• Structural Engineering and Mechanics
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• v.14 no.4
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• pp.491-504
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• 2002

A state-space method is proposed to analyze the aerodynamically coupled flutter problems of long-span bridges based on the modal coordinates of structure. The theory about complex modes is applied in this paper. The general governing equation of the system is converted into a complex standard characteristic equation in a state space format, which contains only two variables. The proposed method is a single-parameter searching method about reduced velocity, and it need not choose the participating modes beforehand and has no requirement for the form of structure damping matrix. The information about variations of system characteristics with reduced velocity and wind velocity can be provided. The method is able to find automatically the lowest critical flutter velocity and give relative amplitudes, phases and energy ratios of the participating modes in the flutter motion. Moreover, the flutter analysis of Jiangyin Yangtse suspension bridge with 1385 m main span is performed. The proposed method has proved reliable in its methodology and efficient in its use.

• 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.

• Journal of Korean Society of Rural Planning
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• v.18 no.1
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• pp.9-15
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• 2012

This study used GIS method for the characteristic analysis of farmstead location in study area. The present study surveyed the coordinates of location for 76 livestock farmsteads with big size in rural areas within city of Cheonan. Based on the surveyed data, this study analyzed the spatial characteristics of location for the farmsteads by using both new evaluation criteria and their corresponding GIS (geographic information system) layers developed in this research. The criteria consist of six factors, which are 2 geographic factors for slope(SLO) and aspect(ASP) of earth surface, 3 accessability factors for distance from water area(DWA), road(DRO), and built-up area(DBA), including type of landuse(TLA). In the analysis results of six criteria using the grid funcations of GIS, the highest distributed ratios of the farmsteads per criterion were found at the lower slope area less then 2% in SLO, the area with south and south-east direction in ASP, the area with distance between 500m and 1,000m in both DWA and DRO, the area within 500m in DWA, and the paddy and upland area in TLA. As new finding of this study, these analysis results seemed that the farmsteads have been located at the better places with the priority to build and manage conveniently and economically.

• Economic and Environmental Geology
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• v.13 no.3
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• pp.159-166
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• 1980

A model study was conducted for the investigation of apparent resistivity variation along with electric resistivity variation of host rock and dip variation of bed. Experiments were carried out for the cases of horizontal and dipping beds in a water tank by using Wenner and Schlumberger arrays and by changing salinity of water. The ratios of resistivity values of the bed to that of brine were 1 : 10, 1 : 50, 1 : 100 and 1 : 500. Natural coally-shale of $55cm{\times}35cm{\times}3.5cm$ was used as a bed for experimental model, and brine as a host rock. Equi-resistivity curves and characteristic curves were obtained for each case of the experiment. The equi-resistivity curve was drawn both on the cross section parallel to strike of bed and longitudinal section perpendicular to it. The characteristic curve was drawn on the cross section. In the case of dipping bed of different dips, the curves are parallel to the boundary of the bed in the upper part of the bed, and are inclined to the opposite direction with the same angle of the dip of bed in the lower part. We can deduce, from the equi-resistivity curves, the location, shape and dip of the bed. It is shown in the characteristic curves that when the ratio of resistivity value of bed to that of host rock increases, the slope of curves becomes steeper, location of low-resistivity zone lower, and the width of it narrower. The slope of curves also becomes steeper when dip of bed increases. We can deduce, from the characteristic curves, the ratio of resistivity values between adjacent beds. It was found out from the experiments that electric resistivity method could be applicable to prospecting for underground geology with an electric resistivity contrast of 1 : 10. This fact strongly suggests that distinction of coal from coally-shale could be possible in a certain field condition.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.3
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• pp.85-94
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• 2006

Practially useful method of steel fiber for construction work is presented in this study. The most important purpose of this study is to develop a model which can predict mechanical behavior of the structure according to aspect ratio and volume fraction of steel fiber. Experiments on compressive strength, elastic modulus, and splitting strength were performed with self-made cylindrical specimens of variable aspect ratios and volume fractions. The experiment showed that compressive strength was not in direct proportion to volume fraction which doesn't seem to have great influence over compressive strength. However, splitting strength showed almost direct proportion to aspect ratio and volume fraction. Improvement of optimal efficiency was confirmed when the aspect ratio was 70. Experiments on flexural strength, fracture energy, and characteristic length were carried out with self-manufactured beams with notch. As a result, increases of flexural strength, fracture energy, and characteristic length according to increase of volume fraction tend to be prominent when aspect ratio is 70. The steel fiber improves concrete to be more ductile and tough. Moreover, regression analysis was the performed and predictable model was developed after determining variables. With comparison and analysis of suggested estimated values and measured data, reliance of the model was verified.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.11
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• pp.3041-3053
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• 1995

Cylindrical chokes are used widely as components of hydraulic equipments. The dynamic characteristics between flowrate and pressure drop through the cylindrical chokes were discussed by the frequency characteristics of the chokes. It was assumed no pressure recovery occurred near the downstream of the choke. The pulsating jetflow from the outlet of cylindrical chokes show very complex behaviours which are quite different from the steady jet flow but it's not clarified quantitatively. In order to utilize the chokes as a flowmeter, it is indispensable to discuss the estimation of the dynamics of pressure drop in the downstream jetflow region of cylindrical chokes. In this experimental study, it is clarified that the reattachment length depended on pressure wave is compared with it depended on velocity wave. A pulsating flow is verified by visualization method. In the present study, the flow characteristic variables of laminar pulsating flow are investigated analytically and experimentally in a circular pipe. Characteristic parameters of the ratios of inertia(.PHI.$_{t,1}$) and viscous(.PHI.$_{z,1}$) term to pressure term are introduced to describe the flow pattern of laminar pulsating flow. flow.low.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.06a
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• pp.678-681
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• 2007

In this study, an implementation of a system for measuring more accurate blood pressure by non-invasive methods of oscillometric was performed. The system were composed of pressure control, signal measurement, blood pressure signal processing units and wireless sensor network parts. For verify the validity of the system, tests of characteristics evaluations for pressure measurement unit, extraction of characteristic ratios for blood pressure estimation, blood pressure tracking by oscillometric method were performed. A group of five adult male was selected for the clinical test of the implemented system. The results of the oscillometric method in comparison with auscultatory method are that the maximum ratios of PAD of average, systolic and diastolic arterial pressure are 1.38%, 1.63% and 2.97% with SEP of 5.00, 3.72 and 4.34.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.11
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• pp.1009-1017
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• 2010

As rotating machines play an important role in industrial applications such as aeronautical, naval and automotive industries, many researchers have developed various condition monitoring system and fault diagnosis system by applying various techniques such as signal processing and pattern recognition. Recently, fault diagnosis systems using artificial neural network have been proposed. For effective fault diagnosis, this paper used MLP(multi-layer perceptron) network which is widely used in pattern classification. Since using obtained signals without preprocessing as inputs of neural network can decrease performance of fault classification, it is very important to extract significant features of captured signals and to apply suitable features into diagnosis system according to the kinds of obtained signals. Therefore, this paper proposes the decision method of the proper feature vectors about each fault signal for neural-network-based fault diagnosis system. We applied LPC coefficients, maximum magnitudes of each spectral section in FFT and RMS(root mean square) and variance of wavelet coefficients as feature vectors and selected appropriate feature vectors as comparing error ratios of fault diagnosis for sound, vibration and current fault signals. From experiment results, LPC coefficients and maximum magnitudes of each spectral section showed 100 % diagnosis ratios for each fault and the method using wavelet coefficients had noise-robust characteristic.

• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1771-1776
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• 2020

Adverse effects in the measured gamma spectrum caused by radioactive statistical fluctuations, gamma ray scattering, and electronic noise can be reduced by energy spectrum denoising. Wavelet threshold denoising can be used to perform multi-scale and multi-resolution analysis on noisy signals with small root mean square errors and high signal-to-noise ratios. However, in traditional wavelet threshold denoising methods, there are signal oscillations in hard threshold denoising and constant deviations in soft threshold denoising. An improved wavelet threshold calculation method and threshold processing function are proposed in this paper. The improved threshold calculation method takes into account the influence of the number of wavelet decomposition layers and reduces the deviation caused by the inaccuracy of the threshold. The improved threshold processing function can be continuously guided, which solves the discontinuity of the traditional hard threshold function, avoids the constant deviation caused by the traditional soft threshold method. The examples show that the proposed method can accurately denoise and preserves the characteristic signals well in the gamma energy spectrum.

• Carbon letters
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• v.9 no.3
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• pp.210-217
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• 2008

Petroleum pitch and coke with wet mixture method or with dry mixture method were investigated to develop the composite anodic carbon material of high power lithium ion battery. Cokes coated with pitch were obtained by the heat treatment of mixture of cokes and pitch with different weight ratios at $800{\sim}1200^{\circ}C$. The charge and discharge characteristic of the consequent composite anodic carbon material assembled in batteries was tested. Cokes with wet mixture method have a smooth surface and their capacity changed little with changing temperature and content as compared to the cokes with dry mixture method. Although the reversible capacities showed different values by the anode manufacturing method, the composite anode with the mixture of 20 wt% of petroleum pitch and 80 wt% of coke showed the higher power capability and initial efficiency than the pitch based anode. However, the reversible capacity of the composite anode showed the reduced value as compared with the pitch based anode.