Ask for electromagnetic induction modelling

Hi all, I'm new in this forum.
I'm doing on a project of electromagnetic generator, I have a magnet bar with 10 cm length (composes of 3 blocks of sub-magnet with 2.5 cm each along its length). It moves inside a tube with 30 cm length and wrapped with coil central outside the tube (coil wrapped region from the length of 10 cm to 20 cm of the tube). The tube is lifted at its tips to make the magnet moving and inducing electric through the coil. The following is information of the components.

1. Wrap coil 120 turns for a layer, there are 6 layers, the total is 720 turns.
2. The outside magnetic flux density (B) along it length by Gauss meter measurement is about 1 Tesla.
3. The measurement of the coil resistance (R) and inductance (L) is 5 ohm and 6.3 mH respectively.

I would like to do an electrical model of the generator system (EMF voltage source + impedance). Can anyone guide me about this?Electromagnetic generator system.pdf
How to calculate the EMF voltage, especially, dB/dt (the magnetic flux changing rate)?

I attached the generator output waveform and additional information for your analysis.

Thank you.
Bundit B.