Monolithic Coupling of the Pressure and Rigid Body Motion Equations in Computational Marine Hydrodynamics

In Fluid Structure Interaction(FSI) problems encountered in marine hydrodynamics, the pressure field and the velocity of the rigid body are tightly coupled. This coupling is traditionally resolved in a partitioned manner by solving the rigid body motion equations once per nonlinear correction loop, updating the position of the body and solving the fluid flow equations in the new configuration. The partitioned approach requires a large number of nonlinear iteration loops per time–step. In order to enhance the coupling, a monolithic approach is proposed in Finite Volume(FV) framework,where the pressure equation and the rigid body motion equations are solved in a single linear system. The coupling is resolved by solving the rigid body motion equations once per linear solver iteration of the pressure equation, where updated pressure field is used to calculate new forces acting on the body, and by introducing the updated rigid body boundary velocity in to the pressure equation. In this paper the monolithic coupling is validated on a simple 2D heave decay case. Additionally, the method is compared to the traditional partitioned approach(i.e. "strongly coupled" approach) in terms of computational efficiency and accuracy. The comparison is performed on a seakeeping case in regular head waves, and it shows that the monolithic approach achieves similar accuracy with fewer nonlinear correctors per time–step. Hence, significant savings in computational time can be achieved while retaining the same level of accuracy.

Optimal control of attitude for coupled-rigid-body spacecraft via Chebyshev-Gauss pseudospectral method

The attitude optimal control problem （OCP） of a two-rigid-body space- craft with two rigid bodies coupled by a ball-in-socket joint is considered. Based on conservation of angular momentum of the system without the external torque, a dynamic equation of three-dimensional attitude motion of the system is formulated. The attitude motion planning problem of the coupled-rigid-body spacecraft can be converted to a dis- crete nonlinear programming （NLP） problem using the Chebyshev-Gauss pseudospectral method （CGPM）. Solutions of the NLP problem can be obtained using the sequential quadratic programming （SQP） algorithm. Since the collocation points of the CGPM are Chebyshev-Gauss （CG） points, the integration of cost function can be approximated by the Clenshaw-Curtis quadrature, and the corresponding quadrature weights can be calculated efficiently using the fast Fourier transform （FFT）. To improve computational efficiency and numerical stability, the barycentric Lagrange interpolation is presented to substitute for the classic Lagrange interpolation in the approximation of state and con- trol variables. Furthermore, numerical float errors of the state differential matrix and barycentric weights can be alleviated using trigonometric identity especially when the number of CG points is large. A simple yet efficient method is used to avoid sensitivity to the initial values for the SQP algorithm using a layered optimization strategy from a feasible solution to an optimal solution. Effectiveness of the proposed algorithm is perfect for attitude motion planning of a two-rigid-body spacecraft coupled by a ball-in-socket joint through numerical simulation.

On the Stability Analysis of a Coupled Rigid Body

In this research article, we investigate the stability of a complex dynamical system involving coupled rigid bodies consisting of three equal masses joined by three rigid rods of equal lengths, hinged at each of their bases. The system is free to oscillate in the vertical plane. We obtained the equation of motion using the generalized coordinates and the Euler-Lagrange equations. We then proceeded to study the stability of the dynamical systems using the Jacobian linearization method and subsequently confirmed our result by phase portrait analysis. Finally, we performed MathCAD simulation of the resulting ordinary differential equations, describing the dynamics of the system and obtained the graphical profiles for each generalized coordinates representing the angles measured with respect to the vertical axis. It is discovered that the coupled rigid pendulum gives rise to irregular oscillations with ever increasing amplitude. Furthermore, the resulting phase portrait analysis depicted spiral sources for each of the oscillating masses showing that the system under investigation is unstable.

MODEL OF CENTRIFUGAL EFFECT AND ATTITUDEMANEUVER STABILITY OF A COUPLEDRIGID-FLEXIBLE SYSTEM

The influences of nonlinear centrifugal force to large overall attitude motion of coupled rigid-flexible system was investigated. First the nonlinear model of the coupled rigid-flexible system was deduced from the idea of “centrifugal potential field', and then the dynamic effects of the nonlinear centrifugal force to system attitude motion were analyzed by approximate calculation; At last, the Lyapunov function based on energy norm was selected, in the condition that only the measured values of attitude and attitude speed are available, and it is proved that the PD feedback control law can ensure the attitude stability during large angle maneuver.

MODELING AND ANALYSIS OF A COUPLED RIGID_FLEXIBLE SYSTEM

Correct predictions of the behavior of flexible bodies undergoing large rigid-body motions and small elastic vibrations is a subject of major concern in the field of flexible multibody system dynamics. Because of failing to account for the effects of dynamic stiffening, conventional methods based on the linear theories can lead to erroneous results in many practical applications. In this paper, the idea of 'centrifugal potential field', which induced by large overall rotation is introduced, and the motion equation of a coupled rigid-flexible system by employing Hamilton's principle is established. Based on this equation, first it is proved that the elastic motion of the system has periodic property, then by using Frobenius' method its exact solution is obtained. The influences of large overall rigid motion on the elastic vibration mode shape and frequency are analysed through the numerical examples.

薄壁四点接触球轴承-腕部关节系统接触动力学分析

在机器人实际工况中,针对含有薄壁四点接触球轴承的机器人腕部关节系统的运动稳定性问题,对腕部系统模型进行了简化设计和仿真研究。在考虑薄壁结构的弹性变形和动态接触作用耦合影响的基础上,建立了刚柔耦合工业机器人腕部关节系统模型,分析了不同受载工况和正反转驱动下的变形规律和动态特性。首先,基于多体动力学和Hertz接触理论,设计了包含薄壁四点接触球轴承和中空轴及基座的腕部关节系统刚柔耦合接触动力学仿真模型;然后,考虑薄壁中空轴、基座、轴承套圈和保持架的结构弹性变形、钢球和套圈滚道、保持架的动态接触作用,研究了机器人腕部关节系统两种实际工况对保持架和钢球角速度、保持架和薄壁基座振动位移、钢球与套圈的动态接触力的影响;最后,计算分析了两种工况下腕部关节系统的动态载荷规律和振动响应特性。研究结果表明:在相对较大的径向载荷作用下,保持架和钢球会出现打滑现象,速度呈现周期波动,保持架和基座具有更好的运动稳定性,其薄壁轴承内部载荷降低,主副接触对均承担联合载荷,轴承内部载荷稳定性也更好。该仿真模型及结果可以为薄壁腕部关节系统的动力学分析与设计提供参考。

基于多体动力学模型的柴油机曲轴振动特性分析

为了减少发动机故障分析曲轴系统的扭转振动,建立了由活塞、连杆、曲轴、飞轮和硅油阻尼器组成的曲轴系统三维模型。利用多体动力学仿真软件ADAMS,建立了由多自由度组成的刚性混合动力发动机系统的多体动力学模型,对其进行扭振响应仿真,对曲轴的扭振进行分析。该仿真结果具有较高的精度,该计算方法具有一定的工程应用价值。

Quasi-Hamiltonian principle of liquid-filled elastic body dynamics

Liquid-filled elastic body dynamics is an important branch of fluid-solid coupling mechanics. It deals with the study of motion of a body and the liquid contained in the body under the interaction between the two,for example,a liquid-filled satellite,a fuel tank of an airplane,etc. The research on liquid-filled elastic body dynamics is usually done by the variational method since the method has a feature of treating things as a whole. Considering the elastic motion of the liquid-filled body and the surface tension effect on the liquid-gas interface,liquid-solid interface and gas-solid interface,the present paper establishes a quasi-Hamiltonian variational principle for the above-mentioned system. After finding the stationary-value conditions of its functional obtained,a complete system of governing equations consisting of the stationary value conditions,preconditions and constraint conditions is established,and then the equations are reduced into some known ones in a special case.

Modeling and simulation of railway vehicle vertical dynamic behavior by considering the effect of passenger-carbody coupling vibration

In order to reflect the vertical random vibration characteristics of railway vehicles more truly and effectively,this paper regards the human body as a single-degree-of-freedom system attached to the bottom of the carriage,and establishes a vertical dynamic model of railway vehicles by considering the influence of the coupling vibration effect between the passenger and the car body.The correctness of the model is verified by the real vehicle test.Then,the influence of the passengers on the vertical vibration characteristics of railway vehicles is analyzed,and the influence of the railway vehicle vibration on the vertical vibration characteristics of passengers is discussed in this paper.The research made in this paper can provide an effective model reference for the analysis of the vertical random vibration characteristics of railway vehicles and passengers,and for the optimization design of the suspension system parameters.

推土机刚柔耦合仿真分析研究

推土机是重要的工程机械,广泛应用于工程建设中。针对某款推土机在使用过程中出现的推杆裂纹情况,基于柔性体理论,将推土机的左右推杆转换成柔性体,建立推土机的刚柔耦合模型,对刚柔耦合模型进行仿真分析。仿真结果可为解决推土机推杆强度和轻量化提供理论基础,具有实际应用价值。

基于CFD/CSD耦合的高速射弹尾拍载荷特性研究

为提高射弹尾拍载荷的预测精度,建立了一套基于计算流体动力学(CFD)/计算结构动力学(CSD)双向耦合分析的计算方法和程序。射弹流体计算主控方程采用耦合SSTk-ω湍流模型和Schnerr-Sauer空化模型的Navier-Stokes方程,射弹结构计算采用基于模态叠加法简化的结构动力学方程,流固耦合界面插值采用径向基函数法,网格变形采用弹簧网格法。分别对泡型计算方法和流固耦合方法进行验证,在此基础上,计算对比1 000 m/s速度下射弹刚体和弹性体的尾拍泡型、结构变形和尾拍流体载荷特性差异。计算表明:弹性体尾拍过程,射弹泡型会产生弹身“二次拍击”、“局部沾湿”和沾湿面积增大等特殊现象,结构变形由弹性一弯模态主导,较大的变形引起流体载荷增大27%~105%,尾拍姿态角增大13%,尾拍频率增加20%,流固耦合效应对尾拍泡型、尾拍载荷和尾拍弹道均产生了较强的影响。

刚柔耦合分析在杠杆式基础制动装置中的应用

目前铁路货车所采用的基础制动装置大多为杠杆式制动装置。相比于单元式制动装置,杠杆式制动装置运动情况复杂,制动效率较低。对于货车车辆基础制动装置的研究,传统分析方法主要为现场试验法和理论计算法。而这两种方法的应用受到试验成本高、研发周期长、测量误差大以及计算复杂的限制。刚柔耦合分析采用ADAMS和ANSYS仿真软件进行多体动力学联合仿真,对货车基础制动装置性能进行分析研究。通过对比仿真分析数据、理论计算数据和现场试验数据,验证了基础制动装置刚柔耦合分析方法的正确性,对研究货车制动性能及解决基础制动装置所存在的问题提供了一种新的手段。

捕捉缓冲机构刚柔耦合多体动力学仿真研究

大部分动力学仿真分析采用的都是刚性构件,在现实生活中把构件看成刚性系统来处理可以满足要求,但这忽略了构件变形的影响。为了得到更真实有效的数据,就必须把模型的部分构件看作柔性体来处理。为研究某捕捉缓冲机构的动力学性能,从理论层面介绍动力学的研究方法和刚柔耦合研究的整体思路,并利用ANSYS和ADAMS导出的.MNF文件和.LOD文件,从刚柔耦合多体动力学的角度对捕捉缓冲机构进行了综合实验分析和对比。通过刚柔耦合研究实现了动力学和结构学的联合仿真,得到了更精确的仿真数据,在获得动力学测量数据的基础上又获得了结构学数据,使仿真结果更为全面,同时也为对结果要求较高的多体动力学工程仿真问题提供了参考。

一种新型商用车驾驶室多轴道路虚拟试验研究

为了提高商用车驾驶室多轴道路模拟试验台的控制精度,精确复现路谱采集信号,提出了一种基于运动学与动力学分析的驾驶室多轴道路虚拟试验台控制策略。依据机构学原理描述了试验台的结构,并进行了运动学分析和计算,利用位姿反解算法及含雅可比矩阵正解算法进行了闭环反馈的自由度解耦。实测驾驶室相关参数并与ADAMS软件相结合建立了驾驶室、部分车架及试验台的刚柔耦合多体动力学模型,创建Femfat-lab、MATLAB/Simulink和ADAMS软件接口进行自适应联合仿真计算,实现了试验台的自由度解耦控制。将多轴虚拟试验台与实车试验内部响应信号相结合,选择信噪比较高的信号为目标信号进行迭代分析,获取实车位置等效位移激励。选取典型的比利时路面载荷谱作为模型输入条件,从而重现与道路试验相结合的真实路谱。研究结果表明,与室内道路模拟试验台架及常规虚拟迭代结果相比,驾驶室采用多轴虚拟试验台的迭代次数明显减少,得到的时域、频域响应信号与目标信号的变化趋势相吻合,且各通道相对误差均方根值(RMS)均小于设定值,迭代精度高,从而验证了所提方法的可行性,为后续驾驶室疲劳寿命预测提供了可靠的载荷谱。

仿鸡脖子刚柔耦合结构的仿生机理及大变形建模

观察表明,禽类颈部普遍具有刚柔耦合的特点,在运动过程中,可以辅助身体运动,使得头部产生大变形.在机器人、航空航天等领域普遍需要具有大变形、变刚度等特征的结构实现相关功能.受禽类脖子结构的启发,提出了一种仿鸡脖子刚柔耦合结构,阐明仿鸡脖子的仿生机理并建立大变形模型.首先,从鸡颈部的生物解剖出发,发现仿鸡脖子结构势必具有多自由度刚柔耦合的特征,因此,根据鸡脖子骨骼的构型构造出单节仿生标准单元,根据肌肉的连接方式厘清节间弹性连接,建立起仿鸡脖子刚柔耦合结构的力学模型;然后,通过定义连接矩阵描述节间弹性元件的分布和作用,由此得到任意运动下的标准单元的力平衡方程;最后,选取了几种具有代表性的工况,通过有限元分析验证理论建模方法的准确性并展示结构的非线性变刚度特征;在4种典型平面弯曲工况下得到不同变形与发力肌肉群的对应关系.文章提出的仿鸡脖子刚柔耦合结构建模具有仿生机理清晰、适合大变形计算及结构具有非线性刚度特征等特点,也解释了禽类颈部变形机理.

考虑桨叶伺服控制的浮式风机多刚体动力学建模与验证

浮式风机是深远海域风力发电的关键结构,分析其在复杂海况下的动力学响应特征对保障远海风能开发具有重要意义。在初步设计和方案比选阶段,需要开发能够定量把握浮式风机动力学主要特征、且分析高效的一体化分析模型。为此,针对大型Spar式海上浮式风机,建立了多刚体动力学全耦合分析模型。基于Lagrange方程,推导了考虑桨叶转动与桨距控制的8自由度刚体运动方程。结合所建议的多刚体模型,基于Spar式浮式风机1∶50缩尺模型试验实测数据,建立了与试验物理模型相应的一体化多刚体数值模型,并进行了静力、纯风、纯浪以及风-浪联合条件下数值分析结果与试验观测结果的对比分析。采用本文建模理论,建立了OC3-Spar式浮式风机足尺结构数值分析模型,并与常用的风机结构分析软件FAST的计算结果进行了对比分析。通过与上述缩尺物理模型试验和足尺数值模型软件分析对比,验证了浮式风机多刚体动力学分析模型的有效性。

幕墙清洗机的毛刷清洁效果分析

以幕墙清洗机的毛刷刷丝为研究对象,针对尼龙66材质的刷丝在不同驱动力下研究刷丝的变形程度与清洁效果的关系。建立柔性体模型,再进行接触式仿真,得出该型刷丝约在3.0 N时的变形程度最大、覆盖的清洁面积最大的结论。通过对毛刷结构在不同驱动力下的实物实验和清洗机外场实验,交叉验证仿真结果可行,清洁效果显著。为工程实践中毛刷清洁作业提供参考。

弹性薄壳动力学比拟的曲面论基础

将Kirchhoff动力学比拟从弹性细杆推广到弹性薄壳,需要相应的经典曲面论新的表达形式,即用刚体动力学的概念和方法描述曲面的基本性质,形成广义Kirchhoff动力学比拟方法.从曲面非正交网格的两个刚性正交轴系出发,用其姿态坐标和Lamé系数表达曲面偏微分方程;用弯扭度和Lamé系数表达曲面的第一和第二基本二次型,得到了法曲率的表达式,由此计算了主曲率和主方向,验证了与经典曲面论的一致性;给出算例以说明该文方法的应用,这一方法可以用来表达曲面的Rodrigues方程、Weingarten公式和Gauss公式,以及曲面论的基本方程.分析表明了这一方法对表述曲面微分几何的可行性,具有推导简洁和直观的优点.这有助于为广义Kirchhoff比拟及其后续发展奠定数学基础.

基于动网格技术的飞机舱弹分离过程CFD/RBD耦合数值仿真

飞机舱弹分离瞬间特性严重影响导弹/炸弹的打击精度。采用计算流体动力学(CFD)和刚体动力学(RBD)模型耦合求解的数值仿真方法,应用网格弹性光顺和局部重构相结合的动网格技术,有效地避免了刚体运动而引起的网格畸变,仿真计算了炸弹舱弹分离后俯仰角度变化过程.仿真结果表明,舱弹分离时向炸弹施加1个合适的抛射力矩,有助于炸弹在下降过程中快速地调整其打击姿态。

考虑车体柔性的敞车动力学性能研究

以C70E敞车为研究对象,基于柔性多体系统动力学理论,利用动力学软件SIMPACK建立考虑车体柔性的刚柔耦合动力学模型,仿真计算空重车工况车辆振动响应和动力学性能,与线路试验和多刚体动力学模型结果对比,研究车体柔性对敞车动力学性能的影响。结果表明:研究敞车车体振动特性时,有必要考虑车体柔性影响,柔性车体主要影响车体中部振动;对于车辆运行平稳性,车辆高速运行时需考虑车体柔性的影响;对于曲线通过安全性,空车工况需要考虑车体柔性的影响。