Gulf Oil Spill Velocimetry-Based Flow Rate Estimate


by russ_watters
Tags: estimate, flow, gulf, rate, spill, velocimetrybased
russ_watters
russ_watters is offline
#1
May18-10, 08:51 PM
Mentor
P: 21,999
In the thread in P&WA on the issue of the oil spill, I expressed my skepticism that the rate of the spill could be accurately measured via analysis of underwater video clips. That skepticism was strengthened by the recent statement by Prof Steven Wereley, the originator of the first such estimate, that his earlier estimate was "consderably" low, despite his previous claim of a 20% margin for error. So I'd like to gain a better understanding of his method and if it is reasonable to believe it can be accurate in this case.

For background information....
Here is the wiki on particle image velocimetry: http://en.wikipedia.org/wiki/Particle_image_velocimetry
Here is the Wereley's 1998 patent on the subject: http://patft.uspto.gov/netacgi/nph-P...ND+velocimetry
Here is Wereley's 2006 patent on the subject: http://patft.uspto.gov/netacgi/nph-P...ND+velocimetry
Phys.Org News Partner Science news on Phys.org
Better thermal-imaging lens from waste sulfur
Hackathon team's GoogolPlex gives Siri extra powers
Bright points in Sun's atmosphere mark patterns deep in its interior
magpies
magpies is offline
#2
May18-10, 09:03 PM
P: 229
Well here is the problem so far I have only seen clips from one of the places the oil is leaking and it looks like a ton of oil is coming out. However I heard from cnn that there are multiple places the oil is leaking from. If I could see all the places the oil is coming from I would just add about how much oil is coming out at any moment and then just do the math to figure out how much should have came out factoring for that the oil probably came out faster as more pressure when the oilfield first started to leak. I mean im not totally sure the people in charge of this even know the main places it's leaking. I heard someone suggest droping an atomic bomb down there to try and seal it up however at that pressure im not sure what an atom bomb will do to seal anything. I saw a video on how to extract oil from water with straw. It might be a good idea to buy some straw for your drinking water in the far future depending on how bad this gets.
russ_watters
russ_watters is offline
#3
May18-10, 09:10 PM
Mentor
P: 21,999
The primary source of skepticism about this method could be accurately applied to the gulf oil spill is the quality of the video. The video is low resolution and presumably shot at a pretty high shutter speed due to the depth, which presumably would make it very difficult to lock-on to particles and track them to measure their velocity.

Here's the primary claim from the first patent:
1. A method of measuring motion within a fluid body comprising the steps of: (a) injecting a plurality of solid particles into the fluid body in dispersed relation to move therewith; (b) applying a short pulse of light through an objective lens to the fluid body so as to broadly illuminate the fluid body, and then repeating the application of the light pulse after a known time delay; (c) after each pulse of the applied light, observing through the same objective lens the light scattered from the individual solid particles; (d) wherein only light from the solid particles lying within the depth of field of the objective lens will produce well-focused discrete images of discrete particles, thereby determining a two-dimensional measurement plane in the flowing fluid; and (e) comparing discrete images of discrete particles successively observed in the measurement plane as a function of time to determine the motion of the fluid body.
This says that the method uses depth of field effects of photography to ensure you can focus on a thin plane of particles injected into the fluid stream and a strobe light operating on the nanosecond range to illuminate discrete particles. Neither of those conditions are available in this video and they seem to me to be pretty important and specific requirements.

The 2003 patent appears to me to be a microscopic version of the same thing.

From a company specializing in the technique:
Particle Image Velocimetry (PIV) measures whole velocity fields by taking two images shortly after each other and calculating the distance individual particles travelled within this time. From the known time difference and the measured displacement the velocity is calculated. Since the flow can be quite fast one has to avoid blurred images and that‘s one reason to use laser pulses. They are only 6-10 ns long and freeze any motion. The other reason is that only laser light can be focused into a thin enough light sheet so that only particles in that plane are imaged. Otherwise the scattered light from particles in other planes would make this measurement impossible. A special camera is utilized so that it can store the first image (frame) fast enough to be ready for the second exposure. The "dead" time between the frames when the camera is "blind" is very short down to 100 ns.

magpies
magpies is offline
#4
May18-10, 09:25 PM
P: 229

Gulf Oil Spill Velocimetry-Based Flow Rate Estimate


If I could get my hands on the size of the oilfield I could probably just figure it out by factoring for the size of the pipe the oil travels out of with all pressures and stuff...
mheslep
mheslep is offline
#5
May19-10, 06:08 PM
PF Gold
P: 3,021
Quote Quote by russ_watters View Post
Here is the Wereley's 1998 patent on the subject:
Here is Wereley's 2006 patent on the subject:
From the 2006 patent:
(b) applying a short pulse of light through an objective lens to the fluid body so as to broadly illuminate the fluid body, and then repeating the application of the light pulse after a known time delay;
So the patented method is not applicable, as it requires active controlled illumination.
IcedEcliptic
IcedEcliptic is offline
#6
May19-10, 08:53 PM
P: 274
Perhaps you could see he would be willing to address these concerns here? You never know, and his info is available at the Purdue U site https://engineering.purdue.edu/Engr/...ource_id=11641 . Divining what his methodology is from, a 12 and 4 year old patent respectively seems to be more amusing than scientific.

How does this square with a similar estimate using pencil and paper by Chiang? In addition, when we know that surface estimates are meaningless in the presence of deep plumes, and the use of dispersants at such a depth?

Quote Quote by May 13th article
BP has said repeatedly that there is no reliable way to measure the oil spill in the Gulf of Mexico by looking at the oil gushing out of the pipe. But scientists say there are actually many proven techniques for doing just that.

Steven Wereley, an associate professor of mechanical engineering at Purdue University, analyzed videotape of the seafloor gusher using a technique called particle image velocimetry.

A computer program simply tracks particles and calculates how fast they are moving. Wereley put the BP video of the gusher into his computer. He made a few simple calculations and came up with an astonishing value for the rate of the oil spill: 70,000 barrels a day -- much higher than the official estimate of 5,000 barrels a day.

The method is accurate to a degree of plus or minus 20 percent.


Given that uncertainty, the amount of material spewing from the pipe could range from 56,000 barrels to 84,000 barrels a day. It is important to note that it's not all oil. The short video BP released starts out with a shot of methane, but at the end it seems to be mostly oil.


"There's potentially some fluctuation back and forth between methane and oil," Wereley said.

But assuming that the lion's share of the material coming out of the pipe is oil, Wereley's calculations show that the official estimates are too low.

"We're talking more than a factor-of-10 difference between what I calculate and the number that's being thrown around," he said.

At least two other calculations support him.

Timothy Crone, an associate research scientist at the Lamont-Doherty Earth Observatory, used another well-accepted method to calculate fluid flows. Crone arrived at a similar figure, but he said he'd like better video from BP before drawing a firm conclusion.

Eugene Chiang, a professor of astrophysics at the University of California, Berkeley, also got a similar answer, using just pencil and paper.

Without even having a sense of scale from the BP video, he correctly deduced that the diameter of the pipe was about 20 inches. And though his calculation is less precise than Wereley's, it is in the same ballpark.


"I would peg it at around 20,000 to 100,000 barrels per day," he said.

Chiang called the current estimate of 5,000 barrels a day "almost certainly incorrect."

Given this flow rate, it seems this is a spill of unprecedented proportions in U.S. waters.

"It would just take a few days, at most a week, for it to exceed the Exxon Valdez's record," Chiang said.

BP disputed these figures.

"We've said all along that there's no way to estimate the flow coming out of the pipe accurately," said Bill Salvin, a BP spokesman.

Instead, BP prefers to rely on measurements of oil on the sea surface made by the Coast Guard and the National Oceanic and Atmospheric Administration. Those are also contentious. Salvin also says these analyses should not assume that the oil is spewing from the 21-inch pipe, called a riser, shown in the video.

"The drill pipe, from which the oil is rising, is actually a 9-inch pipe that rests within the riser," Slavin said.


But Wereley says that fact doesn't skew his calculation. And though scientists say they hope BP will eventually release more video and information so they can refine their estimates, what they have now is good enough.


"It's possible to get a pretty decent number by looking at the video," Wereley said.
On the technical side, mheslep is simply wrong, in that the method requires this laser pulse. It is PREFERABLE, and necessary to achieve the desired sub-pixel accuracy. Note then, that Wereley's figures differ from controlled PIV confidence in assemblymen by orders of magnitude.

Quote Quote by Wikipedia regarding accuracy of PIV
Displacement can typically be accurate down to 10% of one pixel on the image plane.
Clearly this was not achieved in the absence of markers added, or a controlled pulse or binocular setup. That reduces accuracy, but does not necessarily invalidate the estimate as offered, nor the conclusion that surface estimates are grossly misleading by comparison. Perhaps if BP or the USCG would allow the addition of a small number of markers, this could be achieved. One wonders why this has yet to occur given that we are hours away from this having been an issue for a month.
gwangi
gwangi is offline
#7
May20-10, 06:31 PM
P: 4
I'm new here and unfamiliar with the rules on specificity to subject matter being discussed so please excuse me for introducing a tangential question about the oil leak. I recently asked this question in Earth forum but it seems I should have asked it here.
According to news media sources the vast majority of the oil is either slowly settling to the bottom, billowing around at various depths, or slowly surfacing. Nobody seems to know.
I've been thinking that the potential impact of the leak would depend on the answer.
I've been wondering how much the density of the crude is affected by the pressures at that depth. These long chain hydrocarbons are subject to compressibility so density should increase. But, enough to keep the stuff down there?
My tech college math skills are thirty years unused and not in the engineering field, so basically I'm a layman.

came across this but I'm unsure of how to apply it, or even whether it's pertinent to the question:
http://www.engineeringtoolbox.com/bu...ity-d_585.html

Can anyone tell how the pressure is affecting the density of the stuff?
Q_Goest
Q_Goest is offline
#8
May20-10, 07:27 PM
Sci Advisor
HW Helper
PF Gold
Q_Goest's Avatar
P: 2,878
Hi gwangi,
Quote Quote by gwangi View Post
According to news media sources the vast majority of the oil is either slowly settling to the bottom, billowing around at various depths, or slowly surfacing. Nobody seems to know.
I've been thinking that the potential impact of the leak would depend on the answer.
I've been wondering how much the density of the crude is affected by the pressures at that depth. These long chain hydrocarbons are subject to compressibility so density should increase. But, enough to keep the stuff down there?
Interesting question. Petroleum is of course, a mixture of various hydrocarbons, and I have no idea what hydrocarbons are being released but I suspect it is fair to say they are relatively heavy with carbon chains in the neighborhood of 15 to 25 carbons. Let's assume the carbon chains follow the general rule CnH2n+2 and look at a couple of different hydrocarbons at 2500 psia and 40 F. There are reports of tar balls washing ashore, so I'll include an even heavier hydrocarbon. Here's what the density looks like:
C16H34: 34 lb/ft3
C24H50: 50 lb/ft3
C30H62: 52 lb/ft3

From this, it looks like these hydrocarbons are less dense than seawater, so they should come to the surface. Why is there a layer of these hydrocarbons reported deep under the surface? I don't know...
IcedEcliptic
IcedEcliptic is offline
#9
May20-10, 07:32 PM
P: 274
Quote Quote by Q_Goest View Post
Hi gwangi,

Interesting question. Petroleum is of course, a mixture of various hydrocarbons, and I have no idea what hydrocarbons are being released but I suspect it is fair to say they are relatively heavy with carbon chains in the neighborhood of 15 to 25 carbons. Let's assume the carbon chains follow the general rule CnH2n+2 and look at a couple of different hydrocarbons at 2500 psia and 40 F. There are reports of tar balls washing ashore, so I'll include an even heavier hydrocarbon. Here's what the density looks like:
C16H34: 34 lb/ft3
C24H50: 50 lb/ft3
C30H62: 52 lb/ft3

From this, it looks like these hydrocarbons are less dense than seawater, so they should come to the surface. Why is there a layer of these hydrocarbons reported deep under the surface? I don't know...
The temperatures and introduction of dispersants have been implicated, but it is still uncertain. There seems to be the range from "sheen" to "tar" and the mayonnaise-like slick in between. Hopefully congress will demand a public analysis of what BP is siphoning so we can have a better idea of how to answer these questions. The disaster has occurred, we must at least learn from this.
mheslep
mheslep is offline
#10
May20-10, 08:24 PM
PF Gold
P: 3,021
Quote Quote by Q_Goest View Post
Hi gwangi,

Interesting question. Petroleum is of course, a mixture of various hydrocarbons, and I have no idea what hydrocarbons are being released but I suspect it is fair to say they are relatively heavy with carbon chains in the neighborhood of 15 to 25 carbons. Let's assume the carbon chains follow the general rule CnH2n+2 ...
Apparently naphthenes are the majority share of petroleum; they follow CnH2(n+1-g) with g the number of H rings, and would thus be a little less dense - C24H48 and so on.
mheslep
mheslep is offline
#11
May20-10, 08:54 PM
PF Gold
P: 3,021
Apparently the traditional standard spill model used is the Worldwide Oil Spill Model (WOSM)
http://ieeexplore.ieee.org/stamp/sta...umber=00607708
russ_watters
russ_watters is offline
#12
May21-10, 12:26 PM
Mentor
P: 21,999
From my post in the politics forum, here are the differences I see between the measurement methods he's patented and what is available to him with the gulf spill:

1. Low-speed photography, using a standard camera.
2. Poor light source (no laser or strobe light).
3. Opaque fluid.
4. No pre-selected, suspended particles.
5. No specialized depth-of-field focusing.
6. Uncertain opening size (even if he got the size right, breaking-off a pipe can change the geometry of the outlet).
7. Unstable flow.
8. Uncertain and inconsistent mixture of liquid and gas.
9. Uncertain camera angle.
russ_watters
russ_watters is offline
#13
May21-10, 12:29 PM
Mentor
P: 21,999
Quote Quote by IcedEcliptic View Post
Perhaps you could see he would be willing to address these concerns here? You never know, and his info is available at the Purdue U site https://engineering.purdue.edu/Engr/...ource_id=11641 . Divining what his methodology is from, a 12 and 4 year old patent respectively seems to be more amusing than scientific.
I'm trying to understand/assess the method he used to measure the flow rate. That is the purpose of this thread. A link to his homepage is not helpful.
On the technical side, mheslep is simply wrong, in that the method requires this laser pulse. It is PREFERABLE, and necessary to achieve the desired sub-pixel accuracy.
Do you have a source for that?
Clearly this was not achieved in the absence of markers added, or a controlled pulse or binocular setup. That reduces accuracy, but does not necessarily invalidate the estimate as offered, nor the conclusion that surface estimates are grossly misleading by comparison.
Do you have a source for that?

What I'm searching for myself is for any reference that says it is possible to do the measurements without such features, not personal opinions of laypeople that it should still be possible.
IcedEcliptic
IcedEcliptic is offline
#14
May21-10, 12:31 PM
P: 274
Quote Quote by russ_watters View Post
From my post in the politics forum, here are the differences I see between the measurement methods he's patented and what is available to him with the gulf spill:

1. Low-speed photography, using a standard camera.
2. Poor light source (no laser or strobe light).
3. Opaque fluid.
4. No pre-selected, suspended particles.
5. No specialized depth-of-field focusing.
6. Uncertain opening size (even if he got the size right, breaking-off a pipe can change the geometry of the outlet).
7. Unstable flow.
8. Uncertain and inconsistent mixture of liquid and gas.
9. Uncertain camera angle.
There are at least 8 cameras in place, and there is a binocular method. Your reasons certainly explain why a method that usually has significant sub-pixel resolution yielded a result with more leeway than accuracy, but it does not invalidate the method. The presentation by the media has been flawed, and one can argue that Wereley is to blame for that in part if that is pleasing.

I still wonder, with so many ROVs and so much access, why is the US government, BP, and other not using test particles in the effluent and reaching averages? This would seem to be critical in any attempt to back-fill, given the need to understand the pressures involved.
russ_watters
russ_watters is offline
#15
May21-10, 12:40 PM
Mentor
P: 21,999
Quote Quote by IcedEcliptic View Post
Your reasons certainly explain why a method that usually has significant sub-pixel resolution yielded a result with more leeway than accuracy, but it does not invalidate the method.
What method? I've found no reference anywhere to a method existing to do what is being suggested Wereley did. Do you have one?
The presentation by the media has been flawed....
What method? Flawed how? Can you explain exactly what he's doing and if there is any precedent for the method?
IcedEcliptic
IcedEcliptic is offline
#16
May21-10, 12:49 PM
P: 274
Quote Quote by russ_watters View Post
What method? I've found no reference anywhere to a method existing to do what is being suggested Wereley did. Do you have one? What method? Flawed how? Can you explain exactly what he's doing and if there is any precedent for the method?
I'm afraid that without you having read the relevant book, and piracy being illegal, it would be difficult. For the flaws in the media presentation, your own posts have been more than adequate in that regard, in the 'politics' thread as you say it.
.FastEddy.
.FastEddy. is offline
#17
May21-10, 01:12 PM
P: 2
The method does not image single particles nor track the movement of single particles.

The field of view is segmented and Auto-correlation is performed on Fourier transforms of "snapshots" of assemblies of particles at different times to extract flow fields - so the particles are used as markers for the bulk fluid flow.

In this case, I assume, the frames are used instead of laser flash illumination.

Auto-correlation in Fourier space has a similar effect to confocal imaging, it decreases the depth of focus of the conventional image (preferentially weights the contribution of particles that are exatly at the plane of focus).
mheslep
mheslep is offline
#18
May21-10, 01:52 PM
PF Gold
P: 3,021
Regarding the eight cameras, I'd not heard that, but Wereley's stated he made his estimate from the same single grainy video we have all seen.

Without an operable valve upstream of the leak, and a pump that can over come the leak pressure, inserting any tracers into the flow must be nearly impossible.


Register to reply

Related Discussions
The new Hubble rate estimate of 74 means a new critical density. Cosmology 10
Calculate the individual flow rate - based on the pressure drop? Mechanical Engineering 0
Inferring quantity based on changing repitition rate Set Theory, Logic, Probability, Statistics 3
Estimate for the liquid flow-rate into a gas scrubber Materials & Chemical Engineering 2
Theoretical Deposition Rate based on RPM -- Help ARRGGG!! General Engineering 11