• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.1113-1118
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• 2006

A numerical investigation of single phase heat and flow characteristics in circular tubes with a single set of spiral micro fins was performed with varying geometrical parameters like fin height, spiral angle, and number of fins. The properties of $40^{\circ}C$ water was used as a working fluid to simulate a condenser and the RNG $k-{\epsilon}$ turbulence model was adopted. Calculation results were obtained in fully developed turbulent flow with constant surface heat flux boundary condition. Relative terms were introduced to investigate the substitution effect of conventional smooth tubes. The dimensionless terms were the heat transfer enhancement factor, the pressure drop penalty factor, and the efficiency index. Additionally, a numerical optimization was carried out to maximize thermal performance with the concept of the robust design. A statistical analysis showed that fin height interacts with number of fins and spiral angle.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1A
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• pp.53-60
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• 2009

This paper deals with the geometrical nonlinear analyses of post-buckled columns with variable cross-section. The objective columns having variable cross-section of the width, depth and square tapers are supported by both hinged ends. By using the Bernoulli-Euler beam theory, differential equations governing the elastica of post-buckled column and their boundary conditions are derived. The solution methods of these differential equations which have two unknown parameters are developed. As the numerical results, equilibrium paths, elasticas and stress resultants of the post-buckled columns are presented. Laboratory scaled experiments were conducted for validating the theories developed in this study.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2388-2394
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• 2024

In our previous works, two different spherical burnable poison particles (BPPs) as B₄C and Gd₂O₃ in pin-in block type HTGR core had utilized to suppress the excess reactivity and to control long-term reactivity during the burnup period. In the present work, we performed the neutronic analysis of a prismatic HTGR operating at 850 ℃ with thermal power of 100 MW containing spherical and cylindrical BPPs and then studied the self-shielding effect of BPPs and shape effect. The calculations were performed when the surface area (1) or volume (2) of cylindrical BPPs equals to that of the spherical BPPs. The calculations showed that the neutronic parameters were slightly better for the second case than the first one, such as the excess reactivity of the reactor core at the beginning of the cycle were more suppressed, the core lifetime were more extended, and the fuel-burning were more efficiently. The neutron spectrum in each region of the cylindrical BBPs slightly differs than that of the spherical BPPs. Therefore, the self-shielding effect of BPPs on reactor core performance depends on the particle's geometrical shape.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.3
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• pp.258-263
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• 2008

Performance of injector equiped with screw type swirler which is suitable for supersonic cruise engine combustor was investigated using theoretical, numerical, and experimental methods. Based on discharge coefficient and spray angle which represent the performance of injectors, the geometrical parameters which affect these performance parameters were defined, control group injectors were designed, and variation of performance parameters according to the geometrical parameters were examined. Within the defined range, measured value of performance of injectors was smaller than result of theoretical prediction, and prediction result from numerical simulation using VOF method agreed with the result of experiments very well. The viscous barrier was not observed, and minimum discharge coefficient and maximum spray angle, 0.05 and 104 respectively, was obtained for this type of injector.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.73-73
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• 2014

Several geometrical models (e.g., cone and flux rope models) have been suggested to infer 3-D parameters of CMEs using multi-view observations (STEREO/SECCHI) and single-view observations (SOHO/LASCO). To prepare for when only single view observations are available, we have made a test whether the cone model parameters from single-view observations are consistent with those from multi-view ones. For this test, we select 35 CMEs which are identified as CMEs, whose angular widths are larger than 180 degrees, by one spacecraft and as limb CMEs by the other ones. For this we use SOHO/LASCO and STEREO/SECCHI data during the period from 2010 December to 2011 July when two spacecraft were separated by $90{\pm}10$ degrees. In this study, we compare 3-D parameters of these CMEs from three different methods: (1) a triangulation method using the STEREO/SECCHI and SOHO/LASCO data, (2) a Graduated Cylindrical Shell (GCS) flux rope model using the STEREO/SECCHI data, and (3) an ice cream cone model using the SOHO/LASCO data. The parameters used for comparison are radial velocities, angular widths and source location (angle ${\gamma}$ between the propagation direction and the plan of the sky). We find that the radial velocities and the ${\gamma}$-values from three methods are well correlated with one another (CC > 0.8). However, angular widths from the three methods are somewhat different. The correlation coefficients are relatively not good (CC > 0.4). We also find that the correlation coefficients between the locations from the three methods and the active region locations are larger than 0.9, implying that most of the CMEs are radially ejected.

• Advances in nano research
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• v.14 no.3
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• pp.211-224
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• 2023

This work presents a modified analytical model for the bending behavior of axially functionally graded (AFG) carbon nanotubes reinforced composite (CNTRC) nanobeams. New higher order shear deformation beam theory is exploited to satisfy parabolic variation of shear through thickness direction and zero shears at the bottom and top surfaces.A Modified continuum nonlocal strain gradient theoryis employed to include the microstructure and the geometrical nano-size length scales. The extended rule of the mixture and the molecular dynamics simulations are exploited to evaluate the equivalent mechanical properties of FG-CNTRC beams. Carbon nanotubes reinforcements are distributed axially through the beam length direction with a new power graded function with two parameters. The equilibrium equations are derived with associated nonclassical boundary conditions, and Navier's procedure are used to solve the obtained differential equation and get the response of nanobeam under uniform, linear, or sinusoidal mechanical loadings. Numerical results are carried out to investigate the impact of inhomogeneity parameters, geometrical parameters, loadings type, nonlocal and length scale parameters on deflections and stresses of the AFG CNTRC nanobeams. The proposed model can be used in the design and analysis of MEMS and NEMS systems fabricated from carbon nanotubes reinforced composite nanobeam.

• Nuclear Engineering and Technology
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• v.55 no.11
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• pp.4096-4101
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• 2023

Radon is a radioactive gas produced from the uranium-238 series. Radon gas affects public health and is the second cause of lung cancer. The study samples were collected from one area of the city of Jazan, southwest of the Kingdom of Saudi Arabia. The influence of engineering and physical parameters on the emanation coefficient of gas and other gas parameters was studied. Parameters for radon were measured using a CR-39 Solid-State Nuclear Track Detector (SSNTD) through a sealed emission container. The results showed that the emanation coefficient was affected directly by the change in the grain size of the soil. All parameters of measured radon gas have the same behavior as the emanation coefficient. The relationship between particle size and emanation coefficient showed a good correlation. The values of the emanation coefficient were inversely affected by the mass of the sample, and the rest of the parameters showed an inverse behavior. The results showed that increasing the volume of the container increases the accumulation of radon sons on the wall of the container, which increases the emission factor. The rest of the parameters of radon gas showed an inverse behavior with increasing container size. The results concluded that changing the engineering and physical parameters has a significant impact on both the emanation coefficient and all radon parameters. The emanation coefficient affects the values of the radiation dose of an alpha particle.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1264-1267
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• 2002

In order to achieve an advanced human-computer interface system, it is necessary to analyze and synthesize facial motions just as they are in an interactive way, and to protect them from unwanted use and/or illegal use for their privacy, various uses in applications and the costs of obtaining motion parameters. To estimate facial motion, a method of using skin color distribution, luminance, and geometrical information of a face is employed. Digital watermarks are embedded into facial motion parameters and then these parameters are scrambled so that it cannot be understood. Experimental results show high accuracy and efficiency of the proposed estimation method and the usefulness of the proposed watermarking method.

• Journal of the korean Society of Automotive Engineers
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• v.6 no.1
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• pp.36-45
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• 1984

The conventional heat transfer analysis methods based on the one-dimensional theory are not adequate to be applied for the purpose of finned surface design because the two-dimensional effects in fact are induced within the supporting wall by the presence of the finnes. In this study, the two-dimensional heat transfer of a straight fin assembly is analyzed by using the integral method. It is shown that all the effects of the system parameters i.e., the heat transfer parameters and geometrical parameters, on both the total heat transfer rate and the surface temperature effectiveness can be seen from the present analysis. The optimum combinations of these parameters for the design of finned surfaces may be estimated.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.6
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• pp.601-610
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• 2008

This paper deals with a new geometrical surface modeling method of forebody's hull form which is fully defined by form parameters. The complex hull form in the forebody can be modeled by the combination of three parts: bare hull, bulbous bow and blending part which connects a bare hull and a bulbous bow. All these subdomain parts are characterized by each own form parameters and constructed with simple surface model. For this, we need only 2-dimensional hull form data and then the form parameters are calculated automatically from these data. Finally, the smooth hull form surfaces are generated by parametric design and fair-skinning. In the practical point of view, we show that this new method can be useful and efficient modeling tool by applying to the hull form surface modeling of Panamax container's forebody.