Restart for Solidification

atulverma · May 6, 2009, 04:21

hi!
I am facing a problem with restart for solidification.
After filling the die when I am giving restart for solidification after few time steps its shows the solid fraction as 1 or 0 and the temperature also goes to some maximum value and some where it goes to zero.Thus after few more iterations it shoes negative temperature and the solution ends.
I am using the same grid(multi mesh block) for restart.
I am keeping the air entrainment model on even during solidification and turning on the density as the function of temperature and scalar(solute).
Segregation model is on during filling as well as during solidification.
What all things should be taken care of when giving a restart?

Atul

melissa · May 6, 2009, 15:36

Hi~
What are your boundary conditions for the restart do you still have velocity?
MC

atulverma · May 6, 2009, 18:13

hi melissa!
thanks for replying..here is the further explanation...
No ,I am using symmetry boundary conditions,I used a shot sleeve arrangement to fill the die and the boundaries and the boundary conditions remains same.I give restart little before the complete filling and in the restart simulation after few time steps the piston attains 0 velocity.Also the pressure iterations do not converge as the piston is still pushing the fluid after the die is completely filled.So after some iterations compressibility is invoked.I am switching on the density as a function of temperature and scalar(solute) only in the restart.
The simulation is terminated with " negative fluid temperature" message.Also the temperature before goes to value near Melting point of the pure Solvent in most of the parts and remaining it shows zero temperature.Also the solution well runs for zero velocity field.

1)Is this due to failure of pressure iterations,but I do not see any relation?
2)Air Entrainment Model should be used while modeling solidification or not?
3)Restart based on temperature and internal energy have any effect on the solution?
4)Having multi mesh blocks during solidification creates problem..?

It seems that the temperature and internal energy and thus the solid fraction are not calculated properly.
thanks
Atul

melissa · May 6, 2009, 18:40

Hi~
The reason for the pressure iterations is such that since you have a velocity boundary at the restart fluid will continue to be pushed through causing pressure iterations. Use fill fraction for fill conditions when filling. Model setup tab.
Then for restart turn off the density evaluation and set the boundary to symmetry.
MC

May 6, 2009, 04:21	Restart for Solidification	#1
atulverma New Member Atul Verma Join Date: Apr 2009 Location: Bangalore Posts: 17 Rep Power: 17	hi! I am facing a problem with restart for solidification. After filling the die when I am giving restart for solidification after few time steps its shows the solid fraction as 1 or 0 and the temperature also goes to some maximum value and some where it goes to zero.Thus after few more iterations it shoes negative temperature and the solution ends. I am using the same grid(multi mesh block) for restart. I am keeping the air entrainment model on even during solidification and turning on the density as the function of temperature and scalar(solute). Segregation model is on during filling as well as during solidification. What all things should be taken care of when giving a restart? Atul

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May 6, 2009, 15:36		#2
melissa Member MC Join Date: Mar 2009 Posts: 56 Rep Power: 17	Hi~ What are your boundary conditions for the restart do you still have velocity? MC

May 6, 2009, 18:13		#3
atulverma New Member Atul Verma Join Date: Apr 2009 Location: Bangalore Posts: 17 Rep Power: 17	hi melissa! thanks for replying..here is the further explanation... No ,I am using symmetry boundary conditions,I used a shot sleeve arrangement to fill the die and the boundaries and the boundary conditions remains same.I give restart little before the complete filling and in the restart simulation after few time steps the piston attains 0 velocity.Also the pressure iterations do not converge as the piston is still pushing the fluid after the die is completely filled.So after some iterations compressibility is invoked.I am switching on the density as a function of temperature and scalar(solute) only in the restart. The simulation is terminated with " negative fluid temperature" message.Also the temperature before goes to value near Melting point of the pure Solvent in most of the parts and remaining it shows zero temperature.Also the solution well runs for zero velocity field. 1)Is this due to failure of pressure iterations,but I do not see any relation? 2)Air Entrainment Model should be used while modeling solidification or not? 3)Restart based on temperature and internal energy have any effect on the solution? 4)Having multi mesh blocks during solidification creates problem..? It seems that the temperature and internal energy and thus the solid fraction are not calculated properly. thanks Atul

May 6, 2009, 18:40		#4
melissa Member MC Join Date: Mar 2009 Posts: 56 Rep Power: 17	Hi~ The reason for the pressure iterations is such that since you have a velocity boundary at the restart fluid will continue to be pushed through causing pressure iterations. Use fill fraction for fill conditions when filling. Model setup tab. Then for restart turn off the density evaluation and set the boundary to symmetry. MC