• Wind and Structures
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• 제24권2호
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• pp.95-118
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• 2017

The present study revealed comparison the pressure distribution on the surfaces of regular cross plan shaped building with angular cross plan shaped building which is being transformed from basic cross plan shaped building through the variation of internal angles between limbs by $15^{\circ}$ for various wind incidence angle from $0^{\circ}$ to $180^{\circ}$ at an interval of $30^{\circ}$. In order to maintain the area same the limbs sizes are slightly increased accordingly. Numerical analysis has been carried out to generate similar nature of flow condition as per IS: 875 (Part -III):1987 (a mean wind velocity of 10 m/s) by using computational fluid dynamics (CFD) with help of ANSYS CFX ($k-{\varepsilon}$ model). The variation of mean pressure coefficients, pressure distribution over the surface, flow pattern and force coefficient are evaluated for each cases and represented graphically to understand extent of nonconformities due to such angular modifications in plan. Finally regular cross shaped building results are compared with wind tunnel results obtained from similar '+' shaped building study with similar flow condition. Reduction in along wind force coefficients for angular crossed shaped building, observed for various skew angles leads to develop lesser along wind force on building compared to regular crossed shaped building and square plan shaped building. Interference effect within the internal faces are observed in particular faces of building for both cases, considerably. Significant deviation is noticed in wind induced responses for angular cross building compared to regular cross shaped building for different direction wind flow.

• 융합신호처리학회논문지
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• 제21권2호
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• pp.80-85
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• 2020

최근 학생 및 사무직 종사자에게서 근골격계 질환의 발병률이 증가하고 있으며, 바른 자세의 유지 및 교정 훈련의 필요성이 요구되고 있으나, 관련 연구는 부족한 현실이다. 기존 연구에서는 의자 방석부분에 멤브레인 센서 또는 압력센서를 배치하여 무게의 편중을 보거나, 사용자를 구속하는 센서를 부착하여 체위 변환을 측정하였다. 본 연구에서는 착용편의성을 고려한 체위 변환 감지 센서 디바이스를 개발하였으며, 측정한 각도를 분석앱을 통해 확인하였다. 앉은 자세에서 체위 변환을 측정하기 위하여 경추 및 척추에 IMU 센서로 구성된 센서 디바이스를 부착한다. 두 개의 센서에서 측정되는 체위의 변화값을 각도로 변환하였으며, 각도값은 실시간으로 분석앱을 통해 보여 진다. 본 연구에서는 체위 변화에 따른 실시간 변화값의 측정 가능성과, 착용편의성, 각도 측정의 경향성을 확인해 보았다. 향후 연구에서는 보다 정밀한 각도의 연산 및 동잡음의 보정을 위한 연구를 진행해야 한다.

• 한국항공우주학회지
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• 제43권4호
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• pp.318-325
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• 2015

극초소형 위성은 극히 제한적인 크기로 인하여 태양전지판 장착을 위한 표면적이 제한적이다. 또한 자세제어 방식에 따라서는 태양전지판에 대한 태양 입사각이 계속적으로 변화하며 이는 전력생성에 있어 주요 변수이다. 본 논문에서는 태양전지판에 대한 태양입사각이 전력생성에 불리한 조건에도 프레넬렌즈를 이용해 전력생성효율 향상이 가능한 극초소형 위성용 집광형 태양전력시스템을 제안하였다. 제안된 집광형 태양전력시스템의 전력생성효율 극대화 가능성 입증을 위하여 태양광 모사기와 상용 프레넬렌즈를 이용한 전력측정시험을 수행하였으며, 시험결과를 기반으로 상용 S/W인 STK를 활용해 영구자석 안정화 자세제어 방식이 적용된 극초소형 위성의 궤도 전력생성효율 분석을 수행하였다.

• 대한원격탐사학회지
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• 제38권1호
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• pp.111-126
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• 2022

Land use and land cover (LULC) mapping is an important factor in geospatial analysis. Although highly precise ground-based LULC monitoring is possible, it is time consuming and costly. Conversely, because the synthetic aperture radar (SAR) sensor is an all-weather sensor with high resolution, it could replace field-based LULC monitoring systems with low cost and less time requirement. Thus, LULC is one of the major areas in SAR applications. We developed a LULC model using only KOMPSAT-5 single co-polarized data and digital elevation model (DEM) data. Twelve HH-polarized images and 18 VV-polarized images were collected, and two HH-polarized images and four VV-polarized images were selected for the model testing. To train the LULC model, we applied the conditional generative adversarial network (cGAN) method. We used U-Net combined with the residual unit (ResUNet) model to generate the cGAN method. When analyzing the training history at 1732 epochs, the ResUNet model showed a maximum overall accuracy (OA) of 93.89 and a Kappa coefficient of 0.91. The model exhibited high performance in the test datasets with an OA greater than 90. The model accurately distinguished water body areas and showed lower accuracy in wetlands than in the other LULC types. The effect of the DEM on the accuracy of LULC was analyzed. When assessing the accuracy with respect to the incidence angle, owing to the radar shadow caused by the side-looking system of the SAR sensor, the OA tended to decrease as the incidence angle increased. This study is the first to use only KOMPSAT-5 single co-polarized data and deep learning methods to demonstrate the possibility of high-performance LULC monitoring. This study contributes to Earth surface monitoring and the development of deep learning approaches using the KOMPSAT-5 data.

• 한국전자파학회논문지
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• 제22권9호
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• pp.840-846
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• 2011

본 논문에서는 EGS(Electromagnetic Gradient Surface) 구조의 반사 특성과 함께 RCS 특성을 입사파의 다양한 입사각과 편파에 따라 분석하였다. EGS에 입사되는 입사파의 입사각 ${\theta}_i$를 $0^{\circ}$에서 $50^{\circ}$까지 $10^{\circ}$ 간격으로 변화시켜가면서 수직 및 수평 편파를 고려하여 반사 특성 및 RCS 감소율을 비교 분석하였다. EGS의 입사각 ${\theta}_i$가 $0^{\circ}$로 입사하는 입사파의 경우엔 편파에 따른 반사 특성 및 RCS 감소율이 크게 차이가 나지 않았음을 확인하였으며, 입사파의 입사각의 크기가 커지게 될수록 편파에 따른 반사 특성의 차이가 더 크게 나타남을 보였다. RCS 특성의 경우, 입사파의 입사각의 크기가 커지게 되어도 EGS의 수직 방향에서의 RCS 감소율은 약 2 dB 차이를 보이며, 입사각과 편파에 따른 RCS 특성은 유지됨을 확인하였다.

• 한국산학기술학회논문지
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• 제16권6호
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• pp.4131-4136
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• 2015

본 논문은 반사방지막의 성능을 더 정확히 비교 및 분석하기 위하여 기존 방법과 달리 반사방지막에 수직입사가 아닌 입사각이 $8^{\circ}$에서 $60^{\circ}$까지 변화한다고 가정하고 단층 구조와 다층 구조의 반사방지막의 평균반사율을 계산하고 비교하였다. 입사파의 파장범위를 400 nm ~ 1200 nm 라고 가정하고, 분석에 사용된 반사방지막의 구조는 두께 180 nm인 1차 및 5차 함수의 굴절률 분포를 갖는 6층 구조와 균일한 굴절률 분포를 갖는 단층구조이다. 분석 결과로써 180 nm 단층구조의 경우 평균반사율이 19.6 % 이고, 같은 두께의 6층 구조의 1차 함수 굴절률 분포에서는 14.2 % 이고, 5차 함수 경우에는 11.6 %의 결과를 얻어 균일한 굴절률 분포의 단층구조 보다 5차 함수 굴절률 분포를 갖는 6층 구조의 경우 약 8%의 반사율 감소 효과를 보았다. 이러한 결과는 향후 광소자 및 광 필터에 적용되는 반사방지막 제작에 용용 될 수 있다고 판단된다.

• The Journal of Korean Physical Therapy
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• 제13권1호
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• pp.127-137
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• 2001

Low back pain is significant problem in today's society, with lifetime incidence rate reported between 50% and 90%. Many factors associated with LBP are reported. The purpose of this studies were to be evaluated static standing posture aberrations in chronic LBP in comparison with healthy individuals. The samples including 80 subjects recruited to the following two groups:patients and control(normal) Questionnaires were completed by 40 LBP patients and 40 controls at the department of Physical Therapy, Saejong neurosurgical clinic in Taegu city from October 1, 1999 to March 30, 2000. The angle of lumbar lordosis was measured on lateral x-ray films with standing position. In LBP groups. the mean degree of lumbar lordosis, sacral inclination, and lumbosacral joint angle were 29.9 ${\pm}$ 9.3, 34.8 ${\pm}$ 8.2, and 12.7 ${\pm}$ 5.7 respectively. Control groups, the mean degree of lumbar lordosis, sacral inclination and lumbosacral joint angle were 35.3 ${\pm}$ 7.8, 34.9 ${\pm}$ 6.4 and 12.5 ${\pm}$ 4.3 respectively. there were significantly decreaseds in lumbar lordosis in Low back pain group. lumbar lordosis on the working posture had significant differences among groups(sitting position patients 31.4 ${\pm}$ 9.3, standing position patients 29.4 ${\pm}$ 9.3, sitting position control 35.0 ${\pm}$ 6.4, standing position control 35.5 ${\pm}$ 8.8, respectively) (p=0.034). sacral inclination on the working posture had differences among groups(sitting position patients 35.9 ${\pm}$ 8.7.standing position patients 33.6 ${\pm}$ 7.6, sitting position control 33.9 ${\pm}$ 5.9. standing position control 35.6 ${\pm}$ 6.8, respectively). lumbersacral joint angle on the working Posture had differences among groups(sitting position patients 12.0 ${\pm}$ 5.6, standing position patients 13.4 ${\pm}$ 5.9, sitting position control 11.2 ${\pm}$ 3.0. standing position control 13.4$^{\circ}$, respectively).

• 한국항공우주학회지
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• 제30권5호
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• pp.109-117
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• 2002

옆미끄럼이 있는 조건에서 LEX를 갖는 삼각날개의 와류 특성을 유동의 가시화에 의한 실험적 방법으로 연구하였다. 모델은 $65^{\circ}$ 후퇴각의 갖는 평판 날개이다. 자유 유동속도는 6.2 m/s이며, 이 속도와 날개뿌리 시위를 기준으로 한 레이놀즈 수는 $4.4\times10^5$ 이다. 받음각 범위와 옆미끄림각 범위는 각각 $16^{\circ}\sim28^{\circ}$와 $0^{\circ}\sim-15^{\circ}$ 이다. 미세수적과 레이저 평면광에 의한 가시화는 오공 프로브에 의한 측정으로부터 얻을 수 없었던 보다 자세한 와유동 구조를 관찰 할 수 있도록 하였다. 옆미끄럼각이 있는 경우, 바람쪽은 LEX 와류와 날개 와류의 상호작용과 붕괴가 촉진되는 반면, 바람반대쪽은 두 와류의 상호작용과 붕괴가 억제되었다.

• Earthquakes and Structures
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• 제24권1호
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• pp.65-79
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• 2023

A simplified analytical solution for seismic response of tunnel cross section in horizontally layered ground subjected to oblique incidence of SH wave is deduced in this paper. The proposed analytical solution consists of two main steps: free-field response in layered field and tunnel response. The free field responses of the layered ground are obtained by one-dimensional finite element method in time domain. The tunnel lining is treated as a thick-wall cylinder to calculate the tunnel response, which subject to free field stress. The analytical solutions are verified by comparing with the dynamic numerical results of two-dimensional ground-lining interaction analysis under earthquake in some common situations, which have a good agreement. Then, the appropriate range of the proposed analytical solution is analyzed, considering the height of the layered ground, the wavelength and incident angle of SH wave. Finally, by using the analytical solutions, the effects of the ground material, burial depth of the tunnel, and lining thickness and the slippage effect at the ground-lining interface on the seismic response of tunnels are investigated. The proposed solution could serve as a useful tool for seismic analysis and design of tunnels in layered ground.

• Structural Engineering and Mechanics
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• 제77권4호
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• pp.473-479
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• 2021

The propagation of plane waves in a linear, homogeneous and isotropic nonlocal generalized thermoelastic solid medium is considered in the framework of Lord and Shulman generalization. The governing field equations are formulated and specialized in a plane. Plane wave solutions of governing equations show that there exists three plane waves, namely, P, thermal and SV waves which propagate with distinct speeds. Reflection of P and SV waves from thermally insulated or isothermal boundary of a half-space is considered. The relevant boundary conditions are applied at stress free boundary and a non-homogeneous system of three equations in reflection coefficients is obtained. For incidence of both P and SV waves, the expressions for energy ratios of reflected P, thermal and SV waves are also obtained. The speeds and energy ratios of reflected waves are computed for relevant physical constants of a thermoelastic material. The speeds of plane waves are plotted against nonlocal parameter and frequency. The energy ratios of reflected waves are also plotted against the angle of incidence of P wave at a thermally insulated stress-free surface. The effect of nonlocal parameter is shown graphically on the speeds and energy ratios of reflected waves.