At Stationmar AS we have developed a (patent pending) technology that neutralizes all vertical movements due to ocean waves in a semi-submersed structure. This is done through the design of a purpose-built rise canister connected to a trapped air container system that is being built into the columns of the semi-submersible structure.
Neutralize heave motion
The Stationmar Heave Movement Neutralization (HMN) technology is a naturally passive system that requires very limited interference only during extreme conditions. Simply by the special design of the rise canister and the trapped air container will the vertical energy be neutralized during operating conditions.
This is how it works
In the column, below the lowest water level, a rise canister is built in. The water level in the riser canister is balanced by a pressurized air volume in the hull above the water table. As a wave passes by, the water level rises around the column, which means that more of the column will be submerged. This increased submerged volume increases buoyancy to the hull which will tend to lift the hull in relation to the seabed. The increased water level height ads hydrostatic pressure to the trapped air volume above the water in the riser canister below. The added hydrostatic pressure compresses the air which allows increased water level in the riser canister. This reduces buoyancy of the hull exactly correspondingly to the added buoyancy by the column above. The volume of the air and the shape of the riser canister ensures that the multiple
of pressure and volume – p x V – is constant, thus the system is energy neutral.
The above animation is just showing the principles of the heave motion technology. For implementation in a floating wind turbine, see “Sakayan” in the Application section, which also show a foundation that eliminates the pitch & roll motions of a floating wind turbine. This also demonstrates an additional system called ENPAC, which ensures that the heave motion also works for the short periods with high frequency short waves.