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4. Heat Transfer

4. Heat Transfer. Heat Transfer Enhancements. Radiosity method extended to 2-D Transient thermal analyses are much faster. 4.1 2-D Radiosity. Heat Transfer Enhancements. Heat Transfer Enhancements 2-D Radiosity.

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4. Heat Transfer

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  1. 4. Heat Transfer

  2. Heat Transfer Enhancements • Radiosity method extended to 2-D • Transient thermal analyses are much faster Training Manual 001419 15 Aug 2000 4-2

  3. 4.1 2-D Radiosity Heat Transfer Enhancements

  4. Heat Transfer Enhancements2-D Radiosity • Extends ANSYS 5.6 new feature to provide for efficient handling of 2D radiation problems • Uses Radiosity method introduced in ANSYS 5.6 • View factors can be queried • Supports temperature-dependent emissivity Training Manual 001419 15 Aug 2000 4-4

  5. Heat Transfer Enhancements… 2-D Radiosity • Supports open and closed radiating systems • Supports 2d plane and axisymmetric problems • Supports multiple enclosures • Applicable to: PLANE13, PLANE35, PLANE55, PLANE67, PLANE77 Training Manual 001419 15 Aug 2000 4-5

  6. Heat Transfer Enhancements… 2-D Radiosity • New V2DOPT command activates 2-D radiosity: V2DOPT, GEOM, NDIV, HIDOPT, NZONE GEOM: Choice of geometry 0 = planar (default) 1 = axisymmetric NDIV: Number of divisions for axisymmetric geometry HIDOPT: View factor option 0 = hidden (default) 1 = non-hidden NZONE: Number of zones for view factor calculation, default = 200. Training Manual 001419 15 Aug 2000 4-6

  7. Heat Transfer Enhancements… 2-D Radiosity • GUI implementation of V2DOPT: Main Menu > Radiation Opt > -Radiosity Meth- View Factor . . . • Set Plane or Axisymmetric • Select Hidden (default)or Non-hidden method Training Manual 001419 15 Aug 2000 4-7

  8. 4.2 Fast Transient Solver Heat Transfer Enhancements

  9. Heat Transfer EnhancementsFast Transient Solver • Dramatically reduces transient thermal solution time, especially for nonlinear analyses, while maintaining solution accuracy. • Improved tabular boundary condition efficiency • Increased element calculation speed Training Manual 001419 15 Aug 2000 4-10

  10. Heat Transfer Enhancements… Fast Transient Solver • Speed-up achieved by: • Direct matrix assembly • Selective reform strategy • Improved solver strategy Training Manual 001419 15 Aug 2000 4-11

  11. Heat Transfer Enhancements… Fast Transient Solver Direct Matrix Assembly • Formulate and assemble element matrices in memory • Split [K] matrix into sub-[K] matrices as needed: • [K]solid for temperature-dependent solids • [K]nl for highly nonlinear elements • [K]surf for surface boundary conditions • Similarly, split [C] is split into sub-[C] matrices for in-memory storage • Assemble sub-matrices and solve equations Training Manual 001419 15 Aug 2000 4-12

  12. Heat Transfer Enhancements… Fast Transient Solver Selective Reform Strategy • Decision to reform [K] and [C] matrices is based on maximum change in the temperature-dependent material property between current time point and previous reform time point. • Controlled by Reform Tolerance (default is 5%) • Entire matrix is reformed if any element’s material property evaluation exceeds tolerance Training Manual 001419 15 Aug 2000 4-13

  13. Heat Transfer Enhancements… Fast Transient Solver Selective Reform Strategy (cont'd) • Used for temperature-dependent solid matrices [K]solid and[C]solid • Nonlinear matrices and surface boundary condition matrix terms are re-computed every substep • Supported by ICCG and JCG solvers Training Manual 001419 15 Aug 2000 4-14

  14. Heat Transfer Enhancements… Fast Transient Solver Improved Solver Strategy • Both ICCG and JCG now use the previous solution as a starting point for pre-conditioning • Drastically reduces the number of iterations to converge • Auto time-stepping now considers three criteria for controlling time step size • Maintain time-step such that the maximum property change (since the last reform step) stays at the Reform Tolerance • Evaluate Rayleigh criteria and adjust time step (pre-existing criteria) • Heuristic criteria based on maximum temperature change per time step (implemented at Release 5.4) Training Manual 001419 15 Aug 2000 4-15

  15. Heat Transfer Enhancements… Fast Transient Solver Improved Solver Strategy (cont'd) • No equilibrium iterations are performed • Memory guidelines: 1 GB per 1 Million DOF’s Training Manual 001419 15 Aug 2000 4-16

  16. Heat Transfer Enhancements… Fast Transient Solver Other efficiencies gained: • Tabular boundary conditions now processed more efficiently • Temperature-dependent material property tables combined into a single table look-up • OUTRES with the “none” option now more efficient • Surface boundary condition processing is now more efficient Training Manual 001419 15 Aug 2000 4-17

  17. Heat Transfer Enhancements… Fast Transient Solver Procedure • THOPT, Option, ReformTol, nTabPoints, TempMin, TempMax • Option: • NONLIN - Use Full reform Strategy (default) • QUASI - Use Selective Reform Strategy • LINEAR - Do not reform element matrices • ReformTol - Material property change tolerance for matrix reform. Defaults to 0.05 (5%). • nTabPoints - Number of temperature points for the Fast Material table. Defaults to 64. • TempMin, TempMax - Min and Max temperatures for Fast Material table, obtained from MPTEMP command. Training Manual 001419 15 Aug 2000 4-18

  18. Heat Transfer Enhancements… Fast Transient Solver Procedure (cont'd) • Requires either ICCG or JCG solver • Typical command sequence antype,trans thopt,quasi,.05,64, eqslv,iccg Training Manual 001419 15 Aug 2000 4-19

  19. Heat Transfer Enhancements… Fast Transient Solver Procedure (cont'd) • For non-zero initial conditions, set NSUB > 1 to resolve temperature dependencies. Typical command sequence: antype,trans thopt,quasi,.05,64,0,1200 autots,off timint,off nsubst,3 ! Resolve temperature dependencies eqslv,iccg time,... ... solve timint,on ... Training Manual 001419 15 Aug 2000 4-20

  20. Heat Transfer Enhancements… Fast Transient Solver • Example • Transient non-linear thermal analysis (benchmark performed by a large customer) • Statistics • 119,600 SOLID70 tetrahedral elements • 34,588 SURF152 surface-effect elements • 9 MASS71 lumped thermal elements • 8 FLUID116 thermal-flow elements • 29,300 DOF’s • Unsymmetric matrices • Tabular boundary conditions • Mission duration - 1200 sec. Training Manual 001419 15 Aug 2000 4-21

  21. Heat Transfer Enhancements… Fast Transient Solver Benchmark results Compaq Alpha 4100 5/533: Performance increase (45/2) = 22.5 Training Manual 001419 15 Aug 2000 4-22

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