• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.4
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• pp.517-526
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• 2019

In the present study, unsteady flows around a projectile ejected from an aircraft platform have been numerically investigated by using a three dimensional compressible RANS flow solver based on unstructured meshes. The relative motion between the platform and projectile was described by six degrees of freedom(6DOF) equations of motion with Euler angles and a chimera technique. Initial behavior of the projectile for varying conditions, such as roll and pitch-yaw command on the control surface of the projectile, flight Mach number, and platform pitch angle, was investigated. The ejection stability of the projectile was degraded as Mach number increases. In the transonic condition, the initial behavior of the projectile was found to be unstable as increase of platform pitch angle. By applying the command to control surfaces of the projectile, initial stability was highly enhanced. It was concluded that the proposed simulation data are useful for estimating the ejection behavior of a projectile in design phase.

• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.31-36
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• 2021

Recently, automobile air conditioning systems have applied an alternative refrigerant that can replace the high GWP refrigerant R134a due to the global warming problem. This study simulated the performance of an automobile climate control system with an internal heat exchanger and TXV. Refrigerant R1234yf was applied as the working fluid. Amesim, a commercial software program, was used to model the main components of the compressor, condenser, TXV, evaporator, and internal heat exchanger. As the outside temperature increased from 30℃ to 40℃, the cooling capacity of the system decreased by 3.1%, and the power consumption of the compressor increased by 17.1%. In addition, The performance characteristics of the refrigeration cycle were simulated by increasing the fin pitch of the condenser from 0.8 mm to 1.4 mm. When the fin pitch was larger than 1.0 mm, the condenser capacity decreased, and the system COP was lowered by 5.9%. When the fin pitch of the condenser was 0.8 mm, which was smaller than 1.0 mm, there was no significant change in the system performance. Hence, the optimal performance was observed at a fin pitch of 1.0 mm.

• Wind and Structures
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• v.32 no.2
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• pp.127-142
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• 2021

Wind load acting on a standalone structure is different from that acting on a similar structure which is surrounded by other structures in close proximity. The presence of other structures in the surrounding can change the wind flow regime around the principal structure and thus causing variation in wind loads compared to a standalone case. This variation on wind loads termed as interference effect depends on several factors like terrain category, geometry of the structure, orientation, wind incident angle, interfering distances etc., In the present study, a three building configuration is considered and the mean pressure coefficients on each face of principle building are determined in presence of two interfering buildings. Generally, wind loads on interfering buildings are determined from wind tunnel experiments. Computational fluid dynamic studies are being increasingly used to determine the wind loads recently. Whereas, wind tunnel tests are very expensive, the CFD simulation requires high computational cost and time. In this scenario, Artificial Neural Network (ANN) technique and Support Vector Regression (SVR) can be explored as alternative tools to study wind loads on structures. The present study uses these data-driven approaches to predict mean pressure coefficients on each face of principle building. Three typical arrangements of three building configuration viz. L shape, V shape and mirror of L shape arrangement are considered with varying interfering distances and wind incidence angles. Mean pressure coefficients (Cp mean) are predicted for 45 degrees wind incidence angle through ANN and SVR. Further, the critical faces of principal building, critical interfering distances and building arrangement which are more prone to wind loads are identified through this study. Among three types of building arrangements considered, a maximum of 3.9 times reduction in Cp mean values are noticed under Case B (V shape) building arrangement with 2.5B interfering distance. Effect of interfering distance and building arrangement on suction pressure on building faces has also been studied. Accordingly, Case C (mirror of L shape) building arrangement at a wind angle of 45º shows less suction pressure. Through this study, it was also observed that the increase of interfering distance may increase the suction pressure for all the cases of building configurations considered.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.6
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• pp.375-382
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• 2020

Owing to the rapid development of infrared guided weapon systems, the threat to aircraft survivability is constantly increasing, and research on infrared stealth technologies are being conducted to ensure aircraft survival. In this study, we analyze the minimum infrared signature of an aircraft according to its flight altitude by considering the characteristics of infrared guided missiles, which detect the contrast signature between the aircraft and background. We conducted computational fluid dynamics simulations for the convective coefficient, and heat transfer simulations were performed considering convection, conduction, and radiation for flight conditions. Thus, we obtained the surface temperature distribution of the aircraft and analyzed the aircraft infrared signature based on the flow characteristics around it. Furthermore, the optimum emissivity for the minimum infrared signature was derived, and the effect of the infrared signature was analyzed when this optimum emissivity was applied to the fuselage surface for each flight condition.

• International Journal of Computer Science & Network Security
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• v.21 no.2
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• pp.120-130
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• 2021

The spinal cord or CSF surgery is a very complex process. It requires continuous pre and post-surgery evaluation to have a better ability to diagnose the disease. To detect automatically the suspected areas of tumors and symptoms of CSF leakage during the development of the tumor inside of the brain. We propose a new method based on using computer software that generates statistical results through data gathered during surgeries and operations. We performed statistical computation and data collection through the Google Source for the UK National Cancer Database. The purpose of this study is to address the above problems related to the accuracy of missing hybrid KNN values and finding the distance of tumor in terms of brain cancer or CSF images. This research aims to create a framework that can classify the damaged area of cancer or tumors using high-dimensional image segmentation and Laplace transformation method. A high-dimensional image segmentation method is implemented by software modelling techniques with measures the width, percentage, and size of cells within the brain, as well as enhance the efficiency of the hybrid KNN algorithm and Laplace transformation make it deal the non-zero values in terms of missing values form with the using of Frobenius Matrix for deal the space into non-zero values. Our proposed algorithm takes the longest values of KNN (K = 1-100), which is successfully demonstrated in a 4-dimensional modulation method that monitors the lighting field that can be used in the field of light emission. Conclusion: This approach dramatically improves the efficiency of hybrid KNN method and the detection of tumor region using 4-D segmentation method. The simulation results verified the performance of the proposed method is improved by 92% sensitivity of 60% specificity and 70.50% accuracy respectively.

• Journal of Drive and Control
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• v.17 no.4
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• pp.141-151
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• 2020

The aim of this study was to analyze the safety factor of range-shift gear pairs on multi-purpose agricultural implement machinery for an optimal design of a transmission system. Gear-strengths such as bending and contact stress and safety factors were analyzed under three load conditions: an equivalent engine torque at plow tillage, a rated engine torque, and the maximum engine torque. Root and contact safety factor were calculated to be 3.88, 5.14, 2.24, 2.11, 2.21, 0.99 and 0.78, 0.94, 0.65, 0.68, 0.84, 0.85, respectively, under equivalent engine torque condition at the plow tillage. The root and contact safety factor were calculated to be 1.91, 2.53, 1.10, 1.04, 1.07, 0.48 and 0.55, 0.66, 0.46, 0.48, 0.59, 0.59, respectively, under rated engine torque condition. The root and contact safety factor were calculated to be 1.60, 2.11, 0.92, 0.87, 0.90, 0.40 and 0.51, 0.61, 0.42, 0.44, 0.54, 0.54, respectively, under the maximum engine torque condition. The multi-purpose agricultural implement machinery could be conducted under plow tillage operation. However, gear specifications for tooth surface need modification because the gear surface would be broken at all driving conditions as safety factors are lower than 1.

• Journal of the Korean Society of Visualization
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• v.19 no.2
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• pp.56-62
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• 2021

Solid oxide fuel cells (SOFCs) is the high efficiency fuel cell operating at high temperatures ranging from 700-1000℃. Design of the flow paths of the fuel and air in SOFCs is important to improve cell performance and prevent cell degradation. However, the uneven distribution of current density in the traditional type having one inlet and outlet causes cell degradation. In this regard, the parallel flow path with two inlet and outlets was designed and compared to the traditional type based on computational fluid dynamics (CFD) simulation. To check the cell performance, hydrogen distribution, velocity distribution and current density distribution were monitored. The results validated that the parallel designs with two inlets and outlets have a higher cell performance compared to the traditional design with one inlet and outlet due to a larger reaction area. In case of uniform-type paths, more uniform current density distribution was observed with less cross-sectional variation in flow paths. In case of contracted and expanded inflow paths, significant improvement of performance and uniform current density was not observed compared to uniform parallel path. Considering SOFC cell with uniform current density can prevent cell degradation, more suitable design of SOFC cell with less cross-sectional variation in the flow path should be developed. This work can be helpful to understand the role of flow distribution in the SOFC performance.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.143-154
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• 2020

The mathematical modeling applying experimental coefficients to a conventional model was validated through the hydraulic test for the components and the full system of a small-sized liquid rocket engine's propellant supply system. According to the simulations, pressures difference for the fluid resistance components and the pump were mainly predicted. In order to improve the modeling accuracy, the loss coefficients obtained by the empirical method were applied to the modeling. Based on the governing equation of the flow or the well known empirical equation, the method of deriving the empirical coefficients was summarized and the coefficients were presented for the commercial products used in this study. The prediction results by modeling were in good agreement with the experimental data. Through the comparison with the experimental data, the factors affecting the accuracy of the simulation were analyzed and improving methods of the accuracy was proposed.

• Textile Coloration and Finishing
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• v.34 no.1
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• pp.27-37
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• 2022

In this study, a study and interpretation of the spinning process in copolymerized aramid spinning was conducted. In order to proceed with the spinning process modeling and analysis, the spinning process was modeled through the physical property modeling of the spinning solution and the structural modeling of the spinneret, and structural stability and flow of the spinneret for this spinning were analyzed. After modeling the spinning solution and the spinneret in a virtual space, the pack pressure and flow rate when the spinning solution was discharged were simulated. Macroscopically, the structural stability of the spinneret was confirmed at the standard pack pressure (100 kg·f/cm²), and microscopically, the flow rate and pressure drop data of the spinning solution according to the L/D(Length (L)/Diameter (D)) value were analyzed. Based on the research and development of virtual engineering modeling and analysis, we present the possibility of changing the shape and mechanical properties of copolymer aramid fibers according to the spinning process.