• Composites Research
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• v.26 no.2
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• pp.141-145
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• 2013

The mode II interlaminar fracture toughness was evaluated for CFRP laminates with different types of nonwoven tissues and the source of increased mode II interlaminar fracture toughness was examined by SEM analysis in this paper. The interlaminar fracture toughness in mode II is obtained by an end notched flexure test. The experiment is performed using three types of non-woven tissues: 8 $g/m^2$ of carbon tissue, 10 $g/m^2$ of glass tissue, and 8 $g/m^2$ of polyester tissue. On the basis of the specimen with no non-woven tissue, interlaminar fracture toughness on mode II at specimens inserted with non-woven carbon and glass tissues and polyester tissues increases as much as 166.5% and 137.1% and 157.4% respectively. The results show that mode II interlaminar fracture toughness of CFRP laminates inserted with nonwoven tissues increased due to the fiber bridging, fiber breakage, and hackle etc. by SEM analysis.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.583-591
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• 2012

In this paper, using a folded parasitic patch, a hybrid metamaterial antenna having the enhanced bandwidth is presented. To obtain a broad bandwidth of the antenna, a zeroth-order resonance(ZOR) mode of a mushroom antenna and a $TM_{010}$ mode of a conventional patch antenna are combined. By employing an etched rectangular hole and a folded parasitic patch in the conventional patch antenna, a resonance frequency of the $TM_{010}$ mode can be down-shifted toward that of the ZOR mode without changing the size of the antenna. Therefore, the proposed antenna has broad bandwidth which ranges from the ZOR mode to the $TM_{010}$ mode. As a result, a fractional bandwidth of the proposed antenna is measured as 12 % and a radiation efficiency is above 75 % in whole band.

• Proceedings of the Korean Society of Computer Information Conference
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• 2022.07a
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• pp.493-494
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• 2022

본 논문에서는 독립형 하이브리드 발전을 위한 효율적안 운영방법을 제안한다. 별도의 정원이 없는 오지에서 독립적으로 동작하기 위해 태양광과 풍력 또는 소수력을 활용하여 두 가지 이상의 발전을 이용하여 발전할 수 있는 하이브리드 발전을 이용한다. 또한 발전된 전원을 야간에도 사용할 수 있도록 저장할 수 있는 배터리를 내장하여 동작할 수 있도록 한다, 배터리의 이용은 발전이 발생되는 구간과 발전이 되지 않는 구간으로 나누어 설계하였다. 발전이 이루어지는 구간은 하나의 발전과 2개의 발전으로 분리하여 하나의 발전만 이루어지는 구간은 일반적인 CC/CV(정전류/전전압) 방식을 이용하여 일반 충전을 수행하고 두 개의 발전이 동시에 이루어지는 구간은 CC(전전류) 모드를 최대한 활용하는 급속 충전을 수행한다. 본 논문에서 제안한 방법은 2개 이상의 발전을 활용하여 독립적인 기능 수행이 가능한 하이브리드 발전을 이용한 독립형 장치로서 장소와 환경의 제한이 적어 실용가능성을 나타내었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.8
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• pp.677-683
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• 2015

Hybrid rocket combustion displays low frequency instability(LFI, 10~30Hz) at a certain condition. Vortex shedding in the post-chamber is suspected to cause the occurrence of LFI. This study focused on the visualization of flow image using light emissions from high temperature combustion gas. Results shows that combustion pressure oscillates at a frequency of about 18 Hz, which is in phase with oscillations of light emission. Since LFI is not a property of thermo-acoustic instability, this result suggested there exists a physical coupling of pressure fluctuations with light emissions proportional to chemical reaction. Also POD analysis shows that dominant symmetric spatial modes in the stable combustion shift suddenly into asymmetric spatial pattern with the appearance of LFI. Especially, the appearance of mode 3 is a typical change of flow dynamics in unstable combustion representing a rotational fluid motions associated with vortex shedding.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.5
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• pp.251-257
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• 2014

Digital RDA system is retransmit into the opposite direction of the incident signals. Digital RDA system have a disadventage that this system do not signal classification in multipath environment. because multipath signal is shown as vector sum of multipath signal, digital RDA system required complex signal process for multipath signal classification. In this paper, to solve these problem we propose hybrid digital RDA system which combination of the MUSIC algorithm and the digital RDA system. Proposed system has two modes. First mode is digital RDA mode. Secornd mode is digital beamforming mode. Digital RDA mode is used in situations where the less the impact of multipath. Digital beamforming mode is applied to multipath effects is greater. In secornd mode, we find optimal path using MUSIC algorithm. After than the proposed system uses only the optimal path. Through the proposed system in a multipath environment with digital RDA can be used to supplement a disadvantage.

• Composites Research
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• v.22 no.6
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• pp.32-38
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• 2009

In this study, the energy absorption capabilities and failure modes of four different kinds of circular tubes made of carbon, Kevlar and carbon-Kevlar hybrid composites with epoxy resin have been evaluated. In order to achieve these goals, these tubes were fabricated with unidirectional prepregs and compressive tests were conducted for the tubes under 10mm/min loading speed. From the test results, carbon/epoxy tubes were collapsed by brittle fracturing mode and showed the best energy absorption capabilities, while Kevlar/epoxy tubes were crushed by local buckling mode and worst. The hybrid [$90_C/0_K$] tubes were failed in a local bucking mode and showed good post crushing integrity, whereas [$90_K/0_C$] tubes were failed in a lamina bending mode and bad post crushing integrity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.11
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• pp.1407-1413
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• 2013

The swing motion drive unit of a hybrid excavator is composed of an electrical motor instead of a hydraulic motor that is used in hydraulic excavators. The method to assess and guarantee the reliability of a hybrid excavator should consider combining the mechanical and the electrical failure mode effects. In particular, the swing reduction gear set of a hybrid excavator is operated under severe outdoor conditions; therefore, an accelerated life test, which is based on field operating condition, should be conducted for the newly developed reduction gear set. In this study, various qualitative methods for reliability engineering, such as FMMA, FMECA, FTA, and QFD, were used to develop the accelerated life test method for the swing drive reduction gear set for the hybrid excavator.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.791-791
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• 2009

Hybrid air-foil magnetic bearing combines two oil free bearing technologies to take advantage of the strengths of each bearing with minimizing each other weaknesses. This paper presents bending mode vibration control of a flexible shaft supported by the hybrid air-foil magnetic bearing. An experiment set-up of a flexible shaft supported by the hybrid air-foil magnetic bearing is built. In order to verify the effectiveness of the hybrid bearing, unbalance responses of the flexible shaft supported by three different bearings: air-foil, magnetic and hybrid bearings are compared. Effect of load sharing between air-foil and magnetic bearings are investigated through changing control gain and offset displacements of magnetic bearing.

• New & Renewable Energy
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• v.2 no.2 s.6
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• pp.23-27
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• 2006

The power split hybrid powertrain is considered to be one of the most prospective configuration for the hybrid electric vehicle (HEV). Toyota Prius, representing this type of vehicle, showed outstanding performances in fuel efficiency, emission reduction and acceleration. The excellence is largely due to the fact that it utilizes almost all operation modes of HEV. Those modes include ZEV (Zero Emission Vehicle) driving, idle stop, fuel cut-off, power assist, active charging, regenerative braking and so forth. In this paper, a few of the mode operations were simulated using AVL Cruise. Also, control logics to operate the powertrain in each mode were developed. The states of powertrain components were displayed and analyzed. By controlling the three components (engine, motor and generator), it was possible to run the powertrain in several hybrid operation modes.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.63-64
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• 2014

본 논문에서는 비상전원 기능을 갖는 고효율 3kW급 하이브리드 ESS를 제안한다. 제안하는 시스템은 정상운전모드 시 태양광에너지를 배터리에 충전하거나 가정용부하에 공급 또는 여분의 전력을 계통에 보낼 수 있고 전력 수요가 많을 시에는 배터리의 에너지를 이용하여 부하평준화를 할 수 있을 뿐 아니라 계통사고 시 부하에 끊김없는 에너지를 공급 할 수 있는 비상전원기능을 갖는다. 각 운전모드에 대한 제어알고리즘과 각 부 전력변환기의 효율을 시제품을 통하여 검증하였다.