One approach under study considers the presentation of the vibratory environment in 

 the form of statistical distribution functions, i.e., a mean level may be established together 

 with a standard deviation. The latter will define the probability of the data falling within 

 the prescribed band. 



V. DESIGN PROCEDURES AND STANDARDS 



The practicing naval architect has not the time to study the exponentially increasing 

 volume of technical literature to overcome problems important for the design of a ship. To- 

 day, he must have the ability to translate the theoretical approach into practical application. 

 Most theoretical analyses and predictions are based on ideal properties and may be inappli- 

 cable or require a correction factor. However, it is most important that the naval architect 

 be aware of the fundamental concepts which are significant and should be considered in the 

 earliest design stage. It is, therefore, necessary to provide him with a guide useful in the 

 early design stages and which will permit the verification of ship response by reliable cal- 

 culations at a time when design changes are possible. He should also be provided \vith 

 standards, norms, and specifications useful in vibration control. Vibration characteristics 

 are seldom considered in the preliminary design procedure, but are important to avoid later 

 problems of mechanical suitability, habitability, and operability. Mr. McGoldrick's TMB Re- 

 ports 1451 of December 1960 and 1609 of April 1962 will assist in better communication be- 

 tween the scientist doing research and development work and the practicing naval architect. 



A. DESIGN PROCEDURES 



The objective is to establish rational methods to be used during the design stage of 

 a naval vessel to prevent vibration levels which will interfere with proper functioning of ship- 

 board equipment. Reasonably simple methods of predicting hull and machinery response 

 should be provided. Shaft rpm and blade frequency should be chosen to avoid hull resonances, 

 where possible. The choice of propellers and details of hull design should be studied to ob- 

 tain minimum exciting forces. 



It is the objective of the Vibration Division to develop a computer process or proces- 

 ses which would logically fit into the design procedure. For example, it is quite logical 

 that such a program of vibration analysis could be utilized in the early stages of preliminary 

 design as an accepted influence on preliminary lines, machinery details, general arrangement, 

 choice of propellers, etc. This program presumably would replace the limited vibration anal- 

 yses that are now carried out, generally after the fact. It is obvious, however, that such a 

 program required the following basic ingredients before one design can be compared to an- 

 other 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; 



14 



