Dynamic positioning (DP) float-over installation is a new method for maritime structure installation, which uses a DP vessel to transport the topside of a jacket. When the DP vessel moves between the jacket leg, collision will happen because of environmental forces. To protect DP vessel and jacket, fenders are installed on the jacket leg. It is important to consider the collision between DP vessel and fenders. In this paper a numerical simulation for DP float-over installation is carried out, which simulates the dynamics of the DP vessel, and its collision with the fenders. The results are compared with model test.
A dynamically positioned (DP) vessel is defined as a vessel that maintains its position and heading by means of active thrusters. (Zhao et al., 2002). Float-over installation is an offshore installation method. Topside is assembled on land and transported to the place of installation by vessel. Float-over installation is suitable for large platform installation. This method saves time and costs of installation. It has been widely used in recent years. DP float-over installation is a kind of installation method in which the vessel uses DP system to provide propulsion. In general DP float-over installation includes following process: standby operation, docking operation, mating operation and undocking operation. In docking operation, when the vessel moves between the jacket leg, the vessel will collide with jacket leg due to the influence of environmental forces. To protect the vessel and jacket leg, fenders will be installed on the jacket leg. The collision has a significant influence to the DP vessel. It is important to study the influence of fender force to the vessel.
Wang et al. (2010) reviewed various floatover technologies based on the advancements in offshore installation and decommissioning technology. Applications of different float-over technologies is revealed. Maher et al. (2001) elaborated the process of float-over installation and carried out a numerical simulation and model test of float-over installation of SPAR. The technical feasibility of float-over installation is demonstrated. Hu et al. (2017) investigated nonlinear dynamics and impact loads during float-over installations. A more efficient model called state-space model is applied to evaluate part of the radiation force. The model, incorporating the multi-body interactions, is applied to study the nonlinear impact on Leg Mating Unit (LMU) by considering the sway, heave and roll motions of the float-over system. Serraris (2009) carried out a time-domain simulation for a drilling ship and compared the result with model test. The effects of different PID and Kalman coefficients are investigated. The choice of coeffcients has a significant influence on position keeping accuracy. Sun et al. (2012) investigated the interaction effects due to diffraction by a large volume substructure and an installation vessel. A two-stage hydrodynamic analysis was proposed. The multi-body diffraction problem is first solved without any constraints between the bodies, and in the second stage the constrained equations of motion are solved.
