• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2009년도 추계학술대회 논문집
• /
• pp.609-610
• /
• 2009

• 한국전자파학회논문지
• /
• 제25권5호
• /
• pp.585-591
• /
• 2014

본 연구에서는 roof-top 기저함수와 모서리 효과(edge-effect)를 저감시키기 위해 개선된 윈도우 함수를 적용한 2차원 모멘트법의 수치 해석 기법과 그 결과들을 제시한다. 모멘트법을 이용한 2차원 수치 산란 모델은 roof-top 기저함수를 적용하여 임의 방향 표면 전류 성분 표현과 계산 효율을 높였으며, 수치적으로 생성된 표면 양 끝단의 모서리에서 발생되는 산란 특성을 제거하기 위해 입사각별 가중치를 둔 개선된 윈도우 함수를 제안한다. 또한, 거칠기가 있는 표면의 산란 특성 분석을 위한 개선된 2차원 수치 해석 기법의 정확도를 검증하기 위해서 SPM(Small Perturbation Model)의 계산결과와 비교/분석하였다.

• 한국인터넷방송통신학회논문지
• /
• 제10권2호
• /
• pp.1-6
• /
• 2010

근거리 무선 통신시스템은 사무실과 가정의 응용으로 빠르게 확장하고 있다. 무선 네트워크의 개발은 더 높은 data rate의 요구를 만족하도록 수행되었다. 이것으로 높은 주파수에서 동작하는 통신시스템 개발의 필요성이 강조된다. 따라서 근거리 무선 통신 네트워크는 테라헤르츠 주파수 쪽으로 옮겨갈 것으로 기대된다. 실내의 벽과 바닥, 천장에 의해 발생하는 전파 환경 분석은 3차원 광선방출기법을 이용하였다. 또한 테라헤르츠 주파수에서의 rough한 건물 벽면의 특성을 파악하기 위해 광학적으로 두꺼운 smooth한 건물 재질의 반사 모델로부터 접근하여 나타내었다. 전파환경 시뮬레이션 결과평균 수신 전력이 참고문헌의 결과와 유사한 결과를 얻을 수 있었다. 또한, 실내 공간의 크기가 $6m(L){\times}5m(W){\times}2.5m(H)$에서 콘크리트 벽의 경우 RMS 지연시간은 9.11 ns로 계산되었다.

• 건축역사연구
• /
• 제19권5호
• /
• pp.65-80
• /
• 2010

The purpose of this paper is to investigate into the meaning of the New Brutalism sensed in the late church buildings of the Swedish architect Sigurd Lewerentz (1885-1975). St Mark's (1956-64) and St Peter's (1962-66) churches, his grand finale designs, have a unique architectural vocabulary of rough brickwork. The brick treatment is the basis on which Reyner Banham (1966) discussed him concerning the New Brutalism, and the point that this research focuses on. This paper explores the brutalist character of the buildings from two aspects - interpretational level of individual buildings and historical level of a broader view. First, the character of two churches could be interpreted with the phrase of 'play between brutality and sacredness'. The rough surface of brick and mortar in the buildings symbolises brutality and the vault of their chapels' ceiling sacredness. And the two characteristics meet and play on the rough vault surface. Second, in the historical point of view, this paper argues that the buildings made a giant leap for Swedish modern architecture, which had been at a deadlock owing to the compromising attitude of the New Empiricism since 1940s. And the Swedish New Empiricism (or the New Humanism), spread to Britain as "Welfare State architecture" after World War II, brought about reaction of the young British architects such as the Smithsons and became the background that made the new brutalist mood. However, considering that the term of the New Brutalism was first used in Sweden by Hans Asplund, Lewerentz's brutalist late churches - which seemingly had nothing to do with the British nor the Corbusian lineage - are also meaningful in that they confirmed the tendency in its homeland. In conclusion, this paper argues that St Mark's and St Peter's churches with the brutalist characteristics should be regarded as crucial buildings not only in Lewerentz's personal career but also in Swedish and international architectural history.

• International Journal of Fluid Machinery and Systems
• /
• 제2권4호
• /
• pp.353-362
• /
• 2009

In the process of turbine modernizations, the investigation of the influences of water passage roughness on radial flow machine performance is crucial and validates the efficiency step up between reduced scale model and prototype. This study presents the specific losses per component of a Francis turbine, which are estimated by CFD simulation. Simulations are performed for different water passage surface roughness heights, which represents the equivalent sand grain roughness height. As a result, the boundary layer logarithmic velocity profile still exists for rough walls, but moves closer to the wall. Consequently, the wall friction depends not only on roughness height but also on its shape and distribution. The specific losses are determined by CFD numerical simulations for each component of the prototype, taking into account its own specific sand grain roughness height. The model efficiency step up between reduced scale model and prototype value is finally computed by the assessment of specific losses on prototype and by evaluating specific losses for a reduced scale model with smooth walls. Furthermore, surveys of rough walls of each component were performed during the geometry recovery on the prototype and comparisons are made with experimental data from the EPFL Laboratory for Hydraulic Machines reduced scale model measurements. This study underlines that if rough walls are considered, the CFD approach estimates well the local friction loss coefficient. It is clear that by considering sand grain roughness heights in CFD simulations, its forms a significant part of the global performance estimation. The availability of the efficiency field measurements provides an unique opportunity to assess the CFD method in view of a systematic approach for turbine modernization step up evaluation. Moreover, this paper states that CFD is a very promising tool for future evaluation of turbine performance transposition from the scale model to the prototype.

• 한국전자통신학회논문지
• /
• 제6권3호
• /
• pp.343-348
• /
• 2011

이동통신의 급속한 보급과 발전에 의하여, 시가지에서의 전자파전파의 특성을 해명해야할 뿐만 아니라, 산림, 계곡 등의 외부 공간과 실내 공간 등의 전파난청 지역으로 불려오던 공간에 있어서도 안정적으로 통신을 이용할 수 있는 무선통신환경 개선의 중요성이 높게 요구 되고 있다. 더욱이, 이동통신의 디지털화와 더불어 건물 등에 의한 반사에 의해서 생기는 멀티패스에 기인하는 수신펄스의 시간지연이 고속디지털통신의 장해가 되고 있다. 이러한 도심 시가지에대한 전자파전파의 특성을 보다 정밀하게 추정하기 위해서는 건물 벽면의 구조 등의 영향도 고려 대상으로 포함 시킬 필요성이 있다. 따라서 본 논문에서는 FVTD(finite volume time domain)법을 적용하여, 기초적인 자료 보완을 위하여, 즉 주기적 구조에 의한 산란 특성과 불규칙적 표면을 포함하는 복합형 구조에 의한 2차원 전파환경 모델들에 대한 산란 특성을 조사 하였다.

• Geomechanics and Engineering
• /
• 제21권4호
• /
• pp.357-369
• /
• 2020

Different from the conventional planar fracture and simplified Newton model, for power-law slurries with a lower water-cement ratio commonly used in grouting engineering, flow model in geological rough fractures is built based on ten standard profiles from Barton (1977) in this study. The numerical algorithm is validated by experimental results. The flow mechanism, grout superiority, and water plugging of pseudo plastic slurry are revealed. The representations of hydraulic grouting properties for JRCs are obtained. The results show that effective plugging is based on the mechanical mechanisms of the fluctuant structural surface and higher viscosity at the middle of the fissure. The formulas of grouting parameters are always variable with the roughness and shear movement, which play a key role in grouting. The roughness can only be neglected after reaching a threshold. Grouting pressure increases with increasing roughness and has variable responses for different apertures within standard profiles. The whole process can be divided into three stationary zones and three transition zones, and there is a mutation region (10 < JRCs < 14) in smaller geological fractures. The fitting equations of different JRCs are obtained of power-law models satisfying the condition of -2 < coefficient < 0. The effects of small apertures and moderate to larger roughness (JRCs > 10.8) on the permeability of surfaces cannot be underestimated. The determination of grouting parameters depends on the slurry groutability in terms of its weakest link with discontinuous streamlines. For grouting water plugging, the water-cement ratio, grouting pressure and grouting additives should be determined by combining the flow conditions and the apparent widths of the main fracture and rough surface. This study provides a calculation method of grouting parameters for variable cement-based slurries. And the findings can help for better understanding of fluid flow and diffusion in geological fractures.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
• /
• pp.494-497
• /
• 1994

We propose a novel velocity detection method of moving object based on a speckle pattern on the target surface using a self-mixing laser diode (SMLD). By this measurement, it was confirmed that the speckle signal has its waveform independent of the target velocity, and has its averaged frequency directly proportional to the target velocity. So it will be possible to detect the velocity of the target transversely translating against the laser light beam using a compact measuring system.

• 대한치주과학회:학술대회논문집
• /
• 대한치주과학회 2007년도 제47회 종합학술대회 연제초록
• /
• pp.109-110
• /
• 2007

• International journal of advanced smart convergence
• /
• 제12권1호
• /
• pp.101-107
• /
• 2023

Machine tools are widely used in mechanical manufacturing corporations, as well as in engineering courses at universities in Vietnam. The PINACHO S-90/200 lathe is particularly popular. This paper aims to research and select an optimal cutting depth to minimize power costs and ensure surface roughness quality when machining upper plain cylindrical turning products with the PINACHO S-90/200 lathe on C45 steel material.