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Bergen ( Norway)

Crete (Greece)

Hamburg(Germany)

Eighth Congress of International Maritime Association of Mediterranean) novembre 1997 Istanbul (Turkey)

Fourth International Conference on FAST Sea Trasportation, luglio 1997 - Sydney (Australia)

The paper deals with the first part of a wide experimental project on three geosim models of a high-speed catamaran, whose hull form corresponds to the one of a full scale catamaran operating in the Naples Gulf. The research is carried out jointly at INSEAN (Rome Towing Tank) and at Naples University towing tank, with the following main aims: - to compare different techniques of towing direction of the models in the resistance tests; - to obtain indications on the validity of the model-ship correlation based on Froude methodology also by means of the direct measurement of the wave resistance component; - to investigate on both viscous and wave interference phenomenon. Up to now, systematic cairn water tests have been completed only on the scale model ? = 13 and the results obtained, analyzed and discussed can be already considered a contribution to the solution of the above-mentioned problems.

A combined analytical/numerical approach is proposed to address the problem of the ship roll motion under the combined action of wind and waves. The approach is modular allowing an easy update of the methodology on the basis of new research outcomes. Realistic environmental conditions regarding both wind and waves are considered. The spatial correlation of wind gusts is taken into account by means of an “aerodynamic admittance” function. The proposed analytical procedure allows obtaining approximate statistical averages of the roll motion without necessarily resorting to time consuming Monte Carlo simulations. On the basis of the results obtained, an estimation of the capsize probability can be carried out. It seems that the effect of wind gustiness could be considered negligible when compared to the effect of waves and of mean wind speed if the ship roll period is not too large. Finally, the presented approach moves towards the concept of “performance based analysis”, recently introduced at IMO as the basis for future developments of Intact Stability, in a clear and formal way.

This paper presents the results of a research program carried out on different trimaran hull forms and configurations suitable for medium size fast ferries. Resistance tests on large size scale models of the two different hull forms of main hull and outriggers, both isolated and combined in different configurations have been carried out at the towing tank of Naples University. For each isolated hull and trimaran configuration the total resistance and running trim have been assessed. Wave pattern analysis was also performed by experimental tests and by numerical computations, so that the influence of each resistance component has been highlighted. The results of this work could be used as a reference in trimaran hull design and optimization.

This article presents the further development of the automated deck layout design. Efficient spatial arrangement is crucial for ships having large number of people on board e.g. ro-pax. Procedure starts with the list of required rectangular compartments while it ends with their optimal locations within available deck space. A two-phase multi-criteria procedure is developed consisting of the automated layout generation phase and of the decision making phase. Compartments are limited by their minimal dimensions lengthwise and crosswise and by required minimal area. Heuristic algorithm for placing, creating and modifying compartments within available deck space is developed. By allowing dimensional variability of each rectangular compartment, considerable improvement in flexibility of the Pareto-optimal solutions is reached. Pareto-optimal layout designs make possible the trade-off between different optimal solutions in the multi-attribute environment. The procedure is applied to the deck layout design of the ro-pax vessel. The graphical output helps to visualize different solutions.

Different types of cargo tanks for gas sea-transport by Liquefied Gas Carriers are described. Design of bilobe tanks, as a complex task, according to the Classification Rules and the USCG Requirements is analysed. This includes selection of special material for high pressure and low temperature, determination of internal pressure consisting of design vapour pressure and liquid pressure that depends on ship motion in rough sea. Furthermore, it includes calculation of tank scant-lings, i.e. shell thickness, and design of longitudinal bulkhead, swash bulkhead, vacuum rings and stiffening rings. Stabil-ity of cylindrical shells and torispherical dished ends is considered. Special attention is paid to the FEM analysis of the stiffening rings. The design procedure is illustrated in case of an LPG Carrier with one ordinary cylindrical tank and huge bilobe tank. Some comments are given how to improve tank design for production.

This paper addresses, starting from an extensive series of tests in longitudinal regular waves, the problems connected with the threshold formulation for parametric rolling and its amplitude modelling above threshold. Both head and following waves have been considered, also in view of the greater attention to head sea conditions called during IMO/SLF discussion on the revision of the Intact Stability Code. Particular attention is given to the nonlinear damping, nonlinear restoring and nonlinear parametric excitation terms. The mathematical models so developed are “compared” with experimental results by means of an ad hoc parameter estimation technique. The experimental results show that a preliminary analysis of the possibility of the onset of parametric rolling can be done by using standard hydrostatic packages allowing for the computation in longitudinal waves. The amplitude above threshold needs, however, a nonlinear approach. The subject is discussed in connection with a series of experiments on scale models of naval ships (a frigate and a destroyer) which exhibited large amplitude rolling in head waves in some loading conditions.

Paper presents the methodology of decision-making for ship/structure multi-criteria design problems. Following points are discussed: Decision support problem identification and formulation. Formulation of the ship or ship structure mathematical module in the decision-making system. Design mapping vs. evaluation mapping. Multi-attribute versus multi-objective approaches/techniques for decision making. Problem manipulations and solution strategies. Concept of non-dominance for filtering the efficient solutions (Pareto frontier). Inter and intra attribute preferences. Attribute normalisation using fuzzy functions. Determination of consistent relative importance of attributes. Designer's heuristic preferences regarding multiple attributes and selection among efficient solutions using Lp-norms. Interactive selection of preferred design with selection of the attribute weights, distance norms, targets, membership grade, etc. Sensitivity analysis. Robustness. Visualisation Applications to the ship structures in practical design environment developed for the efficient design process

Presidente del Comitato Organizzatore del FAST 2003 ed Editor dei Proceedings: Prof.Pasquale Cassella

Southampton ( U.K.)

Publisher Summary This chapter summarizes the results of a research program on high speed trimarans, jointly performed at Genoa, Naples, and Trieste Universities. Two geosim models of a trimaran hull equivalent to high speed vessels operating in the bay of Naples were built. Resistance tests were carried out to assess the best trim and configuration regarding the hydrodynamic resistance. Resistance and wave pattern tests were carried out separately on the main hull, on the outrigger, and on the trimaran. Due to very slender hulls the wave resistance of the considered trimaran is a low percentage of the total resistance and the wave interference phenomenon is generally beneficial to the trimaran. Preliminary seakeeping tests in regular waves show very significant differences of heave and pitch motions of the trimaran with respect to those of its main hull. The reported data seem to indicate a significant beneficial effect of the outriggers on the seakeeping performances.

Streamline differential equations take the indeterminate form et the stagnation point and because of this there appears the difficulty in starting step of numerical integration of these equations. A solution of this problem is given by determining the slopes of streamlines at the stagnation point. It turns out that in three-dimensional potential flow of an incompressible fluid, when the spatial derivatives of velocity components in the stagnation point are non-equal zero, (and this is always fulfilled in the case of the stagnation point of hydrodynamical singularities generating ship forms), the streamline enters the forward stagnation point perpendicularly to the streamlines which leave this point. Three pairs of slopes, which are the roots of two symmetric quadratic equations in two unknowns, define the reference system whose axes are principal-axes of the rate of deformation tensor.

The paper describes the designing procedure of a shipyard able to build a wide assortment of final products. The building of all kind of off-shore objects, special ships of various types, steel structural blocks for ship conversions as well as all kinds of land steel constructions is foreseen. The core of paper is related to the designing philosophy that has to be respected to meet the flexibility and economy of production. The flexibility of the production process is a big goal in all areas of the shipyard’s technology. The layout of the shipyard with working areas, stores and buffers are presented.

Race on for deepwater acreage moves the offshore technology into deeper and deeper seawater. In the last decade exploration drilling has progress up to 2 300 meters of sea depth. In the same time, the oil industry was coping with low oil price and companies had to rationalise their activities. As results we see today many old generation floating platforms used in the conditions which exceed their original design limits. In the article it is given the analytical model used as the base in the feasibility study of upgrading the anchoring system on one old generation semi-submersible drilling platform. The simple analytical model of the composite anchor line calculated the anchor line stiffness properties. The model, which describes the force-displacement relation of the composite anchor line, includes the classical catenary, suspended elastic cable and concentrate buoyant/gravity force in their connection. Besides the static analysis also the dynamic analysis including the first and the second order wave forces was considered. The optimum choice should have to be defined with respect to relation between environmental loading, operating conditions, pre-tension forces and safety factor.

Case studies in structural design and optimization show that structural optimization is a mature tool offering significant savings to the shipyard: decrease in weight and price of construction steel, increase of deadweight, fast calculation of the most complex ships, obtaining of special class ( e.g BV ) which assume 3-D FEM model. The models of double wall tanker, reefer/ro-ro ship, large first class passenger vessel and ro-pax ship are used to demonstrate those benefits.

The main propulsion shafting belongs to a narrow group of the most vital systems on the ship. It influences reliability of the propulsion plant as well as the overall design of the vessel. As high-strength steels possess a favorable property to allow reduced shafting diameters, which results in enlarged torsional flexibility of the shaftline, in this paper, the flexible shafting system approach is presented. In general, this concept offers better torsional vibration behavior of the propulsion system, reduces overall investment costs, enables smoother shaftline alignment and finally, permits shaftline, as well as the engine room, length reduction. Unfortunately, this approach introduces some unfavorable side effects. Therefore, some practical design and manufacturing notes are also given. Finally, two real-life main propulsion shafting design examples are presented. The sea trial vibration measurements proved the concept as well as the performed analyses.

Experimental and theoretical investigations have shown that a linear analysis of the ship motions in waves gives acceptable predictions accuracy over a wide variety of sea conditions and vessel types if the incident wave amplitude is relatively small and if the resonance phenomenon is not present. Unfortunately both, behaving the ship in the extreme sea conditions and in the resonance range is unavoidable part of analysis in ship design. Much effort has been put in developing the suitable numerical tools to calculate the large amplitude ship response on practical and easy way. In spite of the fast recent computers and more accurate three-dimensional models, the simple preparation of input data make the traditional strip method (slender body theory) still very popular. In the article it is shown the extension of the traditional strip method for calculation of coupled heaving and pitching motion in vertical plane for large amplitudes. The non-linear effects due to large amplitude motion and variation of the wetted surface are taken into account through the variable hydrodynamic and restoring coefficients. An instantaneous draft is computed and these coefficients are interpolated for that draft. To solve the coupled non-linear time depended equations of motions, the trigonometric series and perturbation method is applied. The comparison of results with experimental values confirms the numerical results. The influence of resonant phenomena and ship speed variation on the perturbation coefficients is investigated for different wave amplitudes.

Washington D.C. (USA)

Proceedings of Third International Synmposium Conference on Hydrodynamics ottobre 1998- Seoul (Korea)