MOBS Example 1 



In order to evaluate the hydrodynamic form effectiveness on a 

 floating platform, a configuration similar to Figure 2 is assumed. The 

 hypothetical platform is 300 feet by 300 feet with 36 buoyant columns 

 of 20 foot diameter and 100 foot submerged length and with 12 hydrodynamic 

 forms. Assuming a 2 knot current and a 40 knot wind environment 

 (references 7 and 8) the required propulsion system output is estimated 

 as 17,100 hp (refer to Appendix A). For a sea state condition of 5 the 

 hydrodynamic form net rate of energy extraction is approximately 240 hp. 

 The effect of the hydrodynamic forms for this configuration and environ- 

 ment is 1.47o of the estimated required propulsion system output. 



MOBS Example 2 



A second case is considered in which all of the 36 buoyant columns 

 of the configuration assumed in Example 1 have the hydrodynamic shape. 

 The same environment of a 2 knot current and a 40 knot wind is assumed. 

 The estimated propulsion system requirement is the same value of 17,100 

 hp. For a sea state condition of 5 the hydrodynamic form rate of energy 

 extraction is approximately 960 hp which is 5.67o of the estimate required 

 propulsion system output. 



A parametric study is beyond the scope of this preliminary study. 

 However, the results of the above examples strongly indicate that the 

 effectiveness of the hydrodynamic form is not too significant. 



MODEL TEST 



Introduction 



To supplement the analytical study and to improve insight into the 

 problem a floating platform model test was conducted in the NCEL wave 

 tank. The model consisted of an aluminum sheet platform with thirty 

 wooden buoyant columns of one inch diameter and fourteen inch length 

 as shown in Figure 2. Attached as shown in the figure were eight wooden 

 hydrodynamic forms of twelve inch length and one and one half inch 

 equivalent diameter. 



Test Procedure 



The average drift velocity of the model was measured over a drifting 

 length of five feet for wave steepness ratios up to 0.130 (H/T to 8.0). 

 Drift velocities were measured for two orientations of the model: the 

 normal orientation in which the concave side of the hydrodynamic form is 

 facing in the direction of wave travel and the orientation opposite to 

 this in which the concave side faces opposite to the direction of wave 

 travel. The effect of the hydrodynamic forms in the normal orientation 



48 



