Wave Effects on Vortex-Induced Motion (VIM) of a Large-Volume Semi-Submersible Platform

2012 ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Guilherme F. Rosetti ◽  
André L. C. Fujarra ◽  
Kazuo Nishimoto ◽  
Allan C. Oliveira
Keyword(s):  
Experimental Study ◽  
Free Surface ◽  
Large Volume ◽  
Periodic Motion ◽  
Transverse Direction ◽  
Irregular Waves ◽  
Regular Waves ◽  
Sea State ◽  
Wave Effects ◽  
Induced Motion

Aiming to complete the results presented before by Gonçalves et al. (2011) – Experimental Study on Vortex-Induced Motions (VIM) of a Large-Volume Semi-Submersible Platform, OMAE2011, the present work brings new experimental results on VIM of a large-volume semi-submersible platform, particularly concerning its coexistence with waves in the free surface. The VIM tests were performed in the presence of three regular waves and also three different conditions of sea state. According to the results, considerable differences between the presence of regular or irregular waves were observed. The motion amplitudes in the transverse direction decreased harshly when the regular waves were performed and no VIM was observed. In the case of sea state condition tests, the amplitudes decreased slightly but a periodic motion characterized by the VIM was observed. The results herein presented concern transverse and yaw motion amplitudes, as well as spectral analyses.

scholarly journals Numerical Evaluation of the Hydropneumatic Power of the Oscillating Water Column Wave Energy Converter Submitted to Regular and Irregular Waves

2021 ◽  
pp. 32-43
Author(s):  
Augusto Hack da Silva Koch ◽  
Maycon da Silveira Paiva ◽  
Caroline Barbosa Monteiro ◽  
Phelype Haron Oleinik ◽  
Liércio André Isoldi ◽  
...  
Keyword(s):  
Free Surface ◽  
Water Column ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Oscillating Water Column ◽  
Regular Waves ◽  
Energy Converter ◽  
Sea State ◽  
Electric Generator

The purpose of this study is to computationally analyze the hydropneumatic power available in the air duct of an Oscillating Water Column (OWC) Wave Energy Converter (WEC) device when subject to realistic sea state data (irregular waves) and when submitted to the regular waves representative of this sea state. The OWC WEC is mainly composed of a hydropneumatic chamber and an air duct where a turbine and electric generator are coupled. The chamber is open below the free surface while the duct is open to the atmosphere. The oscillating movement of the water-free surface inside the chamber causes the air to flow, moving the turbine and generating electricity. To execute this study, a bi-dimensional computational model was considered and numerical simulations of wave generation were carried out using ANSYS Fluent, which is a Computational Fluid Dynamics (CFD) software based on the Finite Volume Method (FVM). The Volume of Fluid (VOF) multi-phase model was applied in the treatment of the water-air interaction. To evaluate the average hydropneumatic power available in the duct, the static pressure, velocity, and air mass flow rate were monitored. The results were analyzed, showing that the available power is 250% greater when the device is subject to realistic irregular waves rather than subject to representative regular waves.

An Experimental Investigation of Cylindrical Floater VIM in Current and Waves

2014 ◽  
Author(s):  
Masakatsu Saito ◽  
Toshifumi Fujiwara ◽  
Katsuya Maeda
Keyword(s):  
Wave Height ◽  
Safety Evaluation ◽  
Offshore Structures ◽  
Irregular Waves ◽  
Regular Waves ◽  
Cross Sectional ◽  
Strong Current ◽  
Induced Motion ◽  
Different Characteristics ◽  
Motion Amplitude

VIM (Vortex Induced Motion) is one of the important issues in the safety evaluation for cylindrical floating offshore structures. The VIM is basically placed as a phenomenon to occur in strong current, but that also appears in current and waves in the sea where offshore structures are installed. The authors have recognized the phenomenon that the motion amplitude of a cylindrical floater in current and irregular waves together is larger than the sum of the motion amplitude in current and in irregular waves respectively in a VIM experiment. This VIM amplification phenomenon in the current and waves is remarkable when wave height is relatively low that has high occurrence frequency in the sea. It is, therefore, expected that the amplification phenomenon has large influence on the accumulative fatigue damages of the offshore structure’s mooring system. In order to make clear this VIM amplification phenomenon, the authors have conducted detailed VIM experiment in waves using a circular cross sectional mono-column floater model. The results of the VIM experiment in current and waves are described in detail in this paper. The results of the experiment in irregular waves show different characteristics for VIM amplitude in current. The results in regular waves show the effect of wave height and wave period on VIM amplitude in waves. Using those results, the mechanisms of the VIM amplification in waves are investigated.

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

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.

Experimental Study on Hydrodynamics of Hybrid Deep-V Monohull With Different Built-Up Appendages

2018 ◽  
Author(s):  
Shuzheng Sun ◽  
Hui Li ◽  
Muk Chen Ong
Keyword(s):  
Model Test ◽  
Performance Model ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Hydrodynamic Characteristics ◽  
Vertical Acceleration ◽  
Test Results ◽  
Regular Waves ◽  
Sea State ◽  
Seakeeping Performance

The hydrodynamic characteristics of a hybrid deep-V monohull with different built-up appendages are investigated experimentally in order to improve the resistance and seakeeping performance. Model tests have been carried out to study the hydrodynamic performance between a bare deep-V vessel and a deep-V monohull with different built-up appendage configurations (i.e. a hybrid deep-V monohull). From the model test results, it is found that the existence of the appendages will reduce the amplitude of pitching angle and bow vertical acceleration compared to that of the bare deep-V vessel in heading regular waves. However, the resistances for the hybrid deep-V monohull with built-up appendages are increased 15.6% for Fn = 0.264, and 0.1% for Fn = 0.441 compared to the resistance of the bare deep-V vessel. The model test results of seakeeping performance in irregular waves show that the hybrid deep-V monohull gives a better seakeeping performance than the deep-V vessel. The pitching angle and bow vertical acceleration of the hybrid deep-V monohull containing a built-up appendage are reduced 15.3% and 20.6% compared to the deep-V monohull in irregular waves at Fn = 0.441 in 6th class sea state (H1/3 = 6m).

Numerical Investigation of Hydrodynamic Performance of a Light Buoy with Different Mooring Configurations in Regular Waves

2021 ◽  
pp. 1-26
Author(s):  
Xin Li ◽  
Yimei Chen ◽  
Lilei Mao ◽  
Huiyu Xia
Keyword(s):  
Experimental Data ◽  
Yangtze River ◽  
Coupled Model ◽  
Coupling Model ◽  
Numerical Approach ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Regular Waves ◽  
Induced Motion ◽  
Wave Induced

Abstract The single-moored light buoys employed in the lower reaches of the Yangtze River play an important role in indicating ship navigation and ensuring safety. To clarify the interaction between waves and floating buoys moored to the riverbed, this paper develops a numerical approach to investigate the wave-induced motion performance of a light buoy and reveal the effects of different mooring configurations to extend its service life. A new open-source SPH based numerical model named DualSPHysics coupled with MoorDyn is implemented. This coupled model is validated by simulating the motion of a moored rectangle buoy in regular waves, and compared with experimental data and the numerical results of REEF3D code, a new mesh-based CFD model. The validation results show that the coupled model reproduces experimental data well and has a smaller deviation in comparison with REEF3D. Then the coupling model is applied to simulate the hydrodynamic performance of the real-size light buoy employed in Yangtze River and investigate effects of encounter angle between wave propagation direction and mooring chain. The results demonstrate the capability of this coupled mooring model to simulate the motion of a moored buoy in regular waves, and this numerical approach will be extended to simulate the light buoy in more complex environments such as irregular waves, flow or extreme weather in further work.

Experimental Study on Vortex-Induced Motions (VIM) of a Large-Volume Semi-Submersible Platform

2011 ◽  
Author(s):  
Rodolfo T. Gonc¸alves ◽  
Guilherme F. Rosetti ◽  
Andre´ L. C. Fujarra ◽  
Kazuo Nishimoto ◽  
Allan C. Oliveira
Keyword(s):  
Experimental Study ◽  
Model Test ◽  
Large Volume ◽  
Cross Flow ◽  
Induced Motion ◽  
Line Cross

A great deal of work has been developed on the spar and monocolumn vortex-induced motion (VIM) issue. However, there are very few published works concerning VIM of semi-submersible platforms, partly due to the fact that VIM studies for this type of platform recently became interesting particularly due to the increasing semi-submersible dimensions (columns diameter and height. In this context, a meticulous experimental study on VIM for this type of platform concept is presented here. Model test experiments were performed to check the influence of many factors on VIM, such as different headings and hull appendages. The results comply with in-line, cross-flow and yaw motion amplitudes, as well as with combined motions in the XY plane.

Computational Fluid Dynamics Simulations of Regular and Irregular Waves Past a Horizontal Semi-Submerged Cylinder

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Shengnan Liu ◽  
Muk Chen Ong ◽  
Charlotte Obhrai ◽  
Sopheak Seng
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Wave Height ◽  
Stokes Equations ◽  
Wave Force ◽  
Numerical Results ◽  
Irregular Waves ◽  
Wave Forces ◽  
Regular Waves ◽  
Peak Period

Two-dimensional (2D) numerical simulations have been performed to investigate both regular and irregular waves past a fixed horizontally semisubmerged circular cylinder. The 2D simulations are carried out by solving Navier–Stokes equations discretized by finite volume method. Volume of fluid (VOF) method is employed to capture the free surface in the numerical wave tank (NWT). Validation studies have been performed by comparing the numerical results of free surface waves past the cylinder with the published experimental and numerical data. The present numerical results are in good agreement with both the experimental and the other numerical results in terms of hydrodynamic forces and free surface elevation. Subsequently, the effects of the wave height and the wavelength on wave–structure interaction are investigated by conducting numerical simulations on the regular and the irregular waves past a semisubmerged cylinder at different wave heights and the wavelengths. The averaged and maximum vertical wave forces on the cylinder increase with the increasing wave height. The numerical results for the irregular waves are compared with those induced by the regular waves in terms of the maximum and averaged vertical wave forces. When the significant wave height and the spectral peak period of the irregular waves are equal to the wave height and the wave period of the regular waves, the maximum vertical wave force induced by the irregular waves is larger than that induced by the regular waves, meanwhile, the average vertical wave forces have the contrary relationship.

Experimental Study of Turbulent Flow Induced by Regular and Irregular Waves Above a Rock-Armored Slope

2014 ◽  
Author(s):  
Konstantina A. Galani ◽  
Giannis D. Dimou ◽  
Athanassios A. Dimas
Keyword(s):  
Experimental Study ◽  
Turbulent Flow ◽  
Velocity Profiles ◽  
Irregular Waves ◽  
Wave Crest ◽  
Regular Waves ◽  
Mean Velocity ◽  
Peak Period ◽  
Wave Trough ◽  
Wave Heights

The aim of the present work is the experimental study of the turbulent flow induced by waves above a physical model of a rock-armored slope of 1/3. The armor consisted of two layers of rocks with characteristic diameter D50 = 4.4cm. Measurements of the instantaneous velocity fields were conducted using an underwater planar PIV system. Four cases of incoming waves were tested, two cases of regular waves of 1st order Stokes theory with wave period of 1.134s and wave heights of 0.04m and 0.08m, respectively, and two cases of irregular waves, generated from a JONSWAP spectrum, with a peak period of 1.134s and significant wave heights of 0.04m and 0.08m, respectively. For the regular waves, the period-averaged velocity profiles show the existence of a strong undertow current heading towards deep water, while turbulence is not homogeneous with larger horizontal fluctuations. The phase-averaged horizontal velocity profiles present systematically larger values during wave trough passage than during wave crest passage. Furthermore, as the depth becomes smaller, the waveform loses its symmetry, with the wave trough becoming wider and the wave crest steeper. For the irregular waves, the mean velocity profiles show the existence of an undertow current weaker in magnitude than the one in the regular waves, while turbulence is still not homogeneous with larger horizontal fluctuations. For both wave cases, spanwise vorticity, which is generated at the rough surface of the rock-armored slope, is transported landward by the turbulent velocities.

Experimental Study Into Vortex Induced Motion Response of Semi Submersibles With Square Columns

2008 ◽  
Author(s):  
Oriol Rijken ◽  
Steven Leverette
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Mooring System ◽  
Test Program ◽  
Sea State ◽  
Response Characteristics ◽  
Test Conditions ◽  
Induced Motion ◽  
Four Square ◽  
Model Programs

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.

Large-Scale Wave Kinematics Measurements of Regular Waves and Large-Amplitude Wave Groups

2010 ◽  
Author(s):  
Lisa Minnick ◽  
Christopher Bassler ◽  
Scott Percival ◽  
Lauren Hanyok
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Near Field ◽  
Field Measurements ◽  
Primary Objective ◽  
Irregular Waves ◽  
Ship Motions ◽  
Regular Waves ◽  
Wave Groups ◽  
Wave Kinematics

An experiment was performed to measure and characterize wave kinematics in an experimental basin. The experiment is part of an ongoing effort to improve predictions and measurements of ship motions in waves, including more accurate characterization of the near-field wave environment and its influence on ship motions. The primary objective of this experiment was to measure and characterize the wave kinematics of regular waves of varying steepness and scaled irregular seaways, including irregular waves with embedded wave groups. Measurements, including free-surface elevations and velocity field measurements under the free surface, are presented and discussed.

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