Question 1
Paper 2Medium9 marksA panel in a vibrating screen is driven by a motor. Large oscillations help the screen separate particles, but excessive vibration can loosen joints in the supporting machine. The panel has a natural frequency of
The following amplitudes were measured after the oscillations had reached a steady state. Treat the driving frequency at which the greatest amplitude is recorded as the resonant frequency for these measurements.
| Driving frequency / Hz | Amplitude with weak damping / mm | Amplitude with strong damping / mm |
|---|---|---|
| 2.0 | 2 | 3 |
| 2.5 | 3 | 5 |
| 3.0 | 6 | 8 |
| 3.5 | 10 | 7 |
| 4.0 | 9 | 5 |
| 4.5 | 5 | 3 |
| 5.0 | 2 | 2 |
State what is meant by the natural frequency of the panel.
For each damping condition, determine the driving frequency at which the greatest amplitude was recorded.
Using the data, compare the effects of increasing the damping on the greatest amplitude and on the frequency at which it occurs.
The screen is driven at Select the damping condition that would produce more effective particle separation, and explain why the panel has a large response at this driving frequency.
Explain why engineers might nevertheless choose strong damping, even if this reduces the screen’s effectiveness.