Nonparametric Shock Absorber Modelling Based on Standard Test Data

Summary The possibility of improving the results of a rough road simulation by a - compared to the classic forcevelocity relation - more complex, but still an easy-to-handle shock absorber model based only on standard harmonic excitation test data is investigated. While a force-displacement-velocity relation proves not well suited for the problem under consideration, a force-velocity-acceleration relation yields a noticeable gain of accuracy with little effort. Special attention is given to the problems arising particularly in a full vehicle simulation.     

A container terminal simulation model with animation capabilities

The objective of this paper is to introduce a computer simulation model with on-screen animation graphics, which can simulate the operations of a container terminal equipped with straddle carriers. The movements of the equipment are simulated as realistically as possible, to include time losses due to the mismatch in the sequence of equipment movements and to traffic congestion. Trucks are normally served in a specified area, but in some cases, straddle carrier drivers can call the truck to be served directly in the container storage areas. The experience of operators is incorporated in the model, in the form of a knowledge base, that is used to simulate the above process and determine the service discipline. The model was designed to evaluate different configurations (changes in yard layout, equipment number and productivity, truck arrival pattern and service discipline) of the simulated system. The proposed model was used to examine the differences between “the observed” operations strategy and the strategy dictated by the operational rules of the port of Piraeus. The results indicate that “the observed” strategy leads to shorter truck service time but increase the traffic conflicts in the terminal's internal transport networks.     

Force Control in Electrohydraulic Active Suspensjons

For a simple vehicle active suspension system complete optimality and zero steady state body displacements may be achieved if the axle and body accelerations, and other easily measured quantities, are included in the performance index. Apart from not requiring an observer, this also allows the optimal feedback gains to be determined for an arbitrary body spring rate. In a theoretical example, model parameters matching those of an experimental test rig are employed. The results of computer simulations, with and without an electrohydraulic servovalve and actuator, are compared to demonstrate the effects of inner loop gain on force control. Aspects of the system behaviour including lockup are commented upon.     

Theoretical Analysis of the Steering Behaviour of Articulated Frame Steer Vehicles

A theoretical analysis of the steering behaviour of articulated frame steer vehicles is presented. It includes details of the hydraulic steering system as well as the equations governing motion of the front and rear body units. Both oscillatory and exponential instabilities can occur with this type of vehicle. The most sensitive design feature is the steering system, which governs the effective torsional stiffness around the pivot. Other important features which influence stability are speed and centre of gravity positions of the bodies.     

Physically Realisable Feedback Controls for a Fully Active Preview Suspension Applied to a Half-Car Model

An optimal preview type active suspension with feedback control based on easily measured relative displacements, velocities and accelerations is proposed. Measurements relative to the road, except by the preview sensor, are not required and the front and rear spring rates are quite arbitrary. Also, state estimators or observers are unnecessary and as a practical alternative the body accelerometers may be replaced by load cells. The effects of preview on the performance, for a theoretical step type road input and an analogous random road input, are described. The definition of the optimum preview function, and its consequent effects on performance, receives attention and an example is given.     

Robust Scalable Vehicle Control via Non-Dimensional Vehicle Dynamics

A temporal and spatial re-parameterization of the linear vehicle Bicycle Model is presented utilizing non-dimensional ratios of vehicle parameters called p-groups. Investigation of the p-groups using compiled data from 44 published sets of Vehicle Dynamics reveals a normal distribution about a line through p-space. The normal distribution suggests numerical-values for an 'average' vehicle and maximum perturbations about the average. A state-feedback controller is designed utilizing the p-space line and the expected p-perturbations to robustly stabilize all vehicles encompassed by the normal distribution of vehicle parameters. Experimental verification is obtained using a scaled vehicle.