• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.3
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• pp.147-155
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• 2022

The accumulated ice and snow during the operation of aircraft and railway vehicles can degrade aerodynamic performance or damage the major components of vehicles. Therefore, it is crucial to predict the temporal growth of ice for operational safety. Numerical simulation of ice is widely used owing to the fact that it is economically cheaper and free from similarity problems compared to experimental methods. However, numerical simulation of ice generally divides the analysis into multi-step and assumes the quasi-steady assumption that considers every time step as steady state. Although this method enables efficient analysis, it has a disadvantage in that it cannot track continuous ice evolution. The purpose of this study is to construct a surrogate model that can predict the temporal evolution of ice shape using reduced-order modeling. Reduced-order modeling technique was validated for various ice shape generated under 100 different icing conditions, and the effect of the number of training data and the icing conditions on the prediction error of model was analyzed.

• Journal of applied mathematics & informatics
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• v.30 no.3_4
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• pp.635-646
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• 2012

This paper is concerned with an SIRS epidemic model with spatial diffusion and time delay representing the length of the immunity period. By using a new cross iteration scheme and Schauder's fixed point theorem, we reduce the existence of traveling wave solutions to the existence of a pair of upper-lower solutions. By constructing a newfashioned pair of upper-lower solutions, we derive the existence of a traveling wave solution connecting the uninfected steady state and the infected steady state.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.321-327
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• 2010

A simplified analytical modeling for micro-sized single metal particle combustion in air was conducted in the present study. The metal particle combustion consists of two distinct reaction regimes, ignition and quasi-steady burning, and the thermo-fluidic phenomena in each stage are formulated by virtue of the conservation and transport equations. Reliability of the model is shown by rigorous validation of the method with emphasis laid on the characterizing the commanding parameters. Effects of Initial particle size, initial oxide film thickness, convection, ambient pressure and temperature are examined and addressed with validation.

• Journal of applied mathematics & informatics
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• v.39 no.5_6
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• pp.601-616
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• 2021

Retrial queueing models have been studied extensively in the literature. These have many practical applications, especially in service sectors. However, retrial queueing models have their own limitations. Typically, analyzing such models involve level-dependent quasi-birth-and-death processes, and hence some form of a truncation or an approximate method or simulation approach is needed to study in steady-state. Secondly, in general, the customers are not served on a first-come-first-served basis. The latter is the case when a new arrival may find a free server while prior arrivals are waiting in the retrial orbit due to the servers being busy during their arrivals. In this paper, we take a different approach to the study of multi-server retrial queues in which the signals are generated in such a way to provide a reasonably fair treatment to all the customers seeking service. Further, this approach makes the study to be level-independent quasi-birth-and-death process. This approach is different from any considered in the literature. Using matrix-analytic methods we analyze MAP/M/c-type retrial queueing models along with Poisson signals in steady-state. Illustrative numerical examples including a comparison with previously published retrial queues are presented and they show marked improvements in providing a quality of service to the customers.

• Ecology and Resilient Infrastructure
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• v.1 no.2
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• pp.61-67
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• 2014

Dam construction changes flow regime and stream morphology in the downstream reach. These affect the ecosystem of downstream reach. This study provides the assessment of the impact of dam construction on the downstream fish habitat. For this, physical habitat simulations are carried out. The quasi-steady model is used for hydraulic simulation, The hydraulic model used in the present study is capable of simulating the morphological change due to sediment transport. The change of the fish habitat condition is investigated using the flow scenarios before and after the dam construction. Simulation results indicate that the habitat suitability decreases frequently due to hydropeaking after dam construction. In addition, erosion is expected to occur in a reach downstream of dam. This is a long term effect due to the shut-down of sediment supply from the upstream reach.

• Journal of the Korean Society of Combustion
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• v.13 no.3
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• pp.17-23
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• 2008

The spray combustion and spray cooling depends on droplet evaporation. So, evaporation model for spray has been requested and lots of investigation has been done and various reliable models have been developed also for last few decades. In the present study, One dimensional quasi-steady spherically symmetric droplet evaporation model for micro-gravity is developed. The gas phase was assumed as steady state and the thermophysical properties are calculated as a function of temperature, pressure and composition and the properties used in the model was validated by NIST web data and overall evaporation history results was compared with experimental results by Nomura and Qasim and gave satisfactory agreements. Through this model, diverse phenomenon was investigated, especially regarding the effects of ambient pressure and temperature. The effects of pressure for the droplet evaporation time were studied. The high pressure increased the droplet surface temperature and made effect on the evaporation time depend on atmospheric temperature. The role of the ambient temperature was investigated and explained. The basic investigation for the evaporation process according to variation of droplet diameter and surface temperature were also investigated and the well-known phenomena, like D-square-law, were reported, too.

• Journal of the Korean Society for Railway
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• v.7 no.3
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• pp.180-185
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• 2004

The present study investigates the effect of fire growth model on fire development characteristics in a carriage. The parallel processing version of FDS code is used to simulate the fire driven flow in a carriage and two types of fire growth model which are flame spread model and t$^2$ model are examined for the same geometrical condition. The heat release rates(HRR) of both model are similar each other until 30 s after ignition, but the flame spread model predicts 5 times higher than those of the t$^2$ fire model during the quasi-steady fire period. Maximum heat release rate in the case of flame spread model reaches about to 12 MW at 100 s after fire ignition. Also, various database of fire properties for combustible materials and more elaborate combustion model considering the flame spreading phenomena are required for better predictions of fire development characteristics using numerical simulation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1087-1095
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• 1994

Chain drive power transmission system was developed for a low head hydro-turbine which generates power by energy transformation on the turbine blades attached to chains. Also, experimental and theoretical analysis for the sprocket wheel tooth load distribution were performed. The tooth load was measured by the specially designed load sensor. It was found that the tooth load distribution for the steady state operation was in good accordance with the quasi-static state results showing the peak load at the final meshing tooth. The trend of the experimental results agreed with the theoretical results based on the spring model analysis and difference in the magnitude of the maximum tooth load was considered to be the effect of the variable spring constant due to the moving contact point between the roller and sprocket wheel tooth.

• Journal of IKEEE
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• v.22 no.4
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• pp.985-991
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• 2018

In this paper, an equivalent circuit reflecting the internal loss of the LLC resonant half bridge converter was proposed and a steady state characteristic equation including the loss factors was derived. Using the results, the frequency characteristics of I/O voltage gain and input impedance were compared with the lossless model In order to verify the proposed model and the derived equation, the main components of the 1kW class LLC resonant half bridge converter were selected under the same conditions and the steady state characteristics such as voltage gain and input impedance were compared. In particular, to compare more closely the steady state error of the two models, we observed the change in switching frequency with respect to the load current, which is considered to be the most important in the actual circuit design stage. As a result, it is confirmed that the error of the operating frequency is significantly improved from the proposed model and the analysis result.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.549-552
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• 2002

The objective of this study is to clarify the detailed performances of the impulse type radial turbine and to present an optimum configuration of the turbine. The impulse type radial turbine has been manufactured and investigated experimentally under steady and sinusoidally oscillating flow conditions by model testing. Then, the starting characteristics under sinusoidally flow conditions have been evaluated by a numerical simulation using a quasi-steady analysis. As a result, the running and starting characteristics of the impulse type radial turbine for wave energy conversion have been clarified. Furthermore, the recommended configuration is presented, especially for setting angles of inner and outer guide vanes.