Finite element (FE) model updating is often used to associate FE models with corresponding existing structures for
the condition assessment. FE model updating is an inverse problem and prone to be ill-posed and ill-conditioning when
there are many errors and uncertainties in both an FE model and its corresponding measurements. In this case, it is
important to quantify these uncertainties properly. Bayesian FE model updating is one of the well-known methods to
quantify parameter uncertainty by updating our prior belief on the parameters with the available measurements. In
Bayesian inference, likelihood plays a central role in summarizing the overall residuals between model predictions and
corresponding measurements. Therefore, likelihood should be carefully chosen to reflect the characteristics of the
residuals. It is generally known that very little or no information is available regarding the statistical characteristics of
the residuals. In most cases, the likelihood is assumed to be the independent identically distributed Gaussian distribution
with the zero mean and constant variance. However, this assumption may cause biased and over/underestimated
estimates of parameters, so that the uncertainty quantification and prediction are questionable. To alleviate the potential
misuse of the inadequate likelihood, this study introduced approximate Bayesian computation (i.e., likelihood-free
Bayesian inference), which relaxes the need for an explicit likelihood by analyzing the behavior similarities between
model predictions and measurements. We performed FE model updating based on likelihood-free Markov chain Monte
Carlo (MCMC) without using the likelihood. Based on the result of the numerical study, we observed that the
likelihood-free Bayesian computation can quantify the updating parameters correctly and its predictive capability for the
measurements, not used in calibrated, is also secured.
In this paper, a piezoelectric energy harvesting device consisting of a proof mass and a corrugated cantilever beam is proposed in order to enhance its performance (i.e., an increase in output voltage as well as a reduction in resonant frequency). The sinusoidal or trapezoidal shape of a cantilever beam is able to make the bonding area of piezoelectric materials (e.g., polyvinylidene fluoride (PVDF) film) much larger, resulting in higher output voltages. Moreover, the natural frequency of the device can be significantly decreased due to low flexural rigidity of the beam member. This lownatural frequency device would fit well for civil engineering applications because most civil structures such as bridges and buildings have low natural frequencies. In order to examine the geometrical characteristics of the proposed device, an analytical development and a numerical simulation are carried out. Besides, shaking table tests are conducted with a prototype of energy harvesting device. It is demonstrated from numerical and experimental studies that the proposed energy harvester can shift down its resonant frequency considerably and generate much higher output power as compared with a conventional one having a flat (or straight) cantilever beam.
It is well known that the dynamic properties of a structure such as natural frequencies depend not only on damage but
also on environmental condition (e.g., temperature). The variation in dynamic characteristics of a structure due to
environmental condition may mask damage of the structure. Without taking the change of environmental condition into
account, false-positive or false-negative damage diagnosis may occur so that structural health monitoring becomes
unreliable. In order to address this problem, an approach to construct a regression model based on structural responses
considering environmental factors has been usually used by many researchers. The key to success of this approach is the
formulation between the input and output variables of the regression model to take into account the environmental
variations. However, it is quite challenging to determine proper environmental variables and measurement locations in
advance for fully representing the relationship between the structural responses and the environmental variations. One
alternative (i.e., novelty detection) is to remove the variations caused by environmental factors from the structural
responses by using multivariate statistical analysis (e.g., principal component analysis (PCA), factor analysis, etc.). The
success of this method is deeply depending on the accuracy of the description of normal condition. Generally, there is
no prior information on normal condition during data acquisition, so that the normal condition is determined by
subjective perspective with human-intervention. The proposed method is a novel adaptive multivariate statistical
analysis for monitoring of structural damage detection under environmental change. One advantage of this method is the
ability of a generative learning to capture the intrinsic characteristics of the normal condition. The proposed method is
tested on numerically simulated data for a range of noise in measurement under environmental variation. A comparative
study with conventional methods (i.e., fixed reference scheme) demonstrates the superior performance of the proposed
method for structural damage detection.
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