Wave-in-Deck Load Analysis for a Jack-Up Platform

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Thomas E. Schellin ◽  
Milovan Perić ◽  
Ould el Moctar
Keyword(s):  
Stokes Equations ◽  
Wave Theory ◽  
Breaking Waves ◽  
Navier Stokes ◽  
Design Parameters ◽  
Wave Loads ◽  
Wave Direction ◽  
Two Phase ◽  
Highly Nonlinear ◽  
Jack Up

This paper describes the prediction of environmental loads on a typical three-leg jack-up platform under freak wave conditions. Considered were cases where the air gap is small and the hull is subject to impact-related wave-in-deck loads. The technique to predict wave loads was based on the use of a validated CFD code that solves the Reynolds-averaged Navier–Stokes equations. This code relies on the interface-capturing technique of the volume-of-fluid type to account for highly nonlinear wave effects. It computes the two-phase flow of water and air to describe the physics associated with complex free-surface shapes with breaking waves and air trapping, hydrodynamic phenomena that had to be considered to yield reliable predictions. The Stokes fifth-order wave theory initialized volume fractions of water, velocity distributions in the solution domain, and time-dependent boundary conditions at inlet and outlet boundaries. This paper demonstrates that this technique can be a valuable numerical tool for preliminary designs as well as subsequent safety assessments. In particular, it shows that effects of different operating and design parameters on wave-in-deck loads, such as wave direction, wave height, wave period, and wind speed, can be evaluated with an affordable computing effort.

Wave-Deck-Load Analysis for a Jack-Up Platform

2009 ◽  
Author(s):  
Thomas E. Schellin ◽  
Milovan Peric´ ◽  
Ould el Moctar
Keyword(s):  
Stokes Equations ◽  
Volume Fraction ◽  
Wave Theory ◽  
Breaking Waves ◽  
Design Parameters ◽  
Wave Direction ◽  
Wave Load ◽  
Two Phase ◽  
Highly Nonlinear ◽  
Jack Up

The paper analyzes freak wave-in-deck load effects on a typical three-leg jack-up platform stationed in the North Sea. Considered were cases where the air gap is small and the hull is subject to impact-related wave-in-deck loads. Wave load predictions were based on the use of a validated CFD code that solves the Reynolds-averaged Navier-Stokes equations. The code relies on the interface-capturing technique of the volume-of-fluid type to account for highly nonlinear wave effects. It computes the two-phase flow of water and air to describe the physics associated with complex free-surface shapes with breaking waves and air trapping, hydrodynamic phenomena that had to be considered to yield reliable predictions. Stokes 5th order wave theory was used to initialize volume fraction of water and velocity distribution in the solution domain, as well as to prescribe time-dependent boundary conditions at inlet and outlet boundaries. It was demonstrated that CFD methods can be used to predict the load phenomena under extreme wave conditions and thus serve as a valuable tool for both initial design and subsequent assessment of safety aspects. In particular, we demonstrated that effects of different operating and design parameters on wave-in-deck loads, such as wave direction, wave height, wave period, and wind speed, can be evaluated with an affordable computing effort using personal computers.

Wave Load and Structural Analysis for a Jack-Up Platform in Freak Waves

2007 ◽  
Author(s):  
Ould el Moctar ◽  
Thomas E. Schellin ◽  
Milovan Peric
Keyword(s):  
Structural Model ◽  
Stokes Equations ◽  
Nonlinear Effects ◽  
Breaking Waves ◽  
Wave Loads ◽  
Wave Load ◽  
Two Phase ◽  
Freak Waves ◽  
Highly Nonlinear ◽  
Jack Up

The paper analyzed effects of freak waves on a mobile jack-up drilling platform stationed in exposed waters of the North Sea. Under freak wave conditions, highly nonlinear effects, such as wave run-up on platform legs and impact-related wave loads on the hull, had to be considered. Traditional methods based on the Morison formula needed to be critically examined to accurately predict these loads. Our analysis was based on the use of advanced CFD techniques. The code used here solves the Reynolds-averaged Navier-Stokes equations and relies on the interface-capturing technique of the volume-of-fluid type. It computed the two-phase flow of water and air to describe the physics associated with complex free-surface shapes with breaking waves and air trapping, hydrodynamic phenomena that had to be considered to yield reliable predictions. Lastly, the FEM was used to apply the wave-induced loads onto a comprehensive finite element structural model of the platform, yielding deformations and stresses.

Wave Load and Structural Analysis for a Jack-Up Platform in Freak Waves

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Ould el Moctar ◽  
Thomas E. Schellin ◽  
Thomas Jahnke ◽  
Milovan Peric
Keyword(s):  
Finite Element ◽  
Structural Model ◽  
Stokes Equations ◽  
Breaking Waves ◽  
Wave Loads ◽  
Wave Load ◽  
Two Phase ◽  
Freak Waves ◽  
Highly Nonlinear ◽  
Jack Up

This paper analyzed the effects of freak waves on a mobile jack-up drilling platform stationed in exposed waters of the North Sea. Under freak wave conditions, highly nonlinear effects, such as wave run-up on platform legs and impact-related wave loads on the hull, had to be considered. Traditional methods based on the Morison formula needed to be critically examined to accurately predict these loads. Our analysis was based on the use of advanced computational fluid dynamics techniques. The code used here solves the Reynolds-averaged Navier–Stokes equations and relies on the interface-capturing technique of the volume-of-fluid type. It computed the two-phase flow of water and air to describe the physics associated with complex free-surface shapes with breaking waves and air trapping, hydrodynamic phenomena that had to be considered to yield reliable predictions. Lastly, the finite element method was used to apply the wave-induced loads onto a comprehensive finite element structural model of the platform, yielding deformations and stresses.

Current generation by deep-water breaking waves

2016 ◽  
Vol 803 ◽  
pp. 275-291 ◽  
Author(s):  
N. E. Pizzo ◽  
Luc Deike ◽  
W. Kendall Melville
Keyword(s):  
Wave Field ◽  
Water Column ◽  
Deep Water ◽  
Stokes Equations ◽  
Laboratory Data ◽  
Breaking Waves ◽  
Navier Stokes ◽  
Mean Flow ◽  
Two Phase ◽  
Navier Stokes Equations

We examine the partitioning of the energy transferred to the water column by deep-water wave breaking; in this case between the turbulent and mean flow. It is found that more than 95 % of the energy lost by the wave field is dissipated in the first four wave periods after the breaking event. The remaining energy is in the coherent vortex generated by breaking. A scaling argument shows that the ratio between the energy in this breaking generated mean current and the total energy lost from the wave field to the water column due to breaking scales as $(hk)^{1/2}$, where $hk$ is the local slope at breaking. This model is examined using direct numerical simulations of breaking waves solving the full two-phase air–water Navier–Stokes equations, as well as the limited available laboratory data, and good agreement is found for strong breaking waves.

scholarly journals 3-D Oil spill modelling. Natural dispersion and the spreading of oil-water emulsions in the water column

2013 ◽  
Vol 13 (4) ◽  
pp. 325-338 ◽  
Keyword(s):  
Surface Wave ◽  
Water Column ◽  
Oil Spills ◽  
Stokes Equations ◽  
Probability Model ◽  
Breaking Waves ◽  
Navier Stokes ◽  
Two Phase ◽  
Dispersed Oil ◽  
Oil Emulsions

A 3-D hybrid turbulence model, simulating the transport and fate of oil spills in various waters, is used to evaluate the influence of natural dispersion on the spreading of water-in-oil emulsions formed in the water column. The model combines the Navier-Stokes equations for two-phase flows, the RNG k-ε submodel, and parameterized expressions of the basic processes affecting the fate of oil spills. The model also considers the presence of waves, the wind- and wave- induced surface drifts, and the influence of surface wave breaking on the oil spills. Using a stochastic probability model of breaking waves, the loss of surface wave energy into turbulence, due to breaking, is derived and the rate of natural dispersion of oil mass and that of oilwater emulsions formed in the water column is evaluated, under a variety of sea state conditions. Results in the form of oil concentration profiles with depth, graphs showing the variation of the fraction of water (mass) absorbed by the dispersed oil, at various depths and times, as well as graphs showing the oil mass balance, at the sea surface, at various times are compared with counterpart profiles, and graphs obtained from the literature, and useful conclusions are drawn.

Numerical Modeling of Evolution of Boundary Between Incompressible Gas and Liquid in Two-Dimensional Region

2006 ◽  
Vol 4 ◽  
pp. 224-236
Author(s):  
A.S. Topolnikov
Keyword(s):  
Numerical Modeling ◽  
Interphase Boundary ◽  
Incompressible Liquid ◽  
Stokes Equations ◽  
Numerical Code ◽  
Navier Stokes ◽  
Two Phase ◽  
Navier Stokes Equations ◽  
Incompressible Media ◽  
Good Agreement

The paper is devoted to numerical modeling of Navier–Stokes equations for incompressible media in the case, when there exist gas and liquid inside the rectangular calculation region, which are separated by interphase boundary. The set of equations for incompressible liquid accounting for viscous, gravitational and surface (capillary) forces is solved by finite-difference scheme on the spaced grid, for description of interphase boundary the ideology of Level Set Method is used. By developed numerical code the set of hydrodynamic problems is solved, which describe the motion of two-phase incompressible media with interphase boundary. As a result of numerical simulation the solutions are obtained, which are in good agreement with existing analytical and experimental solutions.

scholarly journals Experimental and Numerical Study on Water Filling and Air Expelling Process in a Pipe with Multiple Air Valves under Water Slow Filling Condition

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2511
Author(s):  
Jintao Liu ◽  
Di Xu ◽  
Shaohui Zhang ◽  
Meijian Bai
Keyword(s):  
Numerical Model ◽  
Stokes Equations ◽  
Numerical Study ◽  
Practical Method ◽  
Navier Stokes ◽  
Physical Processes ◽  
Two Phase ◽  
Saint Venant Equations ◽  
Water Filling ◽  
Air Valve

This paper investigates the physical processes involved in the water filling and air expelling process of a pipe with multiple air valves under water slow filling condition, and develops a fully coupledwater–air two-phase stratified numerical model for simulating the process. In this model, the Saint-Venant equations and the Vertical Average Navier–Stokes equations (VANS) are respectively applied to describe the water and air in pipe, and the air valve model is introduced into the VANS equations of air as the source term. The finite-volume method and implicit dual time-stepping method (IDTS) with two-order accuracy are simultaneously used to solve this numerical model to realize the full coupling between water and air movement. Then, the model is validated by using the experimental data of the pressure evolution in pipe and the air velocity evolution of air valves, which respectively characterize the water filling and air expelling process. The results show that the model performs well in capturing the physical processes, and a reasonable agreement is obtained between numerical and experimental results. This agreement demonstrates that the proposed model in this paper offers a practical method for simulating water filling and air expelling process in a pipe with multiple air valves under water slow filling condition.

NUMERICAL SOLUTIONS OF 2D AND 3D SLAMMING PROBLEMS

2021 ◽  
Vol 153 (A2) ◽  
Author(s):  
Q Yang ◽  
W Qiu
Keyword(s):  
Free Surface ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Type Equation ◽  
The Body ◽  
Navier Stokes ◽  
Time Step ◽  
Navier Stokes Equations ◽  
Highly Nonlinear ◽  
2D And 3D

Slamming forces on 2D and 3D bodies have been computed based on a CIP method. The highly nonlinear water entry problem governed by the Navier-Stokes equations was solved by a CIP based finite difference method on a fixed Cartesian grid. In the computation, a compact upwind scheme was employed for the advection calculations and a pressure-based algorithm was applied to treat the multiple phases. The free surface and the body boundaries were captured using density functions. For the pressure calculation, a Poisson-type equation was solved at each time step by the conjugate gradient iterative method. Validation studies were carried out for 2D wedges with various deadrise angles ranging from 0 to 60 degrees at constant vertical velocity. In the cases of wedges with small deadrise angles, the compressibility of air between the bottom of the wedge and the free surface was modelled. Studies were also extended to 3D bodies, such as a sphere, a cylinder and a catamaran, entering calm water. Computed pressures, free surface elevations and hydrodynamic forces were compared with experimental data and the numerical solutions by other methods.

scholarly journals Development of Hybrid Airlift-Jet Pump with Its Performance Analysis

2018 ◽  
Vol 8 (9) ◽  
pp. 1413 ◽  
Author(s):  
Dan Yao ◽  
Kwongi Lee ◽  
Minho Ha ◽  
Cheolung Cheong ◽  
Inhiug Lee
Keyword(s):  
Boundary Conditions ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Jet Pump ◽  
Two Phase

A new pump, called the hybrid airlift-jet pump, is developed by reinforcing the advantages and minimizing the demerits of airlift and jet pumps. First, a basic design of the hybrid airlift-jet pump is schematically presented. Subsequently, its performance characteristics are numerically investigated by varying the operating conditions of the airlift and jet parts in the hybrid pump. The compressible unsteady Reynolds-averaged Navier-Stokes equations, combined with the homogeneous mixture model for multiphase flow, are used as the governing equations for the two-phase flow in the hybrid pump. The pressure-based methods combined with the Pressure-Implicit with Splitting of Operators (PISO) algorithm are used as the computational fluid dynamics techniques. The validity of the present numerical methods is confirmed by comparing the predicted mass flow rate with the measured ones. In total, 18 simulation cases that are designed to represent the various operating conditions of the hybrid pump are investigated: eight of these cases belong to the operating conditions of only the jet part with different air and water inlet boundary conditions, and the remaining ten cases belong to the operating conditions of both the airlift and jet parts with different air and water inlet boundary conditions. The mass flow rate and the efficiency are compared for each case. For further investigation into the detailed flow characteristics, the pressure and velocity distributions of the mixture in a primary pipe are compared. Furthermore, a periodic fluctuation of the water flow in the mass flow rate is found and analyzed. Our results show that the performance of the jet or airlift pump can be enhanced by combining the operating principles of two pumps into the hybrid airlift-jet pump, newly proposed in the present study.

Subsidence of the Ekofisk Platforms: Wave in Deck Impact Study — Various Wave Models and Computational Methods

2002 ◽  
Author(s):  
Bogdan Iwanowski ◽  
Henrik Grigorian ◽  
Ingar Scherf
Keyword(s):  
Computational Methods ◽  
Stokes Equations ◽  
Type Equation ◽  
Navier Stokes ◽  
Stokes Wave ◽  
Wave Loads ◽  
Wave Impact ◽  
Navier Stokes Equations ◽  
Wave Models ◽  
Displacement Approach

Subsidence of the Ekofisk platforms creates several operational challenges. For safety of the platforms, it is of great importance to find the wave impact loads acting on the platforms’ decks. The paper describes how such loads can be computed. Three theoretical wave models are discussed in the paper: the Airy wave, Airy wave modified through Wheeler stretching and the 5th order non-linear Stokes wave. The wave loads for these wave models are computed by various methods. The method based on momentum displacement approach and Morison-type equation developed by Dr. Kaplan is used as a reference point. The loads are also computed through a solution of complete Navier-Stokes equations, with the Volume of Fluid (VOF) method used to trace motion of the fluid’s free surface. Results of different wave models and different computational methods are compared and discussed.

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