Mooring Loads Due to Parallel Passing Ships - State Lands ...

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Fxpred (lbs) Fypred (lbs) Mpred (lbs) 0.400 0.300 0.200 0.100 0.000 1.000 0.800 0.600 0.400 0.200 0.000 1.000 0.800 0.600 0.400 0.200 0.000 0.000 0.100 0.200 0.300 0.400 Fxmeas (lbs) 0.000 0.200 0.400 0.600 0.800 1.000 Fymeas (lbs) 0.000 0.200 0.400 0.600 0.800 1.000 Mmeas (lbs) Figure 23. Comparison of measured peak loads to values predicted with PASS-MOOR with revised correction factors in equation (10). NFESC TR-6056-OCN 34
Figure 23 indicates that the revised correction factors in equation (10) result in predicted loads from PASS-MOOR that are in good agreement with measured loads. As expected, there is no bias toward over or under-predicting loads. Scatter is generally comparable to that obtained using the empirical model in Figure 18. CONCLUSIONS This study has produced a new set of laboratory scale model data for the loads on a moored ship induced by a passing ship. A total of 144 tests were carried out covering a range of ship speeds, water depths, ship drafts or displacements, and separation distances. Results are for a Series 60 hull form, which is a generic form of commercial vessels that has been widely used in naval architecture laboratories. The degree to which results apply to other hull forms is unknown and additional tests using other hull forms appears needed. Measured values of peak mooring loads (surge force, sway force, and yaw moment) were first analyzed empirically. A new set of predictive equations was developed to permit simplified estimates of the mooring loads. These equations capture the observed variability in loads with ship separation distance, ship speed, and the draft-t-depth ratio. The simplified equations may be useful for simple hand calculations or for use in spreadsheet predictions. Measured values were also used to evaluate two of the available methods of predicting mooring loads. The first method, a set of empirical equations by Flory (2002), was found to be unreliable. The formulation in the model for representing the differences in displacement of the passing and moored vessels, and for representing the effect of vessel separation did not accurately reproduce observed variations in loads. The second method, the PASS-MOOR spreadsheet by Seelig (2001), was more consistent in its performance, but under-predicted measured surge and sway forces. Because PASS-MOOR is used by NAVFAC to predict mooring loads, correction factors used in PASS-MOOR to represent he effects of vessel separation and the draftto-depth ratio were r e-derived using the new lab data. The revised or re-calibrated PASS-MOOR was then found to provide acceptable predictions of mooring loads. Despite the large number of tests carried out, additional model tests would prove useful. One lesson learned from the analysis of data is that the mooring loads closely follow a quadratic variation with ship speed. Many tests were carried out with different ship speeds that, in hindsight, were not really needed because of the simple and well-behaved variation of loads with speed. In future tests, it therefore appears that fewer ship speeds should be tested while additional permutations of other parameters should be investigated. These tests used only one hull form, and certainly additional tests should be carried out with additional hull forms. Tests also used only two vessel displacements and this is really insufficient to fully document the variation of loads on a moored ship as vessels having different displacements (or different lengths, beams, and drafts) pass by. NFESC TR-6056-OCN 35
Page 1 and 2: L I T N AV A L F A C I E N G I N E
Page 3 and 4: INTRODUCTION A series of scale mode
Page 5 and 6: distance (normalized by ship length
Page 7 and 8: Figure 3a. View of towing carriage
Page 9 and 10: Figure 5. Original test frame used
Page 11 and 12: Ship Models Figure 7. View of load
Page 13 and 14: Test Conditions Test conditions are
Page 15 and 16: Sign Convention The coordinate syst
Page 17 and 18: Interpretation of Figure 10 is aide
Page 19 and 20: fx normalized fy normalized mom (no
Page 21 and 22: Force (lb) or Moment (ft-lb) 0.7000
Page 23 and 24: Some results from Table 5 are prese
Page 25 and 26: CX- CY+ CM- 0.100 0.090 0.080 0.070
Page 27 and 28: FYpred FXpred Mpred 1.000 0.800 0.6
Page 29 and 30: Flory’s equations are somewhat aw
Page 31 and 32: Seelig Method in PASS_MOOR The pred
Page 33 and 34: FXpred FYpred Mpred 0.400 0.300 0.2
Page 35: Cy - empirical 35.0 30.0 25.0 20.0
Page 39 and 40: Appendix A Tabulation of Test Condi
Page 41: 111 4.1 1.75 3.0 1.534 0.042 0.052

Mooring Loads Due to Parallel Passing Ships - State Lands ...

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