• Advances in aircraft and spacecraft science
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• 제4권1호
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• pp.1-19
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• 2017

Fatigue life prediction of a multi-row countersunk riveted lap joint was performed numerically. The stress and strain conditions in a highly stressed substructure of the joint were analysed using a global/local finite element (FE) model coupling approach. After validation of the FE models using experimental strain measurements, the stress/strain condition in the local three-dimensional (3D) FE model was simulated under a fatigue loading condition. This local model involved multiple load cases with nonlinearity in material properties, geometric deformation, and contact boundary conditions. The resulting stresses and strains were used in the Smith-Watson-Topper (SWT) strain life equation to assess the fatigue "initiation life", defined as the life to a 0.5 mm deep crack. Effects of the rivet-hole clearance and rivet head deformation on the predicted fatigue life were identified, and good agreement in the fatigue life was obtained between the experimental and the numerical results. Further crack growth from a 0.5 mm crack to the first linkup of two adjacent cracks was evaluated using the NRC in-house tool, CanGROW. Good correlation in the fatigue life was also obtained between the experimental result and the crack growth analysis. The study shows that the selected methodology is promising for assessing the fatigue life for the lap joint, which is expected to improve research efficiency by reducing test quantity and cost.

• 정보통신설비학회논문지
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• 제2권4호
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• pp.5-16
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• 2003

Parallel Coupler Access Encoder(PCAE)와 Parallel Coupler Access Decoder(PCAD)를 이용한 FO-CDMA(Fiber-Optic Code Division Multiple Access)시스템에서 광정합필터 특성을 실험을 통해 분석하였다. PCAE와 PCAD를 구성하고 있는 즉, 1xN splitter와 Nx1 combiner사이에 접속된 광지연선로의 길이비율을 광직교코드 생성알고리즘에 의해 결정하였고, 부/복호화 과정 및 시그템 성능을 peak to side-lobe ratio(PSR)를 구하여 기존에 제시된 결과와 비교하였다. 기존의 연구에서는 SCAE 및 SCAD를 이용하여 일차신호만을 고려하여 시스템의 성능을 분석하여 성능평가가 정확하지가 않았다. SCAE 및 SCAD는 커플러수를 증가함에 따라 여러 형태의 간섭신호들을 가지므로, 이러한 신호들이 시스템 성능을 현저히 열화 시킨다. 본 논문에서는 $\alpha$(coupling coefficient)값이 커질수록 PCAE와 PCAD를 이용한 PSR이 향상됨을 밝혔고 FO-CDMA 통신망의 성능을 개선하기 위해서는 SCAE와 분석 SCAD 구조보다는 PCAE와 PCAD 구조가 적합함을 제시하였다.

• 비파괴검사학회지
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• 제29권3호
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• pp.235-241
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• 2009

Composite wood materials are very sensitive to water and inspection without any coupling medium of a liquid is really needed to wood materials due to the permeation of coupling medium such as water. However, air-coupled ultrasound has obvious advantages over water-coupled experimentation compared with conventional C-scanner. In this work, it is desirable to perform contact-less nondestructive evaluation to assess wood material homogeneity. A wood material was nondestructively characterized with non-contact and contact modes to measure ultrasonic velocity using automated data acquisition software. We have utilized a proposed peak-delay measurement method. Also through transmission mode was performed because of the main limitation for air-coupled transducers, which is the acoustic impedance mismatch between most materials and air. The variation of ultrasonic velocity was found to be somewhat difference due to air-coupled limitations over conventional scan images. However, conventional C-scan images are well agreed with increasing the resin-infiltrated time as expected. Finally, we have developed a measurement system of an ultrasonic velocity based on data acquisition software for obtaining ultrasonic quantitative data for correlation with C-scan images.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2471-2478
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• 2020

Pumps are essential machinery in the various industries. With the development of high-speed and large-scale pumps, especially high energy density, high requirements have been imposed on the vibration and noise performance of pumps, and cavitation is an important source of vibration and noise excitation in pumps, so it is necessary to improve pumps cavitation performance. The modern pump optimization design method mainly adopts parameterization and artificial intelligence coupling optimization, which requires direct correlation between geometric parameters and pump performance. The existing cavitation performance calculation method is difficult to be integrated into multi-objective automatic coupling optimization. Therefore, a fast prediction method for pump cavitation performance is urgently needed. This paper proposes a novel cavitation prediction method based on impeller pressure isosurface at single-phase media. When the cavitation occurs, the area of pressure isosurface S_iso increases linearly with the NPSH_a decrease. This demonstrates that with the development of cavitation, the variation law of the head with the NPSH_a and the variation law of the head with the area of pressure isosurface are consistent. Therefore, the area of pressure isosurface S_iso can be used to predict cavitation performance. For a certain impeller blade, since the area ratio R_s is proportional to the area of pressure isosurface S_iso, the cavitation performance can be predicted by the R_s. In this paper, a new cavitation performance prediction method is proposed, and the feasibility of this method is demonstrated in combination with experiments, which will greatly accelerate the pump hydraulic optimization design.

• Geomechanics and Engineering
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• 제37권1호
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• pp.73-84
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• 2024

Owing to the high strength and abrasive characteristics of cobble-boulders, cutters are easily worn and damaged during shield tunneling, making construction inefficient. In the present work, the stress on the ripper and scraper on the cutterhead was analyzed by the PFC3D-FLAC3D coupling model of shield tunneling to get insight into the performance of the cutterhead for cutting underground cobble and boulders. The numerical calculation results revealed that the increase in trajectory radius leads to a rising stress on the cutters, and the stress on the front cutting surface is greater than that on the back of the cutters. Moreover, the correlation between cutter wear and stress is revealed based on field measurement data. The distribution of the cutter stress is consistent with the cutter wear and breakage characteristics in actual construction, in which more extensive cutter stress is exhibited, extreme cutter wear appears, and more cutter breakage occurs. Finally, the relationship between the cutterhead opening area's layout and cutter wear distribution was investigated, indicating that the cutter wear extent is the most severe in the region where the radial opening ratio dropped sharply.

• 한국지구과학회지
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• 제39권3호
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• pp.211-227
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• 2018

본 연구에서는 한국기상청의 장기예측시스템 현업모형인 GloSea5의 성층권 극소용돌이 강화사례에 대한 예측성을 진단 및 검증하였다. 진단에 사용된 통계량은 이상상관계수(ACC, Anomaly Correlation Coefficient)와 평균제곱근 예측성(MSSS, Mean Squared Skill Score)으로, 1991-2010년간 발생한 14개 극소용돌이 강화사례에 대한 GloSea5의 예측성한계는 ACC를 기준으로 13.6일, MSSS를 기준으로 18.5일로 나타났다. 모형의 평균제곱오차(MSE, Mean Squared Error)의 각 성분을 정량적으로 비교분석한 결과, 예측성을 저하시키는 가장 큰 요인은 맴돌이(에디)오차로, 그 중 에디의 위상오차가 전체 예측오차의 큰 부분을 차지하는 것으로 나타났다. 또한 극소용돌이 현상이 수평적으로 큰 규모를 가지는 만큼 동서파수 1의 에디와 관련한 오차가 더 작은 규모의 에디에 비해 가장 크게 예측오차에 기여하는 것으로 나타났다. 한편, 분석한 사례들에 대하여 GloSea5의 대류권 순환에 대한 예측성은 성층권 예측성과는 큰 관련이 없는 것으로 나타났다. 이는 단순히 GloSea5 모형이 성층권-대류권 접합과정을 잘 모의하지 못하기 때문에 나타난 결과로 유추할 수 있다. 하지만, 극소용돌이 강화에 의한 영향에 비해 대류권에서 내부변동성의 절대적인 크기가 종종 크게 나타난다는 점을 감안하면, 모형에서 성층권-대류권 접합을 잘 모의하고 있더라도 극소용돌이 강화 자체만의 영향이 뚜렷하게 나타나지 않았을 가능성 또한 간과하면 안 될 것이다.

• 한국항공우주학회지
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• 제44권7호
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• pp.585-592
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• 2016

하이브리드 로켓의 연소실험에서 관찰된 500 Hz 대역의 연소압력과 연소반응 변동이 안정한 연소에서 발생하는 원인과 LFI로 발전하는 과정을 분석하기 위하여 $CH^*$ 화학발광 이미지와 PMT(photomultiplier tube)에 의한 광자방출 측정으로 연소반응 변화를 가시화하였다. 안정한 연소에서는 500 Hz 대역의 연소압력과 연소반응 변동의 위상차이가 180 도 정도를 이루며 전단층 유동을 따라서 정상적인 연소가 발생하였다. 그러나 불안정 연소가 발생하면, 500 Hz 주파수의 두 변동의 위상차는 60~70 도로 양의 관계(positive coupling)를 이루며 상하 대칭의 와류 발생과 국부적 소염이 나타나는 주기적 변화를 반복한다. 또한 천이구간에서는 매우 불규칙적인 와류와 상하 대칭의 전단층 유동 형상이 번갈아 관찰되고 있다. 이것은 연소의 영향으로 와류가 발생하는 것으로 보염기 후류에서 발생한 BVK 유동불안정과 유사한 특성을 보여준다, 따라서 하이브리드 로켓 연소의 저주파수 연소불안정은 500 Hz 대역의 연소반응 변동에 의한 와류의 발생과 이로 인한 국부적인 소염이 점진적으로 발전하여 완전한 주기적 소염으로 이어졌고, 20 Hz의 연소불안정으로 발전하는 것으로 판단하였다.

• Journal of Acupuncture Research
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• 제30권4호
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• pp.25-33
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• 2013

Objectives : To assess the test-retest reliability and the intratest repeatability in measuring the cervical range of motion of healthy subjects with wireless microelectromechanical system inertial measurement unit(MEMS-IMU) system and to discuss the feasibility of this system in the clinical setting to evaluate the cervical spine musculoskeletal. Methods : 12 healthy people who were evaluated as no- or mild-disability with neck disability index were participated. Their cervical motion were measured with IMU twice in consecutive two days for the test-retest reliability study. Intratest repeatability was calculated in the two tests separately. The calculated intraclass correlation coefficients(ICC) were discussed and compared with the those of the previous studies. Results : Cervical range of motion data were acquired and statistically processed: left rotation($61.64^{\circ}$), right rotation($65.12^{\circ}$), extension($61.98^{\circ}$), flexion($52.81^{\circ}$), left bending($39.31^{\circ}$), right bending($41.08^{\circ}$). ICCs were 0.77~0.98(intratest repeatability) and 0.74~0.93 (test-retest reliability) in the primary motion. In the coupling motion, intratest repeatability ICCs were 0.93~ 0.99(transverse primary plane), 0.88~0.97(saggital primay plane), and 0.77~0.93(coronal primary plane). Test-retest reliability of coupling motion were 0.90~0.97(transverse primary plane), 0.00~0.72(saggital primary plane), and 0.04~0.76(coronal primary plane). Conclusions : Several types of range-of-motion devices are now on use in many fields including medicine, but the practicality of the devices in clinical use is questionable for the convenient and economical aspects. In this study, we presented the reliability of cervical range of motion test with the developed wireless MEMS-IMU system and discussed its potential utility in clinical use.

• Bulletin of the Korean Chemical Society
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• 제33권5호
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• pp.1675-1680
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• 2012

Three new cyanide-bridged $Cr^{III}Mn^{II}$ binuclear complexes, $[Mn(phen)_2Cl][Cr(bpmb)(CN)_2]{\cdot}H_2O$ ($\mathbf{1}$) (phen = 1,10-phenanthroline, $bpdmb^{2-}$ = 1,2-bis(pyridine-2-carboxamido)-4-methyl-benzenate), $[Mn(phen)_2Cl][Cr(bpmb)-(CN)_2]{\cdot}H_2O$ ($\mathbf{2}$) ($bpdmb^{2-}$ = 1,2-bis(pyridine-2-carboxamido)-4,5-dimethyl-benzenate), and $[Mn(phen)_2Cl]-[Cr(bpClb)(CN)_2]{\cdot}CH_3OH{\cdot}H_2O$ ($\mathbf{3}$) ($bpClb^{2-}$ = 1,2-bis(pyridine-2-carboxamido)-4-chloro-benzenate) were obtained based on $Mn(phen)_2Cl_2$ and a series of dicyanidechromate(III) building blocks. Single crystal X-ray diffraction analysis shows the structures of the three complexes are dimeric type with two different metal centers linked by a cyanide group from corresponding dicyanidechromate(III) building block. Magnetic investigations indicate the existence of relatively weak antiferromagnetic coupling between Cr(III) and Mn(II) ions with best-fit constants $J_{CrMn}=-2.78(5)cm^{-1}$ for $\mathbf{1}$, $J_{CrMn}=-3.02(2)cm^{-1}$ for $\mathbf{2}$ and $J_{CrMn}=-2.27(3)cm^{-1}$ for $\mathbf{3}$ based on the spin exchange Hamiltonian = $-2J_{CrMn}\hat{S}_{Cr}\hat{S}_{Mn}$. The magneto-structural correlation of cyanide-bridged $Cr^{III}Mn^{II}$ complexes has been discussed at last.

• Journal of Welding and Joining
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• 제30권6호
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• pp.42-48
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• 2012

Due to increase in demand of stable and long pipelines in natural gas industry, wide range of researches are being performed on automation welding to improved welding quality with respect to weld process parameters in real time measurement. In particular, the coupling between the pipe manufacturing process and location of the weld seam, the measured size of the gap that exists in the weld position and the weld angle depending on whether the movement of molten weld. This is due to absence of controlling welding penetration position, depending on the required size of the angle of the setting. In addition, the optimum welding conditions must be considered while selecting, the correlation between these variables and the systematic correlation has not yet been identified. Therefore, in most welded pipe root-pass weld solely depends on the experience of workers in relation to secure a stable weld quality. In this study, automation welding system is implemented to select a suitable root-pass STT (Surface Tension Transfer) welding method using the optimal welding conditions. To successfully accomplish this objective, there were various welding conditions used for welding experiment to confirm that the assessment required for construction through the pipe and automatic welding process is proposed to optimize this plan.