IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Offshore wind energy has emerged as a major frontline competitor for producing sustainable and carbon free energy. With the recent advancement in engineering the researchers and developers are challenging the conventional wisdom of existing technology to improve the economics of wind power. Offshore wind turbines are rated in megawatts (MW) and costs approximately $1.5 million per MW for an installed capacity of 5 MW. On an average basis 5% to 15 % of this total capital investment goes into transportation and installation which is basically due to high day rates of jack up barges and other dynamic position vessels. An innovative floater conceived and designed by Nagan Srinivasan wherein the concept of self installation is introduced has been undertaken for hydrodynamic analysis during the transition phase in this study. Analysis has been carried out for different drafts and statistics of responses summarized for seastate 5. © 2014: The Royal Institution of Naval Architects and IIT Madras.

Department of Ocean Engineering

RINA, Royal Institution of Naval Architects - International Conference on Computational and Experimental Marine Hydrodynamics, MARHY 2014

Hydrodynamic analysis of self-installing mono column wind float during transition phase

Spars are floating complaint structures used for deepwater oil explorations. The heave motion response of spar is very important for the selection of suitable drilling and production equipments. Spar platform can possibly be subjected to heave resonant oscillations during the swell conditions. To reduce the heave motions one of the most effective methods is to use damping devices in the form heave plate which is attached to the keel of the spar. This will reduce the heave response in two ways; by increasing the added mass of the spar and by increasing the viscous damping by vortex shedding process. In the present study the influence of damping plates on the heave response of the spar is studied using WAMIT software. The configurations of the heave plates taken into considerations include single circular heave plate with different diameter configuration and twin circular heave plates with different spacing configurations. The effect of disc diameter and spacing on the heave added mass is studied. The diameter ratio defined as the ratio of the diameter of the heave plate to the diameter of the spar (Dd/Ds) considered for study are in the range of 1.1 to 1.4 and it is observed that as the plate diameter increases the reduction in the heave response also increases. Based on the study a plate diameter which is 20% to 30% more than the spar diameter found to be effective in heave motion reduction. For different spacing configurations, spacing ratio (L/Dd) 0.1 to 0.4 is considered. It is observed that as the spacing ratio increases the heave motion of the spar reduces. A spacing ratio in the rage of 0.2 to 0.4 is found to be effective in heave motion reduction. It is also inferred from the study that the effect of the heave plates on the pitch and surge motions is minimal (no effect). Copyright 2014, Offshore Technology Conference.

World University root node

Proceedings of the Annual Offshore Technology Conference

Hydrodynamic Response of Spar with Disc

Tension Leg Platforms (TLPs) are one of the reliable structures in the offshore industry in deep waters because of its motion characteristics in heave, roll and pitch degrees of freedom (dof). Heave motion is very important in offshore facilities and have to be kept as minimum as possible. As the water depth increases TLPs suffers from some limitations and hence has to be modified to cater to deeper waters. One such concept proposed is Tension Based Tension Leg Platform (TBTLP). In this paper, experimental investigations carried out on a 1:150 scaled model of a Tension Based Tension Leg Platform in regular waves in 3 m water depth is reported. These are the first ever experiments which were carried out on a scaled model of the new concept. To investigate the effects of Tension Base, experiments were also conducted on the TLP (without Tension Base). Responses have been compared in terms of Response Amplitude Operators (RAOs) for surge, heave and pitch dof for TBTLP and TLP. Numerical modeling of the TLP and TBTLP responses using ANSYS® AQWA™ software is included as well for comparisons. © 2014 ANAME Publication. All rights reserved.

GENERAL

Fulltext

Journal of Naval Architecture and Marine Engineering

Experimental investigations on tension based tension leg platform (TBTLP)

This paper presents the details of sea trials conducted on a water jet propelled high speed craft. This ship is an Inshore Patrol Vessel fitted with interceptors. The trials were conducted to establish the speed, manoeuvring performance and endurance of the ship. The speed trials were conducted with interceptors and without interceptors and the dynamic trim of the vessel was recorded along with speed. The interceptors contributed to a considerable increase of speed by dynamic reorientation of the ship. Under manoeuvring performance, the turning circle manoeuvre and the crash stop manoeuvre were conducted to establish the turning and stopping characteristics of the ship respectively. The turning characteristics of the ship were established by steering the jet to 30 degrees and completing one full turning circle at maximum continuous rating of the engine. The stopping characteristics were established by conducting crash stop manoeuvre (ahead to astern). For reversing the ship's direction of motion the water jet was reversed by deploying the buckets. The performance of the deck machinery, endurance of engines was also established during the sea trials. The obtained values from various sea trials are presented and compared with the recommendations of the standards. © 2014: The Royal Institution of Naval Architects and IIT Madras.

Sea trials of a water jet propelled high speed craft

Polymetallic nodules found in the deep ocean basins contain many economically valuable metals and are viewed as potential resources to supplement depleting onshore reserves and tackle increasing demand. The present work focuses on the preliminary design through analysis of a bottom weighted rigid riser which would form a part of the future full scale prototype nodule mining system under development by the National Institute of Ocean Technology (NIOT), India, operating in a water depth of around 6500m in the Central Indian Ocean Basin. A semisubmersible platform is chosen as a surface support vessel and the hydrodynamic analysis of a conceptual semisubmersible platform is carried out with WAMIT [3] to determine the heave Response Amplitude Operators (RAOs). The initial riser diameter, material grade and wall thickness configuration are arrived at using basic engineering principles and semi-coupled dynamic analysis of the platform riser system is carried out using ORCAFLEX [8] software to determine the loads imposed on the riser. The wall thickness is optimized to meet requirements of offshore standard DNV OS F 201 [6]. Vortex Induced Vibration (VIV) and Fatigue Analysis are then carried out using ORCAFLEX. Copyright © 2014 by ASME.

Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE

Preliminary design through analysis of a bottom weighted rigid riser for subsea mining

Tension Leg Platforms (TLPs) are one of the best options for offshore industry in deep waters due to proven motion response characteristics. These are water depth sensitive structures and the motion responses in vertical plane motions (heave, roll and pitch) are critical for a TLP. Tension Based TLP (TBTLP) is a new concept and finds application in much deeper waters. A provision of a tension base at mid-depth results in an economical design of TLP. In fact, the TLP installed at a certain depth without any modifications can be made to be deployed in much deeper water depths by means of a tension base. In this paper, the concept of TBTLP is highlighted and hydrodynamic analysis of the chosen platform has been carried out using ANSYS AQWA package. The motion responses in terms of Response Amplitude Operators (RAOs) of TBTLP with one Tension Base in surge, heave and pitch have been obtained and compared with a TLP without a tension base. Copyright © 2012 by ASME.

Hydrodynamic analysis of Tension Based Tension Leg Platform

The estimation of the motion response of a floating semisubmersible 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 semisubmersible 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. Copyright © 2011 by ASME.

Hydrodynamic analysis of semisubmersibles for a large scale desalination plant

Free Floating Wave Energy Converter (FFWEC) is a Wave energy extraction device patented (US patent No: 7823380B2) by Gp. Capt. S.M Ghouse. Feasibility studies on the device was undertaken by Department of Ocean Engineering, Indian Institute of Technology (IIT) Madras. A FFWEC model was designed and fabricated and was subjected to experimental analysis. The results of the experimental study are presented with discussions. © 2011 IEEE.

2011 International Conference on Electrical and Control Engineering, ICECE 2011 - Proceedings

Feasibility studies on the Free Floating Wave Energy Converter (FFWEC) concept

Ship dynamics in ocean waves involve frequency-dependent added mass and radiation damping which can be estimated either by potential theory-based calculations or by experiments. With uniform forward speed, the added mass and damping matrices become asymmetric. In this paper, we attempt to use a system identification approach, specifically the reverse multiple input-single output (R-MISO) method, for coupled heave-pitch response (two degrees of freedom) of a ship moving with uniform forward speed in random ocean waves. The system mass matrix has both frequency-independent and frequency-dependent components, whereas its damping matrix has only frequency-dependent components. The frequency-dependent components of the mass and damping matrices are asymmetric. The excitation force and moment due to linear monochromatic waves which act on the system are assumed to be known and can be either calculated or obtained from experiments. For numerical illustration, a ship whose hydrodynamic behaviour has been computed by strip theory has been considered. The motion, as well as the loading, is simulated assuming Pierson-Moskowitz spectrum in conjunction with response amplitude operators from the strip theory code, and these results are analysed by the R-MISO method yielding frequency-dependent asymmetric coupled added mass and radiation damping coefficients satisfactorily. © 2010 Taylor &amp; Francis.

Ships and Offshore Structures

System identification of coupled heave-pitch motion of ships with forward speed in random ocean waves

Dynamics of a large moored floating body in ocean waves involves frequency dependent added mass and radiation damping as well as the linear and nonlinear mooring line characteristics. Usually, the added mass and radiation damping matrices can be estimated either by potential theory-based calculations or by experiments. The nonlinear mooring line properties are usually quantified by experimental methods. In this paper, we attempt to use a nonlinear system identification approach, speciakally the reverse multiple input-single output (R-MISO) method, to coupled surge-pitch response (two-degrees-of-freedom) of a large floating system in random ocean waves with linear and cubic nonlinear mooring line stiffnesses. The system mass matrix has both frequency independent and frequency dependent components whereas its damping matrix has only frequency dependent components. The excitation force and moment due to linear monochromatic waves which act on the system are assumed to be known that can either be calculated or obtained from experiments. For numerical illustration, a floating half-spheroid is adopted. The motion as well as the loading are simulated assuming Pierson-Moskowitz (PM) spectrum and these results have been analyzed by the R-MISO method yielding frequency dependent coupled added mass and radiation damping coefficients, as well as linear and nonlinear stiffness coefficients of mooring lines satisfactorily. Copyright © 2006 by ASME.

Journal of Offshore Mechanics and Arctic Engineering

System identification of a coupled two DOF moored floating body in random ocean waves

A new frequency domain system identification method for estimation of hydrodynamic derivatives embedded in linear steering equations for ship maneuvering in calm seas is presented. The frequency domain multiple input-single output models developed for identification involves determination of constant, 'zero-frequency' hydrodynamic derivatives. The method is robust, non-iterative and computationally light and it does not require any starting estimates. In this method, the time domain operations are converted to linear operations in the frequency domain. The responses of the ship in a few standard maneuvers have been simulated in the numerical examples and the proposed method is applied to this data in order to estimate the hydrodynamic derivatives for all possible 'identifiable' combinations.

International Shipbuilding Progress

A frequency domain system identification method for linear ship maneuvering

Dynamics of a large moored floating body in ocean waves involves frequency dependent added mass and radiation damping as well as the linear and nonlinear mooring line characteristics. Usually, the added mass and radiation damping matrices can be estimated either by potential theory-based calculations or by experiments. The nonlinear mooring line properties are usually quantified by experimental methods. In this paper, we attempt to use a nonlinear system identification approach, specifically the Reverse Multiple Inputs-Single Output (R-MISO) method, to a single-degree-of-freedom system with linear and cubic nonlinear stiffnesses. The system mass is split into a frequency independent and a frequency dependent component and its damping is frequency dependent. This can serve as a model of a moored floating system with a dominant motion associated with the nonlinear stiffness. The wave diffraction force, the excitation to the system, is assumed known. This can either be calculated or obtained from experiments. For numerical illustration, the case of floating semi-ellipsoid is adopted with dominant sway motion. The motion as well as the loading are simulated with and without noise assuming PM spectrum and these results have been analyzed by the R-MISO method, yielding the frequency dependent added mass and radiation damping, linear as well as the nonlinear stiffness coefficients quite satisfactorily.

Parameter identification of a large floating body in random ocean waves by reverse MISO method

The determination of the drag and inertia coefficients, which enter into the wave force model given by Morison's equation, is particularly uncertain and difficult when a linear spectral model is used for ocean waves, and the structure is compliant and has nonlinear dynamic response. In this paper, a nonlinear System Identification method, called Reverse Multiple Inputs-Single Output (R-MISO) is applied to identify the hydrodynamic coefficients as well as the nonlinear stiffness parameter for a compliant single-degree-of-freedom system. Four different types of problems have been identified for use in various situations and the R-MISO has been applied to all of them. One of the problems requires iterative solution strategy to identify the parameters. The method has been found to be efficient in predicting the parameters with reasonable accuracy and has the potential for use in the laboratory experiments on compliant nonlinear offshore systems. © 2001 Elsevier Science Ltd. All rights reserved.

Ocean Engineering

Parameter identification of a compliant nonlinear SDOF system in random ocean waves by reverse MISO method

Dynamics of a large moored floating body in ocean waves involves frequency dependent added mass and radiation damping as well as the linear and nonlinear mooring line characteristics. Usually, the added mass and radiation damping matrices can be estimated either by potential theory-based calculations or by experiments. The nonlinear mooring line properties (usually cubic nonlinearity characterised by a constant) are usually quantified by experimental methods. In this paper, we attempt to use a nonlinear system identification approach, specifically the Reverse Multiple Inputs-Single Output (R-MISO) method, to a single degree of freedom system with linear and cubic nonlinear stiffnesses. The system mass is split into a frequency independent and a frequency dependent component and its damping is frequency dependent. This can serve as a model of a moored floating system with a dominant motion associated with the nonlinear stiffness. The wave diffraction force, the excitation to the system, is assumed known. This can either be calculated or obtained from experiments. For numerical illustration, the case of floating semi- ellipsoid is adopted with dominant sway motion. The motion as well as the loading are simulated assuming PM spectrum and these results have been analysed by the R-MISO method, yielding the frequency dependent added mass and radiation damping, linear as well as the nonlinear stiffness coefficients quite satisfactorily.