A single degree of freedom system is represented as a \(2 \mathrm{~kg}\) mass attached to a spring possessing a stiffness of \(4 \mathrm{~N} / \mathrm{m}\) and a viscous damper whose coefficient is \(2 \mathrm{~N}-\mathrm{sec} / \mathrm{m}\). (a) Determine the response of the horizontally configured system if the mass is displaced 1 meter to the right and released from rest. Plot and label the response history of the system. (b) Determine the response and plot its history if the damping coefficient is \(8 \mathrm{~N}-\mathrm{sec} / \mathrm{m}\).

Short Answer

Expert verified
Question: Calculate and compare the response of a single degree of freedom system with an initial displacement of 1 m, mass of 2 kg, and spring stiffness of 4 N/m when subjected to (a) a viscous damper coefficient of 2 N·s/m and (b) a viscous damper coefficient of 8 N·s/m. Briefly describe the differences in the response histories. Answer: For case (a) with a viscous damper coefficient of 2 N·s/m, the system is underdamped, and its response is given by the equation: $$x(t) = e^{-\frac{\sqrt{2}}{4}t}( \cos\left(\frac{\sqrt{15}}{2}t\right) + \frac{\sqrt{2}}{\sqrt{15}}\sin\left(\frac{\sqrt{15}}{2} t\right))$$ For case (b) with a viscous damper coefficient of 8 N·s/m, the system is critically damped, and its response is given by the equation: $$x(t) = (1 + \sqrt{2}t)e^{-\sqrt{2}t}$$ The underdamped system (case a) exhibits oscillatory behavior, with the amplitude of oscillations decaying over time due to damping, whereas the critically damped system (case b) returns to the equilibrium position as quickly as possible without any oscillations.

Step by step solution

01

Obtain the governing equation of motion

The governing equation of motion of the system can be represented by the following differential equation: $$m \ddot{x} + c \dot{x} + kx = 0$$ where m is the mass, c is the viscous damping coefficient, k is the spring stiffness, and x is the displacement of the mass. In our case, we have: - m = 2 kg - k = 4 N/m - Case (a): c = 2 N·s/m - Case (b): c = 8 N·s/m
02

Analyze the type of damping

To determine the type of damping, we need to calculate the damping ratio \(\zeta\). The damping ratio is given by: $$\zeta = \frac{c}{2\sqrt{mk}}$$ For case (a), the damping ratio is: $$\zeta_a = \frac{2}{2\sqrt{2\cdot4}} = \frac{1}{4}$$ For case (b), the damping ratio is: $$\zeta_b = \frac{8}{2\sqrt{2\cdot4}} = 1$$ Since \(\zeta_a < 1\) for case (a), we have an underdamped system. For case (b), \(\zeta_b = 1\), which indicates a critically damped system.
03

Calculate the natural frequency and damped frequency

The natural frequency \(\omega_n\) is given by: $$\omega_n = \sqrt{\frac{k}{m}}$$ So, \(\omega_n = \sqrt{\frac{4}{2}} = \sqrt{2} ~\mathrm{rad/s}\) For the underdamped case (a), we need to calculate the damped frequency \(\omega_d\). The damped frequency is given by: $$\omega_d = \omega_n\sqrt{1-\zeta^2}$$ $$\omega_d = \sqrt{2}\sqrt{1-\left(\frac{1}{4}\right)^2} = \frac{\sqrt{15}}{2} ~\mathrm{rad/s}$$
04

Find the response of the system

For the underdamped case (a), the response is given by: $$x(t) = e^{-\zeta \omega_n t}(A\cos(\omega_d t) + B\sin(\omega_d t))$$ We also have the initial conditions: - Initial displacement: \(x(0) = 1 ~\mathrm{m}\) - Initial velocity: \(\dot{x}(0) = 0 ~\mathrm{m/s}\) Applying the initial conditions, we get: $$A = 1$$ and $$B = \frac{\omega_n \zeta}{\omega_d}$$ The response of the system for case (a) is: $$x(t) = e^{-\frac{\sqrt{2}}{4}t}( \cos\left(\frac{\sqrt{15}}{2}t\right) + \frac{\sqrt{2}}{\sqrt{15}}\sin\left(\frac{\sqrt{15}}{2} t\right))$$ For the critically damped case (b), the response is given by: $$x(t) = (A + Bt)e^{-\omega_n t}$$ Applying the initial conditions as before, we get: $$A = 1$$ and $$B = \omega_n$$ The response of the system for case (b) is: $$x(t) = (1 + \sqrt{2}t)e^{-\sqrt{2}t}$$
05

Plot the response history

To plot the response history, generate time values (e.g., from 0 to 10 seconds with 0.1-second increments) and calculate corresponding displacement values using the response equations we found for each case: - Case (a): \(x(t) = e^{-\frac{\sqrt{2}}{4}t}( \cos\left(\frac{\sqrt{15}}{2}t\right) + \frac{\sqrt{2}}{\sqrt{15}}\sin\left(\frac{\sqrt{15}}{2} t\right))\) - Case (b): \(x(t) = (1 + \sqrt{2}t)e^{-\sqrt{2}t}\) Then, plot the displacement against time for both cases and label the response histories accordingly.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

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 \(12 \mathrm{~kg}\) spool that is \(1 \mathrm{~m}\) in radius is pinned to a viscoelastic rod of negligible mass with effective properties \(k=10 \mathrm{~N} / \mathrm{m}\) and \(c=8 \mathrm{~N}-\mathrm{sec} / \mathrm{m}\). The end of the rod is attached to a rigid support as shown. Determine the natural frequency of the system if the spool rolls without slipping.

A \(30 \mathrm{~cm}\) aluminum rod possessing a circular cross section of \(1.25 \mathrm{~cm}\) radius is inserted into a testing machine where it is fixed at one end and attached to a load cell at the other end. At some point during a torsion test the clamp at the load cell slips, releasing that end of the rod. If the \(20 \mathrm{~kg}\) clamp remains attached to the end of the rod, determine the frequency of the oscillations of the rod-clamp system. The radius of gyration of the clamp is \(5 \mathrm{~cm}\). Fig. P2.7 Fig. P2.7

The timing device shown consists of a movable cylinder of known mass \(m\) that is attached to a rod of negligible mass supported by a torsional spring at its base. If the stiffness of the spring is \(k_{T}\), where \(k_{T} / m g L>1\), determine the period of small angle motion of the device as a function of the attachment length, \(L\), if the spring is untorqued when \(\theta=0\).

A railroad car of mass \(m\) is attached to a stop in a railroad yard. The stop consists of four identical metal rods of length \(L\), radius \(R\) and elastic modulus \(E\) that are arranged symmetrically and are fixed to a rigid wall at one end and welded to a rigid plate at the other. The plate is hooked to the stationary railroad car as shown. In a docking maneuver, a second car of mass \(m\) approaches the first at speed \(v_{1}\). If the second car locks onto the first upon contact, determine the response of the two car system after docking.

See all solutions

Recommended explanations on Physics Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free