液压减振器随机热力学模型与油温变化研究

为了获得具有更多信息和更加接近工程实际的液压减振器油温热力学模型,将随机不确定性理论引入到液压减振器油温传统热力学模型中进行研究。将液压油密度、导热系数、比热容和运动粘度作为随机变量,运用求解函数数字特征的代数综合法建立减振器随机热力学模型,进而获得油液传热过程规律。将油温随机热力学模型研究结果和传统模型的计算结果与实验结果进行比较,证明随机不确定性理论的引入可行且随机热力学模型比传统模型更加优越。     

Nonlinear dynamic responses of twin-tube hydraulic shock absorber

Basically on the multi-body system dynamics, the virtual prototype of the hydraulic shock absorber for the bench test is developed in the ADAMS environment. Dynamic behaviors of the absorber are studied by both computer simulation and real test. Numerical predictions of dynamic responses are produced by the established virtual prototype of the absorber and compared with experimental results. It has been shown from the comparison that the vibration behaviors of the prototype with hysteretic damping characteristics are considered to be more identical with the bench test results than those of the same prototype with piecewise linear damping properties are. The current virtual prototype of the shock absorber is correct and can be a developing terrace for the optimizing design of the absorber and matching capability of the whole car.     

一种直降式滑橇减震器性能研究

为验证无人机伞降回收系统的直降式滑橇着陆装置的动力学性能,对其着陆缓冲过程进行数学模拟构造了该装置的动力学模型,通过数值求解得出了该装置缓冲过程的动态特性。对其着陆压缩过程的动力学模型进行了简化,计算结果可用于减震器参数的确定。落震试验结果表明:动力学模型能准确模拟着陆装置的缓冲过程;以5m/s着陆时过载仅为6.8g;本文所采用动力学模型的数值求解结果与实验结果一致,误差小于5%。     

汽车模拟碰撞用液压缓冲器的动态仿真

汽车模拟碰撞(台车试验)用缓冲装置是汽车零部件安全试验中一个非常关键的设备。应用孔口节流理论，建立了汽车模拟碰撞用液压缓冲器的力学模型，同时对主要参数对模型的影响进行了具体的讨论。试验证明，进行参数优化后，计算曲线能够很好地模拟试验曲线。该仿真过程可以为类似液压缓冲器的理论建模和调试提供依据。     

A review of development and implementation of an active nonlinear vibration absorber

Summary We present an account of an implementation of an active nonlinear vibration absorber that we have developed. The control technique exploits the saturation phenomenon that is known to occur in quadratically-coupled multi-degree-of-freedom systems subjected to primary excitation and possessing a two-to-one internal resonance. The technique is based on introducing an absorber and coupling it with the structure through a sensor and an actuator, where the feedback and control signals are quadratic. First, we consider the case of controlling the vibrations of a single-degree-of-freedom system. We develop the equations governing the response of the closed-loop system and use the method of multiple scales to obtain an approximate solution. We investigate the performance of the control strategy by studying its steady-state and transient characteristics. Additionally, we compare the performance of the quadratic absorber with that of a linear absorber. Then, we present theoretical and experimental results that demonstrate the versatility of the technique. We design an electronic circuit to emulate the absorber and use a variety of sensors and actuators to implement the active control strategy. First, we use a motor and a potentiometer to control the vibration of a rigid beam. We develop a plant model that includes Coulomb friction and demonstrate that the closed-loop system exhibits the saturation phenomenon. Second, we extend the strategy to multi-degree-of-freedom systems. We use PZT ceramics and strain gages to suppress vibrations of flexible steel beams when subjected to single- and simultaneous two-mode excitations. Third, we employ Terfenol-D, a nonlinear actuator, and accelerometers to control the vibrations of flexible beams. In all instances, the technique is successful in reducing the response amplitude of the structures. Received 3 May 1999; accepted for publication 3 June 1999     

An elastic oscillation model for goods in a shortage market

I.IntroductionTheelasticrelation.elasticreplacementandgenerallyelastictheor}'amonggoods,sincetheconceptofelasticit}'ineconomicswasintroducedbyK.Marxeinthemiddleoflastcentury,havebeenlargel}'andwidelydiscussed.Fromthephysicalfact.thevariouskindsofelasticit…     

Shift of shock position for a class of nonlinear singularly perturbed problems

Thenonlinearsingularlyperturbedproblemisaveryattentiveobjectofstudyintheinternationalacademiccircles[1].Recently ,manyscholarsstudiedagreatdealofwork .Forexample,Boh啨[2 ],ButuzovandSmurov[3],O’Malley ,Jr.[4 ],Butuzov ,NefedovandSchneider[5 ]andKelley[6 ]andsoon .TheauthorconsideredaclassofsingularlyperturbednonlinearboundaryvalueproblemsfortheordinarydifferentialequationinRefs .[7～ 1 0 ] ,reactiondiffusionequationsinRefs.[1 1～ 1 3 ] ,singularlyperturbedproblemswithnonlocalboundarycond…     

Design of a tuned vibration absorber for a slender hollow cylindrical structure

Abstract

In this paper, details of the design work for a tuned vibration absorber to be used on a hollow cylindrical structure is presented. The vibration problem is of resonant type and the tuned vibration absorber is designed to suppress the displacement vibration response of the free end of the slender hollow structure dominated by the contribution of its lowest transverse vibration modes. The structure is modeled using a commercial finite element software. Finite element model of the structure is verified using experimentally obtained frequency response functions and modal parameters. Effective parameters of the tuned vibration absorber design are then determined based on finite element analysis simulations of the vibration suppression performance of the tuned vibration absorber as it is used on the structure. Details of the tuned vibration absorber design are determined and a prototype is fabricated. Prototype tuned vibration absorber is then characterized experimentally both as a standalone system and also as it is used on the main structure. Vibration reduction performance of the physical prototype of the tuned vibration absorber is also compared with its vibration reduction performance estimated from finite element analysis simulations so that the analysis based design process can be validated.

Communicated by Dumitru Caruntu.     

An alternative reduced order model for electrically actuated micro-beams under mechanical shock

This study focuses on the effect of mechanical shock on dynamic pull-in instability of eclectically actuated micro-beams through an alternative reduced order model (ROM). The model's predictions for dynamic pull-in voltages are compared with available finite element (FE) results and six modes Galerkin approximations in the literature. It is shown that present results for high shock accelerations agree with FE predictions better than those obtained using six modes approximations. Furthermore, the present model can remove the limitation of previous methods in capturing dynamic pull-in instability for cases under enormous shock accelerations.     

An improved Jones-Nelson nonlinear material model and rubber composite lamina analysis

A Jones-Nelson model has been applied to depict nonlinear stress-strain relations of composite laminae, where mechanical properties were expressed by strain energy density. The nonlinear material matrix is only a function of the strain energy density. Then a material model could be conveniently applied under complex stress condition. In this paper, by introducing large displacement stress-strain measurement and varying-Poisson's ratio idea, an improved Jones-Nelson material model is presented, where the expanding problem of material properties and convergence problems are overcome. Meanwhile a discuss of the reorientation of fiber and a material nonlinear analysis of rubber composite lamina under super large deformation conditions are made. The prediction results of improved material model are in fairly good agreement with those of the experiments.     

一种固流耦合结构的抗冲击力学特性实验研究

针对一种新型固流耦合减振器原理样机开展了多参数匹配冲击力学特性实验研究,结果表明其具有良好的抗大冲击能力,并表现出强非线性动态力学特征,同时通过改变一些主要的参数器件测试其力学工作特性,研究了共力学特性的设计可控性。     

The line spring model with arbitrary loads on crack surfaces and its applications in thermal shock analysis

In this paper the line spring model taking account of arbitrary loads on crack surfaces, and the corresponding constitutive relations, are proposed. The general expressions of the additional outfield loads, which are equivalent to the distributed loads on crack surfaces, are derived. The model is used to compute stress intensity factors in a hollow cylinder with an axial surface crack subjected to thermal shock. Several results of calculations are presented and discussed.     

一个改进的混凝土非线性双剪切强度准则

通过对混凝土、岩石等材料强度理论的分析研究,基于普遍形式强度理论及双剪切强度理论,考虑混凝土在多轴荷载作用下材料强度性质在π平面和拉伸压缩子午线上不同的变化规律,将混凝土的强度准则定义为两个较大主剪切应力平方和的函数;并考虑其对应剪切应力作用面上的正应力和静水压力的影响,推导了一个考虑中间主应力效应和复杂极限面情况的非线性双剪切强度准则;通过实验数据获得了相关参数。结果表明该强度准则可以较好地描述混凝土材料的破坏特性。     

求解预定位移水平的改进弧长法

为了在使用弧长法进行结构非线性分析时能够收敛到指定的位移,基于广义弧长的概念,对传统弧长法进行改进。改进后的方法不仅能够自动跟踪结构非线性平衡路径,同时能求得位于结构平衡路径的任意区段的任意预定位移时的受力状态。数值算例表明本文计算方法的精确度、效率以及可靠性较好。     

An improved nonlinear reduced-order modeling for transonic aeroelastic systems

In this study, an improved nonlinear reduced-order model composed of a linear part and a nonlinear part is explored for transonic aeroelastic systems. The linear part is identified via the eigensystem realization algorithm and the nonlinear part is obtained via the Levenberg–Marquardt algorithm. The impulsive signal is chosen as the training signal for the linear part and the sinusoidal signal is used to determine the order of the linear part. The training signal for the nonlinear part is selected as the filtered white Gaussian noise with the maximal amplitude and frequency range to be designed via the aeroelastic responses. An NACA64A010 airfoil and an NACA0012 airfoil are taken as illustrative examples to demonstrate the performance of the presented reduced-order model in modeling transonic aerodynamic forces. The aeroelastic behaviors of the two airfoils are obtained via computational fluid dynamics to solve the Euler equation and the Navier–Stokes equation, respectively. The numerical results demonstrate that the presented reduced-order model can successfully predict the nonlinear aerodynamic forces with and without viscous flows. Moreover, the presented reduced-order model is capable of capturing the flutter velocity and modeling complex aeroelastic behaviors, including limit-cycle oscillations, beat phenomena and nodal-shaped oscillations at the transonic Mach numbers with high accuracy.     

Modifications for an explicit algebraic stress model

An extension of the explicit algebraic stress model, developed by Gatski and Speziale [Gatski TB, Speziale CG. On the explicit algebraic stress models for complex turbulent flows. Journal of Fluid Mechanics 1993; 254: 59–78] is proposed. The extension implicates some essential characteristics of second‐order closure models. The strain‐dependent coefficients are modified, resulting in an alleviation of the numerical instabilities involved in the model. A new near‐wall damping function f_μ in the eddy viscosity relation is introduced. To enhance dissipation in near‐wall regions, the model constant C_ϵ1 is modified and an extra positive source term is included in the dissipation equation. In addition, a realizable time scale is incorporated to remove the wall singularity. Computed results show that the modified Gatski–Speziale (MGS) model predictions are in better agreement with the direct numerical simulation (DNS) and experimental data than those of the original Gatski–Speziale (OGS) model. Copyright © 2001 John Wiley & Sons, Ltd.     

An improved three-dimensional model for interface pressure calculations in free-surface flows

A three-dimensional method for the calculation of interface pressure in the computational modeling of free surfaces and interfaces is developed. The methodology is based on the calculation of the pressure force at the interfacial cell faces and is mainly designed for volume of fluid (VOF) interface capturing approach. The pressure forces at the interfacial cell faces are calculated according to the pressure imposed by each fluid on the portion of the cell face that is occupied by that fluid. Special formulations for the pressure in the interfacial cells are derived for different orientations of an interface. The present method, referred to as pressure calculation based on the interface location (PCIL), is applied to both static and dynamic cases. First, a three-dimensional motionless drop of liquid in an initially stagnant fluid with no gravity force is simulated as the static case and then two different small air bubbles in water are simulated as dynamic cases. A two-fluid, piecewise linear interface calculation VOF method is used for numerical simulation of the interfacial flow. For the static case, both the continuum surface force (CSF) and the continuum surface stress (CSS) methods are used for surface tension calculations. A wide range of Ohnesorge numbers and density and viscosity ratios of the two fluids are tested. It is shown that the presence of spurious currents (artificial velocities present in case of considerable capillary forces) is mainly due to the inaccurate calculation of pressure forces in the interfacial computational cells. The PCIL model reduces the spurious currents up to more than two orders of magnitude for the cases tested.

Also for the dynamic bubble rise case, it is shown that using the numerical solver employed here, without PCIL, the magnitude of spurious currents is so high that it is not possible to simulate this type of surface tension dominated flows, while using PCIL, we are able to simulate bubble rise and obtain results in close agreement with the experimental data.     

钢筋混凝土框架—剪力墙结构非线性抗震分析的一种空间力学模型

将钢筋混凝土框架－剪力墙结构离散为能模拟梁、柱、墙抗震性能的单元，采用杆系－层间模型进行结构的非线性抗震分析。本文的空间力学模型可考虑局部楼板变形对结构地震反应的影响，并可沿任意角度输入相互垂直的两个地震动水平分量，适用于框架一剪力墙复杂结构的非线性抗震分析。     

结构非线性分析中求解预定荷载水平的改进弧长法

本文对目前广泛应用于结构非线性分析之中的弧长法进行改进。改进后的弧长法除保持原有优点外，能够在自动跟踪结构非线性平衡路径的同时，进一步求得位于结构平衡睡径任一区段的任意预先指定的荷载水平及相应的变形。本文的方法可以推广应用于求解预先指定的应力或位移。数值算例表明了本文方法的计算精度、效率及可靠性。     

One-dimensional model for microscale shock tube flow

A one-dimensional model for the numerical simulation of transport effects in small-scale, i.e., low Reynolds number, shock tubes is presented. The conservation equations have been integrated in the lateral directions and three-dimensional effects have been introduced as carefully controlled sources of mass, momentum and energy, into the axial conservation equations. The unsteady flow of gas behind the shock wave is reduced to a quasi-steady flow by choosing a coordinate system attached to the shock. The boundary layer problem is thereby reduced to a laminar solution, similar to the Blasius solution, with the exception that the wall velocity can be nonzero. The resulting one-dimensional equations are then solved numerically using a two-step Lax-Wendroff/ MacCormack scheme with flux correction transport. For validation purposes, comparisons are performed against previously published shock structure and low Reynolds number shock tube experiments; good agreement is observed. The model has been used to predict the performance of a 10μm shock tube and the result of this simulation shows the possibility of shock wave disappearance at lower pressure ratios for a micro-scale shock tube.