scholarly journals Vortex Shedding From Hulls in Close Proximity With Relative Motion

2018 ◽  
Author(s):  
Ian A. Milne ◽  
J. Michael R. Graham
Keyword(s):  
Vortex Shedding ◽  
Significant Contribution ◽  
Pressure Field ◽  
Computational Results ◽  
Floating Bodies ◽  
Damping Coefficients ◽  
Close Proximity ◽  
Forced Roll ◽  
Offshore Industry ◽  
Liquid Natural Gas

The safe and efficient offloading of liquid natural gas (LNG) in a side-by-side configuration has emphasised the need to accurately quantify the hydrodynamic responses of floating bodies when located in very close proximity. A new series of computational results are presented for the forced roll of a hull in the presence of a second body representative of a floating FLNG facility. The vortex shedding phenomenon which provides a significant contribution to the damping of an isolated hull, is demonstrated to be modified by the presence of the second body. The total damping coefficients were found to be significantly reduced by approximately 50 percent for the very small gap widths considered. It is shown that in addition to the modification of the local shedding dynamics, the variation in the pressure field owing to the presence of the second body also contributes significantly to the reduction in the damping. The findings will be of particular interest to the offshore industry for improving and optimising offloading practices.

Experimental and Numerical Studies on Ship Motion Responses Coupled with Sloshing in Waves

2009 ◽  
Vol 53 (02) ◽  
pp. 68-82 ◽  
Author(s):  
Bo-Woo Nam ◽  
Yonghwan Kim ◽  
Dae-Woong Kim ◽  
Yong-Soo Kim
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Impulse Response Function ◽  
Ship Motion ◽  
Computational Results ◽  
Floating Bodies ◽  
Motion Responses ◽  
Significant Difference ◽  
Response Amplitude Operators ◽  
Liquid Natural Gas

This study considers the motion responses of floating bodies in waves coupled with sloshing-induced internal forces and their effects on sloshing-induced impact loads. The linear ship motion is solved using an impulse-response-function (IRF) method, while the nonlinear sloshing flow is simulated using a finite difference method. The considered models are a liquid natural gas floating production, storage, and offloading unit (LNG FPSO) with two partially filled tanks and a modified S175 hull with an antirolling tank. In the case of the LNG FPSO model, both numerical and experimental studies are carried out. Three degree-of-freedom motion responses are allowed in the presence of regular waves, and the measured response amplitude operators (RAOs) are compared with computational results. For the modified S175 hull, the computational results are compared with other existing computational results. It is observed that the present method provides a fair agreement with experimental and other numerical results, showing significant coupling effects on both motion responses and sloshing flows. The numerical study extends to the observation of pressure field inside the tanks, and a significant difference in internal pressure is also shown.

Experimental Investigation of Hydrodynamic Coefficients of a Wave-Piercing Tumblehome Hull Form

2007 ◽  
Author(s):  
Christopher C. Bassler ◽  
Jason B. Carneal ◽  
Paisan Atsavapranee
Keyword(s):  
Experimental Investigation ◽  
System Modeling ◽  
Flow Simulation ◽  
Roll Damping ◽  
Hull Form ◽  
Damping Coefficients ◽  
Calm Water ◽  
Forced Roll ◽  
Future Work ◽  
Damping Model

A systematic series of calm-water forced roll model tests were performed over a range of forward speeds using an advanced tumblehome hull form (DTMB model #5613-1) to examine the mechanisms of roll damping. This experimental investigation is part of an ongoing effort to advance the capability to assess seakeeping, maneuvering, and dynamic stability characteristics of an advanced surface combatant. The experiment was performed to provide data for development and validation of a semi-empirical roll damping model for use in validation of ship motion and viscous flow simulation codes, as well as to provide a basis for future work with additional experiments, contributing to the development of an improved analytical roll damping model. Two hull configurations were tested: barehull with skeg, and bare hull with skeg and bilge keels. Measurements of forces and moments were obtained over a range of forward speeds, roll frequencies, and roll amplitudes. Stereo particle-image velocimetry (SPIV) measurments were also taken for both zero and forward speeds. Test data was used to calculate added mass/inertia and damping coefficients. Two different system modeling techniques were used. The first method modeled the system as an equivalent linearly-damped second-order harmonic oscillator with the time-varying total stiffness coefficient considered linear. The second technique used equivalent linear damping, including higher-order Fourier components, and a non-linear stiffness formulation. Results are shown, including plots of added inertia and damping coefficients as functions of roll frequency, roll amplitude, and forward speed and SPIV measurements. Trends from the experimental data are compared to results from traditional component roll damping formulations for conventional hull from geometries and differences are discussed.

Modelling of multi-bodies in close proximity under water waves—Fluid forces on floating bodies

2011 ◽  
Vol 38 (13) ◽  
pp. 1403-1416 ◽  
Author(s):  
Lin Lu ◽  
Bin Teng ◽  
Liang Sun ◽  
Bing Chen
Keyword(s):  
Water Waves ◽  
Floating Bodies ◽  
Fluid Forces ◽  
Close Proximity

scholarly journals Surge motion on a floating cylinder in water of finite depth

2003 ◽  
Vol 2003 (57) ◽  
pp. 3643-3656 ◽  
Author(s):  
Dambaru D. Bhatta
Keyword(s):  
Velocity Potential ◽  
Separation Of Variables ◽  
Finite Depth ◽  
Added Mass ◽  
Computational Results ◽  
Complex Matrix ◽  
Interior Region ◽  
Exterior Region ◽  
Damping Coefficients ◽  
Calm Water

We derived added mass and damping coefficients of a vertical floating circular cylinder due to surge motion in calm water of finite depth. This is done by deriving the velocity potential for the cylinder by considering two regions, namely, interior region and exterior region. The velocity potentials for these two regions are obtained by the method of separation of variables. The continuity of the solutions has been maintained at the imaginary interface of these regions by matching the functions and gradients of each solution. The complex matrix equation is numerically solved to determine the unknown coefficients. Some computational results are presented for different depth-to-radius and draft-to-radius ratios.

Analysis of Aerodynamic Characteristics in the Bottom of a Car

2013 ◽  
Vol 373-375 ◽  
pp. 20-23
Author(s):  
Hai Tao Bao ◽  
Cheng Wang
Keyword(s):  
Numerical Simulation ◽  
Velocity Field ◽  
Pressure Field ◽  
Final Analysis ◽  
Aerodynamic Characteristics ◽  
Specific Reference ◽  
Computational Results ◽  
The Future ◽  
Cfd Method

The aerodynamic characteristics of ordinary vehicle have been studied by lots of scholars, while few people pay enough attention to the aerodynamic characteristics in the bottom of the car. As the requirements of regulations for the performance of the car continues to increase, Analysis of Aerodynamic Characteristics of the car is much more necessary now. In this paper , by using CFD method and getting benefit from the established CFD software, we gave external velocity field and pressure field of the car. The data was analyzed and summarized and the computational results are obtained. In the final analysis for the flatness in the bottom of the car influence on aerodynamic characteristics.This paper has done some useful attempts, and it will provide specific reference significance to the numerical simulation on design of the car in the future.

Theoretical and numerical investigations of wave resonance between two floating bodies in close proximity

2017 ◽  
Vol 29 (5) ◽  
pp. 805-816 ◽  
Author(s):  
Lei Tan ◽  
Guo-qiang Tang ◽  
Zhong-bing Zhou ◽  
Liang Cheng ◽  
Xiaobo Chen ◽  
...  
Keyword(s):  
Floating Bodies ◽  
Numerical Investigations ◽  
Wave Resonance ◽  
Close Proximity

Numerical Investigation of Flow around a Triangle Cylinder Using a Multiscale Turbulence Model

2013 ◽  
Vol 444-445 ◽  
pp. 253-258
Author(s):  
He Dong ◽  
Ge Gao ◽  
Zhi Qiang Li ◽  
Yang Yang Tang ◽  
Huan Xu ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Numerical Method ◽  
Numerical Investigation ◽  
Strouhal Number ◽  
Turbulence Model ◽  
Vortex Shedding ◽  
Average Method ◽  
Variable Interval ◽  
Computational Results ◽  
Time Average

The unsteady flow around a triangle cylinder was simulated using the multiscale turbulence model based on the variable interval time average method. The numerical method used in this simulation is an unstructured staggered mesh scheme. The computational results show that the multiscale turbulence model can successfully simulate vortex shedding characteristics. The Strouhal number and time-averaged velocity profiles also agree better with experiments than that of the standard k-ε model.

Using CFD to Assess Low Frequency Damping

2012 ◽  
Author(s):  
Alessio Pistidda ◽  
Harald Ottens ◽  
Richard Zoontjes
Keyword(s):  
Standard Procedure ◽  
Low Frequency ◽  
Added Mass ◽  
Model Tests ◽  
Viscous Damping ◽  
Viscous Effects ◽  
Floating Bodies ◽  
Time Step ◽  
Damping Coefficients ◽  
Quadratic Component

During offshore installation operations, floating bodies are often moored using soft mooring which are designed to withstand the environmental forces. Large amplitude motions often occur due to excitation by slowly varying wind and wave drift forces. To analyze these motions the dynamic system has to be accurately described, which includes an estimation of the added mass and damping coefficients. In general, the added mass can be accurately calculated with traditional potential theory. However for the damping this method is not adequate because viscous effects play an important role. Generally these data are obtained using model tests. This paper validates the CFD methodology as an alternative to model tests to evaluate the viscous damping. The aim is to define a standard procedure to derive viscous damping coefficients for surge, sway and yaw motion of floating bodies. To estimate viscous damping in CFD, a 3D model of the launch and float-over barge H-851 was used. For this barge, model test data is available which could be compared with the results of the CFD analysis. For the simulations, the commercial package STAR-CCM+ with the implicit unsteady solver for Reynolds-Averaged Navier-Stokes (RANS) equations was used. The turbulence model implemented was the k-Omega-SST. Numerical errors have been assessed performing sensitivity analysis on time step and grid size. Damping has been investigated by performing decay simulations as in the model tests, taking the effect of coupling among all motions into account. The P-Q fitting method has been used to determine the linear and quadratic component of the damping. Numerical results are validated with those obtained from the towing tank. Results show that CFD is an adequate tool to estimate the low frequency damping in terms of equivalent damping. More investigations are required to determine the linear and quadratic component.

Dynamic Properties of a Heliostat Structure Determined by Numerical and Experimental Modal Analysis

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
J. Felipe Vásquez-Arango ◽  
Reiner Buck ◽  
Robert Pitz-Paal
Keyword(s):  
Modal Analysis ◽  
Vortex Shedding ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Simple Approach ◽  
Operating Conditions ◽  
Mode Shapes ◽  
Fe Model ◽  
Damping Coefficients ◽  
Operating Points

An experimental and numerical modal analysis was performed on an 8 m2 T-shaped heliostat structure at different elevation angles. The experimental results were used to validate a finite element (FE) model by comparing natural frequencies and mode shapes. The agreement between experiments and simulations is good in all operating points investigated. In addition, damping coefficients were determined experimentally for each mode, in order to provide all necessary information for the development of a dynamic model. Furthermore, potentially critical operating conditions caused by vortex shedding were identified using a simple approach.

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