Birdstrike Analysis
Birdstrike Analysis
(OP)
I am working on birdstrike analysis on aircraft structures, using Gelatin bird. Could any one describe the method of ALE apporach to carry out the birdstrike analysis using ls-dyna.
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RE: Birdstrike Analysis
Once upon a time no "jello birds" but real ones, although already deceased, were launched into a running engine:
- multiple (small) bird ingestion requirement: 3 sparrow size per square feet of intake area, in 1 s time interval between each, an engine has to swallow and to keep on running with reduced thrust or power (if I remember correctly power reduction must not be more than 40% but don’t remember bird impact speed).
- single (large) bird ingestion requirement: 2 lb bird, bird speed = max take-off speed, engine speed = take off speed (rating); no engine particle (minced blades) should be able to pierce any engine casing, all debris must stay within engine envelope, they may leave engine only through exhaust.
So approach was rather direct and analysis was quite forensic.
RE: Birdstrike Analysis
RE: Birdstrike Analysis
http://www.ansys.com/ansys/lsdyna.htm
TTFN
RE: Birdstrike Analysis
RE: Birdstrike Analysis
conclusion: a fast chick is a real bullet
RE: Birdstrike Analysis
RE: Birdstrike Analysis
We snuff the birds out right before we shoot them.
RE: Birdstrike Analysis
STF
RE: Birdstrike Analysis
Eventually, the ASPCA stopped that, too; so we got FAA permission to use dressed chickens from the local grocery store. We did freeze them and we do suspect that one early test went badly because of insufficient thawing. But I agree that it is highly unlikely that anyone anywhere actually shot a fully frozen chicken.
The dressed chicken made a lot less of a mess, but the real secret to having a clean shot on a windshield is to turn the whole assembly upside down, so the chicken spray goes mostly down instead of up and all over everywhere. Finally, by doing the shots in a local field, we found that the local critters cleaned up almost all of it by the next day.
It is amazing what damage an 8 lb bird can do at 300 kt. High speed cameras show it becoming ssentially "hydraulic", sometimes forcing an opening between fasteners and squirting through like a water jet to cut through internal airframe pieces, which then go flying about the cockpit.
My initial thought on using a dynamic fea method is that it will take a good deal of testing to reliably calibrate the simulation for each structural arrangement.
RE: Birdstrike Analysis
"there are fast chicken and there are living chicken, but there is no living and fast chicken"
RE: Birdstrike Analysis
Both these methods were based upon test and were pretty accurate, as we sized the design based on the analysis and later did certification tests, all of which passed.
Can't remember the name/number of the 2 analyses mentioned, but maybe an internet searh will reveal.
RE: Birdstrike Analysis
you wrote:
'I am working on birdstrike analysis on aircraft structures, using Gelatin bird. Could any one describe the method of ALE apporach to carry out the birdstrike analysis using ls-dyna.'
ALE Approach:
I am also not familiar with this terminology. I am familiar with the use of 'Eulerian' and 'Lagrangian' computer techniques for conducting birdstrike analyses. My experience lies with DYTRAN(MSC software). The exercises of performing these analyses have been extremely interesting, however the value added to the development of typical aircraft structure (leading edges, transparencies, radomes, etc)is questionable and depends upon the nature and scope of your project.
Our typical design process involves the use of proprietary software which is based in part on the RAE paper mentioned by Graham and which is supplemented by internal 'curved and flat panel' test data. The energy dissipation curves extracted from this method are applied to a non-linear finite element model typically is used for internal load development.
We have certified structure by analysis alone(supported by historical data and by new product testing alone (last full-scale test conducted in Aug of 2001). While several DYTRAN models have been developed internally: As yet we have not made use of this technique for purpose of certification.
The RAE referenced above is:
"The design of leading-edge and intake wall structure to resist impact." Royal Aircraft Establishment, Technical Report 72056, Farnborough, Hants, March 3, 1972.
A good reference for your question about the gelatin bird would be:
"Validation of a bird susbstitute for development and qualification of aircraft transparencies.", Chalita, A., Flight Dynamics Laboratory, Write-Patterson Air Force Base, Ohio, AFFDL-TR-77-60, Oct. 1980.
RE: Birdstrike Analysis
http://wildlife.pr.erau.edu/Pictures3.ht...
Hawk?
http://www.americanaeroservices.com/imag...
Pigeon
http://www.americanaeroservices.com/imag...
RE: Birdstrike Analysis
RE: Birdstrike Analysis
You will get in the ball park, occasionally, but will never calculate the precise outcome. After development testing and incorporation of the results into the vehicle design, a physical test is required to validate your method and prove that you met the specs.
By the way, summer is a bad time of year to conduct this work. Hosing the inside of the bunker down barely improves the smell.
The birds are dead for a long time; frozen and then thawed before the shot. Adjust the weight by clipping off parts or injecting water.
If you're working on a thesis, then never mind; no one in industry cares about your results.