Discussion Forum

Hi everyone,

(all the contents and photo are in the .doc file, please download it, Thanks)

I’m trying to build a laser-material interaction model based on the “heat transfer module” and “moving mesh module”. During those days, I have encountered some problems. Could you give me some guidance? Thanks in advance for your response.
The model geometry is a simple rectangle (2D).

Setting of heat transfer module:
A laser beam is treated as a heat flux boundary on 4th (boundary number or the upper boundary) boundary (the heat flux is limited in a certain range-narrow than the length of the 4th boundary), while the other three boundaries are “thermal insulation”.


P.s. All the details are illustrated in the attachment. The numbers with circle means boundary, while the one without circle is domain. The above diagram simplifies the actual triangular mesh.

Setting of ALE module:
An attribution- prescribed mesh displacement (the y direction displacement is activated and the x direction is not activated) is applied to the upper boundary (number 4), while other is fixed. Thanks.

Physical basics:
When the material temperature is getting higher than T_e (usually equal to the evaporation temperature or melting point), this part of material will be removed, so the new boundary is created.

Ideas for the ALE and prescribed mesh displacement:
1. Using the “mphinterp” function to extract the Temperature at each point on the boundary 4, because this function can estimate the expression at arbitrary point instead of only the nodal pint (only the quantity of the nodal point is less – poor accuracy).

2. Find the new points (the blue point in the attachment photo), where the temperature is just equal to T_e (or around the T_e, considering the discrete position) also using the function “mphinterp”. Assuming the new coordinate is (x, y’) at a specific x (identical to the x value of the old points for the reason of a good compare and calculation).

3. Define a variable ”dis_y”, which is the subtraction of the y coordinate value between new and old points. i.e. dis_y=y-y’

4. Using dis_y to present the prescribed mesh displacement in the ALE.

5. The COMSOL moves the upper boundary according to the prescribed mesh displacement “dis_y”. Furthermore the new boundary is created like the blue dashed line in the attachment.

Question I: Can the prescribed mesh displacement of the ALE fulfill the aim?
I have watched some models using ALE, some of them use the dependent variable (in my case, the temperature can be used). But if I build the model only according to the temperature instead of using the rate of evaporation (where a velocity of the boundary is dependent on the dependent variable ‘Temperature’, and this velocity can be set into the velocity of the mesh). Is here an accessible method if the ALE method can’t do it? Thanks sincerely.

Question II: Can these function like “mhpinterp”be used in building a model?
Usually, the kinds of function are defined as postprocessing function. As far as I known (maybe what I known is quite little), there is no reference or guidance illustrating the use in building model, while there are many illustrating their use in postprocessing. In my case, there is any other ways to fulfill my aim? Thanks for your guidance.

Thanks for your response.
Best wishes to you and your family.

Yours
FM Huang
Dec. 7th .2011