Measurement of six degree-of-freedom ground motion by using eight accelerometers

A new integrated measuring system with eight force-balance accelerometers is proposed to obtain a direct measurement of six degree-of freedom （DOF） ground motions, including three rotational and three actual translational acceleration components without gyroscopes. In the proposed measuring system, the relationship between the output from eight force-balance accelerometer and the six DOF motion of the measuring system under an earthquake are described by differential equations. These equations are derived from the positions and directions of the eight force-balance accelerometers in the measuring system. The third-order Runge-Kutta algorithm is used to guarantee the accuracy of the numerical calculation. All the algorithms used to compute the six DOF components of the ground motion are implemented in a real-time in Digital Signal Processor （DSP）. The distortion of the measured results caused by position and direction errors of the accelerometers in the measuring system are reduced by multiplying a compensation coefficient C to the output and subtracting static zero drift from the measured results, respectively.

Effects of Degrees of Motion Freedom on Free-Fall of A Sphere in Fluid

Free-fall of a sphere in fluid is investigated at a Galileo number of 204 by direct numerical simulations(DNS). We mainly focus on the effects of different degrees-of-freedom(DOFs) of the sphere motion during free-fall. The characteristics of free-fall are compared with those of flow past a fixed sphere. Additional numerical tests are conducted with constraints placed on the translational or rotational DOFs of the sphere motion to analyze different DOFs of sphere motion. The transverse motion contributes significantly to the characteristics of free-fall; it results in the retardation of the vortex shedding, leading to the decrease of the Strouhal number. In addition, the transversal sphere motion exhibits the tendency to promote the sphere rotation. On the contrary, the effects of the sphere rotation and vertical oscillations during free-fall are negligible.

Design and Analysis of a Novel Compliant Mechanism with RPR Degrees of Freedom

A novel compliant mechanism with RPR degrees of freedom(DOF)is proposed where R and P represent rotation and translation DOFs,respectively.The proposed compliant mechanism is obtained from dimension synthesizing a 2-RPU-UPR rigid parallel mechanism with the method of optimization of motion/force transfer characteristic.R,P and U represent rotation,translation and universal pairs,respectively.Firstly,inverse kinematics and Jacobian matrix are analyzed for the dimensional synthesis.Then,output transmission indexes of branches in the parallel mechanism are given.Dimensional synthesis is completed based on the normalized design parameter.And optimization of flexure joints based on constrained energy is carried out.Afterwards,the novel compliant mechanism is obtained by direct replacing method.Mechanical model of the compliant mechanism including static stiffness and input stiffness is built based on the pseudo-rigid body modeling method and virtual work principle.Finally,FEA simulation by Ansys Workbench is carried out to verify DOF,effectiveness of the dimension synthesis,and compliant model.Optimization of motion/force transfer characteristic is first applied for the design of compliant mechanisms to suppress drift of rotation axis in the paper.

Numerical Modeling of a New Flight Simulator Enabling Continuous 360⁃Degree Spinning and Translational Motion

This paper presents a new nine⁃degree⁃of⁃freedom parallel mechanism,which can be applied as a flight simulator.The mechanism is composed by Stewart turntable and another three⁃axis turntable.The Stewart platform can realize six⁃degree⁃of⁃freedom movement in space,but the working space is limited.After the three⁃axis turntable is installed,the rotation space can be increased to simulate more realistic flight conditions.This paper analyzes the new flight simulator from kinematics and dynamics aspects.In addition,the flight simulator is simulated and analyzed based on the MATLAB/Simulink simulation system.The results obtained from the numerical simulations is planned to be used for the practical manufacturing and applications of the new platform.

6-DOF motion estimation using optical flow based on dual cameras

Because of its characteristics of simple algorithm and hardware, optical flow-based motion estimation has become a hot research field, especially in GPS-denied environment. Optical flow could be used to obtain the aircraft motion information, but the six-(degree of freedom)(6-DOF) motion still couldn't be accurately estimated by existing methods. The purpose of this work is to provide a motion estimation method based on optical flow from forward and down looking cameras, which doesn't rely on the assumption of level flight. First, the distribution and decoupling method of optical flow from forward camera are utilized to get attitude. Then, the resulted angular velocities are utilized to obtain the translational optical flow of the down camera, which can eliminate the influence of rotational motion on velocity estimation. Besides, the translational motion estimation equation is simplified by establishing the relation between the depths of feature points and the aircraft altitude. Finally, simulation results show that the method presented is accurate and robust.

Numerical Simulation about the Characteristics of the Store Released from the Internal Bay in Supersonic Flow

To understand the influence of the initial release conditions on the separation characteristics of the store and improve it under high Mach number(Ma=4)flight conditions,the overset grid method and the Realizable k−εturbulence model coupled with an equation with six degrees of freedom are used to simulate the store released from the internal bay.The motion trajectory and the attitude angle of the store separation under the conditions of different centroid,velocity,height and control measures are given by the calculated result.Through analysis,the position of the centroid will affect the separation of the store,which needs to be considered in the design.Increasing the launching height is conducive to the separation of the store.If the store has an initial velocity,it can leave the internal bay more quickly and reduce the probability of collision with the wall.Cylindrical rod and slanted aft wall control measures can improve the attitude of the store and make the store fall more smoothly.

下腰椎椎体在不同负荷下屈伸运动特点的分析

目的探索不同负重状态下直立位腰椎L_(3)、L_(4)椎体屈伸运动过程中体运动轨迹,分析负重状态下腰椎在体运动的规律和特点。方法招募2018年8月至2020年8月10名无症状的青年志愿者,使用双荧光透视系统DFIS与CT相匹配技术,经平扫CT获取L_(3)~S_(1)的图像进行三维重建。于放射线透视不同负重下0、5、10 kg完成下腰椎的前屈到直立到后伸动作获得X线影像,通过轮廓重叠实现二维到三维图像的匹配,还原下腰椎椎体的三维运动轨迹。结果下腰椎在前屈到站立位时:不同负重下腰椎椎体0、5、10 kg的X轴的运动位移分别为-1.05(-2.42,1.72)、0.63(0.15,4.26)、-0.39(-0.75,3.12)mm。X轴运动位移比较5 kg>10 kg>0 kg,差异有统计学意义(P<0.05)。γ角度分别为-0.26(-1.30,5.43)、0.93(0.24,5.42)、-0.95(-2.12,4.32)°。γ角度比较5 kg>0 kg>10 kg,差异有统计学意义(P<0.05)。下腰椎在站立到后伸位时:不同负重下腰椎椎体0、5、10 kg X轴的运动位移分别为0.90(-0.82,3.74)、-0.91(-1.55,4.26)、0.07(-0.92,3.25)mm。Z轴的运动位移分别为-0.25(-0.54,1.78)、0.40(-0.68,2.37)、-0.19(-0.92,1.03)mm。X轴运动位移比较0 kg>10 kg>5 kg,Z轴运动位移比较5 kg>10 kg>0 kg,差异有统计学意义(P<0.05)。α角度分别为0.91(-0.82,2.85)、-0.61(-0.14,3.79)、0.54(-0.82,3.87)°。γ角度分别为1.15(0.24,5.32)、0.92(-0.67,5.45)、0.65(-1.24,5.32)°。α角度比较0 kg>10 kg>5 kg,γ角度比较0 kg>5 kg>10 kg,差异有统计学意义(P<0.05)。结论负重5 kg下腰椎椎体在体运动的位移和旋转角度和0 kg相比差异有统计学意义,可能与腰椎退行性疾病有一定关联。下腰椎退行性疾病可能与X轴位移的关系更为密切。

子母无人机多体分离气动特性模拟

子母机多体分离过程中气动干扰特性的分析是集群无人机发射技术的重要研究方向。基于动态嵌套非结构多面体网格技术,耦合求解流场非定常N-S方程与刚体六自由度运动方程,实现了子母机多体分离过程的精确模拟。首先,对母机的气动干扰区和子母机的分离方式进行分析,其次,计算得到整体状态时子母机以及子机与子机之间的气动干扰特性,最后,根据多体分离过程中子机运动状态的变化情况,进行安全特性评估。研究结果表明:相对于减速分离,加速分离能够快速脱离气动干扰区,安全性更高,并且随着子机数量的增加,子机机翼的距离不断减小,在一定程度上减弱了子机的翼尖涡对翼面的影响,增大了子机的升力。

基于弹性网络回归的地震动参数排序与比选

为合理选取地震动参数以有效减小结构损伤预测的不确定性,基于弹性网络回归技术对多个地震动参数进行了比选。基于多种地震动参数以及大量单自由度(SDOF)模型的增量动力分析结果建立弹性网络回归模型,定义回归模型中回归系数值以及回归系数值为非零值的个数分别为地震动参数的敏感性系数和频数。基于地震动参数敏感性和频数分析结果对多种地震动参数进行排序,研究结构恢复力模型、地震动集和结构极限状态对地震动参数排序结果的影响。基于一座8层钢框架结构分析结果验证了基于弹性网络回归的地震动参数比选方法的有效性。结果表明:选取代表性的地震动参数加入最小二乘回归模型时,不同结构极限状态下回归分析中残差标准差显著减小。基于大量SDOF体系的地震动参数排序结果比选出了受地震动集、结构恢复力模型和结构极限状态影响较小的地震动参数。结果可为结构抗震能力预测用地震动参数的比选提供理论基础。

球面2-DOF冗余驱动并联机器人静力学全解

以球面2-DOF冗余驱动并联机器人为研究对象,在考虑构件弹性的情况下,采用传统的拆杆法建立机构的静力学平衡方程,利用积分法求出各杆件变形,再运用小变形叠加原理建立机构的变形补充协调方程,共得到42个方程,但该机构为冗余机构,共有43个未知数,为此采用输入力优化方法,得到该机构静力学全解。通过数值算例,绘制输出轴在外载荷作用下沿给定轨迹的受力图。研究为该机构在工程中的结构设计与应用提供了静力学理论基础。

弹塑性SDOF系统的地震输入能量谱

以4种场地土条件下40条强震记录为输入,分析了弹塑性单自由度(Single Degree of Freedom,SDOF)系统的地震输入能量谱,并对地震动强度和SDOF系统参数对地震输入能量谱的影响进行了研究。结果表明:能量谱峰值主要由地震动强度决定,阻尼比和延性系数有很大影响。在长周期范围,延性系数一定时,随着阻尼比的增大,能量谱值也有所增大;随延性系数增大,能量谱值随阻尼比增加而增大的趋势有所减缓。采用归一化方法,根据能量谱的特征建议了简化三段式地震输入能量谱,并根据能量谱分析结果的统计,建议了弹塑性SDOF系统能量谱峰值和能量谱曲线参数的确定方法。

基于等损伤的主余震序列型地震动PGA放大系数谱研究

大地震发生后往往会伴随强余震发生,强烈余震会加重结构的破坏程度,在抗震设计及结构损伤评估中考虑余震的影响是一重要课题。采用NGA-West2数据库建立主余震序列型地震动记录数据集,基于损伤等效思想定义主余震作用下PGA放大系数α,针对单自由度体系结构,通过动力时程分析建立不同相对强度、不同场地条件下平均PGA放大系数谱,进一步通过回归分析构建PGA放大系数谱的预测方程,分析统计结果的离散性。结果表明:PGA放大系数谱受场地条件影响较小,受主余震相对强度影响显著;放大系数谱值随周期增大而减小。谱预测方程能够提供目标损伤下结构的主震PGA放大需求,并可以作为设计谱调整系数使用,以实现在结构抗震设计及结构损伤评估中考虑余震的影响。

弹性SDOF系统的地震输入能量谱

本文以4种场地土条件下40条强震记录为输入,对弹性单自由度(SDOF)系统的地震输入能量谱进行了研究。首先研究了SDOF系统参数和地面运动参数对弹性地震输入能量谱的影响。结果表明,在中长周期范围,弹性SDOF系统的阻尼比和地面运动强度对能量谱峰值有较大影响;在长周期范围,随弹性SDOF系统阻尼比的增大,能量谱值也有所增大。随后,采用归一化能量谱方法,并根据能量谱曲线的特征,建议了简化三段式地震输入能量谱。在此基础上,根据4种场地土条件下40条强震记录能量谱计算结果的统计分析,建议了能量谱峰值和能量谱曲线参数的确定方法。

基于改进迭代学习的并联6-DOF运动平台控制策略研究

为了改善并联6-DOF运动平台的轨迹跟踪效果提出了一种新颖的控制算法。该控制方法结合了非奇异Terminal滑模控制(NTMSMC)和迭代学习控制(ILC),非奇异Terminal滑模控制器可以在有限的时间到达和消除控制器奇异,将其作为第一控制器来处理模型参数不确定性、未知的非线性和外部干扰;在到达滑模面之后,用PD型迭代学习控制器作为第二控制器来消除周期性轨迹跟踪误差。Simulink仿真结果表明,这种组合控制器与其它控制器(如PID控制、滑模控制、迭代学习控制)相比有更高的轨迹跟踪精度和较强的鲁棒性。

自主式水下机器人滑模容错自动化控制方法

针对因水下机器人工作环境噪声影响较大、难以提取故障特征点,导致控制精准度较低的问题,该文提出一种滑模容错自动化控制方法。建立机器人五自由度空间方程以及故障执行器的动力学方程,计算机器人每个关键滑模点的不确定性因素变化矢量,推导得到机器人的离散故障状态方程。根据机器人在期望状态下的滑模特性,将故障状态参数代入后,识别定位到故障点,提取机器人线性反馈的控制规律,设定机器人在滑模容错控制函数中的双曲正切函数,计算产生滑模动态的控制输入值,实现自动化控制。实验结果证明,所提方法在第25 s处即发现故障,输出信号幅值稳定在-28 Hz~28 Hz之间,具有良好的自动化控制能力。

Spar平台多自由度耦合的涡激运动数值模拟研究

为研究Spar平台在均匀流作用下多自由度耦合的涡激运动特性,本文基于STAR-CCM+求解器建立了考虑流固耦合的Spar平台涡激运动数值模型,探讨了纵荡、横荡、垂荡、纵摇和横摇五个自由度的耦合效应。结果表明:Spar平台在横荡、垂荡与横摇三个自由度发生明显“涡激共振”现象,并且垂荡与横摇自由度“涡激共振”现象发生的速度区间基本一致;横荡与横摇自由度保持着较高的耦合性,横荡共振时横荡与横摇的运动主频保持1:1的关系,横摇共振时横荡运动频谱的次峰频率等于横摇运动主频;纵荡、垂荡与纵摇三个自由度存在复杂的非线性耦合运动关系,不仅纵荡、垂荡的运动主频始终存在于纵摇频谱中,而且纵摇与纵荡、纵摇与垂荡的耦合程度在不同的折合速度范围内存在差异。

考虑风险极限的建筑钢结构抗震延性检测仿真

抗震延性是衡量建筑结构在地震荷载下是否具备足够延性和韧性的重要指标。传统的静力测试方法往往需要破坏性取样,对结构造成一定的损伤。为了解决传统方法中存在的问题,提出考虑风险极限的建筑钢筋结构抗震延性检测方法。通过三参数模型获取地震加速度反应谱,以描述地震的强度作用;建立建筑钢筋等效单自由度体系,并获取建筑钢筋的结构特征参数;在考虑风险极限的情况下,通过地震中建筑钢筋延性能力与地震中风险极限下建筑钢筋的延性需求值的对比,完成建筑钢筋结构的抗震延性检测。实验结果表明,所提方法的建筑钢筋结构抗震延性检测精度在85%以上,且准确度高、整体应用效果好。

基于Leap Motion的机械臂交互控制研究

针对多旋转自由度机械臂的便捷控制问题,建立了一种联接体感设备Leap Motion与六自由度机械臂的交互控制系统。在体感输入和机械臂运动响应模型中,利用基于几何方法的机械臂运动学逆解,提出一种增加求解约束,二分搜索末端抓取器最优空间位姿的解法。这种解法运行效率高,求解过程直观,能够在对数级时间内求解。经过仿真和实物实验验证,该解法具备处理大量体感输入数据,实现机械臂实时响应的能力,为非触控式的体感机械臂控制提供了一种可行方案。

THE NOVEL ANNULAR ENVELOPE CYLINDRICAL WORM AND FUZZY OPTIMAL DESIGN OF ITS DRIVE

The cylindrical worm processed by annular grinding wheel envelope in two degree of freedom motion state is a novel worm. This paper explains the shaping principle of such a worm. To improve meshing quality and the properties of contact and lubrication, the multi objective optimization has been conducted for the first time to the parameters of such a worm pair by the fuzzy optimal method. The results show that, the shape of the contact line is visibly more sloped than before being optimized, lubrication angle is apparently bigger, and the distribution of contact lines is much improved.

Numerical Simulation of a Planing Vessel at High Speed

Planing vessels are applied widely in civil and military situations.Due to their high speed,the motion of planning vessels is complex.In order to predict the motion of planning vessels,it is important to analyze the hydrodynamic performance of planning vessels at high speeds.The computational fluid dynamic method（CFD） has been proposed to calculate hydrodynamic performance of planning vessels.However,in most traditional CFD approaches,model tests or empirical formulas are needed to obtain the running attitude of the planing vessels before calculation.This paper presents a new CFD method to calculate hydrodynamic forces of planing vessels.The numerical method was based on Reynolds-Averaged Navier-Stokes（RANS） equations.The volume of fluid（VOF） method and the six-degrees-of-freedom equation were applied.An effective process was introduced to solve the numerical divergence problem in numerical simulation.Compared with experimental results,numerical simulation results indicate that both the running attitude and hydrodynamic performance can be predicted well at high speeds.