Page 1 of 3 123 LastLast
Results 1 to 8 of 20

Thread: NoiseCam goes 3D

  1. #1
    Forum God > 400 posts Club Member
    Join Date
    Mar 2009
    Posts
    978

    Default NoiseCam goes 3D

    We've now been using the NoiseCam system for 3 years to identify noise sources on individual hovercraft and several craft are now quieter as a result of targetted remedial action. The existing system gives a 2D picture of where loud noise sources are as a series of red spots on a cross sectional graphic of the craft. Sometimes though 2D doesn't tell the full story - yes that noise comes from the silencer but where along it? - the outlet at the back or that leaking joint at the front?

    To answer that and improve picture quality I've been developing a 3D upgrade with now 24 microphones and new software. Here are some of the first test 3D noisepics. Each noisepic shows the noise in 3 pics, the first from the right hand side of the craft, then a plan view, then the familiar head on view we got from the 2D system.

    This is a noisepic of a car air horn, producing an 833hz tone, placed on top of the engine on my F35. I've shown a graphic of the horn so you can see that the noise is pretty accurately located. Ideally the spot would be round. As you can see its elongated particularly vertically. Thats due to astigmatism problems on the current microphone array, I've got to do some more work on that.
    air horn test.jpg

    This is a noisepic of the noise at 312hz produced by turbulent air hitting the fan. The turbulence was deliberately created by a 150mm square plate in front of the fan. (actually gaffer tape across 9 squares of the fan guard) As you can see there are two sources, one emitting from the front of the duct and other where the turbulent plume emerges from the rear of the fan. The 2 sources are about 180degrees out of phase (one blows when the other sucks!) confirming its a dipole source. The source is very directional - its much louder to the front of the craft than at the sides.
    plate test 1.jpg

    This is a noisepic of the same 312hz but I've used some new software features to more accurately locate the louder of the two sources - the front one.
    plate test 2.jpg

    Keith Oakley

  2. #2
    Forum God > 400 posts
    Join Date
    Mar 2009
    Posts
    485

    Default Re: NoiseCam goes 3D

    I never cease to be impressed by this system! If this had been commercially available it would have helped me with a serious issue at work over Christmas - knowing where the noise came from would have been very helpful.

    In the end, I used a "scanning laser vibrometer" - a device that measures the oscillation of the surface in a line-of-sight and superimposes the motion over a photograph of the specimen - great for locating mechanical resonances in silencers, etc. But at 1200 per day, a little pricey!

    Ian
    Ian Brooks
    Gloucester, UK
    http://www.hoverclub.org.uk

  3. #3
    Extremely active > 250 posts!
    Join Date
    Mar 2009
    Posts
    259

    Default Re: NoiseCam goes 3D

    Quote Originally Posted by Ian Brooks View Post
    I never cease to be impressed by this system! If this had been commercially available it would have helped me with a serious issue at work over Christmas - knowing where the noise came from would have been very helpful.

    In the end, I used a "scanning laser vibrometer" - a device that measures the oscillation of the surface in a line-of-sight and superimposes the motion over a photograph of the specimen - great for locating mechanical resonances in silencers, etc. But at 1200 per day, a little pricey!

    Ian
    Borrow a 3 year old kid.
    They can hear and detect a packet of crisps being opened from 300 metres

    Kip

  4. #4
    Forum God > 400 posts Club Member
    Join Date
    Mar 2009
    Posts
    534

    Default Re: NoiseCam goes 3D

    Very impressive Keith, well done indeed!

    Out of interest, could this system be used on the cruising craft at some stage?

    I would love to make mine quieter and would be very interested in a starting point.

    Keep up the good work, even if I do not understand a word you say :-))))))

    Brian.

  5. #5
    Extremely active > 250 posts! Club Member
    Join Date
    Mar 2009
    Posts
    337

    Default Re: NoiseCam goes 3D

    excellent work kieth, you really must put this work forward for a Masters by research, having said that it's uniqueness could easily qualify for Phd

    others should see and learn from your findings

  6. #6
    Forum God > 400 posts
    Join Date
    Mar 2009
    Posts
    662

    Default Re: NoiseCam goes 3D

    Would love too see how the Sevs do.
    In the beginning there was the Cube; I know where is came from and it has the power to create Hover life. But with great power comes great Fun.

  7. #7
    Forum God > 400 posts Club Member
    Join Date
    Mar 2009
    Posts
    978

    Default Re: NoiseCam goes 3D

    The Sevtecs are just as prone to obstructions in front of the prop/fan as any other design. I think John R gained a couple of dba off by moving 2 jockey pulleys further away from the prop.

    I've tested over 130 craft so far, cruising craft as well as racing - for example if Brian's Osprey5 is similar to others I've tested then the splitter is a major source of noise.

    This is part of a paper I presented to a recent international scientific conference on this 'seeing noise' technology in Germany. Most of the other papers came from Profs & Phd folk from Europe and N America. Sadly mine was the only one from the UK. To some extent we can achieve more than the professionals. For example when I discovered the silencer is a major problem on F3 TZRs, and Ricky Goosey came up with a silencer that knocks 12dba off, without hurting performance, it was reasonably easy to get that fitted to the whole F3 fleet. Conversely if a major EU funded R&D programme finds noise from Airbus wing flaps for example, its a big exercise to get maybe 2dba off. It probably doesn't even start until a new aircraft is being designed.

    I'll post some more pics over the next few days on the Builders Corner Forum with generic recommendations for members as to how to minimise noise.

    Keith Oakley

  8. #8
    Very active > 100 posts Club Member
    Join Date
    Mar 2009
    Posts
    144

    Default Re: NoiseCam goes 3D

    Good work Keith,

    I want to reduce the noise signature of the next Sev build as much as possible. I am interested if a change from 25mm square tube to 25mm round tube on engine framing makes much difference, factoring in the distance from the prop or fan?

    Steve

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •