ABS 225-2016 GUIDANCE NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVATING UNITS.pdf

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1、 Guidance Notes on Structural Analysis of Self-Elevating Units GUIDANCE NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVATING UNITS APRIL 2016 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2016 American Bureau of Shipping ABS Plaza 16855 Northchase D

2、rive Houston, TX 77060 USA ii ABSGUIDANCE NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVATING UNITS .2016 Foreword Foreword The guidance contained herein should be used in conjunction with the ABS Rules for Building and Classing Mobile Offshore Drilling Units for the purpose of ABS Classification of a Se

3、lf-Elevating Unit. The guidance indicates acceptable practice in a typical case for types of designs that have been used successfully over many years of service. The guidance may need to be modified to meet the needs of a particular case, especially when a novel design or application is being assess

4、ed. The guidance should not be considered mandatory, and in no case is this guidance to be considered a substitute for the professional judgment of the designer or analyst. In case of any doubt about the application of this guidance ABS should be consulted. A self-elevating unit is referred to herei

5、n as an “SEU”, and the ABS Rules for Building and Classing Mobile Offshore Drilling Units, are referred to as the “MODU Rules”. These Guidance Notes become effective on the first day of the month of publication. Users are advised to check periodically on the ABS website www.eagle.org to verify that

6、this version of these Guidance Notes is the most current. We welcome your feedback. Comments or suggestions can be sent electronically by email to 0Hrsdeagle.org. Terms of Use The information presented herein is intended solely to assist the reader in the methodologies and/or techniques discussed. T

7、hese Guidance Notes do not and cannot replace the analysis and/or advice of a qualified professional. It is the responsibility of the reader to perform their own assessment and obtain professional advice. Information contained herein is considered to be pertinent at the time of publication, but may

8、be invalidated as a result of subsequent legislations, regulations, standards, methods, and/or more updated information and the reader assumes full responsibility for compliance. This publication may not be copied or redistributed in part or in whole without prior written consent from ABS. Table of

9、Contents GUIDANCE NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVATING UNITS CONTENTS SECTION 1 Introduction 1 1 Overview . 1 3 General Requirements of Strength Analysis . 1 5 Information Required for Strength Analysis 1 5.1 Units Data . 1 5.3 Gravity and Functional Load 2 5.5 Environmental Data . 2 7 Met

10、hods of Analysis 8 7.1 Static Response 8 7.3 Dynamic Response . 8 TABLE 1 Wind Pressure Height Coefficients . 3 FIGURE 1 Plot of Wind Force Height Coefficient vs. Height above Design Water Surface . 4 FIGURE 2 Current Velocity Profile . 7 FIGURE 3 Water Depth 7 SECTION 2 Loads . 9 1 Overview . 9 3 G

11、ravity and Functional Loads . 9 5 Wind Load . 10 5.1 Wind Load on Open Truss . 10 5.3 Wind Load on Leg . 11 5.5 Dynamic Effects and Vortex Induced Vibration . 11 7 Wave and Current Loads 11 7.1 Validity and Application of the Morisons Equation 11 7.3 Hydrodynamic Coefficients 12 7.5 Wave Theories 19

12、 7.7 Asymmetry 20 7.9 Stretching 20 7.11 Shielding 21 7.13 Wave Approach Angle . 21 7.15 Breaking Wave and Slamming 21 7.17 Stepping Wave through Structures 22 ABSGUIDANCE NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVATING UNITS .2016 iii 9 Large Displacement Load (P- Effect) 22 9.1 Large Displacement M

13、ethod 22 9.3 Geometric Stiffness Method 22 11 Dynamic Load (Inertial Effect). 24 11.1 Magnitude of Inertial Load . 24 11.3 Distribution of Inertial Load 24 13 Leg Inclination . 24 TABLE 1 P- Effect Approaches 23 FIGURE 1 Non-cylindrical Chords 13 FIGURE 2A Drag Coefficient of Tubular Chord with Rack

14、: Deterministic Analysis . 14 FIGURE 2B Drag Coefficient of Triangular Chords: Deterministic Analysis . 14 FIGURE 3 One Bay of Lattice Leg . 17 FIGURE 4 Split-Tube Chord Section 17 FIGURE 5 Triangular Chord Section 18 FIGURE 6 Wave Theories Applicability Regions (After API RP2A) . 19 FIGURE 7 Wheele

15、r Stretching of Wave . 21 SECTION 3 Structural Analysis Models . 25 1 Overview . 25 3 Structural Model 25 3.1 Hierarchy of Models . 25 3.3 Hull Model 27 3.5 Leg Model 28 3.7 Leg-to-Hull Connection Model . 30 3.9 Foundation Modeling . 36 TABLE 1 Applicability of Leg Models . 25 TABLE 2 Applicability

16、of Hull Models . 25 TABLE 3 Applicability of Connection Models . 26 TABLE 4 Comparisons of Global Models . 26 FIGURE 1 Simplified Guide Modeling 33 FIGURE 2 Linearization of Guides . 35 FIGURE 3 Eccentricity of Spudcan 37 SECTION 4 Structural Analyses 38 1 Overview . 38 1.1 Two-Step Procedure Analys

17、is . 38 1.3 Step 1 Dynamic Analysis and Inertial Load Set 38 1.5 Step 2 Quasi-static Analysis . 39 1.7 Critical Storm Load Directions . 40 1.9 Exception . 40 iv ABSGUIDANCE NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVATING UNITS .2016 3 Specification of Wave Parameters and Spudcan-Soil Stiffness . 41 3

18、.1 Introduction 41 3.3 Spectral Characterization of Wave Data for Dynamic Analysis . 42 3.5 Spudcan-Soil Rotational Stiffness (SC-S RS) . 42 5 Dynamic Analysis Modeling 43 5.1 Introduction 43 5.3 Stiffness Modeling . 43 5.5 Modeling the Mass 45 5.7 Hydrodynamic Loading 45 5.9 Damping 45 7 Dynamic Re

19、sponse Analysis Methods . 46 7.1 General 46 7.3 Random Wave Dynamic Analysis in Time Domain . 46 7.5 Other Dynamic Analysis Methods . 53 9 Dynamic Amplification Factor and Inertial Load Set . 55 9.1 Introduction 55 9.3 Inertial Load Set based on Random Wave Dynamic Analysis . 55 9.5 Inertial Load Se

20、t based on SDOF Approach . 56 9.7 Inertial Load Set Applications 56 FIGURE 1 Flowchart of Two-step Procedure . 41 FIGURE 2 The Drag-Inertia Method Including DAF Scaling Factor . 50 FIGURE 3 Graphical Representation of DAF Scaling Factor, FDAF, Applied in the Drag-Inertia Method . 51 SECTION 5 Commen

21、tary on Acceptance Criteria . 57 1 Introduction . 57 3 Categories of Criteria 57 5 Wave Crest Clearance and Air Gap . 57 7 Overturning Stability 57 9 Structural Strength 58 9.1 Yield Criteria 58 9.3 Buckling Criteria 59 9.5 Hybrid Members 59 9.7 Punching Shear . 60 9.9 P- Effect on Member Checking 6

22、0 11 Fatigue of Structural Details 60 13 Strength of the Elevating Machinery . 60 15 Spudcan Check . 61 15.1 Preload Condition 61 15.3 Normal Operating and Severe Storm Conditions 61 17 Other Checks 61 FIGURE 1 Chords Section Stress Points . 60 ABSGUIDANCE NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVAT

23、ING UNITS .2016 v APPENDIX 1 Equivalent Section Stiffness Properties of a Lattice Leg . 62 1 Introduction . 62 3 Formula Approach 62 3.1 Equivalent Shear Area of 2D Lattice Structures 62 3.3 Equivalent Section Stiffness Properties of 3D Lattice Legs . 63 TABLE 1 Equivalent Shear Area of 2D Lattice S

24、tructures . 64 TABLE 2 Equivalent Moment of Inertia Properties of 3D Lattice Legs 65 FIGURE 1 Shear Force System for X Bracing and its Equivalent Beam . 62 APPENDIX 2 Equivalent Leg-to-Hull Connection Stiffness Properties 66 1 Introduction . 66 3 Empirical Formula Approach . 66 3.1 Horizontal Stiffn

25、ess 66 3.3 Vertical Stiffness 66 3.5 Rotational Stiffness 66 5 Unit Load Approach 67 5.1 Unit Axial Load Case . 67 5.3 Unit Moment Case . 67 5.5 Unit Shear Load Case . 67 APPENDIX 3 References 68 vi ABSGUIDANCE NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVATING UNITS .2016 Section 1: Introduction SECTIO

26、N 1 Introduction 1 Overview These Guidance Notes provide suggested practices that can be used in the structural analysis of a self-elevating unit (also referred to herein as an SEU or a unit) in the elevated condition. The emphasis is on analyses that are used to assess the structural strength of th

27、e unit to resist yielding and buckling failure modes considering the static, and as needed the dynamic, responses of the unit in accordance with the ABS Rules for Building and Classing Mobile Offshore Drilling Units (MODU Rules). As an aid to users of the Rules, these Guidance Notes also provide exp

28、lanations on the intent and background for some of the related criteria contained in the Rules. 3 General Requirements of Strength Analysis A units modes of operation in an elevated condition should be investigated using anticipated loads, including gravity, functional and environmental loads. The O

29、wner is to specify the environmental conditions for which the plans for the unit are to be approved. Owners or designers are to thoroughly investigate the environmental and loading conditions for each water depth considered in the Classification. It is the Owners responsibility to ensure that the un

30、it is not exposed to conditions more severe than those for which it has been approved. A unit with an Unrestricted Classification is designed considering a minimum wind speed of 100 knots in the elevated severe storm condition, and 70 knots in the elevated normal drilling condition. The wave and oth

31、er conditions that accompany these winds are to be as specified by the Owner. These other conditions, especially those related to waves and currents may not be the maximum values that are expected during the operational life of the unit. Accordingly other sets of environmental and other design param

32、eters are typically specified by the Owner and are included in the scope of the units Classification. 5 Information Required for Strength Analysis Sufficient information needs to be obtained to adequately perform the structural analysis on the unit. 5.1 Units Data Basic information about the units c

33、onfiguration is required for the analysis. These data are summarized below. 5.1.1 Structural Information Most of the structural information is obtained from relevant drawings and reports. These data can be categorized as: The primary sizes, scantlings and locations of structural members The detailed

34、 sections, connections and localized designs of structural members The material properties of structural members The characteristics of some machinery equipment that affect structural response ABSGUIDANCE NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVATING UNITS .2016 1 Section 1 Introduction In particul

35、ar, the properties of leg-to-hull connections are of great importance and need special attention: The basic configuration and arrangement of connections, which include pinions, chocks (if any), upper/lower guides, jacking case, shock pads (if any), etc. The stiffness and capacity of pinions and choc

36、ks (if any) The gap between leg chords and upper/lower guides The detailed structural configuration of jacking case The detailed structural configuration of upper/lower guides 5.1.2 Other Information Other data that are required for the SEU strength analysis include: Wind projected areas of the hull

37、, deckhouses, derrick, drilling floor and leg in each direction The capacity and moving range of the cantilever The capacity of jacking system 5.3 Gravity and Functional Load The gravity loads include: steel weights, equipment and outfitting weights, the weights of liquid and solid variable quantiti

38、es; and live loads. The gravity loads should be taken into account for the structural design and stability. The load effects due to operations such as drilling, work over and well servicing (rotary/hook loads and tensioner loads) should also be taken into account as functional loads. For all modes o

39、f operation, the combinations of gravity and functional loads are specified by the Owner for the operations considered in the design. However, maximums (or minimums) of the combinations that produce the most unfavorable load effects on the units strength or stability should be used in the design. To

40、tal elevated load defined in 3-1-1/16 of the MODU Rules consists of the lightship weight excluding legs and spudcans, all shipboard and drilling equipment and associated piping, the liquid and solid variables and combined drilling (functional) load. The total elevated load is normally used to identi

41、fy the capacity of an SEU in the elevated mode. The following information needs to be collected: The magnitude and distribution of the lightship weight The magnitude and distribution of variable loads The magnitude and location of functional loads The magnitude and distribution of the total elevated

42、 load Extreme limits of center of gravity for the whole hull and the corresponding load magnitude Weight, center of gravity and buoyancy of the legs including non-structural parts. 5.5 Environmental Data Environmental loads contribute most of the horizontal forces acting on a unit, which are usually

43、 the controlling factors to determine the capacity of the unit. Below, the environmental data requirements as per 3-1-3 of MODU Rules are discussed. Each of the following environmental parameters that affect the loads acting on a jack-up unit is discussed: Wind Wave Current Water depth 2 ABSGUIDANCE

44、 NOTES ON STRUCTURAL ANALYSIS OF SELF-ELEVATING UNITS .2016 Section 1 Introduction Airgap and wave clearance Geotechnical data 5.5.1 Wind The MODU Rules specify that for unrestricted offshore service, a unit should be designed for an operating wind velocity of at least 36 m/s (70 knots) and at least

45、 51.5 m/s (100 knots) for a severe storm condition. 5.5.1(a) Wind Profile. The wind velocity increases with height above the still water level. The MODU Rules specify a profile as given in Section 1, Table 1 to be applied when calculating the wind pressure. This is not a complete listing of the tabl

46、e as given in the Rules, but may be sufficient for most elevated SEU analyses. (A complete listing is given in 3-1-3/Table 2 of the MODU Rules.) It is important to note that this is NOT a wind velocity profile. Velocity profile factors are squared during the calculation of wind force. In order to co

47、mpare the wind pressure coefficients with a wind velocity profile, it is necessary to either square the velocity profile ordinates, or take the square root of the Rules pressure coefficients. TABLE 1 Wind Pressure Height Coefficients Height (m) Height (ft) Ch 0-15.3 0-50 1.0 15.3-30.5 50-100 1.1 30.

48、5-46.0 100-150 1.2 46.0-61.0 150-200 1.3 61.0-76.0 200-250 1.37 76.0-91.5 250-300 1.43 91.5-106.5 300-350 1.48 Section 1, Figure 1 gives a plot of the MODU Rules specified height coefficient, Chin conjunction with various others. The “API 1 min Force Profile” is the wind force profiles as suggested

49、in API RP 2A, but modified from a velocity profile, to a force profile. The basic form of these profiles is: Vh= Vrefnrefhh1where Vh= wind velocity at elevation h above the mean sea level Vref= wind velocity at the reference height href= reference height 10 meters (33 feet) 1/n= exponent of the velocity profile. Note that if the exponent of the velocity profile is 1/nthe exponent of the force profile will be 2/nIn older versions of API RP 2A it was suggested that the exponent should range between 1/13for gus