• International Journal of Fluid Machinery and Systems
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• 제3권3호
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• pp.260-270
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• 2010

Reducing the losses of the tip clearance flow is one of the keys in an unshrouded centrifugal compressor design and development because tip clearances are large in relation to the span of the blades and also centrifugal compressors produce a sufficiently large pressure rise in single stage. This problem is more acute for a low flow high-pressure ratio impeller design. The large tip clearance would cause flow separations, and as a result it would drop both the efficiency and surge margin. Thus a design of a high efficiency and wide operation range low flow coefficient centrifugal compressor is a great challenge. This paper describes a recent development of high efficiency and wide surge margin low flow coefficient centrifugal compressor. A viscous turbomachinery optimal design method developed by the authors for axial flow machine was further extended and used in the centrifugal compressor design. The compressor has three main parts: impeller, a low solidity diffuser and volute. The tip clearance is under a special consideration in this design to allow impeller insensitiveness to the clearance. A patented three-dimensional low solidity diffuser design method is used and applied to this design. The compressor test results demonstrated to be successful to extend the low solidity diffusers to high-pressure ratio compressor. The compressor stage performance showed the total to static efficiency of the compressor being about 85% and stability range over 35%. The test results are in good agreement with the design.

• 한국추진공학회지
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• 제2권1호
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• pp.88-94
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• 1998

이 연구에서는 100인승 항공기 급의 저익-주익장착나셀(wing mounted nacelle)의 추진기관 장착설계 방법을 제시하였다. 장착설계 방법을 구체적으로 설명하기 위해 세부적인 설계제한조건(design constraint)과 설계요구조건(design requirement and objectives)을 정의하고, 그러한 기준을 근거로 실례의 항공기(K100)를 사용하여 주익장착방식의 장착설계를 수행하였다. 장착설계는 간섭항력(interference drag), roll clearance, ground clearance, nose gear collapse margin, rotor burst, 연료탱크용량 등의 설계제한사항들을 고려하여 엔진성능을 만족시킬 수 있는 최적의 나셀 장착위치(spanwise, FS, WL)와 장착각도(toe-in, incidence, droop angle), wing dry bay의 위치와 크기를 결정하여 향후에 개발될 주익장착방식의 추진기관 장착설계에 활용될 수 있는 설계절차를 구축하였다.

• 한국자동차공학회논문집
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• 제12권4호
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• pp.191-197
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• 2004

This paper presents experimental results for human drivers' driving patterns and an Adaptive Cruise Control(ACC) strategy. Analyses have shown that female drivers' driving characteristic values such as time-gap and minimum clearance are larger than those of male drivers'. Human drivers tend to have more clearance margins at high speed than at low speed. At low speed, drivers are much more sensitive to the desired clearance than at high speed. A multi-vehicle detection method is presented to improve ride quality of an ACC. Simulation results have shown that the proposed ACC can provide superior performance compared to the ACC strategy which uses a single-vehicle detection method.

• 조명전기설비학회논문지
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• 제24권12호
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• pp.177-183
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• 2010

Overhead transmission lines in domestic area have been built by several different design standards of dip and ground clearance. This paper describes an experimental study for evaluating load capacity and dip margin in overhead transmission lines. Such design standards for selection of overhead transmission conductors, dip and ground clearance, as well as electrical equipment technical standard are discussed. Based on daily load and weather data, several characteristics such as line utilization factor, load factor, conductor temperature and dip, etc. are analyzed, and compared with the specified levels of design standards. As a result, it is verified that DLR method can be a clue of the solving of the problem, for occurring in old transmission conductors which may be rarely operating below standards.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 강연회 및 연구개발 발표회 논문집
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• pp.203-209
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• 1998

Rotordynamic analysis of a multistage turbine pump using finite element method is performed to investigate the effects of seal wear on Its system behavior. Stiffness and damping coefficients of the 2-axial grooved bearing are obtained as functions of rotating speed. Stiffness and damping coefficients of plane annular seals are calculated as functions of rotating speed as well as seal clearance. As the clearance of seals become larger, these stiffness and damping coefficients decrease drastically so that there can be significant changes in whirl natural frequencies and damping characteristics of the pump rotor system. Although a pump is designed to operate with a sufficient seperation margin from the 1st critical speed, seal wear due to long operation may cause a sudden increase in nitration amplitude by resonance shift and reduce seal damping capability.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1998년도 제10회 학술강연회논문집
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• pp.4-4
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• 1998

이 연구에서는 100인승 항공기 급의 저익-주익장착나셀(wing mounted nacelle)의 추진기관 장착설계 방법을 제시하였다. 장착설계 방법을 구체적으로 설명하기 위해 세부적인 설계제한조건(design constraint)과 설계요구조건(design requirement and objectives)을 정의하고, 그러나 기준을 근거로 실례의 항공기(K100)를 사용하여 주익장착방식의 장착설계를 수행하였다. 장착설계는 간접항력(interference drag), roll clearance, ground clearance, nose gear collapse margin, rotor burst, 연료탱크용량 등의 설계제한 사항들을 고려하여 엔진성능을 만족시킬 수 있는 최적의 나셀 장착위치(spanwise, FS, WL)와 장착각도(toe-in, incidence, droop angle), wing day의 위치와 크기를 결정하여 향후에 개발될 주익장착방식의 추진기관 장착설계에 활용될 수 있는 설계절차를 구축하였다.

• 소음진동
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• 제7권6호
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• pp.1015-1023
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• 1997

Rotordynamic analysis of a multistage turbine pump using finite element method is performed to investigate the effects of seal wear on its system behavior. Stiffness and damping coefficents of the 2-axial grooved bearing are obtained as functions of rotating speed. Stiffness and damping coefficients of plane annuler seals are calculated as functions of rotating speed as well as seal clearance of seals become larger, these stiffness and damping coefficients decrease drastically so that there can be significant changes in whirl natural frequencies and damping characteristics of the pump rotor system. Although a pump is designed to operate with a sufficient seperation margin from the 1st critical speed, seal wear due to long operation may cause a sudden increase in vibration amplitude by resonance shift and reduce seal damping capability.

• 한국유체기계학회 논문집
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• 제14권5호
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• pp.31-38
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• 2011

Optimization using a hybrid multi-objective evolutionary algorithm coupled with response surface approximation has been performed to improve the performance of a transonic axial compressor with circumferential casing grooves. In order to optimize the operating stability and peak adiabatic efficiency of the compressor with circumferential casing grooves, tip clearance, angle distribution at blade tip and the depth of the circumferential casing grooves are selected as design variables. Three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model are discretized by finite volume approximations. The trade-off between two objectives with the interaction of blade and casing treatment is determined and discussed with respect to the representative clusters in the Pareto-optimal solutions compared to the axial compressor without the casing treatment.

• KSTLE International Journal
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• 제4권1호
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• pp.1-7
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• 2003

A turbo pump unit provides high pressure oxygen and fuel in a space shuttle main engine (SSME). This paper focused on rotordynamics, investigating its characteristics based on a numerical simulation of turbo pump finite element model. Speeds up to 50,000 rpm are considered, as well as the special problems related to elastic-ring, seal hydrodynamic force, shroud force and clearance-excitation farce. The rotordynamic prediction shows that the elastic-ring which is inserted between the casing and the outer race of ball bearing allows far an acceptable separate margin of first critical speed. Additionally, the results show that the floating ring seal, which have a peculiar ring, adds substantial stiffness and damping to the system as well as exhibits superior performance in terms of rotordynamic stability of system compared to the plain seal.

• 한국항공운항학회지
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• 제15권3호
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• pp.70-76
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• 2007

The benefits for using reduced takeoff thrust are many, ranging from lower maintenance and operating costs to improved engine and dispatch reliabilities. Some pilots, however, are apprehensive about using reduced thrust. They are particularly reluctant to use the maximum permissible level of reduced thrust. Two common arguments are (1)If reduced thrust is used, then the airplane will not be able to clear the obstacles if an engine fails during takeoff, and (2)If the maximum allowable assumed temperature is used, then there will be no stopping margin left if the takeoff is aborted. There is the notion that using reduced thrust sacrifices safety. The intent of this discussion is to: (1)Show that reduced thrust performance meets all regulatory requirements (2)Show that the Assumed Temperature method includes inherent extra performance margins (3)Show how to maximize performance margins while maximizing thrust reduction.