• 대한기계학회논문집B
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• 제30권6호
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• pp.505-513
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• 2006

The pressure drop characteristics in a rotating two-pass duct with rib turbulators are investigated in the present study. Three ducts of different aspect ratios (W/H=0.5, 1.0 and 2.0) are employed with a fixed hydraulic diameter ($D_h$) of 26.7 mm. $90^{\circ}$-rib turbulators with $1.5mm{\times}1.5mm$ cross-section are attached on the leading and trailing surfaces. The pitch-to-rib height ratio (p/e) is 1.0. The distance between the tip of the divider and the outer wall of the duct is 1.0 W. The thickness of divider wall is 6.0 mm o. 0.225 $D_h$. The Reynolds number (Re) based on the hydraulic diameter is kept constant at 10,000 and the .elation number (Ro) is varied from 0.0 to 0.2. As duct aspect ratio increases, high friction factor ratios show in overall regions. The reason is that the rib height-to-duct height ratio (e/H) increases, but the divider wall thickness-to-duct width ($t_d/W$) decreases. The rotation of duct produces pressure drop discrepancy between the leading and trailing surfaces. However, the pressure drop discrepancy of the high duct aspect ratio (AR=2.0) is smaller than that of the low duct aspect ratio (AR=0.5) due to the decrement of duct hight (H).

• 대한기계학회논문집B
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• 제26권1호
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• pp.159-169
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• 2002

The present study investigates in detail the combined effects of the Coriolis and centrifugal farce on the development of laminar flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a rotating curved region, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal farce due to the curvature of U-bend. When the values of Rossby number and curvature ratio are large, the flow field in a rotating U-bend can be represented by two dimensionless parameters ; the Dean number K$\_$LC/=Re/√λ and a body ratio F=λ/Po. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards, the directions of the two secondary flows are the same. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct with a larger f7c. On the other hand, in case of negative rotation, where two farces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces.

• 한국유체기계학회 논문집
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• 제13권5호
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• pp.43-53
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• 2010

This study investigates a design optimization of a rotating two-pass rectangular cooling channel with staggered arrays of pin-fins. The radial basis neural network method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The ratio of the diameter to height of the pin-fins and the ratio of the streamwise spacing between the pin-fins to height of the pin-fin are selected as design variables. The optimization problem has been defined as a minimization of the objective function, which is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Results are presented for streamlines, velocity vector fields, and contours of Nusselt numbers, friction coefficients, and turbulent kinetic energy. These results show how fluid flow in a two-pass square cooling channel evolves a converted secondary flows due to Coriolis force, staggered arrays of pin-fins, and a $180^{\circ}$ turn region. These results describe how the fluid flow affects surface heat transfer. The Coriolis force induces heat transfer discrepancy between leading and trailing surfaces, having higher Nusselt number on the leading surface in the second pass while having lower Nusselt number on the trailing surface. Dean vortices generated in $180^{\circ}$ turn region augment heat transfer in the turning region and in the upstream region of the second pass. As the result of optimization, in comparison with the reference geometry, thermal performance of the optimum geometry shows the improvement by 30.5%. Through the optimization, the diameter of pin-fin increased by 14.9% and the streamwise distance between pin-fins increased by 32.1%. And, the value of objective function decreased by 18.1%.

• 대한기계학회논문집B
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• 제28권4호
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• pp.441-448
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• 2004

A numerical study was conducted to show the effect of aspect ratio on the analogy of the developing laminar flows between in orthogonally rotating straight duct and in a stationary curved duct of rectangular cross-section. In order. to clarify the similarity of two nows, dimensionless parameters (equation omitted) and Rossby Ro= $w_{m}$$\Omega$ $d_{h}$, in a rotating straight duct were used as a set corresponding to Dean number, (equation omitted), and curvature ratio, λ=R/ $d_{h}$, in a stationary curved duct. Four. different aspect ratios A=0.25, 0.5, 2 and 4 were considered. Under the condition that the magnitudes of Ro and λ were large enough to satisfy the 'asymptotic invariance property' and the aspect ratio was larger than 1, there were strong quantitative similarities between the two flows such as flow patterns, friction factors, and maximum axial velocity magnitudes fur the same values of $K_{LR}$ and $K_{LC}$ . On the other hand, as the aspect ratio decreased below 1 (A=0.25 and 0.5), the difference of the secondary flow intensity between these two flows was enhanced and therefore the analogy of two flows was not so evident as that of the larger aspect ratio (A=2 and 4). 4).nd 4).

• 대한기계학회논문집B
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• 제41권3호
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• pp.161-169
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• 2017

터빈 블레이드의 내부냉각 설계 강화를 위해 설치된 경사요철과 가이드 베인에 대한 연구를 진행하였다. 채널의 입구로 들어오는 공기와 요철이 만나는 각도를 기준으로, 서로 상반된 두 가지 요철배열을 전연면과 후연면에 평행하게 배치하였다. 채널의 종횡비(AR)는 5:1이고, 요철의 각도는 $60^{\circ}$, 요철의 높이와 요철간 간격 비($e/D_h$)는 0.075이다. 레이놀즈 수는 10,000으로 고정하였다. 요철배열에 따른 2차 유동과 딘 와류의 상호작용이 곡관부와 전체 채널의 열전달 결과와 유동특성에 어떠한 영향을 미치는지 확인할 수 있었다. 결론적으로 첫 번째 유로의 요철배열이 팁 면의 열전달 분포에 지배적인 요인이며, 곡관부에서 유동의 분포에도 영향을 미쳤다. 또한 U자 형상 가이드 베인을 사용하였을 때 모든 요철에서 팁 면의 열전달 값이 상승하였으며, 특히 공기와 요철의 충돌각도가 양의각도일 때 가장 높은 냉각성능계수를 보였다.

• Journal of Advanced Research in Ocean Engineering
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• 제1권3호
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• pp.157-167
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• 2015

In order to provide simple and accurate wave theory in design of offshore structure, an analytical approximation is introduced in this paper. The solution is limited to flat bottom having a constant water depth. Water is considered as inviscid, incompressible and irrotational. The solution satisfies the continuity equation, bottom boundary condition and non-linear kinematic free surface boundary condition exactly. Error for dynamic condition is quite small. The solution is suitable in description of breaking waves. The solution is presented with closed form and dispersion relation is also presented with closed form. In the last century, there have been two main approaches to the nonlinear problems. One of these is perturbation method. Stokes wave and Cnoidal wave are based on the method. The other is numerical method. Dean's stream function theory is based on the method. In this paper, power series method was considered. The power series method can be applied to certain nonlinear differential equations (initial value problems). The series coefficients are specified by a nonlinear recurrence inherited from the differential equation. Because the non-linear wave problem is a boundary value problem, the power series method cannot be applied to the problem in general. But finite number of coefficients is necessary to describe the wave profile, truncated power series is enough. Therefore the power series method can be applied to the problem. In this case, the series coefficients are specified by a set of equations instead of recurrence. By using the set of equations, the nonlinear wave problem has been solved in this paper.

• 대한기계학회논문집B
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• 제24권5호
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• pp.699-708
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• 2000

To make compact evaporator, experiments that show characteristics of evaporating heat transfer and pressure drop in the helically coiled small diameter tube were taken in this research. The experiments were performed with HCFC-22 in the helically coiled small diameter tube; inner diameter=1.0(mm), tube length=2.0(m), and curvature diameter=31, 34, 46.2(mm). The experiments were also carried out with the following test conditions; saturation pressure=0.588(MPa), mass velocity=$150{\sim}500(kg/m^2s)$, and heat flux=$1{\sim}5(kW/m^2)$. The experiment results are that the empirical correlation to predict heat transfer coefficient for single phase flow in helically coiled small diameter tube was obtained. It was found that dry-out is occurred at low-quality region for evaporation heat transfer because of breaking of annular liquid film. The friction factor of single phase flow of helically coiled tube was agreed with Prandtl's correlation. Finally, It was proposed for correlation that can precisely predict the friction factor of two phase flow of helically coiled tube.

• Journal of Forest and Environmental Science
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• 제37권3호
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• pp.243-250
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• 2021

Information on butterflies in the Niger Delta Region is relatively scanty because monitoring of their activities and distribution has not been fully documented and these are paramount to establish their conservation protocols. The study therefore aimed at evaluating the species richness distribution pattern, and relative abundance of butterflies in the University of Port Harcourt. The University Park was purposively selected for this study. The park was stratified into three different habitat types (secondary forest, farmland, and residential/garden). A sampling of each stratum was done three times; twice in the morning between 8:00 am and 12:00 pm as well as once in the evening between 4:00 pm and 6:00 pm along a 100 m line transects for 16 months (May 2017-August 2018). Data collected were analyzed for species diversity indices, evenness, and similarity index. A total of 1,932 individual butterflies belonging to 28 species, 18 genera, and five 5 families were identified in the study area. Species diversity and evenness were higher on farmland (1-D=0.909; H'=2.615; E=0.833), and least in the residential area/gardens (1-D=0.744; H'=1.975; E=0.659). The family Nymphalidae (39.0%) had the highest number of species occurrence while Hesperidae (0.4%) had the lowest composition. Anthene larydas (24.12%) had the highest relative abundance in the entire study area, followed by Acraea serena (17.49%). The study, therefore, recommends continuous monitoring of butterfly species diversity and composition also in other regions.

• International Journal of Computer Science & Network Security
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• 제22권12호
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• pp.153-159
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• 2022

The article discusses the use of smart technologies in the training of future specialists. Today, learning using smart technologies is becoming a new educational standard, where information is presented in a logical sequence, computer training systems have powerful functions for the educational process. The functions of smart technologies are highlighted. It is noted that smart technologies are successfully used in the field of education and professional training. The concept of "smart education" is characterized. Smart education is an educational paradigm that underlies a new type of education system. The implementation of the smart education paradigm is aimed at the process of obtaining competencies and competencies for flexible and adapted interaction with the social, economic and technological environment. Smart education should ensure that the benefits of the global information society can be used to meet educational needs and interests. A special place is occupied by computer-based educational multimedia systems that allow you to deepen your knowledge, reduce the duration of training, and increase the number of students per teacher. The main principles of smart education are highlighted. Improving the efficiency of training in a modern higher education institution is impossible without the introduction of smart technologies in the organization of the educational process.

• Clinics in Shoulder and Elbow
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• 제26권4호
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• pp.351-356
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• 2023

Background: Total elbow arthroplasty (TEA) is uncommon, but growing in incidence. Traditionally an inpatient operation, a growing number are performed outpatient, consistent with general trends in orthopedic surgery. The aim of this study was to compare TEA outcomes between inpatient and outpatient surgical settings. Secondarily, we sought to identify patient characteristics that predict the operative setting. Methods: Patient data were collected from the American College of Surgeons National Quality Improvement Program. Preoperative variables, including patient demographics and comorbidities, were recorded, and baseline differences were assessed via multivariate regression to predict operative setting. Multivariate regression was also used to compare postoperative complications within 30 days. Results: A total of 468 patients, 303 inpatient and 165 outpatient procedures, were identified for inclusion. Hypoalbuminemia (odds ratio [OR], 2.5; P=0.029), history of chronic obstructive pulmonary disorder or pneumonia (OR, 2.4; P=0.029), and diabetes mellitus (OR, 2.5; P=0.001) were significantly associated with inpatient TEA, as were greater odds of any complication (OR, 4.1; P<0.001) or adverse discharge (OR, 4.5; P<0.001) and decreased odds of reoperation (OR, 0.4; P=0.037). Conclusions: Patients undergoing inpatient TEA are generally more comorbid, and inpatient surgery is associated with greater odds of complications and adverse discharge. However, we found higher rates of reoperation in outpatient TEA. Our findings suggest outpatient TEA is safe, although patients with a higher comorbidity burden may require inpatient surgery. Level of evidence: III.