• Geomechanics and Engineering
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• 제15권4호
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• pp.973-986
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• 2018

The objective of this paper is to present abacuses obtained from a parametric study of deep-lined tunnels using a numerical finite element model. This numerical model was implemented in software GEOMEC91, which is a two-dimensional axisymmetric model that considers the progress of excavation and the placing of the lining through the activation and deactivation of elements. It is adopted a step of excavation constant (1/3 of radius), constant velocity and circular cross section along the tunnel axis. It is used for rock mass a viscoplastic constitutive law with von-Mises criterion of viscoplasticity without hardening whose deformation rate over time is given by the Bingham model. The lining uses a linear elastic constitutive law. In total are 1716 analysis presented in 60 abacuses that show the value of ultimate convergence ($U_{eq}$) due to tunneling speed. In addition, it is shown an example of the use of the abacuses to determine the ultimate convergence ($U_{eq}$) of the tunnel and pressure ($P_{eq}$) on the lining.

• 한국정밀공학회지
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• 제30권8호
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• pp.790-796
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• 2013

Micro-speaker diaphragms play an important role in generating a desired audio response. The diaphragm is generally a circular membrane, and the cross section is a double dome, with an inner dome and an outer dome. To improve the sound quality of the speaker, a number of corrugations may be included in the outer dome region. In this study, the role of these corrugations is investigated using two kinds of finite element method (FEM) calculations. Structural FEM modeling was carried out to investigate the change in stiffness of the diaphragm when the corrugations were included. Modal FEM modeling was then carried out to compare the natural frequencies and the resulting vibrational modes of the plain and corrugated diaphragms. The effects of the corrugations on the vibration characteristics of the diaphragm are discussed.

• Wind and Structures
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• 제29권6호
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• pp.441-455
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• 2019

In this study, vortex induced vibrations of a cylinder mounted on a flexible rod are analyzed. This simple configuration represents the key element of new conception bladeless wind turbine (Whitlock 2015). In this study the structure oscillations equation coupled to the wake oscillation equation for this configuration are solved using analytical perturbation method, for the first time. An analytical expression that predicts the lock-in phenomena range of wind speed is derived. The discretized equations of motion are also solved using RKF45 numerical method. The equations of motion are discretized by Galerkin method. Free vibration mode shape of the structure taking into account the discontinuity of the cross section are used as comparison function. Numerical results are compared to the analytical results, and they show a satisfying agreement. The effect of system parameters on the oscillations of structure and wake as well as on the lock-in domain are presented. Moreover, it is shown that the values of wind speed triggering the start and the stop of the lock-in phenomenon, for increasing wind speed are different from those values obtained during the reverse process, i.e., when the wind speed decreases.

• 대한기계학회논문집B
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• 제22권11호
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• pp.1509-1520
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• 1998

An experiment was carried out for the fully developed turbulent flow of water in tube coils on the condition of uniform heat flux. The present work was conducted for various ranges for Dean number(1794~1321), Prandtl number (2.5~4.5), curvature ratio parameters (22~60). Heat transfer to steady viscous flow in coiled tubes of circular cross section was studied for fully developed velocity and temperature fields under the thermal boundary condition of uniform heat flux. The peripherally local Nusselt number correlated as a function of Dean and Prandtl numbers. We studied the flow in heat coiled tubes under the influence of both centrifugal and buoyancy forces in order to gain insight into the flow pattern. In the present study, we obtained three emperical formulas, $Nu_v=0.0231Re^{0.84}Pr^{0.4}(a/R)^{0.13}$ (vertical) $Nu_c=0.0241Re^{0.86}Pr^{0.4}(a/R)^{0.08}$ (corrugated) $Nu_h=0.0227Re^{0.84}Pr^{0.4}(a/R)^{0.09}$ (horizontal).

• 한국구조물진단유지관리공학회 논문집
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• 제16권6호
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• pp.1-8
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• 2012

이 연구는 횡보강근의 배근형상에 따른 횡구속된 콘크리트의 성능을 평가하였다. 주요 변수는 횡보강근의 항복강도와 횡보강근의 배근형상으로 하였다. 총 27개의 직사각형 형태의 실험체를 제작하였으며, 단조 집중하중상태에서 실험을 수행하였다. 이 연구에서는 배근형상을 사각형인 R-type, 원형인 C-type 및 이 연구에서 제안한 사각과 팔각이 혼합된 O-type으로 계획하였다. 실험결과, 이 연구에서 제안한 배근형상이 사각형 나선철근과 비교하여 뛰어난 연성능력을 가짐을 확인할 수 있었다.

• 한국소음진동공학회논문집
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• 제25권7호
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• pp.510-517
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• 2015

The free vibration and stability analysis of a spinning composite shaft modelled as a thin-walled closed beam is performed for several design parameters, such as ply angle, aspect ratio, and spin speed. The governing equations of spinning shafts based on the Timoshenko beam theory are derived via Hamilton's variational principle. Coriolis acceleration and anisotropy of constituent materials are incorporated in the derivation. The equations of motion are then transformed to the standard form of an eigenvalue problem for free vibration and stability analysis. Analytical results both for uniform circular cylindrical shaft and rectangular cross-section shaft are obtained by using extended Galerkin method, and the results are compared with those from FEM ANSYS analysis for a verification.

• 한국염색가공학회지
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• 제26권2호
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• pp.114-123
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• 2014

This research investigated the physical properties of PET coolness filaments and their knitted fabrics including dyeing characteristics of these knitted fabrics according to the different dyeing time and temperature. The coolness filament(S) with non-circular cross-section and hydrophilic property was spun and another commercialized coolness(A) and regular(R) PET filaments were prepared for comparing coolness and another physical properties. Qmax of coolness knitted fabric made with S filament was higher than that of R-PET filament, and the maximum value of Qmax of S knitted fabric was shown at the dyeing conditions of temperature, $110^{\circ}C$ with 30 min. or 40min. It was shown that hand of S knitted fabric was a little harsh comparing to A and regular knit specimens, but shape retention and wearing performance of garment made with S knit specimen were estimated as good owing to high bending and shear rigidity. K/S of S knitted fabric was higher than those of regular PET and A knit specimens. Dyeing fastness of coolness knitted fabric showed between 4th and 5th grade.

• 대한조선학회논문집
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• 제38권1호
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• pp.62-71
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• 2001

레이다 반사면적(RCS)은 레이더 탐지에, 그리고 음향 표적강도(TES)는 소나 탐지에 직접 관련이 있기 때문에 이 두 신호는 함정설계 초기단계에서 검토되어야 하는 중요한 요소 중의 하나이다. 따라서 본 연구에서는 곡면패치 물리광학법을 도입하여 완전반사 곡면구조물의 RCS와 TES를 계략적으로 예측하는 기법을 개발하였다. 수치기법의 검증을 위하여 원형 실린더, 구, NACA3317 날개의 RCS를 계산한 후 가용한 자료와 비교 검토하였다. 또한 본 연구의 기법을 잠수함에 확장 적용하여 수상 항해시의 RCS와 잠수 항해시의 TES를 각각 계산하였다. 그리고 레이더 파와 소나 음파의 입사방위와 고각에 따른 주요 반사구조물의 위치를 확인하였다.

• 한국전자파학회논문지
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• 제19권10호
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• pp.1115-1121
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• 2008

본 논문에서는 유전체의 유전 상수를 결정하기 위하여 유전체 슬랩을 원통형 공진기에 삽입하여 측정하는 기술을 제안한다. 유전 상수는 빈 공진기와 유전체 슬랩이 삽입된 공진기의 공진 주파수 편차에 의해 측정된다. 특성 방정식은 정확한 필드 해석에 의해 정의되었다 측정 장치는 HP8719A 벡터 네트웍 분석기와 금속 재질의 원통형 공동 공진기를 이용하였다. 이론적인 증명은 실험과 3D 시뮬레이터인 CST사의 MWS 4.0에 의해 확인되었다. 측정 된 결과는 전반적으로 만족하였다. 측정 된 테플론과 베이클라이트의 비유전율은 각각 2.03과 4.44이다.

• Wind and Structures
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• 제18권1호
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• pp.83-101
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• 2014

Lamps installed on stay cables of cable-stayed bridges may alter the configuration of circular cross section of the cables and therefore result in aerodynamically unstable cable vibrations. The background of this study is a preliminary design of lamp installation on the cable-stayed He-dong Bridge in Guangzhou, China. Force measurements and dynamic response measurements wind tunnel tests were carried out to validate the possibility of cable galloping vibrations. It is observed that galloping will occur and the critical wind velocity is far less than the design wind velocity at Guangzhou City stipulated in Chinese Code. Numerical simulations utilizing software ANSYS CFX were subsequently performed and almost the same results as the wind tunnel tests were obtained. Moreover, the pressure and velocity contours around cable-lamp model obtained from numerical simulations indicated that the upstream steel wire in the preliminary design is the key factor for the onset of the galloping vibrations. A modification for the preliminary design of lamp installation, which suggests to remove the two parallel steel wires, is proposed, and it effectiveness is validated in further wind tunnel tests.