In this research, an internal model based method is proposed to estimate the displacement profile of a bridge subjected to a moving traffic load using a combination of acceleration and strain measurements. The structural response is assumed to be within the linear range. The deflection profile is assumed to be dominated by the fundamental mode of the bridge, therefore only requiring knowledge of the first mode. This still holds true under a multiple vehicle loading situation as the high mode shapes don’t impact the over all response of the structure. Using the structural modal parameters and partial knowledge of the moving vehicle load, the internal models of the structure and the moving load can be respectively established, which can be used to form an autonomous state-space representation of the system. The structural displacements, velocities, and accelerations are the states of such a system, and it is fully observable when the measured output contains structural accelerations and strains. Reliable estimates of structural displacements are obtained using the standard Kalman filtering technique. The effectiveness and robustness of the proposed method has been demonstrated and evaluated via numerical simulation of a simply supported single span concrete bridge subjected to a moving traffic load.
Because of the relatively narrow bandwidth of the linear approaches, using nonlinear oscillators to harvest energy from ambient vibrations has been a primary trend in this field. Frequency response, used extensively in evaluating linear approaches, has been used as the primary metrics for nonlinear harvesters. Existing results have demonstrated that nonlinear devices may offer “broadband” performance. However, such “broadband” performance can only be obtained from a single-frequency excitation. It does not represent satisfactory performance of such devices under multi-frequency excitations because of the inapplicability of the principle of superposition. Conversely, existing nonlinear devices may perform worse than their linear counterparts for excitations with multiple dominant frequencies. This paper provides some new insights into the potential of using nonlinear systems to harvest energy from vibrations with multiple frequencies. A previous study has shown that a nonlinear harvester can achieve its maximum performance only at the so-called global resonance condition under which the properties of excitation matches those of the response. Through the global resonance mechanism, the energy can be dissipated and compensated in multiple frequencies with the maximum efficiency. A device design concept based on the matching between the potential well of the device and the characteristics of the excitation is proposed in this study. Numerical results are included to demonstrate the effectiveness of the proposed method. In this study, focus is placed on periodic response; chaos and response under random excitations are not considered.
In this study, we investigated a promising method for measuring three-axis force based on an optical tactile sensing
system. Such system consists of a waveguide, an array of tactile cell, a light source and an image sensor (a CCD
camera). When the tactile cells are subjected to external forces, the condition for total internal reflection of the attached
waveguide is spoiled. The original symmetrical planar waveguide then changes to an asymmetrical one, leading to light
leakage in the transverse direction, which is used as the sensing mechanism for the applied forces. A numerical study
involving three-dimensional finite element analysis was carried out to study the deformation of tactile cells due to
contact forces. A linear relationship between the applied three-axis force and the spot sizes of the image of the leaked
light was obtained and validated by experiments.
In this paper, multivariable linear regression analysis was employed to obtain the relationship among facial geometric
features, and a discriminant function was used to evaluate the significance of different features. Finally, classification
rates were compared with different combinations of geometric features. The results showed that the geometric feature
with more significance probably improved the classification performance in the cases studied.
Two micro-optomechanical accelerometers based on Multi-Mode Interference (MMI) couplers were designed and
evaluated in this study. The optical components were optimized with the Parameter Scan Method. According to the
photoelastic effect, the change in refractive index of a waveguide made of crystal materials is related to the mechanical
strains in the waveguide. In this study, such change was calculated using the mechanical strains obtained from the Finite
Element Analysis (FEA) results. Beam Propagation Method (BPM) was used to study the relationship between the input
acceleration and the output optical power and thus the performance of the proposed accelerometers. The results show the
two designs are suitable for different acceleration ranges.
In order to measure three-axis force, two four-part tactile sensing systems based on piezoelectricity and optics were
designed and fabricated. The feasibility and reliability of the two systems were evaluated both numerically and
experimentally. A general formula between the applied three-axis force and the four-part tactile sensing signals was
developed. It is expected that this formula should benefit the design and fabrication of new tactile sensing systems.
Sensing technology and sensor development have received increased attention in the recent years, and a number of types
of sensors have been developed for various applications for materials and structures. In this paper, we will discuss the
concept of combining sensing of global vibration and local infrared imaging techniques. The global vibration-based
techniques determine the health condition of structures by the changes in their dynamic properties or responses to
external disturbs or excitations. Infrared Imaging is introduced here to detect local defects or problems so that to provide
more direct and accurate assessment about the severity and extent of the damage. The progress on developing a hybrid
structural health monitoring system is presented through the results on both the global sensing algorithm study and local
infrared imaging investigation on a steel C channel.
Proc. SPIE. 6529, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2007
KEYWORDS: Numerical simulations, Linear filtering, Buildings, Structural health monitoring, Finite element methods, Damage detection, System identification, Electronic filtering, Systems modeling, Filtering (signal processing)
Two parameter estimation approaches have been developed for system modeling and health monitoring of multi-story
buildings based on structural vibration responses under seismic excitation and/or applied forces. In the first approach,
parameter estimation is performed in a decentralized fashion, i.e. parameters are estimated for each story individually,
while in the second approach, the parameters are estimated in a centralized manner for the entire structure. In order to
reduce the effect of random noise, drift with D.C. off-set as well as low-frequency disturbances in the measured data,
three kinds of filter (i.e., high-pass filter, moving average filter and Kalman filter) have been used for data preprocessing.
Numerical simulations based on lumped parameter models and a finite element model of a realistic building have been
conducted. The results show that, the performance of the decentralized approach is better than the centralized one in the
This paper presents a method for structural health monitoring using acceleration measurements. In a previous study a method for detecting, locating, and quantifying structural damages has been developed by directly using the time domain structural vibration measurements. However, only displacement and velocity measurements were used in that study. In this paper, acceleration measurements are used as feedback. Because it is more practical to measure acceleration using accelerometers, it is preferable to use acceleration rather than displacement and velocity measurements for the purpose of structural damage detection and assessment. However, using acceleration measurements is more difficult since the effects of different damages can not be decoupled completely as in the cases of displacement and velocity measurements. One approach of circumventing this difficulty is presented and it involves increasing the order of time derivatives of the linear system. The effectiveness of the proposed method using acceleration feedback is evaluated with illustrative examples of a three and an eight-story model. Results obtained are found to be comparable with results from simulations using displacement measurements as feedback.
A basic eigenvector orientation approach has been used to evaluate the possibility of controlling the onset of panel flutter using a flat panel (wide beam) as an illustrative example. The onset of flutter can be defined as the instance when two modes coalesce. Since eigenvectors for two consecutive modes are usually orthogonal, an indication of the onset of flutter condition can be observed earlier when they start to lose their orthogonality. Using eigenvector orientation method for the prediction of the flutter boundary (indicated by a gradual loss of orthogonality between two eigenvectors) was developed in a previous study and thus can provide a 'lead time' for possible flutter control. In this study, a basic simple beam element is used to model the panel (wide beam). As a first step, piezoelectric layers are assumed to be bonded on the top and bottom surface of the panel to provide counter-bending moments at joints between elements. The standard linear quadratic control theory is used for controller design and full state feedback is considered for simplicity. The controllers are designed to modify the system stiffness matrix in such a way to re-stabilize the system at the onset of flutter; as a result, flutter occurrence is offset to higher flutter speed. Controllers based on different control objectives are considered and the effects of control moment locations are studied as well. Potential applications of this basic method can be straightforwardly applied to plates and shells of laminated composites using finite element method.
This study proposes a semi-model-based method for detecting, locating and quantifying damages that may exist in a structure after a seismic event. The basic concept of the proposed method is to design a monitor for each structural component that needs to be monitored. The monitor is designed based on a residual generator technique and is sensitive only to the damage of the targeted component. The input signals to this monitor are the structural dynamic responses and the excitation. The monitor produces zero or close to zero output when there is no damage in the corresponding component. It produces an obvious nonzero output when the condition of that component has changed. The occurrence and the location of the structural damage can be determined by the display of nonzero output. Furthermore, the severity of the damage can be assessed by using a time-domain system identification technique on the input-output data of the monitor. The proposed method requires some prior knowledge about the structure being monitored. However, as the method can be used to assess and update the structural property of the components, precise modeling of the structure prior to the implementation of the technique is not necessary. A three-story lumped mass shear beam model under a seismic excitation was chosen as a numerical example. Results show that the proposed method can accurately detect, locate and quantify structural damages.