2008 International ANSYS Conference Strongly Coupled FSI Simulation Moving Compressible Pressure Pulse through a Tube

Transcription

1 2008 International ANSYS Conference Strongly Coupled FSI Simulation Moving Compressible Pressure Pulse through a Tube Daniel L. Cler, US Army RDECOM/ ARDEC/ WSEC/ Benet Labs 1

2 Overview Background Problem Description Objectives and Assumptions Workflow Results Future Work Conclusion 2

3 A Collage of Real Life Multiphysics Applications Examples of multiphysics are plentiful Realistic FSI analysis is needed to address design and performance issues. Wing flutter, engine noise, VIV, oil exploration, offshore structures, air crafts and components, defense equipment, pumps, valves, arteries, bones,... Courtesy of Pluere Total deformation contours on a pump impeller in a coupled structural and flow analysis Typical torsional blade modes: impact of gas on swept surfaces ANSYS Adv.v1,n3,2007, Coupled FSI of bio-med valve FSI of distributor header Courtesy: CADFEM 3

4 Background Multiphysics Solutions: State-of-the-Art Much has been achieved In-depth single discipline solutions Ability to make these solutions communicate Efforts to facilitate communication at data level MPCCI, dedicated solvers, and communicators Multi-disciplinary applications need real world collaboration of discipline specialists Analysis tools need framework to share multiple data fields that represent the true physics Technology maturity is providing new opportunities Need for improvement stays ahead of the progresses made Hardware and software capabilities entice practitioners with increased demand of complex real life analysis towards Simulation Driven Product Development 4

5 Current Reality Integrated Process in Workbench Geometry Model Base level coupling CHT Solid Mesh CFD with CHT Thermal Stress Setup Thermal Loads from CFX Thermal Stress Solution 5

6 P / T Spikes A Sample Engineering Case Consider a problem with flow physics involving High speed compressible flow in a tube From pavement / concrete digger to oil well drills Time From BB guns to more serious defense equipment From musical instruments to pneumatic control equipment... Very high cyclic pressure and thermal loads over long time Simple principle Use potential energy of compressed fluid through systematic release in kinetic form Focus on optimized delivery of an object or a force on a target The release segment of these cycles involve a reaction force Engineering challenge Minimize the reaction impact without any degradation on the forward motion, direction and force fields Important to analyze the response of the tube material Accuracy of the target motion, direction and force fields Long term fatigue behavior of the equipment (tube) 6

7 Engineering Solution Consider a lightweight structure attached at the end of the tube to reduce the recoil action Loads on the new attachment device Pressure pulse from inlet end of the tube Thermal loads from the source of the pressure pulse Design objective Maximize braking by smart design to minimize forces and moments (torques) on the tube Smartness defined by minimum space and material use without loss of strength or life 7

8 Engineering Solution The case studied here is a muzzle block The attachment geometry is for exemplification only and is not for any real equipment or any design The total engineering of such system require analysis of multiple fields of physics Propulsion system, material science, aero-acoustics, turbulence, fatigue life estimation, stress-concentration and micro-cracks, solidification, heat treatment, machining, surface finish, etc. This study focuses only on analysis of coupled FSI problem to demonstrate maturity of the analysis tool 8

9 Objectives Explore the state of the art in simulation for two-way fluid structure interaction to predict the pressure, thermal loads, on the fluid side and deformations of the structures Multiple loading cycles in a single analysis Objective is NOT to do all the detailed simulation of 1 cycle Requirements: Two way coupled, unsteady, FEA & CFD analysis Robust, easy to use, flexible Automated with minimal user intervention Optimization tools Develop the initial Proof-of-Concept! Feasibility study Focus on correctness of physics by establishing proper coupling 9

10 Assumptions Fluid simulation Blow down simulation No moving solid-load in the tube Typical chamber pressure is compensated Half geometry, vertical symmetry Fluid material properties NASATM 4647 ; NASA/TP FEA simulation Flexible multi body dynamics Tube inlet is fixed in space Solid material properties Alloy Steel 10

11 Workflow and Data Transfer Pre-processing ANSYS Simulation: Solid mesh, mechanical simulation setup ICEM CFD: Fluid mesh ANSYS CFX-Pre: CFD, FSI simulation setup Solver and Execution ANSYS Multiphysics: A single integrated, fully coupled environment FEA Solver: ANSYS Simulation CFD solver: CFX-Solver Data Transfer CFD to FEA: Wall heat flux and total force FEA to CFD: Wall temperature and displacement Data transfer between ANSYS and CFX solvers is fully automated Post-processing ANSYS CFX Post Solid and Fluid field variables can be post processed together 11

12 Fluid Domain and Mesh Mesh Generated using ICEM CFD Blocking concept, hexahedral mesh Initial proof of concept mesh Number of Nodes FLUID Domain Chamber: High pressure, high temperature Barrel Muzzle block Outer domain: External flow Ground 12

13 Solid Domain and Mesh Mesh Generated using ANSYS Simulation Easy to use, highly automated and fast! Hex mesh in the barrel Tet mesh in the muzzle block Pulse Source 13

14 Workflow Snapshots Mechanical Simulation Setup Boundary Conditions : Solid Material: Steel Alloy Analysis Type : Flexible Dynamics Coupled Field Element Solve for thermal and structural stresses 14

15 Workflow Snapshots CFD Simulation Setup Material properties Density: Ideal Gas mixture Temperature dependent properties NASATM 4647; NASA/TP Physical Models SST K- turbulence model Natural convection Initial condition 1atm and 300K, zero velocity Source term approach for initial high P and T Mass and energy sources corresponding to 820 atm and 1120 K at pulse source Applied at the first time step of each cycle Adaptive Time stepping Time step size ramp up from 7e-6 s (min) to 0.25 s (max) B.C. types Green : Opening Red : FSI interface Cyan : Ground Open face: Symmetry 15

16 Workflow Snapshots FSI simulation set-up in ANSYS CFX Pre FSI Simulation Setup External coupling Interface load transfer CFD solver controls 16

17 Workflow Snapshots FSI simulation start-up using ANSYS CFX-Solver CFX Solver input ANSYS Solver input 17

18 MFX Multi-Field Solver Supports Simulation between Multiple Executables FEA CFD Third Party Coupling Scheme Not Required Uses Client/Server architecture TCP/IP Heterogeneous Networks (LAN/WAN/Internet) Supports Large Models Solution on Two Machines CFX Solution can use Parallel Processing Supports Nonconformal Meshes Transfers Surface Loads Automatically Morphs CFD Mesh ANSYS Multi-Field Solver Sequential load transfer coupling MFS Coupling within a single executable Coupling of structural, thermal, electric and electromagnetic fields in ANSYS Multiphysics. MFX Coupling between multiple executables ANSYS/CFX FSI Other combinations in future releases! 18

19 Results Solvers output CFX & ANSYS Cooling period b/w the pressure pulses ~10sec CFX Output ANSYS Output Total force (N) Fx, Fy, Fz on FSI interface Maximum mesh displacement (m) in the Fluid Domain 19

20 Workflow Snapshots Post Processing Coupled simulation post-processing in ANSYS CFX Post Common Graphical User Interface Can analyze intermediate time step data Easy to create/save animations Geometry definition Post surfaces Animation controls 20

21 Results CFD 16 - Cycles Mach Symmetry Plane Symmetry Plane 21

22 Results CFD 5 - cycles Temperature iso-surface, 500K Pressure iso-surface, 0.1 atm(g) 22

23 Results Mechanical 7- cycles Temperature on FSI interface Temperature on the Muzzle block 23

24 Results Mechanical 5 - cycles Structural deformation x

25 Future Work Appropriately finer mesh Inclusion of additional physics Radiation model Real gas effects Including moving solid loads Moving solid considered rigid Approximated by a moving interior plane in layering Fully coupled 1-DOF solid s motion Significant time saving Source terms to model energy impulse of the cartridge detonation Improve run time performance Effects of tightness of the convergence criteria on solution accuracy Ensure parallel performance 25

26 Conclusion Two way coupled FEA & CFD Demonstrate seamless two way fluid/thermal and structural coupling for high speed compressible flow simulation Easy to Use Single, intuitive environment for the entire FSI simulation setup Robust Minimal user intervention for the FSI run Robust FEA and CFD solvers, even with larger time step size Automation with minimal user intervention Full automation through scripts possible Flexible Ability to add advanced models to include more physics Optimization Design Explorer in Workbench 26

27 Questions and Answers 27

28 Multi-field Solver Field Interface Loads Transferred Across Field Interface Physics Fields SEND RECEIVE Structural Displacement Force, Temperature Thermal Temperature, Heat Generation, Heat Flux Displacement, Heat Generation Electric Field Force, Heat Generation Displacement, Temperature Magnetic Force, Heat Generation Displacement, Temperature Fluid Surface Force, Surface Temperature Displacement, Surface Temperature HF Electromagnetic Heat Generation Temperature Please refer to ANSYS coupled field analysis guide for thorough details. 28

29 MFX Multi-field Solver Do Mapping ANSYS Master CFX Slave Time Loop Time Controls Time Loop Stagger Loop Stagger Loop ANSYS Solver Stagger Controls (ANSYS to CFX) Load Transfers Stagger Controls (Bidirectional) CFX Solver End Stagger Loop End Stagger Loop End Time Loop Time Controls End Time Loop 29