试验机弹性储能对岩石力学性能测试的影响

在材料试验机上进行岩石力学性能测试时，如何准确测量岩石的变形是整个测试分析的基础．为了具体考察试验机刚度对岩石变形测量的影响程度，在两台不同的试验机上进行了岩石的单轴压缩试验，通过对加卸载过程中试验系统及岩石能量变化的分析，详细研究了试验系统弹性储能对岩石变形测量的影响，进而给出了基于试验机刚度的修正计算方法，来确定岩石在测试过程中的变形．     

Tensile Test Machine for Unsymmetrical Materials

A novel solution to overcome the shortcoming of conventional tensile test machines in dealing with unsymmetrical materials and off-axis testing of composites is presented. Conventional testing machines are designed on the basis of subjecting a specimen to axial load to determine the stiffness and strength of the material. For specimens with unsymmetrical cross-section this method is no longer valid due to induced additional bending stresses. To overcome this problem a novel tensile test machine was designed, which allows bending deformation, thus subjecting the specimen to pure tension instead of axial loading. To validate the design, the machine was fabricated and employed for tensile testing of an aluminum specimen with unsymmetrical cross-section. The comparison of test results from a conventional machine and from analytically calculations, based on pure tension, reveals that conventional machine generates significant errors, while the results from new machine are in good agreement. The machine was then used to test a functionally graded beam.     

金属拉伸试验方法的关键及其对策

本文首先指出金属拉伸试验方法的关键问题是试验时的应力速率及应变速率控制,首次提出应用传感器及计算机技术,以一只比例节流阀为控制器构成旁路节流式微机控制电液系统,具有压力和速度双重控制功能,在液压式万能材料试验机上获得良好的应力速率及应变速率控制的试验结果,为我国液压材料试验机功能扩展和开发新一代机型奠定基础,以适应２１世纪静强度检测的需要。     

复杂工程结构构件的预应力光弹性分析方法及应用

本文提出了一种后张法预应力光弹性实验方法与技术，并用该方法解决了三峡工程升船机的试验机－清江隔河岩水利枢纽第二级垂直升船机承重结构的楼板与深梁的预应力分析问题，实验结果已被工程单位所采用。     

A Control Algorithm for a 3D Hopping Machine

The paper addresses several control problems for a three-dimensional hopping machine. The machine consists of a ponderable torso and an imponderable leg. The leg is a kinematic chain with joints allowing rotation and translation. The leg is attached at the torso's center of mass. The force in the leg is developed by a linear spring. A control system is synthesized within the framework of a periodic linear quadratic problem. The efficiency of the controller is exemplified by a case where the hopper changes the direction of its motion     

Control of motion of a legged locomotion machine with minimal-power motor

We consider the problem of control of motion of a many-legged statically stable locomotion machine ensuring the choice of a minimal-power motor. We show that the machine frame can be used as a kinetic energy recuperator, thus providing a significant decrease in the reactive power.     

Productivity of tillage loosening and separating machines in an aggregate with tractors of various capacities

Currently, chemical methods of weed control are increasingly being replaced by mechanical weeding. One of the promising mechanical devices for weed control is a rotary loosening and separating stratifier. This tillage machine can provide high quality tillage to a depth of up to 18 cm. Its performance is determined by the width of the grip of the gun and the speed of movement and is limited by the traction capabilities of the tractor. Using the Goryachkin formula for the traction resistance of a tillage machine, the authors obtained the dependence of productivity on the width of the grip and the speed of movement at different depths of tillage. The obtained dependencies on the example of tractors John Deere 8330, HTZ 16131-05 and MTZ 1523.3 showed the presence of a pronounced maximum, which led to the solution of the optimization problem. The article presents a method for calculating the optimal width of the grip and the speed of movement that ensure the maximum productivity of the tillage machine, depending on the depth of processing and the specific resistance of the soil. The use of optimal parameters of the tillage machine allows you to increase its productivity by 2–3 times.     

Optimal design of paper machine headboxes

A shape optimization problem for incompressible flows within a stabilized finite element framework is studied. The goal is to develop and test numerical realizations of optimal shape design problems that could be applied to non‐trivial industrial problems. The resulting algorithm is applied to the optimization of the geometry of a tapered header in a paper machine headbox. Copyright © 2000 John Wiley & Sons, Ltd.     

A Note on a Walking Machine Model

The paper continues studies intended to find out whether it is possible to create a prototype walking machine with relatively simple components. In this connection, the control problem is solved for a two-dimensional model of biped machine. It has a torso and two telescopic legs. Each leg includes a ponderable section of constant length and an imponderable section of variable length. The machine, regarded as a system with variable constraints, implements a single-stance gait (one stance leg at a time) with a step of constant duration. The contact of the swing leg with the ground is analyzed within the framework of Carnot's theorem (perfectly inelastic impact). It is assumed that the force developed in the stance leg is due to the deformation of the leg's spring and that this deformation can be controlled. An algorithm is proposed to synthesize a control system that takes into account collisions occurring at reverse of the roles of the legs. This algorithm is based on methods of optimizing periodic systems. The algorithm is compared with approaches used by other authors     

基于支持向量机回归的结构系统可靠性及灵敏度分析方法

提出了一种基于支持向量机回归近似极限状态方程的系统可靠性分析方法,所提方法首先由支持向量机拟合系统各失效模式的极限状态方程,将复杂或隐式极限状态方程近似等价为显式极限状态方程,然后根据系统各个失效模式的逻辑结构,由高精度的显式极限状态方程方法计算系统的失效概率和参数灵敏度.与线性展开和响应面法近似极限状态方程相比,文中方法由于采用了基于结构风险最小化原理的支持向量机回归,因而在拟合非线性极限状态方程上表现优越,计算精度高.与直接蒙特卡洛模拟相比,由于该方法采用较少的样本即可近似出概率等价的显式极限状态方程,因而计算效率大幅提高.工程实例表明:所提方法可以处理串联、并联和混合系统的可靠性与可靠性灵敏度分析,具有工程运用价值.     

基于网格搜索的支持向量机砂土液化预测模型

在使用支持向量机对砂土液化进行预测时,不可避免地会遇到惩罚因子和核函数参数如何选取的问题,目前还没有确定这两个参数的选择模式,解决这一问题比较常用的办法有经验公式法、遗传算法和网格搜索法.对此本文基于网格搜索方法,使用LIBSVM软件包,寻找砂土液化训练样本的结构风险最小值所对应的支持向量机最优参数;使用最优参数,建立了支持向量机砂土液化预测模型.研究结果表明:预测样本的正确率可达87.5%,而且预测结果稳定;同时通过比较BP神经网络的砂土液化预测情况,可知支持向量机有更好的泛化能力,收敛速度也更快.     

Application of the Wavelet Multi-resolution Analysis and Hilbert transform for the prediction of gear tooth defects

In machine defect detection, namely those of gears, the major problem is isolating the defect signature from the measured signal, especially where there is significant background noise or multiple machine components. This article presents a method of gear defect detection based on the combination of Wavelet Multi-resolution Analysis and the Hilbert transform. The pairing of these techniques allows simultaneous filtering and denoising, along with the possibility of detecting transitory phenomena, as well as a demodulation. This paper presents a numerical simulation of the requisite mathematical model followed by its experimental application of acceleration signals measured on defective gears on a laboratory test rig. Signals were collected under various gear operating conditions, including defect size, rotational speed, and frequency bandwidth. The proposed method compares favourably to commonly used analysis tools, with the advantage of enabling defect frequency isolation, thereby allowing detection of even small or combined defects.     

Subcritical Hopf Bifurcation in the Delay Equation Model for Machine Tool Vibrations

We show the existence of a subcritical Hopf bifurcation in thedelay-differential equation model of the so-called regenerative machine toolvibration. The calculation is based on the reduction of the infinite-dimensional problem to a two-dimensional center manifold. Due to the specialalgebraic structure of the delayed terms in the nonlinear part of the equation,the computation results in simple analytical formulas. Numerical simulationsgave excellent agreement with the results.     

基于深度置信网络的松动部件质量估计方法研究

为解决以往核电站冷却系统松动部件质量估计方法存在的精度不高的问题,提出了一种基于深度置信网络的松动部件质量估计方法。基于平板模型上的不同质量钢球跌落实验,利用冲击信号的自功率谱与对应钢球质量来训练深度置信网络模型,进一步对跌落钢球质量进行了分类预测,并与支撑向量机和神经网络模型预测方法进行了比较。结果表明:深度置信网络方法能对跌落钢球质量进行较好的分类预测,分类平均正确率达到94%以上,预测结果好于支撑向量机(87.57%)和神经网络(91.64%),具有较高的跌落钢球质量预测精度。     

Theoretical and experimental investigations of gear-rattling

Rattling vibrations in gear boxes are a noise problem of modern cars following the requirement to be as quiet as possible. The paper presents an uniform approach to model such vibrations based on classical impact theory and applying modern methods of topological dynamics. Some comparisons of theory and measurements utilizing a test set-up of a rattling machine are presented. They demonstrate the practical relevancy of the presented theory.     

A mathematical model of the ring-spinning process

This paper develops a mathematical model of the ring-spinning process that takes into account its non-stationary nature. A complex system of differential equations is obtained, which from a mathematical point of view constitutes a ‘free-boundary’ problem. Its solution involves definition of suitable boundary conditions related to the mechanical characteristics of the process and of the spinning machine itself. The boundary conditions which determine the solution are pointed out. A numerical solution of the system of differential equations can be obtained by the Finite-Segments method, as shown in an example.     

Concept evaluations of three novel forwarders for gentler forest operations

In-terrain transport of wood from sensitive areas with soft soil has always been difficult to perform in without extensive rutting and soil distortion. To carry out logging in wintertime, on frozen ground, is increasingly difficult as prolonged, rainy fall seasons and milder winters have decreased the window of opportunity for such operations. This creates strong demands for forest machines that can master soft soils. Exposure to whole body vibrations is a serious problem for operators of forest machines, which is also related to the machine-ground interaction. Both the soil and operator benefit from damped chassis suspension.Vibrations and soil distortion indicate loss of tractive energy. Instead of moving the machine, energy is lost in deformation of the ground and tractive elements, adding to motion resistance and to machine vibrations. Three recent developments of concept machines with improved soil interaction properties, reducing soil impact and improving operator comfort are presented. Two rubber tracked forwarders and one wheeled pendulum arm machine with active damping have been constructed, tested and analyzed.Results from standardized rutting and vibration tests of the concept machines are presented. Notable improvements regarding soil impact and rutting, operator comfort and fuel consumption were found. Some remaining technical challenges are also discussed.     

Inverse dynamics of a 3-PRC parallel kinematic machine

Recursive matrix relations for kinematics and dynamics analysis of a three-prismatic-revolute-cylindrical (3-PRC) parallel kinematic machine (PKM) are performed in this paper. Knowing the translational motion of the platform, we develop first the inverse kinematical problem and determine the positions, velocities and accelerations of the robot’s elements. Further, the inverse dynamic problem is solved using an approach based on the principle of virtual work and the results in the framework of the Lagrange equations with their multipliers can be verified. Finally, compact matrix equations and graphs of simulation for input force and power of each of three actuators are obtained. The investigation of the dynamics of this parallel mechanism is made mainly to solve successfully the control of the motion of such robotic system.     

On the integrability of the motion of a heavy particle on a tilted cone and the swinging Atwood machine

In the present note we study the motion of a particle under uniform gravity on a tilted smooth cone. We point out some integrable cases of that problem. In particular, we establish that motion on the cone with semi-vertical angle π/6 and one generator vertical is integrable. Moreover, we show that the swinging Atwood machine is equivalent to a special version of the motion on the tilted cone. This analogy makes it easier to analyze motion of SAM from a geometrical point of view.     

基于恒等映射多层极限学习机的高速列车踏面磨耗预测模型

针对高速列车车轮踏面磨耗单一模型无法对各种复杂工况下列车车轮踏面磨耗进行定量计算的问题, 提出一种基于恒等映射多层极限学习机的高速列车车轮踏面磨耗测量方法. 首先将恒等映射引入到多层极限学习机中, 提出一种基于恒等映射的多层极限学习机模型(identity multilayer extreme learning machine, I-ML-ELM), 采用机器学习公共数据集对该模型进行性能验证, 数值结果表明I-ML-ELM模型具有较好的准确性与泛化性; 然后基于车辆-轨道耦合动力学理论建立高速列车的车辆-轨道耦合动力学模型, 模拟列车运行的不同工况, 观测和分析高速列车的车轮踏面磨耗情况, 并通过I-ML-ELM预测模型对高速列车车轮踏面磨耗量进行学习及预测; 最后应用高速列车车轮踏面磨耗的实际测量值对I-ML-ELM预测模型进行进一步的验证, 结果表明: I-ML-ELM预测模型的各项性能参数指标在整体上优于以下五种网络: ELM, FLN, ML-ELM, ML-KELM和DLSFLN, 通过高速列车线路实测数据的进一步验证表明, 本文提出的基于I-ML-ELM的高速列车车轮踏面磨耗预测模型能较好地反映不同参数对高速列车车轮踏面磨耗值的影响规律.