• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.650-657
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• 2001

This paper explains the process of designing a shielded encircling remote field eddy current (RFEC) probe to inspect nuclear fuel cladding tubes and investigates resulting signal characteristics. To force electromagnetic energy from exciter coil to penetrate into the tube, exciter coil is shielded outside by laminations of iron insulated electrically from each other. Effects of shielding and the proper operating frequency are studied by the finite element analysis and the location for sensor coil is decided. However, numerically simulated signals using the designed probe do not clearly show the defect indication when the sensor passes a defect and the other indication appeared as the exciter passes the defect is affected by the shape of shielding structure, which demonstrates that the sensor is directly affected by exciter fields. For this reason, the sensor is also shielded outside and this shielding dramatically improves signal characteristics. Numerical modeling with the finally designed probe shows very similar signal characteristics to those of inner diameter RFEC probe. That is, phase signals show almost equal sensitivity to inner diameter and outer diameter defects and the linear relationship between phase signal strength and defect depth is observed.

• Composites Research
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• v.35 no.4
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• pp.269-276
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• 2022

In this paper, a composite stiffened panel was fabricated using a three-dimensional weaving method that can reduce the risk of delamination, and mechanical properties such as buckling load and natural frequency were investigated. The preform of the stringer and skin of the stiffened panel were fabricated in one piece using T800 grade carbon fiber and then, resin (EP2400) was injected into the preform. The compression test and natural frequency measurement were performed for the stiffened panel, and the results were compared with the finite element analyses. In order to compare the performance of 3D weaving structures, the stiffened panels with the same configuration were fabricated using UD and 2D plain weave (fabric) prepregs. Compared to the tested buckling load of the 3D woven panel, the buckling loads of the stiffened panels of UD prepreg and 2D plain weave exhibited +20% and -3% differences, respectively. From this study, it was confirmed that the buckling load of the stiffened panel manufactured by 3D weaving method was lower than that of the UD prepreg panel, but showed a slightly higher value than that of the 2D plain weave panel.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.412-421
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• 2023

Ultrasound brain stimulation is spot-lighted by its capability of inducing brain cell activation in a localized deep brain region and ultimately treating impaired brain function while the efficiency and directivity of neural modulation are highly dependent on types of stimulus waveforms. Therefore, to optimize the types of stimulation parameters, we propose a cell-cultivable ultrasonic transducer having a series stack of a spin-coated polymer piezoelectric element (Poly-vinylidene fluoride-trifluorethylene, PVDF-TrFE) and a parylene insulating layer enhancing output acoustic pressure on a glass-coverslip which is commonly used in culturing cells. Due to the uniformity and high accuracy of stimulus waveform, tens of neuronal cell responses located on the transducer surface can be recorded simultaneously with fluorescence microscopy. By averaging the cell response traces from tens of cells, small changes to the low intensity ultrasound stimulations can be identified. In addition, the reduction of stimulus distortions made by standing wave generated from reflections between the transducers and other strong reflectors can be achieved by placing acoustic absorbers. Through the proposed ultrasound transducer, we could successfully observe the calcium responses induced by low-intensity ultrasound stimulation of 6 MHz, 0.2 MPa in astrocytes cultured on the transducer surface.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.5
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• pp.442-449
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• 2009

A two-dimensional cross-section analysis program based on the finite element method has been developed for composite blades with solid, thin-walled and compound cross-sections. The weighted-modulus method is introduced to determine the laminated composite material properties. The shear center and the torsion constant for any given section are calculated according to the Trefftz' definition and the St. Venant torsion theory, respectively. The singular value problem of cross-section stiffness properties faced during the section analysis has been solved by performing an eigenvalue analysis to remove the rigid body mode. Numerical results showing the accuracy of the program obtained for stiffness, offset and inertia properties are compared in this analysis. The current analysis results are validated with those obtained by commercial software and published data available in the literature and a good correlation has generally been achieved through a series of validation study.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.130.2-130.2
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• 2010

한전 전력연구원에서는 2009년 12월부터 125 kW급 용융탄산염 연료전지 발전시스템의 성능평가를 위한 운전이 진행되고 있다. 현재 진행 중인 "250 kW급 열병합 용융탄산염 연료전지 Proto Type개발" 과제의 최종시작품인 250 kW급 발전시스템은 125 kW급 MCFC 스택 2기로 설계되어, 125 kW급 시스템의 시험운전은 매우 중요한 기술적 성과가 될 것이다. 현재 125 kW급 MCFC 스택은 10,000 $cm^2$의 유효전극면적을 갖는 단위전지들로 구성되었으며, 적층 스택의 온도 및 농도분포의 최적화를 위해 내부 매니폴드 및 Co-flow Type 열교환기 기반의 분리판을 개발 적용하였다. 연료극의 전극 구성은 Ni-Al alloy로, 공기극의 전극 구성은 Lithiated-NiO로 이루어졌다. 그리고 매트릭스는 ${\alpha}-LiAlO_2$로 제작되었고, 전해질은 Li과 K Carbonate가 68 : 32 비율로 섞인 용융염을 사용하였다. 본 125 kW급 용융탄산염 연료전지 시스템의 운전평가는 고적층 스택의 온도 및 농도 분포를 확인하고, 최적화된 스택 운전 조건을 도출하는 것을 그 목적으로 하고 있다. 125kW급 스택 1기의 규모의 주변기기 시스템은 외부개질기, 촉매연소기, 이젝터, 고온순환 블로어 및 공기블로어 등으로 이루어져 있다. 고온형 연료전지 시스템에서 연료극과 공기극의 균일한 온도 및 압력 확보는 매우 중요하며, 이를 위하여 외부개질기 및 촉매연소기 연동을 통한 온도편차를 최소화하고, 기존 고온용 순환 블로어 대신 이젝터를 개발 도입하여 압력균형을 조절하였다. 125kW급 MCFC 시스템은 2009년 12월부터 전처리 운전을 시작하여 2010년 1월 말부터 PCS로 전기를 생산하고 있다. 평균전압 0.83V에서 100kW의 출력을 기록하였으며, 피크부하 120 kW, 누적출력량 30 MWh를 초과달성하였다.

• Journal of Korea Foresty Energy
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• v.20 no.1
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• pp.73-80
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• 2001

This study was carried out to investigate the strength and technical feasibility of arch type laminated lumber from the domestic small lumbers(Pinus densiflora S. et Z. and Larix kampferi Catt.). Arch type lumbers manufactured with different compositions of laminae. It was designed to improve the strength and stiffness. Strength S. rt Z. U;timate load Carr. laminated lumbers were higher than that of the Pinus densiflora S. et Z. Ultimate load of 7-ply laminated lumbers were 2 times higher than the 5-ply laminated lumbers. The strength of finger jointed lumbers were found to be about 15.8% less than that of the no joint lumber. One solution for this problem is to use veneer as face lamina. The veneer laminated lumbers was considerably greater than that of the non-veneer laminated lumbers. It was suggested that this small lumber may be a candidate for high valued product member to provide the proper combination of laminae.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.3 s.32
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• pp.77-82
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• 2004

In this paper, warpages of heterogeneous LTCC substrates comprised of high K/low K hi-layered structure were investigated. The effect of glass content in high K LTCC layer on the warpage of substrate during co-firing process was examined. Shrinkage and dielectric properties of high K and low K green sheets were measured. In-situ camber observation by hot stage microscopy showed different camber development of heterogeneous LTCC substrates according to glass content in high K green sheet. High K green sheet containing $50\%$ glass was matched to low K green sheet in the shrinkage. Therefore, LTCC substrate of Low K/High K+$50\%$ glass structure showed flat surface after sintering.

• Composites Research
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• v.27 no.4
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• pp.174-181
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• 2014

This study describes viscoelasticity analysis of carbon-fiber reinforced polymer matrix composite material. One of the most important problem during high temperature molding process is residual stress. Residual stress can cause warpage and cracks which can lead to serious defects of the final product. For the difference in thermal expansion coefficient and change of resin property during curing, it is difficult to predict the final deformed shape of carbon-fiber reinforced polymer matrix composite. The consideration of chemical shrinkage can reduce the prediction errors. For this reason, this study includes the viscoelasticity and chemical shrinkage effects in FE analysis by creating subroutines in ABAQUS. Analysis results are compared with other researches to verify the validity of the subroutine developed, and several stacking sequences are introduced to compare tested results.

• Computational Structural Engineering
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• v.3 no.3
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• pp.113-123
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• 1990

The paper is concerned with the elasto-plastic and geometrically nonlinear analysis of shell structures using an improved degenerated shell element. In the formulation of the element stiffness, the combined use of three different techniques was made. They are; 1) an enhanced interpolation of transverse shear strains in the natural coordinate system to overcome the shear locking problem ; 2) the reduced integration technique in in-plane strains to avoid the membrane locking behavior ; and 3) selective addition of the nonconforming displacement modes to improve the element performances. This element is free of serious shear/membrane locking problems and undesirable compatible/commutable spurious kinematic deformation modes. In the formulation for plastic deformation, the concept of a layered element model is used and the material is assumed von Mises yield criterion. An incremental total Lagrangian formulation is presented which allows the calculation of arbitrarily large displacements and rotations. The resulting non-linear equilibrium equations are solved by the Netwon-Raphson method combined with load or displacement increment. The versatility and accuracy of this improved degenerated shell element are demonstrated by solving several numerical examples.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.45-52
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• 2012

A variety of retrofit material such as CFRP, GFRP, and PolyUrea have been developed for strengthening RC structures and infrastructures. From previously reported research results, the capacity of strengthened concrete structures was dictated by the behavior of the interface between retrofit material and concrete. In this study, bond-shear test was carried out to estimate the bond behavior between retrofit material and concrete using a newly developed test grip. The test results of load and slip relation and energy absorption capacity of each retrofit material were obtained. These test results will provide basic information for retrofit material selection to achieve target retrofit performance.