附加非线性阻尼夹层的间隙弹性机构减振分析

为了实现含间隙弹性机构低成本的振动控制,提出了部分附加约束阻尼合金夹层的方法.采用符合接触边界条件的非线性弹簧阻尼模型描述碰撞分离过程,建立了多间隙连杆机构的刚体动力学模型;用曲线拟合描述阻尼合金的损耗因子随应变变化的规律,在考虑剪切的基础上给出了依赖于应变和频率非线性阻尼本构关系式;在计入阻尼层非线性阻尼特性和普通材料结构阻尼特性的2节点10自由度的夹层单元模型的基础上,建立了部分附加阻尼合金夹层的系统运动弹性动力学方程.计算结果说明了所提方法对控制含间隙弹性机构的振动是有效的.     

摆动式柔性递纸机构的动力学分析及研究

分析了定心上摆式递纸机构的运动过程,建立了机构的动力学模型.该模型为一存在弹性变形的四杆机构,运用Lagrange方程建立了该模型的动力学运动方程,通过摄动分析对模型进行了求解,得到了与实际运行相一致的结论.分析表明,弹性连杆机构动力学系统中存在内共振和组合共振,运动副间隙、机构边界条件、阻尼和机构尺度均可能引起机构产生非线性振动,而机构弹性构件的变形是导致机构产生非线性振动的关键因素.     

多间隙运动副平面连杆机构动态特性研究

采用非线性弹簧力和非线性阻尼描述含间隙运动副元素的碰撞接触过程，以此为基础建立了多间隙运动副平面连杆机构动力学模型；通过数值仿真研究了多间隙运动副对平面连杆机构动态特性的影响，进而讨论了在高速机构设计中应采取的设计方法；并首次指出了高速运转条件下，运动副元素由于弹性变形而存在的连续变形接触现象和多间隙运动副之间的相互影响特性。     

含间隙弹性连杆机构的KED分析

将传统的ＫＥＤ分析方法与以牛顿法为基础的含间隙刚性机构二阶段模型相结合,建立了较为简洁的含间隙弹性连杆机构动力学模型,采用了ＫＥＤ求解思路,分析了运行副间隙和结构阻尼对弹性连杆机构动态响应的影响,算例表明,该方法是正确可行的。     

非线性接触模型在多间隙机构混沌分析中的应用

分析了含间隙运动副副元素的碰撞分离过程,指出线性弹簧阻尼模型不能满足接触边界条件并产生力突变;采用符合接触边界条件的非线性弹簧阻尼模型描述碰撞分离过程,并通过实例分析了模型积分求解方法;建立了多间隙曲柄摇杆机构的动力学模型,对含间隙机构的非线性特性进行了分析和讨论,说明多间隙机构动力学行为中存在混沌现象。     

含间隙平面连杆机构动态特性研究

采用非线性弹簧接触力和非线性阻尼描述了含间隙运动副副元素的碰撞接触过程,以此为基础建立了含间隙平面连杆机的动力学模型,通过大量的数值仿真,研究了运动副间隙对机构动态特性的影响及副元素的相对运动过程。首次指出了高速运转条件下,运动副副元素由于弹性变形而出现的连续变形接触现象。     

基于FMD理论的间隙机构动力学研究

以FMD理论为基础建立了更精确的含间隙弹性连杆机构动力学模型 ,模型中计入了含间隙刚性机构运动与弹性杆件变形运动的强耦合作用 ,利用求解刚性方程的数值积分法与求解弹性变形运动的模态分析法相结合 ,较为简洁地求得了含间隙弹性机构的动态响应。通过算例表明 ,该建模和求解方法是准确的而且对于机构优化设计更具有普遍意义     

基于ADAMS的往复发动机敲缸故障仿真研究

基于多刚体系统动力学方法和非线性弹簧阻尼接触模型,在ADAMS中对含活塞-缸壁间磨损间隙的曲柄滑块机构进行动力学建模及动态仿真.研究该机构在考虑外载荷、构件惯性力、重力、材料接触刚度及阻尼等条件存在时,不同程度磨损下的活塞接触动力学响应,计算并比较了磨损间隙条件下的活塞侧推力、拍击力及活塞2阶运动特性参数等数据;阐明了运动副间隙引起活塞敲缸现象的发生机理.该工作为内燃机配缸间隙的选择、磨损间隙的故障诊断及振动控制提供了参考依据.     

含间隙铰机构尺寸优化及减磨效用研究

提出了机构尺寸优化、多体动力学、磨损预测三者的集成分析框架。铰接副由非线性弹簧阻尼模型结合修正库伦摩擦力来表达,采用Archard模型结合有限元接触模型进行磨损预测,并通过广义简约梯度法实现整体优化计算,最后针对连杆机构铰接副磨损问题进行详细分析计算。结果表明构件的角加速度峰值可有效表征机构振动和磨损程度,优化后摇杆的最大加速度幅值降低了71%,机构运动平稳性大幅提升;间隙铰接副轴套低磨损区域明显扩大,最大磨损深度降幅为36%,证明了该算法对含间隙机构摩擦学优化问题的有效性。     

变长度曲柄-连杆机构的动力学分析

以变长度曲柄-连杆机构为研究对象.从弹性力学分析入手,建立了变长度曲柄-连杆机构的非线性动力学模型;用数值计算方法对非线性动力学方程进行了求解.实例计算的分析结果表明选择适当的变化规律,改变曲柄长度,可以降低机构的动态响应.这为振动响应的控制研究开辟新的思路.     

阻尼合金非线性本构关系及其在弹性机构动力学中的应用

对所开发的阻尼合金材料,测量其在不同力幅脉冲激励下的响应,发现其损耗因子随着应变值的上升而增大。在对多种拟合模型比较基础上,选取二次曲线函数描述该阻尼合金的比阻尼能力随应变的变化规律。将所得变化规律与等效粘性阻尼理论相结合,给出了一种依赖于应变和频率的非线性阻尼本构关系式。根据变形体虚功原理,导出了包含该非线性阻尼关系的弹性连杆机构系统运动微分方程。将状态变量法与Pade逼近法相结合,给出了一种求解该复杂非线性系统的数值算法。数值计算与试验结果吻合,表明了所提理论方法的正确性和有效性。     

含间隙连杆机构非线性行为研究

分析了间隙铰接触的特点，指出线性弹簧阻尼模型不能满足接触边界条件并产生力突变；采用符合接触边界条件的非线性弹簧阻尼模型描述碰撞分离过程，建立了含间隙曲柄摇杆机构的动力学模型，对含间隙机构的非线性特性进行了分析和讨论，说明含间隙机构动力学行为中存在混沌现象。     

含间隙曲柄滑块机构运动副动态磨损研究

含间隙曲柄滑块机构中运动副的润滑情况不同于滑动轴承,其相对速度不足以形成动压润滑而处于边界润滑状态下.为了分析此状态下的动态磨损问题,考虑到含间隙运动副边界润滑时轴套的切向弹性变形和切向阻尼,结合考虑间隙运动副碰撞接触的非线性弹簧阻尼模型,提出边界润滑条件下的间隙副接触力模型,进而在此基础上推导出间隙副的动态磨损模型,并对含间隙曲柄滑块机构的运动副动态磨损进行数值分析.计算结果表明副元素间呈现出连续弹性变形现象,在连续变形接触处,动态磨损量较大使磨损加剧,并出现非均匀磨损.     

Dynamic analysis of planar mechanical systems with clearance joints using a new nonlinear contact force model

We investigated the dynamic behavior of planar mechanical systems with clearance joints. First, the contact effect in clearance joint was studied using a new nonlinear contact force model, and the rationality of this model was verified by the results of numerical simulations, which are based on a journal and bearing contact model. Then, the dynamic characteristics of a planar slider-crank mechanism with clearance were analyzed based on the new nonlinear contact force model, and the friction effect of clearance joint was also considered using modified Coulomb friction model. Finally, the numerical results of the influence of clearance size on the acceleration of slider are presented, and compared with the published experimental results. The numerical and experimental results show that the new nonlinear contact force model presented in this paper is an effective method to predict the dynamic behavior of planar mechanical system with clearance joints, and appears to be suitable for a wide range of impact situations, especially with low coefficient of restitution.     

Effects of joint on dynamics of space deployable structure

Joints are necessary components in large space deployable truss structures which have significant effects on dynamic behavior of these joint dominated structures.Previous researches usually analyzed effects of one or fewer joint characters on dynamics of jointed structures.Effects of joint stiffness,damping,location,number,clearance and contact stiffness on dynamics of jointed structures are systematically analyzed.Cantilever beam model containing linear joints is developed based on finite element method,influence of joint on natural frequencies and mode shapes of the jointed system are analyzed.Analytical results show that frequencies of jointed system decrease dramatically when peak mode shapes occur at joint locations,and there are cusp shapes present in mode shapes.System frequencies increase with joint damping increasing,there are different joint damping to achieve maximum system damping for different joint stiffness.Joint nonlinear force-displacement is described by describing function method,one-DOF model containing nonlinear joints is established to analyze joints freeplay and hysteresis nonlinearities.Analysis results show that nonlinear effects of freeplay and hysteresis make dynamic responses switch from one resonance frequency to another frequency when amplitude exceed demarcation values.Joint contact stiffness determine degree of system nonlinearity,while exciting force level,clearance and slipping force affect amplitude of dynamic response.Dynamic responses of joint dominated deployable truss structure under different sinusoidal exciting force levels are tested.The test results show obvious nonlinear behaviors contributed by joints,dynamic response shifts to lower frequency and higher amplitude as exciting force increasing.The test results are further compared with analytical results,and joint nonlinearity tested is coincident with hysteresis nonlinearity.Analysis method of joint effects on dynamic characteristics of jointed system is proposed,which can be used in optimal design of joint parameters     

Dynamic behaviour analysis of planar mechanical systems with clearance in revolute joints using a new hybrid contact force model

In this study, the dynamic behaviour of planar mechanical systems including revolute joints with clearance is investigated using a computational methodology. The contact model in revolute joint clearance is established using a new nonlinear continuous contact force model, which is a hybrid contact force model, and the friction effect is considered using modified Coulomb friction model. And then, the dynamic characteristics of planar mechanical system with revolute joint clearance are analysed based on the new contact model. Numerical results for two simple planar mechanisms with revolute clearance joints are presented and discussed. The correctness and validity of the new contact force model of revolute joint clearance is verified through the demonstrative application examples. Clearance size and friction effect are analysed separately. The numerical simulation results show that the proposed contact force model is a new method to predict the dynamic behaviour of planar mechanical system with clearance in revolute joints.     

微间隙共形圆柱接触力模型的适用性分析

针对目前间隙铰接副接触力模型无法有效表述不同材料耗散阻尼效应,以及不适用于微间隙共形接触的问题,分析各种接触力模型中弹性接触力和耗散阻尼力计算方法的优缺点,提出一种普适性的圆柱内接触力分析模型。该模型将接触力描述为接触深度的显式函数,并将其适用范围有效地扩展至微间隙和低恢复系数工况。采用含间隙铰接副的曲柄-滑块机构进行动力学分析,对所提出接触力进行验证,计算结果表明:所提出的普适性接触力模型体现了微间隙时更高的接触刚度和低恢复系数时显著的阻尼效应,从而可为不同材料和间隙尺寸的间隙铰接副力学分析提供更为完备的计算模型。     

Effects of Contact Pressure and Sliding Speed on the Unlubricated Friction and Wear Properties of Zn-15Al-3Cu-1Si Alloy

The unlubricated friction and wear properties of Zn-15Al-3Cu-1Si alloy were studied over a range of contact pressure (1–5 MPa) and sliding speed (0.5–2.5 ms^?1) for a sliding distance of 2,500 m using a block-on-disc type test machine. It was observed that as the contact pressure increased, the friction coefficient of the alloy decreased but its working temperature, surface roughness, and wear volume increased. Sliding speed had no significant effect on the friction coefficient of the alloy but increased its working temperature, surface roughness, and wear volume. It was also observed that the formation of a hard and brittle surface layer had a great influence on the wear behavior of the experimental alloy. The hardness and thickness of this layer increased with increasing contact pressure and sliding speed. However, contact pressure was found to be much more effective on the hardness of the surface layer of this alloy. Both adhesion and abrasion were observed to be the dominant wear mechanisms for the alloy under the given sliding conditions. The results obtained from the friction and wear tests are discussed in terms of the test conditions and microstructural changes that take place during sliding.