Homework- Lecture 14
Problem 14.1
The base of a spring mass system is subjected to the periodic displacement shown in Figure 4.32
in Rao.
a) Determine the steady state response of the mass assuming m = 0.5 kg, k = 8000 N/m, ζ =
0.06, Y = 5 mm and τ = 0.4 s.
b) How many terms do you need to keep in your Fourier Series?
c) Solve this problem using Simulink and compare your solutions. Assume zero initial
conditions so if you’d like to use a transfer function block (it is located in the
“continuous” block set – all you have to do is input the numerator and denominator
polynomials) that would be fine. Be sure to include a snapshot of your Simulink model
and a plot of your output. It should looks something like the figure below.
Problem 14.2
A standard second order system (m = 0.25 kg, k = 1000 N/m, c = 0.3 N-s/m) is forced with a
periodic force as shown below (only the portion of the force for t>0 is shown and the equations
are only valid for the cycle between 0<t<6). The force is zero between 1.5 and 4.5 s.
Determine
a) the Fourier series for the input force (write down the first 3 non-zero terms below)
b) the steady state response of the system (write down the first 3 non-zero terms below).
c) about how many terms do you need in your steady state solution to have a good
approximation? (Run your simulation for various numbers of terms to answer this question –
make sure you are past resonance.)
For both these problems clearly show what you need to put in your Maple worksheets and
include a printout of your Maple worksheet.
t−5.1100
6
1.5
4.5
3
5.4100 −t
Time (s)
Force (N)