• 한국항공우주학회지
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• 제39권5호
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• pp.424-432
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• 2011

원심압축기 임펠러의 최적화연구를 수행하기 위하여 임펠러의 형상변수와 설계변수에 관한 연구를 수행하였다. 최적화된 결과로부터 성능향상이 달성되었는지를 평가하기 위하여 기존에 실험되어진 임펠러를 선택하였으며, 이 임펠러에서 최적화를 위한 설계변수를 선정하였다. 임펠러 유로에서 허브와 쉬라우드에서의 형상은 베지어곡선으로 재설계되었다. 또한 임펠러 허브와 팁에서의 블레이드 캠버선도 베지어곡선으로 표현하였다. 각각의 형상곡선은 6-8개의 조정점으로 충분히 일치하는 곡선을 얻게 되었으며, 이 중 형상의 변화에 큰 영향을 미치는 조정점을 선택하여 8개의 설계변수로 최적화가 가능함을 보여주었다. 따라서 기존에 사용되고 있는 원심압축기 임펠러의 점 데이터를 활용하여 최적화 형상을 위한 연구가 진행될 수 있음을 보여주었다.

• Smart Structures and Systems
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• 제12권5호
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• pp.501-521
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• 2013

This paper is concerned with static and dynamic shape control of a laminated Bernoulli-Euler beam hosting a uniformly distributed array of resistively interconnected piezoelectric patches. We present an analytical one-dimensional model for a laminated piezoelectric beam with material discontinuities within the framework of Bernoulli-Euler and extent the model by a network of resistors which are connected to several piezoelectric patch actuators. The voltage of only one piezoelectric patch is prescribed: we answer the question how to design the interconnected resistive electric network in order to annihilate lateral vibrations of a cantilever. As a practical example, a cantilever with eight patch actuators under the influence of a tip-force is studied. It is found that the deflection at eight arbitrary points along the beam axis may be controlled independently, if the local action of the piezoelectric patches is equal in magnitude, but opposite in sign, to the external load. This is achieved by the proper design of the resistive network and a suitable choice of the input voltage signal. The validity of our method is exact in the static case for a Bernoulli-Euler beam, but it also gives satisfactory results at higher frequencies and for transient excitations. As long as a certain non-dimensional parameter, involving the number of the piezoelectric patches, the sum of the resistances in the electric network and the excitation frequency, is small, the proposed shape control method is approximately fulfilled for dynamic load excitations. We evaluate the feasibility of the proposed shape control method with a more refined model, by comparing the results of our one-dimensional calculations based on the extended Bernoulli-Euler equations to three-dimensional electromechanically coupled finite element results in ANSYS 12.0. The results with the simple Bernoulli-Euler model agree well with the three-dimensional finite element results.

• 한국항공우주학회지
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• 제37권5호
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• pp.476-482
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• 2009

본 논문에서는 Fluent의 Spalart-Allmaras 난류모델을 적용하여 연소실 내부에 설치된 핀틀 형상이 핀틀 추진기관 추력 크기에 미치는 영향을 수치해석으로 분석하였다. 핀틀이 존재하면 노즐목을 지나는 질량 유량율은 이론적으로 예측된 값 보다 항상 작았으며, 핀틀 직경이 커질수록 노즐목에서 경계층 두께가 차지하는 비율이 증가되어 노즐목의 질량 유량율이 더욱 감소하였다. 핀틀 직경이 커질수록 핀틀 팁에 나타나는 재순환 영역의 압력에 의한 추력은 증가하지만 노즐 및 연소실 압력에 의한 추력은 감소하여 총 추력은 핀틀 직경이 작은 것 보다 감소하였다. 핀틀 추진기관의 비추력은 큰 차이가 없었다.

• 한국정밀공학회지
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• 제17권12호
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• pp.145-150
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• 2000

Micro punching is one of general methods to fabricate simple holes such as permanent ink-jet printer nozzles. A thin punch, that is need for micro punching, usually has been obtained by mechanical machining. There are some method to obtain a thin punch from a cylindrical rod, e.g., microgrinding and WEDG (Wire Electro-Discharge Grinding). Inefficiently, only one punch can be obtained from these machining methods. In contrast with these methods, many punches can be fabricated simultaneously by electrochemical process. Electrochemical process has usually aimed to obtain very sharp probe for atomic force microscopy (AFM) or scanning tunneling microscopy (STM), and it has not been considered the whole shape of a probe in spite of good merits. In this paper, an ultrathin punch with a tapered shape and a cylindrical tip is newly fabricated by electrochemical process.

• Restorative Dentistry and Endodontics
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• 제9권1호
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• pp.115-119
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• 1983

The purpose of this study was to compare the solubility of enamel and dentin to an etchant after fluoride application. Specimens were collected from extracted anterior and bicuspid and each tooth was cut into several pieces. These specimen were allocated in 7 group; 1%, 2%, 3% NaF, 1%, 8%, 20% $SnF_2$, and control group. Five specimens in each group was exposed to pre-determined fluoride solution for 3 minutes, and washed with running water. These specimens were etched by Hipol (commercial label) etchant for 30 seconds. Following are the findings obtained through S.E.M. 1. All specimens with acid etching revealed preferential removal of prism periphery leaving prism core. 2. Specimens treated with 1%, 2% NaF solution showed that the shape of prism tip was thin and sharp like a needle. The case of 3% NaF showed rather round shape at prism end. 3.1% of $SnF_2$ case showed similar findings with the control group but 8% and 20% $SnF_2$ case revealed needle shape at the prism and was less clear than NaF case. Preferential removal of prism periphery was partialy observed and un decalcified area is fused to prism forming reidge. 4. Dentine treated by fluoride compound in low concentration showed the orifice of dentinal tubule was clearly enlarged whereas in high concentration the orifice was not widened.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.378-383
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• 2007

As the Minimally Invasive Surgery (MIS) is developed, an interventional procedure becomes the major of the spine surgery in the world. Despite of the use of the expensive medical equipments, the success chance of the nucleoplasty is about 30%. The reason is that the shape of the cannular needle is similar to that of the conventional injector and looks like the straight. Because the tip of these straight needles is not able to reach in the vicinity of the disc bulging or the protrusion, which are the cause of the low back pain and because the far indirect plasma discharge results in the decompression, the nucleoplasty has the limit. Many incurable diseases has not been solved due to the unexistence of the advanced technique for the MIS human body cannula device. If 3-D direction controllable cannular catheter (whose direction is accurately controlled after inserting into the bodies to cure the lesion) is developed, it is expected that new devised cannular catheter can cure many incurable diseases simultaneously. Therefore, the aims of this research are to develop the new devised cannular catheter of SMA direction controller for the medical situation, which has been produced through many previous trial-error procedures, and to produce the commercial medical device.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.833-836
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• 2007

Load/Unload technology has more benefits than the conventional CSS technology. However, it remains unsolved technical problem on the unloading process. While the slider climbs up the ramp at the outer edge of the disk, the possibility of the slider-disk contact by lift-off force and rebound of the slider increases. This paper focuses on no slider-disk contact. To prevent the slider-disk contact, we apply the disk bump on disk outer edge proceeding unload. Firstly, in the simulation, the bump dimension is determined by changing bump design parameters. Secondly, dynamic stability of slider have to be checked on disk bump before unload analysis, and unload analysis is performed by applying stable bump shapes to unload simulation. Thirdly, we select optimal bump shape to improve unload performance by unload analysis. Finally, in the experiment, the disk bump is mechanically manufactured by pressing disk surface using diamond tip. That is variously processed by changing pressing pressure. After confirming bump shape by nano-scanner, proper bump shape is applied to real experimental unload process. Through this investigation, we propose the optimal bump design to prevent the slider-disk contact, and then we can realize improved unloading performance.

• 한국정밀공학회지
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• 제33권1호
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• pp.31-35
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• 2016

For reaction injection molding (RIM) polyurethane was mixed in the mixing head by impingement mixing, injected into the mold, and cured quickly, as soon as the mold is filled. The shape of the nozzle in the mixing head is critical to improve the quality of polyurethane. To achieve homogeneous mixing, an intensive turbulence energy in the mixing nozzle is essential. In this study, a mixing nozzle for RIM was designed, and mixing efficiency was investigated based on experiment. Experiments were conducted with different combinations of nozzle tips and exit diameter to measure the mixing efficiency by measuring jet force and investigating mixing image with high speed camera. Jet force increased gradually and reaches steady state conditions. The jet force depended on shape of nozzle tip and outlet sizes. These results suggest that optimized nozzle configurations are necessary for high efficiency mixing with RIM.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.380-387
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• 2000

In this paper, a successful result of modification of an axial flow fan and a shroud for noise reduction of a window type air conditioner is presented especially in order to verify the importance of blade shape improvement and the searching for the optimal shape of shrouds. Effective ways to work out the result as mentioned above are to make the tip of the blade varied in thickness and to have special shapes. From the viewpoint of the shape in a shroud, several cases were examined and the particular value of a design parameter of the shroud was acquired to get the best noise reduction of an air conditioner. Through the application of the methods, the air conditioner became less noisy by 4.5 dB(A) in terms of air-borne noise produced only by the axial flow fan and consumed less energy by 20.9% compared to the current one.

• Journal of Biosystems Engineering
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• 제18권1호
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• pp.15-20
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• 1993

Wearness has been a major failure criterion in Korean-made rotary blade. However, few studies have been conducted to improve it. In this study, the fundamental data obtained from the measurement of wearness and failure of rotary blade were analyzed to provide a guideline for the design of rotary blades. For the straight part(about 20-23 em from bolt hole) from the bolt hole to bending point of rotary blade, modifications were proposed for improvements, however, for the portion from bending point to tip was made no design recommendations because the failure behavior of that portion was difficult to analyze with the experimental data. The results are summarized as follows. 1. The current V-shape section has to be moved about 5 em toward the bending point of rotary blade. 2. The section modulus at the portion about 5-7 em distant from bolt hole has to be increased about 15-20 %. 3. The V-shape section has to be changed into U-shape to reduce the on account of recieving initial stress in blades. 4. The radius of curvature of the neck(the portion about 5-7 cm apart from bolt hole) has to be made larger to decrease the stress concentration.