Numerical study on scale effect of nominal wake of single screw ship

: A design procedure for minimizing propeller-induced vibration in hull structural elements is recommended. This procedure begins when the ship's vibration specifications are defined and continues through the design and construction process until the vibration levels measured during sea trials are compared with the specifications. Consideration is given to the hydrodynamic excitation and structural response of the propeller-induced vibration problem, with both analytical and experimental techniques being used in the design process. The recommended procedure is presented and discussed in the form of a flow diagram with 27 separate design steps. The process also contains five evaluation milestones. At these points, the design is assessed, and, if deficiencies are found, corrective action can be taken before the design proceeds. The recommended complete procedure is presented in this report for the first time. Many of the aspects of this procedure are still being developed, in particular, the influence of propeller cavitation on hull pressures and a simple but accurate treatment of water inertia. These indefinite aspects have to be treated empirically using judgement and experimental data. The portions of the procedure which are available are illustrated in an example using a single-screw, containerized and unitized cargo ship. (Author)

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A design procedure for minimizing propeller-induced vibration in hull structural elements

Numerical investigation of scale effect of nominal wake of four-screw ship

An overset RaNS prediction and validation of full scale stern wake for 1,600TEU container ship and 63,000 DWT bulk carrier with an energy saving device

Procedures for the design, analysis and model tests of a new type preswirl, namely, the biased preswirl stator system for a 300,000 DWT VLCC are described. It is well-known that the preswirl stator, which recovers the propeller slipstream rotational energy, is selected as the most reliable energy saving device due to its simplicity and reliability. The proposed biased stator, with more blades on the port side than on the starboard side, effectively recovers rotational energy loss by taking the advantage of non-symmetric wake flow characteristics between the port and starboard sides of the propeller disk. To design the biased stators effectively, a design program based on lifting surface theory has been successfully applied to the propeller design and analysis. Resistance and self-propulsion tests are carried out with the designed stator-propeller system to verify its effect. A modified model test analysis method for the preswirl stator-propeller system is used based on the 1978 ITTC standard method. The experimental results show that a 5.7% efficiency gain for the ship with the biased preswirl stator with 4 blades can be obtained compared to the ship without a stator. This gain is almost equivalent to that of the existing symmetric stator with 6 blades, and hence it is considered that this biased preswirl stator has merits in terms of light weight, low cost and small volume etc.

Design and experimental study on a new concept of preswirl stator as an efficient energy-saving device for slow speed full body ship

This paper deals with the problem of the prediction of the effective wake distribution in the propeller plane of a ship, using the measured nominal wake of a model as a starting point The chosen prediction method consists of two successive steps viz a scale effect correction to obtain the nominal wake field of the actual ship and the prediction of the difference between nominal and effective wake With regard to the scale effect, a method is introduced based on a threefold contraction of the model nominal wake field in dependency of its harmonic content An empirical approach is used to account for the scale effect on the diffusion of the wake peak in the centerplane which starts as soon as the flow has left the stern Further, the scale effect on bilge vortices, assuming that they are generated near the same point on ship and model, is calculated Application of the method shows promising results It is felt, however, that our knowledge of the scale effect on generation of bilge vortices is unsufficient at present The need for more correlation data is emphasized Concerning the transition from nominal to effective wake, a rough estimate is made of the influence of the propeller-hull interaction on the flow by a) an approximation of the influence of the image of the propeller in the hull, b) a concentric contraction of the wake field to account for changes in the boundary layer profile and c) the calculation of the effect of screw race contraction on the axial velocity distribution in the bilge vortex, if present

M Hoekstra

Papers

Prediction of full scale wake characteristics based on model wake survey