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

• 한국전문물리치료학회지
• /
• 제15권3호
• /
• pp.1-7
• /
• 2008

Multi-sensory systems, including the visual, somatosensory, and vestibular ones, are involved in maintaining standing balance. The organization of these sensory systems is as important as the efficiency of each individual system in maintaining optimal balance. The purpose of the present experiment was to investigate the developmental changes in static standing balance and sensory organization under altered sensory conditions. This study involved 64 children (from 4 to 15 years of age) and 17 young adults. The children were divided into four age groups: 4~6, 7~9, 10~12, and 13~15 years. Static standing balance was assessed with the one-leg standing test under four different sensory conditions: the children stood on a firm surface with (1) eyes open or (2) closed, and they stood on a foam surface with eyes (3) open or (4) closed. In balancing ability, the age groups exhibited significant differences. The function of sensory organization for balance control was poorer for the children than for the young adults. The functional efficiency of the somatosensory system of the children aged 7~9 years was at the young adults' level, and the visual function of the children aged 10~12 years had also reached the young adults' level. However, the functional efficiency of the vestibular system of children was significantly lower than that of the young adults, even at the age of 15 years. This may indicate that sensory organization and standing balance are still developing after the age of 15 years.

• 산업진흥연구
• /
• 제8권4호
• /
• pp.257-266
• /
• 2023

이 연구는 중국 서부지역의 대학을 중심으로 진행되었으며, 2017년부터 2021년까지 12개 대학의 연구수준을 정적 효율성과 동적 효율성을 모두 고려하여 조사하였다. 정적 효율성은 데이터 포락 분석(DEA)을 사용하여 검사하였고, 동적 효율은 Malmquist 모델을 사용하여 분석하였다. 분석결과, 서부12개 대학의 과학연구 효율성은 일반적으로 높지 않았으며 '쌍일류' 건설의 맥락에서 대학의 과학연구 효율성은 증가하는 추세를 보이고 있으며, 과학연구 효율성의 원인으로 최근 몇 년 동안 효율성이 크게 증가하였다. 연구 활동의 TFP (Total Factor Productivity)는 기술진보지수의 영향을 받아 초기에 증가하다가 감소하다가 다시 증가하는 패턴을 보였다. 연구 결론은 서부 대학들의 과학연구 활동을 위해 자원을 합리적으로 배분하여 효과적인 과학연구 메커니즘을 갖추어서, 관리기준을 개선하여야 한다. 이에 과학혁신과 이에 상응하는 성과를 촉진하여, 궁극적으로 중국 서부의 과학기술 수준을 높일 수 있어야 하겠다.

• Steel and Composite Structures
• /
• 제21권2호
• /
• pp.323-342
• /
• 2016

To study the effect of collar-plate reinforcement on the static strength of tubular T-joints under axial loading, fundamental research work is carried out from both experimental test and finite element (FE) simulation. Through experimental tests on 7 collar-plate reinforced and 7 corresponding un-reinforced tubular T-joints under axial loading, the reinforcing efficiency is investigated. Thereafter, the static strengths of the above 14 models are analyzed by using FE method, and it is found that the numerical results agree reasonably well with the experimental data to prove the accuracy of the presented FE model. Additionally, a parametric study is conducted to analyze the effect of some geometrical parameters, i.e., the brace-to-chord diameter ratio ${\beta}$, the chord diameter-to-chord wall thickness ratio $2{\gamma}$, collar-plate thickness to chord wall thickness ratio ${\tau}_c$, and collar-plate length to brace diameter ratio $l_c/d_1$, on the static strength of a tubular T-joint. The parametric study shows that the static strength can be greatly improved by increasing the collar-plate thickness to chord wall thickness ratio ${\tau}_c$ and the collar-plate length to brace diameter ratio $l_c/d_1$. Based on the numerical results, parametric equations are obtained from curving fitting technique to estimate the static strength of a tubular T-joint with collar-plate reinforcement under axial loading, and the accuracy of these equations is also evaluated from error analysis.

• 한국콘텐츠학회논문지
• /
• 제20권10호
• /
• pp.496-509
• /
• 2020

본 연구는 최근 엔터테인먼트 산업의 핵심 분야로 각광받으며 향후 국가 경제의 새로운 성장 동력으로 주목을 받고 있는 게임산업 중 온라인 및 모바일 게임 기업 25곳을 대상으로 2014년부터 2018년까지 5년간의 효율성 분석을 진행하였다. 정태적 효율성 분석을 위해 DEA를, 동태적 효율성 분석을 위해 DEA-Window를 사용하였다. 투입 변수로 자산, 종업원 수, 비용을 선정하였으며 산출 변수로 영업이익과 매출을 선정하였다. 연구의 주요 결과로는 규모 효율성은 2014년을 제외하고 전체 평균이 0.85를 넘는 준수한 결과를 보였으나, 기술 효율성은 전체 기간 중 0.80을 넘은 연도가 없었다. 또한 기업 규모의 관점에서 상위 기업과 하위 기업의 효율성 차이가 큰 것으로 나타났으며, 효율성 평균의 추이는 2014년부터 2016년까지 상승하다가 2017년부터 하락하는 결과를 나타냈다.

• 대한기계학회논문집A
• /
• 제29권5호
• /
• pp.707-715
• /
• 2005

In this work, Scalar Passive code in Lattice Boltzmann Method is employed to simulate two-phase flow of low Reynolds number in a micro-channel. The mixing characteristics in a micro-channel is a function of Peclet number. The mixing length increases with the Peclet number. It is found that with the inclusion of static elements at the channel, rapid mixing of two liquids can be achieved, as shown by the results of computer simulations. The enhancement in mixing performance is thought to be caused by the generation of eddies and by lateral velocity component when the mixture flows past static elements. The results indicate that the size of static element has more effect on the mixing than the number of static element.

• 한국산업안전학회:학술대회논문집
• /
• 한국안전학회 2003년도 춘계 학술논문발표회 논문집
• /
• pp.508-513
• /
• 2003

The objective of this paper is to investigate the lining board's capacity by using the static loading test and fatigue test. Specimens that constitute the H & Channel type lining board are adopted. The test is to inspect the possibility of retrofit and efficiency, which is required to upgrade the structure's capacity and to examine the effects of the improvements of specimen by using structural analysis, stress analysis, static loading test and fatigue test, respectively. The accumulated test results of stress condition and deflection by bending will be used to analyze the relation between the cause of fatigue crack occurrence and the behavior of both structure system and the steel.

• KIEE International Transactions on Power Engineering
• /
• 제4A권3호
• /
• pp.141-145
• /
• 2004

FACTS devices, such as the Thyristor Controlled Series Compensator (TCSC) and Static Var Compensators (SVC), can help increase system load margin to improve static voltage stability. In power systems, because of the high cost and the effect value, the optimal placement for FACTS devices must be determined. This paper investigates the use of the series device (SVC) and the parallel device (TCSC) from the point of load margin to increase voltage stability. It considers the sensitivity of load margin to the line reactance and eigenvector of the collapse. The study has been carried out on the IEEE 14 Bus Test System to verify the validity and efficiency of the method. It reveals that incorporation of FACTS devices significantly enhance load margin as well as system stability.

• Current Optics and Photonics
• /
• 제8권4호
• /
• pp.375-381
• /
• 2024

In this report, we present the design, fabrication, and experiment of a static solar system for electric vehicle (EV) applications. The static concentration component is composed of compound parabolic concentrators (CPCs) couplings with multi-junction solar cells, where a flat silicon panel is added to the bottom of the CPV structure to maximize power generation. This design allows the system to collect both direct sunlight and diffused sunlight. The CPCs were fabricated with acrylic with a geometric concentration ratio of 4×. We built a prototype with a (3 × 3) cell array of CPCs with a thickness of 25 mm, which is as thin as conventional flat photovoltaic panels, and performed an outdoor experiment that showed that after six hours of operation, the system had an acceptance angle of approximately 43° and an average daily efficiency of 22.85%.

• Wind and Structures
• /
• 제8권6호
• /
• pp.443-454
• /
• 2005

Wind loading is very important, even dominant in some cases, to large-span single-layer reticulated shells. At present, usually equivalent static methods based on quasi-steady assumption, as the same as the wind-resistant design of low-rise buildings, are used in the structural design. However, it is not easy to estimate a suitable equivalent static wind load so that the effects of fluctuating component of wind on the structural behaviors, especially on structural stability, can be well considered. In this paper, the effects of fluctuating component of wind load on the stability of a single-layer reticulated spherical shell model are investigated based on wind pressure distribution measured simultaneously in the wind tunnel. Several methods used to estimate the equivalent static wind load distribution for equivalent static wind-resistant design are reviewed. A new simple method from the stability point of view is presented to estimate the most unfavorable wind load distribution considering the effects of fluctuating component on the stability of shells. Finally, with comparisive analyses using different methods, the efficiency of the presented method for wind-resistant analysis of single-layer reticulated shells is established.