UUV Buoyancy Drift Correction via Subsea Station Material Transfer
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Solution Overview
Problem
Unmanned underwater vehicles (UUVs) experience buoyancy drift over long periods of immersion due to water absorption and shrinkage of buoyancy blocks under hydrostatic pressure, leading to unpredictable buoyancy changes and difficulty in depth control, especially in deep water.
Innovation Solution
A method and system for adjusting the buoyancy of UUVs using a subsea station where buoyancy drift is measured and corrected by transferring buoyancy-adjustment material, such as granular solids or liquids, between the UUV and the station, allowing for autonomous correction without surface support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If permanent buoyancy blocks are used in UUVs, then neutral buoyancy is achieved over a range of depths, but buoyancy drift occurs over long periods due to water absorption and shrinkage
Solution Approach 1:
The patent applies a dynamic buoyancy adjustment system that allows the UUV to modify its buoyancy characteristics in real-time. A variable buoyancy device is incorporated alongside the permanent buoyancy blocks, enabling the vehicle to compensate for buoyancy drift by adjusting the volume of buoyant material. This dynamic adjustment mechanism transforms the static buoyancy system into an adaptive one, maintaining neutral buoyancy throughout extended missions.
Solution Approach 2:
The patent implements a feedback control system that continuously monitors the UUV's depth and buoyancy state. Depth sensors and pressure transducers provide real-time data to a control system, which calculates the required buoyancy adjustment and actuates the variable buoyancy device accordingly. This closed-loop feedback mechanism ensures that buoyancy drift is detected and corrected automatically, maintaining stable operation over long durations.
2Duration of action of moving object
If UUVs remain deep underwater for long periods, then extended missions are enabled, but buoyancy control becomes difficult due to unpredictable buoyancy changes
Solution Approach 1:
The patent employs a self-regulating buoyancy control system that automatically compensates for buoyancy changes without requiring manual intervention. The system uses onboard sensors to detect depth and buoyancy state, then autonomously adjusts the variable buoyancy device to maintain neutral buoyancy. This self-service capability allows the UUV to operate independently for extended periods, performing extended missions while maintaining ease of depth control through automated compensation of buoyancy drift.
3Ease of operation
If thrusters are used to maintain depth, then depth control is achieved, but excessive energy is consumed and sediment is stirred up near the seabed
Solution Approach 1:
The patent uses buoyancy forces as a counterweight to gravitational force, creating neutral buoyancy that naturally balances the UUV at its operating depth. By configuring the permanent and variable buoyancy devices to match the vehicle's weight, the system eliminates the need for continuous thruster operation to maintain depth. This anti-weight approach allows the UUV to hold station without energy consumption, and when operating near the seabed, prevents thruster downwash from stirring up sediment by removing the need for upward thrusting.
4Reliability
If variable buoyancy systems are added to correct drift, then buoyancy stability is improved, but device complexity increases
Solution Approach 1:
The patent employs a flexible bladder or membrane-based variable buoyancy device that can change volume in response to pressure differential. This flexible shell structure allows for simple, reliable buoyancy adjustment without complex mechanical components. The bladder can be inflated or deflated using basic pneumatic or hydraulic actuation, providing variable buoyancy capability while maintaining relatively simple system architecture. This approach improves buoyancy stability without proportionally increasing device complexity.
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 approach stabilizes the buoyancy of UUVs, reducing the need for excessive thruster use and enabling longer, more accurate underwater missions by maintaining consistent depth control without the need for frequent surface refueling or complex systems.
Implementation Method 1
the permanent buoyancy is provided by permanently buoyant elements such as buoyancy blocks of syntactic foam
Implementation Method 2
The buoyancy drift may be measured using depth sensors or pressure transducers on the UUV
Implementation Method 3
The buoyancy drift is corrected by transferring an appropriate amount of buoyancy-adjustment material to the UUV from, or from the UUV to, the subsea station
Data Source
AI summary
A method of adjusting buoyancy of an Unmanned Underwater Vehicle (UUV) includes measuring buoyancy drift of the UUV when underwater. After docking the UUV with a subsea station, a quantity of a flowable buoyancy-adjustment material held onboard the UUV is changed by transferring that material from the station to the UUV or from the UUV to the station. A buoyancy adjustment system for a UUV includes: an onboard tank for holding a variable quantity of the buoyancy-adjustment material and upwardly-opening and downwardly-opening passageways communicating with the tank for transferring the buoyancy-adjustment material to or from the UUV. The subsea station includes: a dock for docking a UUV; a holding tank for holding the buoyancy-adjustment material; and at least one upwardly-opening or downwardly-opening passageway aligned with the dock and communicating with the holding tank for transferring the buoyancy-adjustment material to or from the docked UUV.