Nonlinear Dynamics

, Volume 43, Issue 1–2, pp 197–208 | Cite as

A Two-Strand Ply Hanging Under Its Own Weight



We consider an idealised model for a plied structure such as may form when a straight rod or filament is subjected to a high twisting moment. Examples are found in textile yarns, interwound DNA molecules and bacterial macrofibres. Plied structures, generally composed of more than two strands, are also used widely in engineering (mooring ropes, cables in lift shafts), although here the strands are often not intrinsically straight. The ply is assumed to consist of two strands of thin circular elastic rod winding around each other while touching on a straight line of contact. Each strand is therefore constrained to lie on a cylinder. Using a variational approach we give an unconstrained Hamiltonian formulation for this problem. We also derive an exact expression for the contact force acting between the two strands. We study the symmetry-breaking effect of gravity on the ply configuration as well as on the contact force.

Key Words

constraints contact force elastic rod gravity two-strand ply variational analysis 


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Copyright information

© Springer Science + Business Media, Inc. 2006

Authors and Affiliations

  1. 1.Centre for Nonlinear Dynamics, Civil Engineering BuildingUniversity College LondonLondonU.K.

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