• Wind and Structures
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• 제15권5호
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• pp.385-407
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• 2012

Bridge hanger vibrations have been reported under icy conditions. In this paper, the results from a series of static and dynamic wind tunnel tests on a circular cylinder representing a bridge hanger with simulated thin ice accretions are presented. The experiments focus on ice accretions produced for wind perpendicular to the cylinder at velocities below 30 m/s and for temperatures between $-5^{\circ}C$ and $-1^{\circ}C$. Aerodynamic drag, lift and moment coefficients are obtained from the static tests, whilst mean and fluctuating responses are obtained from the dynamic tests. The influence of varying surface roughness is also examined. The static force coefficients are used to predict parameter regions where aerodynamic instability of the iced bridge hanger might be expected to occur, through use of an adapted theoretical 3-DOF quasi-steady galloping instability model, which accounts for sectional axial rotation. A comparison between the 3-DOF model and the instabilities found through two degree-of-freedom (2-DOF) dynamic tests is presented. It is shown that, although there is good agreement between the instabilities found through use of the quasi-steady theory and the dynamic tests, discrepancies exist-indicating the possible inability of quasi-steady theory to fully predict these vibrational instabilities.

• 대한조선학회논문집
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• 제35권3호
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• pp.14-25
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• 1998

본 논문은 자유수면 위를 가까이 비행하는 표면효과익선(Wing-in Ground Effect Craft)의 날개에 작용하는 정상(steady) 및 비정상(unsteady) 동유체력을 포텐셜 기저 패널법을 사용하여 수치해석을 수행한 결과이다. 파가 없는 고정수면 위를 비행하는 정상문제의 경우에 대해서는 단면변화, 앙각(angle of attack), 가로-세로비(aspect ratio), 날개 끝단판(end-plate)의 부착 유무 및 비행고도에 따른 양력 및 항력을 계산하여 풍동실험 결과와 비교하였다. 비정상문제에서는 이미 정의된 파표면 위를 표면효과익이 날아가는 경계치 문제로 해석하였다. 파장, 파고, 비행고도의 변화에 따른 날개에 작용하는 비정상 동유체력을 계산하여 파가 있을 경우 표면효과의 영향을 살펴보았다.

• 한국자동차공학회논문집
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• 제23권1호
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• pp.139-147
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• 2015

This paper is the second investigation on the evaluation methods of flow characteristics in a steady flow bench. In the previous work, several assumptions used in the steady flow bench were examined and it was concluded that the assumption of the solid rotation might cause serious problems. In this study, intake valve angle is selected as a main parameter for the assessment because the main flow direction to cylinder governed by this angle has the strongest influence on the in-cylinder flow pattern. For this purpose, four heads, which have the different angle, are prepared and the flow characteristics are estimated both by the conventional impulse swirl meter and a particle image velocimetry at 1.75 times bore position apart from the cylinder head, which is widely used plane in the steady flow measurement. The results show that both of the eccentricity and the velocity profile distort the flow characteristics when using the ISM at 1.75 plane, however, the effects of two factors act in the opposite direction. In addition, the profile's influence is much greater than that of the eccentricity.

• Korea-Australia Rheology Journal
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• 제15권2호
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• pp.55-61
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• 2003

The steady shear flow properties of vaseline generally used as a base of the pharmaceutical dosage forms were studied in the consideration of wall slip phenomenon. The purpose of this study was to show that how slip may affect the experimental steady-state flow curves of semisolid ointment bases and to discuss the ways to eliminate (or minimize) wall slip effect in a rotational rheometer. Using both a strain-controlled ARES rheometer and a stress-controlled AR1000 rheometer, the steady shear flow behavior was investigated with various experimental conditions ; the surface roughness, sample preparation, plate diameter, gap size, shearing time, and loading methods were varied. A stress-controlled rheometer was suitable for investigating the flow behavior of semisolid ointment bases which show severe wall slip effects. In the conditions of parallel plates attached with sand paper, treated sample, smaller diameter fixture, larger gap size, shorter shearing time, and normal force control loading method, the wall slip effects could be minimized. A critical shear stress for the onset of slip was extended to above 10,000 dyne/$\textrm{cm}^2$. The wall slip effects could not be perfectly eliminated by any experimental conditions. However, the slip was delayed to higher value of shear stress by selecting proper fixture properties and experimental conditions.

• Steel and Composite Structures
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• 제33권3호
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• pp.463-472
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• 2019

Initial thermo-elastic and steady state creep deformation of a rotating functionally graded simple blade is studied using first-order shear deformation theory. A variable thickness model for cantilever beam has been considered. The blade geometry and loading are defined as functions of length so that one can define his own blade profile and loading using any arbitrary function. The blade is subjected to a transverse distributed load, an inertia body force due to rotation and a distributed temperature field due to a thermal gradient between the tip and the root. All mechanical and thermal properties except Poisson's ratio are assumed to be longitudinally variable based on the volume fraction of reinforcement. The creep behaviour is modelled by Norton's law. Considering creep strains in stress strain relation, Prandtl-Reuss relations, Norton' law and effective stress relation differential equation in term of effective creep strain is established. This differential equation is solved numerically. By effective creep strain, steady state stresses and deflections are obtained. It is concluded that reinforcement particle size and form of distribution of reinforcement has significant effect on the steady state creep behavior of the blade.

• Wind and Structures
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• 제35권2호
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• pp.109-120
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• 2022

The force coefficients of rotating plates in the acceleration stage will vary with rotation rate from 0 to stable rotation rate w₀, which are important for quasi-steady theory of plate-like windborne debris to simulate the trajectory. In this paper, a wind tunnel experiment is carried out to study the effects of geometry and the Reynolds number on the variations of mean force coefficients of rotating plates. The rotational lift coefficients are sensitive to both geometry effect and Reynolds number effect, while the rotational drag and moment coefficients are only sensitive to geometry effect. In addition, new empirical formulas for the rotational lift coefficient and moment coefficients are proposed. Its accuracy is verified by comparing the predicted results with existing test data. Based on the experimental data of rotating plates, a new rotational force model for quasi-steady theory, which can be applied to a wider scope, is proposed to calculate the trajectory of plate-like windborne debris. The results show that the new model provides a better match with the tested trajectories than previous quasi-steady theories.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 학술대회 논문집 전문대학교육위원
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• pp.51-54
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• 2007

In this paper, the dynamic models of a SOFC are rearranged. It consists of electrochemical model, thermal model, voltage equation and several loss equations. Experiment results of the real SOFC system are shown to evaluate the steady voltage characteristics. Control problems on tracking steady voltage by air flow is discussed and an adaptive controller is designed to withstand to the variation of stack current. Simulation is done to prove the solution of control algorithms.

• 전자공학회논문지A
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• 제31A권10호
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• pp.114-118
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• 1994

To resolve thd discrepancy between the existing channel thermal noise theory of MOSFETs and a new theory called the stady-state Nyquist theorem, we have measured the channel thermal noise of specially designed MOSFETs with both uniform and nonuniform channels. the experimental results clearly show that the correct theory of the channel thermal nois in MOSFETs should be the steady-state Nyquist theorem.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.460-465
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• 2001

In the present study, steady and unsteady flow characteristics inside an industrial mixer with flat turbine type impeller are studied. For the flow analysis, STAR-CD is used with an automatic mesh generator developed in the present study. flow results are compared to the an available experimental data to show validity or the present simulation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1986년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 17-18 Oct. 1986
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• pp.232-237
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• 1986

Theoretical studies are performed for a nonisothermal CFSTR in which consecutive reactions take place. The local dynamic stability of an unstable steady state is investigated with relation to variations in the controller gain when the temperature is subjected to a proportional control. The control has significant in fluences upon the stability of the high temperature steady state as well as that of the intermediate steady state.