• Wind and Structures
• /
• 제34권1호
• /
• pp.137-149
• /
• 2022

In this paper, the fluctuating lift and drag forces on 5:1 rectangular cylinders with two different geometric scales in three turbulent flow-fields are investigated. The study is particularly focused on understanding the influence of the ratio of turbulence integral length scale to structure characteristic dimension (the length scale ratio). The results show that both fluctuating lift and drag forces are influenced by the length scale ratio. For the model with the larger length scale ratio, the corresponding fluctuating force coefficient is larger, while the spanwise correlation is weaker. However, the degree of influence of the length scale ratio on the two fluctuating forces are different. Compared to the fluctuating drag, the fluctuating lift is more sensitive to the variation of the length scale ratio. It is also found through spectral analysis that for the fluctuating lift, the change of length scale ratio mainly leads to the variation in the low frequency part of the loading, while the fluctuating drag generally follows the quasi-steady theory in the low frequency, and the slope of the drag spectrum at high frequencies changes with the length scale ratio. Then based on the experimental data, two empirical formulas considering the influence of length scale ratio are proposed for determining the lift and drag aerodynamic admittances of a 5:1 rectangular cylinder. Furthermore, a simple relationship is established to correlate the turbulence parameter with the fluctuating force coefficient, which could be used to predict the fluctuating force on a 5:1 rectangular cylinder under different parameter conditions.

• 한국추진공학회지
• /
• 제14권2호
• /
• pp.29-38
• /
• 2010

하이브리드 로켓을 위한 파라핀 왁스/LDPE 혼합 연료에 관한 실험적 연구를 수행하였다. 혼합 연료 의 성능 평가를 위해 혼합 연료의 다양한 연소 특성을 순수 파라핀, HTPB, HDPE, SP-1a 연료와 비교하였다. 순수 파라핀의 후퇴율은 HDPE에 비해 large-scale과 lab-scale 모터에서 각각 10.2, 9.8배 증가 하였다. Lab-scale 혼합 연료의 후퇴율은 HDPE에 비해 3.4배 증가하여 HTPB, HDPE 연료보다는 높은 후퇴율을 나타냈으나 순수 파라핀, SP-1a에 비해서는 낮은 후퇴율을 나타냈다. 혼합 연료의 특성속도와 비추력은 순수 파라핀, HTPB, HDPE 보다 높았고 SP-1a 연료와 대등하였다. 이로부터 혼합 연료가 효과적인 하이브리드 로켓 연료가 될 수 있음을 확인하였다.

• 한국진공학회지
• /
• 제7권s1호
• /
• pp.57-77
• /
• 1998

Heteroepitaxial $Y_2O_3$ films were grown on a Si(111) substrate by ionized cluster beam deposition(ICBD) in ultra high vacuum, and its qualities such as crystllitnity, film stress, and morphological characteristics were investigated using the various measurement methods. The crystallinity was investigated by x-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED). Interface crystallinity was also examined by Rutherford backscattering spectroscopy(RBS) channeling, transmission electron microscopy(TEM). The stress of the films was measured by RBS channeling and XRD. Surface and interface morphological characteristics were investigated by atomic force microscopy (AFM) and x-ray scattering method. Comparing the interface with the surface characteristics, we can conclude that many defects at the interface region were generated by interface reaction between the yttrium metal and SiO2 layer and by ion beam characteristic such as shallow implantation, so that they influenced the film qualities. The film quality was dominantly depended on the characteristic temperature range. In the temperature range from $500^{\circ}C$ to $600^{\circ}C$, the crystallinity was mainly improved and the surface roughness was drastically decreased. On the other hand, in the temperature range from $600^{\circ}C$ to $700^{\circ}C$, the compressive stress and film density were dominantly increased, and the island size was more decreased. Also the surface morphological shape was transformed from elliptical shape to triangular. The film stress existed dominantly at the interface region due to the defects generation.

• 간호행정학회지
• /
• 제2권1호
• /
• pp.125-139
• /
• 1996

Organizational commitment is characterized by a strong belief in and acceptance of the organization's goal and values ; a willingness to exert considerable effort on behalf of the organization ; a strong desire to maintain membership in the organization. The purpose of this study was to identify the variables which influence the organizational commitment and to test the relationship between the clinical nurses' organizational commitment and turnover intention. The subjects were 412 nurses who were working on general wards at three General Hospitals in Chounbuk. The data were collected by self-reporting questionnaire from Sept. 20 to Sept. 31, 1995. The instruments used in this study were Likert-type scale which were Organizational Commitment Scale by Mowday et al, and Turnover Intention Scale by Mobley et al. The questionnaire of organizational characteristics was made through reviewing literature. The data were analyzed by frequency, percentage, t-test, one-way ANOVA, Scheffe test, Pearson's correlation coefficient, and stepwise multiple regression with $SPSS-PC^+$ program. Major findings are as follows : 1. Mean scores for organizational commitment were 3.008 and turnover intention 3.167 on a 5 point scale. 2. Age and clinical experience were positively related to organizational commitment(r=.4806, p=.000; r=.4792, p=.000). 3. In the personal variables, hospital type(F=21.374, p=.000), education level(F=5.481, p=.001), position(F=30.867, P=.000), and marital status(t=-5.63, p=.000) of the nurses showed significant differences in organizational commitment. 4. The variables to the organizational characteristic were statistically significant in organizational commitment : formalization(r=.3458, p=.000), human-centered organizational characteristic(r=.4302, p=.000), performance- centered organizational characteristic(r=-.1502, p=.000), payment(r=.2234, p=.000), promotion(r=.2710, p=.000), benefit & service(r=.2325, p=.000), and resource inadequacy(r=-.2172, p=.000). 5. For the purpose of identifying the predicting variables in organizational commitment, stepwise multiple regression is conducted. The results show that age, human-centered organizational characteristic, formalization, hospital type, resource inadequacy, promotion, and benefit & service were significant variables and explained 46% of the variance. 6. Organizational commitment was significantly negatively correlated with turnover intention(r=-.6442, p=.000). As a result of stepwise multiple regression analysis, organizational commitment is the most powerful variable predicting turnover intention and explained 41.5% of the variance. In conclusion, this study shows that the higher the organizational commitment level, the lower the turnover intention. Therefore, for effective turnover management, it is important to improve the organizational commitment among clinical nurses. In order to enhance the organizational commitment by the clinical nurses, it will be useful to consider significant organizational characteristics variables identified in this study.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2008년도 제30회 춘계학술대회논문집
• /
• pp.149-152
• /
• 2008

30톤급 액체로켓엔진 실물형 연소기의 형상에 따른 연소특성속도에 대한 연구를 수행하였다. 본 연구에서 연소기의 형상은 연소기 헤드와 분리가 가능한 내열재 및 채널 냉각형 연소실(${\varepsilon}$=3.2), 그리고 일체형인 팽창비가 각각 3.5와 12인 재생냉각형 연소기이다. 연소압력은 약 53${\sim}$60 bar 그리고 추진제 유량은 약 89 kg/s이고, 적용된 분사기는 리세스수가 1.0인 동축 와류형이다. 설계점 연소시험에서 팽창비가 12인 일체형 재생냉각 방식의 연소기가 가장 큰 연소특성속도를 보였는데 이는 추진제인 케로신이 분무되기 전 챔버 냉각으로 인한 온도 상승에 따른 엔탈피의 증가 및 연소압력의 증가에 기인한 것이다.

• 자원환경지질
• /
• 제19권spc호
• /
• pp.113-119
• /
• 1986

A characteristic mineralogical zonal distribuion is observed in a large scale(whole ore- body) small scales(handy specimens). They show similar chemical variations: most of elements except CaO were supplied by hydrothermal fluids to form skarns. Garnets occuring in the pyroxene-garnet skarn have a wide range of chemical composition ranging from andradite to grossularite, while individual grains of the garnets also show a similar zonation of chemical composition varied between grossularite and andradite. Highly contained Mo-bearing scheelites are generally concentrated in the central part of the Sang- dong skarn orebody. Similarly, some large grains of scheelite show a nice zonation due to different contents of Mo, highly enriched in the core of the scheelite crystal. This geochemical similarity in the large scale and small scales suggests the Sangdong skarn formation was achieved under a certain chemical environment, and detailed studies on a small scale texture could be a clue to understand a whole ore deposit.

• 아동학회지
• /
• 제29권6호
• /
• pp.245-257
• /
• 2008

Subjects in this study on causal relationships among playfulness, interactive peer play, teacher-child relationships, and creative characteristics were 286 3- to 5-year-old children. Instruments were the Rating Scale for Creative Characteristic of Preschoolers (Lee et al., 2002), Children's Playfulness Scale (Bemett, 1990), Penn Interactive Peer Play Scale (Fantuzzo et al., 1995), and Student Teacher Relationship Scale (Pianta, 1991). Results showed : (1) significant relationships among social spontaneous, cognitive spontaneous and children's humor in sub-areas of children's playfulness, friendliness in sub-areas of teacher-child relationships, play interaction in sub-areas of interactive peer play and creative characteristics. (2) Children's creative characteristics directly influenced social spontaneous, cognitive spontaneous and children's humor in sub-areas of children's playfulness and of play interaction in sub-areas of interactive peer play.

• 한국정밀공학회지
• /
• 제9권3호
• /
• pp.122-131
• /
• 1992

In this paper an approximate solution method for the large-scale Traveling Salesman Problem (TSP) is presented. The method starts with the subdivision of the problem domain into a number of cluster by considering their geometric characteristic. Each cluster has a limited number of nodes so as to get a local solution. They are linked go give the least pathe which covers the whole domain and become TSPs solution with start-and end-node. The approximate local solution in each cluster are obtained based on geometrical properties of the cluster, and combined to give an overall approximate solution for the larte-scale TSP.

• 연구논문집
• /
• 통권26호
• /
• pp.51-56
• /
• 1996

In the case of a heat exchanger, scale is made in the tube by the chemical reactions of Ca and Mg ions contained in the water, and heat transfer rate is reduced because of increment of heat resistance in the pipe of the heat flow. Thus it brings to reduce the energy efficiency and to make environmental pollution by the use of chemicals for the prevention and removement of scale. In this paper, we discussed the design of electronic generator for ultrasonic scale preventor and analyzed the fundamental characteristic for ultrasonic transducer.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2008년도 춘계학술대회 논문집
• /
• pp.2011-2014
• /
• 2008

A linear induction motor for urban railway transit is accompanied with the end-effect and large air-gap comparing with a rotary induction motor. These cause amount of difference between simulation results and experiments. In order to figure out the difference, experiments based on a real-scale test bed are indispensable, however building a test-line and a test vehicle is so difficult that authors are going to make a small-scale model and simulate it for comparison. In this paper, A rotary-type small-scale model of a linear induction motor is designed. Thrust and normal force of the model have been analyzed with the variation of frequency and speed by using a Finite Element Method(FEM).