• 한국음향학회지
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• 제31권4호
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• pp.205-213
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• 2012

동해와 남해에서 능동 음향센서 배열 신호를 측정하고, 신호의 공간 상관성을 분석하였다. 주변소음, 표적신호, 해수면과 후방산란 신호, 해상풍, 수직 수온을 25시간 동안 동시에 관측하였다. 남해 측정에서는 분석결과로 부터 주변소음의 공간 상관성이 표적신호 보다 매우 낮고, 표적신호는 전체 음향센서에서 0.5 이상의 상관성을 보였다. 동해 측정에서는 해수면 잔향 신호의 공간 상관성은 해수면 입사각이 클때 높고, 상관성이 0.5이상인 무차원화된 배열의 최대길이는 26도의 입사각에서 3.0, 32도의 입사각에서 3.5였다. 배열센서의 형상과 배열성능을 결정하는 기준이 되는 공간 상관성 파악을 위해서는 향후에 다양한 시공간 변동을 포함한 지속적인 관측이 필요하다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.477-482
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• 2009

로켓노즐 유동은 성능에 대단히 중요한 영향을 미치나, 고온 고압의 가스 유동 특성으로 직접적인 측정이 매우 어렵다. 이러한 문제 해결을 위해 수력학적 상사(hydraulic analogy)기법이 개발되었으며, 본 연구에서는 고온 고압의 로켓 노즐 유동에 대한 수력학적 상사의 적용 가능성이 시험되었다. 로켓 모타의 축대칭 De Laval 노즐 내부 유동현상에 관한 연구가 수력학적 상사를 이용하여 설계된 2차원 수문형 시험장치(2-D Sluice-Type Water-Table)에서 수행되었다. 정량적인 시험을 위해서는 $k{\neq}2$인 기체 유동에 대한 비상사성 문제 해결이 필요하며, 본 연구에서는 시험대를 경사시켜 유동방향 중력가속도 영향을 감소시킴으로서 점성에 의한 비상사성 문제 해결을 시도하였다. 유동 가시화를 통해 수력학 상사에 대한 이해를 깊이할 수 있었으며, 수력학적 상사 실험(2차원 등엔트로피 유동)의 관련 분야에 대한 다양한 적용 가능성이 확인되었다.

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1611-1625
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• 2020

We propose a scaled-down experimental model of vertical air-natural convection channels by applying the modified Ishii-Kataoka scaling method with the assistance of numerical analyses to the Reactor Vault Cooling System (RVCS) of the Proto-type Gen-IV Sodium-cooled fast reactor (PGSFR) being developed in Korea. Two major non-dimensional numbers (modified Richardson and Friction number) from the momentum equation and Stanton number from the energy balance equation were identified to design the scaled-down experimental model to assimilate thermal-hydraulic behaviors of the natural convective air-cooling channel of RVCS. The ratios of the design parameters in the PGSFR RVCS between the prototype and the scaled-down model were determined by setting Richardson and Stanton number to be unity. The friction number which cannot be determined by the Ishii-Kataoka method was estimated by numerical analyses using the MARS-KS system code. The numerical analyses showed that the friction number with the form loss coefficient of 2.0 in the scale-down model would result in an acceptable prediction of the thermal-hydraulic behavior in RVCS. We also performed experimental benchmarking using the scaled-down model with the MARS-KS simulations to verify the appropriateness of the scale-down model, which demonstrated that the temperature rises and the average air flow velocity measured in the scale-down model.

• 대한기계학회논문집
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• 제16권5호
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• pp.943-951
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• 1992

본 연구에서는 삭막에 의한 표면후퇴 현상을 해석하기 위하여 Brogan이 제시 한 front node dropping기법을 적용하여 여러개의 상이한 재료로 구성된 조합 내열 부품에서 삭마와 숯이 동시에 발생하는 경우에 대한 내부 열반응 예측도 가능하게 하 였다. 이 수치기법은 해석하고자 하는 부분에 대한 격자생성(mesh generation)을 수 행하여 각 격자점의 좌표를 고정한 후, 삭마에 의하여 표면이 후퇴될 때 첫번째 격자 점은 두번째 격자점과 일치될 때 까지 존재하다가 제거되고, 두번째 격자점도 세번째 격자점과 일치될 때까지 존재하다가 제거된다. 이때 나머지 격자점의 위치는 항상 일정하게 고정되며 삭마가 정지될 때까지 이 과정이 계속된다. 또한 본 연구분야에 수치해석 기법으로 유한해석법(FAM:finte analytic method)을 국내외 최초로 적용하여 비선형성이 심한 것을 효과적으로 처리하므로써 안정한 해를 얻을 수 있었다. 유한 해석법은 1981년 Chen이 제안한 기법으로, 국소 격자계에 대하여 선형화된 지배 방정 식의 엄밀해를 구하여 전체 문제 영역에 확장하는 방법이다. 이 방법은 수치 계산식 의 유도과정이 매우 복잡하기는 하나, 그 결과가 정확하고 안정한 해를 얻을 수 있어 서 점차 적용 사례가 증가하고 있으며 본 문제의 수치 해석에 매우 적합한 기법으로 판단된다.

• 한국가구학회지
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• 제21권3호
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• pp.237-247
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• 2010

This research was carried out to examine the properties of black charcoal board, in order to find the proper manufacturing condition for the black charcoal-board made of the charcoal. The charcoal in this study was distillated from domestic wood waste, and it were also the purpose of this study to see if the black charcoal-board has the advantageous properties of charcoal as a well-being building material against the sick house problem. Domestic wood waste was consisted of MDF 40%, PB 30%, plywood 15% and wood 15%, respectively. Black charcoal board was produced by hot pressing with following conditions; temperature $170^{\circ}C$, three stage pressing cycle of $40-10-40\;kgf/cm^2$(1min.-2.5min.-5min.) and non formaldehyde adhesives [P15%+M5%:MDI(M), poly vinyl acetate emulsion(P). Fine mixed particle size [#6-12(16.9%), #12-18(16.7%), #12-40(47.2%), #40-60(9.5%), #60-100(5.9%), less than #100(3.8%)] gave better results than larger particle size [over #6(33.8%), #12-18(17.7%), #12-40(37.7%), #40-60(6.4%), #60-100(2.6%), less than #100(1.8%)]. Final moisture content of the mat was best at 36%. Black charcoal-board showed less MOR and IB(internal bond), more WA(water absorption) than that of white charcoal-board. Black charcoal board showed not only the same gas adsorption and dimensional stability as white charcoal board but also good cutting, nailing and drilling for indoor environment systems.

• 한국추진공학회지
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• 제21권4호
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• pp.1-11
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• 2017

나로우주센터에 구축된 터보펌프 실매질시험설비는 터빈 구동을 위해 가스 발생기 대신 알코올버너 연소 가스를 사용한다. 그러나 터빈 입구에서 압력과 온도가 증가하여 터보펌프의 회전수가 정상상태를 유지하지 못하였다. 본 연구는 시험 환경을 정확히 파악하고자 알코올버너와 공급 배관에 대한 시스템 해석 코드를 개발하였으며 적용하였다. 해석 결과는 시험 결과와 일치하였고 터빈 입구의 압력과 온도 변화가 배관 열전달에 기인함을 정량적으로 확인하였다. 터빈 입구 조건에 공급 배관 단열 효과는 크지 않으나 길이는 매우 영향이 컸다. 본 연구를 통해 경험적으로 알았던 시험 조건의 영향을 정량적으로 명확히 파악했으며 시험 운용에 적용할 수 있었다.

• Journal of Welding and Joining
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• 제26권4호
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• pp.79-84
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• 2008

Use of sheet metal structure is increased in various fields such as automobile, aerospace and communication equipment industry. When this structure is welded, welding distortion is generated due to the non-uniformity of temperature distribution. Recently welding distortion becomes a matter of great importance in the structure manufacture industry because it deteriorates the product's quality by bringing about shape error. Accordingly many studies for solving the problems by controlling the welding distortion are being performed. However, it is difficult to remove all kinds of distortion by welding process, though various kinds of methods for reducing distortion are applied to production. Consequently, straightening process is operated if the high precision quality is requested after welding. The local heating method induces compression plastic deformation by thermal expansion in the heating stage and then leaves constriction of length direction in the cooling stage. Accordingly, in the case of sheet metal structure, straightening effect is expected by heating for the part of distortion. This study includes numerical analysis of straightening effect by the local heating method in distortion comes from production of welded sheet metal structure. Particularly straightening effect followed by dimensions of heating area is analyzed according to the numerical analysis. The numerical analysis is performed by constructing 3-dimensional finite element model for 0.4mm stainless steel-sheet metal. Results of this study confirm that straightening effect changes as heating area increases and the optimum value of heating area that proves the maximum straightening effect exists.

• Advances in nano research
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• 제8권1호
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• pp.83-94
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• 2020

An analytical formulation and solution process for the buckling analysis of porous magneto-electro-elastic functionally graded (MEE-FG) beam via different thermal loadings and various boundary conditions is suggested in this paper. Magneto electro mechanical coupling properties of FGM beam are taken to vary via the thickness direction of beam. The rule of power-law is changed to consider inclusion of porosity according to even and uneven distribution. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. Change in pores along the thickness direction stimulates the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM beam under magneto-electrical field via Hamilton's principle. An analytical model procedure is adopted to achieve the non-dimensional buckling load of porous FG beam exposed to magneto-electrical field with various boundary conditions. In order to evaluate the influence of thermal loadings, material graduation exponent, coefficient of porosity, porosity distribution, magnetic potential, electric voltage and boundary conditions on the critical buckling temperature of the beam made of magneto electro elastic FG materials with porosities a parametric study is presented. It is concluded that these parameters play remarkable roles on the buckling behavior of porous MEE-FG beam. The results for simpler states are proved for exactness with known data in the literature. The proposed numerical results can serve as benchmarks for future analyses of MEE-FG beam with porosity phases.

• Nuclear Engineering and Technology
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• 제41권9호
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• pp.1143-1156
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• 2009

The SPACE code that is based on a multi-dimensional two-fluid, three-field model is under development for licensing purposes of pressurized water reactors in Korea. Among the participating research and industrial organizations, KAERI is in charge of developing the physical models and correlation packages for the constitutive equations. This paper introduces a developed wall-to-fluid heat transfer package for the SPACE code. The wall-to-fluid heat transfer package consists of twelve heat transfer subregions. For each sub-region, the models in the existing safety analysis codes and the leading models in literature have been peer reviewed in order to determine the best models which can easily be applicable to the SPACE code. Hence a wall-to-fluid heat transfer region selection map has been developed according to the non-condensable gas quality, void fraction, degree of subcooling, and wall temperature. Furthermore, a partitioning methodology which can take into account the split heat flux to the continuous liquid, entrained droplet, and vapor fields is proposed to comply fully with the three-field formulation of the SPACE code. The developed wall-to-fluid heat transfer package has been pre-tested by varying the independent parameters within the application range of the selected correlations. The smoothness between two adjacent heat transfer regimes has also been investigated. More detailed verification work on the developed wall-to-fluid heat transfer package will be carried out when the coupling of a hydraulic solver with the constitutive equations is brought to completion.

• Membrane and Water Treatment
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• 제13권5호
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• pp.235-243
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• 2022

The paper presents the effect of operating temperatures and flow rates on the distillate flux that can be obtained from a hydrophobic membrane having the characteristics: pore size of 0.15 ㎛; thickness of 130 ㎛; and 85% porosity. That membrane in the present investigation could be the direct contact (DCMD) or the air-gap membrane distillation (AGMD). To model numerically the membrane distillation processes, the two-dimensional computational fluid dynamic (CFD) is used for the DCMD and AGMD cases here. In this work, DCMD and AGMD models have been validated with the experimental data using different flows (Parallel and Counter-current flows) in non-steady-state situations. A good agreement is obtained between the present results and those of the experimental data in the literature. The new approach in the present numerical modeling has allowed examining effects of the nature of materials (Polyvinylidene fluoride (PVDF) polymers, copolymers, and blends) used on thermal properties. Moreover, the effect of the area surface of the membrane (0.021 to 3.15 ㎡) is investigated to explore both the laminar and the turbulent flow regimes. The obtained results found that copolymer P(VDF-TrFE) (80/20) is more effective than the other materials of membrane distillation (MD). The mass flux and thermal efficiency reach 193.5 (g/㎡s), and 83.29 % using turbulent flow and an effective area of 3.1 ㎡, respectively. The increase of feed inlet temperatures and its flow rate, with the reduction of cold temperatures and its flow rate are very effective for increasing distillate water flow in MD applications.