정상인에서 운동 후 심근의 color tissue doppler velocity와 strain rate의 변화

이병호 경희대학교 대학원 2003 국내석사

(A) Study of deformation around the Korea strait prior to Mw9.0 Tohoku earthquake

Tasliman, Michael Timothy Sungkyunkwan university 2020 국내석사

On 11 March 2011, a great earthquake with magnitude 9.0 has occurred in Tohoku, Japan, more than 1,000 km from South Korea. In fact, seismicity rate in South Korea has increased since the 2011 Tohoku earthquake, although detailed evaluation of its effects on the Korean Peninsula remains incomplete. Now, the high precision space geodesy techniques play a key role in monitoring the crustal strain state and energy variation. This study attempts to evaluate crustal deformation around the Korean Strait after 2011 Tohoku earthquake through a detailed analysis recorded by GPS. Moreover, this study found a different fault characteristics in Japan affect the station displacement prior to GPS data observed among 2011 to 2012. After a year, the strain in Japan found in direction WNW-ESE, while in Korea found in direction WSW-ENE. This finding suggest the likelihood of the existence of a certain tectonic line between the southern part of Korea peninsula and Japan.

Microscale Fluid-Structure Interactions Between Viscous Internal Flows and Elastic Structures

Anand, Vishal Purdue University ProQuest Dissertations & Theses 2020 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

This thesis examines the problem of low Reynolds number viscous fluid-structure interactions (FSIs) at the microscale. A myriad of examples of such phenomena exist, both in nature (blood flow in arteries, air flow in lungs), as well as in the laboratory (microfluidics devices, soft robotics). For this thesis, we restrict to internal flows in conduits with deformable walls. Specifically, two types of conduits of different cross-sectional shapes are considered: microchannels and microtubes. Both of these geometries are slender and thin. Different types of material behavior are considered, via constitutive laws, in the solid domain, namely linearly elastic, hyperelastic and viscoelastic; and in the fluid domain, namely Newtonian and power-law fluids with shear-dependent viscosity. Similarly, the geometry and dimensions of the structures allow us to use shell and plate theories in the solid domain, and the lubrication approximation of low Reynolds number flow in the fluid domain.First, we study a rectangular microchannel with a deformable top wall of moderate thickness, conveying a power-law fluid at steady conditions. We obtain a nonlinear differential equation for pressure as a function of imposed steady flow rate, consisting of infinite expansions of hypergeometric functions. We also conduct simulations of FSI using the commercial computer-aided engineering (CAE) software ANSYS, to both benchmark our perturbative theory and to establish the limits of its applicability.Next, we study fluid-structure interactions in a thin microtube constituted of a linearly elastic material conveying a generalized Newtonian fluid. Here, we employ the Donnell shell theory to model the deformation field in the structure of the tube. As a novel contribution, we formulate an analytical expression for the (radial) deformation of the tube using the method of matched asymptotic expansions, taking into account the bending boundary layers near the clamped ends. Using our perturbative theory, we also improve certain classical but partial results, like Fung's model and the law of Laplace, to match with direct numerical simulations in ANSYS.Subsequently, we explore FSI in hyperelastic tubes via the Mooney-Rivlin model. In a thin-walled vessel, we formulate a novel nonlinear relationship between (local) deformation and (local) pressure A similar approach for the thick-walled tube, yields a nonlinear ODE to be solved numerically. Due to strain hardening, the hyperelastic tube appears stiffer and supports higher pressure drops than a linearly elastic tube.Finally, we study transient compressible flow being conveyed in a linearly viscoelastic tube. By employing a double perturbation expansion (for weak compressibility and weak FSI), a predictive relationship between the deformed radius, the flow rate and the (local) pressure is obtained. We find that, due to FSI, the Stokes flow takes a finite time to adjust to any changes emanating from the boundary motion. In the case of oscillatory pressure imposed at the inlet, acoustic streaming is shown to arise due to FSI in this compressible flow.Fundamentally, the goal of the research in this thesis is to generate a catalog of flow rate-pressure drop relationships for different types of fluid-structure interactions, depending on the combinations of fluid mechanics and structural mechanics models (behaviors). These relationships can then be used to solve practical problems. We formulate a theory of hydrodynamic bulge testing, through which the elastic modulus is estimated from the pressure drop and flow rate measurements in a microchannel with a (thick and pres-stressed) compliant top wall, without measuring the deformation. A sensitivity analysis, via Monte Carlo simulation, shows that the hydrodynamic bulge test is only a slightly less accurate than the traditional bulge test, but is less susceptible to uncertainty emanating from the noise in measurements.

충돌하중을 받는 차체 쉘 구조물의 동적 붕괴 해석

강신유 서울대학교 1992 국내박사

변형률 속도를 고려한 금속 재료의 고속 충돌 연구

이경한 한국항공대학교 일반대학원 2021 국내석사

고속으로 운행되는 항공기나 차량의 발전에 따라 차량 충돌, 항공기 엔진 블레이드 파손 사고 등의 순간적인 큰 하중과 높은 응력이 발생하는 고속 충격 상황을 고려하여 설계되어야 한다. 고속 충격을 받는 기계 및 구조물의 많은 부분에 금속 재료가 사용되기 때문에 금속 재료의 고속 변형 거동에 관한 이해가 필요하다. 동적 혹은 충격 하중을 받는 재료 변형 거동은 충돌 속도, 재료 물성, 파동 전파, 마찰 등 다양한 변수에 의해 영향을 받으며, 이에 대한 정확한 거동을 표현할 수 있 는 동적 모델을 검토하고 선정할 필요가 있다. 금속 재료 동적 모델의 유효성을 평가하는 방법으로 Taylor 충격 시험이 있다. 테일러 충격 시험은 원통형 시편을 높은 속도로 강체에 충돌시키는 시험이며, 충돌하는 과정에서 시편에 높은 변형률 속도가 발생하는 것을 관찰할 수 있다. 따라서 본 연구에서는 범용으로 사용되는 알루미늄에 대한 동적 경화 모델의 유효성을 테일러 충격 시험을 통해 평가하는 것이다. 테이러 충격 시험에서 시편과 타겟이 수직으로 충돌하게 하기 위해 사봇 형상, 타겟 장치를 설계하였다. 다양한 속도로 발사한 시편을 고속 카메라를 통해 영상 촬영을 하고, Johnson-Cook 소성 모델과 Zerilli-Armstrong FCC 모델을 적용한 유한요소해석을 진행하여 충격 시험 결과와 비교/분석 하였다. As the development of high speed aircraft or vehicles, it should be designed in consideration of high speed impact situations in which instantaneous large loads and high stress are generated. Since metallic materials are used in many parts of machines and structures it is necessary to understand the high speed deformation behavior of metallic materials. The deformation behavior of materials subjected to a dynamic or impact load is affected by many variables such as impact velocity, material properties, wave propagation, and friction. Therefore, it is necessary to review and select a dynamic model that can express accurate behavior of material. The Taylor impact test is a method of evaluating the effectiveness of the dynamic model of metallic materials. The Taylor impact test is the test in whicha cylindrical specimen is crushed with a rigid body at a high speed, and it can be observed that a high strain rate occurs in the specimen during the crush process. In this study, the validity of the dynamic hardening model for aluminum, which is generally used, is evaluated through the Taylor Impact test. In order to make the specimen and the target collide vertically in the test, a sabot shape and target device were designed. The specimens fired at various speeds were photographed through a high speed camera, and finite element analysis was performed using the Johnson-Cook plasticity model and the Zerilli-Armstrong FCC model to compare and analyze the impact test results.

(A) study on formation of nanocracks in Pd thin films on an elastomeric substrate : nanogap-based hydrogen gas sensors

김성연 Graduate School, Yonsei University 2016 국내박사

기존의 플렉서블 (flexible), 벤더블 (bendable), 롤러블 (rollable), 폴더블 (foldable)이 가능한 플라스틱 재료의 기판 또는 점탄성 (viscoelastic) 물질의 기판에 제작한 박막 표면의 인위적인 크랙 형성은 임의로 잡아당기거나 구부리는 방법, 수소 취성 방법, 액체 질소에 노출 시키는 방법 등을 이용하였다. 그러나 이러한 방법은 임의로 크랙을 형성할 수는 있으나 크랙이 형성되는 방향, 형성되는 크랙의 평균 너비, 크랙 밀도 등을 제어할 수는 없었다. 본 연구는 점탄성 재료인 폴리디메틸실록산 (polydimethylsiloxane, PDMS) 기판 위에 증착된 팔라듐 (Pd) 박막에 나노 크기의 크랙 (crack)이 형성되는 정도를 제어하는 공정과 그를 응용한 수소 가스 센서에 관한 연구이다. 주재료와 경화제의 비율을 10:1로 합성하여 제작한 점탄성의 특성을 가지는 0.6-0.75 mm두께의 폴리디메틸록산 기판 위에 초고진공 직류 마그네트론 스퍼터 (Ultra-High Vacuum Direct Current Magnetron Sputter, UHV DC Magnetron Sputter)를 이용하여 약 10 nm 두께로 증착된 팔라듐 박막을 마이크로인장시험기를 이용하여 인장 속도 100-800 μm/s 및 인장 변형률 30-120% 로 정량적인 조절하여 Load-Unload Cycling 으로 기계적 거동을 하게 되면, 박막과 기판의 기계적 거동의 차이에 의해 나노 크기 크랙의 수직/수평 방향성과 밀도, 평균 너비와 같은 크랙 형성 정도를 제어할 수 있었다. 이를 팔라듐 박막 기반의 수소 가스 센서로 응용하게 되면 형성된 크랙의 평균 너비가 좁고, 그 밀도가 높을수록 팔라듐 박막의 부피팽창은 용이해지고, 표면적은 넓어지기 때문에 확산속도가 빨라지게 되어 공기 중에서 저농도의 수소를 검지가 가능하다. Load-Unload의 Cycling 인장 속도 및 인장 변형률 조절을 통해서 인장 방향에 대해 수직, 수평 방향의 나노 크기의 크랙이 형성 가능하다는 것을 확인할 수 있었다. 또한 시편의 표면 형태 분석을 통해 인장 속도와 인장 변형률이 증가함에 따라 평균 크랙 밀도가 증가한다는 사실을 확인하였으며, 90% 이상의 인장 변형률로 시편을 인장시키면 인장 방향에 대해 수평방향으로 크랙이 형성되기 시작한다는 것을 발견하였다. 이러한 결과를 토대로 수소 가스 센싱에 적용시켰을 때, 평균 크랙 밀도가 높은 경우 수소 가스 센싱이 용이하며, 인장 변형률 120 %로 연신/압축 사이클을 한 경우 상압의 공기 중에서 가장 낮은 수소 검지 농도 (50 ppm)를 가지는 것을 확인하였다. 본 연구는 간단하고 손쉬운 공정을 통해 박막과 기판의 기계적 거동의 차이를 이용하여 정량적인 방법으로 박막에 형성되는 크랙의 평균 너비와 밀도, 크랙 형성 방향을 손쉽게 조절할 수 있음으로써, 이를 이용한 가스 센서에서 검지 능력이 향상되는 것을 확인하였다. 이러한 나노 크기의 크랙 제어을 제어할 수 있는 공정을 이용하여 가스 센서 뿐만 아니라, 스트레인 센서 등 플렉서블, 벤더블, 롤러블, 폴더블이 가능한 폴리머 기판을 이용한 센서를 기반으로 하는 다양한 전기ᆞ전자소자에서 전기적 특성을 제어 및 향상시킬 수 있을 것으로 기대된다. We report the effects of various tensile velocities and strains on the nanocrack formation in a palladium thin film on an elastomeric polydimethylsiloxane substrate and its hydrogen gas sensing properties. We achieved quantitatively nanocrack formation by stretching/compression cycles with adjusting the mechanical tensile velocity and strain applied to a palladium thin film on an elastomeric polydimethylsiloxane substrate. This method can be used to modulate nanocrack formation along both the x- and y-axes over a large area. From the microstructural analyses, we found that the tensile velocity has a significant effect on the crack density but little effect on the average crack width. However, in tensile strain variation, increase in the applied tensile strain of 90 % gives rise to the appearance of horizontal cracks in y-axis in addition to the increased number of vertical cracks in x-axis. When the strain reaches to 120 %, lots of ordered nanocracks are abundantly propagated on the palladium surface in both directions. The palladium nanogap sensor prepared under a high tensile velocity showed a high performance with a low detection limit of 500 ppm of hydrogen in air. In addition, sensing property measurement showed a dramatic enhancement with the lowest detection limit of 50 ppm hydrogen in air at 120 %, which is attributed from the large surface area in the palladium nanocrack pattern readily allowing volume expansion. From these results, this mechanism presents a simple tool for controlling the sensing properties of hydrogen gas sensors with a low detection limit even in air.

일축 압축 시 발생하는 미소 전위에 관한 기초 연구

김종욱 전북대학교 대학원 2007 국내석사

We monitored micro-electric potentials which were generated by rocks and mortar specimens failure while the specimens were compressed uniaxially, which are a basic study for application of a micro-electric potential measurement to landslides and slope degradations monitoring. The granites, limestones and sandstones were used and the hand made mortar specimens which kept up uniform composition were used for the measurements with various conditions. First, basic physical properties, resistivity and acoustic velocity of the specimens were measured as the basic property informations. Then, assembling the multi channel electric potential measurement system, we measured the loading power, the vertical and horizontal strain, micro-electric potentials in same time. The strength of micro-electric potential of the saturated rocks and mortar specimens increased in proportional to the increase of the loading power and the strains, and there were no increases in case of the dried specimens. But the sandstone specimens had increases of the strengths in both saturated and dried cases. Comparing the data from 4 pairs of electrodes were installed to the circumference of a specimen at interval of 90 degree, we found the strength of the micro-electric potential of some electrode pair got stronger as locations of the specimen failure got closer to that electrode. It was possible to check the relationship of physical properties and micro-electric potential.

Evaluation of velocity vector imaging (VVI) in dogs with chronic mitral valve insufficiency : 만성 이첨판 폐쇄 부전증이 있는 개에서 속도벡터영상 (VVI)을 통한 평가

Lee, Sung wook 강원대학교 대학원 2013 국내석사

Chronic mitral valve insufficiency (CMVI) is the most common acquired heart disease seen in dogs. CMVI is characterized by chronic myxomatous mitral valvular degeneration and develops on one of the valves on the left side of heart, which is known as the mitral valve. This condition causes leakage and backflow of blood into the left atrium during systole and subsequently leads to volume overload in left atrium, left ventricle and pulmonary vein, causing fatal pulmonary edema. Although several echocardiographic indices are being used to diagnose CMVI in small animals, these indices have some limitation for accurate evaluation of ventricular function. Traditionally, global left ventricular (LV) systolic function is assessed by the LV ejection fraction. However, the echocardiographic parameter for quantifying regional systolic function has yet been developed in small animals. Recently, a method called velocity vector imaging (VVI) using speckle tracking technology has been developed in human medicine. The VVI is a novel echocardiographic imaging technique based on two- dimensional gray scale echocardiographic images. In this study, we evaluated diagnostic value of VVI in dog with heart failure from CMVI. For evaluating VVI, the LV echocardiographic images from the papillary muscle level of the short axis plane were obtained from twenty-two healthy small-breed dogs and twenty-one small-breed dogs with CMVI (graded by ISACHC heart failure scheme) in this study. The LV dimensions were also assessed in a short-axis plane with conventional 2-dimensional echocardiography. We compared both indices in two groups of dogs to evaluate the diagnostic value of the VVI. The mean radial velocity (p< 0.01), mean radial strain (p < 0.001), and mean radial strain rate (p < 0.05) were significantly decreased in dogs with CMVI than in control dogs. Also, each section of the ventricular wall motion was much more irregular in dogs with CMVI (indicating ventricular dyssynchrony). Dogs with CMVI in our study mostly had ISACHC class III of heart failure and showed decreased radial strain, SR, and velocity, compared to the normal healthy dogs. This suggests that there will be significant disruptions in myocardial fibres in dogs with advanced stage of CMVI and the assessment of myocardial strain can be a good alternative method for predicting the progression of heart failure in dogs with CMVI. Keywords: chronic mitral valve insufficiency, echocardiography, strain, velocity vector imaging. 만성 이첨판 폐쇄 부전증(Chronic mitral valve insufficiency: CMVI)은 개에서 가장 흔하게 발생하는 후천성 심장질환이다. 이 질환의 특징은 이첨판의 점액 변성으로, 심실이 수축하는 동안 변성된 판막 사이로 혈액이 역류하여 좌심방과 폐정맥에 과부하를 유발한다. 다양한 방법의 심장초음파를 이용하여 만성 이첨판 폐쇄 부전증을 진단할 수 있지만, 심실의 기능을 정확히 평가하기에는 몇 가지 한계가 있다. 본 연구는 반점 추적 기술(Speckle tracking technology: STT)을 바탕으로 한 새로운 영상 기법인 속도 벡터 영상(Velocity vector imaging: VVI)을 통해 심각한 만성 이첨판 폐쇄 부전증을 가지고 있는 21마리의 소형견과 건강한 22마리의 소형견을 비교 평가하였다. 또한, 이면 심초음파(2-dimensional echocardiography)를 이용하여 좌심실의 기능을 함께 비교 평가하여 속도 벡터 영상의 진단적 가치를 확인해 보았다. 연구 결과 mean radial velocity (p < 0.01), mean radial strain (p < 0.001), 그리고 mean radial strain rate (p < 0.05)는 정상 그룹에 비해 심각한 만성 이첨판 폐쇄 부전 그룹에서 유의성 있게 감소되어 나타났다. 키워드: 만성 이첨판 폐쇄 부전증, 심장 초음파, strain, 속도 벡터 영상.

Investigation of Dynamic Properties of GFRP and Its Material Model for Finite Element Analysis of Low-Velocity Impact

김승원 성균관대학교 일반대학원 2026 국내석사

Local flow properties and flame-vortex interactions in turbulent hydrogen nonpremixed flames with coaxial air

김문기 서울대학교 대학원 2007 국내박사