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In the event of earthquakes, greater resilience
In another project, ATLSS researchers are evaluating the potential for magnetorheological (MR) dampers to minimize seismic damage to structures. They study the dampers using hybrid simulation, which integrates two types of data – data generated by numerical models of structural components that are well understood and can be modeled analytically and data collected simultaneously from lab experiments on components that are not well understood.
MR dampers, say Sause and James Ricles, professors of structural engineering, improve the resilience of a multi-story steel-framed structure to earthquakes by minimizing its drift and vibration during a seismic event. During an earthquake, says Ricles, floors in a high-rise can drift laterally, damaging beams and columns and pipes and wires. a building that looks sturdy can still be deemed unsafe to use and can cost more to repair than to be demolished and rebuilt.
Hybrid simulation, says Sause, increases the amount of information researchers can gather from an experiment.
“Hybrid simulation allows us to evaluate the performance of very large buildings under the dynamic loading of an earthquake in real time and also to compare designs,” says Sause. “such data would be too expensive to collect from physical experiments alone.”
Sause and Ricles evaluated the benefit of using MR dampers by performing hybrid simulations of a nine-story building subjected to conditions equivalent to those of the Northridge Earthquake. The actual building was condemned after the earthquake.
The building, which was rendered unusable by the Northridge Earthquake, would not have had to be condemned if it had been fitted with MR dampers.
“MR dampers are unique,” says Ricles. “Their properties can be controlled by varying an applied electrical current. The fluid inside the damper contains iron particles, which form linear chains that align with the induced magnetic field when a current is applied.
“This alignment increases the viscosity of the fluid and restricts its ability to move through the orifices of the damper. The result is a change in the yield strength and energy dissipation capability of the fluid.”
“The dampers significantly reduce the vibration and drift of the structure,” says Yunbyeong Chae, a Ph.D. student. The building that was rendered unusable by the Northridge Earthquake, he adds, would not have had to be condemned if it had been fitted with MR dampers.
The test was performed at the NEES Real-Time Multi-Directional Earthquake Simulation Facility in the ATLSS Center, with funding from NSF and the state of Pennsylvania.
For the grid, an intelligent interface
No part of America’s infrastructure, says Rick Blum, is more overdue for a fresh coat of intelligent systems than the electrical grid that generates, transmits and distributes power to more than 300 million people.
Blum, professor of electrical and computer engineering, is one of a cluster of Lehigh researchers studying the smart grid. The group also includes Shalinee Kishore, associate professor of electrical and computer engineering; Lawrence Snyder, associate professor of industrial and systems engineering; and Liang Cheng, associate professor of computer science and engineering. The group formed a year ago when engineering faculty, meeting with experts from industry, government and national labs, determined that Lehigh’s expertise in systems engineering was ideally suited to help overhaul the grid.
“The electrical grid,” says Blum, “needs to be able to respond to demand and to control distribution in real time. We have to figure out when consumers need power, how much they need and how much power is being generated at a given time by a given plant.
“The smart grid will increase energy efficiency and decrease carbon emissions. It will integrate renewable energy sources like wind and solar. Because power generated by these sources is variable, the prices charged for power must become variable as well.”
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Information architecture overlaying the smart grid, says Kishore, will more efficiently match supply with demand.
“The smart grid will send information on real-time prices directly to consumers, allowing them to make decisions regarding the purchase of power,” she says.
“Homes will have energy management controllers [EMCs] and smart meters. Your EMC will be programmed to know your power usage patterns and preferences. It will look at prices in real time and make decisions for you.”
Communication between EMCs and the grid, says Kishore, will enable consumers to use power when it is priced most cheaply. Communication among EMCs will allow car batteries to be charged and dishwashers to be run on a schedule that spreads out demand for power.
This leveling effect, says Snyder, will help power companies avoid costly periods of peak demand and even costlier brownouts and blackouts.
“A utility always tries to meet peak demand, but this is very expensive,” says Snyder. “The peak usually lasts a short period of time. But a utility has to maintain expensive equipment – usually older, more polluting equipment – to be able to turn on power as needed no matter what.”
Kishore and Snyder are developing mathematical models that optimize communication among EMCs and between EMCs and the grid. The model, says Snyder, is similar to a CSMA (carrier sense multiple access) protocol that enables a node in a network of sensors to transmit information only when it detects that other nodes in the network are idle.
“Let’s say your EMC wants to run the air conditioner, dishwasher and clothes dryer,” says Snyder, who is developing an optimization algorithm for the model. “It asks the other EMCs in the network, ‘Do i have enough power?’ They might respond, ‘No, you have to delay one of your tasks.’
“This is like rationing, but it’s structured so that users never really feel it.”
Without communication among each other, says Kishore, too many EMCs might schedule tasks during periods of low power demand, distorting usage and pricing patterns. Kishore and Snyder have run tests showing that this distortion would actually cause a greater spike in peak demand. To avoid this, a smart grid would act in concert with EMCs to manage the number of power-driven tasks performed at various times during the day. It would implement its decisions to achieve fairness without infringing on customers’ privacy.
“Pricing is just one mechanism to achieve efficiency,” says Kishore. “Communication is also essential. Our scheme shows you can develop coordinator-based communications protocols that allow the leveling of peak usage.”
