Offshore Wind Gravity Foundation with Hollow Caisson
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Solution Overview
Problem
Current gravity foundations for offshore wind turbines face challenges in design, fabrication, transportation, and installation, particularly at deeper depths, due to limitations in existing technologies, including high costs, resource demands, and instability during towing and sinking phases.
Innovation Solution
A prefabricated reinforced concrete caisson with a circular cross-section and solid concrete ballast, fabricated on a floating dock, providing stability during towing and sinking, and allowing for adjustable ballast levels and mast heights to accommodate varying depths, enabling direct towing and sinking without auxiliary equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional gravity foundations are used for offshore wind turbines at depths greater than 35m, then the foundation stability is compromised, but increasing foundation size and weight to maintain stability significantly increases fabrication costs and transportation difficulties
Solution Approach 1:
The foundation is divided into multiple hollow cells arranged in concentric rings, creating a modular structure that provides both stability and buoyancy. This segmentation allows the foundation to maintain structural integrity while reducing material requirements compared to a solid concrete structure of equivalent size.
Solution Approach 2:
The foundation employs concentric rings of hollow cells nested within each other, creating a multi-layered cellular structure. This nested configuration optimizes the distribution of structural strength and buoyant force while minimizing the overall material volume required for deep-water applications.
2Ease of manufacture
If gravity foundations are fabricated on land and transported to offshore sites, then fabrication processes are well-established, but transportation and installation costs increase significantly, especially for deep water installations
Solution Approach 1:
The foundation is pre-assembled as a complete hollow cellular structure on the floating dock before being towed to the installation site. This preliminary assembly of the entire foundation structure, rather than transporting components, significantly reduces transportation time and simplifies installation operations.
Solution Approach 2:
A floating dock serves as an intermediary platform for fabricating and assembling the foundation structure in a controlled environment before deployment. This intermediary facility enables offshore-style construction with land-based quality control, reducing both transportation time and installation complexity.
3Object-affected harmful factors
If the caisson is designed to fully submerge during sinking to reduce wave loads, then wave resistance decreases, but stability during the sinking process becomes difficult to maintain
Solution Approach 1:
The foundation employs adjustable ballast levels that can be dynamically modified during the sinking process. By controlling the amount of water in the hollow cells, the foundation can maintain optimal stability characteristics at each stage of sinking while progressively reducing wave resistance as it submerges.
Solution Approach 2:
The sinking process incorporates monitoring and adjustment mechanisms that provide feedback on the foundation's stability and orientation. This feedback enables real-time adjustments to ballast distribution and sinking rate, maintaining stability throughout the process while achieving full submersion to minimize wave loads.
4Reliability
If solid concrete ballast is added to increase foundation weight for deeper installations, then stability against wave loads improves, but fabrication complexity and cost increase
Solution Approach 1:
The hollow cellular structure serves multiple functions simultaneously: it provides structural strength, generates buoyancy for towing and sinking operations, and offers ballast capacity through water filling. This multi-functionality eliminates the need for separate solid concrete ballast, reducing fabrication complexity while maintaining stability.
Solution Approach 2:
The foundation utilizes changes in water density and ballast level as adjustable parameters to control stability and sinking behavior. By varying the amount of water in the hollow cells, the foundation can achieve the necessary weight and stability for deep-water installations without adding complex ballast systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces fabrication and transportation costs, enhances safety and efficiency by allowing for standardized processes, and extends the applicability of gravity foundations to depths of 35-50 meters without significant modifications, while maintaining structural integrity and reducing wave loads.
Implementation Method 1
solid concrete ballast at the bottom of the cells, with the thickness varying based on the conditions of the site, whose purpose is to guarantee stable conditions during the towing and sinking of the structure
Implementation Method 2
prefabricated reinforced concrete caisson... fabricated on a floating dock, providing stability during towing and sinking
Data Source
Figure 1
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Figure 3
AI summary
Gravity foundation for offshore wind turbines, fabricated using floating dock technology, comprising a caisson (1) with a circular cross-section, with hollow cells (11, 12, 13) for interior voiding, closed on the top by one or more covers (16), whose central cell (13) is extended into a post-tensioned concrete mast (2), on which the metal tower (4) that supports the wind turbine is attached. The cells (11, 12, 13) of the caisson are filled with solid ballast (8) for the purpose of lowering its centre of gravity, such that the design of the foundation as a whole can be towed and sunk on the open sea without the need for special vessels or the use of additional means of flotation, because it has sufficient naval stability during all of the its phases.