Variable Mass Load Marine Vibrator Depth Compensation
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Solution Overview
Problem
Marine vibrators experience an undesirable increase in resonance frequency due to the 'air spring' effect caused by increasing internal gas pressure as depth increases, which affects their ability to operate effectively at low frequencies for marine seismic surveys.
Innovation Solution
A variable mass load is added to the outer shell of the marine vibrator, which shifts the resonance frequency lower by increasing with depth, compensating for the air spring effect and maintaining resonance frequency independence of water depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the marine vibrator is pressure balanced with external hydrostatic pressure to minimize structural weight, then the structural weight is reduced, but the resonance frequency undesirably increases due to the air spring effect
Solution Approach 1:
A variable mass load is added to the marine vibrator to counterbalance the increasing air spring stiffness at depth. The mass load increases with depth to compensate for the pressure-balanced air spring effect, thereby maintaining a constant resonance frequency while preserving the pressure-balanced lightweight structure.
Solution Approach 2:
The mass load of the marine vibrator is made variable with depth to change the system's inertial properties. By increasing the mass load as depth increases, the resonance frequency is kept constant despite the changing stiffness characteristics of the pressure-balanced air spring.
2Weight of moving object
If the internal gas pressure increases with depth to maintain pressure balance, then the structural weight is minimized, but the bulk-modulus (stiffness) of the internal gas rises causing resonance frequency increase
Solution Approach 1:
The variable mass load acts as a counterweight to the increasing stiffness of the internal gas. As the bulk-modulus of the internal gas increases with depth, the added mass compensates for this stiffness increase, maintaining constant resonance frequency while allowing the pressure-balanced lightweight structure to function.
3Strength
If the stiffness of the structure and internal gas increases with depth, then the structural integrity is maintained, but the resonance frequency increases undesirably
Solution Approach 1:
The mass parameter of the marine vibrator is changed as a function of depth to compensate for the increasing stiffness. By making the mass load variable with depth, the resonance frequency remains constant even as the structural integrity is maintained through increased stiffness at greater depths.
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
The variable mass load allows the marine vibrator to maintain a consistent resonance frequency across varying depths, enhancing its ability to generate low-frequency acoustic energy efficiently and effectively for seismic surveys.
Implementation Method 1
the bulk-modulus (stiffness) of the internal gas also rises. This increase in bulk-modulus or 'air spring' of the internal gas tends to be a function of the operating depth of the source
Implementation Method 2
the stiffness of the structure and the internal gas are primary determining factors in the source's resonance frequency. Accordingly, the resonance of the marine vibrator may undesirable increase when the vibrator is towed at depth
Implementation Method 3
the marine vibrator may be pressure balanced with external hydrostatic pressure. As the internal gas (e.g., air) in the source increases in pressure
Data Source
AI summary
Embodiments related to addition of a variable mass load to the shell of a marine vibrator to compensate for air spring effects. An embodiment provides a marine vibrator, comprising: an outer shell; a driver disposed at least partially within the outer shell and coupled thereto; and a mass load coupled to an exterior surface of the outer shell; wherein the marine vibrator has a resonance frequency selectable based at least in part on the mass load.