In some cases, you may want to fix the values of some of the material parameters so that they do not vary during the fitting calculation. For example, the value of a parameter may be fixed due to physical requirements. The reference temperature for the Arrhenius law is a parameter that is commonly fixed.
Once you have specified the type of fluid model you want to fit (as described in Selecting the Type of Fluid Model), follow the steps below to fix the values of any material parameters that you want to keep constant during the fitting calculation. See Material Data Parameters for details about the material parameters for different viscosity models.
Select Material Data in the top-level Ansys Polymat menu.
Material Data
Click the menu button near the top of the Ansys Polymat application window. Ansys Polymat will inform you that fixing is enabled, and the menu button will remain highlighted.
Select the menu item for the material property for which you want to fix the value of one or more parameters (for example, Shear-rate dependence of viscosity).
Choose the desired law (for example, Bird-Carreau law).
Select the parameter to be fixed (for example, Modify fac), and enter the value.
Important: You will need to select the parameter even if you plan to keep the default value. By default, the value will not be fixed; you need to tell Ansys Polymat that it is a fixed value, and this is done in the menu that appears after you have specified the value.
Select the appropriate menu item to indicate that you are setting a fixed value for the parameter (for example, fac is a fixed value).
Select Upper level menu.
Repeat the previous three steps to define fixed values for any other parameters that you do not want to be varied during the fitting calculation.
When you have fixed values for all of the appropriate material parameters, click Upper level menu twice to return to the Material Data menu.
If relevant, click the menu item for the next material property for which you want to fix the value of one or more parameters (for example, Temperature dependence of viscosity), and follow the same procedure for selecting the desired law and setting the related fixed values.
Click the menu button again to disable the fixing of values. Ansys Polymat will inform you that fixing is disabled, and the menu button will no longer be highlighted.
(optional) Specify values for any other relevant properties (for example, Density or Thermal conductivity). Note that these values will have no effect on the fitting procedure, but setting them will allow you to save a material data file containing a full description of the fluid model.
Select Upper level menu to return to the top-level Ansys Polymat menu.