Wireless sensor network and its application
to structural health monitoringTomonori NagayamaAssistant professor University of Tokyo
2010/08/06
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A historic decade of wireless smart sensor research
Berkeley MoteMica2 (2004)
BTnode rev3 (2004)EYES (2003)WINS 1 (1999)
U3 (2002)
Prototype by Prof. Lynch (2002)
Intel Imote (2004)
Imote2 (2006)
In 2000, US Defense Advanced Research Projects Agency (DARPA)’s Networked Embedded Systems Technology (NEST) program funded projects aiming to build dependable, real-time, distributed, embedded applications comprising 100-100,000 simple computing nodes.
Since then a variety of WS platforms have been developed
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Application examples:
• Soil moisture & temperature• Ambient temperature & humidity
eKo, MEMSIC Corporation
-Agricultural application-
Application examples:
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Energy monitoring solution
Ecowizard, Crossbow Japan
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Application examples:
MEMS inclinometer
Volumetric water content meter
Sensor units
Data link by Cell Phone Network (KDDI)
Data link by wireless chip MU-2(< 600m for each node)
Data can be accessed through internet
Warning to adjacent residents
Low-cost, easy instllation
Database for regional disaster mitigation programs
時間
傾斜
土壌水分
法尻部の土壌水分
No wiring work Low cost, easy instlation
(1) Sensor units with inclinometer and watercontent sensor.
(3) Data is collected at the gateway unit.
(4) Data is transferred via cell phone network to Internet. (every 10 mins.)
(5) Central server receives dataand issue warning if abnormal data is found.
(2) Data is relayed by mult-hopping among sensor units.
Assoc. Prof. T. Uchimura, University of Tokyo
-Landslide monitoring-
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The prototype system is installed on steep slopes in Kobe City, Japan.
Senjo-Dani Slope
Ogawa-Dani Slope(which failed due to 1995 Hyogoken-Numbu earthquake)
-Landslide monitoring-
Installation takes less than 30 min per unit
Ubiquitous Structural Monitoring System
Application examples: -seismic response monitoring-
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Application examples:
◇US‐Korea‐Japan joint research project (UIUC/KAIST/Univ. of Tokyo) ◇70‐111 multimetric sensor nodes ◇8/2008 to 1/2011
-Bridge vibration monitoring-
What can we obtain from dense structural vibration measurements?How can WSN contribute to bridge engineers?
Various purposes of structural vibration monitoring
• To monitor and control the construction process• To validate the structural designs and characterize
performance (e.g., develop database)• To characterize loads in situ• To assist with building/bridge maintenance• To detect and localize damage before it reaches a
critical level, thus increasing the safety to the public• To reduce the costs and down-time associated with
repair of damage• To assist with emergency response efforts, including
building evacuation and traffic control
(Prof. B. F. Spencer, Jr. UIUC)
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5P accelerometers (19pts)
How much can we know about the bridge How much can we know about the bridge from measurement by dense arrays of sensors?from measurement by dense arrays of sensors?
Measurement: more than 3 weeks
Sensors: 40 pts (dense array)Sampling: 100Hz
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5P0 1 2-0.8
-0.4
0
0.4
0.8
min
galTime history
Spatial view
Structural vibration monitoring: case study
Obtained: up to 23rd modeObtained: up to 23rd mode
Identification resultsModes
ζr fr(Hz)
1st 0.0235 0.1302nd 0.0122 0.1523rd 0.0066 0.221…
10th 0.048 1.3217th 0.031 3.2019th 0.055 3.86
Damping & freq.
-300 0 300-0.4
0
0.4
-300 0 300-0.4
0
0.419-th mode
Distance from tower(m)
Mod
al a
mp.
1st mode
Change in stiffness (KN/m)
Wind velocity (m/s)0 5 10
-80
-40
0
0 5 100
50
100Change in damping (KNs/m)
Wind velocity (m/s)
Result 1: Aerodynamic damping & stiffness
Identified
Ref. state.
Ref. state
Wind tunnel
Aerodynamic
Result 2 Bearing damping & stiffness
Coulomb friction
Coulomb frictionRMS Acceleration(cm/s )
Change in damping (MNs/m)
RMS Acceleration(cm/s )
Change in stiffness (MN/m)
0 1 2
0
4
8
0 1 2-12
-8
-4
0
Bearing