• 한국정밀공학회지
• /
• 제32권3호
• /
• pp.307-314
• /
• 2015

In this paper, the embedding type novel liquid metal strain gauge was developed for measuring the deformation of wind turbine blades. In general, the conventional methods for the SHM have many disadvantages such as frequency distortion in FBG sensors, the low gauge factor and mechanical failures in strain gauges and extremely sophisticated filtering in AE sensors. However, the liquid metal filled in a pre-confined micro channel shows dramatic characteristics such as high sensitivity, flexibility and robustnes! s to environment. To adopt such a high feasibility of the liquid metal in flexible sensor applications, the EGaIn was introduced to make flexible liquid metal strain gauges for the SHM. A micro channeled flexible film fabricated by the several MEMS processes and the PDMS replication was filled with EGaIn and wire-connected. Lots of experiments were conducted to investigate the performance of the developed strain gauges and verify the feasibility to the actual wind turbine blades health monitoring.

• 한국유체기계학회 논문집
• /
• 제16권1호
• /
• pp.17-23
• /
• 2013

Recently so much attention has been focused on renewable energy and, since its sources to exploit are already almost saturated in the country, the practical alternative to this situation could be a micro-turbine which uses the low head and low flow. From a point of view of local micro-turbine design capacity and manufacturing technology, the problems such as the accumulation of technical skills, the expansion of related industries, the national policy expansion and the turbine efficiency to improve are still vulnerable and it's true that there are also negative views about the economic feasibility, the technicity and the operation management of the micro-turbine. However, if the improvement can be done in technology of low-head double regulation micro-turbine to generate more outputs and the operation management can be reliably realized, the micro-turbine will be re-evaluated as an appliable source of renewable energy, even the output is small, and by a paradigm shift, it could realize a power generation as an economic and rational system.

• 한국표면공학회지
• /
• 제46권1호
• /
• pp.22-28
• /
• 2013

$WS_2$ particles were added to micro-diamond blades with Cu/Sn binding metal as lubricants to improve cutting efficiency. It was found in previous works that the added $WS_2$ lubricant could reduce remarkably the momentary energy consumption during dicing tests but increased wear rate slightly owing to weak bonding between lubricant particles and bond metals. In the present work, the surface of $WS_2$ lubricant particles were etched for activating the surface of $WS_2$ particles that provide even distribution of particles during powder mixing process and improvement of wetting at the interfaces between $WS_2$ particles and molten Cu/Sn bond metals during pressurized sintering so that could provide the improved strength of micro-blades and result in extended life. Chipping behavior of workpiece with the types of micro-blades including $WS_2$ were compared because it is important in semiconductor and micro-packaging industries to control average roughness and straightness of sliced surface which is closely related with quality.

• 한국정밀공학회지
• /
• 제20권11호
• /
• pp.47-54
• /
• 2003

Research during the past several years has established the effectiveness of acoustic emission (AE)-based sensing methodologies for machine condition analysis and process. AE has been proposed and evaluated for a variety of sensing tasks as well as for use as a technique for quantitative studies of manufacturing process. STD11 has been known as difficult-to-cut materials. The micro-grooving machine was developed for this study and the experiments were performed using CBN blade for machining STD11. Evaluating the machining conditions, frequency spectrum analysis of acoustic emission (AE) signals according to each conditions were applied. Fuzzy clustering method for associating the preprocessor outputs with the appropriate decisions was followed by frequency spectrum analysis. FFT is used to decompose AE signal into different frequency bands in time domain, the root mean square (RMS) values extracted from the decomposed signal of each frequency band were used as features.

• 청정기술
• /
• 제23권1호
• /
• pp.90-94
• /
• 2017

현재 풍력발전은 우리나라에서 가장 주목 받고 있는 신재생에너지 분야로 많은 연구가 진행 중이다. 풍력발전을 구성하는 요소 중 핵심 요소인 블레이드에 손상이 발생할 경우에 발전 효율에 직접적인 영향을 미치므로 효율적인 유지보수를 위해 초기에 결함을 측정하는 기술이 매우 중요한 상태이다. 그러나 기존의 초음파 비파괴 검사 및 열화상 비파괴 검사는 소요시간이 길고 실시간 모니터링이 어려우므로 초기 결함 측정이 불가능하다. 기존의 문제를 보완하고자 본 논문에서는 표면파를 이용한 블레이드 표면상태 실시간 모니터링에 관한 연구를 수행하였다. 압전센서 기반의 시스템을 구성하여 블레이드 표면샘플에 대해 공정 변수 별 기초 성능 실험을 하였고, 소형 블레이드에 대해 공정변수 별 실험을 통해 블레이드의 크랙, 벗겨짐, 장애물 등을 실시간으로 모니터링이 가능한지 연구 하였다.

• 한국습지학회지
• /
• 제23권3호
• /
• pp.234-241
• /
• 2021

본 논문은 자유수면을 갖는 와류수차의 성능에 풀리의 영향을 이해하는 것이다. 실험은 개수로 유입구 유량 0.0069 ~ 0.0077 m³/s 범위에서 물리적 인자(와류높이, 유속, 유효낙차 등)에 따른 수차의 회전수, 전압 및 전류를 측정해 분석하였다. 실험결과에 따르면 와류수차의 전압, 전류 및 회전수는 블레이드 형태와 상관없이 풀리비가 증가할 경우 감소하였다. 직선형 블레이드와 비틀린 블레이드의 효율은 풀리비 0.45 지점에서 52 %인 반면 소형 비틀린 블레이드의 효율은 풀리비 0.21 지점에서 54 %이다. 와류수차의 최대 발전량은 풀리비 0.5 지점 내에서 발생했다. 와류수차의 효율은 풀리비에 따라 0.2 ~ 58 % 범위에서 관찰되었다.

• 한국표면공학회지
• /
• 제45권1호
• /
• pp.37-42
• /
• 2012

$WS_2$ powder was added to the Cu/Sn bond metal of diamond micro-blades for machining of semi-conductor and IC chips to improve cutting efficiency. The effect of $WS_2$ additive on cutting efficiency was investigated and compared with the micro-blades with $MoS_2$ developed in previous research. Flexural strength, frictional coefficient, and wear resistance of blades decreased with $WS_2$ but wear depth increased. It was found that the blades including $WS_2$ consumed less momentary energy than the blades containing $MoS_2$ during dicing test. Micro-blades containing $WS_2$ exhibited lower flexural strength than the blades with $MoS_2$ resulting from higher amount of sintering defects relevant to the less effectiveness of $WS_2$ on fluidity. The effect of $WS_2$ and $MoS_2$ on fluidity during sintering was analyzed in terms of mismatching degree between the longitudinal direction of lubricant particles and the perpendicular direction to the compact loading. The blade with 8.1 vol.% of $WS_2$ showed the best cutting efficiency.

• 한국수소및신에너지학회논문집
• /
• 제27권1호
• /
• pp.121-126
• /
• 2016

Hydraulic performance of a micro-bubble pump has been analyzed by numerical simulation and experimental measurements. Flow recirculation apparatus between the pump inlet and outlet reserviors has been adopted to measure pump performance according to flow conditions sequentially. To analyze three-dimensional flow field in the micro-bubble pump, general analysis code, CFX, is employed. SST turbulence model is employed to estimate the eddy viscosity and compared the pump performance to k-${\varepsilon}$ model. Unstructured grids are used to represent a composite grid system including blade, casing and inlet casing. It is found that the numerical model used in the present study is effective to evaluate the pump performance. From the numerical simulation, low velocity region due to pressure loss is decreased where pump efficiency has maximum value. Detailed flow field inside the micro-bubble pump is also analyzed and compared.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2005년도 금형가공,미세가공,플라스틱가공 공동 심포지엄
• /
• pp.175-180
• /
• 2005

In this study, we have developed a novel wire straightener which uses the direct heating method (DHM) fer straightening the micro wire. Also, we have developed a shearing device for cutting the micro wire. In order to avoid the surface oxidization, we supplied the inert gas(Ar) during the heating process and examined the effect of gas flow rate. The effects of the tension and the current applied to the tungsten micro wires were also thoroughly studied. From various experiments and analyses, we could obtain fine straightness $(\approx1\;{\mu}m/1000\;{\mu}m)$ and roundness $(<{\pm}2{\mu}m\;/100{\mu}m)$ when the tension is $500\~~600gf$ and the current is about 1.5A. for burrfree cutting, counter-punch method which two cutters moving contrary was used. The cutting blade has various U-groove angle where upper $10^{\circ}$, $mid:25^{\circ}$, lower $0^{\circ}$. After the shearing process, we confirmed the shearing section.

• 한국기계가공학회지
• /
• 제19권8호
• /
• pp.8-14
• /
• 2020

In the air current pulverizing type grinding method, the blade wings fitted inside a casing are rotated at a high speed to generate a cornering air current, which facilitates the collision of materials with one another, leading to the pulverizing phenomenon. In contrast to mechanical grinding, grit pulverizing leads to fine grinding and less acid waste and degeneration of the material. Moreover, this approach prevents the loss of nutritional value, while allowing the milling grain to have an excellent texture. However, the existing air current pulverizing type machines consist of prefabricated blades, which cannot be rotated at a speed higher than 5,000 rpm. Consequently, the grinding process becomes time consuming with a low productivity. To overcome these problems, in this study, the shape and structure of the air current pulverizing type wings were optimized to allow rapid grinding at more than 8,000 rpm. Moreover, the optimal design for the ripening parts for the air current pulverizing type device was determined by performing a computational fluid dynamics analysis based on airflow analyses to produce machinery that can grinding materials to the order of micrometers.