Dendrite tip velocity

[CharMIC]

Hi,

Is there an inbuilt function in MICRESS to calculate the dendrite tip velocity in directional solidification simulations.

BR
Chamara

[Bernd]

Hi CharMIC,

apart from the .vel output which is very inaccurate, there is no inbuilt general function in MICRESS to determine velocities. However, if there is only one dendrite, or if you are interested in the leading one, you can use the "Front Position" output in the .TabL file. It is only accurate within 1 grid cell, but by interpolation you can achieve a very exact velocity calculation. The number given
here is the z-coordinate of the uppermost cell in the domain which is not completely liquid.

There are other methods like tracking the profile of the solid phase fraction by virtual EDX linescans with DP_MICRESS and fitting the profile in order to determine the center of the interface. However, this is complicated and probably not really more exact. You would need that for determination of the absolute position in an exact way.

In contrary, the optional "front_temp" output in .TabF would give you the average front temperature which is not helpful for dendrites.

Bernd

[CharMIC]

Hej Bernd,

Thanks for the reply. Is it possible to use the methods that you have mentioned above to measure the growth rate (solidification front velocity)?

BR
Chamara

[Bernd]

Yes,

using "Front Pos." as function of time you easily can calculate the average front velocity (by taking the derivative and divided by the temperature gradient).
In cases without moving_frame, it is equivalent to the total fraction of solid.

Edit: Of course I meant "Front Pos." and not "front Temp." as erroneously written before...

Bernd

[CharMIC]

Hej Bernd,

I want to fine the relationship between undercooling and the growth rate velocity in directional solidification case.

I have already performed directional solidification simulation starting with many initial grains at the bottom of the domain with different cooling rates and thermal gradients. Is it possible to use these simulation results for the above purpose

OR

Do I have to simulating a single dendrite growth under different cooling rates and thermal gradients and use that results?.

Also How can I calculate the undercooling using .driv file?

BR
Chamara

[Bernd]

Hi Chamara,

as I have explained further above in this thread, an automatic evaluation of the dendrite tip velocity and position/undercooling is only possible for the leading dendrite (if it is always the same one), or if you have only one dendrite at all. However, you always can make evaluations by hand if you pick the position of the tip of each dendrite for different time steps and evaluate local temperature using the .temp output (or calculated it from the position).

The .driv output gives no information about tip undercooling, because it displays only the deviation from equilibrium which depends on temperature, concentration and local curvature and kinetic undercooling. Tip undercooling, instead, is just the difference between liquidus temperature and local temperature at the tip.

Bernd

[CharMIC]

Hej Bernd,

Many thanks for the input.

I saw in the MICRESS manual (Manual for 6.4, page 75-76) that undercooling can be calculated form the driving force out put file and transformation entropy.
That was the reason why I have mentioned it above.

[Bernd]

Yes, this is true. However ΔT here (in the manual) is the solutal undercooling which is calculated as function of local concentration and temperature. If we speak about dendrite tip undercooling, usually only the temperature is considered.

[CharMIC]

Many thanks Bernd.

One more thing, I can see "Front Temp" results in .TabL. Is this for the temperature at the "Front Pos"

[Bernd]

Yes, this is exactly the case.