基于恢复系数的碰撞过程模型分析

论述了恢复系数的含义及作用,并在此基础上介绍了几种碰撞过程模型.通过详细推导恢复系数与模型参数之间的关系,使得不同的碰撞过程模型可统一用恢复系数表示能量损失,并用接触刚度表示变形.这也阐明了碰撞过程模型与刚性模型之间的区别和联系,把动态接触理论和古典碰撞理论统一了起来.通过对一个单球碰撞系统进行数值仿真,不仅验证了关系推导的正确性,而且对各种模型从精度、效率、微观接触过程等方面进行了比较.     

化工厂弹性定量评价方法

化学过程工业中安全是首要因素.传统的安全评价方法仅揭示化工厂当前的风险程度和安全水平,为了反映化工厂面临内外部变更时避免事故和减少事故损失的能力,提出了化工厂弹性指数.在应用层次分析法和模糊综合评价法分析化工厂的危险容忍能力的基础上,结合本质安全指数,给出了弹性指数的计算方法.案例研究表明,弹性指数能反映化工厂弹性的大小,可以协助管理人员在生产和安全问做出正确决策,在确保安全的同时尽可能追求高产高效.     

关于液滴撞击弹性固体变形预测仿真

在液滴撞击弹性固体问题中,由于流固两相的动力学特性复杂且传统网格法求解困难,研究中通常将固体结构视为刚性壁面,不考虑固体在冲击下的变形情况及变形对液滴的影响,导致数值仿真精度较低。根据光滑粒子动力学(Smoothed Particle Hydrodynamics,SPH)方法的基本原理和理论,采用连续介质力学的控制方程,引入非牛顿流体和弹性固体所遵循的本构关系,分析流固两相的相互作用,提出一种流固边界的耦合处理算法,建立流固耦合动力学模型,对非牛顿液滴撞击弹性固体的动态过程进行数值仿真。仿真结果表明,上述数值方法能够精细地预测出撞击过程中非牛顿液滴的形态变化和弹性固体结构的微变形情况,并探讨了具有不同弹性模量的固体在液滴撞击下的可变形性及对液滴的影响。     

利用Poisson方法实现图像前景提取

图像前景提取是运用图像处理算法快速、准确地提取出图像中人们感兴趣的信息,它是图像研究的基础和重要的工作.图像前景提取的重点工作是研究出高效、准确的算法来确定图像中的每个像素点是属于需要提取的前景还是需要舍弃的背景.用Alpha值来表示该像素点属于前景的部分,称为掩模值.根据图像的表达公式可知,求解Alpha值是一个病态问题,快速、准确地进行前景提取成为图像研究的重点.介绍了前景提取的基本概念,详细介绍了Poisson前景提取算法并对关键代码进行分析,对Poisson前景提取算法进行了分析与展望.     

横向撞击下弹性支承轴向受力梁的动力响应

研究了具有弹性支承轴向受力梁在横向撞击下的动力响应.基于Timoshenko梁理论,综合考虑了梁端支承的抗推刚度、抗转刚度和撞击点处的平衡条件,导出了撞击体系的动力学微分方程,采用积分变换方法求解,得到时域内的各种动力响应.通过对不同支承条件下撞击力、横向位移、弯矩的对比分析,说明了弹性支承对结构动力响应的影响.最后分析了弹性支承下轴压力对结构的影响情况,得出了一些有益的结论.     

含陀螺效应的声表面波波动方程的求解

含陀螺效应的声表面波(SAW)波动方程的求解是分析旋转压电基体SAW传播特性和设计SAW角速度传感器的理论基础.以旋转条件下压电基体声表面波方程的建立和求解为研究内容,推导了含陀螺效应的Christoffel方程的一般表达式,提出了在求解中必须注意对解耦波的判别及进行相应的处理,设计了计算机数值求解的软件,并给出了流程.以新型压电材料硅酸镓镧作为求解的实例,验证了算法的可行性.理论与算法可为与陀螺效应有关的SAW器件的设计提供参考.     

ΔE效应对磁弹性传感器的影响与分析

分析了磁弹性传感器共振频率的测量原理。主要分析直流偏置磁场变化对共振频率测量的影响,提出了传感器尺寸和最佳直流偏置磁场的对应关系。通过实验得出ΔE效应对传感器共振频率测量准确性的影响。     

超声弹性图像去噪方法研究

超声弹性成像能直观展现各组织的弹性信息,已经成为肿瘤检测的重要工具。由于成像系统中的固有特性,使得图像遍布着大量伪影噪声,降低了图像的可辨读性。为了获取伪影噪声较少且组织边缘结构清晰的弹性图像,本文提出一种分数阶偏微分图像去噪方法,并通过各向异性算法有效平衡了梯度阈值k与微分阶数v的关系。人体体模弹性图像和仿真弹性图像的测试结果表明,该算法能有效改善弹性图像质量,增强边缘结构信息,且去噪后图像的信噪比及噪声比例差得到显著提升。     

弹性力学极坐标公式利用矩阵形式的对比教学

利用弹性力学平面问题中有很强规律性且容易记忆的基本方程的直角坐标矩阵形式,按极坐标系与直角坐标系之间物理量、微分算子的对应关系,考虑特殊情况,可列出基本方程及物理量的极坐标矩阵表达形式.两种坐标系下的公式具有一定的对应规律,得到的极坐标矩阵形式体现出很强的规律性和记忆特点,矩阵形式易化成一般表达式.教学中可利用这些规律进行对比讲授,从而使学生对较为复杂且采用通常方法不易记忆的基本方程或物理量的极坐标形式变得有规可循,容易记忆和掌握.     

复杂装备系统弹性度量方法研究

由于复杂装备系统缺少可工程应用的弹性度量方法, 且传统可靠性工程难以描述装备从故障到修复全过程的性质, 因此考虑装备系统在工作过程中性能变化的连续性以及扰动、故障和修复的不确定性, 利用可靠性工程相关参数, 针对无子系统的简单装备提出一种混合型弹性度量方法. 在此基础上, 考虑子系统对复杂系统的影响, 以及复杂系统故障和修复概率, 提出一种针对复杂装备系统的弹性度量方法. 最后, 通过基于弹性理论的组件重要度计算案例, 评估复杂装备系统各个子系统性能变化对整个装备的影响重要程度, 验证了方法的可行性和有效性.     

A coefficient of restitution of rock materials

At a macroscopic scale, even a purely elastic contact between rock particles is accompanied by energy dissipation. The resulting hysteretic loop of the stress/strain path during such a loading and unloading event suggests that grains recover slower to their original shape than when they were first deformed. This contact behaviour may be simulated in distinct element codes by utilizing a hysteretic damping contact model. In this research, values for the elastic coefficient of restitution for components of a molasse conglomerate were measured using a newly developed drop-test apparatus. These values can be used to calibrate or to verify constitutive models that incorporate strain-rate-independent, elastic hysteretic damping.     

Delay time compensation based on coefficient of restitution for collision hybrid motion simulator

A hybrid motion simulator embeds a hardware experiment in a numerical simulation loop. However, it is often subjected to the inherent problem of an energy increase in the collision of two pieces of hardware in a loop because of the delay time. This paper proposes a delay time compensation method based on contact dynamics model for a collision hybrid motion simulator under delay time and establishes a compensation method for coupled translational and rotational motion. The model developed in this paper describes linear uniform motion of a floating object during the period of the delay time until the force and torque are observed and non-linear motion according to environmental stiffness after the initial delay time period in contact. By using the above model, compensation parameters are designed based on desired coefficient of restitution with iterative calculation. The proposed method achieves accurate delay time compensation and simultaneously realizes a variable desired coefficient of restitution over a wide range of frequencies. Furthermore, the compensation method for multi-dimensional motion is established under the assumption that the friction effect is very small. The efficiency of the proposed method is verified through collision experiments for the coupled motion in two dimensions.     

Compensation for dead band of force measurement based on the coefficient of restitution in a hybrid simulator

In order to develop space robotic technologies, the feasibility and reliability of the systems have to be verified by repetitive operation tests. A hybrid simulator (also referred to as a Hardware-in-the-loop simulator) is one of the effective ways to examine orbital operations on the ground. The simulator embeds a hardware experiment in a numerical simulation loop. However, it is known that the hybrid simulator has a serious problem that energy increase arises in contact with a hardware experiment in the loop. In general, the energy increase in the hybrid simulator occurs due to the dead time in the system. However, this paper presents that dead band in force/torque measuring also causes the energy increase. The dead band in the force/torque measuring is necessary to avoid unexpected motion of the hybrid simulator due to the noise data in the force/torque sensor. This paper proposes two compensation methods for the energy increase problem due to the dead band. The first method is to insert a virtual damper to absorb the increased energy during the contact. The second method is to extrapolate force/torque data that is lost through the dead band processing right after the contact. The experimental verification with uniaxial contact in hybrid simulator is carried out to validate the proposed compensation methods.     

Solution to indeterminate multipoint impact with frictional contact using constraints

This work presents a method for determining the post-impact behavior of a rigid body undergoing multiple, simultaneous impact with friction. A discrete algebraic model is used with an event-driven function which finds impact events. In this work, the indeterminate nature of the equations of motion encountered at impact is examined. Velocity constraints are developed based on the rigid body assumption to address the equations and an impact law is used to determine the impulsive forces. The slip-state of each impact point is then determined and appropriate methods are used to resolve the post-impact velocities. These techniques are applied to a 3-D model of a ball which is forced to impact a corner between the ground and two wall planes. Additionally, a rocking block example is considered. Simulations are presented for 2-D and 3-D cases of the ball example, and a 2-D model of the rocking block problem to demonstrate the effectiveness of the proposed approach.     

Analytical model of variable characteristic of coefficient of restitution and its application to ball trajectory planning

In this article, we investigate the behavior of the coefficient of restitution (COR) which is an important parameter in many impact-related fields. In many cases, the COR is considered as a constant value, but it varies according to many variables. In this paper, we introduce an analytical variable COR model considering aerodynamics along with its verification through experiment. To introduce and analyze the variable characteristic of the COR model, the collision phenomenon between a pendulum and two kinds of ball is employed as an example and aerodynamics such as drag force is considered for analyzing the after-effect of the collision. Collision velocity of the pendulum, dynamic parameters of colliding bodies, contact time, drag coefficient, the air density, and the cross-sectional area of the ball are found as the typical variables of analytical COR model. This observation generalizes the result in previous researches. To verify new COR model, the travel distances for the curve-fitted constant COR model and the curve-fitted variable COR model are compared through simulation and experiment. Moreover, comparison between constant COR and variable COR is presented in several points of view. Finally, using the variable COR model, the travel distance of the ball for given collision velocity can be estimated.     

The relationship amongst coefficient matrices in symmetric Galerkin BEM for 2D elastic problems

Based on the assumption that solutions from different methods are the same, the relationship amongst weakly singular, strongly singular and hypersingular matrices associated with symmetric Galerkin BEM is derived for 2D elastic problems. Hypersingularity is avoided through matrix manipulations so that only weakly and strongly singularities need to be solved. Compared with the advantages brought about by symmetry, the additional computation caused by matrix manipulations is not so important in many cases, especially for time domain dynamic problems or when one wants to couple BEM with other symmetric schemes. Both static and dynamic problems have been studied, and three numerical examples are included to show the effectiveness and accuracy of the present formulation.     

轴向受力梁结构线弹性碰撞问题求解

研究了质点对轴向受力的Euler-Bernoulli梁结构任意位置的横向撞击问题.把撞击体系简化为质量-弹簧体系模型,采用积分变换方法,对撞击体系的控制微分方程、边界条件和连续条件进行Laplace变换,在频域内求得其解析表达式,然后采用Crump逆变换方法进行数值反演,得到时域内的各种动力响应.数值算例给出了撞击力、弯曲应力和剪力随时间变化的曲线,通过与有限元比较验证了本方法的正确性.最后研究了撞击位置、轴向压力、撞击质量、撞击速度和柔度系数等参数对撞击力的影响,得出了一些有用的结论.     

Assessing the impact of using the Internet for competitive intelligence

The Internet, as an information-rich resource and an interorganizational communications tool, has transformed the way that firms gather, produce and transmit competitive intelligence (CI). Yet, there is little empirical work on the impact of the Internet on CI and the subsequent effects on the organization. This study fills that gap by studying downstream impact of Internet usage on both CI and the organization. A questionnaire survey is used to gather data for the study. The findings indicate that research and external use of the Internet is significantly related to quality of CI information. However, the relationship between internal use and quality of CI information is not significant. The study also provides empirical evidence that quality of CI information is positively related to organizational impact. Implications of the results are discussed.     

Estimation of the maximum correlation coefficient using Bernstein copula

In this paper, the estimation of a nonlinear stochastic dependence between signals in information-measuring and control systems is considered. The maximum correlation coefficient and corresponding optimal transformations of the signals are estimated using the Bernstein approximation. Some basic concepts of the copula theory are discussed. Main calculation formulas for the maximum correlation coefficient in the case of a degenerate stochastic kernel are presented. An estimation algorithm for the maximum correlation coefficient and corresponding optimal (nonlinear) transformations of random signals is proposed. An example of correlation estimation for random signals is given.