It sways!

I just got back from CP and when I was standing in line for Wicked Twister, I noticed it swayed about 3 feet back and forth, both towers too..it got me wondering.. Great ride though!

~*kP

Its supposed to sway....if it wouldn't then it would of snapped off already....swaying releases the tension on the unsupported track

Blah blah blah... does everyone just say that it has to sway (or else...), not really knowing what they are talking about?

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Jes
Jes's Roller Coasters DJ Jes MCS Please, Feel Free To Call Me Jes!
Six Flags Worlds Of Adventure 2002 Ride-Ops Crew!

i know that they are supposed to sway....just like the twin towers did :'( ....and any other free standing structure or track or anything free standing needs to sway.

I think they sway a bit more than 3 feet, it just looks like that from the ground.

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Break the scream barrier NOW!
Wicked twists: 4
Danger: Hgih Voltage!

Actually 3 feet is about right. :)

The easiest way to understand why the towers sway is to think of them undergoing simple harmonic motion, which can be modeled using trig functions. Simple harmonic motion involves an object set in motion about a point and the force required to restore this object to its original state or lowest potential energy. An example that you can try at home is getting a rock, tying a string to it, and swinging it back and forth. This is a pendulum. If you quit swinging it, the restoring forces of gravity and wind resistance will act on it, slowly causing it to lose momentum. The forces of gravity and air are dampeners. If you were observing a spring in harmonic motion, the strength of the spring would also determine how quickly its motion is dampened. Stiffer springs=greater dampening. If you want, you can stop here. It gets a little more complex, but same idea.

Now think about the unsupported track on Wicked Twister being like a hybrid of the spring and the pendulum, with the point of rotation being about the last support below the unsupported track. Since the train was previously traveling in a direction parallel to the ground, it would like to continue traveling parallel to the ground. Therefore, a horizontal force dependant upon the radius of the pullout will be applied to the track. Additionally, when the train tavels up the tower, it is rotating about a virtual center that the mass of the train does not occupy. Therefore, centifugal forces (or center seeking forces) are occuring that translate into the track itself. We can now think of these cetrifugal forces as many little lateral point forces that are acting on the track, some of which may or may not cancel each other out. If we added the vectors of all these little forces and the vector of the horizontal force, we would end up with a net resultant vector. This would determine the direction in which the tower would sway, most likely in the direction of the station since I'm assuming the horizontal force comprisises the greatest magnitude of that vector.

This now allows us to think of the complex spiraling shape as a steel member which has had a net force applied at a certain distance away from its axis of rotation (the last support before free standing track). As the force is applied, a moment about this point occurs. The moment is also greatest here which means the track at this point needs to be strong enough to be able to widthstand this force. It will deflect though, as steel is an elastic material. As the train descends back to the ground, the force is removed and the track tries to restore itself to its previous position and state of zero motion. Its motion or frequency will be dependant on its initial dsplacement (or deflection), and the ratio of the track's mass to stiffness (strength of the steel in combination with the moment resisting capacity of the truss design). Therefore, the track will never move more than how much the train initially displaces it. The ratio of the mass to stiffness will determine the primary dampening factor that allows the track to return to zero movement, as we are working opposite gravity here.

Of course I haven't included any equations here, but using some eq's from physics and statics could roughly get you there. You can be assured that accurately figuring out the design of WT's structure has been entrusted to computers, though, as doing this manually would be very tedious due to the shear number of caluculations that would be involved and the accuracy required. Since the track is like a continuous beam, forces are always being traslated every where, making this an indeterminant structure. That doesn't mean it's magic as to how the structure stays up, it's just impossible to design accurately using methods of statics. So you end up turning to a computer program that has been written by those with advanced engineering degrees to get the job done.

Hmm...now that my tangent has ended up putting me in the realm of computers and engineering...Moral to this story:

We really can thank modern methods of structural and mechanical analysis using computers for the wonderful coasters from the likes of B&M and Intamin that we are seeing. Without these tools, these rides would never be a reality

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-Dave Kochman
Pittsburgh

**Corrected some typos for your reading pleasure.
*** This post was edited by DaveTKoch 5/30/2002 3:00:23 AM ***

Wow, Dave. You picked a hell of a time to reappear in Jeff's Wacky Coaster Site Network!

Something I noticed was that the center of the train's rotation would appear to be the train's center of gravity if it was hung by one end. In that respect, the train has motion that moves straight up, causing me to think that the track does more to guide the train around than actually support it.

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Jeff
Webmaster/GTTP, Sillynonsense.com
"As far as I can tell it doesn't matter who you are. If you can believe, there's something worth fighting for..." - Garbage, "Parade"

...much like Demon Drop's free-fall section...

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Jes
Jes's Roller Coasters DJ Jes MCS Please, Feel Free To Call Me Jes!
Six Flags Worlds Of Adventure 2002 Ride-Ops Crew!

Yeah Jeff, you're probably right now that I think back to the videos. For some reason, I was thinking that the train's center of gravity was outside the center of rotation, but in fact, the track lays outside the center of rotation keeping the train within the pocket. As has been discussed in previous threads, this is the key to creating smooth transitions on coasters.

Thanks for the warm welcome; I figured it was a good time to come back and unleash all of my pent up rage on the fine members of this board. ;)

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-Dave Kochman
Pittsburgh

Dave, your methods have one flaw. I have a bit of a background in physics and one thing we do alot is assume that alot of forces are perfect. I work at Cedar Point and have noticed something else. In your discussion you stated that the track sways about a fixed point, the uppermost green support. However, both of the green towers sway as well. Therefore, there are forces applied to the swaying yellow track that are not harmonic with the natural sway of the yellow track.

Not many people have noticed that the green supports sway as well. There is a whole set of structural flaws I've noticed in them. However, with the two swaying at different frequencies, the green supports have a greater momentum acting on the yellow than the yellow on the green. This causes the yellow track above the last green support to sway irregularly, and not in some simple harmonic motion.

I know that steel is an elastic material, however I also know that there was something wrong with the computers' calculations. Because, Thursday May 30th, at 10:30 AM ride maintenance was welding the yellow track just above the green support on the northern most tower. You can see the black scorching very well from just outside the beach gate enterance. They were welding this section, because they discovered the track had cracked that morning during testing. Yes, I am not making this up. The track on Wicked Twister has already cracked, and been welded to repair it.

Thanks for correcting me, Zane.

I actually haven't seen WT in person yet, so I was infact postulating from the observations of someone else. I should've stated that. OOPS! (There goes scientific method out the window...)

I took the fact that the base of the towers do not have perfect moment resisting capacity for granted. That makes alot of sense, though, given that no structure is perfect. Like you said, this then becomes a more complex case of wave interference.

You're comment regarding the stress fracture is interesting. However, the stress fracture was probably not an immediately serious issue, but it's better to be safe than sorry.

Typically, steel can develop minor stress fractures during production. Under standard production conditions, these are merely surface blemishes, analogous to the hairline cracks that developed during the molding processes for the iCube by Apple Computer.

The next category of stress fracture is caused by normal wear and tear. These types of cracks, although not typically harmful, should be monitored for further development--especially considering the environment where they occur. They will give plenty of notice before they finally fail, but who wants that under any situation. Given the nature of the amusement industry, I'm sure Cedar Point has a zero tolerance policy for these cracks and immediately takes action. That's probably what you were seeing then: nothing serious, just some preventative maintenance. Maybe someone with ride inspection experience can chime in here...

That does make me curious as to how much preventative maintenance SFWOA's version has required thus far, though.

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-Dave Kochman
Pittsburgh

*** This post was edited by DaveTKoch 6/1/2002 12:37:10 AM ***

All I am going to say is:It's supposed to sway if it did not sway the track would snap like a twig.

Thank You

"And Enjoy Your Day At Cedar Point,America's Rollercoast."
*** This post was edited by RaptorTwister 6/1/2002 9:09:34 AM ***

yup....i agree with raptortwister.....its supposed to sway....and i don't know why people are making such a big deal out of this....if there would be a problem with the track...or if it was endanger of snapping off they would have shut it down already.

My explanation above was intended to give Zero-G and others a little more indepth understanding of the physics behind the swaying. There's nothing to "agree" about here, no one ever asserted that it's not supposed to sway.

In my second post, I was merely providing a little more information regarding steel and allowable stresses. I wouldn't say a "big deal" was made of anything, but rather the opposite.

All posts at forums are not argumentative in their nature, many are just meant to be informative.

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-Dave Kochman
Pittsburgh

i think a big deal is made about this....not only in this forum ...but on other sites and forums...and i hear people talking about the sway all the time and that it can snap off....i even heard sombody making bets on which tower would snap off first...as a joke ofcourse....but still i do hear alot of nonsense about the swaying

Of couse you do - but you also hear a lot of people ask if Magnum is really sinking or is sold to Japan! :) It's also kind of like when a ride goes down mechanical and some guests immediately proceed to tell others that one of the trains flew off the track. Just nonsense. Some of them are just fooling around, some of them are just dumb. I've got news for you - Magnum sways too! Not as badly, but when you're up there, you can definitely feel/see some swaying action. Most tall structures sway - it's nothing to worry about.

-Matt
2001 Magnum Crew

All this talk about swaying makes me think about the que for Racer at Kennywood, a main support pole for the turn-around above the que is situated in the middle of the que and it sways in a circular motion every time the trains pass.  Very obvious especially  with the creaking noise of the wood.

Anyway, in all honestly, the swaying comforts me.  Because the track sways, I  know that it is not overly rigid.  An easy example of the concept of rigidity can be seen in the winter time.  After a nice sleet storm leaving a good solid layer of ice on everything you see even the most lively looking twigs can easily be  snapped straigt off of the shrubs outside.  This is because the twig is frozen completely through turning even the usually quite plyable plant material in the twig into a much more rigid structure.  While the rigid structure does not bend while put under stress, it quickly reaches a point where the stress is too great and cleanly breaks off.  Apply stress to the same twig come summer time and it will bend instead of breaking.  In fact you will  probably be able to bend it completely in half without breaking.

Needless to say this example easily shows that a completely rigid, unmoving structure would be easily snapped.  While While a fairly rigid yet still plyable structure allowing for a small amount of

I agree with RaptorTwister that Twister is supposed to sway. I do not know how it was designed or what tests it was put through before actually being put into use. All that I do know, is that the man who welded all three cracks in the track said "I do not feel safe even standing under the thing."

well....first of all ...isn't there 4 cracks in the track...2) there was like 2 people welding the tracks....and how do you know what the guy said.

- Dennis

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