• 대한의용생체공학회:의공학회지
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• 제20권3호
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• pp.283-290
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• 1999

Mr(Magnetic Resonance ) 영상은 인체 기관의 상태에 관한 많은 정보를 가지고 있어 이것을 분석하여 가시화하면 의료 진단에 유용하게 이용될 수 있다. MR 영상의 가시화는 영상의 획득, 전처리, 조직 분류, 보간, 렌더링의 단계로 이루어진다. 이 단계 중 Mr 영상의 불완전성 때문에 현재 조직 분류 및 보간이 문제로 되어 있다. 본 논문에서는 머리 MR 영상을 대상으로 조직 분류 및 보간에 대한 기법을 제안하고 제안된 기법을 바탕으로 뇌를 3차원 가시화한다. 조직 분류 기법에서는 뇌조직 성분 구성 등 임상 실험에 의해 밝혀진 뇌에 대한 구조적인 지식을 단계적으로 이용한다. 보간 기법은 오목 윤곽선에 사용할 수 있게 동적 탄성 보간기법을 개선하였다. 제안한 구조적인 분류 기법 및 보간 기법을 다른 기법과 비교 평가한다.

• 대한치과보철학회지
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• 제24권1호
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• pp.73-83
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• 1986

The purpose of this study was to evaluate the distortion of 6-unit etched bridge during the firing cycle. Thirty frameworks were constructed. Twenty of the frameworks received a normal application of porcelain and firing sequence ; ten served as controls and subjected to the same firing sequence without the porcelain application. The results were as follows ; 1. Distortion did occur in the body of curved, long-span etched bridge frameworks during the porcelain firing cycle. 2. This distortion was a result of changes in the metal as well as the contraction of fired porcelain. 3. The greatest distortional changes occurred during the degassing stage and final glaze stage of the porcelain firing cycle. 4. Distortion incurred by the application and firing of the porcelain was reversible. When the porcelain was chemically removed from the frameworks, there was an elastic rebound. 5. Distortion was clinically important.

• 한국해양공학회지
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• 제15권2호
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• pp.11-21
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• 2001

The focus of this paper is on the numerical investigation of obliquely incident wav interactions with a system composed of fully submerged and floating dual buoy/vertical-flexible-membrane breakwaters placed in parallel with spacing between two systems. The fully submerged two systems allow surface and bottom gaps to enable wave transmission over and under the system. The problem is formulated based on the two-dimensional multi-domain hydro-elastic linear wave-body interaction theory. The hydrodynamic interaction of oblique incident waves with the combination of the rigid and flexible bodies was solved by the distribution of the simple sources (modified Bessel function of the second kind) that satisfy the Helmholz governing equation in fluid domains. A boundary element program for three fluid domains based on a discrete membrane dynamic model and simple source distribution method is developed. Using this developed computer program, the performance of various dual systems varying buoy radiuses and drafts, membrane lengths, gaps, spacing, mooring-lines stiffness, mooring types, water depth, and wave characteristics is thoroughly examined. It is found that the fully submerged and floating dual buoy/membrane breakwaters can, if it is properly tuned to the coming waves, have good performances in reflecting the obliquely incident waves over a wide range of wave frequency and headings.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.343-343
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• 2008

Newly designed structure of a thin ultrasonic rotary motor was proposed. Thin brass plate was used as a cross shaped vibrator and eight ceramic plates were attached on the upper and bottom sides of the brass plate as in Figure 1. The thin type ultrasonic motor has the structure adherent piezoelectric ceramic on the top and bottom surface of the thin elastic body. The direction of polarization is decided so as to occur the elliptical displacement in regular sequence at touch point A, B, C and D of stator contacted with rotor. By applying two electric fields which have 90 degree phase difference on the ceramics, each contact points make rotational displacements as in figure 2. Finite element analysis program ATILA was used to find the optimal size of the stator. As a result of the simulation, elliptical displacements of the tips were obtained at off-resonance frequencies. The maximum displacements of the contact tips were obtained at the length of 16[mm], width of 6[mm] and thickness of 0.4[mm]. Changes of the resonance frequencies were inversely proportional to the length of ceramic and proportional to the width of ceramic. Elliptical motions of the contact tips. of the stator were consistently obtained at off resonance frequencies. From a prototype motor, speed of 600[rpm] was obtained at 20[Vrms].

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.324-324
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• 2008

Piezoelectric ceramics is an active element that makes stator to vibrate to generate rotational force in ultrasonic motors. In drive of ultrasonic motors, many factors that affect to the resonance characteristics of piezoelectric ceramics exist. For example, those factors are bonding condition with elastic body, the magnitude of electric field, the normal force for frictional drive and the emission of heat due to vibration and friction and so on. Therefore, it is important to research the inclination of property variation of piezoelectric ceramics in circumstance that has complex elements. In this paper, we focused and analyzed the resonance characteristics of ultrasonic motor due to the magnitude of the driving voltage and normal force.

• 전산구조공학
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• 제10권4호
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• pp.229-238
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• 1997

본 논문에서는 반복하중에 의해 손상을 입은 아스팔트 콘크리트의 점탄성 구성모델에 대한 역학적 접근방법을 제시하였다. 모의변수로 나타낸 탄성-점탄성 일치원리는 아스팔트 콘크리트의 점탄성과 시간의존 손상의 증가를 별도로 평가하도록 적용되었다. 선형-점탄성 파괴역학에 사용되고 있는 미소균열의 증가법칙이 물체내 손상증가를 나타내는데 성공적으로 사용되었다. 응력과 모의변형도로 나타나는 구성방정식은 먼저 변형도조절에 대해 세워졌으며, 응력과 모의변형도를 모의응력과 변형도로 간단하게 대체함으로써 응력조절 구성방정식으로 변형되었다. 모의응력으로 나타낸 변형된 구성방정식은 응력조절모드에서 파괴에 이르는 아스팔트 콘크리트의 모든 역학적 거동을 충분히 예측하고 있다.

• Structural Engineering and Mechanics
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• 제36권4호
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• pp.401-419
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• 2010

This paper focuses on the development, verification and application of a three-dimensional nite element code for coupled thermal and structural analysis of roller compacted concrete arch dams. The Ostour Arch dam located on Ghezel-Ozan River, Iran, which was originally designed as conventional concrete arch dam, has been taken for the purpose of verication of the nite element code. In this project, RCC technology has been ascertained as an alternative method to reduce the cost of the project and make it competitive. The thermal analysis has been carried out taking into account the simulation of the sequence of construction, environmental temperature changes, and the wind speed. In addition, the variation of elastic modulus with time has been considered in this investigation using Concard's model. An attempt was made to compare the stresses developed in the dam body five years after the completion of the dam with those of end of the construction. It was seen that there is an increase in the tensile stresses after five years over stresses obtained immediately at the end of construction by 61.3%.

• 한국기계가공학회지
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• 제16권5호
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• pp.19-24
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• 2017

In this research, a practical stiffness calculation method is developed and applied for modifying the height of the headstock, turret, and tailstock of a CNC lathe to enlarge the turntable diameter. The casting structure is assumed to be a rigid body and the linear motion element to be an elastic spring to simplify the turret stiffness calculation model. The stiffness of the sliding guide and ball screw of the original lathe is measured with a push tester and LVDT sensor, and the turret stiffness of the modified lathe is predicted and compared with experimental results to verify the model. The measured stiffness of the original turret is $0.17kN/{\mu}m$ and that of the modified turret is $0.11kN/{\mu}m$, i.e., an 18% difference from the predicted result. The verified stiffness calculation model can be used to develop another modified lathe.

• 한국공작기계학회논문집
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• 제17권2호
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• pp.30-37
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• 2008

An object transport system is driven by a conveyor belt system or a magnetic levitation system. It is an indispensable device in many fields and especially it is very important in the factory automation. However, the conventional transport system can damage precision optical components by the contact force and destroy the inner structure of semiconductor by the magnetic field. The new transport system for transporting without damage is required. The ultrasonic transport system is a device that transports objects on the elastic body using ultrasonic wave. In this paper, an object transport system using the ultrasonic wave is developed for transporting precision elements without damage. Traveling waves are generated by the ultrasonic wave generator fixed in both ends of the beam. The traveling wave of the ultrasonic transport system is theoretically analyzed. Transport direction of the object is examined according to phase difference and frequency. The theoretical results are verified by experiments.

• Wind and Structures
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• 제16권5호
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• pp.411-431
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• 2013

A computational study of vortex-induced transverse vibrations of a cylinder with low mass-damping is presented. An Arbitrary Lagrangian-Eulerian (ALE) formulation of the Unsteady Reynolds-Averaged Navier-Stokes equations (URANS), along with the Spalart-Allmaras (SA) one-equation turbulence model, are coupled conservatively with rigid body motion equations of the cylinder mounted on elastic supports in order to study the amplitude and frequency response of a freely vibrating cylinder, its flow-induced motion, Vortex Street, near-wake flow structure, and unsteady loading in a moderate range of Reynolds numbers. The time accurate response of the cylinder from rest to its limit cycle is studied to explore the effects of Reynolds number on the start of large displacements, motion amplitude, and frequency. The computational results are compared with published physical experiments and numerical studies. The maximum amplitudes of displacements computed for various Reynolds numbers are smaller than the experimental values; however, the overall agreement of the results is quite satisfactory, and the upper branch of the limit-cycle displacement amplitude vs. reduced velocity response is captured, a feature that was missed by other studies. Vortex shedding modes, lock-in phenomena, frequency response, and phase angles are also in agreement with experiments.