This section presents an example of a transient thermal analysis.
The example analysis this chapter describes is a transient heat transfer analysis of a casting process.
Note: A pictorial version of this example appears in the Thermal Tutorial on the Ansys customer site.
This example tracks the temperature distribution in the steel casting and the mold during a three-hour solidification process. The casting is made in an L-shaped sand mold with four-inch thick walls. Conduction occurs between the steel and the sand mold, and convection occurs between the sand mold and the ambient air.
The example performs a 2D analysis of a slice that is one unit thick. Half symmetry is used to reduce the size of the model. The lower half is the portion modeled.
To analyze the entire thickness of the model, use PLANE55 with KEYOPT(3) = 3 and specify the THK real constant. In this case, the temperate results will not be any different than modeling a one-unit thickness, but the heat flow results (PRRSOL, PRRFOR, PRNSOL, PRESOL) will be different.
Sand and steel, the materials used in the sample analysis of the casting, have these properties:
| Item | U.S. Customary Measurement Units |
|---|---|
| Material properties for sand: | |
| Conductivity (KXX) | 0.025 Btu/(hr-in-F) |
| Density (DENS) | 0.054 lb/in3 |
| Specific heat (C) | 0.28 Btu/(lb- °F) |
|
Material properties for steel: Conductivity (KXX): | |
| at 0 °F | 1.44 Btu/(hr-in- °F) |
| at 2643 °F | 1.54 |
| at 2750 °F | 1.22 |
| at 2875 °F | 1.22 |
| Enthalpy (ENTH): | |
| at 0 °F | 0.0 Btu/in3 |
| at 2643 °F | 128.1 |
| at 2750 °F | 163.8 |
| at 2875 °F | 174.2 |
| Initial conditions: | |
| Temperature of steel | 2875 °F |
| Temperature of sand | 80 °F |
| Convection properties: | |
| Film coefficient | 0.014 Btu/(hr-in2- °F) |
| Ambient temperature | 80 °F |
Material properties for the sand are constant. The steel casting has temperature-dependent thermal conductivity and enthalpy.
The solution method for this example uses automatic time stepping to determine the proper time step increments needed to converge the phase change nonlinearity. The transition from molten to solid steel uses smaller time steps.
The example casting solidification analysis is included in the Thermal Tutorial on the Ansys customer site.
The following example input builds and solves the casting model. Comments (text preceded by the exclamation mark or ! character) explain what functions the commands perform.
/TITLE,CASTING SOLIDIFICATION !Give the analysis a title /PREP7 K,1,0,0,0 K,2,22,0,0 K,3,10,12,0 K,4,0,12,0 /TRIAD,OFF !Turn triad symbol off /REPLOT ! A,1,2,3,4 !Connect keypoints to define mold area SAVE RECTNG,4,22,4,8 !Create a primitive rectangle APLOT !Display areas AOVLAP,1,2 !Overlap the areas ADELE,3,,,1 !Delete area 3 SAVE ! MP,DENS,1,0.054 !Define sand properties MP,KXX,1,0.025 MP,C,1,0.28 ! MPTEMP,1,0,2643,2750,2875,,, !Define steel properties MPDATA,KXX,2,1,1.44,1.54,1.22,1.22,,, MPDATA,ENTH,2,1,0,128.1,163.8,174.2 MPPLOT,KXX,2,,,,, !Plot steel conductivity MPPLOT,ENTH,2,,,,, !Plot steel enthalpy SAVE ! ET,1,PLANE55 !Use element PLANE55 ! SAVE SMRT,5 !Specify smart element sizing level 5 MSHAPE,0,2D !Mesh with quadrilateral-shaped elements MSHKEY,0 !Specify free meshing AMESH,5 !Mesh mold area, area 5 ! TYPE,1 !Set element type attribute pointer to 1 MAT,2 !Set element material attribute pointer to 2 REAL !Set element real const set attribute pointer ESYS,0 !Set the element coord sys attribute pointer AMESH,4 !Mesh casting area, area 4 ! SAVE SFL,1,CONV,0.014,,80,, !Apply film coefficient and bulk temperature SFL,3,CONV,0.014,,80,, SFL,4,CONV,0.014,,80,, SAVE FINISH /SOLU ! ANTYPE,4 !Specify transient analysis ! APLOT ASEL,S,,,4 !Select casting area, area 4 NSLA,S,1 !Select nodes associated with casting area NPLOT !Display casting area nodes IC,ALL,TEMP,2875 !Apply initial condition of 2875F on casting NSEL,INVE !Select nodes of steel area, area 5 /REPLOT !Display mold area nodes IC,ALL,TEMP,80 !Apply initial condition of 80F on mold ALLSEL,ALL !Select all entities SAVE ! TIME,3 !Set time at end of load step AUTOTS,-1 !Program chosen automatic time stepping DELTIM,0.01,0.001,0.25,1 !Specify time step sizes KBC,1 !Specify stepped loading ! OUTRES,ALL,ALL !Write to file at every step SAVE /STAT,SOLU !Display solution options /REPLOT !Display all nodes APLOT !Display areas SOLVE FINISH ! /POST26 !Time-history postprocessor EPLOT !Display elements cntr_pt=node(16,6,0) !Define postprocessing variable NSOL,2,cntr_pt,TEMP,,center !Specify nodal data to be stored PLVAR,2 !Display nodal temperature versus time FINISH /EOF