• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.2087-2098
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• 2003

The development of numerical mathematical model to calculate both the static and dynamic characteristics of a multi-shaft gas turbine consisting of a single combustion chamber, including advanced cycle components such as intercooler and regenerator is presented in this paper. The numerical mathematical model is based on the simplified assumptions that quasi-static characteristic of turbo-machine and injector is used, total pressure loss and heat transfer relation for static calculation neglecting fuel transport time delay can be employed. The supercharger power has a cubical relation to its rotating velocity. The accuracy of each calculation is confirmed by monitoring mass and energy balances with comparative calculations for different time steps of integration. The features of the studied gas turbine scheme are the starting device with compressed air volumes and injector's supercharging the air directly ahead of the combustion chamber.

• New & Renewable Energy
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• v.4 no.4
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• pp.3-9
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• 2008

In design PV (photovoltaic) system, there are many important factors to consider for best site selection. It is essential to understand to know the amount of sunlight available and how to minimize the shadings. This study presents basic concepts for understanding sun's position and insolation. also it gives easy tools for topography analysis. Finally, this study shows some theoretical calculations of power generation losses by topographic obstacle's elevations and disadvantages in economic feasibility, that is about 7million won loss per year for case of 10 degree topography elevation with assuming average Korea's topography elevation as 5 degree.

• Journal of The Korean Astronomical Society
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• v.26 no.1
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• pp.1-12
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• 1993

In order to explore the time dependence of the closure parameters of the two-fluid calculations for supernova remnants and the terminal shocks of stellar winds, we have considered a simple model in which the time evolution of the cosmic-ray distribution function was followed in the test-particle limit using the Bohm diffusion model. The particles are mostly accelerated to relativistic energy either in the free expansion phase of the SNRs or in the early phase of the stellar winds, so the evolution of the closure parameters during these early stages is substantial and should be followed correctly. We have also calculated the maximum momentum which is limited by either the age or the curvature of these spherical shocks. We found that SNRs expanding into the medium where the gas density decreases with the distance from the explosion center might be necessary to explain the observed power-law distribution of the galactic cosmic rays. The energy loss due to the escaping energetic particles has been estimated for the terminal shocks of the stellar winds.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.05a
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• pp.123-126
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• 1994

We discussed the thermal analysis for recording media with the variation of the laser pulse duration and the power and the temperature distribution for the optimized Te-based antireflection structure by using the computer calculations. If the radial diffusion of heat is negligible, we can calculate the maximum temperature at the spot center in recording layer by Simple Method, and the temperature profile considering the specific heat and the latent heat by Numerical Method. As a result, the effect of the heat sinking which acted as a loss for the hole formation can be minimized by introducing the pulse of the hole formation duration( $\tau$ ) shorter than the thermal time constant( $\tau$$\sub$D/) of dielectric layer. This requirments can be satisfied as using the dielectric thickness of the 7nd ART condition or the dielectric materials with low thermal diffusivity.

• Journal of Power System Engineering
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• v.6 no.3
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• pp.36-41
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• 2002

A swashplate type piston motor with a tripod joints is introduced to improve compactness and starting torque in conventional types of motor. If the driving torque of motor shaft is transmitted by utilizing the mechanism, its friction torque loss would be drastically reduced and mechanical efficiency would be improved because the lateral force on the piston of the rod type motor with tripod joints mechanism is relatively smaller than that of the conventional plunger type motor. In particular, kinematics analysis for the mechanism are done as a preliminary study to investigate the feasibility of the mechanism in the axial piston motor. General formulas are derived from the displacement and velocity analysis of the mechanism, showing relationships between output shaft and shoe holder motion. A series of numerical calculations are carried out for a medium size motor with 160cc/rev using the formulas and their graphical plots are shown as well.

• Nuclear Engineering and Technology
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• v.30 no.6
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• pp.531-540
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• 1998

The DYLAM-3 code which overcomes the limitation of event tree/fault tree was applied to LOOP (Loss of Off-site Power) in the mid-loop operation employing HEPs (Human Error Probabilities) supplied by the ASEP (Accident Sequence Evaluation Program) and the SEPLOT (Systematic Evaluation Procedure for Low power/shutdown Operation Task) procedure in this study. Thus the time history of core uncovery frequency during the mid-loop operation was obtained. The sensitivity calculations in the operator's actions to prevent core uncovery under LOOP in the mid-loop operation were carried out. The analysis using the time dependent HEP was performed on the primary feed & bleed which has the most significant effect on core uncovery frequency. As the result, the increment of frequency is shown after 200 minutes duration of simulation conditions. This signifies the possibility of increment in risk after 200 minutes. The primary feed & bleed showed the greatest impact on core uncovery frequency and the recovery of the SCS (Shutdown Cooling System) showed the least impact. Therefore the efforts should be taken on the primary feed & bleed to reduce the core uncovery frequency in the mid-loop operation. And the capability of DYLAM-3 in applying to the time dependent concerns could be demonstrated.

• Nuclear Engineering and Technology
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• v.41 no.7
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• pp.945-952
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• 2009

The Three Mile Island Unit 2 (TMI-2) accident provides unique full scale data, thus providing opportunities to check the capability of codes to model overall plant behavior and to perform a spectrum of sensitivity and uncertainty calculations. As part of the TMI-2 analysis benchmark exercise sponsored by the Organization for Economic Cooperation and Development Nuclear Energy Agency (OECD NEA), several member countries are continuing to improve their system analysis codes using the TMI-2 data. The Republic of Korea joined this benchmark exercise in November 2005. Seoul National University has analyzed the TMI-2 accident as well as the currently proposed alternative scenario along with a sensitivity study using the Modular Accident Analysis Program Version 4.03 (MAAP4.03) code in collaboration with the Korea Hydro and Nuclear Power Company. Two input files are required to simulate the TMI-2 accident with MAAP4: the parameter file and an input deck. The user inputs various parameters, such as volumes or masses, for each component. The parameter file contains the information on TMI-2 relevant to the plant geometry, system performance, controls, and initial conditions used to perform these benchmark calculations. The input deck defines the operator actions and boundary conditions during the course of the accident. The TMI-2 accident analysis provided good estimates of the accident output data compared with the OECD TMI-2 standard reference. The alternative scenario has proposed the initial event as a loss of main feed water and a small break on the hot leg. Analysis is in progress along with a sensitivity study concerning the break size and elevation.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.6
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• pp.345-354
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• 2022

It is easy for a ship passing through confined waters to be exposed in dangers of collisions and grounding due to different hydrodynamic responses. Since marine accidents can cause significant impacts on environments, global economy, and human lives, it is necessary to study the effect of shallow water on hydrodynamic performance of a ship. In this paper, the effect of water depth on resistance performance was investigated using CFD analysis as an initial study for improving navigational safety of a large container ship under confined waters. After a CFD set-up for deep water condition was validated and verified by comparing CFD analysis with model test results, CFD calculations according to ship speed and water depth were conducted. The features were investigated in terms of tendency and physical knowledge related to resistance performance. The increase of resistance due to shallow water effect was reviewed with empirical formula suggested from SWABE JIP. Speed loss due to shallow water effect was additionally reviewed from estimated delivered power according to ship speed and water depth.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1145-1152
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• 2024

To realize an initial objective of the negative ion-based neutral beam injection (N-NBI) at the Comprehensive Research Facility for Fusion Technology (CRAFT) test facility, which targets an H⁰ beam power of 2 MW at an energy of 200-400 keV and a pulse duration of 100 s, it is crucial to study the cesium dynamics of the negative ion source. Here a numerical simulation program CSFC3D is developed and applied to simulate the distribution and time dynamics of cesium during short pulses. The calculations show that most of the cesium on the plasma grid (PG) area originates from the release of cesium that is accumulated within the ion source in the plasma phase. Increasing the wall temperature reduces the loss of cesium on the wall of the ion source. Furthermore, the thickness of the cesium monolayer is directly influenced by the PG temperature. Both simulated and experimental results demonstrate that maintaining the PG temperature between 180 ℃ and 200 ℃ is essential for enhancing the performance of the ion source and optimizing the cesium behavior.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.71-71
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• 2003

The study on magnetic field combined radiation therapy, as a new technique to modify the dose distributions using external magnetic field, has been investigated. The goal of the study is to develop the techniques for dose localization, as a particle beam, from the strong magnetic fields. In this study, in order to study the principle of dose deposition in external fields, as a basic approach, we have calculated approximately the paths of traveling electrons in water under external magnetic fields with numerical methods. The calculations are performed for a primary particle by cumulating the steps which are defined as small path lengths which energy loss can be ignored. In this calculation, the energy loss and direction change for a step was calculated by using total stopping power and Lorentz force equation respectively. We have examined the deflected paths of the electron through water as a function of external magnetic field and incident electron s energy. Since we did not take account of the multiple scattering effects for electrons through water, there are errors in this calculation. However, from the results we can explain the principle of dose variation and dose focusing for electron beams under strong magnetic fields in water.