Directional Stability of Truck-Dolly-Trailer System

The present state of knowledge on the handling behaviour of truck-dolly-trailer system is based on parametric studies made through simulation or eigen value analysis. Any convincing study using the equations to the stability boundaries have not been reported so far due to algebraic complexities. This paper fills the gap. Effects of system parameters are assessed using equations to the stability boundaries obtained from Routh-Hurwitz criterion. The system equations of motion are derived from a bondgraph model of a linearised system.     

A Comparison of Tyre Representations in a Simple Wheel Shimmy Problem

A simple system capable of wheel shimmy is analysed in three different ways and the results are compared. The tyre in each case is taken to be representable by a “taut string”, and the three ways involve (a) developing a digital tyre simulation which operates sequentially with a digital simulation of the mechanical system, (b) representing the tyre responses by linear constant coefficient differential equations derived empirically to match the string responses, and (c) as in (b) but employing fundamentally derived equations which approximate the exact string responses. The approximations are shown to give good results at reduced frequencies typical of the wheel shimmy phenomenon.     

Currency adjustment factors: some alternative strategies

The purpose of this paper is to consider some of the issues arising from currency fluctuations or currency disparities and in particular their effects upon freight earnings through the application of a currency adjustment factor (CAF).

The operation of CAFs has been a source of great concern to shippers and shipper's councils since their introduction some seven years ago. The basis of this concern has been the widening differential of applicable CAFs as a surcharge on basic freight rates. The CAF system has been regarded by many as iniquitous and punitive. Conferences have been accused of insulating themselves from currency losses due to exchange-rate variability consequent upon the introduction of flexible exchange rates in 1971. However, this mounting pressure has brought the operation of the CAF formula under close scrutiny especially from four sources.

(a) Some member Councils of the European Shippers' Council (ESC).

(b) The Japanese Shippers' Council (JSC).

(c) The question of the legality of differential CAFs under the Treaty of Rome

(d) Complaints from North Continental Maltsters.     

Transit system evaluation: Guideway bus vs. light rail transit

This paper describes a set of specialized spreadsheets that model the cost and performance of transit system options including light rail transit, guideway bus, express bus, and ride sharing. These spreadsheets are demonstrated by comparing a guideway bus (GWB) transit system and a light rail transit (LRT) system proposed for construction in an active rail corridor. The comparisons for assumed levels of transit ridership include guideway geometry, travel time, headways, vehicle requirements, grade crossing protection, and capital and operating costs. The planned GWB system runs on an exclusive dual guideway in the rail right-of-way, and the alternative LRT system operates on the existing rails with new bridges and track as needed for a dual guideway system. The analysis compares the two options for mode splits between 0.5% and 50%. Results show that while both options have approximately the same travel time, the GWB system costs approximately 30% less than the LRT system. The cost difference results primarily from lower GWB vehicle purchase and operating costs. The spreadsheets are available through the McTrans Center at the University of Florida, Gainesville, Florida.     

Longitudinal Oscillations of Vehicle/Trailer Combinations Induced by Overrun Braking

A mathematical model for the representation of longitudinal oscillations which can occur in car/trailer systems in braking, when the trailer brakes are applied through compression of the towing hitch, is described. The model is used to show how the trailer braking system parameters affect the steady deceleration performance of the vehicle combination, and the stability, in the linear system sense, of the steady motions. The sensitivity of the stability to other system design parameters is also examined.

Digital simulation of the motions occurring in response to a step input of car braking torque is reported, with the results confirming the predictions of the linear stability analysis, and also showing the influence of backlash in the trailer brake actuating mechanism.

The system is shown to be capable of self-excitation in a “shunting” mode, in which the car and trailer motions are in antiphase, with the stability/damping property critically dependent on drawbar damping, and only weakly dependent on other system parameters. The characteristic frequency of the “shunting” mode oscillations is shown to be controllable via the stiffness of the trailer brake linkage, but this frequency is closely related to the steady drawbar deflection which occurs in uniform deceleration.

The model behaviour described provides a basis for the design of relevant systems whose longitudinal dynamic characteristics will be satisfactory.     

A shipbuilder's view of safety

Shipbuilders do not consider themselves leaders in furthering safety. There has been rapid growth in safety legislation but actual improvement has been modest. Casualty rates could most effectively be reduced in future by removing older ships. The responsibilities for safety in the longer term need consideration.     

Currency adjustment factors

The manner in which CAFs have been applied to cargo carried by lines appears to be both arbitrary and secretive. This note intends to give some clarification as to how the CAF is calculated and the manner in which it is applied.

The operation of the two methods, i.e. the monthly review and the radical review, is merely a device which enables conferences to adjust effective charges so as to leave lines without a loss in real revenue, although minor losses and gains will be inevitable as the operation of the CAFs take time to be implemented.

Finally it is hoped to point out the volatilc nature of CAF changes impinges upon the uncertainty of lines' costs.     

Human Control of Road Vehicles

This paper reviews the present state of knowledge of human control of road vehicles. Lateral and longitudinal control of motorcycles and automobiles are discussed, whenever information is available. Although knowledge has increased greatly in the last decade, the major part of this concerns lateral control and most is of an ad hoc nature. Adequate mathematical models for longitudinal motion of the vehicle are yet to be developed. Their development is a necessary step in the attainment of a complete understanding of longitudinal control.