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Experimental Investigation of Porous Structures in Splash Zone
| Content Provider | Semantic Scholar |
|---|---|
| Author | Gupta, Prateek |
| Copyright Year | 2018 |
| Abstract | The design of a structure is based on the strength requirements to sustain the operational as well as installation loads. An accurate estimation of such loads is also necessary for resource and mission planning of marine operations involving the deployment or installation of these structures. The hydrodynamic loads on a structure are often expressed as a summation of added mass and damping force components (as in Morison’s equation) which can in-turn be calculated from analytically, experimentally or numerically determined added mass and drag coefficients. The purpose of this work is to experimentally determine hydrodynamic loads on porous structural components such as perforated plates and rod screens in different cases of fluid flow. It is observed that the hydrodynamic loads, for a porous plate placed in a uniformly oscillating flow in infinite fluid (such as forced oscillations in deep water), are damping dominated due to high damping to added mass ratio. The objective of the current work is to investigate the damping or drag dominance, in different conditions of fluid flow, for two different type of porous plates: perforated plate with sharp edged circular openings, and rod screen with equally spaced circular rods. First, the KC number (or porous KC number) varying hydrodynamic coefficients for porous plates are determined from forced oscillations in deep water. Then water-entry drag coefficient is determined from the force impulse observed during constant velocity water-entry for both types of plates. Finally, the rod screen type porous plate is subjected to incident waves, while it is held fixed and fully submerged at a small water depth. Results indicate that damping can be as high as 1.5 to 3.0 times the added mass for a porous structure in forced oscillation case whereas it can be, surprisingly, 10 to 100 times when subjected to incident waves. In case of constant velocity waterentry, it is observed that the slamming impact peak has negligible contribution to the force impulse and thus, the total force is drag dominated. This indicates that a strong emphasis should be placed on estimation of damping or drag loads on such structures. Further, the empirical method suggested by DNV-GL to estimate zero amplitude (KC = 0) added mass and the added mass reduction factor curve to obtain conservative estimates of added mass for a porous structure were compared with the results from current work. In case of first a validity range, in terms of KC number, is defined where it can be applicable to obtain conservative estimates of added mass. Additionally, linearized damping model was discussed for deep water forced oscillation tests. The water-entry drag was found to be significantly influenced by free surface phenomenon like attachment of air bubbles and delayed wetting of top surface. Negative added mass was observed in some cases of wave tests. III |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://brage.bibsys.no/xmlui/bitstream/handle/11250/2564495/19483_FULLTEXT.pdf?isAllowed=y&sequence=1 |
| Alternate Webpage(s) | https://brage.bibsys.no/xmlui/bitstream/handle/11250/2564495/19483_COVER.pdf?isAllowed=y&sequence=3 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
