October 16, 2010

Pneumatically Stabilized Platform, PSP

If we want to create a Very Large Floating Structure, VLFS, in the open ocean, and as commented in the previous blog, we need a type of structure that attenuates the waves. Semisubmersibles are ideal for that, as in the MOB. But other ideas and technologies are also being developed. The very well known Pneumatically Stabilized Platform, PSP, is a very promising structure.

The PSP, designed by Float Incorporated is a type of pneumatic platform composed of a number of cylindrical shaped components packed together in a rectangular pattern to form a module. Each cylinder is sealed at the top, open to the ocean at its base, and contains air slightly above atmospheric pressure. Most conventional floating platforms acquire their floatation forces by directly displacing the water with their hulls. However, the PSP utilizes indirect displacement: the platform rests on trapped air that displaces the water; the primary buoyancy force is provided by air pressure acting on the underside of the deck. The water in each cylinder moves up and down, and the air pressure in the trapped airspace changes. These spaces are connected through pneumatic lines and valves, so that these pressure changes result in air moving between cells. This dampens the waves and distributes their force in order to reduce peak load on the structure. If air turbines are attached to these lines, it becomes a wave-powered electricity generator.

The PSP has some characteristics of a platform (it can support loads) and some of a breakwater (it attenuates waves). It is built out of concrete, very modular and fairly reconfigurable. However, the design for a floating airport off the San Diego coast was rejected in 2003 as too expensive, so it remains an unproven technology.

The original idea came from the Wave Pumps developments thirty years ago. The main advantage towards seasteading designs is that the problems of energy source and wave attenuation can be solve at the same time (if we are in an area where we have enough waves to produce the required energy for the seastead).

A similar idea for attenuating wave movement is developed in anti-heeling and anti-rolling systems with tanks of the active/controlled type, where the water flow between tanks is controlled with automatic valves. This technology is currently used in ships to avoid the roll movements and not for the heave movements as in the PSP. But in any case, it is a recent but proven technology and not very expensive. So perhaps we could expect that in some years, the PSP could be commercially profitable, because the structure itself made of concrete seems not to be the problem.