Containerization in Nigeria: trends and patterns

Containerization was introduced into Nigeria in the late 1960s, not through a delibrate policy but through the unilateral action of shipping companies.In spite of this,the percentage of the country's external trade cargo that is containerized grew from only about 0.03 in 1968-69 to about 8.6 in 1981.

Containerization of cargo is more significant in the import than in the export trade. Perhaps because of the capital-intensive nature of this technology, there is a concentration of containerization facilities in the ports of Lagos and Port Harcourt. Whereas this is a cost-efficient development, there are various inefficient aspects in the inland distribution of containers.     

适用于重载的滚动轴承

介绍了为增加货车轴重而开发的短轴承以及将短轴承进行标准化而遇到的问题。     

Vertical Vibration Analysis of Vehicle/Imperfect Track Systems

Summary This paper studies the vertical vibration of a vehicle traveling on an imperfect track system. The car body and sleepers are modeled as Timoshenko beams with finite length, and the rail is assumed as an infinite Timoshenko beam with discrete supports. Imperfection of the track system comes from a sleeper lost partial support by the ballast. Since deflection of the rail is limited within a certain interval where the vehicle is passing over, the infinite domain problem can be transformed into a finite domain problem with moving boundary. In this work, the equations of motion of the car body, rail and sleepers are discretized first by the finite element method. The discretized equations of motion for the vehicle and track systems are then assembled, respectively. Finally, the Newmark method is applied to obtain the response of the vehicle and track systems at each time step. The effect of the vehicle speed on the response of the vehicle and track systems is investigated.     

Queue-dependent vehicle dispatching with options and optimal fleet size

A queue-dependent vehicle dispatching rule, with options to use special vehicles (rented, reserve, shared etc.) for relieving long waiting lines, is considered. The transportation system under consideration has one source terminal and a fleet of N regular vehicles. Passengers are assumed to arrive individually at the source terminal according to a Poisson process. An efficient recursive algorithm is derived to analyse the performance of the system. An average cost criterion is used to determine the firm's fleet size and dispatching strategy for a simpler system. This is a variant of a “Random vehicle dispatching with options” rule proposed by Zuckerman and Tapiero (1980).     

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.     

Motivating ship managers to use management support technology

Ship managers have been slow in their response to using information technology (IT) in spite of the dynamic environment encouraging technological support for a number of critical tasks. The reason is in part the conservatism of the shipping industry, but the main reason seems to be the poor quality of systems provided, creating a credibility gap and usage reluctance. This paper suggests five principles for the development of 'user seductive' systems and illustrates their successful use in a number of case histories of management support systems development.