International Shipbuilding Progress - Volume 48, issue 4

Authors: Fang, Ming-Chung | Chiou, Shan-Chin

Article Type: Research Article

Abstract: A time simulation technique with fuzzy control algorithm is evaluated to predict the motion response of the SWATH ship with controllable stabilizer fins in longitudinal regular and irregular waves. In the paper, a mathematical model including the effect of surge force, viscous force, and the fin force is developed to simulate the SWATH ship motion. The stabilizer fin control using the fuzzy algorithm is applied to reduce the pitch motion of the SWATH ship. Basically the …fuzzy controller consists of five parts: (1) Fuzzifier (2) Rule base (3) Data base (4) Inference engine (5) Defuzzifier. The calculations of the corresponding hydrodynamic coefficients at each time step follow the simplified technique developed before, which needs only one set of initial input data of the ship configuration. After comparing with the previous technique, i.e. "bang-bang" control, we find that the present fuzzy control appears to be more practical for operating stabilizer fins. Therefore, incorporating the fuzzy control algorithm, the hydrodynamic model developed here may offer more valuable contributions to the SWATH ship design with controllable fin effects. Show more

Citation: International Shipbuilding Progress, vol. 48, no. 4, pp. 277-303, 2001

Authors: Senjanović, Ivo | Tomašević, Stipe | Parunov, Joško

Article Type: Research Article

Abstract: The differential equation of pontoon vibration is derived as a prismatic beam on an elastic foundation, which simulates the buoyancy variation due to rigid body motion. The transient vibration caused by an impulse is solved analytically by applying the mode superposition method. Stability and accuracy of the results are analysed by checking the convergence of deflection, bending moment and shear force harmonic coefficients. Contribution of the higher modes to the total response is also considered. A …criterion is given for a proper choice of necessary number of natural modes in the mode superposition method. Results of a numerical example are elaborated and analysed in detail, and the ship dynamic behaviour due to an impact load is made clearer. Show more

Citation: International Shipbuilding Progress, vol. 48, no. 4, pp. 305-331, 2001

Authors: Bereznitski, A.

Article Type: Research Article

Abstract: In spite of effort of many researches the role of hydroelasticity is not well understood for slamming problems. In this paper the slamming problem is studied numerically. Based on results of calculations some conclusions are given, setting a range within which hydroelasticity plays an important role. It was found that the ratio between the impact duration and the period of first mode of vibration of dry structure is the key factor in taking the decision when …the solution of the structural response should include hydroelastic effects. An estimation of the error in prediction of the structural response if the effect of hydroelasticity is neglected is also discussed in this paper. Several different models and numerical codes are used for the problem of a wedge-shaped structure penetrating water at small deadrise angles. The effect of hydroelasticity is studied as a function of different parameters influencing the impact interaction. These parameters include stiffness of the structure, presence of entrapped air between the structure and the water surface, and penetration of water at different deadrise angles. Show more

Citation: International Shipbuilding Progress, vol. 48, no. 4, pp. 333-351, 2001

Authors: Liu, P. | Bose, N. | Colbourne, B.

Article Type: Research Article

Abstract: This paper first describes procedures and methodologies to automatically produce marine propeller geometry with optional auxiliary bodies such as nozzles, blockages and rudders. This process is designed and implemented for a general boundary element method (the panel method) to deal with both lifting body and non-lifting body flows. The generated geometry is represented by quadrilateral and triangular panels that can be used by other mesh generation codes to produce 3D volumetric mesh for CFD …work. The vertices of these generated panels are set so that the normal of the surfaces points inside the body. The order of the panels and their side indices are aligned for numerical procedures such as differentiation of the perturbation doublet potential for surface tangential velocities and Kutta condition at the trailing edge. A DXF file format was also implemented as one of the output files that can be used for propeller manufacturing via CNC and for commercial CFD codes that use geometry data input. Based on the near field wake modeling studies performed by the authors and previous experimental investigations on far wake turbulent jet measurements, a far wake model for a propeller panel method is implemented to enhance the capability of predicting the velocities and momentum impact on the risers under a floating production storage off-loading (FPSO) system during operation. This far wake model consists of contraction wake (within one propeller diameter downstream), transition wake (one to two diameters downstream), and inflation wake (two diameters beyond). Near field velocity prediction of this far wake model is validated using previous LDV measurement. Further experimental studies are scheduled for LDV/PIV measurement up to 20-diameter downstream. Show more

Citation: International Shipbuilding Progress, vol. 48, no. 4, pp. 353-383, 2001