Students explore sustainable building with bamboo


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LAST FALL, two undergraduates approached Sigrid Adriaenssens, an associate professor of civil and environmental engineering, about working together on their senior-thesis projects, from different angles.

Lu Lu, who is from Chongqing, China, wanted to work on sustainable construction with a focus on design and digital modeling. Russell Archer, who is from East Orange, New Jersey, wanted to physically test building materials. Adriaenssens served as the adviser for both students, who graduated in 2016.

With the help of a graduate student in Adriaenssens’ lab, the seniors identified a partner, the Administrative Department of Environmental Management (DAGMA), in Cali, Colombia. The students and the group collaborated on a project involving bamboo architecture and construction — the entrance canopy to a park to be used by schoolchildren.

Bamboo grows quickly and is lightweight but strong. It has been used as a building material for centuries, but little engineering analysis has been done on it. Lu focused on the structural form of the canopy, and Archer analyzed the effectiveness of the fishmouth joints used in the designs.

Last March, with funding from the School of Engineering and Applied Science, they traveled to Cali to meet with the DAGMA architects and engineers, share their results, and inform the design and construction of the bamboo canopy.

“I couldn’t have imagined I would be traveling to Colombia,” said Archer, who plans to pursue a master’s degree in structural engineering. “I’m really impressed by the broadness of the entire project.”

“I really enjoyed this project because engineering is not only hard-core science — you calculate something but that’s it,” Lu said. “There’s a very strong social component.”

–By the Office of Communications

CITIES: Resilient • Adaptable • Livable • Smart

Innovations in building materials, design, water systems and power grids are helping to make cities more livable, say researchers in Princeton’s School of Engineering and Applied Science

By Bennett McIntosh

Cities. They sprawl and tangle, juxtaposing ancient public squares and glistening skyscrapers. They provide homes for half of humanity, and economic and cultural centers for the rest.

It has taken us thousands of years to build today’s urban centers, and yet, they’re expected to double in land-area in just the next few decades. “Half the urban infrastructure we will be using in 2050 has not yet been built,” said Elie Bou-Zeid, a Princeton associate professor of civil and environmental engineering.

Though this growth is inevitable, the way these cities will expand is not. Rather than repeat the sprawling and uncoordinated development patterns of the past, researchers like Bou-Zeid and others in Princeton’s School of Engineering and Applied Science are exploring new ways to build urban infrastructures to serve our growing population, changing civilization and warming planet.

These intelligent cities will require buildings that heat and cool themselves on a limited energy budget. They’ll require bridges and other infrastructure built with the flexibility to adapt to a changing global climate and rising sea levels. And they’ll require innovations in the networks that supply cities with water and energy. These ideas — from new building materials to continent-spanning electrical grids — have the potential to shift urban development away from the present-day jumble of strip malls, suburbs and shantytowns toward the resilient cities of the future.

Clever buildings

The basic unit of these smarter, resilient cities is the intelligent building. Assistant Professor Forrest Meggers, who has a background in architecture and engineering, has a number of plans for making buildings smarter about how they heat and cool their indoor spaces. Often these heating and cooling systems involve water, which readily absorbs heat that is then shed through evaporation.

In one structure called the Thermoheliodome, the interior is coated with mirrors at odd angles to reflect heat toward water-cooled pipes. In another, the interior cools itself with evaporation through an external membrane that traps liquid water while allowing water vapor to escape. By demonstrating the effectiveness of these innovative ideas, Meggers, who has a joint appointment in the School of Architecture and the Andlinger Center for Energy and the Environment, hopes to show other architects that it is possible to make more effective and more attractive heating and cooling systems.

Meggers’ structures take advantage of two different ways heat is transferred: It can be carried by molecules of warm air or water, or it can radiate like light directly from surface to surface. Thermometers, which measure air temperature, don’t capture the effects that radiative heating and cooling can have on a building’s occupants, so Meggers developed a radiative heat-sensing camera. About the size of a thermostat, the camera captures a 360-degree view that researchers can use to build a 3-D model of the radiative surfaces in any room.

To investigate urban radiant-heat exchanges, Meggers’ students took similar devices to New York City, about 50 miles northeast of Princeton. The resulting thermal photographs enabled them to see how heat lingers in alleyways and clusters around window-mounted air conditioners. By seeing the heat, architects and engineers can improve their designs for optimal energy efficiency.

Optimal cooling is the goal of one project that Meggers collaborated on with Dorit Aviv, who earned her master’s degree in architecture in 2013 and is now a doctoral student at Princeton. The building is called the Cool Oculus and is designed to keep cool in the desert heat through a combination of evaporation and shifting shape. The researchers built the Cool Oculus as a prototype on the Princeton campus, and have secured a grant from the New York-based Tides Foundation to build a full-scale model and measure its capabilities.

During a hot day, mist flows into the Oculus’ central chimney and evaporates to cool the air within, which sinks as a refreshing breeze into the building. Meanwhile, the structure’s foundation absorbs excess heat, which it releases at night when the chimney widens to expose the foundation to the cool night sky. Combined, these effects can turn 100-degree desert heat into a comfortable 75 degrees.

Inspired by nature

The Oculus moves on a daily cycle, but Sigrid Adriaenssens, an associate professor of civil and environmental engineering, has designed structures whose real-time response to heat is built into the material itself. In a transparent case above her desk, Adriaenssens displays three structures that could pass for the leaves of a cyborg Venus flytrap. They each are made of white translucent shells curving off a central metallic strut.

The resemblance to a flytrap is not coincidental. Adriaenssens designed the structures with inspiration from the waterwheel plant, an aquatic cousin of the flytrap. This shape allows the entire structure to open or close in response to a small movement of the central strut. The strut, in turn, is made of two metals that expand differently when heated, so the shell expands significantly with a small increase in temperature. Adriaenssens envisions that these shells, which were developed with funding from the Andlinger Center for Energy and the Environment, could cover a building’s entire façade. On hot days, the shells would expand and block heat from streaming in through the windows.

Structures like these, which make clever use of materials and their form, will be the key to affordable and efficient structures in future cities, according to Adriaenssens. To make these structures, Adriaenssens and her team use computer simulations to calculate the structure’s optimal form. Like optimized forms in nature, Adriaenssens’ structures often show striking curves, from spiraling earthen garden walls and arching steel footbridges, to shell-shaped pavilions with slats to keep out direct sunlight while allowing in scattered light and breezes. Nor are the spreading leaves Adriaenssens’ only dynamic structure: To protect coastlines from storm surges while keeping them visually uncluttered, she has designed thick elastic spherical membranes that will inflate and press together to hold off the waves.

Water world

Where does the water that surges around Adriaenssens’ barriers go? Where does the water that cools Meggers’ buildings come from? To plan something as complex as a future city’s water system requires not just understanding the interactions between structures like these, but understanding how the structures and the people affect each other. Such an undertaking requires cooperation between researchers from many different fields, and an understanding of the successes and failings of many different cities, according to Bou-Zeid.

Bou-Zeid first grew interested in cities when he was a mechanical engineering undergraduate at the American University of Beirut in Lebanon. “I thought I would be designing racecars or airplanes, but environmental problems that involve the interaction of humans with their surroundings are more interesting,” he said. During his graduate and postdoctoral studies, Bou-Zeid investigated how cities — with their skyscraper-created wind canyons and their innumerable sources of heat and steam — fundamentally alter the movement of air around them.

Bou-Zeid is interested in how this airflow affects an invisible but critical part of cities’ water systems: evaporation. Before a city is built, water evaporates out of plants and earth, cooling the area. But in built-up areas, dark asphalt absorbs heat. Water flows off impermeable pavement into storm systems before it has the chance to evaporate and take heat away with it, trapping heat in the buildings and the streets. This trapped heat can warm cities by 10 to 15 degrees Fahrenheit higher than the surrounding countryside. The so-called urban heat island raises energy consumption and contributes to climate change as we burn fossil fuels to cool ourselves.

Parks, greenbelts and green roofs covered in plants can solve this problem by encouraging cooling through evaporation, Bou-Zeid said. But it is not as simple as planting trees: While Baltimore’s greenbelts have cooled it significantly, drier cities like Denver and Phoenix may be better off saving water by cooling with traditional air conditioning. “How do you compare the value of a gallon of water and a kilowatt-hour of energy in different cities?” Bou-Zeid asked.

Bou-Zeid’s attempts to answer this question, and similar studies by other researchers in every aspect of the water cycle, led to the formation of the Urban Water Innovation Network. The Network, supported by a five-year grant from the National Science Foundation, includes engineers, architects and social scientists from 14 institutions who are studying how six American cities interact with water. Bou-Zeid, Princeton’s team lead for the network, is working with colleagues at the University of Maryland and Arizona State University to create software that will model everything water can do in a city. Such software could be used to predict the benefit of new water projects while accounting for local climate and geology.

The wildest possible experiments

To ensure that the urban landscape is accurately represented in such simulations, professor James Smith is leading a team of researchers from five universities in the network to produce extremely accurate maps of the rainfall and flooding in each of the cities. For Smith, the William and Edna Macaleer Professor of Engineering and Applied Science and professor of civil and environmental engineering, such studies of real cities are the only way to understand urbanization’s present and future effects.

“In cities,” he said, “the wildest possible experiments are being carried out for you.” Rivers are rerouted. Vast tracts of land are paved over. Artificial shorelines and skylines change the flow of water and air. It is up to researchers to watch and learn from these unprecedented alterations to the land and environment.

Collaboration within the network leads in surprising directions. Meggers, also a member of the network, found a way to combine his interest in efficient heat transfer with the water systems. With Sybil Sharvelle, a professor at Colorado State University, he is designing wastewater systems that recapture the heat from showers and other uses of hot water.

When the project ends in 2020, the network will release a report detailing its findings and recommendations for the cities under study. The research covers an environmentally diverse collection of cities so that the suggestions can be useful to cities across the country and, in some cases, around the world. In the meantime, the network connects researchers and government officials to craft individual recommendations on short-term projects. “We ask the policymakers what they need to know, and try to understand their constraints so that our recommendations can be implemented,” Bou-Zeid said.

It’s not the first time Bou-Zeid has worked to make small, efficient changes to cities. Simply painting black roofs white so that they reflect more light keeps buildings cooler and saves energy and money.

New York City has implemented this idea via their °CoolRoofs program, through which thousands of volunteers have painted roofs white since 2009. These efforts provided Bou-Zeid with more data than he could ever have achieved in a laboratory. He is using data from this experiment in conjunction with his models of urban air and heat flow to determine the cost and energy savings of painting roofs white.

Networks and grids

Painting roofs white is a relatively easy modification to make to a city, but other modifications require a new way of thinking. Our cities are already in need of upgrades to electricity supply and delivery systems. Going forward, our electricity will increasingly come from renewable sources such as solar and wind power, which, while better for the environment, can vary due to wind shifts and cloud cover.

With renewable energy making up only about 10 percent of power production in the United States, this variability is not yet an issue, said Warren Powell, a professor of operations research and financial engineering who studies networks such as electrical grids and transportation systems. “But I see us hitting problems at about 20 percent renewables,” Powell said.

This variability makes it hard to fully replace coal, the traditional workhorse of electricity generation, and natural-gas turbines, which can be ramped up quickly. “When the dust clears in 40 years, we’re still going to have some fossil energy,” Powell said. While large, efficient batteries could store wind and solar power and release it as needed, the marginal cost of battery storage increases as more batteries are added to the grid. “It is going to be hard to fight this curve,” he said.

Changes in how the power grid operates could help. Powell recently began a project in Brazil, where a drought has cut into Brazil’s heavy dependence on hydroelectric power. Powell has begun working with a group of Brazilian power companies to study strategies for managing the variability from the influx of wind power. Because of wind’s variability, this is not simply a matter of replacing one power source with another. Instead, Powell will be supervising the development of Brazil’s first grid model that can closely simulate the variability of wind. This model will be used to develop robust management policies and energy portfolios that would help Brazil optimize an energy system that depends heavily on  wind and solar.

New technologies deployed smartly will help, Powell said. For example, self-driving electrical vehicles can decrease congestion in dense cities and lend their batteries to the electrical grid, selling power when the city needs it most and recharging overnight from the grid’s excess capacity.

Ultimately, these changes in technologies and policy must work within the economic and social constraints of existing cities. Failing to understand and anticipate urban changes and growth leads to not just bad policy, but unenforceable policy, Bou-Zeid said. If a city tries to prevent urban growth, for example, by limiting new housing, the city will often still grow, but in unregulated and unhealthy shantytowns on the periphery. “You must accept urban expansion — you have to work with it,” Bou-Zeid said.

But the size and inertia of cities is an opportunity, too, Meggers said. “Cities have the power to make a change.”

If researchers and policymakers at Princeton and in cities around the world can collaborate, making clever use of form, physics and interacting components as a part of urban planning, then that change will be a positive one.

RESILIENT SHORES: After Sandy, climate scientists and architects explore how to co-exist with rising tides

Coastal Resilience
AFTER THE WIND, RAIN AND WAVES of Hurricane Sandy subsided, many of the modest homes in the Chelsea Heights section of Atlantic City, New Jersey, were filled to their windows with murky water. Residents returned to find roads inundated by the storm surge. Some maneuvered through the streets by boat.

This mode of transport could become more common in neighborhoods like Chelsea Heights as coastal planners rethink how to cope with the increasing risk of hurricane-induced flooding over the coming decades. Rather than seeking to defend buildings and infrastructure from storm surges, a team of architects and climate scientists is exploring a new vision, with an emphasis on living with rising waters. “Every house will be a waterfront house,” said Princeton Associate Professor of Architecture Paul Lewis. “We’re trying to find a way that canals can work their way through and connect each house, so that kayaks and other small boats are able to navigate through the water.”

The researchers aim for no less than a reinvention of flood hazard planning for the East Coast. A new approach, led by Princeton Professor of Architecture Guy Nordenson, rejects the strict dividing line between land and water that coastal planners historically have imposed, favoring the development of “amphibious suburbs” and landscapes that can tolerate periodic floods. These resilient designs can be readily modified as technologies, conditions and climate predictions change.

Discovery2014_CR_textbox1To plan for future flood risks, Princeton climate scientists are using mathematical models of hurricanes to predict storm surge levels over the next century, taking into account the effects of sea level rise at different locations. Four design teams — from Princeton, Harvard University, the City College of New York and the University of Pennsylvania — are using these projections to guide resilience plans for specific sites along the coast: Atlantic City; Narragansett Bay in Rhode Island; New York City’s Jamaica Bay; and Norfolk, Virginia. [See Planning for resilience up and down the coast.]

The designs will serve as a guide for the U.S. Army Corps of Engineers’ North Atlantic Coast Comprehensive Study, a plan to reduce the risk of flood damage to coastal communities, which is due to Congress in January 2015. “The Army Corps understands that they have to revisit what it means to make structures that are resilient,” said Enrique Ramirez, a postdoctoral research associate in architecture at Princeton and the project’s manager. He serves as a liaison between the design teams and Army Corps officials in regional districts.

The idea for the project grew out of Nordenson’s work on a pre-Sandy project to develop creative proposals for adaptation to rising sea levels in New York Harbor. The project culminated in a book, On the Water: Palisade Bay, and a 2010 exhibition, Rising Currents, at the New York City Museum of Modern Art. The proposals included repairing and lengthening existing piers, as well as planting wetlands and building up small islands inside the harbor. “It was forward thinking because we showed that there are benefits to building things in the water,” Nordenson said. Other Princeton contributors to On the Water were engineering professors James Smith and Ning Lin (then a graduate student) and climate scientist Michael Oppenheimer of the Woodrow Wilson School of Public and International Affairs.

Hurricane Sandy heightened the urgency of long-term coastal planning. While advising a New York State commission on future land use strategies, Nordenson began discussing a broader plan for the East Coast with Joseph Vietri of the U.S. Army Corps of Engineers and Nancy Kete of the Rockefeller Foundation. This discussion led to the Structures of Coastal Resilience project, which is funded by the Rockefeller Foundation and began in October 2013. The project is managed by Princeton’s Andlinger Center for Energy and the Environment and will extend resilient design concepts to other coastal regions, as well as integrate hurricane storm surge predictions with projections of local sea level rise.

One of the project’s goals is to encourage a reconsideration of the absolute flood zone boundaries on maps produced by the Federal Emergency Management Agency (FEMA), which determine building code requirements and insurance rates. Climate science shows that the geographical borders of flood risk should be based on the probabilities and outcomes of different storm events, not the placements of artificial levees that may be overtopped by high storm surges. Indeed, many of the homes and businesses ravaged by Hurricane Sandy were not located in flood hazard zones on FEMA’s maps. “Sandy really brought home the message that we have to do a lot better in the future,” said Oppenheimer, the Albert G. Milbank Professor of Geosciences and International Affairs. “Because while we sit here thinking about it, the risk is only increasing.”

Click to enlarge. The low-lying barrier island that is home to Atlantic City is particularly vulnerable to storm surges, especially in parts of the city, such as residential Chelsea Heights, that were built on wetlands. Researchers are exploring ways to make existing neighborhoods (Panel A) more resilient in the face of occasional storm surges. By raising houses, using roads as low levees and letting abandoned lots return to wetland conditions, these neighborhoods can become “amphibious suburbs” (Panel B). A similar approach can be applied to existing canal neighborhoods (Panel C), making them more resilient and tolerant of flooding (Panel D).

Click to enlarge. The low-lying barrier island that is home to Atlantic City is particularly vulnerable to storm surges, especially in parts of the city, such as residential Chelsea Heights, that were built on wetlands. Researchers are exploring ways to make existing neighborhoods (Panel A) more resilient in the face of occasional storm surges. By raising houses, using roads as low levees and letting abandoned lots return to wetland conditions, these neighborhoods can become “amphibious suburbs” (Panel B). A similar approach can be applied to existing canal neighborhoods (Panel C), making them more resilient and tolerant of flooding (Panel D).

Smarter building codes are also needed, according to Lin, an assistant professor of civil and environmental engineering, who heads the effort to predict storm surge levels. Current building code books primarily address earthquake risks. “A tiny few chapters are for wind, and very few pages are for flooding,” Lin said. Large-scale, long-term projects such as levees and seawalls have been the standard approach to coastal protection. But the Coastal Resilience team puts forth a different view, one of coping with occasional flooding rather than fighting it. “We will never be able to prevent such hazards. We can only be prepared to reduce their impact,” Lin said.

Resilient designs call for supporting, revitalizing and in some cases reengineering natural features such as wetlands and beach dunes. This so-called “soft infrastructure” can reduce the impact of waves, improve water quality and create new recreational spaces for coastal residents and visitors. Rather than the exclusive construction of barriers, the project’s plans include “layered systems of natural and engineered structures that will respond in different ways to different hazards,” Nordenson said. “It is a more nuanced and more resilient approach.”

Flexible design is also an important component of the project. Ideally, the sizes and arrangements of structures will be adaptable as predictive models improve. Scientists continue to debate how climate change will affect the strength and frequency of storms. “But we are trying to take what we know right now and do the best job we can in accounting for the uncertainties in what we know, and use that to explore how we should be thinking about adaptation,” said Smith, the William and Edna Macaleer Professor of Engineering and Applied Science and chair of the Department of Civil and Environmental Engineering at Princeton.

Meteorological measurements show that the extreme winds of a swirling hurricane transfer energy to the ocean surface. The winds and the storm’s low air pressure cause a dome of water to rise, generating a surge of high water when the storm makes landfall. “When you think of the storm, you think of the wind and the rain. That’s what seems scary,” said Talea Mayo, a postdoctoral research associate who is working with Lin to model storm surges. But the coastal storm surge was the main cause of deaths and property damages from Hurricane Sandy.

To predict future storm surges, Lin and Mayo are using thousands of synthetic hurricanes modeled by Kerry Emanuel, an atmospheric scientist at the Massachusetts Institute of Technology. “Anytime you’re studying hurricanes, especially so far north, your historical data are really limited because there just aren’t enough events,” Mayo said. “So instead of basing our risk analysis on historical data, we use synthetic data.”

Hurricane damage 1944

Storms have caused significant damage to Atlantic City’s iconic boardwalk throughout its existence. Shown here is South Inlet during the Great Atlantic Hurricane of 1944. Image from the archive of the Coastal and Hydraulics Laboratory, Engineer Research and Development Center, Vicksburg.

Emanuel’s team uses existing models of global climate circulation patterns to generate 3,000 synthetic, physically possible storms for nine different climate change scenarios at each of the four study sites — a total of more than 100,000 storms. These hurricanes exist only in computer code, but their wind speeds, air pressure levels and patterns of movement are based on physical laws and information from recorded storms. Mayo and Lin plug these parameters into algorithms that work like sophisticated versions of high school physics problems: solve the equations for conservation of mass and momentum to estimate maximum water levels at each site. Variations in tide levels, coastline shapes and seafloor topographies add additional layers of complexity.

To make reasonable projections of future flood hazards, the models must also account for sea level rise. According to geoscientist Chris Little, an associate research scholar working with Oppenheimer, storm surges are a short-term version of sea level rise. “They both contribute to coastal flooding,” Little said. “Climate change will be felt through the superposition of changes in long- and short-term variations in sea level.”

And when it comes to sea level rise, local projections are crucial for planning efforts. A constellation of factors influence regional differences in sea levels, including the vertical movement of the Earth’s surface, changes in ocean circulation and the melting of glacial ice. Little and Oppenheimer were among the authors of a study published in June 2014 in the journal Earth’s Future, which used model-based and historical tide gauge data for sites around the globe to project local sea levels over the next two centuries.

“We live in a hotspot, where the local sea level rise has been higher in the past than the global mean, and we expect it to continue to be higher in the future,” Oppenheimer said — as much as 40 percent higher than the worldwide average. One reason for this is that the land along the East Coast is slowly sinking (by a millimeter or two each year), a legacy of the ice sheet that covered much of North America until about 12,000 years ago. The ice sheet depressed Earth’s crust over present-day Canada, causing the liquid mantle beneath to bulge southward. Now that the glaciers have melted, the mantle is being gradually redistributed, flowing out from under the East Coast of the United States.

Sea levels respond slowly to changes in climate, including the current warming trend, caused in part by increased carbon dioxide levels from human activity. Because future carbon emissions depend on human decisions, predictions of sea level rise come with built-in uncertainty. This project attempts to meet this challenge head-on: “A major purpose of the project is to think about doing a more thorough job of assessing the uncertainty in these flood zones,” Little said. “I think it’s difficult but worthwhile.”

Resilient designs call for planning and reengineering natural features such as salt marshes, submerged aquatic vegetation and wetlands, as in this imagined coastline for Staten Island, south of Manhattan.

Resilient designs call for planning and reengineering natural features such as salt marshes, submerged aquatic vegetation and wetlands, as in this imagined coastline for Staten Island, south of Manhattan.

Because of this uncertainty, climate scientists deal in probabilities. The Princeton team has projected flood levels for storms with return periods of 100, 500 and 2,500 years. A return period of 100 years is akin to a “100-year flood” — this means that in any given year there is a 1 percent chance of that flood level occurring. These forecasted flood risks are key to making smart building and design decisions in the face of climate change. “Every decision-maker is going to look and decide what risk is tolerable for their region in the context of how much it would cost to defend against that risk,” Oppenheimer said.

The design teams are beginning to test their plans against the climate scientists’ predictions. Simulated local water levels will reveal which structures may be inundated by future storms and at what probabilities. These analyses may prompt the designers to adjust the heights of buildings, roads or beach dunes in their blueprints. And as the science improves, this process will repeat itself. “Over time, others can start to add things that we haven’t been able to include, like the relationship of the wind and the flood,” Nordenson said.

True resilience necessitates a change in outlook. In Atlantic City, the focus area for Lewis and the Princeton group, a narrow channel of water separates the Chelsea Heights neighborhood from the city’s famous boardwalk and high-rise casinos, where many residents work. “You have extensive areas of suburban neighborhoods that are built on wetlands,” said Lewis. “Two binary positions are retreat, where you return these to wetlands, and fortification, which is the seawall approach. And both of them are problematic.”

The team recognizes the social and economic importance of maintaining the neighborhood. But barricading it behind a seawall may be prohibitively expensive, not to mention unattractive. More important, metal or concrete seawalls can actually exacerbate flooding when areas behind them are inundated by heavy rain. Lewis and his team have a fundamentally different vision for places like Chelsea Heights: “We’re looking at developing an amphibious suburb,” he said. “We want water to come in. If there are berms [earthen seawalls] that are put in, they should be built with a series of valves.”

The plans for Chelsea Heights include raised homes and roads interspersed with canals and revitalized wetlands. Lewis hopes these ideas will be useful to policymakers and to the Army Corps of Engineers, which may apply the Princeton team’s concepts to Chelsea Heights and other similar communities along the New Jersey shore. By the end of this century, grassy suburban lawns may be transformed into salt marshes.

PLANNING FOR RESILIENCE UP AND DOWN THE COAST

Natural features play a pivotal role in the designs for two of the project’s other focal regions, New York’s Jamaica Bay and Rhode Island’s Narragansett Bay.

  • The plan for Jamaica Bay includes the use of local dredged materials to build up land for marsh terraces, which can serve to reduce wind fetch as well as improve water quality and encourage sediment deposition, according to Catherine Seavitt, an associate professor of landscape architecture at the City College of New York. In particular, her team hopes to expand the restoration of a native wetland grass, Spartina alterniflora, an effective attenuator of wind and waves that also provides valuable ecological habitat.
  • Michael Van Valkenburgh and Rosetta Elkin lead the Harvard design effort for Narragansett Bay. One of their plans involves relocating two critical reservoirs that supply drinking water to the city of Newport. The reservoirs are currently vulnerable to coastal flooding; the proposed project would use dredged material from the original reservoir to fill in and extend the existing maritime forest, now a rare ecosystem along the New England coast. The larger forest, designed by the team, would mitigate coastal erosion, attenuate wave action, and become a valuable recreational area for surrounding communities.
  • The project’s other site, the Norfolk, Virginia, area of Chesapeake Bay, calls for a more extensive reshuffling of settlement and infrastructure, according to Dilip da Cunha, an adjunct professor of landscape architecture at the University of Pennsylvania. Of the four sites, Norfolk is expected to see the most dramatic sea level rise, and is home to the world’s largest naval station and a vital commercial port. The UPenn team’s designs stem from the natural network of fractal-like interfaces where land and water meet. The plan seeks to bolster “fingers of higher ground” that will be more robust to gradual sea level rise as well as storm surges. “The higher grounds could be for housing, schools and other facilities, and the low grounds could accommodate various things, from marsh grasses to football fields,” da Cunha said. “Things that can take water in the case of a storm event, but will not endanger lives.”

-By Molly Sharlach

Shell Structures for Architecture: Form Finding and Optimization

Shell Structures for Architecture

Shell Structures for Architecture

Edited by: Sigrid Adriaenssens, Philippe Block, Diederik Veenendaal and Chris Williams, with a foreword by Pritzker Prize Winner Shigeru Ban
Publisher: Routledge: Taylor and Francis, 2014

This book presents contemporary design methods for shell and gridshell structures, covering formfinding and structural optimization techniques. Edited by experts including Princeton Assistant Professor of Civil and Environmental Engineering Sigrid Adriaenssens, the book introduces architecture and engineering practitioners and students to structural shells and provides computational techniques to develop complex curved structural surfaces, in the form of mathematics, computer algorithms and design case studies.

Wetlands provide solutions for agricultural runoff

Wetlands

When a dry spell made their intended experiments impossible, researchers made a serendipitous discovery: a novel biochemical reaction that could help clean up wastewater and remediate wetlands. (Photo by Peter Jaffe)

A PATCHWORK OF SMALL LAKES, forests and marshes surrounded by farms and suburbs, the Assunpink Wildlife Management Area in central New Jersey is an ideal place to track the effects of agricultural nitrogen runoff on wetland soil chemistry. Princeton professor Peter Jaffe and his students arrived at the study site in 2004, along with an ecology research group from Rutgers University.

But a drought made their intended experiments impossible; they couldn’t study the wetlands when they had dried out. Instead, Jaffe, a professor of civil and environmental engineering, asked his students to take soil samples back to the lab, where they added different sources of nitrogen to the samples and analyzed changes in their chemistry.

In some of the samples, the researchers observed something unexpected: in the absence of oxygen, a polluting form of nitrogen called ammonium was transformed into harmless nitrogen gas. In these samples, electrons — charged particles — were moving from ammonium, which comes from fertilizer runoff, to iron, a plentiful metal in the soil. Jaffe’s group documented this reaction for the first time.

Although Jaffe’s original goal was to examine how nitrogen runoff from fertilizer affects metal transport in wetland ecosystems, he wondered if this newly discovered natural phenomenon could be useful for cleaning up nitrogen pollution. To investigate it further, he secured funding from the National Science Foundation and Princeton’s Project X, a program that funds risky but promising projects, and returned to the site in 2011 with postdoctoral research associate Shan Huang. “My first fear was that we wouldn’t see anything,” Jaffe said. “But our findings were reproducible.”

Huang and Jaffe brought fresh soil samples back to the lab. To mimic the underground environment at the field site, Huang placed the small bottles of mud in a chamber without oxygen and bathed them in water spiked with ammonium. She monitored levels of ammonium and forms of iron in the samples and found that the ammonium was indeed being converted into nitrite, a precursor of nitrogen gas.

As Huang monitored the reaction, she noticed something intriguing. “After six months, the reaction became more and more efficient,” she said. “We thought there should be some bacteria responsible for the reaction.” When Huang sterilized the soil by heating it under high pressure, the ammonium removal stopped, suggesting that microorganisms were the force behind the chemical transformations.

Those microorganisms were carrying out a reaction, now known as Feammox, that oxidizes ammonium — takes the electrons from it — and transfers the electrons to iron (Fe is the symbol for the element iron). The oxidized ammonium became nitrite, and other bacteria converted the nitrite to nitrogen gas.

Since the Jaffe team’s initial discovery of Feammox, two other groups have observed the process, in a laboratory sewage treatment reactor and in soil from a Puerto Rican rainforest. But Jaffe and Huang were the first to identify the bacterium that carries out the reaction. Huang isolated this bacterial species from the others present in the soil. “We tried hundreds of different growth conditions, and finally got a pure culture,” she said. “It was 50 percent hard work and 50 percent luck.” The winning recipe had an acidic pH, similar to the soil environment where the bacteria were found.

The bug, which belongs to a family of soil microbes called Acidimicrobiaceae, functions without oxygen and at a relatively low temperature — about 68 degrees Fahrenheit, compared with 86 degrees for other microbes that oxidize ammonium in the absence of oxygen. “This is really good when you think about applying this in wastewater treatment plants,” said Melany Ruiz-Urigüen, a graduate student who is working to optimize the Feammox reaction. “It means you wouldn’t have to heat the water, and that saves a lot of energy.”

Ruiz-Urigüen is also testing whether the bacteria can use inexpensive sources of iron, such as scrap metal. The Feammox reaction requires iron oxide, which is found on rusty steel — a plentiful industrial waste. For Ruiz-Urigüen’s latest experiments, she uses steel wool pads purchased from a home improvement store. She sprays the metal mesh with a salty solution and lets it rust for two weeks before adding it to a reactor.

In the wetland environment, Feammox bacteria likely depend on plants to supply oxidized iron for the reaction. Oxygen leaks out of plant roots, forming orange nodules where it reacts with iron in the soil; this natural rust can seep into areas without oxygen, where Feammox bacteria thrive. To investigate how the Feammox process might work in an engineered wetland, graduate student Zheyun Zhang is monitoring the reaction in greenhouse pots planted with cattails and bulrushes. “We want to use the plants to recycle the iron,” Zhang said. “Plants are very cheap. And it’s a natural process.”

Jaffe and his team hope to improve the Feammox process and harness it to clean up pollution — not only of nitrogen runoff, but perhaps also of certain toxic metals that may act as stand-ins for iron. The success of this fortuitous discovery gives the researchers confidence as they strive to turn Feammox into a useful technology.

–By Molly Sharlach

Green roofs’ energy savings hinge on climate

Green roofs

Green roofs, such as these above the dormitory at Princeton’s Butler College, must be designed so that they take advantage of local climate conditions. (Photo by Brian Green)

Urban planners who want green roofs in their cities need to remember that the roofs may not work the same way in different climates. Green roofs, which are covered with a layer of a vegetation to keep the building cool, perform differently according to the amount of solar radiation and precipitation present, according to Elie Bou-Zeid, an assistant professor of civil and environmental engineering.

In a study published in the journal Building and Environment, Bou-Zeid and his team found that the green roofs on the campuses of Princeton and Tsinghua University in Beijing performed similarly when the researchers controlled for the radiation and precipitation levels in the two areas, indicating the levels’ importance in green roof function. With support from the U.S. Department of Energy through Pennsylvania State University’s Energy Efficiency Building Hub and the National Science Foundation of China, the researchers used surface temperature, heat convection from the Earth’s surface to the atmosphere, and the amount of incident energy conducted through the roof as performance measures.

Bou-Zeid

Elie Bou-Zeid, an assistant professor in civil and environmental engineering, stands with a wireless sensing station that measures wind speed and direction, air temperature, relative humidity, surface temperature, and incoming and reflected solar radiation from black and white roofs. (Photo by Elle Starkman)

Bou-Zeid said he hopes his work will help city planners account for the specific climatic conditions in their cities when integrating rooftop gardens into their building decisions, and assess the potential benefits of irrigation that improves green roof performance in dry periods.

Highly effective green roofs are important in cities, which suffer from the “urban heat island” phenomenon: a sustained period of excessive heat in metropolitan areas caused by buildings that absorb heat and release it into the atmosphere, a lack of vegetation, and high human activity. Increasing the number of green spaces will trap rainwater, Bou-Zeid explained, thereby providing a “heat sink” in which evaporation of that water encourages heat loss and cools things down.

The New York City Office of the Mayor is taking the heat waves of the city particularly seriously, Bou-Zeid said. New York’s asphalt and concrete roads and buildings actively absorb heat, making the area sometimes up to seven degrees warmer than its neighbors. Bou-Zeid is working with representatives from the NYC Cool Roofs program, a citywide initiative to promote the use of reflective, white rooftop coating, to examine which areas of the city will suffer most during a heat wave. He later hopes to relate physical maps of area-specific heat stress in the city to physical health indicators.

“Heat waves are the deadliest natural disasters,” Bou-Zeid said. He noted that the 2003 European heat wave, which produced the Northern Hemisphere’s hottest-ever August, caused up to 70,000 deaths in the region. “They are silent killers.”

–By Tara Thean

Inventions Bridge the Gap between lab and marketplace

Road trip

A road trip offered Mark Zondlo and his team the opportunity to test their new air quality sensors. (Photo by Lei Tao)

The college experience often involves at least one road trip, but most students do not bring along their faculty adviser. But last spring, two graduate students crammed into a rented Chevy Impala with Professor Mark Zondlo and a postdoctoral researcher to drive eight hours a day across California’s Central Valley, testing their new air-quality sensors, which were strapped to a rooftop ski rack.

The sensors are an example of technologies being developed at Princeton that have the potential to improve quality of life as commercial products or services. Although teaching and research are Princeton’s core missions, the campus is home to a vibrant entrepreneurial spirit, one that can be found among faculty members who are making discoveries that could lead to better medicines as well as students working to turn a dorm-room dream into the next big startup.

“Princeton has a number of initiatives aimed at supporting innovation and technology transfer,” said John Ritter, director of Princeton’s Office of Technology Licensing, which works with University researchers to file invention disclosures and patent applications, and with businesses and investment capitalists to find partners for commercialization. “Our goal is to accelerate the transfer and development of Princeton’s basic research so that society can benefit from these innovations,” he said.

Crossing the valley

One of the ways that Princeton supports this transfer is with programs that help bridge the gap between research and commercialization, a gap that some call the Valley of Death because many promising technologies never make it to the product stage. One such program is the Intellectual Property Accelerator Fund, which provides financial resources for building a prototype or conducting additional testing with the goal of attracting corporate interest or investor financing.

Zondlo, an assistant professor of civil and environmental engineering, is one of the researchers using the fund to cross the valley — in this case literally as well as figuratively. Earlier this year, Zondlo and his research team, which consisted of graduate students Kang Sun and David Miller and postdoctoral researcher Lei Tao, tested their air-quality sensor in California’s Central Valley, a major agricultural center that is home to some of the worst air pollution in the nation.

Their goal was to compare the new portable sensors to existing stationary sensors as well as to measurements taken by plane and satellite as part of a larger NASA-funded air-quality monitoring project, DISCOVER-AQ.

One of the new sensors measures nitrous oxide, the worst greenhouse gas after carbon dioxide and methane. Nitrous oxide escapes into the air when fertilizers are spread on farm fields. Currently, to measure this gas, workers must collect samples of air in bottles and then take them to a lab for analysis using equipment the size of refrigerators.

Zondlo’s sensor, which is bundled with two others that measure ammonia and carbon monoxide, is portable and can be held in one hand, or strapped to a car roof. “The portability allows measurements to be taken quickly and frequently, which could greatly expand the understanding of how nitrous oxide and other gases are released and how their release can be controlled,” Zondlo said.

The sensors involve firing a type of battery-powered laser, called a quantum cascade laser, through a sample of air, while a detector measures the light absorption to deduce the amount of gas in the air. The researchers replaced bulky calibration equipment, necessary to ensure accurate measurements in the field, with a finger-sized chamber of reference gas against which the sensor’s accuracy can be routinely tested.

The decision to commercialize the sensor arose from the desire to make the device available to air-quality regulators and researchers, Zondlo said. “Our sensor has precision and stability similar to the best sensors on the market today, but at a fraction of the size and power requirements,” said Zondlo, a member of the Mid-Infrared Technologies for Health and the Environment (MIRTHE) center, a multi-institution center funded by the National Science Foundation (NSF) and headquartered at Princeton. “We are already getting phone calls from people who want to buy it.”

Lighting up the brain — with help from a synthetic liver

Far from the dusty farm roads of California, Princeton faculty member John (Jay) Groves sits in his office in the glass-enclosed Frick Chemistry Laboratory, thinking about the potential uses for a new synthetic enzyme. Modeled on an enzyme isolated from the liver, the synthetic version can carry out reactions that human chemists find difficult to pull off.

One of these reactions involves attaching radioactive fluorine tags to drugs to make them visible using a brain-imaging method known as positron emission tomography (PET) scanning.

PET scans of the radiolabeled drugs could help investigators track experimental medicines in the brain, to see if they are reaching their targets, and could aid in the development of drugs to treat disorders such as Alzheimer’s disease and stroke, according to Groves, Princeton’s Hugh Stott Taylor Chair of Chemistry. The synthetic enzyme adds fluorine tags without the toxic and corrosive agents used with radioactive fluorine today.

Groves’ initial work was supported by the NSF, but to develop the technology for use in pharmaceutical research, the Groves team, which includes graduate students Wei Liu and Xiongyi Huang, is receiving funding from a Princeton program aimed at supporting concepts that are risky but have potential for broad impact. The Eric and Wendy Schmidt Transformative Technology Fund was created with a $25 million endowment from Google executive chairman Eric Schmidt, a 1976 alumnus and former trustee, and his wife, Wendy.

“The Schmidt funding is enabling us to explore ways to optimize the chemical reaction and create a prototype of an automated system,” Groves said. “This will allow us to create a rapid and noninvasive way to evaluate drug candidates and observe important metabolites within the human brain.”

Aiding the search for planets

Tyler Groff

Postdoctoral researcher Tyler Groff is creating an improved system for adjusting the blurry images seen through telescopes due to atmospheric turbulence, heat and vibrations. (Photo by Denise Applewhite)

Inspired by the search for planets outside our solar system, Princeton postdoctoral researcher Tyler Groff conceived of a technology that could enhance the quality of images from telescopes. Groff received Schmidt funding to develop a device for controlling the mirrors that telescopes use to correct blurring and distortion caused by atmospheric turbulence, heat and vibrations.

This technology, known as adaptive optics, involves measuring disturbances in the light coming into the telescope and making small deformations to the surface of a mirror in precise ways to correct the image. These deformations are made using an array of mechanical devices, known as actuators, each capable of moving a small area of the flexible reflective surface up or down. But existing actuators are limited in the amount of correction they can provide, and the spaces between the actuators create dimples in the mirror, producing a visible pattern in the resulting images that astronomers call “quilting.”

Groff envisioned replacing the array of rigidly attached actuators with flexible ones made from packets containing iron particles suspended in a liquid, or ferrofluid. Just as iron filings can be moved by waving a magnet over them, applying varying magnetic fields to the ferrofluid changes the shape of the fluid in ways that deform the mirror.

The ferrofluid mirror enables highquality images while being more resistant to vibrations and potentially more power efficient, which will be important for future satellite-based telescopes, said Groff, who works in the laboratory of Jeremy Kasdin, professor of mechanical and aerospace engineering. A ferrofluid mirror can also achieve something that a rigid actuator mirror cannot: it can assume a concave or bowl-like shape that aids the focusing of the telescope on objects in space. “A telescope that uses ferrofluid mirrors would be able to see dim objects better,” Groff said, “which would greatly enhance our ability to probe other solar systems.”

From drug discovery to space exploration, Princeton’s dedication to supporting technology transfer and potentially disruptive but high-risk research ideas is yielding tremendous benefits for the advancement of science and the improvement of people’s lives.

Box: From student project to startup

Carlee Joe-Wong (Photo by Steve Schultz)

Carlee Joe-Wong (Photo by Steve Schultz)

In 2009 when Princeton undergraduate Carlee Joe-Wong started working on the technology that would become the DataMi company, she didn’t even own a smartphone. Today, the startup company co-founded by Joe-Wong provides mobile traffic management solutions to wireless Internet providers, and also helps consumers manage their data usage through an app, DataWiz, that has been downloaded by more than 200,000 Apple and Android users.

Joe-Wong became involved in the study of mobile data usage in the spring of her junior year when Professor Mung Chiang challenged her to explore ways that wireless providers could reduce congestion by adjusting their prices based on the variations in network supply and demand. “I mostly just worked on the project in my dorm room,” Joe-Wong said. “I thought it would be cool if it was adopted but I didn’t think that I would be the one helping to make that happen.” After graduation, Joe-Wong became a graduate student working with Chiang on mathematical algorithms that predict the most effective methods for balancing network use across “peak” minutes and “valley” minutes.

“With companies charging $10 per gigabyte, mobile consumers today need to intelligently manage their data,” said Chiang, the Arthur LeGrand Doty Professor of Electrical Engineering. “What the DataWiz app does is tell you when, where and what app used how much of your quota.”

In May 2013 the team, under the engineering leadership of associate research scholar Sangtae Ha, opened an office for DataMi one block off campus. Needless to say, Joe-Wong now has a smartphone.

Taking it to the streets with help from Princeton’s eLab

ELab students

From left: Nathan Haley, Christine Odabashian, Luke Amber and Leif Amber. (Photo by Denise Applewhite)

A love of motorcycles brought them together: three Princeton undergraduates decided to explore building and marketing an electric motorcycle to provide a superior riding experience at significantly lower emissions than gasoline powered models.

The team was one of nine groups selected to participate in the 10-week eLab Summer Accelerator Program, an initiative of the Keller Center in the School of Engineering and Applied Science, which teaches entrepreneurship by offering resources, mentoring and working space.

Throughout the summer, the team members worked on ways to market the bike while simultaneously building a prototype. “We geared the product toward people who enjoy taking weekend trips,” said Nathan Haley, Class of 2014, an economics major.

Haley was joined by Luke Amber, Class of 2015, and Christine Odabashian, Class of 2014, both majors in mechanical and aerospace engineering. The team also included Luke’s older brother, Leif Amber, a graduate student in electrical engineering at Clarkson University.

-By Catherine Zandonella

Site-specific shades offer sun protection

Sun shade

Civil and environmental engineering graduate student Matthew Horner sits with Assistant Professor Sigrid Adriaenssens beneath a prototype of a pavilion designed to block harmful UV radiation by accounting for the sun’s path within its specific geographic location. (Photo by Denise Applewhite)

Children exposed to a lot of sunlight have a higher chance of developing skin cancer as adults, according to the Centers for Disease Control and Prevention. With this in mind, structural designer and assistant professor in the Department of Civil and Environmental Engineering Sigrid Adriaenssens is creating a sun shade designed to account for the sun’s path within a specific geographic location. This would allow the shade to work anywhere, protecting against the sun’s power and helping reduce skin cancer — the most common form of cancer in the United States.

Adriaenssens’ approach is to produce a dome shaped grid for the sun shade that works with surrounding climatic conditions and uses the least amount of building material possible. To do this, her team uses data from the National Oceanic and Atmospheric Administration and NASA coupled with their sun path algorithms to identify specific sunlight angles in the sun shade’s location and ensure that the grid shades for only those angles. This allows the structure to block damaging UV radiation, but lets through light that doesn’t affect the target shade area.

The inspiration for the shade’s design came in part from existing commercial sun shades, which are typically “one design fits all” and thus ineffective at actually shading their target areas. Individuals sitting under a patio set with a sun shade, for example, can find that the perimeter of the table around which they are sitting is not shaded at all, Adriaenssens explained.

Adriaenssens uses a “dialectic” strategy in her work, which is a reference to the dialectic form of discourse that looks for a solution to a problem by using various arguments, or design drivers in this case. For Adriaenssens, the drivers include engineering considerations such as structure and material as well as questions of environmental performance.

“I think sometimes you can design, in a very economic way, very elegant systems,” she said, noting that she encourages the dialectic approach among her students. Adriaenssens’ colleagues, including Assistant Professor of Civil and Environmental Engineering Mark Zondlo, Postdoctoral Research Associate Landolf Rhode- Barbarigos, and graduate students Matthew Horner and Dan Reynolds, recently erected a prototype sun shade near the Princeton University Stadium.

Other sun-related projects that adapt to different environmental conditions are on Adriaenssens’ radar. One of her models takes its cue from plants such as the waterwheel plant (Aldrovanda vesiculosa), which uses two lobes that rapidly snap shut to catch prey. The mechanics of this motion serve as the basis for shading structures that open and close based on the amount of sunlight present at a given time, ensuring lower manufacturing costs and energy consumption.

Adriaenssens hopes that the high efficiency of her creations will ensure a low-resource path to useful designs, especially in cities. With 70 percent of the world population predicted to live in urban environments by 2050, carbon emissions from existing and additional buildings — and the construction materials for creating them — required to support their needs will only increase, she explained.

“We must find more efficient ways to provide people with a good quality of life using fewer resources,” she said. “My research is all about how we can develop an engineering design framework for a future-oriented urban environment.”

–By Tara Thean