The moral of this story is double
check your input parameters or Hey's Law
"Garbage in - Garbage Out". In the
question, I stated that the time I guessed the air
impulse to be was 4 seconds. Not unreasonable.
However, I input 4 into the Duration of air impulse
box, forgetting that it was in milliseconds. The above
output is the result of that mistake.
The reason for the maxima is that the
air impulse is calculated in steps of 1ms and
therfore the computer model takes the integer of the
air impulse time ie 3.2 becomes 3.0 and 3.7 becomes
3.0. In fact, the variables page will not allow you
manually to use anything other than whole numbers.
The band to the right of the 1ms line
produces an error that is caused by the impulse being
less than 1ms. To the left, there are the steps for
2, 3 and 4ms, blending off into a continuum.
If I had used 4000 instead of 4, the
picture would have been completely different.