初创型企业股票期权的激励机制研究

高新技术创业型企业建立适应市场规律的有效激励机制是提高人才资本增值效应、完善公司治理结构的重要问题。本通过对股票期权的激励特点和初创型企业管理模式的分析，提出了关于初创型企业的股票期权计划的思路和对策。     

规则迎浪中船舶参数横摇的三维时域预报方法研究

参数横摇是船舶因复原特性改变而引起的典型非线性现象。文章采用三维时域方法预报规则迎浪中船舶的参数横摇运动。该方法引入匹配面将流域分为内域和外域,内域中采用Rankine源来满足物面条件和线性自由面条件,而外域中应用时域格林函数来满足线性自由面条件和远场辐射条件。数值方法中,Froude-Krylov力和恢复力是通过对船舶瞬时湿表面积积分获得,同时考虑了横摇、垂荡和纵摇三自由度之间的耦合作用,以及非线性横摇阻尼的影响。数值结果与试验结果吻合很好,说明该方法可以有效地预报参数横摇。     

A survey of wheel–rail contact models for rail vehicles

Accurate and efficient contact models for wheel–rail interaction are essential for the study of the dynamic behaviour of a railway vehicle. Assessment of the contact forces and moments, as well as contact geometry provide a fundamental foundation for such tasks as design of braking and traction control systems, prediction of wheel and rail wear, and evaluation of ride safety and comfort. This paper discusses the evolution and the current state of the theories for solving the wheel–rail contact problem for rolling stock. The well-known theories for modelling both normal contact (Hertzian and non-Hertzian) and tangential contact (Kalker's linear theory, FASTSIM, CONTACT, Polach's theory, etc.) are reviewed. The paper discusses the simplifying assumptions for developing these models and compares their functionality. The experimental studies for evaluation of contact models are also reviewed. This paper concludes with discussing open areas in contact mechanics that require further research for developing better models to represent the wheel–rail interaction.     

Influence of wheel and rail profile shape on the initiation of rolling contact fatigue cracks at high axle loads

The influence of wheel and rail profile shape features on the initiation of rolling contact fatigue (RCF) cracks is evaluated based on the results of multi-body vehicle dynamics simulations. The damage index and surface fatigue index are used as two damage parameters to assess the influence of the different features. The damage parameters showed good agreement to one another and to in-field observations. The wheel and rail profile shape features showed a correlation to the predicted RCF damage. The RCF damage proved to be most sensitive to the position of hollow wear and thus bogie tracking. RCF initiation and crack growth can be reduced by eliminating unwanted shape features through maintenance and design and by improving bogie tracking.     

A theoretical model of speed-dependent steering torque for rolling tyres

ABSTRACT

It is well known that the tyre steering torque is highly dependent on the tyre rolling speed. In limited cases, i.e. parking manoeuvre, the steering torque approaches the maximum. With the increasing tyre speed, the steering torque decreased rapidly. Accurate modelling of the speed-dependent behaviour for the tyre steering torque is a key factor to calibrate the electric power steering (EPS) system and tune the handling performance of vehicles. However, no satisfactory theoretical model can be found in the existing literature to explain this phenomenon. This paper proposes a new theoretical framework to model this important tyre behaviour, which includes three key factors: (1) tyre three-dimensional transient rolling kinematics with turn-slip; (2) dynamical force and moment generation; and (3) the mixed Lagrange–Euler method for contact deformation solving. A nonlinear finite-element code has been developed to implement the proposed approach. It can be found that the main mechanism for the speed-dependent steering torque is due to turn-slip-related kinematics. This paper provides a theory to explain the complex mechanism of the tyre steering torque generation, which helps to understand the speed-dependent tyre steering torque, tyre road feeling and EPS calibration.     

Survey of programs on contact mechanics developed by J.J. Kalker

In his extensive career, Joost Kalker worked on many contact phenomena. For this, he developed various theories, which were accompanied by algorithms and computer programs. Most notably, these are the FASTSIM algorithm for quickly evaluating the nonlinear creep-force law in vehicle dynamic simulations, the CONTACT program for the exact theory of rolling contact in 3D elastic halfspaces, and the USETAB program that uses a large table calculated with CONTACT, in order to improve over the FASTSIM algorithm in speed, accuracy and versatility as well.     

改善小型高速艇总体性能的措施研究

结合某项产品的设计论证和船模试验,对小型高速艇的总体性能进行了研究,提出了减小船体阻力、改善耐波性和减小船体振动的若干措施。     

冲击碾压法处理湿陷性黄土路基的施工技术

黄土地区的湿陷性黄土路基常因处治不当而发生变形沉陷.陕西省禹阎高速公路某标段湿陷性黄土路段处理的施工实践,收到了良好的效果.     

轨道车辆三电平中点自平衡电路拓扑研究

在有轨电车超级电容供电系统中,作为充电装置的三电平直流变换器中储能电容存在有均压以及中点平衡问题,中点不平衡将导致装置的工作异常,严重的将引起直流变换器的损坏.对此,传统方法一般是通过电路拓扑结构及控制策略调节电力电子器件开关管占空比来解决.通过分析传统充电装置中三电平中点电位不平衡的原因,针对超级电容型轨道车辆充电系...