The following approach is necessary tx> understand and predict the propeller forces 

 induced by Item 1: 



a. Conduct model wake measurements in the plane of the propeller at the correspond- 

 ing displacement, trim, and speed of the ship to determine the longitudinal (wake) and tan- 

 gential velocity components. 



b. Analyze the harmonic content of the circumferential wake at various radii within 

 the propeller plane. This will permit the selection of a propeller with the optimum number 

 of blades for minimum thrust and torque forces. 



c. Calculate thrust and torque force fluctuations as derived from the wake survey. 



d. Calculate the off-center thrust (eccentricity) in radial and angular directions. 



e. Calculate the horizontal and vertical bearing forces. 



Inadequate information exists on the fluctuating pressures produced on the surface of the 

 ship by propeller action to permit computation of the forces generated. Tests are currently 

 planned to obtain additional information in this area. Information is also required to deter- 

 mine the magnitude of the forces transmitted through the bearings. Static and dynamic mass 

 unbalance due to geometrical imperfections or lack of symmetry will excite forces and mo- 

 ments at shaft speeds. 



It is considered important, in the design of a ship, to be able to predict the response 

 of the primary hull girder to known exciting forces. This would permit an evaluation of the 

 capability of the ship to perform its intended function and to provide a basis of general ap- 

 proval of the more important design aspects. It is obvious, however, that such a program 

 requires the following basic ingredients before one design can be compared to another or 

 before a design can be evaluated against a given control factor: 



1. A "Basic Computer Program" (Here we are referring to a "Basic Computer Program" 

 as a series of coded problems.) which permits the study of the response of a mechanical 

 system; 



2. A computer program which permits the rapid computation of the exciting forces; 



3. A better understanding of damping mechanisms; 



4. Improved knowledge of virtual mass; 



5. Suitable vibration specifications or limits of acceptability for vibration of the system 

 under study; and 



6. Full-scale program of applicability studies. 



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