International Shipbuilding Progress - Volume 44, issue 437

Authors: Thiart, G.D.

Article Type: Research Article

Abstract: The paper presents a vortex lattice method for the calculation of lift on a straight hydrofoil of finite span near the free surface of an infinitely deep fluid. The velocity field induced by the vortex lattice satisfies the linearized free surface boundary condition and the radiation condition. Lift calculations are compared with experimental results for a 5.11 aspect ratio hydrofoil of the circular arc type. Two options regarding the path of the trailing vortices are examined, i.e. that the trailing vortices leave the hydrofoil directly from the camber surface or via the trailing edge. It is shown that for moderate …effective angles of attack the results are very similar, and that the first option, which is simpler and computationally more efficient than the second, is sufficiently accurate for practical purposes. The method was also used to compute the variation of hydrodynamic characteristics with depth of submergence and Froude number for a flat plate of finite span. Results are presented for aspect ratios of 2, 5 and 10 respectively. Show more

DOI: 10.3233/ISP-1997-4443701

Citation: International Shipbuilding Progress, vol. 44, no. 437, pp. 5-26, 1997

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

Article Type: Research Article

Abstract: The time-domain analysis is applied to study the added resistance of a restrained floating body moving with a steady forward speed in waves. It is treated as an initial-boundary value problem and solved by the time-domain Green function method. The body boundary condition is satisfied exactly on each instantaneous wetted body surface, and the linearized free surface condition is applied. The added resistance computation is carried out by integrating pressures on the wetted body surface. A submerged spheroid and a surface-piercing vertical circular cylinder are selected as numerical examples. Good agreements are obtained by comparing with the transformed results from …the frequency-domain computation. Wave exciting force on Series 60 CB =0.7 is also computed to verify the computational method. Show more

DOI: 10.3233/ISP-1997-4443702

Citation: International Shipbuilding Progress, vol. 44, no. 437, pp. 27-57, 1997

Authors: Zhang, Rongjun | Sun, Zhenqi | Xu, Hanzhen

Article Type: Research Article

Abstract: Nowadays, autopilots have been used widely in ship steering, while the robustness of the autopilots designed on the basis of the adaptive control theory is need to be enhanced. This paper presents a theoretical frame of a robust autopilot using the theory of Variable Structure Systems (VSS). Having computed the wave forces and moments acting on a ship, a Variable Structure Control System (VSCS) is investigated for the autopilot of a ship steering in random sea. A kind of nonlinear switching plane and a modified control law are employed to remove the frequent back-and-forth steering. Simulations show that the proposed …simple control system is robust to the modeling errors and changes of environment and speed, so it is worthy to be applied to real ship steering/control. Show more

DOI: 10.3233/ISP-1997-4443703

Citation: International Shipbuilding Progress, vol. 44, no. 437, pp. 59-75, 1997

Authors: Klein Woud, J. | Smit, K. | Vucinic, B.

Article Type: Research Article

Abstract: A research project has been carried out with the objective to develop a structured and systematic method for the design of a maintenance programme during the engineering phases of ship's life. With the method the life cycle costs for maintenance can be minimized with at the same time acceptable safety risks. The method consists of failure mode analysis, a quantified operational and safety risk analysis and maintenance concept design, which involves cost optimization.

DOI: 10.3233/ISP-1997-4443704

Citation: International Shipbuilding Progress, vol. 44, no. 437, pp. 77-100, 1997