Category: Engineering

Some links: 93

Reversible

Carol Vogel reports on the restoration of the Metropolitan Museum of Art’s Adam, a 15th-century marble by Tullio Lombardo, which is again on display. The sculpture was smashed into dozens of pieces when its supporting pedestal gave way, in 2002. Vogel notes “a new attitude adopted by museums around the world to share such innovative work not just professionally but with the public,” although concerns had been expressed (as reported by Randy Kennedy in 2010) about the slowness of the reconstruction as well as lack of media access. In any event, now that the sculpture is back, the museum has produced an impressive suite of videos summarizing the story.

Related: Restoration of a Mark Rothko.

Flying

The Old River Control Auxiliary Structure is a rank of seven towers, each buff with a white crown. They are vertical on the upstream side, and they slope toward the Atchafalaya. Therefore, they resemble flying buttresses facing the Mississippi. The towers are separated by six arciform gates, convex to the Mississippi, and hinged in trunnion blocks secured with steel to carom the force of the river into the core of the structure. Lifted by cables, these tainter gates, as they are called, are about as light and graceful as anything could be that has a composite weight of twenty-six hundred tons. Each of them is sixty-two feet wide. They are the strongest the Corps has ever designed and built. A work of engineering such as a Maillart bridge or a bridge by Christian Menn can outdo some other works of art, because it is not only a gift to the imagination but also structural in the matrix of the world. The auxiliary structure at Old River contains too many working components to be classed with such a bridge, but in grandeur and in profile it would not shame a pharaoh.

—John McPhee, “Atchafalaya” (1989)

Cool running

Jonathan Erickson’s recent newsletter post for Dr. Dobb’s highlights a couple of the low-tech water development projects of Engineers without Borders: specifically, projects to bring clean drinking water to two villages in Honduras, designed and managed by USC students Liana Ching and Jackie Reed. Their scheme rests on

…a pair of 10,000-gallon storage tank[s] with a chlorination system (via tablets) upstream, away from the pollution.

But designing a system that would work in a remote village with no electricity is no small feat. The design they eventually came up with is a self-sustaining dam and water pump that uses paddles to carry water to a tank before it gets distributed by pipes to the villages.

“The students had to learn from scratch,” says Mansour Rahimi, their advisor and an associate professor of industrial and systems engineering. “There is no software, no tables or books on this.” Dana Sherman, a senior lecturer also in the industrial and systems engineering department, added that “the project involves so much more than just designing and installing a pump system…[it also involves] implementing a system that does not require consistent or difficult maintenance.”

Wildlife and wind power in California

The California Energy Commission has adopted a set of voluntary guidelines for wind power projects in the state, as reported by The Birding Community E-Bulletin. The document’s abstract:

These voluntary guidelines provide information to help reduce impacts to birds and bats
from new development or repowering of wind energy projects in California. They
include recommendations on preliminary screening of proposed wind energy project
sites; pre-permitting study design and methods; assessing direct, indirect, and
cumulative impacts to birds and bats in accordance with state and federal laws;
developing avoidance and minimization measures; establishing appropriate
compensatory mitigation; and post-construction operations monitoring, analysis, and
reporting methods.

The guidelines were developed in conjunction with the California Department of Fish and Game.

Squeezed

Suhas Sreedhar explains why the old Bruce Springsteen CDs that I’ve ripped sound so much quieter than newer tracks. The dynamic range of CDs (as opposed to vinyl) and digital signal compression technology made it happen.

In the 1980s, CDs were mastered so that songs generally peaked at about -6 dBFS [0 decibels full scale, the loudest point of the dynamic range] with their root mean square (RMS)—or average levels—hovering around -20 dBFS to -18 dBFS. As multidisc CD changers began to gain prominence in households toward the end of the decade, the same jukebox-type loudness competition started all over again as record companies wanted their CDs to stick out more than their competitors’. By the end of the 1980s, songs on CDs were amplified to the point where their peaks started pushing the loudness limit of 0 dBFS. At this point, the only way to raise the average levels of songs without having their loudest parts clipped—the digital equivalent of distortion, where information is lost because it exceeds the bit capacity—was to compress the peaks.

And as music players become smaller and more rugged (I moved from a sports-model water-resistant Walkman to a hard-drive-based iPod and aspire to a solid-state one), we’re taking them more places with us and we expect the music to be there. Music on the subway as the train rumbles through a tunnel is a commonplace now.

But the problem doesn’t just lie on the production end. If people are listening to songs in a noisy environment—such as in their cars, on trains, in airport waiting rooms, at work, or in a dormitory—the music needs to be louder to compensate. Dynamic-range compression does just that and more. Not only does it raise the average loudness of the song, but by doing so it eliminates all the quiet moments of a song as well. So listeners are now able to hear the entire song above the noise without getting frustrated by any inaudible low parts.

This might be one of the biggest reasons why most people are completely unaware of the loss of dynamics in modern music. They are listening to songs in less-than-ideal environments on a constant basis. But many listeners have subconsciously felt the effects of overcompressed songs in the form of auditory fatigue, where it actually becomes tiring to continue listening to the music.

Wildlife & Wind Energy Conference

Wind power isn’t quite the unambiguously benign source of electricity that some have made it out to be—for example, the author of the article for Worldchanging. That’s our big takeaway from the Wildlife & Wind Energy Conference, hosted by the Geography Department of Kutztown University and organized by Donald S. Heintzelman. It was perhaps fitting that attendees encountered blustery weather conditions enroute to the venue, located in Berks County, Pennsylvania, in the Appalachian Mountains, not far from the renowned Hawk Mountain Sanctuary.

The first surprising thing that I learned is how large a state-of-the-art wind turbine is. A typical wind turbine is rated at 1.5 MW, stands 70 meters tall, and its three blades span a diameter of approximately 50 meters. Perhaps, then, it’s not surprising that many consider a row of these turbines arranged along a ridgeline to be a blot on the landscape, although I find the monopole towers supporting three thin blades to be one of the more graceful engineered objects that you might encounter: certainly more attractive than a bristling microwave tower or spiderly powerline structure. The language we use to describe a wind generation facility has become politicized: while supporters popularize the term “wind farm,” cons favor “wind plant.” Finally, most troubling is that wind turbines pose a real threat to flying wildlife, primarily birds and bats. And hence the conference.

Unfortunately, the sessions appeared to be designed more to muster opposition to new wind projects in Pennsylvania and elsewhere in the Appalachians than to entertain a wide spectrum of viewpoints. Two speakers from government were briefly heard, plus a last-minute replacement, out of more than two dozen speakers on the printed agenda, and no industry or trade association officials spoke. Q&A time was given short shrift. We heard from citizen scientists but no engineers.

And it’s too bad, because almost everyone agrees that not only is mortality from collisions with the turbines a serious problem, but also that there’s very little good science that’s been done to understand exactly how serious it is, and why. What’s worse, operators of controversial facilities like Mountaineer Wind Energy Center in West Virginia, after suffering bad publicity from reports of bat kills, have restricted access by researchers to their sites. We didn’t learn at this conference how wind turbine mortality differs from kills at stationary communications towers. We know something, but not a lot, about the different effects on migrating and foraging wildlife, on raptors, songbirds, and bats. We have some anecdotal evidence about the effects of weather: fog and low ceilings can exacerbate. Likewise, it was suggested that quiet-running, preferred by human neighbors, may pose more of a wildlife hazard. What research has been done into mortality is disputed: how do we know that field searchers have found all the carcasses before scavengers have?

More than one speaker struck a defiant NIMBY attitude, among them Laura Jackson of a Bedford County grassroots organization. Speakers cast longing looks at the development potential for Chesapeake Bay and offshore wind farms, but no one spoke about the possible effects on marine mammals, birds, and amphibians.

The most pragmatic notes were sounded by David Riposo, master’s candidate at the University of Maryland’s Marine, Estuarine, and Environmental Science Department, who cited Pacala and Socolow’s “stabilization wedges” concept, which concludes that wind power is but one of many measures that need to be taken to address looming climate change problems; and by Michael Fry of the American Bird Conservancy. The ABC hosted a two-day workshop in 2004, and has taken a qualified positive policy stance on wind power, and Fry’s remarks focused on mitigation and incremental improvements.

Also noteworthy was a last-minute speaker from the Government Accountability Office, who provided hard copies of a September, 2005 report that I haven’t finished digesting. She noted that a National Academy of Sciences report was due for publication in January, 2007. One of the points made by the GAO report, and amplified by other speakers, is that the federal government has a limited role in regulating wind power development. In many states, the burden of oversight falls to counties and municipalities.