Critical load position for cavities beneath CRCP slab under vehicle loading

In order to study the critical load position that causes cavities beneath the continuously reinforced concrete pavement（ CRCP） slab under vehicle loading, the elliptical load is translated into the square load based on the equivalence principle.The CRCP slab is analyzed to determine the cavity position beneath the slab under vehicle loading. The influences of cavity size on the CRCP slab＇s stress and vertical displacement are investigated. The study results showthat the formation of the cavity is unavoidable under traffic loading, and the cavity is located at the edge of the longitudinal crack and the slab corner.The cavity size exerts an obvious influence on the largest horizontal tensile stress and vertical displacement. The slab corner is the critical load position of the CRCP slab. The results can be used to assist the design of CRCP in avoiding cavities beneath slabs subject to vehicle loading.

Velocity Feedback in Load Simulator with a Motor Synchronizing in Position

The velocity feedback in a load simulator with a motor synchronizing in position is achieved by installing a tachometer generator between tile shaft and shell of the loading motor, and thes not only decreases the disturbance torque of tile load simlilator greatly but also improves its dynamic performance.

A Precision-Positioning Method for a High-Acceleration Low-Load Mechanism Based on Optimal Spatial and Temporal Distribution of Inertial Energy

High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit （IC） packaging equipment. In this paper, we derive the transient nonlinear dynamicresponse equations of high-acceleration mechanisms, which reveal that stiffness, frequency, damping, and driving frequency are the primary factors. Therefore, we propose a new structural optimization and velocity-planning method for the precision positioning of a high-acceleration mechanism based on optimal spatial and temporal distribution of inertial energy. For structural optimization, we first reviewed the commonly flexible multibody dynamic optimization using equivalent static loads method （ESLM）, and then we selected the modified ESLM for optimal spatial distribution of inertial energy; hence, not only the stiffness but also the inertia and frequency of the real modal shapes are considered. For velocity planning, we developed a new velocity-planning method based on nonlinear dynamic-response optimization with varying motion conditions. Our method was verified on a high-acceleration die bonder. The amplitude of residual vibration could be decreased by more than 20% via structural optimization and the positioning time could be reduced by more than 40% via asymmetric variable velocity planning. This method provides an effective theoretical support for the precision positioning of high-acceleration low-load mechanisms.

Finite Element Analysis of soft Foundation Strengthening by Vacuum Loading from Lower Position

Strengthening soft foundation by vacuum loading from lower position is a new method of accelerating the consolidation of dredger fill. This paper presents the mechanism of soft foundation strengthening by vacuum loading from lower position and evaluates the effectiveness of this method under various boundary conditions by means of finite element method (FEM) on the basis of Biot's consolidation theory.

Effect of loading point position on fracture mode of rock

Anti symmetric four point bending specimen with different loading point positions was used to study effect of loading point position on fracture mode of rock in order to explore a feasible method for achieving Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock, K ⅡC . Numerical and experimental results show that the distance between the inner and outer loading points, L 1+ L 2, has a great influence on stresses at notch tip and fracture mode. When L 1+ L 2>0.5 L or 0.1 L < L 1+ L 2<0.5 L , maximum principal stress σ 1 exceeds the tensile strength σ t. The ratio of τ max / σ 1 is relatively low or high and thus Mode Ⅰ or mixed mode fracture occurs. When L 1+ L 2< 0.1 L , σ 1 is smaller than σ t and the ratio of τ max / σ 1 is much higher, which facilitates the occurrence of Mode Ⅱ fracture.

基于级联惯性负载转矩观测器的永磁伺服电机复合抗扰控制

针对永磁伺服电机在运行时位置跟踪精度差和抗干扰性能弱等问题,提出一种模型预测位置控制与非奇异快速终端滑模速度控制相结合的复合模型预测控制策略。该控制策略采用非奇异快速终端滑模设计速度控制器,以有效提高响应速度及系统鲁棒性;采用模型预测位置控制提高位置跟踪精度;同时,采用基于转动惯量观测和负载转矩观测器相结合的级联惯性负载转矩观测器观测负载转矩并进行前馈补偿,进一步提高系统的抗干扰性能。通过仿真和实验结果可得,所提复合模型预测控制可有效提高永磁伺服电机的动态响应速度和抗负载扰动能力。

Indirect Adaptive Robust Trajectory Tracking Control of Hard Rock TBM with Load Variation of Tunneling Face

Posture adjustment of open-type hard rock tunnel boring machine(TBM) can be achieved by properly adjusting the hydraulic pressure of gripper cylinder and torque cylinders. However, the time-varying inhomogeneous load acting on tunneling face of TBM and complex stratum working condition can cause the trajectory deviation. In this paper,the position and posture rectification kinematics and dynamics models of TBM have been established in order to track the trajectory. Moreover, there are uncertain parameters and uncertain loads from complex working conditions in the dynamic model. An indirect adaptive robust control strategy is applied to achieve precise position and posture trajectory tracking control. Simulation results show when the position deviation only occurs in Y-axis and the current orientation is parallel with the designed axis, the deviation can be corrected by controlling the pressure of gripper cylinder and the actual trajectory meets the designed axis when TBM is pushed forward 0.14 m in X-axis. If the deviation only occurs in Z-axis, then the deviation can be corrected by controlling torque cylinders. If the position deviation occurs both in Y-axis and Z-axis at the same time, the pressure of gripper cylinder and torque cylinders should be controlled at the same time to rectify the deviation. Simulation results are shown to illustrate the e ectiveness and robustness of the proposed controller. This research proposes an indirect adaptive robust controller that can track the planned tracking trajectory smoothly and rapidly.

Characteristics of gravity signal and loading effect in China

The complex geographical environment in China makes its gravity signals miscellaneous.This work gives a comprehensive representation and explanation in secular trend of gravity change in different regions,the key features of which include positive trend in inner Tibet Plateau and South China and negative trend in North China plain and high mountain Asia（HMA）.We also present the patterns of amplitudes and phases of annual and semiannual change.The mechanism underlying the semiannual period is explicitly discussed.The displacement in three directions expressed in terms of geo-potential spherical coefficients and load Love numbers are given.A case study applied with these equations is presented.The results show that Global Positioning System（GPS） observations can be used to compare with Gravity Recovery and Climate Experiment（GRACE） derived displacement and the vertical direction has a signal-noise-ratio of about one order of magnitude larger than the horizontal directions.

Generation of electromotive force in igneous rocks subjected to non-uniform loading

When one end of an air-dry igneous rock block was uniaxially loaded in laboratory, there appeared an electromotive force that made electric currents flow from the stressed volume to the unstressed volume. Quartz-free rocks such as gabbro also generated this force, stronger than quartz-bearing rocks such as granite. This indicates that the piezoelectric effect of quartz and the electrokinetic effect of pore water do not make a large contribution toward generating the electromotive force. We focus on peroxy bond that is one of the abundant lattice defects in igneous rock-forming minerals. When mechanical loading deforms the lattice structure around this defect and breaks its bond, its energy levels change and act like an accepter. As an electron is trapped at this defect from a neighbor 02- site, a positive hole is activated there. They attempt to diffuse toward the unstressed volume through the valence band and are simultaneously affected by the attractive electric force with the electrons trapped in peroxy bonds. This leads to a polarization in the stressed volume and the generation of electromotive force between the stressed and unstressed volumes. Similar electromotive force may be generated in the Earth＇s crust where inhomogeneous stress/strain is changing.

Session RPE and Speed High Intensity Distance in Meters(D_SHI mt):A Valid Method to Analyze Training Load in Soccer Players

The purpose of this study is to verify the physiological effect and describe the intensity of training in response to internal and external loads,through Session Rate of Perceived Exertion and Speed High Intensity Distance in Meters reports,on professional soccer players engaged in weekly training(199 Sessions,43 weeks)and league games(32 official matches).Twenty-two male professional soccer players(n=22)of the Italian national championship under-19 are involved in this study during the season 2014-2015.Daily,Weekly and Monthly RPE(perceived exertion)Session(Borg CR-10 Scale)is a good indicator of the amount of work done:training time multiplied by perceived effort(TL=Training Time×RPE).With Arbitrary units(a.u.)produced by the individual and used for team-based data analysis,we analyze the intensity produced by workout depending on the working time.Furthermore,by means of global positioning system technology(K-Sport,Montelabbate PU,Italy 10 Hz),we statistically established the existing relationship with high intensity speed distance(>16 km/h)and session rate of perceived exertion to describe how the internal(represented by the sum of the stresses that the body undergoes an external load;is strictly subjective)and external loads(the objective quantification of the means used in training km routes,running speed,slope,type of recovery),are correlated(r=0.87,p<0.01,95%CI).The statistical analysis highlights how these methods are suitable to quantifying the high-intensity work done by the soccer player during the workout and the game.

The evolution characteristics of positive and negative earthquakes before strong quakes in Kanto area and the Hyugo earthquake in Japan

This paper studies the evolution charateristics of positive and negative quakes before Hyugo earthquake of M =7.2 and several strong quakes in Kanto area in Japan.The results show that the earthquakes over a certain megnitude are mainly positive ones a certain time before the main shock in or near the focal regions of most strong quakes,and form a concentratingintervals of positive quakes,The main quakes generally locate in or near the areas of positive quake distribution.Negative quakes often occur several months before the main shocks (not excluding positive ones), with the decrease of LURR (Loading/Unloading Response Ratio) values.It possibly shows that earthquake generating process has come to a short term stage.These characteristics may help to predict the time and location of the future earthquakes,and have been applied to the preliminary prediction of the time and the location of the earthquake of M =6.6 on Sep.11,1996 in Kanto area.

含逆变型分布式电源和分支负荷的配电网自适应电流差动保护

电流差动保护具有良好的选择性和灵敏性。但是,逆变型分布式电源(inverter-interfaced distributed generator,IIDG)和分支负荷接入改变了配电网的故障特性,现有配电网的电流差动保护面临拒动或误动的风险。为解决以上问题,该文在计及P/Q控制的IIDG和分支负荷的故障等值建模基础上,从故障点、IIDG和分支负荷的相对位置出发,挖掘配电网线路两端正序电流差的幅值特征以及正序电流故障分量的相位特征。在此基础上,提出一种正序电流幅值与故障分量相角阈值配合的双比例制动系数自适应差动保护方案,并且利用幅相平面分析所提保护判据的可靠性和灵敏性。最后通过PSCAD/EMTDC验证了所提保护方案的有效性,仿真结果表明该方案适应不同故障类型、位置和过渡电阻,且不受IIDG以及分支负荷接入的影响。

液阻全桥网络负载口独立电液系统节能控制策略仿真

针对传统电液控制系统节流损失大、能耗高、效率低的问题,采用液阻全桥网络搭建了具有负载口独立控制特性的新型电液控制系统,详细研究了该系统在典型四象限负载下的节能控制策略。液阻全桥网络电液系统由5个二位二通比例阀组成,根据其具有的负载口独立控制特性,将系统归纳为传统三位四通、负载口独立和负载敏感3种控制模式。传统三位四通下,两负载口开度控制模拟三位四通进出口耦合形式;负载口独立模式下,采用一腔控制流量另一腔阀口全开的控制策略;负载敏感模式下,控制泵出口压力比进油腔压力高一个定值,从而实现负载敏感功能。在超越负载下,3种模式都使用流量再生回路进行节能控制。AMESim+Matlab联合仿真结果表明,与传统的三位四通模式相比,三位四通流量再生、负载口独立、负载口独立流量再生、负载敏感模式分别节能43.38%、65.27%、77.91%、83.58%。

基于刚度可调的气动位置伺服系统摩擦补偿控制

气动伺服系统的低刚度、低气源压强、流量易饱和等特性,导致系统在工作过程中能量耗散较大,系统易受摩擦影响,且补偿效果不明显。尤其是当系统的运动方向改变时,会产生明显的“平顶现象”,严重影响气动伺服系统的跟踪精度。采用负载口独立控制结构,消除因两腔耦合而导致的能量耗散,使系统流量特性尽可能地位于线性区间;针对气动系统中存在的摩擦中部分参数不确定,以及外界干扰、动态负载的不确定性,设计非线性自适应鲁棒控制方法;将系统的刚度调节与自适应鲁棒控制进行协同控制,提高气动位置伺服系统的动态性能。仿真和实验结果均表明:具有刚度调节的自适应鲁棒控制能够明显降低系统能量耗散,提高系统位置跟踪精度,有效改善摩擦引起的“平顶现象”。

结构动载荷识别研究进展

作用于工程结构上的动载荷由于环境等限制难以通过直接测量的方式获取,基于动响应信息间接识别或重构动载荷已成为一种十分有效的途径。动载荷识别经过数十年的发展,已经形成了一系列行之有效的方法。本文总结了动载荷识别方法的研究历程及主要成果,系统性阐述了典型时、频域方法以及基于函数拟合思想、正则化策略、贝叶斯框架、数据驱动等动载荷识别方法,并讨论了各方法的优缺点以及适用范围。此外,还针对载荷识别过程中普遍存在的结构参数不确定问题以及输入条件不确定问题进行了总结。动载荷位置识别也是动载荷识别问题的重要组成部分,本文对现有位置识别方法进行了归纳分析。探讨了动载荷识别方法的工程应用,并分析了现有方法的局限性。结合当前实际工程应用中日益迫切的需求及动载荷识别领域面临的问题,展望了未来动载荷识别亟需攻克的技术难题以及可能的发展方向和重点领域。

基于EKF的PMSM无位置传感器控制

为了获得永磁同步电机转子的位置信息,提出了一种五阶扩展卡尔曼滤波器(EKF)的算法;在传统的四阶EKF中引入对负载转矩的估算,并将其前馈至电流环以解决速度环对外界负载扰动响应慢的问题;通过设计改进的递推最小二乘法实时辨识电机的转动惯量,优化了系统的观测性能和鲁棒性,基于Simulink搭建仿真模型,结果表明该观测器性能优秀且提高了系统的抗扰动性能;最后,通过硬件实验实现了电机位置误差仅在0.02 rad以内,且负载转矩观测误差在4%以内,有效改善了系统在有负载波动时的动态特性。

集装箱船典型装载工况下的重心位置估算方法

对于集装箱船结构评估中加速度公式所需重心位置进行研究。以10艘集装箱船为研究对象,选取规范校核的典型装载工况,参照《散货船和油船共同结构规范》中的公式开展重心位置对比。研究发现,采用《散货船和油船共同结构规范》中的公式所得结果与实际值相差较大,该公式不适用于集装箱船。在此基础上,中国船级社在其《集装箱船结构规范》中提出一种新的集装箱船重心位置估算公式。另选5艘集装箱船,通过将采用该估算公式所得结果与实际值相对比,验证该估算公式合理、实用。

变负载直驱力矩电机位置误差预测模型研究

为提高直驱力矩电机在变外载荷工况下的位置精度,使用基于狼群算法(WPA)优化支持向量回归(SVR)神经网络,建立直驱力矩电机位置误差预测模型。搭建试验台,将磁粉制动器与力矩电机用联轴器连接,利用磁粉制动器对直驱力矩电机施加变化外载荷。以可变外载荷数据和直驱力矩电机运行时电流数据作为输入,以直驱力矩电机位置误差作为输出。实验结果表明:所建立的WPA—SVR预测模型精度高于SVR预测模型,能够有效预测直驱力矩电机变负载下位置误差。

旋转机构零位姿态传感器设计及测量方法

面向新型旋转成像载荷姿态角测量需求,针对现有传感器无法同时测量无接触旋转机构零位三轴姿态角的问题,提出了一种基于光电传感的旋转载荷零位姿态测量方法,并研制了零位姿态传感器,使用光电传感器获取过零波形,采用最小二乘法得到过零时的时间信息,通过时间和转速获得精确的旋转角和定转子相对位移。在此基础上,通过坐标变换求解出零位时的三轴姿态信息。分析平台舱和旋转舱平动、转动对传感器的测量精度的影响,建立传感器测量误差与光源组件轴安装误差、采样误差、传感器安装误差等的理论模型,仿真分析各因素对零位测量误差的影响。搭建了磁悬浮旋转支撑机构测试平台,对比所设计零位姿态传感器测量结果与电涡流位移传感器和旋变传感测量结果,分析所设计传感器的测量精度。结果表明,所设计传感器位移测量误差均值不大于2.4μm,转动角度测量误差均值不大于3.7"。所设计传感器能够准确检测出定转子间隙变化时的零位姿态信息,可为高精度的载荷舱姿态控制提供参考。

机械臂负载移动性能与运动调控研究

工业的不断发展对机械臂的负载要求越来越高,而负载的增加会对机械臂末端的精度造成影响.本文以Franka七轴串联机械臂为对象,采用M-DH法和雅可比迭代法对其正、逆运动学展开分析;采用三次函数插值法进行关节空间的轨迹规划.基于拉格朗日方程建立了机械臂的动力学模型,并通过Admas和Simulink联合动力学仿真验证了动力学模型的有效性.最后基于定位控制,对末端位置误差收敛速率、负载质量、控制参数之间的关系展开研究.