• 한국전자파학회논문지
• /
• 제13권1호
• /
• pp.19-25
• /
• 2002

본 논문에서는 전력증폭기를 슬롯이 적재된 삼각형 마이크로스트립 패치 안테나와 동일 평면의 기판에 집적화하여 전력증폭기 출력단의 제 3 고조파 튜닝을 안테나가 수행함으로써 전력효율을 향상시키는 효과와, 실제 집적화에 따른 송.수신 신호의 분리 문제를 위해 이중공진, 이중급전을 이용한 능동 집적 안테나의 특성을 고찰하였다. 제 3 고조파에서 방사를 억제 구조로서 안테나에 슬롯을 적재시킨 능동 집적 안테나를 설계, 제작하여 측정한 결과, B급 전력증폭기와 안테나를 각각 제작하여 결합한 형태보다 약 5 %의 전력효율 개선 효과를 얻을 수 있었다. 또한, 송.수신 분리에 대하여서도 IMT-2000주파수 대역의 수신 port에서 송신 주파수의 신호를 -35 dB 이하로 격리시키는 특성을 나타냄을 관찰할 수 있었다.

• Structural Engineering and Mechanics
• /
• 제69권4호
• /
• pp.467-477
• /
• 2019

Digital image correlation (DIC) is now a popular and extensively used full-field metrology technique. In general, DIC is performed by using a turnkey solution offered by various manufacturers of DIC. In this paper, a simple and economical set-up for DIC is proposed which uses easily accessible digital single-lens reflex (DSLR) camera rather than industrial couple-charged device (CCD) cameras. The paper gives a description of aspects of carrying a DIC experiment which includes experimental set-up, specimen preparation, image acquisition and analysis. The details provided here will be helpful to carry DIC experiments without specialized DIC testing rig. To validate the responses obtained from proposed DIC set-up, tension and fatigue tests on specimens made of IS 2062 Gr. E300 steel are determined. Tensile parameters for a flat specimen and stress intensity factor for an eccentrically-loaded single edge notch tension specimen are evaluated from results of DIC experiment. Results obtained from proposed DIC experiments are compared with those obtained from conventional methods and are found to be in close agreement. It is also noted that the high resolution of DSLR allows the use of proposed approach for fracture characterization which could not be carried out with a typical turnkey DIC solution employing a camera of 2MP resolution.

• 한국강구조학회 논문집
• /
• 제26권4호
• /
• pp.289-297
• /
• 2014

본 연구에서는 고강도강재(HSA800)의 단주 편심압축실험을 통해 휨-압축 부재의 강도를 평가하였다. 편심압축실험은 축력비에 따라 휨-압축의 조합력을 받는 부재의 P-M 상관관계를 알아보기 위해 HSA800강재의 각형강관과 H형강을 대상으로 실험을 수행하였으며, 가력 편심거리를 조정하여 다양한 P-M 조합에 대해 강도평가 실험을 수행하였다. 실험결과 실험최대 평균응력은 국부좌굴에 의한 최대내력이 결정된 실험체에 대해서는 판폭두께비가 증가함에 따라 감소하는 경향을 보였다. 발현강도의 여유는 축력이 낮을수록 상대적으로 휨강도에 대해 큰 마진을 보이고 있었고, 실험체 모두 현행 설계기준의 P-M 상관관계를 안전측으로 충족하였다.

• Steel and Composite Structures
• /
• 제51권6호
• /
• pp.661-678
• /
• 2024

The utilization of geopolymer recycled aggregate concrete (GRAC) as the infilled core of the concrete-filled steel tubular (CFST) columns provides superior economic and environmental benefits. However, limited research exists within the field of geopolymer recycled aggregate concrete considered a green and sustainable material, in addition to the limitation of the design guidelines to predict the behavior of such an innovative new material combination. Moreover, the behavior of high-strength concrete is different from the normal-strength one, especially when there is another material of high-strength properties, such as the steel tube. This paper aims to investigate the behavior of the axially loaded square high-strength GRACFST columns through the nonlinear finite element analysis (NLFEA). A total of thirty-two specimens were simulated using ABAQUS/Standard software with three main variables: recycled aggregate replacement ratio (0, 30, and 50) %, width-to-thickness ratios (52.0, 32.0, 23.4, and 18.7), and length-to-width ratio (3, 5, 9, and 12). During the analysis, the response in terms of the axial load versus the longitudinal strain was recorded and plotted. In addition, various mechanical properties were calculated and analyzed. In view of the results, it has been demonstrated that the mechanical properties of high-strength GRACFST columns such as ultimate load-bearing capacity, compressive stiffness, energy absorption capacity, and ductility increase with the increase of the steel tube thickness owing to the improvement of the confinement effect of the steel tube. In contrast, the incorporation of the recycled aggregate adversely affected the mentioned properties except the ductility, while the increase of the recycled aggregate replacement ratio improved the column's ductility. Moreover, it has been found that the increase in the length-to-width ratio significantly reduced both the failure strain and the energy absorption capacity. Finally, the obtained NLFEA results of the ultimate load-bearing capacity were compared with the corresponding predicted capacities by numerous codes. It has been concluded that AISC, ACI, and EC give conservative predictions for the ultimate load-bearing capacity since the confinement effect was not considered by these codes.

• 한국해양환경ㆍ에너지학회지
• /
• 제6권2호
• /
• pp.38-45
• /
• 2003

본 연구는 항만공사시 발생되는 부유토사의 거동특성을 분석하기 위하여 항만공사 중 가장 비중이 높은 공정 중의 하나인 사석공사를 대상으로 부유토사 발생거동에 대해 조사하였다. 조사는 방파제조성을 위한 기초사석투하시, 준설토투기장 호안조성시 사석투하를 위해 바지선상에서 사석적재시 및 속채움용 사석투하시를 대상으로 하였다. 본 조사결과에 의하면 방파제 기초사석(0.001~0.03㎥)투하시 부유토사의 발생이 현저히 나타났으며, 확산범위는 대조기의 경우 약 500m이상까지 확산됨을 알 수 있었다. 사석적재시(바지선상)의 부유토사의 거동특성에 대한 조사결과 바지선으로부터 해상으로 흘러내리는 사석으로 인해 부유토사가 발생하여 바지선 주변에서는 늪은 탁도를 나타냈다. 수심별 조사결과 표층의 경우 부유토사는 바지선 주변에 국한되고 곧 침강하여 넓은 범위로 확산하지는 않았다. 그러나 저층의 경우에는 약 100m까지 확산되었으며 그 이후 SS농도가 급격히 저하되어 배경농도를 나타냈다. 포크레인을 이용한 속채움용 사석(0.03㎥이하)투하시의 부유토사 거동특성에 대한 조사결과 표층의 경우 약 300m까지, 저층의 경우는 300m 이상까지 확산됨을 알 수 있었다. 본 연구결과에서 흥미로운 사실은 항만공사시 발생하는 부유토사는 표층의 경우 취송류의 영향을 많이 받고 저층의 경우 조류의 영향을 받으며, 부유토사의 확산은 표층보다는 저층으로 더 멀리 확산된다는 사실을 알 수 있었다

• 한국통신학회논문지
• /
• 제29권8C호
• /
• pp.1133-1141
• /
• 2004

비디오 데이터를 효율적으로 처리하기 위해서는 비디오 데이터가 가지고 있는 내용에 대한 정보를 데이터베이스에 저장하고 사용자들의 다양한 질의를 처리할 수 있는 의미기반 검색 기법이 요구된다. 본 논문에서는 주석기반 검색과 특징기반 검색을 이용하여 대용량의 비디오 데이터에 대한 사용자의 다양한 의미검색을 지원하는 에이전트 기반에서의 자동화되고 통합된 비디오 의미기반 검색 시스템을 제안한다. 사용자의 기본적인 질의와 질의에 의해 추출된 키 프레임의 이미지를 선택함으로써 에이전트는 추출된 키 프레임의 주석에 대한 의미를 더욱 구체화시킨다. 또한, 사용자에 의해 선택된 키 프레임은 질의 이미지가 되어 제안하는 특징기반 검색기법을 통해 가장 유사한 키 프레임을 검색한다. 설계하고 구현한 시스템은 실험을 통한 성능평가에서 90% 이상의 높은 정확도를 보였다.

• Structural Engineering and Mechanics
• /
• 제32권5호
• /
• pp.635-648
• /
• 2009

This paper describes fire performance of eight axially restrained reinforced concrete (RC) columns under a combination of two different load ratios and two different axial restraint ratios. The eight RC columns were all concentrically loaded and subjected to ISO834 standard fire on all sides. Axial restraints were imposed at the top of the columns to simulate the restraining effect of the rest of the whole frame. The axial restraint was effective when the column was expanding as well as contracting. As the results of the experiments have shown, the stiffness of the axial restraint and load level play an important role in the fire behaviors of both HSC and NSC columns. It is found that (a) the maximum deformations during expanding phase were influenced mostly by load ratio and hardly by axial restraint ratio, (b) For a given load ratio, axial restraint ratio had a great impact on the development of axial deformation during contraction phase beyond the initial equilibrium state, (c) increasing the axial restraint increased the value of restraint force generated in both the NSC and HSC columns, and (d) the development of column axial force during the contracting and cooling phase followed nearly parallel trend for columns under the same load ratio.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집C
• /
• pp.281-286
• /
• 2001

Tilting pad journal bearings have been widely used in a high speed rotating machinery, such as steam turbines and gas turbines, owing to their inherent stability characteristics. However, some peculiar fatigue failure in the babbitt metal due to spragging has been continuously occurred at the leading edge of the upper pads. The spragging is defined as the pad vibration initiated on the upper unloaded pads in a tilting pad journal bearing. This paper describes both several kinds of bearing failure related with spragging and the theoretical investigation on the prevention of the spragging phenomenon using the variation of preload. Results show that positive preload(m>0.5) assures all pads remain statically loaded under all operating conditions. For the change of design parameter to prevent spragging, thermo-hydrodynamic lubrication and rotor dynamic analysis were performed to verify temperature limitation on bearing and vibration problems on rotor bearing system.

• Journal of Electrical Engineering and Technology
• /
• 제10권6호
• /
• pp.2315-2325
• /
• 2015

Induction motors are widely used in industrial processes since they offer a very high degree of reliability. But like any other machine, they are vulnerable to faults, which if left unmonitored, might lead to an unexpected interruption at the industrial plant. Therefore, the condition monitoring of the induction motors have been a challenging topic for many electrical machine researchers. Indeed, the effectiveness of the fault diagnosis and prognosis techniques depends very much on the quality of the fault features selection. However, in induction-motor drives, rotor defects are the most complex in terms of detection since they interact with the supply frequency within a restricted band around this frequency, especially in the no-loaded case. To overcome this drawback, this paper deals with an efficient and new method to diagnose the induction-motor rotor fault based on the digital implementation of the monitoring algorithm based on the association of the Time Synchronous Averaging technique and Discrete Wavelet Transform. Experimental results are presented in order to show the effectiveness of the proposed method. The obtained results are largely satisfactory, indicating a promising industrial application of the combined “Time Synchronous Averaging – Discrete Wavelet Transform” approach.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2006년도 추계학술대회
• /
• pp.316-319
• /
• 2006

There is a worldwide interest in the development and commercialization of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) for vehicular and stationary applications. One of the major objectives is the reduction of loaded electrode materials, which is comprise of the Pt-based noble metals. In this paper, a novel chemical strategy is described for the preparation and characterization of carbon-supported and surface-alloys, which were prepared by using a successive reduction process. After preparing Au colloid nanoparticles, the deposition of Au colloid nanoparticles occurred spontaneously in the carbon black-dispersed aqueous solution. Then nano-scaled active materials were formed on the surface of carbon-supported Au nanoparticles. The structural and electrochemical analyses indicate that the active materials were deposited on the surface of Au nanoparticles selectively and that an at toying process occurred during the successive reducing process The carbon-supported & surface-alloys showed the higher electrocatalytic activity than those of the particle-alloys and commercial one (Johnson-Matthey) for the reaction of methanol and formic acid oxidation. The increased electrocatalytic activity might be attributed to the effective surface structure of surface-alloys, which have a high utilization of active materials for the surface reaction of electrode.