• Journal of Industrial Technology
• /
• v.18
• /
• pp.131-138
• /
• 1998

Numerical modeling for electromagnetic exploration methods are essential to understand behaviours of electromagnetic fields in complex subsurfaces. In this study, a finite element method was adopted as a numerical scheme for the 2.5-dimensional forward problem. And a finite element equation considering linear conductivity variation was proposed when 2.5-dimensional differential equation to couple eletric and magnetic field was implemented. Model parameters were investigated for near-field with large source effects and far-field with responses dominantly by homogeneous half-space. Numerical responses by this study were compared with analytic solutions in homogeneous half-space and compared with other three dimensional numerical results.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2002.03a
• /
• pp.117-124
• /
• 2002

The major purpose of this study is to determine the dynamic behavior of soil-pile-structure interaction system considering the underground cavity. For the analysis, a numerical method fur ground response analysis using FE-BE coupling method is developed. The total system is divided into two parts so called far field and near field. The far field is modeled by boundary element formulation using the multi-layered dynamic fundamental solution that satisfied radiational condition of wave. And this is coupled with near field modeled by finite elements. For the verification of dynamic analysis in the frequency domain, both forced vibration analysis and free-field response analysis are performed. The behavior of soil non-linearity is considered using the equivalent linear approximation method. As a result, it is shown that the developed method can be an efficient numerical method to solve the seismic response analysis considering the underground cavity in 2D problem.

• Steel and Composite Structures
• /
• v.34 no.5
• /
• pp.625-641
• /
• 2020

The realistic modeling of the beam-column semi-rigid connection in steel frames attracted the attention of many researchers in the past for the seismic analysis of semi-rigid frames. Comparatively less studies have been made to investigate the behavior of steel frames with semi-rigid connections under different types of earthquake. Herein, the seismic behavior of semi-rigid steel frames is investigated under both far and near-field earthquakes. The semi-rigid connection is modeled by the multilinear plastic link element consisting of rotational springs. The kinematic hysteresis model is used to define the dynamic behavior of the rotational spring, describing the nonlinearity of the semi-rigid connection as defined in SAP2000. The nonlinear time history analysis (NTHA) is performed to obtain response time histories of the frame under scaled earthquakes at three PGA levels denoting the low, medium and high-level earthquakes. The other important parameters varied are the stiffness and strength parameters of the connections, defining the degree of semi-rigidity. For studying the behavior of the semi-rigid frame, a large number of seismic demand parameters are considered. The benchmark for comparison is taken as those of the corresponding rigid frame. Two different frames, namely, a five-story frame and a ten-story frame are considered as the numerical examples. It is shown that semi-rigid frames prove to be effective and beneficial in resisting the seismic forces for near-field earthquakes (PGA ≈ 0.2g), especially in reducing the base shear to a considerable extent for the moderate level of earthquake. Further, the semi-rigid frame with a relatively weaker beam and less connection stiffness may withstand a moderately strong earthquake without having much damage in the beams.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.22 no.2
• /
• pp.43-50
• /
• 2022

In this paper, we designed and verified a Far-field measurement system for measuring the performance of an antenna operating in millimeter wave(W-band). For the antenna test, a measurement system should be selected according to the type of antenna, measurement items, measurement environment and period, etc. In the case of near-field measurement, it takes a lot of time because the number of measurement items increases when the antenna has multiple channels or various beams. Such an antenna can reduce the measurement time through Far-field measurement, and only necessary measurement items can be measured. Therefore, this study secured precise alignment of the far-field measurement system using a high-power laser and improved the measurement accuracy by applying a double amplifier system. The designed system was built in the anechoic chamber and verified by comparison with the verified Near-field measurement system.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.14 no.4
• /
• pp.471-477
• /
• 2014

In this paper, a modeling and co-simulation methodology is proposed to predict the radiated electromagnetic interference (EMI) from on-chip switching I/O buffers. The output waveforms of I/O buffers are simulated including the on-chip I/O buffer circuit and the RC extracted on-chip interconnect netlist, package, and printed circuit board (PCB). In order to accurately estimate the EMI, a full-wave 3D simulation is performed including the measurement environment. The simulation results are compared with near-field electromagnetic scan results and far-field measurements from an anechoic chamber, and the sources of emission peaks were analyzed. For accurate far-field EMI simulation, PCB power trace models considering IC switching current paths and external power cable models must be considered for accurate EMI prediction. With the proposed EMI simulation model and flow, the electromagnetic compatibility can be tested even before the IC is fabricated.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1996.06a
• /
• pp.59-62
• /
• 1996

A numerical study of a two-dimensional acoustic field is carride ort for a spinning vortex pair located neat a wall to investigate the effect of the wall from the spinning quadrupole source in unsteady vortical flows. Based on the known incompressible flow field, the perturbed compressible acoustic terms derived from the Euler equations are calculated. Non-reflecting boundary conditions on the free field and the solid boundary conditions are developed for a generalized curvilinear coordinates system to investigate the effect of a curced wall. It is concluded that the sound generated by the quadrupole sources of unsteady vortical flows in the presence of a flat wall or a circular cylinder can be calculated by using the source terms of hydrodynamic flow fluctuations in both near and far acoustic fields simultaneously.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2002.09a
• /
• pp.106-113
• /
• 2002

In this study, a numerical analysis method for soil-pile interaction in frequency domain problem is presented. The total soil-pile interaction system is divided into two parts so called near field and far field. In the near field, beam elements are used for a pile and plain strain finite elements for soil. In the far field, dynamic fundamental solution for multi-layered half planes based on boundary element formulation is adopted for soil. These two fields are coupled using FE-BE coupling technique In order to verify the proposed soil-pile interaction analysis, the dynamic responses of pile on multi-layered half planes are simulated and the results are compared with the experimental results. Also, the dynamic response analyses of interface spring elements are performed. As a result, less spring stiffness makes the natural frequency decrease and the resonant amplitude increase.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.21 no.1
• /
• pp.1-6
• /
• 1984

Calculation of the launch-condition dependent near field pattern, modal power distribution and far field pattern of the SGS mode scrambler by ray optical approch fits well with the experiment. These results were applied to explain how to establish the stable mode launching into the grated index multimode fiber under test by the SGS mode scrambler. The effective use of the 5G5 mode scrambler is found to restrict the launching NA as well as possible. This was also confirmed by experiment.

• Proceedings of the Optical Society of Korea Conference
• /
• 2009.02a
• /
• pp.197-198
• /
• 2009

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.19 no.4
• /
• pp.105-111
• /
• 2019

In this paper, a performance analysis of waveguide broad-wall slot array antenna for millimeter-wave seeker in Ka-band was performed as using near-field measurement. The measurement of slot array antenna was conducted in both far-field and near-field. And the validation of near-field test in millimeter band was confirmed. It was confirmed that the beam pattern characteristics including beam width and side lobe level of the slot array antenna that performed the verification were the same. Differenced in the side lobe level of azimuth and elevation beam pattern were verified to be less than 1dB. Additionally, the new antenna aperture distribution was extracted as using back-projection method modifying the near-field data and then introduced the method conducting performance analysis of array antenna.