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Comments on “dynamic analysis of three-dimensional marine cables”
Ocean Engng, Vol. 22, No. 7, pp. 761, 1995 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0029-8018/95 $9.50 + .00
Pergamon 0029--8018(94)00026-3
LETTER TO THE EDITOR COMMENTS ON "DYNAMIC ANALYSIS OF T H R E E - D I M E N S I O N A L M A R I N E CABLES" P. A. A. Laura Institute of Applied Mechanics (CONICET), Universidad Nacional del Sur, 8000 Bahia Blanca, Argentina (Received for publication 19 September 1994)
The writer wishes to compliment the author for his extremely important and timely contribution (Huang, 1994). His numerical approach for analyzing the dynamic behaviour of marine cable systems, based upon the lump-mass-and-spring model, deserves considerable credit. It may be of some interest to point out that equations (15) contained in his paper are of the type E1 o4w - S 02w : pAo 02w OX4
OX2
(1)
Ot2
which governs transverse vibrations of an elastic, homogeneous beam of constant cross-sectional area Ao and moment of inertia I, of a material characterized by 9 (mass density) and E (Young's modulus) subject to a tensile force S. If the axial force is of a compressive nature, one has S = - N and, replacing in (1), one obtains E1 04W 0214P 02W Ox4 + N ~x 2 = pAo Ot2
(2)
which coincides with the type of partial differential equations (15) obtained by Huang. With regard to the elastic properties of the cable and its deformation, an important consideration is the "modified Poisson's effect" (Laura et al., 1970). The "modified Poisson's ratio" reflects--essentially--geometry changes within the cable itself (this is true in the case of wire ropes, synthetic cables, etc.). Experimental results reported in the literature almost 25 years ago show, in some instances, values of the "modified Poisson's ratio" higher than 0.50. This effect is quite important when determining drag forces and added water mass, and has not been taken into account when determining cable configurations. Acknowledgements--Research on cable dynamics and failure of cables is sponsored by Secretaria de Ciencia
y Tecnologfa (Universidad Nacional del Sur) under Program 1993-1994 (Director: Professor R. E. Rossi). REFERENCES Huang, S. 1994. Dynamic analysis of three-dimensional marine cables. Ocean Engng 21, 587-605. Laura, P.A.A., Vanderveldt, H.H. and GaIfney, P.G. 1970. Mechanical behavior of stranded wire rope and feasibility of detection of cable failure. Mar. Technol. J. 4, 19-32.
761
Pergamon 0029--8018(94)00026-3
LETTER TO THE EDITOR COMMENTS ON "DYNAMIC ANALYSIS OF T H R E E - D I M E N S I O N A L M A R I N E CABLES" P. A. A. Laura Institute of Applied Mechanics (CONICET), Universidad Nacional del Sur, 8000 Bahia Blanca, Argentina (Received for publication 19 September 1994)
The writer wishes to compliment the author for his extremely important and timely contribution (Huang, 1994). His numerical approach for analyzing the dynamic behaviour of marine cable systems, based upon the lump-mass-and-spring model, deserves considerable credit. It may be of some interest to point out that equations (15) contained in his paper are of the type E1 o4w - S 02w : pAo 02w OX4
OX2
(1)
Ot2
which governs transverse vibrations of an elastic, homogeneous beam of constant cross-sectional area Ao and moment of inertia I, of a material characterized by 9 (mass density) and E (Young's modulus) subject to a tensile force S. If the axial force is of a compressive nature, one has S = - N and, replacing in (1), one obtains E1 04W 0214P 02W Ox4 + N ~x 2 = pAo Ot2
(2)
which coincides with the type of partial differential equations (15) obtained by Huang. With regard to the elastic properties of the cable and its deformation, an important consideration is the "modified Poisson's effect" (Laura et al., 1970). The "modified Poisson's ratio" reflects--essentially--geometry changes within the cable itself (this is true in the case of wire ropes, synthetic cables, etc.). Experimental results reported in the literature almost 25 years ago show, in some instances, values of the "modified Poisson's ratio" higher than 0.50. This effect is quite important when determining drag forces and added water mass, and has not been taken into account when determining cable configurations. Acknowledgements--Research on cable dynamics and failure of cables is sponsored by Secretaria de Ciencia
y Tecnologfa (Universidad Nacional del Sur) under Program 1993-1994 (Director: Professor R. E. Rossi). REFERENCES Huang, S. 1994. Dynamic analysis of three-dimensional marine cables. Ocean Engng 21, 587-605. Laura, P.A.A., Vanderveldt, H.H. and GaIfney, P.G. 1970. Mechanical behavior of stranded wire rope and feasibility of detection of cable failure. Mar. Technol. J. 4, 19-32.
761