I've seen small weights on lower-power lines that I've read were some sort of vibration dampeners, and googling
weights on power lines
brings up many interesting threads, perhaps most notably this:
https://en.m.wikipedia.org/wiki/Stockbridge_damper
weights on power lines
brings up many interesting threads, perhaps most notably this:
https://en.m.wikipedia.org/wiki/Stockbridge_damper
Learning all the time benb - thanks for the interesting link!
I've extracted this image showing a modern Stockbridge vibration damper installed on an overhead power cable:
Two of the three major modes of oscillation are called 'gallop' and 'flutter' - names that are right up Steve's street! 😉
I've extracted this image showing a modern Stockbridge vibration damper installed on an overhead power cable:
Two of the three major modes of oscillation are called 'gallop' and 'flutter' - names that are right up Steve's street! 😉
It seems we are dealing with Aeroelasticity, a branch of physics and engineering that studies the interaction between moving fluids and flexible solid bodies.
A Stockbridge vibration damper targets flutter, aka aeolian vibration, which is a dynamic instability of an elastic structure (the cylindrical overhead cable) in a fluid flow (the wind).
The wind induces vortexes which produce low amplitude (conductor diameter) high frequency (5 to 150 Hz) oscillations of the cable.
I believe the oscillations are explainable in terms of the 'von Kármán Vortex Street': https://aerospaceengineeringblog.com/the-von-karman-vortex-street-and-tacoma-narrows-disaster/
Quote: "Each time an eddy is shed from the cylinder, the symmetry of the flow pattern is broken and a difference in pressure is induced between the two sides of the cylinder. The vortex shedding therefore produces alternating sideways forces that can cause sideways oscillations. If the frequency of these oscillations is the same as the natural frequency of the cylinder, then the cylinder will undergo resonant behaviour and start vibrating uncontrollably."
A Stockbridge vibration damper targets flutter, aka aeolian vibration, which is a dynamic instability of an elastic structure (the cylindrical overhead cable) in a fluid flow (the wind).
The wind induces vortexes which produce low amplitude (conductor diameter) high frequency (5 to 150 Hz) oscillations of the cable.
I believe the oscillations are explainable in terms of the 'von Kármán Vortex Street': https://aerospaceengineeringblog.com/the-von-karman-vortex-street-and-tacoma-narrows-disaster/
Quote: "Each time an eddy is shed from the cylinder, the symmetry of the flow pattern is broken and a difference in pressure is induced between the two sides of the cylinder. The vortex shedding therefore produces alternating sideways forces that can cause sideways oscillations. If the frequency of these oscillations is the same as the natural frequency of the cylinder, then the cylinder will undergo resonant behaviour and start vibrating uncontrollably."
There was nothing very unusual in the Spanish weather on Monday... it was a calm day with a gentle Easterly, except around Gibralter where the wind hit a fresh 25 mph easterly due to the usual tunneling effect with the Atlas mountains in Morocco. I thought the whole episode was pitiful. People complaining that they felt "so isolated from the World" when their 'phone packed up for two hours! Time will tell, but likely a knock-on effect of one system tripping an adjacent one. Most useful organisations I have worked for have a Disaster Recovery contingency set up. You know, boxes with charged torches, mobile phones, axes and first aid boxes and a plan to cope with electric doors that should default open in a crisis and can pose security risks, and stuck lifts that need manual winding override.
I was usually the the only person who kept an eye on them, because when you need them, you need them badly. So when we lost power in the Naval Dockyard and the whole of Portsmouth about 7 years ago, we had a radio and torches that worked, and soon found a working coffee machine! You can imagine that all the Naval ships were in hurry to get dockside power back up for about 20 warships, and that is complicated. The single night duty electrician was STRESSED! But a good training exercise, one feels. You find out who is good in a crisis, and who is a waste of space, and, trust me, most people are a waste of space...
Richard Feynman said Star Clusters let us see Gravity at work, and he was right. Here is the Beehive Cluster M44 in Cancer I took last night:
That is Mars on the right which will cross the Beehive on May 5, but the half moon will ruin the photograph. Left is the reddest star in the sky, X Cancri, which is a red supergiant the size of the Earth's orbit and a variable Carbon star varying from mag 5 to 7. The Beehive is about 700 million years old, 700 million LY away, and contains a good mix of stars.
Very different from the newer gassier Pleiades at 100 million years old and 400 LY away:
Also in Cancer is a very faint smudgy cluster called M67. This is 4 Billion years old, 3000 LY away, and has a lot of Sun-like stars, here photographed including infra-red.
https://en.wikipedia.org/wiki/Messier_67
Interestingly most of them rotate in around 27 days like our own, so there is some principle there.
This cluster has lost most of its gaseous mass, down to one tenth the original, presumably through solar winds, But there is also a tendency called mass segregation that has driven away the lighter stars.
Those few of you who understood my rubber ball experiments and calculations will realise that the lighter masses acquire the most speed in interactions.
This goes for mixed gases too, where equipartition of energy means the lighter molecules move faster in a mixed gas,
The overall effect is that clusters tend to disperse, but it is not known if that is how our own star arose.
You see, you are now possibly a trained observer of star clusters, able to see what is going on in time. Not just part of the bovine herd at the trough munching up whatever dull fodder, usually about Black Holes and the monthly bulletins of the imminent collapse of the Standard Model of Physics, the internet throws at you.
I was usually the the only person who kept an eye on them, because when you need them, you need them badly. So when we lost power in the Naval Dockyard and the whole of Portsmouth about 7 years ago, we had a radio and torches that worked, and soon found a working coffee machine! You can imagine that all the Naval ships were in hurry to get dockside power back up for about 20 warships, and that is complicated. The single night duty electrician was STRESSED! But a good training exercise, one feels. You find out who is good in a crisis, and who is a waste of space, and, trust me, most people are a waste of space...
Richard Feynman said Star Clusters let us see Gravity at work, and he was right. Here is the Beehive Cluster M44 in Cancer I took last night:
That is Mars on the right which will cross the Beehive on May 5, but the half moon will ruin the photograph. Left is the reddest star in the sky, X Cancri, which is a red supergiant the size of the Earth's orbit and a variable Carbon star varying from mag 5 to 7. The Beehive is about 700 million years old, 700 million LY away, and contains a good mix of stars.
Very different from the newer gassier Pleiades at 100 million years old and 400 LY away:
Also in Cancer is a very faint smudgy cluster called M67. This is 4 Billion years old, 3000 LY away, and has a lot of Sun-like stars, here photographed including infra-red.
https://en.wikipedia.org/wiki/Messier_67
Interestingly most of them rotate in around 27 days like our own, so there is some principle there.
This cluster has lost most of its gaseous mass, down to one tenth the original, presumably through solar winds, But there is also a tendency called mass segregation that has driven away the lighter stars.
Those few of you who understood my rubber ball experiments and calculations will realise that the lighter masses acquire the most speed in interactions.
This goes for mixed gases too, where equipartition of energy means the lighter molecules move faster in a mixed gas,
The overall effect is that clusters tend to disperse, but it is not known if that is how our own star arose.
You see, you are now possibly a trained observer of star clusters, able to see what is going on in time. Not just part of the bovine herd at the trough munching up whatever dull fodder, usually about Black Holes and the monthly bulletins of the imminent collapse of the Standard Model of Physics, the internet throws at you.
The range of velocities in a star cluster is known as its velocity dispersion. Because giant molecular clouds that give birth to stars are cold, they have low energy and therefore low velocity dispersions of just a few kilometres per second, which they should pass on to their fledgling stars. This means that the stars of a cluster should all be moving at more or less the same low velocity, which allows their mutual gravity to keep a hold of them for longer.
Overlaid as yellow dots are the locations of over 1000 young stars that make up the newly discovered Ophion family.
However, news is just in of a star cluster named Ophion, where the velocity dispersion is much larger than normal at 20 kilometres per second. With such a high velocity dispersion, Ophion will quickly fly apart. Unlike the Pleiades, which is a tight gaseous cluster of stars that has been around for 100 million years, the Ophian cluster at barely 20 million years old seems to be playing by different rules.
It is possible that supernovae explosions in the vicinity of Ophion have blown away the interstellar gas in the cluster and that losing so much mass in the form of all this gas had a feedback effect, loosening the cluster's hold on its stars.
https://www.sciencenewstoday.org/op...zzle-the-star-family-that-broke-all-the-rules
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This newish 20M-y-o star cluster, "Ophion" seems to be enormous as a sky object. It is 700 LY away but fills about a twentieth of the sky, across many constellations. I read the Paper about the Data Release 3 from the Lagrange2, 1 meter ESA space telescope, Gaia.
It is recently decommisioned after 10 years of excellent observations of our own galaxy, but there is still more data freely available to come for astrophysicists.
The thing seems to be centred on blue Rho Ophiucus above the pretty pentagon in Scorpio which includes red Antares, in a busy direction of the galaxy centre and you would guess it is about 100 LY in extent.
Scorpio is sadly low in the sky in Europe, so a difficult object to photograph. But a rich region that includes Sagittarius A* and a galactic satellite cluster called M54, along with the pink Lagoon gas nebula.
I suppose a lot of the bluer stars are part of this cluster. Perhaps a supernova scattered them and the gas mass, I don't know.
I found this artists impression of our younger galaxy 10 Bn years ago interesting. It is more like Triangulum M33 with lots of pink star forming regions:
Veritasium has lots of interesting videos about supernovae and what happens if one goes off near, say 100LY, from our own star.
And on cosmic timescales this happens quite regularly... 🙁
It is recently decommisioned after 10 years of excellent observations of our own galaxy, but there is still more data freely available to come for astrophysicists.
The thing seems to be centred on blue Rho Ophiucus above the pretty pentagon in Scorpio which includes red Antares, in a busy direction of the galaxy centre and you would guess it is about 100 LY in extent.
Scorpio is sadly low in the sky in Europe, so a difficult object to photograph. But a rich region that includes Sagittarius A* and a galactic satellite cluster called M54, along with the pink Lagoon gas nebula.
I suppose a lot of the bluer stars are part of this cluster. Perhaps a supernova scattered them and the gas mass, I don't know.
I found this artists impression of our younger galaxy 10 Bn years ago interesting. It is more like Triangulum M33 with lots of pink star forming regions:
Veritasium has lots of interesting videos about supernovae and what happens if one goes off near, say 100LY, from our own star.
And on cosmic timescales this happens quite regularly... 🙁
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I haven't watched the Ve video yet, but can refer you to a recent article on how supernovae may have triggered two of Earth's most devastating mass extinctions: https://www.sciencenewstoday.org/co...o-of-earths-most-devastating-mass-extinctions
These are the Ordovician-Silurian extinction around 445 million years ago and the late Devonian extinction approximately 372 million years ago.
Together they annihilated a staggering 60% to 70% of all species on Earth - mostly marine life because at that time life was mainly confined to oceans.
If a supernova explosion were to occur within about 30 light-years of Earth, the human race would basically be f****d! On the bright side, one could regard this event as a 'reset button' that would allow life on Earth to set off on a new evolutionary path.
Personally, I think we have more chance of blowing ourselves to kingdom come than perishing in a supernova detonation!
Goodnight Vienna!
These are the Ordovician-Silurian extinction around 445 million years ago and the late Devonian extinction approximately 372 million years ago.
Together they annihilated a staggering 60% to 70% of all species on Earth - mostly marine life because at that time life was mainly confined to oceans.
If a supernova explosion were to occur within about 30 light-years of Earth, the human race would basically be f****d! On the bright side, one could regard this event as a 'reset button' that would allow life on Earth to set off on a new evolutionary path.
Personally, I think we have more chance of blowing ourselves to kingdom come than perishing in a supernova detonation!
Goodnight Vienna!
My efforts to photograph Mars near the Beehive cluster fell to the last two nights cloudy weather, and the Moon will now be problematic.
About half the Charles Messier "comet like" objects are star clusters, and I have collected quite a few now in a spot the smudge sort of game.
Dear Doctor Becky has been involved in an internet series (The Numberphile team?) about all 110 of them. Here she talks about M44, The Beehive in an interesting way:
It sums up some of the things we have been talking about like mass segregation and how you detect large exoplanets by detecting wobbling star velocities as low as 300m/s.
Fierce mathematics though:
Well by some people's standards anyway, it's not the Dirac Equation.... 🤣
I took in a few of them, and M7 near the tail of Scorpio in that previous picture was used by Jupiter, Pluto and Kuiper Belt asteroid mission "New Horizons" as a LORRI camera check:
Not much chance of a good photo in the UK though. That's right on the horizon.
https://en.wikipedia.org/wiki/New_Horizons
Being an Astrophysicist looks like a great life. A World where people actually know what they are talking about and talk less rubbish than in most walks of life, and some very nifty engineering.
About half the Charles Messier "comet like" objects are star clusters, and I have collected quite a few now in a spot the smudge sort of game.
Dear Doctor Becky has been involved in an internet series (The Numberphile team?) about all 110 of them. Here she talks about M44, The Beehive in an interesting way:
It sums up some of the things we have been talking about like mass segregation and how you detect large exoplanets by detecting wobbling star velocities as low as 300m/s.
Fierce mathematics though:
Well by some people's standards anyway, it's not the Dirac Equation.... 🤣
I took in a few of them, and M7 near the tail of Scorpio in that previous picture was used by Jupiter, Pluto and Kuiper Belt asteroid mission "New Horizons" as a LORRI camera check:
Not much chance of a good photo in the UK though. That's right on the horizon.
https://en.wikipedia.org/wiki/New_Horizons
Being an Astrophysicist looks like a great life. A World where people actually know what they are talking about and talk less rubbish than in most walks of life, and some very nifty engineering.
Dr. Becky is an excellent communicator! Her video contains cool stuff on 'Hot Jupiters'.
A Hot Jupiter is Jupiter-like gas giant that orbits very close to its parent star, making the exoplanet hot and the star wobble.
https://simple.wikipedia.org/wiki/Hot_Jupiter
A 'year' on a typical Hot Jupiter lasts hours, or at most a few days. For comparison, Mercury takes almost three months to complete one orbit around the Sun.
As more and more Hot Jupiters are detected, our solar system, once thought to be the norm, is starting to seem like a misfit.
BBC talking rot this month... shocking. 🙁
Sophia Herod seems a nice weather forecaster, but had me scratching my head after remarks about this being a good time to spot the centre of the galaxy and Eta Aquarid (Halley's Comet) meteors tomorrow morning:
But a conjunction of Mars, Moon and Venus 22-24 May? Whatever is she talking about? They are nowhere near each other. I know Mars is in the Beehive with the Moon right now, and Venus is a morning star.
Ah, I think the video is two years old:
From which we can calculate that Mars orbits every 23 Months... 😎
Sophia Herod seems a nice weather forecaster, but had me scratching my head after remarks about this being a good time to spot the centre of the galaxy and Eta Aquarid (Halley's Comet) meteors tomorrow morning:
But a conjunction of Mars, Moon and Venus 22-24 May? Whatever is she talking about? They are nowhere near each other. I know Mars is in the Beehive with the Moon right now, and Venus is a morning star.
Ah, I think the video is two years old:
From which we can calculate that Mars orbits every 23 Months... 😎
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Because the radiant of the Eta Aquarid meteors is in the Water Jar of the Aquarius constellation, they are best observed in the Southern Hemisphere where they are considered to constitute the best meteor shower of the year.
Aquarius Constellation
I believe that here in the UK the Aquarids will appear to radiate from a position low on the eastern horizon and, at best, we might expect to see about 10 meteors per hour.
The meteor shower peaks on Tuesday morning (May 6th). https://www.space.com/stargazing/me...at-to-expect-from-the-crumbs-of-halleys-comet
Aquarius Constellation
I believe that here in the UK the Aquarids will appear to radiate from a position low on the eastern horizon and, at best, we might expect to see about 10 meteors per hour.
The meteor shower peaks on Tuesday morning (May 6th). https://www.space.com/stargazing/me...at-to-expect-from-the-crumbs-of-halleys-comet
The way Sabine said "Weyl gravity" sounded to me like "Wild gravity", which would actually appear to be an apt title for the new theory paper! 😉
Although she repeatedly uses the phrase "Let's be open minded", Sabine is forced to conclude that the new hypothesis is "mathematically wrong" and "makes no physical sense whatsoever".
That's telling them!
