Appendix £ 

 OTHER CABLE STRUMMING PREDICTION MODELS 



The "wake-oscillator" model described in the previous appendix is but one of the several models 

 for predicting the response of bluff structures to vortex shedding-induced forces. However, most of 

 these other models have not been sufficiently extended to the case of an arbitrary flexible body such as 

 a cable. The several categories of predictive models are: 



• Empirical models, in which the hydrodynamic forces are derived from experiments; 



• Random vibration models, in which the vortex forcing and cable response are modeled as 

 stochastic processes; 



• Discrete vortex methods, in which the flow field parameters and the hydrodynamic forces 

 are computed from the motions of arrays of discrete vortices inserted into the flow; 



• Numerical solution of the Navier-Stokes equations, in which the complete equations of 

 unsteady fluid motion are integrated numerically. 



The first two methods have been developed specifically toward applications to predicting the 

 vortex-excited oscillations of flexible members such as cables. The third and fourth methods are, 

 except for special cases, limited to problems in two dimensions. These methods have not been 

 extended to practical design problems but they have employed in basic fluid dynamic studies. 



E.l The Prediction of Strumming Parameters from Measured Force Coefficients. The equation for the 

 resonant cross flow vibration of an elastically-mounted, rigid cylindrical structure, with the vortex and 

 vibration frequencies locked on, can be written in general as 



161 



