• 한국가스학회지
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• 제22권1호
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• pp.1-8
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• 2018

수소연료전지 자동차 압력 용기에는 연료전지 스택으로 수소의 흐름을 제어하기 위해 전자 밸브가 부착되고 있다. 전자 밸브의 솔레노이드는 전기 신호에 의해 유로를 개폐하는 역할을 하며, 전원이 인가되는 시간이 경과함에 따라 온도가 상승하여 일정 온도에서 포화된다. 특히 온도의 상승은 솔레노이드의 흡인력을 감소시키므로 안정적인 수소 공급을 위해서 설계 시 포화 온도와 온도에 따른 흡인력 특성 파악이 요구된다. 본 연구에서는 솔레노이드 설계 변수에 따른 포화 온도 계산식을 제안하고 열 유동 해석을 통해 타당성을 확인하였다. 또한, 온도에 따른 흡인력 변화를 분석하기 위해 전자기장 해석을 수행하였으며 온도 특성 실험을 통해 포화 온도와 흡인력 해석 결과를 검증하였다. 포화온도는 계산식과 해석결과를 비교하였을 때 $5.3^{\circ}C$, 해석 결과와 실험 결과를 비교하였을 때 $5.9^{\circ}C$의 오차가 발생하였으며, 흡인력은 1.0 N, 최대 2.1 N의 오차가 발생하였다.

• 한국기계가공학회지
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• 제20권10호
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• pp.27-37
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• 2021

The use of additive manufacturing processes for the repair and remanufacturing of mechanical parts has attracted considerable attention because of strict environmental regulations. Directed energy deposition (DED) is widely used to retrofit mechanical parts. In this study, finite element analyses (FEAs) were performed to investigate the influence of the substrate phase and inclination angle on the heat transfer characteristics in the vicinity of Hastelloy X regions deposited via DED. FE models that consider the bead size and hatch distance were designed. A volumetric heat source model with a Gaussian distribution in a plane was adopted as the heat flux model for DED. The substrate and the deposited powder were S45C structural steel and Hastelloy X, respectively. Temperature-dependent thermal properties were considered while performing the FEAs. The effects of the substrate phase and inclination angle on the temperature distributions and depth of the heat-affected zone (HAZ) in the vicinity of the deposited regions were examined. Furthermore, the influence of deposition paths on depths of the HAZ were investigated. The results of the analyses were used to determine the suitable phase and inclination angle of the substrate as well as the appropriate deposition path.

• 대한기계학회논문집 C: 기술과 교육
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• 제3권3호
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• pp.165-173
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• 2015

본 논문에서는 PRT(Personal Rapid Transit) 차량의 수직이송을 위한 장치를 개발하는 과정에서 수행된 주요 구조물의 정적 구조적 안전성 평가 결과를 다룬다. 지금까지 노선상에서 승객이 탑승한 상태에서 운영중인 차량의 수직이송에 대한 연구는 전무하며, 이는 기존의 2 차원 적인 교통운영 체계의 한계를 극복하는데 기여할 수 있을 것으로 기대된다. 특히, 본 연구에서 제안된 수직이송장치는 순환컨베이어 방식으로 연속 이송이 가능해서 통행량이 많은 지역에도 적용이 가능하다. 본 시스템이 물류분야에서 많이 사용되어 왔지만, 수직이동 시 차량의 무게에 의한 하중은 일반적인 물류의 수송과는 다르게 집중하중 형태로 컨베이어에 가해지기 때문에 이에 대한 구조적 안정성 평가는 필수적이다. 본 논문에서는 상용 유한요소 해석 프로그램인 $Ansys^{(R)}$를 이용해서 수직이송 장치의 기본 설계(안)의 구조적 안정성을 수치해석적 방법에 의해 평가하고자 한다.

• 전기화학회지
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• 제10권3호
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• pp.179-183
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• 2007

The corrosion behavior of metal covered with mortar under a wet-dry cyclic condition were investigated to apply for the measurement of corrosion rates of reinforcing steel in concrete structure. The carbon steel in mortar having t=3 mm cover thickness was exposed to the alternate condition of 6 h immersion in chloride containing solution and 18 h drying at $25^{\circ}C$ and 50%RH. The electrochemical phenomena of a carbon steel and mortar interface was explained by an equivalent circuit consisting of a solution resistance, a charge transfer resistance and a CPE(Constant Phase Element). The corrosion rates were monitored continuously during exposure using an AC impedance technique. Simultaneously, the current distribution over the working electrode during impedance measurement was analyzed from the phase shift, $\theta$, in an intermediate frequency. The result showed that corrosion rate monitoring using an AC impedance method is suitable under the given exposure conditions even during the drying period when the metal is covered with the wetted mortar.

• Computers and Concrete
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• 제23권4호
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• pp.235-243
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• 2019

The discontinuous Galerkin method (DGM) has become widely used as it possesses several qualities, such as a natural ability to dealing with discontinuities. DGM has its major success related to fluid mechanics. Its major importance is the ability to deal with discontinuities and still provide high order of approximation. That is an important advantage when simulating cracking propagation. No remeshing is necessary during the propagation, since the crack path follows the interface of elements. However, DGM comes with the drawback of an increased number of degrees of freedom when compared to the classical continuous finite element method. Thus, it seems a natural approach to combine them in the same simulation obtaining the advantages of both methods. This paper proposes the application of the combined continuous-discontinuous Galerkin method (CDGM) to crack propagation. An important engineering problem is the simulation of crack propagation in concrete structures. The problem is characterized by discontinuities that evolve throughout the domain. Crack propagation is simulated using CDGM. Discontinuous elements are placed in regions with discontinuities and continuous elements elsewhere. The cohesive zone model describes the fracture process zone where softening effects are expressed by cohesive zones in the interface of elements. Two numerical examples demonstrate the capacities of CDGM. In the first example, a plain concrete beam is submitted to a three-point bending test. Numerical results are compared to experimental data from the literature. The second example deals with a full-scale ground slab, comparing the CDGM results to numerical and experimental data from the literature.

• Structural Engineering and Mechanics
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• 제68권5호
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• pp.527-536
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• 2018

The free vibration frequency responses of the graded flat and curved (cylindrical, spherical, hyperbolic and elliptical) panel structures investigated in this research considering the rectangular and tilted planforms under unlike temperature loading. For the numerical implementation purpose, a micromechanical model is prepared with the help of Voigt's methodology via the power-law type of material model. Additionally, to incur the exact material strength, the temperature-dependent properties of each constituent of the graded structure included due to unlike thermal environment. The deformation kinematics of the rectangular/tilted graded shallow curved panel structural is modeled via higher-order type of polynomial functions. The final form of the eigenvalue equation of the heated structure obtained via Hamilton's principle and simultaneously solved numerically using finite element steps. To show the solution accuracy, a series of comparison the results are compared with the published data. Some new results are exemplified to exhibit the significance of power-law index, shallowness ratio, aspect ratio and thickness ratio on the combined thermal eigen characteristics of the regular and tilted graded panel structure.

• Nuclear Engineering and Technology
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• 제51권7호
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• pp.1805-1815
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• 2019

While nickel-based alloys have been widely used for power plants due to corrosion resistance and good mechanical properties, during the last couple of decades, failures of nuclear components increased gradually. One of main degradation mechanisms was primary water stress corrosion cracking at dissimilar metal welds of piping and reactor head penetrations. In this context, precise estimation of welding effects became an important issue for ensuring reliability of them. The present study deals with a series of finite element analyses and crack growth rate evaluation of Alloys 690/152. Firstly, variation of residual stresses and equivalent plastic strains was simulated taking into account welding of a cylindrical block. Subsequently, extraction and pre-cracking of compact tension (CT) specimens were considered from different locations of the block. Finally, crack growth curves of the alloys and heat affected zone were developed based on analyses results combined with experimental data in references. Characteristics of crack growth behaviors were also discussed in relation to mechanical and fracture parameters.

• 한국환경과학회지
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• 제4권5호
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• pp.103-103
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• 1995

In the Chinhae Bay, Korea, sedimentation rates and sedimentary record of anthropogenic metal loads were determined by $^{210}Pb$ dating and heavy metal analysis of four sediment cores . The sedimentation rates varied from 0.16g/$cm^2$/yr(3.1mm/yr) at Sta. Ct, located within narrow waterway to 0.24g/$cm^2$/yr(4.8mm/yr) at Sta. Cl, located in Haengam Bay. Maximum contents of Mn, Zn, Cu and Cr were observed at Sta. C2 located near the mouth of Masan Bay, while minimum contents were observed at Sta. CB. Mn/Fe ratios at Sta. C2 and Sta. C4 showed gradually increasing and decreasing downward, respectively, in the upper layer of sediment cores. This suggests that Mn may be diagenetically redistributed in highly reduced environment. At Sta. C2, the concentrations of Zn and Cu began to increase from 1920s by anthropogenic input and have been remarkablely increasing since mid 1960s. At Sta. C3, located near Sungpo, anthropogenic input of these two elements has also slightly increased after 1970s. However, pollution of these two elements was not significant in Haengam Bay(Sta. Cl) and Chiljun watenway(Sta. C4). The pollution of Co, Ni and Cr was not remarkable in all core samples except surface sediment of Sta. C2. The total input of anthropogenic Zn and Cu since 1920s was estimated to be 28∼792 ㎍/cm2 and 0∼168㎍/cm2, respectively. Sta. C2 showed remarkablely higher values relative to other stations: anthropogenic loads of Zn and Cu constituted 27% and 29% of the total sedimentary inventories at the present day, respectively. Fe, Ni, Cr and Co contents showed good correlation(r>0.8) with each other. Anthropogenic Zn and Cu also showed a very good positive correlation(>0.9). However, correlation between these two group of element was quite scattered, indicating different sources and geochemical behaviors.

• 한국환경과학회지
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• 제4권5호
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• pp.489-500
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• 1995

In the Chinhae Bay, Korea, sedimentation rates and sedimentary record of anthropogenic metal loads were determined by $^{210}Pb$ dating and heavy metal analysis of four sediment cores . The sedimentation rates varied from 0.16g/$cm^2$/yr(3.1mm/yr) at Sta. Ct, located within narrow waterway to 0.24g/$cm^2$/yr(4.8mm/yr) at Sta. Cl, located in Haengam Bay. Maximum contents of Mn, Zn, Cu and Cr were observed at Sta. C2 located near the mouth of Masan Bay, while minimum contents were observed at Sta. CB. Mn/Fe ratios at Sta. C2 and Sta. C4 showed gradually increasing and decreasing downward, respectively, in the upper layer of sediment cores. This suggests that Mn may be diagenetically redistributed in highly reduced environment. At Sta. C2, the concentrations of Zn and Cu began to increase from 1920s by anthropogenic input and have been remarkablely increasing since mid 1960s. At Sta. C3, located near Sungpo, anthropogenic input of these two elements has also slightly increased after 1970s. However, pollution of these two elements was not significant in Haengam Bay(Sta. Cl) and Chiljun watenway(Sta. C4). The pollution of Co, Ni and Cr was not remarkable in all core samples except surface sediment of Sta. C2. The total input of anthropogenic Zn and Cu since 1920s was estimated to be 28~792 $\mu\textrm{g}$/cm2 and 0~168$\mu\textrm{g}$/cm2, respectively. Sta. C2 showed remarkablely higher values relative to other stations: anthropogenic loads of Zn and Cu constituted 27% and 29% of the total sedimentary inventories at the present day, respectively. Fe, Ni, Cr and Co contents showed good correlation(r>0.8) with each other. Anthropogenic Zn and Cu also showed a very good positive correlation(>0.9). However, correlation between these two group of element was quite scattered, indicating different sources and geochemical behaviors.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.656-660
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• 2002

The fiber reinforced composite material is widely used in the multi-industrial field where the weight reduction of the infrastructure is demanded because of their high specific modulus and specific strength. Pressure vessels using this composite material in comparison with conventional metal vessels can be applied in the field where lightweight and the high pressure is demanded from the defense and aerospace industry to rocket motor case due to the merits which are energy curtailment by the weight reduction and decrease of explosive damage precede to the sudden explosion which is generated by the pressure leakage condition. In this paper, for nonlinear finite element analysis of E-glass/epoxy filament winding composite pressure vessel receiving an internal pressure, the standard interpretation model is developed by using the ANSYS 5.7.1, the general commercial program, which is verified as the accuracy and useful characteristic of the solution based on Auto LISP and ANSYS APDL. Both the preprocessor for doing exclusive analysis of filament winding composite pressure vessel and postprocessor that simplifies result of analysis have been developed to help the design engineers.