Wednesday, September 30, 2009

A landmark paper in physical modeling.


A groundbreaking physical modeling study was published this week in PNAS (subscription required). NSF has a press release here. Christian Braudrick and others at EPS-Berkeley used a 17m flume filled with a mix of lithic and plastic particles to achieve what they call "the successful experimental generation of a lateral migrating, bedload-dominated, meandering channel with repeated cutoffs."
Using the lithic/plastic sediment mix, and stopping flow periodically to replant alfalfa used to create hydraulic roughness and bank cohesion, they created a remarkable simulation of river behavior over a 136 hour run. The photo above shows the remarkable resemblance of the channel and floodplain to a larger fluvial system.
Building on Bill Dietrich’s work on meandering and bedload transport through bends, the authors observed that matching outside bank erosion rates to bar deposition was critical, and that fine sediments (in this case the plastic particles) were necessary to fill in the chutes that form between point bars and the higher floodplain to allow the bar surface to build as channel migration occurred. Very good stuff that beautifully matches with my observations of our models and what happens in real rivers.
I’ve been immersed in this topic lately, so this paper was a very timely and pleasant surprise. Especially since the authors used plastic media similar to that in our Emriver models and concluded that their scaling, both geometrical and temporal, of roughly 1/50 to 1/100 produced realistic results.
Just yesterday (!) I arrived at a similar scale conclusions based on Reynolds number analysis and measurements of our models: Our Em4 is capable of scaling small streams (e.g., with a 7m bankfull width) at 1/50. At this scale the media particles would scale to a D50 of ~40mm (same as the paper). We’re still working on the alfalfa issue (and cohesive banks), but clearly this research supports use of models like our Em4 for research on real world rivers. The figure below shows how Reynolds numbers for a small real world stream would scale to a physical model; below 1/75 or so the distortion is reasonable and you can expect fully turbulent flow and a decent Froude relationship.
The authors addressed time scales in some detail in the suppliments to the paper--very good stuff, because that's been nearly ignored in the engineering literature on modeling because most of that work uses models that are not time-dependent.
You can see a movie of the experiment at PNAC, apparently not behind a paywall, here.
The paper’s title is Experimental evidence for the conditions necessary to sustain meandering in coarse-bedded rivers; authors are Christian Braudrick, William Dietrich, Glen T. Leverichb, and Leonard Sklarb.
Photo NSF and PNAC.

Sunday, September 27, 2009

Approaching the elegance of an insect.




The NY Times published an article on insect aerodynamics last week (and also a beautiful photo series featuring recent science photos).

I've been immersed in micro-hydraulics for a few weeks now. Our Emriver models work in this realm of centimeter-deep flows and low Reynolds numbers. I've been going through the literature trying to make sense of it. No small feat; authors can't even agree on basic things, and most of the work's in engineering, with severely restricted experiments, not freely meandering channels like the ones we use. I keep going back to Steven Vogel's wonderful book Life in Moving Fluids. Vogel explains these things much better than the engineers who write about hydraulic modeling do.

The Times article scientists used a combination of mathematical models and tethered insets in wind tunnels. While there is much work to be done on the use of low density plastic media in river models, I argue that the mathematical models are not any better at prediction. Which is one of the reasons we keep building the physical ones. And because they're a lot more fun.

From the Times article:
The researchers suggest there is a lesson in this for engineers who are trying to develop tiny flying vehicles that mimic insects. Camber and the ability to twist while flapping are the keys to success, they say. But insects are far advanced when it comes to wing materials that can flap and twist thousands of times without cracking or tearing. The researchers note in the paper that it may be difficult for engineers “even to approach the elegance of an insect.”
I'd argue the workings of an alluvial river are certainly as complex as an insects wings, and we have a long way to go in our understanding, and need all the tools we can find.

Photo from the article in Science.

Sunday, September 20, 2009

Em4 installation at St. Louis University.



We installed an Emriver Em4 model at the St. Louis University (SLU) Department of Earth and Atmospheric Sciences on Friday.

Several faculty members there are interested in the model. Since we're only two hours away, and there really is no substitute for seeing the model firsthand, I decided to loan it to them for for a trial run.

The model sits on the third floor of Maclwane Hall, with a beautiful view to the east and north, including the Arch. Despite the three story climb for the 4m x 1.5 meter box (bottom photo) the installation went without a hitch.

As is always the case, everybody was wowed. These models are magnificent tools.

We worked with faculty in the Department of Earth and Atmospheric Sciences to arrange this, including David Kirchner and Ana Londono, who joined SLU last year.

Ana (second photo, center) is shown teaching her first class only an hour after the model became operational.

We're very excited about this, and hope SLU will decide to give this Em4 a permanent home. They're close enough for collaborative work, and SLU is in a great geographical location for workshops on movable bed models that we hope to initiate next year.

We'll be visiting again next week for a meeting with interested faculty.

SLU has a rich history. The department of geophysics (renamed in 1969) was founded as the first in the western hemisphere in 1925.

Update:  Google Maps location of the lab and model here.  If you're driving, best to park in the Laclede Garage on the east side of Grand Ave.

Friday, September 11, 2009

Extreme accomplishment at LRRD.

I haven't done an update in a while, so fans of LRRD, here goes:

We have several potential Em4 clients now, and are very excited to be installing one at a university in Missouri next week (can't quite say who yet). We designed the Em4 to be adapted to both museums and academic teaching/research, and it's getting attention in both areas. We're now working with a museum developer for the Science Museum of Minnesota on an Em4 museum variant. We've also made contact with a Danish firm that can help us get models to the EU.

We've had great reviews on the Em4 installed at Winona State. (They also have six Em2s. All NSF-funded.) Toby Dogwiler and Cathy Summa there have done a wonderful job of teaching with the models. We're anxiously waiting for formal reviews--what we've heard so far is very encouraging. A nice article on their lab here.

We now have 50 Em2 models in the wild. Here's a map showing where they live. Aside from warm reviews from users, I'm happy to know we got the engineering right--except for a couple of bad pumps, we've had zero parts, safety, or other user problems. And, from user polling, no suggestions for improvements. This is what 20 years of careful tweaking yields!

Budgets seem to have recovered a bit from the panic of last fall and winter, and we've had many orders this year. And, overall, the economy has picked up. We narrowly missed NSF funding this spring, disappointing because there was stimulus money available. I can't think of a small business who could put it to better use.

We've made so many contacts this year--we have a long list of people interested in the Em2 model who're limited by the economy or waiting for the new fiscal year. And we've connected with many scientists who're interested in the models and collaborative research and curriculum development. Our visit to the American Fisheries Society (AFS) national meeting in Nashville last week was very encouraging--the biologists who need to educate stakeholders can see the great potential our Em2 models have to do this.


It's a great lift to get out of the office and meet literally hundreds of people who're fascinated with our models. We're looking forward to doing this again soon at the Portland meeting of the Geological Society of American (GSA) in October. I'm giving a talk there on use of plastic media in geoscience models.


Our new business manager, Stephanie Rhodes, is transforming much of the way we work, especially with her marketing savvy.

In the consulting/research arena, we're talking with the managers of the Cache River in southern Illinois about directing research at this Ramsar site, which is a geologically and biologically unique. This site will also feature in work done by SIUC's new $3.2 million NSF-IGERT program. Many of our SIUC collaborators are working on this project, and we're happy they've gained this funding. I hope to soon be adjunct in three departments at SIUC, adding Geology to Geography and Zoology.

Things are looking up, partly from the economic recovery, and also because of our hard work making connections, writing grants, continuing R&D, and marketing of our wonderful river models.

Bottom photo, taken about this time in 2008, of Jesse and Cara and the first Em4 model. Top photo full caption/credit for the photo above: Winona State University Geoscience majors Kristen Dieterman, left, and Valerie Johnson examine how water can form a river on one of the Emriver stream tables in WSU’s flume laboratory in the Science Learning Center. (Katie Derus)

Tuesday, September 1, 2009

LRRD at AFS Nashville.




We're at the annual meeting of the American Fisheries Society (AFS) in Nashville now. Though the depressed economy has attendance down to about 1,500 (half last year's), we're having a great time. Our booth, featuring an Emriver Em2, is getting a lot of attention.

Fish biologists are fun. They face huge challenges--aquatic ecosystems are integrators of human impact, and suffer accordingly--but the fisheries scientists and management biologists I've known do this hard work with a good attitude.

Cara's doing a wonderful job, as always, and my wife Kate's here to help as well, which makes me very happy.

We've made many new connections and I've reconnected with clients I haven't seen in years. And we've enjoyed talking to the many international students and scientists.

And of course we've been mobbed with excited visitors the whole time!