Theories Discussion > Katabatic wind
The wind plays its own music
WAB:
--- Quote from: Star man on February 24, 2019, 03:44:58 PM ---Thank you Richard and thank you WAB for your responses to my post.
Again the details always seem to raise more questions.
--- End quote ---
It is quite normal situation. It is so be always.
--- Quote from: Star man on February 24, 2019, 03:44:58 PM ---Good luck on your trip WAB. Safe journey to you.
--- End quote ---
Thanks! We very much will try! grin1
As well as in all four previous expeditions … grin1
--- Quote from: Star man on February 24, 2019, 03:44:58 PM --- Are you going to try and take equipment to measure infrasound?
--- End quote ---
It is very painful question for me … Even simply good measuring instrument of noise (or noisemeter) costs not less Э2000 (Euro …. Or ~ $2500 that the same, and for me it is unreal). Therefore I try be use only the appendix to the smart phone in form of program. I understand that it is completely not professional device, but I do not have choice …
There it is possible receive even some spectrograms and almost in the necessary range, but ….
So I need do only that turns out, instead of that I very much would want. Even if it is not absolutely that is most good.
--- Quote from: Star man on February 24, 2019, 03:44:58 PM ---It might be interesting to understand the forces on the tent due to various wind speeds. I will have a look at this when I get some time.
--- End quote ---
It will be interesting for reading …
--- Quote from: Star man on February 24, 2019, 03:44:58 PM ---Regards
star man
--- End quote ---
With not smaller (it is big) respect
WAB
WAB:
--- Quote from: Star man on February 25, 2019, 03:46:56 PM ---I have completed some simple calculations of wind force on the tent. I have used a formular that is used to estimate the wind loading on civil structures. I had broken it down into detail, but for some reason all my text has just vanished so here is the simple version:
F= AxPxCd
A is cross sectional area normal to wind direction
P is the wind pressure = 0.613 x V^2. V is I metres per second
Cd is the drag coefficient which is about 1.4 for a smallish rectangle
At 100 miles per hour the force on the tent would be about 870kg
At 80 miles per hour it would be about 620 Kg
Most of this force would be spread out across th fabric on the side exposed to the wind and also taken up by the tension in the rope and then transmitted to the supports that the rope is attached to.
All in all it doesn't seem that significant. For 100 miles per hour it may have been approaching the limit for the rope but probably not for the tent fabric. If there was a weak point (tears) on the fabric this may have concentrated the force at the corners of these tears causing the material to tear further. It's difficult to say though. The tent supports may have been pulled, but I believe these were still standing when the tent was found. Was the rope still in one piece?
Overall I don't think it looks like it would support the High wind theory. Obviously a reconstruction of the tent in a wind tunnel would be a better test. Does anyone have a wind tunnel available to test the hypothesis?
Regards
Star man
--- End quote ---
Dear Star man!
I will a little specify your calculations.
At first I will copy yours formula how it is accepted in aerodynamics (your formula correct, but little less detailed for understanding):
Fresist = Cx* ro*V2* S/2
Where it is designated
Сх – it is the same as at you Сd = factor of front resistance (without units),
ro - here it is necessary write in Greek letter «ro», but I do not have it in my computer alphabet and I write its in Latin (it is measure kg/m3),
V - speed of stream if it laminar also is absent interface layer(it is measure m/s),
S - the area of cross-section size, just as at you Ax (it is measure м2)
Now we take more real values of the sizes entering into this formula:
1. Cx - for tent it is necessary take that here such:
Lilac colour is designates interface layer, but I will tell about it later.
Therefore Cx cannot be = 1,4 in any way.
For Cube the party directly Cx =
The right extreme column – it is the settlement value, the second on the right - experimental measurements.
For Cube an edge to air stream Cx =
For Hemisphere the basis to air stream Cx =
It will be the maximum value though on experiment in colder conditions for Hemisphere the basis to air stream it was equal Cx = 1,44.
Therefore Cx it is necessary to take = between Cx = Cube the party directly and Cx = Cube an edge to air stream, or between 1,05 and 0,8. We take Cx =0,95. It will be the maximum approach to reality. It is will be dimensionless size.
2.ro – it is air density at the given height from earth level. I do not know whence you took value of density, but for earth level at tо = + 15оС it will be = 1,22 kg/m3, and for height in 1000 m and at tо =-10oC it will be = 1,112 kg/m3
3.V – it is speed of stream. You have 2 values, therefore for 80 mph V = 35,76 m/s, and for 100 mph V = 44,7 m/s
4.S – it is the area. For tent in our case we take on the maximum value, taking into account that the tent has partially been driven in slope as 4 m (it is length) of *1,3 m (it is height taking into account the driven part) = 5,2 м2.
The scheme of the driven tent is:
The tent has not been dug completely. It is not meaningful, and it will be worse for people because it will fall asleep more snow.
Preparation of the same platform in accuracy for tent, video which is made on that place where the tent placed in 1959 is shown on it:
https://drive.google.com/file/d/0B6J-XIhYsx39ZWlHOXkwZmVVbjg/view?usp=sharing
after that the same, platform as it has been made and at Dyatlov group in 1959 (for this purpose has been levelled that the tent bottom would be on more flat place).
These are our experiments in the winter 2014. The temperature was-21…-22o C, the wind was small, approximately as 5 … 7 m/s, “Shura” (Alesander Alekseenkov) has been dressed approximately how many participants of Dyatlov group after have escaped from tent. It was the illustration of possible working capacity of these people below, after place where Zina has been found, but without that they have taken place to this place in the conditions of snowstorm at wind nearby V = 15 … 18 m/s (or approximately 35 pmh).
If made out calculation for these values for 80 mph force of pressure on tent = 3512,34 Н or 358 kgF (forces) turns out, and for 100 mph force of a pressure on tent = 4390,42 Н or 447,54 kgF (forces) turns out.
That "mute" does not coincide with your calculations … grin1
The resume:
- Pressure will be even less because there will be its losses on an interface;
- area of section of tent will be less because is sagging;
- fabric cannot be absolutely rigid; the tent costs not exactly on perpendicular to stream and е. с …
Therefore it is possible draw conclusion, what not loading on tent because of wind was the main reason of that they have escaped from tent …
The reason here exists internal and it is connected with psychology as all participants and group as whole.
WAB:
--- Quote from: sarapuk on February 26, 2019, 11:50:44 AM ---
......................................
A KATABATIC WIND can reach 200 MPH, or hurricane force. And as you correctly say , even for high wind the forces are still survivable. The Dyatlov Tent doesnt appear to have suffered such high forces, making it even less likely that wind played a part in their leaving the Tent.
--- End quote ---
I do not think that were such wind. Because I had possibility feel on myself wind approximately 50 m/s. At such wind, even on flat part of the earth, the man cannot keep vertical position. Even if he bears backpack with the big weight and small resistance to wind. Certainly, their tent at such wind could not keep the form. However it was steady. In 2014 we have made experiment with similar tent on its stability to wind. But today I cannot write any more (at us 3 o'clock in the morning). Next time I will try to show photo with this tent in one day, in 4 days, in 2 weeks and in 3 or 4 weeks. It not we photographed all last photos …
Star man:
--- Quote from: WAB on February 26, 2019, 03:56:21 PM ---
--- Quote from: Star man on February 25, 2019, 03:46:56 PM ---I have completed some simple calculations of wind force on the tent. I have used a formular that is used to estimate the wind loading on civil structures. I had broken it down into detail, but for some reason all my text has just vanished so here is the simple version:
F= AxPxCd
A is cross sectional area normal to wind direction
P is the wind pressure = 0.613 x V^2. V is I metres per second
Cd is the drag coefficient which is about 1.4 for a smallish rectangle
At 100 miles per hour the force on the tent would be about 870kg
At 80 miles per hour it would be about 620 Kg
Most of this force would be spread out across th fabric on the side exposed to the wind and also taken up by the tension in the rope and then transmitted to the supports that the rope is attached to.
All in all it doesn't seem that significant. For 100 miles per hour it may have been approaching the limit for the rope but probably not for the tent fabric. If there was a weak point (tears) on the fabric this may have concentrated the force at the corners of these tears causing the material to tear further. It's difficult to say though. The tent supports may have been pulled, but I believe these were still standing when the tent was found. Was the rope still in one piece?
Overall I don't think it looks like it would support the High wind theory. Obviously a reconstruction of the tent in a wind tunnel would be a better test. Does anyone have a wind tunnel available to test the hypothesis?
Regards
Star man
--- End quote ---
Dear Star man!
I will a little specify your calculations.
At first I will copy yours formula how it is accepted in aerodynamics (your formula correct, but little less detailed for understanding):
Fresist = Cx* ro*V2* S/2
Where it is designated
Сх – it is the same as at you Сd = factor of front resistance (without units),
ro - here it is necessary write in Greek letter «ro», but I do not have it in my computer alphabet and I write its in Latin (it is measure kg/m3),
V - speed of stream if it laminar also is absent interface layer(it is measure m/s),
S - the area of cross-section size, just as at you Ax (it is measure м2)
Now we take more real values of the sizes entering into this formula:
1. Cx - for tent it is necessary take that here such:
Lilac colour is designates interface layer, but I will tell about it later.
Therefore Cx cannot be = 1,4 in any way.
For Cube the party directly Cx =
The right extreme column – it is the settlement value, the second on the right - experimental measurements.
For Cube an edge to air stream Cx =
For Hemisphere the basis to air stream Cx =
It will be the maximum value though on experiment in colder conditions for Hemisphere the basis to air stream it was equal Cx = 1,44.
Therefore Cx it is necessary to take = between Cx = Cube the party directly and Cx = Cube an edge to air stream, or between 1,05 and 0,8. We take Cx =0,95. It will be the maximum approach to reality. It is will be dimensionless size.
2.ro – it is air density at the given height from earth level. I do not know whence you took value of density, but for earth level at tо = + 15оС it will be = 1,22 kg/m3, and for height in 1000 m and at tо =-10oC it will be = 1,112 kg/m3
3.V – it is speed of stream. You have 2 values, therefore for 80 mph V = 35,76 m/s, and for 100 mph V = 44,7 m/s
4.S – it is the area. For tent in our case we take on the maximum value, taking into account that the tent has partially been driven in slope as 4 m (it is length) of *1,3 m (it is height taking into account the driven part) = 5,2 м2.
The scheme of the driven tent is:
The tent has not been dug completely. It is not meaningful, and it will be worse for people because it will fall asleep more snow.
Preparation of the same platform in accuracy for tent, video which is made on that place where the tent placed in 1959 is shown on it:
https://drive.google.com/file/d/0B6J-XIhYsx39ZWlHOXkwZmVVbjg/view?usp=sharing
after that the same, platform as it has been made and at Dyatlov group in 1959 (for this purpose has been levelled that the tent bottom would be on more flat place).
These are our experiments in the winter 2014. The temperature was-21…-22o C, the wind was small, approximately as 5 … 7 m/s, “Shura” (Alesander Alekseenkov) has been dressed approximately how many participants of Dyatlov group after have escaped from tent. It was the illustration of possible working capacity of these people below, after place where Zina has been found, but without that they have taken place to this place in the conditions of snowstorm at wind nearby V = 15 … 18 m/s (or approximately 35 pmh).
If made out calculation for these values for 80 mph force of pressure on tent = 3512,34 Н or 358 kgF (forces) turns out, and for 100 mph force of a pressure on tent = 4390,42 Н or 447,54 kgF (forces) turns out.
That "mute" does not coincide with your calculations … grin1
The resume:
- Pressure will be even less because there will be its losses on an interface;
- area of section of tent will be less because is sagging;
- fabric cannot be absolutely rigid; the tent costs not exactly on perpendicular to stream and е. с …
Therefore it is possible draw conclusion, what not loading on tent because of wind was the main reason of that they have escaped from tent …
The reason here exists internal and it is connected with psychology as all participants and group as whole.
--- End quote ---
Thanks for presenting the more detailed calculation. I am sure it is more accurate.
I used a simple formula to gain a rough idea of the forces and the Cd value is a very rough alignment. I am familiar with the fluid dynamics but was just looking for something simple to understand the credibility of the theory. I think with the same conclusion.
Regards
Star man
WAB:
--- Quote from: Star man on February 27, 2019, 04:57:23 AM ---
...............................
Thanks for presenting the more detailed calculation. I am sure it is more accurate.
--- End quote ---
I am grateful to you that you have not taken offence to my specification, sometimes at forums it understand as desire wound the opponent. I wanted approach understanding of this question to the validity only. Aerodynamics one of components of my speciality.
And I once again am grateful to you that I could look at that I have written earlier. One picture There was gone. It is the scheme of installation of tent on a slope. Here it is image:
Probably I have forgotten insert the reference to it because there were already 2 or 3 o'clock in the night.
I will try insert it into the initial text if still probably edit it.
--- Quote from: Star man on February 27, 2019, 04:57:23 AM --- I think with the same conclusion.
--- End quote ---
It is clear, if people aspire to the end result and at them the understanding is in one channel they will come to the same conclusion.
Planes which develop under the same tasks in the different countries are similar absolutely. Because physics laws are identical in all countries.
--- Quote from: Star man on February 27, 2019, 04:57:23 AM ---Regards
Star man
--- End quote ---
I too yours Regards . grin1
WAB
PS. I have glanced here only for some minutes, therefore I cannot write anything till March, 15th or later.
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