The analysis system also includes a statistical evaluation of vibration amplitudes and 

 provides histograms, mean values, and standard deviations of certain selected frequencies. 



4. Test Procedures 



Test procedures are refined so that analysis of modes of vibration are possible. This 

 also permits the separation of bending and torsion in the coupled torsion bending modes, and 

 the separation of the three rotational and three translational vibrations, when needed. Test 

 procedures also permit phase determinations between different locations and permit the de- 

 velopment of relative amplitude curves. 



D. METHODS OF DATA PRESENTATION 



Data are presented in the form of tables which list frequencies and corresponding am- 

 plitudes. Selected frequencies are shown in the form of curves for the whole speed range. 

 These frequencies are usually blade or shaft frequencies. 



The vibratory level at a selected location may be presented in the form of amplitude 

 spectra, and the vibration amplitude of a selected frequency may be shown in the form of an 

 average value or maximum value. 



E. DESIGN EVALUATION 



Design evaluation, so far, usually covers the vibratory level of a ship class (first of 

 the class vibration survey) and compares the results with those obtained in other classes. 



An evaluation of test results usually is made to identify the source of vibration, when 

 it is considered excessive. Remedies are suggested whenever possible. 



Response characteristics of hull to unit force excitation are calculated, and experi- 

 mental results are compared with calculated values to obtain the hull mobility. The same 

 procedure is used for surface ships as well as for submarines. 



Other evaluations concern the selection of locations for machinery or the necessary 

 reduction of vibratory forces by use of vibration reducers. 



F. ENVIRONMENTAL STUDIES 



Environmental studies are required to determine acceptability of equipment in meeting 

 specifications. Studies are made on radar platforms, masts, electronic mounts, crew quarters, 

 etc. 



There is no "norm" yet established which will present the vibratory environment at 

 any given location. The approach used is described in MIL-STD-167. Generally, values of 

 environment are presented in two ways, displacement versus frequency or acceleration versus 

 frequency. 



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