• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.39-45
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• 2005

The aim of this research is to predict the thickness and loading noise of the round-tip shaped Hartzell propeller currently used in the general aviation aircraft. Before implementing the noise analysis, the pressure distribution on the propeller was obtained by using the free wake panel method and unsteady Bernoulli's equation. The noise signal at observer position can be obtained by using the FW-H equation. The noise prediction results for the propeller indicates that the thickness noise has s symmetric directivity pattern with respect to the tip path plane, while the noise due to loading shows higher noise directivity toward downstream than the upstream direction from the rotor plane. The loading noise is dominant rather than the thickness noise in normal operating condition.

• Journal of the Society of Disaster Information
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• v.10 no.1
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• pp.1-14
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• 2014

This paper presents the three-dimensional stress analysis of orthotropic thick plates using the three-dimensional spline strip method based on the theory of elasticity. The orthotropic plates are made of Aragonite crystal and sitka spruce. To demonstrate the convergence and accuracy of the present method, several examples are solved, and results are compared with those obtained by other exact and numerical methods based on the theory of elasticity. Good convergence and accuracy are obtained. The effects of thickness/width ratio, aspect ratio and boundary conditions on normal stress distributions of Aragonite crystal plates and sitka spruce plates are investigated. Moreover, the difference of weak orthotropic and strong orthotropic properties given to the characteristics of stress distributions are also shown.

• KDI Journal of Economic Policy
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• v.10 no.4
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• pp.61-81
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• 1988

우리나라 택시산업(産業)에 대한 정부규제(政府規制)는 크게 보아 요금규제(料金規制), 면허규제(免許規制) 그리고 서비스관련규제(關聯規制)로 나눌 수 있다. 정부규제에 의한 문제점으로서는 요금규제(料金規制)에 의한 초과수요(超過需要)의 존재와 제한적인 면허발급제도(免許發給制度)에 의해 발생한 면허에 대한 프리미엄과 이의 배분을 둘러싼 여러가지 비효율(非效率)과 형평(衡平)의 문제(問題)라고 할 수 있다. 우리나라 택시산업(産業)은 비호출방식(非呼出方式)의 노상유객(路上誘客)을 주로 하는 소위 순항식(巡航式)(cruising)시장(市場)이기 때문에 자유경쟁(自由競爭)의 상태에서는 시장정보전달(市場情報傳達)의 불완전성(不完全性)으로 인한 시장실패(市場失敗)의 가능성(可能性)이 존재한다고 할 수 있다. 따라서 이것을 보정(補正)하기 위한 가격규제(價格規制)의 필요성(必要性)은 인정할 수 있으나, 정부에 의한 제한적인 사업면허(事業免許)의 발급(發給)과, 임의적인 증차결정(增車決定) 및 배분방식(配分方式)은 그 정당성(正當性)이 의문시된다고 할 수 있다. 따라서 장기적(長期的)으로 택시에 대한 면허제(免許制)는 폐지되어야 할 것이다. 그러나 택시증차(增車)의 문제는 도시교통혼잡의 문제와 관련이 있으므로, 중(中) 단기적(短期的)으로는 현행의 직접규제방식(直接規制方式)을 개선하여 일정한 자격을 갖춘 출원자(出願者)에게는 일정금액의 공탁금(供託金)만 납부하면 의무적으로 면허를 내어주는 간접규제방식(間接規制方式)으로의 전환을 고려해야 할 것이다. 또한, 태당(台當) 1일(日) 승객회전률(乘客回轉率)의 증가를 통한 승차난완화(乘車難緩和)를 위해 현행(現行) 요금체계(料金體系)를 개선해야 할 것이다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.4
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• pp.417-425
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• 2007

The differential quadrature method(DQM) is applied to computation of eigenvalues of the equations of motion governing the free out-of-plane vibration for circular curved beams including the effects of rotatory inertia and transverse shearing deformation. Fundamental frequencies are calculated for the members with clamped-clamped end conditions and various opening angles. The results are compared with exact solutions or numerical solutions by other methods for cases in which they are available. The DQM provides good accuracy even when only a limited number of grid points is used.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.9
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• pp.743-748
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• 2016

Ship's diesel engines have intrinsic problem to make vibrations caused by cylinder explosion and unbalanced rotating mass. These vibrations might induce noises, are transferred to hull and neighboring structures and cause secondary vibrations. This paper suggests the use of an additional dynamic absorber with a sub-vibration system to reduce the aforementioned vibrations. This dynamic absorber is designed based on an analysis of the free vibration of the engine shafting system and the forced vibrations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.3
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• pp.528-536
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• 1987

In a turbulent free shear flow, the large scale motion is characterized by the intermittent flow which arises from the interaction between the turbulent fluid and the irrotational fluid of the environment through the mean velocity gradient. This large scale motion causes a bulk convection whose effect is similar to the spatial diffusion process. In this paper, the total diffusion process is proposed to be approximated by weighted sum of the bulk convection due to the large scale motion and the usual gradient diffusion due to small scale motion. The diffusion term in conventional .kappa.-.epsilon. model requires on more equation of the intermittency transport equation. A production term of this equation means mass entrainment from the irrotational fluid to the turbulent one. In order to test the validity of the proposed model, a plane jet is predicted by this method. Numerical results of this model is found to yield better agreement with experiment than the standard .kappa.-.epsilon. model and Byggstoyl & Kollmann's model(1986). Present hybrid diffusion model requires further tests for the check of universality of model and for the model constant fix.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.373-384
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• 1989

The motions of a spinning rotor and a fluid enclosed in its cavity are known to have mutual interactions, which change the frequencies of forced vibrations and cause instabilities. These phenomena are of technical importance for fluid-cooled turbines as well as spin-stabilized satellites or rockets containing liquid fuels. In this paper the characteristics of unstable whirling of a rotor containing a partitioned cavity filled with two kinds of liquids are investigated experimentally. It studies the influence of rotational speed and filling ratio of two kinds of liquids on unstable whiring. As a result, it is found that the whirl velocity is approximately equal to, or slightly lower for large masses of trapped fluid than rotor critical speed. In case of a spinning rotor partially filled with two kinds of liquids the boundary surface plays a similar role to the free surface, and cases unstable forward whirl.

• The Journal of Korea Robotics Society
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• v.10 no.2
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• pp.119-132
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• 2015

Two novel parallel mechanisms (PMs) employing two or three PaPaRR subchains are suggested. Each of those two PMs has translational 3-DOF motion and employs only revolute joints such that they could be adequate for haptic devices requiring minimal frictions. The position analyses of those two PMs are conducted. The mobility analysis, the kinematic modeling, and singularity analysis of each of two PMs are performed employing the screw theory. Then through optimal kinematic design, each of two PMs has excellent kinematic characteristics as well as useful workspace size adequate for haptic applications. In particular, by applying an additional redundantly actuated joint to the 2-PaPaRR type PM which has a closed-form position solution, it is shown that all of its parallel singularities within reachable workspace are completely removed and that its kinematic characteristics are improved.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.18-24
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• 2003

A three node triangular element with drilling rotations incorporating improved higher-order zig-zag theory(HZZT) is developed to analyze the vibration of pretwisted composite plates with embedded damping layer. Shear force matching conditions are enforced along the interfaces between the embedded damping patch and the border patch by matching the shear forces of the embedded damping patch to the shear forces of the adjacent border patch. The natural frequencies and modal loss factors are calculated for cantilevered pretwisted composite blade with damping core with the present triangular element, and compared to experiments and MSC/NASTRAN using a layered combination of plate and solid elements.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.12
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• pp.5984-5989
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• 2011

The buckling strength of a pin-ended column may be increased significantly by reinforcing it with an assemblage of cross-arm members rigidly connected to the modpoint of the column and stayed members connecting the ends of the columns and cross-arm members. The purpose of the stays and cross-arm members is to introduce restraint against translation and rotation and thereby decrease the effective buckling length of the column. In this study, buckling strengths of the reinforced columns were quantitatively evaluated from analytical solutions and elastic/inelastic finite elements analysis and the results were compared each other. It was found that the reinforcing system may increase the buckling strength up to 8 times compared to ones without reinforcing system.