James Etchells (TEC-MCV) 19 th European Workshop on Thermal and ECLS Software 11 th 12 th October 2005

Transcription

1 James Etchells (TE-MV) 19 th European Workshop on and ELS Software 11 th 12 th October Introduction and discussion of background and important issues 2. omparison of TLP and FEA for S/ thermal analysis 3. Presentation of developed tools with accompanying examples 4. ombination of tools to allow hybrid FEA/TLP analysis 5. onclusions 6. Questions Sheet 2

2 ! "# $ % & Traditionally S/ thermal analysis uses Lumped Parameter (TLP) method Physical system represented as an abstract network of conductors and capacitances Based on 1 st order Finite Difference discretisation of governing PDE Industry standard tools: ESATAN, SINDA In the past lumped parameter methods were used for many application domains e.g. Structural, Fluid Flow,, Electromagnetic complex problems abstracted and analysed using limited computing resources of the day Recently FEA gained widespread popularity especially for structural analysis Shift to FEA made possible by vast improvements in computational hardware Excellent pre/post processing tools, AD import, mesh generation Intrinsic link with physical geometry However, the S/ thermal analysis community is reluctant to embrace FEA But the method has much to offer so why the reluctance? Sheet 3 ' "# ( ) * FEA often considered inefficient compared with TLP Inappropriately large thermal models with FEA unsuitable for system level analysis Perception that FEA is non-physical method negative conductors often cited Lack of ontrol functionality in FEA tools Valid point but problem lies with current FEA tools NOT the method Lack of dedicated radiation analysis tools for FEA Some FEA tools support radiation exchange but very limited (only geometric VF s) No support for specular reflectivity, environmental fluxes, orbit definition, kinematics etc. engineers often not interested in precise temperature fields More interested in system level heat flows But very precise temperature fields will be required for future scientific missions ultural inertia - over 40 years of experience with TLP engineers have confidence in TLP and experience with the tools Sheet 4

3 ) * GMM Radiative onductor Generation ontrol Post Process Structural Mapping TLP FEA GMM built in radiative analysis tool geometry only used for radiation, no AD link Powerful radiative anal. tools (e.g. ESARAD) - specularity, orbit definition, heat fluxes onductor generation required for TMM often done manually major bottleneck anal. and control in TLP tool with functionality for fluid loops, subroutines, etc. Post-pro with spreadsheets, ad-hoc scripts etc - mapping temps to structural FE difficult FEA pre-processors extremely powerful for building geometry meshing and AD import Limited radiative anal. functionality in current FE tools no specularity or orbital fluxes No conductor generation necessary conduction matrix from mesh and material props. Lack of functionality for thermal control element library designed for structures Excellent post-processing tools contour plotting on mesh, x-y plotting, etc. Mapping temperatures. to structural FE mesh is made easier - intrinsic link with geometry Sheet 5 Several targets were identified: ( +, & 1. It should be possible to use the functionality of FE pre-processors to create a GMM 2. Important to be able to use S/ radiative analysis tool (e.g. ESARAD) with FE mesh Also important to map exchange favtors and 3. Hybrid TLP/FEA thermal analysis (c.f. Desktop) is attractive ombine benefits of FEA (e.g. no conductor gen.) & TLP (e.g. control elements) Hybrid TLP/FEA thermal analysis using TLP tool as general equation solver Allows gradual integration of FEA users must gain experience and confidence Sheet 6

4 ! # - ' TLP FEA GMM Radiative onductor Generation ontrol Post Process Structural Mapping ey benefit of FEA is functionality in pre-processing tools Automatic meshing, AD import, point-and-click modelling, link to parametric data or concept model possible We can use this functionality to create GMM for analysis of radiation exchange NAS2TAS was developed converts radiative part of NASTRAN FE model to STEP-TAS Allows development of GMM in any pre-processor that supports NASTRAN BDF (Patran, FEMAP, ATIA) Patran/NASTRAN chosen due to availability at ESTE ABAQUS, SAMEF, ANSYS etc. could have been used Use of STEP-TAS as neutral format allows any supported radiative tool to be used for analysis urrently ESARAD and THERMIA supported TRASYS, RadAD in future Sheet 7! # - ' ESARAD erg Develop GMM in Preprocessor NASTRAN BDF NAS2TAS STEP-TAS stp TASverter THERMIA SYSBAS TRASYS inp Sheet 8

5 .! # / / " * 0 Real practical example where NAS2TAS was used Validated ESARAD model of LSS existed but Boolean cutting operations used THEMIA LSS model was required cutting operations not supported in THERMIA Patran used to build faceted model powerful modelling functionality and meshing ESARAD with cutting MS Patran THERMIA Sheet 9 ' # 1 2, TLP FEA GMM Radiative onductor Generation ontrol Post Process Structural Mapping Many FEA codes have some in built radiation exchange functionality but limited No support for specular reflectivity, calculation of environmental heat fluxes, mission definition etc. But NASTRAN permits user to supply pre-defined radiative couplings RADMTX matrix RADMTX Writer maps REF s and heat fluxes from radiative analysis tool to NASTRAN GR s and HF s calculated with radiative tool and written to ESATAN input deck Both ESARAD and THERMIA can produce ESATAN input decks Tool was developed to map REF s and HF s from ESATAN deck to NASTRAN Mapping via an ESATAN deck reader implemented in python analysis carried out using FEA in NASTRAN Sheet 10

6 ' # 1 2, Develop FE Model in Preprocessor NASTRAN BDF NASTRAN FE Solver NASTRAN Results Post-process FEA e.g. Patran NAS2TAS/ TASverter Include Files: radmtx.dat fluxes.dat ESARAD erg THERMIA SYSBAS RADMTX Writer Radiative ESATAN Model.d Sheet 11 ' # 1 2, Sheet 12

7 3 # ' - TLP FEA GMM Radiative onductor Generation ontrol Post Process Structural Mapping FEA does not require conductor generation huge advantage over TLP methods Disadvantage of FEA tools is the lack of flexibility for subroutines, control loops etc. But TLP codes such as ESATAN/SINDA just solve systems of equations Thus it is possible to cast FEA equations (matrices) in TLP form and solve in TLP tool FE2TAN tool maps NASTRAN conduction elements to ESATAN conductors & capacitances Hybrid FEA/TLP approach possible due to use of ESATAN for thermal analysis User can combine all functionality of ESATAN with detailed FE model - subroutines, fluid loops Sheet 13 ' - # / 3 2 e = $ONDUTORS GL(1,2) = - 12 GL(1,3) = - 13 GL(1,4) = - 14 GL(2,3) = - 23 GL(2,4) = - 24 GL(3,4) = e = $INITIAL 1 = = = = Sheet 14

8 ' - # Optional ESATAN template.optional GR s User Logic ontrol reate FE Model in preprocessor e.g. Patran NASTRAN.BDF FE2TAN ESATAN Model.d ESATAN Solver ESATAN results urrently TRIA3, QUAD4, TETRA, ELAS, DAMP elements can be written to TAN ELAS analogous to TLP linear conductor DAMP analogous to TLP lumped capacitance Non-isotropic material properties and temperature dependence not yet supported Functionality to include radiation exchange (GR s) between FE grid points ESATAN template file can be used to define structure of model solution routines etc. Element conduction/capacitance matrices formed using code written from scratch Validation of the methods used is thus an issue but we can compare with NASTRAN Sheet 15 4 ' - # * & Q W/m -2 Q W/m -2 Q W/m -2 FE2TAN Results: Solution in ESATAN Boundary Temperature Problem Definition reate Patran/NASTRAN Mesh NASTRAN Results Sheet 16

9 * ( # $ ( NASTRAN.BDF FEM Pre/Post Processor (PATRAN, FEMAP) NAS2TAS/TASverter --from_bdf TASverter --from_gff --to_patran Input Deck for Radiative Tool with TASverter writer ESARAD: erg THERMIA: SYSBAS ernel e.g. erk TAN template e.g. ere Radiative Tool ESARAD/THERMIA User Logic Procedural ontrol TLP components ESATAN results.gff ESATAN deck ESATAN Model.d GR s, Fluxes FE2TAN Model.d GL s, GR s, Fluxes ESATAN/ThermXL Sheet # $ ( ) / 5 * Electronics units with power dissipation mounted on a shelf reject heat to DS via radiator Single phase fluid loop chosen to transport heat to radiator Optimisation of fluid loop requires accurate temperature field prediction on shelf FEA excellent method to model conduction on electronics shelf accurately BUT no capability to model fluid loops in NASTRAN must use TLP Sheet 18

10 6. # * D500 = 'NASTRAN Grid Point 500', T = E+02[]; D501 = 'NASTRAN Grid Point 501', T = E+02[]; D502 = 'NASTRAN Grid Point 502', T = E+02[]; D503 = 'NASTRAN Grid Point 503', T = E+02[]; B99999 = 'DEEP SPAE', T = 3.0[]; $ONDUTORS #NASTRAN QUAD4 HEAT ONDUTION ELEMENT. ELEMENT ID 1 GL(1,2) = E-02; GL(1,23) = E-02; GL(1,22) = E-02; GL(2,23) = E-02; GL(2,22) = E-02; GL(23,22) = E-02; #END OF NASTRAN ELEMENT 1 ESATAN deck sample NASTRAN radiation enclosure geometry mapped to ESARAD NAS2TAS and TASverter NASTRAN conductive model mapped to ESATAN FE2TAN Fluid loop ESATAN model defined manually GF s and GL s Standard pipe flow Prandtl, Nusselt number approach with expressions coded in $VARIABLES1 Steady state thermal analysis with ESATAN results written to GFF format GFF file mapped back to Patran for post-processing TASverter GFF reader Sheet # 7 Nodal results data imported to Patran ontour plotting available on geometry Data extraction and XY plotting Temperatures linked to geometry Mapping to structural mesh more simple Sheet 20

11 6. # 7 Flow direction Sheet 21, & Integrate NAS2TAS as a reader module in future TASverter release Including development of a formal test suite unit tests etc. FE2TAN tool should produce STEP-TAS network model not ESATAN model reate STEP-TAS conductors nrf_network_node_relationship s Extension to include temperature dependent properties and more elements Extension of TASverter GFF reader to read ESARAD results into STEP-TAS GFF reader supports ESATAN type results but ESARAD rpt. is also a valid GFF file Develop ESARAD/THERMIA primitives that are more compatible with FE s Shells analogous to curved finite elements allows higher order elements to be used Raytracing between finite element nodal points not isothermal faces Research into model reduction FE models can have many degrees of freedom how to interface with system level model Reduction of linear conduction models is simple non-linear (radiation) difficult Sheet 22

12 * Several tools were developed to aid integration of FEA into S/ thermal analysis Long term goal is a co-existence of TLP/FEA this project should be seen as a first step engineers should be able to choose the analysis method best suited for a given application Important aspect of the development was use of neutral formats (STEP-TAS) STEP-TAS can aid the development of new methodologies Generality and tool-independence of ideas is extremely important - all the ideas used in the tools can be applied directly to other tools Users can try the tools and gain some experience and confidence with FEA All the methodologies use existing tools minimum financial investment or time commitment All tools and documentation available on the web - Tutorials for the tools are almost complete and will also be published Sheet 23 & During the course of my YGT period I received support from many people. I would particularly like to thank: Harrie Rooijackers Supervisor for my YGT period Simon Appel Everybody in TE-MV/TE-MT at ESTE Sheet 24