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Floating wind turbines represent a cost-efficient energy solution in deep water where bottom-fixed wind turbine becomes excessively expensive. However, mooring design is quite challenging for all shallow water depths including the transition water depth between bottom-fixed and floating wind turbines, in the order of 50-80 m, for which floating con...
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... Some scholars have conducted research on the coupling effect between floating structures and mooring systems in shallow water. Xu et al. (2021) designed seven mooring concepts for a semi-submersible floating wind turbine in shallow water and compared their performance in terms of static characteristics, dynamic responses, and capital cost. The numerical results showed that the traditional catenary mooring configuration is not suitable for shallow water environments. ...
Large-scale floating photovoltaics (FPV) are garnering increased attention as a sustainable solution for renewable energy production and efficient utilization of ocean spaces. These FPV arrays are predominantly deployed in shallow water environments, which present significant challenges in mooring system design due to substantial tidal fluctuations. In such settings, mooring systems may become slack and lose functionality at low tide or risk damage from excessive stiffness at high tide. The primary aim of this study is to develop a mooring system tailored to FPV arrays, capable of withstanding extensive tidal variations without causing damage to the floating modules due to high mooring line tension. Employing HydroD, a hydrodynamic analysis tool based on potential flow theory, alongside OrcaFlex, a time-domain coupled analysis tool predicated on the lumped mass method, we conducted a comparative assessment of six distinct mooring configurations. These configurations, varying in mooring line materials and components, were evaluated from static, dynamic, and fatigue analysis standpoints across a range of tidal levels. The results indicate that taut mooring systems integrated with buoys or clumps consistently exhibit superior performance in all test scenarios. Accordingly, these systems are highly recommended for securing FPV arrays in shallow water environments characterized by severe tidal variations, offering optimal stability and resilience.
... In [37], the authors discussed the effects of buoys on the dynamics of a semi-submersible platform, and explored how the system's operational capacity could be increased by adding more buoys to the system in deep and very deep waters. Finally, several configurations of catenary and taut mooring systems for a semi-submersible 5MW WT in shallow waters, involving different materials, mooring components and anchors, were examined in [38]. The material of the mooring lines has also been found to be a key parameter affecting the strength of the system [39,40]. ...
In this study, the effect of a 10MW DTU wind turbine (WT) on a semi-submersible platform is examined from the point of view of its dynamic behaviour as part of a mooring system with attached buoys. The platform has a rectangular geometry, and consists of four offset and one main cylindrical members. The structure is assumed to receive both wave and wind loading simultaneously. A coupled analysis within the frequency domain is performed using two boundary element method software packages, NEMOH and HAMS. The results are presented in the form of parametric graphs for each of the software packages used and for varying wave directions. The graphs show the hydrodynamic loads exerted on the platform, the wave elevation, the added masses, the hydrodynamic damping coefficients, the mooring line tensions, and the Response Amplitude Operators (RAOs) for the motion of the platform.
... The catenary configuration is usually applied to the floating platforms at water depths between 100 m and 250 m, where it can be considered an optimum solution for the stationkeeping of the system [195]. Based on Figure 13, which shows the cost evolution of a traditional steel chain catenary system regarding water depth, in the case of shallow waters with a depth smaller than 100, the highly dynamic condition in which the floater operates calls for a more expensive station-keeping system [196]. Additionally, the additional mooring line length increases the cost as the water depth exceeds values larger than 250 m. Figure 13. ...
... On the other hand, the taut configuration can be used in water depths smaller than 100 m or larger than 250 m [196]. An example of a taut system used at a water depth shallower than 100 m is the Ideol platform installed close to the French coastline at a water depth of nearly 30 m [197]. ...
Recently, more wind turbine systems have been installed in deep waters far from the coast. Several concepts of floating wind turbine systems (FWTS) have been developed, among which, the semi-submersible platform-due to its applicability in different water depths, good hydrodynamic performance, and facility in the installation process-constitutes the most explored technology compared to the others. However, a significant obstacle to the industrialization of this technology is the design of a cost-effective FWTS, which can be achieved by optimizing the geometry, size, and weight of the floating platform, together with the mooring system. This is only possible by selecting a method capable of accurately analyzing the FWTS-coupled hydro-aero-structural dynamics at each design stage. Accordingly, this paper provides a detailed overview of the most commonly coupled numerical and physical methods-including their basic assumptions, formulations, limitations, and costs used for analyzing the dynamics of FWTS, mainly those supported by a semi-submersible-to assist in the choice of the most suitable method at each design phase of the FWTS. Finally, this article discusses possible future research directions to address the challenges in modeling FWTS dynamics that persist to date.
... However, alternative designs using fiber rope are also considered as future solutions. 6 In an FOWF with shared moorings, adjacent FOWTs are connected by shared lines so that the total number of mooring lines and anchors is reduced compared to the conventional practice. However, shared moorings introduce coupling of neighboring FOWTs and add extra complexity to an FOWF system. ...
Conventional mooring systems contribute significantly to the cost of floating wind projects, and innovative solutions with cost‐saving potentials are desired. In the present paper, we investigate the fundamental dynamic behavior of an innovative tethered‐buoy mooring system for a prototype wind farm in which two spar floating offshore wind turbines (FOWTs) are moored to five submerged tethered buoys. Numerical decay tests are used to characterize the fundamental frequencies and oscillatory modes of the system. The influence of net buoyancy is established through a parametric study. Finally, the dynamic response of the tethered‐buoy mooring system is compared against two alternative shared mooring configurations with catenary mooring lines. Time‐domain simulations are carried out for one accidental scenario with a parked and an operational FOWT, and one extreme scenario with two parked FOWTs. The results show that net buoyancy has a significant influence on platform motions and mooring loads. Compared to alternative configurations with catenary mooring lines, the tethered‐buoy mooring system exhibits substantially lower mooring tension loads and practically eliminates the threat of snap events. The reduction in the maximum characteristic fairlead tension is up to 85%. The mean positional offset of the wind turbines in the loading direction is larger, up to 36% of the water depth, however, the relative motions are comparable. The mean distance between the FOWTs is even smaller for the tethered‐buoy system. With the application of dynamic inter‐array cables, the proposed tethered‐buoy system can be a promising mooring solution for floating offshore wind farms.
... Pham et al. [14] proposed a practical modeling procedure for conducting numerical mooring analyses for a floating wind turbine considering the dynamic axial stiffness of nylon lines. Xu et al. [15] studied seven mooring concepts for a 5 MW semi-submersible floating wind turbine to identify structurally reliable and economically attractive mooring solutions. Xiang et al. [16] tested the dynamic response of a spar-type floating wind turbine foundation with a taut mooring system using a finite element method (FEM)-based tensile mooring line model. ...
The influence of mooring systems with lines of different material on the dynamic response of a floating wind turbine is studied using a 5 MW OC4-DeepCwind semi-submersible wind turbine as a representative prototype in this study. Two types of mooring systems were designed using the MoorDyn module in OpenFAST software (v3.1.0): one uses chains, and the other uses a hybrid mooring line composed of chains and high-strength polyethylene (HMPE) ropes. A wind turbine with two types of mooring systems was simulated using the OpenFAST software. The results show that the floating wind turbine moored with the hybrid lines exhibited a larger heave and pitch motion than that moored using chains alone. At the same time, the surge displacement was smaller than that of the wind turbine using chains alone. In terms of mooring line tension, the mean and amplitude values of the hybrid mooring system at the location examined were smaller than those of the chain mooring system. Thus, using HMPE ropes in the mooring system can significantly reduce line loads. In addition, the HMPE ropes used in the floating wind turbine mooring system did not affect the power generation of the wind turbine. This study provides promising support data and observations for applying high-strength polyethylene (HMPE) ropes in mooring systems for floating wind turbines.
... Several recent papers have examined the mooring of floating wind turbines. Xu et al. (2021) looked at seven different mooring concepts for 50-m water depth, including a taut synthetic line. Its stiffness was modelled using the approach developed for polyester within the SYROPE JIP (Falkenberg et al., 2017), with a linear dynamic stiffness dependence on mean tension. ...
... Yuan et al. (2014) introduced an innovative hybrid mooring system using clump weights and buoys to transform the mooring line from taut to catenary shape, resulting in reduced tension without a significant impact on motion response. Xu et al. (2018Xu et al. ( , 2021 performed different mooring lines arrangement utilizing taut and catenary mooring lines with further components (clump weight and buoy) for hydrodynamic and mooring tension analysis. Neisi et al. (2022) proposed two hybrid mooring systems, Multi-Segmented Mooring lines including Buoy and Single clamp Weight (MSM-BSW) and Buoy and Multi clump Weight (MSM-BMW), for floating wind turbine platforms, demonstrating reduced surge and pitch motions with the taut line in the BSW concept. ...
The mooring system can effectively reduce the dynamic response of floating wind turbine platforms (FOWT), especially in extreme environmental conditions. Investigating mooring line failure is crucial for ensuring safety in FOWT operations. MSM-BMW is the multi-segment mooring (MSM) arrangement of the catenary and taut lines, consisting of the buoy multi-clump weight (BMW) that is proposed as a new concept to reduce platform hydrodynamic response. The aim of this study is to assess the performance of FOWTs in both intact and mooring system failure scenarios for two mooring systems: OC4-DeepCwind, representing the primary configuration, and MSM-BMW, representing a hybrid mooring system. The boundary element method has been used in the time domain under irregular wave conditions in different wave directions. To simulate mooring line failure, a specific mooring line was intentionally detached from the floating platform at a predetermined time. The hydrodynamic platform responses, mooring line tensions and their statistical responses were checked. Based on the result the BMW concept presents a better performance in both intact and failure modes in comparison primary mooring system (OC4) that significantly reduces platform offset.
Keywords:
OC4-DeepCwind, Multi-segment arrangement, MSM-BMW, Mooring line failure, FOWT responses, mooring tension.
... Although strength reduction could be more significant over long-term operation, the safety factor designed for synthetic fiber ropes still encompasses the required range. Through experimental investigation and decay analysis, Xu et al. (2021) found that polyester effectively 2 of 25 restricts the heave motion of Wave Energy Converts (WECs) more than nylon due to its higher stiffness and greater damping [7]. Consequently, they highlighted nylon as a more favorable material for WECs compared to polyester. ...
... Although strength reduction could be more significant over long-term operation, the safety factor designed for synthetic fiber ropes still encompasses the required range. Through experimental investigation and decay analysis, Xu et al. (2021) found that polyester effectively restricts the heave motion of Wave Energy Converts (WECs) more than nylon due to its higher stiffness and greater damping [7]. Consequently, they highlighted nylon as a more favorable material for WECs compared to polyester. ...
... Using the T-N curve method, Wu et al. (2015) performed analytical numerical analysis to calculate the fatigue damage for low frequency and wave frequency tension [9]. Additionally, Xu et al. (2021) provided experimental data to investigate the dynamic tension response in hybrid moorings, proposing seven different mooring concepts considering the ultimate limit state (ULS) [10]. ...
Floating offshore wind turbines (FOWTs) are one of the innovative solutions to achieve net-zero emissions. Given that Taiwan has abundant wind power resources in its western waters and wind farms are evaluated as potential sites, a strategic emphasis on the extensive expansion of wind power is imperative. This paper chooses four different designs of hybrid mooring systems, comparing them with the conventional pure chain mooring arrangement in shallow water regions in Taiwan through integrated numerical simulations, ANSYS AQWA, and Orcina OrcaFlex. The use of synthetic fiber ropes in hybrid moorings provides substantial economic and operational advantages, making them the preferred alternative to traditional chains in deepwater offshore renewable energy (ORE) mooring configurations. Hybrid mooring enables the FOWT to survive in extreme sea conditions and is presented as the ultimate limit state (ULS) and fatigue limit state (FLS). In addition, hybrid mooring not only reduces mooring line costs but also minimizes the footprint area on the seabed, enhancing economic competitiveness and optimizing marine space utilization. However, it increases the entanglement risk that may pose a potential threat to marine mammals. Building on prior research, this paper proposes a unique approach to calculate the mooring line swept volume, which is essential for entanglement assessment and marine spatial planning.
... Brommundt et al. [68] created a numerical tool for catenary mooring system optimization, and a case study using a semisubmersible floating wind turbine with two different water depths was carried out [69]. ...
... The design of MLs needs to consider the working environment and level of technological maturity, in addition to the material cost. For instance, at intermediate water depths (e.g., 50-80 m) (Xu et al., 2021), the advantage of less effective weight using synthetic rope may be insufficient to overcome its disadvantage in terms of cost. The primary technical consideration of MLs is their performance in terms of reliability. ...
Global warming caused by the emission of fossil fuel consumption has become critical, leading to the inevitable trend of clean energy development. Of the power generation systems using solar energy, the floating photovoltaic (FPV) system is a new type, attracting wide attention because of its many merits. The latest progress in the research and applications of FPVs from multiple aspects is summarized in this paper. First, the development of FPVs is briefly described with a summary of typical installed FPV systems. Innovative photovoltaic design concepts and hybrid usage with other renewable energies are emphasized for offshore applications. Furthermore, critical structural design considerations are discussed, particularly emphasizing critical aspects such as load estimations, wave-structure interaction analysis, floating structure types, and mooring system design. Finally, several significant future challenges to the development and applications of marine FPV systems are identified, including survivability in the open sea, long-term reliability, and environmental impact. It aims to provide a broad overview of the development status, offering limited insights into the trends and challenges for marine FPV systems.
