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.

Hydrodynamic Response of Three Column Semi-Submersible Floater Supporting Vertical Axis Wind Turbine

2017 ◽  
Author(s):  
Rajeswari Krishnan ◽  
Nallayarasu Seeninaidu
Keyword(s):  
Numerical Simulations ◽  
Wind Turbine ◽  
Wind Farms ◽  
Vertical Axis ◽  
Offshore Wind ◽  
Scale Model ◽  
Vertical Axis Wind Turbine ◽  
Ocean Engineering ◽  
Motion Response ◽  
Wave Basin

Offshore wind energy extraction has gathered momentum around the world due to its advantages over onshore wind farms at various fronts. The floating support system with vertical axis wind turbine might prove to be feasible concept in medium to deep waters. In this context, this paper addresses an investigation of hydrodynamic analysis of three column semi-submersible with Vertical Axis Wind Turbine (VAWT) in parked condition under regular and random waves. Free decay experiments were conducted for using scale model (1:75) in a laboratory wave basin at the Department of Ocean Engineering in Indian Institute of Technology Madras, India. Computational Fluid Dynamics (CFD) simulations were used to assess damping characteristics and validated with the experiments. Numerical simulations of hydrodynamic motion response of the floater were carried out using potential flow theory based commercial software (ANSYS AQWA). The damping values obtained from experiments were used in numerical simulations to obtain motion response and Response Amplitude Operator (RAO). The motion response obtained from the study was used to verify the suitability of the system for deployment in east and west coast of India.

Model Basin Tests of Ocean Wave Responses for a 40-MW OTEC Pilot Plant

1982 ◽  
Vol 104 (1) ◽  
pp. 46-51 ◽  
Author(s):  
J. F. George ◽  
D. Richards
Keyword(s):  
Puerto Rico ◽  
Pilot Plant ◽  
Additional Data ◽  
Cold Water ◽  
Green Water ◽  
Scale Model ◽  
Water Pipe ◽  
Stability Margins ◽  
Mooring Forces ◽  
Wave Conditions

A 1/30th-scale model of a floating 40-MW OTEC pilot plant has been subjected to wave conditions that the prototype would experience as a plant moored off Puerto Rico or Hawaii, or as a cruising plantship in the South Atlantic Ocean east of Brazil. The model, in its unmodified baseline configuration, survived the design wave conditions for the three sites, with more than adequate stability margins. A modified configuration was also tested to reduce the possibility of taking on “green water” which was a concern at the Puerto Rico and Hawaii sites. Additional data were obtained on seawater system parameters, cold water pipe motions, and mooring forces.

Coupled Analysis Approach in OTEC System Design

2012 ◽  
Author(s):  
Shan Shi ◽  
John Halkyard ◽  
Nishu Kurup ◽  
Lei Jiang
Keyword(s):  
System Design ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Cold Water ◽  
Large Diameter ◽  
Working Fluid ◽  
Coupled Analysis ◽  
Ammonia Vapor ◽  
Water Pipe ◽  
Floating Platform

Ocean Thermal Energy Conversion (OTEC) technologies based on floating platforms generate electrical energy by utilizing the temperature difference between the deep ocean water and the surface water. One typical offshore floating OTEC system uses the temperature difference to drive a heat engine, utilizing a closed-loop Rankine cycle with a working fluid such as ammonia (NH3). Cold water is pumped through a large flexible pipe from approximately 1000m depth to heat exchangers which condense the ammonia vapor. Warm water from the surface is pumped through heat exchangers to evaporate the liquid ammonia to drive the turbine. An OTEC floating platform could be a semisubmersible, a spar, or other typical offshore hull form with a taut or a catenary mooring system. As opposed to oil and gas production platforms, the OTEC system consists of a large diameter cold water pipe (CWP) which will participate in the global performance of the floating platform. Its unique behavior also includes the contribution of CWP entrained water which behaves differently in lateral and vertical directions due to its open bottom design. The hydrodynamic behavior of the large scale cold water pipe is an important consideration in the system design and analysis. The study presented in this work includes the application of a fully coupled analysis program with an accurate cold water pipe dynamic model in OTEC floating system analysis. The study could be useful for future guidance and reference on OTEC floating platform designs.

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.

Numerical Study of the Mean and Filtered Characteristics of Turbulent Jets Impinging on Convex and Flat Surfaces Using LES

2012 ◽  
Author(s):  
Adra Benhacine ◽  
Zoubir Nemouchi ◽  
Lyes Khezzar ◽  
Nabil Kharoua
Keyword(s):  
Convex Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbulent Jets ◽  
Scale Model ◽  
Wall Jet ◽  
Potential Core ◽  
Flat Surfaces ◽  
Free Jet ◽  
Eddy Simulation

A numerical study of a turbulent plane jet impinging on a convex surface and on a flat surface is presented, using the large eddy simulation approach and the Smagorinski-Lilly sub-grid-scale model. The effects of the wall curvature on the unsteady filtered, and the steady mean, parameters characterizing the dynamics of the wall jet are addressed in particular. In the free jet upstream of the impingement region, significant and fairly ordered velocity fluctuations, that are not turbulent in nature, are observed inside the potential core. Kelvin-Helmholtz instabilities in the shear layer between the jet and the surrounding air are detected in the form of wavy sheets of vorticity. Rolled up vortices are detached from these sheets in a more or less periodic manner, evolving into distorted three dimensional structures. Along the wall jet the Coanda effect causes a marked suction along the convex surface compared with the flat one. As a result, relatively important tangential velocities and a stretching of sporadic streamwise vortices are observed, leading to friction coefficient values on the curved wall higher than those on the flat wall.

Preliminary Design of a 1-MWe OTEC Test Plant

1982 ◽  
Vol 104 (1) ◽  
pp. 3-8 ◽  
Author(s):  
T. Kajikawa
Keyword(s):  
Cold Water ◽  
Working Fluid ◽  
Test Plant ◽  
Mooring System ◽  
Preliminary Design ◽  
Closed Cycle ◽  
Water Pipe ◽  
Thermal Energy Conversion ◽  
Design Value ◽  
Ocean Thermal Energy

An ocean-based, 1-MWe (gross) test plant has been planned to establish the feasibility of OTEC (ocean thermal energy conversion) power generation in the revised Sunshine Project. The preliminary design of the proposed test plant employs a closed-cycle power system using ammonia as the working fluid on a barge-type platform with a rigid-arm-type, detachable, single-buoy mooring system. Two types each of titanium evaporators and condensers are to be included. The steel, cold-water pipe is suspended from the buoy. The design value of the ocean temperature difference is 20 K. The paper presents an overview of the preliminary design of the test plant and the tests to be conducted.

scholarly journals A Numerical Study of Fluid Structure Interaction of a Flexible Submerged Cylinder Mounted on an Experimental Rig

2015 ◽  
Author(s):  
Erkan Cakir ◽  
Ayhan Akinturk ◽  
Alejandro Allievi
Keyword(s):  
Numerical Study ◽  
Coupled Analysis ◽  
Mapping Algorithms ◽  
Automatic Mapping ◽  
Structural Responses ◽  
Submerged Cylinder ◽  
Physics Model ◽  
System Coupling ◽  
Force Data ◽  
Experimental Rig

The aim of the study is to investigate VIV effects, not only on a test cylinder but also on the experimental rig being towed under water at a prescribed depth and operating speeds. For this purpose, a numerical Multi-Physics model was created using one way coupled analysis simultaneously between the Mechanical and Fluent solvers of ANSYS software package. A system coupling was developed in order to communicate force data alternately between the solvers with the help of automatic mapping algorithms within millesimal time periods of a second. Numerical investigation into the dynamic characteristics of pressure and velocity fields for turbulent viscous fluid flow along with structural responses of the system, stressed the significance of time and space scales for convergence and accuracy of our Finite Volume (FV) CFD calculations.

OTEC-1 Cold Water Pipe Recovery Engineering of Lift and Towing Systems

1984 ◽  
Author(s):  
D. Tracy ◽  
G. Tettlebach ◽  
T. McNatt
Keyword(s):  
Cold Water ◽  
Water Pipe
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