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On the resistance prediction of offshore mobile platforms
Başlık:
On the resistance prediction of offshore mobile platforms
Yazar:
Grekoussis, Christos, author.
ISBN:
9780438060876
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (275 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: N. S. Miller.
Özet:
The methods and data available for predicting the drag resistance of the Semi-Submersible Platforms in uniform flow are reviewed. It is shown that considerable uncertainty exists about the methods used as well as about the data and their applicability in the various Reynolds number regimes. Resistance predictions thus can vary by more than 100% depending on the method and data used. To improve the estimation procedures Tank model tests were carried out on a short Circular Cylinder and five different designs of Semi-Submersible Platforms representing a wide range of current full scale designs being in use. It is shown that at subcritical Reynolds number flow conditions, the vertical column drag resistance is best estimated by assuming 2-Dimensional flow conditions and suitable interference corrections due to proximity of the columns with each other. The drag resistance of the caissons is best estimated in general using 3-Dimensional flow conditions avoiding the use of any 2-Dimensional flow interference corrections. The hull resistance is predicted as the sum of its skin friction and the form drag of the end shape. Suitable orientation to the direction of the flow has been found to account for a significant reduction of total drag. Full scale Semi-Submersibles will operate in the supercritical and transcritical Reynolds number regimes where the subcritical drag interference data are not applicable. Drag interference measurements were carried out in a wind tunnel on groups of two and three Circular Cylinders in line with the flow at various spacings and combinations of spacings among them. The results obtained cover the critical and supercritical Reynolds number regimes (2 x 10e5 to 10e6). A simulation technique was used to create in this range of Reynolds number, flow conditions pertinent to the transcritical regime and drag coefficients of the Cylinders were obtained. In the critical and supercritical regimes the proximity effects will in generally increase the drag coefficient of the cylinders from its value of the single isolated cylinder at the same Reynolds number. Under the simulated transcritical flow conditions the drag coefficient of the second and subsequent cylinder will be lower than the isolated single cylinder values. However the percentage reductions will be lower than those observed in the subcritical Reynolds number regime, but still significant from the design point of view. Therefore subcritical Reynolds number regime drag interference, corrections should be avoided in the critical, supercritical and transcritical regimes. Also prediction of the drag coefficient of the second and subsequent cylinder of three or more cylinders in line by the use of the results of equivalent cases of two cylinders in line should be exercised with care since it may lead to serious underestimations in certain cases.
Notlar:
School code: 0547
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684855.1) | 684855-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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