• 한국지반환경공학회 논문집
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• 제15권1호
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• pp.43-51
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• 2014

부등침하로 인한 각변위는 구조물의 안정성과 사용성에 영향을 미치는 중요한 요소 중 하나이다. 실무에서는 현재 Bjerrum이 제안한 각변위기준이 널리 사용되고 있다. 하지만 현재 도로 성토 현장에서 적용하고 있는 계측시스템은 구조물의 각변위를 적합하게 나타내지 못하고 있다. 이와 같은 문제는 충분하지 못한 계측 수, 부정확한 계측기 설치, 계측된 자료의 해석에 있어 각변위 기본개념의 잘못된 이해 등과 관련이 된다. 본 연구에서 도로 성토 현장에서 얻어진 데이터의 분석을 통해 이와 같은 문제점을 규명하였다. 도로 성토 현장에서 적용할 수 있는 자동화된 상대변위 계측시스템이라는 개선된 계측시스템을 제안하였다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1994년도 추계학술대회
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• pp.71-74
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• 1994

In cementless total hip arthroplasty(THA), an initial stability of the femoral component is mandatory to achieve bony ingrowth and secondary long term fixation. Bone ingrowth depends strongly on relative micromotion and stress distributions at the interface. Primary stability of the femoral component can be obtained by minimizing the magnitude of relative micromotions at bone-prosthesis interface, Hence an accurate evaluation of interface behavior and stress/strain fields in the bone implant system may be relevant for better understanding of clinical situations and improving THA design. However, complete evaluation of load transfer in the bone remains difficult to assess experimentally, Hence, recently finite element method (FEM) was introduced in orthopaedic research field to fill the gap due to its unique capacity to evaluate stress in structure of complex shape, loading and material behavior. The authors developed the 3-dimensional numerical finite element model which is composed of totally 1179 elements off and 8 node blick. We also analyzed the micromotions at the bone-stem interface and mechanical behavior of existing bone prosthesis for a loading condition simulating the single leg stance. The result indicates that the values of relative motion for this well fit Multilock stem were $150{\mu}m$ in maximum, $82{\mu}m$ in minimum, and the largest relative motion developed in medial region of proximal femur with anterior-posterior direction. The proximal region of the bone was much larger in motion than the distal region and the stress pattern shows high stress concentration on the cortex near the tip of the stem. These findings indicates that the loading in the proximal femoral bone in the early postoperative situation can produce micromotions on the interface and clinically cementless TEA patient should not be allowed weight bearing strictly early in the postoperative period.

• Journal of Astronomy and Space Sciences
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• 제31권2호
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• pp.177-186
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• 2014

The Immersion Grating Infrared Spectrometer (IGRINS) is a near-infrared wide-band high-resolution spectrograph jointly developed by the Korea Astronomy and Space Science Institute and the University of Texas at Austin. IGRINS employs three HAWAII-2RG Focal Plane Array (H2RG FPA) detectors. We present the design and fabrication of the detector mount for the H2RG detector. The detector mount consists of a detector housing, an ASIC housing, a Field Flattener Lens (FFL) mount, and a support base frame. The detector and the ASIC housing should be kept at 65 K and the support base frame at 130 K. Therefore they are thermally isolated by the support made of GFRP material. The detector mount is designed so that it has features of fine adjusting the position of the detector surface in the optical axis and of fine adjusting yaw and pitch angles in order to utilize as an optical system alignment compensator. We optimized the structural stability and thermal characteristics of the mount design using computer-aided 3D modeling and finite element analysis. Based on the structural and thermal analysis, the designed detector mount meets an optical stability tolerance and system thermal requirements. Actual detector mount fabricated based on the design has been installed into the IGRINS cryostat and successfully passed a vacuum test and a cold test.

• Korea-Australia Rheology Journal
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• 제16권4호
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• pp.183-191
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• 2004

High Deborah or Weissenberg number problems in viscoelastic flow modeling have been known formidably difficult even in the inertialess limit. There exists almost no result that shows satisfactory accuracy and proper mesh convergence at the same time. However recently, quite a breakthrough seems to have been made in this field of computational rheology. So called matrix-logarithm (here we name it tensor-logarithm) formulation of the viscoelastic constitutive equations originally written in terms of the conformation tensor has been suggested by Fattal and Kupferman (2004) and its finite element implementation has been first presented by Hulsen (2004). Both the works have reported almost unbounded convergence limit in solving two benchmark problems. This new formulation incorporates proper polynomial interpolations of the log­arithm for the variables that exhibit steep exponential dependence near stagnation points, and it also strictly preserves the positive definiteness of the conformation tensor. In this study, we present an alternative pro­cedure for deriving the tensor-logarithmic representation of the differential constitutive equations and pro­vide a numerical example with the Leonov model in 4:1 planar contraction flows. Dramatic improvement of the computational algorithm with stable convergence has been demonstrated and it seems that there exists appropriate mesh convergence even though this conclusion requires further study. It is thought that this new formalism will work only for a few differential constitutive equations proven globally stable. Thus the math­ematical stability criteria perhaps play an important role on the choice and development of the suitable con­stitutive equations. In this respect, the Leonov viscoelastic model is quite feasible and becomes more essential since it has been proven globally stable and it offers the simplest form in the tensor-logarithmic formulation.

• 대한의용생체공학회:의공학회지
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• 제17권1호
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• pp.61-70
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• 1996

In cementless total hip arthroplasty(THA), an initial stability of the femoral component is mandatory to achieve bony inyowth and secondary long term fixation. Primary stability of the femoral component can be obtained by minimizing the magnitude of relative micromotions at bone stem interface. An accurate evaluation of interf'ace micromotion and stress/strain fields in the bone-implant system may be relevant for better understanding of clinical situations and improving THA design. Recently finite element method(FEM) was introduced in'orthopaedic research field due to its unique capacity to evaluate stress in structure of complex shape, loading and material behavior. The authors developed the 3-dimensional finite element model of proximal femur with $Multilock^{TM}$ stem of 1179 blick elements to analyse the micromotions and mechanical behaviors at the bone-stem inteface in early post-operative period for the load simulating single leg stance. The results indicates that the values of relative motion for this well fit stem were $150{\mu}m$ in maximum $82{\mu}m$ in minimum and the largest relative motion was developed in medial region of Proximal femur and in anterior-posterior direction. The motion in the proximal bone was much greater than in the distal bone and the stress pattern showed high stress concentration on the cortex near the tip of the stem. These findings indicate that the loading on the hip joint in the early postoperative situation before achieving bony ingrowth could produce large micromotion of $150{\mu}m$ and clinicaly non-cemented THA patient should not be allowed weight bearing strictly early in the postoperative period.

• 한국추진공학회지
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• 제17권5호
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• pp.70-79
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• 2013

마이크로 가스터빈용 하이브리드/이중 선회제트 연소기의 비반응 유동 및 혼합특성에 관한 수치해석 연구가 수행되었다. 고정된 열부하에서 pilot 버너의 위치, 선회 각 및 방향이 주요 변수로 검토되었다. 결과로서, pilot 버너의 위치, 선회 각 및 방향의 변화는 버너 출구 근처의 난류 유동장, 특히 중앙 재순환영역 및 난류강도의 큰 변화를 초래하며, 화염안정성 및 배기성능의 큰 변화를 동반하게 된다. 실험결과와의 비교를 통해, 하이브리드/이중 선회제트 연소기의 개발을 위하여 화염안정성 및 배기의 측면에서 pilot 버너의 최적 위치, 선회각$45^{\circ}$ 그리고 정방향 선회유동 조건들이 선택되었다.

• Bulletin of the Korean Chemical Society
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• 제11권4호
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• pp.276-281
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• 1990

The equivalent conductance of univalent cation (potassium, silver, thallium and ammonium) perchlorates in methanol containing 18-membered crown ethers, 18-crown-6 (18C6) and 1,10-dithia-18-crown-6 (DT18C6) were measured at different temperatures. The equivalent conductances of ammonium perchlorate were increased by increasing content of DT18C6 exceptionally, due to more favorable solvations than complexations. From the equivalent conductance changes, the formation constants for 1:1 compmlexes have been determined, and the values of enthalpy and entropy changes have been calculated. The complexations of 18C6 and DT18C6 with the univalent cations under investigation are all exothermic and the ${\Delta}$S values are all negative and no considerable differences around 50 J/ (k mol). The selectivity order of 18C6 is $K^+ > Tl^+ > Ag^+ > NH_4^+$, while that of DT18C6 is $Ag^+ > Tl^+ > NH_4^+ > K^+$. By sulfur substitutions in 18C6 result in significant decrease in stability, but the stability of $Ag^+$-DT18C6 complex are $10^4$ times larger than those of $K^+$. This increase of stabilities for $Ag^+$-DT18C6 complex are primary due to the result of favorable exothermic heat of reaction between the polarizable soft cation and soft sulfur centers. In NMR experiment, the stepwise additions of cation perchlorates into crown ether solutions induced two major spectral changes. First, the resonance all shift down field and the cation induced shifts were linear up to 1:1 cation/crown ratio, above which no further changes were observed. On the basis of these results, it could be concluded that 1:1 complex is formed. Second, the magnitudes of cation induced shifts were different each other in same ligand. By addition of silver ion to the solution of DT18C6, the largest shift of proton peak near the sulfur atom was observed. These effects are also arisen from the results of covalent bonding between "soft-soft" interactions.

• E2M - 전기 전자와 첨단 소재
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• 제12권7호
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• pp.7-11
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• 1999

Fully sealed field emission display in size of 4.5 inch has been fabricated using single-wall carbon nanotubes-organic vehicle com-posite. The fabricated display were fully scalable at low temperature below 415$^{\circ}C$ and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1V/${\mu}{\textrm}{m}$ and field emis-sion current of 1.5mA at 3V/${\mu}{\textrm}{m}$ (J=90${\mu}{\textrm}{m}$/$\textrm{cm}^2$)were observed. Brightness of 1800cd/$m^2$ at 3.7V/${\mu}{\textrm}{m}$ was observed on the entire area of 4.5-inch panel from the green phosphor-ITO glass. The fluctuation of the current was found to be about 7% over a 4.5-inch cath-ode area. This reliable result enables us to produce large area full-color flat panel dis-play in the near future. Carbon nanotubes (CNTs) have attracted much attention because of their unique elec-trical properties and their potential applica-tions [1, 2]. Large aspect ratio of CNTs together with high chemical stability. ther-mal conductivity, and high mechanical strength are advantageous for applications to the field emitter [3]. Several results have been reported on the field emissions from multi-walled nanotubes (MWNTs) and single-walled nanotubes (SWNTs) grown from arc discharge [4, 5]. De Heer et al. have reported the field emission from nan-otubes aligned by the suspension-filtering method. This approach is too difficult to be fully adopted in integration process. Recently, there have been efforts to make applications to field emission devices using nanotubes. Saito et al. demonstrated a car-bon nanotube-based lamp, which was oper-ated at high voltage (10KV) [8]. Aproto-type diode structure was tested by the size of 100mm $\times$ 10mm in vacuum chamber [9]. the difficulties arise from the arrangement of vertically aligned nanotubes after the growth. Recently vertically aligned carbon nanotubes have been synthesized using plasma-enhanced chemical vapor deposition(CVD) [6, 7]. Yet, control of a large area synthesis is still not easily accessible with such approaches. Here we report integra-tion processes of fully sealed 4.5-inch CNT-field emission displays (FEDs). Low turn-on voltage with high brightness, and stabili-ty clearly demonstrate the potential applica-bility of carbon nanotubes to full color dis-plays in near future. For flat panel display in a large area, car-bon nanotubes-based field emitters were fabricated by using nanotubes-organic vehi-cles. The purified SWNTs, which were syn-thesized by dc arc discharge, were dispersed in iso propyl alcohol, and then mixed with on organic binder. The paste of well-dis-persed carbon nanotubes was squeezed onto the metal-patterned sodalime glass throuhg the metal mesh of 20${\mu}{\textrm}{m}$ in size and subse-quently heat-treated in order to remove the organic binder. The insulating spacers in thickness of 200${\mu}{\textrm}{m}$ are inserted between the lower and upper glasses. The Y\ulcornerO\ulcornerS:Eu, ZnS:Cu, Al, and ZnS:Ag, Cl, phosphors are electrically deposited on the upper glass for red, green, and blue colors, respectively. The typical sizes of each phosphor are 2~3 micron. The assembled structure was sealed in an atmosphere of highly purified Ar gas by means of a glass frit. The display plate was evacuated down to the pressure level of 1$\times$10\ulcorner Torr. Three non-evaporable getters of Ti-Zr-V-Fe were activated during the final heat-exhausting procedure. Finally, the active area of 4.5-inch panel with fully sealed carbon nanotubes was pro-duced. Emission currents were character-ized by the DC-mode and pulse-modulating mode at the voltage up to 800 volts. The brightness of field emission was measured by the Luminance calorimeter (BM-7, Topcon).

• 한국지반공학회논문집
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• 제19권5호
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• pp.211-221
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• 2003

스웨덴$\"{A}"{s}"{p}"{o}$지하실험실에서는 방사성폐기물 처분공 사이 암반에서의 파쇄 및 안정성을 예측할 수 있는 능력을 평가하기 위해 $\"{A}"{s}"{p}"{o}$ 암주 안정성 실험 (APSE)이라고 하는 현지 가열 실험이 준비되고 있다. 계획된 시험 조건하의 암주에서의 균열 진전 과정을 합리적으로 예측하기 위해 경계요소 수치해석 코드인 FRACOD가 적용되었다. 암석경계와 무결암석 내에서의 균열 진전을 모사하기 위해 코드를 개선하였다. 또한 굴착 및 열하중에 의해 발생하는 응력분포를 FRACOD모델에 적용하기 위해 새로운 경계요소를 이용한 역해법을 개발하였다. 이 글은 계획된 시험조건에 대한 예측 모델링 결과를 제시한다. 굴착에 의한 응력분포는 암주 벽면에 약간의 균열을 발생시켰다. 120일 동안의 가열에 의해 암주 벽면 중앙부에서 전형적인 전단 균열들의 개시 및 전파가 일어났지만, 전반적으로 암주 내부는 고려되는 조건하에서 안정한 상태를 유지하였다. 기존 절리들의 존재와 균열 물성에 따른 영향이 또한 논의되었다. 해석 결과를 통해 FRACOD가 심부 터널 및 보어홀에서 취성 암반의 균열 진전 현상을 적절히 모델링할 수 있음을 알 수 있다. 취성 암반의 균열 진전 현상을 적절히 모델링할 수 있음을 알 수 있다.

• 한국산학기술학회논문지
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• 제20권11호
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• pp.250-258
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• 2019

과거 지진 발생으로 인하여 발전소 내 전력 운용설비의 전도로 인한 피해가 크게 발생하여 이에 대한 국내 발전소 운용설비 정착부에 대한 내진 안정성 평가는 매우 중요하다. 본 연구에서는 현재 국내 발전소 내 설치된 발전설비 현장조사를 통하여 콘크리트 슬래브에 설치된 발전설비 정착부 앵커볼트의 구조성능을 평가하였다. 대상구조물인 대청댐의 경우, 고정부 설치용으로 선 설치 앵커볼트가 사용되었으며 규격은 M10 J형 선설치 앵커볼트와 M12 J형 선설치 앵커볼트로 시공되었다. ASTM E 488-96 기준을 고려하여 앵커볼트 인발 및 전단 성능평가를 수행하였으며 평가된 앵커볼트의 성능을 국내외 설계기준(KCI 2012, ACI 318, EOTA TR45)과 비교, 분석하였다. 그 결과 M10, M12 J형 선설치 앵커볼트들은 모두 설계하중 값보다 높게 저항하는 것으로 나타나 현재 시공 상태가 설계기준은 충분히 만족하다는 결과를 얻었다. 하지만 이는 실험적 평가를 통한 결과일 뿐이므로 향후 수치해석 평가를 통하여 보다 폭넓게 분석될 필요가 있을 것으로 판단된다.