**5. Installation methodology**

#### **5.1. Monopile**

The length of monopile is 30 m with diameters of 6 m and requires huge hydraulic hammers for driving the pile. These hammers are usually equipped on a floating barge or jack-up platforms. Jack-up platforms are generally used under severe sea-state conditions and floating barges for relatively calm sea conditions. The jack-up platforms are associated with high rentals and less deck space than floating barges. In case of floating barges, the large deck space on the barge can reduce the time and costs needed for the transportation of monopiles and transition pieces by using the barge as a floating storage. Considering the low-wave climate along potential sites of Tamil Nadu, floating barge would be an ideal solution. However, these vessels (floating barges/specialized jack-up platforms) are not available in India and have to be hired from Europe or to be developed in India. Hence, the cost of mobilization and demobilization will be high during the installation phase of offshore wind project.

The installation methodology for a monopile using specialized vessel is shown in **Figure 11**. The ship is loaded with four to five monopiles in the port and sailed to the wind farm. The monopile will be lowered through a guide with the help of a deck crane and driven using a hydraulic hammer. Once the monopile is driven to the required depth, the transition piece is installed over it. The gap between the monopile and the transition piece is grouted for appropriate transfer of loads and to adjust the alignment of platform. The main advantage of the monopile is easy and quick installation. On the other hand, its disadvantages include high cost due to unavailability in India and additional charges for mobilization and demobilization.

#### **5.2. Gravity-based foundation**

The installation methodology for gravity-based foundation is shown in **Figure 12**. The gravitybased foundation is constructed on a steel platform nearby the fishing harbor. The monopole is then installed through the inner ring of the foundation. In the second stage, the landside edge of the platform is raised by hydraulic jacks. The gravity-based foundation is slid into the water. Due to buoyancy effects, the structure will float. The gravity-based foundation is then towed to the required position using a tug. Before lowering the foundation, the seabed has to be leveled using a gravel bed. The foundation is then positioned using tugs and then lowered by ballasting water into it. The hollow chambers inside the foundation are filled with plain cement concrete to increase the stability of the foundation.

**Figure 11.** Installation methodology of monopile.

**5. Installation methodology**

**Figure 10.** FEM models gravity-based foundation.

**Figure 9.** Deflected profiles for monopile and jacket structures.

162 Stability Control and Reliable Performance of Wind Turbines

The length of monopile is 30 m with diameters of 6 m and requires huge hydraulic hammers for driving the pile. These hammers are usually equipped on a floating barge or jack-up platforms. Jack-up platforms are generally used under severe sea-state conditions and floating barges for relatively calm sea conditions. The jack-up platforms are associated with high rentals and less deck space than floating barges. In case of floating barges, the large deck space on the barge can reduce the time and costs needed for the transportation of monopiles and transition pieces by using the barge as a floating storage. Considering the low-wave climate along potential sites of Tamil Nadu, floating barge would be an ideal solution. However, these

**5.1. Monopile**

wind parameters by installing an onshore mast in a narrow strip extending into the sea. LiDAR-based offshore wind data collection platforms are successfully commissioned in Gulf of Khambhat for MNRE-NIWE and Gulf of Kutch for M/S Suzlon with technical support from

Offshore Wind Feasibility Study in India http://dx.doi.org/10.5772/intechopen.74916 165

Considering the bathymetry and geotechnical conditions along potential sites, three substructure concepts, monopile, gravity-based foundation, and jacket, were analyzed. A preliminary design based on aerodynamic loads on turbine, hydrodynamic loads on the structures, pilesoil interaction, and floatation analysis for gravity-based structures is carried out to arrive at suitable substructure concepts for Gujarat and Tamil Nadu. Installation methodologies were developed for identified substructure concepts for Indian scenario and the infrastructure needs assessed. These studies will also assist in arriving at the cost for implementation of the

The authors wish to express their sincere thanks to Dr. Satheesh C. Shenoi, Director, NIOT, for his keen interest and encouragement. They also express their gratitude to the National Institute of Wind Energy and M/s Suzlon for their support in LiDAR project. The authors

[1] European Wind Energy Association. The European Offshore Wind Industry-Key Trends

[5] Energy Next. March 2013. [Online]. http://www.energynext.in/japan-to-increase-its-off-

[2] Global Wind Energy Council. Global Wind Statistics 2014. Brussels, Belgium; 2014

[3] European Wind Energy Association. Wind Energy Scenarios for 2020. July 2014

[4] FOWIND. Offshore Wind Policy and Market Assessment. December 2014

thankfully acknowledge the support extended by MoES in funding the project.

Satya Kiran Raju Alluri\*, Devender Gujjula, Krishnaveni B, Dhinesh Ganapathi,

S.V.S. Phanikumar, M.V. Ramanamurthy and M.A. Atmanand

National Institute of Ocean Technology, Chennai, Tamil Nadu, India

\*Address all correspondence to: raju@niot.res.in

shore-wind-capacity-to-40-times-by-2020/

and Statistics 2014; 2015

NIOT for recording the continuous wind data and validation.

offshore wind farm projects.

**Acknowledgements**

**Author details**

**References**

**Figure 12.** Installation methodology of gravity foundation.

The static stability of the foundation is carried out, and the draft is estimated to be 4 m from the bottom. As the foundation needs to be towed for a long distance, it is essential to identify the natural frequencies and response amplitude operations (RAO). Natural frequencies and RAOs are computed for three translation modes and three rotation modes. It is observed that the natural frequency is far away from the encounter frequency of waves (5–10 s).
