• Structural Monitoring and Maintenance
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• v.4 no.1
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• pp.33-52
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• 2017

A cantilever beam with a breathing crack is studied to improve the breathing crack identification sensitivity by the parametric optimization of sample entropy and wavelet transformation. Crack breathing is a special bi-linear phenomenon experienced by fatigue cracks which are under dynamic loadings. Entropy is a measure, which can quantify the complexity or irregularity in system dynamics, and hence employed to quantify the bi-linearity/irregularity of the vibration response, which is induced by the breathing phenomenon of a fatigue crack. To improve the sensitivity of entropy measurement for crack identification, wavelet transformation is merged with entropy. The crack identification is studied under different sinusoidal excitation frequencies of the cantilever beam. It is found that, for the excitation frequencies close to the first modal frequency of the beam structure, the method is capable of detecting only 22% of the crack depth percentage ratio with respect to the thickness of the beam. Using parametric optimization of sample entropy and wavelet transformation, this crack identification sensitivity is improved up to 8%. The experimental studies are carried out, and experimental results successfully validate the numerical parametric optimization process.

• Journal of IKEEE
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• v.24 no.2
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• pp.570-578
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• 2020

In this paper, we propose an efficient method for implementing the adaptive second-order Volterra filter. To reduce computational load, the UCFD-SVF has been proposed. The UCFD-SVF, however, shows deteriorated convergence performance. We propose a new method that initializes the adaptive filter weights periodically on the fact that the energy of the filter weights is slowly increased. Furthermore, we propose another method that the interval for the weight initialization is variable to guarantee the performance and we shows the method gives the better performance under the non-stationary environment through the computer simulation for the adaptive system identification.

• International Journal of High-Rise Buildings
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• v.1 no.3
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• pp.203-209
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• 2012

The purpose of this paper is to present the state of practice being used in the Philippines for the performance-based seismic design of reinforced concrete tall buildings. Initially, the overall methodology follows "An Alternative Procedure for Seismic Analysis and Design of Tall Buildings Located in the Los Angeles Region, 2008", which was developed by Los Angeles Tall Buildings Structural Design Council. After 2010, the design procedure follows "Tall Buildings Initiative, Guidelines for Performance-Based Seismic Design of Tall Buildings, 2010" developed by Pacific Earthquake Engineering Research Center (PEER). After the completion of preliminary design in accordance with code-based design procedures, the performance of the building is checked for serviceable behaviour for frequent earthquakes (50% probability of exceedance in 30 years, i.e,, with 43-year return period) and very low probability of collapse under extremely rare earthquakes (2% of probability of exceedance in 50 years, i.e., 2475-year return period). In the analysis, finite element models with various complexity and refinements are used in different types of analyses using, linear-static, multi-mode pushover, and nonlinear-dynamic analyses, as appropriate. Site-specific seismic input ground motions are used to check the level of performance under the potential hazard, which is likely to be experienced. Sample project conducted using performance-based seismic design procedures is also briefly presented.

• International Journal of Korean Welding Society
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• v.1 no.2
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• pp.36-44
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• 2001

To get the appropriate welding process variables, mathematical modeling in conjunction with many experiments is necessary to predict the magnitude of weld bead shape. Even though the experimental results are reliable, it has a difficulty in accurately predicting welding process variables for the desired weld bead shape because of nonlinear and complex characteristics of welding processes. The welding condition determined for the desired weld bead shape may cause the weld defect if the welding current/voltage/speed combination is improperly selected. In this study, the $2^{n-1}$ fractional factorial design method and correlation parameter were used to investigate the effect of the welding process variables on the fillet joint shape, and the multiple non-linear regression analysis was used for modeling the gas metal arc welding(GMAW）parameters of the fillet joint. Finally, a fuzzy rule-based method and a neural network method were proposed so that the complexity and non-linearity of arc welding phenomena could be effectively overcome. The performance of the proposed neuro-fuzzy system was evaluated through various experiments. The experimental results showed that the proposed neuro-fuzzy system could effectively check the welding conditions as to whether or not weld defects would occur, and also adjust the welding conditions to avoid these weld defects.

• Proceedings of the KIEE Conference
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• 2004.04a
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• pp.133-135
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• 2004

As a result of the recent advances in magnetic materials, the Magnetic Amplifier(Magamp) technique is one of the reliable and cost-effective postregulation method for multiple-output power supply. This is true for high-current postregulated output since at highter output current the efficiency of linear postregulation is unacceptably low, while the complexity of more efficient switch mode postregulator is associated with a significant cost. Magamp have some advantages of higher power density, simple control circuit, good regulation, high frequency and high performance. In this paper, Operation principle of proposed approach and a performance of magamp control circuit with TL431 is described. The comparative analysis of magamp circuit and buck regulator circuit with 20W load condition is conducted. Experimental verifications on multi-output flyback converter are conducted. Simulations and experimental results show that the proposed approach is efficiency and voltage regulation of the auxiliary output is excellent.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.6
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• pp.1070-1079
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• 2016

In this paper, the design of recursive radial basis function neural networks based on incremental fuzzy c-means is introduced for processing the big data. Radial basis function neural networks consist of condition, conclusion and inference phase. Gaussian function is generally used as the activation function of the condition phase, but in this study, incremental fuzzy clustering is considered for the activation function of radial basis function neural networks, which could effectively do big data processing. In the conclusion phase, the connection weights of networks are given as the linear function. And then the connection weights are calculated by recursive least square estimation. In the inference phase, a final output is obtained by fuzzy inference method. Machine Learning datasets are employed to demonstrate the superiority of the proposed classifier, and their results are described from the viewpoint of the algorithm complexity and performance index.

• Smart Structures and Systems
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• v.26 no.2
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• pp.135-146
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• 2020

This paper deals with an application of adaptive blind source separation (BSS) method, equivariant adaptive separation via independence (EASI), and Teager Energy Operator (TEO) for online identification of structural modal parameters. The aim of adaptive BSS methods is recovering a set of independent sources from their unknown linear mixtures in each step when a new sample is received. In the proposed approach, firstly, the EASI method is used to decompose structural responses into independent sources at each instance. Secondly, the TEO based demodulation method with discrete energy separation algorithm (DESA-1) is applied to each independent source, and the instantaneous frequencies and damping ratios are extracted. The DESA-1 method can provide the fast time response and has high resolution so it is suitable for online problems. This paper also compares the performance of DESA-1 algorithm with Hilbert transform (HT) method. Compared to HT method, the DESA-1 method requires smaller amounts of samples to estimate and has a smaller computational complexity and faster adaption due to instantaneous characteristic. Furthermore, due to high resolution of the DESA-1 algorithm, it is very sensitive to noise and outliers. The effectiveness of the proposed approach has been validated using synthetic examples and a benchmark structure.

• The Journal of the Acoustical Society of Korea
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• v.22 no.6
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• pp.496-504
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• 2003

In this paper, the error tolerance of each array element to ensure a given specified error level for the array pattern is analyzed using the Genetic Algorithm. In the conventional deterministic method for synthesis of sonar way problems the computational resource required in the simulation grows rapidly as the number of way elements increases. To alleviate this numerical inefficiency, the Monte-Carlo method may be considered as an alternative technique for array syntheses. However, it is difficult to apply the method to the synthesis of array patterns because of its relatively lower accuracy in spite of moderate computational complexity. A new analysis method for estimating error tolerances in sonar arrays is Proposed since the Genetic Algorithm has significant promise to efficiently solve way synthesis problems. Through several numerical tests in linear and planar arrays, it is demonstrated that the proposed method can provide accurate results for error tolerances of sonar arrays.

• Journal of Construction Engineering and Project Management
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• v.5 no.4
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• pp.1-6
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• 2015

Due to unique characteristics of small construction companies, safety management is comprised of complex problems. This paper aims to better understand the complexity and dynamics of safety management in small construction companies. A system dynamics (SD) model was built in order to capture the causal interdependencies between factors at different system levels (regulation, organization, technical and individual) and their effects on safety outcomes. Various tests were conducted to build confidence in the model's usefulness to understand safety problems facing small companies from a system dynamics view. A number of policies were analyzed by changing the value of parameters. The value of a system dynamics approach to safety management in small construction companies is its ability to address joint effects of multiple safety risk factors on safety performance with a systems thinking perspective. By taking into account feedback loops and non-linear relationships, such a system dynamics model provides insights into the complex causes of relatively poor safety performance of small construction companies and improvement strategies.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12B
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• pp.1637-1647
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• 2001

Multi-Code CDMA (MC-CDMA) can not only be integrated easily with a conventional system, but also achieve good spectral efficiency and high processing gain. However, it suffers from high value of peak-to-average power ratio (PAPR). In this paper, we propose the Multi-Phase CDMA (MP-CDMA) system that can provide variable rate service and is not susceptible to the non-linear characteristics of amplifier. The clipping is introduced between at the output of multi-code modulator and at the input of MPSK modulator in order to improve the performance of MPSK chip demodulator and reduce the system complexity, The system performances are compared for the different Number of codes and different clipping levels, respectively. The optimum clipping level is also evaluated for the different number of codes in both, AWGN and frequency flat fading channel.