Experimental study on vortex-induced motions of a semi-submersible platform with four square columns, Part II: Effects of surface waves, external damping and draft condition

Intended as a contribution towards understanding the multiple processes entailed in the development of coastal sand bars due to wave action, this theoretical and experimental study deals with the Bragg reflection of long-crested surface waves in a water channel whose bed is corrugated sinusoidally. The present findings complement and in a few respects improve upon those in previous investigations, particularly Davies & Heathershaw (1984).In §2 a linearized theory is presented, being directed to the elucidation of experimental situations where monochromatic waves propagate into a channel with a limited stretch of corrugations on its bed and an imperfectly absorbing beach at its far end. Allowance is made fully for dispersive effects (§2.2) and approximately for small frictional effects (§2.3). Points of interpretation (§2.4) include accounts of degenerate but non-trivial solutions that apply at frequencies terminating the stopping band, wherein the spatial wavefield has an exponential envelope. The experimental results presented in §4 derive from measurements of the wavefield over a stretch of 24 corrugations, at various frequencies both inside and outside the stopping band. Quantitative comparisons (§4.2 and 4.3) demonstrate close agreements with the theory.

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Experimental Study of the Effect of the Pontoon Presence on the Flow-Induced Motion of a Semi-Submersible Platform With Four Square Columns

Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium on Offshore Technology ◽

10.1115/omae2019-95250 ◽

2019 ◽

Author(s):

Rodolfo T. Gonçalves ◽

Hideyuki Suzuki ◽

Fredi Cenci ◽

André L. C. Fujarra ◽

Shinichiro Hirabayashi

Keyword(s):

Experimental Study ◽

Fatigue Life ◽

Transverse Direction ◽

The Other ◽

Mooring Line ◽

Towing Tank ◽

Spacing Ratio ◽

Floating System ◽

Induced Motion ◽

Four Square

Abstract The Flow-Induced Motions (FIM) is an essential topic on multi-column platforms due to the effect on the mooring line fatigue life. Vortex-Induced Motions (VIM) or galloping behavior can be observed for an array of four columns with square sections. The presence of pontoons showed to be important for changing the flow around the array and promote different amplitude behavior of the motions in the transverse direction mainly. This article aims to understand the effect of the presence of two pontoons on the FIM of a semi-submersible platform (SS) with four columns and square sections. Model tests of a floating system supported elastically utilizing four springs were performed in a towing tank. Five different pontoon ratios were tested, namely P/L = 0, 0.25, 0.50, 0.75 and 1.00; where P is the pontoon height, and L is the length of the square column face. The draft condition was kept constant as H/L = 1.5; where H is the draft of the platform. The spacing ratio of the columns was S/L = 4; where S is the distance between column centers. Three incidence angles of the current were carried out, i.e., 0-deg incidence represents the condition in which the two pontoons are aligned to the current, 45-deg incidence represents the non-symmetric condition in which the pontoons are 45 degrees positioned to the current, and 90-deg incidence represents the condition in which the two pontoons are perpendicular to the current. The transverse amplitudes decreased with increasing the pontoon ratio for 0 and 45-deg incidences. On the other hand, the transverse amplitudes increased with increasing the pontoon ratio for 90-deg incidence. The pontoon presence needs to be well investigated to choose the best condition to avoid raising the FIM.

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Experiments on the Excitation of Resonances of Elastic Objects by Acoustic Pulses and Theoretical Interpretation

Applied Mechanics Reviews ◽

10.1115/1.3121350 ◽

1991 ◽

Vol 44 (11S) ◽

pp. S16-S19 ◽

Cited By ~ 1

Author(s):

Xiao-Ling Bao ◽

Herbert U¨berall ◽

Jan Niemiec

Keyword(s):

Experimental Study ◽

Surface Waves ◽

Theoretical Interpretation ◽

Oblate Spheroids ◽

Vibrational Resonances

We have carried out tank experiments on the excitation of vibrational resonances of submerged elastic objects by incident short acoustic pulses. We have studied steel spheres, cylinders with hemispherical endcaps, and prolate as well as oblate spheroids. Theoretical interpretations of the resonance positions are provided by the matching of the phases of surface waves excited by the incident pulses, that encircle the object along closed paths. Some results of a French experimental study (G Maze and J Ripoche, University of Le Havre) are interpreted using the same approach.

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Experimental study of surface waves over anisotropic solids

10.1190/1.1888835 ◽

1991 ◽

Author(s):

Chih‐Hsiung Chang ◽

Q. Luo ◽

G. H. F. Gardner

Keyword(s):

Experimental Study ◽

Surface Waves

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Experimental study on the intensification of turbulence in mixed layer by surface waves

Deep Sea Research Part B Oceanographic Literature Review ◽

10.1016/0198-0254(85)93680-5 ◽

1985 ◽

Vol 32 (12) ◽

pp. 999

Keyword(s):

Experimental Study ◽

Surface Waves ◽

Mixed Layer

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Experimental Study of the Effect of the Pontoon Dimensions on the Flow-Induced Motions (FIM) of a Semi-Submersible Platform With Four Square Columns

Volume 8: CFD and FSI ◽

10.1115/omae2020-18009 ◽

2020 ◽

Author(s):

Rodolfo T. Gonçalves ◽

Hideyuki Suzuki ◽

Matheus A. Marques ◽

Leandro S. P. Silva ◽

Chenling Tian ◽

...

Keyword(s):

Experimental Study ◽

Fatigue Life ◽

Transverse Direction ◽

Vertical Direction ◽

Model Tests ◽

Mooring Line ◽

Towing Tank ◽

Spacing Ratio ◽

Floating System ◽

Four Square

Abstract The Flow-Induced Motions (FIM) is an essential topic on multi-column platforms due to the effect on the mooring line fatigue life. Vortex-Induced Motions (VIM) or galloping behavior can be observed for an array of four columns with square sections. The presence of pontoons showed to be important for changing the flow around the array and promoting different amplitude behaviors of the motions in the transverse direction mainly. This article aims to understand the effect of the presence of four pontoons on the FIM of a semi-submersible platform (SS) with four square section columns. Model tests of a floating system supported elastically utilizing four springs were performed in a towing tank. Five different pontoon ratios were tested, namely P/L = 0, 0.25, 0.50, 0.75, and 1.00; where P is the pontoon height (the dimension in the vertical direction), and L is the length of the square column face. The draft condition was kept constant as H/L = 1.5; where H is the draft of the platform. The spacing ratio of the columns was S/L = 4; where S is the distance between column centers. Two incidence angles of the current were carried out, namely 0 and 45 degrees. The amplitudes in the transverse direction (direction perpendicular to the incidence current) decreased by increasing the pontoon ratio for 0 and 45-deg incidences. The pontoons positioned aligned to the flow significantly reduced the amplitudes in the transverse direction since the pontoon presence in this position modified the incident wake in the downstream columns. The pontoon presence needs to be well investigated to choose the best condition to avoid raising the FIM or mitigating the FIM.

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