Active nonlinear energy sink using force feedback under transient regime

Nonlinear Dynamics - In this paper, an active nonlinear energy sink (ANES) based on force feedback is investigated. The proposed device is composed of a pair of collocated actuator and force...     

Transient filament stretching rheometer

The filament stretching device which is used increasingly as an apparatus for measuring extensional properties of polymeric liquids is analysed. A force balance that includes the effects of inertia and surface tension is derived. The force balance may be used to correct for the effects of inertia and surface tension, provided online measurements of the filament surface shape are available. In addition, the question of initial asymmetry due to gravity is addressed.     

Nonlinear equivalent model and its identification for a delayed absorber with magnetic action using distorted measurement

For an absorber with the magnetic action and the delayed feedback, the equivalent strongly nonlinear model of the magnet force is proposed. We develop an identification algorithm with correcting distorted output measurement to identify and estimate the relevant parameters of the equivalently nonlinear model and the time delay in the feedback loop. The detailed steps of the algorithm are given analytically. We configure an experimental device of a delayed electromechanical absorber with action of the nonlinear magnetic force. The new algorithm is employed to identify the relative parameters of the device, such as time delay, damping and nonlinear stiffness, based on data of the output measurement with distortion. The results show that it is reasonable that the magnet action may be equivalent to the cubic nonlinear force. One may also see that the new algorithm may treat the experimental distorting measurement and correct it as long as the measurement still keeps periodicity. As an important result, values of the identified parameters with the correcting distortion are closer to those of the original measurement than those without the no correcting distortion for some excitation frequencies. It means that the algorithm may correct the polluted measurement, so that the quality of the identification is greatly improved. The new algorithm may be useful for design of nonlinear electromechanical absorber with time-delayed feedback.     

Stability of a system of two immiscible fluids in magnetohydrodynamics

Stability is investigated with allowance for the induced magnetic field and the force of gravity. Calculations are made for specific values of the parameters corresponding to the conditions in an electrolyzer. The parameters of a feedback regulator capable of stabilizing unstable steady states in accordance with the signals from a detector that measures the deviation of some parameter from the steady-state value are found.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 88–94, November–December, 1991.     

矩形弹性壳液耦合系统中的重力波分析

根据非线性动力学理论，建立了矩形壳液耦合系统的非线性振动方程组，通过数值求解，发现当激振频率为壳体固有频率与重力波频率之和，且激振力足够大时，会产生大幅低频重力波，通过实验验证，发现了壳液耦合系统中存在的大幅低频重力波现象，实验结果与理论结果基本吻合。     

海洋重力测量误差补偿技术

海洋重力场信息在勘探矿源和导航定位等方面都具有重要意义.进行海洋重力实时测量时,重力仪会受到各种外界扰动力的影响,再加上重力敏感器本身稳定性和惯性平台系统性能影响,重力敏感器的输出需要进行一系列数据处理和补偿后才能得到当地重力异常值,研究了重力敏感器安装角误差标定、零位漂移估计和格值修正等重力数据预处理方法.分析了海洋重力测量数据处理流程,主要包括零点漂移补偿、水平加速度误差补偿、厄特弗斯效应修正、高度修正和噪声滤波处理等.对每个数据处理过程都提出了具体补偿算法,并分析了补偿后的重力测量误差,将以上重力数据处理方法应用到实际重力测量,结果表明重力仪能够准确测量出当地重力值,其精度为1 mGa1.     

Disturbance compensation of a dual-arm underwater robot via redundant parallel mechanism theory

Disturbance compensation is one of the major issues for underwater robots to hover as a mobile platform and to manipulate an object in an underwater environment. This paper presents a new strategy of disturbance compensation for a mobile dual-arm underwater robot using internal torques derived from redundant parallel mechanism theory. A model of the robot was analyzed by redundant serial and parallel mechanisms at the same time. The joint torque to operate the robot is obtained from a redundant serial mechanism model with null-space projection due to redundancy. The joint torque derived from the redundant parallel kinematic model is calculated to perfectly compensate for disturbances to the mobile platform and is included in the solution of the joint torque based on the serial redundant model. The resultant joint torque can generate force on the end-effector for required tasks and forces for disturbance compensation simultaneously . A simulation shows the performance of this disturbance compensation strategy. The joint torque based on the algorithm generates the desired task force and the disturbance compensation force together, and a little additional joint torque can generate a large internal force effectively due to the characteristics of a redundant parallel mechanism. The proposed method is more effective than compensation methods using thrusting force on the mobile platform.     

Design of multi-degree motion haptic mechanisms using smart fluid-based devices

This article presents two different types of haptic masters capable of 4-degree- of-freedom (DOF) force feedback utilizing magnetorheological fluid (MR) and electrorheological (ER) fluid. The proposed ER master consists of a spherical joint for 3-DOF rotational motion and a linear device for 1-DOF translational motion, the MR haptic master consists bi-directional clutches associated with a planetary gear system and one-directional clutch with a bevel gear system. After showing the configuration of each haptic mechanism, the torque and force models of the actuators are derived based on the field-dependent Bingham model. After undertaking optimal design with spatial limitation and desired torque level, two different types of haptic master systems are manufactured. The torque and force responses are experimentally evaluated to validate practical feasibility of the proposed haptic masters for medical application.     

不等径颗粒间液桥力学参数及形态的试验研究

作为一种自然界中广泛存在的力, 液桥力的研究对制药、重金属回收、颗粒分离等领域具有十分重要的意义. 利用纳米多功能拉伸试验机测量不等径颗粒间液桥拉伸过程中的液桥力?位移曲线, 同时配合CCD工业相机记录拉伸全过程液桥形态的变化. 首先分析了液桥力?位移曲线形态、最大液桥力、断裂距离随粒径比及液桥体积的变化规律, 其次基于圆环假设及Y-L方程对本文试验结果的合理性进行验算, 最后针对圆环假设在液桥力计算中存在的不足分析了其原因, 并结合重力对液桥形态的影响对液桥拉伸全过程的形态变化进行了具体分析. 结果表明: 最大液桥力受粒径比的影响较大而受液桥体积的影响较小, 与最大液桥力相反, 断裂距离受液桥体积的影响较大而受粒径比的影响较小; 圆环假设可以较好地预测最大液桥力大小但对拉伸过程中的液桥力预测不准, 这是由于当液桥力达到最大值后液桥的外轮廓已不能用圆环表示; 根据重力对液桥形态的影响, 将拉伸过程液桥外轮廓的变化简化为重力影响可以忽略时的圆环形?抛物线形, 重力影响处于过渡阶段或影响较小时的长轴与短轴之比不断增大的椭圆形, 以及重力影响不可忽略时的“冷却塔形”?双曲线形.      

旋转重力梯度仪的加速度计动态调节方法与需求分析

适合陆基使用的旋转重力梯度仪采用多个加速度计的组合输出,能有效地抑制平台的共模噪声,实现对地球表面微小重力梯度变化信号的测量.其关键技术之一就是对多个加速度计进行动态匹配调节,通过实时反馈来降低多种噪声和误差,从而降低对研制单个加速度计的性能要求.本文结合旋转重力梯度仪中加速度计的匹配调节方法,以重力梯度测量分辨率达到1E为目标分析,结果表明对加速度计的标度因子一致性匹配需要达到10-11的量级,对二阶非线性因子调节同样需要达到～10-11g/g2的量级.     

The optimum height of application of force and eccentricity of a wheeled vehicle running on a loose sandy soil

In earthmoving sites, multi-wheeled vehicles are used to excavate a sandy soil or to pull other construction machinery. In this paper, the mechanism of a 5.88 kN weight, two-axle, four-wheel vehicle running on a loose sandy soil is theoretically analysed. For given terrain-wheel system constants, the combination of the effective braking force of the front wheel during pure rolling state and the effective driving force of the rear wheel during driving action will clarify the relation between effective effort of the vehicle and slip ratio and the relation between amounts of sinkage the front and rear wheels and slip ratio, etc. The maximum effective tractive effort of the vehicle varies with the height of application force and the position of the center of gravity of the vehicle. The optimum height of application of force and the eccentricity of the center of gravity to obtain the largest value of the maximum effective tractive effort can be explained with an analytical simulation program. Results of this study showed that the optimum height of application force should be 30 cm and the optimum eccentricity of the center of gravity is 0.05 for a vehicle considered for this study.     

旋转加速度计重力梯度仪标度因子调整方法及误差补偿研究

在旋转加速度计重力梯度仪的重力梯度测量原理的基础上,本文提出了加速度计标度因子的在线调整方法。此方法对加速度计组合输出信号中的标度因子不平衡信息进行解调,通过反馈实现标度因子的调整,同时可实现对重力梯度仪系统误差的补偿。     

Numerical study of convection in a fluid layer in the presence of vibratory forces

We consider the influence of modulation of the gravity force field on the stability of the equilibrium of a horizontal fluid layer heated from below. The fluid is bounded above and below by semi-infinite solid masses. The upper mass has infinite thermal conductivity, and the lower mass zero thermal conductivity. We propose to analyze numerically the dependence of the critical Rayleigh number on the frequency and amplitude of the gravity force modulation.     

A New Mathematical Model for Force Gravity Drainage in Fractured Porous Media

In force gas/oil gravity drainage process in fractured porous media, gas is flowing in both matrix and fractures leading to produce a finite gas pressure gradient. Consequently, viscous force plays an important role for displacing matrix oil toward fractures in addition to gravity force that is required to be modeled appropriately. A new analytical model for estimation of steady state oil saturation distribution with assumption of fixed gas pressure gradient throughout the matrix is presented. Moreover, based on some results of this analytical model a different numerical formulation is developed to predict the performance of oil production process. Comparison of the results obtained from this numerical model with the results of a conventional simulator demonstrates that the newly developed model can be applied with satisfactory accuracy. Numerical simulations show that the viscous displacement in fractured porous media can reduce the capillary threshold height, and thus it suggests the force gravity drainage as a favorable production mechanism when the matrix length is close to the threshold height.     

一种可用于运载火箭的SINS/GNSS自主导航方案

研究了一种可用于运载火箭的SINS/GNSS自主导航方案。起飞前捷联惯组采用基于惯性系重力加速度积分的解析粗对准和卡尔曼滤波精对准,起飞后采用SINS/GNSS卡尔曼滤波组合导航反馈实时修正姿态、速度和位置。仿真结果表明捷联惯组水平自主对准误差0.01°,方位自主对准误差1.5°,起飞后经组合导航修正后的姿态误差小于0.2°,速度误差小于0.4m/s,位置误差小于40m,考虑所有误差的蒙特卡罗仿真结果满足火箭入轨精度要求,此方案具有较高的工程应用价值。     

高精度惯导系统重力扰动的阻尼抑制方法

重力扰动已经成为高精度长航时惯导系统的主要误差源之一。针对船用高精度惯导系统的重力扰动抑制问题,从舰船INS误差模型出发,推导了重力扰动在惯导系统中的传播特性。仿真结果表明垂线偏差将引起系统较大的舒拉振荡误差。为抑制重力扰动对系统的影响,引入常速度误差反馈阻尼网络和相位超前串联阻尼网络。分析了重力扰动在水平阻尼网络中的传递特性,实现了相应滤波器的设计。在此基础上完成了实验验证,海上试验结果表明,所引入的两种阻尼网络都能够阻尼掉重力扰动引起的舒拉振荡型导航误差,其中,相位超前串联阻尼网络效果更优,抑制率达到70%以上。     

Fundamentals of a liquid (soap) film tunnel

 The continuously running liquid film tunnel (LFT) is a novel device suitable for the study of two-dimensional flows. In this innovation, the films start from a reservoir, run over a horizontal or non-horizontal wire frame and get pulled/washed by a water sheet or by gravity of liquid film. How-ever, despite the simple design and widespread application of LFT, its working mechanisms are not well understood. In the present work, an experimental effort for explaining these mechanisms is reported. The results show that both film velocities and film flow rates increase with water sheet velocity up to a saturation level. This behavior is described via a force balance between the shear force produced by the water sheet and the opposing pulling force of reservoir and boundary layer frictions. The results also show that the average film thickness depends on the surfactant concentration. This is as predicted by a model based on Langmuir’s adsorption theory, in which the liquid film contains two external monolayers of surfactant and a slab of surfactant solution in between. When a film is drawn from the reservoir to the water sheet, the surfactant molecules start migrating from the former to the latter. To restore the thermodynamic equilibrium, the dragged film pulls more surfactant due to Marangoni elasticity, and thus a flow is established. The film flow soon reaches an equilibrium rate as required by the force balance mentioned above. Received: 15 August 1996/Accepted: 12 November 1996     

Dynamics of a Spherical Body in a Liquid with Rotational Vibration of the Cavity

The average dynamics of a single solid sphere in a liquid-filled cylindrical cavity in the presence of high-frequency rotational oscillation about the axis of symmetry is studied experimentally. In the cavity there is an impermeable membrane which forces the liquid as a whole to vibrates together with the cavity. Various orientations of the vessel in the gravity force field are considered. The action of an average force of vibrational nature on the sphere and the dependence of this force on the vibration parameters and the body dimensions and density are studied. The force is measured with respect to the floating threshold for the heavy body, when the average vibrational force balances or exceeds the action of the gravity force.     

Stabilization control for offshore steel jacket platforms with actuator time-delays

This paper is concerned with the stabilization control for the offshore steel jacket platforms subject to wave-induced force. Two state feedback stabilization control schemes are proposed to reduce the vibration amplitudes of the systems. One scheme is that for the systems without actuator time-delay, a state feedback controller is designed. Compared with the nonlinear controller, both the control force and the vibration amplitudes of the systems under the state feedback controller are much reduced; and compared with the dynamic output feedback controller and the integral sliding mode controller, the required control force under the state feedback controller are significantly reduced. The other scheme is that based on the integral inequality approach, a delay-dependent state feedback controller, which can be solved by using the cone complementarity algorithm, is developed to control the systems with actuator time-delays. Compared with the state feedback controller, the delay-dependent state feedback controller is less conservative with actuator time-delays. In addition, it is capable of improving the control performance of the offshore platforms significantly, which are illustrated by simulation results.