International Shipbuilding Progress - Volume 50, issue 1-2

Authors: Thornhill, Eric | Oldford, Dan | Bose, Neil | Veitch, Brian | Liu, Pengfei

Article Type: Research Article

Abstract: A set of bare hull resistance tests were performed on a 1/8 scale model of an 11.8 m long planing hull. The model was tested over a range of speeds and ballast conditions in calm water. Measurements were made of tow force, running trim,and sinkage. Wetted areas and lengths were determined using underwater video. Flush mounted pressure taps gave gauge pressures at various locations on the hull surface. Wave profiles were measured using an array of …capacitance probes positioned laterally in the tank. Boundary layer velocity profiles were resolved at two locations on the hull for several model speeds using a laser Doppler velocimeter (LDV). Pressures under the aft region of the hull were found to be lower and velocities just outside of the boundary layer were found to be higher than predicted by simple planing theory. Show more

Citation: International Shipbuilding Progress, vol. 50, no. 1-2, pp. 5-18, 2003

Authors: Helvacioğlu, Şebnem | İnsel, Mustafa

Article Type: Research Article

Abstract: Ship design applications are carried out mainly by human experts who generally utilise computerised deterministic analysis techniques. Application of stochastic methods, and formalisation of heuristic methods in computer aided ship design have not been widely utilised yet. This work investigates whether such a heuristic method, namely expert system approach, can be satisfactorily applied into ship design. An expert system program package called ALDES (Accommodation Layout Design Expert System) was developed by using CLIPS expert …system shell in order to asses the current approach. Preliminary dimensions of a container ship were calculated by a heuristic approach supported by a database of similar ships, empirical formulation, and deterministic analysis techniques. The hull was subdivided into main compartments by locating decks, double bottom, and transverse bulkheads. The number of crew was calculated by utilising manning regulations, then the superstructure layout was developed by assigning spaces for access, passageways, public and private rooms. Two cases were selected to test the current approach: firstly the effects of design heuristics were analysed in an evacuation analysis, and secondly a preliminary concept design for a fast containership was conducted. In conclusion, this study presents a case study approach in which an expert system is applied into ship design domain successfully with layout design emphasis. Show more

Citation: International Shipbuilding Progress, vol. 50, no. 1-2, pp. 19-34, 2003

Authors: Soares, C. Guedes | Garbatov, Y. | von Selle, H.

Article Type: Research Article

Abstract: The paper addresses the evaluation of the fatigue life of ship structures based on a probabilistic approach that considers the stochastic nature of the ocean environmental loading and the service profile of the ship. The method is based on a linear spectral analysis of the stress range response. The local stress range response transfer functions are obtained by using a three-dimensional finite element model. The response process for each short-term sea state is modelled by a …Rayleigh distribution. The long-term response period and long-term stress range distribution are then determined and are fitted as a Weibull distribution. The Palmgren-Miner linear cumulative damage model is applied. An example calculation is presented for a tanker and the influence of several scatter diagrams on the fatigue life of structural details is examined. Show more

Citation: International Shipbuilding Progress, vol. 50, no. 1-2, pp. 35-55, 2003

Authors: Degiuli, Nastia | Werner, Andreja | Doliner, Zdravko

Article Type: Research Article

Abstract: The Landweber, Hogben and Baba methods of experimental determination of wave pattern resistance based on wave height measurements in several longitudinal measurement cuts have been introduced in this paper. The programme of numerical simulation and experimental determination of wave pattern resistance was conducted in a tank of finite width and infinite depth for a trimaran whose individual hulls are Wigley parabolic models, for the Froude number range 0.254–0.420, with a total of 12 runs. The above …mentioned methods are based on an identical hydrodynamic model, and identical analytic expressions. A comparison of the calculation results (amplitude spectrum, wave resistance, reconstructed waveforms) is given by numerical simulation of experimental determination of wave pattern resistance. It has been shown that all three methods are equal and that they give the same results if criteria based on frequency content determination and resolution in frequency are respected. Experimental determination of wave pattern resistance by applying the same methods and respecting the same criteria was carried out and results show the consistency of the basic approach. Calculation of theoretical wave resistance based on the linear wave theory and Michell's approximation of ship's hull has been carried out, whereby the comparison between theoretical predictions and experimentally determined wave pattern resistance has shown poor agreement. Show more

Citation: International Shipbuilding Progress, vol. 50, no. 1-2, pp. 57-87, 2003

Authors: Vaaraniemi, Kalle | Pramila, Antti | Enlund, Håkan | Olkinuora, Pauli

Article Type: Research Article

Abstract: By using geometrically and materially nonlinear Finite Element Analysis the dimensionless ultimate moment as a function of the slenderness of a right angled isosceles bracket (arm length/thickness) is calculated for a range of Young's modulus/yield strength values covering most of the practical cases. Both simply supported and fixed boundary conditions on the sides connected to the flanges of the beams are considered. As the dimensionless results are in an EXCEL-table, the generation of several design alternatives …is very fast and the designer can choose the final size by taking into account also other criteria which are important in the case under consideration. For stiffened brackets the ultimate moment is presented as a function of the dimensionless stiffness of the stiffener for different arm length/thickness ratios and for different gap lengths at the end of the stiffener. These results can be used for avoiding overdimensioning of the stiffener. Illustrative examples are presented. Show more

Citation: International Shipbuilding Progress, vol. 50, no. 1-2, pp. 89-108, 2003

Authors: Lee, Seung Keon | Fujino, Masataka

Article Type: Research Article

Abstract: The MMG mathematical model [1] is well known and widely used for describing the manoeuvring motion of a ship. The MMG model is a modular type mathematical model which has proven to be useful in predicting various aspects of manoeuvring motion. However, this model was originally developed for the single-propeller singlerudder ship. Nowadays there are many multi-propeller multi-rudder ships, but little is known about the manoeuvring characteristics of the multi-propeller multi-rudder ship. In this …paper, the authors develop the mathematical model to predict the manoeuvring motion of a twin-propeller twin-rudder ship, which was selected as one of the most popular configurations of multi-propeller multi-rudder ships. Initially, the various parameters included in the mathematical model for manoeuvring motion are investigated experimentally for a twin-propeller twin-rudder ship. The authors subsequently modified the mathematical model of the single-propeller single-rudder ship, and proposed a new mathematical model for the twin-propeller twin-rudder ship [2]. Finally, the predicted manoeuvring motion of the twin-propeller twin-rudder ship was compared with the test results of a free-sailing model in order to examine the validity of the proposed mathematical model. Show more

Citation: International Shipbuilding Progress, vol. 50, no. 1-2, pp. 109-123, 2003

Authors: Segal, Zelik | Segal, Alexander

Article Type: Research Article

Abstract: The paper presents results of theoretical and experimental investigations about hydrodynamic characteristics of vertical axis propeller blades moving on curvilinear trajectories with variable angles of attack. Inductive velocities are computed according to a three-dimensional vortex system, and design of the blades motion was carried out using experimental characteristics of underwater wings in curvilinear flow.

Citation: International Shipbuilding Progress, vol. 50, no. 1-2, pp. 125-145, 2003

Authors: Brockett,, Terry E.

Article Type: Research Article

Abstract: Available performance data of selected open, contra-rotating and ducted propulsors operating in a uniform onset field are assembled to display the maximum efficiency as a function of thrust-loading coefficient, C_T = T/(½ρV^2 R_{R^2} ). Satisfactory correlation is presented between this observed best efficiency and estimates from a numerical method based on an inviscid lifting-line representation of the rotor, or other blade row, plus, when appropriate, an axi-symmetric …panel-method analysis of the duct and hub surfaces. Viscous drag is added empirically as a local blade-section friction coefficient. For the open-propeller series and various sets of conventional accelerating ducted propulsors, the maximum efficiency of the ducted propulsors is greater by several percent at a C_T = 1 and by about 5 percent (straight difference in values) at a C_T approaching 10. The contra-rotating configuration displays a greater increase in the observed maximum efficiency at reduced C_T values compared to the accelerating ducted propulsor but at C_T > 2 the accelerating ducted units develop greater efficiency. Only at reduced thrust levels is there an indicated beneficial interaction between the blade rows of a contra-rotating propulsor compared to a simple thrust division without interactions. Show more

Citation: International Shipbuilding Progress, vol. 50, no. 1-2, pp. 147-169, 2003