Fatigue life prediction of welded stiffened 350WT steel plates

The propagation of fatigue cracks under constant amplitude cyclic loading was studied in welded stiffened steel plates. The residual stresses in the stiffened plates were measured using the neutron diffraction strain-scanning technique. A finite element model of the stiffened plate was constructed to simulate the residual stresses by an uncoupled thermal and thermo-mechanical analysis. Both the finite element model and the neutron diffraction measurements indicated that in general the residual stresses were tensile near the welded stiffeners and compressive between the stiffeners and ahead of the starter notch tip. Fatigue testing indicated that the fatigue crack growth rates of the stiffened plates were in general lower than that of a corresponding unstiffened plate, especially near the notch tip where compressive residual stresses existed. Both the finite element method and Green's function predicted the fatigue crack growth rates with reasonable accuracy.     

GPS-based speed collection method for road traffic noise mapping

One of the most difficult and expensive tasks in making noise pollution maps is the collection and processing of the data needed to create acoustic models. In the case of road traffic noise maps, obtaining speed data for light and heavy vehicles a problem that has usually been avoided by using a road’s speed limit or by making assumptions based on experience from similar road types. Here global positioning systems-based techniques are applied for acquiring vehicle speed data and adapted to fulfill the requirements of noise prediction models.     

L’intégration territoriale des gares sur lignes à grande vitesse en France : une approche typologique

Construction of high-speed railway lines (Lignes à Grande Vitesse — LGV in French) in France and in other European countries has brought considerable changes in railway accessibility for the areas linked to this fast transport network. The new stations on the high-speed lines take maximum advantage of such relational gains. However, mass transit access to these stations often constitutes a problem. Their locations, which are frequently exurban, are not determined by considerations involving efficient mass transit service links, and especially railway links. This situation creates difficulties for prior and subsequent passenger travel, and it means that the local players have to develop new access routes of variable quality. The present article puts forward a quality analysis covering territorial integration of high-speed railway stations via typology of the interactions between these new service points and the established stations in central locations. In a context marked by the increasing burdens placed on local authorities regarding financing for new high-speed railway infrastructures, we examine whether these changes in the players’ roles encourage enhanced consideration as to positioning of high-speed railway stations in relation to accessibility criteria for mass transit.     

Designing a non-linear tracking controller for vehicle active suspension systems using an optimization process

In this paper, a new non-linear tracking controller for vehicle active suspension systems is analytically designed using an optimization process. The proposed scheme employs a realistic non-linear quarter-car model, which is composed of a hardening spring and a quadratic damping force. The control input is the external active suspension force and is determined by minimizing a performance index defined as a weighted combination of conflicting objectives, namely ride quality, handling performance and control energy. A linear skyhook model with standard parameters is used as the reference model to be tracked by the controller. The robustness of the proposed controller in the presence of modeling uncertainties is investigated. The performed analysis and the simulation results indicate that both vehicle ride comfort and handling performance can be improved using the minimum external force when the proposed non-linear controller is engaged with the model. Meanwhile, a compromise between different objectives and control energy can easily be made by regulating their respective weighting factors, which are the free parameters of the control law.     

Safety in Greek coastal shipping: The role and risk of human factor revisited

The comprehensive analysis presented in this paper investigates the links and comparative assets between human factor and other factors that are important determinants of maritime transport risk. In this outline, the identification of factors, such as age and ship size, that can be statistically linked (i.e. statistical significance) to whether an accident in a passenger vessel can be attributed to human factor or other causes is addressed accordingly. This way, the role of human factor in relation to safety of Greek coastal shipping is revealed and the spotlight is able to focus on the various aspects and points that manifest the importance of human element in the maritime industry. The risk assessment of the transportation with Greek passenger ships is being used in order for the safety level of Greek coastal shipping to be adequately estimated. Moreover, the comparison between the values of risk for accidents caused by human factor and those attributed to other causes is an established way to bring to the fore the unbroken relationship between the human factor and marine accidents’ consequences. The paper is concluded with interesting insights and comments drafted through the aforementioned tasks.     

Scientific requirements for an abyssal benthic laboratory

For over thirty years man has studied “outer space” and installed satellites which watch the surface of the Earth. The great depths of the world ocean are, however, practically unknown and there is an urgent need to put abyssal benthic laboratories into “inner space” in order to study basic phenomena of interest to marine science and climatology as well as man's impact on the oceans.In view of the numerous problems related to global change, as a first step emphasis should first be on the role of the oceans and their inherent processes, which are the focus of such international programmes as the World Ocean Circulation Experiment (WOCE) and the Joint Global Ocean Flux Study (JGOFS). Multi-disciplinary registration of key events at selected key sites investigating the variability in time and space are of the utmost importance. The same methods and techniques must be used for the study of human impacts on the deep oceans caused by mining of metalliferous resources and by waste disposal as well as in basic studies. However, the investigation of the inner space of our planet has certain requirements. As long-term and large-scale investigations become more and more important, development of automized systems, largely independent from research vessels will be required. This will demand high capacities of energy for all technical functions as well as high storage capacities for data and samples. As a consequence the needs for two different—although overlapping—functional approaches are defined for future deep-sea deployments.(A) A system for long-term registration of the natural variability and long-term monitoring of human impacts: (B) A system for short-term observations and short-time experimentations. This report summarizes their technological demands. The envisioned interdisciplinary technology should deliver information on physical, biological and geochemical processes and their variabilities in the deep oceans. The prospected systems need to have the ability for real time video observation, data transfer and experimental manipulation, as well as sensing and sampling facilities with large storage capacities for long-term deployments.Prospective costs of the described multipurpose abyssal benthic laboratory will presumably exceed the funds for deep-sea research of a single country. A joint European effort could solve this problem and help to manifest a leading role for European marine science in international deep-sea and global change research.     

Inertial waves in the Ibiza channel

Currentmeter data taken in the Ibiza Channel show the almost permanent presence of near-inertial motions below the mixed layer. They correspond to downwards progressing waves with a vertical group velocity of some m/day. The presence of the Balearic Front sensibly affects the propagation of these inertial waves. Although situations exist in which the passage of atmospheric fronts along the Channel is clearly the generating force of these near-inertial motions we find others in which the energy density in mid-depths is higher than in any other depth. These last situations are closely related to the arrival to the Channel of some of the different water masses which flow around there. A clear correspondence between the presence of relatively strong inertial waves and a noticeable vertical shear of the subinertial flow, evidenced by an averaged Richardson number, is also observed. In some circumstances, the vertical shear of the whole flow (inertial plus subinertial) is higher than the stability limit, that is, Ri < 0.25, favoring the braking of the internal waves. This could be a plausible cause of their decay and a reason to explain why they do not penetrate further than certain depths.     

The Nonlinear Behaviour of a MacPherson Strut Wheel Suspension

Three nonlinear models of a MacPherson strut wheel suspension have been studied. The nonlinearities considered are due to the nonlinear geometrical effects in the mechanism, the amplitude limitation due to the bumpstop, the progressive stiffness of the bumpstop and the different damping coefficients for the shock absorber in bump and rebound. The models have been derived according to physical parameter values of. the MacPherson strut wheel suspension of the car SAAB 9.000. The most suitable model was further studied with special attention to nonlinear phenomena. For harmonic forcing the system had phenomena such as multiple solutions and subharmonics. For some parameter values the solution was very sensitive to changes in the integration tolerances in the numerical integration routine. No chaotic steady state solutions were found for the parameter values studied.     

Optimal Preview Control of Rear Suspension Using Nonlinear Neural Networks

The performance of neural networks to be used for identification and optimal control of nonlinear vehicle suspensions is analyzed. It is shown that neuro-vehicle models can be efficiently trained to identify the dynamical characteristics of actual vehicle suspensions. After trained, this neuro-vehicle is used to train both front and rear suspension neuro-controllers under a nonlinear rear preview control scheme. To do that, a neuro-observer is trained to identify the inverse dynamics of the front suspension so that front road disturbances can be identified and used to improve the response of the rear suspension. The performance of the vehicle with neuro-control and with LQ control are compared.     

Contributors to this issue

Contributors to this issue