# Help with non-linear block spring mass system

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Cristian Rohozneanu on 1 Feb 2024
Answered: Fangjun Jiang on 1 Feb 2024
How can I add a block for the nonlinear term so that I can simulate the system?
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Fangjun Jiang on 1 Feb 2024
The nonlinear part is the k() function. It is simple enough to construct it using blocks.
The block diagram is far from the correct implementation. Use two integrators to construct q1, two integrators for q2, two integrators for q3. And then construct the rest.
Cristian Rohozneanu on 1 Feb 2024
This implementation of the scheme is done without considering the nonlinear term, in the first part I didn't need it, I just need to add now and simulate the system with the nonlinear part.

Fangjun Jiang on 1 Feb 2024
1. Use two integrators connected in series to construct q1. The output is q1, the input is "q1 two dot". In the middle, it is "q1 dot".
2. Do the same for q2 and q3
3. Then you have Delta1=q1-q2, Delta2=q2-q3
4. k(Delta1)=K0*Delta1+K1*(Delta1)^3 should be easy. You can even make it a function to apply the same for Delta2
5. Then connect the signal lines in Simulink according to the last three lines of your equations. You will have the correct Simulink implementation of your mathmatical equations.