Showing papers on "Vehicle dynamics published in 1984"

Re-entry vehicle dynamics

Abstract: Re-entry vehicle dynamics , Re-entry vehicle dynamics , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

A Nonlinear Analysis of the Generic Types of Loss of Stability of the Steady State Motion of a Tractor-Semitrailer∗

Abstract: SUMMARY All different types of loss of stability which occur generically for a tractor semitrailer vehicle are studied when varying two parameters namely the speed V of the vehicle and the position d of the center of mass of the trailer. For a fixed value of d and varying V it turns out that only two cases either a divergence or a Hopf bifurcation can occur typically. By means of a nonlinear analysis the post-bifurcation behavior for both cases is treated showing that it is critical in both cases. This latter result means that the system is an imperfection sensitive one for which the calculation only of the linear stability limit, does not have very much practical meaning, because small perturbations of the system (changes of parameters) can lead to a drastic reduction of the critical speed. Our paper furthermore indicates how a nonlinear investigation of stability problems in vehicle dynamics with no restriction to the number of degrees of freedom of the system can be done in a straight forward manner.

Nonlinear Lateral Stability Analysis of Road Vehicles Using Liapunov's Second Method

Abstract: One important road vehicle dynamics problem is the determination of the lateral stability of the vehicle. In this paper, stability results for a nonlinear model of the lateral stability problem are obtained using Liapunov's Second Method. The nonlinearities in the model are present because of the nonlinear relationships that exist between the lateral forces on the tires and the tire slip angles. Two Liapunov functions are presented which reproduce the well known stability criterion, the critical speed equation, for the classical linear model of the lateral stability problem. These two functions are then used to obtain stability conditions for the nonlinear problem. Finally, the stability results obtained with the two Liapunov functions are compared with each other and with digital computer simulations of the nonlinear equations of motion.

Analysis of Aircraft Attitude Control Systems Prone to Pilot-Induced Oscillations

Abstract: An optimal control model of the human pilot is applied to the study of aircraft attitude control systems. Attention is focused upon documented examples where an aircraft's linear pitch attitude dynamics have led to the incidence of pilot-induced oscillations. In particular, the effects of control system time delays, or higherorder vehicle dynamics that can be represented by time delays, are examined. A simple criterion for determining an aircraft's susceptibility to pilot-induced oscillations is offered. The criterion is based upon the open-loop pilot/vehicle crossover frequency as predicted by the optimal control model. The modeling procedure offers insight into the manner in which higher-order vehicle dynamics effect pilot equalization requirements and closed-loop pilot/vehicle performance.

Vehicle-bridge interaction

Abstract: SUMMARY With the emergence of high-speed trains, dynamic loads on bridges have changed. A method for estimation of the time-dependent vehicle-bridge interaction forces has been developed in the present paper. The increase (or decrease) of the bridge response due to dynamic effects is determined. The moving constant-force problem is reviewed in some detail. Results obtained by the present method for the moving-mass problem are compared with existing experimental and theoretical results as reported in the literature. A parametric study of bridge responses is made. The parameters varied are the vehicle speed, the ratio of vehicle mass to bridge mass, the ratio of vehicle eigenfrequency to bridge eigenfrequency, and the relative damping of the vehicle. Finally, the influence of an initial bridge deflection is discussed.

The influence of correlated random road excitation processes on vehicle vibration

Abstract: An improved mathematical description of the interaction between vehicle and road requires complexity in vehicle modeling as well as in road modeling. Therefore the vehicle dynamics are represented by a multibody system with 19 degrees of freedom, and the modeling of the road unevennesses is done by a special kind of shape filter approach, which takes all correlations between the road-excitation processes on a two-or multi-axle vehicle into consideration. The approach has been tested for a first order shape filter by comparison with measured data. To show the influence of correlated random road excitation processes on vehicle vibration the vertical car body accelerations are calculated for different road models, For the coverning abstract of the conference see TRIS 395019. (Author/TRRL)

A multibody approach for dynamic investigation of rolling systems

Abstract: In the classical multibody models which are used for vehicle dynamics, the contact forces applied to the wheels are considered as external forces and must be supplied in analytical from for each particular application. Moreover, when geometrical constraints arise because several wheels are in contact with a non-planar rolling path, they also have to be specified analytically.

Nonlinear Trajectory Control of Autonomous Underwater Vehicles Using the Sliding Methodology

Abstract: A new variation on sliding control is shown to be very effective for the control of underwater vehicles. The method deals with nonlinearities directly, is highly robust to imprecise models, and is intuitively appealing. The method is demonstrated using a nonlinear vehicle simulation.

Handling behaviour of off-road vehicles

Abstract: Research relevant to the lateral dynamic behavior of off-road vehicles is reviewed. This includes work on off-road vehicle dynamics and tire forces, but the lateral behavior of road vehicles is also reviewed where it is considered relevant. Although the lateral dynamics of road vehicles, both alone and in combinations, are fairly well understood, off-road vehicles have received little attention. It is concluded that the lack of lateral tire force data in off-road conditions is the factor which at present limits the predictions of off-road handling and steering behavior.

Automated vehicle dynamic analysis with flexible components

Abstract: A method is presented for nonlinear, transient dynamic analysis of vehicle systems that are composed of interconnected rigid and flexible bodies. The finite element method is used to characterize deformation of each elastic body and a component mode technique is employed to reduce the number of elastic generalized coordinates. Equations of motion and constraints of the coupled system are formulated in terms of a minimal set of modal and reference generalized coordinates. A Lagrange multiplier technique is used to account for kinematic constraints between bodies and a generalized coordinate partitioning technique is employed to eliminate dependent coordinates. The method is applied to a planar truck model with a flexible chassis and nonlinear suspension components. Simulation results for transient dynamic response as the vehicle traverses a bump, including the effect of bump-stops, and random terrain show that flexibility of the chassis can be routinely accounted for and predicts significant effects on vibratory motion of the vehicle. Compared with a rigid body model, flexibility of the chassis increases peak acceleration of the chassis and induces high-frequency vertical acceleration in the range of human resonance, measured in this paper as driver absorbed power, which deteriorates ride quality of off-road vehicles.

Vehicle Deceleration Pulse Characterization By Harmonic Analysis

Abstract: A technique for vehicle deceleration characterization by harmonic analysis is presented. The objective of this pulse shape analysis is to provide a backbone curve for a crashing vehicle which not only preserves significant vehicle response information, but also is representative of the deceleration that is experienced by a vehicle during a frontal barrier crash test. The technique improves some of the other techniques available in the literature as it is more generally applicable and can be systematically applied to any deceleration data. Applications of the method have been made to a number of barrier crashes of different carlines with various structural design configurations. The method has demonstrated the capability of reproducing crush characteristics of vehicles of identical structure, reflecting the characteristics due to velocity effect, and differentiating pulses of vehicles with different structural configurations. The reconstructed pulse can be used (1) for determining the energy-crush relationship for studying energy absorption of body structures/components and (2) as an input forcing function to an occupant mathematical simulation model for investigating the combined system performance of the vehicle structure and occupant restraint during the design phase.

The connection of theoretical simulation and experiments in passenger car dynamics

Abstract: The requirement to simulate the response of an arbitrary combined input influencing the lateral and longitudinal dynamics of the vehicle states the features for a complex 4 wheel model. Each wheel surface contact is considered separately and the tire characteristics include combined slip values of any quantity. The problem to provide the corresponding data for the evaluation is indicated for some parameters. The comparison of simulation and measurement gives the justification for using this model to analyse the driving manoeuvres and to calculate effects of design changes-the essential problem of car development. For the coverning abstract of the conference see TRIS 395019. (Author/TRRL)

Vehicle response on flexible track

Abstract: This paper describes the state-of-the-art of analyzing vehicle response on flexible track as a continuation and update of an earlier survey. While concentrating on MAGLEV systems, the activities on conventional high-speed railways in various countries are covered as well, because of the similarity of methods and the possibility of comparison and contest of the two systems.

Vibration and dynamics of off-road vehicles

Abstract: The dynamic behaviour of off road vehicles is becoming increasingly important as vehicles are required to operate at faster speeds, carry greater loads and also be more reliable and comfortable to ride. The dynamics of several off road vehicles have been investigated using IBM's continuous system modelling package with a view to improving the vehicles performance. Three different vehicles have been investigated: a 25 tonne articulated dump truck manufactured by DJB engineering Ltd, a Vickers MK 3B/3 battle tank and a small hovercraft designed for agricultural use. The modelling of the vehicle components incorporated many of the non linearities which are present in vehicle suspensions both by chance and by design such as friction and hydroelastic suspension characteristics. The predictions of the models were then compared to actual measurements which could be made on prototype vehicles. For the covering abstract of the conference see TRIS 451834. (Author/TRRL)

Dynamics and handling characteristics of single track vehicles during braking and acceleration

Abstract: The dynamic behavior and handling characteristics of single track vehicles are significantly different during braking and acceleration. The linearised equations of motion for small perturbations from straight running for a variable speed situation are derived. The tire model employed with the vehicle model is based on the actual scooter tire data measured in the laboratory under longitudinal slip conditions. The tire side force due to turn slip is accounted through a mathematical approximation. Vehicle handling characteristics are evaluated using steering torque and steering stiffness values under braking and acceleration. For the covering abstract of the conference see TRRL 395019. (Author/TRRL)

Railway vehicle modelling by the constraint equation method

Abstract: SUMMARY A method for the dynamic analysis of railway vehicles is proposed. The method is based on both the using of constraint equations, and on the building of the mathematical model by means of the initial data. The calculation models are nonlinear, due both to the connecting elements, and to the wheel-rail contact modelling. Solving of differential equations is achieved by time step integration. The method has been applied to the analysis of a freight wagon and a train unit.

Vehicle Dynamics Applications

Abstract: The computerized generation of equations of motion is presented for a simple vehicle with rigid wheels representing a nonholonomic system. Then, the stochastic excitation process of a spatial road, the equations of motion of a complex automobile vehicle, the human sensation of mechanical vibrations and numerical methods for the analysis of random vehicle vibrations are discussed.

On the optimal design of a vehicle lateral controller

Abstract: An optimization approach is used to design a velocity-adaptive, lateral controller to meet requirements pertaining to lateral-position tracking accuracy, robustness, and ride comfort. The resulting nonlinear controller required full-state feedback and thus an observer, which was nonlinear with velocity, was included. The observer/controller compensator was implemented using a 16-bit microcomputer and evaluated in a laboratory study wherein vehicle lateral dynamics were simulated on an analog computer. Excellent lateral control -- close tracking |lateral-position error| < 0.024 m in curve tracking), a good insensitivity to disturbance forces and probable ride comfort -- resulted. The selected control algorithm was realized using some 5% of the available computation time. Thus the microcomputer could also be employed for other control functions and vital-function monitoring.

Computer simulation of the dynamic behaviour of road vehicles

Abstract: In this paper is presented a method of modelization of vehicle suspensions considered as plane mechanisms. The kinematic and dynamic analysis is done with a method previously developed by the authors, that uses basic coordinates as lagrangian coordinates. To modelize realistically the vehicle suspension, a wheel-road subsystem has been incorporated into the program. The wheel is modelized with two basic points in the extremes of a radius, and the road is represented by several spans defined locally with cubic splines and allowing slope discontinuity between them. In this method, rolling and sliding conditions, impact and loss of contact events, and Coulomb friction can be considered. A set of tests that ascertains the true conditions at the contact point is described. Finally an examples solved by this method is presented. For the covering abstract of the conference see TRIS 395019. (Author/TRRL)

A microprocessor-based vehicle longitudinal controller

Abstract: A longitudinal controller was designed to meet the following requirements: a velocityinvariant response, physical realizability, a comfortable ride, a small, vehicle-position error, short ramp lengths for merging entries, and minimal effects from disturbance inputs. A reduced-order observer was used to derive the required state feedback signals, the controller was designed to obtain a velocity-invariant response, and was realized on a microcomputer. The vehicle longitudinal dynamics were simulated on an analog computer, and the performance of the controlled system was evaluated. It was concluded that all design requirements were met. The designed digital controller is an attractive candidate for implementation, and at the very least, indicates the type of longitudinal performance one can expect from a realistically designed controller over the speed range 0-30 m/s.

Hybrid laboratory test method for anti-lock systems

Abstract: This paper describes a hybrid simulation method for evaluating anti-lock system hardware with electronic wheel speed sensors mounted in a real vehicle. The method allows the testing of stability, steerability and braking efficiency. The vehicle to be tested is stationary during the test and connected to a fast digital computer programmed for real time simulation of the dynamics of a four wheel vehicle during combined braking and steering. The wheel speed sensor signals are generated by the computer and transmitted to the real anti-lock system controller. Brake pressure transducers on the real vehicle deliver input signals to the simulated vehicle. The validity of the method is demonstrated by simulations compared with field test results obtained with a heavy truck with compressed air brakes equipped with three different antilock systems. The following tests were performed: straight braking on homogeneous ice, on dry asphalt and on a split friction track (ice/frozen gravel); j-turn tests on ice with constant steer input applied at the same time as the brakes. For the covering abstract of the conference see TRIS 395019. (Author/TRRL)

Rational Flow Modeling

Abstract: The methodology used to develop computational techniques capable of predicting the dynamic response of submersible vehicles in highly dynamic maneuvers is discussed. Applications of the techniques are presented for both aerodynamic and submersible configurations documenting the results of prediction of normal force and pitching moment for the complete vehicle, spanwise normal force distributions on tail surfaces, and the vorticity distribution on the flow field at three axial stations.

The steering behaviour of off-road vehicles

Abstract: The handling behaviour of off-road vehicles is analysed using techniques which are well established for the study of road vehicle dynamics. As might be expected, the major differences in behaviour between on and off road vehicles are dominated by their relative tyre/ground characteristics. The specific features which characterise off-road vehicle performance and contrast it with that of road vehicles are identified as; (a) lateral and longitudinal tyre force generation on a deformable surface, (b) dynamic tyre response, (c) variety of steering configurations used, (D) importance of non-linear regime. For the covering abstract of the conference see TRIS 395019. (Author/TRRL)

Properties of non-linear two-force elements used in vehicle dynamic systems under stationary stochastic excitation. part 2 - realistic complex elements

Abstract: Realistic two-force elements used in vehicle dynamic systems have very often complex output force-inputs relations. Determination of their properties under stationary stochastic excitation must be therefore carried out experimentally for every excitational case. Evaluation of the measurements of one type of a passenger car telescopic hydraulic suspension damper and of one type of a heavy duty truck leaf spring is shown in this part of the paper. Transfers of the dtscussed elements, representing the frequency responses of the elements to the input deflectional process and defined in the first part of this paper, form the base for the evaluation. For Part 1 see TRIS 451960. (Author/TRRL)