Abstract:  A mathematical scheme was proposed and derived to study the dynamics of towed low tension cable with both bending and torsion moment. According to the principle of the classic lumped mass method, a 4DOF (three degrees of translational motion and one degree of rotate motion) mathematical model was formulated, which is employed to analyze the effect of bending and torsion moment on cable. When modeling, the methods were given to determine the three dimensional bending moment, torsion moment and shear force, while a new variable, zerotorsion moment angle, was introduced to eliminate the effect of cables translational motion on torsion moment and finally get the actual torsion moment, then taking the cables buoyancy, weight, drag and tension into consideration so as to result in the whole mathematical model. Three simulation cases were presented subsequently, the results show good agreement with actual dynamic characters of bending and torsion moments effect, which thus validates the proposed mathematical scheme; these results also turn out some valuable conclusions.  

Key words: towed cable, bending and torsion moment, lumped mass method, numerical simulation