|Other titles||Caracterisation des efforts du second ordre en faible profondeur avec un fond incliné|
|Author(s)||Rouault Marie Christine1, Molin Bernard2, Le Boulluec Marc3, Petrie François4|
|Affiliation(s)||1 : PRINCIPIA SAS, Zac Athelia 1, 13705 La Ciotat, France
2 : Ecole Centrale Marseille, Technopôle de Château Gombert, 38 rue Joliot Curie, 13451 Marseille, France
3 : IFREMER RDT–HO, BP 70, 29280 Plouzané, France
4 : OCEANIDE, Port de Brégaillon, 83502 La Seyne sur Mer, France
|Meeting||13èmes Journées de l'Hydrodynamique, Chatou, 21-23 novembre 2012|
|Source||Actes des 13èmes Journées de l'Hydrodynamique, Chatou, 21-23 novembre 2012, ISSN : 1161-1847. Session 2 : Interactions fluide - structure 1, pp.1-12|
|Abstract||An experimental campaign was previously reported on the slow-drift motion of a rectangular barge moored in irregular beam seas. The 24 m long false bottom of the basin is raised and inclined at a slope of 5% from 1.05m below the free surface to 0.15m above (see figure 1).
The barge is moored in different water depths (from 54 cm to 21 cm). The measured slowdrift component of the sway motion is compared with state of the art calculations based on Newman approximation. The principal results are, for the beam sea configuration:
- at 54 cm depth: good agreement between the experimental results and the Newman simulation
- at 21 cm depth: the Newman calculation overpredicts the forces.
When the flat bottom set-down contribution is added, the calculated value is much larger than the measured one. It has often been observed that the flat bottom expression of this component leads to over-conservative second order loads. A second order model is then proposed to account for the shoaling effect of a bi-chromatic sea-state propagating in decreasing water depth.
Newman’s approximation provides an estimate of the real part P. Q is mostly a contribution of the second order incident part in flat bottom. When R < 1 and 0
A second experimental campaign test is made with the same slope bottom configuration but with the barge moored successively in different locations and positions with respect to the wave (head, beam and 30°).
The previous second order model is adapted to take into account the difference of depth between the front of the barge and the aft of the barge in the DIODORE TM software.
For the head sea cases, the Newman approximations under-estimate the low frequency motions, and the correction of the set down gives better comparisons with the measured values.
In parallel to the development of the set-down modified method, a numerical model based on the Boussinesq formulation with high order is tested to extract the different components of the generated wave on the slope bottom. The tests studied from the campaign in BGO First basin are regular waves, bi-chromatic, bi-chromatic+irregular. Analysis of the difference frequency component and the set down contribution are emphasized with comparison with semi-analytical solutions.
Rouault Marie Christine, Molin Bernard, Le Boulluec Marc, Petrie François (2012). Second order loads characterization in shallow water with a slope bottom. Actes des 13èmes Journées de l'Hydrodynamique, Chatou, 21-23 novembre 2012, ISSN : 1161-1847. Session 2 : Interactions fluide - structure 1, pp.1-12. https://archimer.ifremer.fr/doc/00170/28174/