4. Heat Transfer

Training Manual Aug Heat Transfer Enhancements Radiosity method extended to 2-D Transient thermal analyses are much faster

4.1 2-D Radiosity Heat Transfer Enhancements

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

Training Manual Aug 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. Heat Transfer Enhancements … 2-D Radiosity

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

4.2 Fast Transient Solver Heat Transfer Enhancements

Training Manual Aug Heat Transfer Enhancements Fast 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 Aug Heat Transfer Enhancements … Fast Transient Solver Speed-up achieved by: –Direct matrix assembly –Selective reform strategy –Improved solver strategy

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

Training Manual Aug Heat Transfer Enhancements … Fast Transient Solver Compaq Alpha /533: Performance increase (45/2) = 22.5 Benchmark results