 April - June 1997 
Earthquakes: How Can We Design Structures Less Likely to Fail [e-lab Home Page] [Energy Lab Home Page] [MIT Home Page] .
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Improving Piston Engines Through Better Ring Design major
challenge for designers of internal combustion engines is how to seal shut
the "combustion chamber" at the top of the cylinder while the
piston is moving up and down. Three rings are mounted on each piston and
extend to the cylinder wall to form a seal. But as the piston moves, the
rings shift in ways that can contribute to three major engine problems:
friction, wear, and oil consumption. A detailed model developed by Energy
Laboratory researchers can help engine designers identify new piston and
ring designs that will reduce those problems. For a given engine design
and operating conditions, the model describes how the rings move, how much
friction and wear occur as they encounter other metal surfaces, and how
much lubricating oil escapes into the combustion chamber, especially when
the rings become unseated. Experimental studies have verified the model's
ability to predict ring and oil film behavior. Using the model, the MIT
researchers have defined a new friction-reducing shape for the grooves
in which the rings are mounted. They have also identified a type of ring
behavior that may contribute significantly to oil consumption--a behavior
that can be altered by changing the shape of the rings.
[e-lab Home Page] Copyright © Massachusetts Institute of Technology 1997. Material in this bulletin may be reproduced if credited to e-lab. |
uring the past
decade, earthquakes in California and in Japan have caused the dramatic
collapse of freeways, bridges, and other structures built according to
stringent earthquake-resistant design codes. A new Energy Laboratory study
shows that today's building codes may be inadequate because they are based
on incorrect assumptions about earthquake motions--assumptions derived
when seismic data were relatively scarce. An MIT team has analyzed earthquake
records gathered during the past decade and found that ground motions are
more intense than previously thought possible. Moreover, they can vary
substantially over short distances, producing differential motions that
can endanger and even collapse large-span structures such as freeways and
bridges. While theoretical simulations and scale models have been useful
in earthquake engineering, they cannot accurately predict how strong ground
motions cause structures to fail, hence what building codes and retrofitting
techniques will prevent damage. Therefore, the MIT researchers have designed
a 30-by-30-meter "shake table" that can hold a full-sized 10-story
building or other large structure. Novel electromagnetic "pistons"
move individual panels in the table so as to replicate the complex ground
motions of an earthquake. A table-top model of the "electromagnetic
seismic simulator" (EMSS) has demonstrated the feasibility of the
concept. The EMSS is planned to be located at the Idaho National Engineering
and Environmental Laboratory as part of a major facility for testing the
responses of full-scale structures to earthquakes, wind, and aging.