• Steel and Composite Structures
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• 제51권4호
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• pp.391-406
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• 2024

The present research investigates the combination resonance behaviors of porous FG shallow shells reinforced with oblique stiffeners and subjected to a two-term excitation. The oblique stiffeners considered in this research reinforce the shell internally and externally. To model the stiffeners, Lekhnitskii's smeared stiffeners technique is utilized. According to the first-order shear deformation theory (FSDT) and stress functions, a nonlinear model of the oblique stiffened shallow shell is established. With regard to the FSDT and von-Kármán nonlinear geometric assumptions, the stress-strain relationships for the present shell system are developed. Also, in order to discretize the nonlinear governing equations, the Galerkin method is implemented. To obtain the required relations for investigating the combination resonance theoretically, the method of multiple scales is applied. For verifying the results of the present research, generated results are compared with previous research. Additionally, a comparison with the P-T method is conducted to increase the validity of the generated results, as this method has illustrated advantages over other numerical methods in terms of accuracy and reliability. In this method, the piecewise constant argument is used jointly with the Taylor series expansion, which is why it is named the P-T method. The effects of stiffeners with different angles, and the effects of material parameters on the combination resonance behaviors of the present system are addressed. With the findings of this research, researchers and engineers in this field may use them as benchmarks for their design and research of porous FG shallow shells.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.269-272
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• 2008

고체 추진기관의 추력을 조절하기 위하여 사용되는 핀틀은 초음속 유동장 내부에 위치하기 때문에 핀틀 팁의 형상과 노즐의 Contour형상에 따라 초음속 노즐 내부는 복잡한 유동장 패턴을 가지게 된다. 본 연구는 핀틀 노즐성능에 대한 연구로 Needle형 핀틀을 사용하여 수행한 공압 시험과 수치해석을 이용하여 핀틀의 위치에 따른 초음속 노즐 내부 유동장 변화가 핀틀 노즐의 추력성능에 미치는 영향에 대하여 분석하였다. 연구의 결과, 노즐 내부에 3가지 충격파가 존재하고 경사충격파의 위치가 핀틀의 위치에 따라 진동함을 알 수 있었다.

• 대한기계학회논문집
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• 제16권10호
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• pp.1990-1997
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• 1992

본 연구에서는 미소진폭의 파형벽을 가진 유로내에 응축성 기체인 습공기가 초음속으로 흐르는 경우의 유동에 대하여 정체점에서의 상대습도와 온도의 변화에 따 른 유동장내의 상태량의 변화와 경사충격파의 거동 등을 2차원 수직해석을 통하여 규 명하였다.

• Archives of Plastic Surgery
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• 제37권4호
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• pp.504-508
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• 2010

Purpose: Traumatic telecanthus can result from nasoethmoid-orbital fractures. Repair of the medial canthal tendon (MCT) using transnasal wiring is regarded as a choice of method to treat telecanthus, however, is often complicated by incomplete anchoring and drift of canthus, extrusion of wire, in-fracture of orbital bone, and eye damage. The authors introduced oblique transnasal wiring method through the Hiraga's epicanthopalsty incision instead of well-known classical bicoronal approach. Methods: Five patients with traumatic telecanthus were treated with this method. Though the Hiraga's epicanthoplasty incision, we could approach the operative field; the medial orbital wall and detached MCT. Oblique transnasal wiring was performed as following steps. After slit skin incision on the contralateral nasal recession area, drill holes were made from this point to the superior and posterior point of lacrimal sac of deformed eye. A 2-0 wire was double-passed through the holes and MCT. Traction was applied to ensure pulling the MCT and the wires were twisted in the contralateral nose, securing the MCT in the correct position. Results: All patients except 1 person showed improvement and rapid recovery. On average each canthus was moved 5.6 mm medially. In all cases, there were no eyelashes disappear, lacrimal canaliculitis, lacrimal duct injury, or infections. Conclusion: The Hiraga's epicanthoplasty incision could give sufficient operative field to reattach the MCT in traumatic telecanthus patients. And the oblique transnasal wiring technique is effective for the Asians who have flat nose and exophthalmic eye. The authors conclude that this technique could be a simple, safe and scarless method to correct traumatic telecanthus.

• Applied Microscopy
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• 제46권2호
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• pp.93-99
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• 2016

The thickness of specimen is an important factor in microscopic researches. Thicker specimen contains more information, but it is difficult to obtain well focused image with precise details due to optical limit of conventional microscope. Recently, a microscope unit that combines improved illumination system, which allows real time three-dimensional (3D) image and automatic z-stack merging software. In this research, we evaluated the usefulness of this unit in observing thick samples; Golgi stained nervous tissue and ground prepared bone, tooth, and non-transparent small sample; zebra fish teeth. Well focused image in thick samples was obtained by processing z-stack images with Panfocal software. A clear feature of neuronal dendrite branching pattern could be taken. 3D features were clearly observed by oblique illumination. Furthermore, 3D array and shape of zebra fish teeth was clearly distinguished. A novel combination of two channel oblique illumination and z-stack imaging process increased depth of field and optimized contrast, which has a potential to be further applied in the field of neuroscience, hard tissue biology, and analysis of small organic structures such as ear ossicles and zebra fish teeth.

• Wind and Structures
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• 제7권6호
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• pp.421-447
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• 2004

This paper presents a time domain approach for predicting buffeting response of long suspension bridges under skew winds. The buffeting forces on an oblique strip of the bridge deck in the mean wind direction are derived in terms of aerodynamic coefficients measured under skew winds and equivalent fluctuating wind velocities with aerodynamic impulse functions included. The time histories of equivalent fluctuating wind velocities and then buffeting forces along the bridge deck are simulated using the spectral representation method based on the Gaussian distribution assumption. The self-excited forces on an oblique strip of the bridge deck are represented by the convolution integrals involving aerodynamic impulse functions and structural motions. The aerodynamic impulse functions of self-excited forces are derived from experimentally measured flutter derivatives under skew winds using rational function approximations. The governing equation of motion of a long suspension bridge under skew winds is established using the finite element method and solved using the Newmark numerical method. The proposed time domain approach is finally applied to the Tsing Ma suspension bridge in Hong Kong. The computed buffeting responses of the bridge under skew winds during Typhoon Sam are compared with those obtained from the frequency domain approach and the field measurement. The comparisons are found satisfactory for the bridge response in the main span.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.501-517
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• 2020

Three-dimensional numerical simulations were performed to study the effects of flow direction and flow velocity on the flow regime behind a curved pipe represented by a curved circular cylinder. The cylinder is based on a previous study and consists of a quarter segment of a ring and a horizontal part at the end of the ring. The cylinder was rotated in the computational domain to examine five incident flow angles of 0-180° with 45° intervals at Reynolds numbers of 100 and 500. The detailed wake topologies represented by λ2 criterion were captured using a Large Eddy Simulation (LES). The curved cylinder leads to different flow regimes along the span, which shows the three-dimensionality of the wake field. At a Reynolds number of 100, the shedding was suppressed after flow angle of 135°, and oblique flow was observed at 90°. At a Reynolds number of 500, vortex dislocation was detected at 90° and 135°. These observations are in good agreement with the three-dimensionality of the wake field that arose due to the curved shape.

• 디지털콘텐츠학회 논문지
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• 제12권1호
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• pp.49-55
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• 2011

비 자성 금속 screw를 이용한 고정술을 시행한 환자를 대상으로 검사하는 자기공명영상에서는 자장의 기하학적 변형을 일으켜 영상에 자화율 인공물을 유발시킨다. 이에 본 연구에서는 자화율 인공물 발생 시 주파수 경사 방향 변환에 따른 영상의 왜곡 정도를 비교, 확인하고자 하였다. 우선 티타늄 성분의 비 자성 금속 screw을 삽입한 자체 팬텀을 제작하여 관심영역을 설정하고 주파수 경사 방향을 축상면에서는 전측-후측을 우측-좌측 방향으로 변환하였고 관상면에서는 우측-좌측을 위측-아래측으로 변환하였고 시상면에서는 상측-하측을 전측-후측으로 변환하여 관심영역의 왜곡 정도를 비교, 관찰 하였다. 결과적으로 주파수 경사 방향을 변환 하였을 때 관심 영역의 왜곡차이를 확인 할 수 있으며 향후 경사 방향을 적절하게 변경함으로써 진단적 효율을 높일 수 있을 것으로 사료된다.

• 대한기계학회논문집A
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• 제35권9호
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• pp.1113-1118
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• 2011

고체-고체 접촉계면의 특성을 평가하기 위하여 초음파 수직 입사에 의한 반사 투과법이 주로 이용되어왔다. 하지만 수직입사방법은 용접부 검사와 같은 현장적용에 한계가 있는 단점이 있다. 이러한 한계를 극복하기 위한 방법으로 초음파 경사입사법이 대안이 될 수 있다. 그러나 경사입사법의 경우, 초음파의 모드변환이 발생하고 수신신호는 접촉면의 수직 계면강성뿐만 아니라 수평 계면강성의 영향을 받으므로 이를 고려한 분석이 필요하다. 본 연구에서는 경사입사에 따른 접촉계면에서의 초음파 반사와 투과특성에 대한 이론적 모델을 제안하였다. 그리고 경사입사에 대한 초음파 반사율 및 2 차 고조파 측정실험 결과 이론적 예측과 잘 일치함을 확인하였다. 결과적으로 경사입사법은 접촉계면 특성평가를 위한 효과적인 기법이라 할 수 있다.

• Structural Engineering and Mechanics
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• 제77권1호
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• pp.137-149
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• 2021

In engineering design, the axial equivalent elastic modulus of laminated FRP pipe was mostly calculated by the average elastic modulus method or the classical laminated plate theory method, which are based on relatively simplified assumptions, and may be not accurate enough sometimes. A new analytical calculation method for the axial equivalent elastic modulus of laminated FRP pipe was established based on three-dimensional stress state. By comparing the results calculated by this method with those by the above two traditional analytical methods and the finite element method, it is found that this method for the axial equivalent elastic modulus fits well not only for thin-walled pipes with orthotropic layers, but also for thick-walled pipes with arbitrary layers. Besides, the influence of the layer stacking on the axial equivalent elastic modulus was studied with this method. It is found that a proper content of circumferential layer is beneficial for improving the axial equivalent elastic modulus of the laminated FRP pipe with oblique layers, and then can reduce its material quantity under the premise that its axial stiffness remains unchanged. Finally, the meso-mechanical mechanism of this effect was analyzed. The improving effect of circumferential layer on the axial equivalent elastic modulus of the laminated FRP pipe with oblique layers is mainly because that, the circumferential fibers can restrain the rigid body rotations of the oblique fibers, which tend to cause the significant deformations of the pipe wall units and the relatively low axial equivalent elastic modulus of the pipe.