LOADS ACTING ON A SHIP AND THE ELASTIC RESPONSE OF A SHIP 



265 



Table 3 Vertical Bending Moment Sheet (from Adm. Ship Weld. Comm. R. 8, 1953) 



FRAME No. 300 ALL FORCES ARE IN TONS RECORD 6E7 



the ship is in the following sea and that the frequency of 

 wave encounter is, therefore, low. The conditions ap- 

 proach the static ones and the dynamic forces are not as 

 important as in two head-sea cases discussed earlier; 

 i.e., the Lewis and Dalzell destroyer model and Schna- 

 del's MS San Francisco. Nevertheless, the accelera- 

 tion forces shown on the second line of Table 3 are im- 

 portant. 



The "hydrostatic forces" are believed to be obtained 

 from the pressure-gage readings and, therefore, include 

 the Smith effect and the hull-wave interference. In 

 the theoretical section of Report No. 8, the authors em- 

 phasize the necessity of taking Smith effect into account 

 but consider hull-wave interaction to be unimportant. 

 The present author was not able to follow their logic 

 in this connection and finds this conclusion to be in dis- 

 agreement with Schnadel's work, with the conclusion of 

 the theory outlined in Section 2 and with the model test 

 data outlined in Section 4 which follows. 



The curves of shear forces and of bending moments are 

 shown in Fig. 10 for various instances defined by the 

 film frame nimibers. The interval between consecutive 

 film frames on this record is 0.48 sec. The in.sert figure 

 shows a good agreement t)etween the bending moments 

 computed from the pressure and acceleration measure- 

 ments (solid curve) and computed from strain-gage 

 readings (dotted curve). Examination of Table 3 shows, 

 however, that this agreement was secured only after 

 drastic corrections of the closing errors in shear-force 

 and bending-moment diagrams. The failure of these 

 diagrams to close indicates the failure to account cor- 

 rectly for all forces acting on the ship. The authors of 



the report, however, presented a discussion expressing 

 the opinion that no significant errors in bending moments 

 had been caused by these discrepancies. 



In the summary tables of Report R-8, the range of 

 hogging to sagging stress during the observation (3E7. 

 just discu.ssed, is given as 150,000 ton.s-feet in the vertical 

 direction and 50,000 tons-feet in the lateral direction. 

 The wind NNW force 7 to 8 and sea WNW-7 were re- 

 corded in the ship's log. The trial party recorded the 

 wind as WNW, force 8 to 9. Maxima of the ship's 

 pitching amplitudes were ±7.6 deg and rolling amplitude 

 ±10 deg. The mean period of pitching was 12.1 ,sec. 

 Average ship's speed was 10.6 knots. 



4 Bending Moment— Ship Model Experiments 



Measurements of bending moments on ship models in 

 towing tanks were made by E. V. Lewis, Lewis and Dal- 

 zell, Sato, Akita and Ochi, and K. Ochi.'- In the present 

 section the discussion will be limited to the slow-acting 

 loads occiu'ring in the course of normal pitching and 

 heaving in head seas. Slamming and other rapidly 

 occurring loads will be discussed as a separate matter in 

 Section 5. 



4.1 E. V. Lewis, T-2 Tanker. E. V. Lewis (1954) 

 conducted a series of towing-tank tests on the model 

 of T2-SE-A1 tanker.'^ The test arrangement is shown 



'* Haiiaoka (19.57) also refers to liending monients measured on 

 an idealized ship model. Furthermore, attention sho\ild fie called 

 to two translations by Ochi (15-1958/; and c). 



'^ These tests were sponsored by the Hull Structure Committee 

 of SNAME through its S-:5 panel". 



