Acoustic excitation of hull surfaces by propeller sources

We present preliminary results from our new ship motion model that includes both strong and weak three-dimensional interactions between environmental surface waves and ship bodies in arbitrary water depth. The linear solutions of steady flow using the new model agree well with those obtained using the Green function methods. When the Froude number Fn is large, the fully nonlinear solutions of our model are significantly different from linear solutions, even in calm water. The interactions between the ship and incident gravity waves are completely different from those in linear solutions even with small Fn and moderate-amplitude surface waves (e.g., Fn = 0.25 and a significant wave height of about 1–3m).     

Simulation model for the study of overhead rail current collector systems dynamics, focused on the design of a new conductor rail

Overhead rigid conductor arrangements for current collection for railway traction have some advantages compared to other, more conventional, energy supply systems. They are simple, robust and easily maintained, not to mention their flexibility as to the required height for installation, which makes them particularly suitable for use in subway infrastructures. Nevertheless, due to the increasing speeds of new vehicles running on modern subway lines, a more efficient design is required for this kind of system.

In this paper, the authors present a dynamic analysis of overhead conductor rail systems focused on the design of a new conductor profile with a dynamic behaviour superior to that of the system currently in use. This means that either an increase in running speed can be attained, which at present does not exceed 110 km/h, or an increase in the distance between the rigid catenary supports with the ensuing saving in installation costs.

This study has been carried out using simulation techniques. The ANSYS programme has been used for the finite element modelling and the SIMPACK programme for the elastic multibody systems analysis.     

The comparison of general cargo ship economic performance by simulation

Cargo ship designs offered by shipbuilders differ in characteristics such as deadweight, speed, fuel consumption and cargo equipment. The best vessel for high freight markets and high fuel prices may not be the best for low freight markets and low fuel prices. A model has been developed to compare by simulation a number of multi-purpose general cargo vessels suitable for the trade of a Turkish shipowner. The model simulates the operation of each vessel under a variety of operating scenarios, e.g. fuel prices and freight profiles over the ships' lives, and estimates the distribution of resulting net present values. The techno-economic simulation model incorporates variables including ship size, speed, first cost, fuel consumption, load factor and port days.

Results are presented for six standard vessels of around 20 000 dwt operating over a long and a short route. Although the ranking of the six varies with assumptions, one design is shown to be superior under most operating conditions.     

An economic assessment of fluidized-bed boilers in Australian merchant ships

Fluidized-bed boiler systems have sparked the enthusiasm of many in the past few years as an answer to many technological problems as alternate energy sources are investigated. Although still barely out of the experimental stage, ship designers are mooting the possibility of fluidized-bed combustion technology being applied in ship propulsion. This paper outlines briefly its process and discusses the economics of such a venture.     

Generalised time and the problem of equity in transport studies

The generalised time expenditure on travel,g _t, may be defined asg _t =t +m/λ where t is the amount of time spent, m is the amount of money spent, and λ is the value of time. Generalised time is expressed in units of time, unlikeg _c, the generalised cost (g _c =m + λt), which measures the same quantities in units of money. Data on all trips from two studies are analysed to show that, as household income increases, the money spent per mile travelled increases, but the time spent per mile decreases. The use of generalised time gives a different picture of the relationship between income and the total time and money spent on travel to that given by the use of generalised cost. The choice between using generalised time and generalised cost in evaluation is fundamentally a choice between assuming that the marginal utility of time and that of money is constant. The procedures at present recommended by the Department of the Environment in U.K. have elements of both assumptions, with some loss of consistency. There are some a priori reasons for expecting constant marginal utility of time to be a more plausible assumption than constant marginal utility of money. Time is, by its nature, equitably and unalterably distributed, not subject to the accidents of inheritance, theft, chance, inflation, social system or government decree. Everybody starts off with 24 hours a day. Although the amount of “free” time varies, of course, it probably varies within a much smaller range than the amount of wealth, certainly for the employed population. In allocating time between various activities, the use of words likespend, save, waste, lose, gain, and so on is a reflection of how deeply rooted in language and thought is the concept of time as a fundamental currency. This approach is strengthened by recent developments in two areas where generalised cost has been found to be a useful tool of analysis — (a) in explaining and predicting the behaviour of travellers, and (b) in evaluating the social costs and benefits arising from transport projects. Only non-working time will be considered here. It is suggested that in some circumstances generalised time would allowbehaviourally correct relationships between non-working time and money to be used in evaluation. This paper — which is a revised version of “A Hypothesis of Constant Time Outlay on Travel” (Paper F29: Planning and Transport Research and Computation Ltd. Sussex, June 1973) — is based upon work carried out with the financial support of the Social Science Research Council.     

Modeling and Dynamics of Friction Wedge Dampers in Railroad Freight Trucks

A mechanical model for the vertical response of the bolster and friction-wedge suspension elements in a railroad freight truck is developed. The model incorporates linear stiffnesses and dry friction contact between rigid elements. Numerical bifurcation diagrams for sticking events, obtained for parameterizations of the amplitude and frequency of a harmonic track excitation, and for various friction laws, reveal distinct parameter-dependent dynamic responses: strongly nonlinear stick-slip oscillations, observed away from period-1 resonance; and weakly nonlinear, nearly harmonic responses, observed near the period-one resonance. The analytical method of harmonic balance is applied to develop a first order approximation for the period-1 response, and, as should be expected, is found to correspond well with the numerical results in the large amplitude limit and near the resonance location. Given that such weakly nonlinear, large amplitude, period-1 responses are not common for the speeds and system parameters of most freight vehicles, we conclude that friction-wedge models based on some form of equivalent linearization may be inadequate for simulating freight car dynamics in many cases of practical importance.     

INTERFERON γ－INDEPENDENT EFFECTS OF INTERLEUKIN 12 ADMINISTERED DURING ACUTE OR ESTABLISHED INFECTION DUE TO LEISHMANIAMAJOR

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CONSTRUCTING POLYCOMPETITOR CDNAS FOR QUANTITATIVE PCR

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A model and algorithm for multicriteria route-mode choice

Using an idea proposed independently by Quandt and Schneider, the paper declares mode choice to be a special instance of route choice. It describes a (non-logit) model which includes in its route-choice mechanism the decision variables traditionally associated with mode choice. With the assumption that each traveller selects the route which minimizes his own personal linear choice function, it is clear that the routes with a nonzero chance of being picked are only those not dominated by any other path (e.g. are not both costlier and longer than any other path). The precise probability of a route being chosen is just the integral over the appropriate portion of the probability density of the coefficients of the choice function. The integration limits are implied by the amount of each disutility on each of the undominated routes. An algorithm is given which is quite efficient in finding these paths in a large and complex multimodal network.