《ABS-127-2004.pdf》由会员分享，可在线阅读，更多相关《ABS-127-2004.pdf（34页珍藏版）》请在三一文库上搜索。
1、 GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO ICE LOADS APRIL 2004 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2004 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Copyr
2、ight American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-,- This Page Intentionally Left Blank Copyright American Bureau of Shipping Provided by IHS
3、 under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO ICE LOADS . 2004 iii Foreword These Guidance Notes
4、 provide a procedure for performing nonlinear finite element analysis of side structures subject to ice loads. This document is referred to herein as “these Guidance Notes” and its issue date is 15 April 2004. Users of these Guidance Notes are encouraged to contact ABS with any questions or comments
5、 concerning these Guidance Notes. Users are advised to check with ABS to ensure that this version of these Guidance Notes is current. Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or n
6、etworking permitted without license from IHS -,-,- This Page Intentionally Left Blank Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-
7、,- ABS GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO ICE LOADS . 2004 v GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO ICE LOADS CONTENTS SECTION 1 Introduction1 1 Background1 3 Purpose1 5 Applications1 7 Key Components of these
8、Guidance Notes 2 9 Contents of these Guidance Notes2 SECTION 2 Structural Idealization3 1 Introduction3 3 Extent of Structural Modeling.3 5 FEM Elements .3 7 Mesh Size4 FIGURE 1 FE Model Extent (Inner Skin Removed for Clarity)5 FIGURE 2 Mesh of Side Longitudinal and Bracket at Connection to Web Fram
9、e.5 SECTION 3 Material Model7 SECTION 4 Load Model.9 FIGURE 1 Ice Load as Line Load on Side Longitudinal9 SECTION 5 Boundary Conditions.11 TABLE 1 Boundary Conditions for FEM Model.12 FIGURE 1 Boundary Conditions for FEM Model.11 SECTION 6 FEM Solution13 1 Incremental Solution13 3 Convergence13 Copy
10、right American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-,- vi ABS GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT T
11、O ICE LOADS . 2004 SECTION 7 Acceptance Criteria.15 1 General 15 3 FMA Approach: Comparative Study15 5 Permanent Deformation.15 APPENDIX 1 Nonlinear FEM Theory and Software.17 1 Material Nonlinearity17 3 Geometrical Nonlinearity17 5 Incremental Solutions 17 7 Convergence Criteria.18 9 Commercial FEM
12、 Packages 18 APPENDIX 2 Example of Nonlinear FEM Applications.19 1 Problem Definition19 3 FEM Modeling19 5 Ice Load .21 7 Analysis Results.21 9 Alternative Design23 FIGURE 1 FEM Model.20 FIGURE 2 Load Path (Loading and Unloading Phases).21 FIGURE 3 Von Mises Stress Contour.22 FIGURE 4 Pressure vs. D
13、eflection (Loading and Unloading Phases)23 FIGURE 5 Pressure vs. Deflection of Different Designs.23 APPENDIX 3 The Finnish Maritime Administration (FMA) “Tentative Note for Application of Direct Calculation Methods for Longitudinally Framed Hull Structure”, 30 June 2003 .25 Copyright American Bureau
14、 of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO ICE LOADS . 2004 1 S E
15、 C T I O N 1 Introduction 1 Background According to the Finnish-Swedish Ice Class Rules, it is stipulated that longitudinal frames shall be attached to all supporting web frames and bulkheads by brackets. In a subsequent paragraph, it is stated that “For the formulae and values given in this section
16、 for the determination of hull scantlings, more sophisticated methods may be substituted subject to approval by the administration or the classification society.” Ice load measurements conducted with ships navigating in the Baltic show that loads several times higher than the design loads are often
17、encountered. It is deemed that designing up to the yield point with these high loads would be uneconomical, and so, some excess of the nominal design load is acceptable. In certain extreme cases, some plastic deformation will occur, leaving behind a permanent set. The design of the longitudinal fram
18、es can be checked by using a FEM program capable of nonlinear structural analysis. In such an analysis, the permanent set can be calculated and the ultimate load carrying capacity of the frames can be predicted. These Guidance Notes expound upon the ideas and notions introduced in the Finnish Mariti
19、me Administration (abbreviated as “FMA” in these Guidance Notes) “Tentative Note for Application of Direct Calculation Methods for Longitudinally Framed Hull Structure”, 30 June 2003. 3 Purpose The purpose of these Guidance Notes is to clearly define a procedure to conduct a nonlinear FEM analysis o
20、f side structures subject to ice loads. In accordance with Ice Class Rules, the results of such an analysis may be used to substitute for standard Rules formulae and values. Certain design requirements, such as constraints on longitudinal frame spacing and the bracket attachment requirement between
21、web frames and bulkheads, may be relaxed. These Guidance Notes provide more technical details to supplement the Finnish Maritime Administration “Tentative Note for Application of Direct Calculation Methods for Longitudinally Framed Hull Structure”, 30 June 2003. 5 Applications The requirement that t
22、he maximum frame spacing of longitudinal frames “shall not exceed 0.35 metre for ice class IA Super and IA and shall in no case exceed 0.45 metre” stems from the fact that the ice loading is concentrated along a narrow horizontal strip, typically only 250 mm wide. In order to limit the possible cata
23、strophic consequences of longitudinal frames collapsing, there is a Rule requirement to install brackets between longitudinal frames and transverse webs. These brackets increase the ultimate load-carrying capability of the frames by effectively reducing their span. However, the installation of such
24、brackets may lead to higher production costs, and it is desirable to use nonlinear FEM to justify a design decision to omit such brackets in order to optimize structural design. Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale,
25、 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-,- Section 1 Introduction 2 ABS GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO ICE LOADS . 2003 7 Key Components of these Guidance Notes The key components of applying a non
26、linear FEM analysis of side structures subject to ice loads include: Structural idealization Material nonlinearity and geometrical nonlinearity Loads and boundary conditions Failure or acceptance criteria These analysis components can be expanded into additional topics, as follows, which become the
27、subject of particular Sections in the remainder of these Guidance Notes. 9 Contents of these Guidance Notes These Guidance Notes are divided into the following Sections and Appendices: Section 1 Introduction Section 2 Structural Idealization Section 3 Loads Model Section 4 Boundary Conditions Sectio
28、n 5 FEM Solutions Section 6 Acceptance Criteria Appendix 1 Nonlinear FEM Theory and Software Appendix 2 Calculation Example Appendix 3 The Finnish Maritime Administration (FMA) “Tentative Note for Application of Direct Calculation Methods for Longitudinally Framed Hull Structure”, 30 June 2003 Copyr
29、ight American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO IC
30、E LOADS . 2004 3 S E C T I O N 2 Structural Idealization 1 Introduction In order to create a three-dimensional model that can be analyzed in a reasonable amount of time, a subsection of the vessels side structure is considered. Indeed, as long as enough structure is modeled to sufficiently move the
31、boundary effects of fixity away from the area of interest, there is no benefit in modeling a greater area of the ship structure. The result on the longitudinal frame of interest will remain the same, although the analysis time could increase tenfold. 3 Extent of Structural Modeling The three-dimensi
32、onal structural model is to be justified as being representative of the behavior of side structures subject to ice load. Longitudinal direction. In principal, the structural model is to extend a minimum of three webs (three-bay model) with an extra half-frame spacing on the forward and aft ends. Ver
33、tical extent. In principal, the structural model is to extend between the two horizontal stringers that include the ice belt region. Typically, the ice belt is applied in the area of a single longitudinal frame that is halfway between the stringer extent. The model should contain at least one three-
34、 dimensional longitudinal frame above and below the frame of interest. Modeling more than three three-dimensional longitudinal frames will require more time for modeling and analysis with little to no appreciable difference in the result. Ship width direction. The FEM model extends to and includes t
35、he inner skin. Structures to be modeled include: Side shell and side longitudinal frames Web frames, web stiffeners and brackets, if any Inner skin and the attached longitudinals 5 FEM Elements Shell elements are generally used for representing the side shell, inner skin, web frames and web and flan
36、ge of the side longitudinal within the ice belt. Beam elements can be used for side longitudinals outside of the ice belt. The flange of the side longitudinals within the ice belt can be modeled using either shell element or beam element. Copyright American Bureau of Shipping Provided by IHS under l
37、icense with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-,- Section 2 Structural Idealization 4 ABS GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO ICE LOADS . 2004 7 Mes
38、h Size Mesh size should be selected such that the modeled structures reasonably represent the nonlinear behavior of the structures. Areas where high local stress or large deflections are expected are to be modeled with fine meshes. Section 2, Figure 1 shows an example of the FEM mesh. It is preferab
39、le to use quadrilateral elements that are nearly square in shape. The aspect ratio of elements should be kept below 3-to-1. In general, the web of a longitudinal is to be divided into at least three elements (see Section 2, Figure 2). The flange of a side longitudinal can be modeled by one shell ele
40、ment or by a beam element. The side shell, web frames and inner skin can be divided into elements that are of the same size as that for the web of side longitudinal. Structures away from the ice belt may be represented using a coarser mesh. Tapering of fine mesh to relatively coarse mesh is acceptab
41、le. When modeling brackets, the mesh should be finer in order to carry at least three elements in the area where the bracket meets the longitudinal flange (see Section 2, Figure 2). It is recommended to keep element edges normal to the bracket boundary and avoid using triangular-shaped elements. Als
42、o, it is preferable not to use quadrilaterals oriented in such a way that only one point touches a bracket boundary. Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitt
43、ed without license from IHS -,-,- Section 2 Structural Idealization ABS GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO ICE LOADS . 2004 5 FIGURE 1 FE Model Extent (Inner Skin Removed for Clarity) FIGURE 2 Mesh of Side Longitudinal and Bracket at Connection to Web F
44、rame Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-,- This Page Intentionally Left Blank Copyright American Bureau of Shipping Provi
45、ded by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS GUIDANCE NOTES ON NONLINEAR FINITE ELEMENT ANALYSIS OF SIDE STRUCTURES SUBJECT TO ICE LOADS . 2004 7 S E C T I O N 3 Mater
46、ial Model Material nonlinearity results from the nonlinear relationship between stress and strain once the elastic yield limit of the material has been reached. The behavior of materials beyond yield is typically characterized by the slope of the stress-strain curve that indicates the degree of hard
47、ening. In general, it is recommended to use an elastic-perfectly plastic material model for shipbuilding steel that does not account for strain hardening effects. This simplification yields conservative results. The elastic-perfectly plastic material model for mild steel is characterized by the foll
48、owing parameters: Yield Stress 235 MPa Youngs Modulus (elastic) 206,000 MPa Poissons Ratio 0.3 Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:09:50 MDTNo reproduction or networking permitted without license from