (RCF) initiated at deep (10–25 mm) defects is derived and employed together with a fatigue index for more shallow (4–10 mm) subsurface RCF initiation. Integrated simulations of high-frequency dynamic train–track interaction and prediction of RCF impact are then carried out to evaluate the influence of short-pitch rail corrugation on RCF of railway wheels. Parametric studies are carried out to identify operational conditions likely to generate high RCF impact. Simulation results show how rail corrugation causes a major increase in RCF impact at high-speed operations and that corrugation magnitudes measured in-field are sufficient to generate subsurface initiated RCF. At high speeds the main cause for increased fatigue impact is the increase in dynamic load magnitudes. At lower speeds and higher axle loads also the effect of poor contact geometry will have an influence.     

Effect of rail corrugation on vertical dynamics of railway vehicle coupled with a track

The effect of rail corrugation on the vertical dynamics of railway vehicle coupled with a curved track is investigated in detail with a numerical method when a wheelset is steadily curving. In the calculation of rail corrugation we consider the combination of Kalker‘s rolling contact theory modified, a model of material loss on rail running surface, and a dynamics model of railway vehicle coupled with a curved track. In the establishment of the dynamic model, for simplicity, one fourth of the freight car without lateral motions,namely a wheelset and the equivalent one fourth freight car body above it, is considered. The Euler beam is used to model the rails and the track structure under the rails is replaced with equivalent springs, dampers and mass bodies. The numerical results show the great influence of the rail corrugation on the vibration of the parts of the vehicle and the track, and the some characters of rail corrugation in development.     

Effects of corrugation angle on developing laminar forced convection and entropy generation in a wavy channel

This paper investigates the effects of corrugation angle (β) on the developing laminar forced convection and entropy generation in a wavy channel with numerical methods. The studied cases cover β = 10-, 15-, 20-, 25-, 30- and 35°, whilst Reynolds number (Re) is varied as 100, 200 and 400. The analyzed flow characteristics include recirculating flows, secondary vortices, temperature distributions, and friction factor as well as Nusselt number. In particular, the effects of corrugation angle on the distributions and magnitudes of local entropy generation resulted from frictional irreversibility (S _P ^′′′) and heat transfer irreversibility (S _T ^′′′) are separately discussed in detail in the present paper. Based on the minimal entropy generation principle, the optimal corrugation angle and favorable Re are reported.     

聚乙烯泡沫单填充纸瓦楞管的轴向跌落冲击缓冲吸能特性

利用聚乙烯闭孔泡沫单填充纸瓦楞管开展轴向跌落冲击试验,对比分析了结构参数和冲击参数对其缓冲吸能特性参数（比吸能、行程利用率、压缩力效率、比总体效率）的影响。结果表明,X向单填充管的动态缓冲吸能特性优于Y向单填充管,而静态缓冲吸能特性差于Y向单填充管。正四边形单填充管的动态缓冲吸能特性优于正五、六边形单填充管,X向正四边形单填充管的比吸能相较于正五、六边形管分别提高了114.4%和182.3%。对于跌落冲击压缩,单填充管的比吸能、行程利用率、比总体效率随着管长比的增大而减小,管长比为1.4的X向单填充管的比吸能相较于管长比为2.2和3.0的单填充管分别增加了45.8%和117.9%,而压缩力效率随着管长比的增大而增大。随着跌落冲击质量或冲击能量的增加,比吸能、行程利用率、压缩力效率和比总体效率皆呈增大趋势,冲击质量对X向单填充管的影响较大,而冲击速度则对Y向单填充管的影响较大。

     

On the two-phase Stefan problem with interfacial energy and entropy

Archive for Rational Mechanics and Analysis -     

Structural damage detection using convolutional neural networks combining strain energy and dynamic response

Meccanica - Based on the classification ability of a convolutional neural network (CNN), this paper proposes a structural damage detection method in which a CNN is used to classify the location and...     

Towards entropy detection of anomalous mass and momentum exchange in incompressible fluid flow

An entropy‐based approach is presented for assessment of computational accuracy in incompressible flow problems. It is shown that computational entropy can serve as an effective parameter in detecting erroneous or anomalous predictions of mass and momentum transport in the flow field. In the present paper, the fluid flow equations and second law of thermodynamics are discretized by a Galerkin finite‐element method with linear, isoparametric triangular elements. It is shown that a weighted entropy residual is closely related to truncation error; this relationship is examined in an application problem involving incompressible flow through a converging channel. In particular, regions exhibiting anomalous flow behaviour, such as under‐predicted velocities, appear together with analogous trends in the weighted entropy residual. It is anticipated that entropy‐based error detection can provide important steps towards improved accuracy in computational fluid flow. Copyright © 2002 John Wiley & Sons, Ltd.     

谐波型波磨激扰下轮轨系统接触蠕滑特性

将钢轨波浪形磨耗理想化为三种波长和波深组合的连续谐波激扰,通过多体动力学软件UM,分析不同波长和波深工况下谐波激扰对轮轨接触蠕滑特性的影响。研究表明,当波长固定、波深增大时,钢轨轮对垂向振动加速度和纵向蠕滑率/力的平均值均增大,横向蠕滑率/力平均值均减小。当波深固定、波长增大时,钢轨轮对垂向振动加速度平均值和纵向蠕滑率/力平均值均减小,横向蠕滑率/力平均值均增大。纵横向蠕滑率/力均含有与初始不平顺频率值相接近的特征频率成分,纵向蠕滑率/力特征频率随着波深的增大趋向高频段发展,横向蠕滑率/力特征频率集中在低频段,且随着波深增大逐渐减小。当波深为0.3 mm时,纵横向蠕滑率/力强度相当,能量主要集中在低频,频率比较单一;当波深达到0.6 mm和0.9 mm时,蠕滑率/力以纵向蠕滑率/力为主,表现出多频率特征。在波长相同的条件下,随着运营时间的增加,磨耗量在低频段增加较小,在中高频段增加较大。     

Weighted dynamic transfer network and spectral entropy for weak nonlinear time series detection

Nonlinear Dynamics - This work proposes a novel method to construct weighted dynamic transfer network to map time series to complex networks. Firstly, we map time series into symbolic series by...     

Thermodynamical properties of triangular quantum wires: entropy,specific heat,and internal energy

In the present work, thermodynamical properties of a GaAs quantum wire with equilateral triangle cross section are studied. First, the energy levels of the system are obtained by solving the Schrödinger equation. Second, the Tsallis formalism is applied to obtain entropy, internal energy, and specific heat of the system. We have found that the specific heat and entropy have certain physically meaningful values, which mean thermodynamic properties cannot take any continuous value, unlike classical thermodynamics in which they are considered as continuous quantities. Maximum of entropy increases with increasing the wire size. The specific heat is zero at special temperatures. Specific heat decreases with increasing temperature. There are several peaks in specific heat, and these are dependent on quantum wire size.     

Detecting asynchrony of two series using multiscale cross-trend sample entropy

Nonlinear Dynamics - We develop a new cross-sample entropy, namely the multiscale cross-trend sample entropy (MCTSE), to investigate the synchronism of dynamical structure regarding two series with...     

Complexity analysis of the time series using inverse dispersion entropy

Nonlinear Dynamics - The primary object of this study is to measure the complexity of different types of signals. We undertake the experiment to support the hypothesis of inverse dispersion entropy...     

Numerical investigation of BB-AMR scheme using entropy production as refinement criterion

In this work, a parallel finite volume scheme on unstructured meshes is applied to fluid flow for multidimensional hyperbolic system of conservation laws. It is based on a block-based adaptive mesh refinement strategy which allows quick meshing and easy parallelisation. As a continuation and as an extension of a previous work, the useful numerical density of entropy production is used as mesh refinement criterion combined with a local time-stepping method to preserve the computational time. Then, we numerically investigate its efficiency through several test cases with a confrontation with exact solution or experimental data.     

A two stage method for structural damage detection using a modal strain energy based index and particle swarm optimization

A two-stage method is proposed here to properly identify the site and extent of multiple damage cases in structural systems. In the first stage, a modal strain energy based index (MSEBI) is presented to precisely locate the eventual damage of a structure. The modal strain energy is calculated using the modal analysis information extracted from a finite element modeling. In the second stage, the extent of actual damage is determined via a particle swarm optimization (PSO) using the first stage results. Two illustrative test examples are considered to assess the performance of the proposed method. Numerical results indicate that the combination of MSEBI and PSO can provide a reliable tool to accurately identify the multiple structural damage.