• Solar Energy
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• v.15 no.1
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• pp.29-38
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• 1995

This paper concerns the study of a two-stage binary absorption cycle employing the refrigerant/absorbent combinations of $LiBr/H_2O$ and $NH_3/H_2O$. This cycle consists of coupling two single-effect absorption cycles so that the first stage absorber and condenser produces heating water to evaporate refrigerant in the evaporator of the second stage. The effect of operating variables such as evaporator temperature, condenser and absorber temperature, and generator temperature on the coefficient of performance and temperature lift have been studied for two-stage binary absorption heat pump systems. It is found that this cycle has a large temperature lift at $105^{\circ}C$ of optimum generator temperature to obtain $50^{\circ}C$ of condenser temperature.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.8 no.1
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• pp.83-95
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• 2000

Lift, drag, pitching moment, what we call longitudinal aerodynamic coefficient, effects airplanes directly, so the method to find the accurate result quickly is an important factor from the beginning of the aircraft design. There are different ways to find aerodynamic coefficient such as empirical methods, numerical analysis methods, wind tunnel tests, and finally through an actual flight tests, but choosing the best methods depends on the due date or the cost. The accuracy varies on each design level, but all this methods have relationship to complement and balance each other, so by combining proper methods, the best result can be obtained. At this paper, empirical methods and numerical analysis method were experimented, compared, and reviewed to find the availability of each method and by combining two methods accurate result was obtained. So, we applied this methods to predict the aerodynamic coefficient on cruise configuration aircraft, and was able to obtain more accurate result on the low speed longitudinal aerodynamic coefficient. Also by watching there result, we are able to predict the errors before the actual wind tunnel test.

• Journal of the Korean Professional Engineers Association
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• v.34 no.3
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• pp.64-67
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• 2001

In resent the weight of structure is heavier and bigger than before. Engineers use many heavy equipments to erect buildings and bridges. The heavy equipment is very useful to lift any weight. But most engineers do not know the impact of the weight when the equipment lifts the weight. In this study one researched into the impact of the weight in the crane work which lifts the weight in the construction site. Also along the number of pulley sheave the impact of the weight was researched. From the impact field test the impact coefficient of a single pulley sheave crane was 0.65 and the four pulley sheaves crane was 0.13. The result shows that the impact coefficient of a single pulley crane is more than 5 time of the impact coefficient of the four pulley sheaves crane and that engineers must consider the impact effect of the crane work in the construction site.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3080-3085
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• 2007

Shape optimization of the 3-dimensional WIG airfoil with 3.0-aspect ratio has been performed by using the multi-objective genetic algorithm. The WIG ship effectively floating above the surface by the ram effect and the virtual additional aspect ratio by a ground is one of next-generation and cost-effective transportations. Unlike the airplane flying out of the ground effect, a WIG ship has possibility to capsize because of unsatisfying the static stability. The WIG ship should satisfy aerodynamic properties as well as a static stability. They tend to strong contradict and it is difficult to satisfy aerodynamic properties and static stability simultaneously. It is inevitable that lift force has to scarify to obtain a static stability. Multi-objective optimization technique that the individual objectives are considered separately instead of weighting can overcome the conflict. Due to handling individual objectives, the optimum cannot be unique but a set of nondominated potential solutions: pareto optimum. There are three objectives; lift coefficient, lift-to-drag ratio and static stability. After a few evolutions, the non-dominated pareto individuals can be obtained. Pareto sets are all the set of possible and excellent solution across the design space. At any selections of the pareto set, these are no better solutions in all design space

• International Journal of Aeronautical and Space Sciences
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• v.18 no.3
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• pp.403-413
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• 2017

Dual-point aerodynamic design optimization is conducted for DLR-F6 wing-body-nacelle-pylon configuration adopting an efficient surface mesh movement method for complex junction geometries. A three-dimensional unstructured Euler solver and its discrete adjoint code are utilized for flow and sensitivity analysis, respectively. Considered design conditions are a low-lift condition and a cruise condition in a transonic regime. Design objective is to minimize drag and reduce shock strength at both flow conditions. Shape deformation is made by variation of the section shapes of inboard wing and pylon, nacelle vertical location and nacelle pitch angle. Hicks-Henne shape functions are employed for deformation of the section shapes of wing and pylon. By the design optimization, drag coefficients were remarkably reduced at both design conditions retaining specified lift coefficient and satisfying other constraints. Two-point design results show mixed features of the one-point design results at low-lift condition and cruise conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.1
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• pp.20-36
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• 2024

In this study, probabilistic models for the wave- and lifting forces were derived directly from long-term in-situ wave data embedding the Korean marine environment characteristics varying from sea to sea based on the Three-Parameter Weibull distribution. Korean marine environment characteristics varying from sea to sea carved out their presence on the probability coefficients of probabilistic models for wave- and lifting forces. Energetic wave conditions along the southern coast of Korea distinguish themselves from the others with a relatively large scale coefficient, small location coefficient, and shape coefficient around 1.3. On the other hand, mild marine environment along the western coast has a small variability, leading to small scale-coefficient, large location coefficient and shape coefficient around 2.0. In the sea off Mokpo, near the boundary between the South- and West Seas, marine environment was characterized by small scale-coefficient, large location coefficient, and shape coefficient around 1.2, implying that marine environments characteristics of the South-and West Sea coexist in the sea off Mokpo.

• Wind and Structures
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• v.23 no.5
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• pp.385-403
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• 2016

The across-wind dynamic loads on L-shaped tall buildings with various geometric dimensions were investigated through a series of wind tunnel testing. The lift coefficients, power spectral densities and vertical correlation coefficients of the across-wind loads were analyzed and discussed in details. Taking the side ratio and terrain category as key variables, empirical formulas for estimating the across-wind dynamic loads on L-shaped tall buildings were proposed on the basis of the wind tunnel testing results. Comparisons between the predictions by the empirical formulas and the wind tunnel test results were made to verify the accuracy and applicability of the proposed formulas. Moreover, a simplified procedure to evaluate the across-wind dynamic loads on L-shaped tall buildings was derived from the proposed formulas. This study aims to provide a simple and reliable way for the estimation of across-wind dynamic loads on L-shaped tall buildings.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.3
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• pp.26-33
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• 1998

An experimental study has been conducted for the three-dimensional in-cylinder swirl flow under steady conditions. Velocity fields are measured by using an LDV at various valve lifts. Effects of geometry of inlet ports on swirl flows are investigated for standard and helical ports. Swirl distributions evaluated from velocity measurements are compared with those obtained from an impulse torque swirl meter. Results show that the helical port generates more intensive swirl than the standard one but it causes red- uction in air flow coefficient. At the lower valve lift, no significant difference is observ- ed in non-dimensional swirl values between two ports because of limited pre-swirl effect, while it becomes significant as the valve lift increases.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.75-82
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• 1995

The free surface effects on the aerodynamic performance of 2-D wings are investigated based on the potential flow approximation. The wing is represented b source and vortex distributions on the wing surface. The steady free surface effect is taken into account by source distribution on the free surface and the velocity potentials of air and water flows are obtained. Using three different techniques, namely, positive image method, inverse image method and source distribution method, numerical results are obtained for wave elevation, pressure distribution and lift coefficient with various foil sections. The wave elevation calculated by the inverse image method is shown to be very small even at higher speeds so that the free surface effect on the performance of wings is regraded negligible. However, the wave elevations by the positive image method and source distribution method are relatively high at higher speeds and accordingly the free surface effects on wings can not be neglected.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.1
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• pp.150-156
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• 2006

A Flapping foil Produces an effective angle of attack, resulting in a normal force vector with thrust and lift components, and it can be expected to be a new highly effective propulsion system. A heaving foil model was made and it was operated within a circulating water channel at low Reynolds numbers. The unsteady thrust and lift acting on the heaving foil were measured simultaneously using a 6-axis force sensor based on force and moment detectors. We have been examined various conditions such as heaving frequency and amplitude in NACA 0010 Profile. The results showed that thrust coefficient and efficiency increased with reduced frequency and amplitude. We also Presented the experimental results on the unsteady fluid forces of a heaving foil at various Parameters.