Subsea Structure Tilting Method for Splash Zone Load Reduction
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Solution Overview
Problem
Existing methods for lowering subsea structures with flat support bases into the water through the splash zone result in significant load changes on the structure and hoisting equipment, leading to potential damage due to the full area of the support base contacting the water, and limited operational windows due to harsh weather conditions.
Innovation Solution
The method involves lifting the subsea structure into a horizontal position, tilting it into a tilted position while suspended in the air to reduce the area of contact with water, lowering it through the splash zone in this position to minimize load changes, and then tilting it back horizontally once submerged, using offset hoisting cables for controlled movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the subsea structure is lowered into the water in a horizontal position with the flat support base parallel to the water surface, then the structure is stable and easy to handle, but the full area of the support base contacts the water simultaneously causing large dynamic load changes that can damage the structure and hoisting equipment
Solution Approach 1:
The subsea structure is tilted to a predetermined angle (10-45 degrees) before entering the splash zone, so that only a portion of the flat support base contacts the water first. This preliminary positioning action reduces the contact area and mitigates the dynamic load changes that would otherwise occur when the full base contacts the water simultaneously, thereby preventing damage to the structure and hoisting equipment while maintaining operational stability
2Strength
If the subsea structure is tilted to reduce water contact area, then the dynamic load changes are reduced, but the structure becomes more difficult to handle and requires complex hoisting operations
Solution Approach 1:
The hoisting system dynamically adjusts the tilt angle of the subsea structure during the lowering operation. The structure is tilted to the optimal angle (10-45 degrees) specifically when passing through the splash zone to minimize load changes, and then returned to horizontal position after submersion. This dynamic adjustment optimizes both damage prevention and operational ease at different stages of the process
Solution Approach 2:
The tilting operation is performed periodically - tilting to the predetermined angle before entering the splash zone, maintaining this angle during the critical water entry phase, and then returning to horizontal position after submersion. This periodic action pattern ensures damage prevention during the critical phase while maintaining ease of operation during stable phases
3Loss of time
If the subsea structure is lowered quickly through the splash zone, then the exposure time to harsh weather conditions is reduced, but the control precision and safety during the critical water entry phase are compromised
Solution Approach 1:
The subsea structure is pre-positioned at the optimal tilt angle (10-45 degrees) before entering the splash zone, so that when it does enter, the water contact is already optimized to minimize dynamic loads. This preliminary preparation allows for quick passage through the splash zone while maintaining safety and control precision, as the critical positioning is done in advance rather than during the rapid water entry
Solution Approach 2:
The hoisting system continuously monitors the position, angle, and load parameters of the subsea structure during lowering, and adjusts the tilting and lowering rates in real-time based on feedback from sensors. This feedback control ensures that the structure maintains the optimal tilt angle during splash zone passage, balancing quick transit with safety and control precision
Data Source
Figure 1~1A
Figure 2
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AI summary
The present invention relates to a method for lowering a subsea structure to be installed on the seabed into the water through the splash zone, said subsea structure comprising subsea equipment arranged on a substantially flat support base for preventing the subsea equipment to sink into the seabed. The method according to the invention comprises: lifting the subsea structure into the air in a horizontal position in which the flat support base extends substantially parallel to the horizontal plane; tilting the subsea structure while suspended in the air from the horizontal position into a tilted position in which the flat support base is angled with respect to the horizontal plane; lowering the subsea structure into the water through the splash zone in the tilted position; and tilting the subsea structure while suspended in the water below the splash zone back into the horizontal position.