Hydrostatic Shock: Wikipedia Article

[Michael Courtney]

Dr. Amy Courtney assisted me in re-writing the Hydrostatic Shock article on Wikipedia. We believe it is now much improved, with a more complete discussion and more complete reference list.

See:

http://en.wikipedia.org/wiki/Hydrostatic_shock

Thanks,

Michael Courtney

 

[Crash_Test_Dhimmi]

Nice article, But it needs a list of Preferred rounds for my shopping list, er uhmmm for further research.

 

[max popenker]

Forgive my stupidness, but why you call it Hydrostatic when it is caused by shock wave, and therefore is the result of a DYNAMIC process?

 

[geophysicishooter]

I was slighltly dissappoited at the conspicuous absence of any mention of the the wave equation.

Also, according to my learning, the dissapation of wave energy is not exponential. it's a function of 1/r^2 , where r is the (radial) distance from the point of wave origin.

Other than that, I thought it was a good piece.

 

[Red Tornado]

Wow, nice job. That's probalby the most complete and well researched wiki article I've read.
RT

 

[benEzra]

Also, according to my learning, the dissapation of wave energy is not exponential. it's a function of 1/r^2 , where r is the (radial) distance from the point of wave origin.

It may be nonlinear; the exponential model is just an approximation. From the article:

"Lee et al. present an analytical model showing that unreflected ballistic pressure waves are well approximated by an exponential decay, which is similar to blast pressure waves.[23]"

The reference is Lee M, Longoria RG, Wilson DE, "Ballistic Waves in High-Speed Water Entry," Journal of Fluids and Structures, 11, 819-844, 1997. I'd like to find the text of that.

BTW, Dr. Courtney, that is an excellent article, and a very fair treatment of the other side as well, IMO. Kudos to the both of you.

 

[RNB65]

Well written article but it's not clear to me which side of the "light and fast" vs "slow and heavy" debate it favors. Perhaps both are more or less equally effective?
-

 

[Conqueror]

It is somewhat dubious, and IIRC against wikipedia policy, to cite oneself in an academic article. That said, your piece is well-written. Being that the argument is not "settled," the ideal of neutrality might suggest you pay more than brief lip service to those who disagree with your stance.

Good work overall.

 

[Michael Courtney]

It is somewhat dubious, and IIRC against wikipedia policy, to cite oneself in an academic article. That said, your piece is well-written. Being that the argument is not "settled," the ideal of neutrality might suggest you pay more than brief lip service to those who disagree with your stance.

Good work overall.

It is neither dubious nor contrary to wikipedia policy to cite one's own work as long as those works qualify as reliable sources. Scientists cite their own papers all the time.

We do cite several prominent authors (Fackler, Patrick, MacPherson) who have raised objections to remote ballistic pressure wave effects. Much of the internet type of debate on the subject does not meet the Wikipedia standards for reliable sources.

I was slighltly dissappoited at the conspicuous absence of any mention of the the wave equation.

Also, according to my learning, the dissapation of wave energy is not exponential. it's a function of 1/r^2 , where r is the (radial) distance from the point of wave origin.

Other than that, I thought it was a good piece.

The exponential decay is the time dependent part, the spatial dependence is 1/r^2, as you have surmised. We cover this ground in some of our papers, but did not include it in this piece.

Forgive my stupidness, but why you call it Hydrostatic when it is caused by shock wave, and therefore is the result of a DYNAMIC process?

We prefer the term "ballistic pressure wave" but "hydrostatic shock" is the colloquial term that is in wide use and it is the prevailing term in use by joe sixpack for remote effects of the penetrating projectiles.

In fluid physics, the general usage is to describe macroscopic motion of fluids imparted by a sudden pressure pulse as "hydrodynamic shock." If all the fluid motion is microscopic, then the term "hydrostatic shock" is often used since the motion associated with the pressure pulse cannot be easily observed.

I suppose it would be optimally correct to describe the motion of temporary cavitation as "hydrodynamic" and remote pressure wave effects beyond the region of macroscopic motion as "hydrostatic." Chamberlin preferred the term "hydraulic" which is more general and applicable to both.

Wow, nice job. That's probalby the most complete and well researched wiki article I've read.
RT

Thanks.

Michael Courtney

 

[SoCalShooter]

very nice article but this is not going to end the 45acp vs 9mm discussion or the 5.56 vs .308

 

[hankdatank1362]

You guys remind me of why I dropped out of engineering college. Thankyou for reminding me just how out of place I was. I'm much better off in criminal justice classes.

Geez, and to think I had a hard time with thermodynamics / heat transfer classes. :banghead:

 

[Wes Janson]

So, which do you carry...9 or 45? ;P

 

[Michael Courtney]

So, which do you carry...9 or 45? ;P

Dr. Amy Courtney and I both prefer the .357 Sig for our personal uses.

Michael Courtney

 

[Richard.Howe]

Hydrodynamic, guys. Hydrostatic is, well, static. 8 years studying thermofluid physics earns me the right to be persnickety...and everyone's entitled to their own weird pet peeves.

 

[Michael Courtney]

"Hydrostatic" was in widespread colloquial use long before we came to the subject, and we felt that there was too much momentum in the usage of the common man to change the vocabulary over technical details.

In addition, we have seen a number of papers in the physics literature that use the term "hydrostatic" in cases where the wave passes without macroscopic motion of the medium. "Hydrodynamic" seems to be applied when the fluid is in macroscopic (easily detectable) motion.

Thanks,

Michael

 

[antsi]

The debate between bullets that are "light and fast" vs. bullets that are "slow and heavy"

This phrasing strikes me as odd.

Where are the light and fast bullets going to be debating against the slow and heavy bullets? Will the debate be open to the public? What are the bullets going to be debating about?

 

[W.E.G.]

The "ballistic" results showed considerable hydrostatic effect.

 

[st_albert]

It is somewhat dubious, and IIRC against wikipedia policy, to cite oneself in an academic article. That said, your piece is well-written. Being that the argument is not "settled," the ideal of neutrality might suggest you pay more than brief lip service to those who disagree with your stance.

I don't know where you're coming from but it is apparent that you don't know anything about the scientific literature. To "cite oneself" may (though I doubt it) be against Wikipedia policy, but it is certainly NOT against policy in the science literature. In fact, it is expected. And your ideas about "neutrality" are incomprehensible in the scientific context. One cites every relevant peer-reviewed artlcle known to the author, and "res ipsa loquitur."

"What DO they teach them in schools these days?" -- Dr. Digory (C.S.Lewis), circa. 1944

Albert

 

[st_albert]

@ Dr. Courtney: I seem to recall that at some point in the past, you posted some equations that estimated the magnitude of the hydraulic shock that would result from impact of a projectile given its velocity and the diameter of the meplat. I have not been able to find that post (maybe it was on some other forum? but I thought it was here.)

Could you re-post those equations? Thanks!

And a personal comment: Thanks for your patience (here and elsewhere) in dealing with what at times seems to be a "religious" argument between the "fast and light" versus the "slow and heavy" proponents. Although I don't necessarily accept all of your hypotheses, I truly respect your efforts to present the facts as you see them, and remain above the fray vis a vis the "religious" arguments. You have truly taken the high road, IMHO.

Nobody asked, but here's my take on the effect of hydraulic shock in the context of handgun velocities: I remember when I was in 5th grade, being hit by a baseball bat thrown by an over-entheusiastic batter. Yes, I was standing where I shoudn't have been. I got hit in the solar plexus. It didn't penetrate enough to cause even a bruise, and the velocity and kinetic energy were way below that achieved even by a mediocre handgun round, I'm sure. But it sure as heck incapacitated me, momentarily! I've had similar experiences in Karate classes.

So here's what I think. The Great Debate revolves around what you consider to be "incapacitation." One school requires immediate death or permanent paralysis (CNS damage). In this case, impact placement and sufficient penetration are all that matter. Since impact placement is under control of the shooter, only penetration (and to some extent expansion since that increases the probability of effective placement) matters. Call this the "Fackler School" for lack of a better term. In this school of thought, if you succeed in meeting the criteria, the attacker cannot possibly continue. He is, or shortly will be, dead.

On the other hand, another school (call it the St_Albert school... you can see where I'm going) relaxes the concept of incapacitation to where it means "the perp can no longer prosecute the attack." Under this school of thought, any "Fackler" success will also be a success. But there may be other successes also (akin to the baseball bat incident above). But these extra successes are far less certain. What if the perp is high on PCP and could care less about pain? Are there other considerations that would make the perp less vulnerable to hydraulic shock effects? I don't know.

Then there's your argument (as I see it) that hydraulic shock may induce very real and absolute effects in the CNS that can't be "overridden" by drugs such as PCP. If confirmed, that woud support St_albert's hypothesis and move it closer to the "Fackler" school of "incapacitation no matter what."

Personally, prejudicially, I hope you can show that hydraulic effects can indeed induce damage long-range to the CNS.

But even if you don't, the St_albert school will continue to believe that for self defense:

A quality Self-Defense hollowpoint, in any caliber for which it will expand, is preferred;

After that, a blunt projectile at a (relatively) high velocity (thus greater hydraulic shock -- whatever that means) is good;

And always prefer penetration to expansion. (Since my observation is that overpenetration is much less likely than missing the target completely).

OK, I'm putting on my Nomex (T) underwear. Let the discussion begin!

St_Albert

 

[Michael Courtney]

This phrasing strikes me as odd.

Where are the light and fast bullets going to be debating against the slow and heavy bullets? Will the debate be open to the public? What are the bullets going to be debating about?

Very witty. Had me laughing out loud. Thanks for sharing.

Michael

 

[Michael Courtney]

I've been thinking recently about the topic of hydrostatic shock, and I figured I'd go ahead and do a brain dump, with some observations and questions that I have.

High speed projectiles appear to have three distinct effects when hitting an object. We'll assume ballistic gelatin for now, as it's standardized and roughly replicates tissue.

Hydrostatic shock. This is a compression wave that travels through the medium--in other words, a sound wave. And with regards to comments above, water IS slightly compressible, otherwise compression waves would NOT travel through it.

Temporary cavitation. This is tissue that is displaced by the projectile, but springs back. Unlike the compression wave, which travels at the speed of sound in the medium, this is a displacement wave, and travels much slower, though it can readily exceed the speed of the projectile. This effect only exists in elastic mediums, like ballistic gelatin, which will spring back wherever the tensile strength of the material is not exceeded.

Permanent cavitation. This is the hole that remains after the medium comes to rest. This is cause by stressing the material to beyond its elastic limits, typically by direct contact of the projectile, but may also result from remote stretching exceeding the material strength, such as the "splash" of a high speed impact crater.

All of these are demonstrable, and measurable. A hydrophone will measure the hydrostatic shock in μPa, the temporary cavity can be seen in high speed photographs (and its size and speed estimated from them), and the permanent cavity volume is readily measured by filling with fluid, and its perimeter may be estimated if a transparent medium is used. That these phenomena exist is pretty much beyond question. The question is, how much impact does each have in relation to wounding? This is where the issue becomes very murky.

Martin Fackler referred to temporary cavitation as the inertial component of the ballistic pressure wave. So while it is wrong to suppose that the temporary cavity describes everything about ballistic pressure wave effects, it is also incorrect to assert that temporary cavitation is completely distinct from it.

Permanent cavities are sufficient to cause lethal wounds; this can be readily demonstrated by looking at wounds by low velocity penetrations, such as knife wounds and similar mechanical trauma. These impacts produce negligible amounts of hydrostatic shock and temporary cavities, and kill by direct destruction of vital organs and blood loss.

Temporary cavities are more contentious, but are again sufficient to cause lethal wounds. Many organs are relatively inelastic, and can be damaged by stretching; this damage may arguably be called a permanent cavity, and shows up in ballistic gelatin as radial tears along the wound path, largest near the point of entry. A good example of a temporary cavity with little or no hydrostatic shock or permanent cavity is blunt trauma such as a punch to the abdomen. This elastically displaces the tissue, tears blood vessels, and can rupture organs. An example of this is the ruptured appendix said to have claimed Houdini's life.

There will be a pressure wave radiating outward from most blunt impacts, but it is to small to create much effect beyond the expected range of most blunt force trauma. The exception seems to be blunt ballistic impacts (such as bullets stopped by kevlar), where remote wounding effects have been noticed.

Now for the most contentious part, the effect of hydrostatic shock on wounding. Various assertions are made about wave pressures required for incapacitation, ranging from 45 psi to 1500 psi. Information on where the pressure is measured, or how the pressure waves attenuate as they propagate through the body, doesn't seem to be available.

The Suneson et al. papers implanted pressure transducers in the thighs, abdomen, neck, and brain. These experiments show that a local pressure wave magnitude of roughly 1500 PSI can create a remote pressure wave magnitude of roughly 45 PSI in the brain, 18 inches away. Other available data also suggest an average decrease in pressure magnitude of roughly a factor of 30 between the local pressure wave 18 inches or so away and the pressure reaching the brain.

Research from a wide variety of fields demonstrates that pressure magnitudes from 15-30 PSI produce neurological effects in the brain.

The body is not a homogeneous medium, and compression waves reflect and refract significantly at the junction between areas of dissimilar density. This doesn't necessarily cause greater attenuation, however. Just like the internal reflection in an optic fiber, certain conditions in an acoustic medium can reduce attenuation and cause sound to travel much farther than the inverse square law would predict.

The Suneson et al. papers demonstrate this clearly.

Michael Courtney

 

[Michael Courtney]

A lithotripter, according to one reference I found, generates pressure waves on the order of 100 MPa, while the hydrostatic shock causing value of 1500 psi you cite translates to 10 MPa. While some tissue destruction has been shown to happen from lithotripter use, the most significant side effects appear to be greater risk for hypertension and adult onset diabetes, not sudden loss of consciousness. An examination of the methods by which these shockwaves can cause cell damage and hemorrhaging showed that it was due to cavitation, which is caused by negative pressure waves in excess of 1 MPa. This damage was only seen in areas adjacent to the application of the shockwave. Lithotripsy also involves thousands of these 100 MPa shockwaves in a session.

We believe that pressure wave magnitudes from different bullets can reasonably be compared assuming comparable shot placements. However, ballistic pressure wave magnitudes cannot really be directly compared with pressure waves from other sources because other sources have vast differences in wave direction, duration, area, and frequency characteristics.

Lithotriptors have been designed and refined over several decades to break up kidney stones with minimal damage to surrounding tissue. The location of lithotripsy wave is focussed and the direction carefully controlled to minimize damage to soft tissues. Likewise, frequency and duration are also designed not to damage soft tissue.

You simply cannot conclude much about ballistic pressure wave injury or blast pressure wave injury from lithotriptor waves. It is known that a blast pressure wave of 50 PSI will usually result in blast lung and other internal injuries. However, much larger lithotriptor waves cause no such damage.

I recently reviewed a grant proposal suggesting the use of lithotriptor waves to study blast injury. There were some hints that the investigators intended to modify the lithotriptor waves to more closely resemble blast waves and focus the lithotriptors on the tissue under study. In principle, this might be a sound approach to studying injury due to blast pressure wave or ballistic pressure waves. However, in practice, considerable care needs to be taken to assure that the modified lithotriptor waves are an accurate representation of the blast/ballistic waves they are intended to model.

Michael Courtney

 

[Michael Courtney]

None of the cited papers I've looked at claiming to show incapacitation from remote injuries appear to decouple hydrostatic shock (sound waves) from effects caused by the temporary or permanent cavitation, which are both dynamic effects (pushing material around).

Unless you've got an alternate explanation about how permanent and temporary cavitation in the thigh of pigs and dogs causes remote neural damage in the brain, then the Suneson et al. and Wang et al. papers are compelling evidence for remote ballistic pressure wave damage in the brain, since the brain is well beyond the reach of the temporary cavity. Likewise, the Sturtevant paper documents remote CNS injury due to focussing of pressure waves on the spinal cord beyond the reach of the temporary cavity. Yet another paper (ref 36) documents experimental observations of incapacitation and death induced by ballistic pressure waves without a wound channel or temporary cavity.


Michael Courtney

 

[Michael Courtney]

If hydrostatic shock can be shown to be a significant wounding factor, then it should be simple enough to design bullets to maximize the level of hydrostatic shock; certainly there are designs intended to maximize temporal cavities (like the THV and Devel concave ogive bullets) and permanent cavities (like large meplat, flat nosed solids) so there is no reason there could not be a design to maximize hydrostatic shock. Bullet shape will certainly have an effect on hydrostatic shock; just listen to the sound waves generated by a diver entering the water in different ways. The energy and velocity will be the same for a given diver falling the same distance, but the sound levels between a clean, head-first dive and a belly flop will be very different (as will penetration and splash). Based on the diving analogy, I suspect that hydrostatic shock will be strongly coupled to the temporary cavity size.

BPW magnitude and temporary cavity size are highly correlated, as you supposed. This is because both are caused by the instantaneous force between bullet and tissue which is exactly equal to the local rate of the bullets kinetic energy loss, dE/dx.

The challenge for new bullet designs is not just increasing BPW magnitude, but also meeting constraints imposed by penetration requirements, manufacturing costs, and legal requirements. The THV is illegal in the US. The devel was interesting, but the company apparently failed for reasons unrelated to bullet effectiveness.

Michael Courtney

 

[Michael Courtney]

I haven't read the work of Suneson, but if the article writer is explaining it accurately, it's bad science. If you shoot a pig -even an anaesthetised pig- in the leg, well, you'll get a massive spike in intra-cranial pressure (which is what the researcher's transducers are measuring). But you'd get that same spike if you passed a suction catheter down the animals' throat- discomfort causes spikes in ICP.

That's nothing new (and doesn't really justify shooting pigs). It doesn't in itself indicate the presence of a pressure-wave emanating from the axis of injury up to the brain; why didn't the researchers think of placing intra-abdominal and intra-thoracic transducers which would be able to demonstrate the transmission of a pressure-wave?

The Suneson et al. experiments used pressure transducers implanted in both thighs, the abdomen, the soft tissue of the neck, the carotid artery in the neck, and the brain. These experiments demonstrated that the pressure wave propagated from the location of impact (the thigh) to the abdomen, neck, and brain at approximately the speed of sound in water. The pressure waves in the brain were less than a millisecond in duration and comprised of frequencies up to 250 kHz. This is much different from a "discomfort spike." One would also have a difficult time explaining how the proposed "discomfort spike" caused the observed damage in both brain and spinal cord.

Michael Courtney