An Investigation of the Drag Induced on a Tool in a Granular Medium

An investigation of the drag induced by pulling a tool through a granular medium is reported. The work is aimed at understanding the drag on an offshore cable-laying tool with the objective of producing a model capable of predicting the force required to pull the tool through a granular medium. Experiments were run at 1g in a laboratory rig comprising a channel, containing the granular medium and a frame, in which the tool was inserted into the sand to a fixed depth and pulled through it at a constant velocity. The width, length and depth of insertion of the tool, the shape of the tool face and velocity of towing were investigated in dry sand only. The results show little change in drag force with velocity, over the range investigated, but indicate a power law relation to the depth of insertion. Increase in face width produces a near proportional increase in drag while increases in length produce smaller increases in drag force. The use of a rounded nose on the tool reduces the drag by a factor of up to 30%. A numerical model is proposed which is matched to the data and used to predict the loads on a full-scale device.