• Structural Engineering and Mechanics
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• v.39 no.1
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• pp.1-20
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• 2011

This study investigates the feasibility of detecting structural damage using the HHT method. A damage detection index, the ratio of bandwidth (RB) is proposed. This index is highly correlated or approximately equal to the change of equivalent damping ratio for an intact structure incurring damage from strong ground motions. Based on an analysis of shaking table test data from benchmark models subjected to adjusted Kobe and El Centro earthquakes, the damage detection index is evaluated using the Hilbert-Huang Transform (HHT) and the Fast Fourier Transform (FFT) methods, respectively. Results indicate that, when the response of the structure is in the elastic region, the RB value only slightly changes in both the HHT and the FFT spectra. Additionally, RB values estimated from the HHT spectra vs. the PGA values change incrementally when the structure response is nonlinear i.e., member yielding occurs, but not in the RB curve from the FFT spectra. Moreover, the RB value of the top floor changes more than those from the other floors. Furthermore, structural damage is detected only when using the acceleration response data from the top floor. Therefore, the ratio of bandwidth RB estimated from the smoothed HHT spectra is an effective and sensitive damage index for detecting structural damage. Results of this study also demonstrate that the HHT is a powerful method in analyzing the nonlinear responses of steel structures to strong ground motions.

• Journal of Bio-Environment Control
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• v.32 no.2
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• pp.106-114
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• 2023

With rising concerns about pesticide spray drift by aerial application, this study attempt to evaluate aerodynamic property and collection efficiency of spray drift according to the leaf area index (LAI) of crop for preventing undesirable pesticide contamination by the spray-drift tunnel experiment. The collection efficiency of the plant with 'Low' LAI was measured at 16.13% at a wind speed of 1 m·s^-1. As the wind speed increased to 2 m·s^-1, the collection efficiency of plant with the same LAI level increased 1.80 times higher to 29.06%. For the 'Medium' level LAI, the collection efficiency was 24.42% and 43.06% at wind speed of 1 m·s^-1 and 2 m·s^-1, respectively. For the 'High' level LAI, it also increased 1.24 times higher as the wind speed increased. The measured results indicated that the collection of spray droplets by leaves were increased with LAI and wind speed. This also implied that dense leaves would have more advantages for preventing the drift of airborne spray droplets. Aerodynamic properties also tended to increase as the LAI increased, and the regression analysis of quadric equation and power law equation showed high explanatory of 0.96-0.99.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.293-300
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• 2007

In Korea, the seismic design regulations was established since 1988 about regularity scale of structures. However, It was not established about seismic performance and evaluation method as the most existing buildings was constructed before Earthquake-Resistant Design(1988). In this study, for model structures which are 4 units of non-seismic designed apartment and 3 units of seismic designed in Korea performed seismic performance evaluation by suggested KISTC (2004). And the result compare to evaluate Capacity Spectrum Method by using MIDAS Gen and SDS. As a result, we observed that suggested KISTC's method have overestimated for shear stress and drift index. The purpose of this study provides most conformity seismic performance evaluation process and the appropriate method of calculating the seismic performance index in Korea.

• Physical Therapy Korea
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• v.19 no.3
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• pp.115-123
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• 2012

It is important to assess foot posture when investigating the relationship between lower extremity dysfunctions and foot types. Although several measurements of static foot posture have been used, there is no consensus regarding clinical measurements for foot posture. The aim of this study is to explore the differences among navicular drift (NDt), foot posture index (FPI), arch index (AI), dorsal arch height ratio (DAHR), normal navicular height truncated (NNHt) and to discover the most effective measurement. After foot types were classified by navicular drop test (NDp), clinical measurements of NDt, FPI, AI, DAHR, and NNHt were performed on 64 subjects' feet. ANOVA analysis was used for the variance of the difference between the NDp and the five kinds of clinical measurements, and the level of significance was set at ${\alpha}$=.05. The results showed that all five clinical measurements demonstrated significant differences with navicular drop. In post-hoc, FPI and NNHt showed significant differences in all foot types. The five clinical measurements are suitable the classification of foot types through the NDp. Therefore, it could be possible to assess correct and objective foot posture by using FPI and NNHt.

• Structural Engineering and Mechanics
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• v.30 no.4
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• pp.445-466
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• 2008

This paper presents a novel structural damage detection method with a new damage index based on the statistical moments of dynamic responses of a structure under a random excitation. After a brief introduction to statistical moment theory, the principle of the new method is put forward in terms of a single-degree-of-freedom (SDOF) system. The sensitivity of statistical moment to structural damage is discussed for various types of structural responses and different orders of statistical moment. The formulae for statistical moment-based damage detection are derived. The effect of measurement noise on damage detection is ascertained. The new damage index and the proposed statistical moment-based damage detection method are then extended to multi-degree-of-freedom (MDOF) systems with resort to the leastsquares method. As numerical studies, the proposed method is applied to both single and multi-story shear buildings. Numerical results show that the fourth-order statistical moment of story drifts is a more sensitive indicator to structural stiffness reduction than the natural frequencies, the second order moment of story drift, and the fourth-order moments of velocity and acceleration responses of the shear building. The fourth-order statistical moment of story drifts can be used to accurately identify both location and severity of structural stiffness reduction of the shear building. Furthermore, a significant advantage of the proposed damage detection method lies in that it is insensitive to measurement noise.

• Earthquakes and Structures
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• v.7 no.3
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• pp.365-384
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• 2014

The intensity of a ground motion can be measured by a number of parameters, some of which might exhibit robust correlations with the damage of structures subjected to that motion. In this study, 204 near-fault pulse-type records are selected and their seismic parameters are determined. Time history and damage analyses of a tested 3-storey reinforced concrete frame representing for low-rise reinforced concrete buildings subjected to those earthquake motions are performed after calibration and comparison with the available experimental results. The aim of this paper is to determine amongst several available seismic parameters, the ones that have strong correlations with the structural damage measured by a damage index and the maximum inter-story drift. The results show that Velocity Spectrum Intensity is the leading parameter demonstrating the best correlation, followed by Housner Intensity, Spectral Acceleration and Spectral Displacement. These seismic parameters are recommended as reliable parameters of near-fault pulse-type motions related to damage potential of low-rise reinforced concrete structures. The results also reaffirm that the conventional and widely used parameter of Peak Ground Acceleration does not exhibit a good correlation with the structural damage.

• Earthquakes and Structures
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• v.23 no.4
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• pp.339-352
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• 2022

Due to the large volume and generally as a public building, the damage of large-span space structures under various non-conventional loads will cause greater economic losses, casualties, and social impacts, etc. Therefore, it is particularly important to evaluate the seismic performance of large-span space structures. This paper taked a multipurpose sports center as an example and considered its synergistic deformation based on the method of equivalent damping ratio. Furthermore, The ABAQUS software was used to analyze the time-history and energy response of the multipurpose sports center under the action of rare earthquakes, and proposed a quantitative damage index to assess the overall damage of the structure. Finally, the research results indicated that the maximum inter-story drift ratio of the multipurpose sports center under the action of rare earthquakes was less than its limit value. The frame beams presented different degrees of damage, but the key members were basically in an elastic state. The bearing capacity did not reach the limit value, which satisfied the intended seismic performance target. This study taked an actual case as an example and proposed a relevant damage evaluation system, which provided some reference for the analysis of the seismic performance of large-span space structures.

• Journal of Power Electronics
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• v.11 no.2
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• pp.228-236
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• 2011

The ${\Delta}\;V_{10}$ or 10-Hz flicker index, as a common method of measurement of voltage flicker severity in power systems, requires a high computational cost and a large amount of memory. In this paper, for measuring the ${\Delta}\;V_{10}$ index, a new method based on the Adaline (adaptive linear neuron) system, the FFT (fast Fourier transform), and the PSO (particle swarm optimization) algorithm is proposed. In this method, for reducing the sampling frequency, calculations are carried out on the envelope of a power system voltage that contains a flicker component. Extracting the envelope of the voltage is implemented by the Adaline system. In addition, in order to increase the accuracy in computing the flicker components, the PSO algorithm is used for reducing the spectral leakage error in the FFT calculations. Therefore, the proposed method has a lower computational cost in FFT computation due to the use of a smaller sampling window. It also requires less memory since it uses the envelope of the power system voltage. Moreover, it shows more accuracy because the PSO algorithm is used in the determination of the flicker frequency and the corresponding amplitude. The sensitivity of the proposed method with respect to the main frequency drift is very low. The proposed algorithm is evaluated by simulations. The validity of the simulations is proven by the implementation of the algorithm with an ARM microcontroller-based digital system. Finally, its function is evaluated with real-time measurements.

• Journal of the Optical Society of Korea
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• v.15 no.3
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• pp.237-243
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• 2011

Thermal characteristics, such as diffusivity and temperature induced change in the fiber mode index of rotation sensing fiber coil are critical factors which determine the time varying, thermo-optically induced bias drift of interferometric fiber-optic gyroscopes (IFOGs). In this study, temperature dependence of the transient effect is analyzed in terms of the thermal characteristics of the fiber coil at three different temperatures. By applying an analytic model to the measured bias in the experiments, comprehensive thermal factors of the fiber coil could be extracted effectively. The validity of the model was confirmed by the fact that the extracted values are reasonable results in comparison with well known properties of the materials of the fiber coil. Temperature induced changes in the critical factors were confirmed to be essential in compensating the transient effect over a wide temperature range.

• Journal of Industrial Technology
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• v.28 no.B
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• pp.101-109
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• 2008

In general, non-stationary or chaos time series forecasting is very difficult since there exists a drift and/or nonlinearities in them. To overcome this situation, we suggest a new prediction method based on multiple model TS fuzzy predictors combined with preprocessing of time series data, where, instead of time series data, the differences of them are applied to predictors as input. In preprocessing procedure, the candidates of optimal difference interval are determined by using con-elation analysis and corresponding difference data are generated. And then, for each of them, TS fuzzy predictor is constructed by using k-means clustering algorithm and least squares method. Finally, the best predictor which minimizes the performance index is selected and it works on hereafter for prediction. Computer simulation is performed to show the effectiveness and usefulness of our method.