ABS 124-2014 GUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELFELEVATING UNITS.pdf

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1、 GUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS FEBRUARY 2014 Guide to Color Coding Used in Online Version of the Guidance Notes The following summarizes the colors corresponding to Rule Changes, Corrigenda items and editorial changes in the Guidance Notes files which are avai

2、lable for download. Rule Changes: Changes effective 1 February 2014 Corrigenda: CORRIGENDA/EDITORIALS 1 September 2014 Editorials: Editorial Changes Guidance Notes on Dynamic Analysis Procedure for Self-Elevating Units GUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS FEBRUARY 20

3、14 (Updated September 2014 see next page) American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2014 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Updates September 2014 consolidation includes: February 2014 versio

4、n plus Corrigenda/Editorials ABSGUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS .2014 iii 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 Classificat

5、ion of a Self-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 b

6、eing assessed. 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 referr

7、ed to herein 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 v

8、erify that this version of these Guidance Notes is the most current. We welcome your feedback. Comments or suggestions can be sent electronically by email to rsdeagle.org. iv ABSGUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS .2014 Table of Contents GUIDANCE NOTES ON DYNAMIC AN

9、ALYSIS PROCEDURE FOR SELF-ELEVATING UNITS CONTENTS SECTION 1 Introduction 1 1 Background . 1 3 Basic Concepts of the Inclusion of Dynamic Effects into Structural Analysis . 1 5 Exception 2 FIGURE 1 Flowchart of the Two-Step Procedure 3 SECTION 2 Specification of Wave Parameters and Spudcan-Soil Stif

10、fness . 4 1 Introduction . 4 3 Spectral Characterization of Wave Data for Dynamic Analysis 4 5 Spudcan-Soil Rotational Stiffness (SC-S RS) 5 SECTION 3 Dynamic Analysis Modeling 6 1 Introduction . 6 3 Stiffness Modeling . 6 3.1 Leg Stiffness 6 3.3 Hull Stiffness 7 3.5 Leg-to-Hull Connection Stiffness

11、 . 7 3.7 P-Delta Effect (P-) . 7 3.9 Foundation Stiffness 8 5 Modeling the Mass 8 7 Hydrodynamic Loading . 8 9 Damping 8 SECTION 4 Dynamic Response Analysis Methods . 10 1 General . 10 3 Random Wave Dynamic Analysis in Time Domain 10 3.1 General 10 3.3 Random Wave Generation 10 3.5 Calculation of St

12、ructural Response 11 3.7 Prediction of Extreme Responses 12 5 Other Dynamic Analysis Methods . 17 5.1 Single-Degree-of-Freedom Approach 17 ABSGUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS .2014 v FIGURE 1 The Drag-Inertia Method Including DAF Scaling Factor . 14 FIGURE 2 Grap

13、hical Representation of DAF Scaling Factor, FDAF, Applied in the Drag-Inertia Method . 15 FIGURE 3 Dynamic Amplification Factor (SDOF) 19 SECTION 5 Dynamic Amplification Factor and Inertial Load Set . 20 1 Introduction . 20 3 Inertial Load Set based on Random Wave Dynamic Analysis . 20 5 Inertial Lo

14、ad Set based on SDOF Approach 21 7 Inertial Load Set Applications . 21 APPENDIX 1 Equivalent Section Stiffness Properties of a Lattice Leg . 22 1 Introduction . 22 3 Formula Approach 22 3.1 Equivalent Shear Area of 2D Lattice Structures 22 3.3 Equivalent Section Stiffness Properties of 3D Lattice Le

15、gs . 23 5 Unit Load Approach 26 5.1 Unit Axial Load Case . 26 5.3 Unit Shear Load Case . 26 5.5 Unit Torsional Moment Case . 27 TABLE 1 Equivalent Shear Area of 2D Lattice Structures . 24 TABLE 2 Equivalent Moment of Inertia Properties of 3D Lattice Legs 25 FIGURE 1 Shear Force System for X Bracing

16、and its Equivalent Beam . 22 APPENDIX 2 Equivalent Leg-to-Hull Connection Stiffness Properties 28 1 Introduction . 28 3 Empirical Formula Approach. 28 3.1 Horizontal Stiffness . 28 3.3 Vertical Stiffness 28 3.5 Rotational Stiffness . 28 5 Unit Load Approach 29 5.1 Unit Axial Load Case . 29 5.3 Unit

17、Moment Case . 29 5.5 Unit Shear Load Case . 29 APPENDIX 3 Equivalent Hydrodynamic Coefficients of Lattice Legs 30 1 Introduction . 30 3 Equivalent Diameter 30 5 Equivalent Drag Coefficient 30 7 Equivalent Mass Coefficient 32 9 Current Associated with Waves 33 vi ABSGUIDANCE NOTES ON DYNAMIC ANALYSIS

18、 PROCEDURE FOR SELF-ELEVATING UNITS .2014 FIGURE 1 One Bay of Lattice Leg . 31 FIGURE 2 Split-Tube Chord Section 31 FIGURE 3 Triangular Chord Section 32 FIGURE 4 Current Velocity Profile . 33 APPENDIX 4 References 34 ABSGUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS .2014 1 Se

19、ction 1: Introduction SECTION 1 Introduction (1 February 2014) 1 Background These Guidance Notes present acceptable practice for an important aspect in the Classification of self-elevating units (SEUs). The technical criteria contained in the original version of these Guidance Notes published in 200

20、4 were based on the results of a Joint Industry Project sponsored by Owners, Designers, Builders, Operators and Classification Societies. The criteria were subsequently published as Reference 1. That reference is specifically aimed at providing assessment criteria for the site-specific use of the SE

21、U. Reference 1 was also used in the development of the International Standards Organization (ISO) Standard 19905-1 Reference 6 for site-specific assessment of mobile offshore units Jack-Ups. There were changes in both required and acceptable methods of assessment when the ISO 19905-1 standard was de

22、veloped from Reference 1. The changes that are relevant to Classification were incorporated into this revision of these GNs. The fundamental difference between site-specific evaluation and Classification is that the latter is not site-specific in nature. Instead, the Owner specifies conditions for w

23、hich the unit is to be reviewed for Classification. The basic dimensions of the envelope of conditions that the Owner may specify for Classification are: i) Water depth (plus air gap and penetration depth into the seabed) ii) Environmental conditions of wind, wave and current iii) Total elevated loa

24、d iv) Spudcan-soil rotational stiffness (The last item is a consideration introduced by ABS in 2003 when dynamic response is assessed for Classification.) Therefore, a major theme of these Guidance Notes is to designate the portions of the criteria in References 1 and 6 that can be applied without m

25、odification and the portions of the criteria that may need to be adapted for Classification purposes. 3 Basic Concepts of the Inclusion of Dynamic Effects into Structural Analysis Because the natural period of an SEU is typically in the range of 5 to 15 seconds, there may be a concern that there wil

26、l be dynamic amplification (resonance) with waves in this period range. It is therefore often desirable to account for the dynamic effects of the SEU in the elevated condition due to waves (and waves with current). The basic approach most commonly used to include dynamic effects into structural anal

27、ysis is characterized as a “quasi-static” method, which entails a two-step procedure. In the first step, a Dynamic Analysis model of the structural system is analyzed. Then, the static response to the same loads is obtained using the same model. A Dynamic Amplification Factor (DAF) is obtained as th

28、e ratio of the most probable maximum extreme (MPME) of a response when dynamics is considered to the most probable maximum extreme (MPME) of the same response statically considered. DAFs can be obtained for various structural responses, such as the global overturning moment of the unit, base shear f

29、orce or the lateral displacement of the elevated hull (i.e., surge and sway). From the DAFs, an “inertial load set” is established that simulates the dynamic effects. The loads considered to produce the dynamic response are those induced by waves or waves acting with current. Usually, it is sufficie

30、nt that the level of structural system idealization used to determine DAFs is, as often described, an “equivalent model”, which is an “equivalent 3-leg idealization” coupled with an “equivalent hull structural model”. The need to appropriately account for the stiffness of the leg-to-hull interaction

31、 and spudcan-soil interaction adds some minor complexity to this simplified modeling approach. Section 1 Introduction 2 ABSGUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS .2014 In the second step, the “inertial load set” is imposed, along with all of the other coexisting loads,

32、 onto the usual, detailed static structural model that is used to perform the “unity checking” for structural acceptance based on the Rules. Because this model now includes the “inertial load set” to simulate the dynamic response, it is often also referred to as the Quasi-Static model. The two-step

33、procedure is summarized as: i) Use an “equivalent” model to perform a random wave dynamic analysis deriving the DAFs and subsequently the inertial load set caused by wave-induced structural dynamics. Alternatively, the DAFs may also be estimated using the single degree-of-freedom (SDOF) approach giv

34、en in 4/5.1.2 as an alternative to the random wave dynamic analysis, above. However, care should be exercised since the SDOF approach may significantly over or underestimate the DAF. See the limitations of the SDOF approach for deriving the DAFs given in 4/5.1.4. ii) Use a “detailed” model to perfor

35、m, with static gravity and wind loads and quasi-static wave loads plus the derived inertial load set, a static structural analysis deriving the stresses for unity checks in accordance with the ABS strength requirements in the MODU Rules for the leg chords, braces and the jacking pinions. The flowcha

36、rt of the two-step procedure is shown in Section 1, Figure 1. More details on the modeling procedure and the determination and application of the inertial load set are given in these Guidance Notes as follows: Specification of Wave Parameters and Spudcan-Soil Stiffness Section 2 Dynamic Analysis Mod

37、eling Section 3 Dynamic Response Analysis Methods Section 4 Dynamic Amplification Factor and Inertial Load Set Section 5 5 Exception Since 2008 the ABS MODU Rules require that wave induced dynamic response is to be included in the SEU design, except when the dynamic amplification factor (DAF) obtain

38、ed from SDOF given in 4/5.1 is less than 1.1 considering the SEU as pin-ended at least 3 m (10 ft) below sea bed. However, caution should still be exercised since the SDOF approach may underestimate the dynamic response when the ratio of the natural period of the SEU to the wave period exceeds unity

39、 (1.0) or is less than 0.6. See also the limitations for use SDOF given in 4/5.1.4. Section 1 Introduction ABSGUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS .2014 3 FIGURE 1 Flowchart of the Two-Step Procedure (1 February 2014) Two-step AnalysisStep 1Determine inertial load se

40、tDAF by SDOFPerform random wave dynamic analysis with “equivalent model”Calculate DAF iaw 4/5.1.2 1.0Set = 1.0Calculate = Tn/0.9TpCalculate dynamic and static MPME values and DAF iaw 4/3.7DAF 4.72srpH , then use Tp= 4.72srpH if Tp25 m) Tp= peak period associated with Hsrp(also used with Hs), in seco

41、nds Section 2 Specification of Wave Parameters and Spudcan-Soil Stiffness ABSGUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS .2014 5 Equation (2.2) is the Wheeler stretching adjustment that accounts some nonlinear effects around the free surface in shallower water depth. The JO

42、NSWAP spectrum with a peak enhancement factor of 3.3 and the above calculated Hsand Tpshould be used to represent the considered sea state. The short-crestedness of waves should not be considered. 5 Spudcan-Soil Rotational Stiffness (SC-S RS) Since 2003, the ABS MODU Rules permits consideration of “

43、spudcan-soil rotational stiffness” for cases involving dynamic response. The maximum extent to which this rotational stiffness can be applied to the system, Krs,fixed, is defined by the following equation. Krs,fixed= E I /(L Cmin)where E = Youngs modulus, 209GPa for steel I = moment of inertia, in m

44、4L = the sum of the distance, in m, from the underside of the hull to seabed plus the seabed penetration (minimum 3 meters) 4.35(I/As)0.5 Cmin= (1.5 J)/(J + F) J = 1 + 7.8 I/(AsL2) F = 12 I Fg/(A Y2)A = axial area of the equivalent leg, in m2As= shear area of the leg, in m2Y = the distance, in m, be

45、tween the centerline of one leg and a line joining the centers of the other two legs for a 3-leg unit; the distance, in m, between the centers of leeward and windward rows of legs; in the direction of being considered Fg= 1.125 for a three leg unit and 1.0 for a four leg unit The Owner may select va

46、lues of SC-S RS ranging from zero (the pinned ended condition) up to the maximum value indicated. 6 ABSGUIDANCE NOTES ON DYNAMIC ANALYSIS PROCEDURE FOR SELF-ELEVATING UNITS .2014 Section 3: Dynamic Analysis Modeling SECTION 3 Dynamic Analysis Modeling (1 February 2014) 1 Introduction To determine a

47、DAF, a simplified Dynamic Analysis model, as indicated below, may be used. The usual level of modeling employed in this case is designated as an “equivalent model”. Inaccurate or inappropriate modeling can have a major effect on the calculated structural responses, therefore, special care should be

48、exercised to assure that the modeling and application of the dynamic loading is done appropriately. The stiffness of the Dynamic Analysis model should also be consistent with that of the “detailed” model used for the Quasi-Static structural analysis to check the adequacy of the structure by the perm

49、issible stress unity check criteria of the MODU Rules. 3 Stiffness Modeling The level of stiffness modeling of the “equivalent model” for dynamic analysis discussed in this section includes Leg stiffness Hull stiffness Leg-to-hull connection stiffness (stiffness of jacking system, proper load transfer direction of guides, pinions and clamps, etc.) P-Delta effect Foundation stiffness (leg-to-seabed interactions) 3.1 Leg Stiffness The stiffness of a leg is characterized by the following equivalent cross sectional properties: Cross sectional area