• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1993년도 봄 학술발표회논문집
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• pp.95-99
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• 1993

Conventional tuned mass dampers are located on the top floor of tall buildings, which reduce the fundamental mode response of buildings. Higher modes may have a greater contribution toward the acceleration response of tall buildings. To reduce this, additional tuned mass dampers are required and could be substituted as building equipments. This paper shows, with a numerical ezample, how the lecate tuned mass damper in order to reduce the higher mode response effectively

• 대한조선학회논문집
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• 제40권5호
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• pp.53-59
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• 2003

Ocean space utilization using VLFS(Very Large Floating Structures) can provide environmental impact free space by allowing sea water flow freely through the floating structure. Use of Pontoon type VLFS for that purpose needs employment of breakwaters for reduction of wave effects. Therefore, in order to maximize advantage of environmental impact free structure, the breakwater should be the one that can allow water flow freely through it, too. In this paper hydroelastic response of a pontoon type structure is analyzed considering breakwaters which allow water flow through its opening at bottom of the breakwaters. Mode superposition technique is used for solving equation of flexible body while interactions between the pontoon and breakwaters is considered based on generalized mode concept. Bi-quadratic nine node higher-order boundary element method is adopted for more accurate numerical treatment near sharp edged body shape. Performance of various combinations of breakwaters is investigated.

• 소음진동
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• 제9권5호
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• pp.914-921
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• 1999

There are many theoretical investigations to analyze higher order mode of reactive type single expansion chambers with offset inlet/outlet locations. But the conventional method has the restriction that the ratio between the area of inlet(or outlet) pipe and that of chamber must be natural number. In the paper, a new method was suggested to apply the Kim's method to silencer with circular cross-section. Not only the offset location but also the magnitude of cross-section area of inlet/outlet pipe can be considered by the suggested method. The predictions by this new method also compared with those by the finite element method and Munjal's method in order to verify the accuracy of the suggested method presented here.

• 한국인터넷방송통신학회논문지
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• 제16권2호
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• pp.93-99
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• 2016

본 논문은 무인기용 Ku 대역 위성추적 안테나 시스템의 다중모드 모노펄스 추적 시스템을 위한 소형구조 도파관 고차모드 커플러를 설계, 제작 및 성능시험을 수행하였다. 제안된 고차모드 커플러는 이동형 탑재용 위성추적 안테나 시스템에 적용이 가능하도록 장착성을 감안, 동축 구조의 도파관 구조를 이용하였다. 또한 제안된 커플러를 이용하여 출력된 추적 오차 신호의 패턴을 측정하고 설계된 주파수 대역내에서 적정한 추적 오차가 도출됨을 확인하였다. 제안된 커플러 구조는 향후 정밀추적이 요구되는 다중모드 모노펄스 위성추적시스템에 이용될 것으로 기대된다.

• 대한조선학회지
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• 제21권1호
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• pp.21-34
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• 1984

This paper is concerned with the experimental investigation of transverse vibration characteristics in water of rectangular plates having an inner free cutout. Systematic experiments are carried out to investigate effects of the surrounding water on the added mass and the natural frequency of the plates due to the changes of the aspect ratio, hole size and eccentricity. The main subject is the clamped rectangular plate with a circular hole. For the purpose of comparative evaluations, some other common-type boundary conditions and hole shapes such as ellipses and rectangles are also investigated. Some of the results obtain are as follows; 1) For each given aspect ratio of the plate, there is a hole area ratio which gives a minimum value of the nondimensional frequency parameter for each mode. The hole area ratio increases as the order number of the mode increases. 2) The nondimensinal mass-increment parameter decreases as the aspect ration or the order number of the mode increases. For each given aspect ratio, the parameter the fundamental mode decreases monotonically as the hole area ratio increase. In cases of the second and higher order modes, however, each mode has a hole area ratio which gives a maximum value of the parameter for each aspect ratio more then 2/3. 3) Comparing elliptic holes with rectangular ones with same hole area ratio, nondimensional frequency parameters are almost same for each given ratio of the shorter axises to the longer one. 4) The influences of difference in boundary condion on nondimensional frequency parameters in water are similar to those in air.

• 한국농공학회지
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• 제35권4호
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• pp.38-46
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• 1993

This study is to analyze effect of exposure environment and mode of ASR on the engineering properties of synthetic lightweight aggregate concrete, such as dynamic modulus of elasticity and ultrasonic pulse velocity. The results of this study are summarized as foflows ; 1. The expansion rate of each exposure environment in 380$^{\circ}$C and NaCI 4% solution was shown higher than in 20$^{\circ}$C and normal water. The expansion rate of each exposure mode was largely shown in order of fjill immersion, wetting/drying, half immersion. 2. The dynamic modulus of elasticty and ultrasonic pulse velocity of each exposure environment in 38$^{\circ}$C and NaCl 4% solution was shown less than in 20$^{\circ}$C and normal water. The dynamic modulus of elasticity and ultrasonic pulse velocity of each exposure mode was shown smaller in order of full immersion, wetting/drying, half imersion.3. The relation between dynamic modulus of elasticity and ultrasonic pulse velocity was highly significant. The dynamic modulus of elasticity was increased with increase of ultrasonic pulse velocity. The decreasing rate of the dynamic modulus of elasticity was shown 2.1~3.4 times higher than the ultrasonic pulse velocity at each age, exposure environment and mode, respectively. 4. The expansion of each exposure environment and mode was increased with increase of curing age. The dynamic modulus of elasticity and ultrasonic pulse velocity of those concrete was increased with increase of curing age. At the curing age 28 days, the highest properties was showed at each type concrete, it was gradually decreased with increase of curing age. Specially, at the curing age 98 days of full immersion, the rate of expansion of type D was shown 3.95 times higher than the type A. But the dynamic modulus of elasticity and ultrasonic pulse velocity was decreased 17% and 8.3%.

• Journal of the Optical Society of Korea
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• 제18권6호
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• pp.650-656
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• 2014

We propose a novel active fiber design for selectively generating cylindrical vector beams (CVBs) or cylindrical vector modes (CVMs) which can be applied to conventional fiber lasers. A fiber is designed to have a ring-shaped core refractive index profile which can lead to the best overlap between the active dopant distribution profile and the lowest-order CVM (LCVM) field profile. Therefore, the overlap factor (OVF) of the LCVM becomes even higher than that of the fundamental mode. We emphasize that this condition cannot be satisfied by a conventional step-index core fiber (SICF) but by the ring-doped core fiber (RDCF). Because the lasing threshold is inversely proportional to the OVF, the LCVM can predominantly be stimulated even without going through special procedures to impose extra loss mechanisms to the fundamental mode. We numerically verify that the OVF of the LCVM with the doped ions can significantly exceed that of the fundamental mode if the proposed fiber design is applied. In addition, an RDCF of the proposed fiber design can also operate in a regime containing no higher-order modes besides the LCVM, so that it can selectively and efficiently generate the LCVM without being disrupted by the parasitic lasing of the higher-order modes. We highlight that an optimized RDCF can lead to a >30 % higher OVF ratio than a SICF having the same doped area. The proposed model is expected to be useful for enhancing the efficiency of generating CVBs in an all-fiber format.

• 한국정보통신학회논문지
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• 제14권1호
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• pp.38-44
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• 2010

본 논문에서는 고차모드 시간영역 유한차분법(FDTD)을 이용하여 원통형 메타물질 Slab의 주파수 영역 특성을 정확하게 구하는 방법을 연구하였다. 메타물질의 해석방법에는 분산매질 FDTD방정식이 가장 광범위하게 사용되는데 주파수 분산특성을 갖는 유전율과 투자율 모델을 가정하기 때문에, 주파수 응답특성을 구하기 위해서는 주파수 영역에서 차분방정 식을 전개해야 한다. 본 논문에서는 고차모드 FDTD 방법을 유도하여 기존의 분산매질 FDTD 방법과 비교하여 유전체물질에서는 동일한 결과를 얻을 수 있지만 메타물질 해석에서는 오차가 발생을 한다는 것을 확인하였다. 원통형 메타물질 Slab을 해석하기 위해서 고차모드 FDTD 방법을 이용하면 계산오차를 줄일 수 있고 정확한 주파수 특성을 얻을 수 있다. 본 논문에서 제안한 방법을 사용하면 메타물질을 이용한 다양한 회로구조에 대하여 정 확한 주파수 특성을 얻을 수 있다.

• 한국지열·수열에너지학회논문집
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• 제8권1호
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• pp.7-12
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• 2012

This study proposes a hybrid geothermal system combined with heating mode and snow-melting mode for winter season in order to increase the annual operating efficiency of the GSHP(Ground Source Heat Pump). The purpose of this study is to get effectiveness of the hybrid geothermal system by the site experiments. In case of snow-melting only mode, the GSHP COP is 0.7 higher than system COP in average. And in case of hybrid mode, heating GSHP COP is 0.5 higher than snow-melting GSHP COP. And it is also found out that all COP obtained through measurement periods is higher than nominal COPs given by GSHP manufacturer. As a conclusion, it is clear that the proposed hybrid geothermal system is expected as a highly efficient system.

• 한국전자파학회논문지
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• 제27권5호
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• pp.424-429
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• 2016

본 논문은 인공전송선로 중 하나인 LUC(Low-pass filter Unit Cell)을 이용한 이중모드 링-공진기 대역통과 여파기를 제안한다. 기존의 링 공진기 대역통과 여파기는 한 파장 링 공진기를 기반으로 설계하므로 소형화에 어려움이 있고, 정수배 파장의 고조파로 인한 원치 않는 동작의 문제점이 있다. 저역통과 특성을 지닌 인공전송선로 중 하나인 LUC를 이용하여 링-공진기를 구성함으로써 소형화와 고조파 저지 특성을 구현하였다. 링-공진기와 입력 및 출력 단의 인터디지탈 결합선로 인버터를 이용하여 2단 대역통과 여파기를 설계 및 제작하였다. 제작된 여파기는 이중모드, UWB 전 대역저지, 날카로운 스커트 특성을 나타냈으며, 기존의 링-공진기 대역통과 여파기의 링 면적을 약 60 % 감소시켰다.