锻压过程宏-细观跨尺度仿真研究

采用基于Voronoi图的微结构模型,针对Cr5锻件锻压过程中晶体之间滑移趋势进行了有限元仿真研究。并根据晶粒接触滑移角度的不同,对锻压过程中不同应力区域晶粒应力、滑移剪切力的不均匀分布进行了统计和分析。将宏观有限元分析的特定区域的分析结果耦合成相应尺寸的细观模型的边界条件,从而实现了针对应力集中区域的宏-细观跨尺度的仿真。所得结果表明,材料内部滑移趋势受接触滑移角度影响很大,位于宏观滑移区的材料,在细观模型中的滑移趋势同样明显。     

大型饼类锻件镦粗夹层裂纹缺陷形成机理研究

针对大型饼类锻件镦粗过程出现的夹层裂纹缺陷问题,本文采用有限元技术,建立锻件镦粗过程的热力耦合理论分析模型,计算了镦粗过程中等效应变、等效应变速率及其对应梯度的演变规律。通过对各场变量演变分布的分析,提出了基于变形程度与变形速度梯度组合式的夹层缺陷判断模型,并获得了锻件心部夹层裂纹的形貌和分布。通过对比计算结果与实验测试数据,二者吻合良好。     

锻造操作机机构受力性能的多目标优化设计

考虑到锻造操作机的重载特性,为避免因受力不均造成局部受力过大而危及机械结构的安全性,本文以某DDS锻造操作机为例,进行操作机的机构受力性能优化设计。通过灵敏度分析,以关键的机构受力构件在整个工作空间上的平均受力作为优化目标,基于多目标遗传算法NSGA II对操作机的主运动机构进行尺寸优化设计,以合理分配机构受力。与原设计相比,优化后的操作机具有更为良好的整体受力性能。本文的研究工作有助于操作机的机构设计。     

循环载荷下随动硬化模型的数值迭代算法

在Von-Mises屈服准则及正交流动准则的前提下,建立了循环载荷下叠加型A-F(Armstrong-Frederick)非线性随动强化模型的迭代算法,并根据塑性应变增量的收敛控制实现内部的平衡迭代。为验证本文数值方法的正确性,以Chaboche和Ohno-Abde-Karim随动硬化模型为例,将本文方法的计算结果与通用有限元软件ANSYS的分析结果及试验数据进行了比较,均吻合良好,验证了本文算法的可靠性。     

耦合蠕变损伤的粘塑性模型用于疲劳-蠕变交互作用的研究

该文对550℃下30CrMoNiV5-11转子钢进行了轴向应力控制的带保持时间的疲劳实验.按照Le-maitre有效应力的概念,采用Kachanov损伤演化方程,推导了耦合损伤的粘塑性流动方程和随动硬化方程,使用返回映射和向后欧拉方法实现应力更新,并在有限元软件ANSYS的接口程序UMAT中嵌入用户程序.对试样疲劳-蠕变交互行为进行模拟,结果表明,耦合蠕变损伤变量后,模拟结果较不含损伤变量模型的模拟结果精度大为提高.     

基于子模型法的大跨斜拉桥扁平钢箱梁应力分析

为了掌握扁平流线型钢箱梁应力水平及其分布,本文以润扬斜拉桥为工程背景,建立了整体有限元模型和局部有限元子模型。在对整体有限元模型进行分析的基础上,应用子模型法对润扬斜拉桥主梁各关键截面进行了有限元受力分析,运用试验结果验证了有限元结果的可靠性。在此基础上研究了主梁各关键截面的应力水平及其分布特点,并进一步总结了试验荷载下润扬斜拉桥扁平钢箱梁的受力特点。结果表明了子模型法应用于扁平钢箱梁局部应力分析的有效性和可靠性,其结果可为润扬斜拉桥扁平钢箱梁的安全监测提供科学依据。     

重载操作机钳臂结构多工况拓扑优化设计

钳臂是重载操作机夹持机构的重要组成部分,其力学性能和疲劳性能直接影响着操作机的正常使用功能.本文针对重载锻压操作机钳臂结构进行了典型工况下的力学性能分析,在此基础上对钳臂结构进行了多工况拓扑优化,给出了材料布局以及力的最优传递路径,并进一步进行尺寸优化.结果表明,优化后的钳臂结构在保持良好力学性能的同时,减少了材料用量...     

损伤因素对单层平面索网静力性能影响研究：有限元分析与试验验证

运用通用有限元软件ANSYS建立三维有限元模型,对横索与竖索连接节点失效、索预应力损失和锚固端失效这三种损伤因素的不同损伤工况下,单层平面索网结构的受力性能进行了非线性有限元分析,并与相应的试验结果进行了全面对比分析。结果表明：本文的有限元模型能够准确地分析计算上述三种损伤因素对单层平面索网结构受力性能的影响,包括结构...     

考虑空气耦合的薄膜结构动力分析

假定空气是可压缩、无粘性和有势的,推导了薄膜结构的非线性刚度矩阵和空气与薄膜结构耦合作用的气动力表达式。根据薄膜结构的受力特点,建立了薄膜结构与空气耦合系统的运动方程。采用有限元方法对无限域的空气进行简化,建立了空气与薄膜结构的耦合有限元模型,模拟了空气对薄膜结构的附加质量和声致阻尼影响。考虑薄膜结构的几何非线性,对结构在空气中的自由振动和受迫简谐振动进行了系统分析,同时探讨了流体环境对薄膜结构动力响应的影响因素。     

有限元方法在爆炸动力学中的应用

从动量和能量守恒方程出发，结合爆炸动力学的特点，建立适于模拟爆炸动力学过程的有限元方法，并对两个问题进行了模拟计算。计算结果与实验结果符合表明，通过选择合适的物质模型，有限元方法对爆炸动力学问题的模拟是可行的。     

Non-linear dynamic response of a rotating radial Timoshenko beam with periodic pulse loading at the free-end

Consideration is given to the dynamic response of a Timoshenko beam under repeated pulse loading. Starting with the basic dynamical equations for a rotating radial cantilever Timoshenko beam clamped at the hub in a centrifugal force field, a system of equations are derived for coupled axial and lateral motions which includes the transverse shear and rotary inertia effects, as well. The hyperbolic wave equation governing the axial motion is coupled with the flexural wave equation governing the lateral motion of the beam through the velocity-dependent skew-symmetric Coriolis force terms. In the analytical formulation, Rayleigh-Ritz method with a set of sinusoidal displacement shape functions is used to determine stiffness, mass and gyroscopic matrices of the system. The tip of the rotating beam is subjected to a periodic pulse load due to local rubbing against the outer case introducing Coulomb friction in the system. Transient response of the beam with the tip deforming due to rub is discussed in terms of the frequency shift and non-linear dynamic response of the rotating beam. Numerical results are presented for this vibro-impact problem of hard rub with varying coefficients of friction and the contact-load time. The effects of beam tip rub forces transmitted through the system are considered to analyze the conditions for dynamic stability of a rotating blade with intermittent rub.     

圆筒内旋转细长管与流体界面耦合的数值方法

圆筒内旋转细长管是石油钻采工程中特有结构,细长管不仅与圆筒发生碰撞接触,还与管内流体和管外环空流体耦合,是一个复杂的非线性流固耦合系统。细长管固体域离散成梁单元,采用非线性碰撞接触动力学方程描述;管内外流体离散成六面体单元,采用计算流体动力学方程描述,在耦合界面处用任意拉格朗日欧拉法动网格来处理运动界面。根据梁单元位移...     

中心刚体-旋转悬臂板耦合系统碰摩动力特性解析法研究

针对大型旋转机械叶片与机壳间发生的碰摩故障,建立了中心刚体-旋转悬臂板耦合系统碰摩动力学模型,考虑了离心刚化效应,利用Hamilton原理推导出运动微分方程。基于实验和有限元分析碰摩力的结果,给出了碰摩力的近似数学表达式,得到了系统振动响应解析解,通过与文献中实验结果的对比,验证了模型及方法的准确性,讨论了叶片梁模型和薄板模型在不同点碰摩及线碰摩情况下各自的适用范围,分析了转速对碰摩动力响应的影响。结果表明：论文解析解具有较高精度;薄板模型能够更全面地反映叶片各种不同碰摩情况下的动力特性,比梁模型更准确、可靠;随着转速的增大,碰摩力导致薄板自由端幅值突变,这是引发工程中叶片掉角,甚至折断的重要原因。     

Theoretical analysis of transient waves in a simply-supported Timoshenko beam by ray and normal mode methods

The dynamic transient responses of a simply-supported Timoshenko beam subjected to an impact force are investigated by two theoretical approaches – ray and normal mode methods. The mathematical methodology proposed in this study for the ray method enable us to construct the solution for the interior source problem and to extend to solve the complicated problem for the multi span of the Timoshenko beam. Numerical results based on these two approaches are compared. The comparison in this study indicates that the normal mode method is more computationally efficient than the ray method except for very short time after the impact. The long-time transient responses are easily calculated using the normal mode method. It is shown that the average long-time transient response converges to the corresponding static value. The Timoshenko beam theory is more accurate than the Bernoulli–Euler beam theory because it includes shear and rotary inertia. This study also provides the slender ratio for which the Bernoulli–Euler beam can be used for the transient-response analysis of the displacement. Moreover, the resonant frequencies obtained from finite element calculation based on the three-dimensional model are compared with the results calculated using the Timoshenko beam and Bernoulli–Euler beam theories. It is noted in this study that the resonant frequency can be accurately determined by the Timoshenko beam theory if the slender ratio is larger than 100, and by the Bernoulli–Euler beam theory if the slender ratio is larger than 400.     

An improved dynamic model for a silicone material beam with large deformation

Dynamic modeling for incompressible hyperelastic materials with large deformation is an important issue in biomimetic applications. The previously proposed lower-order fully parameterized absolute nodal coordinate formulation (ANCF) beam element employs cubic interpolation in the longitudinal direction and linear interpolation in the transverse direction, whereas it cannot accurately describe the large bending deformation. On this account, a novel modeling method for studying the dynamic behavior of nonlinear materials is proposed in this paper. In this formulation, a higher-order beam element characterized by quadratic interpolation in the transverse directions is used in this investigation. Based on the Yeoh model and volumetric energy penalty function, the nonlinear elastic force matrices are derived within the ANCF framework. The feasibility and availability of the Yeoh model are verified through static experiment of nonlinear incompressible materials. Furthermore, dynamic simulation of a silicone cantilever beam under the gravity force is implemented to validate the superiority of the higher-order beam element. The simulation results obtained based on the Yeoh model by employing three different ANCF beam elements are compared with the result achieved from a commercial finite element package as the reference result. It is found that the results acquired utilizing a higher-order beam element are in good agreement with the reference results, while the results obtained using a lower-order beam element are different from the reference results. In addition, the stiffening problem caused by volumetric locking can be resolved effectively by applying a higher-order beam element. It is concluded that the proposed higher-order beam element formulation has satisfying accuracy in simulating dynamic motion process of the silicone beam.     

Terminal sliding mode control for coordinated motion of a space rigid manipulator with external disturbance

The control problem of coordinated motion of a free-floating space rigid manipulator with external disturbance is discussed. By combining linear momentum conversion and the Lagrangian approach, the full-control dynamic equation and the Jacobian relation of a free-floating space rigid manipulator are established and then inverted to the state equation for control design. Based on the terminal sliding mode control （SMC） technique, a mathematical expression of the terminal sliding surface is proposed. The terminal SMC scheme is then developed for coordinated motion between the base＇s attitude and the end-effector of the free-floating space manipulator with external disturbance. This proposed control scheme not only guarantees the existence of the sliding phase of the closed-loop system, but also ensures that the output tracking error converges to zero in finite time. In addition, because the initial system state is always at the terminal sliding surface, the control scheme can eliminate reaching phase of the SMC and guarantee global robustness and stability of the closed-loop system. A planar free-floating space rigid manipulator is simulated to verify the feasibility of the proposed control scheme.     

A simplified method for time domain simulation of cross-flow vortex-induced vibrations

A new method for time domain simulation of cross-flow vortex-induced vibrations of slender circular cylindrical structures is developed. A model for the synchronization between the lift force and structure motion is derived from already established data for the cross-flow excitation coefficient. The proposed model is tested by numerical simulations, and the results are compared to experimental observations. When a sinusoidal cross-flow motion is given as input to the algorithm, the generated force time series are generally in good agreement with experimental measurements of cross-flow force in phase with cylinder velocity and acceleration. The model is also utilized in combination with time integration of the equation of motion to simulate the cross-flow vibration of a rigid cylinder. The resulting amplitude and frequency of motion as functions of reduced velocity are compared to published experimental results. In combination with the finite element method, the model is used to simulate cross-flow vibrations of a flexible cylinder in shear flow. Comparison with experiments shows that the model is capable of reproducing important quantities such as frequency, mode and amplitude, although some discrepancies are seen. This must be expected due to the complexity of the problem and the simple form of the present method.     

均布力偶作用下细长梁力学分析

通过铁木辛柯梁理论分析了反向均布表面剪应力——等效均匀分布力偶作用下的等截面均质细长梁挠度和应力分布规律,并与有限元法的计算结果对比发现：当边界条件中剪力不为零时,弯曲挠度和正应力分析必须考虑剪力的影响,即Euler梁理论不能满足分析的要求;若存在剪力为零边界时,可使用Euler梁分析弯曲挠度和正应力;剪应力分布向通常规律一样,仍沿高度方向呈抛物线分布,即使对于剪力为零的横截面也可能存在剪应力,这是由于表面剪应力的影响使得梁的上下表面存在剪应力,并且剪应力在横截面内正负可以发生变化。     

机械臂臂杆刚度主动控制下的末端振动特性研究

机械臂在运动过程中会因臂杆柔性引发结构变形和弹性振动,降低机械臂末端的定位精度和运动稳定性,将结构振动控制方法用于机械臂的振动抑制研究具有重要意义. 基于变刚度主动控制的设计思想,提出了臂杆刚度主动控制方法,通过改变机械臂臂杆的轴向受力状况来主动改变机械臂的刚度. 采用变形耦合法描述了机械臂的非线性变形,进而结合假设模态法和拉格朗日方程建立了臂杆的变刚度动力学模型,并进行了数值仿真. 在此基础上,设计了基于臂杆刚度主动控制方法的单自由度实验台,分析了不同预紧力下机械臂末端的振动特性. 数值仿真和实验结果表明,随着预紧力的增加,机械臂末端的振动幅值得到衰减,验证了臂杆刚度主动控制方法的有效性. 通过采用响应面法建立了机械臂末端的振动响应与预紧力的关系,并基于内部映射牛顿法的子空间置信域法优化算法对预紧力进行了优化分析,得到了最优预紧力. 该研究可为机械臂的精细动力学建模和振动抑制提供一定的理论依据,并为研究经济型低刚度材料的刚化问题提供了方向,以利用廉价低刚度材料取代目前所应用的昂贵高刚度材料.      

RESEARCH ON VIBRATION CHARACTERISTICS OF THE MANIPULATOR END UNDER ACTIVE CONTROL OF ARM STIFFNESS$^{\bf 1)}$

机械臂在运动过程中会因臂杆柔性引发结构变形和弹性振动,降低机械臂末端的定位精度和运动稳定性,将结构振动控制方法用于机械臂的振动抑制研究具有重要意义. 基于变刚度主动控制的设计思想,提出了臂杆刚度主动控制方法,通过改变机械臂臂杆的轴向受力状况来主动改变机械臂的刚度. 采用变形耦合法描述了机械臂的非线性变形,进而结合假设模态法和拉格朗日方程建立了臂杆的变刚度动力学模型,并进行了数值仿真. 在此基础上,设计了基于臂杆刚度主动控制方法的单自由度实验台,分析了不同预紧力下机械臂末端的振动特性. 数值仿真和实验结果表明,随着预紧力的增加,机械臂末端的振动幅值得到衰减,验证了臂杆刚度主动控制方法的有效性. 通过采用响应面法建立了机械臂末端的振动响应与预紧力的关系,并基于内部映射牛顿法的子空间置信域法优化算法对预紧力进行了优化分析,得到了最优预紧力. 该研究可为机械臂的精细动力学建模和振动抑制提供一定的理论依据,并为研究经济型低刚度材料的刚化问题提供了方向,以利用廉价低刚度材料取代目前所应用的昂贵高刚度材料.