• Journal of Aerospace System Engineering
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• v.11 no.5
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• pp.6-12
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• 2017

This paper deals with mathematical modeling of a 75-ton open-cycle Liquid Propellant Rocket Engine (LPRE) and the steady state simulation based on a nominal operating point. Each component of open-cycle LPRE may be classified into seven major categories using thermodynamics and dynamics characteristics. To simplify the simulation model of LPRE in this paper, we used four govern equations with assuming no heat transfer process. We confirmed the mathematical model of LPRE by using the error ratio and comparing the experiment data and simulation data in steady state, and checked the stability with the linearized model. Finally, we demonstrated the simulation model as compared to the transient response of experimental data.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.317-319
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• 2019

In this paper, a three level duty cycle controlled half bridge LLC converter for EV charger application is presented. The topology and operating regions of the converter are discussed. The equations of the converter are derived in time domain. A small signal model of the converter is developed by perturbation and linearization of the steady state model about their operating point using Extended Describing function.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.1
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• pp.93-101
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• 2000

In a gas-turbine engine, fan blades in flow path are confronted with many kinds of loading. The study of the excited force by the wake of struts has proposed and the possibility of fatigue failure about rotating fan blades by the excited force at the steady state is evaluated. Equations of the excited force of wakes has been derived at the steady state and the maximum pressure distributions measured at the transient state are proposed. Dynamic characteristics and the fatigue strength of fan blades by experimental test were obtained. To evaluate HCF(High Cycle Fatigue) damage of fan blades, FEM analysis was performed with a steady state harmonic response, which was followed by high cycle fatigue damage factor from goodman diagram.

• Journal of Power System Engineering
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• v.22 no.1
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• pp.34-40
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• 2018

In this paper, Performance of 1MW OTEC system using R32 with varying seawater temperature range is studied. Steady state cycle is designed and its output and generation efficiency were 1,014kW and 2.72%, respectively. Compared to dynamic cycle, system performance and change during long term operation is studied. The simulation is performed by decreasing surface seawater temperature from $29^{\circ}C$ to $25^{\circ}C$ with 20 minute of reaction time. Dynamic cycle with same condition applied to steady state cycle and it showed output and efficiency of 1,020kW and 2.75% respectively. Seawater temperature decreased from $29^{\circ}C$ and the vapor fraction of refrigerant decreased below 1 at $28^{\circ}C$. While the vapor fraction was above 1, the turbine output decreased by 0.017kW per second. After the seawater temperature reached $26.2^{\circ}C$, the turbine output decreased by 1.03kW per second. However, Driving the turbine below the saturation temperature caused the occurrence of surging and the influx of liquid refrigerant. When the liquid separator having a capacity of 1.0 m3 was used, the flow into the turbine was confirmed after 5 minutes from the first liquid refrigerant coming into the separator.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.2
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• pp.181-189
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• 1998

A general steady-state model for simulation on domastic refrigerator has been developed. The system model consists of various standard components such as evaporator compressor condenser capillary tube and cabinet. Cabinet is not system component but influence characteristic on domastic refrigerator. The purpose of this paper is to compare between characteristics of HFC 134a with CFC 12 in the domastic refrigerator and to predict the steady state cycle performance which is various specifications of cycle components under the continuous running conditions. As the results of simulation the coefficient of performance of both condenser and evaporator increases with increasing UA the increasing rate for condenser is greater than for evaporator.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.252-257
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• 2000

An efficient method is developed for mold thermal cycle analysis in repeated forming process, which is well suited to the analysis in TV glass production. plunger, which is a mold to press-form the glass, undergoes temperature fluctuation during a cycle due to the repeated contact and separation from the glass, which attains a cyclic steady state in the end. If analyzed straightforwardly of this problem, it leads to more than 80 cycles to get reasonable solution, and it is yet hard to setup stopping creteria due to extremely slow convergence. An exponential fitting method is proposed to solve the problem, where an exponential function is found to best approximate temperature values of 3 consecutive cycles, and new cycle is restarted with the function value at infinite time. From numerical implementation, it is found that the method reduces the number of cycles dramatically to only $6{\sim}15$ cycles to reach accurate solution within $1^{\circ}$ error. A system for the analysis is contructed, in which the thermal analysis is performed by commercial software ANSYS, and the fitting of the result is done by IMSL library.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.3
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• pp.198-206
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• 1993

Experimental results of two stage Gifford-McMahon cryorefrigerator are described. In-prototype experiments, drive mechanism is Scotch Yoke type driven by stepping motor, copper meshes and lead balls are used for regenerator's materials in the first stage and the second stage, respectively. To find optimal conditions of the cryopump, no load temperature and refrigeration capacity according to the variation of cycle frequency and operating pressure are measured, and the cool down and load characteristics at particular cycle frequencies are presented. In general, as the cycle frequency is lowered, no load temperature is dropped but refrigeration capacity is diminished. As the representative result, in a case that the cycle frequency is 70rpm and steady state pressure is 14 atm, no load temperature of second stage is lowered to 10.5K in 55 minuters, and in this situation the refrigeration capacity of the first stage is 42W at 80K, that of the second stage is 11 W at 20K.

• International Journal of Automotive Technology
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• v.8 no.3
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• pp.361-373
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• 2007

In previous work, an approach based on maximizing the efficiency of an internal combustion engine while ignoring the power conversion efficiency of other powertrain components, such as the electric motor and power battery or ultracapacitor, was implemented in the steady-state optimization of an internal combustion engine for hybrid electric vehicles. In this paper, a novel control algorithm was developed and successfully justified as the basis for maximal power conversion efficiency of overall powertrain components. Results indicated that fuel economy improvement by 3.9% compared with the conventional control algorithm under China urban transient-state driving-cycle conditions. In addition, using the view of the novel control algorithm, maximal power generation of the electric motor can be chosen.

• Proceedings of the Safety Management and Science Conference
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• 2007.04a
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• pp.309-322
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• 2007

This paper shows application guide of dependability data from the field, life cycle costing, and maintainability. Moreover, this study introduces mathematical expressions and predictions for reliability, availability and maintainability. This paper also shows compliance test procedures for steady-state availability, and application of Markov techniques.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1729-1737
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• 2002

A mathematical model for the prediction of carbon-dioxide absorption rate during the transient state of rotary type absorber is developed. The rotary type absorber operates using a fast rotating porous structure and clean water. The model for the transient state rotary type absorbers is based on the steady state model of packed tower absorber. The paper manipulates the operating data of an arbitrary quasi-steady state condition of rotary type absorber for the determination of the coefficients involved in the model developed. The prediction accuracy is evaluated from the measured data of rotary type absorber operated under fast transient state. The measured data include the mole fraction of carbon dioxide in mixed gas and the pressure of absorber. The relative error in carbon dioxide prediction is estimated to be 20% at maximum. The model is successfully applied for the prediction of the behavior of a closed cycle diesel engine.