• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.457-464
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• 2001

The aeroacoustic phenomena in the simple rectangular open cavity are well published by many researchers. But the geometry shapes of aircraft landing gear wells, weapon bays, etc. are more complicate than that of the simple retangular cavity. They are more similar to the cavity having cover-plates at adges, or Helmholtz resonator. Therefore, the effects of cover-plates existing on edges of rectangular open cavity are numerically investigated in this paper. The compressible Navier-Stokes equations are solved for two-dimensional cavities with laminar boundary layers upstream. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Physically correct numerical boundary conditions and buffer zone techniques are implemented to produce time-accurate solutions in the whole computation domain. The computational domain is large enough to directly resolve a portion of the radiated acoustic field. Results show that the cover-plates existing on edges of cavity reduce the noise convected from cavity, make the frequency of noise become higher, and change the directivity pattern. So these results can be used in the design of a low noise cavity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.836-842
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• 2001

The more sophisticated patterns of propagation model is presented in this paper, which includes three different source characteristics. The spherical, cosine and dipole radiation characteristics compared and sound event level and the maximum sound level are calculated by experiment and calculation. It is shown that patterns of propagation has dipole characteristics for low speed range(below about 150km/h) at electric multiple system. We know that push-pull high speed system(maximum speed: 300km/h) has cosine characteristics of noise propagation. For this purpose, We conduct the experiment of noise and know the empirical formula of noise level and radiation coefficient K. This model of simulation is conducted through point source array model at wheel/rail contact point by using program and experimental formula. We can guess prediction of profile, flat and wear of wheel by above modeling in near field.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.67-71
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• 2003

The propagation characteristics of the impulse wave discharged from the exit of a perforated pipe is investigated through a simple shock tube facility. The pressure histories and directivities of the impulse wave propagating outside from the exit of pipe with several different configurations are analyzed for the range of the incident weak shock wave Mach number between 1.02 and 1.2. In the shock tube experiments, the impulse wave are visualized by a Schlieren optical system for the purpose of understanding its propagation characteristics. The experimental results show that for the near sound field the impulse noise strongly propagates toward to the pipe axis, but for the far sound field the impulse noise uniformly propagates toward to the omnidirections, indicating that the directivity pattern is almost same regardless of the pipe type. Especially, it is shown that the perforated pipe has a little performance to reduce the impulse noise only for the near sound field

• Journal of Sensor Science and Technology
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• v.7 no.1
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• pp.9-16
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• 1998

This paper describes how the directivity pattern of the scattered sound pressure is distributed when a plane acoustic wave is incident on a rigid or soft spherical shell underwater. A coupled Finite Element-Boundary Element method is developed as a numerical technique. The result of the coupled FE-BE method is agreed with theoretical solution for algorithmic confirmation.

• The Journal of the Acoustical Society of Korea
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• v.18 no.4E
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• pp.3-9
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• 1999

Deep-water sonar transducers of FFR (Free Flooded Ring) type have been designed using a coupled FE-BEM. The proposed sonar transducers are composed of piezoelectric ceramic tubes and structural steel materials for simple fabrication. In order to have an omnidirectional beam pattern around 30kHz, a conic steel is placed below a piezoelectric tube or a steel disc is placed between two piezoelectric tubes. The dynamics of the sonar transducer is modelled in three dimensions and is analyzed with external electrical excitation conditions. Various results are available such as directivity patterns and transmitting voltage responses. The most optimal structure and dimensions of the steel material were calculated, so that the beam patterns of the sonar transducers had +/- 3dB omnidirectivity at 30kHz.

• ETRI Journal
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• v.39 no.6
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• pp.813-819
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• 2017

A slotted rectangular nameplate antenna design with a patch bearing the name of the first author is presented. A $6.8mm{\times}26mm{\times}1.6mm$ substrate of FR-4 epoxy material having a relative permittivity of 4.4 and a dielectric loss tangent of 0.02 is used. Additionally, the feeding technique used is a coaxial mechanism. The standard antenna design parameters, including the reflection coefficient, bandwidth, radiation pattern, gain, directivity, and voltage standing wave radio (VSWR) for the proposed prototype are analyzed using a high-frequency structure simulator (HFSS) v-15, and are compared to the measured results. The designed structure may be considered for different satellite- and radio-determination applications at the respective resonant frequencies.

• Journal of the Korean Institute of Telematics and Electronics
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• v.19 no.4
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• pp.6-14
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• 1982

Both the power increasing of a television broadcasting channel for the purpose of minimiaing weak signal areas and depressing of radiation pattern to prevent some interference in known quadrants may be needed in TV broadcasting. This study shows that, the two needs mentioned above are solvable by adjusting the phases of feeding points, or redesigning the lengths of feeder lines between transmitter outend and feeder inputs in super gain antenna. A theoretical study on lengths of coaxial cables and a practical procedure of designing cable lengths, which is simple and inexpensive to apply, is presented.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1921-1926
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• 2004

The tone generation mechanism and aeroacoustic characteristics have been investigated for flow over open cavities using direct acoustic numerical simulations. Physically the tone generation mechanism of open cavity is more complicated when flow instabilities are excited by the correlation effects of flow parameters. From non-dimensional parameter studies in very low Mach number range, it is shown that characteristics of cavity resonance inherently involve typical acoustic pattern at each discrete tone frequency, and especially in laminar flow the fundamental tone frequency is determined within flow instability criterion of laminar shear layer as well as cavity geometry, length to depth ratio.

• Journal of the Korean Institute of Telematics and Electronics
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• v.10 no.5
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• pp.21-30
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• 1973

A snaked-line array antenna is investigated for the use of high gain antenna at X-band frequency by studing its attenation constant and the radiation pattern. Attenuation constant which is equivalent to the radiation resistance varies roughly as a function of the square of sinh$\theta$a where sin$\theta$a corresponds to the amplitude of sinusoidal form of snaked-line. The directivity is determined by the number of snaked-line antennas and the periodic units of a snaked line.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.256-262
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• 1997

The characteristics of the unstable impinging circular jet were investigated based on the frequency characteristics and the sound field of the impinging-tones. Two symmetric modes Si and S2, associated with low frequency and high frequency respectively, and one helical mode H have been observed by measuring frequency and phase-distribution around the jet. Radiation characteristics of impinging-tone were studied by measuring axial directivity. It was founded that the radiation patterns of symmetric and helical mode are different and it is toward the plate as the impinging distance increased. By estimating the convection velocity of the unstable jet, it was founded that the convection speed decreases with the frequency and its decreasing pattern varies with unstable modes S1, S2 and H, respectively.