• Journal of the Institute of Convergence Signal Processing
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• v.19 no.3
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• pp.133-138
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• 2018

VR technology is a technology that allows a user to experience virtual reality close to reality by wearing an HMD (Head Mounted Display) device. Recently, as the interest in VR technology increases due to the 4th industrial revolution, various HMD devices are spreading. As a result, VR technology is being rapidly applied to various fields, but many of them still experience VR nausea. VR nausea is caused mainly by visual factors, unlike motion nausea, such as car nausea, sea nausea, and air nausea. Such occurrence of VR nausea may be caused by the characteristics of visual information of VR video contents, the hardware characteristics of HMD devices blocking the external visual field, or the physical specificity of individuals, and it is difficult to distinguish the causes. In this paper, we aim to analyze the characteristics of Visually Induced Motion Nausea images focusing on VR video content, which is the cause of VR nausea, in order to search for minimization of Cyber sickness occurrence.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.1
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• pp.29-36
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• 2008

Spray characteristics for APU gas turbine engine are investigated. In the test, four flight conditions such as sea level idle, sea level max power, 20,000 feet idle, 20,000 feet max power are used as spray experimental conditions. Spray visualization was performed by using ND-YAG laser bean PDPA(Phase Doppler Particle Analyzer) was used for measuring the particle diameter and velocity from 20 mm to 100 mm from discharge orifice. From the test result, SMD is $90{\sim}95\;{\mu}m$ 맛 20,000 ft idle condition and SMD is $60{\sim}75\;{\mu}m$ at sea level idle condition. Also SMD is $55{\sim}65\;{\mu}m$ at 20,000 ft max power condition and SMD is $30{\sim}70\;{\mu}m$ at sea level max power condition. In the case of 20,000 ft idle condition, combustion instability could be occurred due to the higher drop diameter. Therefore it is necessary to decrease the droplet diameter in the high altitude condition.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.148-148
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• 2013

스퍼터 이온펌프(Sputter Ion Pump)는 주로 화학흡착으로 동작하며 기계적 진동이 없고, 기름 등의 오염 물질을 배출하지 않으며, 수명이 길어 초고청정 진공이 요구되는 표면실험장치, 표면분석계, 입자가속기 등에서 널리 사용 되고 있다. 일정한 지름을 갖는 다수의 원통 양극과 그 양단에 두개의 음극판을 배치시킨 후, 양극과 음극 사이에 수 kV의 전압을 걸고 원통의 축방향으로 자장을 인가하면 페닝 방전이 발생한다. 냉음극에서 방출된 전자는 양극으로 비행하면서 가스를 이온화한다. 이온분자는 가스흡수성 게터재료로 된 음극에 충돌하여 스퍼터링을 일으키며 게터막를 주변에 증착시킨다. 이온 및 중성 가스는 게터 고체막 속에 주입 포획되는 형태로 배기된다. 스퍼터 이온펌프는 $10^{-5}$ Pa 부근에서 최대 배기속도를 가지며, 압력이 낮아질 수록, 특히 $10^{-10}$ Pa영역 이하에서는 그 배기속도가 급격히 저하되며, $10^{-10}$ Pa영역에서는 배기능력을 거의 상실한다. 따라서 스퍼터 이온펌프 단독으로 진공시스템을 배기할 때 도달압력은 $10^{-9}$ Pa 영역에 머무르게 되며, $10^{-10}$ Pa 이하의 극고진공을 얻기 위해서는, $10^{-8}$ Pa 이하의 압력에서 배기 속도가 압력과 무관한 흡착펌프(getter pump)와 이온펌프를 조합하여 사용한다. 본 실험에서는 $600^{\circ}C$ 이상의 온도로 진공로에서 탈개스시킨 진공용기를 배기속도 450, 60, 30, 20, 5, 3 l/s의 6종류의 이온펌프와 배기속도 400 l/s, 100 l/s의 non-evaporable getter (NEG) 펌프를 조합시켜 배기하여 그 배기 특성을 비교하였다. 도달 압력은 이온펌프의 배기속도가 클수록 낮아지는 경향을 보여주었다. 450 l/s 이온펌프와 400 l/s NEG를 조합하여 배기시킬 때 도달 압력은 ~$2{\times}10^{-10}$ Pa을 기록하여 가장 낮았으며, 3 l/s 이온펌프와 400 l/s NEG를 조합하였을 때는 $ 2{\sim}3{\times}10^{-8}$ Pa을 기록하였다. 450 l/s 이온펌프와 400 l/s NEG를 조합한 경우 잔류가스의 대부분이 수소였으나, 3 l/s 이온펌프와 400 l/s NEG의 조합한 경우에는 메탄의 잔류량이 수소 보다 많았다. 이 결과는 메탄을 배기하지 못하는 NEG의 배기 특성을 보완하기 위해서는 일정 배기속도 이상의 이온 펌프가 필요함을 보여준다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.9
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• pp.1100-1106
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• 2012

This paper has presented the analysis of the micro-Doppler signatures scattered from the blades of the rotating propeller using the modified HHT method, one of the joint time-frequency analysis methods. The field scattered from the blade edge of the propeller was calculated using equivalent current method(ECM). After the acquisition of the scattered field data in the time domain, the modified HHT method was applied to analyze the micro-Doppler signature. The analysis results showed not only a good agreement with the realistic dynamic characteristic of the blade but also sinusoidally varing characteristics of the micro-Doppler signatures generated from rotating objects. It could be concluded that the joint time-frequency analysis via the modified HHT provided the discriminative characteristics for recognizing a small aircraft target with small RCS value.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2008.06a
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• pp.310-317
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• 2008

Although aerial LiDAR had been launched commercially several years ago, it is still difficult to study data acquisition conditions and effects with various datasets because of its acquisition cost. Thus, this research was performed to study data acquisition conditions and effects with virtually various datasets. For this research, 3D tree models and forest stand models were built to represent graded tree sizes and tree plantation densities. Also, a variable aerial LiDAR acquisition model was developed. Then, through controlling flight height parameter, one of the data acquisition parameters, virtual datasets were collected for various data acquisition densities. From those datasets, forest canopy volumes and maximum tree heights were estimated and the estimated results were compared. As the results, the estimated is getting closer to the expected during the data acquisition density increase. This research would be helpful to perform further studios on relations between forest inventory accuracy and LiDAR cost.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.60-67
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• 1997

This paper presents the results of 3rd wind tunnel test for the wings of WIG R/C test models, 'Hanjin-1' & 'Hanjin-2'. We made 'Hanjin-1' in last May 1995 and had a success in test flight. And in order to grasp the aerodynamic characteristics of wings in ground effect, the measurements of lift and drag were carried out for the various kinds of wing. It was shown that lift and lift-drag ratio increase with decrease of the clearance, but the feature was considerably depended on the shape of wing section. In this case we select the three kind of wing. section, and then compare their characteristics especially for a stability in longitudinal motion. They are NACA6409 for 'Hanjin-1' and the two kinds of DHMTU for ekranoplans of Russia. Experimental results show that the pitching moments of DHMTU wing sections are smaller than NACA6409.

• Journal of Convergence for Information Technology
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• v.7 no.2
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• pp.37-42
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• 2017

In order to estimate chaff RCS, we suggest here a novel method using the probability distribution. Normally, a chaff is assumed that it is a thin dipole antenna and the RCS can be calculated by the scattering wave theory. Most of the theoretical methods presented were mainly focusing on a single chaff cloud. In this paper, the RCS calculation was done for two or more chaff clouds and the changes of RCS with azimuth angle were observed. Matlab was used for presenting the probability distribution of chaff clouds and RCS calculation. A more accurate RCS estimation method is suggested by estimating the number of chaffs except the blocked elements.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.150-161
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• 2005

A test was performed to collect the data to validate an analytic method for vent hole sizing on the nose fairing of a launch vehicle. The bake-out chamber at KARI was used to simulate the ambient pressure drop, and pressure difference data were collected for a model with various kinds of vent holes which was installed in the chamber. The characteristics of the test facility and measurement equipments were evaluated for the measurement of the transient behaviors. The measured data were processed in consideration of the characteristics of the facility and equipments, and the effects of vent hole size and configuration on the pressure variation in the model were analyzed based on the data.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2482-2487
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• 2007

Numerical simulations are conducted for the analysis of a thermal mass air flow sensor with periodic heating pulses on silicon-nitride ($Si_3N_4$) thin membrane structure. This study aims to find the locations of temperature sensors on the thin membrane and the heating pulse conditions, that the higher sensitivity can be achieved, for the development of a MEMS fabricated mass air flow sensor which is driven in periodic heating pulse. The simulations, thus, focus on the membrane temperature profile according to variation of the flow velocity, heating duration time and imposed power. The flow velocity of the simulations is ranging from 3 m/s to 35 m/s, heating duration time from 1 ms to 3 ms and imposed power from 50 mW to 90 mW. The corresponding Reynolds numbers vary from 1000 to 10000.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.5
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• pp.10-18
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• 2011

A new film cooling method to protect the pylon injector from aerodynamic heating for a scramjet combustor is proposed and verified with numerical methods. The conditions for the Mach 8 flight at an altitude of 35km are considered. Air is considered as a coolant. Three-dimensional Navier-Stokes equations with $k-{\omega}$ SST turbulence model are used. A downward injection of coolant from the top of the pylon gives higher cooling effects with less mass flow rate of coolant than the upward coolant injection from bottom of the pylon. Also, the downward injection shows little flow separation due to the favorable pressure gradient and does not disturb the flowfields near pylon injector, which results in reduction of pressure losses.