Numerical Simulation of Non-linear Joint Using Displacement Discontinuity Method

An iterative algorithm for modeling of non-linear joint by the displacement discontinuity method (DDM) was described, and the effect of the non-linear joint on the in-situ stress field was investigated in this paper. The Barton-Bandis (BB) non-linear joint model and failure criterion were adopted in the new DDM program. Using this program, the stress field around the non-linear joint was obtained, the parameters analysis of the joint was carried out, and the deformation and stress distribution of the joint were studied. The simulation results show that: (1)the in-situ stress is significantly affected by the joint; (2)the increase of stiffness, friction angle, and thickness of the joint affect the stress concentration in different ways; (3)the influence distance of the joint changes with the angle of the joint; (4)the deformation and stress of the joint change with the point position.

Fractional Order Linear Active Disturbance Rejection Control for Linear Flexible Joint System

A linear flexible joint system using fractional order linear active disturbance rejection control is studied in this paper.With this control scheme,the performance against disturbances,uncertainties,and attenuation is enhanced.Linear active disturbance rejection control(LADRC)is mainly based on an extended state observer(ESO)technology.A fractional integral(FOI)action is combined with the LADRC technique which proposes a hybrid control scheme like FO-LADRC.Incorporating this FOI action improves the robustness of the standard LADRC.The set-point tracking of the proposed FO-LADRC scheme is designed by Bode’s ideal transfer function(BITF)based robust closed-loop concept,an appropriate pole placement method.The effectiveness of the proposed FO-LADRC scheme is illustrated through experimental results on the linear flexible joint system(LFJS).The results show the enhancement of the robustness with disturbance rejection.Furthermore,a comparative analysis is presented with the results obtained using the integer-order LADRC and FO-LADRC scheme.

Linear inversion-imaging method based on joint primary refl ected waves and surface-related multiples

In marine seismic exploration,especially in deep-water and hard ocean-bottom cases,free-surface multiples are strongly developed.Compared with primary waves,the wider illumination aperture of the multiples is beneficial for high-resolution seismic imaging.In this study,by introducing a new compound source composed of primaries and free-surface multiples and by ignoring internal multiples,we derive a new linearized forward problem(free-surface-multiple prediction model)under a weak-scattering assumption(i.e.,first-order Born approximation).On the basis of the new linearized problem,we propose a joint inversion-imaging method by simultaneously using the primaries and free-surface multiples under the general framework of least square inversion.To eliminate the crosstalk artifacts introduced by the cross-correlation of multiples with different orders,we prove that the crosstalk artifacts can be gradually eliminated during the inversion if a proper step length is selected.Synthetic-andfield-data tests demonstrate the effectiveness of the proposed method.

基于局部Transformer的泰语分词和词性标注联合模型

泰语分词和词性标注任务二者之间存在高关联性,已有研究表明将分词和词性标注任务进行联合学习可以有效提升模型性能,为此,提出了一种针对泰语拼写和构词特点的分词和词性标注联合模型。针对泰语中字符构成音节,音节组成词语的特点,采用局部Transformer网络从音节序列中学习分词特征;考虑到词根和词缀等音节与词性的关联,将用于分词的音节特征融入词语序列特征,缓解未知词的词性标注特征缺失问题。在此基础上,模型采用线性分类层预测分词标签,采用线性条件随机场建模词性序列的依赖关系。在泰语数据集LST20上的试验结果表明,模型分词F1、词性标注微平均F1和宏平均F1分别达到96.33%、97.06%和85.98%,相较基线模型分别提升了0.33%、0.44%和0.12%。

基于无网格方法的机械结合面接触分析

典型的无网格方法采用移动最小二乘函数(moving least squares,MLS)作为近似函数,但由于MLS不具备Kronecker delta函数性质,本质边界施加困难。LRPIM是采用径向基点插值形函数的无网格方法,本质边界条件无需特殊处理,可以直接施加,在保持高精度的前提下提高计算效率。将LRPIM应用于机械结合面接触问题的计算。根据位移连续条件推导了含接触特性的线性互补方程,建立了基于LRPIM的计算模型,采用线性互补算法利用数值积分计算了几种典型的接触问题,得到了接触面压力分布和接触变形,分析了插值函数形状参数和积分域尺寸对计算结果的影响。研究结果表明,插值函数形状参数α_(c)对接触力的影响较小,而形状参数q取-0.5~1.2时有较好的收敛效果;积分域无量纲尺寸a_(qx)、a_(qy)大于1.5时计算结果开始收敛,大于2.5时出现发散现象,取值2.1时收敛效果最佳。将计算结果与已有结果进行比较,表明本研究方法有较高的求解精度。

基于传感器获取骨架信息的舞蹈动作分类

为了对视频中的舞蹈动作规范性实现有效分类,提出了一种基于Kinect传感器获取人体骨骼运动数据的舞蹈分类方法。通过视频每帧中舞蹈动作的六个核心角度生成级联向量,运用主成分分析(PCA)将高维向量投影到低维空间,结合线性判别分析(LDA)得到具有识别能力的特征向量。设计了基于校正线性单元(ReLU)的极限学习机分类器(ELMC),利用ReLU函数解决神经网络设计中的梯度消失问题,在不需权值学习的情况下实现了舞蹈动作的快速分类处理。实验结果表明:与传统方法相比,文中方法具有更好的分类结果且最大分类率可达到96.5%。

考虑横纵向误差协调的智能汽车路径跟踪控制研究

针对传统轨迹跟踪控制方法应用场景局限,精度不高的问题,为实现车辆横纵向联合控制从而提升无人驾驶汽车在结构化场景下的轨迹跟踪效果,本文建立了自然坐标系下的车辆跟踪误差模型,设计基于LQR与PID相结合的车辆横纵向耦合控制器。在横向控制层面,为消除系统稳定误差,通过引入前馈控制量实现系统的整体稳定,减小车辆在实际运行过程中产生的横向误差,提升控制过程的稳定性;在纵向控制层面,运用PID控制策略进行调节,实现车辆的实际速度与规划速度,实际位置与规划位置之间的精确匹配。通过MATLAB/Simulink与Carsim搭建联合仿真平台,针对日常泊车、驶入主路以及超车多种工况进行仿真验证。仿真结果表明:本文所设计的横纵向联合控制器将车辆的轨迹跟踪误差控制在可接受范围之内的同时,轨迹跟踪效果满足乘客对车辆乘坐舒适性的要求,故本文设计的控制器具备一定的稳定性和准确性。

基于特征模型的5阶关节伺服系统扰动补偿策略

针对工业机器人关节伺服系统负载时变和模型不确定性问题,提出将线性扩张状态观测器和基于特征模型的全系数自适应控制相结合的控制策略。建立双惯量柔性关节动力学模型并得到关节伺服系统5阶扩张状态方程。基于该模型设计5阶线性扩张状态观测器,通过该观测器估计系统总扰动并进行扰动补偿,并证明观测器收敛性。基于特征建模的方法,通过实验数据和梯度下降法对特征参数进行辨识,并基于参数值设计全系数自适应控制律,将该控制律结合线性扩张状态观测器设计一种控制策略,对系统进行精确控制。实验结果表明,新的控制策略使系统在变负载扰动工况下的定位精度达到0.003°,正弦信号跟踪误差保持在0.92°以内,系统具有较强的鲁棒性和控制精度。

基于GWO-PSO算法的四旋翼飞行器LADRC参数整定

针对线性自抗扰控制器参数整定繁琐的问题,提出了一种基于灰狼算法与粒子群算法联合改进(GWO-PSO)的控制器参数整定方法。将粒子群算法中的粒子种群替换为灰狼算法中的灰狼种群,提高其全局搜索能力;改进收敛因子使其以指数形式变化,提高其寻优精度;在绝对误差积分准则(ITAE)的基础上改进适应度函数,使其与超调量和系统误差相关联,并根据线性自抗扰控制器控制的四旋翼飞行器模型特点,将控制器参数ω0、ωc和b0作为改进算法中的种群进行整定。仿真结果表明,经改进算法优化的控制器,能够满足控制系统的动态性能和稳态性能要求。

硅橡胶绝缘材料温度及场强依赖特性对XLPE绝缘直流电缆预制接头内电场分布的影响

为选择合适的电缆接头绝缘材料,以改善电缆接头内的电场分布,探究了接头绝缘常用材料硅橡胶的电导温度及场强依赖特性对XLPE直流电缆预制接头中电场分布的影响。首先,针对10 kV电压等级XLPE绝缘直流电缆预制接头结构建立相应的仿真模型。然后,改变硅橡胶材料的电导非线性特征参数,得到对应接头在满载运行状态下的绝缘内电场分布。结果表明:随着硅橡胶材料电导活化能的增大或电导场强依赖系数的减小,接头绝缘交界面处的场强增大,且应力锥根部场强增幅明显;从经济性角度考虑给出硅橡胶与XLPE绝缘材料的电导活化能之比和电导场强依赖系数之比推荐值分别为不高于0.95和不低于0.50,可作为工程上选择确定合适接头绝缘材料的参考。

考虑道路受阻的森林火灾应急资源联合调度优化研究

针对森林火灾发生后可能存在的交通路网受阻情况,探讨一类新的森林火灾应急资源联合调度优化策略,构建了兼顾资源受限和道路受阻的森林火灾应急资源联合调度的混合整数线性规划模型。为减少森林火灾造成的资源损失,优化目标设定为最小化消防救援时间,并且根据问题特性设计两种编码方式的改进人工蜂群算法。最后,通过典型实例和随机仿真算例进行实验验证。实验结果表明:(1)对于实际案例和中小规模仿真案例,采用商业求解器CPLEX求解模型,能够在5 min内获得最优的消防救援方案;(2)对于大规模森林火灾,提出的改进人工蜂群算法求解性能优于商业求解器CPLEX,只需10 s就能够获得更高质量的消防救援方案,可为道路受阻下的森林火灾应急救援团队提供有效的消防救援方案。

基于线性强化结构应变法的低周疲劳分析

焊接结构的低周疲劳分析对于轨道车辆尤为重要。为了有效评估焊接结构的低周疲劳,提出一种基于线性强化本构的结构应变数值计算方法。该方法基于经典板壳理论和弹塑性力学。通过考虑材料的应变硬化行为,将材料的真实应力应变关系简化为线性强化本构关系。利用有限元分析软件ABAQUS和Fe-safe计算焊接结构焊趾位置的结构应力,给出基于径向回退算法的线性强化本构塑性修正模型。利用MATLAB编写结构应变数值计算程序对结构应力进行塑性修正,并计算结构应变。基于该结构应变,给出了考虑板厚效应和载荷模式的等效结构应变范围计算公式,利用主应变-寿命曲线分析低周疲劳数据,建立了广泛用于轨道车辆的Q450高强度耐候钢材料制成的3种焊接接头的有限元模型。采用结构应力法的主应力-寿命曲线和结构应变数值计算方法的主应变-寿命曲线对试验获得的疲劳数据进行分析,并对比2种方法计算的等效结构应变范围。结果表明,各焊接接头的试验数据均分布在主应变-寿命曲线的线性窄带内,验证了结构应变数值计算法的可行性;与结构应力法相比,结构应变数值计算方法能更好地反映低周疲劳过程中材料的应变硬化现象,更适用于焊接结构的低周疲劳评估。该方法对轨道车辆焊接板结构的低周疲劳评估具有研究价值。与传统的通过提取节点力的方式计算结构应力和结构应变参数的方法相比,利用MATLAB编写结构应变数值计算程序极大地提高了结构应变参数计算的效率。

Stress-strain characteristics of linear friction welding of TC11 and TC17 alloys

Abstract Transient stress and strain fields of dissimilar titanium alloys （TCll and TC17 ） joint during linear friction welding （ LFW） were investigated by a two-dimensional model with ABAQUS/Explicit. The results showed that in the X-axis, the maximum compressive stress of 850 MPa occurred in the center zone of friction interface , and the maximum tensile stress of 190 MPa distributed at the flash; in the Y-axis, the maximum compressive stress of 1 261 MPa located at the junction region between the welding fixture and edge of the specimen, and the maximum tensile stress of 320 MPa distributed in the connecting portion between the flash and edge of the specimen. In addition, areas of plastic strain increased gradually during welding process. In the X-axis, tensile strain mainly existed at the heads of the specimens; in the Y-axis, compressive strain mainly occurred at the heads of the specimens.

Shear strength criteria for rock,rock joints,rockfill and rock masses:Problems and some solutions

Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has recently been better defined,and correct curvature or correct deviation from linear Mohr-Coulomb（MC） has finally been found.Standard shear testing procedures for rock joints,using multiple testing of the same sample,in case of insufficient samples,can be shown to exaggerate apparent cohesion.Even rough joints do not have any cohesion,but instead have very high friction angles at low stress,due to strong dilation.Rock masses,implying problems of large-scale interaction with engineering structures,may have both cohesive and frictional strength components.However,it is not correct to add these,following linear M-C or nonlinear Hoek-Brown（H-B） standard routines.Cohesion is broken at small strain,while friction is mobilized at larger strain and remains to the end of the shear deformation.The criterion ＇c then σn tan φ＇ should replace ＇c plus σn tan φ＇ for improved fit to reality.Transformation of principal stresses to a shear plane seems to ignore mobilized dilation,and caused great experimental difficulties until understood.There seems to be plenty of room for continued research,so that errors of judgement of the last 50 years can be corrected.

Comparison and analysis of two Coulomb friction models on the dynamic behavior of slider-crank mechanism with a revolute clearance joint

The objective of this study is to investigate the effects of the Coulomb dry friction model versus the modified Coulomb friction model on the dynamic behavior of the slider-crank mechanism with a revolute clearance joint. The normal and tangential forces acting on the contact points between the journal and the bearing are described by using a Hertzian-based contact force model and the Coulomb friction models, respectively.The dynamic equations of the mechanism are derived based on the Lagrange equations of the first kind and the Baumgarte stabilization method. The frictional force is solved via the linear complementarity problem(LCP) algorithm and the trial-and-error algorithm.Finally, three numerical examples are given to show the influence of the two Coulomb friction models on the dynamic behavior of the mechanism. Numerical results show that due to the stick friction, the slider-crank mechanism may exhibit stick-slip motion and can balance at some special positions, while the mechanism with ideal joints cannot.

基于非线性超声的电缆接头硅橡胶热老化状态检测

针对硅橡胶的热老化问题,引入非线性超声检测方法展开相关的试验研究。对电缆接头硅橡胶试样在200℃下进行不同时长的热老化试验,测试分析老化试样的相对非线性系数、微观结构、表面形貌的变化趋势。结果表明:随着热老化时间的增加,硅橡胶的相对非线性系数呈现明显的上升趋势,基于测试结果拟合得到相对非线性系数与热老化时间之间具有良好的线性关联度,可决系数R2>0.95;热老化后硅橡胶的有机成分逐渐减少,交联程度逐渐增大,表面开始出现局部孔洞、裂纹、填料析出等微观缺陷,微观结构发生一定程度的劣化,导致超声非线性效应增强。

服装数控裁剪机滑轨结合面动态特性分析

滚动直线导轨是服装数控裁剪机床中的关键部件之一。分析导轨结合面动态特性,研究其对数控裁剪机的加工精度及运行平稳性的影响。通过分析数控裁剪机的工作原理,根据滑轨结合面基础接触特性理论,利用SolidWorks三维软件建立滑轨结构实体模型,联合ANSYS软件中Workbench模块建立数控裁剪机滑轨结构仿真模型,并搭建模态测试系统,研究了数控裁剪机滑轨在负载下导轨结合面的力学特性。结果表明:数控裁剪机滑轨结构前六阶模态固有频率的试验结果与有限元仿真分析结果基本吻合,误差值小于10%,并利用有限元仿真得到的谐响应分析结果,计算出服装数控裁剪机滑轨的法向刚度为249.6 N/μm和切向刚度为170.2 N/μm。该研究结果可以为数控裁剪机床的振动分析和振动控制的研究及其动态特性分析和结构优化设计提供理论依据。

考虑地连墙槽段接缝影响的竖井应力和变形规律研究

由地下连续墙(简称“地连墙”)筑成的圆形围护结构径向变形小,在竖井工程中得到广泛应用,但在计算中如何合理考虑其环向效应是亟待解决的科学问题。为揭示地连墙槽段接缝泥皮对圆形超深竖井应力变形的影响,在某输水隧洞超深竖井数值分析中,采用实体单元模拟地连墙Ⅰ、Ⅱ槽段接缝泥皮,并在地连墙-岩土、混凝土衬砌-地连墙、地连墙-缝间填充物之间均设置接触面,对泥皮缝宽、材料特性进行了参数敏感性研究,获得了竖井支护结构的受力特征。结果表明:地连墙受力以竖向应力与竖向弯矩为主,随缝宽的减小或者缝模量的提高,地连墙的径向位移、竖向弯矩与竖向压力均减小,而环向压力增大;在开挖至土岩交界面时地连墙径向位移与竖向弯矩最大,开挖至坑底时环向弯矩最大。圆形衬砌受力以环向为主,其与地连墙受力方向互补,弥补了地连墙槽段接缝泥皮的环向削弱作用。研究成果可为竖井的设计优化与施工提供技术支撑。

FD-MIMO下行系统中基于空时码下的联合选码方法

对于三维多输入多输出(Full-Dimension Multiple Input Multiple Output,FD-MIMO)下行系统,基站侧配备N根传送天线,用户端仅有单接收天线的场景,提出了基于空时码与联合选码结合的传送方案,以及低复杂度的解码方法。在充分利用空时码能够克服信道深度衰落的特性基础上,通过两次发送信息构建等价信道,从而实现线性解码。此外,还给出了基于此信道模型下的反馈开销的下限值及复杂度的分析。最后,对所提方案进行了仿真,其结果与理论分析一致。

胫骨平台骨折合并髁间棘骨折术后膝关节功能恢复效果影响因素分析

目的分析胫骨平台骨折合并髁间棘骨折患者术后膝关节功能恢复效果的影响因素。方法选取2020年5月至2021年3月驻马店市第一人民医院收治的40例胫骨平台骨折合并髁间棘骨折患者作为研究对象,收集患者性别、年龄、职业、骨折Schatzker分型、受伤原因、受伤至手术时间、手术方式、髁间棘骨折块是否游离、康复起始时间、是否使用支具、付费方式、末次随访时美国特种外科医院(HSS)评分等资料,采用多重线性回归分析影响术后膝关节功能恢复效果的相关因素。结果40例患者术后随访6~7个月[(6.40±0.24)个月],末次随访时HSS评分为75~100分[(88.55±6.54)分]。单因素分析结果显示,不同年龄、职业、骨折Schatzker分型、受伤原因以及髁间棘骨折块游离情况患者HSS评分差异均具有统计学意义(t/F=9.741、3.436、4.763、4.482、4.879,P<0.001、P=0.043、P=0.001、P=0.009、P<0.001);多重线性回归分析结果显示,骨折Schatzker分型、髁间棘骨折块是否游离是胫骨平台骨折合并髁间棘骨折患者术后膝关节功能恢复效果的独立影响因素(95%CI为-13.420~2.113、11.482~23.121,P=0.006、P<0.001)。结论骨折Schatzker分型、髁间棘骨折块是否游离是影响胫骨平台骨折合并髁间棘骨折患者术后膝关节功能恢复效果的重要因素,临床应根据患者具体情况制定针对性干预措施,以提高治疗效果。