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Surface waves from the ray point of view : delivered at the Fifteenth ONR Symposium on Naval Hydrodynamics, Hamburg, 3 September 1984 ; seventh Georg Weinblum memorial lecture
Citation Link: https://doi.org/10.15480/882.931
Publikationstyp
Technical Report
Date Issued
1984
Sprache
English
Author(s)
TORE-DOI
Surface waves from the ray point of view : delivered at the Fifteenth ONR Symposium on Naval Hydrodynamics, Hamburg, 3 September 1984 ; seventh Georg Weinblum memorial lecture
Surface waves for the ray point of view VII. Georg-Weinblum-Gedächtnisvorlesung. Using the same procedure for the calcu1ation of the far field spectrum as in the case of the pressure patch, we have shown again that in asymptotic theory the boundary of the ship generates waves; for an observer above the hull only the upper side of the hull can generate waves. One set of these waves must have their wave vectors normal to the ship's hull, just as in the case of the pressure patch. However, because of the condition that the displacement flow follows the ship hull these waves have zero group velocity. They therefore propagate on a ray in ship coordinates tangent to the ship's hull and cannot leave the hull. These results are the same as those of Keller (1979). Another set of waves leave the aft portion of the hull on rays initially parallel to the ship's path, provided that the inclination of the hull is not steeper than -20°. We provide formula for calculating the strength of these waves which are in general both transverse and divergent. In principal this set of waves includes a fan at the bow (or stern) provided that a stagnation point exists at the point of the bow; the strength of these waves depends entirely on the gradient of the pressure (elevation) in the displacement at that point. We conclude that our present knowledge is inadequate either to know whether the conventional ray theory is valid near the ends of the hull or if it is, to use it effectively.
Surface waves for the ray point of view VII. Georg-Weinblum-Gedächtnisvorlesung. Using the same procedure for the calcu1ation of the far field spectrum as in the case of the pressure patch, we have shown again that in asymptotic theory the boundary of the ship generates waves; for an observer above the hull only the upper side of the hull can generate waves. One set of these waves must have their wave vectors normal to the ship's hull, just as in the case of the pressure patch. However, because of the condition that the displacement flow follows the ship hull these waves have zero group velocity. They therefore propagate on a ray in ship coordinates tangent to the ship's hull and cannot leave the hull. These results are the same as those of Keller (1979). Another set of waves leave the aft portion of the hull on rays initially parallel to the ship's path, provided that the inclination of the hull is not steeper than -20°. We provide formula for calculating the strength of these waves which are in general both transverse and divergent. In principal this set of waves includes a fan at the bow (or stern) provided that a stagnation point exists at the point of the bow; the strength of these waves depends entirely on the gradient of the pressure (elevation) in the displacement at that point. We conclude that our present knowledge is inadequate either to know whether the conventional ray theory is valid near the ends of the hull or if it is, to use it effectively.
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Bericht_Nr.446_M.P.Tulin_VII._Georg_Weinblum_Memorial_Lecture_Surface_Waves_from_the_Ray_Point_of_View.pdf
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