Self-locking and Stability of the Bowline Knot

Abstract

We investigate the self-locking of the bowline knot through numerical simulations, experiments, and theoretical analysis. Specifically, we perform two complementary types of simulations using the 3D finite-element method (FEM) and a reduced-order model based on the discrete-element method (DEM). For the FEM simulations, we develop a novel mapping technique that automatically transforms the centerline of the rod into the required knot topology prior to loading. In parallel, we conduct experiments using a nearly inextensible elastic rod tied into a bowline around a rigid cylinder. One end of the rod is pulled to load the knot while the other is left free. The measured force-displacement response serves to validate both the FEM and DEM simulations. Leveraging these validated computational frameworks, we analyze the internal tension profile along the rod's centerline, revealing that a sharp drop in tension concentrates around a strategic locking region, whose geometry resembles that observed in other knot types. By considering the coupling of tension, bending, and friction, we formulate a theoretical model inspired by the classic capstan problem to predict the stability conditions of the bowline, finding excellent agreement with our FEM and DEM simulations. Our methodology and findings offer new tools and insights for future studies on the performance and reliability of other complex knots.