Analytical and Experimental Analysis of Static Friction Forces of Moving Cables Inside Curved Pipes

In-pipe robots are a powerful tool for hydrate plug removal inside ultradeepwater pipes. Most of these robots operate with the energy supplied by umbilical cables. The present work focuses on the development of a general strategy for computing the required forces for pulling such cables confined in ducts of generic length and geometry. Based on classical mathematical models applied in cable friction evaluation, a new equation set was developed and implemented in a computational algorithm designed to evaluate the static friction force related to the cumulative effects along the arbitrary set of curves present in a generic pipe. Therefore, the proposed computational routine can calculate the static friction forces associated with a cable inside a given pipe, whose coordinates are fed by the user. To evaluate the simulation performance, the achieved results were compared with the data obtained through experimental tests performed using a cable with polymeric coating positioned inside ducts. Different geometries, loads, and lubricating conditions were tested, and the analytical model could suitably estimate the required force to move an umbilical cable inside pipes.