WOLFRAM SYSTEM MODELER
This information is part of the Modelica Standard Library maintained by the Modelica Association.
The function is used for continuous fading of variable inputs within a defined range. It allows a differentiable and smooth transition between function outputs, e.g., laminar and turbulent pressure drop or correlations for certain ranges.
The tanh-function is used, since it provides an existing derivative and the derivative is zero at the borders [nofunc, func] of the interpolation domain (smooth derivative for transitions).
In order to work correctly, the internal interpolation range in terms of the external arbitrary input x needs to be scaled such that:
f(func) = 0.5 π f(nofunc) = -0.5 π
In the picture below the input x is increased from 0 to 1. The range of interpolation is defined by:
Description: input value for that result = 100%
Description: input value for that result = 0%
Description: input variable for continuous interpolation
Description: output value