Whip Antenna: Newsletter Challenge (09/19/06)

"You perform a finite element analysis of the antenna with the max wind load assumed and your analysis tells you everything looks ok"

Analysis of Max-wind-load-assumed considers Max wind speed, but omits max ground speed of vehical combined with max wind speed as a head wind.

It looks like the truck was parked overnight, so ground speed should not enter into the problem! What about lightning striking nearby, inducing some magnetic force on the antenna?

"You perform a finite element analysis of the antenna with the max wind load assumed and your analysis tells you everything looks ok"

Analysis of Max-wind-load-assumed considers Max wind speed, but omits max ground speed of vehical combined with max wind speed as a head wind.

In response to this comment, doesn't it say that the truck was in the parking lot?

maybe the handbook only recorded, say, the 30-second average maximum windspeed and not the instantaneous gust speed, which would be significantly higher?

regards -paul

Wild guess (assuming the truck never moved through out the night). Thunderstorms usually have varying wind speeds and wind directions. While the gust may have a top velocity that meets the requirement, the direction tends to change and the duration is not constant.

So, the antenna tends to act like a spring and the whip may actually bend more in changing violent wind gusts if the direction of the wind suddenly changes.

Also, you may need to consider mechanical resonance frequencies with the antenna. Since it is essentially a spring grounded at one end it could vibrate at a sympethetic frequency.

I doubt it was struck with lightning. Metal whips melt and curl. Fiberglass would shatter into splinters due to the violent expansion of water molecules inside the whip when they vaporize.

However, more likely it was hit by a flying monkey during the storm. A simple check of the parking lot security camera would confirm this.

It probably hit a resonant frequency. See the Tacoma bridge narrows disaster.

The truck was parked - so no vehicle speed.

The thunderstorm was 'ordinary' and probably nowhere near the

100 year maximum wind.

N.

Alternative theory. Mischievous young boy entered lot and broke it off.

Hit by lightning or freezing rain built up enough to snap it under weight.

I like the flying monkey idea. There's a comedian does a routine about hurricanes and some dink in Florida who was going to tie himself to a tree and ride out a hurricane. The comedian's answer to that idea is: "Let me tell you about hurricanes. It's not THAT the wind is blowing, it's WHAT the wind is blowing..."

But in Real Life (a small town in South Dakota) the resonant frequency explanation is more likely. Unless the wind overturned the truck.

I had a whip antenna bend on my truck bend almost at right angles, but that had something to do with a "Clearance 6'4"." sign on the parkade.

clue-- one of the prototypes on the truck in the parking lot. there was more than one and they came in contact forcibly causng the break(fracture) ha

We are all assuming it was the aerial that snapped - or was it the aerial to mounting joint?

Why is everybody assuming the truck was not moving?

"This was one of the prototypes on the truck in the parking lot."

All the sentence says is that the truck is now in the parking lot, it does not specify that the truck was parked there when it broke. It seems possible that it broke out on the road somewhere, the truck stopped picked it up and drove back to the office with it. Then the truck was left in the parking lot for analysis.

A combination of acceleration and braking at the antennas resonant frequency, with high winds, in freezing rain, after squirrels knawed at the tasty material properties, with a flying monkey perched at the top. Seems obvious.

This is a little like the physics question "How can you determine the height of a tall building using a barometer." There are many many answers, the best being "Offer to give the building super the barometer if he tells you the height of the building."

Given that whip antennas are well-known technology, I'd hope that the FEA was not so flawed that it failed to consider that the antenna might already be moving at 75 MPH when it encounters the 100 year wind.

Then there are plenty of oportunities for goofing up on the FEA. One would hope that the engineer first got a solid approximation of the stresses involved, and considered their many possible causes.

The obvious anwer is that a 12 foot whip is too long for use on a truck: even if it were mounted at ground level it would not fit under most bridges. Perhaps there was a collision with some structure.

Next, I'd guess that the FEA was set up to look only at the constant wind load and failed to look at resonance, which would have a significant effect in the gusty conditions associated with a thunderstorm.

Or: A competing company hired a kid to break the antenna to delay the market launch.

Or: The 100 year wind is the wind speed exceeded with a 1% probablilty. In a thunderstorm, winds can exceed the 100 year value: no structure can be reasonably expected to withstand a tornado, or severe microburst.

Or: Maybe the prototype was incorrectly built, e.g., with a notch that would not be likely in production.

Maybe the FEA program itself is limited in ways the engineer did not understand, such as not incorporating effective 3d CFD code.

Did the truck have more then one prototype on it? Maybe one antenna collided with another.

The engineer should consider many things before deciding to hand in his resignation.

Obviously, the boss broke it himself and was trying to see how you would handle failure and what steps you might take to correct the "problem".

OK, most of the good answers were already given, so I had to come up with something original, now didn't I? Flying monkees, indeed! (grin)

Sherlock Holmes said, "When you eliminate the impossible, whatever you have left, no matter how improbable, must be the truth."

If we assume, as some others did, that either the truck was not moving, or that ground speed as a head wind was included in the FEA, and there were no monkees or boys doing mischief, and the 100-year max. wind speed was indeed the true instantaneous maximum wind speed, and your boss is not a sadistic jerk (well, at least that he did not snap the antenna), then the improbable must have happened, i.e. there was a gust of wind that exceeded the 100-year maximum. Either that, or you made a big mistake! Better go back and recheck your calculations.

Not too many years ago here in the St. Louis area we had river levels that caused severe flooding. In one area there was a levee built to withstand the highest "100-year flood". Well, the waters DID top the levee, it broke, flooding the Chesterfield valley area and all homes and business in up to 6 feet or so of muddy Missouri River water. After the flooding ended the levee was rebuilt, however now we have a "500-year flood" levee, much higher than the original and business have not only rebuilt, but many new projects, including a gigantic shopping/entertainment center, have been constructed in the Chesterfield valley area.

Do you think it will ever be topped? Well, probability says it could happen only once in 500 years, so we are likely to be safe for a few hundred years or so, but you never know. After all, it is only a probability!

"...the boss broke it himself and was trying to see how you would handle failure..."

That's good! ;-)

Rime ice developed on the antenna thereby increasing its diameter and wind profile, increasing the leverage effects of an "average wind. That or a monkey.

Even if rim ice did develop on the antenna, freezing conditions would cause the most ice to build up at the point of greatest torque, the base of the antenna. Ice is fairly strong in compression, and with higher strength reinforcing the base more so and lesser higher up (due to gravity effects causing the freezing water to flow toward the base primarily, creating an inverted icicle) it is unlikely that icing alone would cause the breakage. Also, the ice would dampen out any resonance effects.

First who said that the truck didn't move? second, I guess that the given length of the whip,(12') is given on purpose. Truck height, say is 12' plus the whip another 12' way over the max permitted height on any highway for example. Obviously wind is not the problem. surface area = wind resistance would be so small that under normal construction practice, 100-year max wind plus a 70mph max truck speed will not present any engineering challenge. Or did the truck drive to the Aleutian Islands that night ?

Wangito

The original question said that this was ONE of the prototypes being tested. It did NOT say whether the prototypes were identical nor how many there were. Good engineering practice would not base a decision on one solitary test result. For whatever reason, including my explanation above or any of the others given here, this could have been a statistical anomoly, or "flyer" as it is often called, or a "fluke" as some people would call it. If your investigation finds no other problems, further testing may be necessary to determine if this was an anomoly or there is some real probablility of failure. Further testing may also lead to discovery of the failure mode or modes and underlying causes.

Real engineering is still completed in the real world, with real world testing, not on paper, not in a computer model, not even in a laboratory.

"Real engineering is still completed in the real world, with real world testing, not on paper, not in a computer model, not even in a laboratory."

Tell that one to Boeing next time you're in a 7xx.

The story mentions being well below the stress due to bending, but what about repeated bending fatigue due to whipping, or is that part of the FEA?

It's hard to model the effect of vortices whipping off the antenna.

Probably Vandalism. Rotton Buggers!

I'm going to have to go with the flying monkeys, even though the low bridge/high antenna is more probable!

I'll put my vote in for fatigue failure

Rotten buggers? Are you sure its not them critters from the movie "TREMORS" at work?

Perhaps the guy that designed the antenna should get a job working on Boston's Big Dig. He'd fit right in there, in fact he'd probably get a promotion. Given that the project was originally scheduled to be finished, he should be able to get a good 10 years of work in.

Force equals mass times acceleration.

What went wrong is that you forgot to consider the additional force produced by the extra mass of the water (rain) when accelaerated by the wind.

I forgot to take into account harmonic effects as the antenna oscillation combined positively with wind velocity to cause the amplitude and velocity of antenna flex to exceed the maximums indicated by my analysis. As this over flexing continued for a time the metal was heated and softened (just as in breaking a wire by repeated flexing) until it eventually failed and broke. I also forgot the lessons already learned when I sometimes see power/telephone lines begin to oscillate wildly (in even moderate speed wind--even "singing" as they fail wildly, held fast between two poles) due to harmonic reinforcement; or lessons from reading about and seeing films of galloping gertie when I visited there and saw the replacement bridge.

This one's on the right track.

I meant to say constructive resonance reinforcement. It was one of those days where the exact word just refuses to light up in the brain.

Those of us in South Texas know that the problem was directly related to that thunderstorm and it has nothing to do with wind velocity. It doesn't take much hail to shatter that antenna if several strike in quick succession. Watch what it can do to fiberglass greenhouse panels.

Come on now. What is the probability of several successive hail strikes on a mobile antenna; and of poorly compacted ice shattering the thin-edged metal without itself being shattered first? --even in Texas where all things are probable? --and even south Tex. where huffing/puffin is a far greater hazard than storms to any antenna? If you had said a twister blew a cow into the antenna I might bite...but it's south Texas. Not so many torndoes down that way.

PS: Do folks in south Texas know that what you know, they know?

"Watch what it can do to fiberglass greenhouse panels."

Fibreglass greenhouse panels, motorbike fuel tanks, helmet visors, fist size and bigger hail slanting in at 45 degrees and who knows what speed hurts when when you ride your bike through it. Three or more in the one spot, by jove you're right, scratch that whip aerial.

Regardless of whether the truck actually moved, the antenna seems to have been intended for mobile service. A fact that you may have overlooked in your calculations. In a thunderstorm there would be added force from the water drops which are considerably more dense than the air alone which may have exceeded your worst case senario..

It got wet.

Assumptions:

• Though the antenna was from one of the truck in the parking lot, it was just ASSUMED that it staionary when the antenna broke.
• Max wind speed used for calculation perhaps was based on stationary object.

Could the truck be driven against the wind before being parked?

No one has mentioned the effect of lower temperatures on the antenna. the flexibility of the antenna will be significantly reduced as the temparature drops closer to freezing as in a thunderstorm, combine that with an excessive wind speed and the antenna will break

Close to freezing...in a thunderstorm? On the ground or in the sky? Are you now saying that it's a winter thunderstorm...and that the drops are sleet or snow? Are you saying that the antenna could have been saved by turning on the radio, so the the radio waves conducted in the antenna could keep the antenna warmer, so it wouldn't break?

could the wind have kicked up a plastic bag or other object that could have snagged and broke the antenna?

It really depends on how large a bag the wind could have picked up, and how large the bag was, and of what shape, so that it could snag theantenna without also snagging the truck? But the point of the challenge is not about could haves and possibilities? It's about must haves....based on information made known by, or implicit in the statements of, the challenger.

If there is a security tape of the parking lot, look at it . It's possible that some-one was feeling malicious and broke it off as they were walking through the lot.

The maximum wind speed is a speed from sensors at the airport or other weather reporting site. Thunderstorms can generate 100mph+ winds in micro bursts. You wil not get surface icing from a thunderstorm, unless the truck was flying. Thunderstorms are warm air machines so I think a micro burst or hail would have taken out the antenna.

He may not have taken in to account the fatigue factor of the material.

I notice no one has suggested that it may have been a case of 'truck fatigue' - perhaps it was the truck that snapped leaving the antenna with nowhere to go?

Assuming that it wasn't a flying monkey, vandal boss or any of the other one-off type events, AND, assuming the truck had indeed been parked overnight - then the total absence of temperature related effects upon the antenna material indicate a combination of temperature change associated with wind shear.

LMAO :) Truck fatigue!!! Those guys posting about ice and such must be from antartica. wheres there mostly ice and freezing rain and peguins dressed as monkeys flying arond !!! flying around - how about a pile of feathers and some guts spattered on the antenna. WELL... they never posted anything about freezing rain either.

I like the resonnace thing myself. and those guys are fast - to fast. they made the thing - didn't let the fiberglass setup and it just fell over. Not the dudes fault at all. its the shirts watching the iso whose at fault. sparkyc:

There could be two causes...

1. the material properties would be dissimilar if the temperature was too low and hence a reduction in the impact strength. A impact may very well be expected during the tunderstorm.

2. The other could be that of the low frequency Aeolin vibrations.

I don't see where the material is named in the problem.

Quite simply the truck driver broke it..........she reversed the van under a low roof (must be a woman as they can't reverse)

Two things went wrong. 100 year max wind does not include gust wind speed and sheding vortices caused a failure of the antennna.

You must be single!

It was probably your mother trying to back up on you. It's a shame she missed =D

She swerved to miss the flying monkeys.

Check if the antenna exceeds the height barrier of the car park.

The truck, parked in the empty parking lot, was subject to passing vandals who broke it off just for fun.

We obviously forgot about harmonics and the Von Karman Vortex Street. The Von Karman Vortex Street is a phenomenon involving wind flow around a cylindrical object. The slightest disturbance to the flow causes the air to detatch from one side of the cylinder, so that the attached air on the opposite side flows further around the cylinder on that side. Eventually, however, flow on that side is forced to detatch, and it then attaches on the opposite side. This cycle stabilizes at a speed dependent on the wind speed and cylinder size.

Obviously the aerodynamic forces on the cylinder are higher on the attached side than the stalled side, so you end up with cyclic side forces on the cylinder. You may have witnessed a flagpole experiencing this phenomenon, bending from side to side rythmically.

The real problem comes about when the Von Karman cyclic rate matches a harmonic frequency of the cylinder, or in this case antenna. At harmonics the antenna deflections increase, rather than being damped. With airplanes we refer to it as flutter, and it can tear an airplane apart in an instant!!!!

Lewbloms

It's a prototype. Maybe a POC item with rough finish, stress cracks, etc. Prototypes have a short life span. If it died, try again and keep better observation of what events occur. A twelve foot antenna is going to attract overhead signs, bridges, overpasses, Flying Spaghetti Monsters, etc. It is difficult to conduct statistical analysis on a single sample.

Cyclic loading causing failure? This is the definition of fatigue failure if the amplitude of the antenna's oscillation does not exceed too large a value to cause immediate catastrophic failure. Also, wouldn't the antenna's diameter be too small to cause such behavior? I have never seen similar sized antennas snapping off in a strong wind here in the Midwest. It sounds like you do agree with me, you just don't want to admit it.

It is likely harmonics. You can see this on a regular radio antenna on a car at highway speed. The antenna vibrates in two or more nodes, and the fatigue effect can cause failure.

Good point. And, often whip antennae are strapped down.

I know this is long, but bear with me here:

The most likely answer is probably a fatigue failure due to the variable loading condition supplied by the thunderstorm winds. The question states that the stress result obtained by the engineer was within the yield criteria, but as we all know, the fatigue strength of the material decreases with increased loading/unloading cycles.

For simplicity's sake, let us say the antenna is made from steel, this way we can use the concept of endurance limit. Now, for the static yield result, it was stated that the stress was "well within" the yield and ultimate strengths, which could place the stress result, in my conservative opinion, anywhere from 50% to 75% of the ultimate strength. Also, for steels which would form a good antenna, the laboratory endurance limit is roughly ½ of the ultimate tensile strength. So, it is seen that the stress result obtained is already very close to the laboratory endurance limit before any fatigue strength factors are considered.

Next, a number of "field" variables will play a role in reducing the real life endurance limit from that predicted in the laboratory's perfect conditions. First, the geometry of the antenna will reduce the fatigue strength because it is different than the fatigue lab specimen. Second, the surface finish of the antenna will reduce the fatigue strength due to differences from the lab specimen. Third, other factors, such as the material's homogeneity and the environment chemistry the antenna is placed in will also reduce the fatigue strength. For simplicity's sake, lets again assume that only surface finish will play a role here. Assuming the antenna is manufactured through a cold-forming process, such as extrusion or drawing, the fatigue strength reduction factor is around 0.65.

So, taking the simplified cases into consideration, it is seen that the antenna's fatigue failure is the most likely culprit. The FEA result is known to be "well-within" the material's ultimate strength, thus conservatively putting the stress result in the range of 50-75% of the ultimate strength. Giving the question the benefit of the doubt, let's say we are at 50% of ultimate strength for the FEA stress result. Now, applying only the surface finish reduction factor of 0.65 to the laboratory fatigue results, and recalling that the endurance limit of the steel is likely ½ of the ultimate strength, we have a modified "real-world" endurance limit of 0.325*UltimateStrength. Obviously, this is MUCH less than the 0.500*UltimateStrength predicted by the FEA stress result, therefore the most likely cause of failure for the antenna, barring any sabotage from competitors, is FATIGUE FAILURE. And keep in mind, my assumption is that it simply failed sitting in the parking lot. Had the truck been on the road, the stress could have been much higher, thus breaking the antenna even faster due to the increased wind load.

Adam Dye

Project Manager/Graduate Asst.

Metal Forming Research Group

Northern Illinois University

Fatigue has been mentioned a number of times as a possibility, which it certainly is - eventually. But let's remember that this is a prototype antenna. In other words, it is rather new. Fatigue failure generally requires cycles in the 10 to the 7th range, which I seriously doubt is the case here.

Lewbloms

Your reply is duly noted, however by effecticely reducing the fatigue strength by such a large factor (about 30% of the lab fatigue), the issue is no longer that of such high cycles. Also, fatigue failure is defined as failure falling anywhere between 1000 to 1 million (10^6) load/unload cycles. Because the fatigue strength has been reduced so much, the number of cycles to failure has been effectively been cut down by a significant amount to possibly lie within the 1000 to 10000. Such a value could be easily attained with a violent thunderstorm wind causing a lot of very dramatic dynamic loading on the antenna.

Also, keep in mind that I have only used the surface finish reduction factor. In fact, there are roughly 5 or 6 factors which should be considered for design work, each of which would continue to lower the fatigue strength, thus effectively lowering the number of cycles to failure.

Thank you for your reply,

Adam Dye

Project Manager/Grad Asst

Metal Forming Research Group

Northern Illinois University

You let your Boss get to work before you!!!

This brings up images of the Tacoma Narrows Bridge. While the analysis of static stress may be valid it didn't take into account resonance. Turbulence in the wind stream will start the antenna vibrating at the resonant frequency and unless the antenna is well damped, vibrations will build. The stress levels at resonance can far exceed those under static conditions.

I would suggest fatigue failure from vortex shedding exitation.

I'm figuring that lightning strike would overheat the metal and reduce the material strength. Combine this with a simultaneous loading condition from wind and viola. There's a lot more to materials than just their strength.

But let's also entertain the proverbial, "were you in metric?" Just for fun.

"Materials scientists have good tempers.

One more thing, although possibly insignificant, was the fracture brittle or ductile. If the fracture was brittle, preform a test on a new antenna, if its fracture is ductile, some degree of work hardening could have occured due to bending, reducing the antennas ductility.

Was the material tested for strength when recieved, in order to confirm the manufacturers strength specifications. Also i can't remember the exactly how to do it, but look into the testing specifications, most of the time the material strength is only known to a certain degree ie. if the UTS is 200MPa, it could mean that a test specimine will break at 200MPa or above 95% of the time. Same with how well you know the stresses if you know them to a estimated 90% accuracy that with fatigue and under extream conditions the maximum bending stress will be less than 190MPa, there is still a probability that your actual stress will be 207MPa and your material UTS is 191MPa (snap). This is after taking all stress, cyclic loading, worst case senario into acount (ice buildup, below ductile brittle transition temp, resonance, heating during cylclic loading, work hardening ect.)

Responses #52 and #56 are erudite and interesting. But I'm going with response #27. The additional factor, rain, makes for a different antenna --a water-covered one--than the one for which our poor engineer based his calculations.

Maybe it's a question of Flutter. The antenna could withstand the static load, but under certain conditions of wind speed it enters in resonance.

OK. I have re-read the problem. (Remember they used to tell us to do that in school?)

The question is: "What went wrong?"

The answer is: "The antenna broke."

Nobody asked "Why?"

By the way, for the non-Canadians among us, what happened to the antenna was that it was seen by a Weights and Measures inspector who determined that it was labelled "12 foot antenna" and broke it for not being labelled "3.65 meter antenna".

Alternately, as all radio bands are measured in meters, the waves themselves snapped it for being FPS.

Personally I would fire the boss for wasting an engineer's time, when one can buy:

Array Solutions - part number AS-12-HD ($270.00) (Military grade) or

MFJ - MFJ-1956 (Telescopic whip) ($29.95)

with a credit card and a two minute web search.

Hmmm, if they were designing an antenna and making prototypes it is unlikely the antennas were for internal use, but rather to manufacture for sale to users. If they were mounted on a Truck, then they may be competing with Array Solutions (or looking to be a supplier to them) or designing for the non-military market. Also, the MFJ telescopic whip would not work because you do not mount telescopic whips on moving vehicles! They are not strong enough. Telescopic whips are for portable applications. (STL Engineer is a FCC Licensed General Class Amateur Radio Operator, callsign withheld for privacy)

"max wind load assumed " --- may not have included the additional momentum imparted to the antenna by the rain. A twelve foot fishing pole will be bent more by a 10 mph current then by an 10 mph wind.

He has forgotten to calculate the strength of the antenna joint with the body of the Truck. Max load occurs at the antenna base joint and needs stiffening of the body of the truck where the antenna is mounted.

Gopinath... baddepudi40@yahoo.com

I put an FM antenna on my truck, and drove it repeatedly at 80 mph. No problem. I put a Jack-In-The-Box antenna ball on it, and it went nuts, but it received OK, and it seemed like it wouldn't be a problem. After a week or two, the antenna snapped (which is a real pain, because it took me a while to find out that pretty much nobody but Pep Boys sells car antennas).

This gives us several points of information:

1. Don't stick a Jack-In-The-Box antenna ball on an antenna, even if it's wearing an Oakland A's helmet.

2. Don't forget to do the infinite element analysis too.

3. Wind bounces stuff around. Find out how much you can bend an antenna without breaking it, and then see how much it bends in the wind. Simulate the wind by putting in on a truck and driving fast.

I fully support the #38 answer: Some object flying because of the wind kicked the antenna.

Most people who got hurt in windstorms had been kicked by a flying object: Pieces of roof, tree branches, etc. (I never heard about real flying monkeys, but…)

Under these circumstances, other then finite element analysis and various technicalities, you better buy insurance.

If the CR 4 challenge is no longer an engineering-premised challenge, but merely a riddle, pray tell how there can ever be an unravelling if the poser of the riddle has omitted every datum and circumstance needed to solve it. How can a riddle have dozens of different solutions, and still be a valid riddle?

The wind speed in the thunderstorm was accelerated, above the max wind load for the antenna, as it changed direction around the building and over the body of the truck.

A couple of things spring to mind.

1. Down burst winds
2. Ice

The first deals with high shear winds that can have the punch of a tornado. Since inciental damage was not mentioned, it would be a good to check for area damage to trees bushes fences, etc.

Don't know the time of the year but in the Great Lakes area it is not unreasonable to see freezing rain and thunderstorms within a commute. If there was freezing rain then the physics of the antenna in the wind is quite different.

Mother Nature just loves to give humility lessons to us folks.

Well I am no expert, but there seems to be one thing that is overlooked by this engineer. Precipitation. Combine your high winds with a heavy downpour or hail (which is common for thunderstorms) and there will be more forces at work then the engineer took into consideration. (as it is written up)

I am intrigued by the vortex and shredding theories, which are completely outside my realm of understanding. There is quite likely something there.

I just thought I'd bring out the one obvious ommision that most others seem to be over loking as well.

Afterthoughts...

What about the pitch and roll effects of the vehicle due to the wind on it?

Also would "dry" wind have different effects on the antenna then a "wet" wind?

I saw somewhere that the wind will cool one side of an object (in this case a mountain) and heat the other side.

Would any of these principles come into play with something so small?

The antenna was never attached to the truck. So when the thunderstorm winds kicked up, it rolled off of the truck and onto the surface of the parking lot. Then in the morning, the boss ran it over with his Lexus. Remember to attach it next time. If it was attached - it was the monkeys.

During the thunderstorm the wind bent the antenna enough that a large bird (hawk, eagle, condor) was able to perch on it. The weight of the bird was enough to break the antenna.

It was a twister and the truck was flipped over and broke the antenna. Hee Hee

Quote "This was one of the prototypes on the truck in the parking lot." What went wrong?

Firstly it does not say, one of the aerials you specified, it just says a prototype

Secondly the simple answer is It broke!

Thirdly what it does not tell you is that the office is in a complete mess looks like something got reversed thro the office wall last night the size of a pick up truck and guess what the aerial just happened to land on your bosses desk as it got snapped off the back of the truck and he has passed it on to you!

Fourthly Who left the truck in reverse come on own up now!

IMO...

The engineer failed to realize that simulation is only one portion of a proper evaluation, and he/she failed to realize that after the simulation showed no possibility of failure, he/she should also run physical testing of actual specimen to account for material and manufacturing defect, not to mention sanity-checking the finite analysis software.

And btw, the story doesn't say whether or not the antenna was broken by a bending action, or if it might have been hit by debrie...

Arrogance looks like the "man in charge", Humility always checks twice.

When the antenna bent it made contact with another part of the truck, for example the trailer, and that sharp angle caused a stress concentration at the bend point.

prototype on the truck could not be 12 ft, so.... say 6 ft, you lower the critical stress load and .....snap!

Where did the monkey, flying or not, come from?

Thunderstorms are ususally not assocaited with ice build up in my experience. I'd be more willing to say that it is due to:

a) The truck going beneath a low clearance bridge, garage door opening, etc.

b) A material failure if it is one antenna

c) Something about the geometry of the parking lot - a nearby building for instance, that caused the wind to behave in an abnormal manner - perhaps cyclonic.

What went wrong? You were ask to analyse the antenna to see whether it will snap due to weather and you only analysed the effect of wind.
Lots of posters have supplied details of the difference between the effects of a thunderstorm and a schoolroom model of a uniform high-speed wind. Also, if you want to use them in Siberia, you need to check the effects of temperatures varying between -55C and +45C (-67F to + 113F) and the range in the middle of the USA will be nearly as wide, but a bit warmer- so you need to check tensile strengths at different temperatures.
As an alternative to the flying monkey, consider a stationary truck - if the wind blows the antenna against the truck, it will initially bounce back and then be blown onto it again; with a varying speed of wind gust, it could hit the truck dozens of times and it may not take long for stress fatigue to snap it.
Just be glad that a prototype snapped before the firm had tried to manufacture (or had bought) a million of them. Now run tests to find out why the prototype snapped and whether it meets the specification of the sample that you analysed.

No one seems to have considered that the antenna was not just subjected to wind, but to wind and rain, a much more dense material than just wind alone, and that it would be able to exert much more force. As stated in a previous post, it's what is IN the wind that counts.

The resonance thing is good but if you think you can blow in a whip to resonate it I suggest you try. Let us know if you succeed. Thanks.

if it was a prototypes and not the one tested , the prototype could have been mounted wrongly , material stress , or some drunk idiot passed and broke it , or the most comum human error

In the discussions, which I read before writing this reply, I herd no mention of the antenna reaching its resonant frequency as a consequence of vortex shedding which to my mind would be a very likely explanation.

Vortex shedding is a common occurrence when a thin circular cylinder is placed transversely in a fluid stream. It takes place between Reynolds number 250 and 200000 and was discovered by Von Kārmān or something like that. Anyways, Vincent Strouhal or someone created an empirical formula for calculating the shedding frequency.

If the range of shedding frequencies corresponds with the resonant frequency (or one of its harmonics) of the cylinder, then something has to be done to break up the vortices or change the resonant frequency of the cylinder.

You must have skipped over #52, as I basically came to the same conclusion as you. That is also the official answer, posted in the latest newsletter.

I was wondering when, where, and if they ever posted an official answer to these "puzzlers". Can you download the newsletter from somewhere on the web, or only by e-mail subscription?

The globalspec letter was emailed, a day late. Constructive resonance reinforcement was the answer.

It will be nice though if the CR4 teams picks this up as a suggestion to, perhaps, post solutions (say, as a reply under the challenge) after they've been "officially" released in the weekly enewsletter.

Click on "Specs & Techs" at the top of this page, then pick the 9/26 issue. It is in there.

Lewbloms

But, as you may find out, you might have to wait for several days...before a particular, week-after-challenge, issue gets added to the list. So, even with the "Specs & Techs" facilitiy (that doesn't tell you that it's a past issues facility) having the solution posted to its board would be nice.

On the contrary, resonance was mentioned by even the earliest posters. I believe that the $10,000 check should be sent to me because I said that "Maybe the FEA program itself is limited in ways the engineer did not understand, such as not incorporating effective 3d CFD code." Fluent, for instance, hooks into most FEA programs and nicely models vortex shedding. This link shows an animation from Fluent, showing VK vortex action.

http://www.enseeiht.fr/hmf/travaux/CD0102/travaux/optmfn/gpfmho/01-02/grp6/pages/re400.htm

I'll have to admit that, even though the $10,000 would be nice to have, the prize should really be split between posters 4 and 5 (anonymous hero and Nick james) both of whom mentioned resonance (I'd assumed they meant aerodynamically induced or reinforced resonance in both cases, and the resonance cited in Nick's post was clearly aero induced.)

But then STL has the best real world answer, for which there should be a $15,000 award:

'Obviously, the boss broke it himself and was trying to see how you would handle failure and what steps you might take to correct the "problem".'