scholarly journals Estimation of the Motion Performance of a Light Buoy Adopting Ecofriendly and Lightweight Materials in Waves

2020 ◽  
Vol 8 (2) ◽  
pp. 139 ◽  
Author(s):  
Se-Min Jeong ◽  
Bo-Hun Son ◽  
Chang-Yull Lee
Keyword(s):  
Fluid Dynamics ◽  
Wave Motion ◽  
Viscous Damping ◽  
Motion Simulation ◽  
Incoming Wave ◽  
Damping Coefficients ◽  
Free Decay ◽  
Computational Fluid Dynamics Cfd ◽  
Motion Performance ◽  
Decay Tests

In this study, the methods and results of numerical simulations to estimate the motion performance of a newly developed lightweight light buoy in waves and to check the effect of conceptually developed appendages on that performance were introduced. The results from a potential-based motion analysis with viscous damping coefficients obtained from free decay tests using computational fluid dynamics (CFD) and those obtained from wave motion simulation using CFD were compared. From these results, it was confirmed that viscous damping should be considered when the frequency of an incoming wave is close to the natural frequency of the buoy. It was estimated that the pitch and heave motions of the light buoy became smaller when the developed appendages were adopted. Although the quantitative superiority of the appendages was different, the qualitative superiority was similar between both results.

Effect of Bilge Radius and Bilge Keel Height on Roll Damping Performance of Floating Structures

2021 ◽  
Author(s):  
Chang Seop Kwon ◽  
Joo-Sung Kim ◽  
Hyun Joe Kim
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Kinetic Energy ◽  
Floating Body ◽  
Rectangular Section ◽  
Roll Damping ◽  
Floating Structures ◽  
Free Decay ◽  
Computational Fluid Dynamics Cfd ◽  
Bilge Keel

Abstract A round bilge with a bilge keel structure is a key element which can alleviate roll motions of ships and floating structures by transferring the roll momentum of a floating body into the kinetic energy of water. This study presents a practical guide to properly designing a bilge radius and bilge keel height of a barge-shaped and tanker-shaped FPSOs. A parametric study to figure out the effect of bilge radius and bilge keel height on the roll damping performance is conducted through a series of numerical roll free decay simulations based on Computational Fluid Dynamics (CFD). The bilge radius is normalized by the half breadth of ship, and the bilge keel height is normalized by the maximum bilge keel height which is limited by the molded lines of a side shell and bottom shell. In addition, it is investigated to identify how the roll damping performance of a rectangular section differs from the result of a typical round bilge section with maximum available bilge keel height.

scholarly journals Bilge Keel Induced Roll Damping of an FPSO With Sponsons

2016 ◽  
Author(s):  
Babak Ommani ◽  
Nuno Fonseca ◽  
Trygve Kristiansen ◽  
Christopher Hutchison ◽  
Hanne Bakksjø
Keyword(s):  
Free Surface ◽  
Two Dimensions ◽  
The Body ◽  
Proximity Effects ◽  
Roll Damping ◽  
Damping Coefficients ◽  
Free Decay ◽  
Strip Theory ◽  
Decay Tests ◽  
Bilge Keel

The bilge keel induced roll damping of an FPSO with sponsons is investigated numerically and experimentally. The influence of the bilge keel size, on the roll damping is studied. Free decay tests of a three-dimensional ship model, for three different bilge keel sizes are used to determine roll damping coefficients. The dependency of the quadratic roll damping coefficient to the bilge keel height and the vertical location of the rotation center is studied using CFD. A Navier-Stokes solver based on the Finite Volume Method is adopted for solving the laminar flow of incompressible water around a section of the FPSO undergoing forced roll oscillations in two-dimensions. The free-surface condition is linearized by neglecting the nonlinear free-surface terms and the influence of viscous stresses in the free surface zone, while the body-boundary condition is exact. An averaged center of rotation is estimated by comparing the results of the numerical calculations and the free decay tests. The obtained two-dimensional damping coefficients are extrapolated to 3D by use of strip theory argumentations and compared with the experimental results. It is shown that this simplified approach can be used for evaluating the bilge keel induced roll damping with efficiency, considering unconventional ship shapes and free-surface proximity effects.

Hydrodynamic Response of Buoy Form Spar With Heave Plate Near Free Surface

2021 ◽  
Author(s):  
Pooja Hegde ◽  
S. Nallayarasu
Keyword(s):  
Fluid Dynamics ◽  
Free Surface ◽  
Hydrodynamic Characteristics ◽  
The Past ◽  
Damping Characteristics ◽  
Free Decay ◽  
Hydrodynamic Response ◽  
Computational Fluid Dynamics Cfd ◽  
Heave Plate ◽  
Pitch Damping

Abstract Hydrodynamic response of spar with appendages such as heave plate has been investigated in the past, mostly attached at the bottom of the spar. The effect of geometry and appendages on the hydrodynamic response of spar has been investigated in this article. A curved neck form with a heave plate near the free surface is proposed as an energy dissipation device for both heave and pitch responses. Numerical simulation using Computational Fluid Dynamics (CFD) is used for capturing the flow around the curved neck with heave plate and corresponding damping characteristics. CFD free decay simulations have been carried out to obtain heave and pitch damping and were noted to be higher than the conventional spar with heave plate at the bottom. Comparison of the proposed geometry and heave plate at the free surface with a conventional heave plate at the bottom of the spar has been made, and significant changes to the response and hydrodynamic characteristics have been noted. It is observed that the buoy form spar combined with the heave plate located near the surface (within 10% of the draft) helps dissipate energy and thus reduce the heave response.

scholarly journals CFD Modelling to Investigate Design of a Whaleback-Type Forecastle for Greenwater Protection

2019 ◽  
Author(s):  
Lifen Chen ◽  
Xiantao Zhang ◽  
Paul H. Taylor ◽  
Scott Draper ◽  
Hugh Wolgamot
Keyword(s):  
Fluid Dynamics ◽  
Structural Integrity ◽  
Numerical Models ◽  
Vertical Component ◽  
Preliminary Design ◽  
Cfd Modelling ◽  
Incoming Wave ◽  
Opposite Trend ◽  
Computational Fluid Dynamics Cfd ◽  
Run Up

Abstract In extreme weather permanently moored FPSOs may be overtopped by large amounts of greenwater, resulting in damage to deck structures and downtime. Thus, the preliminary design process for FPSOs has often included structural protection to mitigate loads from greenwater on deck and ensure structural integrity of top side structures at the bow in harsh sea conditions. This paper numerically investigates greenwater at the bow of an FPSO fitted with a ‘whaleback’ or ‘duck-bill’ shaped forecastle that is represented as an angled extension to the freeboard. In this study, the whaleback forecastle is intended to completely deflect the greenwater flow off the forecastle head. Previously validated numerical models based on OpenFOAM, an open source Computational Fluid Dynamics (CFD) package, are used. The (vertical) run-up height and the forces on the whaleback are analysed based on the CFD results to quantify the effectiveness of the design. It is found that the parameter tan β (FE/λp) that combines the coupled effect of the whaleback geometry and the incoming wave is important for determining the run-up height. The use of this parameter leads to a crude method for fast estimates of the effectiveness of such structures. Increase of the slope of the whaleback forecastle increases the run-up height, thus, increases the horizontal greenwater loading on such structure, however, the direct effect of the slope on the horizontal greenwater loading is found to be limited. An opposite trend is observed for the vertical greenwater loading in which the forecastle slope still plays a significant role even if the effect of run-up height is excluded, as a result of overtopping volume. Additionally, the vertical component of greenwater loading dominates the total greenwater loading on the whaleback forecastle.

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