• Elastomers and Composites
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• 제50권4호
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• pp.251-257
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• 2015

The rubber seal is a part inserted into servo cylinder to keep the air pressure constant. In order for efficient movements of the servo cylinder, the frictional coefficient of the rubber seal needs to be minimized while the sealing is maintained. In this work the friction characteristics of rubber seal specimen are tested on metal plate at various conditions. The experimental conditions include roughness level, applied pressure, lubrication, and rubbing speed. The design of experiment approach is taken to assess the effect of each parameter. The nonlinear frictional response of the rubber is applied to the FEM model simulating the servo cylinder movement. The result demonstrates that precise optimization of the servo cylinder movement must be preceded by preliminary experiments coupled with the theory and FEM model.

• 한국방재안전학회논문집
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• 제11권2호
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• pp.53-60
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• 2018

본 연구에서는 강판에 발생한 국부적인 손상의 진단을 위해 강자성의 연속체 구조물에 적합한 비파괴진단 기법인 누설자속 기법을 적용하였다. 강판시편의 두께 변화에 따른 누설자속 기반 진단 기법의 민감도를 분석하기 위해 각각 다른 두께를 가지는 몇 가지의 강판시편을 준비하였고, 각각의 시편에 3가지 깊이의 인공결함을 가공하였다. 홀센서와 자화요크를 이용하여 일정한 자화밀도를 가지는 누설자속 센서헤드를 제작하여 강판시편으로부터 누설자속 신호를 계측하였다. 센서헤드로부터 수집된 자속신호의 품질향상을 위해 일련의 신호처리 과정을 거쳤으며, 각 손상지점으로부터 계측된 누설자속 신호의 확인을 통해 국부손상 감지의 가능성을 확인하였다. 강판두께에 따른 누설자속 기법의 손상감지 민감도의 분석을 위해 각각 다른 두께의 강판시편으로부터 검출된 MFL 신호에서 P-P value를 정량적으로 추출하였고 그 값을 비교 분석 하였다.

• 한국융합학회논문지
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• 제13권2호
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• pp.31-37
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• 2022

이 연구는 실습용 아두이노 자동차 키트 개발 사례를 제시하는 데 그 목적이 있다. 이를 위해 기존 아두이노 자동차 키트의 문제점을 분석하고 이에 대한 개선 방안을 반영한 다양한 시제품을 개발하였다. 개발된 키트는 교육 현장에서 적용하여 문제점과 개선점을 파악하였으며, 이를 수정 보완하여 최종 실습용 아두이노 자동차 키트로 개발하였다. 개발한 아두이노 자동차 키트는 상판과 하판으로 구성된 2개의 판을 결합하는 방식을 이용하여 아두이노 자동차와 관련된 다양한 실험이나 실습이 수행할 수 있게 하였다. 또한, 상판과 하판을 결합할 수 있는 별도의 결합 수단을 사용하여 볼트나 너트를 이용하지 않고 쉽고 빠르게 자동차의 차체를 구성할 수 있는 특징이 있었다. 개발된 키트는 단순하며 쉬운 조립 방식을 사용하여 자동차의 차체 조립에 드는 시간을 획기적으로 줄였기 때문에 자동차를 이용하여 프로그래밍 교육을 체험할 수 있는 키트로 널리 활용될 수 있을 것이다.

• 융복합기술연구소 논문집
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• 제6권2호
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• pp.35-40
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• 2016

Ignitor tip is a component of burner to start the burning process in power plant. This is used to ignite the coal to a constant operating state by fuel mixed with air and kerosene. This component is composed of three components so that air and kerosene are mixed in the proper ratio and injected uniformly. Because the parts with the designed shape are manufactured in the machining process, they have to be made of three parts. These parts are designed to have various functions in each part. The mixing part mixes the supplied air and kerosene through the six holes and sends it to the injecting part at the proper ratio. The inject part injects mixed fuel, which is led to have a constant rotational direction in the connecting part, to the burner. And the connecting plate that the mixed fuel could rotate and spray is assembled so that the flame can be injected uniformly. But this part causes problems that are worn by vibration and rotation because it is mechanically assembled between the mixing part and the inject part. In this study, 3D printing method is used to integrate a connecting plate and an inject part to solve this wear problem. The 3D printing method could make this integrated part because the process is carried out layer by layer using a metal powder material. The part manufactured by 3D printing process should perform the post process such as support removal and surface treatment. However, while performing the 3D printing process, the material properties of the metal powders are changed by the laser sintering process. This change in material properties makes the post process difficult. In consideration of these variables, we have studied the optimization of manufacturing process using 3D printing method.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.248-253
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• 2014

Air Gap Membrane Distillation (AGMD) is one of several technologies that can be used to solve problems fresh water availability. AGMD exhibits several advantages, including low conductive heat loss and higher thermal efficiency, due to the presence of an air gap between the membrane and condensation wall. A previous study by Bhardwaj found that the condensation surface properties (materials and contact angle) affected the total collected fresh water in the solar distillation process. However, the process condition differences between solar distillation and AGMD might result in different condensation phenomena. In contrast, N. Miljkovic showed that a hydrophobic surface has higher condensation heat transfer. Moreover, to the best of our knowledge, there is no study that investigates the effect of condensation surface properties in AGMD to overall process performance (i.e. flux and thermal efficiency). Thus, in this study, we treated the AGMD condensation surface to make it hydrophobic or hydrophilic. The condensation surface could be made hydrophilic by immersing and boiling plate in deionized (DI) water, which caused the formation of hydrophilic aluminum hydroxide (AlOOH) nanostructures. Afterwards, the treated plate was coated using hexamethyldisiloxane (HMDSO) through plasma-enhanced chemical vapor deposition (PECVD). The result indicated that condensation surface properties do not affect the permeate flux or thermal efficiency significantly. In general, the permeate flux and thermal efficiency for the treated plates were lower than those of the non-treated plate (pristine). However, at a 1 mm and 3 mm air gap, the treated plate outperformed the non-treated plate (pristine) in terms of permeate flux. Therefore, although surface wettability effect was not significant, it still provided a little influence.

• 한국공간구조학회논문집
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• 제21권4호
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• pp.57-64
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• 2021

This paper conducted a comparative analysis of the shear buckling characteristics of trapezoidal and sinusoidal corrugated steel plates considering of their initial imperfection. Initial imperfection refers to the state where the shape of the corrugated plate is initially not perfect. As such, an initially imperfect shape was assumed using the eigen buckling mode. To calculate the buckling stress of corrugated steel plates, the linear buckling analysis used a boundary condition which was applied to the plate buckling analysis. For the comparison of trapezoidal and sinusoidal corrugation, the shape parameters were assumed using the case where the length and slope of each corrugation were the same, and the initial imperfection was considered to be from 0.1% to 5% based on the length of the steel plate. Here, for the buckling analysis, ANSYS, a commercial FEA program, was used. From the results of buckling analysis, the effect of overall initial imperfection showed that the larger the initial imperfection, the lower the buckling stress. However, in the very thin model, interaction or local buckling was dominant in the perfect shape, and in this case, the buckling stress did not decrease. Besides, the sinusoidal model showed higher buckling stress than the trapezoidal one, and the two corrugation shapes decreased in a similar way.

• 한국정보전자통신기술학회논문지
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• 제12권2호
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• pp.113-119
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• 2019

우리는 선행연구로 다기능 마찰력 측정기를 개발해 왔고 본 논문에서는 적응화 평활화 방법을 적용하여 마찰력 측정기의 성능을 개선하고자 하였으며, 스크래치 테스트를 통해 시편에 대한 마찰력과 마찰면의 모니터링 기능을 심도 있게 분석하였다. 일반적으로 강판을 가공하여 사용하고자 할 때 마찰을 줄이기 위해서 윤활유를 사용하지만, 윤활유는 환경오염의 큰 원인이기 때문에 본 연구에서는 윤활강판을 사용하였다. 특히, 윤활강판의 마찰계수는 유기, 무기 등의 시편의 종류 및 코팅층의 상태에 따라 변화하기 때문에 합금화 용융아연도금강판과 같은 다양한 시편에 대한 정밀한 실험을 통해 분석하였다. 이를 토대로 적응화 평활화법을 이용하여 잡음이 제거된 정확한 마찰계수를 측정할 수 있는 측정기의 성능을 향상시킬 수 있음을 검증하였다. 그 결과로서 마찰계수 0.16에 대하여 적응화 평활화법을 이용한 경우 저감률이 0.0417%임을 보였다.

• Smart Structures and Systems
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• 제16권5호
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• pp.781-806
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• 2015

A unified formulation of finite layer methods (FLMs), based on the Reissner mixed variational theorem (RMVT), is developed for the three-dimensional (3D) coupled electro-elastic analysis of simply-supported, functionally graded piezoelectric material (FGPM) plates with open- and closed-circuit surface conditions and under electro-mechanical loads. In this formulation, the material properties of the plate are assumed to obey an exponent-law varying exponentially through the thickness coordinate, and the plate is divided into a number of finite rectangular layers, in which the trigonometric functions and Lagrange polynomials are used to interpolate the in- and out-of-plane variations of the primary field variables of each individual layer, respectively, such as the elastic displacement, transverse shear and normal stress, electric potential, and normal electric displacement components. The relevant orders used for expanding these variables in the thickness coordinate can be freely chosen as the linear, quadratic and cubic orders. Four different mechanical/electrical loading conditions applied on the top and bottom surfaces of the plate are considered, and the corresponding coupled electro-elastic analysis of the loaded FGPM plates is undertaken. The accuracy and convergence rate of the RMVT-based FLMs are assessed by comparing their solutions with the exact 3D piezoelectricity ones available in the literature.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.855-859
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• 2004

We develop a new four-node flat shell element which is accurate, efficient, and suitable to be used on general purpose. The new element has a hybrid Trefftz element with drilling degrees of freedom as a membrane part. We define the two independent displacement field: the internal displacement field that satisfies governing equations in the domain a priori and the boundary displacement field that is usually used as a conventional finite element method. The hybrid Trefftz variational formulation connects these two displacement fields on the boundary of the domain. To add drilling degrees of freedom, we introduce the Allman's quadratic displacement field to the boundary displacement field. As a result, our flat shell element has 6 degrees of freedom per a node. We also use the well-known DKMQ plate bending element for the plate part of the proposed element. The DKMQ element satisfies Mindlin-Reissner‘s plate theory along the edge of the element and gives proper behavior regardless of the thickness. A series of numerical experiments shows that the performance of the new element such as accuracy, rate of convergence, robustness to mesh quality, and so on.

• 전산구조공학
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• 제3권3호
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• pp.101-111
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• 1990

p-version 유한요소법을 사용한 바닥 슬래브의 탄성해석은 어떤 종류의 요형모서리, 개구 그리고 손상단면을 갖는 점에서 응력특이성을 수반하게 된다. Reissner-Mindlin의 평판이론에 근거한 C.deg.- 평판 계층요소를 사용한 결과가 이론치 및 참고문헌에 발표된 수치해석값과 비교되었다. h-, p-와 hp-version의 수렴속도는 전체적 차원에서의 자유도 증가에 따른 에너지 노름값을 사용하여 예측할 수 있다. 만약에 자유도의 항으로 나타내지는 정확도를 여러 해석방법을 비교하는 기준으로 삼으면 본 연구에서 새로 제안되는 p-version 유한요소해석법의 근사해는 종래의 h-version에 근거하여 현재 까지 발표된 어떤 것 보다 훨씬 효율적 접근방법이라 하겠다. 해석예로는 150.deg. 둔각을 갖는 마름모꼴평판과 손상단면을 갖는 정방형평판이 사용되었다.