Modeling and motion simulation of a three-wheeled mobile robot with front wheel driven and steered taking into account wheels�� slip

The problem of modeling of dynamics of a three-wheeled mobile robot with front wheel driven and steered is analyzed in this paper. Kinematical structure and kinematics of the robot are described. A universal methodology of analytical modeling of robot??s dynamics is applied. This methodology takes into account wheel-ground contact conditions and wheels?? slip. Its essence is the use of a contact model of deformable tire with rigid ground and division of the robot??s dynamics model into parts connected with wheels, including tire model, and with the mobile platform. The tire model used in this paper results from empirical dependencies determined during investigations of car tires. Ground geometry and type are specified in the environment model. Tire-ground interface is characterized by coefficients of friction and rolling resistance. The robot model takes into account the presence of friction in kinematical pairs. The model of servomotors is included as well. The important part of this work is simulation research performed using Matlab/Simulink package. Simulation research includes solving of the forward and inverse dynamics problems as well as the tracking control task. During simulations, the robot was moving on concrete and on a piece of ice. The simulation research enabled verification of the elaborated solutions.     

MECHANICAL AND ACOUSTIC RESPONSE OF AN UNDERWATER STRUCTURE SUBJECTED TO MECHANICAL EXCITATION

In this paper, an underwater structure is modeled as a cylindrical shell with internal bulkheads, and closed by a truncated conical shell, and it consists of metal substrate and sound absorbing coating, whose FGM core is considered. Suppose the inner cavity and outer space of the structure are filled with air and fluid mediums, the mechanical response of the underwater structure is calculated with Galerkin method while the acoustic response is investigated by means of the Helmholtz integral. Some numerical examples are given and the effect of geometrical size and material parameters on mechanical and acoustic response is discussed.     

Interaction between a submerged evacuated cylindrical shell and a shock wave—Part I: Diffraction–radiation analysis

The interaction between a submerged elastic circular cylindrical shell and an external shock wave is addressed. A linear, two-dimensional formulation of the problem is considered. A semi-analytical solution is obtained using a combination of the classical analytical approach based on the use of the Laplace transform and separation of variables, and finite difference methodology. The study consists of two parts. Part I focuses on the simulation and analysis of the acoustic fields induced during the interaction. Both the diffraction (absolutely rigid cylinder) and complete diffraction–radiation (elastic shell) are considered. Special attention is paid to the lower-magnitude shell-induced waves representing radiation by the elastic waves circumnavigating the shell. The focus of Part II is on the numerical analysis of the solution. The convergence of the series solution and finite-difference scheme is analysed. The computation of the response functions of the problem is discussed as well, as is the effect of the bending stiffness on the acoustic field. The membrane model of the shell is considered to analyse such an effect, which, in combination with the models addressed in Part I, allows for the analysis of the evolution of the acoustic field around the structure as its elastic properties change from an absolutely rigid cylinder to a membrane. The results of the numerical simulations are compared to available experimental data, and a good agreement is observed.     

Interaction between a submerged evacuated cylindrical shell and a shock wave—Part II: Numerical aspects of the solution

The interaction between a submerged elastic circular cylindrical shell and an external shock wave is addressed. A linear, two-dimensional formulation of the problem is considered. A semi-analytical solution is obtained using a combination of the classical analytical approach based on the use of the Laplace transform and separation of variables, and finite difference methodology. The study consists of two parts. Part I focuses on the simulation and analysis of the acoustic fields induced during the interaction. Both the diffraction (absolutely rigid cylinder) and complete diffraction–radiation (elastic shell) are considered. Special attention is paid to the lower-magnitude shell-induced waves representing radiation by the elastic waves circumnavigating the shell. The focus of Part II is on the numerical analysis of the solution. The convergence of the series solution and finite-difference scheme is analysed. The computation of the response functions of the problem is discussed as well, as is the effect of the bending stiffness on the acoustic field. The membrane model of the shell is considered to analyse such effect, which, in combination with the models addressed in Part I, allows for the analysis of the evolution of the acoustic field around the structure as its elastic properties change from an absolutely rigid cylinder to a membrane. The results of the numerical simulations are compared to available experimental data, and a good agreement is observed.     

Design of an Active Noise Control System Using a Distributed Actuator

A distributed acoustic actuator for active noise control, consisting of a piezoelectric PVDF film, bonded at each side of a carrier structure, is simulated and built. The piezoelements are driven in anti-phase, resulting in a bending motion of the actuator, and thus in the necessary out-of-plane displacement for sound radiation. An analytical model for the acoustic actuator is derived, relating the actuator's displacement to the applied voltage, taking into account the influence of the piezoelectric film on the actuator's stiffness. The model is used to optimise the specifications for the piezoelectric film and the carrier structure, resulting in the highest sound power output in a frequency range from 30–500 Hz. An analytical model for the behaviour of a double panel partition is derived. The analytical model is combined with the model for the acoustic actuator, describing an actively controlled double panel partition with a distributed acoustic actuator integrated in the cavity. A controller is added to the system to control the sound power transmitted through the double panel partition. Simulation results show that a substantial increase of transmission loss can be achieved in the low frequency region (30–500 Hz) with this configuration. This revised version was published online in July 2006 with corrections to the Cover Date.     

A high-fidelity approach for vehicle mobility simulation: Nonlinear finite element tires operating on granular material

Assessing the mobility of off-road vehicles is a complex task that most often falls back on semi-empirical approaches to quantifying the vehicle–terrain interaction. Herein, we concentrate on physics-based methodologies for wheeled vehicle mobility that factor in both tire flexibility and terrain deformation within a fully three-dimensional multibody system approach. We represent the tire based on the absolute nodal coordinate formulation (ANCF), a nonlinear finite element approach that captures multi-layered, orthotropic shell elements constrained to the wheel rim. The soil is modeled as a collection of discrete elements that interact through contact, friction, and cohesive forces. The resulting vehicle/tire/terrain interaction problem has several millions of degrees of freedom and is solved in an explicit co-simulation framework, built upon and now available in the open-source multi-physics package Chrono. The co-simulation infrastructure is developed using a Message Passing Interface (MPI) layer for inter-system communication and synchronization, with additional parallelism leveraged through a shared-memory paradigm. The formulation and software framework presented in this investigation are proposed for the analysis of the dynamics of off-road wheeled vehicle mobility. Its application is demonstrated by numerical sensitivity studies on available drawbar pull, terrain resistance, and sinkage with respect to parameters such as tire inflation pressure and soil cohesion. The influence of a rigid tire assumption on mobility is also discussed.     

Vibroacoustic responses of a heavy fluid loaded cylindrical shell excited by a turbulent boundary layer

A fully coupled structural–acoustic model of a cylindrical shell under external turbulent boundary layer excitation is herein developed. The numerical process requires computation of the wall pressure cross spectral density function as well as sensitivity functions for the fluid-loaded cylindrical shell. A semi-empirical model from literature is used to describe the wall pressure field induced by the turbulent boundary layer in the wavenumber–frequency domain. An analytical expression of the wall pressure field for a flat surface is adapted to describe the wall pressure field for a cylindrical surface. Circumferential sensitivity functions are derived using a wavenumber-point reciprocity principle. Results for the near-field and far-field acoustic pressure spectra are presented. Contributions of individual circumferential modes to the acoustic pressure spectra are examined, showing distinct trends below and above the ring frequency. The proposed method is computationally efficient and provides an effective approach to investigate vibroacoustic responses for maritime platforms.     

Sound scattering and its cancellation by an elastic spherical shell in free space and near a free surface

Sound scattering by an elastic spherical shell is analysed using linear acoustics and linear structural dynamics. It is suggested to utilize the shell’s structural dynamics to reduce or even eliminate the scattered sound field, thus making it practically acoustically invisible. This can be achieved using a prescribed external pressure distribution acting on the shell’s wall. Exact analytical solutions are found for that external pressure distribution, eliminating the scattered wave when the sphere is in free space or near a free surface and is subject to an incoming planar monochromatic sound wave. The latter is assumed to propagate in a direction perpendicular to the free surface (if it exists). The case of a few pressure-actuators acting on the shell’s wall is also modelled and an optimal solution which reduces the sound scattering by these actuators is found. An aluminium shell of 1 m radius and 5 mm thickness, situated in fresh water is analysed for sound frequencies of up to 10 kHz. The scattered wave fields are presented as well as the external pressure distributions that eliminate these scattered sound field, i.e. achieving acoustic cloaking. Significant reduction in the scattered wave energy and the target strength of more than 10 dB are also realized using a few pressure-actuators as long as the distance between the actuators is no more than three times the incident wave length for the investigated cases.     

基于轮胎非线性特性的汽车动力学问题

长期以来,人们对轮胎的非线性进行了大量的理论与试验研究,总结出各种理论模型与经验模型。利用这些非线性轮胎模型建立汽车动力学的非线性常微分方程组,通过数值积分,可以获得汽车在各种工况条件下的稳态与瞬态转向特性。但这些模型的普遍缺点是不能用于对汽车行驶的稳定性作定性分析。本文提出了一种轮胎非线性侧特性的摄动模型,利用近似解析方法,讨论了轮胎非线性特性对汽车的转向特性、动态响应和汽车行驶稳定性的影响,导     

Submerged fluid-filled cylindrical shell subjected to a shock wave: Fluid–structure interaction effects

A submerged fluid-filled circular cylindrical shell subjected to a shock wave propagating in the external fluid is considered. The study focuses on a number of acoustic and structural effects taking place during the interaction. Specifically, the influence of the acoustic phenomena in the fluid on the stress–strain state of the shell is analysed using two different visualization techniques. The effect that the parameters of the shell have on the internal acoustic field is addressed as well, and the ‘shock transparency’ of various shells is discussed. Special attention is paid to the analysis of the contribution of the terms in the shell equations representing bending stiffness, and the limits of applicability of the membrane theory of thin shells are discussed in the fluid–structure interaction context. The possibility of cavitation in the internal fluid is investigated, and the effect that cavitation could have on the structural dynamics of the shell is discussed. The present paper is a follow-up of the author's earlier study of the interaction between fluid-filled cylindrical shells and external shock waves.     

轮胎结构分析的一般壳体精化理论

基于一般壳体理论和Reddy型剪切精化理论，发展出适用于充气轮胎的结构非线性分析的一般壳体精化理论。为获得一个具有解析结构的近似解，将Bezier多项式用于分片描述轮胎几何形状和位移场，应用Rayleigh-Ritz法构造轮胎在充气内压作用下的内力，变形和层间应力的解，这一模型具有任意铺层性，复杂曲面逼近便捷和求解精度可控等优点。为比较起见，文中还对轮胎结构作了三维有限元数值分析。两种方法的综合比较表明，该文提出的轮胎模型不仅预测结果精确，而且大大节省计算量。     

铁路客车室内噪声预测与控制技术研究

为探索铁路客车室内低频噪声预测分析与控制的可行办法,提高车室内噪声品质,本文基于有限元和边界元结合的方法给出了铁路客车结构-声场耦合系统振动分析模型的建模方法;通过对比分析结构振动模态、车室内空腔声学模态以及结构-声场耦合系统模态的相关性,澄清车室内噪声形成机理;对客车结构-声场耦合系统在0 Hz～200Hz频率范围内进行谐响应分析之后,确定了室内噪声观测平面及测试点在不同频率下的声压级,通过对客车车身面板声学贡献度的分析,确定主要噪声源和对内部声场影响较大的面板,为降低噪声而试图对客车结构进行修改提供了理论依据.     

Eigenproblems of two-dimensional acoustic cavities with smoothly varying boundaries by using the generalized multipole method

This paper presents a semi-analytical approach to solve the eigenproblem of a two-dimensional acoustic cavity with smoothly varying boundaries. The multipole expansion for the acoustic pressure is formulated in terms of Bessel and Hankel functions to satisfy the Helmholtz equation in the polar coordinate system. Rather than using the addition theorem, the multipole method and directional derivative are both combined to propose a generalized multipole method in which the acoustic pressure and its normal derivative with respect to non-local polar coordinates can be calculated. The boundary conditions are satisfied by uniformly collocating points on the boundaries. By truncating the multipole expansion, a finite linear algebraic system is acquired. The direct searching approach is applied to identify the natural frequencies using the singular value decomposition technique. Several numerical examples are presented, including those of an annulus cavity, a confocal elliptical annulus cavity and an arbitrarily shaped cavity with an inner elliptical boundary. The accuracy and numerical convergence of the proposed method are validated by comparison with results of the available analytical method and the commercial finite-element code ABAQUS. No spurious eigensolutions are found in the proposed formulation. Due to its semi-analytical character, excellent accuracy and fast rate of convergence are the main features of the proposed method.     

Off-road tire modeling and the multi-pass effect for vehicle dynamics simulation

Off-road operations are critical in many fields and the complexity of the tire-terrain interaction deeply affects vehicle performance. In this paper, a semi-empirical off-road tire model is discussed. The efforts of several researchers are brought together into a single model able to predict the main features of a tire operating in off-road scenarios by computing drawbar pull, driving torque, lateral force, slip-sinkage phenomenon and the multi-pass behavior. The approach is principally based on works by Wong, Reece, Chan, and Sandu and it is extended in order to catch into a single model the fundamental features of a tire running on soft soil. A thorough discussion of the methodology is conducted in order to highlight strengths and weakness of different implementations. The study considers rigid wheels and flexible tires and analyzes the longitudinal and the lateral dynamics. Being computationally inexpensive a semi-empirical model is attractive for real time vehicle dynamics simulations. To the best knowledge of the authors, current vehicle dynamics codes poorly account for off-road operations where tire-terrain interaction dominates vehicle performance. In this paper two soils are considered: a loose sandy terrain and a firmer loam. Results show that the model realistically predicts longitudinal and lateral forces providing at the same time good estimates of the slip-sinkage behavior and tire parameters sensitivity.     

Harmonic radiation from a liquid-filled spherical acoustic lens with an internal eccentric spherical source

Radiation of sound from a modally vibrating shell-encapsulated (eccentric) spherical source is analyzed in an exact manner using the classical method of separation of variables. The proposed model is a realistic idealization of a spherical acoustic lens with focal point inside the lens when used as a sound projector. The analytical results are illustrated with a numerical example in which the modal acoustic radiation impedance load on the source and the radiated far-field pressure are evaluated for representative values of the parameters characterizing the system. Numerical results clearly illustrate that in addition to frequency, surface velocity distribution and eccentricity of the source, the dynamic interaction of the encapsulating shell can be of great consequence in sound radiation.     

球壳中球形夹杂对SV波的三维散射与动应力集中研究

结构中夹杂将导致应力集中,是降低结构承载能力重要影响因素,尤其是动载作用情况下,弹性波衍射和叠加将加剧应力集中程度。弹性波衍射方程建立和求解非常复杂,目前主要研究对象集中在二维模型情况,三维有限域内夹杂引起的动应力集中现象在大型结构中比较常见,有界域边界不仅作为边界条件,同时也是散射波波源,提高了求解难度。一般通过近似方法,将三维模型简化为二维情况,往往导致求解结果过于保守不能解释实际问题。本文针对三维球壳包含夹杂一般情况,分别以球壳和夹杂中心建立球坐标以描述球壳内、外壁和夹杂表面散射波势函数,并引入一种球波函数加法公式实现不同坐标下势函数转换,以求解应力集中状态。最后针对三维情况,给出多个动应力集中因子分布状态以描述动应力集中程度。文中研究为一般情况下含夹杂球壳结构的强度分析提供了理论支撑。     

扁壳结构弯曲与扭转振动控制试验研究

扁壳结构的弯曲与扭转振动控制对该类结构的应用具有重要意义。本文采用不影响壳体结构的粗压电纤维复合材料(MFC)作动器对其弯曲与扭转振动进行主动控制。建立局部表面粘贴MFC作动器的开口圆柱扁壳的动力学解析模型,得到了作动力和作动力矩的解析表达式,分析了扁壳结构上MFC作动器在弯曲与扭转振动控制中的作动机理。针对一开口碳纤维圆柱扁壳,设计了模糊PD控制器,开展了定频与随机激励下壳体弯曲与扭转振动控制试验,并与传统PD控制试验效果进行了对比。结果表明:MFC作动器在壳体弯曲和扭转振动控制方面作动能力突出;模糊PD控制器的控制效果优于传统PD控制器的控制效果。     

Energetics of axisymmetric fluid-filled pipes up to high frequencies

The energetics of motions of axisymmetric fluid-filled pipes are presented in this paper, in view of high-frequency modelling. This study deals in particular with derivations of local energy equations well suited for the prediction of averaged response of coupled fluid–structure systems. The derivation of the latter requires special manipulation of the kinematic dynamics based here on the notion of propagation modes. Thus, the focus is on the Donnell–Mushtari cylindrical shell with an internal acoustic fluid, a typical example of waveguides with multiple transmission mechanisms. “Exact” and statistical approaches are developed for this system. A state-space representation is first proposed; it allows the characterization of propagating modes in a general manner. This propagating content then leads to the formulation of the local energy approach for this canonical problem.     

Flow-excited resonance of trapped modes of ducted shallow cavities

The self-excitation mechanism of the acoustic diametral modes of an axisymmetric internal cavity–duct system is studied for a Mach number range up to 0.4. The effect of cavity dimensions on the excitation mechanism is investigated experimentally and numerically. Experiments are conducted on three cavity depths and six cavity lengths for each depth. Numerical simulations of the mode shapes are also performed to determine the effect of cavity dimensions on the particle velocity field of the diametral modes. For all the tested configurations, the diametral modes are strongly excited at relatively low Mach numbers (as low as 0.1). The pulsation amplitude at resonance is found to increase as the cavity becomes shorter or deeper, relative to the main pipe diameter. The test results provide new insights into the excitation mechanism of diametral modes, the effect of the cavity length to depth ratio on the Strouhal numbers of acoustic resonances caused by various shear-layer modes of the cavity, and into the effect of the particle velocity field of the acoustic modes on the mode selectivity mechanism which determines the dominant acoustic mode during resonance.