Containerization and liner conferencs: A polemic

By the mind-1960s there was a great deal of inefficiency in the Europe/Australia liner trade which reflected the ultra-conservative management of the British shipping lines under the benign protection of the conference system. Containerization per se was not necessary to realising a large gain in efficiency and therefore permitting a reduction in the level of freight rates. The introduction of containerization with cellular container ships and under the aegis of a strengthened conference monopoly has meant that shippers have been denied much of the potenital beneifit.     

Variation of whitecap coverage with wave-field conditions

Field observations were carried out at a sea observation tower to investigate how whitecap coverage on the ocean surface responds to wave-field conditions. Images of whitecaps were taken for every 4 h or 7 h in the daytime using a 3CCD digital video camera fixed at 14 m elevation, and they were stored automatically in a hard disk video recorder at a time interval of 1 s. The determination of whitecap coverage was made by means of a digital image processing. The 1/3 power of whitecap coverage increases linearly with increasing the 10-m neutral wind speed. On the basis of the deflection angle between the propagating directions of wind waves and swell, wave-field conditions are classified into four cases. The present results show that whitecaps are produced most actively under the condition of the pure windsea and they tend to be suppressed by the presence of swell. It is difficult to find a certain relation between the deflection angle and whitecap coverage. Whitecap coverage also increases with the wave age in the same wind-speed conditions.     

Tractor Handling during Control Loss on Sloping Ground

Tractor behaviour on sloping ground following a control loss due to rear wheel locking is examined. A mathematical model to predict the tractor trajectory is presented and the results obtained from this model are compared with those obtained from experiments with a remotely controlled tractor.

Reasonable agreement is reached between measured and predicted results - the discrepancies arise from limited tyre data or local random variations in slope, ground roughness or tyre/ground frictional values.

Within these limitations, the model is used to examine possible driver strategies following a control loss. Applying and maintaining full lock for this particular type of accident appears to improve safety; it certainly tends to avoid the worst situation in which the tractor accelerates backwards down the slope and reaches dangerously high speeds although inevitably it increases the likelihood of a low speed overturn.     

A note on the age of radioactive tracers

The age of a water mass is often estimated experimentally using the radio-age computed from the distribution of a radioactive tracer (radiocarbon, helium–tritium). Deleersnijder et al. [J. Mar. Syst. 28 (2001) 229.] have shown that the radio-age underestimates the age of the water and is larger than the age of the radioactive tracer used for its evaluation. This result is generalized here to radio-ages computed from the ratio of two radioactive tracers. The differences between the different ages are also studied analytically and numerically as functions of the decay rate of the radioactive tracers.For small decay rates, the difference between the age of the water mass and the radio-age is shown to be proportional to the decay rate. It depends also on the level of mixing in the system; even radioactive tracers with small decay rates can provide poor estimates of the age of the water mass in a strongly diffusive flow. For small half lives, both the radio-age and the age of radioactive tracers decrease as the inverse of the square root of the decay rate.The same analysis applies to some extent to the estimates of the age of a water mass from stable tracers with known time dependent sources (e.g. chloroflurocarbons).     

An experimental testbed for mobile offshore base control concepts

 The concept of a mobile offshore base (MOB) reflects the need to stage and support military and humanitarian operations anywhere in the world. A MOB is a self-propelled, modular, floating platform that can be assembled into lengths of up to 2 km, as required, to provide logistic support to US military operations where fixed bases are not available or adequate. It accommodates the take-off and landing of C17 aircraft, and can be used for storage, as well as to send resources quickly to shore. In most concepts, the structure is made of three to five modules, which have to perform long-term station-keeping in the presence of winds, waves, and currents. This is usually referred to as dynamic positioning (DP). In the MOB, the alignment is maintained through the use of thrusters, connectors, or a combination of both. In this paper, we consider the real-time control of scaled models of a MOB. The modules are built at the 1 : 150 scale, and are kept aligned by rotating thrusters under a hierarchical hybrid control scheme. This paper describes a physical testbed developed at the University of California, Berkeley, under a grant from the US Office of Naval Research, for the purpose of evaluating competing MOB control concepts. Received: June 4, 2002 / Accepted: October 30, 2002 Acknowledgments. This material is based on work supported by the MOB Program of the US Office of Naval Research under grant N00014-98-1-0744. The authors would like to thank the Link Foundation for its support. Many thanks go to Stephen Spry for his experimental work. The photographs are courtesy of Bill Stone, Gerald Stone, and Jay Sullivan of the PATH Publications staff. Address correspondence to: A.R. Girard (e-mail: anouck@eecs.berkeley.edu)     

Federal ports policy

In contrast to the centralized port-planning framework that is utilized in some industrialized countries, the US relies on a complex and fragmented framework in which responsibility for the planning, development and operation of landside maritime infrastructure rests with State and local governments. It has been argued that the separation of the federal government from port policy was rooted in the port preference clause of the Constitution. This paper is an effort to determine whether the current decentralized port policy in fact stems from the Constitution and, to that end, reviews how over the years the US Supreme Court has construed the port preference clause in the Constitution. It was found that there is no evidence to support the assertion that the port preference clause has restricted the development of Federal port policy. Moreover, the decentralized and fragmented decision-making process that is evident today does not imply the absence of federal impact. Rather, it reflects federal involvement through multiple agencies and regulatory processes and is a conscious effort, consistent with other areas of transport infrastructure development, to retain local decision-making for infrastructure investments. It is concluded by raising the issue whether current federal involvement in ports (that is, existing federal port policy), through dredging, landside transportation improvements or subsidized capital, among other things, needs to be reappraised before a new round of capital intensive investment begins.     

Modeling the modal choice decision process

Most models of modal choice are macroanalytic in nature — focusing on the behavior of large groups of travelers — and have limited explanatory power. Transportation managers need to know more about the decision processes of individual travelers in selecting a mode for a particular trip, if they are to be able to develop strategies for influencing these decisions. A microanalytic model of modal choice is therefore developed in flow-chart form, clarifying the stages in the modal choice decision process for any given trip. Individual consumers are seen as trying to satisfy a particular travel need by first specifying the characteristics of the trip itself and then specifying the “ideal” modal attributes required for this trip. Next, the perceived characteristics of a limited number of modes are evaluated against this “ideal” solution and the consumer is assumed to select that mode which provides the best match. The model explicitly recognizes the impact of psychological variables on modal choice as well as the consumer's need for information if he or she is to evaluate realistically all alternatives.     

Steering and Dynamic Stability of Railway Vehicles

For railway vehicles having coned wheels mounted on solid axles there is a conflict between dynamic stability and steering ability

It is shown that the stiffness and kinematic properties of all possible interwheelset connections are characterised by two properties describing the distortional characteristics of the vehicle in plan. Within this framework, the various possibilities for steered wheelsets are considered, and several past and current proposals are reviewed. Using the linear approach to dynamic stabibty and curve negotation the performance of existing and newly proposed configurations is discussed

For any symmetric, two-axle vehicle it is shown that for perfect steering on a curve there should be zero bending stiffness between the wheelsets. It is further shown that if the bending stiffness is zero, the vehicle lacks dynamic stability as the critical speed of instability, is zero. In this case, the vehicle undergoes a steering oscillation which occurs at the kinematic frequency of a single wheelset and which is a motion in which pure rolling occurs

Similar results are obtained with vehicles with three or more axles if adjacent axles are connected by shear structures. However, it is shown that it is possible to satisfy both the requirements of perfect steering and a non-zero critical speed if the vehicle has zero bending stiffness and if, in addition to adjacent wheelsets being connected in shear, at least one pair of non-adjacent axles are connected by a shear structure.     

Aircraft and maintenance scheduling support,mathematical insights and a proposed interactive system

In this paper we first review the current practice of operative aircraft and maintenance scheduling at the Hungarian Airlines. The ideas to be included in the proposed operative scheduling support system mean new contributions from both the algorithmic and human-computer interaction points of view. The algorithm is based on new graph theoretical results which were motivated by the necessity of combining a given flight schedule with the strict maintenance requirements of the aircraft. Aircraft rotation corresponds in mathematical terms to the coloring of an interval graph with colors representing the tail numbers in such a way that the vertices corresponding to maintenance checks are colored in advance. The human-computer interface is built on the Microsoft Windows graphics environment, which allows a simultaneous, visual and active contact with all necessary information and methods.