S7.

Solution:

The problem can be solved by applying Duhamel-theorem.
$$ y(t)=f(t)h(0)+\int_{0}^{t}f(\tau )\frac{dh(t-\tau)}{d\tau}d\tau$ , or let’s apply the other formula:

$$ y(t)=f(0)h(t)+\int_{0}^{t} \frac{d f(\tau) }{d\tau} h(t-\tau)d\tau$

The latter formula will be used in order to determine the output response:
$$ y(t)=-(F_0\text{sin}\varphi)A(e^{s_1t}- e^{s_2t})+\int_{0}^{t} \frac{d F_0\text{sin}(\omega \tau+\varphi) }{d\tau} \left [ -A(e^{s_1(t-\tau)}- e^{s_2(t-\tau)}) \right ] d\tau$

$$ y(t)=-(AF_0\text{sin}\varphi)(e^{s_1t}- e^{s_2t})-\int_{0}^{t} \frac{d F_0\text{sin}(\omega \tau+\varphi) }{d\tau} A \left [ (e^{s_1(t-\tau)}- e^{s_2(t-\tau)}) \right ] d\tau$

$$ y(t)=-AF_0\text{sin}\varphi(e^{s_1t}- e^{s_2t})+\int_{0}^{t} AF_0\omega \text{cos}(\omega \tau+\varphi) \left [ (e^{s_1(t-\tau)}- e^{s_2(t-\tau)}) \right ] d\tau$

$$ y(t)=-AF_0 (e^{s_1t}- e^{s_2t}) \text{sin}\varphi + AF_0\omega \int_{0}^{t} \text{cos}(\omega \tau+\varphi) \left [ (e^{s_1(t-\tau)}- e^{s_2(t-\tau)}) \right ] d\tau$

Let’s execute the following integral $$ \int_{0}^{t} e^{s_1(t-\tau)}\text{cos}(\omega \tau+\varphi) d\tau$ .

Partial integral method will be used.
$$ u= \text{cos}(\omega \tau+\varphi) \quad {u}'=-\omega \text{sin}(\omega \tau+\varphi) \quad \quad {v}'= e^{s_1(t-\tau)} \quad v=\frac{-1}{s_1} e^{s_1(t-\tau)}$

$$ \int_{0}^{t} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau = \left [ -\frac{1}{s_1} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) \right ]_0^t-\frac{\omega}{s_1}\int_{0}^{t} e^{s_1(t-\tau)} \text{sin}(\omega \tau+\varphi) d\tau$

$$ \int_{0}^{t} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau = \frac{1}{s_1} \left [e^{s_1t} \text{cos}(\varphi)-\text{cos}(\omega t+\varphi) \right ] -\frac{\omega}{s_1}\int_{0}^{t} e^{s_1(t-\tau)} \text{sin}(\omega \tau+\varphi) d\tau$

Let’s apply again the partial integral method.
$$ u= \text{sin}(\omega \tau+\varphi) \quad u'=\omega \text{cos}(\omega \tau+\varphi) \quad \quad v'= e^{s_1(t-\tau} \quad v=\frac{-1}{s_1} e^{s_1(t-\tau)}$

$$ \frac{\omega}{s_1}\int_{0}^{t} e^{s_1(t-\tau)} \text{sin}(\omega \tau+\varphi) d\tau =\frac{\omega}{s_1} \left [ \left [-\frac{1}{s_1} e^{s_1(t-\tau)}) \text{sin}(\omega \tau+\varphi) \right ]_0^t+\frac{\omega}{s_1} \int_{0}^{t} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau \right ]$

$$ \frac{\omega}{s_1}\int_{0}^{t} e^{s_1(t-\tau)} \text{sin}(\omega \tau+\varphi) d\tau =\frac{\omega}{s_1} \left [\frac{1}{s_1} e^{s_1 t} \text{sin}(\varphi) - \frac{ \text{sin}(\omega t+\varphi) }{s_1} \right ]+\frac{\omega^2}{s_1^2}\int_{0}^{t} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau$

Now the $$ \int_{0}^{t} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau$ integral element can be expressed as follow:
$$ \int_{0}^{t} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau = \frac{1}{s_1} \left [e^{s_{1}t} \text{cos}(\varphi)-\text{cos}(\omega t+\varphi) \right ] - \frac{\omega}{s_1^2} \left [ e^{s_{1}t} \text{sin}( \varphi) - \text{sin}( \omega t + \varphi) \right ] - \frac{\omega^2}{s_1^2}\int_{0}^{t} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau$

The unknown integral element:

$$ (s_1^2+\omega^2) \int_{0}^{t} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau = \left [ -s_1\text{cos}(\omega t +\varphi)+\omega \text{sin}(\omega t + \varphi) + e^{s_1t}( s_1\text{cos}(\varphi)-\omega \text{sin}(\varphi)) \right ]$

$$ \int_{0}^{t} e^{s_1(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau = \frac{1}{ s_1^2+\omega^2}\left [ -s_1\text{cos}(\omega t +\varphi)+\omega \text{sin}(\omega t + \varphi) + e^{s_1t}( s_1\text{cos}(\varphi)-\omega \text{sin}(\varphi)) \right ]$

Completely same way can be written the other integral element:

$$ \int_{0}^{t} e^{s_2(t-\tau)} \text{cos}(\omega \tau+\varphi) d\tau = \frac{1}{ s_2^2+\omega^2}\left [ -s_2\text{cos}(\omega t +\varphi)+\omega \text{sin}(\omega t + \varphi) + e^{s_2t}( s_2\text{cos}(\varphi)-\omega \text{sin}(\varphi)) \right ]$

After substituting both integral elements, the response will be the following!
$$ y(t)=AF_0(e^{s_2t}- e^{s_1t}) \text{sin}\varphi + F_{0}A\omega \left [\frac{1}{ s_1^2+\omega^2}\left [ -s_1\text{cos}(\omega t +\varphi)+\omega \text{sin}(\omega t + \varphi) + e^{s_1t}( s_1\text{cos}(\varphi)-\omega \text{sin}(\varphi)) \right ]\right] -$

$$ - F_{0}A\omega \left [ \frac{1}{ s_2^2+\omega^2}\left [ -s_2\text{cos}(\omega t +\varphi)+\omega \text{sin}(\omega t + \varphi) + e^{s_2t}( s_2\text{cos}(\varphi)-\omega \text{sin}(\varphi)) \right ] \right]$

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