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)     

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.     

Steel product flows: works-to-port: an application of the 'transportation problem'

The pattern of landward flows of steel products between manufacturing works and ports in the United Kingdom used for export is examined, and the spatial implications of various levels of hypothetical rationalization in the distribution of port facilities discussed. While extreme spatial concentration of port facilities for handling general steels would seem both impracticable and undesirable, the analysis suggests that a greater degree of rationalization than at present could be achieved without increasing overall landward transport costs.     

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.     

Analysis of wheel speed vibrations for road friction classification

ABSTRACT

With higher level of vehicle automation, it becomes increasingly important to know the maximum possible tyre forces during normal driving. An interesting method in this respect is estimating the tyre–road friction from the resonance peak in the wheel speed signal, excited by road roughness. A simulation environment using the MF-Swift tyre model is proposed, which gives insight in the correctness and functioning of this method. From implementing the estimation algorithm and considering the tyre torsional vibration system, it is concluded that frequencies and damping ratios can be estimated with reasonable accuracy and that the trends observed with changing road friction are consistent. Furthermore, the proposed simulation environment gives opportunity to investigate other issues like robustness of the estimation method to road roughness. Additionally, the tyre modelling aspect of the estimation method is analysed and improvements are proposed.     

Optimal tyre usage for a Formula One car

Variations in track temperature, surface conditions and layout have led tyre manufacturers to produce a range of rubber compounds for race events. Each compound has unique friction and durability characteristics. Efficient tyre management over a full race distance is a crucial component of a competitive race strategy. A minimum lap time optimal control calculation and a thermodynamic tyre wear model are used to establish optimal tyre warming and tyre usage strategies. Lap time sensitivities demonstrate that relatively small changes in control strategy can lead to significant reductions in the associated wear metrics. The illustrated methodology shows how vehicle setup parameters can be optimised for minimum tyre usage.     

Knock in dual-fuel diesel combustion with an E85 ethanol/gasoline blend by multi-dimensional simulation

In this paper, knocking combustion in dual-fuel diesel engine is modeled and investigated using the CFD code coupled with detailed chemical kinetics. The ethanol/gasoline blend E85 is used as the primary fuel in a dual-fuel combustion concept based on a light-duty diesel engine equipped with a common-rail injection system. The E85 blend is injected and well mixed with intake air in the intake manifold and is ignited by the direct injection diesel fuel. A 46-species, 187-reaction Multicomponent mechanism is adopted to model the auto-ignition process of the E85/air/diesel mixture ahead of the flame front. Based on the model validation, knocking combustion under boost and full load operating condition for 0 %, 20 %, 50 %, as well as 70 % E85 substitute energy is simulated. The effects of E85 substitute rate and two stage injection strategies on knock intensity, power output, as well as location of the auto-ignition initiation is clearly reproduced by the model. The calculation result shows that, for a high E85 rate of 50 % and 70 % with single injection strategies, the most serious knock and the origin of auto-ignition always occurs far away from where the flame of diesel spray is first generated, at the center of combustion chamber, due to higher pressure wave, relatively richer E85 mixture and longer distances of flame propagation. The two stage injection strategies with a small amount of diesel pilot injection ahead of the main injection primarily influence the ignition behavior of the directly injected fuel, leads to a lower pressure rise rate and a reduced propagation distance, both of which contribute to the attenuation of knock intensity for a higher E85 rate.     

Non-natural equilibrium contour design for radial tire and its influence on tire performance

Two types of radial tire 11.00R20 and 385/65R22.5 are chosen as the research objects, and their carcass contours are redesigned by using Sakai Hideo’s, Frank’s and the new non-natural equilibrium contour design theories, which were based on analyzing the current non-equilibrium contour design theories of radial tire. Then the tire wear, rolling resistance and grip performance of the two radial tires designed by different non-natural equilibrium contour design theories are comprehensively analyzed with the finite element software ABAQUS. The results show that Frank’s contour design theory can reduce tire wear; the new non-natural equilibrium contour design theory can enhance tire wear, rolling resistance performance, etc. It is also found that the tire carcass contour has great influence on tire performance, especially on the tire rolling resistance. The new non-natural equilibrium contour theory provides a guidance to reduce the tire rolling resistance, and it can break through the target conflicts in tire performance. The tire with the new non-natural equilibrium carcass contour can enhance its comprehensive performance.     

Performance evaluation of slim low-risk-deployment dual-type passenger airbag system with dispersed inflation pressure

Motor vehicle passenger airbags have been proven to be effective for reducing the possibility of passenger injury during a crash. However, the inflation of the airbag sometimes causes serious injury when a passenger is positioned close to the airbag. The United States Federal Motor Vehicle Safety Standard (FMVSS) 208 requires the use of a low-riskdeployment (LRD) passenger airbag system. This paper proposes a newly developed airbag system comprising two slim airbags mounted on the instrument panel. A series of tests were conducted using the FMVSS 208 test procedures to demonstrate the effectiveness of the proposed system. It was found that the system not only satisfied the injury criteria of FMVSS 208, but was also effective for protecting passengers of all sizes.     

Effect of regenerative braking energy on battery current balance in a parallel hybrid gasoline-electric vehicle under FTP-75 driving mode

In recent years, a hybrid electric vehicle (HEV) has been considered a successful technology. Especially, in case of a full HEV, the motor can drive the vehicle by itself at low velocity or assist the engine at high load. To improve the hybrid electric vehicle’s efficiency, a regenerative braking system is also applied to recover from kinetic energy. In this study, an experimental control apparatus was set up with a parallel hybrid electric vehicle mounted on a chassis dynamometer to measure ECU (engine control unit) and MCU (motor control unit) signals, including the current and state of charge in the battery. In order to analyze regenerative braking characteristics, user define braking driving cycle was introduced and carried out using different initial velocities and braking times. The FTP 75 driving cycle was then adapted under different initial SOC (state of charge) levels. The experiment data was analyzed in accordance with the vehicle velocity, battery current, instant SOC level, motor RPM, engine RPM, and then vehicle driving mode was decided. In case of braking driving cycle, it was observed that SOC were increased up to 1.5 % when the braking time and the velocidy were 6 second and 60 km/h, respectively. In addition, using the FTP 75 driving cycle, mode 1 was most frequently operated at SOC 65 conditions in phase 1. In phase 2, due to frequent stop-go hills, percentage of mode 1 was increase by 22 %. Eventually, despite of identity, it was shown that the characteristics of phase 3 differed from phase 1 due to the evanishment of the effects of initial SOCs.