Transcript No Slide Title

4. Heat Transfer
Heat Transfer Enhancements
• Radiosity method extended to 2-D
• Transient thermal analyses are much faster
NEW FEATURES 5.7
Training Manual 001419
15 Aug 2000
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4.1 2-D Radiosity
Heat Transfer Enhancements
Heat Transfer Enhancements
2-D Radiosity
• Extends ANSYS 5.6 new feature to provide for
efficient handling of 2D radiation problems
• View factors can be queried
• Supports temperature-dependent emissivity
NEW FEATURES 5.7
• Uses Radiosity method introduced in ANSYS 5.6
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Heat Transfer Enhancements
… 2-D Radiosity
• Supports open and closed radiating systems
• Supports 2d plane and axisymmetric problems
• Applicable to: PLANE13, PLANE35, PLANE55,
PLANE67, PLANE77
NEW FEATURES 5.7
• Supports multiple enclosures
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Heat Transfer Enhancements
… 2-D Radiosity
• New V2DOPT command activates 2-D radiosity:
V2DOPT, GEOM, NDIV, HIDOPT, NZONE
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
NEW FEATURES 5.7
GEOM:
NZONE: Number of zones for view factor calculation,
default = 200.
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Heat Transfer Enhancements
… 2-D Radiosity
• GUI implementation of V2DOPT:
Main Menu > Radiation Opt > -Radiosity Meth- View Factor . . .
– Select Hidden (default)
or Non-hidden method
NEW FEATURES 5.7
– Set Plane or Axisymmetric
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4.2 Fast Transient Solver
Heat Transfer Enhancements
Heat Transfer Enhancements
Fast Transient Solver
• Improved tabular boundary condition efficiency
• Increased element calculation speed
NEW FEATURES 5.7
• Dramatically reduces transient thermal solution
time, especially for nonlinear analyses, while
maintaining solution accuracy.
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Heat Transfer Enhancements
… Fast Transient Solver
• Speed-up achieved by:
– Direct matrix assembly
– Improved solver strategy
NEW FEATURES 5.7
– Selective reform strategy
Training Manual 001419
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Heat Transfer Enhancements
… Fast Transient Solver
Direct Matrix Assembly
• 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
NEW FEATURES 5.7
• Formulate and assemble element matrices in
memory
• Assemble sub-matrices and solve equations
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Heat Transfer Enhancements
… Fast Transient Solver
Selective Reform Strategy
– Controlled by Reform Tolerance (default is 5%)
– Entire matrix is reformed if any element’s material property
evaluation exceeds tolerance
NEW FEATURES 5.7
• 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.
Training Manual 001419
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Heat Transfer Enhancements
… Fast Transient Solver
Selective Reform Strategy (cont'd)
• Nonlinear matrices and surface boundary condition
matrix terms are re-computed every substep
• Supported by ICCG and JCG solvers
NEW FEATURES 5.7
• Used for temperature-dependent solid matrices
[K]solid and [C]solid
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Heat Transfer Enhancements
… Fast Transient Solver
Improved Solver Strategy
– 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
NEW FEATURES 5.7
• Both ICCG and JCG now use the previous solution
as a starting point for pre-conditioning
– 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)
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Heat Transfer Enhancements
… Fast Transient Solver
Improved Solver Strategy (cont'd)
• No equilibrium iterations are performed
NEW FEATURES 5.7
• Memory guidelines: 1 GB per 1 Million DOF’s
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Heat Transfer Enhancements
… Fast Transient Solver
Other efficiencies gained:
• 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
NEW FEATURES 5.7
• Tabular boundary conditions now processed more
efficiently
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Heat Transfer Enhancements
… Fast Transient Solver
Procedure
– 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%).
NEW FEATURES 5.7
• THOPT, Option, ReformTol, nTabPoints, TempMin,
TempMax
– 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.
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Heat Transfer Enhancements
… Fast Transient Solver
Procedure (cont'd)
• Requires either ICCG or JCG solver
antype,trans
thopt,quasi,.05,64,
eqslv,iccg
NEW FEATURES 5.7
• Typical command sequence
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Heat Transfer Enhancements
… Fast Transient Solver
Procedure (cont'd)
antype,trans
thopt,quasi,.05,64,0,1200
autots,off
timint,off
nsubst,3
! Resolve temperature dependencies
eqslv,iccg
time,...
...
solve
timint,on
...
NEW FEATURES 5.7
• For non-zero initial conditions, set NSUB > 1 to
resolve temperature dependencies. Typical
command sequence:
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Heat Transfer Enhancements
… Fast Transient Solver
• Example
– 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
NEW FEATURES 5.7
– Transient non-linear thermal analysis (benchmark
performed by a large customer)
– Tabular boundary conditions
– Mission duration - 1200 sec.
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Heat Transfer Enhancements
… Fast Transient Solver
Benchmark results
Pratt & Whitney 3-D Benchmark
NEW FEATURES 5.7
45
40
35
30
CPU Time 25
(Hours) 20
15
10
5
0
Full Reform
Selective Reform
Solver Strategy
Compaq Alpha 4100 5/533: Performance increase (45/2) = 22.5
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