ABSTRACT 



For the purpose of vibration and load analysis a ship hull is often regarded 

 as a flexural beam. This report describes a method and numerical computer (digital) 

 program to calculate ship section properties (i.e., equivalent beam parameters) 

 needed for the beam vibration equations and its internal shear distribution, using 

 data tabulations obtained from hull plans by a pre-established orderly procedure. 

 The program has been written in FORTRAN and can be used on an IBM 650, 704, 

 709, or 7090. Comparison between digital computer and hand calculations for a 

 sample problem shows excellent agreement. 



INTRODUCTION 



For several years the David Taylor Model Basin has been concerned with the compu- 

 tation of the natural frequencies and mode shapes of a ship huU,^ the whipping response of 

 a ship subject to slamming loads, ^'^ and the flutter response of hull-appendage systems.'* 

 In solving these problems, the ship hull has been treated as a beam and the physical para- 

 meters (i.e., equivalent beam parameters) have been computed for a ship subdivided into n 

 sections of equal or unequal length (usually n = 20).^ These parameters include the inertia 

 properties (mass, location of center of gravity, and moments of inertia), bending (location of 

 neutral axis and bending flexibilities), shear (location of shear center and shear flexibilities), 

 and torsional flexibility parameters. 



The accurate calculation of ship properties has been a laborious task because it 

 requires a detailed examination of ship scantlings, a tabulation of pertinent basic data (such 

 as location and cross-sectional areas of longitudinals), and the performance of routine but 

 lengthy calculations. It is therefore of interest to develop a digital computer program for 

 calculating the inertia-elastic parameters of a ship hull to materially reduce the time, labor, 

 cost, complexity, and errors associated with the present method of hand calculation of these 

 properties. 



The objective of this report is to describe a method and numerical computer program 

 for calculating the section properties (i.e., equivalent beam parameters) of the hull starting 

 with information derived from drawings of the hull. These parameters are to be used in the 

 finite-difference form of the beam vibration equations developed in Reference 1; these equa- 

 tions have been used in vibration, slamming, and hydroelasticity problem areas in which the 

 hull is also treated as a beam.^""* The theory, program derivation, and operation associated 

 with the determination of these parameters are presented. ^-^ This includes the mathematical 

 development of the necessary equations and a description of the input and output statements 



References are listed on page 86. 



