Analysis of Catenary Mooring Systems Based on Truncated Mooring Experiments

2018 ◽  
Author(s):  
Sheng Xu ◽  
Chunyan Ji ◽  
C. Guedes Soares
Keyword(s):  
Water Depth ◽  
Model Tests ◽  
Mooring System ◽  
Coupled Dynamic Analysis ◽  
Motion Responses ◽  
Wave Basin ◽  
Six Dof ◽  
Floating Systems ◽  
Fully Coupled ◽  
Reasonable Model

Considering the activities of floating systems pushing to the ultra-deepwater, the full scale mooring system needs to be truncated in order to carry out model tests in wave basin with reasonable model scale. In this paper, a Semi-Submersible moored by a catenary mooring system, which operates in 1500m water depth is truncated at 200m water depth. The mooring induced damping of truncated mooring system and prototype mooring system in 100 year typhoon condition in South China Sea are studied experimentally and numerically. The de-couple technique is applied to obtain truncated mooring damping, which is implemented by inputting the vessel six DOF motion responses and solving the mooring tensions, then decompose mooring tension in x, y and z directions. The vessel six DOF motion responses were measured in the model tests. For the full depth mooring system, the fully coupled dynamic analysis is carried out to study mooring induced damping. The results of truncated mooring damping will be compared with full depth mooring damping.

Experimental and Numerical Study on Large Truncation of Deepwater Mooring Line

2009 ◽  
Author(s):  
Yihua Su ◽  
Jianmin Yang ◽  
Longfei Xiao ◽  
Gang Chen
Keyword(s):  
Dynamic Response ◽  
Water Depth ◽  
Numerical Study ◽  
Unit Length ◽  
Low Frequency ◽  
Model Tests ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Wave Basin

Modeling the deepwater mooring system in present available basin using standard Froude scaling at an acceptable scale presents new challenges. A prospective method is to truncate the full-depth mooring lines and find an equivalent truncated mooring system that can reproduce both static and dynamic response of the full-depth mooring system, but large truncation arise if the water depth where the deepwater platform located is very deep or the available water depth of the basin is shallow. A Cell-Truss Spar operated in 1500m water depth is calibrated in a wave basin with 4m water depth. Large truncation arises even though a small model scale 1:100 is chosen. A series of truncated mooring lines are designed and investigated through numerical simulations, single line model tests and coupled wave basin model tests. It is found that dynamic response of the truncated mooring line can be enlarged by using larger diameter and mass per unit length in air. Although the truncated mooring line with clump presents a “taut” shape, its dynamic characteristics is dominated by the geometry stiffness and it underestimates dynamic response of the full-depth mooring line, even induces high-frequency dynamic response. There are still two obstacles in realizing dynamic similarity for the largely truncated mooring system: lower mean value of the top tension of upstream mooring lines, and smaller low-frequency mooring-induced damping.

FourStar™ Dry-Tree Semisubmersible Development

2010 ◽  
Author(s):  
Neil Williams ◽  
Steve Leverette ◽  
Sean Bian ◽  
Sean Large ◽  
Peimin Cao
Keyword(s):  
Water Depth ◽  
Model Tests ◽  
Wave Basin

This paper discusses the development of a dry-tree semisubmersible (DTS) platform concept appropriate for deployment in non-hurricane/non-cyclonic environments worldwide, and the verification of the concept through wave basin model tests. An example configuration is presented for an application in 2,100 m water depth offshore Brazil.

The Ocean Cleanup System 001 Performance During Towing and Seakeeping Tests

2019 ◽  
Author(s):  
Joost Sterenborg ◽  
Nicola Grasso ◽  
Rogier Schouten ◽  
Arjen Tjallema
Keyword(s):  
Fluid Structure Interaction ◽  
Model Tests ◽  
Operating Conditions ◽  
Image Correlation ◽  
Plastic Pollution ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Wave Basin ◽  
Floating System ◽  
Floating Systems

Abstract One of the aims of The Ocean Cleanup is to develop technologies to extract plastic pollution from the world’s oceans. Several concepts of passive floating systems were considered that are supposed to confine plastics to ease their collection. Such concepts consist of a floating member and a submerged flexible skirt and have in common that their span is generally more than 500 meters. Consequently, fluid-structure interaction plays an important role in the response of such a floating system. To support numerical simulations, MARIN carried out extensive model tests on a 120 meter system section of the final concept, with focus on the fluid-structure interaction (FSI) of the submerged skirt in operating conditions and in towing configuration. The ability to capture plastics was not investigated in these model tests. Novel for wave-basin tests were non-intrusive measurements using underwater Digital Image Correlation (DIC) to obtain the displacements and deformations of the flexible skirt. DIC proved to be a capable measurement technique for this type of structure in combination with a wave basin. Detailed quantitative data on skirt motions and deformations were delivered and the last concept of the cleanup system was tested in the towing configuration and operational configuration.

Time-Domain Coupled Dynamic Analysis of Mooring Systems in Extreme Sea Condition

2018 ◽  
Author(s):  
Xuliang Han ◽  
ShiSheng Wang ◽  
Bin Xie ◽  
Wenhui Xie ◽  
Weiwei Zhou
Keyword(s):  
Dynamic Analysis ◽  
Body Surface ◽  
Time Domain ◽  
Mooring Line ◽  
Mooring System ◽  
Dynamic Coupling ◽  
Spar Platform ◽  
Coupled Dynamic Analysis ◽  
Motion Responses ◽  
The Time Domain

In order to predict the coupled motion and external wave load for the design of deepwater floating structure system, based on the three-dimensional time-domain potential flow theory, this paper present the indirect time-domain dynamic coupling method and the body nonlinear dynamic coupling method. The perturbation expansion theory is adopted to evaluate hydrodynamic on the fixed mean wetted body surface for the former method. The transient free surface Green function has been extended and applied to calculate the nonlinear hydrodynamic on the instantaneous wetted exact body surface for the latter method. The finite element model is employed to solve dynamic response of mooring line. Then asynchronous coupled method is adopted to achieve the coupled dynamic analysis of platform and mooring lines. The time-domain motion responses and spectrum analysis of Spar platform are verified and compared with the traditional indirect time-domain coupling dynamic method when the mooring system is completed. Also the time-domain motion responses and statistical characteristic of Spar platform are investigated with one mooring line broken in extreme sea condition. Some conclusions are obtained, that is, dynamic coupling effects are significant and transient position hydrodynamic calculation of platform has a great influence on the low frequency motion. The results also show that the influence on the global performance of mooring system is different when the broken line is in different place. A remarkable influence occurs when the broken mooring line is in the head-wave direction.

Experimental Determination of Resonant Response in the Narrow Gap Between Two Side-by-Side Fixed Bodies in Deep Water

2016 ◽  
Author(s):  
Wenhua Zhao ◽  
Hugh Wolgamot ◽  
Scott Draper ◽  
Paul H. Taylor ◽  
Rodney Eatock Taylor ◽  
...  
Keyword(s):  
White Noise ◽  
Numerical Simulations ◽  
Water Depth ◽  
Deep Water ◽  
Model Tests ◽  
Full Scale ◽  
Resonance Phenomenon ◽  
Resonant Response ◽  
Gap Resonance ◽  
Wave Basin

Floating liquefied natural gas (FLNG) facilities are a new type of offshore structure, which have been developed as a game changer in offshore hydrocarbon development for unlocking stranded gas reserves. One of the key challenges associated is offloading from FLNG facilities to LNG carriers. Offloading may proceed with vessels in a side-by-side configuration, which allows offtake by un-modified vessels and minimizes requirements for new hardware or procedures (e.g. compared to a tandem operation). Significant challenges remain, however, and reliable offloading is critical for successful FLNG implementation. In this scenario, the two vessels are separated by a narrow 4 m wide gap. The resonant response of the sea surface in the gap has been predicted by numerical simulations [1] to be a few times that of the incident waves at particular frequencies. As a consequence, the gap resonant response may play a role in determining the operational window for side-by-side offloading operations, and thus has attracted a lot of attention recently. There have been studies on this topic both numerically and experimentally. However, many of these studies are in 2 dimensions (2D), for relatively large gaps and relatively shallow water depth, which may pose difficulties when extending the results to a real project. It is unclear what will happen for a gap resonance if the gap width gets narrower (say 4 m in full scale) and the water depth gets deeper (say 600 m in full scale). In this study, we conducted a series of model tests at a scale of 1:60 in a large wave basin, and focused on deep water and, crucially, narrow gaps, which are closer to a real project geometry. To facilitate future numerical simulations, we used two identical fixed bodies in the model tests and the vessels were simple barge-like shapes. Using white noise waves as the excitation, which covers a broad brand, the response of the fluid in the gap has been measured at several points. In these experiments, different modes of the gap resonance have been observed. Response amplitude operators (RAOs) of the gap resonance have been obtained through spectral analyses, which provide valuable information for the design of side-by-side operations and will benefit future numerical simulations. Test runs in white noise waves with different significant wave heights were also performed, to study the nonlinearities of the gap resonance phenomenon.

Experimental Study of Hydrodynamic Responses of a Single Floating Storage Tank With Internal Fluid

2017 ◽  
Author(s):  
Zhang Chi ◽  
Allan R. Magee ◽  
Wan Ling ◽  
Chien Ming Wang ◽  
Øyvind Hellan
Keyword(s):  
Shallow Water ◽  
Model Tests ◽  
Constant Current ◽  
Single Model ◽  
Floating Structure ◽  
Drag Forces ◽  
Oil Storage ◽  
Internal Fluid ◽  
Wave Basin ◽  
Six Dof

When floating structure with internal fluid compartment is close to other structures, the multibody interaction problem needs to be addressed in addition to the internal fluid influence. Furthermore, shallow water effects become important, especially when the gap between the floating structure and the sea floor is small. These issues are encountered when designing a novel floating oil storage facilities in nearshore area. To investigate these issues, floating models under 1:50 scale are built to perform model tests. The test set-up uses a set of flexible constraints working as fenders placed on frames to restrain the motions of the models in the horizontal plane. Various tests in waves are carried out to measure motion responses of single model in waves with different filling levels and stiffness of “fenders”. The reaction forces on the “fenders” are also measured. Several regular wave conditions are selected to perform tests on double model system to investigate multibody interactions under the influence of internal fluid and effects of waves between the tanks. The drag forces for both single model and double models are measured by performing model tests under constant current from different directions, to check the shielding effects. The tests are performed in shallow-water wave basin, and the constant currents tests are performed by towing the models in a flume tank. Both facilities are located at National University of Singapore (NUS). This paper presents the detailed setting of the model tests. The single model’s RAOs with 20% filling level of internal fluid are given to demonstrate the influence of internal fluid on the motions. The performances of a single tank, including six DOF motions are shown. The results will be used for validation of numerical analysis results in the near future.

Validation of the HVS Semisubmersible Global Performance by Model Tests

2013 ◽  
Author(s):  
Johyun Kyoung ◽  
C. K. Yang ◽  
Jim O’Sullivan ◽  
Thiago Miliante
Keyword(s):  
Model Tests ◽  
Wind Loading ◽  
Mooring System ◽  
Test Results ◽  
Analysis Program ◽  
Global Motion ◽  
Nonlinear Motion ◽  
Wave Basin ◽  
Global Performance ◽  
Induced Motion

Validation of the HVS (Heave and VIM Suppressed) semi-submersible’s global performance is carried out through wave basin model tests and correlation with numerical analysis. As an application for a wet-tree floater, Technip designed the HVS semisubmersible to have reduced heave and VIM (Vortex Induced Motion) response. The HVS semisubmersible has blisters attached to the columns. The blister breaks the coherence of the vortex shedding along the length of the column and as a result reduces the VIM response. The redistribution of pontoon volume because of the blister reduces the heave excitation loading. The blister also provides adequate buoyancy for quayside integration. To validate the improved hull global performance, the wave basin model tests were performed. In the tests, collinear hurricane environments of the Gulf of Mexico were considered for two different headings. Truncated mooring was applied to simulate prototype mooring system. Wind loading was applied by means of a dynamic controlled wind winch. Current was generated by a wire attached to a system of pulleys. The measured hull responses were correlated with MLTSIM, a Technip in-house time-domain nonlinear motion analysis program. Through the correlation with model test results, the improved HVS semisubmersible global motion in hurricane environments is validated.

scholarly journals Study on the Coupled Dynamic Responses of a Submerged Floating Wind Turbine under Different Mooring Conditions

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 418 ◽  
Author(s):  
Conghuan Le ◽  
Yane Li ◽  
Hongyan Ding
Keyword(s):  
Wind Turbine ◽  
Natural Frequencies ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Intermediate Water ◽  
Mooring System ◽  
Irregular Wave ◽  
Coupled Dynamic Analysis ◽  
Motion Responses

A submerged floating offshore wind turbine (SFOWT) is proposed for intermediate water depth (50–200 m). An aero-hydro-servo-elastic-mooring coupled dynamic analysis was carried out to investigate the coupled dynamic response of the SFOWT under different mooring conditions subjected to combined turbulent wind and irregular wave environments. The effects of different parameters, namely, the tether length, pretension and the tether failure, on the performance of SFOWT were investigated. It is found that the tether length has significant effects on the motion responses of the surge, heave, pitch and yaw but has little effects on the tower fore-aft displacements and the tether tensions. The increased pretension can result in the increase of the natural frequencies of surge, heave and yaw significantly. The influence of tether failure on the SFOWT performance was investigated by comparing the responses with those of the intact mooring system. The results show that the SFOWT with a broken tether still has a good performance in the operational condition.

Hybrid Verification of a Deepwater FPSO Using Truncated Model Tests and Numerical Simulations

2021 ◽  
Author(s):  
Xiangbo Liu ◽  
Ching Theng Liong ◽  
Nitesh Kumar ◽  
Kie Hian Chua ◽  
Allan Ross Magee ◽  
...  
Keyword(s):  
Numerical Model ◽  
Numerical Modelling ◽  
Water Depth ◽  
Return Period ◽  
Line Length ◽  
Model Tests ◽  
Mooring Line ◽  
Mooring System ◽  
Test Results ◽  
Set Up

Abstract This paper presents verification of a deep water FPSO with a semi-taut mooring system using model tests and numerical modelling commonly referred to as the hybrid method. The vessel under investigation is a FPSO of 310m in length and 47m in beam with an internal turret mooring system of 12 lines in 2000m water depth. Two configurations of the mooring systems i.e. inline and bisecting are investigated for sea-states up to 1000yr return period. A full depth mooring system has been developed for the FPSO and model tests will be carried out to verify the model. Due to limitations to the size of the model basins, the model tests will be carried out for a truncated mooring setup. Non-linear horizontal stiffness of a single mooring line and the complete mooring system with truncation is compared to that of the existing full depth mooring system. Discrepancies in the vertical forces due to truncation of line length will be discussed in the paper. A numerical model of the truncated set-up will be calibrated using model test results.

A Novel Passive Riser Tensioning System for a Dry Tree Spread Moored Barge

2004 ◽  
Author(s):  
Amit Katarya
Keyword(s):  
Model Test ◽  
Vertical Motion ◽  
Model Tests ◽  
Test Results ◽  
Test Set ◽  
Payload Capacity ◽  
Set Up ◽  
Floating Systems ◽  
Moon Pool ◽  
Fully Coupled

Dry tree risers on floating systems are presently supported either by TLPs or SPARs, both of which have limited payload capacity and no storage. A spread-moored barge having dry trees, storage and integrated drilling facilities has been developed. Model tests were performed for the riser tensioning system used on such a barge for offshore West Africa conditions. The risers are attached to a rectangular platform in a moon pool of the barge. This platform is supported by means of an articulated Rocker Arm System (RAS) located on the vessel main deck. The RAS has built-in counter weights hinged on pedestals fixed to the barge deck. In this arrangement gravity is used to tension the risers and when the barge heaves, the counterweights in the rocker arm system essentially decouple the barge vertical motion from the riser platform. This system provides a heave-restrained platform for dry trees with minimal dynamic loading of the risers. The model tests confirmed the feasibility of the new design. The paper describes the basic components of the gravity tensioning system. The model test set up and results from the model test are shown. Comparison of model test results with a fully coupled analytic model consisting of the barge and articulated tensioning system is also presented.

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