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| CONTENTS | |
| Volume 15, Number 1, March 2025 |
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- Impact of padeye depth of suction caisson anchors and clump weights on floating offshore wind turbines Hiroyoshi Hirai
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| Abstract; Full Text (2409K) . | pages 1-21. | DOI: 10.12989/ose.2025.15.1.001 |
Abstract
Little analytical study has been conducted to elucidate the interactions among the suction caisson anchors, mooring chains, and the platforms of floating offshore wind turbines (FOWTs). In this paper, an analytical approach will be developed to clarify the effect of the padeye depth of suction caisson anchors in sands and the mooring clump weight on the response of the comprehensive system of the FOWT. First, to predict the tensile behavior of suction caisson anchors in sand, the equations relevant to the vertical and lateral yield resistances, the bearing capacity, and pullout were presented. Second, considering the characteristics of the moorings dependent on the horizontal load applied to FOWTs and the clump weight, an analytical approach was proposed regarding the relationships among the mooring chain configuration, the caisson padeye depth, the tensile load induced at the caisson padeye, the magnitude and location of the clump weight, and the horizontal load at the spar fairlead. Last, the relationships among the displacement, the tensile capacity, and pullout of the suction caisson anchor in sand subjected to the inclined tensile loads induced at the caisson padeye were revealed when the designed horizontal load is exerted on the spar fairlead.
Key Words
clump weight; floating offshore wind turbines; mooring; pullout; sand; suction caisson anchor; three-dimensional displacement method; ultimate load
Address
Hiroyoshi Hirai: Applied Geotechnical Institute, Inc., 807, Oizumi, Hokuto, Yamanashi, 409-1502, Japan
- Development of variable-fidelity FOWT digital twins in extreme sea environments: Part I – mid-fidelity analysis Hyoungchul Kim, Ikjae Lee, Moohyun Kim, Hyunchul Jang and Bonjun Koo
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| Abstract; Full Text (3326K) . | pages 023-42. | DOI: 10.12989/ose.2025.15.1.023 |
Abstract
In the coming years, more Floating Offshore Wind Turbines (FOWT) are projected to be installed beyond the continental shelf in the USA and worldwide. Accurate and reliable modeling of various environmental loadings and the resulting dynamic responses are crucial for the structural design, operation, and safety of FOWTs. To develop accurate and reliable FOWT design tools, a collaborative effort between academia (Texas A & M University), industry (Technip Energies), and class society (American Bureau of Shipping), supported by the Ocean Energy Safety Institute (OESI), has been undertaken. In this project, accurate and reliable digital twin (DT) models were developed based on the high-fidelity CFD models and mid-fidelity potential-flow models. In the mid-fidelity models, the wind turbine and platform dynamically interact, exchanging loads and motions at each time step. Aerodynamic loadings on the blade elements, considering wind-inflow data, tower and blade elasticity, and blade-pitch control are included. Hydrodynamic loading is calculated using potential-flow theory with Morison' s equation, and the FEM is used to model the behavior of mooring lines. The present study is presented in two separate papers. This paper, Part I, focuses on the development and validation of two mid-fidelity DT models (OrcaFlex and MLTSIM-OpenFAST) for a 15MW semi-submersible wind turbine model. The results from the two mid-fidelity DT simulations were verified through several system identification tests and for various extreme environmental conditions. In future work, the capabilities of these models will be extended to consider the effects of submarine earthquakes and tsunami waves, expanding the design loading cases of current design guidelines.
Key Words
digital twins; FOWT; mid-fidelity fully coupled numerical analysis; validation
Address
Hyoungchul Kim, Hyunchul Jang and Bonjun Koo: TechnipEnergies, 15377 Memorial Dr, Houston, TX 77079, USA
Ikjae Lee and Moohyun Kim: Department of Ocean Engineering, Texas A&M University, Haynes Engineering Building,
727 Ross St, College Station, TX 77843, USA
- Development of variable-fidelity FOWT digital twins in extreme sea environments: Part II – high-fidelity CFD analysis Hyunchul Jang, Hakun Jang, Moohyun Kim and Bonjun Koo
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| Abstract; Full Text (2373K) . | pages 043-62. | DOI: 10.12989/ose.2025.15.1.043 |
Abstract
In the coming years, more Floating Offshore Wind Turbines (FOWT) are projected to be installed beyond the continental shelf in the USA and worldwide. Accurate and reliable modeling of various environmental loadings and the resulting dynamic responses are crucial for the structural design, operation, and safety of FOWTs. To develop accurate and reliable FOWT design tools, a collaborative effort between academia (TAMU), industry (Technip Energies), and class society (ABS), supported by the Ocean Energy Safety Institute (OESI), has been undertaken. In this project, accurate and reliable digital twin (DT) models were developed based on high-fidelity CFD models and mid-fidelity potential-flow models. These DT models simulate the coupled dynamics of the floater-turbine-control-mooring system and were validated against 5MW OC3 semisubmersible model test results. The present study is presented in two separate papers. This paper, Part II, focuses on the development and validation of CFD-based high-fidelity DT model for a 15MW semi-submersible wind turbine model. In the high-fidelity coupled analysis methodology, aero-servo-elastic behaviors of the wind turbine blade and tower are simulated by OpenFAST, and the hydrodynamic loads on the floating platform and mooring system are simulated by Technip Energies' CFD-based numerical wave basin tool. The high-fidelity DT simulations were performed for various extreme environmental conditions, and the CFD results were used to calibrate the empirical coefficients of mid-fidelity tools. The development and the validation of mid-fidelity DT models are presented separately in another paper, Part I.
Key Words
Computational Fluid Dynamics (CFD); Floating Offshore Wind Turbine (FOWT); global motion analysis; irregular wave; OpenFAST; numerical wave basin
Address
Hyunchul Jang, Hakun Jang and Bonjun Koo: TechnipEnergies, 15377 Memorial Dr, Houston, TX 77079, USA
Moohyun Kim: Department of Ocean Engineering, Texas A&M University, Haynes Engineering Building,
727 Ross St, College Station, TX 77843, USA
- Equivalent plate method for calculating responses of multi-body floating structure with beam connectors Byoung Wan Kim
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| Abstract; Full Text (4520K) . | pages 63-89. | DOI: 10.12989/ose.2025.15.1.063 |
Abstract
This paper proposed an equivalent plate method to simply analyze multiple floating bodies connected with many beam structures. Proposed method assumes a complicated beam grillage structure as a simple plate by introducing equivalent bending thickness and equivalent distributed mass. With this scheme, we can get a approximate but simpler model to reduce Finite Element Method (FEM) computation. A multi-body floating solar platform with 400 floaters, 200 mooring lines and 100 connector beams were analyzed as a numerical example. Added mass, hydrodynamic damping and wave forces of floating bodies were formulated by Higher Order Boundary Element Method (HOBEM) and the elastic equations of beam or plate were formulated by FEM. By solving the combined equation, body motions, mooring lines tensions and section forces such as shear forces, bending moments and torsion moments in regular & irregular waves were obtained. Responses by wind or current were also investigated. All the results by the equivalent proposed method were compared with the original beam grillage analysis results to check efficiency and accuracy of the proposed method.
Key Words
beam connectors; body motion; equivalent plate analysis; FEM; floating solar platform; HOBEM; mooring line tension; multiple floating bodies; section force
Address
Byoung Wan Kim: Korea Research Institute of Ships & Ocean Engineering (KRISO), Daejeon, South Korea
University of Science and Technology (UST), Daejeon, South Korea
Abstract
Herein, we present the design and development of a 'Finite Element Analysis (FEA)' based model incorporating temperature dependent material properties for impact analysis of blasts on underwater vehicles. Our primary idea is the incorporation of temperature dependent material properties in explosion studies for the design and development of new age shield engineering designs, especially focused towards the applications relevant to the underwater vehicles (e.g. autonomous underwater vehicles, submarines, submersibles, and torpedoes, etc.). We present extensive results that are key towards bench marking. Furthermore, we show and analyse the effect of explosion on square plates of different materials and distribution of stresses, strains and displacements after explosion/impact, etc., are examined in-detail. Our proposed FEA based model is governed by the basic numerical analysis, finite element analysis and thermal/material science. We implement our model in ABAQUS*TM and Matlab**TM software solution systems and develop subroutines to ensure seamless integration. In our model the focus is on large deformation finite element analysis, and we use the Jones-Wilkins-Lee (JWL) equation of state, Johnson Cook parameters, along with temperature dependent material properties. Presented results examine the role of explosion at various heights in the z axis direction on plates of different materials and the '2, 4, 6-Tri Nitro Toluene (TNT)' is used as a representative explosive material. Finally, based upon the results and their analyses suitable design guidelines related to material selection and applications are derived.
Key Words
explosion; finite element analysis; impact analysis; large deformation analysis; material properties; temperature dependent material properties
Address
Pankaj Meena and R. Sharma: Design and Simulation Laboratory, Department of Ocean Engineering, IIT Madras,
Chennai (TN) - 600036, India
