• 한국해양공학회지
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• 제25권6호
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• pp.91-96
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• 2011

In this paper, friction welded joints were constructed to investigate the mechanical properties of welded 15-mm diameter solid bars of Mg alloy (AZ31B). The main friction welding parameters were selected to endure reliable quality welds on the basis of visual examination, tensile tests, impact energy test, Vickers hardness surveys of the bonds in the area and heat affected zone (HAZ), and macrostructure investigations. The study reached the following conclusions. The tensile strength of the friction welded materials (271 MPa) was increased to about 100% of the AZ31B base metal (274 MPa) under the condition of a heating time of 1 s. The metal loss increased lineally with an increase in the heating time. The following optimal friction welding conditions were determined: rotating speed (n) = 2000 rpm, heating pressure (HP) = 35 MPa, upsetting pressure (UP) = 70 MPa, heating time (HT) = 1 s, and upsetting time (UT) = 5 s, for a metal loss (Mo) of 10.2 mm. The hardness distribution of the base metal (BM) showed HV55. All of the BM parts showed levels of hardness that were approximately similar to friction welded materials. The weld interface of the friction welded parts was strongly mixed, which showed a well-combined structure of macro-particles without particle growth or any defects. In addition, an acoustic emission (AE) technique was applied to derive the optimum condition for friction welding the Mg alloy nondestructively. The AE count and energy parameters were useful for evaluating the relationship between the tensile strength and AE parameters based on the friction welding conditions.

• 전력전자학회논문지
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• 제12권6호
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• pp.500-509
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• 2007

본 논문에서는 FPGA를 사용하여 진행파형 초음파모터의 2상 입력 전원 전압의 주파수, 전압, 전압차 및 2상 간의 위상차 조절이 가능하고, 최대 8대의 초음파모터를 동시에 제어할 수 있는 PC기반 8채널 USB통신 초음파모터 디지털 제어기를 제안한다. 제안한 제어기는 FPGA를 사용한 디지털 논리에 의해 각각의 파라미터를 실시간으로 조절할 수 있을 뿐만 아니라 속도 및 위치 센서인 로터리 엔코더의 카운터 회로를 FPGA 회로에 내장시킴으로써 별도의 외부 회로 구성이 불필요하여 제어기의 크기나 생산비용의 절감을 기대할 수 있다. 제안한 새로운 방식의 제어기의 성능을 검사하기 위해서 홀딩토크가 다른 2가지 타입의 초음파모터에 대한 각 파라미터 조절에 따른 무부하 속도 특성을 실험하였다.

• 대한전자공학회논문지TC
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• 제48권12호
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• pp.35-41
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• 2011

본 논문에서는 손실매질의 다층구조로 이루어진 마이크로 스트립선로의 손실특성의 개선을 위한 새로운 구조를 제안한다. MIS 구조로 된 전송선로의 Si와 SiO2층 사이에 0전위를 가진 도체를 일정한 간격의 주기적인 배열로 고안된 새로운 모델의 MIS구조에 대한 유한차분법을 이용한 해석방법이 사용된다. 특히 전송선로에 대한 유전체의 영향을 줄이기 위하여 0전위를 가진 주기적인 결합의 도체로 이루어진 구조가 시간영역의 신호를 통해 시험된다. 다양한 0전위 도체의 간격(갭)에 따른 주파수 의존적인 추출된 전송선로 파라미터와 등가회로 파라미터가 주파수 함수로서 나타내진다. 또한 본 논문에서 고안된 구조에 대해 특성임피던스와 유효유전상수의 큰 변화 없이 대칭 결합선로의 quality factor가 개선됨을 볼 수 있다.

• 대한기계학회논문집A
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• 제35권10호
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• pp.1229-1235
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• 2011

신뢰성이 가장 우수한 프레팅 피로손상 파라미터를 찾아내기 위해 알루미늄 합금 A7075-T6 을 대상으로 피로시험을 수행하였다. 시편 표면에 홈을 가공하여 패드 접촉압력에 따라 패드-시편 접촉면에서 프레팅 피로균열이 발생하거나 또는 홈에서 일반 피로균열이 발생할 수 있게 하였다. 광학현미경을 이용하여 균열의 발생위치와 방향을 측정하고, 문헌에서 가장 많이 사용되는 프레팅 피로손상 파라미터들의 신뢰성을 평가하였다. 파라미터 값과 최대손상평면 방향을 산출하는데 필요한 응력과 변형률 자료는 유한요소해석으로 산출하였다. 전단모드 피로파손을 가정하는 Fatemi-Socie 파라 미터와 McDiarmid 파라미터가 가장 신뢰성이 높은 것으로 판명되었다.

• Nuclear Engineering and Technology
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• 제48권4호
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• pp.859-869
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• 2016

Component-scale modeling of boiling is predominantly based on the Eulerian-Eulerian two-fluid approach. Within this framework, wall boiling is accounted for via the Rensselaer Polytechnic Institute (RPI) model and, within this model, the bubble is characterized using three main parameters: departure diameter (D), nucleation site density (N), and departure frequency (f). Typically, the magnitudes of these three parameters are obtained from empirical correlations. However, in recent years, efforts have been directed toward mechanistic modeling of the boiling process. Of the three parameters mentioned above, the departure diameter (D) is least affected by the intrinsic uncertainties of the nucleate boiling process. This feature, along with its prominence within the RPI boiling model, has made it the primary candidate for mechanistic modeling ventures. Mechanistic modeling of D is mostly carried out through solving of force balance equations on the bubble. Forces incorporated in these equations are formulated as functions of the radius of the bubble and have been developed for, and applied to, low-pressure conditions only. Conversely, for high-pressure conditions, no mechanistic information is available regarding the growth rates of bubbles and the forces acting on them. In this study, we use direct numerical simulation coupled with an interface tracking method to simulate bubble growth under high (up to 45 bar) pressure, to obtain the kind of mechanistic information required for an RPI-type approach. In this study, we compare the resulting bubble growth rate curves with predictions made with existing experimental data.

• Annals of Laboratory Medicine
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• 제38권6호
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• pp.512-517
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• 2018

Background: Complete blood count (CBC) results play an important role in peripheral blood smear (PBS) examinations. Many descriptions in PBS reports may simply be translated from CBC parameters. We developed a computer program that automatically generates a PBS draft report based on CBC parameters and age- and sex-matched reference ranges. Methods: The Java programming language was used to develop a computer program that supports a graphical user interface. Four hematology analyzers from three different laboratories were tested: Sysmex XE-5000 (Sysmex, Kobe, Japan), Sysmex XN-9000 (Sysmex), DxH800 (Beckman Coulter, Brea, CA, USA), and ADVIA 2120i (Siemens Healthcare Diagnostics, Eschborn, Germany). Input data files containing 862 CBC results were generated from hematology analyzers, middlewares, or laboratory information systems. The draft reports were compared with the content of input data files. Results: We developed a computer program that reads CBC results from a data file and automatically writes a draft PBS report. Age- and sex-matched reference ranges can be automatically applied. After examining PBS, users can modify the draft report based on microscopic findings. Recommendations such as suggestions for further evaluations are also provided based on morphological findings, and they can be modified by users. The program was compatible with all four hematology analyzers tested. Conclusions: Our program is expected to reduce the time required to manually incorporate CBC results into PBS reports. Systematic inclusion of CBC results could help improve the reliability and sensitivity of PBS examinations.

• 한국음향학회지
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• 제38권4호
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• pp.433-441
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• 2019

본 논문에서는 입 주변에 방사한 초음파 신호가 반사되어 돌아올 때 발생하는 초음파 도플러 신호를 LSTM(Long Short Term Memory) 순환 신경망 (Recurrent Neural Networks, RNN)을 이용해 음성 패러미터를 추정하는 방법을 소개하고 다층 퍼셉트론 (Multi-Layer Perceptrons, MLP) 신경망을 이용한 방법과 성능 비교를 하였다. 본 논문에서는 LSTM 순환 신경망을 이용해 초음파 도플러 신호로부터 음성 신호의 푸리에 변환 계수를 추정하였다. LSTM 순환 신경망을 학습하기 위한 입력 및 기준값으로 초음파 도플러 신호와 음성 신호로부터 각각 추출된 멜 주파수 대역별 에너지 로그값과 푸리에 변환 계수가 사용되었다. 테스트 데이터를 이용한 실험을 통해 LSTM 순환 신경망과 MLP의 성능을 평가, 비교하였고 척도로는 평균 제곱근 오차(Root Mean Squared Error, RMSE)가 사용되었다.각 실험의 RMSE는 각각 0.5810, 0.7380로 나타났다. 약 0.1570 차이로 LSTM 순환 신경망을 이용한 방법의 성능 우세한 것으로 확인되었다.

• Coupled systems mechanics
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• 제10권6호
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• pp.509-520
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• 2021

Fiber-reinforced concrete (FRC) is a composite material where small fibers made from steel or polypropylene or similar material are embedded into concrete matrix. In a material model each constituent should be adequately described, especially the interface between the matrix and fibers that is determined with the 'bond-slip' law. 'Bond-slip' law describes relation between the force in a fiber and its displacement. Bond-slip relation is usually obtained from tension laboratory experiments where a fiber is pulled out from a matrix (concrete) block. However, theoretically bond-slip relation could be determined from bending experiments since in bending the fibers in FRC get pulled-out from the concrete matrix. We have performed specially designed laboratory experiments of three-point beam bending with an intention of using experimental data for determination of material parameters. In addition, we have formulated simple layered model for description of the behavior of beams in the three-point bending test. It is not possible to use this 'forward' beam model for extraction of material parameters so an inverse model has been devised. This model is a basis for formulation of an inverse model that could be used for parameter extraction from laboratory tests. The key assumption in the developed inverse solution procedure is that some values in the formulation are known and comprised in the experimental data. The procedure includes measured data and its derivative, the formulation is nonlinear and solution is obtained from an iterative procedure. The proposed method is numerically validated in the example at the end of the paper and it is demonstrated that material parameters could be successfully recovered from measured data.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2453-2458
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• 2007

The performance of polysilicon thin film transistor (p-Si TFT) has an important role in the operation of active matrix liquid crystal displays. To fabricate the p-Si TFTs that have uniform characteristics, understanding of the recrystallization mechanism of silicon is crucial. Especially, the analysis of the transient temperature variation and the liquid-solid interface motion is required to find the mechanism. The thermal conductivity is one of the most important parameters to understand the mechanism. In this work, a KrF eximer laser beam was irradiated to amorphous silicon thin films. We measured the transient reflectivity at the wavelength of 633 nm. We carried out the numerical simulation of one dimension conduction equation so that we determined the most well-fitted thermal conductivity by comparing the numerically obtained transient reflectivity with the experimentally measured one. The experimentally determined thermal conductivity of amorphous silicon thin films is 1.5 W/mK.

• 정보저장시스템학회논문집
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• 제4권1호
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• pp.13-18
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• 2008

Scratches are observed on a polymer cover-layer of near-field recording (NFR) media after a servo test with rotating disc. The scratches are formed by the collision of a solid immersion lens (SIL)-media. One of the possible ways to avoid the scratch problem is to coat a dielectric protective film on the polymer cover-layer which enhances the hardness of the surface. The surface with hard characteristics in the surface reduces the scratch problem in the cover-layer. Not only the mechanical properties but also the optical properties should be controlled. Specifically, the refractive index of the dielectric protective film should be matched with the polymer cover-layer not to lose light at the interface due to the difference of the refractive index. The refractive index of the dielectric film can be tailored by controlling process parameters during sputtering and matched with that of the polymer cover-layer.