This study presents a damage detection algorithm based on the proper orthogonal decomposition technique
for health monitoring of composite structures. A finite element model of a carbon/epoxy composite plate is
used to generate vibration data for healthy and damaged structures. Varying levels of stiffness reduction for
the elements in the damaged zone of the structure simulate impact damage. Different random excitation
inputs are used for each of the three damage locations investigated in order to introduce variation in the
loading conditions of the model. An experimental investigation is also performed using a carbon/epoxy
plate similar to the numerical model. The composite plate is mounted as a cantilever and the fixed end of
the plate is excited with an electro-magnetic shaker. Impact damage is introduced into the plate dropping a
steel ball in one area of the plate from different heights. The results of the damage detection method
indicate that damages can be detected and localized using this algorithm.
KEYWORDS: Bridges, Sensors, Sensor networks, Damage detection, Analog electronics, Digital filtering, Cements, Linear filtering, Instrument modeling, System identification
The development of low-cost wireless sensor networks has resulted in resurgence in the development of ambient
vibration monitoring methods to assess the in-service condition of highway bridges. However, a reliable approach
towards assessing the health of an in-service bridge and identifying and localizing damage without a priori knowledge of
the vibration response history has yet to be formulated. A two-part study is in progress to evaluate and develop existing
and proposed damage detection schemes. The first phase utilizes a laboratory bridge model to investigate the vibration
response characteristics induced through introduction of changes to structural members, connections, and support
conditions. A second phase of the study will validate the damage detection methods developed from the laboratory
testing with progressive damage testing of an in-service highway bridge scheduled for replacement. The laboratory
bridge features a four meter span, one meter wide, steel frame with a steel and cement board deck composed of sheet
layers to regulate mass loading and simulate deck wear. Bolted connections and elastomeric bearings provide a means
for prescribing variable local stiffness and damping effects to the laboratory model. A wireless sensor network
consisting of fifty-six accelerometers accommodated by twenty-eight local nodes facilitates simultaneous, real-time and
high-rate acquisition of the vibrations throughout the bridge structure. Measurement redundancy is provided by an array
of wired linear displacement sensors as well as a scanning laser vibrometer. This paper presents the laboratory model
and damage scenarios, a brief description of the developed wireless sensor network platform, an overview of available
test and measurement instrumentation within the laboratory, and baseline measurements of dynamic response of the
laboratory bridge model.
With the increased demand placed on aging infrastructure, there is great interest in new condition assessment tools for
bridges. The routine deterioration that bridges undergo causes a loss in the intended performance that, if undetected or
unattended, can eventually lead to structural failure. Currently the primary method of bridge condition assessment
involves a qualitative bridge inspection routine based on visual observations. Discussed in this paper are methods of in-situ
quantitative bridge condition assessment using a dense wireless sensor array. At the core of the wireless system is
an integrated network which collects data from a variety of sensors in real-time and provides analysis, assessment and
decision-making tools. The advanced wireless sensor system, developed at Clarkson University for diagnostic bridge
monitoring, provides independent conditioning for both accelerometers and strain transducers with high-rate wireless
data transmission in a large-scale sensor network. Results from a field deployment of a dense wireless sensor network
on a bridge located in New York State are presented. The field deployment and testing aid to quantify the current bridge
response as well as demonstrate the ability of the system to perform bridge monitoring and condition assessment.
Presented in this paper is the environmental testing of Wireless Intelligent Sensor and Actuator Network (WISAN) currently under development at Clarkson University for the use of long-term structural health monitoring of civil infrastructure. The wireless sensor nodes will undergo controlled mechanical vibration and environmental testing in the laboratory. A temperature chamber will be used to perform temperature cycle tests on the sensor nodes. The temperature chamber will also houses a small shaker capable of introducing mechanical loading under the controlled temperature
cycle tests. At low temperatures, the resistance of the electronics processing and storage characteristics will be studied. Also, the testing will look at volume expansion and degradation of characteristics due to freezing, degradation of functions and performance, and mechanical characteristics caused by contraction. At high temperatures, temperature-related changes in sensor nodes due to excessively high temperatures will be investigated. Also studied will be the effects of temperature cycles, including the thermal stresses induced in the nodes and housing and the distortion caused due to expansion and contraction, fatigue, cracks, and changes in electrical characteristics due to mechanical displacement. And finally, mechanical vibration loading will be introduced to the WISAN sensor nodes. Mechanical looseness, fatigue destruction, wire disconnection, damage due to harmonic vibration, defective socket contact, joint
wear, destruction due to harmonics, lead breakage, occurrence of noise and abnormal vibration, cracking will be monitored. The eventual goal of the tests is to verify WISAN's performance under anticipated field conditions in which the sensors will be deployed.
The sensitivity and consistency of a damage index based on instantaneous phase values obtained through vibration measurements of a structure is investigated experimentally. An 'empirical mode decomposition' is performed to decompose structural vibrations into a small number of 'intrinsic mode functions' following the methodology generally known as the Hilbert-Huang Transform. Instantaneous phase information is derived through the Hilbert transform of intrinsic mode functions. The damage index is based on the idea that the difference in phase functions between any two points on a structure is altered if the structure is damaged. Experimental investigations are performed on a beam structure with varying excitations (white noise signals), damage levels, and damage locations. The damage index shows generally consistent results, but its sensitivity to damages needs improvements for practical applications.
KEYWORDS: Sensors, Structural health monitoring, Data acquisition, Sensor networks, Actuators, Bridges, Microcontrollers, Intelligent sensors, Temperature metrology, Data storage
This paper presents Wireless Intelligent Sensor and Actuator Network (WISAN) as a scalable wireless platform for
structural health monitoring. Design of WISAN targeted key issues arising in applications of structural health
monitoring. First, scalability of system from a few sensors to hundreds of sensors is provided through hierarchical
cluster-tree network architecture. Special consideration is given to reliable delivery of wireless data in real-world
conditions. Second, a possibility of autonomous operation of sensor nodes from energy harvesters is ensured through
extremely low power consumption in operational and standby modes of operation. Third, all the sensors and actuators
operate in globally synchronized time on the order of a few microseconds through utilization of the beaconing
mechanism of IEEE802.15.4 standard. Fourth, depending on application requirements, the system is capable of
delivering real-time streams of sensor data or performing on-sensor storage and/or processing with result transmission.
Finally, a capability to work with heterogeneous arrays of sensors and actuators is ensured by a variety of analog and
digital interfaces. Results of experimental tests validate the performance of the WISAN.
Life cycle monitoring of civil infrastructure such as bridges and buildings is critical to the long-term operational cost and safety of aging structures. The widespread use of Structural Health Monitoring (SHM) systems is limited due to unavailability of specialized data acquisition equipment, high cost of generic equipment, and absence of fully automatic decision support systems.
The goals of the presented project include: first, design of a Wireless Intelligent Sensor and Actuator Network (WISAN) and creation of an inexpensive set of instrumentation for the tasks of structural health monitoring; second, development of a SHM method, which is suitable for autonomous structural health monitoring.
The design of the wireless sensor network is aimed at applications of structural health monitoring, addressing the issues of achieving a low cost per sensor, higher reliability, sources of energy for the network nodes, energy-efficient distribution of the computational load, security and coexistence in the ISM radio bands. The practical applicability of the sensor network is increased through utilization of computational intelligence and support of signal generation capabilities.
The automated SHM method is based on the method of modal strain energy, though other SHM methods will be supported as well. The automation tasks include automation of the modal identification through ambient vibrations, classification of the acquired mode shapes, and automatic evaluation of the structural health.
Active control of fixed wing aircraft using piezoelectric materials has the potential to improve its aeroelastic response while reducing weight penalties. However, the design of active aircraft wings is a complex optimization problem requiring the use of formal optimization techniques. In this paper, a hybrid optimization procedure is applied to the design of an airplane wing, represented by a flat composite plate, with piezoelectric actuation to improve the aeroelastic response. Design objectives include reduced static displacements, improved passenger comfort during gust and increased damping. Constraints are imposed on the electric power consumption and ply stresses. Design variables include composite stacking sequence, actuator/sensor locations and controller gain. Numerical results indicate significant improvements in the design objectives and physically meaningful optimal designs.
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