Simulation of Trawl Board and Pipeline Pull-Over Interaction

This paper presents a finite element (FE) model for simulation of trawl board and pipeline pullover interaction. The considered trawl gear system is referred to as a single otter trawl. This system consists of a single trawl net, two trawl boards and a fishing vessel which are connected by steel ropes. The trawl net was modelled by a new simplified trawl net model ensuring high computational efficiency. This trawl net model can simulate the correct tension level in the steel ropes connecting the trawl net and the trawl boards during the pipeline interaction phase, which is crucial to obtain a realistic trawl board interaction behaviour. The trawl boards were modelled as 6-DOF rigid bodies which were assigned a tailormade hydrodynamic load model based on a 3-parameter interpolation scheme both for the added mass and the forward-speed induced loads. Compared to previous work, the applied interpolation scheme was extended and improved in terms of parameter choice and number of parameters. The forward-speed induced loads consist of drag and lift loads. These loads were estimated by flume tank testing considering numerous trawl board configurations in terms of angle of attack, board-seabed inclination angle and gap between the trawl board and the seabed. Detailed measurements of the trawl board applied in the flume tank test were done to obtain an accurate description of the contact geometry, the centre of gravity and the rotational mass properties. The proposed FE model was validated against model test results of trawl board pull-over considering variation of pipeline height, pipeline diameter and trawling velocity. The FE model was found to give very good agreement with the model test in terms of build-up of pipeline interaction forces, peak force level and duration. The FE model is therefore regarded as applicable for use in design analysis of pipeline and trawl board pull-over interaction.