船体梁极限强度英文文献和中文翻译(5)
The yield stress of HST and mild steel is 315Mpa and 235 Mpa respectively. The scantlings of longitudinals are listed in table 5. Table 1 : Principal dimensions of 34,000 ton bulk carrier Length overall 200.00m Length between perpendiculars 191.00m Breadth 23.50m Depth 14.90m Draft 10.68m Block coefficient 0.8619 Frame spacing 0.80m Table 2: The scantlings of longitudinals Stiffener No Type Dimensions (mm) Yield stress(Mpa) 1 Angle bar 350x100x12/17 315 2 Angle bar 300x90x13/17 315 3 Angle bar 250x90x12/16 235 4 Angle bar 250x90x10/15 315 5 Flat bar 200x20 235 6 Flat bar 120x11 235 7 Flat bar 220x11 235 8 T bar 180x12/100x16 235 9 T bar 150x12/100x16 235 For the purpose of representing the actual damage scenario, the location and extent of structural damage should in principle be defined either by real information from the accident or by using statistical data from past casualties. Fig. 4: cross section of 34,000 ton bulk carrier amidship Every accident is different. The resulting damage also varies. Accidents require many parameters to describe the damage a ship sustains after an accident. A comprehensive description can easily fill a couple of pages or more, even though not all of the data is necessary for calculating hull girder strength. There exist some assumptions with regard to damage extents. In the ABS Guide(1995) for assessing hull-girder residual strength, a grounding damage includes bottom girders attached to the damaged bottom shell to a certain depth; collision damage includes deck stringer plate and slope bulkhead plating attached to damaged side shell plating for a specified extent. Paik, et al.(1998) define collision and grounding damages according to this ABS Guide. For sensitivity studies, they analyzed 0.8 to 1.2 times the specified damage extents described in the ABS Guide. For simplicity, the following damage definitions, which are convenient for calculation but retain the main characteristics of accident damages, are given: For a grounding, it is assumed that the bottom shell and the attached bottom longitudinals are lost. No girders are assumed to be damaged after grounding. In this study, a broader range of bottom loss, up to 80% of ship breadth, to simulate minor to severe grounding damages are investigated. At the same time, the damaged bottom structures are studied both symmetrically and asymmetrically. For each type, some cases are analyzed. The following Table 3 and 4 give the detail information on the damaged structure induced by grounding.
For a collision, it is assumed that the side shell and the attached longitudinals are lost. The damage starts from the deck at the side and extends downward. The deck stringer plate is also assumed to be damaged. A broad range of side shell, ranging from 5% to 40% of ship depth, is considered. With regard to this bulk carrier, the deck stringer plate with the breadth of 1100mm is assumed to be damaged. The following collision cases listed in Table 5 are analyzed: Table 3: Damage extent of bottom caused by the grounding symmetrically Case Range of damaged bottom symmetrical about center line (b) Ratio of b to breadth (b/B) 1 2960 mm 0.126 2 7400 mm 0.315 3 14800 mm 0.629 4 18000 mm 0.766 Table 4: Damage extent of bottom caused by the grounding asymmetrically Case Range of damaged bottom from the bilge (b) Ratio of b to breadth(b/B) 1 2750 mm 0.117 2 4350 mm 0.185 3 6750 mm 2.87 4 10270 mm 0.437 Table 5: Damage extent of side caused by the collision Case Range of damaged side from deck (d) Ratio of d to depth (d/D) 1 745 mm 0.05 2 1500 mm 0.1 3 3000 mm 0.2 4 4850 mm 0.325 5 5960 mm 0.4 The residual resistances of damaged ship hull girder are analyzed both in hogging and sagging condition when the damage scenarios listed in the Table 3 to Table 5 are considered. The part of result curves of moment—curvature and the corresponding curves of central position of cross section—curvature are presented in Fig. 5 to Fig. 8. The Fig. 9 to Fig. 10 show the relationship of the residual strength index, which is the ratio of ultimate strength of damaged hull girder to that of intact hull girder, and the damage extent in hogging and sagging states. Fig. 5: Moment—Curvature curve(grounding symmetrically, Hogging) Fig.6: Central position—Curvature curve(grounding symmetrically, Hogging) Fig. 7: Moment—Curvature curve(collision, Hogging) Fig.8: Central position—Curvature curve(collision, Hogging) For the purpose of residual strength assessment, the residual strength index is to be introduced, which is the ratio of ultimate strength of damaged hull girder to that of intact hull girder as following formula: ) () () (Intact MDamaged M RIF index strength residualuu= The Fig. 9 and 10 give the relationship of residual strength index (RIF) and the damage range curve. Fig. 10: Relationship between Residual Strength Index and Damage Extent due to Collision