The research plan also recommended an extensive program of laboratory and field experiments to 

 provide data for validating the analytical models at each stage of development. The laboratory experi- 

 ments were to be conducted in water tunnels, towing tanks and wind tunnels, depending on the particu- 

 lar aspect of the phenomenon being investigated and the scale of model required. 



1.4 Scope of the Report. This report is limited in scope to the problems caused by vortex shedding from 

 marine cable structures and moorings, and to the resonant cross flow or strumming oscillations that 

 often are excited by the vortices. The topics discussed in this report are primarily concerned with, but 

 not limited to, the various elements of the NAVFAC/CEL cable dynamics research program. A discus- 

 sion is given of the basic fluid dynamic characteristics of a cable in an incident flow, including the 

 hydrodynamics forces, resonant dynamic response characteristics and Reynolds number effects. Addi- 

 tional consideration is given to the fluid/structure interaction effects of shear (nonuniform flow) and 

 roughness of the cable surface. Relevant experimental findings from towing channel experiments, 

 small-scale field experiments and large scale field experiments also are discussed. 



Strumming analysis methods for both taut and slack marine cables are described together with the 

 computer codes that are available to implement the various analysis procedures. Emphasis is placed 

 here on the development of design procedures, on the definition of hydrodynamic loads and force 

 coefficients applicable in practice, and on the definition of structural and hydrodynamic response param- 

 eters relevant to marine cable design. Towing cable hydrodynamics is not considered explicitly in this 

 report, though many of the topics discussed also are applicable to that problem as well. 



2. CROSS FLOW STRUMMING OSCILLATIONS 



2.1 Resonant Cross Flow Response Characteristics. The frequency /j of the vortex shedding from a 

 circular cylinder is related to the other main flow parameters (D, the diameter of a cylinder; V, the flow 

 velocity) parameters through the nondimensional Strouhal number defined as follows 



fsD 

 St=^. 



