A METHOD OF APPLYING LINEAR SEAKEEPING PANEL PRESSURE TO FULL SHIP STRUCTURAL MODELS

Transcription

1 A METHOD OF APPLYING LINEAR SEAKEEPING PANEL PRESSURE TO FULL SHIP STRUCTURAL MODELS Ming Ma - DRS Defence Solutions, USA Chengbi Zhao - SCUT, China Nick Danese - COMPIT 2012 Liège, April 2012 /1

2 Introduction State of the art review The MAESTRO / integrated approach MAESTRO-WAVE Comparison Extreme Load Analysis / Design Wave Spectral Fatigue Analysis Conclusion COMPIT 2012 Liège, April 2012 /2

3 Introduction. M.A.E.STR.O. (Dr. Hughes, DRS-DS) FE everywhere FE as a design tool 1980 : adequacy parameters, limit state analysis 1996 : graphical interactive topological modelling 2000 : added mass, DNV HSLC equivalency factors 2004 : sparse solver 2008 : COM-MAESTRO 2011 : MAESTRO - NAPA Steel one click 2012 : MAESTRO - Seakeeping one click Extreme Load Analysis / Design Wave Spectral Fatigue Analysis 16 April 2012 : MAESTRO 10 with released COMPIT 2012 Liège, April 2012 /3

4 Significance of equilibrium for finite element analysis. FE analysis of floating structures requires hydro-s/d balancing. Draf t Unbala nced Trim Unbalanced Deg Model Balan ced 3.96m 4.07m Deg Weight Distribution Balanced Model Buoyancy Distribution VBM VBM 3-node deflection shape 2-node deflection shape COMPIT 2012 Liège, April 2012 /4

5 Transfer hydrodynamic loads to a FE model. Panel based hydrodynamic analysis is computational intensive, coarser meshes Customarily, two different mesh models are maintained: Hydrodynamic (coarser) and Structural (finer) Hull form Hydrostati cs Hydrodynamic mesh Structural mesh Structures Hydrodyn amics Design Spiral In some cases, the hydrodynamic analysis may not use a surface model at all, still need to get panel pressures for FE ( does). COMPIT 2012 Liège, April 2012 /5

6 Load mapping methods. Direct pressure mapping PROS: Intuitive, easy for third party development CONS: unbalanced structural model, inertia relief corrective approach (ABS, 2010) modifies accelerations, potentially unrealistic. Source strength mapping (BV, 2008) PROS: structural model is balanced by definition CONS: may be difficult for third party users (no access to source strengths and mapping facilities) HYDRODYNAMIC MESH STRUCTURAL MESH COMPIT 2012 Liège, April 2012 /6

7 Hydrostatic restoring force matrix. Equations of motion: Hydrostatic restoring matrix: Using pressure integration Hydrostatic restoring forces Inconsistency COMPIT 2012 Liège, April 2012 /7

8 Panel pressure correction methods. BV s proposed approach: adding a gravity term to all FE elements in the complete ship model MAESTRO s approach: adding correction nodal forces using Quadratic Programming to wet nodes only For each panel, the elemental Forces and Moments are: By the original hydrostatic restoring matrix: Quadratic Programming By the pressure integration: COMPIT 2012 Liège, April 2012 /8

9 MAESTRO integrated approach. One mesh used for both FE and hydrodynamics One Graphical User Interface FE model supplies weights, CGs, etc. Embedded linear frequency domain 3D panel hydrodynamic analysis The hydrodynamic model is generated from the FE wet panels and nodes Source strengths mapped to FE mesh = hydrodynamic equilibrium by default Nodal force adjustment uses Quadratic Programming (heave, pitch), not inertia Fully integrated structural analysis Extreme Load Analysis / Design Wave Spectral Fatigue Analysis Failure mode evaluation (structural adequacy, limit states), the heart of first principles FE 9 COMPIT 2012 Liège, April 2012 /9

10 Hydrodynamic comparisons. S175 COMPIT 2012 Liège, April 2012 /10

11 Hydrodynamic comparisons, cont'd. COMPIT 2012 Liège, April 2012 /11

12 Hydrodynamic comparisons, cont'd. COMPIT 2012 Liège, April 2012 /12

13 An integrated solution: NAPASteel FE export ELA/SFA Failure mode evaluation Structural Model FEA Model Hydrodynamic Model VBM RAOs of all sections COMPIT 2012 Liège, April 2012 /13

14 Design Waves. If the static load case is balanced and if the hydrodynamic loads are balanced, then the combined load case is balanced, by definition. Then, the FE response analysis can be run directly. Wet elements automatically receive hydrostatic loads, while Dry elements do not MAESTRO will balance the static load case. will balance the corresponding hydrodynamic load cases using panel pressures on the FE mesh and quadratic programming for heave and pitch correction. COMPIT 2012 Liège, April 2012 /14

15 Design Waves: dynamic, s/p static, combined. Extreme Design Case #1 Extreme Design Case #1 with 180deg Shift Extreme Design Case #4 Extreme Design Case #4 with 180deg Shift Extreme Design Wave Case #4 Extreme Design Wave Case #4 with 180deg Shift COMPIT 2012 Liège, April 2012 /15

16 ELA - Extreme Load Analysis calculation procedure. 12 Headings 30 Frequencies 5 Speeds Cached Unit Wave Load Database (Accelerations, Panel Pressure) Full Ship Structural Model MAESTRO FE model Hull Girder Global Loads RAO Wave Spectrum Short/Long Term Extreme Loads Long/Short Term Environment n i T T z P H, T 0 P ( ) P ( V ) s Extreme Load for Each Sea State Hull Girder Global Loads Response Spectrum Scale y y max dlp Operational Conditions DL Scale UnitWave( ) StaticLoad Equivalent Extreme Regular Wave Hull Girder Ultimate Strength Local Structural Failures ELA Strength Assessment COMPIT 2012 Liège, April 2012 /16

17 SFA Spectral Fatigue Analysis calculation procedure. 12 Headings 30 Frequencies 5 Speeds Cached Unit Wave Stress Response Database Full Ship Structural Model Cached Frequency Domain Stress RAO Database MAESTRO FE model Element Stress RAO Wave Spectrum Coarse Mesh Full Ship Fatigue Damage Screening Long Term Environment Element Stress Response Spectrum Operational Conditions (speed, heading) Stress Range (N/mm2) 1000 B C D E 100 F F2 G W E+04 1.E+05 1.E+06 1.E+07 1.E+08 Number of Cycles D T K p nk AllSeaStates m / 2 m 2 1 pn pi f0i i 2 n 1 i 1 m Fine Mesh Selected Area Fatigue Damage Assessment S-N Curves Stress Range PDF Miner s Rule COMPIT 2012 Liège, April 2012 /17

18 SFA Coarse mesh full model fatigue screening. COMPIT 2012 Liège, April 2012 /18

19 What was that all about? Obtain wet FE mesh from MAESTRO Export it to hydrodynamic code using From the discretized boundary integral equations obtain the panel source strength of each potential Map the source strengths of each panel to the FE mesh Compute hydrodynamic added mass, damping and restoring coefficients by integrating the wet panels (FE panels hydro panels) Construct the equations of motion, obtain the motion RAOs Compute the panel pressures on the FE mesh and the corrective restoring nodal forces Load the FE model by applying panel pressures (unbalanced model) balances the FE model by applying corrective forces using quadratic programming COMPIT 2012 Liège, April 2012 /19

20 Conclusion. : integrates FE and seakeeping Full model, supports any shape Purpose-dense mesh (very coarse to very fine) Runs ELA and SFA at once Fast, use in every day design work (mesh density speed) Neutral format interface file (.wet) Interfaces / integrates with any seakeeping code One-stop ship-shop COMPIT 2012 Liège, April 2012 /20

21 THANK YOU COMPIT 2012 Liège, April 2012 /21