Foorier transformation question

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The discussion focuses on solving the differential equation \(\ddot{v_c}+2\dot{v_c}+2v_c=v_s(t)\) with initial conditions \(\dot{v_c(0)}=2\) and \(v_c(0)=0\). The user seeks to determine if the response for \(v_s(t)=u(t)+\cos(t)\) can be expressed as the sum of the responses \(v_c^u\) and \(v_c^{cos}\). The solution involves transforming the equation into the s-domain using Laplace Transform techniques, leading to the expression \(V_c(s)=\frac{s}{(s^2+2s+2)(s^2+1)}-\frac{2}{s^2+2s+2}\). The user encounters difficulty in simplifying the fractions for further analysis.

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  • Familiarity with Fourier Transforms as a special case of Laplace Transforms.
  • Knowledge of partial fraction decomposition techniques.
  • Basic concepts of control systems and response analysis.
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This discussion is beneficial for engineering students, control systems analysts, and anyone involved in signal processing or differential equations, particularly those working with Laplace and Fourier Transforms.

electron2
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this is the last part of a bigger question
if you i forgot to mention some data please tell

in the last part i got
[itex]\ddot{v_c}+2\dot{v_c}+2v_c=v_s(t)[/itex]
[itex]\dot{v_c(0)}=2[/itex]
[itex]v_c(0)=0[/itex]

i need to find out if the response for [itex]v_s(t)=u(t)+cos(t)[/itex]
equals the sum of [itex]v_c^u[/itex](the response for spet function) and [itex]v_c^cos[/itex] the response for cosine
i start by finding the response for cos(t)
[itex]v_c(t)->V_c(s)[/itex]
[itex]\dot{v_c}->sV_c(s)-v_c(0)[/itex]
[itex]\ddot{v_c}->s(sV_c(s)-v_c(0))-\dot{v_c(0)}[/itex]
[itex]s(sV_c(s)-v_c(0))-\dot{v_c(0)}+2sV_c(s)-v_c(0)+2V_c(s)=\frac{s}{s^2+1}[/itex]
[itex] V_c(s)[s^2+2s+2]+2=\frac{s}{s^2+1}[/itex]
so i get
[itex] V_c(s)=\frac{s}{(s^2+2s+2)(s^2+1)}-\frac{2}{s^2+2s+2}[/itex]
where [itex]\dot{v_c}=j\omega v_c[/itex]

so now i need to break the fractures into a simpler ones
but here its all complex and i don't know how to get
a simpler fractures and there foorier transformation
??

so this is where i got stuck
and i even didnt get closer to the main solution of the problem

??
 
Last edited:
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First of all, unless you put in [itex]s = j\omega[/itex], the s-domain transformation is known as a Laplace Transform. The Fourier Transform is a special case of the Laplace Transform with [itex]s = j\omega[/itex].

As for your query, do you know how to express the right hand side in terms of a partial fraction expansion, in terms of functions of s whose inverse Laplace transform (time domain function) is known to you?
 

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