Session: 09-01-03 Installation, Marine Operations and Maintenance - 3

Paper Number: 80930

80930 - Offshore Wind Turbine Support Structures Along Indian Coast - Multi Criteria Analysis 

Offshore wind is gaining prominence as a clean energy resource for its promising features of low visual intrusion, reduced noise pollution and increased wind speeds. Due to the promising features of offshore wind and replenished land-based resources, India with a coastline of 7600 km has set itself a target of 30 GW of renewable energy by 2030. From the available mesoscale data sets, India has a huge potential for offshore wind along the coasts of Tamil Nadu and Gujarat. The present study is to select a feasible support structure for a 1.5 MW wind turbine in Gulf of Mannar, off the coast of Kanyakumari, Tamil Nadu. The location has a water depth of 40 m with a soil profile of predominantly silty sand and subjected to wave height of 5m.

The installation of turbines is complex and involves huge capital. Of the total capital cost of the offshore wind turbine (OWT), the support structure accounts for 20 – 25 %. The selection of a feasible support structure for the site-specific environmental conditions helps in reducing the capital cost of the OWT. As the location under study falls under shallow water depth, the bottom fixed structures such as monopile, tripile and jacket have been considered as alternatives. The analysis of the alternatives has been carried out using API and DNVGL codal provisions in a finite element based framework, in which the structure is discretized into number of beam elements. The analysis also accounts for soil structure interaction effects for the pile supported structures. Apart from the hydrodynamic loads from waves and currents, OWTs are subjected to aerodynamic loads from the turbine blade rotations. The aerodynamic loads are estimated using Blade Element Momentum Theory based software and are coupled with the hydrodynamic loads using FEM software.

Multi criteria decision analysis (MCDA) is adopted to aid in the decision making regarding the choice of the feasible support structure. Multi- criteria evaluation problem consists of a viable set of alternatives for a given problem. MCDA explicitly evaluates conflicting criteria involved in the decision making. It helps analyse a complex problem using a pre-defined set of variables/ criteria to derive at a logical solution. Among the varies methods of MCDA, for evaluating the alternatives against the criteria Analytical Hierarchy Process (AHP) has been adopted, where the pairwise comparison is made for the given alternatives using pre-defined criteria. The criteria considered for the study are structural configuration, fabrication, transportation and installation of the structure. The criteria again are classified into different sub criteria in order to sort out the weights of all the alternatives. The support structure with the highest weight has been identified as the optimal and feasible structure for the location under study.

 

 

Presenting Author: Mounika Mallela Indian Institute of Technology, Madras

Authors:

Mounika Mallela Indian Institute of Technology, Madras
Nilanjan Saha Indian Institute of Technology, Madras
Satya Kiran Raju Alluri National Centre for Coastal Research
M V Ramana Murthy National Centre for Coastal Research