Kim and Meroiev 



hemispherical end. Damping plates are attached, interchangeably, to 

 the lower end of the float in way of the junction of the cylindrical float 

 body and the hemispherical cap. These circular plates were made of 

 l/16-in plexiglass with a 60-deg included angle bevel on the periphery. 

 Model weight was selected to be 20-lb, resulting in model size suitable 

 for the available apparatus. 



The location of the gimbal-box is such that the center-of-rotat- 

 ion corresponds to the center-of-gravity of the model for a particular 

 "average" set of floats and damping plates. It was felt that the influ- 

 ence on vertical center-of-gravity due to interchanging floats and damp- 

 ing collars would be negligible, being less than about 1/8 inch. Floats 

 are designed so that the height of the gimbal-center is a constant dist- 

 ance above the Stillwater level for all the float variants tested. 



The model moments of inertia, about the pitch and roll axes, 

 were fixed using the "average" sets of floats and damping plates. While 

 changes in floats and float spacings may alter the model's pitch and roll 

 inertias by amounts up to about 3 per cent, the small changes may be 

 expected to approximate those which would be associated with corres- 

 ponding design modifications for full-scale vehicles. 



The geometric characteristics of the models are given in 

 Table 1 for four-float (cruciform) configurations, and in Table 2 for 

 three-float (triangular) configurations. Also shown in these tables are 

 metacentric heights as computed according to the model design draw- 

 ings and as measured in separate tests. The computed and measured 

 values do not agree especially well, which is probably attributable to 

 small discrepancies in the manufacture of the styrofoam floats, which 

 would have an important effect on the waterplane inertias and, conse- 

 quently, on GM (especially for the low values of GM used here). For a 

 few cases where the GM was not measured, estimated values are enter- 

 ed in the table, and these are distinguished by being enclosed in par- 

 entheses. 



The experiments were carried out in Davidson Laboratory Tank 

 No. 2 which is 75-ft square with a water depth of 4.5 ft. The motions 

 apparatus used to follow the model's motions and provide a means of 

 recording the six components of motion with a minimum of interference 

 has been described by Numata [12] in an appendix to his paper on 

 "Hydrodynamic Model Tests of Offshore Drilling Structures." Tests 

 were carried out in irregular waves with a significant height of 2 inches. 



RESULTS 



Figure 3 shows a sample oscillogram taken during a test run. 



798 



