Range of relaxation times: If you want to compare rheological curves obtained for a viscoelastic flow, you will need to specify the minimum and maximum values of the relaxation time for the curves so that they will all be consistent. To set these values, click Modify the range of relaxation times in the Numerical Options for Fitting menu.

  Modify the range of relaxation times

Window of shear rates: If you want to compare rheological curves obtained for a steady shear flow, you will need to specify the minimum and maximum values of shear rate for the curves so that they will all be consistent. To set these values, click Modify the window of shear rates in the Numerical Options for Fitting menu.

  Modify the window of shear rates

Window of angular frequencies: If you want to compare rheological curves obtained for an oscillatory shear flow, you will need to specify the minimum and maximum angular frequencies for the curves so that they will all be consistent. To set these values, click Modify the window of angular frequencies in the Numerical Options for Fitting menu.

  Modify the window of angular frequencies

Window of times: If you want to compare rheological curves obtained for a transient flow, you will need to specify the minimum and maximum values of time for the curves so that they will all be consistent. To set these values, click Modify the window of times in the Numerical Options for Fitting menu.

  Modify the window of times

Weighting for shear viscosity curves: The weighting allows you to assign more importance to one or more curves compared to the others. For example, in the fitting of a viscoelastic model, if you are not interested in fitting the shear viscosity, you should set the weighting for the shear viscosity curves to a much lower value than for the others.

To set the weighting for the shear viscosity curves, click Modify the weight of shear viscosity curves in the Numerical Options for Fitting menu.

  Modify the weight of shear viscosity curves

Weighting for the storage and loss moduli curves: The weighting allows you to assign more importance to one or more curves compared to the others. To set the weighting for the storage and loss moduli curves, click Modify the weight of G’ and G" curves in the Numerical Options for Fitting menu.

  Modify the weight of G’ and G" curves

Weighting for extensional viscosity curves: The weighting allows you to assign more importance to one or more curves compared to the others. For example, in the fitting of a viscoelastic model for a flow that is mainly extensional (for example, fiber spinning), the fitting of the extensional viscosity must be better than the fitting for the others, so you should set the weighting for the extensional viscosity curves to a higher value than for the others.

To set the weighting for the extensional viscosity curves, click Modify the weight of extensional visc. curves in the Numerical Options for Fitting menu.

  Modify the weight of extensional visc. curves

Weighting for the first normal stress difference curves: The weighting allows you to assign more importance to one or more curves compared to others. To set weighting for the first normal stress difference curves, click Modify the weight of N1 curves in the Numerical Options for Fitting menu.

  Modify the weight of N1 curves

Maximum number of iterations: In general, 50 iterations (the default) are enough to get converged results. However, sometimes more iterations are needed, especially for fitting viscoelastic models. Select Modify the max. number of iterations item in the Numerical Options for Fitting menu to modify the default value.

  Modify the max. number of iterations

Activation/deactivation of fitting of relaxation times: By default, relaxation times are not fit. Rather, they are distributed at a regular interval in the range specified (in a logarithmic scale) via the Modify the range of relaxation times option. However, it is possible to optimize the distribution of the relaxation times to obtain a better fit.

When activating the fitting of relaxation times, the range of relaxation times defined above (under the Modify the range of relaxation times option) can be affected. The acceptable range of relaxation times is from (0.999*min_relax_time) to (1.001*max_relax_time). When this option is activated, the fitting can become more complex, requiring a few more iterations, and increasing the calculation time to achieve a converged solution. By default, we do not fit the relaxation times

Select Activate fitting of relaxation times item in the Numerical Options for Fitting menu to enable the fitting of the relaxation times.

  Activate/Deactivate fitting of relaxation times

Identical parameters: When a multi-mode differential viscoelastic model is selected, it is strongly advised that all modes obey the same constitutive equation. This requirement is even enforced for some models. Despite this, a multi-mode model may involve a long series of linear and parameters, which need to be identified on the basis of a few data only. You have the option of enabling the Use identical non-linear parameters menu option, so that parameters of a given type will be assigned the same value for all modes. This may sometimes improve the fitting procedure by increasing the sensitivity of the model properties with respect to parameters.

  Use identical non-linear parameters