关键词： 挖掘机   动力学   工作装置   挖掘轨迹   运动学  

摘要： 大型矿用机械式挖掘机是国内外矿山开采的重要设备之一,其工作装置性能的优劣直接关系到整机性能。工作实践表明,若提高整机性能,须从研究其工作装置的动力学入手。 工作装置的动力学研究是从挖掘机的理论动力特性曲线出发,以极端工况为计算条件,以工作装置的提升和推压系统的自然系统作为计算模型；将斗柄、动臂视为弹性体,有别于以往的刚体动力学模型,根据确定广义坐标的原则,建立9自由度工作装置弹性动力学模型；运用拉格朗日方程建立工作装置的动力学数学模型；采用振型叠加法求得各个自由度的位移响应及各构件的最大动载荷及动载荷系数。在上述工作的基础上,分析各自由度对系统动载荷的贡献度,忽略对整体结构动力学影响较弱的自由度,建立2自由度的当量系统弹性力学模型,并与多自由度的计算结果进行比较,两者均为工程认可。分析了影响系统动载荷的各个因素,并找出降低动载荷的可行途径。 此外,采用动点法对挖掘机的运动学进行了研究,有别于定点法以推压轴中心为参考点,动点法是以推压齿轮与斗柄齿条的啮合点为参考点,基于施力机构的推压、提升速度,求得挖掘轨迹。相较之下,动点法模型更接近于挖掘机的工作原理。且基于铲斗的装满条件,提出比较合理的提升和推压速度匹配方式。 综上,上述工作充实了挖掘机设计理论,同时论文的建模和分析方法对于其它同类型机械系统的分析具有参考意义。

ISBN: (纸本)9787118080308

ISBN: (纸本)9787508495392

关键词： 自由浮动   刚柔耦合空间机械臂   动力学建模   轨迹跟踪控制   振动控制   混沌识别   混沌控制  

摘要： 随着航天技术和机器人技术的不断发展，自由浮动空间机器人越来越体现出其在空间在轨服务中的优越性，是空间技术的重要发展方向。而其中自由浮动柔性空间机械臂具有质量轻、操作空间大、发射成本低等特点，成为当前空间机械臂技术研究的热点。然而，由于空间柔性机械臂在运动中会产生扭曲、弹性、剪切等变形，给这类柔性机械臂的分析和控制带来了许多困难。把冗余度机器人和柔性机器人两方面的研究结合起来，利用机器人的冗余特性能够克服柔性机械臂在运动过程由弹性振动引起的末端误差和运动结束后的余振等问题。本文以一种平面内三连杆的自由浮动刚柔耦合冗余度空间机械臂为研究对象，对其建模与控制进行了深入研究。 首先，基于拉格朗日法、假设模态法和系统动量守恒，推导了一种平面内三连杆的自由浮动刚柔耦合冗余度空间机械臂操作末端刚性负载的动力学模型。 其次，在该空间机械臂动力学模型的基础上，针对末端刚性负载的轨迹跟踪和柔性连杆的弹性振动问题，本文分别设计了基于滑模控制，终端滑模控制，非奇异终端滑模控制以及PID积分滑模控制下，结合主动抑振控制和末端作用力的比例积分控制的混合控制，同时利用模糊理论消除滑模控制的抖振，分析各种控制方法的优缺点，并通过仿真实验验证控制方法的有效性。 再次，基于最小关节驱动力矩优化的建立平面内三连杆的自由浮动刚柔耦合冗余度空间机械臂的混沌动力学模型，然后应用鲁棒补偿控制器调节其末端执行器的跟踪控制，得出了基于鲁棒控制器的角加速度反解表达式，并将其转换为状态方程的形式并在此基础上进行仿真来预测系统中的混沌现象。针对空间机械臂混沌动力学模型中的混沌现象，分别设计线性和非线性延迟反馈控制抑制混沌。通过数值仿真验证了控制方法的有效性。为开展其它更复杂的高冗余度、柔性、双臂自由浮动空间机器人系统中存在的混沌现象的研究工作奠定了基础。 最后，基于Matlab中的GUI设计了平面内三连杆的自由浮动刚柔耦合冗余度空间机械臂动力学系统的可视化仿真平台，形象说明该空间机械臂系统各部分的运动情形。

关键词： Mechanical properties   ROOT CAUSES   service failure   fan-in   Aerodynamics   fixed speed   controllable pitch   blade angle  

摘要： This paper describes research involving an in-service failure of a "variable pitch in motion" fan's blade bearing. Variable pitch in motion fans rotate at a constant speed, with the changing blade angle varying the load. A pitch-change mechanism facilitates the change in blade angle. A blade bearing supports each blade enabling it to rotate. The author observed that as the fan aerodynamic stage loading progressively increased, so did the rate of blade-bearing wear. The reported research addressed two separate, but linked, needs. First, the ongoing need to increase fan pressure development capability required an increase in fan loading. This increase was within the context of an erosive operating regime which systematically reduced fan pressure development capability. The second need was to identify the root cause of blade-bearing failures. The author addressed the linked needs using a computational analysis, improving the rotor inflow aerodynamic characteristics through an analysis of the inlet box and design of inlet guide vanes to control flow nonuniformities at the fan inlet. The results of the improvement facilitated both an increase in fan-pressure-developing capability and identification of the root cause of the blade-bearing failures.

标准号: DIN EN ISO 11806-2-2012

摘要： [SCOPE en]<p>This part of ISO 11806 gives safety requirements and measuresfor their verification for the design and construction of portable,hand-held, powered brush-cutters and grass-trimmers with aback-pack-mounted combustion engine power source and mechanicalpower transmission between the power source and the cuttingattachment. Methods for the elimination or reduction of hazardsarising from the use of these machines and the type of informationon safe working practices to be provided by the manufacturer arespecified.</p><p>This part of ISO 11806, taken together with the relevant clausesof ISO 11806-1 (see 4.1), deals with all significant hazards,hazardous situations and hazardous events, with the exception ofwhole-body vibration from the back-pack power unit, relevant tothese machines when they are used as intended and under conditionsof misuse which are reasonably foreseeable by the manufacturer.</p><p>NOTE 1 A standardized test procedure for measuring whole-bodyvibration from the back-pack power unit is presently notavailable.</p><p>NOTE 2 See Annex A, together with Annex A in ISO 11806-1:2011,for a list of significant hazards.</p><p>This part of ISO 11806 is applicable to portable, hand-held,powered brush-cutters and grass-trimmers manufactured after itsdate of publication.</p><p>This part of ISO 11806 is not applicable to machines equippedwith metallic cutting attachments consisting of more than onepiece, e.g. pivoting chains or flail blades.</p>

关键词： Large-scale multibody models   random excitation   fatigue life   multi-level dynamic substructuring   periodic steady-state response  

摘要： An efficient methodology is presented for predicting dynamic response and fatigue life of large-scale nonlinear mechanical models, subjected to random excitation. The methodology developed is based on a combination of techniques leading to a fast and accurate determination of the dynamic response with a method related to an efficient prediction of fatigue life. Specifically, the first step involves application of an appropriate coordinate transformation, causing a drastic reduction in the degrees of freedom. This opens the way to the application of another numerical method, leading to direct determination of periodic steady-state response of nonlinear systems under periodic forcing. This approach provides a solid foundation for the subsequent application of a rainflow stress cycle counting method, leading to prediction of fatigue failure. The computational accuracy and effectiveness of the methodology is illustrated by a quite involved example model, representing a city bus subjected to road excitation. Typical results are presented for both the stochastic response and the fatigue life by considering excitation arising from selected road profiles with known statistical properties. Special attention is paid to assessing the effect of the nonlinearity, by considering profiles of different quality. Moreover, a critical comparison is performed on results referring to the expected fatigue lifetime, obtained by applying methods in both the frequency and the time domain. In this way, the applicability of classical spectral methods in nonlinear models is also investigated.

关键词： 齿轮传动   非线性振动   间隙非线性振动  

摘要： 文中围绕圆柱齿轮系统非线性动力学问题，说明了齿轮系统啮合过程非线性振动的基本概念，包括基本的力学模型、数学模型、不同类型的分析系统和求解方法；然后分别介绍了齿轮啮合刚度参数振动问题和齿侧间隙非线性振动问题。

ISBN: (纸本)9787111397373

关键词： 机械密封   CFD   腔内介质物理场   热流固耦合   液膜特性   固有振动特性  

摘要： 机械密封装置是动力装备安全运行的重要屏障。高压、高温、高速、高腐蚀等极端工况易造成密封端面的温升过大，将引起密封副形成热锥面或波度、非正常的热磨损及热腐蚀、热裂或龟裂及端面间液膜失稳等失效现象。 本文以石化行业热油泵用高参数波纹管机械密封为研究对象，首先建立了密封腔内工作流场的三维数值模型，设置了边界条件初始条件后，基于计算流体动力学(C FD)数值计算法，选用基压式求解器及RNG k ε湍流模型，通过求解工作流场的三维N S方程、能力方程及连续性方程，得到了工作流场及密封副与接触面处的压力梯度云图、速度梯度云图、温度梯度云图、流场区域的涡量分布、质点运动迹线云图、湍动能及湍能耗散率等热流体动力物理场特性分布，与此同时，得到了上述参数的矢量图、等值线图。 基于腔内流场的热流体动力学特性的研究，建立了以腔内介质、动环、静环及冲洗介质等部分为整体的数值计算模型，实现了热、流、固多场耦合数值计算。首先分别建立了各部分的数值模型，将高参数工况的物料属性及模型的边界条件写入了数值计算模型，其中在流固交界面设置了实际工况热对流系数，选用合理的压力松弛因子及差值格式后，计算得到了液膜的压力梯度及压力系数、摩擦力及摩擦扭矩、温度梯度分布以及液膜质点的运动迹线等流场特性参数分布规律；得到了动、静环的热荷载轴向及径向的梯度分布特性，基于有限元算法，通过求解物理方程、几何方程、虚功方程，得到了在热荷载作用下的动、静环轴向及径向的热应变、热应力及热变形。另外，基于有限元动力学分析原理，数值计算了预热荷载作用下的动环的模态分析，并将其与无热荷载因素下的结果进行了对比分析，得到了密封副在高参数工况下的振动机理。 通过对不同工况条件下的数值计算结果的对比分析，得到了主轴转速、密封压力、介质粘度、介质温度及液膜膜厚等因素对于液膜热流场物理特性、对动、静环的热变形及热应力以及对于动环振动特性的影响规律，这为高参数极端工况下所用机械密封的优化设计提供了依据。