Depth Compensated Heave Compensator Using Area Ratio Back Pressure
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Solution Overview
Problem
Existing subsea heave compensators face challenges due to the impact of hydrostatic pressure, which limits their ability to achieve spring isolation and increases sensitivity to external pressure, potentially rendering them useless due to errors in mass calculations and length constraints.
Innovation Solution
The integration of a compensating cylinder that uses area ratios to provide back pressure on the low-pressure side of the hydraulic cylinder, offsetting the load from the high-pressure piston rod caused by hydrostatic pressure, allowing for depth compensation without increasing the length of the unit, thus maintaining a balanced system unaffected by varying depths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If hydrostatic pressure is applied to the piston rod in subsea heave compensators, then the unit can operate at depth, but the depth effect compresses the rod and limits the ability to soften the spring system
Solution Approach 1:
The patent applies a counterbalancing principle by introducing a compensating cylinder that generates an opposing force to counteract the hydrostatic pressure effect on the piston rod. The compensating cylinder creates a back pressure that offsets the compressive load from hydrostatic pressure, effectively neutralizing the depth effect and allowing the spring system to maintain its desired softness at depth.
Solution Approach 2:
The patent changes the pressure parameters within the hydraulic system by introducing a compensating cylinder that modifies the pressure distribution. By adjusting the pressure in the compensating cylinder, the system can compensate for hydrostatic pressure effects and maintain optimal spring characteristics across different depths.
2Duration of action of moving object
If the spring curve is flattened to achieve greater spring isolation, then the natural period increases, but the system becomes more sensitive to external pressure and errors in mass calculations
Solution Approach 1:
The compensating cylinder provides a counterbalancing force that offsets the sensitivity to external pressure. By neutralizing the hydrostatic pressure effect on the piston rod, the system can maintain a flattened spring curve and extended natural period without experiencing increased sensitivity to pressure variations or mass calculation errors.
3Object-affected harmful factors
If a tail rod is used to eliminate the depth effect, then the hydrostatic pressure effect is offset, but the length of the unit is doubled
Solution Approach 1:
The patent merges the depth compensation function with the existing piston rod structure by integrating a compensating cylinder that operates within the same structural envelope. This combination allows depth effect compensation without requiring a separate tail rod, thereby avoiding the doubling of unit length while still achieving the necessary pressure offset.
Solution Approach 2:
Instead of extending the solution in the longitudinal dimension (adding a tail rod that doubles length), the patent introduces a compensating cylinder that operates in a different dimensional configuration, providing depth compensation within the existing structural footprint and avoiding length increase.
4Duration of action of moving object
If the volume of nitrogen is increased to lengthen the natural period, then spring isolation improves, but the unit becomes more sensitive to external pressure
Solution Approach 1:
The compensating cylinder provides a counterbalancing force that offsets the external pressure sensitivity associated with increased nitrogen volume. By neutralizing the hydrostatic pressure effect on the piston rod, the system can safely increase nitrogen volume to extend the natural period and improve spring isolation without experiencing detrimental pressure sensitivity.
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 effectively mitigates the depth effect, enabling the natural period of the spring/mass system to be increased, enhancing spring isolation and reducing sensitivity to external pressure, thereby improving the reliability and effectiveness of the heave compensator.
Implementation Method 1
The SPHC is an inline tool that uses the principles of spring isolation to generate a net heave compensation effect or spring isolation effect
Implementation Method 2
The tool is a nitrogen over oil spring dampening device
Implementation Method 3
The difficulties with these types of compensators are the effect that hydrostatic pressure has on the units
Implementation Method 4
The novel design of the SPHC is the use of pressure balancing to mitigate/eliminate the depth effect
Data Source
AI summary
A depth compensated passive eave compensator comprises a first cylinder connected at its upper end to a vessel. A piston rod extends from a piston located within the first cylinder through the lower end thereof and is connected to subsea equipment. A second cylinder contains a compressed gas which maintains pressure beneath the piston of the first cylinder. The upper end of the first cylinder is connected to the upper end of a third cylinder having a piston mounted therein. A piston rod extending from the piston of third cylinder extends through the lower end thereof thereby applying the pressure of the sea to the piston of the third cylinder.