## First Step

Due in stages
goodwine
Posts: 1596
Joined: Tue Aug 24, 2004 4:54 pm
Location: 376 Fitzpatrick
Contact:

### First Step

This will be incorporated into Homework 7, but if you want to get started, do the following.

Use the model from Section 4.4.2 in the book for a 1/4-car model. I looked up the values for a Mazda Miata:
• k=6000 kg/m (note the weird units, k = 6000*9.81 N/m)
• m = 250 kg
• b = 5370 N s/m.

Write a computer program (Matlab is fine as long as you trust the answer) to compute how the car moves up and down for different driving velocities and different road types. Once you have that, submit plots for
1. Ride height vs x
2. Suspension compression vs x (the suspension will "bottom out" at 4cm deflection)
3. The net acceleration vs x (if the acceleration is more negative than -9.81 the wheel will leave the road).
For each road type, what is the fastest you can drive (to the nearest 10 km/hr) to satisfy the second and third criteria?

Added October 24, 8:00pm If you use ode45() in Matlab, it needs a function that gives the right hand side of the differential equation. For some reason, it really, really wants that function to be a function of x and t only. But in order for us to compute y and dydt we need to send it other variables too, like wavenos, phi and sk0. The way to deal with this is with an anonymous function. If my right hand side function is called carrhs.m then use the following syntax in ode45():

Code: Select all

``[t z] = ode45(@(t,x) carrhs(t,x,sk0,wavenos,phi,v,m,b,k),[0 timetodrive1km], [icz iczdot])``
The whole part

Code: Select all

``@(t,x) carrhs(t,x,sk0,wavenos,phi,v,m,b,k)``
is the anonymous function. Without the very first part in front of carrhs it won't work.
Bill Goodwine, 376 Fitzpatrick
rlema

### Re: First Step

When presenting the plots, is it okay to present:
a) The road profile for each case
b) Height for a speed that meets criteria given and for a speed that doesn't for each case
c) Same as above but with accelerations
d) Same as above but with compression
goodwine
Posts: 1596
Joined: Tue Aug 24, 2004 4:54 pm
Location: 376 Fitzpatrick
Contact:

### Re: First Step

rlema wrote:When presenting the plots, is it okay to present:
a) The road profile for each case
b) Height for a speed that meets criteria given and for a speed that doesn't for each case
c) Same as above but with accelerations
d) Same as above but with compression
Yes, that would be ok.
Bill Goodwine, 376 Fitzpatrick
mjunker1

### Re: First Step

Do we need to attach our code for this first step in the project?
goodwine