Homework for Vehicle Dynamics class.
Problem 1
Explain what we mean by "Ride" with vehicles.
Problem 2
With the help of analytical description, show how asymmetric objects can cause moment vectors that don't align with the SAE convention axes.
Problem 3
Make an FFT on acoustic data you record with your laptop while your car is running. Show how noise level relates to RPM, gears, speed.
MIC RECORDING ON MATLAB:
Start by using the following commands to record a 5 second sample straight from matlab:
recObj = audiorecorder; disp('Start speaking.')
recordblocking(recObj, 5); % you can change the second element to however long you %want to sample, here it is turning on the mic for 5 seconds. However, you will have %to change the length of the signal once you perform a fast Fourier transform by %multiplying the length of the recording by the sampling frequency of 8000Hz. disp('End of Recording.');
y = getaudiodata(recObj);
To do a fast Fourier transform (going from the time domain to the frequency domain) on your 5 second y data use the following commands:
Freq = fft(y);
Fs = 8000; % sampling frequency
T = 1/Fs; % Sampling period
L = 40000; % Length of signal t = (0:L-1)*T; % Time vector
P2 = abs(Freq/L); P1 = P2(1:L/2+1);
P1(2:end-1) = 2*P1(2:end-1); f = Fs*(0:(L/2))/L;
plot(f,P1) title('Engine Rev Test') xlabel('f (Hz)')
ylabel('|P1(f)|')
You should obtain a plot similar to the one shown here:
What are the major frequencies?
How do these frequencies relate to human perception and what consequences do they have for the ride?
Problem 4
Implement the quarter car model in Matlab analytically. Solve the problem either numerically or analytically with Matlab. Show the natural frequencies of the system. By introducing a GUI, allow the parameters to change.
Problem 5
Describe 2-3 different types of dampers. Show illustrations, explain operation, benefits and disadvantages.
Problem 6
Find the natural frequency of the 4 different corners of your car. [Hint: by pushing it down, measuring the acceleration you can derive the displacement, from which you can reverse engineer the parameters]
Problem 7
Find the natural frequency of your spare tire or bicycle tire. [Hint: if you drop it, "free vibration" is triggered ....]
Problem 8
Test your car's suspension system. Is it underdamped, overdamped, or else? Is it time to replace them yet? Why?
Problem 9
Describe the changes in natural frequency if our spring does not have linear characteristics.
Problem 10
Create an analytical 2DOF model of the pitching and bouncing of the car. Show the motion law (x(t) and theta(t) as the solution to the Equation of motion]. [Hint: you can find derivations online to help you.]
Problem 11
Implement Problem 10 in Matlab with a GUI.
Problem 12
What sort of springs and dampers would your personal car need to get installed in order to turn it into a low rider car?
Problem 13
Experimentally determine the spring constant of your car and the damping coefficient.
Problem 14
Create a tire pressure - tire spring coefficient curve. Use your spare or bicycle tire.
Problem 15
Develop the analytical model, EOM and x(t) and theta(t) for rolling of the car. What can trigger rolling?
Problem 16
Determine the pitching natural frequency of your car. [Hint: keep braking periodically and have an observer video record the pitching of the car. Wherever it's maximum...]
Problem 17
Describe an analytical relationship between the distance of speedbumps, their geometry (length and height), the car's geometry and parameters (k,c) and how they relate to bouncing and pitching. What is causing the discomfort for humans when passing a bump?