Numerical Analysis of Thermal Distortion and Residual Stresses in H13 Steel Due to Vacuum Gas Quenching

IntroductionVacuumgasquenchinginvolvinghighpressuregasasacoolingmedium,is.anincreasinglypoPularheattreatffienttechniquefor1argesteeldieblocks,forexamPleHl3die.ItisconsideredessefltialtounderstandthentheeofthegasflowandtheinfiuencethishasontemPeratureprofilesandresultaflresidualstresseswithintheheattTeatedcomPonent.SimulatingthisprocessinvolvesthesimulationofgasflowinthefurnaceaswellasthesimulationofthethermalbehaviourofthecomPoneni.However,thereisnosinglecomPatersoftwarepackageavailabletot…     

A study of the Alboran sea mesoscale system by means of empirical orthogonal function decomposition of satellite data

This paper presents the results of a combined empirical orthogonal function (EOF) analysis of Advanced Very High Resolution Radiometer (AVHRR) sea surface temperature (SST) data and sea-viewing wide field-of-view sensor (SeaWiFS) chlorophyll concentration data over the Alboran Sea (Western Mediterranean), covering a period of 1 year (November 1997–October 1998). The aim of this study is to go beyond the limited temporal extent of available in situ measurements by inferring the temporal and spatial variability of the Alboran Gyre system from long temporal series of satellite observations, in order to gain insight on the interactions between the circulation and the biological activity in the system. In this context, EOF decomposition permits concise and synoptic representation of the effects of physical and biological phenomena traced by SST and chlorophyll concentration. Thus, it is possible to focus the analysis on the most significant phenomena and to understand better the complex interactions between physics and biology at the mesoscale. The results of the EOF analysis of AVHRR-SST and SeaWiFS-chlorophyll concentration data are presented and discussed in detail. These improve and complement the knowledge acquired during the in situ observational campaigns of the MAST-III Observations and Modelling of Eddy scale Geostrophic and Ageostrophic motion (OMEGA) Project.     

A behavioural car-following model for computer simulation

The ability to predict the response of a vehicle in a stream of traffic to the behaviour of its predecessor is important in estimating what effect changes to the driving environment will have on traffic flow. Various proposed to explain this behaviour have different strengths and weaknesses. The paper constructs a new model for the response of the following vehicle based on the assumption that each driver sets limits to his desired braking and acceleration rates. The parameters in the model correspond directly to obvious characteristics of driver behaviour and the paper goes on to show that when realistic values are assigned to the parameters in a simulation, the model reproduces the characteristics of real traffic flow.     

Carbon and nutrient dynamics in a hypertrophic lagoon in southwestern Taiwan

Dissolved and particulate phases of carbon (DIC, DOC, POC) and nutrients (DIN, DIP, DSi, DON, DOP, PN) were investigated bimonthly from August 1999 to August 2000 to study biogeochemical dynamics of carbon and nutrients in Tapong Bay, a small semi-enclosed and hypertrophic lagoon in southwestern Taiwan. The lagoon has only a tidal inlet for exchanging water between Tapong Bay and Taiwan Strait, which may result in low water exchange rates and various oxygen-deficient conditions in bottom water of the inner bay during warm seasons. The water exchange time of Tapong Bay ranges from 7 days (summer) to 13 days (winter) with a mean of 10 days. Nutrient dynamics were largely ascribed to allochthonous inputs, biological and exported removals in the lagoon. Diffusion fluxes from sediments to overlying water accounted for only about 7.6% of annual DIN inputs and 1.0% of annual DIP inputs. High primary productivity (89 mol C m⁻² year⁻¹) supported by abundant nutrients primarily drove the lagoon into a hypertrophic condition as particulate organic matter was derived mainly from biological production. Excess of DIP appeared to occur throughout the study period in the lagoon. Temperature, solar radiation and turbidity, rather than nutrients, perhaps controlled seasonal variations of primary productivity. The net ecosystem production (NEP) derived from daily changes of DOC and POC inventories was about 6.3 mmol C m⁻² day⁻¹ that was close to 6.7 mmol C m⁻² day⁻¹ simulated from the biogeochemical modeling. Therefore, the net ecosystem production (NEP) rate of organic carbon estimated from the biogeochemical model was reliable, and the NEP was temporally variable with an annual mean of 5.8 mol C m⁻² year⁻¹, implying that Tapong Bay was an autotrophic system. Although calcification proceeded pronouncedly in warm seasons, an invasion of CO₂ was significant in this system. In terms of nitrogen budget, the annual nitrogen fixation exceeded the annual denitrification with a magnitude of 1.30 mol N m⁻² year⁻¹, which may be supported by the abundance of nitrogen fixation microplanktons in the lagoon.     

Application of Nonlinear Control Theory to Electronically Controlled Suspensions

This paper illustrates the use of nonlinear control theory for designing electro-hydraulic active suspensions. A nonlinear, “sliding” control law is developed and compared with the linear control of a quarter-car active suspension system acting under the effects of coulomb friction. A comparison will also be made with a passive quarter-car suspension system. Simulation and experimental results show that nonlinear control performs better than PID control and improves the ride quality compared to a passive suspension.     

New technology and maritime training in the 21<Superscript>st</Superscript> century: Implications and solutions for MET institutions

This paper examines the impact of new technology on MET institutions in the 21^st century and discusses to what extent global MET institutions can enhance and enrich traditional practices through access to new technology and the use of innovative teaching and assessment methods within a sustainable and achievable framework. It notes the diverse standards and access to new technology by MET institutions across the globe and discusses the implications for them if they are to remain competitive and viable. The paper concludes that maritime institutions can benefit from the use of new technology, but only through rational planning and sustainable staged growth. A series of continua of technical development is provided to assist institutions, from the smallest to the largest, to plan for technical development and growth in a rational and feasible way.     

Clustering and performance: the case of maritime clustering in The Netherlands

Over the last years, the concept of clustering has become a central concept for analysing the competitiveness of nations, industries and firms. The cluster concept can be usefully applied to study clustering of maritime activities. Maritime activities, such as shipping, shipbuilding and port and maritime services, are clearly geographically concentrated in a number of maritime clusters. Due to ongoing internationalization in these industries, the concentration of maritime activities in clusters is likely to increase. This observation leads to two important research questions: what are the advantages for firms to locate in clusters and what factors influence the development of maritime clusters? This study identifies four agglomeration economies that attract firms to cluster: a joint labour pool, a broad supplier and customer base, knowledge spillovers, and low transaction costs. Furthermore, it discusses the effects of aspects of the cluster structure, being the presence of internal competition, the heterogeneity of the cluster population, the entry and exit barriers, and the presence of (above mentioned) agglomeration effects. It also briefly discusses the important issue of cluster governance. This overview allows one to develop a theoretical framework to analyse clusters. In the empirical part, this framework is applied to the maritime cluster in The Netherlands. Based on empirical data, from surveys amongst firms in the maritime cluster, studies commissioned by the Dutch maritime Network and regional statistics, the presence of agglomeration economies in the cluster is shown. Secondly, it is shown that the cluster structure is beneficial for the performance. This paper finishes with conclusions and suggestions for further research.     

Collapase analysis of ship hulls

This paper presents an efficient finite element procedure for the collapse analysis of ship hulls under complicated loads. A set of finite elements, such as beam-column elements, stiffened plate elements, and shear panel elements are developed, directly accounting for the geometrical and material non-linearities and initial imperfections.

Elastic-plastic stiffness matrices for elements have been derived by combining elastic large displacement analysis theories with a plastic hinge model. The buckling and post-buckling behaviour of plates is included using an effective width concept. The procedure is effective, since few mode-points are necessary and numerical integration for evaluating stiffness matrices is avoided. Fracture mechanics criteria are introduced in order to account for tension tearing rupture and brittle failure of the material.

Practical applications to ultimate longitudinal strength analysis of ship hulls and tanker collision analysis are presented. The procedure can also be used for collapse analysis of offshore and onshore structures.