Hydroelastic Responses of Pontoon and Semi-Submersible Types of Very Large Floating Structure in Regular Head Waves

2002 ◽  
Author(s):  
T. S. Phan ◽  
P. Temarel
Keyword(s):  
Three Dimensional ◽  
Source Distribution ◽  
Mode Shapes ◽  
Floating Structure ◽  
Floating Structures ◽  
Hydrodynamic Damping ◽  
Very Large Floating Structure ◽  
Head Waves ◽  
Interaction Problem ◽  
Regular Head Waves

The symmetric dynamic behaviour of two types of Very Large Floating Structure (VLFS) is investigated. The structures are of pontoon (or mat like) and semi-submersible type and have the same beam, length and displacement. The responses for these stationary and free-floating structures in regular head waves are investigated using the three-dimensional hydroelasticity theory, applicable to structures with arbitrary shape. The “dry analysis” is carried out by discretising the structures using beam and shell finite elements, as appropriate. The solution of the fluid-structure interaction problem is achieved through a pulsating source distribution whereby the mean wetted surface of either structure is discretised using four-cornered panels. The symmetric dynamic characteristics of both structures are compared, both in vacuo (e.g. natural frequencies and mode shapes) and in water (e.g. generalised added mass and hydrodynamic damping). Predicted responses such as vertical deflections and direct stresses, in regular head waves, are also discussed and compared.

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.

Numerical Research on FPSOs With Green Water Occurrence

2009 ◽  
Vol 53 (01) ◽  
pp. 7-18
Author(s):  
Renchuan Zhu ◽  
Guoping Miao ◽  
Zhaowei Lin
Keyword(s):  
Three Dimensional ◽  
Green Water ◽  
Floating Body ◽  
Incoming Wave ◽  
Model Case ◽  
Floating Structures ◽  
Design And Optimization ◽  
Head Waves ◽  
Wave Heights ◽  
The Impact

Green water loads on sailing ships or floating structures occur when an incoming wave significantly exceeds freeboard and water runs onto the deck. In this paper, numerical programs developed based on the platform of the commercial software Fluent were used to numerically model green water occurrence on floating structures exposed to waves. The phenomena of the fixed floating production, storage, and offloading unit (FPSO) model and oscillating vessels in head waves have been simulated and analyzed. For the oscillating floating body case, a combination idea is presented in which the motions of the FPSO are calculated by the potential theory in advance and computional fluid dynamics (CFD) tools are used to investigate the details of green water. A technique of dynamic mesh is introduced in a numerical wave tank to simulate the green water occurrence on the oscillating vessels in waves. Numerical results agree well with the corresponding experimental results regarding the wave heights on deck and green water impact loads; the two-dimensional fixed FPSO model case conducted by Greco (2001), and the three-dimensional oscillating vessel cases by Buchner (2002), respectively. The research presented here indicates that the present numerical scheme and method can be used to actually simulate the phenomenon of green water on deck, and to predict and analyze the impact forces on floating structures due to green water. This can be of great significance in further guiding ship design and optimization, especially in the strength design of ship bows.

scholarly journals Hydrodynamic Zone of Influence Due to a Floating Structure in a Fjordal Estuary—Hood Canal Bridge Impact Assessment

2018 ◽  
Vol 6 (4) ◽  
pp. 119 ◽  
Author(s):  
Tarang Khangaonkar ◽  
Adi Nugraha ◽  
Taiping Wang
Keyword(s):  
Near Field ◽  
Juvenile Fish ◽  
Three Dimensional ◽  
Floating Structure ◽  
Floating Structures ◽  
Hood Canal ◽  
Data Collection Program ◽  
Zone Of Influence ◽  
Floating Bridge ◽  
Ambient Currents

Floating structures such as barges and ships affect near-field hydrodynamics and create a zone of influence (ZOI). Extent of the ZOI is of particular interest due to potential obstruction to and impact on out-migrating juvenile fish. Here, we present an assessment of ZOI from Hood Canal (Floating) Bridge, located within the 110-km-long fjord-like Hood Canal sub-basin in the Salish Sea, Washington. A field data collection program allowed near-field validation of a three-dimensional hydrodynamic model of Hood Canal with the floating bridge section embedded. The results confirm that Hood Canal Bridge, with a draft of 4.6 m covering ~85% of the width of Hood Canal, obstructs the brackish outflow surface layer. This induces increased local mixing near the bridge, causes pooling of water (up-current) during ebb and flood, and results in shadow/sheltering of water (down-current). The change in ambient currents, salinity, and temperature is highest at the bridge location and reduces to background levels with distance from the bridge. The ZOI extends ~20 m below the surface and varies from 2–3 km for currents, from 2–4 km for salinity, and from 2–5 km for temperature before the deviations with the bridge drop to <10% relative to simulated background conditions without the bridge present.

The Prediction of the Added Resistance for the Trimaran Ship With Different Side Hull Arrangements in Waves

2009 ◽  
Vol 53 (04) ◽  
pp. 227-235
Author(s):  
Ming-Chung Fang ◽  
Yi-Chin Wu ◽  
Deng-Kai Hu ◽  
Zi-Yi Lee
Keyword(s):  
Steady State ◽  
Steady Flow ◽  
Three Dimensional ◽  
Prediction Method ◽  
Source Distribution ◽  
Added Resistance ◽  
Distribution Method ◽  
Related Data ◽  
Head Waves ◽  
Flow Potential

In this paper, a second-order steady-state approach and a three-dimensional pulsating source distribution method are applied to derive the added resistance on a trimaran ship advancing in waves. The added resistance treated here is the secondorder steady-state hydrodynamic force, which can be expressed as products of the ship-motion responses, the radiation potential, diffraction potential, and the incident wave potential, and all related velocity potentials are in three-dimensional form. The steady flow potential is also included in the motion response calculation to investigate its effect on the added resistance. In order to validate the prediction method, the experiments for measuring the added resistance of a trimaran model in head waves were also handled in a National Cheng Kung University (NCKU) towing tank, and the related data are adopted to compare with the theoretical results. The comparisons show that the prediction results obtained in the paper generally agree well with experimental data; the validity of the prediction method applied here can be regarded as acceptable, and the effect of the steady flow potential on the added resistance of the trimaran ship can be neglected.

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.

Effects of Aircushion Division to Hydroelastic Responses of an Aircushion Type Very Large Floating Structure

2003 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Hisaaki Maeda ◽  
Chang-Kyu Rheem
Keyword(s):  
Water Waves ◽  
Final Section ◽  
Three Dimensional ◽  
Offshore Structure ◽  
Floating Structure ◽  
Distribution Method ◽  
Steady Wave ◽  
Elastic Deflection ◽  
Momentum Theory ◽  
Very Large Floating Structure

A target offshore structure in this study is an aircushion supported very large floating structure. The aircushion type VLFSs behave elastically in water waves. Corresponding aircushions are very large or relatively small size. The VLFSs considered in this study are supported by a large aircushion, two aircushions, or several module aircushions. The zero-draft theory is applied to the prediction of the hydrodynamic forces. The zero-draft theory is based on the pressure distribution method. The elastic deflection predicted by the zero-draft method is compared with that by another three-dimensional method in order to confirm the validity of it. In addition, the steady wave drifting forces on VLFSs with the aircushion are shown and their characteristics are examined. Then, the momentum theory is applied to the prediction. In the final section, effects of aircushion division to the elastic deflection and the wave drifting force are investigated. From the results, it is confirmed that the elastic deflection is can be reduced in the specification relation between the wavelength and the length of a module aircushion. In addition, it is possible to ajust the aircushion setting in order to simultaneously reduce the elastic deflection and the steady wave drifting force of the aircushion type VLFS on the case.

An Enhanced 1-Way Coupling Method to Predict Elastic Global Hull Girder Loads

2014 ◽  
Author(s):  
Jens Ley ◽  
Ould el Moctar
Keyword(s):  
Finite Element ◽  
Finite Volume ◽  
Structural Response ◽  
Coupling Method ◽  
Mode Shapes ◽  
Fe Model ◽  
Element Analysis ◽  
Hull Girder ◽  
Hydrodynamic Damping ◽  
Head Waves

This paper introduces a numerical method to predict global hull girder loads of sea-going vessels, taking into account the structural elasticity. A field method based on a Finite Volume discretisation is applied to simulate the nonlinear rigid ship motions and provides the external loads at the hull surface. The structural response is computed in a full transient 3D-Finite-Element Analysis. The lowest global structural mode shapes and eigenfrequencies are covered by the 3D-FE model. The mapping between the Finite Volume mesh and Finite Element grid, is performed by the Mesh-Based Code Coupling Interface (MpCCI). As long as only global vertical bending modes are considered, simplified beam models may sufficiently cover the structural response. However, the use of the 3D-FE model is motivated by the prediction of the global torsional and local loads that are influenced by hydroelastic effects. A 1-way coupling method is applied. To account for hydromass effects, the Finite-Element model is enhanced by acoustic elements. Acoustic wave equations are solved to simulate the sound wave propagation in water and to obtain realistic eigenfrequencies of the wetted hull. Structural and hydrodynamic damping is controlled by the Rayleigh-Damping method. Simulations are performed for an ultra large container vessel sailing in regular head waves. The computed time histories of the vertical bending moment are compared with experimental data and with numerical simulations using a strong 2-way coupling simulation that employs a Finite-Element Timoshenko-Beam.

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.

scholarly journals Hydroelasticity of the barge near island affected by bathymetry based on THAFTS software

2019 ◽  
Vol 234 (1) ◽  
pp. 48-58
Author(s):  
Ye Lu ◽  
Pandeli Temarel ◽  
Ye Zhou ◽  
Chao Tian
Keyword(s):  
Shallow Water ◽  
Three Dimensional ◽  
Water Area ◽  
Dynamic Responses ◽  
Response Analysis ◽  
Three Dimension ◽  
Floating Structure ◽  
Floating Structures ◽  
Hydroelastic Analysis ◽  
Water Depths

Floating structures are sometimes deployed in shallow water areas close to reefs and islands as facilities serving tourists. In contrast to the open sea, the marine environment, such as wave and current, in the nearshore shallow water area will be affected by the non-uniform complex seabed bottom, and the hydrodynamic interaction between the floating structure and the seabed bathymetry should be investigated, instead of being ignored as the case when a uniform seabed is assumed. A hydroelastic analysis method for slowly varying water depths is proposed to calculate the hydroelastic responses of the floating structures, considering the seabed as a fixed boundary condition. This method was integrated into the software THAFTS (Three Dimension Hydroelastic Analysis of Floating and Translating, developed by China Ship Scientific Research Center). Based on the THAFTS software, the three-dimensional hydroelastic motion response analysis of a barge is carried out, in which the effects of different water depths and the complex bathymetry are investigated by comparing the results of the motion and structural responses of the barge. The stress distribution of the barge with the effect of the bathymetry taken into account is presented in this article as well as the modal stresses. The strength evaluation of the barge indicates that the effect of the inhomogeneous seabed plays a large role in the dynamic responses of the barge when it is deployed near reefs.

scholarly journals WAVE INDUCED COUPLED MOTIONS AND STRUCTURAL LOADS BETWEEN TWO OFFSHORE FLOATING STRUCTURES IN WAVES

Brodogradnja ◽  
2018 ◽  
Vol 69 (3) ◽  
pp. 149-173
Author(s):  
Mun Sung Kim ◽  
◽  
Kwang Hyo Jung ◽  
Sung Boo Park ◽  
Keyword(s):  
Three Dimensional ◽  
Hydrodynamic Pressure ◽  
Source Distribution ◽  
Wave Loads ◽  
Gas Field ◽  
Offshore Area ◽  
Floating Structures ◽  
Motion Responses ◽  
Induced Motion ◽  
Wave Induced

As oil or gas field moves deeper offshore area, offshore offloading operations such as Tandem or Side-by-Side arrangement between two floating structures take place in many locations throughout the world and also have many hydrodynamic problems. Therefore, the researches on the motion response and hydrodynamic force including first and second order between two floating structures are needed to have the more safe offloading operability in waves. In this paper, prediction of wave induced motion responses and structural loads at mid-ship section with hydrodynamic interaction effect between two offshore floating structures in various heading waves are studied by using a linearized three-dimensional potential theory. Numerical calculations using three-dimensional pulsating source distribution techniques have been carried out for hydrodynamic pressure distribution, wave exciting force, twelve coupled linear motion responses, relative motions and wave loads of the barge and the ship in oblique waves. The computational results give a good correlation with the experimental results and also with other numerical results. As a result, the present computational tool can be used effectively to predict the wave induced motions and structural loads of multiple offshore floating structures in waves.

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