• Wind and Structures
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• 제37권2호
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• pp.163-178
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• 2023

The paper reviews and discusses the substantive changes to the ASCE 49-21 Standard, Wind Tunnel Testing for Buildings and Other Structures. The most significant changes are the requirements for wind field simulations that utilize (i) partial turbulence simulations, (ii) partial model simulations for the flow around building Appurtenances, along with requirements for determining wind loads on products that are used at multiple sites in various configurations. These modifications tend to have the effect of easing the precise scaling requirements for flow simulations because it is not generally possible to construct accurate models for small elements placed, for example, on large buildings at the scales typically available in boundary layer wind tunnels. Additional discussion is provided on changes to the Standard with respect to measurement accuracy and data acquisition parameters, such as duration of tests, which are also related to scaling requirements. Finally, research needs with respect to aerodynamic mechanisms are proposed, with the goal of improving the understanding of the role of turbulence on separated-reattaching flows on building surfaces in order to continue to improve the wind tunnel method for determining design wind loads.

• Wind and Structures
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• 제19권1호
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• pp.15-33
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• 2014

This paper describes partial turbulence simulation and validation of the aerodynamic pressures on building models for an open-jet small-scale 12-Fan Wall of Wind (WOW) facility against their counterparts in a boundary-layer wind tunnel. The wind characteristics pertained to the Atmospheric Boundary Layer (ABL) mean wind speed profile and turbulent fluctuations simulated in the facility. Both in the wind tunnel and the small-scale 12-Fan WOW these wind characteristics were produced by using spires and roughness elements. It is emphasized in the paper that proper spectral density parameterization is required to simulate turbulent fluctuations correctly. Partial turbulence considering only high frequency part of the turbulent fluctuations spectrum was simulated in the small-scale 12-Fan WOW. For the validation of aerodynamic pressures a series of tests were conducted in both wind tunnel and the small-scale 12-fan WOW facilities on low-rise buildings including two gable roof and two hip roof buildings with two different slopes. Testing was performed to investigate the mean and peak pressure coefficients at various locations on the roofs including near the corners, edges, ridge and hip lines. The pressure coefficients comparisons showed that open-jet testing facility flows with partial simulations of ABL spectrum are capable of inducing pressures on low-rise buildings that reasonably agree with their boundary-layer wind tunnel counterparts.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1435-1450
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• 2004

Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The end wall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the end wall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the end wall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suction-side corner are influenced most strongly by the high free-stream turbulence. In this study, the end wall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.

• 유통과학연구
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• 제20권5호
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• pp.1-11
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• 2022

Purpose: This study attemptsto investigate the moderating effects of environmental turbulence (ET) between learning orientation (LO) and SMEs' performance. Research design, data, and Methodology: To gain insights and provide implications for manufacturing SMEs in Pakistan, this study adopted simple random sampling to collect 379 valid responses. Data were collected through a self-administrative questionnaire from manufacturing SMEs owners/managers. Partial least squares of structural equation modeling have been used to test research hypotheses by using SmartPLS® 3.0 software. Results: The study's primary finding is that LO has a significantly positive effect on SMEs' performance and this relationship is strengthened under the moderating influence of environmental turbulence (ET). Conclusion: Environmental turbulence (ET) enables SMEs to focus on learning capability to get a more competitive advantage. Moreover, SMEs owner/managers ought to emphasize continuous learning that accentuates the capability to compete with environmental changes. Findings support notifying Pakistan's Small and Medium Enterprise Development Authority (SMEDA) in dealings with Manufacturing SMEs in terms of improving their internal capabilities. This research contributes to the literature as it provides a more detailed and in-depth explanation of distribution management-related issues faced by SMEs. This research carries a significant influence on literature and relevant Resource-based view and contingency theories.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.71-79
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• 1999

Numerical analysis on the characteristics of nitrogen oxides (NOx) formation in turbulent nonpremixed hydrogen-air flames was carried out. Lagrange IEM model and Assumed PDF model were applied to consider turbulence-chemistry interaction known to affect the production of NOx. Partial equilibrium assumption was used to predict nonequilibrium effect to which one-half power dependence between EINOx normalized by flame residence time and global strain rate is attributed. As a result. such one-half power dependence could be reproduced only by reaction model including $HO_{2}$and $H_{2}O_{2}$, which means its dependence on Damkohler number; nonequilibrium effect. This dependence was shown better in the region of higher global strain. Besides, the improvement of turbulence model is required to predict mean flow properties quantitatively in the radial direction.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.391-397
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• 2004

The performance characteristics of partial admission supersonic turbines are analyzed by using the commercial CFD program FLUENT6.0. The governing equations were discretized with Euler implicit method in time and 2nd-order upwind scheme of FVM in space. The k-$\varepsilon$ turbulence model was utilized to describe the turbulent flow field. In order to investigate the nozzle--rotor interactions and the effect of partial admission, the flows in supersonic turbine rotor cascades with a nozzle are computed. Extensive computations of partial admission supersonic turbines provide the shock structures and flow patterns in the nozzle and rotor. It is clearly shown that the nozzle flow is highly affected by the shocks or expansion waves propagated from the rotor leading edge. And the rotor flow is also affected by the shocks or wakes originated from the nozzle.

• 한국전자통신학회논문지
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• 제18권3호
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• pp.387-396
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• 2023

현재 기상관측에 사용되는 대표적인 장비는 기상탑과 윈드라이다가 사용되고 있다. 국제 규정에 의하면 기상탑은 단독 측정이 가능하나 윈드라이다 경우 40m 기상탑 혹은 풍력발전기 블레이드 최하단의 높이에 맞는 기상탑을 필수로 설치하고 측정데이타를 보정하여야 한다. 난류는 특성상 100m 이하의 고도에서 빈번하게 발생하며 기상탑 보다는 윈드라이다가 난류의 영향을 많이 받는다. 그럼에도 불구하고 기상탑에 대한 난류 강도는 국제 규정에 명시되어 있으나 윈드라이다 대해서는 별도로 명시하지 않고 있다. 본 연구는 동일한 조건에서 기상탑과 윈드라이다에서 측정된 데이터를 수집하고 불확도 및 난류 강도 비율을 분석한다. 데이터를 분석한 결과 난류 강도 비율이 3%를 초과하는 구간이 부분적으로 존재한다. 따라서 윈드라이다에 대한 난류강도 오차율을 국제 규정에 명시할 것을 제안한다.

• 한국음향학회지
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• 제33권6호
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• pp.358-365
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• 2014

선박용 프로펠러가 수중에서 빠른 속도로 회전할 때, 날개 표면의 국부적인 압력이 낮아짐에 따라 불가피하게 여러 형태의 공동이 발생한다. 이러한 공동현상은 근본적으로 날개 단면의 기하학적 형상 특성과 수동력학적 운용조건에 의해 결정되며, 결과적으로 선박 프로펠러에서 유기되는 수중방사소음은 공동의 발생특성과 직결된다고 할 수 있다. 따라서 저소음 프로펠러 설계를 위해서는 날개 단면의 형상에 따라 발생하는 공동과 그에 따른 소음특성을 이론 및 실험을 통해 정량적으로 평가할 수 있어야 한다. 본 연구에서는 저소음 프로펠러의 설계단계에서부터 적용이 가능한 부분공동성능 해석법 개발 및 날개단면 형상정보 도출을 목표로 선박용 프로펠러 날개 단면에서 발생하는 부분공동 다상 유동의 비점성 수치해석을 수행하였다. 또한 점성해석 상용프로그램인 FLUENT에서 제공하는 난류 및 공동 모델 조합에 따른 결과를 살펴보았으며, 점성 및 비점성 해석 결과를 비교, 평가 하였다.

• The Journal of Asian Finance, Economics and Business
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• 제8권12호
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• pp.529-540
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• 2021

This study proposes a model and attempts to illustrate the relationship between the frequency of dynamic capability utilization and marketing capabilities, and how market, technology, and competitor turbulence may affect these relationships. The findings suggest that in a highly turbulent environment, frequent use of sensing and integration capabilities may cause certain changes in the impact of marketing capabilities, and in a highly competitive environment, marketing capabilities are positively correlated with company performance. The sample consists of 212 enterprises of China with a three-year vertical data span. The partial least square program Smart-PLS was used for data analysis. The careful management of dynamic capabilities (i.e., relational, sensory, and inclusive) is required to address environmental conditions to achieve capacity alignment and ultimately enhance performance. Our findings demonstrate that relationship capabilities are valuable to the organization and might even help improve its sensing and integrating capabilities. In a highly competitive environment, marketing capabilities contribute the most to company performance. The more frequent the environmental turbulence, the higher the impact of integration capabilities on marketing capabilities. This situation necessitates the organization's usage of dynamic capabilities to modify its marketing approach effectively between stable and turbulent environments.

• Nuclear Engineering and Technology
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• 제39권1호
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• pp.43-50
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• 2007

A partial flow blockage in an assembly of a liquid metal reactor could result in a cooling deficiency of the core. To develop a partial blockage detection system, we have studied the changes of the temperature fluctuation characteristics in the upper plenum according to changes of the t10w blockage conditions in an assembly. We analyzed the temperature fluctuation in the upper plenum with the Large Eddy Simulation (LES) turbulence model in the CFX code and evaluated its statistical parameters. Based on the results of the statistical analyses, we developed a neural network model for detecting a partial flow blockage in an assembly. The neural network model can retrieve the size and the location of a flow blockage in an assembly from a change of the root mean square, the standard deviation, and the skewness in the temperature fluctuation data. The neural network model was found to be a possible alternative by which to identify a flow blockage in an assembly of a liquid metal reactor through learning and validating various flow blockage conditions.