Consider the problem of hitting a specified target value. For a cannon ball that is fired at a target, the equation of flight is given by
y = ((F/m)2 sin 2a)/g
where F is the thrust, m is the mass of the cannon ball, a is the angle of projection and g is acceleration due to gravity.
If the target distance y is 150 metres, the mass of the cannon ball is 0.2 kg, g is 9.81 m s -2 what is the best value of thrust (F) and angle of projection (a)?
Most engineers are quick to assign a value of F (say 10 N) and then calculate the angle a = 0.5 sin -1 [y g (m / F) 2 ]. Is this the best answer?
Certainly not. In reality, F, m and a will all have some variability. The objective is to find those values of F and a (assuming for simplicity that m can be accurately determined) that will consistently hit the target despite variations in F
or a.
How do we do it?
Our strategy is as follows:
Instead of merely calculated F and a, an engineer can include variability into the equation and calculate F and a that are robust to not only variations in F and a but also air resistance, wind directions, etc. The results of the conventional design and parameter design are shown
above. |