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A single degree of freedom system is represented as a \(4 \mathrm{~kg}\) mass attached to a spring possessing a stiffness of \(6 \mathrm{~N} / \mathrm{m}\) and a viscous damper whose coefficient is \(1 \mathrm{~N}-\mathrm{sec} / \mathrm{m}\). (a) Determine the response of the horizontally configured system if the mass is displaced 2 meters to the right and released with a velocity of 4 \(\mathrm{m} / \mathrm{sec}\). Plot and label the response history of the system. (b) Determine the response and plot its history if the damping coefficient is \(5 \mathrm{~N}-\mathrm{sec} / \mathrm{m}\). (c) Determine the response and plot its history if the damping coefficient is \(10 \mathrm{~N}-\mathrm{sec} / \mathrm{m}\).

Short Answer

Expert verified
Answer: The response function of a single degree of freedom system depends on the damping ratio (ζ). For different values of ζ, the response function can be divided into three scenarios: 1. Underdamped (\(\zeta < 1\)): \(x(t)=e^{-\zeta\omega_nt}\left[x_0\cos(\omega_d t)+\left(\frac{v_0+\zeta\omega_nx_0}{\omega_d}\right)\sin(\omega_d t)\right]\), where \(\omega_d=\omega_n\sqrt{1-\zeta^2}\). 2. Critically damped (\(\zeta = 1\)): \(x(t)=e^{-\omega_nt}\left[x_0+(v_0+\omega_n x_0)t\right]\) 3. Overdamped (\(\zeta > 1\)): \(x(t)=e^{-\zeta\omega_nt}\left[C_1e^{\omega_n\sqrt{\zeta^2-1}t}+C_2 e^{-\omega_n \sqrt{\zeta^2-1}t}\right]\), where \(C_1\) and \(C_2\) are coefficients determined from the initial conditions.

Step by step solution

01

Setup the equation of motion

For a single degree of freedom system with mass (\(m\)), spring stiffness (\(k\)) and damping coefficient (\(c\)), the equation of motion can be written as: \(m \ddot{x} + c \dot{x} + k x = 0\) We are given that \(m = 4\text{ kg}\), \(k = 6\text{ N/m}\), and the initial displacement \(x_0 = 2\text{ m}\) and velocity \(v_0 = 4\text{ m/s}\).
02

Determine the natural frequency and damping ratio

Compute the natural frequency (\(\omega_n\)) and damping ratio (\(\zeta\)) for the given system. They are calculated as follows: \(\omega_n = \sqrt{\frac{k}{m}}\) \(\zeta = \frac{c}{2 m \omega_n}\)
03

Solve the equation of motion for different damping coefficients

For each damping coefficient, we can now solve the equation of motion to compute the response of the system. Since we have 3 different damping coefficients: \(1\text{ Ns/m}\), \(5\text{ Ns/m}\), \(10\text{ Ns/m}\), we need to compute the response for each case.
04

Determine the response function

Depending on the value of the damping ratio \(\zeta\), the response function \(x(t)\) will have different forms: 1. For \(\zeta < 1\), the system is underdamped, and the response function is: \(x(t)=e^{-\zeta\omega_nt}\left[x_0\cos(\omega_d t)+\left(\frac{v_0+\zeta\omega_nx_0}{\omega_d}\right)\sin(\omega_d t)\right]\) where \(\omega_d=\omega_n\sqrt{1-\zeta^2}\) is the damped natural frequency. 2. For \(\zeta = 1\), the system is critically damped, and the response function is: \(x(t)=e^{-\omega_nt}\left[x_0+(v_0+\omega_n x_0)t\right]\) 3. For \(\zeta > 1\), the system is overdamped, and the response function is: \(x(t)=e^{-\zeta\omega_nt}\left[C_1e^{\omega_n\sqrt{\zeta^2-1}t}+C_2 e^{-\omega_n \sqrt{\zeta^2-1}t}\right]\) where \(C_1\) and \(C_2\) are coefficients determined from the initial conditions.
05

Calculate the response and plot the history

For each damping coefficient, compute the response function using the appropriate formula from Step 4. Then, plot the response history for each case (a), (b), and (c). For (a) \(c=1\text{ Ns/m}\), compute the response and plot the history using the appropriate formula. For (b) \(c=5\text{ Ns/m}\), compute the response and plot the history using the appropriate formula. For (c) \(c=10\text{ Ns/m}\), compute the response and plot the history using the appropriate formula.

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Most popular questions from this chapter

The cranking device shown consists of a mass-spring system of stiffness \(k\) and mass \(m\) that is pin-connected to a massless rod which, in turn, is pin- connected to a wheel at radius \(R\), as indicated. If the mass moment of inertia of the wheel about an axis through the hub is \(I_{O}\), determine the natural frequency of the system. (The spring is unstretched when connecting pin is directly over hub ' \(O\) '.)

A single degree of freedom system is represented as a \(4 \mathrm{~kg}\) mass attached to a spring possessing a stiffness of \(6 \mathrm{~N} / \mathrm{m}\). If the coefficients of static and kinetic friction between the mass and the surface it moves on are \(\mu_{s}=\mu_{k}=0.1\), and the mass is displaced 2 meters to the right and released with a velocity of \(4 \mathrm{~m} / \mathrm{sec}\), determine the time after release at which the mass sticks and the corresponding displacement of the mass.

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