• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1B
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• pp.59-69
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• 2012

Probabilistic design is required to effectively consider the coastal environment of great uncertainty. However, designers who are familiar with the deterministic design method prefer a method which is similar to the existing method but is based on the probabilistic concept. Therefore, the partial safety factor method has been adopted as a new design method over the world. In Korea, Tetrapod is widely used for armoring rubble mound breakwaters. Even though the partial safety factor method developed in the United States and Europe covers Tetrapods, the limited wave and structure conditions in its development make the engineers hesitate about its use in practical breakwater design. In this study, partial safety factors for Tetrapod armor blocks have been developed by analyzing 116 breakwater cross-sections and wave conditions in 16 trade harbors and 15 coastal harbors with the FORM and optimal code calibration approach. Especially, partial safety factors have been proposed depending on the shape parameter of the Weibull extreme wave height distribution. For other types of extreme distributions, it is possible to apply the proposed partial safety factors using the relationship between skewness coefficient and shape parameter. Finally, the proposed partial safety factors have been applied to existing structures to show that they better satisfy the target reliability of the structures than previous partial safety factors.

• Journal of Sensor Science and Technology
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• v.5 no.2
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• pp.29-36
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• 1996

With the three dimensional magnetic field measuring system dealt with in this paper, accurate measurements and analyses of extremely low frequency(ELF) magnetic fields caused by starting and/or operating electric devices and power installations can be conducted. To obtain high performance for lower frequency and spatial components without any distortion, the measuring system is designed as three dimensionally including the multiturn loop-type magnetic field sensors, differential amplifiers and active integrators. As the results of calibration experiments, the frequency response characteristics of the measuring system range from 8[Hz] to about 53[kHz] for each direction of x, y, z axes, and the response sensitivities are 9.54, 9.21, $10.89[mV/{\mu}T]$, respectively. The actual survey experiments by using an oscillating impulse current generator confirm a reliability of the proposed measuring system. Also, through the other experiments by using small-sized induction motors, the magnetic field intensities when starting and steady-state operating mark 15.8, $8.61[{\mu}T]$ as maximum value, respectively. And those intensities decrease steeply according as the measuring distance increases.

• Journal of the Korean earth science society
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• v.32 no.6
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• pp.602-612
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• 2011

Jeju Island, a volcanic island located in South Korea, has been one of the main targets of geophysical and/or geological studies because of its tectonic importance related to the volcanism and tectonic link to the southern part of the Korean Peninsula. Recently, as a number of broad-band magnetotelluric (MT) measurements were made, we have examined the deep part of the island. In such an insular setting, it is not easy to properly recover the deep structures such as the lower crust and the upper crust using MT data, because their low-frequency components are strongly affected by the surrounding sea of the island. In this study, we apply the sea-effect correction to the existing MT data collected at a total of 102 sites in Jeju Island. The sea-effect correction makes remarkable changes in the observed MT data at frequencies below 1 Hz, clearly indicating the existence of a conductive lower crust. The 2-D inversion results for both Jeju Southern Line (JSL) and Jeju Northern Line (JNL) show that the transition zone separating the resistive upper crust and conductive lower crust exists at a depth of 20 km on average.

• Geophysics and Geophysical Exploration
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• v.12 no.3
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• pp.268-277
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• 2009

Recently as the interest in the development of domestic ore deposits has increased, we can easily find some studies on exploration geophysics-based ore deposit survey in literature. Geophysical surveys have been applied to the investigation of both metallic and non-metallic ore deposit. For metallic ore-deposit survey, the 2D electrical resistivity method has been popularly used, because metallic mineral deposits are generally more conductive than surrounding media. However, geological structures are 3D rather than 2D structures, which may lead to misinterpretation in 2D inversion section. In this study, 3D effects are examined for several 3D structures such as a width-varying dyke model and a wedge-shaped model. We also investigate the effects of the direction of survey line. Numerical results show that the width-varying dyke model yields some low resistivity zone in the deep part, which is independent of real ore-body location. For the wedge-shaped model, even though the survey line is located apart from the ore body, the 2D inversion section still shows low resistivity zone in the deep part. When the survey line is not perpendicular to the strike of the ore body, the low resistivity zone is slightly broader but shallower than that obtained along the survey line perpendicular to the strike. For the survey lines that have an angle smaller than $45^{\circ}$ with the strike of the ore body, the inversion results are totally distorted. From these results, we conclude that 2-D survey and interpretation can lead to misinterpretation of subsurface structures, which may be linked to economical loss. Eventually, we recommend to apply 3-D rather than 2-D electrical resistivity survey for ore-deposit survey.

• Journal of Biomedical Engineering Research
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• v.23 no.2
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• pp.109-117
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• 2002

Electrogastrography(EGG) is a noninvasive method for measuring gastric electrical activity on the abdomen resulting from gastric muscle. EGG signals have a very low frequency range (0.0083 ~0.15 Hz) and extremely low amplitude(10~100 uV). Consequently, EGG signal is easily influenced by other noises. Both finite impulse response(FIR) and infinite impulse response (IIR) filters need high orders or have phase distortions for passing very narrow bandwidth of the EGG signal. In this study, we decomposed EGG signals using a wavelet multiresolution method with Daubechies mother wavelet. The EGG signals were decomposed to seven levels. We reconstructed signal by summing the decomposed signals from level four to seven. To evaluate the performance of the wavelet multiresolution filter(WMF) with simulated EGG signal using two kinds of FIR and four kinds of IIR filters., we used two indices; signal to noise ratio(SNR) and reconstruction squared error(RSE). The SNR of WMF had 9.5, 6.9, and 4.7 dB bigger than that of the other filters at different noise levels, respectively. Also, The RSE of WMF had $1.22{\times}10^6, 1.16{\times}10^6, 1.02{\times}10^6$ smaller than that of the other filters at different noise levels, respectively. The WMF performed better in the SNR and RSE than two kinds of FIR and four kinds of IIR filters.

• Geophysics and Geophysical Exploration
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• v.8 no.3
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• pp.224-231
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• 2005

In geophysical field surveys, commercial equipments often fail to resolve the subsurface target or even sometimes fail to be applied because they do not fit to the various field situations or the physical properties of the medium or target. We developed a geophysical measurement system, which can be easily adapted for the various field situations and targets. The system based on PXI with A/D converter and some stand alone equipment such as Network Analyzer was applied to borehole radar survey, borehole sonic measurement and electromagnetic noise measurement. The system for borehole radar survey consists of PXI, Network Analyzer, dipole antennas, GPIB interface is used for PXI to control Network Analyzer. The system for borehole sonic measurement consists of PXI, 24 Bit A/D converter, high voltage pulse generator, transmitting and receiving piezoelectric sensors. The electromagnetic noise measurement system consists of PXI, 24 Bit A/D converter, 2 horizontal component electric field sensors and 2 horizontal and 1 vertical component magnetic filed sensors. The borehole radar system has been successfully applied to detect the width of the artificial tunnel through which the borehole pass and to image buried steel pipe, while the commercial borehole radar equipment failed. The borehole sonic system was tested to detect the width of artificial tunnel and showed a reasonable result. The characteristic of electromagnetic noise was grasped at an urban area with the data from the electromagnetic noise measurement system. The system is also applied to characterize the signal distortion by induction between the electric cables in resistivity survey. The system can be applied various geophysical problems with a simple modification of the system and sensors.