• Smart Structures and Systems
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• 제11권4호
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• pp.349-364
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• 2013

Recently, researchers in the field of structural health monitoring (SHM) have been rigorously striving to replace the conventional NDE techniques with the smart material based SHM techniques, employing smart materials such as piezoelectric materials. For instance, the electromechanical impedance (EMI) technique employing piezo-impedance (lead zirconate titanate, PZT) transducer is known for its sensitivity in detecting local damage. For practical applications, various external factors such as fluctuations of temperature and loading, affecting the effectiveness of the EMI technique ought to be understood and compensated. This paper aims at investigating the damage monitoring capability of EMI technique in the presence of axial stress with fixed boundary condition. A compensation technique using effective frequency shift (EFS) by cross-correlation analysis was incorporated to compensate the effect of loading and boundary stiffening. Experimental tests were conducted by inducing damages on lab-sized aluminium beams in the presence of tensile and compressive forces. Two types of damages, crack propagation and bolts loosening were simulated. With EFS for compensation, both cross-correlation coefficient (CC) index and reduction in peak frequency were found to be efficient in characterizing damages in the presence of varying axial loading.

• 전기학회논문지
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• 제58권5호
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• pp.929-935
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• 2009

As modem industrialized society progresses, the demand for electric power is increasing rapidly. The electric power system is getting amazingly bigger and complicated, which can easily induce serious troubles from the potential of large fault problems and/or system failure. The monitoring and diagnosis of the electric machine for the fault detection and protection has been important part in the electric power system. Most faults in the generator appear in the winding. This paper presents the air-gap magnetic flux characteristic of a small-scale 2-pole synchronous generator according to the faults in the field winding to protect the generator from the fault. The magnetic flux patterns in air-gap of a generator under various fault conditions as well as a normal state are simulated by using finite element method. These results are successfully applied to the detection and diagnosis of the short-circuit condition in rotor windings of a high capacitor generator.

• 전력전자학회논문지
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• 제4권6호
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• pp.491-499
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• 1999

본 논문은 새로운 제어기법의 고성능 전동차 추진용 IGBT VVVF 인버터에 관한 것이다. 현차 적용 전에 견인력 제어성의 우수함과 안정성을 검증하기 위해, 현차 조건에서 발생될 수 있는 경우에 대한 모의 주행시험을 실시하고 그 결과를 보인다. 모의 주행시험은 160톤의 차량을 등가화한 관성부하장치를 이용하여 정상상태는 물론 전압변동 등 각종 과도상태에 대해서도 실시하였다. 본 논문에서는 4병렬 접속된 견인전동기의 토오크 제어성 향상을 위한 벡터제어기법 적용과 공간벡터 변조기법에 동기방식을 적용하여 500Hz이하의 저주파 스위칭으로써 6스텝까지 연속 과변조 제어가 가능한 최적의 PWM방법을 제시한다.

• 국제학술발표논문집
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• The 9th International Conference on Construction Engineering and Project Management
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• pp.145-152
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• 2022

Recently, interest in the precast concrete (PC) construction method has been increasing. The PC construction process consists of i) design, ii) production, iii) transportation, and iv) installation. A PC field manager at the site submits a shipment request form to the factory one to three days before the installation of the PC component. Numerous matters should be considered in writing a shipment request form. Incorrect shipment request forms may cause standby resources, waste of resources, premature work conclusion, or excessive work. These issues can lead to an increase in construction costs, replanning of PC component installation, or rework. In order to prevent such problems, PC component installation should be simulated based on the shipment request form. Accordingly, this study aims to identify factors influencing the operability of shipment request forms for PC construction. To this end, this study derived factors influencing i) initiation of the activity, ii) addition or deletion of activities, and iii) an increase or decrease in the activity execution time. As a result, this study identified flow, the features of PC components, condition of PC components, unloading location, installation location, input equipment and labor, number of anchors, number of supports, weather, strike, and accident. Further studies should verify the factors derived in this study based on focus group interviews.

• Geomechanics and Engineering
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• 제38권2호
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• pp.205-214
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• 2024

Permafrost refers to the condition where the ground is frozen. It is crucial to review and evaluate the ground's characteristics before construction. In this study, electrical resistivity surveying is chosen as the investigative technique to apply and illustrate the results on the state of permafrost ground and to summarize its applicability. Field experiments are conducted in the Yeoncheon area of South Korea, which has a freezing index of 522.6°C·days. The target area is categorized into two ground conditions: the first where the original ground freezes, and the second involves excavating the original ground up to a depth of 3 meters, backfilling it, and then artificially injecting fluid. Thus, frozen ground conditions are simulated under both natural and artificial circumstances. Electrical resistivity surveys are performed under both above-freezing and sub-zero temperature conditions, with the experiments conducted at sub-zero temperatures revealing relatively more high-resistivity zones due to the temperature conditions. In this area, the distribution of soil moisture content is also investigated using the Time Domain Reflectometry (TDR) technique. It is observed that the ground into which water is artificially injected had a relatively higher moisture content, although the difference is minor. Finally, a 3D map of the target ground is constructed based on the measured electrical resistivity values, and through this, the distribution of porosity, a crucial design parameter, is also depicted. This research demonstrates that the electrical resistivity technique can effectively evaluate the state of frozen and unfrozen ground and further suggests that it can detailed extract the characteristics of the target ground.

• 한국지하수토양환경학회지:지하수토양환경
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• 제10권6호
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• pp.20-31
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• 2005

일정한 평균 지하수 유속을 가진 불균질한 등방성 삼차원 대수층 내에서 정류상태로 흐르는 지하수의 흐름과 함께 이동해가는 비반응성 오염물질에 대한 몬테카를로 시뮬레이션이 시행되었다. 대수-정규적으로 분포되어 있는 수리전도도 K(x)가 임의장으로 설정되었으며 시뮬레이션 동안에 발생할 수 있는 불확실성을 감소하기 위해 여러 가지 방법들이 시도되었다. 1600개 오염운들에 대한 이차공간적률의 집합적평균(ensemble average) <$S_{ij}'(t',\;l')$>(i,\;j=1,2,3), 그리고 오염운중심분산 $R_{ij}'(t',\;l')$이 각기 다른 세 가지 불균질도${\sigma}_Y^2=0.09,\;0.23$ 및 0.46에 대해서 시뮬레이션 되었으며 또한 각기 다른 크기의 평균속도에 수직방향인 선형초기오염원(l': 1, 2, 4)에 대해서 입자추적이 행하여 졌다. 시뮬레이션 된 무차원 종적률들은 일차근사법에 의한 비에르고딕 이론적 결과와 비교적 잘 일치하나 시뮬레이션 된 무차원 횡적률들은 일차근사법에 의한 이론적 결과들 보다 더 큰 값을 보인다. 일차근사법에 의한 비에르고딕 이론적 결과는 특히 불균질도가 큰 대수층에 대해서 그리고 큰 무차원 시간에 대해서 시뮬레이션 된 무차원 횡적률들을 과소평가 했다 시뮬레이션 된 집합적 평균이차적률은 에르고딕 상태에 도달하지 못했으며 횡방향으로의 오염운 확장이종방향보다 훨씬 느리게 에르고딕 상태에 접근하는 것으로 관찰되었다. 불균질한 대수층 내에서의 오염운의 진화는 초기 오염원의 모양이나 배열상태 보다는 주로 대수층의 불균질도와 초기 오염원의 크기에 영향을 받는 것으로 밝혀졌다.가 정신의 숭고한 고유-독창성(Originality)이 피드백의 경로를 투과하면서 자신을 남에게 투영시켜 얻어내는 것이 고유성의 변종이다. 피드백은 단순한 작품의 일부가 아니라 작품을 이루는 뼈대이다 기술의 과시만으로는 예술의 행위가 될 수 없다. 작가의 예술성이 관객의 감성에 피드백 되도록 노력해야 한다 그러기 위해서는 예정된 피드백이란 느낌을 관객이 갖지 않도록 하여야 한다. 인터렉티브 미디어 아트는 초기의 형태에서 벗어나 새로운 집적된 피드백 기술로 전환하여야 할 시기가 온 것이다.료된다.시한 개체의 수술 전 방사선학적 평균 고관절 등급은 양측 모두 $3.2\pm0.9$이었고 수술 직후의 좌 우측 평균 고관절 등급은 각각 $2.7\pml.1,\;2.7\pm0.9$ (n=36) 이었다. 수술 직후와 2, 4, 8, 12, 24주 후의 고관절 등급이 수술 전에 비하여 유의적으로 개선된 것을 확인하였다.(P<0.01). 수술 후 정기적인 검사 시에 측정한 Norberg angle, percentage of femoral head coverage도 수술 전과 비교해 유의성 있게 증가하였다(P<0.01). 변형 3중 골반 절골술 직후의 평균 골반직경은 수술 전의 골반직경보다 유의적으로 증가하였으며(P<0.01)(n=36) 수술 후 평균 9.3L2.7주에 절골선 유합이 종료되었다(n=21). 반면 편측 3중 골반 절골술을 실시한 경우에는 수술 후 골반경이 수술 전과 비교해 증가하지 않았다. 변형 3중 골반 절골술후에 장액종 형성(1마리), 스크류 변위(4마리), 스크류 부러짐(1마리), 편측성 신경마비(1마리) 등의 부작용이 발생하였다. 이상의 결과를 토대로,

• 터널과지하공간
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• 제20권1호
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• pp.15-27
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• 2010

국토의 약 70%가 산악지형인 우리나라의 지형적 특성상 각종 건설공사에 따른 대절토 사면의 형성으로 인해 낙석의 위험성이 급증하고 있다. 특히 해마다 반복되는 집중호우 시의 사면 붕괴는 대규모 낙석을 동반하면서 막대한 인적, 물적 피해를 초래하고 있다. 이러한 문제점들을 해결하기 위해 많은 현장조사연구 및 기초연구들이 수행되고 있으나 이들 연구의 대부분은 낙석이 발생할 경우의 보강 및 낙석 위험도 분석 등에 국한되고 있어, 근본적인 낙석의 거동에 관한 검토 및 분석은 미진한 실정이다. 따라서 본 연구에서는 수치해석적 기법을 이용하여 사면의 외적 요소에 따른 낙석의 거동 특성을 규명하였으며, 이를 위해 개별요소법의 하나인 PFC2D가 이용되었다. 사면의 외적 요소로 사면의 표면상태, 구배, 소단 개수, 소단 구배 및 낙석의 크기에 대한 소단의 너비의 비 등이 검토되었으며, 이들 요소에 대한 다양한 변화를 통해 낙석의 거동 메커니즘이 수치해석적으로 분석되었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• 대한조선학회논문집
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• 제50권5호
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• pp.282-290
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• 2013

The effects of the combination of blade number for forward and after propeller on the propeller shaft forces of a contra-rotating propeller (CRP) system are presented in the paper. The research is performed through the numerical simulations based on the Reynolds-Averaged Navier-Stokes equations (RANS). The simulation results of the present method in open water condition are validated comparing with the experimental data as well as the other numerical simulation results based on the potential method for 4-0-4 CRP (3686+3687A) and 4-0-5 CRP (3686+3849) of DTNSRDC. Two sets of CRP are designed and simulated to study the effect of the combination of blade number in behind-hull condition. One set consists of 3-blade and 4-blade, while the other is 4-blade and 4-blade. A full hull body submerged under the free surface is modeled in the computational domain to simulate directly the wake field of the ship at the propeller plane. From the simulation results, the fluctuations of axial force and moment are dominant in the case of same blade numbers for forward and after propellers, whereas the fluctuations of horizontal and vertical forces and moments are very large in the case of different blade numbers.