공동이 있는 수직 분사 초음속 연소기 내의 불안정 연소유동 해석 (Numerical Analysis of Unstable Combustion Flows in Normal Injection Supersonic Combustor with a Cavity)
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- 한국추진공학회:학술대회논문집
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- 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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- pp.91-93
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- 2003
A comprehensive numerical study is carried out to investigate for the understanding of the flow evolution and flame development in a supersonic combustor with normal injection of ncumally injecting hydrogen in airsupersonic flows. The formulation treats the complete conservation equations of mass, momentum, energy, and species concentration for a multi-component chemically reacting system. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations and detailed chemistry of H2-Air is considered. It also accommodates a finite-rate chemical kinetics mechanism of hydrogen-air combustion GRI-Mech. 2.11[1], which consists of nine species and twenty-five reaction steps. Turbulence closure is achieved by means of a k-two-equation model (2). The governing equations are spatially discretized using a finite-volume approach, and temporally integrated by means of a second-order accurate implicit scheme (3-5).The supersonic combustor consists of a flat channel of 10 cm height and a fuel-injection slit of 0.1 cm width located at 10 cm downstream of the inlet. A cavity of 5 cm height and 20 cm width is installed at 15 cm downstream of the injection slit. A total of 936160 grids are used for the main-combustor flow passage, and 159161 grids for the cavity. The grids are clustered in the flow direction near the fuel injector and cavity, as well as in the vertical direction near the bottom wall. The no-slip and adiabatic conditions are assumed throughout the entire wall boundary. As a specific example, the inflow Mach number is assumed to be 3, and the temperature and pressure are 600 K and 0.1 MPa, respectively. Gaseous hydrogen at a temperature of 151.5 K is injected normal to the wall from a choked injector.A series of calculations were carried out by varying the fuel injection pressure from 0.5 to 1.5MPa. This amounts to changing the fuel mass flow rate or the overall equivalence ratio for different operating regimes. Figure 1 shows the instantaneous temperature fields in the supersonic combustor at four different conditions. The dark blue region represents the hot burned gases. At the fuel injection pressure of 0.5 MPa, the flame is stably anchored, but the flow field exhibits a high-amplitude oscillation. At the fuel injection pressure of 1.0 MPa, the Mach reflection occurs ahead of the injector. The interaction between the incoming air and the injection flow becomes much more complex, and the fuel/air mixing is strongly enhanced. The Mach reflection oscillates and results in a strong fluctuation in the combustor wall pressure. At the fuel injection pressure of 1.5MPa, the flow inside the combustor becomes nearly choked and the Mach reflection is displaced forward. The leading shock wave moves slowly toward the inlet, and eventually causes the combustor-upstart due to the thermal choking. The cavity appears to play a secondary role in driving the flow unsteadiness, in spite of its influence on the fuel/air mixing and flame evolution. Further investigation is necessary on this issue. The present study features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the previous works. In particular, the oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is not related to the cavity, but rather to the intrinsic unsteadiness in the flowfield, as also shown experimentally by Ben-Yakar et al. [6], The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The work appears to be the first of its kind in the numerical study of combustion oscillations in a supersonic combustor, although a similar phenomenon was previously reported experimentally. A more comprehensive discussion will be given in the final paper presented at the colloquium.
목적: 이 연구는 맞벌이 가정의 부친의 육아참가 발생과정을 인과관계모델로 구축하여 이 모델에 대한 데이터로의 적합성에 대해 검토하는 것을 목적으로 하였다. 방법: 조사대상은 I 현 A,B시, II현 C시의 어린이집 21곳과 유치원 4곳을 이용하는 2,006세대(A시:499세대, B시:1113세대, C시:98세대)의 부친으로 하였다. 조사내용은 부친의 연령, 학력, 자녀수, 막내자녀나이, 부모역할관, 1일 노동시간, 귀가시간, 육아참가로 구성하였다. 결과: 부친의 육아참가 발생과정 모델의 데이터로의 적합성에 대해 검토한 결과, 적합도 지표는 CFI=0.912, RMSEA=0.082였다. 경로계수를 살펴보면, 막내자녀나이에서 긍정적 부모역할관으로 향하는 경로계수는 0.08, 긍정적 부모역할관에서 육아참가로 향하는 경로계수는 0.19로 통계학적으로 유의하였다. 또한 저해요인으로서 상정한 귀가시간과 1일 노동시간은 부친의 긍정적/부정적 부모역할관으로부터 영향을 받지 않고, 육아참가에 직접효과를 나타내었다. 이때, 귀 시간에서 육아참가로 향하는 경로계수는 -0.43, 노동시간에서 육아참가로 향하는 경로계수는 -0.13, 귀가시간과 노동시간 간의 상관계수는 0.80이었다. 결론: 이상의 결과를 통해 본 연구에서 제기한 모델의 타당성을 증명하였고, 부친의 육아참가 발생 매커니즘에 관한 기초자료로 활용될 수 있음을 시사한다.
위성에서 보다 미세한 공간 분해능으로 신뢰할 수 있는 지상 강우 관측은 도시 수문학적 및 미시적 농업 수요에 필수적이다. 전통적으로 "톱다운" 접근 방식 기반 위성 강우 산출물이 널리 사용되고 있지만 공간 분해능에 한계가 있다. 본 연구는 C-밴드 SAR Sentinel-1 위성 데이터(SM2RAIN-S1)에 적용되는 매개 변수화된 SM2RAIN 모델인 강우 추정을 위한 새로운 "상향식" 접근 방식의 가능성을 평가하여 중부지방에 대한 높은 공간 분해능 지상 강우 추정치(0.01° 그리드/6일)를 생성하는 것을 목표로 한다. 그것의 성능은 중부지방 두 개의 다른 하위 지역, 즉 혼합 산림 중심, 중간 하위 지역, 그리고 경작 중심, 서해안 하위 지역의 1년 기간 동안 기존의 재분석 프로덕트와 우량계 네트워크의 각각의 강우 데이터를 사용하여 공간 및 시간적 가변성에 대해 평가되었다. 평가결과에 따르면 SM2RAIN-S1 프로덕트는 중부지방의 일반적인 강우 패턴을 포착할 수 있고, 서로 다른 토지 피복으로 지역 규모에서 공간 분해능 강우량 측정 가능성을 보유할 수 있으며, 강우량 관측치에 대한 편중된 강우량 추정치가 제공되었다. 또한 SM2RAIN-S1 강우량은 피어슨의 상관 계수(R = 0.69)를 고려할 때 혼합림에서 더 우수했으며, 이는 혼합림에서 토양 수분과 강우의 시간 역학을 포착하는 데 6일 SM2RAIN-S1 데이터의 적합성을 암시했다. 그러나, RMSE와 바이어스 측면에서, 혼합림보다는 경작지의 SM2RAIN-S1 강우 생성물에서 더 나은 성능을 얻었으며, 이는 높은 증발증산 손실(특히 혼합림)에 의해 유도된 더 큰 오류를 SM2RAIN의 추가 개선에 포함해야 한다는 것을 나타낸다.
This study investigates when and how disagreements in online customer ratings prompt more favorable product evaluations. Among the three metrics of volume, valence, and variance that feature in the research on online customer ratings, volume and valence have exhibited consistently positive patterns in their effects on product sales or evaluations (e.g., Dellarocas, Zhang, and Awad 2007; Liu 2006). Ratings variance, or the degree of disagreement among reviewers, however, has shown rather mixed results, with some studies reporting positive effects on product sales (e.g., Clement, Proppe, and Rott 2007) while others finding negative effects on product evaluations (e.g., Zhu and Zhang 2010). This study aims to resolve these contradictory findings by introducing preference heterogeneity as a possible moderator and causal attribution as a mediator to account for the moderating effect. The main proposition of this study is that when preference heterogeneity is perceived as high, a disagreement in ratings is attributed more to reviewers' different preferences than to unreliable product quality, which in turn prompts better quality evaluations of a product. Because disagreements mostly result from differences in reviewers' tastes or the low reliability of a product's quality (Mizerski 1982; Sen and Lerman 2007), a greater level of attribution to reviewer tastes can mitigate the negative effect of disagreement on product evaluations. Specifically, if consumers infer that reviewers' heterogeneous preferences result in subjectively different experiences and thereby highly diverse ratings, they would not disregard the overall quality of a product. However, if consumers infer that reviewers' preferences are quite homogeneous and thus the low reliability of the product quality contributes to such disagreements, they would discount the overall product quality. Therefore, consumers would respond more favorably to disagreements in ratings when preference heterogeneity is perceived as high rather than low. This study furthermore extends this prediction to the various levels of average ratings. The heuristicsystematic processing model so far indicates that the engagement in effortful systematic processing occurs only when sufficient motivation is present (Hann et al. 2007; Maheswaran and Chaiken 1991; Martin and Davies 1998). One of the key factors affecting this motivation is the aspiration level of the decision maker. Only under conditions that meet or exceed his aspiration level does he tend to engage in systematic processing (Patzelt and Shepherd 2008; Stephanous and Sage 1987). Therefore, systematic causal attribution processing regarding ratings variance is likely more activated when the average rating is high enough to meet the aspiration level than when it is too low to meet it. Considering that the interaction between ratings variance and preference heterogeneity occurs through the mediation of causal attribution, this greater activation of causal attribution in high versus low average ratings would lead to more pronounced interaction between ratings variance and preference heterogeneity in high versus low average ratings. Overall, this study proposes that the interaction between ratings variance and preference heterogeneity is more pronounced when the average rating is high as compared to when it is low. Two laboratory studies lend support to these predictions. Study 1 reveals that participants exposed to a high-preference heterogeneity book title (i.e., a novel) attributed disagreement in ratings more to reviewers' tastes, and thereby more favorably evaluated books with such ratings, compared to those exposed to a low-preference heterogeneity title (i.e., an English listening practice book). Study 2 then extended these findings to the various levels of average ratings and found that this greater preference for disagreement options under high preference heterogeneity is more pronounced when the average rating is high compared to when it is low. This study makes an important theoretical contribution to the online customer ratings literature by showing that preference heterogeneity serves as a key moderator of the effect of ratings variance on product evaluations and that causal attribution acts as a mediator of this moderation effect. A more comprehensive picture of the interplay among ratings variance, preference heterogeneity, and average ratings is also provided by revealing that the interaction between ratings variance and preference heterogeneity varies as a function of the average rating. In addition, this work provides some significant managerial implications for marketers in terms of how they manage word of mouth. Because a lack of consensus creates some uncertainty and anxiety over the given information, consumers experience a psychological burden regarding their choice of a product when ratings show disagreement. The results of this study offer a way to address this problem. By explicitly clarifying that there are many more differences in tastes among reviewers than expected, marketers can allow consumers to speculate that differing tastes of reviewers rather than an uncertain or poor product quality contribute to such conflicts in ratings. Thus, when fierce disagreements are observed in the WOM arena, marketers are advised to communicate to consumers that diverse, rather than uniform, tastes govern reviews and evaluations of products.
The wall shear stress in the vicinity of end-to end anastomoses under steady flow conditions was measured using a flush-mounted hot-film anemometer(FMHFA) probe. The experimental measurements were in good agreement with numerical results except in flow with low Reynolds numbers. The wall shear stress increased proximal to the anastomosis in flow from the Penrose tubing (simulating an artery) to the PTFE: graft. In flow from the PTFE graft to the Penrose tubing, low wall shear stress was observed distal to the anastomosis. Abnormal distributions of wall shear stress in the vicinity of the anastomosis, resulting from the compliance mismatch between the graft and the host artery, might be an important factor of ANFH formation and the graft failure. The present study suggests a correlation between regions of the low wall shear stress and the development of anastomotic neointimal fibrous hyperplasia(ANPH) in end-to-end anastomoses. 30523 T00401030523 ^x Air pressure decay(APD) rate and ultrafiltration rate(UFR) tests were performed on new and saline rinsed dialyzers as well as those roused in patients several times. C-DAK 4000 (Cordis Dow) and CF IS-11 (Baxter Travenol) reused dialyzers obtained from the dialysis clinic were used in the present study. The new dialyzers exhibited a relatively flat APD, whereas saline rinsed and reused dialyzers showed considerable amount of decay. C-DAH dialyzers had a larger APD(11.70
The wall shear stress in the vicinity of end-to end anastomoses under steady flow conditions was measured using a flush-mounted hot-film anemometer(FMHFA) probe. The experimental measurements were in good agreement with numerical results except in flow with low Reynolds numbers. The wall shear stress increased proximal to the anastomosis in flow from the Penrose tubing (simulating an artery) to the PTFE: graft. In flow from the PTFE graft to the Penrose tubing, low wall shear stress was observed distal to the anastomosis. Abnormal distributions of wall shear stress in the vicinity of the anastomosis, resulting from the compliance mismatch between the graft and the host artery, might be an important factor of ANFH formation and the graft failure. The present study suggests a correlation between regions of the low wall shear stress and the development of anastomotic neointimal fibrous hyperplasia(ANPH) in end-to-end anastomoses. 30523 T00401030523 ^x Air pressure decay(APD) rate and ultrafiltration rate(UFR) tests were performed on new and saline rinsed dialyzers as well as those roused in patients several times. C-DAK 4000 (Cordis Dow) and CF IS-11 (Baxter Travenol) reused dialyzers obtained from the dialysis clinic were used in the present study. The new dialyzers exhibited a relatively flat APD, whereas saline rinsed and reused dialyzers showed considerable amount of decay. C-DAH dialyzers had a larger APD(11.70
HadGEM2-CC 모델에서의
본 연구에서는 미 국립대기연구소(NCAR)의 열권-이온권 전기역학적 대순환 모델(TIEGCM)을 이용하여 행성간 자기장(IMF)의 방향과 세기 그리고 고도에 따라 여름철 남반구 고위도 하부 열권의 바람에 작용하는 운동량 강제력을 정량적으로 구하였다. 그리고 이들을 서로 비교 분석함으로써 IMF 조건과 고도에 따른 고위도 하부 열권의 풍계(wind system)를 유지시켜주는 주된 물리적인 과정을 살펴보았다. 고위도 하부 열권(<180km)에서 양(
대동맥류 질환에 사용되는 스텐트그라프트의 체외실험을 위한 대동맥류 혈류 팬텀의 유효성과 실현가능성에 대해 평가하고자 한다. 팬텀은 인체의 혈류 조건과 유사한 상황을 재현할 수 있도록 심장부분과 대동맥류 부분으로 구성되었다. 심장부분은 고압력 수중펌프와 솔레노이드 밸브를 사용하여 심장의 대동맥 혈류를 재현하였고, 대동맥류 부분은 지점토를 사용하여 동맥류 모양을 재현하고 그 틀을 투명 실리콘으로 틀을 떠내는 방법으로 제작하였다. 두부분은 실리콘 관으로 연결하였다. 제작된 팬텀에서 밸브의 개폐 시간에 따른 압력(수축기/이완기) 변화를 측정하였으며, 스텐트그라프삽입술 전, 후의 압력변화를 측정하였으며, 통계적 유의성을 알아보았다. 밸브의 개폐 시간에 따른 압력 변화는 통계적으로 유의한 결과를 보였다(P<0.05). 0.5회/초의 개폐조건에서는 팬텀의 대동맥 근위부, 대동맥류, 원위부의 압력은 각각