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

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For tests having common values of water depth, passing ship draft, and separation, results for the various passing ship speeds were averaged to define best fit force and moment coefficients. These values are given in Table 5. It is noted that these results are independent of ship speed and depend only on the displacement ratio, ∆R, the draft-to-depth ratio of the passing ship, D/d, and the separation ratio, S/L. Passin g Table 5 Summary of test results when averaged over all velocities for a given set of test conditions, i.e. for a given ship draft, water depth, and separation. Water Draft Depth spacin g inches inches feet ∆R D/d S/L CX+ CX- CY+ CY- CM+ CM- 3.7 4.1 2.0 1.1 0.90 0.4 0.0378 0.0463 0.2174 0.1053 0.0274 0.0251 3.7 4.1 3.0 1.1 0.90 0.6 0.0310 0.0306 0.1105 0.0582 0.0133 0.0110 3.7 4.1 4.0 1.1 0.90 0.8 0.0221 0.0239 0.0753 0.0506 0.0073 0.0062 3.7 4.5 2.0 1.1 0.82 0.4 0.0309 0.0369 0.1159 0.0606 0.0129 0.0149 3.7 4.5 3.0 1.1 0.82 0.6 0.0226 0.0268 0.0777 0.0360 0.0069 0.0076 3.7 4.5 4.0 1.1 0.82 0.8 0.0194 0.0240 0.0524 0.0388 0.0039 0.0044 3.7 4.9 1.5 1.1 0.76 0.3 0.0266 0.0353 0.0974 0.0558 0.0110 0.0171 3.7 4.9 2.0 1.1 0.76 0.4 0.0216 0.0270 0.0725 0.0360 0.0082 0.0115 3.7 4.9 3.0 1.1 0.76 0.6 0.0132 0.0190 0.0450 0.0247 0.0044 0.0065 3.7 4.9 4.0 1.1 0.76 0.8 0.0138 0.0171 0.0254 0.0185 0.0025 0.0035 3.7 4.9 5.0 1.1 0.76 1.0 0.0118 0.0164 0.0268 0.0264 0.0028 0.0032 3.7 5.5 2.0 1.1 0.67 0.4 0.0183 0.0227 0.0479 0.0253 0.0051 0.0097 3.7 8.4 2.0 1.1 0.44 0.4 0.0120 0.0150 0.0311 0.0152 0.0048 0.0049 3.7 8.4 3.0 1.1 0.44 0.6 0.0089 0.0089 0.0175 0.0103 0.0025 0.0024 3.7 8.4 4.0 1.1 0.44 0.8 0.0078 0.0087 0.0137 0.0010 0.0013 0.0015 3.7 14.5 2.0 1.1 0.26 0.4 0.0072 0.0082 0.0173 0.0087 0.0027 0.0029 3.7 14.5 3.0 1.1 0.26 0.6 0.0055 0.0058 0.0103 0.0054 0.0013 0.0013 3.7 14.5 4.0 1.1 0.26 0.8 0.0041 0.0043 0.0065 0.0052 0.0007 0.0007 1.75 4.1 2.0 0.52 0.43 0.4 0.0170 0.0185 0.0741 0.0439 0.0102 0.0095 1.75 4.1 3.0 0.52 0.43 0.6 0.0124 0.0156 0.0457 0.0602 0.0044 0.0049 1.75 4.1 4.0 0.52 0.43 0.8 0.0137 0.0146 0.0322 0.0250 0.0031 0.0032 1.75 4.5 2.0 0.52 0.39 0.4 0.0131 0.0159 0.0496 0.0255 0.0063 0.0065 1.75 4.5 3.0 0.52 0.39 0.6 0.0090 0.0124 0.0274 0.0147 0.0031 0.0033 1.75 4.5 4.0 0.52 0.39 0.8 0.0092 0.0115 0.0202 0.0126 0.0017 0.0019 1.75 8.4 2.0 0.52 0.21 0.4 0.0059 0.0064 0.0118 0.0063 0.0022 0.0022 1.75 8.4 3.0 0.52 0.21 0.6 0.0039 0.0044 0.0068 0.0052 0.0011 0.0012 1.75 8.4 4.0 0.52 0.21 0.8 0.0031 0.0033 0.0051 0.0047 0.0006 0.0006 NFESC TR-6056-OCN 20
Some results from Table 5 are presented graphically in Figures 16 and 17. These are from tests with largest displacement ratio, ∆R =1.1. In Figure 16, the maximum load coefficients (CX-, CY+, and M-) are plotted against the separation ratio, S/L. As expected, results indicate the largest loads for the smallest separation, S/L=0.4, with loads diminishing as S/L increases. Loads are also largest when underkeel clearance is small, i.e. for D/d=0.90, and diminish as D/d decreases. The sway coefficient, CY+, is two to four times larger than the surge force coefficient, CX-. Figure 17 then shows that same data plotted against the draft-to-depth ratio, D/d. Tests conducted with D/d=0.26 represent the approximate limit of “deep water” with large underkeel clearance. Loads increase dramatically in shallow water approaches unity. For the smallest underkeel clearance tested of D/d=0.90, loads are an order of magnitude larger than the deep water values. Loads increase strongly with increasing D/d, especially for D/d greater than 0.7. Loads also increase most dramatically for the smallest separation ration of S/L=0.4. EMPIRICAL MODEL The smooth variations in load coefficients displayed in Figures 16 and 17 suggest that relatively simple empirical formulations may be obtained for these coefficients. In particular, it may be observed in the data that the coefficients: (1) diminish in an exponential fashion with increasing separation ratio, S/L, and (2) increase in an exponential fashion with increasing draft-to-depth ratio, D/d. Fitting these forms to the data in Table 5 for the peak loads, gives the following relationships: + 26 .( Dd / ) −15 .( S/ L) CX−= 0. 0074 ∆R e e + 36 .( Dd / ) −20 .( S/ L) CY+ = 00126 . ∆R e e + 32 .( Dd / ) −34 .( S/ L) CM−= 0. 0044 ∆R e e The coefficients in equation (2) are developed for a condition in which the displacement ratio, ∆R, equals unity, i.e. for a passing ship has a displacement equal to that of the moored ship. Tests were conducted with two values of the displacement ratio and results suggest that the coefficients then vary in approximately a linear fashion with changes in ∆R. When the passing ship was tested at its largest draft, ∆R = 1.14, while the passing ship at its smallest draft had ∆R = 0.52. Load coefficients in Table 5 vary roughly in this proportion (0.52/1.14 = 0.46). NFESC TR-6056-OCN 21 (2)
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: Force (lb) or Moment (ft-lb) 0.7000
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 and 36: Cy - empirical 35.0 30.0 25.0 20.0
Page 37 and 38: Figure 23 indicates that the revise
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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