Distributed Contact Plan Design for Multi-Layer Satellite-Terrestrial Network

In multi-layer satellite-terrestrial network, Contact Graph Routing(CGR) uses the contact information among satellites to compute routes. However, due to the resource constraints in satellites, it is extravagant to configure lots of the potential contacts into contact plans. What's more, a huge contact plan makes the computing more complex, which further increases computing time. As a result, how to design an efficient contact plan becomes crucial for multi-layer satellite network, which usually has a large scaled topology. In this paper, we propose a distributed contact plan design scheme for multi-layer satellite network by dividing a large contact plan into several partial parts. Meanwhile, a duration based inter-layer contact selection algorithm is proposed to handle contacts disruption problem. The performance of the proposed design was evaluated on our Identifier/Locator split based satellite-terrestrial network testbed with 79 simulation nodes. Experiments showed that the proposed design is able to reduce the data delivery delay.

Multi-point Contact of the High-speed Vehicle-turnout System Dynamics

The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.

Friction Characteristics of Nanoscale Sliding Contacts between Multi-Asperity Tips and Textured Surfaces

Nanoscale sliding contacts of smooth surfaces or between a single asperity and a smooth surface have been widely investigated by molecular dynamics simulations, while there are few studies on the sliding contacts between two rough surfaces. Actually, the friction of two rough surfaces considering interactions between more asperities should be more realistic. By using multiscale method, friction characteristics of two dimensional nanoscale sliding contacts between rigid multi-asperity tips and elastic textured surfaces are investigated. Four nanoscale textured surfaces with different texture shapes are designed, and six multi-asperity tips composed of cylindrical asperities with different radii are used to slide on the textured surfaces. Friction forces are compared for different tips, and effects of the asperity radii on the friction characteristics are investigated. Average friction forces for all the cases are listed and compared, and effects of texture shapes of the textured surfaces are discussed. The results show that textured surface II has a better structure to reduce friction forces. The multi-asperity tips composed of asperities with R=20r0 （r0=0.227 7 nm） or R=30r0 get higher friction forces compared with other cases, and more atoms of the textured surfaces are taken away by these two tips, which are harmful to reduce friction or wear. For the case of R=10ro, friction forces are also high due to large contact areas, but the sliding processes are stable and few atoms are taken away by the tip. The proposed research considers interactions between more asperities to make the model approach to the real sliding contact problems. The results will help to vary or even control friction characteristics by textured surfaces, or provide references to the design of textured surfaces.

An efficient formulation based on the Lagrangian method for contact–impact analysis of flexible multi-body system

In this paper,an efficien formulation based on the Lagrangian method is presented to investigate the contact–impact problems of f exible multi-body systems.Generally,the penalty method and the Hertz contact law are the most commonly used methods in engineering applications.However,these methods are highly dependent on various non-physical parameters,which have great effects on the simulation results.Moreover,a tremendous number of degrees of freedom in the contact–impact problems will influenc thenumericalefficien ysignificantl.Withtheconsideration of these two problems,a formulation combining the component mode synthesis method and the Lagrangian method is presented to investigate the contact–impact problems in fl xible multi-body system numerically.Meanwhile,the finit element meshing laws of the contact bodies will be studied preliminarily.A numerical example with experimental verificatio will certify the reliability of the presented formulationincontact–impactanalysis.Furthermore,aseries of numerical investigations explain how great the influenc of the finit element meshing has on the simulation results.Finally the limitations of the element size in different regions are summarized to satisfy both the accuracy and efficien y.

Contact-impact formulation for multi-body systems using component mode synthesis

The efficiency and accuracy are two most concerned issues in the modeling and simulation of multi-body systems involving contact and impact. This paper proposed a formulation based on the component mode synthesis method for planar contact problems of flexible multi-body systems. A flexible body is divided into two parts： a contact zone and an un-contact zone. For the un-contact zone, by using the fixed-interface substructure method as reference, a few low-order modal coordinates are used to replace the nodal coordinates of the nodes, and meanwhile, the nodal coordinates of the local impact region are kept unchanged, therefore the total degrees of freedom （DOFs） are greatly cut down and the computational cost of the simulation is significantly reduced. By using additional constraint method, the impact constraint equations and kinematic constraint equations are derived, and the Lagrange equations of the first kind of flexible multi-body system are obtained. The impact of an elastic beam with a fixed half disk is simulated to verify the efficiency and accuracy of this method.

Multi-body Contact Problem of Loose-fitted Tyre of Rotary Kiln

According to the character and the condition for shell deformation and force balance, we have set up the mathematical models of the contact angle and the contact pressure distribution between the tyre and the shell, studied The features of a multi-body contact model between the roller and the tyre, and developed the build-up procedure of the contact finite element model between the roller and the tyre. The stress distribution rule of the roller and the tyre is obtained as follows. The contact center is the center of the contact stress circle, and the contact stress is also reduced gradually from the contact center to the contact boundary. The equivalent stress of the tyre varies 5 times per circle, thus making the trye fracture easily.

多市场接触、相互克制战略与企业绩效——基于企业内部机制视角的研究

以往文献对于企业多市场接触进行了深入而广泛的研究,大多数局限于企业外部视角,很少关注企业内部实施机制对其多市场战略的影响。本文主要考察企业内多市场协同与激励机制对企业相互克制战略实施的影响。我们构建了关于多市场接触、相互克制战略、内部协同机制、多市场激励机制等构念的量表,进行了结构方程分析。结果表明:企业间多市场接触促进了相互克制战略的实施,进而会对企业绩效产生积极影响;企业的内部多市场激励机制对多市场战略与企业绩效间关系具有显著的正向调节作用,但是多市场协同机制的调节效果并不显著。本文认为,合理地安排企业内部协同与激励机制,将对企业实施有效的相互克制战略提供重要支持,进而会对企业绩效有较大的提升作用。

Contact dynamics of elasto-plastic thin beams simulated via absolute nodal coordinate formulation

Under the frame of multibody dynamics, the contact dynamics of elasto-plastic spatial thin beams is numerically studied by using the spatial thin beam elements of absolute nodal coordinate formulation（ANCF）. The internal force of the elasto-plastic spatial thin beam element is derived under the assumption that the plastic strain of the beam element depends only on its longitudinal deformation.A new body-fixed local coordinate system is introduced into the spatial thin beam element of ANCF for efficient contact detection in the contact dynamics simulation. The linear isotropic hardening constitutive law is used to describe the elasto-plastic deformation of beam material, and the classical return mapping algorithm is adopted to evaluate the plastic strains. A multi-zone contact approach of thin beams previously proposed by the authors is also introduced to detect the multiple contact zones of beams accurately, and the penalty method is used to compute the normal contact force of thin beams in contact. Four numerical examples are given to demonstrate the applicability and effectiveness of the proposed elasto-plastic spatial thin beam element of ANCF for flexible multibody system dynamics.

Anovelprofile error model to calculate contact error

A new profile model based on multi-scale asperities is developed and contact error is cal- culated. After stratified sampling, the model can get the distribution law of entity points on each cross section. Asperity radius of curvature is estimated by the relationship between circle radius and the section interval. Contact error is related to surface form error. A model equation of contact error plane is calculated through a method based on static equilibrium theory. Three contact asperities which determine the contact error plane on the rough surface are studied. The simulation results show that contact error can be accurately calculated according to the profile error model.

Surrounding rock deformation analysis of underground caverns with multi-body finite element method

Discontinuous deformation problems are common in rock engineering. Numerical analysis methods based on system models of the discrete body can better solve these problems. One of the most effective solutions is discontinuous deformation analysis （DDA） method, but the DDA method brings about rock embedding problems when it uses the strain assumption in elastic deformation and adopts virtual springs to simulate the contact problems. The multi-body finite element method （FEM） proposed in this paper can solve the problems of contact and deformation of blocks very well because it integrates the FEM and multi-body system dynamics theory. It is therefore a complete method for solving discontinuous deformation problems through balance equations of the contact surface and for simulating the displacement of whole blocks. In this study, this method was successfully used for deformation analysis of underground caverns in stratified rock. The simulation results indicate that the multi-body FEM can show contact forces and the stress states on contact surfaces better than DDA, and that the results calculated with the multi-body FEM are more consistent with engineering practice than those calculated with DDA method.

Acceleration Workspace of Cooperating Multi-Finger Robot Systems

We present a mathematical method for acceleration workspace analysis of cooperating multi-finger robot systems using a model of point-contact with friction. A new unified formulation from dynamic equations of cooperating multi-finger robots is derived considering the force and acceleration relationships between the fingers and the object to be handled. From the dynamic equation, maximum translational and rotational acceleration bounds of an object are calculated under given constraints of contact conditions, configurations of fingers, and bounds on the torques of joint actuators for each finger. Here, the rotational acceleration bounds can be applied as an important manipulability index when the multi-finger robot grasps an object. To verify the proposed method, we used a set of case studies with a simple multi-finger mechanism system. The achievable acceleration boundary in task space can be obtained successfully with the proposed method and the acceleration boundary depends on the configurations of fingers.

多市场接触与企业研发绩效——基于多市场接触细分视角

以往研究对于多市场接触与企业研发行为的关系存在争议性的观点,大多数研究遵循要素市场竞争理论,支持多市场接触下企业的研发绩效会得到提升,但也有少数研究通过实证得出了相反的观点。本文为了在一定程度上解释这种矛盾性观点,从多市场接触的细分视角入手,研究了两种不同的多市场接触(偶然的多市场接触与有意识的多市场接触)对于企业研发绩效的影响。结果表明:偶然的多市场接触正向影响企业的研发绩效;有意识的多市场接触负向影响企业的研发绩效;组织冗余加强了偶然的多市场接触与企业研发绩效的正向关系;环境不确定性减弱了偶然的多市场接触与企业研发绩效的正向关系。

Parameters optimization for direct contact membrane distillation based on orthogonal experiment

Parameter optimization integrating operation parameters and structure parameters for the purpose of high permeate flux,high productivity and low exergy consumption of direct contact membrane distillation (DCMD) process was conducted based on Taguchi experimental design. L16(45) orthogonal experiments were carried out with feed inlet temperature,permeate stream inlet temperature,flow rate,module packing density and length-diameter ratio as optimization parameters and with permeate flux,water productivity per unit volume of module and water production per unit exergy loss separately as optimization objectives. By using range analysis method,the dominance degree of the various influencing factors for the three objectives was analyzed and the optimum condition was obtained for the three objectives separately. Furthermore,the multi-objectives optimization was performed based on a weight grade method. The combined optimum conditions are feed inlet temperature 75℃,packing density 30% ,length-diameter ratio 10,permeate stream inlet temperature 30 ℃ and flow rate 25 L/h,which is in order of their dominance degree,and the validity of the optimization scheme was confirmed.

低耗稳定的四间隙平面连杆多目标优化设计

为提高优化设计效率且更符合工程实践,提出了平面连杆机构低耗平稳的一套可量化的优化设计及评价体系。首先,从运动过程低耗稳定角度完成了综合方案设计和技术设计,基于含摩擦副平面连杆理论模型,建立了低耗稳定平面四连杆优化模型;其次,基于遗传算法,获得该机构的曲柄力矩、铰接点受力峰值和与摇杆角加速度pareto解集;最终,采用含四间隙平面连杆理论模型与龙格库塔法,对5组解动力学数值求解并对比选型。结果表明,满足设计要求下,相比于各目标均衡的方案5,方案1驱动力矩微增0.63%,摇杆角加速度降低了0.41%,各铰接点受力下降了2.94%、11.92%、12.92%、12.04%,既可低耗平稳,又助于减小磨损。该体系能有效减少优化时间,以及传统理论模型与实际差距。

550kV气体绝缘母线大电流工况下温升特性分析

探究气体绝缘母线在超高压大电流工况下的温升特性对设备的正常运行以及监测维护意义重大。然而,在长期大电流负荷运行下,因接触异常等原因导致母线在较小封闭空间内产生大量热量,极易造成局部过热严重威胁设备安全运行。针对这一问题,本文以550kV气体绝缘母线为研究对象,构建了考虑接触电阻的3维电磁-温度-流体多场耦合模型,计算其在1.1倍额定电流(8800A)、气压0.3MPa条件下的母线温度分布,并搭建了大电流温升试验平台进行验证,试验测量结果与仿真结果吻合度高。基于验证后的可靠模型,进一步探究了通流水平、SF_(6)气压及接触状态对母线温度分布的影响规律。结果表明:母线最高温度位于盆子凹面处电接触部位顶部(约为54℃),该端触头上方SF_(6)温度比导杆上方高近15℃,凹面处触头径向温度梯度明显低于凸面处触头径向温度梯度;在非等温自然对流的情况下,母线温度整体呈径向上高下低、轴向端部高中间低的规律分布;母线温度随通流水平提高呈非线性上升、随SF_(6)气压增大呈近似线性下降,可在一定范围内提高设备绝缘气体压强以降低设备运行温度;异常电接触处温度随阻值增大近似线性增加,而电接触异常往往是母线过热的主要风险点。研究结果可为超高压大电流气体绝缘设备产品设计及状态监测提供参考。

含多关节间隙平面柔性六杆机构的动力学分析

为提高机构的动力学分析精度,基于平面六杆机构,同时考虑多个关节间隙与构件柔性对多体机构动力学响应的影响。通过实体建模和引用ADAMS软件中“冲击函数”接触力模型,对含有多个间隙关节与柔性连杆的六杆机构进行动力学模拟仿真,研究间隙数量、间隙位置、间隙大小、柔性连杆及其与间隙耦合对系统动力学性能影响。研究结果表明:与单关节间隙相比,多关节间隙会产生更大的接触力,导致构件的加速度波动更加剧烈;间隙关节距离电机位置越近,则对机构的动力学行为影响越明显;考虑连杆柔性时,可以极大地降低间隙对机构动力学波动的影响。

考虑电磁-热-结构耦合的并沟线夹温升特性分析及验证

为更准确地研究并沟线夹的温升特性,分析了导线与并沟线夹之间接触点的实际分布特征,建立了并沟线夹的三维电磁、热、结构多物理场耦合模型。基于结构场分析线夹与导线安装和发生热膨胀后导线的接触压力,并计算接触电阻,通过电磁-热耦合得到线夹的电流密度及温度分布规律,探明最高温度的具体位置。分析了不同载流量与螺栓松脱程度对线夹最高温度的影响。研究结果表明:当电流流经并沟线夹系统时,导线与线夹本体接触点界面外侧的电流密度最大,造成的发热最严重;载流量越小,螺栓松脱对线夹的最高温度影响越小,反之,螺栓松脱对线夹的最高温度影响越大;相对误差在3%内,模型具有较高的准确性。

融合rPPG和人脸三维法向量的非接触情绪感知技术

近年来,基于深度学习的情绪识别技术取得了显著进展。然而,现有方法主要集中在面部图像或视频上,忽略了其他模态信息,导致鲁棒性和稳定性不足。为了解决这一问题,提出了一种融合多模态信息的面部表情识别方法。首先将输入的人脸视频进行远程光电容积脉搏波(Remote Photo plethysmography,rPPG)信号和人脸三维法向量的提取,其次将这两种模态的信息输入其相应的情绪特征提取子网络,提取出对应的情绪特征向量。然后,将这两种模态提取出的情绪特征向量进行融合,生成一个丰富的特征向量,最后将其输入分类器进行情绪分类任务。通过这种多模态信息融合的方式,提高了面部表情识别的准确性和稳定性。对所提方法在不同数据集上进行了验证,实验结果表明,该方法在多样化面部表情识别中的表现优于当前先进的情感识别方法,具有更高的鲁棒性和稳定性。

基于分层分区域虚拟材料方法的丝杠螺母结合部精确建模研究

为了建立精确的滚珠丝杠螺母结合部模型,基于多目标优化方法获取其结合部虚拟材料模型的参数,构建了精确的结合部虚拟梯度材料模型,从而建立了准确的滚珠丝杠螺母结合部动力学模型,并通过实验对此方法建立的动力学模型进行了实验验证。结果表明:基于虚拟梯度材料法建立的结合部模型具有较高的精度,梯度结构材料层的宏观材料特性在空间上呈现与接触应力随滚珠相位角分布相同的变化,据此能够充分表征滚珠轴承中滚珠和滚道接触面间接触应力分布不均匀的特性。

非堆积型多颗粒阻尼器等效力学模型及其减振性能分析

为考虑颗粒群碰撞过程中时间效应对非堆积型多颗粒阻尼器(non-packed particle damper, NPPD)减振性能的影响,在现有考虑惯容的等效单颗粒力学模型(equivalent inertia single-particle model, EISM)研究基础上,提出了基于接触单元法的等效单颗粒力学模型(equivalent inertia single-particle model based on contact element method, EISM-CE),并基于Runge-Kutta算法建立了NPPD单自由度结构运动状态求解算法。设计进行附加NPPD单层钢框架结构振动台试验,探究不同填充率对结构顶层位移频响曲线的影响规律,提出了EISM-CE参数取值原则,进而进行力学模型试验验证及模型对比分析。在模型验证合理性基础上,基于EISM-CE依次进行了自由振动、简谐激励及记录强震动下减振性能及能量变化规律分析。研究结果表明,与现有EISM相比,提出的基于接触单元法的EISM-CE模型及参数取值原则更加合理有效。减振性能数值分析结果表明,不同激励下NPPD均具有较好的减振性能;考虑碰撞时间效应后EISM-CE与EISM对应减振性能及机理分析结果存在一定的差异。