Wave-In-Deck Load on a Jacket Platform, CFD-Derived Pressures and Non-Linear Structural Response

2009 ◽  
Author(s):  
Bogdan Iwanowski ◽  
Rune Gladso̸ ◽  
Marc Lefranc
Keyword(s):  
Free Surface ◽  
Structural Response ◽  
Computational Grids ◽  
Navier Stokes ◽  
Dynamical Response ◽  
Navier Stokes Equation ◽  
Local Flow ◽  
Jacket Platform ◽  
Shell Elements ◽  
Non Linear

The paper presents an industrial application of CFD and non-linear structural response codes in offshore technology. A Wave-In-Deck load due to an extreme wave, acting on a jacket platform, is studied numerically. Particular attention is given to details of local flow and local non-linear dynamical response of the structure. A very detailed FEM model of the platform deck structure, composed of shell elements, is embedded into a non body-conforming CFD grid of computational cells. The applied CFD code is a Navier-Stokes equation solver with an improved Volume of Fluid (iVOF) method employed to displace and re-construct fluid’s free surface and uses a simple, Cartesian grid. The two computational grids, FEM and CFD, are independent. The challenge of a direct mapping of CFD-derived fluid pressures onto structural FEM shell elements is addressed. Then the non-linear dynamical response of the structure is found in time domain. The employed CFD code is ComFLOW while the FEM part is handled by the well-known commercial program LS-DYNA. The composed approach utilizes both robustness of VOF-based methods in tracking of the fluid’s free surface and reliability of FEM structural codes such as LS-DYNA.

Wave-in-Deck Load on a Jacket Platform, CFD Calculations Compared With Experiments

2014 ◽  
Author(s):  
Bogdan Iwanowski ◽  
Tone Vestbøstad ◽  
Marc Lefranc
Keyword(s):  
Free Surface ◽  
Industrial Application ◽  
Computational Models ◽  
Cfd Simulation ◽  
Navier Stokes ◽  
Extreme Wave ◽  
Navier Stokes Equation ◽  
Jacket Platform ◽  
Irregular Wave ◽  
Start Up

The paper presents an industrial application of CFD for calculation of Wave-In-Deck load due to an extreme wave. Particular attention is given to flow kinematics initialization that is necessary to start up a CFD simulation. The applied CFD code, ComFLOW, is a Navier-Stokes equation solver with an improved Volume of Fluid (iVOF) method employed to displace and re-construct fluids free surface. For incoming waves high enough for a negative air-gap and therefore with Wave-In-Deck loads, a jacket platform was tested in model basin, for both regular and irregular wave cases. One of goals of these model tests was verification of CFD codes. The experimental and computational models of the structure are exactly the same. In the paper, the measured Wave-In-Deck forces are compared with CFD results.

Numerical Analysis of a Floating Body With Two-Dimensional Moonpool Including Piston Mode

2010 ◽  
Author(s):  
Jaekyung Heo ◽  
Jong-Chun Park ◽  
Moo-Hyun Kim ◽  
Weon-Cheol Koo
Keyword(s):  
Free Surface ◽  
Viscous Flow ◽  
Experimental Results ◽  
Floating Body ◽  
Navier Stokes ◽  
Linear Potential ◽  
Navier Stokes Equation ◽  
Nonlinear Potential ◽  
Heave Motion ◽  
Piston Mode

In this paper, the potential and viscous flows are simulated numerically around a 2-D floating body with a moonpool (or a small gap) with particular emphasis on the piston mode. The floating body with moonpool is forced to heave in time domain. Linear potential code is known to give overestimated free-surface heights inside the moonpool. Therefore, a free-surface lid in the gap or similar treatments are widely employed to suppress the exaggerated phenomenon by potential theory. On the other hand, Navier-Stokes equation solvers based on a FVM can be used to take account of viscosity. Wave height and phase shift inside and outside the moon-pool are computed and compared with experimental results by Faltinsen et al. (2007) over various heaving frequencies. Pressure and vorticity fields are investigated to better understand the mechanism of the sway force induced by the heave motion. Furthermore, a nonlinear potential code is utilized to compare with the viscous flow. The viscosity effects are investigated in more detail by solving Euler equations. It is found that the viscous flow simulations agree very well with the experimental results without any numerical treatment.

Mechanics of a Free-Surface Liquid Film Flow

1987 ◽  
Vol 54 (4) ◽  
pp. 951-954 ◽  
Author(s):  
Cyrus K. Aidun
Keyword(s):  
Differential Equation ◽  
Free Surface ◽  
Film Flow ◽  
Navier Stokes ◽  
Experimental Measurements ◽  
Navier Stokes Equation ◽  
Higher Order Terms ◽  
Liquid Film Flow ◽  
Surface Liquid ◽  
Similar Equation

The mechanics of a free surface viscous liquid curtain flowing steadily between two vertical guide wires under the influence of gravity is investigated. The Navier-Stokes equation is integrated over the film thickness and an integro-differential equation is derived for the average film velocity. An approximate nonlinear differential equation, attributed to G. I. Taylor, is obtained by neglecting the higher order terms. An analytical solution is obtained for a similar equation which neglects the surface tension effects and the results are compared with the experimental measurements of Brown (1961).

CFD Calculations of Wave-in-Deck Load on a Jacket Platform: Impact Pressure Decrease due to Air Pocket Formation

2011 ◽  
Author(s):  
Rik Wemmenhove ◽  
Marc Lefranc
Keyword(s):  
Two Phase ◽  
Incoming Wave ◽  
Navier Stokes Equation ◽  
Local Flow ◽  
Hydrodynamic Impact ◽  
Jacket Platform ◽  
Air Pocket ◽  
Phase Liquid ◽  
Pocket Formation ◽  
The Impact

The industrial problem of a jacket platform subjected to Wave-In-Deck load due to an extreme wave is studied numerically by a CFD technique. In particular, details of local flow and slamming-like hydrodynamic impact on structural members are studied. The applied CFD code ComFLOW is a Navier-Stokes equation solver with an improved Volume of Fluid (iVOF) method employed to displace and re-construct fluids free surface. Two different fluid models, single-phase (liquid+void) and two-phase (liquid+compressible gas) can be used, the latter model being capable of simulating gas entrapped in liquid. Local air pockets are formed in corners and nooks of the structure as the incoming wave front approaches. The study presents a comparison of hydrodynamic impact pressures found with and without the air entrapment. Numerical realisation of the two-phase model is considerably more expensive computationally and the study shows possibility and various aspects of its simulation. Accuracy of the numerical solution and relevance of the air pocket formation on the impact pressures and therefore on the exerted structural load are discussed.

scholarly journals Effects of Stenting on Blood Flow in a Coronary Artery Network Model

2006 ◽  
Vol 3 (2) ◽  
pp. 77-86
Author(s):  
R. Raghu ◽  
A. Pullan ◽  
N. Smith
Keyword(s):  
Blood Flow ◽  
Coronary Artery ◽  
Finite Difference Method ◽  
Vessel Wall ◽  
Flow Patterns ◽  
Navier Stokes ◽  
Pressure Gradients ◽  
Computationally Efficient ◽  
Navier Stokes Equation ◽  
Local Flow

The effect of stenting on blood flow is investigated using a model of the coronary artery network. The parameters in a generic non-linear pressure–radius relationship are varied in the stented region to model the increase in stiffness of the vessel due to the presence of the stent. A computationally efficient form of the Navier–Stokes equation is solved using a Lax–Wendroff finite difference method. Pressure, vessel radius and flow velocity are computed along the vessel segments. Results show negative pressure gradients at the ends of the stent and increased velocity through the middle of the stented region. Changes in local flow patterns and vessel wall stresses due to the presence of the stent have been shown to be important in restenosis of vessels. Local and global pressure gradients affect local flow patterns and vessel wall stresses, and therefore may be an important factor associated with restenosis. The model presented in this study can be easily extended to solve flows for stented vessels in a full, anatomically realistic coronary network. The framework to allow for the effects of the deformation of the myocardium on the coronary network is also in place.

scholarly journals Simulation of free-surface flow in a tank using the Navier-Stokes model and unstructured finite volume method

2005 ◽  
Vol 219 (3) ◽  
pp. 251-266 ◽  
Author(s):  
X Zhang ◽  
N M Sudharsan ◽  
R Ajaykumar ◽  
K Kumar
Keyword(s):  
Free Surface ◽  
Finite Volume Method ◽  
Finite Volume ◽  
Free Surface Flow ◽  
Offshore Structures ◽  
Surface Flow ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Volume Method ◽  
Unstructured Finite Volume Method

Modelling free-surface flow has very important applications in many engineering areas such as oil transportation and offshore structures. Current research focuses on the modelling of free surface flow in a tank by solving the Navier-Stokes equation. An unstructured finite volume method is used to discretize the governing equations. The free surface is tracked by dynamically adapting the mesh and making it always surface conforming. A mesh-smoothing scheme based on the spring analogy is also implemented to ensure mesh quality throughout the computaiton. Studies are performed on the sloshing response of a liquid in an elastic container subjected to various excitation frequencies. Further investigations are also carried out on the critical frequency that leads to large deformation of the tank walls. Another numerical simulation involves the free-surface flow past as submerged obstacle placed in the tank to show the flow separation and vortices. All these cases demonstrate the capability of this numerical method in modelling complicated practical problems.

scholarly journals Time-domain non-linear aeroelastic analysis via a projection-based reduced-order model

2020 ◽  
Vol 124 (1281) ◽  
pp. 1798-1818 ◽  
Author(s):  
S. Lee ◽  
H. Cho ◽  
H. Kim ◽  
S.-J. Shin
Keyword(s):  
Flow Field ◽  
Time Domain ◽  
Reduced Order Model ◽  
Navier Stokes ◽  
Computational Time ◽  
Order Model ◽  
Navier Stokes Equation ◽  
Reduced Order ◽  
Non Linear ◽  
The Time Domain

ABSTRACTThe aeroelastic phenomenon of limit-cycle oscillations (LCOs) is analysed using a projection-based reduced-order model (PROM) and Navier–Stokes computational fluid dynamics (CFD) in the time domain. The proposed approach employs incompressible Navier–Stokes CFD to construct the full-order model flow field. A proper orthogonal decomposition (POD) of the snapshot matrix is conducted to extract the POD modes and corresponding temporal coefficients. The POD modes are directly projected to the incompressible Navier–Stokes equation to reconstruct the flow field efficiently. The methodology is applied to a plunging cylinder and an aerofoil undergoing LCOs. This scheme decreases the computational time while preserving the capability to predict the flow field accurately. The ROM is capable of reducing the computational time by at least 70% while maintaining the discrepancy within 0.1%. The causes of LCOs are also investigated. The scheme can be used to analyse non-linear aeroelastic phenomena in the time domain with reduced computational time.

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