- #211
Baluncore
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It is not your prerogative to invalidate the literature of science, by demanding your personal terminology replace that employed for the last century.
With just a few minutes of googling, I easily find references (with my emphasis added) that directly contradict your "appropriate distinctions".Squizzie said:I suggest that the term 'detonation phase' be reserved for the brief, supersonic 'Hugoniot' phase, while 'blast wave' is more appropriately used for the extended sonic 'Friedlander phase' due to these distinctions.
I see no reason to do this, especially since the term 'phase' can be and is used to mark the distinctions. The term 'blast wave' appears to be a more general term for how the resulting shock wave and field flow is generated, with the aforementioned phases used to describe the different parts of the blast wave.Squizzie said:I suggest that the term 'detonation phase' be reserved for the brief, supersonic 'Hugoniot' phase, while 'blast wave' is more appropriately used for the extended sonic 'Friedlander phase' due to these distinctions.
While the term 'blast wave' is commonly used to describe the entire phenomenon, it's important to recognize that the blast wave actually consists of two distinct phases, each with its own unique characteristics of propagation speed and pressure profile.Drakkith said:I see no reason to do this, especially since the term 'phase' can be and is used to mark the distinctions. The term 'blast wave' appears to be a more general term for how the resulting shock wave and field flow is generated, with the aforementioned phases used to describe the different parts of the blast wave.
Please use the standard terminology in discussing this topic.
You keep claiming this but you haven't answered my request from post #212. Again I implore you: please support your claim by posting references that explicitly define this "second phase" of a blast wave and explicitly state that the propagation velocity of a blast wave rapidly decays to, and then continues to propagate at, a constant speed of Mach 1. Or is this really just a personal interpretation of what you've read?Squizzie said:While the term 'blast wave' is commonly used to describe the entire phenomenon, it's important to recognize that the blast wave actually consists of two distinct phases, each with its own unique characteristics of propagation speed and pressure profile.
The first phase is characterised by a very high initial propagation speed which decays within milliseconds to the speed of sound, with an abrupt pressure rise, while the second phase exhibits a slower, more gradual decay in pressure and a constant propagation speed.
May I direct your attention to my post #206, where I presented a plot featuring data sets from three reputable sources? I have adopted a log scale for both axes in order to accommodate the vast scale range of the two co-ordinates.renormalize said:You keep claiming this but you haven't answered my request from post #212. Again I implore you: please support your claim by posting references that explicitly define this "second phase" of a blast wave and explicitly state that the propagation velocity of a blast wave rapidly decays to, and then continues to propagate at, a constant speed of Mach 1. Or is this really just a personal interpretation of what you've read?
The Rankine–Hugoniot conditions, describe and model the pressure step transition at one point, only as the shock front pressure rises. The blast-wave air-movement that follows the shock front, is not covered by that analysis.Squizzie said:I suggest that the term 'detonation phase' be reserved for the brief, supersonic 'Hugoniot' phase, while 'blast wave' is more appropriately used for the extended sonic 'Friedlander phase' due to these distinctions.
That's a plot you made. I ask for the original references, not filtered through your personal interpretation, that explicitly state that 1) there are two phases of blast waves and 2) the second phase propagates at a constant Mach 1.Squizzie said:May I direct your attention to my post #206, where I presented a plot featuring data sets from three reputable sources? I have adopted a log scale for both axes in order to accommodate the vast scale range of the two co-ordinates.
Look, I don't really care what else you call it, but trying to use 'blast wave' to describe only one part of the process, when it is commonly used to describe the entire thing from creation to dissipation, is only going to generate confusion.Squizzie said:Unfortunately, a standardised terminology for each of these phases is lacking, introducing challenges into discussions about the speed of a blast wave.
From my reading, the blast wave quickly decays to the speed of sound in the (unheated, uncompressed) medium. You can check the links I posted previously in post #90.renormalize said:You keep claiming this but you haven't answered my request from post #212. Again I implore you: please support your claim by posting references that explicitly define this "second phase" of a blast wave and explicitly state that the propagation velocity of a blast wave rapidly decays to, and then continues to propagate at, a constant speed of Mach 1. Or is this really just a personal interpretation of what you've read?
I agree, except that, according to the quotes in post #212, a propagating atmospheric disturbance is not called a "blast wave" once it slows to the ambient speed of sound. It's no longer a "blast wave" because it is no longer accompanied by significant pressure excursions, else it wouldn't be in "ambient conditions". The disturbance becomes an ordinary high-amplitude sound wave. That's why I ask @Squizzie to cite some references that uses "blast wave" to label a sonic-speed disturbance in ambient conditions.Drakkith said:From my reading, the blast wave quickly decays to the speed of sound in the (unheated, uncompressed) medium. You can check the links I posted previously in post #90.
Yes, you are correct, but in the absence of any other terminology, my approach has been to restrict my use of "blast wave" it to the much longer phase once it has decayed to the speed of sound. It is that phase that Kinney & Graham discuss in Ch 6. "Blast Waves".Drakkith said:Look, I don't really care what else you call it, but trying to use 'blast wave' to describe only one part of the process, when it is commonly used to describe the entire thing from creation to dissipation, is only going to generate confusion.
From my reading, the blast wave quickly decays to the speed of sound in the (unheated, uncompressed) medium. You can check the links I posted previously in post #90.
I'd also like to remind people that communication is a two-way street. Describing and explaining phenomena is often difficult, even with the proper terminology readily available, and it is often more beneficial to take the time to try to understand what someone is trying to say versus taking what they typed out at literal value. Also, there is no harm in agreeing on a 'temporary' set of terms to use for a discussion if such a thing is warranted.
The blast wave appears to undergo an exponential decay towards the speed of sound, and I'm wondering if the shock front is sustained for a significant amount of time very close to the speed of sound before finally transitioning to a regular sound wave. I have yet to see anything in any of the sources I've read in this thread seen anything about when/where/how this transition occurs. That leads me to believe that the blast wave remains a blast wave for a pretty long time/distance and the transition to a sound wave is not particularly important. But that's a guess on my part.renormalize said:I agree, except that, according to the quotes in post #212, a propagating atmospheric disturbance is not called a "blast wave" once it slows to the ambient speed of sound. It's no longer a "blast wave" because it is no longer accompanied by significant pressure excursions, else it wouldn't be in "ambient conditions". The disturbance becomes an ordinary high-amplitude sound wave. That's why I ask @Squizzie to cite some references that uses "blast wave" to label a sonic-speed disturbance in ambient conditions.
I have yet to see anything that made any effort to use 'blast wave' differently in the two phases, so I would highly recommend not doing that. If you really need to label the two phases, perhaps 'early' and 'late' phases would be do, or "supersonic' and 'near-sonic', or something similar.Squizzie said:Yes, you are correct, but in the absence of any other terminology, my approach has been to restrict my use of "blast wave" it to the much longer phase once it has decayed to the speed of sound. It is that phase that Kinney & Graham discuss in Ch 6. "Blast Waves".
The shock front decays exponentially as it heats air, at the same time as it is attenuated by the inverse square law.Drakkith said:The blast wave appears to undergo an exponential decay towards the speed of sound, and I'm wondering if the shock front is sustained for a significant amount of time very close to the speed of sound before finally transitioning to a regular sound wave.
There is no clear point where the transition occurs. The two velocity modes are feathered together. I would expect reflections to make the transition quite patchy near the ground.Drakkith said:I have yet to see anything in any of the sources I've read in this thread seen anything about when/where/how this transition occurs.
By computing the speed between each pair of data points using Vi = (Zi - Zi-1) / (ti- ti-1) with the provided data, you will observe a consistent interval speed of 340 m/s from 70 metres to 500 metres.Baluncore said:Gilbert F. Kinney and Kenneth J. Graham - Explosive Shocks in Air. 2'nd Edn. 1985.
Table XI, page 254, shows one kilogram of TNT as being supersonic to beyond 500 metres. From 100 m to 500 m, the velocity falls by only 0.2%.
I do not understand why you are differentiating the data when the Mach number is given.Squizzie said:By computing the speed between each pair of data points using Vi = (Zi - Zi-1) / (ti- ti-1) with the provided data, you will observe a consistent interval speed of 340 m/s from 70 metres to 500 metres.
They give the accurate velocity as a Mack number in the Mx column.Squizzie said:Could you please provide more details about the meaning and implications of the "only 0.2%" ?
But the difference between Mach 1.003 (at Z=100 m) and Mach 1 ( ~340 m/sec) is 1.02 metres per second. A few degrees of temperature or hectopascals of atmospheric pressure could easily account for those differences in the data.Baluncore said:They give the accurate velocity as a Mack number in the Mx column.
Z = 100 m; Mx = 1.003
Z = 500 m; Mx = 1.001
The difference is only 0.2%, but it is still supersonic at 500 m.
You are seeing numerical round-off noise from the tabulated data in your unnecessary re-computation. That explains why your graph jumps up and down about the speed of sound, while the shock front remains supersonic throughout.
Then you will be unable to work as a scientist in this field.Squizzie said:I'm not convinced that this evidence is sufficient to support the conclusion that the shock front was moving at anything other than Mach 1.
Well, there is also the theory, and I would also say that my plot of the data supports the conclusion.Squizzie said:But the difference between Mach 1.003 (at Z=100 m) and Mach 1 ( ~340 m/sec) is 1.02 metres per second. A few degrees of temperature or hectopascals of atmospheric pressure could easily account for those differences in the data.
I'm not convinced that this evidence is sufficient to support the conclusion that the shock front was moving at anything other than Mach 1.
I think we are both correctly interpreting the data in table XI as it relates to the progress of the shock front as explained on p. 96 of Chapter 6 "Blast Waves":Baluncore said:How can it be a shock front if it is not moving faster than Mach 1.
No. You are proposing the nonstandard interpretation. The responsibility is on your end.Squizzie said:I think we are both correctly interpreting the data in table XI as it relates to the progress of the shock front as explained on p. 96 of Chapter 6 "Blast Waves":
" the peak overpressure values of Table XI also uniquely define the time required for that shock front to travel out to various distances. "
And I have previously identified p. 88 of the same chapter:
"Each individual portion of this pulse moves outward at its own speed, which also is the speed of sound in its own immediate medium. "
So I'm not convinced that your evidence is sufficient to support your contrary conclusion that the shock front was propagating at anything other than steadily at Mach 1 by 100 metres and 280 ms.
Is not Kinney and Graham, from whom I'm drawing my reference, the standard text?Frabjous said:No. You are proposing the nonstandard interpretation. The responsibility is on your end.
Yes, and you are saying that the data they present is wrong. You did not know about it when you started this thread, and now you believe that you can correct it.Squizzie said:Is not Kinney and Graham, from whom I'm drawing my reference, the standard text?
But a shock front is a pressure step that heats the air. It propagates faster in the heated air, so it maintains the step. The shock front must be propagating marginally above Mach 1, to remain as a step.Squizzie said:So I'm not convinced that your evidence is sufficient to support your contrary conclusion that the shock front was propagating at anything other than steadily at Mach 1 by 100 metres and 280 ms.
If you are suggesting that I am contradicting the data in Table XI, I should point out that the"δ(m/s)" and "Mx" values reported in Table XI represent the average speed (Z(m)/ ta), not the interval speed.Frabjous said:Yes, and you are saying that the data they present is wrong.