In order to validate the simulation results and develop heave compensation control strategy, heave compensation model tests were performed. The model test installation included the mining ship motion simulator, the heave compensation system, the lifting pipe simulator, the buffer simulator and the water pool. The mining ship motion simulator was able to perform under the predetermined attitude path smoothly. The heave compensation system includes a heave compensated platform which is to compensate heave motion and a gimbaled platform which is to accommodate pitch and roll. Heave compensation tests of mining ship motion under harmonic wave and random wave were carried out. PID control is selected as the control strategy here. Tests under random wave show that the heave compensation effect is more than 60% and reach the requirement which is set to 50%. The model tests results indicate that this heave compensation system is effective and feasible.
At present, the pipeline lifting mining system is the most popular mining system. The nodules collected by the miner are lifted by the fluid rising force through the lifting pipeline to the mining ship. Under the sea wave, the lifting pipeline moves with the motion of mining ship, which causes large axial stress on lifting pipeline. To make mining operation secure, a heave compensation system is absolutely necessary. Since the 1960s, various studies and analysis have been carried out about heave compensation systems of pipelines in deep-ocean mining. In 1968, a heave compensation system between travelling block and hook used in oil drilling platform was proposed by VETCD Company, USA. It was composed of hydraulic cylinders, accumulator, locking device etc. The hydraulic cylinder displacement is larger than the heave amplitude of wave height and the load of hydraulic cylinders is nearly 600 tons. In 1976, a heave compensation device for marine use was proposed by William David Stevenson of Scotland Brown Brother Company (Stevenson, 1976). It included a passive load supporting system and an active force adjusting system.