Heat Source Simulation in Workbench

Explore the use of Customization Tools for modeling moving heat sources and their applications in different industries.

Understanding Heat Source Dynamics

Modeling moving heat sources offers valuable insights into various industrial processes and applications. Laser heating and materials processing use many laser beams for heating, welding, or cutting materials. Despite in some cases the heat source (q) is not the usual Gaussian intensity profile, this is a well-known approach given by the general equation:

Where,

q is the heat flux on the desired surface [W/m2]

c is the source power intensity [W]

x, y and z define the instantaneous position of the center of the heat flux which  is on the 'path' at the calculated distance (x = v.t) from the 'start point' [mm]. Notice that v is the velocity of the heat source [mm/s] and t the Time [s].

The following picture provides a qualitatively representation, this time in terms of x, y:

Every laser-based material processing method requires delivering the precise quantity of energy to the appropriate location within the specified timeframe to guarantee effective processing. The thermal history during processing significantly influences factors like melt pool dynamics, residual stresses, microstructure, and ultimately the final mechanical properties and dimensional accuracy of the processed part.

Given the high costs associated with trial-and-error experiments, mathematical modeling emerges as a valuable tool to gain insights into these laser-based processes economically. However, modeling allows exploring different laser beam configurations and energy profiles that may be impractical to test experimentally due to the need for specialized laser equipment for each variation.

Then, modeling may help in optimizing laser processing parameters to reliably attain target material characteristics while minimizing expensive experimental iterations. The problem of moving heat sources can be addressed by CFD tools (like CFX and Fluent), or FEA packages.

Moving Heat Source Modeling

The Demo in this blog is performed on the 'Transient-Thermal' module, available in the Workbench environment. It is important to keep in mind that the use of this ACT (Ansys Customization Tool) on the 'Steady-State' module is not recommended. Within the Transient model, the user may include more thermal boundary conditions in the analysis such as convection and radiation during the simulation time. 

Ansys Customization Tools 

The Ansys Store is a platform that offers a wide range of apps to enhance the capabilities of Ansys solutions. These apps, known as Ansys Customization Tools (ACTs), are published ACT extensions designed to perform specific functions within targeted Ansys products.

The store features both free and paid apps developed by Ansys and trusted partners. To acquire a paid app, you need to request a quote for offline fulfillment, while free apps can be downloaded simply by logging in. The store also allows you to filter apps based on the target application, product version, and price.

Customers can benefit from ACTs by downloading free apps that come with source code, allowing them to view, copy, and even modify the code to create custom apps tailored to their specific needs. This can significantly streamline simulation processes and enhance productivity by automating tasks or adding new functionalities to existing Ansys products.

Installing the ACT

First, you must download and install one ACT that was developed for this purpose. Follow these steps:

1. Visit the Ansys Store online.
   
   
2. Search: Heat Source.
   
   
3. You will see the following ACT.
   
   
   
   
   
4. Click on each one to access the description and the Download link. Get the files and unzip the file on your computer.
   
   
5. Now, Open Workbench. Go to Extensions > Install Extension. Search the wbex file within the bin folder in the unzipped files in Step 4.
   
     
   
   Once the ACT is installed, you will see this message as confirmation:
   
   
   
   
   
6. Open the 'ACT Start Page' and then on 'Manage Extensions'
   
   
   
   
   
   
   
7. Click on the gray triangle and then, 'Load Extension'. Nex, you will see that the ACT block is green-colored. The ACT is ready to use.
   
    

Now, go to the Project Desktop. Drag and drop a module of 'Steady-Thermal'. You will see two tabs named 'Moving Heat Flux' and 'Moving Heat Energy'.

Model setup

• Create the geometry and mesh; here the classic Steel plate is modeled (70 x 40 x 10 mm). Notice the geometry has three bodies and a centerline. Please pay attention to the following steps to understand how to prepare your geometry.
  
  
  
  
• Recall that Convection and Radiation are applied on all surfaces except on the bottom, where a perfect insulation is defined. Now, right click on 'Transient-Thermal' > Insert > Moving Heat Flux.
   
  
  
• Setup. A: Geometry
  
  Geometry. Select the blue surfaces on the top (not the body).
  
  Path. Select the lines that define the trajectory of the heat source. This means that the path is part of the geometry. In this case it is a straight line.
  
  Start Point. The selected point will be at the center of the Heat profile as the starting position.
  
  
  
  
  
• Setup B: Heat Source
  
  Index. It is the ID of a given heat source setup when two or more are included.
  
  First Patch?. Type the index of the first Heat Source to be applied.
  
  Last Patch?. Type the index of the last Heat Source in the model. When there is only one Heat Source, the answer is Yes.
  
  Velocity. It is the speed of the heat source. The direction is defined by the Path. Be aware of the units.
  
  Radius of the Beam. Type the beam radius (not the diameter). Again, be aware of the units.
  
  Source Power Intensity. Type the operating intensity of the Heat Source. This means, the maximum value. Recall that this is a Gaussian distribution.
  
  Start and End Time. In a Steady-State simulation, this is defined in the Initial/End Step in Analysis Settings.  Be aware that the total distance must be covered based on the time and the speed of each Heat Source (Distance = Velocity*Time). 
  
  Number of Segments. This is an option to refine the segmentation on the path, which is divided in equidistant points that will serve as the center of the moving heat flux. Only available for the 'Last Patch'.
  
  Minimum Steps for Cooling Phase. The user can add to the total analysis time more that the ‘End Time’ and thus cooling of the plate can be simultaneously simulated. This input defines numbers of substeps for the cooling phase.
  
  Material Removal. Yes/No. This options allows including this effect and demands much more computational resources for processing.
  
  Melting Temperature. Set the limit to apply the material removal.
  
  

Results

• Heat Source without Material Removal

The baseline model is the one solved using 12 cores. The video shown below presents the contours colored by temperature on the plate. Moreover, the graph indicates the reduction in the processing time when using one HPC Pack license. In summary, the speed up is about four times the time of the model with four cores.

Material Removal

As mentioned earlier, this ACT includes the option to remove the elements that exceed a temperature limit; i.e., the melting temperature of the material. To do that, the Element Birth and death capability is activated to "kill" the elements having the mentioned condition. The information is saved in the files named "ekill_curr.txt", "Killed_ele.txt" and "read_kill.txt". Something important to mention refers to the element type, as the material removal only works for linear elements. The processing time for the same geometry and setup, reached approximately 15 hours using 12 cores. 

The value of 400°C was typed only for demonstration purposes.