C. INFLUENCE OF APPENDAGES 



A comprehensive theoretical study has been made for determining the vibration and 

 flutter characteristics of coupled rudder-diving plane ship vibration systems in forward mo- 

 tion subject to hydrodynamic forces on the rudder. Treatment of "Sprung Body Effects," 

 which consider the influence of heavy elastically attached inertias with one or two degrees 

 of freedom such as a nuclear reactor, machinery, cargo, superstructure, radar mast, boiler, 

 etc. on the response of the hull-control surface system, is included. 



Special emphasis is placed upon digital and electric-analog methods of solution for 

 determining the natural frequencies, mode shapes, critical flutter speeds, and damping of 

 this system and/or parts of this system. This study is reported in TMB Report 1507. Meth- 

 ods for evaluating the hydroelastic parameters for a rudder have also been developed. The 

 procedure for computing these parameters including the damping is given in TMB Report 1508. 

 In particular, methods for determining the structural and viscous damping values for control 

 surfaces from measurements on such surfaces in drydock (or at sea) have been developed. 

 A comparison of theory and experiment for marine control-surface flutter has been made for 

 a model. The work was presented at the Fourth Symposium on Naval Hydrodynamics and is 

 also reported in TMB Report 1567. 



III. PROPELLER-EXCITED VIBRATORY FORCES 



A. ANALYSIS OF STRUCTURAL AND MACHINERY RESPONSE TO CYCLIC FORCES AS 

 DETERMINED FROM MODEL WAKE DATA 



The objective of our program is to develop an adequate theory and method of calcu- 

 lating propeller forces, and of computing the response of the hull and machinery to these 

 excitations. It is necessary to know the relationship between the forces generated and the 

 response of the structure to these forces within the frequency range of interest. 



The propeller forces and moments vibrating the ship hull and structures are induced 

 by: 



1. the nonuniform inflow-velocity into the propeller plane which then transmits forces 

 to the hull through the shaft, struts, bossings, or stern bearings; 



2. oscillating fluid pressures generated by the moving pressure fields associated with 

 the blades of the loaded propeller when passing strut arms, bossings, or the hull; and 



3. mechanical forces resulting from geometric imperfections of the propeller or of the 

 rotating or reciprocating machinery members. 



