Connector response of a multibody VLFS subject to wave loading
conference paper
The energy transition requires us to explore all options for generating non-fossil energy and offshore floating PV( OFPV) energy is gaining momentum with recent developments quite promising. The trend is to
combine small individual floaters into a grid using connectors which can be made reasonably flexible. To address the challenges of offshore conditions the connectors need strength and flexibility. In this paper, the authors address the challenge of the conflicting demands of strength and flexibility for offshore floating structures. The first step is to assess the wave excitation loads between individual elements and how these loads influence the flexibility of a connection. A computational model is developed that uses a 3D BEM (Boundary Element Method) to calculate the linearized hydrodynamic coefficients and the wave diffraction and radiation forces. Meanwhile, the Froude-Krylov, hydrostatic, connector, and mooring forces are time and spatially dependent allowing nonlinearities to be captured. The time domain solution provides answers into the nonlinear interaction between the mechanical behaviour of compliant (flexible) connectors with hydromechanic behaviour of rigid floaters. After a successful validation, a three-floater OFPV system is subjected to typical sea-states representing 1 year and 100 year return on periods. The pitch motion response is compared for both sea-states and wave headings. Then, the forces and moments at the connectors are presented for two connector stiffnesses and sea-states. The head sea case has the greatest force in the axial direction and moment in vertical bending but then the forces and moments in the other DOF are greater in bow quarter seas. There is a decrease in forces but increase in moments when the stiffness of the connectors increases. The results also show the importance of dynamic amplification at sea-states with wave peak periods close to the natural frequency of the system. The connectors are shown to influence the natural frequency of the structure such that it behaves somewhere in between a single continuous structure and three independent floating modules. After successfully using the model to investigate the behaviour of a serially connected OFPV the next step will be to expand to a grid which is more representative of the future types of structures that will be deployed.
combine small individual floaters into a grid using connectors which can be made reasonably flexible. To address the challenges of offshore conditions the connectors need strength and flexibility. In this paper, the authors address the challenge of the conflicting demands of strength and flexibility for offshore floating structures. The first step is to assess the wave excitation loads between individual elements and how these loads influence the flexibility of a connection. A computational model is developed that uses a 3D BEM (Boundary Element Method) to calculate the linearized hydrodynamic coefficients and the wave diffraction and radiation forces. Meanwhile, the Froude-Krylov, hydrostatic, connector, and mooring forces are time and spatially dependent allowing nonlinearities to be captured. The time domain solution provides answers into the nonlinear interaction between the mechanical behaviour of compliant (flexible) connectors with hydromechanic behaviour of rigid floaters. After a successful validation, a three-floater OFPV system is subjected to typical sea-states representing 1 year and 100 year return on periods. The pitch motion response is compared for both sea-states and wave headings. Then, the forces and moments at the connectors are presented for two connector stiffnesses and sea-states. The head sea case has the greatest force in the axial direction and moment in vertical bending but then the forces and moments in the other DOF are greater in bow quarter seas. There is a decrease in forces but increase in moments when the stiffness of the connectors increases. The results also show the importance of dynamic amplification at sea-states with wave peak periods close to the natural frequency of the system. The connectors are shown to influence the natural frequency of the structure such that it behaves somewhere in between a single continuous structure and three independent floating modules. After successfully using the model to investigate the behaviour of a serially connected OFPV the next step will be to expand to a grid which is more representative of the future types of structures that will be deployed.
TNO Identifier
981085
Source
Proceedings 15th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS), 09-13 OCTOBER 2022 - DUBROVNIK - CROATIA, pp. 1-12.
Source title
15th International Symposium on Practical Design of Ships and Other Floating Structures PRADS 2022. Dubrovnik, Croatia, October 9th-13th 2022
Pages
1-12