Installation of Offshore Wind Turbine

Abstract

Ingenium AS is developing a new concept for transporting and installing fixed wind turbines, mainly jacket structures. As a part of the installation the jacket is lowered down to the seabed from a free hanging configuration, supported by a hydraulic frame.

This operation is analyzed by use of the computer program Orcaflex, where the structure is modeled as rigid.

Two critical scenarios are identified. In Scenario 1a the jacket is 10 m above seabed. Here, the jacket may collide with the support frame if the motions are sufficiently large. In Scenario 2a, the jacket is 3 m above seabed, and large motions may cause troubles under installation. Both these Scenarios are modeled and investigated by running response analyses in Orcaflex.

The effect of applying a passive heave compensation system is also investigated. Damping characteristics for the system are provided by Ingenium. By these damping characteristics, the heave compensation system is implemented in the Orcaflex models.

Contact between the support frame and the jacket legs may occur if the jacket motions are sufficiently large. The effect of applying a bumper system to reduce the stress in the jacket legs is investigated. This is done by attaching a bumper to the support frame in Scenario 1a, and use different materials with different contact stiffness for the bumper analysis.

All scenarios are run with different environmental conditions. A matrix which defines the different cases for each scenario with respect to load parameters is established. Modal analyses with different line length are performed to see what effect the line length has on the natural frequency of the system.