环形起重设备的局部动力效应和抗震分析

对大型环形起重机设备进行抗震分析时,考虑了局部动力效应的影响及不同标高处系统加速度谱值的变化,推导了大型环形起重机设备在42.5 m标高处的地震作用及地震响应计算公式。编制了相应的计算程序,通过对实际设备的分析与计算,探讨了局部动力效应及加速度谱值变化的影响,这对工程设计具有一定的指导意义。     

考虑局部动力效应影响的大型起重机寿命预测

对大型起重机进行随机地震分析时,考虑了局部动力效应影响及42.5 m标高处的加速度谱值变化。推导出两者有关的计算公式,并编制了相应的计算程序。通过对工程实例的计算,探讨了局部动力效应对起重机寿命预测的影响,得出了一些有益的结论。     

结构局部振动与抗震分析

在进行结构动力分析时，以往均忽略由于结构连续质量所引起的局部效应，因而引起了较大的误差。若要得到精确的动力响应，则必须考虑局部效应，这一点已被诸多实践证明。因此，建议在工程动力分析上应考虑局部动力效应的影响。     

结构局部振动与抗震分析

在进行结构动力分析时，以往均忽略由于结构连续质量所引起的局部效应，因而引起了较大的误差。若要得到精确的动力响应，则必须考虑局部效应，这一点已被诸多实践证明，因此，建议在工程动力分析上应考虑局部动力效应的影响。     

双层储罐结构的地震局部动力效应研究

对层间及内罐同时储液的双层圆柱壳储罐的地震作用进行理论分析。在考虑壳皮单元及附连水的局部动力效应影响的情况下，推导回转壳壳皮单元的局部动力效应和回转壳附连水的局部动力效应计算公式，同时对双层圆柱壳的刚度阵、质量阵考虑了剪切变形的影响，给出动水压力分布规律和动载荷下的动力特性，并用这种方法对一个双层圆柱壳储罐的节点动位移、动内力等进行计算。研究发现，储罐的局部动力效应正比于节点加速度和单元连续质量；由于附连水质量的影响，储罐的局部动力效应较其他结构更为显著。这些结论对工程设计是非常有益的。     

大跨度门机随机地震响应研究

为更好反应地震对门机造成的影响,以大跨度门机为例建立有限元模型。采用多维多点的地震输入方式对大跨度门机进行平稳随机地震分析,分别在行波效应、局部场地效应和相干效应作用下对门机的位移和应力响应规律进行分析比较。计算结果表明:与一致激励相比,行波效应和局部场地效应下的地震激励对门机的最大应力分别增大了8.38%和10.15%;完全不相干效应会使门机的最大应力减少5.58%;由此可得到结论,忽略地震动空间效应会使门机的分析结果有很大的偏差。     

集装箱起重机强震非线性动力模型及损伤研究

集装箱起重机(岸桥)在强震作用下,结构损伤、非线性特征主要是由门腿的变形反复进入非弹性状态及P-Δ效应所致.为综合反映P-Δ效应、屈服硬化、强度和刚度退化等滞回因素对岸桥结构地震延性需求和损伤的影响,基于Bouc-Wen模型,建立岸桥等效单自由度体系(SDOFS),对结构双向地震载荷作用下的动力响应进行量化分析,并与采用双线性模型计算的结果对比,验证Bouc-Wen模型的可靠性.研究表明:不考虑退化效应时,理想双线性模型和Bouc-Wen模型计算结果具有较好的一致性;在地震水平激励下,重力引起的P-Δ效应对岸桥结构地震延性需求影响较大,而竖向地震激励的P-Δ效应影响较小;充分考虑滞回特性对岸桥结构非线性地震损伤指数评估偏于安全.     

考虑土－结构相互作用的风力发电高塔系统地震动力响应分析

研究考虑土－结构相互作用(Soil-structure interaction, SSI)的风力发电高塔系统地震动力响应分析问题。建立风力发电高塔系统“桨叶－机舱－塔体－基础”一体化的多体系统动力学有限元模型。基于多体系统动力学基本原理,风力发电高塔系统被离散为一系列连续的超级单元,而风力发电高塔系统土－结构相互作用则可通过在基础和土体交界面上设置弹簧和阻尼器来实现。在多体系统动力学方法中,可根据材料力学确定难于确定的超级单元参数和依据Lagrange法推导多体动力学控制运动方程。为了研究风力发电高塔系统的动力特性,基于欧洲规范(Eurocode8)对风力发电高塔系统进行了地震作用动力时程分析。研究表明,考虑SSI效应与否对结果影响较大。一般来说,考虑SSI效应会增加塔体基础与地基连接的柔度。同时,SSI效应在不同自由振动中所起的作用不一样,它对弯曲振动尤其是高阶弯曲振动的影响比较大。因此,在对风力发电高塔系统进行地震动力响应分析时,应该考虑SSI效应。     

基于缺陷局部共振内调制机理的复合材料平板损伤识别

相比利用谐波和调制信号的非线性超声无损检测方法,损伤局部共振内调制效应可以大幅增强损伤界面间的非线性行为,且其利用激励频率与损伤局部共振频率间进行调制,输入信号得到简化。当激励信号满足特定的频率条件时,材料的缺陷和损伤局部在超声激励的作用下会产生共振,导致响应信号中出现幅值增强的倍频、超谐波、亚谐波以及激励频率与局部共振频率间的内调制现象。针对损伤局部共振效应构造单自由度非线性模型,并运用多尺度法进行分析,分别考虑平方、立方刚度非线性,推导局部共振内调制现象产生的机理。进行碳纤维复合材料板冲击损伤局部共振调制损伤识别实验分析,验证理论模型分析结果以及缺陷局部共振内调制非线性损伤检测方法的可行性。结果表明,利用缺陷局部共振内调制效应可以有效地识别复合材料板的冲击损伤。     

随机加载下缺口局部应力应变的弹塑性有限元计算

根据材料在塑性变形后引起的各向异性和Bauschinger效应,利用Jhansale模型原理,对缺口件在随机加载下的缺口根部的局部应力和应变进行弹塑性有限元分析,有限元分析采用了随动强化模型,并考虑材料瞬态局部应力应变的响应特性,最后,将本文有限元的局部应力应变历程分析结果与工程上常用的Neuber法进行了比较。     

Effect of thermal non-equilibrium on transient hydromagnetic flow over a moving surface in a nanofluid saturated porous media

This work is made to study the effect of local thermal non-equilibrium (LTNE) on transient MHD laminar boundary layer flow of viscous, incompressible nanofluid over a vertical stretching plate embedded in a sparsely packed porous medium. The flow in the porous medium is governed by simple Darcy model. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. Three temperature model is used to represent the local thermal non-equilibrium among the particle, fluid, and solid-matrix phases. By applying similarity analysis, the governing partial differential equations are transformed into a set of time dependent nonlinear coupled ordinary differential equations and they are solved by Runge-Kutta Fehlberg Method along with shooting technique. Numerical results of the boundary layer flow characteristics for the fluid, particle and solid phases are obtained for various combinations of the physical parameters. It is found that the thermal non-equilibrium effects are strongest when the fluid/particle, fluid/solid Nield numbers and thermal capacity ratios are small. Moreover, the amount of heat transfer is maximum in nanoparticles than that of fluid and solid phases because of enhancement of thermal conductivity in nanofluids.     

气浮轴承支撑下裂纹-碰摩转子系统动力学分析

建立了带有裂纹和碰摩耦合故障的气浮轴承支撑的弹性转子系统的动力学方程。将打靶法思想与四阶龙格库塔法结合,对转子系统由于气膜力、裂纹和局部碰摩故障导致的非线性动力学行为进行了数值模拟,借助分岔图、相图、Poincare映射和频谱图分析了转子系统的运动形态。研究结果表明,随着系统参数的变化,在特定的参数组合下系统存在周期、拟周期和混沌等复杂的非线性动力学现象。     

Construction of a prediction model for the structural stability of a surface grinder using backpropagation neural network

Learning and prediction capability of the backpropagation neural network (BPNN) have been used to build the prediction model for the structural stability of a surface grinder. The Lagrange energy method is applied to derive the dynamic equation of the lumped parameter model of the surface grinder. The major factors influencing the structural stability of the system can be determined after the ratio of kinetic energy of the sub-structure and the ratio of potential energy of the sub-structure interface are obtained. An orthogonal rotatable central composite design is adopted to dispose the treatment combinations of the major factors. The BPNN model is constructed by the treatment combinations of the training patterns and verified by the treatment combinations of the test patterns. In this paper, a 3-layer BPNN model with a 10-neuron hidden layer which converged after 4,072 learning cycles is selected to predict the structural stability of a surface grinder within the planned ranges. The percentage residuals of both training patterns and test patterns are all within 3.41%, thus the prediction accuracy of the BPNN model is excellent so that the engineering demands are well satisfied.     

SLDQY-60型清淤机静力学分析及结构尺寸优化

在大型有限元分析软件ANSYS中,建立了SLDQY-60型清淤机的有限元模型,并根据该清淤机实际工作过程中的8种典型工况,在不同的载荷组合下进行清淤机的静力学分析,校核了清淤机整体结构的强度,结果表明,清淤机船体结构满足强度要求,工作装置局部应力值较大,对这些应力值较大的部分进行结构加强处理,为进一步减轻结构质量,提高清淤机工作效率,在清淤机船体结构满足强度要求的前提下,对船体结构进行结构尺寸优化设计,并对优化后船体结构的刚度进行校核,该研究为清淤机的设计与改进提供理论参考。     

Experimental characterization and analysis of wet belt friction and the vibro-acoustic behavior

The robustness and noise warranty costs of rubber belts used for power transmission are directly affected by the frictional properties under varying environmental conditions. This paper presents an experimental characterization and analysis of the friction and vibro-acoustic behavior of automotive ribbed rubber belts under wet conditions. The experimental results show that the static friction under wet condition is higher than the corresponding kinetic friction by 40%-1040% for different belts; and the wet static friction is also much higher than the dry static friction. The wet kinetic friction is lower than the dry kinetic friction by about 30-40%. The occurrence of wet static friction is associated with the strong noise of the belt system. The spectrogram analysis of recorded sound demonstrates that the sound exhibits an impulsive sound pattern with broadband frequency extending to 20 kHz. In this study, the belt vibration is also measured and the spectrum results correlated with those of the sound measurement. The capillary effect, dry adhesive effect and the boundary lubrication effect are discussed based on adhesion models, which are used to correlate with experimental results and to interpret the effects of relevant parameters. The presented results are based on the start-up running of a newly developed belt-pulley test rig, which are different from some published results based on SAE Standard J2432. The test rig based on SAE Standard J2432 is actually operated as water lubricated coast-down, which is not applicable to characterizing the friction properties of belt in wet start-up running.     

A method for the reduction of skin marker artifacts during walking : Application to the knee

Previous studies have demonstrated the importance of joint angle errors mainly due to skin artifact and measurement errors during gait analysis. Joint angle errors lead to unreliable kinematics and kinetic analyses in the investigation of human motion. The purpose of this paper is to present the Joint Averaging Coordinate System (JACS) method for human gait analysis. The JACS method is based on the concept of statistical data reduction of anatomically referenced marker data. Since markers are not attached to rigid bodies, different marker combinations lead to slightly different predictions of joint angles. These different combinations can be averaged in order to provide a “best” estimate of joint angle. Results of a gait analysis are presented using clinically meaningful terminology to provide better communication with clinical personal. In order to verify the developed JACS method, a simple three-dimensional knee joint contact model was developed, employing an absolute coordinate system without using any kinematics constraint in which thigh and shank segments can be derived independently. In the experimental data recovery, the separation and penetration distance of the knee joint is supposed to be zero during one gait cycle if there are no errors in the experimental data. Using the JACS method, the separation and penetration error was reduced compared to well-developed existing methods such as ACRS and Spoor & Veldpaus method. The separation and penetration distance ranged up to 15 mm and 12 mm using the Spoor & Veldpaus and ACRS method, respectively, compared to 9 mm using JACS method. Statistical methods like the JACS can be applied in conjunction with existing techniques that reduce systematic errors in marker location, leading to an improved assessment of human gait.     

多传感器称重的组合方式及其应用

电子衡器经常需要多传感器组合来实现称重测量。本文通过理论分析,比较系统地讨论了多传感器输出串联、并联、先串后并联和先并后串联等不同组合方式时的测量原理,以及不同的组合方式在实际中的应用情况。     

Post-failure behaviour of impulsively loaded circular plates

The dynamic plastic response of a simply supported circular plate is analysed. Emphasis is given to the plate behaviour after it has broken free from the supports due to a local material failure. The theoretical rigid plastic analysis predicts various features of the response such as the time to failure, residual kinetic energy and the critical velocity at failure. The residual kinetic energy of the plate could be significant enough to cause secondary impact damage. It is shown that the shape of the plate changes after breaking free from the supports, which is important for forensic investigations. The solution for various cases were proven to be exact in the context of the upper and lower bounds theorems of the theory of plasticity.     

A Study of the Static/Kinetic Friction Behavior of PTFE-Based Fabric Composites

Three different polytetrafluoroethylene (PTFE)-based fabric composites were prepared. The static/kinetic friction behaviors of these composites under different loads and speeds were studied. A 3D laser microscope and profile measurement apparatus were used for analysis of the morphology and weave structure of the composites, and the contact temperature of these composites under different loads and speeds was monitored continuously using a high-precision thermal resistor. In addition, a dynamic mechanical analysis (DMA) apparatus was used to explore the thermal and mechanical properties of PTFE-based fabric composites. The results demonstrated that speed/load, weave structure, and fiber form have an important influence on static and kinetic friction behavior of the fabric composites. Generally, the static friction coefficient is greater than the kinetic friction coefficient, except when considering light load conditions. Under light load conditions, the static friction coefficient is equal to the kinetic friction coefficient. In addition, the kinetic friction coefficient first increased and then decreased with increased speed, but the static coefficient increased first and then remained at an almost constant value. At all sliding speeds, the static and kinetic friction coefficients of tape yarn composites are better than those of the multifilament yarn composites. Weave structure has no effect on the static friction coefficient, but it has a significant influence on the kinetic friction coefficient.     

超声振动钻削中局部共振现象的研究与应用

通过建立数学模型 ,分析了超声振动钻削声学系统的动力学规律 ,探讨了工具杆局部共振现象的机理 ,得出了当工具杆发生局部共振时 ,变幅杆与工具杆联接处为位移节点且整个系统处于谐振状态的结论 ,并推导了超声波发生器可调频率范围与刀具杆磨损率的关系