Model tests have invariably tried to simulate the forces of nature - wind, wave and currents. MARIN’s new Offshore Basin will feature top-of-the-range systems in order to ensure more reliable simulation. In a model basin waves are generated by wave flaps, instead of by wind, and it is important to ensure that oscillating flaps don’t induce effects that simply do not exist at sea. In a basin, very complex control is required.
At sea, waves roll on into infinity. However, a model basin is finite, and needs effective beaches to absorb the outgoing waves as much as possible. When waves reflect on the models, they generally return to the wave flaps instead of to the beaches – and this process of reflection can interfere with the required wave spectrum.
The answer is to use an active reflection compensation system on the wave flaps, absorbing reflected waves by comparing the wave elevation on the wave flap with what is theoretically generated and correcting for the difference.
There are three forces which create currents: the tide, main global currents and wind. In a model basin current is pump-generated, and must be re-circulated outside preventing re-circulation in the basin itself. It is a constant challenge to generate a stable current in the basin - yet this is vitally important because of its direct loading on the structure, its interaction with waves and the effect it has on low frequency motions. If the current velocity in a basin varies too much at frequencies close to the natural frequency of a mooring system, this can have substantial effect on the low frequency mooring behaviour.