Motion Responses of Floating Structures Near Small Islands

2015 ◽  
Author(s):  
Peng Yang ◽  
Xuekang Gu ◽  
Chao Tian ◽  
Xiaolong Liu
Keyword(s):  
Water Depth ◽  
Wave Force ◽  
Wave Pattern ◽  
Far Field ◽  
Small Islands ◽  
Hydrodynamic Coefficients ◽  
Floating Structure ◽  
Floating Structures ◽  
Seabed Topography ◽  
Motion Responses

The seabed topography near small islands is usually in rugged state, and the water depth can be changed from tens of meters to a few meters in a short distance. Far field waves advancing towards the shore will experience a complex evolution on the shoal. In this environment, the hydrodynamic responses of a floating structure will be largely affected by the non-uniform wave pattern and changeable seabed, and might be quite different from the general responses of a platform in waves with uniform water depth. In this paper, a coupling hydrodynamic model of floating structures and reef topography was established; the incident wave force, diffraction force, radiation hydrodynamic coefficients, motions of a floating structure were calculated. The model was validated by comparing the predicted results with that of model tests. It is indicated that complex seabed topography has a significant influence on the hydrodynamic responses of the floating structure. Moreover, the motions are increased obviously in certain wave periods, with reference to that in far field waves.

Hydrodynamic coefficients of a floater near a partially reflecting seawall in the presence of an array of caisson blocks

2021 ◽  
pp. 1-23
Author(s):  
K G Vijay ◽  
Santanu Koley ◽  
Kshma Trivedi ◽  
Chandra Shekhar Nishad
Keyword(s):  
Wave Scattering ◽  
Structural Parameters ◽  
Wave Force ◽  
Vertical Force ◽  
Hydrodynamic Coefficients ◽  
Floating Structure ◽  
Surface Gravity Wave ◽  
Damping Coefficients ◽  
Half Wavelength ◽  
Scattering And Radiation

Abstract In the present study, surface gravity wave scattering and radiation by a freely floating rectangular buoy placed near a partially reflecting seawall and in the presence of an array of caisson blocks are analyzed. Various hydrodynamic parameters related to the wave scattering and radiation, such as the added mass and radiation damping coefficients, correspond to sway, heave and roll motions of the floating buoy, horizontal force, vertical force and moment acting on the floating structure, and horizontal wave force acting on the partially reflecting seawall are studied for a variety of wave and structural parameters. The study reveals that the resonating pattern in various hydrodynamic coefficients occurs for moderate values of the wavenumber. Further, when the distance between the floater and the sidewall is an integral time of half wavelength, the resonating behavior in the sway, heave and roll added masses, and associated damping coefficients appears, and the aforementioned hydrodynamic coefficients change rapidly around this zone. These resonance phenomena can be diminished significantly with appropriate positioning of the floater with respect to the sidewall and in the presence of partially reflecting seawall.

Hydrodynamic Interaction of Floating Structure in Regular Waves

2014 ◽  
Vol 66 (2) ◽  
Author(s):  
Hassan Abyn ◽  
Adi Maimun ◽  
Jaswar Jaswar ◽  
M. Rafiqul Islam ◽  
Allan Magee ◽  
...  
Keyword(s):  
Hydrodynamic Interaction ◽  
Oil And Gas ◽  
Irregular Waves ◽  
Source Distribution ◽  
Floating Bodies ◽  
Floating Structure ◽  
Distribution Method ◽  
Floating Structures ◽  
Motion Responses ◽  
Hydrodynamics Coefficients

Floating structures play an important role for exploring the oil and gas from the sea. In loading and offloading, motion responses of offshore floating structures are affected through hydrodynamic interaction. Large motions between floating bodies would cause the damage of moorings, offloading system and may colloid to each other. This research studies on hydrodynamic interaction between Tension Leg Platform (TLP) and Semi-Submersible (Tender Assisted Drilling (TAD)) in regular and irregular waves with scenario as follows: fixed TLP and 6-DOF floating semi-submersible and 6-DOF both TLP and semi-submersible. Under these conditions, hydrodynamics coefficients, mooring and connectors forces, motions and relative motions of TLP and Semi-Submersible will be simulated numerically by using 3D source distribution method. As the scope is big, this paper only presents model experiment of floating TLP and semi-submersible in the regular wave. The experiment is carried out in the UTM Towing Tank.

Numerical Investigation on Interaction Between a Semi-Submersible Platform and its Mooring System

2015 ◽  
Author(s):  
Yuanchuan Liu ◽  
Yao Peng ◽  
Decheng Wan
Keyword(s):  
Mooring Line ◽  
Mooring System ◽  
Floating Structure ◽  
Mooring Lines ◽  
Flow Solver ◽  
Floating Structures ◽  
Marine Renewable Energy ◽  
Motion Responses ◽  
Increasing Demand ◽  
Energy Engineering

With the increasing demand of floating structures in offshore, coastal and marine renewable energy engineering, the interaction between the mooring system and floating structure becomes more and more important. In this paper, motion responses of a semi-submersible platform with mooring system under regular wave conditions are investigated numerically by a viscous flow solver naoe-FOAM-SJTU based on the open source toolbox OpenFOAM. Influence of the mooring system on the platform motion responses is evaluated in two different ways. Investigations are covered for analysis methods adopted for solving mooring lines and the length of each part of a multi-component mooring line. Several important conclusions are drawn.

Analysis on Motions and Green Water of FPSOs in Shallow Water With Non-Collinear Environments

2010 ◽  
Author(s):  
Bin Guo ◽  
Long Fei Xiao ◽  
Jian Min Yang
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Wind Waves ◽  
Single Point ◽  
Green Water ◽  
Floating Structure ◽  
Floating Structures ◽  
Head Waves ◽  
Run Up ◽  
Yaw Angle

The paper presents motions and green water of a FPSO in shallow water with different wave headings. In non-collinear directions of wind, waves and current, the FPSO does not always encounter head waves, which probably induces specialties in motions and green water especially because of the complexity of shallow water hydrodynamics. Time-domain numerical simulation and model test are carried out in order to analyze motions of a single-point moored FPSO. Green water and wave run-up along the side of a fixed FPSO are simulated in a 3-D numerical wave tank, and results are compared with that of model tests. It is shown that the influence of the yaw angle on motions of a FPSO is considerable and green water occurs more frequently around the mid-ship when the FPSO encounters a big wave heading. In the same water depth, roll and pitch motions of the FPSO under higher wave are lower instead but green water occurs; in the same wave situation, the motions of the FPSO in a lower water depth are lower, but green water occurs more severely. In general, water depth has an important influence on green water of FPSOs in shallow water. The hydrodynamic character of large floating structures in shallow water, especially the green water, should be taken into account carefully for determining the design load and freeboard of a large floating structure.

Oscillating Wave Surge Converter-Type Attachment for Extracting Wave Energy While Reducing Hydroelastic Responses of Very Large Floating Structures

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
H. P. Nguyen ◽  
C. M. Wang
Keyword(s):  
Wave Energy ◽  
Wave Force ◽  
Mooring System ◽  
Energy Converter ◽  
Floating Structure ◽  
Incident Wavelength ◽  
Floating Structures ◽  
Horizontal Wave ◽  
Horizontal Wave Force ◽  
Better Than

Abstract This paper presents an oscillating wave surge converter (OWSC)-type attachment, comprising a submerged vertical flap connected to the fore edge of a very large floating structure (VLFS) with hinges and linear power take-off (PTO) systems, for extracting wave energy while reducing hydroelastic responses of VLFS. In terms of reductions in hydroelastic responses of VLFS, the OWSC-type attachment is better than the recently proposed raft wave energy converter (WEC)-type attachment for relatively short waves (T < 7 s) and better than the conventional anti-motion device comprising a submerged vertical flap rigidly connected to the fore edge of VLFS for all wave periods. Importantly, the horizontal wave force acting on the submerged flap for the OWSC-type attachment is smaller than that for the conventional anti-motion device, leading to a more economical mooring system. In terms of wave energy extraction, the OWSC-type attachment is better than the raft WEC-type attachment for intermediate and long waves (T ≥ 7 s). In addition, for maximizing power production, the required flap length for the OWSC-type attachment is much smaller than the required pontoon length for the raft WEC-type attachment (about λ/10 as compared to about λ/3, where λ is the incident wavelength).

A Numerically Efficient Method for Analysis of Very Large Articulated Floating Structures

1998 ◽  
Vol 42 (03) ◽  
pp. 174-186
Author(s):  
C. J. Garrison
Keyword(s):  
Hydrodynamic Interaction ◽  
Near Field ◽  
Three Dimensional ◽  
Computational Effort ◽  
Floating Structure ◽  
Complete Structure ◽  
Field Interaction ◽  
Floating Structures ◽  
Computing Effort ◽  
The Individual

A method is presented for evaluation of the motion of long structures composed of interconnected barges, or modules, of arbitrary shape. Such structures are being proposed in the construction of offshore airports or other large offshore floating structures. It is known that the evaluation of the motion of jointed or otherwise interconnected modules which make up a long floating structure may be evaluated by three dimensional radiation/diffraction analysis. However, the computing effort increases rapidly as the complexity of the geometric shape of the individual modules and the total number of modules increases. This paper describes an approximate method which drastically reduces the computational effort without major effects on accuracy. The method relies on accounting for hydrodynamic interaction effects between only adjacent modules within the structure rather than between all of the modules since the near-field interaction is by far the more important. This approximation reduces the computational effort to that of solving the two-module problem regardless of the total number of modules in the complete structure.

Feasibility of Using Stress Joint in an Existing Flexible Joint Receptacle for a Deepwater SCR

2009 ◽  
Author(s):  
Basim Mekha ◽  
Alok Kumar ◽  
Mike Stark ◽  
Paul Barnett
Keyword(s):  
Bending Moment ◽  
Flexible Joints ◽  
Floating Structure ◽  
Element Analysis ◽  
Flexible Joint ◽  
Floating Structures ◽  
Operational Problem ◽  
Hull Structure ◽  
Hull Design ◽  
Titanium Material

In recent years, most fluid produced or exported has been transported using steel catenary risers (SCRs) attached to deepwater floating structures. The SCRs are terminated at the floating structures using Top Termination Units (TTUs) such as flexible joints or tapered stress joints. The flexible joints are usually designed to allow the riser to rotate with the floating structure motion and reduce the amount of moments transferred to the hull structure. The flexible joints depend on the flexibility and compressibility of the elastomer layers to allow for the rotation of the SCR. The stress joints, alternatively, provide fixed support at the hull and thus larger bending moment that has to be accounted for in the hull design. The stress joints can be made of steel or titanium material. The SCR TTU’s receptacle, which will be welded to the hull porch and contains the TTU basket, has to be designed to meet the force and reaction requirements associated with the selected TTU type. However, in some cases which could be due to failure of the TTU to meet the expected life or the operational requirements, the operators may have to replace the damaged TTU with another one or with a different TTU type. A few examples are available in the Gulf of Mexico. Recently the Flexible Joint TTU of the Independent Hub 20-inch export SCR had an operational problem. During the course of investigating the related issues and studying possible solutions, one option considered was the feasibility of replacing the Flexible Joint (FJ) with Titanium Tapered Stress Joint (TSJ). This paper highlights the issues that have to be considered in the design of the FJ existing receptacle to accommodate the force reactions of a Titanium TSJ. These issues are addressed and the results of the detailed finite element analysis performed are provided. The analysis conclusions, which are related to the feasibility of the existing receptacle to receive the loads imposed by TSJ and the modifications required to achieve this, are presented.

Wave-Island Interactions About Circular Artificial Islands

1984 ◽  
Vol 106 (1) ◽  
pp. 113-119 ◽  
Author(s):  
J. M. Niedzwecki
Keyword(s):  
Closed Form ◽  
Water Depth ◽  
Wave Breaking ◽  
Numerical Procedure ◽  
Wave Pattern ◽  
The Arctic ◽  
Ray Theory ◽  
Closed Form Solutions ◽  
Wave Patterns ◽  
Dimensionless Formulation

The behavior of waves interacting with islands has gained renewed interest with the construction of exploratory drilling islands in the Arctic. This paper focuses upon the behavior of waves incident upon axisymmetric islands characterized by circular contours which vary with water depth. The island profiles of Arthur and Pocinki, which have closed form solutions, and a single tier conical island are examined. A new dimensionless formulation of Arthur’s ray theory and an extremely accurate numerical procedure to evaluate the ray integrals are presented. It is shown that each island profile leads to a distinct wave pattern about the island. These wave patterns are presented in figures which portray the wave capture and wave breaking about circular islands. It is intended that the methodology presented be used to initially assess trends and to evaluate the need for more refined analyses.

scholarly journals Experimental Investigation on Hydrodynamic Coefficients of a Column-Stabilized Fish Cage in Waves

2019 ◽  
Vol 7 (11) ◽  
pp. 418
Author(s):  
Zhao ◽  
Chen ◽  
Bi ◽  
Cui
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Drag Force ◽  
Inertial Force ◽  
Element Model ◽  
Wave Force ◽  
Hydrodynamic Coefficients ◽  
Horizontal Wave ◽  
Horizontal Wave Force ◽  
The Finite Element Model

This study on hydrodynamic coefficients of a column-stabilized fish cage under wave action plays an important role in the anti-wave design of cages. The regular wave test was used to study the horizontal wave force of the jacket and column-stabilized fish cage under different wave heights, periods, and incident angles; the finite element model of the jacket and the column-stabilized fish cage was established according to the test model. On the basis of the calculation of the finite element model, combined with the wave force obtained from the experiment, the hydrodynamic coefficients of the structure was fitted by the least squares method, and then the drag force, inertial force, and total force of the structure under different conditions were calculated. The results show that the hydrodynamic coefficients of the jacket and netting under the wave condition were more obvious with the change of the KC number and wave incident angles. And as the wave height increased, the drag force, the inertial force, and the proportion of the drag force to the horizontal wave force both increased. When the wavelength was large, the same trend occured as the wave period increased. When the wave incident angles were different, the forces of the jacket and the column-stabilized fish cage were always small in lateral low-frequency waves, which is consistent with the change law of hydrodynamic coefficients of the jacket and netting.

Very Large Floating Structures

2007 ◽  
Author(s):  
H. Suzuki ◽  
H. R. Riggs ◽  
M. Fujikubo ◽  
T. A. Shugar ◽  
H. Seto ◽  
...  
Keyword(s):  
Design Procedure ◽  
Offshore Structures ◽  
Floating Structure ◽  
Floating Structures ◽  
Design Procedures ◽  
Novel Technology ◽  
Hydroelastic Analysis ◽  
Behavior Design ◽  
Hydroelastic Response ◽  
Near Future

Very Large Floating Structure (VLFS) is a unique concept of ocean structures primary because of their unprecedented length, displacement cost and associated hydroelastic response. International Ship and Offshore Structures Congress (ISSC) had paid attention to the emerging novel technology and launched Special Task Committee to investigate the state of the art in the technology. This paper summarizes the activities of the committee. A brief overview of VLFS is given first for readers new to the subject. History, application and uniqueness with regard to engineering implication are presented. The Mobile Offshore Base (MOB) and Mega-Float, which are typical VLFS projects that have been investigated in detail and are aimed to be realized in the near future, are introduced. Uniqueness of VLFS, such as differences in behavior of VLFS from conventional ships and offshore structures, are described. The engineering challenges associated with behavior, design procedure, environment, and the structural analysis of VLFS are introduced. A comparative study of hydroelastic analysis tools that were independently developed for MOB and Mega-Float is made in terms of accuracy of global behavior. The effect of structural modeling on the accuracy of stress analysis is also discussed. VLFS entails innovative design methods and procedure. Development of design criteria and design procedures are described and application of reliability-based approaches are documented and discussed.

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