Wave-Induced Damping of Offshore Structures

1987 ◽  
Author(s):  
A.B. Dunwoody ◽  
J.K. Vandiver
Keyword(s):  
Offshore Structures ◽  
Wave Induced

Stability of offshore structures in shallow water depth

2011 ◽  
Vol 2 (2) ◽  
pp. 320-333
Author(s):  
F. Van den Abeele ◽  
J. Vande Voorde
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Fossil Fuels ◽  
Oil And Gas ◽  
Structural Response ◽  
Offshore Structures ◽  
Exploration And Production ◽  
Subsea Pipelines ◽  
Wave Induced ◽  
Shallow Water Depth

The worldwide demand for energy, and in particular fossil fuels, keeps pushing the boundaries of offshoreengineering. Oil and gas majors are conducting their exploration and production activities in remotelocations and water depths exceeding 3000 meters. Such challenging conditions call for enhancedengineering techniques to cope with the risks of collapse, fatigue and pressure containment.On the other hand, offshore structures in shallow water depth (up to 100 meter) require a different anddedicated approach. Such structures are less prone to unstable collapse, but are often subjected to higherflow velocities, induced by both tides and waves. In this paper, numerical tools and utilities to study thestability of offshore structures in shallow water depth are reviewed, and three case studies are provided.First, the Coupled Eulerian Lagrangian (CEL) approach is demonstrated to combine the effects of fluid flowon the structural response of offshore structures. This approach is used to predict fluid flow aroundsubmersible platforms and jack-up rigs.Then, a Computational Fluid Dynamics (CFD) analysis is performed to calculate the turbulent Von Karmanstreet in the wake of subsea structures. At higher Reynolds numbers, this turbulent flow can give rise tovortex shedding and hence cyclic loading. Fluid structure interaction is applied to investigate the dynamicsof submarine risers, and evaluate the susceptibility of vortex induced vibrations.As a third case study, a hydrodynamic analysis is conducted to assess the combined effects of steadycurrent and oscillatory wave-induced flow on submerged structures. At the end of this paper, such ananalysis is performed to calculate drag, lift and inertia forces on partially buried subsea pipelines.

scholarly journals DRIFT CURRENTS OF CLEAN AND SLICK SEA SURFACES

1982 ◽  
Vol 1 (18) ◽  
pp. 143
Author(s):  
Jin Wu
Keyword(s):  
Surface Film ◽  
Offshore Structures ◽  
Sea Surface ◽  
Clean Surface ◽  
Dynamic Interactions ◽  
Drift Current ◽  
Stress Coefficient ◽  
Wind Velocities ◽  
Wave Induced ◽  
Surface Drift

Drift currents near sea surface govern movement and dispersion of man-made discharges near the sea surface, and influence design, deployment, and stability of offshore structures. The wind-induced drift currents and the wave-induced mass transports at the sea surface are separately estimated. The total surface drift current, the sum of wind- and wave-induced components, agree well with oceanic data (Hughes, 1956). The mass transport of waves over slick surface is greater than that over clean surface due to dynamic interactions between the surface film and waves. On the other hand, the wind-stress coefficient of slick surface is smaller than that of clean surface, resulting in a smaller wind-induced drift current over the slick surface. Available laboratory results (Alofs and Reisbig, 1972) on slick movements are reanalyzed to provide basis for estimating movements of slicks of various sizes over waves of different lengths under different wind velocities.

scholarly journals Wave-Induced Seabed Response around a Dumbbell Cofferdam in Non-Homogeneous Anisotropic Seabed

2019 ◽  
Vol 7 (6) ◽  
pp. 189 ◽  
Author(s):  
Linya Chen ◽  
Dong-Sheng Jeng ◽  
Chencong Liao ◽  
Dagui Tong
Keyword(s):  
Shear Modulus ◽  
Vertical Distribution ◽  
Pore Pressure ◽  
Wave Structure ◽  
Offshore Structures ◽  
Hydrodynamic Process ◽  
Response Analysis ◽  
Depth Function ◽  
Wave Induced ◽  
The Vertical Distribution

Cofferdams are frequently used to assist in the construction of offshore structures that are built on a natural non-homogeneous anisotropic seabed. In this study, a three-dimensional (3D) integrated numerical model consisting of a wave submodel and seabed submodel was adopted to investigate the wave–structure–seabed interaction. Reynolds-Averaged Navier–Stokes (RANS) equations were employed to simulate the wave-induced fluid motion and Biot’s poroelastic theory was adopted to control the wave-induced seabed response. The present model was validated with available laboratory experimental data and previous analytical results. The hydrodynamic process and seabed response around the dumbbell cofferdam are discussed in detail, with particular attention paid to the influence of the depth functions of the permeability K i and shear modulus G j . Numerical results indicate that to avoid the misestimation of the liquefaction depth, a steady-state analysis should be carried out prior to the transient seabed response analysis to first determine the equilibrium state caused by seabed consolidation. The depth function G j markedly affects the vertical distribution of the pore pressure and the seabed liquefaction around the dumbbell cofferdam. The depth function K i has a mild effect on the vertical distribution of the pore pressure within a coarse sand seabed, with the influence concentrated in the range defined by 0.1 times the seabed thickness above and below the embedded depth. The depth function K i has little effect on seabed liquefaction. In addition, the traditional assumption that treats the seabed parameters as constants may result in the overestimation of the seabed liquefaction depth and the liquefaction area around the cofferdam will be miscalculated if consolidation is not considered. Moreover, parametric studies reveal that the shear modulus at the seabed surface G z 0 has a significant influence on the vertical distribution of the pore pressure. However, the effect of the permeability at the seabed surface K z 0 on the vertical distribution of the pore pressure is mainly concentrated on the seabed above the embedded depth in front and to the side of the cofferdam. Furthermore, the amplitude of pore pressure decreases as Poisson’s ratio μ s increases.

Loads on Ships and Offshore Structures

2007 ◽  
Author(s):  
P. Temarel
Keyword(s):  
State Of The Art ◽  
Fatigue Loading ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Green Water ◽  
Vortex Induced Vibrations ◽  
Ice Loads ◽  
Offshore Industry ◽  
Multi Body ◽  
Wave Induced

The Loads Committee of the International Ship and Offshore Structures Congress (ISSC) critically reviews the state of the art of environmental and operational loads. Amongst these, elements more relevant to the offshore industry will be presented in this paper. These comprise wave-induced loads, including linear and nonlinear methods, multi-body interactions, slamming, green water, sloshing and rogue waves, cables and risers, vortex-induced vibrations, ice loads, fatigue loading and, verification and validation.

A Coupled VOF-Eulerian Multiphase CFD Model to Simulate Breaking Wave Impacts on Offshore Structures

2016 ◽  
Author(s):  
Pietro D. Tomaselli ◽  
Erik Damgaard Christensen
Keyword(s):  
Wave Breaking ◽  
Bubble Column ◽  
Vertical Cylinder ◽  
Air Entrainment ◽  
Offshore Structures ◽  
Laboratory Scale ◽  
Breaking Wave ◽  
Cfd Model ◽  
Bubble Plume ◽  
Wave Induced

Breaking wave-induced loads on offshore structures can be extremely severe. The air entrainment mechanism during the breaking process plays a not well-known role in the exerted forces. This paper present a CFD solver, developed in the Open-FOAM environment, capable of simulating the wave breaking-induced air entrainment. Firstly the model was validated against a bubble column flow. Then it was employed to compute the inline force exerted by a spilling breaking wave on a vertical cylinder in a 3D domain at a laboratory scale. Results showed that the entrained bubbles affected the magnitude of the force partially. Further analyses on the interaction of the bubble plume with the flow around the cylinder are needed.

scholarly journals Neural Networks Applied to the Wave-Induced Fatigue Analysis of Steel Risers

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
João P. R. Cortina ◽  
Fernando J. M. de Sousa ◽  
Luis V. S. Sagrilo
Keyword(s):  
Neural Networks ◽  
Time Series ◽  
Cross Sections ◽  
Computational Cost ◽  
Offshore Structures ◽  
Fatigue Analysis ◽  
Element Analysis ◽  
Long Time ◽  
Wave Induced ◽  
Hybrid Methodology

Time domain stochastic wave dynamic analyses of offshore structures are computationally expensive. Considering the wave-induced fatigue assessment for such structures, the combination of many environmental loading cases and the need of long time-series responses make the computational cost even more critical. In order to reduce the computational burden related to the wave-induced fatigue analysis of Steel Catenary Risers (SCRs), this work presents the application of a recently developed hybrid methodology that combines dynamic Finite Element Analysis (FEA) and Artificial Neural Networks (ANN). The methodology is named hybrid once it requires short time series of structure responses (obtained by FEA) and imposed motions (evaluated analytically) to train an ANN. Subsequently, the ANN is employed to predict the remaining response time series using the prescribed motions imposed at the top of the structure by the floater unit. In this particular work, the methodology is applied aiming to predict the tension and bending moments’ time series at structural elements located at the top region and at the touchdown zone (TDZ) of a metallic riser. With the predicted responses (tensions and moments), the stress time series are determined for eight points along the pipe cross sections, and stress cycles are identified using a Rainflow algorithm. Fatigue damage is then evaluated using SN curves and the Miner-Palmgren damage accumulation rule. The methodology is applied to a SCR connected to a semisubmersible platform in a water depth of 910 m. The obtained results are compared to those from a full FEA in order to evaluate the accuracy and computer efficiency of the hybrid methodology.

A Method to Upgrade Iceberg Velocity Statistics to Include Wave-Induced Motion

1987 ◽  
Vol 109 (3) ◽  
pp. 278-286 ◽  
Author(s):  
J. H. Lever ◽  
D. Sen
Keyword(s):  
Three Dimensional ◽  
Interaction Model ◽  
Environmental Parameters ◽  
Offshore Structures ◽  
Grand Banks ◽  
Drilling Rig ◽  
Velocity Statistics ◽  
Impact Risk ◽  
Induced Motion ◽  
Wave Induced

Iceberg impact design loads for offshore structures can be estimated by incorporating an ice/structure interaction model in a probabilistic framework, or risk analysis. The relevant iceberg and environmental parameters are input in statistical form. Iceberg velocity statistics are usually compiled from drilling rig radar reports, and hence represent estimates of average hourly drift speeds. Yet it is the instantaneous ice velocity which is the relevant input to the simulation of the iceberg/structure collision process. Thus, risk analyses based on mean drift speed distributions will only yield valid results for the subset of conditions where wave-induced iceberg motion is negligible. This paper describes a method which, for the first time, systematically accounts for wave-induced motion in iceberg impact risk analyses. A linear three-dimensional potential flow model is utilized to upgrade iceberg velocity statistics to include the influence of Grand Banks sea-state conditions on instantaneous ice motion. The results clearly demonstrate the importance of including wave-induced motion in iceberg impact risk analyses.

Dynamic Response of Marine Structures

2007 ◽  
Author(s):  
Miroslaw Lech Kaminski ◽  
John Halkyard
Keyword(s):  
Dynamic Response ◽  
Offshore Structures ◽  
Structural Monitoring ◽  
Induced Response ◽  
Random Response ◽  
Marine Structures ◽  
Benchmark Study ◽  
Wave Induced

The paper presents conclusions, recommendations and offshore relevant elements of the report of the Committee II.2 -Dynamic Response as presented and discussed by the authors at the 16th International Ship and Offshore Structures Congress (ISSC 2006) in Southampton, UK, 20–25 August 2006. This includes wave-induced response, fluid impacts, noise and vibrations, explosion and shock, damping, structural monitoring, countermeasures, uncertainties, random response and a benchmark study.

Response of a Simple Tension Leg Platform Model to Wave Forces Calculated at Displaced Position

1984 ◽  
Vol 106 (4) ◽  
pp. 437-443 ◽  
Author(s):  
P. D. Spanos ◽  
V. K. Agarwal
Keyword(s):  
Structural Response ◽  
Offshore Structures ◽  
Wave Forces ◽  
Structural Members ◽  
Tension Leg Platform ◽  
Single Degree Of Freedom ◽  
Numerical Studies ◽  
Simple Tension ◽  
Stochastic Solution ◽  
Wave Induced

A simple single-degree-of-freedom model of a tension leg platform is used to assess the reliability of the common practice of calculating wave-induced forces at the undisplaced position of offshore structures. This assessment is conducted in conjunction with the Morison equation based modeling of the wave-induced forces on slender structural members. It is shown by numerically integrating the equation of motion that the calculation of wave forces on the displaced position of the structure introduces a steady offset component in the structural response. This is valid for either deterministically or stochastically described wave fields. Several parameter studies are conducted. Furthermore, reliable approximate analytical deterministic and stochastic solution techniques are developed which conform to and, in fact, predict the conclusions drawn from the results of the numerical studies.

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