Optimisation of Corrugated Duct Profiles

This paper presents a method of optimising the distribution of plastic in a twin-walled, corrugated duct. This could be used to achieve maximum stiffness for minimum linear mass or a desired target stiffness for any envisaged market for the product. Spreadsheet optimisation routines1 based on a generalised reduced gradient solver and Langrangian multipliers were shown to balance structural integrity requirements with efficient usage of raw material. Constrained optimisations were produced ensuring all optimal corrugation shapes were feasible for production on conventional extrusion lines. Typical corrugation profiles were shown to be capable of improvement : stiffness increases of as little as 10% to as much as 50% were achievable provided their structural designs were optimised. For the majority of ducts analysed, the optimum profile could be selected from a family of design curves depending on desired diameter, target mean stiffness and target minimum mass. The peaks, or optimal points, on these families of curves were flat. Therefore the inevitable error bound, or tolerance, on any corrugation dimension (induced as an inherent part of the manufacturing process) would have little effect on a duct’s stiffness provided the profile was close to optimal. The authors’ optimisation routines have been calibrated against various duct profiles and were accurate in calculation of the corrugation’s moment of inertia to within ± 0.5 mm.4