• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1000-1002
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• 2017

Here, the unsteady Navier-Stokes solver has been developed using implicit dual time stepping method. The implicit dual time stepping method introduced the pseudo time step for solving the new residual including the steady state residual and real time derivative. For the validation of code, Stokes 2nd problem, the laminar flow on the oscillating flat plate was selected and compare the calculating results with analytic solutions. The calculating velocity profile and skin friction has a good agreement with analytic solutions.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.297-299
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• 2003

This paper proposes a totally new method in the chaos characteristics analysis of power systems, the introduction of topological invariants. Using a return histogram the bifurcation graph was drawn, the periodic orbits and topological invariants the local crossing number, relative rotation rates, and linking number during the process of period-doubting bifurcation and chaos were extracted. This study also examined the effect on the topological invariants when the sensitive parameters were varied. In addition, the topological invariants of a three-dimensional embedding of the strange attractor was extracted and the result was compared with those obtained from differential equations. This could be a new way for a state detection and fault diagnosis in a dynamical system.

• Bulletin of the Korean Chemical Society
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• v.20 no.4
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• pp.411-416
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• 1999

A new kind of differential flow induced chemical wave is introduced by theoretical calculation. A differential flow between the counter acting species of a dynamical activator-inhibitor system may destabilize its homogeneous reference state and cause the medium to self-organize into a pattern of travelling waves through the differential flow instability (DIFI). In a chemical system, also, the differential bulk flow may change the dynamics of the system, thus it has been refered to as the differential flow induced chemical instability (DIFICI). For DlFICI experiments, one directional flow has been commonly employed, resulting in periodic wave patterns generally. In this study, we considered two directional flow for the DIFICI wave by exchanging artificially the flow direction at some period.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.2
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• pp.162-171
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• 2012

A method of hydrodynamic discrete sources is applied for two-dimensional modeling of stepped planing surfaces. The water surface deformations, wetted hull lengths, and pressure distribution are calculated at given hull attitude and Froude number. Pressurized air cavities that improve hydrodynamic performance can also be modeled with the current method. Presented results include validation examples, parametric calculations of a single-step hull, effect of trim tabs, and performance of an infinite series of periodic stepped surfaces. It is shown that transverse steps can lead to higher lift-drag ratio, although at reduced lift capability, in comparison with a stepless hull. Performance of a multi-step configuration is sensitive to the wave pattern between hulls, which depends on Froude number and relative hull spacing.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.8
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• pp.4315-4328
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• 2019

The present study investigated the effects of work satisfaction on quality of life for 119 paramedics, the Korean equivalent of 911 paramedics. Data collection began in July 2017 and lasted for six months. Data was collected from 410 119 paramedics of the J province and the G metropolitan area who consented to study participation. The results showed that the higher the job satisfaction of the participants, the higher the quality of life (r = 0.508, p = 0.008). The factors affecting the quality of life were leisure activity, subjective health, and job satisfaction. For 119 paramedics to improve their quality of life, they need to relieve work stress and fatigue through leisure activities, and recover and maintain their health through sufficient rest. Moreover, returning to work in a healthy state likely leads to increased job satisfaction, and the quality of life will increase accordingly. Therefore, 119 paramedics should be permitted to have plenty of leisure time outside their work hours and should be able to maintain health through periodic health checks.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.11-15
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• 2022

We conducted numerical calculations to obtain the critical current as a function of the magnetic flux through the topologically trivial and non-trivial superconducting quantum interference devices (SQUIDs), with varying the capacitive and inductive couplings of Josephson junctions (JJs). Our calculation results indicate that a nontrivial SQUID is almost indistinguishable from trivial SQUID, considering the effective capacitance coupling. When the SQUID contains 2π- and 4π-periodic supercurrents, the periodicity of the current-flux relation can be distinguished from the purely trivial or nontrivial SQUID cases, and its difference is sensitive to the relative ratio between the topologically trivial and nontrivial supercurrents. We believe that our calculation results would provide a practical guide to quantitatively measure the portion of the topologically nontrivial supercurrents in experiments.

• Journal of Advanced Information Technology and Convergence
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• v.10 no.1
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• pp.57-69
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• 2020

In general, many IoT devices, including smart phones, use LTE, Wi-Fi, and Bluetooth, and these communication modules generate a lot of energy consumption during periodic data transmission. This paper proposes a method of the data transmission mode change for improving energy efficiency in various communication environments that mobile devices may encounter. We propose an algorithm for setting the mode considering energy efficiency, data transmission performance and cost when the mobile device transmits data, and transmitting the data in an optimized manner according to the state of the mobile device. The proposed algorithm is implemented through experiments on energy efficiency for each communication module, and the scenario is used to verify how efficiently the proposed algorithm uses energy.

• Journal of the Korean institute of surface engineering
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• v.55 no.4
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• pp.196-201
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• 2022

This paper deals with anodic oxidation behavior of AZ31 Mg alloy in aqueous solutions containing various NaF concentrations from 0.01 M to 1 M. Three different voltage-time curves and anodic oxide formation behaviors appeared with concentration of NaF in deionized water. When NaF concentration is lower than 0.02 M, the voltage of AZ31 Mg alloy increased linearly and then reached a steady-state value more than 200 V, and large size pits and thin oxide layer were formed. When NaF concentration is between 0.05 M and 0.1 M, the voltage of AZ31 Mg alloy showed large periodic fluctuations of about 30 ~ 50 V around more than 200 V and large number of small particles were observed. If NaF concentration is higher than 0.2 M, PEO films can be formed without visible arcs under solution pH 6.5 ~ 7.5 by F^- ions without help of OH^- ions.

• Geophysics and Geophysical Exploration
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• v.26 no.4
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• pp.238-267
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• 2023

Studies on Earth's rotation and tide since the 19th century are briefly summarized. The theories of precession, nutation, polar motion, and periodic/secular changes in the rate of rotation are described individually. In addition, a brief review of the Milankovitch theory - the hypothesis of the relationship between the Earth's spin/orbital rotational state and the ice ages - is given. Finally, Earth's tides and their theoretical models are briefly explained. Some detailed technical content is summarized in the appendices.

• Advances in Computational Design
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• v.9 no.2
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• pp.137-150
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• 2024

Paper shows the problems of numerical modeling of nonlinear physical processes of elements stress-strain state of construction are considered. Elastic-plastic environment of homogeneous solid material is investigated. The results of computational experiments of physically nonlinear strain process study of isotropic elements of three-dimensional constructions with a system of one - and doubly periodic spherical cavities under uniaxial compression are presented. The effect and mutual influence of stress concentrators in the form of a spherical cavities, vertically located two cavities and a horizontally located system of two cavities on the strain of construction is studied.