Experimental study on vortex-induced motions of a semi-submersible platform with four square columns, part III: Effects of the collinear irregular and regular wave incidence and current

2020 ◽  
Vol 217 ◽  
pp. 107585
Author(s):  
Rodolfo T. Gonçalves ◽  
Leandro A. Pinto ◽  
André L.C. Fujarra
Author(s):  
Rodolfo T. Gonçalves ◽  
Hideyuki Suzuki ◽  
Fredi Cenci ◽  
André L. C. Fujarra ◽  
Shinichiro Hirabayashi

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.


2020 ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Hideyuki Suzuki ◽  
Matheus A. Marques ◽  
Leandro S. P. Silva ◽  
Chenling Tian ◽  
...  

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.


Author(s):  
Oriol Rijken ◽  
Steven Leverette

Vortex Induced Motion (VIM) of a Deep Draft Semi® with four square columns has been observed in model tests and in a prototype configuration. The flow field around the columns causes the vessel to oscillate along one of the vessel’s main diagonals under particular conditions. The observations and conclusions of three series of VIM model programs are combined in this report. Each test program was executed with a unique objective in mind and each setup was unique. Many similarities in response characteristics have been identified. Some of the differences in observed response are identified and discussed. A discussion is provided regarding the scaling of VIM problems, and the importance of the Reynolds number under model test conditions is discussed. The VIM of a typical Gulf of Mexico Deep Draft Semi® may affect the fatigue life of the mooring system and risers. A formulation is developed that predicts the distribution of VIM amplitudes which then can be used to estimate VIM induced fatigue damage. Observations and conclusions are provided of several experiments where VIM response was evaluated in the presence of a fatigue sea state and for a system with increased sway damping.


2011 ◽  
Vol 1 (32) ◽  
pp. 54 ◽  
Author(s):  
Mohamed Kudeih ◽  
Andrew Cornett ◽  
Ioan Nistor

Arrays of vertical cylinders are essential components of many coastal structures, such as bridge piers, platform legs, and pile breakwaters. Thus, estimating the maximum wave and current-induced forces and moments on such structures is most important. Following a thorough literature review, the authors proceeded with an experimental study in order to investigate the forces exerted by random waves and a superimposed current on an array of three vertical cylinders as a function of the inter-cylinder gap and the angle of wave incidence over a wide range of wave and current conditions in shallow water.


2021 ◽  
Author(s):  
Rodolfo Goncalves ◽  
Matheus Marques ◽  
Leandro Silva ◽  
Shinichiro Hirabayashi ◽  
Hideyuki Suzuki ◽  
...  

Author(s):  
Kohyu Satoh ◽  
Naian Liu ◽  
Ji Ping Zhu ◽  
K. T. Yang

The study of dynamics of multiple fires is important to gain a physical insight of the conditions under which destructive phenomena could result in city fires such those caused by earthquakes. Particularly, heavy populated cities such as Tokyo are highly vulnerable. Unfortunately, previous studies on multiple fires and their dynamics are rather limited. An extensive experimental study has been carried out to examine the fire interactions among freestanding equidistant multiple fires in square arrays, to supplement the authors’ previous related studies. Four square arrays, namely, 5×5, 9×9, 15×15 and 17×17, with various inter-fuel pan distances were treated. The burnout time (BOT) from ignition at every fire in the array was experimentally recorded and expressed as multiples of the BOT of a single free-standing fire as a reference. Since the BOT at any fire location in an array is inversely proportional to an average burning rate (BR) at that location, the local BR can then be directly inferred, and their comparisons thus indications of the physical interactions as affected by the fire location, inter-fuel pan distance and size of the fire array. It is shown that all these parameters play remarkable roles in the interactions among multiple fires in square fire arrays.


Sign in / Sign up

Export Citation Format

Share Document