Dynamic Modeling and Analysis of 4UPS-UPU Spatial Parallel Mechanism with Spherical Clearance Joint

Clearance between the moving joints is unavoidable in real working process. At present, many researches are mainly focused on dynamics of plane revolute joint in plane mechanism, but few on dynamics of spatial spherical joint clearance in spatial parallel mechanism. In this paper, a general method is proposed for establishing dynamic equations of spatial parallel mechanism with spatial spherical clearance by Lagrange multiplier method. The kinematic model and contact force model of the spherical joint clearance were established successively. Lagrange multiplier method was used to deduce the dynamics equation of 4 UPS-UPU mechanism with spherical clearance joint systematically. The influence of friction coefficient on dynamics response of 4 UPS-UPU mechanism with spherical clearance joint was analyzed. Non-linear characteristics of clearance joint and moving platform were analyzed by Poincare map, phase diagram, and bifurcation diagram. The results show that variation of friction coefficient and clearance value had little effect on stability of the mechanism, but the chaotic phenomenon was found at spherical clearance joint. The research has theoretical guiding significance for improving the dynamic performance and avoiding of chaos of parallel mechanisms including spherical joint clearance.

Dynamic Analysis of Submarine Pipelines on an Elastic / Viscoelastic Foundation

This paper presents a new finite element method for solving static and dynamic problems in laying operation of pipelines. The effect of the viscoelastic soil behavior is considered by using the Pasternak foundation model. Some examples are also presented.

Dynamic Modeling of Variable Stiffness and Damping for Spatial Linkage Weft Insertion Mechanism with Clearance

In order to further analyze the influence of clearance on the kinematic performance of spatial linkage weft insertion mechanism,it is necessary to study the dynamic characteristics of contact impact force model with the variable stiffness and damping coefficient.Firstly,the parameters in the output process of the system are solved by describing of the flexible joint clearance.Then,based on Lankarani-Nikravesh contact force model,the contact impact stiffness and damping coefficient is modified from fixed values to time-varying coefficients.The dynamic model of spatial linkage weft insertion mechanism with modified clearance is established by Lagrange method,and the dynamic characteristics of the system are calculated.The results show that the joint clearance can directly affect the output performance of the mechanism.With the increase of the clearance value,the curve fluctuations of acceleration,driving torque and collision force are obvious,and it will be further intensified with the increase of spindle speed,which greatly affects the stability of mechanism and fabric quality.Finally,the virtual prototype is established by the SolidWorks software and simulated by the ADAMS software.The simulation results are compared with the numerical results,which verifies the accuracy of the modeling method in this paper.

Oxidation Kinetics of Aluminum Powders in a Gas Fluidized Bed Reactor in the Potential Application of Surge Arresting Materials

In this technical paper, the oxidation mechanism and kinetics of aluminum powders are discussed in great details. The potential applications of spherical aluminum powders after oxidation to be part of the surging arresting materials are discussed. Theoretical calculations of oxidation of spherical aluminum powders in a typical gas fluidization bed are demonstrated. Computer software written by the author is used to carry out the basic calculations of important parameters of a gas fluidization bed at different temperatures. A mathematical model of the dynamic system in a gas fluidization bed is developed and the analytical solution is obtained. The mathematical model can be used to estimate aluminum oxide thickness at a defined temperature. The mathematical model created in this study is evaluated and confirmed consistently with the experimental results on a gas fluidization bed. Detail technical discussion of the oxidation mechanism of aluminum is carried out. The mathematical deviations of the mathematical modeling have demonstrated in great details. This mathematical model developed in this study and validated with experimental results can bring a great value for the quantitative analysis of a gas fluidization bed in general from a theoretical point of view. It can be applied for the oxidation not only for aluminum spherical powders, but also for other spherical metal powders. The mathematical model developed can further enhance the applications of gas fluidization technology. In addition to the development of mathematical modeling of a gas fluidization bed reactor, the formation of oxide film through diffusion on both planar and spherical aluminum surfaces is analyzed through a thorough mathematical deviation using diffusion theory and Laplace transformation. The dominant defects and their impact to oxidation of aluminum are also discussed in detail. The well-controlled oxidation film on spherical metal powders such as aluminum and other metal spherical powders can potentially become an important part of switch devices of surge arresting materials, in general.

Development and Validation of a Scaled Electric Combat Vehicle Tire Model

Pneumatic tire modeling and validation have been the topic of several research papers, however, most of these papers only deal with pneumatic passenger and truck tires. In recent years, wheeled-scaled vehicles have gained lots of attention as a feasible testing platform, nonetheless up to the authors’ knowledge there has been no research regarding the use of scaled tires and their effect on the overall vehicle performance characteristics. This paper presents a novel scaled electric combat vehicle tire model and validation technique. The pro-line lockdown tire size 3.00 × 7.35 is modeled using the Finite Element Analysis (FEA) technique and several materials including layered membrane, beam elements, and Mooney-Rivlin for rubber. The tire-rim assembly is then described, and the rigid body analysis is presented. The tire is then validated using an in-house custom-made static tire testing machine. The tire test rig is made specifically to test the pro-line tire model and is designed and manufactured in the laboratory. The tire is validated using vertical stiffness and footprint tests in the static domain at different operating conditions including several vertical loads. Then the tire is used to perform rolling resistance and steering analysis including the rolling resistance coefficient and the cornering stiffness. The analysis is performed at different operating conditions including longitudinal speeds of 5, 10, and 15 km/h. This tire model will be further used to determine the tractive and braking performance of the tire. Furthermore, the tire test rig will also be modified to perform cornering stiffness tests.

Progress in Thermomechanical Analysis of Friction Stir Welding

This article reviews the status of thermomechanical analysis of the friction stir welding(FSW)process for establishing guidelines for further investigation,filling the available research gaps,and expanding FSW applications.Firstly,the advantages and applications of FSW process are introduced,and the significance and key issues for thermomechanical analysis in FSW are pointed out.Then,solid mechanic and fluid dynamic methods in modeling FSW process are described,and the key issues in modeling FSW are discussed.Di erent available mesh modeling techniques including the applications,benefits and shortcomings are explained.After that,at different subsections,the thermomechanical analysis in FSW of aluminum alloys and steels are examined and summarized in depth.Finally,the conclusions and summary are presented in order to investigate the lack of knowledge and the possibilities for future study of each method and each material.

Temperature Dependency of Dynamic Mechanical Properties of Cement Asphalt Paste by DMTA Method

We investigated the temperature dependency of the dynamic mechanical properties of cement asphalt paste by the dynamic mechanical thermal analysis（DMTA） method. The experimental results show that the dynamic mechanical properties of cement asphalt pastes are sensitive to temperature due to the inclusion of asphalt, and may go through different states within a temperature range of-40 ℃ to 60 ℃, which is different from that of pure cement and asphalt. As the temperature of the cement asphalt paste increases, a considerable change of dynamic mechanical properties, including storage modulus（E＇）, loss modulus（E＇＇） and loss factor（tand） is observed. Moreover, the influence of asphalt to cement（A/C） ratio on the temperature sensitivity of the dynamic mechanical properties of cement asphalt composites was investigated. The temperature dependency of cement asphalt composites is ascribed to the temperature dependency of the asphalt and its interaction with cement paste. A simple fractional model is proposed to describe the viscoelastic behavior of cement asphalt composites.

Model Simplification and Parameter Modification for Offshore Platforms Using Experiment Data

In this paper, a computation method has been developed so as to compare the finite element method (FEM) with the test results directly. The structure is divided into the 'master' and 'slave' degrees of freedom. The simplified model can be obtained with modal reduction. Then the design sensitivity analysis of the eigenvalues and eigenvectors has been carried out using the modal frequency and modal shape of the test. A two-story frame structure and a jacket model structure have been calculated. Meanwhile, the modified coefficient, the FEM computational and experimental values have been given. It has been shown that the FEM model modified using the test modal value is efficient.

高速短距离阻拦装置动力学建模与仿真分析

针对撞击安全性试验中橇车的高速短距离阻拦需求,提出一种基于非密封型阻尼缓冲水缸与高强度柔性阻拦索的新型高速阻拦装置。从该装置的构成与工作原理出发,考虑阻拦索的弹性变形与活塞的惯性效应,建立阻拦过程的动力学模型,获得橇车加速度、水缸压力、阻拦行程等关键动力学参数的变化特征,并与试验数据进行了对比验证,证明了所建立的动力学模型能够较为准确地反映阻拦装置的动力学特征。基于该动力学模型,分析阻拦索刚度、阻尼孔分布形式、阻尼孔面积、活塞质量等参数对阻拦性能的影响规律,结果表明:宜选用轻质高强的柔性绳索作为阻拦绳;选用大斜率双曲线型的节流孔分布方式,水缸的阻尼效果较好;节流孔面积、活塞面积在设计时应进行综合评估;在保证活塞结构强度的前提下,应尽量降低活塞的质量。

基于弹性滚子接触模型的防滑纹对平板式动态汽车衡称重准确度影响分析

动态称重时秤台防滑纹的垂向起伏会引起车辆发生振动,影响称重准确度。为此,建立了车辆称重过程的动力学模型,考虑轮胎的包容特性,建立弹性滚子接触模型,得出的防滑纹等效路面作为动力学模型的输入激励,分析各种因素作用下平板式汽车衡新型防滑纹对称重准确度的影响。仿真结果表明:随着防滑纹宽度增大,车辆的振动力变大,称重误差随之增大;凹坑型防滑纹间距为235 mm时产生的激励频率接近于车辆的固有频率,引起车辆和秤台共振,称重误差最高可达0.21%。三角形状凹坑类型的防滑纹产生的振动力以及称重误差均低于矩形凹坑;车速越快,防滑纹的产生称重误差越大。

考虑磨损故障的双渐开线齿轮传动系统动态特性研究

针对目前双渐开线齿轮(DIG)研究过程中齿廓磨损对双渐开线齿轮动态特性的影响问题,对考虑磨损故障的双渐开线齿轮传动系统动态特性进行了研究。首先,进行了双渐开线齿轮接触线长度与齿面载荷计算,考虑相对滑移距离,建立了等效接触模型;然后,进行了双渐开线齿轮齿面累积磨损量、齿轮齿面累积磨损深度的计算,建立了双渐开线齿轮啮合刚度计算模型,进行了磨损故障的双渐开线齿轮刚度的计算;最后,以一对双渐开线齿轮为研究对象,采用集中质量法建立了6自由度动力学模型,研究了齿面磨损对双渐开线齿轮动力学特性的影响。研究结果表明:在运行1×104次载荷循环后,混合弹流润滑状态下,双渐开线齿轮与普通渐开线齿轮(CIG)在节线附近齿根位置的最大累计磨损量差值为0.00207μm,且双渐开线齿轮节线靠近齿顶位置的磨损小于普通渐开线齿轮的磨损;双渐开线齿轮系统在磨损后振动加速度幅值小于普通渐开线斜齿轮的幅值。通过对不同磨损情况下的时域响应进行研究,发现磨损导致双渐开线齿轮传动系统的振动幅值增大。

基于多尺度时空Transformer的视频动态场景图生成模型

为应对动态视频中物体间关系在时间维度上的动态变化,提出一种基于多尺度时空Transformer的视频动态场景图生成模型,在经典的Transformer架构基础上引入了多尺度建模思想,以实现对视频动态细粒度语义的精确建模。首先,在空间维度上保留了传统模型对物体在全局空间相关性的关注;同时还对物体间的相对位置进行了局部空间相关性建模,以便更好地理解人和物之间的交互动态,提供更准确的语义分析结果。其次,在时间维度上,除了保留传统模型对视频中物体短期时间相关性的关注外,还关注了同一对物体在完整视频中的长期时间相关性,通过更全面地建模物体之间的长期关系,生成更准确、连贯的场景图,在一定程度上缓解了由遮挡、重合等引起的场景图生成问题。最后,通过空间编码器与时间编码器的共同作用,更加精准地建模视频动态细粒度语义,克服了传统的单尺度模型的局限性。实验结果显示,在Action Genome基准数据集上,与基线模型STTran相比,在谓词分类、场景图分类与场景图检测三个任务的Recall@10指标上分别提升了5.0、2.8、2.9个百分点。实验结果表明,多尺度建模思想能够更加精确地建模,并有效地提高在视频动态场景图生成任务上的性能。

底水油藏水平井含水上升规律影响因素分析--以南海东部A油田为例

南海东部A油田是典型的底水油藏水平井增产改造开发区,在开发过程中,不同油层与油井含水上升规律存在明显差异,制约了该油藏的高效开采。基于A油田原始数据建立综合地质模型,结合实际生产动态,归纳出四种含水上升模式并找出对应的影响因素,利用正交试验进行多因素分析并找出主控因素。此典型区块丰富的实际数据,有望为底水油藏高效开发提供参考。

基于COMSOL的电涡流阻尼器抗震性能仿真分析

为了验证所设计的新型电涡流阻尼器力学性能,进行了仿真分析与结构动力响应分析。首先利用COMSOL Multiphysics验证其力学性能,然后进行建筑结构力学模型选择,并选择合适的地震波,验证其抗震性能。并且基于MATLAB软件将结构与电涡流阻尼器力学模型代入计算并分析,最后,进行结构仿真得出结论。研究表明:通过分析得出附加电涡流阻尼器的框架结构具有良好的减震性能,在位移峰值和加速度的控制上具有较好的效果。

飞机网式拦阻系统动力学分析

介绍了飞机拦阻网系统的工作原理,并通过对系统各构件的受力特点分析,建立了飞机在拦阻过程中的动力学模型,从理论上得出了在拦阻网工作过程中飞机速度随位移衰减的关系式,同时可估算飞机滑行距离和网绳拉力．

钢中动态再结晶力学测定及其数学模型

采用物理模拟的方法 ,对 W1 8Cr4V高速钢和 H1 3热作模具钢热变形过程中的动态再结晶规律进行了研究 ,提出采用加工硬化率 -应变图可以判断动态软化的开始和结束所对应的应变 .与传统的采用应力 -应变图的方法相比 ,该方法具有准确、直观的优点 .采用该方法 ,可以判断动态软化的类型 .建立了 W1 8Cr4V高速钢和 H1 3热作模具钢的动态再结晶的动力学。

渤海冬季环流形成机制动力学分析及数值研究

采用涡度方程、海面实测风应力分布和二维数值方法，对渤海冬季环流形成机制进行了研究。结果表明，渤海冬季海面风应力分布东岸大、西岸小，又因海底十分平坦，从而风应力切变形成的负涡度，成为渤海中部及辽东湾海流是顺时外向流动的主要驱动机制。当考虑海面实测风应力分布、潮余流和开边界入流等条件时，用二维数值方法模拟的渤海冬季环流，与实测吻合良好。一系列数值实验进一步表明：上述关于渤海环流形成机制的动力学分析是正确的；潮余流对黄河三角洲外海的北－东北向海流有重要贡献；海峡处北进、南出的流场是由冬季季风与北深、南浅的海底地形共同作用的结果。

燃烧扰动下炉膛压力的特性分析

采用机理分析和数据分析的方法,建立了炉膛压力与锅炉燃料量、送风量和引风量之间的非线性动态数学模型.在不同锅炉负荷下,对模型进行了线性化处理,得到燃料量对炉膛压力的传递函数,并对其进行了频域特性分析.结果表明:在燃料量扰动下,炉膛压力对象的频率特性在不同负荷下均呈现带通滤波特性,且燃烧扰动的主要频率分布在其通带内,控制系统本身难以直接对燃烧扰动进行有效抑制;在低负荷工况下,炉膛压力波动增大是由于对象自身的非线性特性造成的.

锅炉汽包虚假水位特性研究

锅炉汽包在变工况运行时往往产生严重的"虚假水位"现象。对汽包、下降管、水冷壁内汽水工质循环过程进行合理简化,依据物质及能量守恒定律,建立以微分方程形式描述的汽包水位动态模型。将锅炉实际运行数据引入模型,观察模型输出水位与实际水位变化:锅炉稳态时,仅考虑给水流量与蒸汽流量平衡,模型即能够反映汽包水位变化;锅炉运行状态发生剧烈变化时,模型只有引入锅炉热量信号和汽包压力信号修正后,才能够反映汽包水位变化。以实际数据验证了"虚假水位"主要是受锅炉燃烧状态及汽包压力变化影响的结论。

高压断路器操动机构的动力学建模与仿真研究

利用UG软件建立了高压断路器弹簧操动机构的三维实体模型,并导入到机械系统动力学仿真分析软件ADAMS中,动态仿真了断路器的运动特性,验证了虚拟样机模型的正确性。着重仿真分析了断路操动机构器的挡板位置、摩擦力、弹簧劲度系数等因素对高压断路器动态性能曲线的影响,为以后高压断路器的优化设计、状态监测及其故障诊断提供了理论依据。