An official website of the United States government
The trend of offshore wind energy in deeper water that is expected to shift from fixed to floating platforms requires a cost-effective anchor solution for floating offshore wind turbines (FOWTs). Multiline ring anchor (MRA) has been developed as a cost-effective solution for FOWTs due to its capability of anchoring multiple mooring lines, its high efficiency, and its availability to a wide range of soils and loading conditions. While previous preliminary studies on the anchor performance provide useful insights on how the potential advantages of the MRA can improve load capacity, these studies are limited to focusing on optimizing the anchor design in certain soil and loading conditions. By contrast, the MRA will be installed in seabeds under more complex conditions that depend on geological location, water depth of at-place, and environmental conditions, of which wind, current, and wave are major components. These may result in additional substantial extra capital costs, delays in the projects, and safety issues, when the complex conditions are not properly considered. Specifically, the installation time and expenses of the offshore anchor are very susceptible to anchor types, installation methods, and environmental conditions. For this reason, this paper compares two existing offshore anchor installation methods and different anchor types on the basis of their performance under the same severe environmental condition. In evaluating the installability of the MRA, this paper conducts a comparative scenario study. The results show that the anchor installations and anchor handling vessel (AHV) operations
more »
« less
Effect of Keying Flaps on a Multiline Ring Anchor in Soft Clay
The multiline ring anchor (MRA) was devised as a cost-effective means for securing floating offshore wind turbines (FOWTs) to the seabed. FOWTs occurring in arrays create the possibility for attaching mooring lines from multiple units to a single anchor. Additionally, the deep embedment of the MRA into relatively strong soil permits high load capacity to be achievable with a small and lighter anchor, thereby reducing anchor material, transport, and installation costs. However, since the MRA is shorter than a conventional caisson, features such as wing plates and keying flaps are needed to achieve parity in load capacity with a caisson having a comparable diameter. Preliminary studies show that attaching wing plates to MRA in soft clay is highly effective in enhancing its horizontal load capacity, but only marginally effective in improving vertical load capacity. This motivated the current study investigating the use of keying flaps to further enhance vertical load capacity. Two-dimensional finite element analyses were conducted to understand how keying flaps impact the failure mechanism of the stiffeners and provide reliable evaluations of the uplift resistance of the MRA. The results show that the thickness of the stiffener, flap length, and flap angle can affect the failure mechanism and bearing factors. For the optimal design of the stiffener, a comparative study was carried out to compare the effects of keying flaps and thickness of the stiffener. The studies show that introducing keying flaps can have comparable load capacity with thicker stiffeners and that it can be an economical solution for achieving high vertical load capacity while containing material and fabrication costs.
more »
« less
- Award ID(s):
- 1936901
- PAR ID:
- 10497627
- Publisher / Repository:
- ASCE
- Date Published:
- Journal Name:
- International Foundations Congress and Equipment Expo 2021
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The trend of offshore wind energy in deeper water that is expected to shift from fixed to floating platforms requires a cost-effective anchor solution for floating offshore wind turbines (FOWTs). Multiline ring anchor (MRA) has been developed as a cost-effective solution for FOWTs due to its capability of anchoring multiple mooring lines, its high efficiency, and its availability to a wide range of soils and loading conditions. While previous preliminary studies on the anchor performance provide useful insights on how the potential advantages of the MRA can improve load capacity, these studies are limited to focusing on optimizing the anchor design in certain soil and loading conditions. By contrast, the MRA will be installed in seabeds under more complex conditions that depend on geological location, water depth of at-place, and environmental conditions, of which wind, current, and wave are major components. These may result in additional substantial extra capital costs, delays in the projects, and safety issues, when the complex conditions are not properly considered. Specifically, the installation time and expenses of the offshore anchor are very susceptible to anchor types, installation methods, and environmental conditions. For this reason, this paper compares two existing offshore anchor installation methods and different anchor types on the basis of their performance under the same severe environmental condition. In evaluating the installability of the MRA, this paper conducts a comparative scenario study. The results show that the anchor installations and anchor handling vessel (AHV) operations are sensitive to weather conditions and AHV sizes. In view of total weather standby, the results show that anchor types or installation methods have little effect on it due to their relatively shorter duration than other work sequences. However, the MRA can benefit in substantially reducing transport time and costs due to its compact size. The MRA can be more efficient and cost-effective than other alternatives under complex and severe weather conditions.more » « less
-
A multiline ring anchor (MRA) system has been developed as a cost-effective alternative for securing arrays of floating offshore wind turbines (FOWTs) to the seabed. Multiline attachments can improve the economically competitiveness of FOWTs by reducing the capital cost of the support system for the floating structures. FOWTs can be subjected to severe wind and wave conditions resulting in extreme loads to the anchor system. Thus, the reliable design of the anchor system requires proper determination of the extreme mooring line loads acting on the anchor needed to secure FOWTs to the seabed. Previous studies showed the MRA in soft clay has clear advantages over existing anchors under the extreme horizontal loading conditions imposed by catenary moorings; however, its performance relative to conventional anchors under extreme vertical loading imposed by taut mooring systems requires further investigation. This study presents predictions of extreme loads on floating structures secured by taut mooring systems and evaluates the potential for developing an economical anchor for resisting these extreme loads.more » « less
-
Abstract Birds are agile flyers that can maintain flight at high angles of attack (AoA). Such maneuverability is partially enabled by the articulation of wing feathers. Coverts are one of the feather systems that has been observed to deploy simultaneously on both the upper and lower wing sides during flight. This study uses a feather-inspired flap system to investigate the effect of upper and lower side coverts on the aerodynamic forces and moments, as well as examine the interactions between both types of flaps. Results from wind tunnel experiments show that the covert-inspired flaps can modulate lift, drag, and pitching moment. Moreover, simultaneously deflecting covert-inspired flaps on the upper and lower sides of the airfoil exhibit larger force and moment modulation ranges compared to a single-sided flap alone. Data-driven models indicate significant interactions between the upper and lower side flaps, especially during the pre-stall regime for the lift and drag response. The findings from this study are also biologically relevant to the observations of covert feathers deployment during bird flight. Thus, the methods and results summarized here can be used to formulate new hypotheses about the coverts role in bird flight and develop a framework to design covert-inspired flow and flight control devices for engineered vehicles.more » « less
-
This work focuses on the numerical simulation of multi-plate anchor systems (e.g., helical anchors) in sand subjected to vertical loading. In assessing the stiffness and capacity of these multi-plate anchor systems, full awareness of the abilities and limitations of the various analysis methods must be understood. This work first summarizes studies completed by others and then goes on to assess the failure mechanisms of multi-plate anchors in sand and the influence of (1) plate width-to-depth ratio, (2) number of plates, and (3) relative positioning of plates. The analysis makes use of (1) conventional limit analysis, (2) so-called modified limit analysis that employs reduced strength parameters to account for the influence of soil dilatancy, and (3) the displacement-based finite element method, which considers elastic as well as plastic deformation leading to failure. The work critically reflects on limitations in the current analysis methods for helical ground anchors.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1061/9780784483404.023
