Panel mode

[par1]

I am little bit new to air intake system design so have some questions,

The Panel mode frequency should not match the engine firing frequency to avoid any resonance condition.

I have customer requirement for panel mode is min 240 Hz . Now, air intake surface function is also to make sure to minimize the radiating noise to outside from the air cleaner.

(1) Panel is the most flat surface of the system & has max
possible vibration? (the face through max possible
noise radiation)

(2) The interpretation that any radiating noise after 250
hz is OK from the system?

(3) The other surface on the air cleaner may vibrate below
250 Hz so don’t that significant for noise
radiation/match with engine firing frequency or we
need to consider only panel?

 

[Rob45]

It's just a bit difficult to interpret your questions, but I'll give it a try:
First, I think the customer's requirement that the first panel mode exceed 240 Hz (or is it 250?) means that any surface of the aircleaner or ducting must meet this requirement, to avoid these surfaces becoming radiators of induction noise. This requirement would apply to all surfaces, not just flat surfaces.
2) Above that frequency (240 Hz), it is assumed the noise radiated would not be a major concern. for example, if this aircleaner system is for a four-cylinder engine, the 240 Hz requirement means it won't be excited by engine first firing order below 7200 rpm.
3) Regarding this point, I think the safe way to interpret the customer requirement is that "panel" refers to all surfaces of the aircleaner assembly, not merely to flat panels. And to stiffen all surfaces accordingly.
Alternatively, of course, you could possibly use a viscous damping material on surfaces that you could not not sufficiently stiffen.

Does this help?
Regards,
- R

 

[par1]

First let me clarify that min panel mode requirement is 250 Hz & may be questions are difficult to understand as I have lack of understanding

(1) The reason to tell you the flat surface as panel because:

As per my understanding the panel mode & inertance analysis is the same thing & can be calculated using impulse hammer & FFT. (just different customer uses different terminology)

I have inertance test result in front of me & have taken one point on each face for inertance analysis & the requirement was less than 0 to 38 dB.

Is it correct that the selected point has max possibility to transfer induction noise on that face, But how to select that point? (Theoratical analysis?)

(2) Why engine order is 0.5, 1 , 1.5, 2, 2.5 but not in between & if yes than there would at some engine frequency would be 250 Hz & will excite with panel mode? If possible, clarify.

 

[GregLocock]

1) use intensity or SEA or cladding to establish which surfaces are important. Or analysis. Good luck. One way might be to put a loudspeaker on the intake playing white noise and measure the radiated noise and find which frequency comes from which panel.

2) the fundamental process in a 4 stroke is combustion, once every two revolutions. Therefore all (well, most) excitation is at an integer multiple of that frequency, which is half crankshaft speed.



Cheers

Greg Locock

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