Viscous Drag Reducing Cladding with Segmented Air Pockets
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Solution Overview
Problem
Current solutions for reducing viscous drag on marine vessels and pipelines are ineffective due to limitations in materials that mimic the 'Lotus effect,' which fail to maintain non-wetting behavior under hydrostatic pressures and over extended periods, and existing methods like bubbly flow systems require high power and compromise buoyancy.
Innovation Solution
A viscous drag reducing cladding with densely packed air pockets on its outer surface, where each air pocket has a smaller inlet and larger outlet, and is made from hydrophobic materials like PTFE, with an air distribution system that ensures even pressure distribution and prevents biofouling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If non-wetting materials are used to trap air on the surface, then viscous drag is reduced, but the non-wetting behavior fails under hydrostatic pressures and over extended time
Solution Approach 1:
The surface is segmented into numerous discrete air pockets rather than relying on a continuous non-wetting surface. Each pocket is independently pressurized and maintained, allowing the system to function under hydrostatic pressure where traditional continuous non-wetting surfaces fail.
Solution Approach 2:
The air pockets are dynamically pressurized to maintain positive internal pressure that counteracts external hydrostatic pressure. This dynamic pressure maintenance ensures the pockets remain intact and functional at depth, unlike static non-wetting surfaces that collapse under pressure.
2Force
If air is blown through the hull to create large bubbles, then viscous drag is reduced, but power consumption increases and buoyancy is compromised
Solution Approach 1:
Instead of creating a few large bubbles that consume significant power and reduce buoyancy, the system segments the air into numerous small pockets distributed across the surface. This segmentation reduces the total air volume needed while maintaining drag reduction effectiveness.
Solution Approach 2:
Air is supplied locally to specific pockets rather than blowing large volumes through the entire hull. Each pocket receives only the amount of air needed to maintain its internal pressure, significantly reducing total power consumption compared to global bubbly flow systems.
3Force
If air pockets with smaller inlet and larger outlet are used, then viscous drag is significantly reduced, but the system complexity increases
Solution Approach 1:
The air pockets are formed with curved, dome-like geometries that naturally facilitate air flow from the smaller inlet base to the larger outlet apex. This curved geometry simplifies the inlet/outlet configuration compared to angular or flat structures while maintaining the desired flow characteristics.
Solution Approach 2:
The system uses pneumatic principles where air pressure differential naturally drives flow through the pockets from the smaller inlet to the larger outlet. This passive pneumatic design reduces the need for complex active control mechanisms while achieving the desired drag reduction.
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 solution significantly reduces power consumption and greenhouse gas emissions, increases vessel speed and range, decreases propulsive equipment size, and reduces biofouling and noise pollution, while maintaining a dry surface to minimize drag.
Implementation Method 1
The outer surface of each air pocket may comprise a hydrophobic material. The hydrophobic material may comprise polytetrafluorethylene, PTFE, or perfluoroalkoxy copolymer resin, PFA.
Implementation Method 2
The forces from such hydrostatic pressures are far greater than the surface tension forces that non-wetting materials rely on.
Implementation Method 3
If air can be interspersed between the liquid and solid in such a way as to completely separate the liquid from the solid, that the viscous drag in the liquid will effectively be eliminated.
Implementation Method 4
The radius of each air pocket may be less than twice the capillary length of water.
Data Source
AI summary
A viscous-drag-reducing cladding for a ship's hull whereby the wetted area of the hull is reduced by interspersing air between the hull surface and the water. A substantial portion of the submerged area of the ship's hull comprises densely packed air pockets. The dimension of the air pocket is less than twice the capillary length of water. Each air pocket is supplied with pressurised gas by means of a restrictor. The pressurised air is supplied to each air pocket by means of a network of corrugated channels.