1、 GUIDE FOR SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS (FOR THE SFA (years) CLASSIFICATION NOTATION) JUNE 2016 Guide to Color Coding Used in Online Version of the Guide The following summarizes the colors corresponding to Rule Changes, Corrigenda items and editorial changes in the Rules files which
2、are available for download. Rule Changes: NOTICE NO. 1 February 2017 (effective 15 February 2017) Corrigenda: CORRIGENDA/EDITORIALS 1 February 2017 Editorials: Editorial Changes Guide for Spectral- Based Fatigue Analysis for Vessels GUIDE FOR SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS (FOR THE SFA
3、(years) CLASSIFICATION NOTATION) JUNE 2016 (Updated February 2017 see next page) American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 2016 American Bureau of Shipping. All rights reserved. ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Updates February
4、 2017 consolidation includes: June 2016 version plus Notice No. 1 and Corrigenda/Editorials Foreword Foreword This Guide provides information about the optional classification notation, Spectral Fatigue Analysis SFA (years) which is available to qualifying vessels as described in 1-1-3/21 of the ABS
5、 Rules for Conditions of Classification (Part 1). The source document for this Guide is the Guidance Notes on Spectral-Based Fatigue Analysis for Vessels (2004). Promoting the Guidance Notes to a Guide adheres to ABS standard practice as the source document was published more than ten years ago. Fur
6、thermore, classification notations are customarily provided by only Rules or Guides. Promotion to a Guide alleviates any confusion caused by deviation from standard practice. The technical content in the Guide has not been significantly changed from that in the Guidance Notes. However, it has been s
7、ignificantly reorganized such that it more closely aligns with the procedure and steps commonly used to conduct spectral-based fatigue analyses for ship structures. Nomenclature has also been modified such that it is more consistent throughout the document. The organization of the Guide is detailed
8、in Section 2. A flowchart depicting the spectral-based fatigue procedure is given by Section 2, Figure 1. The table below shows how the existing Guidance Notes have been reorganized in the creation of this Guide. Section in SFA Guide Section in SFA Guidance Notes Remarks 1 Introduction 1 Introductio
9、n 2 Spectral-based Fatigue Analysis Procedure 1 Introduction SFA procedure overview was expanded and moved to its own section. 3 Seakeeping Analysis 2 Establishing Fatigue Demand 4 Motion Analysis and Wave-induced Load Components 6 Loading for Global Finite Element Method (FEM) Structural Analysis M
10、odel Seakeeping analysis was addressed in one section instead of across three sections. The content in the seakeeping analysis section is in agreement with the DLA/SFA System. 4 Structural Analysis 5 Wave-induced Load Components 6 Structural Modeling and Analysis Structural analysis was addressed in
11、 one section instead of across two sections. The content in the structural analysis section is in agreement with the DLA/SFA System. 5 Spectral Analysis 9 Fatigue Life (Damage) The discussion of spectral analysis was moved to its own section and expanded. 6 Fatigue Strength Assessment 8 Fatigue Stre
12、ngth 9 Fatigue Life (Damage) The fatigue strength assessment section in the Guide contains most of the content in the fatigue strength and fatigue life sections from the Guidance Notes. This Guide becomes effective on the first day of the month of publication. Users are advised to check periodically
13、 on the ABS website www.eagle.org to verify that this version of this Guide is the most current. We welcome your feedback. Comments or suggestions can be sent electronically by email to rsdeagle.org. ABSGUIDE FOR SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2016 iii Table of Contents GUIDE FOR SPECT
14、RAL-BASED FATIGUE ANALYSIS FOR VESSELS CONTENTS SECTION 1 Introduction 1 1 Purpose and Applicability 1 3 Background . 1 5 Areas for Fatigue Strength Evaluation 2 7 Methodology and Assumptions . 2 SECTION 2 Spectral-based Fatigue Analysis Procedure Overview . 4 1 General . 4 1.1 Seakeeping Analysis (
15、Section 3) . 4 1.3 Structural Analysis (Section 4) . 4 1.5 Spectral Analysis (Section 5) . 5 1.7 Fatigue Strength Assessment (Section 6) . 5 FIGURE 1 Schematic Spectral-based Fatigue Analysis Procedure . 6 SECTION 3 Seakeeping Analysis 7 1 Scope of Seakeeping Analysis . 7 3 Vessel Loading Conditions
16、 . 7 5 Hydrodynamic Models 7 7 Initial Balance Check 8 9 Seakeeping Analysis Methods 8 11 Effects of Ship Motions and Wave Pressures . 8 11.1 Inertial and Gravitational Loads due to Ship Motions . 8 11.3 Real and Imaginary Parts 8 11.5 Pressure Mapping 9 11.7 Intermittent Wetting 9 SECTION 4 Structu
17、ral Analysis . 10 1 General . 10 3 Internal Load . 11 3.1 Liquid Tank Pressures . 11 3.3 Bulk Cargo Pressure 12 3.5 Container Loads 14 3.7 Loads on Lightship Structure and Equipment 15 iv ABSGUIDE FOR SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2016 5 Load Cases and Model Equilibrium 15 5.1 Number
18、of Load Cases 15 5.3 Equilibrium Check . 16 7 Structural Modeling and Analysis . 16 7.1 3-D Global Analysis Modeling . 16 7.3 Analyses of Local Structure . 16 7.5 Hot Spot Stress Concentration 16 FIGURE 1 Ship Coordinate System . 10 FIGURE 2 Liquid Pressure on a Completely Filled Tank . 12 FIGURE 3
19、Liquid Pressure on a Partially Filled Tank 12 FIGURE 4 Depiction of Surface Normal Vector, n, Acceleration Vector, a, and . 13 FIGURE 5 Vertical and Transverse Container Load Components . 15 FIGURE 6 Definition of Hot Spot Stress . 17 SECTION 5 Spectral Analysis . 18 1 General . 18 3 Wave Spectra an
20、d Wave Scatter Diagram . 18 5 Stress Range Distributions . 18 TABLE 1 ABS Wave Scatter Diagram for Unrestricted Service Classification . 19 SECTION 6 Fatigue Strength Assessment . 20 1 General . 20 3 S-N Data . 20 5 Fatigue Strength . 21 7 Combined Fatigue Life from Multiple Loading Conditions 21 9
21、Acceptance Criteria . 22 APPENDIX 1 Basic Design S-N Curves 23 TABLE 1 Parameters for Basic S-N Design Curves 24 FIGURE 1 S-N Curves 23 APPENDIX 2 Outline of a Closed Form Spectral-based Fatigue Analysis Procedure . 25 1 General . 25 3 Key Steps in Closed Form Damage Calculation 25 5 Closed Form Dam
22、age Expression 28 FIGURE 1 Spreading Angles Definition 26 ABSGUIDE FOR SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2016 v This Page Intentionally Left Blank Section 1: Introduction SECTION 1 Introduction 1 Purpose and Applicability Part 5C of the ABS Rules for Building and Classing Steel Vessels (S
23、teel Vessel Rules) presents the simplified fatigue assessment criteria for the classification of various types of specialized vessels covered by the Rules. Part 5A and 5B of the ABS Rules for Building and Classing Steel Vessels (Steel Vessel Rules) contains fatigue assessment guidance for vessels su
24、bject to the “Common Structural Rules for Bulk Carriers and Oil Tankers”. A brief description of the background and objectives of these fatigue criteria is given in Subsection 1/3. In addition to the simplified fatigue strength criteria required for classification by ABS, the Owner may wish to apply
25、 more extensive Spectral-based Fatigue Analysis (SFA) techniques to the vessels structural systems. It may be an added objective of these Spectral-based Fatigue Analyses to demonstrate a longer design fatigue life than that required for classification. Spectral-based Fatigue Analysis techniques are
26、used in addition to the SafeHull Fatigue Assessment technique, a Permissible Stress Range method (discussed in Subsection 1/3). The fatigue life of each critical location in the structural system is assessed for adequacy. The critical locations are to be selected using the results of the SafeHull Fa
27、tigue Assessment technique which is to be employed in the overall structural design and analysis effort. The list of critical structural locations which are to be subjected to Spectral-based Fatigue Analysis is to be submitted to ABS for approval. Provided that Spectral-based Fatigue Analysis is con
28、ducted appropriately, ABS will grant the optional classification notation, SFA (years). The SFA (years) notation is granted if the design fatigue life is equal to 20 years or greater. The value in parentheses is the design fatigue life in years specified by the applicant in 5-year increments. The st
29、ructural system is analyzed to verify that the calculated fatigue life values for the entire system meet or exceed the design fatigue life. The calculated fatigue lives are typically much higher than the design fatigue life. The actual service life of a vessel is dependent on many factors. The SFA (
30、years) notation denotes the design fatigue life of a vessel and is not a guarantee that the vessel or structure will achieve the design fatigue life. For vessels complying with Part 5A and 5B “Common Structural Rules for Bulk Carriers and Oil Tankers” of the Steel Vessel Rules, the design fatigue li
31、fe for Spectral-based Fatigue Analysis is equal to 25 years or greater in 5-year increments. 3 Background In the application of the Steel Vessel Rules, the SafeHull Fatigue Assessment technique is typically used to evaluate fatigue strength. The SafeHull Fatigue Assessment technique is a permissible
32、 stress range approach that is readily applied to large portions of a vessels hull structure. The technique is required for certain vessels such as an oil tanker with a Rule length greater than 150 m for which the technique is detailed in Appendix 5C-1-A1 of the Steel Vessel Rules. The technique was
33、 derived considering unrestricted ocean service wave loads and a design fatigue life of 20 years. Part 5A and 5B “Common Structural Rules for Bulk Carriers and Oil Tankers” of the Steel Vessel Rules requires a design fatigue life of 25 years and multiple fatigue assessment techniques are employed. A
34、 simplified stress analysis method based on beam theory is presented in Part 5A, Pt 1, Ch 9, Sec 4 of the Steel Vessel Rules, a finite element stress analysis approach is described in Part 5A, Pt 1, Ch 9, Sec 5 of the Steel Vessel Rules and structural design following the detailed design standards i
35、s discussed in Part 5A, Pt 1, Ch 9, Sec 6 of the Steel Vessel Rules. ABSGUIDE FOR SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2016 1 Section 1 Introduction Supplementary to the SafeHull Fatigue Assessment technique or methods employed for vessels complying with Part 5A and 5B of the Steel Vessel Ru
36、les, ABS may require the use of additional or alternative techniques to demonstrate the fatigue strength adequacy of structural components. These techniques may include Spectral-based Fatigue Analysis methods. In many instances the structural details cannot be adequately analyzed via the permissible
37、 stress range fatigue assessment approach. An optional classification notation, FL (years), may be requested in cases in which the owner or designer increases the target fatigue lives of some or all of the structural components above the 20 or 25 year minimum value. This notation is discussed in the
38、 Steel Vessel Rules and does not require the use of SFA methods. In order to obtain the SFA (years) notation, SFA methods must be applied to the entire vessel. 5 Areas for Fatigue Strength Evaluation The Steel Vessel Rules provide guidance on which locations should be included in the fatigue assessm
39、ent. Various appendices provide guidance on which locations should be included in the fatigue assessment for different vessel types. For example, 5C-1-A1/3.3 of the Steel Vessel Rules provides guidance for location selection for oil tankers with a Rule length greater than or equal to 150 m and 5C-3-
40、A1/3.3 of the Steel Vessel Rules provides guidance for location selection for bulk carriers with a Rule length greater than or equal to 150 m. 7 Methodology and Assumptions Spectral-based Fatigue Analysis is a complex and numerically-intensive technique and there are multiple valid implementations o
41、f the method. ABS does not wish to eliminate the use of any valid approach by over-specifying the SFA technique. However, it is necessary to be clear about the basic assumptions that form the basis of a valid method and highlight key details that are to be incorporated in the method to produce accep
42、table results. The remainder of this Guide is devoted in large part to the presentation of these topics. A typical spectral fatigue analysis for a structural location is to evaluate its fatigue strength by comparing its stress range distribution against its fatigue capacity. The following definition
43、s are used in the context of this Guide: Stress Range Distribution: Stress range probability density functions calculated per this Guide. Fatigue Capacity: S-N data (S-N curves) representing the number of stress cycles at fatigue failure. Fatigue Strength: Fatigue life (or damage) calculated per thi
44、s Guide. Fatigue Demand: Design fatigue life. The main underlying assumptions of the Spectral-based Fatigue Analysis method are: i) Ocean waves are the source of the fatigue stress range acting on the structural system. ii) The load and structural analyses are assumed to be linear as required for th
45、e frequency domain formulation and the associated probabilistic analysis to be valid. As such, scaling and the superposition of stress transfer functions from unit amplitude waves are considered valid. iii) Non-linearities due to non-linear roll motion and intermittent loads, such as wetting of the
46、side shell in the splash zone, can be effectively accounted for using correction factors. iv) Due to their insignificant contributions in typical load cases it is appropriate to disregard structural dynamic amplification, transient loads and effects such as springing. This allows for the use of quas
47、i-static finite element analysis. For the specific SFA method presented in Appendix 2, it is assumed that the short-term stress variation for a given sea-state is a random, narrow-banded, stationary process. Therefore a Rayleigh distribution can be used to represent the short-term stress range distr
48、ibution. 2 ABSGUIDE FOR SPECTRAL-BASED FATIGUE ANALYSIS FOR VESSELS .2016 Section 1 Introduction The Spectral-based Fatigue Analysis method is applied to each of the selected structural locations by implementing the following process: Determine the stress range distributions. Determine fatigue capac
49、ity (S-N data). Calculate fatigue strength (fatigue life or damage). Section 2 provides an overview of the spectral-based fatigue analysis procedure. A schematic representation of the SFA procedure can be found in Section 2, Figure 1. An effort is made in this Guide to avoid the discussion of complicated formulae and instead to focus on the concepts being presented. It is necessary to present the complex formulae used in the calculation of fatigue damage resulting from the predicted stress range distributions, which are presented in Appendix 2. It sho
