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Changing the quality of the transient process in a nonlinear system (in Mathematica)

Mathematica Asked by dtn on December 25, 2020

I urgently need advice and help.

I have a system of differential equations like this:

$begin{cases} frac{dx}{dt} == y[t] cdot alpha cdot sin(omega t) + frac{d}{dt}(alpha cdot sin(omega t))
frac{dy}{dt} + h cdot y(t) == frac{d}{dt}(e^{-(x[t] – 2)^2}) end{cases}$

Parameters: $alpha = 0.3, h = 1, omega = 2 pi 0.5, x(0)=1/4, y(0)=0$

It corresponds to the following structural scheme:

enter image description here

The code that simulates such a system is shown below:

ClearAll["Global`*"]

pars = {[Alpha]1 = 0.3, h1 = 1, [Omega]1 = 2 Pi 0.5}

extr = Exp[-(x[t] - 2)^2]

sys = 
 NDSolve[{x'[t] == 
    hpf1[t] [Alpha]1 Sin[[Omega]1 t] + 
     D[[Alpha]1 Sin[[Omega]1 t], t], 
   y'[t] + h1 y[t] == D[extr, t], x[0] == 1/4, y[0] == 0}, 
  x, {t, 0, 500}]

The numerical solution is presented below:

Plot[{Evaluate[x[t] /. sys]}, {t, 0, 150}, PlotRange -> Full, 
 PlotPoints -> 50]

enter image description here

It can be seen that the transition process is a transition from the initial point to the final one with a certain character.

I need to change this character i.e. make the transition from one point to another exponentially.
Like this:

enter image description here

What are the ways to solve this problem?

What to do, add a regulator or manipulate the system of differential equations?

One Answer

You might try to play with the parameters using Manipulate. Like this, for example,

extr = Exp[-(x[t] - 2)^2];
ω1 = 2 Pi 0.5;

Manipulate[
 sys = NDSolve[{x'[t] == 
     y[t] α1 Sin[ω1 t] + 
      D[α1 Sin[ω1 t], t], y'[t] + h1 y[t] == D[extr, t],
     x[0] == 1/4, y[0] == 0}, x, {t, 0, 150}];
 Plot[{Evaluate[x[t] /. sys]}, {t, 0, 150}, 
  PlotRange -> All], {α1, 0, 1}, {h1, 0.5, 1.5}]

with the following effect:

enter image description here

I do not know the limits within which you can vary the parameters, but you should know them. Then you can see what these parameters could do.

Have fun!

Correct answer by Alexei Boulbitch on December 25, 2020

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