Theoretical study of the “chevroning” of the profiled elements of streamlined cables

Abstract

This paper sets out to explain a phenomenon which has been observed in streamlined cables. It would appear that profiled elements strung along a cable to diminish drag do not position themselves in weather-cock manner in the flow-bed but are staggered in a very stable and symmetrical way with relation to the direction of flow. A theoretical study of the phenomenon which we shall call ‘chevroning’ is made in the case of a rectilinear vertical cable moving at a constant velocity in a plane. The streamlining comprises an infinite series of flat rectangular profiles. The problem is solved in the framework of the theory of non-linearized lifting surfaces and thanks to the distributions of vortex singularities. Results show that there exist positions of stable equilibrium for different chevron angles according to the lengths of the elements and to the position of the rotation axis. This peculiar behaviour of the elements brings into evidence an induced drag which decreases the efficiency of cable streamlining. Calculations are presented which enable the extra force to be evaluated.