1、 Guidance Notes on SafeHull Finite Element Analysis of Hull Structures GUIDANCE NOTES ON SAFEHULL FINITE ELEMENT ANALYSIS OF HULL STRUCTURES DECEMBER 2004 (Updated February 2014 see next page) American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2004
2、 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Updates February 2014 consolidation includes: December 2004 version plus Corrigenda/Editorials ABSGUIDANCE NOTES ON SAFEHULL FINITE ELEMENT ANALYSIS OF HULL STRUCTURES .2004 iii Table of Contents GUIDANCE NOTES ON SA
3、FEHULL FINITE ELEMENT ANALYSIS OF HULL STRUCTURES CONTENTS SECTION 1 Introduction 1 1 Objectives . 1 3 Scope of Application . 1 5 Overview of Analysis Procedure . 1 7 Required Analyses 2 9 Supplementary Analyses 2 FIGURE 1 Overview of the FEA Model Functions and Analyses for SafeHull TSA . 2 SECTION
4、 2 Global 3D FEA Model . 4 1 General . 4 3 Extent of the Global 3D FEA Model 4 5 Coordinate and Unit System of the Global Model 8 7 Element Types and Combination 9 9 Finite Element Modeling . 10 9.1 Model for Responses 10 9.3 Element Size . 10 11 FEA Model Verification . 16 13 SafeHull Verification
5、Tools 17 TABLE 1 Recommended Baseline Mesh Size and Mesh Order for Global Model . 11 FIGURE 1 Extent of the 3D Global Model and Mesh Arrangement for Tankers 5 FIGURE 2 Extent of the 3D Global Model and Mesh Arrangement for Bulk Carriers 6 FIGURE 3 Extent of the 3D Global Model and Mesh Arrangement f
6、or Container Carriers . 7 FIGURE 4 Model Coordinate System . 8 FIGURE 5 Typical Mesh Arrangement of Aframax Oil Tankers . 12 FIGURE 6 Typical Mesh Arrangement of VLCC Oil Tankers . 13 iv ABSGUIDANCE NOTES ON SAFEHULL FINITE ELEMENT ANALYSIS OF HULL STRUCTURES .2004 FIGURE 7 Typical Mesh Arrangement
7、of Cape Size Bulk Carriers . 14 FIGURE 8 Typical Mesh Arrangement of Container Carriers 15 FIGURE 9 SafeHull Nastran Model Check Tool . 17 FIGURE 10 SafeHull Groups and Displays the Model by Grouping Parts 17 SECTION 3 Loading and Boundary Conditions . 18 1 General . 18 3 Loading and Loading Pattern
8、s 18 5 Load Combination Factor and Load Cases 19 7 Identify Compartments 19 9 Apply Load Components to Compartment Boundaries 20 11 Pressure Superposition and Force Conversion 20 13 Hull Girder Loads and Load Equilibrium . 21 15 Boundary Conditions . 22 15.1 Supporting Rod and Its Property . 22 15.3
9、 Tankers 23 15.5 Bulk Carriers 24 15.7 Containership Models 25 15.9 Boundary Constraint Beams on the Two End Sections . 26 TABLE 1 Steel Vessel Rules Specified Loading Criteria (150 m or More in Length) . 18 TABLE 2 Steel Vessel Rules Specified Loading Patterns 19 TABLE 3 Steel Vessel Rules Specifie
10、d Loading Combination Factors 19 FIGURE 1 SafeHull “View Tank Boundaries” and “Search Log File” Tools . 20 FIGURE 2 SafeHull “View Tank and Frame Load” Tool . 21 FIGURE 3 View Curves of Hull Girder Load in the SafeHull System . 22 FIGURE 4 Spring Supports for Tanker Global Models . 23 FIGURE 5 Sprin
11、g Supports at Fore End of Bulk Carrier Global Models . 24 FIGURE 6 Spring Supports at Aft End for Container Carrier Global Models . 25 FIGURE 7 Spring Supports at Fore End for Container Carrier Global Models . 26 SECTION 4 Evaluation . 27 1 General . 27 3 Checking Global Model Response . 27 5 Plate
12、Panels for Evaluation . 29 7 Yielding Strength . 29 7.1 Yielding Criteria for Watertight Members . 29 7.3 Yielding Criteria for Non-watertight Members 30 ABSGUIDANCE NOTES ON SAFEHULL FINITE ELEMENT ANALYSIS OF HULL STRUCTURES .2004 v 9 Buckling Strength 30 9.1 Buckling Criteria for Watertight Membe
13、rs 30 9.3 Buckling Criteria for Non-Watertight Members 30 11 Fatigue Strength . 30 TABLE 1 Steel Vessel Rules-specified Loading Criteria (150 meters or more in length) 27 FIGURE 1 View FEA Solution in SafeHull System . 28 FIGURE 2 Overall Deformation of Three Cargo Model for Load Case 1 . 28 SECTION
14、 5 Critical Areas 32 1 Tanker . 32 1.1 Transverse Web 32 1.3 Horizontal Stringer Sections 34 1.5 Longitudinal Girder Sections . 34 3 Bulk Carrier . 34 5 Containership 38 FIGURE 1 Critical Areas Tankers 32 FIGURE 2 Critical Areas for Typical General Bulk Carriers . 36 FIGURE 3 Critical Areas for Typi
15、cal Containerships, Transverse Sections 39 FIGURE 4 Critical Areas for Typical Containerships, Deck 5C-1-3/3.1-5.3 5C-1-3/5.5 5C-1-3/5.7 Bulk Carriers 3-2-1/3.1-3.5; 5C-3-3/3.1-5.3 5C-3-3/5.5 5C-3-3/5.7 Container Carriers 3-2-1/3.1-3.5; 5C-5-3/3.1-5.1 5C-5-3/5.3 5C-5-3/5.5 The Steel Vessel Rules als
16、o specifies the loading patterns, considering the wave conditions and all possible cargo or ballast arrangements to create the worst case loading condition. Section 3, Table 2 lists the Steel Vessel Rules specified load patterns. Section 3 Loading and Boundary Conditions ABSGUIDANCE NOTES ON SAFEHUL
17、L FINITE ELEMENT ANALYSIS OF HULL STRUCTURES .2004 19 TABLE 2 Steel Vessel Rules Specified Loading Patterns Vessel Type Hull Girder Loads Tankers 5C-1-3/Figure 1 & Figure 14 Bulk Carriers 5C-3-3/Figure 1 Container Carriers 5C-5-3/Figure 3 5 Load Combination Factor and Load Cases After calculating al
18、l of the previously-mentioned loads for the Steel Vessel Rules-specified loading pattern, the load components are combined by using the load combination factors (LCFs) to create the different load cases. For all load components, there are corresponding LCFs. In some cases, the load component may be
19、divided into sub-components, such as longitudinal, transverse and vertical components. The LCFs and corresponding load cases can be found in the Steel Vessel Rules tables listed in Section 3, Table 3. TABLE 3 Steel Vessel Rules Specified Loading Combination Factors Vessel Type Hull Girder Loads Tank
20、ers 5C-1-3/Table 1 & Table 2 Bulk Carriers 5C-3-3/Table 1 Container Carriers 5C-5-3/Table 1 7 Identify Compartments SafeHull loads the model for each tank (compartment). SafeHull treats the hull external surface as an external tank. Tank identification is one of the most important aspects for Steel
21、Vessel Rules loading. SafeHull provides two tank identification tools: Quick Tank Search tool Extensive Tank Search tool In general, if the users follow the modeling guide described in Section 2, “Global 3D FEA Model”, the quick tank search identifies all tank boundaries in a very efficient manner.
22、When tanks cannot be identified by the quick tank search, the extensive tank search is applied. The extensive tank search identifies any tank boundaries. SafeHull provides a tank search report (log file) to provide information for the tank search. It also provides a graphic viewing tool to view the
23、searched tank boundary elements. The log file and the viewing tool provide information for modeling problems. View the tank boundary search results using the tools provided in Section 3, Figure 1 to verify that all of the tank boundaries are identified correctly. All tank boundaries must be identifi
24、ed correctly before applying the loads. Section 3 Loading and Boundary Conditions 20 ABSGUIDANCE NOTES ON SAFEHULL FINITE ELEMENT ANALYSIS OF HULL STRUCTURES .2004 FIGURE 1 SafeHull “View Tank Boundaries” and “Search Log File” Tools 9 Apply Load Components to Compartment Boundaries Based on the type
25、s of load components, the SafeHull system computes the pressures or forces for each tank according to the Steel Vessel Rules-specified loading criteria (Subsection 3/3, “Loading and Loading Patterns”), loading pattern (Subsection 3/3) and load combination factors (Subsection 3/5, “Load Combination F
26、actor and Load Cases”) of the Rules-defined load cases (Subsection 3/5). The calculated loads are automatically applied to the tank boundary elements (nodes). The loading by tank approach provides a simplified way to examine different types of load components. SafeHull provides the visualization too
27、l (see Section 3, Figure 2) to review the tank load for selected load cases for one or all tanks. The user can also review the pressure distribution of different tanks at a specified frame section. Use the tank-load-reviewing tool to verify both the applied pressure and force direction by vector, in
28、cluding the projected component and magnitude. 11 Pressure Superposition and Force Conversion Once pressure is calculated for each tank, pressure on the common tank boundaries acting on the same element and node are superimposed to obtain the total pressure value. Then, the pressure is converted to
29、nodal force, weighted by the areas of connecting elements. Section 3 Loading and Boundary Conditions ABSGUIDANCE NOTES ON SAFEHULL FINITE ELEMENT ANALYSIS OF HULL STRUCTURES .2004 21 FIGURE 2 SafeHull “View Tank and Frame Load” Tool 13 Hull Girder Loads and Load Equilibrium As mentioned in Subsectio
30、n 3/3, the FE model only contains a portion of the vessel. The local loads acting on the three cargo holds only provide a partial load contribution to the overall hull girder loads. In order to use the three-hold model to predict vessel responses, adjustment must be made for the hull girder load to
31、reach the Rules target values. The SafeHull system automatically adjusts the load by either inertia force or line loads, in addition to adjusting end moments. When adjustment is completed, all loads acting on the finite element model develop the hull girder target bending moment at the middle sectio
32、n of the middle cargo hold, and hull girder target shear forces at the transverse bulkheads of the middle cargo hold. The SafeHull system provides the plots to verify the hull girder load distribution (see Section 3, Figure 3). These plots include the load, hull girder shear and hull girder bending
33、moment distribution curves before and after the adjustment. The accuracy of the hull girder bending moment adjustment can be verified by using a simple beam bending stress calculation, checking the deck or bottom plate stress using the following formula: IMyx= Note: It is recommended that the deck p
34、late be used in the above formula since the local load has a significant affect on the bottom plate. where M = target vertical bending moment y = coordinate of the plate measured from the cross section neutral axis I = moment of inertia of the cross section All three values can be found in SafeHull
35、output files. If the stress, calculated by the above formula, is close to those from the FE results (with several percentages tolerance), the vertical bending moment adjustment can be considered complete. Section 3 Loading and Boundary Conditions 22 ABSGUIDANCE NOTES ON SAFEHULL FINITE ELEMENT ANALY
36、SIS OF HULL STRUCTURES .2004 FIGURE 3 View Curves of Hull Girder Load in the SafeHull System 15 Boundary Conditions In the state of static equilibrium, the free body of the hull girder is subjected to bending and torsional moments, as well as shear forces at two ends. These end actions are expressed
37、 as normal and shearing stresses on the hull girder and as boundary nodal forces imposed on the model. Even though the local and boundary loads are in equilibrium, the finite element model still needs some support in order to be statically stable. These supports are arranged in the way thereby minim
38、izing the effects on the hull girder vertical, horizontal and torsional bending moments distribution on the model. 15.1 Supporting Rod and Its Property Since forces and moments in the hull girder structures are not always completely balanced, it is recommended that special boundary supports be appli
39、ed using rod elements in both the vertical and horizontal directions. These supports should have one end connected to the model and the other end totally fixed. The cross sectional area of the supporting rod elements for tankers and bulk carriers is calculated as: LALAAss77.011=+=where A = cross-sec
40、tional area of the supporting rod element v = Poissons ratio of the material As= shearing area of the entire cross sectional area of the member (such as the cross-sectional area of the considered side shell or longitudinal bulkhead) L = cargo hold length (i.e., one half span of the beam) = length of
41、 the supporting rod element The resulting cross-sectional area, A, is the total equivalent area for the supporting rod elements connected to the same structural member (e.g., shell or longitudinal bulkhead). The area for the supporting rod is equal to A divided by the number of rods. Section 3 Loadi
42、ng and Boundary Conditions ABSGUIDANCE NOTES ON SAFEHULL FINITE ELEMENT ANALYSIS OF HULL STRUCTURES .2004 23 15.3 Tankers The location for the supporting rod elements of three types of tankers is shown in Section 3, Figure 4. In addition to the vertical and horizontal supports, two points on the lon
43、gitudinal bulkheads intersecting with side stringers and close to the vertical hull girder neutral axis must be directly fixed in the longitudinal direction (x). FIGURE 4 Spring Supports for Tanker Global Models CLCLCLSection 3 Loading and Boundary Conditions 24 ABSGUIDANCE NOTES ON SAFEHULL FINITE
44、ELEMENT ANALYSIS OF HULL STRUCTURES .2004 15.5 Bulk Carriers In the SafeHull System for Bulk Carriers loading, torsional moments are to be accounted for in both oblique and beam sea conditions. Unlike a typical tanker which does not have wide cargo hatch openings in the deck structure, a bulk carrie
45、rs cross deck structure experiences large shear and warping stresses due to a significant amount of torsional moment induced in oblique sea conditions. This is mainly due to the location of the shear center of a bulk carrier, which is below the baseline of the hull. The shear center for tankers is l
46、ocated close to the center of gravity. In addition, a bulk carriers open deck structure has relatively less strength than that of a tanker. In order to enable an appropriate application of torsion in the finite element analysis of a three-cargo-hold model, a different set of boundary supports than t
47、hose used for a tanker is required. The supports at the two ends of the finite element model used in tanker structural analysis are changed to supports at only one end. In this scheme, the fore end of the model is supplied with vertical and lateral rod supports. The vertical supports are placed at l
48、ongitudinal bulkheads and the side shell. Horizontal supports are placed at the deck, inner bottom and bottom shell for both the port and starboard sides (see Section 3, Figure 5). FIGURE 5 Spring Supports at Fore End of Bulk Carrier Global Models This spring system provides vertical and transverse
49、supports to the finite element model. In order to have a statically stable structure, additional supports in the longitudinal direction have to be provided. The longitudinal spring supports are placed at the same location as the vertical and/or transverse supports. The rod element, which is representative of the stiffness of the longitudinal spring support, can be chosen from one rod element with medium stiffness among those that represent vertical and horizontal spring supports. In the analysis of the structural response, all nodal points for the spring suppo
