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Psycholinguistics --- Spanish language --- Grammar --- Spaanse taal --- grammatica --- oefeningen --- oefeningen. --- grammatica.

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Dynamic behavior of high speed craft is different from conventional displacement-vessels, dynamic lift leads to a reduction of the wetted surface and therefore small motions cause noticeable variations in hydrodynamic forces and moments. These excitations can induce important instabilities like broaching or parametric rolling causing serious consequences such as crew injury or important damage of the boat. 

This research seeks to investigate the roll behavior of a high speed craft when it is submitted to heave and pitch excitations. In order to do that, a 20° deadrise prismatic hull CFD model is carefully created by choosing the most suitable meshing techniques and solvers for a complex free surface flow. Within the development of the CFD model, it is demonstrated that computational time can be reduced for high speed crafts by employing an inviscid solver instead of turbulent models. In addition, the procedure to employ an overset mesh is presented as the most suitable technique when complex motions are involved. 

Afterwards, a verification study is carried out to assess in detail the successful convergence of both time step and mesh size. Once the optimum time step and mesh size are selected, the CFD model is employed to estimate the hydrodynamic coefficients for a pure roll motion. Besides, the obtained hydrodynamic coefficients are compared with experimental tests performed by Carolyn Judge in the US Naval Academy and 2D+t model approximation developed by Oscar Tascon at the University of Michigan. Even when good agreement between CFD and experiment results is reached, it is shown the complexity to successfully predict higher order hydrodynamic coefficients. 

Furthermore, roll response estimated by means of the reduced order model developed by Oscar Tascon and roll response predicted by CFD computation are compared for identical heave and pitch excitations. It is demonstrated that the selection of hydrodynamic coefficients influences significantly the roll response retrieved by the reduced order model. Finally, it is concluded that the reduced order model is not robust enough since it requires a very accurate prediction of the hydrodynamic coefficients which is very difficult to achieve by employing either experimental or computational methods.

Ingénierie, informatique & technologie > Ingénierie civile