ssc - 419 supplemental commercial design guidance for fatigue ship ...

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Table Title Page3.8 U.S. Navy Standard Operational Profiles for Auxiliaries and Commercial Cargo 3-8Ships3.9 Sea State Probabilities 3-93.10 Effect of Sea Spectrum and Operational Profiles on Predicted Fatigue Lives 3-134.1 ABS Longitudinal Distribution of Slam Induced Vertical Bending Moments (ABS 4-10Rules 5.3A.3.61c)5.1 Design Code S-N Curves (NSWCCD, 1998) 5-66.1 U.S. Navy Design Hull Girder Stress 6-56.2 Comparison of Maximum Bending Moments Computed by SPECTRA8 and ABS 6-6Rules6.3 Actual Section Modulus Compared to ABS Requirement for Naval Ships 6-98.1 Comparison of Hull Girder Inspection Policies 8-149.1 SafeHull Phase A Fatigue Analysis of Longitudinals for Ship G 9-89.2 SafeHull Phase A Fatigue Analysis of Flat Bars for Ship G 9-89.3 Comparison of Tanker and Containership SafeHull Loadings9-27Based on SafeHull Version 6.0 (Rules 2000)9.4 Comparison of SafeHull Phase A and Phase B Analyses for Ship G (CG 47 Class) 9-319.5 SafeHull Phase B Analysis of Fatigue of Flat Bars for Ship G (CG 47) 9-329.6 Comparison of Phase A and Phase B Section Moduli for Ship G 9-349.7 Difference between Tanker and Containership9-34Fatigue Analysis of Typical Stiffener of Ship G11.1 Computation of Permissible Stress Range 11-511.2 Phase A Fatigue Analysis of Longitudinals for Ship G Modified to 30 Years inNorth Atlantic with 35 Percent Operability11-61. Introduction1.1 PurposeThis report represents an attempt to apply to naval ships a method developed for the fatigue analysis ofcommercial ships. All aspects of structural design and construction as well as the operation of the ship at seahave a profound effect on the fatigue life of ship structure. Therefore, a review of these factors, especially ascurrently applied to the design of commercial and naval ships was undertaken as part of the study. Onecommercial method, the containership version of the SafeHull program of the American Bureau of Shipping(ABS), was then applied to 10 naval ships. This application was not straightforward, and requiredmodifications to the input of the program, and interpretation of the program output. This effort represents anexample of the shortcomings and limitations of such an application of a program developed for one type ofships when applied to a different type.As part of this study, the literature concerning commercial and naval methods of design for fatigue wasreviewed. The documents reviewed are listed in the list of references at the end of the report. The principalsubject matters investigated are listed below with a summary of the subject. The subjects will be discussed infurther detail in the remaining chapters of this report.14
1.2 Commercial Approaches and Practices for the Structural Design of the Ship Hull Girder forEnvironmental LoadsThere are considerable differences between the historical approaches to the structural design of militaryand commercial ships for environmental loads. These differences have diminished in recent years as thecommercial procedures have evolved to structural design based on analytically developed loads and detailedstress analysis. In many regards, particularly in the development of loads, a greater level of sophistication iscurrently used in the Dynamic Loading Approach (DLA) of the American Bureau of Shipping (ABS) than iscurrently used by NAVSEA for design. The differences may diminish in the future as the classificationsocieties develop rules for military ships and if the military authorities adopt these rules. The degree ofdifference cannot be ascertained until ships are designed using the new rules, and the scantlings so developedare compared to equivalent ships designed under the old approach. One important factor relative to fatigue lifeof structure will be to determine which approach will result in heavier scantlings and thus have an inherentlygreater fatigue life. In either case, because fatigue assessment has now become standard practice for bothcommercial and military ship designs, either approach should result in improved fatigue lives.1.3 Operational Environments Used in Commercial and USN Ship Design PracticeThe operating environment clearly influences the fatigue life of ship structure, with some environmentsfar worse than others. The number of operational years for which a ship is designed, and thus, for whichavoidance of fatigue damage is necessary, is generally an owner’s option. Commercial ships are normallydesigned for fewer years of operation than naval ships, but spend a greater percentage of that time at sea. Themaster of a commercial ship is less likely to reduce speed or take a more seakindly heading in heavy weatherthan the commanding officer of a naval ship will during peacetime, but at time of war, the naval ship is morelikely to be driven harder.The area of operations of a ship has a great effect on fatigue life. A ship that operates throughout theentire Atlantic Ocean will have a fatigue life that is twice as long as a similar ship operating in only the NorthAtlantic. The more conservative assumption of North Atlantic Operations is generally used for design, butwhen comparing predictions of fatigue failure with service experience, actual operational conditions should beused.1.4 Hull Response MethodsThe principal issue in the prediction of lifetime bending and torsional moments is the importance ofnonlinearities in wave profiles and in the response of ships to waves. They are extremely important inpredicting the maximum lifetime response. In fatigue analysis, however, the majority of the fatigue damageoccurs at lower sea states where the waves and the response of ships to them are linear. Therefore,consideration of nonlinearities is generally not important for predicting a fatigue loading spectrum, with theexception of slam-induced whipping.The commercial and military methods of fatigue analysis currently used in design have a deterministicbasis, using lower-bound probability fatigue data, but not otherwise considering the stochastic nature of loads,strength or analysis. However, there can be large variability in all of these factors, so that actual fatigue life canvary over a full order of magnitude Thus, calibration of fatigue analysis with operating experience can bedifficult, especially if few failure occur in service, making the failure database small.15
Page 1: SSC - 419SUPPLEMENTAL COMMERCIALDES
Page 4 and 5: CONVERSION FACTORS(Approximate conv
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Ship Lifetime Bending and Torsional
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Fatigue Data for Ship Structural De
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Supplemental Commercial Design Guid
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11. Suggested Modifications to the
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Suggested Modifications to the Safe
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12. CONCLUSIONSThe ABS SafeHull Pha
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13. RECOMMENDATIONSThe following re
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14. REFERENCESAASHTO, Standard Spec
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ReferencesHeyburn, R. and D. Riker,
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ReferencesNaval Ships’ Technical
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ReferencesSNAME, Application of Pro
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Guide for the Use of Commercial Des
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Phase A analysis. This guide provid
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Table 1 Stiffener Library Data File
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SafeHull, so it is not necessary to
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Figure 4 General Data for Section D
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to define the Bilge, Gunwale, or In
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Figure 6 The Stiffener Properties S
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Figure 7 2-D Shell Shape Definition
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produce a screen similar to Figure
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in sequence. If errors are found in
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7.2.2.2 Once the SafeHull Phase A h
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many limitations associated with th
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App A-1APPENDIX AFATIGUE ANALYSIS S
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App A-3STF#SafeHullSTF IDTOE ID Dis
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App A-5Table A.2 SafeHull Phase A F
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App A-7STF#Table A.3 SafeHull Phase
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App A-9STF#SafeHullSTF IDTOE ID Dis
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App A-11CutoutLABELID LOCDist.fromB
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App B-2STF#SafeHullSTF IDTable B.1
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App B-10CutoutLABEL ID LOCTable B.2
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App D-2Table D.1 SafeHull Phase A F
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App D-4STF#SafeHullSTF IDTOE IDDist
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App D-6Table D.2 SafeHull Phase A F
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App E-1APPENDIX EFATIGUE ANALYSIS S
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App F-2Table F.1 SafeHull Phase A F
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App F-4FatigueSTF Stiffener " ID Di
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App F-6FatigueSTF Stiffener " ID Di
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App F-8Table F.2 Phase A Fatigue An
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App G-2ST#StiffenerTable G.1 SafeHu
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App G-4ST#StiffenerTOE ID Dist.from
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App G-8CutoutTable G.2 Phase A Fati
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App G-18Table G.4 Phase B Analysis
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App H-3ST#StiffenerSafeHullSTF IDTO
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App H-7CutoutTable H.2 Phase A Fati
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App I-1APPENDIX IFATIGUE ANALYSIS S
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App I-3STF#SafeHullSTF IDTOEID Dist
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App I-13CutoutLABELID LOCTable I.2
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App I-15Table I.3 Phase A Fatigue A
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App I-27CutoutLABELID LOCDist.fromB
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App J-6CutoutLABELID LOCTable J.2 P
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App J-10CutoutLABELID LOCDist.fromB
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APPENDIX KOPNAV Instruction 4700.7J
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(4) Preventive maintenance actions
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the Integrated Logistic Support (IL
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(2) Operational Forces Resource Spo
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APPENDIX LS9086-CN-STM-040Naval Shi
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Naval Ship’s Technical Manual Cha
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Table 079-53-1. Source Documents fo
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1230/004Contaminated Oil Tank Clean
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is, full cleaning) is attributable
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Ships Technical Manual Chapter 631,
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090-1.70 Shaft Alley. Particular em
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cladding or surfacing shall be acco
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APPENDIX MUnderwater Ship Husbandry
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Section 2 Personnel and Equipment R
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the average percent of block areas
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APPENDIX NThe Corrosion Control Inf
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APPENDIX OUnited States CodeTitle 1
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