Design of a hybrid grab mechanism

Abstract

Grabs are essential in the process of unloading a bulk carrier by grabbing bulk material such as iron ore from the cargo hold. Due to varying operational conditions, the consistency and the amount of payload can vary significantly. One of the largest varying operational conditions is the occurrence of irregular bulk surfaces. Therefore, it is highly desired to attain a more predicable unloading capacity. This can be achieved by designing a hybrid grab which combines a regular grab with mechanical (rope) closing with an energy storage system that can deliver extra torque to increase the penetration depth. This hybrid grab will be designed by comparing its components on important assessment criteria and it will be analyzed if its stored energy provides more benefits than the additional weight of the hybrid grab mechanism over multiple grab cycles. Six hybrid grab concepts were formed by combining the sub solutions with several interconnection possibilities which resulted in a final concept score. The supercapacitor concept has been chosen as the main design based on the benefit of supercapacitors having the ability the absorb energy quickly and because the electrical system has the benefit to be connected in a smart system with interactive accelerator sensors input. To investigate the performance of the hybrid grab in terms of unloading capacity, several experiments were replicated with a new simulation setup. The average of unloading capacity of these simulations increased by 20.1%. It was found that for a SWL of 50 ton the hybrid grab could be activated half of the times. This resulted in an unloading capacity increase of 7.7% for the hybrid grab. The peak is reached for allowable load or SWL> 58 [ton] after which the hybrid grab is activated every cycle which results in a payload increase of 16.3%. These results show the excellent performance the hybrid grab can deliver when unloading a bulk carrier.