The 12th International Conference on Hydrodynamics
18 – 23 september 2016, Egmond aan Zee, The Netherlands
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A PRACTICAL CALCULATION METHOD FOR FORWARD-SPEED EFFECT NON CROSS-COUPLING RADIATION FORCES IN ENHANCED UNIFIED THEORY FOR SHIP MOTIONS


Go-down ichd2016 Tracking Number 47

Presentation:
Session: Ship hydromechanics resistance III
Room: Room 1
Session start: 15:30 Mon 19 Sep 2016

Masashi Kashiwagi   kashi@naoe.eng.osaka-u.ac.jp
Affifliation: Osaka University

Jing Zhu   zhu_jing@naoe.eng.osaka-u.ac.jp
Affifliation: Osaka University


Topics: - Ship hydrodynamics resistance, propulsion, powering, seakeeping, manoeuvrability, slamming, sloshing, impact, green water

Abstract:

The enhanced unified theory (EUT) developed by Kashiwagi has been in routine use for predicting seakeeping performance of a ship with forward speed. Although EUT takes into consideration the forward-speed and 3D effects on the inner solution through the matching procedure between the inner and outer solutions, the free-surface boundary condition to be satisfied in the inner problem is that essentially at zero speed. Thus the degree of agreement between experiments and computed results by EUT is not so good especially for cross-coupling terms in the radiation forces for instance between heave and pitch. Although several attempts have been done to incorporate the forward-speed effect in the inner free-surface boundary condition, no reliable calculation method has been established so far. In this paper, in order to develop a robust and practical calculation method with keeping the framework of EUT, we consider introduction of the concept in Ogilvie-Tuck's rational strip theory into the inner solution of EUT. That is to say, the advection term in proportion to the forward speed can be treated as an equivalent pressure applied on the free surface and its solution is incorporated into the inner solution. This practical method can improve the cross-coupling terms in the radiation forces, introducing forward-speed correction which plays an important role in improving the degree of agreement with experiments in ship motions. The improvement in ship-motion predictions is of crucial importance in the prediction of the added resistance.