• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.55-57
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• 2011

TLM method to analyize receiver gain characteristic of the FZPL antenna which is operated at 12GHz and can be applied to satellite TV system, radio telescope, and Geodetic System. Some numerical results computed by TLM method are compared with Kirchhoff's approximation and PO method. As a result, receiver gain characteristic on main axis of the 12GHz FZPL antenna is shown at the front side, which means that the focal length is 15% shorter than designed focal length.

• Proceedings of the Korea Society for Simulation Conference
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• 2003.06a
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• pp.15-18
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• 2003

Most numerical techniques such as FEM, BEM, and MOM are able to analize electromagnetic scattering problems from arbitrary shapes. Although these methods could be applied to compute electromagnetic scattering problems in frequency domain, it was limited for electrodynamic problem in time domain. In this paper, electromagnetic scattering problem from Fresnel zone plate lens are considered. Some numerical results computed by TLM are compared with Kirchhoff's approximation and PO method.

• Interaction and multiscale mechanics
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• v.1 no.3
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• pp.339-355
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• 2008

A Galerkin meshfree method is presented for analyzing shear deformable cylindrical panels. Based upon the analogy between the cylindrical panel and the curved beam a pure bending mode for cylindrical panel is rationally constructed. The meshfree approximation employed herein is characterized by an enhanced moving least square or reproducing kernel basis function that can exactly represent the pure bending mode and thus meets the requirement of Kirchhoff mode reproducing condition. The variational form is discretized using the efficient stabilized conforming nodal integration with a smoothed nodal gradient based curvature. The resulting meshfree formulation satisfies the integration constraint for bending exactness. Moreover, it is shown here that the smoothed gradient preserves several desired properties which are valid for the standard gradient obtained by direct differentiation, such as partition of nullity and reproduction of a constant strain field. The efficacy of the proposed approach is demonstrated by two benchmark cylindrical panel examples.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.49-50
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• 2011

Receiving sensitivity of the power gain by using Soret typed FZPL antenna should be worse when obliquely incident wave is illuminated on the FZPL. To solve this problem, elliptic Fresnel Zone Plate Lens antenna system should be introduced. Some numerical results computed by PO method are compared with Kirchhoff's approximation and measurement result.

• The Journal of the Acoustical Society of Korea
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• v.34 no.3
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• pp.184-191
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• 2015

In this paper, a normal mode reverberation model for a range-independent environment of shallow water is proposed to calculate the reverberation level in the low-frequency range. Normal mode is used to calculate the acoustic energy propagating from the source to the scattering area and from the scattering area to the receiver. Each mode is decomposed into up and down going waves to consider scattering strength at the scattering area. The scattering functional form combines Lambert's law with a Gaussian-like term near the specular direction based on Kirchhoff approximation considering bottom condition. For verification of the suggested model, the result is relatively compared to several solutions of the problem XI and XV in the Reverberation Modeling Workshop I sponsored by the US Office of Naval Research.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.233-236
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• 2000

The acoustical response of fish depends on size and physical structure na, most important, on the presence or absence of a swimbladder. Acoustic scattering models for swimbladdered fish represent a fish by an ideal pressure-release surface having the size and shape as the swimbladder. Target strength experiments of red seabream (Chrysophrys major) have been conducted using 38 (split-beam), 120 (split-beam) and 200kHz (dual-beam) frequencies. At each start of each experiment, the live fish are placed in the cage at the surface, then the cage is lowed to about $4{\cal}m$ depth where it remains during the measurements. To test the acoustic models, predictions of target strength based on swimbladder morphometries of 10 red seabream offish total length from $103{\cal}mm{\;}to{\;}349{\cal}mm$ ($3 <$TL/\lambda$ < 45)are compared with conventional target strength measurements on the same, shock-frozen immediately after caged experiments. X-ray was projected along dorsal aspect to know the morphological construction of swimbladder. and fish body. At high frequencies, Helmholtz-kirchhoff(HK) approximation would greatly enhance swimbladdered fish modeling. Sound scattering model [HK-ray approximation model] for comparison to experimental target strength data was used to model backscatter measurements from individual fish. The scattering data can be used in the inverse method along with multiple frequency sonar systems to investigate the adequacy of classification and identification of fish

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.6
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• pp.1221-1226
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• 2011

In order to analyze the receiver gain characteristic of the Soret-type FZPL lens antenna which is operated at 12GHz, TLM method can be applied. The application of the FZPL lens antenna is often use the receiver for satellite TV system, radio telescope, and Geodetic System. Some numerical results computed by TLM method are compared with Kirchhoff's approximation and PO method. The focal characteristic of receiver gain on main axis of the FZPL is mostly shown at the front side, which means that the position of the receiver should be properly calibrated.

• ETRI Journal
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• v.42 no.6
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• pp.827-836
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• 2020

Measuring the diffraction loss for high frequencies, long distances, and large diffraction angles is difficult because of the high path loss. Securing a well-controlled environment to avoid reflected waves also makes long-range diffraction measurements challenging. Thus, the prediction of diffraction loss at millimeter-wave frequency bands relies on theoretical models, such as the knife-edge diffraction (KED) and geometrical theory of diffraction (GTD) models; however, these models produce different diffraction losses even under the same environment. Our observations revealed that the KED model underestimated the diffraction loss in a large Fresnel-Kirchhoff diffraction parameter environment. We collected power-delay profiles when millimeter waves propagated over a building rooftop at millimeter-wave frequency bands and calculated the diffraction losses from the measurements while eliminating the multipath effects. Comparisons between the measurements and the KED and GTD diffraction-loss models are shown. Based on the measurements, an approximation model is also proposed that provides a simple method for calculating the diffraction loss using geometrical parameters.

• The Journal of the Acoustical Society of Korea
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• v.20 no.5
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• pp.100-109
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• 2001

The backscattered sound energy by fish depends on size and physical structure and, most important, on the presence or absence of a swimbladder. Target strength experiments of red seabream (Pagrus major) were conducted by using 38 (split-beam), 120 (split-beam) and 200 kHz (dual-beam) frequencies with live fishes confined in a net-cage and free swimming in tank without the cage, respectively. For 38, 120, and 200 kHz frequencies, target strength equations are expressed as a function of fish length：TS/sub 38kHz/=20 log/sub 1o(l)/-66.41, TS/sub 120kHz/＝20 log/sub 1o(1)/-71.80, and TS/sub 200kHz/＝20 log/sub 1o(1)/-73.94. To test the acoustic models by using Helmholtz-Kirchhoff ray approximation, predictions of target strength based on swimbladder morphometries are compared with target strength measurements. The target strength of whole fish depends on variations in swimbladder morphology than fish body morphology. In the mean time, when the fish is confined in the net cage, scattering length by the backscattered signal matched with the Gaussian PDF, while under the free-swimming condition, scattering length is close to the Rayleigh PDF.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.4
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• pp.410-415
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• 2013

Acoustic target strength (TS) is one of the most considerable design elements for survival capacities of the submarine. It needs to reduce acoustic TS that submarines are getting larger and larger, Alberich anechoic coatings are widely used as the representative method. In this paper, the finite element method (FEM) is used to analyze the reflection and transmission coefficients of Alberich anechoic coatings, which have periodic unit cells. The FEM results are compared with experimental results in the literature. Moreover, acoustic TS for the submarine is analyzed by using that result. Finally, it is shown that acoustic TS (Case 1: 10dB, Case 2: 6dB) are reduced due to the use of Alberich anechoic coatings.