• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.1
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• pp.54-60
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• 2012

When the transient current with high frequency components such as lightning surges are injected the grounding electrodes, the performance of grounding electrodes should be evaluated as grounding impedance. It is restricted to analyze the grounding impedance by measurement approach since the grounding impedance is very different with the shape and size of grounding electrodes, resistivity and relative permittivity of soil and the frequency component of the injected current. So a variety of simulation approaches have been developed. Typically, the soil resistivity measured with low frequency and relative permittivity between 1 and 80 are used for simulation of the grounding impedance. However, the resistivity and relative permittivity of soil are changed with frequency of injected current. In this paper, the frequency-dependent resistivity and relative permittivity of soil are measured and these parameters are reflected in the simulation of the grounding impedance of a ground rod. The simulated results are compared with the measured results. As a result, the simulated results with frequency-dependent soil parameters show capacitive aspect like measured results in the frequency of lower than 100[kHz] and they are more consistent with the measured results in wide frequency range.

• Journal of Biosystems Engineering
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• v.33 no.4
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• pp.269-275
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• 2008

This study was conducted to design an impedance sensor that can measure soil water content of soils. Partial least square regression (PLSR) was applied to soil impedance data preprocessed with a smoothing method. An optimal sub-spectrum size and wavelength range were determined by comparing the coefficient of determination ($R^2$) and root mean square error (RMSE) of the PLSR models obtained using soil impedance data. various PLS analysis. Based on the PLSR analysis, it would be concluded that the optimal spectrum measurement range was $32.0{\sim}50.0\;MHz$ with the optimal sub-spectrum size of about 18.5 MHz.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.423-430
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• 2002

A feasibility of a trial test method was evaluated analytically, in which the elastic modulus of a soil deposit was tried to estimate by analyzing dynamic signals measured during conducting the SPT. If there existed a reliable relationship between the impedance ratio of a rod to a soil and the amplitude ratio of a reflected to an incident wave signal at the tip of steel rod contacting the soil surface, it was expected that one could determine the impedance of soil, and then roughly estimate the elastic modulus from the impedance. For a simple rod-soil system, the existence of the relevant relationship was verified in this study by analyzing computed wave signals propagating up and down through the rod. On the basis of these results, thus, a potential of the test method to practical applications could be seen. However, apparent theoretical shortcomings possessed in this approach were also realized since the soil part had an unconfined contact area where contacted with the rod. Therefore, it was concluded that further studies needed to be conducted, in which the reliable theoretical relationship between the impedance and the amplitude ratio as well as the effective contacting soil area contributing to wave reflection should be justified.

• Interaction and multiscale mechanics
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• v.2 no.1
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• pp.91-107
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• 2009

In order to accurately estimate the seismic behavior of buildings, it is important to consider both nonlinear characteristics of the buildings and the frequency dependency of the soil impedance. Therefore, transform methods of the soil impedance in the frequency domain to the impulse response in the time domain are needed because the nonlinear analysis can not be carried out in the frequency domain. The author has proposed practical transform methods. In this paper, seismic response analyses considering frequency dependent soil impedance in the time domain are shown. First, the formulation of the proposed transform methods is described. Then, the linear and nonlinear earthquake response analyses of a building on 2-layered soil were carried out using the transformed impulse responses. Through these analyses, the validity and efficiency of the methods were confirmed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.5
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• pp.98-105
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• 2014

Soil discharges near the ground rod play an important role to reduce the ground potential rise and the ground impedance and to help the fault current to spread into the earth. This paper presents the effects of soil discharges on the transient and conventional ground impedances when the lightning impulse voltage was applied to a ground rod with radial needles. The current-voltage (I-V)curves and transient ground impedance curves were calculated based on the measured current and potential traces. Soil discharge behaviors related to I-V curves and transient ground impedance curves were analyzed as a function of the magnitude of lightning impulse voltages. As a result, the soil discharges occurred near the ground electrode contribute to the reduction of conventional ground impedance and limits the ground potential rise effectively under lightning impulse voltages.

• Geomechanics and Engineering
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• v.15 no.2
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• pp.793-803
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• 2018

Based on the theory of porous media, an interaction system of a floating pile and a saturated soil in cylindrical coordinates subjected to vertical harmonic load is presented in this paper. The surrounding soil is separated into two distinct layers. The upper soil layer above the level of pile base is described as a saturated viscoelastic medium and the lower soil layer is idealized as equivalent spring-dashpot elements with complex stiffness. Considering the cylindrically symmetry and the pile-soil compatibility condition of the interaction system, a frequency-domain analytical solution for dynamic impedance of the floating pile embedded in saturated viscoelastic soil is also derived, and reduced to verify it with existing solutions. An extensive parametric analysis has been conducted to reveal the effects of the impedance of the lower soil base, the interaction coefficient and the damping coefficient of the saturated viscoelastic soil layer on the vertical vibration of the pile-soil interaction system. It is shown that the vertical dynamic impedance of the floating pile significantly depends on the real stiffness of the impedance of the lower soil base, but is less sensitive to its dynamic damping variation; the behavior of the pile in poro-visco-elastic soils is totally different with that in single-phase elastic soils due to the existence of pore liquid; the effect of the interaction coefficient of solid and liquid on the pile-soil system is limited.

• Journal of Biosystems Engineering
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• v.34 no.6
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• pp.434-438
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• 2009

This study was conducted to design an cone penetrometer type impedance sensor that can measure soil water content in realtime. The best width between electrical probe was determined by 5 mm. For optimization about realtime application device, linear regression analysis was applied between soil water content and impedance signal. It was concluded that proper combination of excitation frequency, impedance parameter, and model would provide acceptible performance of a soil waler content sensoe. Best model was obatained at a 36.5 MHz with |Z| as a predictor variable, with a coefficient of determination of 0.96 (RMSE=1.35, RPD=4.98).

• Structural Engineering and Mechanics
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• v.87 no.2
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• pp.173-189
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• 2023

For a given structural geometry, the stiffness and damping parameters of the soil and the dynamic response of the structure may change in the face of an equivalent linear soil behavior caused by a strong earthquake. Therefore, the influence of equivalent linear soil behavior on the impedance functions form and the seismic response of the soil-structure system has been investigated. Through the substructure method, the seismic response of the selected structure was obtained by an analytical formulation based on the dynamic equilibrium of the soil-structure system modeled by an analog model with three degrees of freedom. Also, the dynamic response of the soil-structure system for a nonlinear soil behavior and for the two types of impedance function forms was also analyzed by 2D finite element modeling using ABAQUS software. The numerical results were compared with those of the analytical solution. After the investigation, the effect of soil nonlinearity clearly showed the critical role of soil stiffness loss under strong shaking, which is more complex than the linear elastic soil behavior, where the energy dissipation depends on the seismic motion amplitude and its frequency, the impedance function types, the shear modulus reduction and the damping increase. Excellent agreement between finite element analysis and analytical results has been obtained due to the reasonable representation of the model.

• Journal of Electrical Engineering and Technology
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• v.4 no.4
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• pp.531-537
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• 2009

Lightning has a broad frequency spectrum from DC to a few MHz. Consequently, the high frequency performance of grounding systems for protection against lightning should be evaluated, with the distributed parameter circuit model in a uniform soil being used to simulate grounding impedances. This paper proposes a simulation method which applies the distributed parameter circuit model for the frequency-dependent impedance of vertically driven ground rods by considering multi-layered soil structures where ground rods are buried. The Matlab program was used to calculate the frequency-dependent ground impedances for two ground rods of different lengths. As a result, an increase of the length of ground rod is not always followed by a decrease of grounding impedance, at least at a high frequency. The results obtained using the newly proposed simulation method considering multi-layered soil structures are in good agreement with the measured results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.4
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• pp.62-69
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• 2014

This paper deals with the fundamental characteristics of transient and conventional ground impedances associated with soil discharges when the lightning impulse voltage was applied to a small-sized ground rod. The potential rise responses of the test ground rod to impulse currents were observed. The current-voltage (I-V)curves, transient and conventional ground impedance curves were examined.. To analyze the transient behaviors of ground rod attendant upon soil discharges, the impulse responses of ground rod were compared with those of non-inductive resistor. As a consequence, the potential rise and impedance of ground rod were reduced and the currents dispersed into the earth were increased due to soil discharges near the ground rod. Soil discharges are classified into two regimes; ionization and breakdown phenomena. The potential rise and impulse impedance of ground rod are significantly decreased by breakdown processes in soil.