• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.11
• /
• pp.1405-1411
• /
• 2012

Remote handling manipulators are widely used for performing hazardous tasks, and it is essential to ensure the reliable performance of such systems. Toward this end, tendon-driven mechanisms are adopted in such systems to reduce the weight of the distal parts of the manipulator while maintaining the handling performance. In this study, several approaches for the design of a gripper system for a tendon-driven remote handling system are introduced. Basically, this gripper has an underactuated spring mechanism that is combined with a slave manipulator triggered by a master operator. Based on the requirements under the specified tendon-driven mechanism, the connecting position of the spring system on the gripper mechanism and kinematic influence coefficient (KIC) analysis are performed. As a result, a suitable combination of components for the proper design of the target system is presented and verified.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.2
• /
• pp.161-166
• /
• 2010

Elastomeric seals are widely used in dynamic seal applications, and it is well known that the sealing surfaces can be gradually worn out. Abrasive wear is known to be the most dominant factor; however, little research has been carried out on this problem until now. In this study, a new contact problem related to elastomeric seals-a small spherical particle and steel surface-was modeled and analyzed using MARC. Variations of von-Mises and residual stress distributions as well as deformed seal and steel surface shapes with seal materials and interferences are presented. The stress distribution and surface deformation are highly affected by the elastic properties of seal. For PTFE, the maximum von-Mises stress exceeds the yield strength, and plastic deformation occurs on the steel surface. Therefore, the sealing surface can also be worn down by sub-surface fatigue due to intervening hard particles in the sealing surfaces together with the well-known abrasion.

• 한국해양학회지
• /
• v.29 no.3
• /
• pp.239-247
• /
• 1994

Bedform morphology of the giant ripples have been studied on the continental shelf of the Yellow Sea, East China sea and Korea-Tsushima Strait on the basis of side-scan sonar image, sub-bottom profile, sedimentary facies, geomorphology evidence and hydrology. There are well developed giant ripples ranging from 100 to 500 m in wavelengths and from 2 to 10 m in wave height at nine sites in the study area, which are covered by medium to fine sand. Most of them have been formed under the present hydrologic regime where the tidal currents and local currents or turbulence flows are superimposed. In the study area, giant ripples are produced on two different environments. One is at the geomorphic narrow zone such as the Korea Strait where currents are accelerated by the topographic effects, while the other is the sandy flat plain where tidal currents and local currents are harmonized.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.20 no.5
• /
• pp.397-401
• /
• 2000

The corrosion-fatigue characteristics of the 12Cr steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the Rayleigh surface wave. In this study, the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the aged specimens, and then compared to the corrosion-fatigue characteristics. The width of the backward radiation profile decreases as the increase of the aging temperature, which seems to result from the increase of the effective degrading layer thickness. This parameter also shows an inversely proportionality to the exponent, m, in the Paris law which predicts the crack size increasement due to fatigue. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion-fatigue characteristics of the aged materials.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.11 no.6
• /
• pp.87-94
• /
• 2007

Reuse of recycled aggregate from demolished concrete structure is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. The most important mechanical properties of recycled aggregate concrete (RAC) are the compressive strength, the tensile and the flexural strengths, the bond strength and the elastic modulus of such concrete. In particular, the stress-strain relation and fracture process of RAC in compression is especially important in theoretical and numerical analysis as well as engineering design of RAC structures. In this paper, to clarify the characteristics of fracture process in RAC, acoustic emission(AE) method is applied to detect micro-cracking in concrete under compression. From AE parameters, it is found that cracking and fracture behaviors in recycled aggregate concrete fairly differ from that of normal and recycled sand concrete.

• Journal of the Korean Society of Radiology
• /
• v.82 no.6
• /
• pp.1388-1401
• /
• 2021

Postoperative imaging of the rotator cuff may be performed routinely, even if pain or disability develops after surgery or if there are no symptoms. Postoperative images are obtained through MRI or US, and the purpose is to confirm the integrity of the restored tendon in general. Postoperative MRI has a relatively poor diagnostic accuracy compared to that of preoperative images because various materials used in surgeries deteriorate the image quality. US can dynamically check the condition of the restored tendon and avoid artifacts from the surgical instruments used for recovery. Although imaging findings are not always consistent with the clinical symptoms or prognosis, sub-deltoid fluid retention is more important for pain and functional recovery than the thickness of the reconstructed tendon. Strain elastography can also be a useful method for predicting the prognosis.

• Journal of the Korean Magnetics Society
• /
• v.12 no.5
• /
• pp.184-188
• /
• 2002

The Cu/Ni/Cu(002)/Si(100) films which have perpendicular magnetic anisotropy were deposited by e-beam evaporation methods. From the reflection high energy electron diffraction pattern, the films were confirmed to be grown epitaxially on silicon. After 2X lots ions/$\textrm{cm}^2$ C+ irradiation, magnetic easy-axis was changed from surface normal to in-plane as shown in the hysteresis loop of magneto-optical Kerr effects. It became manifest from analysis of X-ray reflectivity and grazing incident X-ray diffraction that even though interface between top Cu layer and Ni layer became rougher, the contrast of Cu and Ni's electron density became manifest after ion irradiation. In addition, the strain after deposition of the films was relaxed after ion irradiation. Strain relaxation related with change of magnetic properties and mechanism of intermixed layer's formation was explained by thermo-chemical driving force due to elastic and inelastic collision of ions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.04a
• /
• pp.34-39
• /
• 1995

최근 승용차의 급격한 수요증가와 더불어 차량의 승차감 개선에 많은 관심이 집중되면서, 저진동 저소음 차량에 대한 연구가 활발히 이루어지고 있다. 이러한 연구의 일부로서, 수치해석법 및 진동실험에 의하여 복잡한 전체 구조물을 해석할 경우, 계산기의 기억용량, 계산시간, 비용이 많이 들게 되고, 한번 해석을 행한 구조물을 부분적으로 변경할지라도 전체의 계산을 다시 수행해야만 한다. 그래서, 복잡한 전체 구조물을 몇 개의 부분구조물로 나누어, 분계의 특성에 맞게 각기 수치해석법이나 모달실험을 적용한 후, 다시 합성하는 방법이 제시되었는데, 이것이 부분구조합성법이다. 이 방법을 사용하면, 유한요소 모델링이 쉬운 분계와 실험이 쉬운 분계를 서로 구분하여 각기 해석한 후 합성함으로써, 각 분계의 특성에 맞는 효율적인 해석을 수행할 수가 있다. 지금까지의 연구를 살펴보면, 유한요소해석에 의한 모드합성법에서는 Hurty가 구속모드법을 제안한 이래, 불구속모드법, 주종계법 등 많은 연구가 있었으나, 실험모달해석을 병행할 경우에는 결합부에서의 회전자유도의 처리문제, 특성 행렬의 동정문제, 많은 절점으로부터 데이타를 얻어야 하는 등의 어려움이 있었다. 이러한 문제를 개선시켜서 Hermanski등은 회전자유도가 보간된 모드합성법(interpolated mode synthesis, IMS)을 연구하여, 적은 실험데이타만을 사용하면서 단순지지 보에 적용함으로써 타당성을 입증하였다. 한편, 차체는 복잡한 부분구조물들로 이루어져 있으므로, 본 연구에서는 유한요소모델링의 용이함, 실험의 간편성, 계산의 효율성등을 추구하며, 실험과 유한요소해석을 병행한 부분구조합성법을 차량의 BIW(body in white)에 적용하는 방법을 연구하게 되었다. 그 기본연구로서 실험과 유한요소해석을 병행하여 회전자유도를 보간하는 방법을 먼저 단순한 판구조물에 적용을 하고, 나아가 실제 BIW를 축소하여 자체 제작한 모형차에 적용시켜 보았다.물은 분계 A(16개의 사각요소)와 분계 B(8개의 사각요소)로 이루어져 있으며 두개의 스프링으로 결합되어 있다. 설계변수는 강성에 국한하였으며 결합부의 결합형태는 탄성결합과 강결합으로 하였다. 감도해석과 축소임피던스 합성법에 의해 구해진 고유진동수와 FRF를 상용 유한 요소 해석 패키지인 MSC/NASTRAN을 통하여 검증하여 이 연구의 타당성을 검토하였다.인풋기어에서의 회전수 변동을 측정하고, 이 실험 데이타를 기초로 하여 엔진 토크 및 변속기에서의 드래그 토크를 계산하여 엔진-변속기 인풋기어의 반한정계 2자유도 진동모델과 비틀림 특성을 가진 클러치 디스크의 프리댐퍼 영역에 대해 시뮬레이션을 수행하여 클러치 비틀림 기구의 설계인자인 비틀림 강성, 히스테리시스 토크에 따른 비틀림 진동 저감 효과를 연구하고자 한다.성을 확인하였다. 여기서는 실험실 수준의 평 판모델을 제작하고 실제 현장에서 이루어질 수 있는 진동제어 구조물에 대 한 동적실험 및 FRS를 수행하는 과정과 동일하게 따름으로써 실제 발생할 수 있는 오차나 error를 실험실내의 차원에서 파악하여 진동원을 있는 구조 물에 대한 진동제어기술을 보유하고자 한다. 이용한 해마의 부피측정은 해마경화증 환자의 진단에 있어 육안적인 MR 진단이 어려운 제한된 경우에만 실제적 도움을 줄 수 있는 보조적인 방법으로 생각된다.ofile whereas relaxivity at high field is not affected by τS. On the other hand, the change in τV does not affect low field profile but strongly in fluences on both inflection fie이 and the maximum relaxivity value. The results shows a fluences on both inflection field and the maximum relaxivity value. Th

• Korean journal of food and cookery science
• /
• v.1 no.1
• /
• pp.74-81
• /
• 1985

For this research, the Atka-fisher which are used commonly in many homes for baking and broilling were broiled by an iron baking method, a pan baking method, a grill baking method and a microwave baking method respectively after 20 hours salting with 3% salt concentration of fish muscle weight. This thesis has an intention of appreciating the tastes according to each baking method through a sensory test, of examining the corelation between the change of texture measured by Rheometer and a sensory test and of comparing the changes of chemical component of the fish. The results were as follow: 1. The appearance of the broiled Atka-fish maintained a good appearance by the iron baking method and the grill baking method. In the color, the iron baking method and the grill baking method by direct :fire resulted a good score too. In the flavor, there was a significant difference between the grill baking method and the microwave baking method while there was no difference between the iron baking method and the pan baking method. The result of tenderness showed that the pan baking method has the highest score. Difference between the iron baking method and the pan baking was not significant. There was no difference in tenderness between the grill baking method and the microwave baking method. The iron baking method showed-the highest score in juciness and the microwave baking method stowed the highest score in acceptability however the differences were not significant. 2. As a result of the measurement of the texture by Rheometer, the iron baking method and the grill baking method showed higher score than other methods in hardness and chewiness. In springiness and cohesiveness, there was no significant difference among methods. As a result of the measurement of the texture by Rheometer, the corelation with a sensory test was considered to be low. 3. After broil, the cooking retention was the highest in the pan baking method and the moisture content was the highest in microwave baking method. Nitrogen content was the highest in the iron baking method. Fat content was the highest in the iron baking method, followed by the grill baking method, the pan baking method, and the microwave baking method. Free amino acid content was the highest in the iron baking method, followed by the grill baking method, the pan baking method and the micro-wave baking method.

• Composites Research
• /
• v.15 no.4
• /
• pp.23-31
• /
• 2002

The two dimensional size effect of specimen gauge section ($length{\;}{\times}{\;}width$) was investigated on the compressive behavior of a T300/924 $\textrm{[}45/-45/0/90\textrm{]}_{3s}$, carbon fiber-epoxy laminate. A modified ICSTM compression test fixture was used together with an anti-buckling device to test 3mm thick specimens with a $30mm{\;}{\times}{\;}30mm,{\;}50mm{\;}{\times}{\;}50mm,{\;}70mm{\;}{\times}{\;}70mm{\;}and{\;}90mm{\;}{\times}{\;}90mm$ gauge length by width section. In all cases failure was sudden and occurred mainly within the gauge length. Post failure examination suggests that $0^{\circ}$ fiber microbuckling is the critical damage mechanism that causes final failure. This is the matrix dominated failure mode and its triggering depends very much on initial fiber waviness. It is suggested that manufacturing process and quality may play a significant role in determining the compressive strength. When the anti-buckling device was used on specimens, it was showed that the compressive strength with the device was slightly greater than that without the device due to surface friction between the specimen and the device by pretoque in bolts of the device. In the analysis result on influence of the anti-buckling device using the finite element method, it was found that the compressive strength with the anti-buckling device by loaded bolts was about 7% higher than actual compressive strength. Additionally, compressive tests on specimen with an open hole were performed. The local stress concentration arising from the hole dominates the strength of the laminate rather than the stresses in the bulk of the material. It is observed that the remote failure stress decreases with increasing hole size and specimen width but is generally well above the value one might predict from the elastic stress concentration factor. This suggests that the material is not ideally brittle and some stress relief occurs around the hole. X-ray radiography reveals that damage in the form of fiber microbuckling and delamination initiates at the edge of the hole at approximately 80% of the failure load and extends stably under increasing load before becoming unstable at a critical length of 2-3mm (depends on specimen geometry). This damage growth and failure are analysed by a linear cohesive zone model. Using the independently measured laminate parameters of unnotched compressive strength and in-plane fracture toughness the model predicts successfully the notched strength as a function of hole size and width.