International Shipbuilding Progress - Volume 46, issue 445

Authors: Haddara, Mahmoud R. | Wang, Yie

Article Type: Research Article

Abstract: Time domain simulation techniques are becoming a widely accepted tool for the evaluation of controllability and manoeuvring performance of conventional surface ships. Different simulation packages are available on a commercial basis. The accuracy of predictions obtained using these models are largely dependent on the level of accuracy in estimating the values of the parameters used in these models. Several methods are available for the determination of the values of these hydrodynamic parameters. However, each one of these existing methods has its own shortcomings. In this paper a new predictive method is outlined for the estimation of the hydrodynamic characteristics for …a ship performing certain standard manoeuvres. The method uses neural networks technique to predict the hydrodynamic parameters of the ship. Parameters normally measured during standard manoeuvre e.g. surge, sway and yaw velocities and rudder angle, will be used as input to the predictive model. The first author has successfully used the same technique in predicting the transverse stability of a ship at sea. Show more

DOI: 10.3233/ISP-1999-4644501

Citation: International Shipbuilding Progress, vol. 46, no. 445, pp. 5-27, 1999

Authors: Wang, Chun-Tsung | Chiu, Forng-Chen | Horng, Shiann-Jorng

Article Type: Research Article

Abstract: Based on Chapman's approach, wave exciting forces on slender ships with forward speed are solved by a two and half dimensional method. The governing equations are derived along characteristic lines. The forward speed effects are incorporated into the free surface and the body surface conditions. Relaxed radiation condition with numerical correcting term introduced by Yamasaki & Fujino is imposed on the open boundary. Wave exciting forces on a Wigley model, and a Series 60 model with forward speed are calculated. The agreement between the wave exciting forces computed by the present method and the experimental data reported by Gerritsma …is very satisfactory. Wave exciting forces computed are also compared with the numerical results from the strip theory and some three dimensional approaches. Show more

DOI: 10.3233/ISP-1999-4644502

Citation: International Shipbuilding Progress, vol. 46, no. 445, pp. 29-41, 1999

Authors: Fang, Ming-Chung | Liou, Yi

Article Type: Research Article

Abstract: Based on the strip theory, the authors use the phase transfer technique to treat the hydrodynamic problems for a twin-hull structure in the paper. Using the method, the total forces on the twin-hull structure can be obtained by calculating the corresponding hydrodynamic coefficients for a single body only. There is no need to calculate the force on each body twice and the hydrodynamic interactions are not included. Practically the present method is suitable for predicting the corresponding hydrodynamic properties of a semisubmersible and a SWATH ship with high speed because the hydrodynamic interactions are not significant for these two cases. …The results obtained in the paper indeed show the present idea is reasonable and therefore the method developed here can be considered as a efficient tool to analyze the hydrodynamic problems for some twin-hull body structures with less interaction effects in waves, either with or without speed. Show more

DOI: 10.3233/ISP-1999-4644503

Citation: International Shipbuilding Progress, vol. 46, no. 445, pp. 43-60, 1999

Authors: Brockett, Terry E.

Article Type: Research Article

Abstract: A numerical exploration of propulsor-stern interaction, with a predominately potential-flow representation of the flow field, is undertaken to evaluate thrust deduction and control-surface loads for an accelerating-duct, decelerating-duct and open propulsor of relatively large diameter on the same axisymmetric hullform. A boundary-element model of the annular foil shroud and the hull is coupled with a lifting-line model of the rotor to determine the flow field. Interaction fields are taken as axi-symmetric. For the examples considered, each propulsor is at nearly the diameter for minimum shaft horsepower. The estimates show that the superior open-water efficiency of the accelerating-duct propulsor is degraded …by an increased thrust-deduction force component in the axial force balance for the propulsor-hull combination system while the propulsive efficiency of a decelerating-duct propulsor approaches that of the open propeller because of hull interaction, making the propulsive efficiency nearly the same for all three propulsors. Based on estimates from a lifting-line model of side force on a representative rudder located forward of the propulsor, increased course-keeping ability from the control surfaces is anticipated for an accelerating-duct propulsor relative to both an open propeller and decelerating-duct propulsor. Show more

DOI: 10.3233/ISP-1999-4644504

Citation: International Shipbuilding Progress, vol. 46, no. 445, pp. 61-89, 1999

Authors: Ye, H.K. | Hsiung, C.C.

Article Type: Research Article

Abstract: Wave exciting forces on a restrained body with steady forward speed in the time-domain were computed by the authors (1995). As one step further, radiation forces and ship motions in regular waves are computed in the present paper. With impulse response functions, the integral-differential equations of motions are solved in the time-domain. The same method is also applied to compute the radiation forces of a catamaran with forward speed. The results show that the time-domain computation for ship motions is particularly meaningful in the cases where the forward speed effect is considered. Added mass and damping coefficient of a …catamaran with the Lewis-form demi-hull are computed for Froude numbers 0.15 and 0.30. Good agreements with experimental results for heave and pitch motions are obtained. A Wigley hull and a Series 60, CB =0.7 hull are also adopted for the motion computation. The computed results for Froude number 0.20 are compared with experimental results. Show more

DOI: 10.3233/ISP-1999-4644505

Citation: International Shipbuilding Progress, vol. 46, no. 445, pp. 91-123, 1999