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Accident of Punta Nevada - Cerro Catedral - 2013, causes wanted


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#1 JoseP

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Posted 28 October 2014 - 07:11 AM

Hi everybody,

I'm new in this forum, so I present myself. My name is José, I'm from Bariloche, Argentina, and I'm Mechanical Engineer. I'm doing a research about last year accident of Punta Nevada (Cuádruple) chairlift in Cerro Catedral. Here I leave you some news about it:

http://www.anbariloc...uera-de-peligro

http://www.anbariloc...-en-el-catedral

Last one contains a video made by one of the injuried by the accident. Unfortunately they're in spanish, but video is very demonstrative of the accident. You can even see the precise moment when cable derails. It is worth to mention the speeds of wind measured in the 5 min interval within the accident took place:

-Wind speed (km/h): 72.6
-Wind gust (km/h): 126.0

It is very interesting to notice that chairs are falling with an acceleration greater than 1G, due to cable tension pulling downwards.

What I'm looking specifically is a technical plan with dimensions about one tower with sheave train, brittle bar, cable catchers, etc, in order to collect necessary information to make a simulation that could reproduce accident conditions. The model of the chailift is a Doppelmayr-CTEC 4-CLF, installed in 1997, and unlike almost all other lifts from this resort it was purchased new, not used or refurbished. It normally operates for the ascent and not for the descent. As can be seen on pictures, is asymmetrical regarding sheave trains. On the ascent side, it has six sheaves, and on the other side has only two of them.

You can find attached some pics of the lift, specifically from the tower where the accident took place.

Attached File  DSC_7109.JPG (221.72K)
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Attached File  DSC_7135.JPG (322.23K)
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Attached File  DSC_7141.JPG (309.43K)
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Attached File  DSC_7168.JPG (258.31K)
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Attached File  DSC_7163.JPG (154.94K)
Number of downloads: 135


I would appreciate very much your help and I thank you in advance. Feel free to post links or information that may help to determinate the causes of the derailment. It is clear that the wind took a big part in the event, but we are considering all other possible factors that may have acted simultaneously and helped the wind gust to derail the cable.

Regards

#2 Kelly

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Posted 06 November 2014 - 06:21 AM

Hello Jose
Thank you for the interesting topic and welcome to the forum. I’ll cover some known values and some guestimated values along with cultural values (word play intended) of a typical ski lifts and ski areas.
For the benefit of the bulk of the forum readers I’ll change the metric values to US customary units.
Thank you for providing the wind speed so let start with that, converted to pressure, as this is a more relevant value. These are corrected for density altitude that existed on this day at this elevation.
Wind pressure is…
72.6 km/h = 4.7 lbs/sqft
126 km/h = 14 lbs/sqft

As I compose this reply it seems to be gathering in length so I’ll breakup my answers into a few posts – the next post will cover surface areas that the wind pushes on as this is another key to the derailment or any wind derailment for that matter.
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#3 Kelly

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Posted 07 November 2014 - 07:51 PM

Surfaces
For the wind to exert a force we need a surface area – the riders (or in this case, one rider works for side load) and the chair surfaces: bail, stem and grip. This can be considered the square footage that the wind pushes between each span.
Chair surfaces = 1.5 sq/ft
Rider surfaces = 5.5 sq/ft
Total surfaces = 7.0 sq/ft
Attached File  Riders-and-chair-surface.jpg (99.49K)
Number of downloads: 66
Some consideration should be given for wind against the haulrope due to its length at each span. There are numerous correction factors based on a round object’s perceived lower surface area – due to rope lay profiles and ice that is attached to the rope let’s say for now the correction factor is not reduced and will remain at 1X.
Rope surface = .125 sq/ft per ft
Attached File  Rope-surface-area.jpg (99.17K)
Number of downloads: 79
Surfaces ~ Total Area x Wind Force
Adding the lower speed steady wind pressure to those surface areas gives us the forces that push the rope away from its intended path.
Chair/Rider: 7.0 x 4.7 = 32.9 lbs per each chair
Rope: .125 x 4.7 = .5875 lbs per each foot

Sheave Groove – The Key Element
Those loads listed above have to be resisted by some aspect of the sheave groove. Let’s be generous and say that a single sheave groove has a side load resistance value of 500 lbs in either direction.
Lets also assume this sheave is in proper alignment with plane of the rope and in new condition.
Attached File  Groove-resistance.jpg (85.44K)
Number of downloads: 79
The tower that derailed has 6 sheaves so it is easy to jump to the conclusion that the groove reactions should be added to give a result of 3000 lbs…but wait, if you look at the profile of the groove notice as the rope moves out of position it also lifts from the bottom of the groove. This lifts the sheave out of the next groove and next groove…no added reaction is realized! The longer sheave assemblies have little additional benefit as the first and last sheave truly matter for wind alignment.
Attached File  Rope-lift.jpg (98.63K)
Number of downloads: 76
Typical wind misalignment
Attached File  4-Sheave-bent.jpg (56.08K)
Number of downloads: 52

Next – Unexpected groove reactions
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#4 Kelly

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Posted 08 November 2014 - 06:32 AM

2 Sheaves – a different story
Groove lift is less severe in a 2 sheave assembly because of the pivot of the secondary evener (much shorter) frame allows the next sheave to capture the side load. Hummm do we have any assemblies where this could occur…why yes, it was the light side of the tower... which did not derail or so it would seem from the photos. More info about this in later post replies.
Attached File  Two-sheave-assy.jpg (96.42K)
Number of downloads: 59
Wind Loads – How they are resisted and where does the force go
Consider the wind pressure as a load on a simple beam with reactions at the supports (the towers or in this case the groove) - the reactions equal the given load. L=R1+R2
Attached File  Simple-beam-load.jpg (96.83K)
Number of downloads: 56

Next – final loading and reactions for a 72km/h wind on a sheave groove
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#5 Kelly

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Posted 11 November 2014 - 05:48 AM

Diagrams for load and distances affecting the tower
For load spacing of the carriers, you have about 6 chairs before the tower and about 6 after the tower. A fairly common spacing is 50’ between chairs and 300’ between towers so I will use this assumption for the remainder of the worksheet. This shows the distance between supports that the sheave groove realizes from side wind load – please don’t confuse this with vertical loads. The tower in question is called "Feature 2" in this diagram.
Attached File  Tower-distances.jpg (35.67K)
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Adding the chairs with a 50’ spacing along with loads from surface pressure from the rider and chair of 32.9 lbs
Attached File  Carrier-spacing.jpg (67.8K)
Number of downloads: 32
…along with distributed or uniform rope load from wind
Attached File  Carrier-loads-and-rope-load.jpg (98.83K)
Number of downloads: 42
This is simple vector graphic showing a side view – the big arrow (the sheave groove force) wins and keeps the cable in the groove.
Attached File  Goove-vector-side-and-sheav.jpg (99.96K)
Number of downloads: 53
Reaction loads at the tower with a 72 km wind
Attached File  Reaction-72-km.jpg (98.76K)
Number of downloads: 42
Those loads impart a reaction into sides the sheave groove(s) at each tower. Notice that the reaction of the center tower is 467 lbs of groove load or 234 for the lead-in and 234 for the lead-out sheave. Considering a 500 lb capture ability of an ideal sheave groove you have a factor* of 2.1. In straightforward terms this is why the cable stays in the groove at winds of this speed.
* I would be hesitant to call this a safety factor as I will point out in a later reply.

Next – 126 km/h reactions
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#6 Kelly

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Posted 15 November 2014 - 05:29 AM

Total Area and Wind Force at 126 km/h
126 km/h = 14 lbs per square foot
Chair/Rider: 7.0 x 14 = 98 lbs per each chair
Rope: .125 x 14 = 1.75 lbs per each foot
Attached File  Reaction-126-km.jpg (99.65K)
Number of downloads: 12
The total reaction from wind load is 1390 lbs. That is a groove reaction of 695 lbs for the lead-in and lead-out sheave – this would be over the 500 lb limit of an ideal sheave’s capture ability – this why the cable moved out of the groove.

Next ~ Sheave design, the compromises
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#7 RibStaThiok

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Posted 15 November 2014 - 11:45 PM

gooooooood. I look forward to what you have to say about the old Riblet design :)
Ryan

#8 aug

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Posted 16 November 2014 - 06:34 AM

While operating during 40 MPH crosswinds may be possible and predictable, the unpredictable 50MPH -60MPH gust can be devastating .
"Maybe there is no Heaven. Or maybe this is all pure gibberish—a product of the demented imagination of a lazy drunken hillbilly with a heart full of hate who has found a way to live out where the real winds blow—to sleep late, have fun, get wild, drink whisky, and drive fast on empty streets with nothing in mind except falling in love and not getting arrested . . . Res ipsa loquitur (it speaks for it self). Let the good times roll." HT

#9 Kelly

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Posted 16 November 2014 - 06:37 AM

Sheave Design – Flange Profiles
The wind continues pushing the cable from the groove across the flat sheave liner; the passengers are still safe in this short time period as the cable approaches the sheave flange…

Sheaves have a secondary device for misalignment and cable capture called a flange. Skilift sheaves come in a variety of styles and shapes, this one dated from 1861 from an ore tramway is an early version developed with a rubber liner, notice it also has very large side flanges (marked in red) to capture the cable if any misalignment develops.
Attached File  1861.jpg (44.66K)
Number of downloads: 67
This one was developed in the 1960’s. The flange profile is slightly shorter to allow a grip to pass without severe contact if misalignment occurs; it’s a good compromise for grip wear-n-tear and flange height.
Attached File  Yan-flange.jpg (99.97K)
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This one from the 1980s has the same flange “height” but the flange is tipped out to allow the grip to pass without touching if misalignment occurs.
Attached File  Yan-80.jpg (86.28K)
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This is the sheave on the tower in question. The flange has a slightly lower profile to allow the grip (the more expensive component) to pass without hitting and to capture the cable if the first device (the groove) has failed to do its job.
Attached File  CTEC-70.jpg (90.37K)
Number of downloads: 136
Flanges have the ability to capture the rope is shown by the vectors below…
Attached File  Flange-vectors.jpg (98.87K)
Number of downloads: 103
…but they are considered a secondary device and should only be used in short term conditions such as initial alignment during construction. They also can be a good visual warning device for operational misalignment but only if the ropeway is being monitored by skilled ropeway technicians.

The reaction for this style of flange is slightly less than the groove – this why the cable fell from the sheave wheel. No reaction summary is needed in this case. The image below shows a typical flange vector vs. a wind vector. Wind wins...
Attached File  Flange-vs-wind.jpg (98.88K)
Number of downloads: 75
Considering groove and sheave flange reactions, there is no redundancy – the reaction does not taper-off, it is instantaneous. This image shows two different styles of force vectors to give you the general idea.
Attached File  DC-vector-idea.jpg (74.6K)
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This is a design critical aspect. More comments on design critical aspects in later posts.
It should be also noted that the wind force pushing on the cable still exists, at this point there is now some momentum with the cable or… as a large object moves it still has the tendency to keep moving.

Next ~ The wind continues as the cable approaches the third backup device
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#10 Kelly

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Posted 18 November 2014 - 09:11 AM

Quote


Technically speaking the cable is actually called a haulrope, wirerope or rope in aerial transportation. For most folks that work on skilifts the term “cable” means: cable TV or a spool of wirerope before it becomes a haulrope. I have used the layman’s term to help illustrate another term - in this case it has no double meaning.


The third device to capture the cable, if it escapes its normal intended path, is aptly named cable catcher.
The design shown below (from a different manufacturer than this chairlift) came from many decades of development and examination of tower deropements. From the perspective of a ropeway technician it is a true work of art.
The circled areas show nice curves that allow the rope/grip combination a smooth passage if the chairlift is still moving, also notice the wide “landing” area – this allows free passage rather than pinching of the cable.
Attached File  Dop-catcher.jpg (98.75K)
Number of downloads: 98
Here is the same concept with an older American manufacturer.
Attached File  Catcher-older.jpg (102.1K)
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The tower picture Jose has provided shows this assembly has 3 catchers.
Attached File  3-catchers.jpg (97.95K)
Number of downloads: 112
Notice if the first set of sheaves derope, there is a rocking motion as the large assembly accepts the new loading points.
Attached File  catchers-rocking.jpg (98.93K)
Number of downloads: 94
Also notice the loading points are not in the same plane either in the X axis or Y axis – if the chairlift is still running the rope will eventually roll off of the last set of sheaves onto the catchers. From a mechanical analysis stand point this becomes very messy in finding a final solution or solutions to the final cable location.
Attached File  3-vs-2-catchers.jpg (99.95K)
Number of downloads: 83
Some of you may have asked yourself, “what if we could keep that assembly from rocking, perhaps it is a design fault that the engineers overlooked?” If you look closely you can see the “anti-rock” devices on the tower assembly, some other devices exist but are hidden from this view angle so it’s doubtful that this was the key issue in the deropement.
Attached File  Anti-rockers.jpg (97.45K)
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Cable catchers also have to be able to accept the grip if it lands near the area. This shows the projections of this grip that can impact a catcher, this is especially true if the grip has tipped or rotated.
Attached File  CETC-projections.jpg (98.73K)
Number of downloads: 86
Another consideration is the grip also has to pass by the side of the sheaves if the chairlift is moving – if the grip impacts the sheave it will move the rope out of position for a catch or if the catch is successful a grip can still move the rope from the catcher if moving. It could impact the first sheave…
Attached File  CTEC-first-crash.jpg (99.02K)
Number of downloads: 79
…or all three
Attached File  Grip-sheave-contacts.jpg (99.62K)
Number of downloads: 79
This manufacturer has an insert grip – it has fewer projections that could impact a catcher.
Attached File  Riblet-catcher-projections.jpg (60.58K)
Number of downloads: 104
A 70s design
Attached File  Yan-70s.jpg (99.03K)
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Addressing the shortcomings of earlier designs this catcher was quite long (shown in green) and guided the grips around the sheaves.
Attached File  Yan-al-catcher.jpg (99.33K)
Number of downloads: 126
As the reader can see catching the cable is not a 100% guaranty just by the simple examples shown above.
Attached File  Cerro-solution.jpg (97.88K)
Number of downloads: 104

Next ~ Other factors associated with deropements and Archimedes finds an answer to the cause of the incident…
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#11 Kelly

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Posted 23 November 2014 - 04:56 PM

The causes presented above for deropements give a good background for the design considerations on carrier and sheave assembly interface.
1. The grip and carrier must be able to pass by the sheave, sheave assembly and tower with ample clearance.
2. If no clearance exists the carrier must be guided for safe passage.
These practical concepts address passenger and wind induced swing...both common sense rules that all chairlift designers follow. Showing an American manufacturer with a clearance angle drawn in red.
Attached File  Yan-70s.jpg (99.03K)
Number of downloads: 59
Due to a much smaller clearance angle this American manufacturer has a “guide” or swing-stopper or “halo” around the complete tower – effective but more costly.
Attached File  Riblet-swing-angle.jpg (98.62K)
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The same manufacturer also addresses swing in the other direction – again, effective but more costly.
Attached File  Riblet-return-swing.jpg (99.6K)
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Going extra measures, this ski area installed wirerope guides for the guides that provide a secondary measure of security from excessive chair swing.
Attached File  Mt-A-guides.jpg (93.55K)
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The reason the designers (and more so with ropeway technicians monitoring windy chairlifts) are really concerned with swing has to do with a concept first written about by a brilliant mathematician and one of the first engineers, Archimedes. http://en.wikipedia....wiki/Archimedes
Archimedes mathematically investigates the simple lever tool along with a pivot point or fulcrum. He is associated with the phrase give me a lever long enough and I shall move the world.
Attached File  Arch-lever.jpg (91.65K)
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Chairlift carriers are quite long, usually pretty stiff and quite frankly make pretty good levers. The sheave or sheave assembly is the fulcrum and guess who is pushing on the carrier…yep the wind. Here is a basic wind lever diagram with French annotations but decipherable in any language. It also addresses tower contact.
Attached File  Code-swing-better.jpg (97.56K)
Number of downloads: 57
Using the lever balance theory for the low wind example:
Rider surface of 5.5 sqft x 4.7 lbs wind pressure = 26 lbs at end of lever
Lever length is 6.5’ to the fulcrum – sheave edge
Fulcrum to cable is .5’
26 x 6.5 = .5X
= 338 lbs pulling rope from the groove
Attached File  26-338.jpg (69.95K)
Number of downloads: 40
Our lever pulls the rope under the 500 lb load that a new groove can resist. No derail would occur.
Let’s see what happens if we increase the wind speed to 85 km/hr which is well under the peak gust given.
85 km/hr = 7.14 lbs wind pressure per each square foot
Rider surface of 5.5 sqft x 7.14 lbs wind pressure = 39.27 lbs at end of lever
39 x 6.5 = .5X
= 510 lbs pulling the rope from the groove
Attached File  35-510.jpg (67.12K)
Number of downloads: 24
The groove force is less than the pulling force - a derail would occur.
It’s more than likely there is enough momentum in the lever to overcome the flange reaction - a deropement would occur.
Those two examples are oversimplifications of swing dynamics – combining an unfortunate strike from chair swing timed with steady wind that is already pushing the rope from the groove can actually move the rope at a very low wind speed.
Most ropeway technicians would agree that swing is the key element rather than wind speed.
Using the lower pressure from Post #3 plus a swing hit; these combined will be greater than the grooves ability to hold the rope – a derail would occur.
Attached File  26-572.jpg (94.69K)
Number of downloads: 18

Next ~ Mechanical equipment must be in the best adjustment possible
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#12 RibStaThiok

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Posted 24 November 2014 - 04:56 PM

Great reading here, thanks for doing this
Ryan

#13 teachme

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Posted 24 November 2014 - 08:18 PM

+1 what Rib said. Best thread for a long time by far.

#14 Kelly

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Posted 26 November 2014 - 05:57 AM

Mechanical devices of this type need periodic attention, even more so if carrying passengers. A ropeway is not like a car or farm tractor with wheel misalignment – a little shake and odd tracking are unacceptable due to the extreme consequences of deropements.
Attached File  tractor.jpg (93.51K)
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In North America most operating guidelines address tower misalignment to a further degree in mentioning they must be checked every day before they carry the public. Onetime quick check during the summer is no longer the practice. Progressive resorts take additional steps to insure proper cable alignment during wind operations by actually riding the ropeways (continuous monitoring) or close monitoring of problematic towers by watching from a snowmobile or operators house.
In my first post I mention that a groove’s reaction or “capture ability” is based on proper alignment with the groove being in new condition – anything less lowers that factor. Progressive resorts will change these problematic or critical sheaves each season so that reaction stays as the design engineer intended.
The sheave assembly below shows misalignment, worn groove and loss of groove capture – the secondary warning device (the sheave flange) is now the only thing keeping the rope on the tower.
Attached File  4-Sheave-angular.jpg (97.42K)
Number of downloads: 128
Tower alignment is fine tuned with the adjustments shown below.
Attached File  Yan-4S-adj-bolts.jpg (94.14K)
Number of downloads: 123
Proper cable to groove interface is not a new concept, this image shows different types of sheave groove profiles of a crane that operated in 1857.
Attached File  1864.jpg (98.62K)
Number of downloads: 95
Going back 200 years to 1644, this classic image documents one of the first above ground* material handling ropeways.
Attached File  1644.jpg (84.43K)
Number of downloads: 77
Using manila rope, students of history can see where the term “wirerope” and ropeway came from. This ropeway is one of the first to use bullwheels in a horizontal position*…now that may seem insignificant but you can see the constructors were concerned with groove alignment and installed guide sheaves (red arrows) at the bullwheel (a giant sheave) entrance and exits. These pictures show the beginnings of the modern day chairlift.
Attached File  1644-BW.jpg (85.25K)
Number of downloads: 66
*Material rope hoists with vertical bullwheels had been in use in mining applications and building construction for 200 years before this ropeway was constructed. Even in these early images you can imagine considerations were taken for proper rope alignment.
Attached File  1400.jpg (97.49K)
Number of downloads: 44

Next ~ Supercomputers help with avoidance of wind deropements or do they just confirm what we already know
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#15 Kelly

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Posted 29 November 2014 - 04:38 AM

I covered wind forces and groove capture with simple vectors, no computer is needed to understand vectors…not even an older desktop like the one I am typing with, oops the term now is called keyboarding. But if we want to predict the wind and just as importantly predict wind trends it’s handy to have a supercomputer. Also to truly understand what happened on this unfortunate day last year it helps to understand what causes wind.
Wind Causes
Wind is causes by two primary interactions…
1. Pressure imbalance: Wind is the result of air moving from high pressure to low pressure – this is mostly associated on a global scale
2. Temperature imbalance: Wind (or air) moves up if hot and down if cold – this interaction is more common on a regional scale.

Up to this point we have discussed pretty solid scientific principles in every post above. Each concept can be tested and confirmed through observation and viewing the result.

Predicting weather, and in this case wind, takes scientific principles and a tiny amount of art or artistic skill. Weather prediction is a different topic so I’ll delay this thread and add a new topic concerning weather modeling and forecasts that will add to our understanding of what happened at this ski resort.

Next ~ Wind prediction tools, some so small we carry them in our pocket
Post edit: Forecast topic with links to different models ~ http://www.skilifts....showtopic=10129
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#16 Kelly

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Posted 04 December 2014 - 04:28 PM

Does a wind forecast exist in Argentina
Whenever I see a derail mentioned in the press I look to see if a weather forecast would have predicted wind, or better yet, a wind trend that might have occurred at the same time as the incident.
Now I am thinking Argentina seems like a developed country that might have the means to forecast weather… perhaps it has a crude weather model copied from a pirated America TV station? Or something from Germany?
With the help of the internet I have found that Argentina has a quite sophisticated weather forecast system run by a supercomputer. This link gives the wind forecast for the 6500’ elevation all across the country. I believe it is updated every 24 hours and gives the forecast wind speed every 3 hours. This is a perfect forecast for ski lifts that operate in exposed areas. This image shows the selections for Argentina wind at many elevations. I think its great Argentina has such a specific wind forecast for ski areas. It’s nice to see it’s accessible unlike the European forecasts shown in the weather topic section accessed by the link above.
Attached File  Argen-wind-forecast.jpg (98.45K)
Number of downloads: 5
Here is the wind forecast link translated into English:
http://translate.goo...u69cKTiVoxZ2NKw
So now I am thinking the supercomputer stuff is hidden or just hard to find – nope can’t be because I found it on Facebook :mellow: https://translate.go...HWvzALNoodDmgEw
Argentina weather is also forecasted by European global forecasts and United States global forecasts. The European forecast is actually the most accurate of all three.
Summarizing
A wind forecast is produced by 3 supercomputers in this area, they may not have been in exact agreement on top speed for the day but they would have been very precise on the wind trend.

Next ~ Cheaper wind forecast tools might be more accurate
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#17 Kelly

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Posted 07 December 2014 - 06:12 AM

Using a cheaper tool to predict wind
So this gets us back to the posts above – what causes wind? As the early sailors knew, or no doubt felt, wind and wind changes directly correlate to pressure change. If you happened to have a barometer (invented in the 1600s) you can predict and track the speed changes.
The basic premise is that wind is… air attempting to balance atmospheric pressure differences.
As the pressure falls wind will increase…a balance is occurring
As the pressure rises wind will decrease…a balance is realized
This is a picture of my barometer (actually a simple weather station) showing falling barometric pressure (red arrow). Trust me it was windy this day.
Attached File  My-barometer.jpg (99.4K)
Number of downloads: 22
Here is a ski area weather station that was recording the same balancing event, notice pressure trend vs wind speed. Pressure changes happen over large distances so when I look at my barometer I am seeing close to what this ski area records eventhough we could be 50 miles apart. As the pressure falls winds will increase…
Attached File  Hoodoo-baro-vs-wind.jpg (98.11K)
Number of downloads: 19
Barometric pressure trends also predict sustained wind. Notice the pressure has stopped dropping but still is quite low, the balancing air (the wind) is still filling in the low pressure area. From this concept we can say…
Large pressure changes bring stronger and longer lasting winds.
Smaller pressure changes bring lighter and shorter lasting winds.
Attached File  Hoodoo-long-term.jpg (97.58K)
Number of downloads: 9
Weather modeling programs like the one in Argentina take into account predicted pressure drop vs time to forecast wind speed trends – the same trends are shown in the above images and also match what the sailors knew in the 1600s.
Attached File  Hoodoo-time-vs-drop-better.jpg (98.38K)
Number of downloads: 8
… even more convenient
Pocket Barometers
Most smart phones have the ability to track local barometric pressure…
Attached File  Phone-app.jpg (99.58K)
Number of downloads: 15
Smart phone app: https://play.google....tware.barometer
Now if Argentina has half the smart phones compared to my region I would be willing to bet there were a hundred phones saying the same thing at this ski area…
“the barometer is decreasing”…that fact will give us the conclusion that winds will increase or at least stay the same…the wind will not decrease.
Use smart phones to predict the weather
In 2010 two University of Washington professors conceived the idea that a network of smart phones would better help predict weather – the concept of more data gives a foundation for an accurate forecast: http://www.washingto...torm-forecasts/
What’s Next?
In case you lose the ability to access wind forecasts they now have smart phone wind meters.
Attached File  Smart-phone-wind-meter.jpg (85.93K)
Number of downloads: 16
I really don’t think many of us would use this device in a ski resort environment… woops there goes my phone with all my contacts and music sliding over the precipice. But by now you can see wind is a pretty predictable event, being well understood by the 1500s. It can be forecasted by: supercomputers, a desk barometer or the one in your pocket.

Summary of wind
-As the pressure falls wind will increase…a balance is occurring
-As the pressure rises wind will decrease…a balance is realized
-Large pressure changes bring stronger and longer lasting winds.
-Smaller pressure changes bring lighter and shorter lasting winds.

Next ~ Examining archived local pressure readings during this incident, would they have predicted any wind trends?
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#18 Kelly

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Posted 11 December 2014 - 08:05 AM

There are no close weather stations with archived data - These charts are from the Bariloche airport and other nearby stations, the trends for wind direction and pressure would have been very close to what was occurring at the ski area and no doubt would have been amplified.

Looking at typical weather parameters gives a strong indication of trend for the next hour or later that day. Here are numbered key features (see charts below) that I noticed during the week. At this point we are putting some of the science back into the art of forecasting.

1. The simple temperature chart is a good starting point, notice the strong rise on Friday.
Attached File  Temp-chart.jpg (99K)
Number of downloads: 10
Large temperature change is usually associated with approaching weather fronts. The passage of fronts always brings gusty mixing air, this happens in a short time frame. The image shows a cross section of a cold front.
Attached File  Frontal-mixing.jpg (99.56K)
Number of downloads: 11
Here is an example of fronts in the Northern Pacific ocean, notice they are associated or “hooked” into low pressure areas. Argentina has the same patterns however the fronts move in the opposite direction.
Attached File  Fronts-N-Pac.jpg (107.93K)
Number of downloads: 9
2,3. On Wednesday the pressure is rising and on Friday the pressure is dropping. I suspect Thursday was a nice day of skiing.
Attached File  Friday-Press.jpg (85.42K)
Number of downloads: 7
Notice the steep slope of the pressure drop, the time-vs-drop ratio is a good indicator of a high wind event.
Attached File  Press-Drop-slope.jpg (37.6K)
Number of downloads: 3
4. Thursday was calm and Friday at around noon there was a sudden increase in wind.
Attached File  Friday-wind.jpg (99.36K)
Number of downloads: 3
1,3,4. Pressure drop, quick temperature change and sudden high winds are typical winter storm events – this exact scenario is shown in the post above.
Attached File  Friday-WPT.jpg (99.73K)
Number of downloads: 2
5. Sailors many centuries ago recognized sudden direction change indicated a sudden weather change. We now recognize wind direction is linked to pressure fields and pressure field movement. The image below shows steady direction on Thursday with a quick change on Friday around mid-day.
Attached File  Friday-direction.jpg (91.65K)
Number of downloads: 3
3,5. Comparing pressure drop and direction change – another sailor warning for a wind event that will strengthen.
Attached File  Friday-Press-vs-Direct.jpg (67.46K)
Number of downloads: 5
On a larger scale - Looking at pressure imbalance, notice the resort “R” is directly between the low and high pressure areas. The lines shown are zones of equal pressure, notice the change is quite dramatic around the resort area. Tight lines equal strong wind. Take a peek at the direction chart above, notice it shows the same west-northwest wind.
Attached File  Friday-flow.jpg (99.14K)
Number of downloads: 5
Sailors had an idea the weather was pushed by some hidden force – today we recognize that the earth has jet streams that guide much of the large weather systems. Here is a map showing Friday’s jet stream guiding or influencing the pressure systems in this region.
Attached File  Friday-jet.jpg (99.04K)
Number of downloads: 8
Ironically as I am composing this post a large wind event is striking the Pacific area of North America. Same pressure drop, same speeds, opposite direction.
Attached File  Wash-wind.jpg (134.71K)
Number of downloads: 11
High winds smash Santa in Washington.
Attached File  Wash-santa.jpg (97.53K)
Number of downloads: 16
Summarizing this post - Weather station read-outs on Friday would have given good indications for increasing wind during the day. There are no indications that the weather will improve. Old sailors and weather forecasters in the Pacific Northwest would also be recognizing those same signs.
Attached File  Friday-BAD.jpg (98.92K)
Number of downloads: 17

Next ~ Do ski lift manufacturers have guidelines for operating in wind conditions?
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#19 Kelly

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Posted 15 December 2014 - 08:00 AM

(click on thumbnail images to open a larger image)
Up to this point we have examples that use different types of science or mechanical solutions to analyze the events surrounding this incident. We know certain wind conditions bring about chair swing as the pictures show below.
Attached File  swing-1.jpg (88.1K)
Number of downloads: 66 Attached File  swing-2.jpg (96.94K)
Number of downloads: 88
It’s also important to include the manufacturer’s limits, and reasoning for those limits, when operating in windy conditions. Let’s examine a typical operating guideline – this one is for surface lifts from Doppelmayr the parent company of the original manufacturer CTEC.
The guideline for wind operations is quite clear for wind limits and reasons not to run the ropeway. It gives suggested top wind speed and mentions that wind direction should also be considered. It also says these parameters are co-mingled so both have to be considered. (Click on thumbnail image to see text)
Attached File  Surface-lift-limits.jpg (99.91K)
Number of downloads: 75
In a separate paragraph it states that gusts can bring about carrier swing with lower wind speeds (see post #3 swing lever).This implies that the ropeway must be continuously monitored for speed and duration of those gust conditions. This is not some hidden fine print in an addendum – they are using clear and concise language to communicate their reasons for these limits.
Attached File  Wind-limits-2.jpg (99.89K)
Number of downloads: 48
Summarizing this post – the manufacturer sets limits, and says for safe operation, the owner/operator must monitor and not exceed those limits for wind: Speed, Direction, and Gusts.
These are clear and reasonable warnings or expectations when operating in windy environments; they could be stated by any manufacturer.

Next ~ Does this style of chairlift have a hidden design defect? Do manufactures have other designs that might be better suited for high wind conditions? Do owners have solutions for high wind operations?
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#20 Kelly

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Posted 01 January 2015 - 05:57 AM

Agency oversight of chairlifts running in wind conditions
Not mentioned in the last post but many States and Providences in North America have oversight authorities that regulate ropeway operations such as running in wind conditions. This is put in place so there are consequences if you are caught cheating or fudging limits or operation guidelines. Even the United Kingdom’s tiny ski industry has oversight regulations. The image below shows the operation guideline page that declares the owner/operator must adhere to the manufacturer’s limits for wind speed.
Attached File  UK-oversight.jpg (96.69K)
Number of downloads: 30
Design Problems
CTEC is a third generation chairlift, the engineers were well seasoned by the time this chairlift was designed and installed. The quality speaks for itself as the company was seen as a strong competitor and later bought by the Austrian ropeway manufacturer Doppelmayr.

Designs that address wind conditions
Sheaves
For as long as wind and ropeways have existed engineers and ropeway technicians have been modifying and improving designs to better cope with wind. A common modification is to improve groove capture.
Attached File  Groove-resistance.jpg (85.44K)
Number of downloads: 41
A typical modification is to reshape the groove to the original profile or to deepen it resulting in a higher side load. The tool I used in the 1970s to deepen sheave grooves was a Stanley round surform rasp.
Attached File  Surform.jpg (41.44K)
Number of downloads: 42
Manufacturers have different groove design philosophies that attempt to balance: grip clearance, ride smoothness, misalignment tolerance and groove capture.
Attached File  Sheave-liner-profiles.jpg (99.43K)
Number of downloads: 45
This one combines the “V” profile with a groove
Attached File  Partek-liner.jpg (99.37K)
Number of downloads: 43
Curved grip, huge catchers
Attached File  YAN catcher.jpg (161.45K)
Number of downloads: 46
Comparing a 1980s design with a 1860s…different year, same groove.
Attached File  1984-1864.jpg (102.1K)
Number of downloads: 53
Carriers
Early designs were keyed around weight reduction to reduce manufacturing and shipping costs. Built with light seats the center of gravity was high, swing and oscillation can occur at a much lower wind speed with this type of carrier.
Attached File  Dopp-CG.jpg (99.81K)
Number of downloads: 60Attached File  SLI-CG.jpg (78.89K)
Number of downloads: 67
Newer designs are heavier making them more resistant to wind swing.
Attached File  Poma-CG-2000.jpg (99.57K)
Number of downloads: 63
Ropeway Type
Realizing the limitations for reducing swing in chairlifts, ropeway manufacturers have also known that hanging a carrier from two cables makes a more rigid connection for the swing to overcome. Three cable ropeways such as trams and double track gondolas have a higher swing resistance, the carriers are much heavier and actually tilt rather than swing in higher wind conditions.
Attached File  P-to-P-3S.jpg (97.46K)
Number of downloads: 56
An even greater resistance can be realized by spreading the ropes apart eliminating the pivot point for side swing. This manufacturer’s brochure advertizes the superior resistance to side swing and states this design can run in 100 km/h winds. The name Funitel is a combination of the French words funiculaire and telepherique or tracked larger cabin ropeway.
Attached File  Funitel.jpg (98.35K)
Number of downloads: 56
The design and idea goes back a number of decades, this one was made by YAN in the 1980s, called a QMC (Quad Mono Cable).
Attached File  YAN-QMC-Lift-line.jpg (98.71K)
Number of downloads: 75
Squaw Valley has the only funitel in the U.S. - Running along the side of a ridge that can see high winds, this ropeway has to run at capacity as it feeds the upper mountain complex of 15 chairlifts and also has to have the ability to download at 100% capacity in low snow conditions.
Attached File  Squaw-Funi.jpg (97.09K)
Number of downloads: 87
Owner Solutions
At another California resort, Mammoth Mt. and Yan designed this wind shelter for Chair 23. The carriers are allowed to swing mid-span.
Attached File  23-A.jpg (98.23K)
Number of downloads: 85Attached File  23-B.jpg (98.36K)
Number of downloads: 85Attached File  23-C.jpg (98.52K)
Number of downloads: 90
Long span tower placement for avalanche paths also has the added benefit of putting more weight on each sheave resulting in a higher groove reaction for wind capture.
Attached File  23-D.jpg (96.93K)
Number of downloads: 76

Summarizing – The owner of this ski area had purchased a ropeway that is documented to run in winds up to around 40 mph or lower if gusts existed. From the pictures supplied no design modifications existed for higher wind operation.

Next ~ Stop switches, the inside story.
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