Hydrodynamic Analysis of Semisubmersibles for a Large Scale Desalination Plant

2011 ◽  
Author(s):  
R. Saravanan ◽  
S. K. Bhattacharyya ◽  
R. Panneer Selvam ◽  
Srinivasan Chandrasekaran
Keyword(s):  
Large Scale ◽  
Hydrodynamic Performance ◽  
Damping Coefficient ◽  
Scale Model ◽  
Viscous Damping ◽  
Ocean Engineering ◽  
Hydrodynamic Analysis ◽  
Desalination Plant ◽  
The Cost ◽  
Rectangular Columns

The estimation of the motion response of a floating semi-submersible type offshore platform for a desalination plant, of capacity 10 million litres per day (MLD) of fresh water, is the focus of the study. The platform needs station keeping by a mooring system using a spar moored in deep water. To cater to these requirements, several design configurations of the semi-submersible were tried out for their hydrodynamic performance in order to choose the best among them, in all cases keeping the cost of components at reasonable levels. The hydrodynamic analysis of the platforms was carried out using the software WAMIT. The natural heave period was the main criterion in finalizing the configuration of the semi-submersible because it has greatest impact on keeping the downtime of platform operation to a minimum. WAMIT yields unrealistically high RAO that is attributed to the effect of viscous damping not being incorporated in the analysis. Experimental investigation was carried out to find the viscous damping coefficient of the configuration of the semi-submersible that was finally chosen among a few alternatives. A 1:50 scale model was tested in the 4m flume at the Department of Ocean Engineering, I.I.T Madras. Free oscillation tests were carried out to find the damping coefficient and natural heave period. Use of experimentally obtained damping values in WAMIT yielded excellent comparison with experimentally obtained response values (RAOs). On the basis of the present work, configuration of a semi-submersible having six rectangular columns and two rectangular pontoons has been finalized for the desalination plant.

Research in Testing of Loess Foundation Pile Hysteretic Property under Horizontal Cyclic Load

2012 ◽  
Vol 433-440 ◽  
pp. 202-206
Author(s):  
Ming Bo Ding ◽  
Xing Chong Chen
Keyword(s):  
Cyclic Load ◽  
Large Scale ◽  
Damping Coefficient ◽  
Scale Model ◽  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
Loess Area ◽  
Hysteretic Property ◽  
Large Scale Model ◽  
Foundation Pile

In this paper, by the large scale model test of pile-soil in remodeling loess foundation, authors research the basic discipline of pile-soil interaction plastic hysteretic property of pile foundation in loess area under horizontal cyclic load and obtain hysteretic curves, skeleton curves and relationship between equivalent viscous damping coefficient and displacement under pile-soil interaction. The paper also discusses the intensity components, plastic and other energy and equivalent viscous damping coefficient cycles occur with varying degrees of degradation of the variation.

Recycle of resin-based analogue material for geo-mechanical model test

2018 ◽  
Vol 37 (2) ◽  
pp. 142-148
Author(s):  
Fan Pengxian ◽  
Wang Jiabo ◽  
Shi Yehui ◽  
Wang Derong ◽  
Tan Jinzhong ◽  
...  
Keyword(s):  
Model Test ◽  
Mechanical Model ◽  
Large Scale ◽  
Economic Benefits ◽  
Model Tests ◽  
Scale Model ◽  
Large Scale Model ◽  
Cyclic Utilization ◽  
The Cost ◽  
Recycled Material

Analogue materials are widely used to simulate prototype rocks in geo-mechanical model tests. The large amounts of solid waste generated by a large-scale model test has always posed problems for studies. The re-use of analogue materials can significantly reduce the cost of geo-mechanical model tests and the resulting environmental problems. However, despite the environmental and economic benefits, there have been few reports on the re-use of analogue materials. In this work, a recycling method for a resin-based analogue material is studied experimentally. More than 300 samples were prepared and tested. By adding a certain amount of resin in solution form to the recycled material, regenerated samples with properties consistent with those of the samples prior to recycling were obtained. Based on a comparative analysis of the test data, an equation is proposed for the calculation of the appropriate amount of resin addition in the recycling process. Thus, a simple and effective recycling method is established for a resin-based analogue material. Verification was performed by independent tests on three group samples with different proportions, and the possibility of repeated recycling was also confirmed. The proposed recycling method makes the cyclic utilization of resin-based analogue material possible and is helpful for reducing the cost and pollution of geo-mechanical model tests.

Development of 3MW Tidal Energy Platform

2013 ◽  
Author(s):  
Erik ter Brake ◽  
Mike Todman ◽  
John Armstrong
Keyword(s):  
Large Scale ◽  
Tidal Energy ◽  
Model Testing ◽  
Offshore Wind ◽  
Scale Model ◽  
Easy Access ◽  
Main Body ◽  
Sudden Increase ◽  
Large Scale Model ◽  
The Cost

The Triton-3 platform is a novel tidal energy harvester capable of producing 3MW from tidal flow. The platform is a floating structure moored to the seabed by a single-point fully articulated anchorage, and carries three power trains and a number of marine auxiliaries. The driver for the design as developed by TidalStream Ltd is to reduce the cost of energy production in order to compete with the current cost of offshore wind. Independently audited cost modelling shows that tidal stream energy can become competitive with offshore wind, achieving a generating cost as low as 10p/kWh at the best sites. This generating cost is estimated to be less than half that which could be achieved at a similar site from a single seabed-located turbine. The driving aspects for the competitive cost are maximising the capacity per mooring point, reducing installation costs by float-out solutions and by providing easy access to the tidal equipment. Access is achieved by allowing the platform to come to the surface by means of de-ballasting. By doing so, there is no need for large workboats and/or diver activities to perform regular inspection and maintenance on the tidal equipment, reducing the cost significantly. The technical aspects that arise when developing the tidal turbine platform for a typical offshore location are investigated by Houlder Ltd and discussed in this paper. A number of technical challenges have been addressed where the rotational stability in both roll and pitch are of interest. The roll of the platform is heavily affected by the performance of the turbines; sudden increase or reduction in thrust will induce significant rolling moments that must not impair the integrity of the platform. Pitching of the platform allows it to reach the surface when de-ballasted for maintenance and inspection. During normal operations, the platform remains aligned with the current and in doing so maximises the performance of the turbines. The paper illustrates how these aspects have been achieved by means of passive solutions. By means of positioning and shaping the main body of the platform, a working configuration has been developed where the rotations of the platform remain within a limited window maximising the potential power production. The concept has been tested by TidalStream during a large-scale model testing campaign where the unit was subject to different current speeds and different turbine configurations and fault cases. This publication compares the results of the large scale model testing with numerical models developed in OrcaFlex and shows the effectiveness of the passive solutions.

Numerical Analysis of Hydrodynamic Performance of Backward Bent Duct Buoy (BBDB)

2012 ◽  
Author(s):  
W. C. Koo ◽  
S. J. Kim ◽  
M. H. Kim
Keyword(s):  
Time Domain ◽  
Hydrodynamic Performance ◽  
Damping Coefficient ◽  
Surface Boundary ◽  
Viscous Damping ◽  
Computational Domain ◽  
Time Domain Simulation ◽  
Free Surface Boundary Condition ◽  
Floating Type ◽  
The Time Domain

The hydrodynamic performance of Backward Bent Duct Buoy (BBDB), a floating-type wave energy converter, was evaluated in the time-domain simulation by using a two-dimensional fully-nonlinear numerical wave tank (NWT) technique. The developed NWT was based on potential theory, boundary element method with constant panels, and the mixed Eulerian-Lagrangian (MEL) approach to capture the nonlinear free-surfaces. The viscous damping at the chamber entrance due to oscillating water column and the shape of body causing generation of vortex shedding were modeled and applied to the free surface boundary condition inside the chamber. The calculated surface elevations inside the chamber with open chamber condition were compared with experimental data to select a proper viscous damping coefficient. Then, the surface elevations with a tuned viscous damping coefficient were calculated for various wave conditions. The results of linear and nonlinear time-domain simulation with two different corner-shaped BBDBs were compared to investigate the mean drift force of BBDB. Energy conservation in the computational domain was checked for all cases.

Analysis of Coupled Hull: Cold Water Pipe Mooring for Offshore Desalination Plant

2007 ◽  
Author(s):  
A. Venkata Subbaiah ◽  
R. Sundaravadivelu ◽  
V. Anantha Subramanian
Keyword(s):  
Cold Water ◽  
Numerical Study ◽  
Scale Model ◽  
Coupled Analysis ◽  
Water Pipe ◽  
Ocean Engineering ◽  
Wave Condition ◽  
Desalination Plant ◽  
Tension Response ◽  
Wave Basin

The design of a 0.25 Million Litres per Day (MLD) low pressure desalination plant in 150m water depth using a Tension Leg Counterweight Platform (TLCP) consisting of a 10m diameter hull, 1m diameter cold water pipe with counterweight and vertical taut mooring has been carried out. A 1:50 scale model of the TLCP is tested in the 30m × 30m × 3m wave basin in Department of Ocean Engineering, IIT Madras. The tensions in mooring lines are measured using load cells. The coupled analysis of the TLCP is studied using the Nonlinear Analysis of Offshore Structures (NAOS) program developed at IIT MADRAS. The measured tension response of mooring line compare well with numerical results. The Surge, Heave, Pitch and Tension response amplitude operators for the TLCP obtained from numerical study are observed to be within the permissible limits for the operational wave condition whereas the TLCP performs satisfactorily for the survival wave condition. The numerical and model studies are carried out for regular waves. The effect of counterweight and pretension on platform motions is studied in this paper.

Damping Coefficient Analyses for Floating Offshore Structures

2010 ◽  
Author(s):  
Edgard B. Malta ◽  
Rodolfo T. Gonc¸alves ◽  
Fabio T. Matsumoto ◽  
Felipe R. Pereira ◽  
Andre´ L. C. Fujarra ◽  
...  
Keyword(s):  
Numerical Models ◽  
Linear Method ◽  
Offshore Structures ◽  
Damping Coefficient ◽  
Irregular Waves ◽  
Scale Model ◽  
Viscous Damping ◽  
Viscous Effects ◽  
Random Decrement Technique ◽  
Decay Test

The damping evaluation of floating offshore systems is based on the viscous effects that are not considered in numerical models using the potential theory. Usually, different techniques for different systems are used to evaluate these hydrodynamic coefficients. The total damping is separated by potential and viscous damping, the first one is evaluated numerically and the second through experiments at reduced scale model. Common techniques considering linear motion equations cannot be applied to all degrees of freedom. Some methods were compared for results of decay test, such as: exponential and quadratic fit. Fourier transform (FT) spectral analysis and Hilbert Huang transform (HHT) can be used to evaluate the signal natural frequency and with HHT this can be done during the time domain. Also, analysis through the Random Decrement Technique (RDT) is presented to demonstrate the damping evaluation for irregular waves. The method to obtain external damping was presented for the different techniques in an ITTC semi-submersible model. The linear method is not sufficient to predict the damping coefficient for all the cases, because in most of them, the viscous damping was better represented by a quadratic fit. The HHT showed to be a good alternative to evaluate damping in non-linear systems.

Numerical Research of Fujiangsha Waterway Based on a Depth-integrated Hydro-sediment-morphodynamic Model

2021 ◽  
Author(s):  
Mengzhe Sun ◽  
Peng Hu ◽  
Youwei Li
Keyword(s):  
Large Scale ◽  
Hydrodynamic Performance ◽  
Scale Model ◽  
Hydrological Process ◽  
Complex Flow ◽  
Point Bar ◽  
Channel Condition ◽  
Numerical Research ◽  
The Impact ◽  
Channel Bar

<p>Fujiangsha waterway is located in the tidal reach of Yangtze River, which is one of the key sections for channel regulation. The channel condition of the waterway is governed by the evolution of the channel bar and point bar. Groins are consequently set on both sides of the channel bar and the left edge of Fujiangsha island. To explore the impact of the regulation works on the evolution of bars and channels, a numerical research is carried out based on a depth-integrated hydro-sediment-morphodynamic model, using the method of nesting large-scale model with local model. The non-negligible impact on the quality and momentum of water flow caused by enormous sediment transport and drastic change of topography, as well as the complex flow condition in both tide and runoff working together, has been taken into account. The simulation successfully reproduces the hydrological process and changes of topography in Fujiangsha waterway. Results show that: 1) there is a silting trend at the head of the channel bar, and the effect of the regulation works in bar protection and sand stabilization is remarkable; 2) The erosion on both sides of the channel bar improves the channel condition, and the hydrodynamic performance of shallow area at the entrance of the south branch has been enhanced; 3) The control on the evolution of point bar is still weak, which will have an adverse effect on channel condition of north branch.</p>

Offshore Drilling Riser VIV Suppression Devices: What’s Available to Operators?

2008 ◽  
Author(s):  
Samuel Taggart ◽  
Michael A. Tognarelli
Keyword(s):  
Large Scale ◽  
Weather Conditions ◽  
Hydrodynamic Performance ◽  
Scale Model ◽  
Market Place ◽  
Offshore Drilling ◽  
Drilling Rig ◽  
Helical Strakes ◽  
Drilling Operations ◽  
Viv Suppression

VIV suppression and drag reduction are key issues for improved operation in offshore drilling. Properly designed helical strakes are effective in the mitigation of VIV fatigue damage for many riser applications. However such strakes tend not to be applicable to offshore drilling riser applications. This is due to increases in drag force due to increased apparent diameter as well as workability problems for drilling operations. For these reasons, effective devices are sought that would mitigate VIV and reduce, or at least not increase, drag for drilling applications. Along with yielding good hydrodynamic performance, a drilling riser VIV suppression device must be compact and robust enough to be used in a drilling-rig environment. It needs to be deployable and recoverable in declared operational sea states. It must also be easy to store and assemble. Finally, and most importantly, it must be efficient to deploy and recover during normal riser operations. This last point is vital to drilling operations in deepwater in hurricane-prone areas. Weather conditions can change quickly and even a non-faired deepwater riser takes 2 to 3 days for a full retrieval. BP continues to research and document suppression device types and to assess their practical performance. A supply choice in the market place is important so that the correct device can be used for particular situations. To this end, we have recently worked with cooperative partners to demonstrate the hydrodynamic performance of a handful of the most promising devices. This paper is a tailored synopsis of previous suppression concepts and the philosophical pathway toward what is available on the market today. At its core are recent circumstances which precipitated a need to quantify and qualify for operational acceptance the performance of two commercially available short aspect ratio fairing devices. (i.e. a dual-fin splitter and an airfoil-shaped fairing). This paper discusses the results of the large-scale model acceptance tests over prototype Reynolds number for these devices. In addition to rigid devices, a relatively newer suppression product that “inflates” in the direction of the relative flow was also assessed by BP for expected hydrodynamic performance. This device shows particular promise for the mitigation of VIV during drilling operations surprises in high currents along with appearing potentially commercially viable.

scholarly journals Influence of Payloads on the Hydrodynamic Response of Semi Submersible Platform

2019 ◽  
Vol 9 (2) ◽  
pp. 1134-1139
Keyword(s):  
Physical Model ◽  
Water Resource ◽  
Regular Wave ◽  
Hydrodynamic Behavior ◽  
Hydrodynamic Analysis ◽  
Wave Flume ◽  
Desalination Plant ◽  
Hydrodynamic Response ◽  
Resource Laboratory ◽  
Rectangular Columns

The hydrodynamic analysis of the semi submersible platform was carried out for height. with and without mooring condition by changing the metacentric A physical model of scale 1 in 100 was tested in 1m widthand 30 m long regular wave flume at CWR (Centre for Water Resource) Laboratory. The model has four rectangular columns and two rectangular pontoons along with mooring. The natural heave, pitch and roll periods of the semi-submersible have greatest impact on the downtime of platform operation.This paper focus on the influence of payloads on the hydrodynamic behavior semisubmersible platform. On the basis of present work, the configuration of Semi-submersible having four rectangular columns and two rectangular pontoons has been arrived at for the proposed desalination plant.

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