Submersible Aquaculture Cage Depth Control via Variable Buoyancy
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Solution Overview
Problem
Offshore aquaculture cages face significant challenges in withstanding harsh marine conditions, such as high waves and currents, making them expensive to design and maintain, as they need to be engineered to withstand extreme storm conditions, which is not economically viable for commercial fish farming.
Innovation Solution
A submersible cage with a variable buoyancy float system that can adjust depth to avoid harsh weather conditions, using a flexible connecting element with a denser material than water to stabilize the cage, allowing it to be submerged during storms and raised for maintenance, with adjustable buoyancy achieved through fluid density changes or volume adjustments, and an air supply for optimal aquatic conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cage is designed to withstand maximum wave effects, then it can survive harsh storm conditions, but the structure becomes expensive and difficult to make commercially viable
Solution Approach 1:
The cage system employs dynamic depth adjustment capability, allowing the cage to move between surface and deep submersion positions based on weather conditions. This dynamic behavior replaces the need for static over-engineering, enabling the structure to adapt to varying environmental loads and avoid the highest waves during storms without requiring expensive reinforcement.
Solution Approach 2:
The system changes its vertical position parameter in response to wave conditions. By adjusting depth based on sea state, the cage modifies its exposure to wave forces, transitioning from surface-level exposure during calm conditions to deep submersion during storms, thereby reducing structural requirements while maintaining reliability.
2Ease of operation
If the cage is kept at floating position for maintenance access, then ease of operation is improved, but exposure to harsh weather conditions increases
Solution Approach 1:
The cage system dynamically adjusts its vertical position based on operational requirements and weather conditions. During maintenance operations, the cage floats at the surface for easy access. When storms approach, the system automatically submerges to protective depths, thereby reducing weather exposure while maintaining operational accessibility when needed.
Solution Approach 2:
The cage periodically transitions between surface and submerged positions according to weather forecasts and operational schedules. This periodic movement allows the system to maximize maintenance access during calm periods while minimizing storm exposure during adverse weather, optimizing both ease of operation and protection from harmful factors.
3Object-affected harmful factors
If the cage is submerged to avoid harsh conditions, then protection from storms is improved, but access for maintenance becomes difficult
Solution Approach 1:
The cage system employs dynamic depth control, allowing it to submerge to protective depths during storms and return to the surface when weather conditions improve. This dynamic positioning provides storm protection when needed while restoring maintenance accessibility after adverse conditions pass, eliminating the need to choose between protection and access.
4Reliability
If heavy structures like oil rigs are used to withstand 30m waves, then survival in harsh conditions is improved, but cost increases prohibitively
Solution Approach 1:
Rather than using heavy static structures like oil rigs, the aquaculture cage employs dynamic depth adjustment to survive harsh conditions. By submerging to protective depths during storms and returning to surface during calm periods, the system achieves comparable reliability to fixed heavy structures but at a fraction of the cost, making offshore aquaculture economically viable.
Solution Approach 2:
The cage system uses lighter, more economical structures that can be dynamically positioned rather than expensive permanent installations. This approach trades the need for costly heavy-duty fixed structures for more affordable movable cages that achieve equivalent protection through strategic depth adjustment, significantly reducing capital investment requirements.
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 design reduces structural and fatigue stresses, lowers engineering requirements, and associated costs, while providing optimal habitat conditions for aquatic animals, increasing growth rates and reducing mortality, and allows for easy maintenance and access, making the system more commercially viable.
Implementation Method 1
By varying the buoyancy of the variable buoyancy float, the cage can be raised to a floating position and submerged to a desired depth
Implementation Method 2
The connecting element is made from a material of a different density to the ambient water. The connecting element is more dense than the ambient water so that it sinks and provides a downwards force on the variable buoyancy float and on the mount structure
Data Source
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AI summary
A submersible cage for offshore aquaculture, comprising: a cage (10) for containing aquatic animals; a variable buoyancy float (15); a flexible element (17) connected at one end to the cage and with the other end arranged such that the weight distribution of the flexible element between the cage and another support (40) can be adjusted by varying the buoyancy of the variable buoyancy float; and a mount structure (40) separate from the cage; wherein the flexible element is connected between the cage and the mount structure; and wherein said flexible element is arranged such that at certain depths of submersion, the flexible element hangs in an arc between the cage and the mount structure. By varying the buoyancy of the variable buoyancy float, the cage can be raised to a floating position (e.g. for maintenance) and submerged to a desired depth. The depth at which the cage is submerged depends on the buoyancy of the variable buoyancy float (15) and can be adjusted freely to suit the conditions. By adjusting the buoyancy to submerge the cage in harsh weather, the cage can be protected from the worst of the conditions. For example, the cage can be submerged to a depth such that it remains well below the troughs of the waves, even in extremely high wave conditions. When the cage is fully submerged it also does not experience high winds and the strengths of storm currents may be weaker at deeper depths. This significantly reduces the stresses that will be experienced by the cage during a storm and thus significantly reduces the engineering requirements and costs.