• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.61-64
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• 2007

This study is dealt with a method to enhance low-frequency diffuse sound field in a scaled reverberation chamber. Because scaled reverberation chamber has not enough room volume, as a result, it shows a few room modes. So it is not build up low-frequency diffuse sound field. A Helmholtz resonator's arrangement is used to improve spatial uniformity of sound pressure at low frequency. The spatial distribution of sound field has been measured before and after control. The standard deviation of sound field has decreased at 315Hz 1/3 Octave band.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.3
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• pp.199-210
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• 1996

The measurements of velocities of internal flow in a scaled-up nozzle were made by laser Doppler velocimetry in order to clarify the effect of internal flow on the characteristics of fuel spray. The investigated length to diameter ratio(L/d) of the orifice were 1, 3, 4, 5 and 8, and inlet radius to diameter ratio(r0/d) were 0 and 0.5. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds number ranging between 15,000 and 28,000, and L/d ranging between 1 and 8 in sharp and round inlet nozzle. The turbulent intensity and turbulent kinetic energy at exit in a sharp inlet nozzle were higher than that in a round inlet nozzle. For sharp inlet nozzle, fluctuating velocities near exit were decreased with increasing L/d.

• Journal of ILASS-Korea
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• v.1 no.1
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• pp.76-84
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• 1996

The nozzle geometry and up-stream inject ion condition affect the characteristics of flow inside the nozzle. such as turbulence and cavitation bubbles. Flow details in fuel nozzle orifice with sudden contraction of cross sectional area have been investigated both experimentally and numerically. The measurements of velocities of internal flow in a scaled-up nozzle with different length to diameter rat io(L/d) were made by laser Doppler velocimetry in order to clarify the effect of internal flow on the characteristics of fuel spray. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds numbers. The turbulent intensity and turbulence kinetic energy in a sharp inlet nozzle were higher than that in a round inlet nozzle. Calculations were also performed for the same nozzles as scaled-up experimental nozzles using the SIMPLE algorithm. External spray behavior under different nozzle geometry and up-stream flow conditions using Doppler technique and visualization technique were also observed.

• Journal of the Korea Computer Graphics Society
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• v.17 no.1
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• pp.39-44
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• 2011

In this paper, we introduce a novel method to reduce image to a small size, such that the quality of the image is improved when it is up-scaled. Recent hardwares including cameras and display devices allow us to capture and display high-resolution images. However, it is not always realistic to store and transmit those high-resolution images due to limitation of storage and network bandwidth. Therefore, high-resolution images are often down-scaled to be stored and transmitted, and then up-scaled back for display. To improve final image quality in this scenario, we first formulate selected up-scale methods as linear transformations. The optimal reduction methods are obtained as its inverse transformation. Based on this basic idea, we develop down-scale kernel that is optimized for each up-scale method. In our experiment, the proposed method could improve the quality of the up-scaled image noticeable.

• Computers and Concrete
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• v.21 no.4
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• pp.385-397
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• 2018

This study is focused on the investigation for similitude the requirements between prototype and scaled models to determine the structural behavior of concrete load bearing systems. The scaling concept has been utilized in many engineering branches, has been assisted to engineers and scientists for obtain the behavior of the prototype by using scaled model. The scaling can be done for two purposes, either scaling up or scaling down depending upon the application. Because, scaled down models are the experimentation on scaled models is cheaper than huge structures. These models also provide facilities for experimental work. Similarity relationships between systems are created either by field equations of the system or by dimensional analysis. Within this study, similarity relationships were obtained by both methods. The similarity relations obtained are applied to different load bearing systems and it is determined that the similarity relation is a general expression. In this study, as an example, column, frame, cantilever beam and simple beam are chosen and 1/2, 1/5 and 1/10 scales are applied. The results are compared with the analytical results which are obtained by creating of the finite element models with SAP2000 software of different scaled load bearing systems. The analysis results of all systems are examined and it is determined that the scale factors are constant depending on the scale types for different load bearing systems.

• Journal of the Korean Society of Safety
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• v.23 no.5
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• pp.30-34
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• 2008

To evaluate the mechanical properties of in-service materials, tensile properties measurement using small-scaled specimen has been carried out. Tensile testing specimens with various dimensions, including standard and sub-size specimen specified in ASTM and ISO and small-scaled specimen, were prepared. Tensile strain in small-scaled specimen was measured using micro-ESPI system set up in this study. This system was used in the specimen with the parallel length of 2 mm and in subsequently measuring the strain under tensile loading. From each type of tensile specimen, stress-strain curves were determined. The dimension effect of the tensile properties was investigated comparing the tensile results obtained from standard specimens and small-scaled specimens. It was shown that the tensile strength for the small-scaled specimen is lower by 15% than those for the standard specimen.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.1
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• pp.12-18
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• 2019

The spherical $SiO_2$ powders were synthesized by the scaled-up ultrasonic pyrolysis (USP). The aqueous $SiO_2$ sol, which contained 20~30 nm $SiO_2$ particles, was used as a precursor for the scaled-up USP. The effects of the USP operating conditions and precursor conditions were systematically investigated, including reaction temperature, gas flow rate, and the concentration of $SiO_2$ sol on the morphologies of synthesized $SiO_2$ particles. the synthesized $SiO_2$ particle showed a pseudo-crystal phase, spherical morphology, and a smooth surface. The size of the spherical $SiO_2$ particle decreased as both reaction temperature increased and precursor concentration decreased. In addition, the synthesized $SiO_2$ particle size was increased by increasing the gas flow rate. Lastly, the scaled-up USP was compared with the lab-scale USP based on the same process conditions. Due to a short retention time in the reaction tube during the USP process, the $SiO_2$ particle synthesized via the lab-scale USP showed a larger particle size.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.145-148
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• 2008

A 50 Newton monopropellant thruster being developed for attitude control in a variety of aerospace application systems is described in this paper. A scaled down thruster with platinum on aluminum oxide in the reaction chamber was tested to determine the catalyst capacity. A scaled up thruster, was designed and fabricated using data obtained on small scale device, was evaluated by decomposition efficiency based on temperature, efficiency of characteristic velocity, and measurement of thrust. The performance of a scaled up thruster was 42 Newton in thrust, 98 % in efficiency of characteristic velocity, and 123 sec in specific impulse at sea level.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.3
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• pp.24-33
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• 2008

A 50 Newton monopropellant thruster being developed for attitude control in a variety of aerospace application systems is described in this paper. A scaled down thruster with platinum on aluminum oxide in the reaction chamber was tested to determine the catalyst capacity. A scaled up thruster which was designed and fabricated using data obtained from a small scale device was evaluated by its decomposition efficiency based on the temperature, the efficiency of characteristic velocity, and the measurement of thrust. The performance of a scaled up thruster was marked by a measured thrust of 42 Newton, 98 % efficiency of the characteristic velocity, a specific impulse of 123 sec at sea level.

• ETRI Journal
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• v.40 no.5
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• pp.561-569
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• 2018

Modern communication systems employ wideband antennas with circular polarization (CP) radiation. In this work, asymmetric modified bow-tie (ABT) and symmetric modified bow-tie (SBT) slotted circularly polarized single-point probe-fed circular patch antennas with dimensions of $40mm{\times}40mm$ for wideband applications are proposed. A 10 dB RL bandwidth of 350 MHz with CP, 3 dB axial ratio (AR) bandwidth of 100 MHz, peak gain of 4.9 dBic, and 10 dB RL bandwidth of 530 MHz with CP, 3 dB AR bandwidth of 140 MHz, peak gain of 5 dBic are obtained for ABT and SBT slotted circular patch antennas, respectively. The proposed SBT slotted patch is scaled up and down to $50mm{\times}50mm$ and $30mm{\times}30mm$, respectively. The proposed scaled-up version offers 10 dB RL and 3 dB AR bandwidths of 340 MHz and 80 MHz, with a peak gain of 5 dBic. The scaled-down version offers 10 dB RL and 3 dB AR bandwidths of 710 MHz and 180 MHz, with a peak gain of 5.25 dBic. These prototypes are suitable to work in IEEE 802.11a WLAN, ISM, and IEEE 802.11ac applications. The measured and simulated results are then discussed and compared.