Hi Jung-Woo,
I understand that you would like to use the simulation time to change the cross-sectional area of a Reluctance block in your model.
Please note that it is not possible to change the parameters of a Simscape block during simulation (see https://www.mathworks.com/help/physmod/simscape/run-time-parameters.html for more information). However, as a workaround, you can use a Variable Reluctance block with a carefully constructed input signal.
The Variable Reluctance block takes a physical signal as input, which it uses as the thickness of the section or air gap in its calculations. However, using the equations given in the block parameters, you can solve for the needed input value as a function of the cross-sectional area, and set the block parameter for the cross-sectional area to a dummy value of 1.
Once you have solved the system, you can use Clock and Gain blocks to obtain a signal that contains your desired input as a function of the cross-sectional area, then connect this signal to a Variable Reference block using a Simulink-PS Converter.
