• Title/Summary/Keyword: contact problem

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Stress Analysis of Fir-Tree Root in Turbine Rotor Using Photoelastic Technique (광탄성기법을 이용한 터빈로터 퍼-트리부의 응력해석)

  • Sin, Gwang-Bok;Gyeong, U-Min;Hong, Chang-Seon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.6
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    • pp.1784-1797
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    • 1996
  • The disk/blade assembly of a turbine engine is made in the shape of a dovetail type or a fir-tree type. Since disk fillet regions or contact surfaces undergo high stress comcentration, fatigue cracks frequentrly occur in the disk/blade assembly. Therefore, it is necessary to analyze the stress distributions in the fir-tree type disk/balde assembly and predict the region of fatigue failure. The stress distributions of the disk/blade assembly were investigated by using the photoelastic method and the finite element method. Two dimensional photoelastic techniques were used to investigate the stress distributions of contact surfaces and fillet regions. TH stress distributions were obtained by the shear-difference method and were compared to the finite element results. It was found that maximum tensile stresses were higher in the fillet region thatn in the contact surfaces of the fir-tree models. The finite element results showed good agreement with the experimental results.

Dynamic Analysis of Catenary System Subjected to Moving Load (이동하중을 받는 일정장력이 작용하는 가선계의 동적해석)

  • Lee, Kyu-Ho;Cho, Yong-Hyun;Chung, Jin-Tai
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.1
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    • pp.99-106
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    • 2011
  • In this study, the dynamic contact of a catenary system is analyzed by using the finite element method. We derive the equations of motion for the catenary system by taking into consideration tension on the catenaries. After establishing the weak form, they are spatially discretized with beam elements. Then, we analytically calculated the wave propagation speed for a string, bar, beam, and the catenaries subjected to tension. Further, finite element computer program for contact dynamic analyses is developed. Finally, we analyze the wave propagation response corresponding to the moving load to the contact line are calculated.

A Study on Design Sensitivity of Elastomeric O-ring Squeezed and Highly Pressurized Under Laterally One-sided Constrained Condition (단 측벽 구속하에서 압축 및 내압을 받는 고무 오링의 설계 민감도 연구)

  • Park, Sung-Han;Kim, Jae-Hoon;Kim, Won-Hoon
    • Journal of the Korean Society of Safety
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    • v.22 no.6
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    • pp.27-34
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    • 2007
  • Static or dynamic elastomeric O-ring seals are installed between joining parts, and play key roles of high pressure-tightening. Sealing performance and structural safety of the O-ring are dependent on groove design, plain diameter, squeeze and applications such as pressure and temperature. In this study, to solve O-ring problem squeezed and highly pressurized under laterally one-sided constrained condition, hyperelastic FE analyses are performed, and FE results are compared with measured ones by computer-aided tomography, deformed shape and extrusion depth of the O-ring. Through the comparisons, FE analysis technique was verified. In order to evaluate design sensitivity, Taguchi method was used to select FE analysis cases. Adjustment parameters are clearance gap, groove comer radius, plain diameter and squeeze. By means of verified FE analysis technique, it has been analysed how the parameters have effects on contact stress fields, internal stress fields, and extrusion depths. Sealing performance has been evaluated based on contact stress fields and contact widths, and structural safety on internal stress and strain, extrusion lengths.

Characterization of Photoinduced Current in Poly-Si Solar Cell by Employing Photoconductive Atomic Force Microscopy (PC-AFM)

  • Heo, Jin-Hee
    • Transactions on Electrical and Electronic Materials
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    • v.13 no.1
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    • pp.35-38
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    • 2012
  • In this study, we have attempted to characterize the photovoltaic effect in real-time measurement of photoinduced current in a poly-Si-based solar cell using photoconductive atomic force microscopy (PC-AFM). However, the high contact resistance that originates from the metal-semiconductor Schottky contact disturbs the current flow and makes it difficult to measure the photoinduced current. To solve this problem, a thin metallic film has been coated on the surface of the device, which successfully decreases the contact resistance. In the PC-AFM analysis, we used a metal-coated conducting cantilever tip as the top electrode of the solar cell and light from a halogen lamp was irradiated on the PC-AFM scanning region. As the light intensity becomes stronger, the current value increases up to $200{\mu}A$ at 80 W, as more electrons and hole carriers are generated because of the photovoltaic effect. The ratio of the conducting area at different conditions was calculated, and it showed a behavior similar to that generated by a photoinduced current. On analyzing the PC-AFM measurement results, we have verified the correlation between the light intensity and photoinduced current of the poly-Si-based solar cell in nanometer scale.

A Study on the Finite Element Analysis of Tire under Rolling and Loading Conditions (회전 및 하중을 받는 타이어의 응력해석에 관한 연구)

  • Hwang, Joon;Namgung, Suk
    • Journal of the Korean Society for Precision Engineering
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    • v.12 no.3
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    • pp.101-109
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    • 1995
  • Axisymmetric and quasi-static finite element analysis of an inflated tire rotating with constant angular velocity and contact to road has been performed. Centrifugal force effect was added to load stiffness matrix and equation of effective material properties were calculated by the Halpin-Tsai formulation. In this report, radial truck/bus tire was analyzed. It was inflated and rotated at speeds up to 140 km/h. Then, contact problem was performed to calculate stress-strain field of tire wiht flat rigid road under the load due to the self-weight of a vehicle. Significant changes of stress-strain field of tire were observed in the finite element analysis. Shear stress, strain and strain energy density were rapidly increased at the dege of #2 belt at freely rotating state. This concentrated stress and strain made belt edge sparation. Under the condition of flat riged road contact, strain energy density of #2 belt, carcass turn-up part were concentrated and bigger values than only freely rotation state. Therefore, dynamic behaivor of tire has to considered as design factors which are affected to belt edge separation and bead breakage.

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Heart Rate Signal Extraction by Using Finger vein Recognition System (지정맥 인식 시스템을 이용한 심박신호 검출)

  • Bok, Jin Yeong;Suh, Kun Ha;Lee, Eui Chul
    • Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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    • v.9 no.6
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    • pp.701-709
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    • 2019
  • Recently, heart rate signal, which is one of biological signals, have been used in various fields related to healthcare. Conventionally, most of the proposed heart rate signal detection methods are contact type methods, but there is a problem of discomfort that the subject have to contact with the device. In order to solve the problem, detection study by non-contact method has been progressed recently. The detected heart rate signal can be used for finger vein liveness detection and various application using heart rate. In this paper, we propose a method to obtain heart rate signal by using finger vein imaging system. The proposed method detected the signal from the changes of the brightness value in the time domain of the infrared finger vein images and converted it into the frequency domain using the image processing algorithm. After the conversion, we removed the noise not related to the heart rate signal through band-pass filtering. In order to evaluate the accuracy of the signal, we analyzed the correlation with the signal obtained simultaneously with the finger vein acquisition device and contact type PPG sensor approved by KFDA. As a result, it was possible to confirm that the heart rate signal detected in non-contact method through the finger vein image coincides with the waveform of actual heart rate signal.

Evaluation of proximal contact strength by postural changes

  • Kim, Hee-Sun;Na, Hyun-Joon;Kim, Hee-Jung;Kang, Dong-Wan;Oh, Sang-Ho
    • The Journal of Advanced Prosthodontics
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    • v.1 no.3
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    • pp.118-123
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    • 2009
  • STATEMENT OF PROBLEM. Proper proximal contact is important for maintaining and stabilizing the dental arch. However, the proximal contact strength (PCS) is not a constant value and can be affected by a variety of factors. PURPOSE. This study examined the influences of postural changes on the posterior PCS. MATERIAL AND METHODS. Twelve adults with a normal occlusion and had not undergone prosthetic treatment or proximal restoration were participated in this study. A metal strip was inserted into the proximal surface and removed at a constant velocity. The contact strength was measured in every contact point between canine to second molar in both arches. The PCSs were obtained initially in the upright position, secondly in the supine position and finally in the upright position again. All measurements were repeated after a 2 hour period. Statistical analysis was carried out using the Friedman test (P < .05). RESULTS. Generally, a decrease in PCS occurred when the posture was changed from the initial upright to supine position, while it increased when the posture was changed from the supine to upright position. A significant change was observed in all areas except for between the canine-first premolar in the maxilla and between the first molar-second molar in the mandible areas. CONCLUSION. The posterior PCS, which dentists generally believe to be a static feature of occlusion, is affected significantly by posture.

Contact lens Prescription and Satisfaction with Astigmatism Eye (난시안의 콘택트렌즈 처방과 만족도에 관한 연구)

  • Kim, Mi-Yeon;Kim, Yeong-Mi;Kim, Tae-Hun;Sung, A-Young
    • Journal of Korean Ophthalmic Optics Society
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    • v.11 no.4
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    • pp.317-322
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    • 2006
  • For this study we made up a question investigation to analyze a grade of satisfaction and a side effect about the prescription actual condition of contact lens of person with astigmatism among the person who has a error of refraction. The whole patient of refractive error was 46 person, there were 11 person who only wear spectacles by correction of visual acuity among person to a question investigation and 35 person who only wear contact lens. Under investigation 35 person who only wear contact lens, there were 25 person who experience the problem which occurs because of contact lens wearing for a long time. The most patient who made up a question investigation very choose remainder item except for item of very satisfaction. The their reason that could not satisfaction was non corrected astigmatism, wrong prescription, wrong Base curve, out of life span etc.

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Non-contact Ultrasonic Inspection Technology of Fillet Weldments (필렛 용접부의 비접촉 초음파 검사 기법)

  • Park, Ik-Keun;Lee, Chul-Ku;Kim, Hyun-Mook;Park, Tae-Sung;Kim, Yong-Kwon;Cho, Yong-Sang;Song, Won-Joon;Ahn, Houng-Kun
    • Journal of Welding and Joining
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    • v.23 no.5
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    • pp.37-42
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    • 2005
  • The non-destructive Inspection of the fillet weldment has difficulties due to its geometrical complexity and uneasy access. The surface shear horizontal wave (SH-wave), however, has been successfully applied to the detection of cracks on the surface and sub-surface of the filet weldment heel part. The conventional ultrasonic inspection using the surface SH-wave is usually a contact method using piezoelectric transducer. Thus, it is not suitable for a field application because the reliability and repeatability of inspection are significantly affected by test conditions such as couplant, contact pressure and pre-process. In order to overcome this problem, a non-contact SH-wave inspection method using EMAT is propose. The experimental results with this non-contact method are compared with those with a conventional ultrasonic method in fillet weldment with slit type defects. It is shown that the non-contact inspection technique requires simple procedure and less time in the fillet weldment inspection.

MIXED FINITE VOLUME METHOD ON NON-STAGGERED GRIDS FOR THE SIGNORINI PROBLEM

  • Kim, Kwang-Yeon
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.12 no.4
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    • pp.249-260
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    • 2008
  • In this work we propose a mixed finite volume method for the Signorini problem which are based on the idea of Keller's finite volume box method. The triangulation may consist of both triangles and quadrilaterals. We choose the first-order nonconforming space for the scalar approximation and the lowest-order Raviart-Thomas vector space for the vector approximation. It will be shown that our mixed finite volume method is equivalent to the standard nonconforming finite element method for the scalar variable with a slightly modified right-hand side, which are crucially used in a priori error analysis.

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