Tension Leg Platform Installation via Decoupled Pull-Down Lines
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Solution Overview
Problem
The installation of tension leg platform (TLP) based floating objects, such as offshore wind turbines, is hindered by instability during mooring line installation, requiring calm sea states to avoid instability, and the process is complex due to coupling of tensioning systems with mooring lines.
Innovation Solution
A method using an installation vessel and a remotely operated underwater vehicle (ROV) to attach mooring legs and tensioning lines to anchor points, decoupling the pull-down operation from mooring leg installation, allowing for better stability and simplified operations by lowering the floating object with tensioned pull-down lines and then rising it with mooring lines in tensioned mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the TLP is stabilized during installation of mooring lines using traditional ballasting method, then the installation can be completed, but the floating object can only be installed under (very) calm sea states to avoid risk of instability
Solution Approach 1:
The installation process is segmented into distinct phases: first installing anchor points and pull-down lines to create initial stability, then installing mooring lines while the structure is stabilized, and finally transitioning to operational mode. This segmentation allows stability to be maintained during the critical mooring line installation phase without requiring calm sea states for the entire operation.
Solution Approach 2:
Anchor points and pull-down lines are installed beforehand to create a preliminary stabilization system before the actual mooring line installation begins. This preliminary action ensures the floating object is stabilized during the vulnerable installation phase, enabling operations in higher sea states.
2Ease of operation
If the tensioning system is coupled with the tendons using pull-down lines connected to the top of tensioners, then the pull-in operation can be performed, but the process becomes complex and requires coordination of multiple operations
Solution Approach 1:
The pull-down line tensioning operation is extracted and separated from the mooring line installation process. The pull-down lines are installed and tensioned independently to stabilize the structure, then mooring lines are installed while the structure remains stabilized, simplifying the overall process by decoupling these operations.
Solution Approach 2:
Pull-down lines serve as an intermediary stabilization mechanism during installation. They provide the necessary tension and stability during mooring line installation, then are released and removed after serving their purpose, acting as a temporary mediator that simplifies the main installation operation.
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 method enhances stability during installation, allows for higher sea-state operations, simplifies the connection of mooring legs, and improves safety and efficiency by reducing the need for on-board equipment and personnel, enabling more flexible project planning.
Implementation Method 1
tensioning the pull-down lines such that the floating object is lowered with respect to the water surface to an installation elevation level below an operational elevation level
Implementation Method 2
the floating object rises upward from the installation elevation level to the operational elevation level where the mooring lines are in tensioned mode
Data Source
AI summary
A method for installing a TLP based floating object at anchor points. The floating object includes a central body and buoyancy assemblies positioned around the central body in a horizontal plane, with each buoyancy assembly connected to the central body and connectable to one of the anchor points. The method includes: attaching a mooring leg including a mooring line at each anchor point; for each anchor point connecting a pull-down line between the buoyancy assembly and the anchor point; tensioning the pull-down lines so the floating object is lowered to an installation level below an operational level; for each anchor point connecting the mooring leg with the buoyancy assembly in slack mode; and after connecting the mooring lines with the buoyancy assemblies, paying out the pull-down lines so the floating object rises upward from the installation level to the operational level where the mooring legs are tensioned.