• Composites Research
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• 제29권6호
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• pp.369-374
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• 2016

In this study, a structural optimal design of 10 MW composite blade was performed using bend-twist coupled(BTC) design concept. Bend-twist coupling of blade means the coupling behavior between the bending and torsional deflections due to the composite lamina with fiber angle biased from the blade longitudinal axis. This can potentially improve the overall performance of composite blade and reduce the dynamic loading. Parametric studies on layup angle, thickness and area of off-axis carbon UD were conducted to find the optimum coupling effect with weight reduction. Comparing the results of fatigue load analysis between conventional model and BTC applied model, the damage equivalent load(DEL) of blade root area were decreased about 3% in BTC model. To verify the BTC effect experimentally, a 1:29 scaled model was fabricated and the torsion at the tip under deflection behavior of blade stiffener model was measured by static load test.

• The Transactions of the Korean Institute of Power Electronics
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• 제25권5호
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• pp.412-419
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• 2020

In this study, a 70 W buck converter using GaN metal-oxide-semiconductor field-effect transistor (MOSFET) is developed. This converter exhibits over 97 % efficiency, high power density, and 48 V-to-12 V/1.2 V/1 V (triple output). Three gate drivers and six GaN MOSFETs are placed in a 1 ㎠ area to enhance power density and heat dissipation capacity. The theoretical switching and conduction losses of the GaN MOSFETs are calculated. Inductances, capacitances, and resistances for the output filters of the three buck converters are determined to achieve the desired current, voltage ripples, and efficiency. An equivalent circuit model for the thermal analysis of the proposed triple-output buck converter is presented. The junction temperatures of the GaN MOSFETs are estimated using the thermal model. Circuit operation and temperature analysis are evaluated using a circuit simulation tool and the finite element analysis results. An experimental test bed is built to evaluate the proposed design. The estimated switch and heat sink temperatures coincide well with the measured results. The designed buck converter has 130 W/in³ power density and 97.6 % efficiency.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제13권12호
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• pp.2655-2661
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• 2009

In this paper, an accurate noise parameters for thermal noise modeling of short channel MOSFET is derived and extracted. Fukui model for calculating the noise parameters of a MOSFET is modified by considering effects of parasitic elements in short channel, and it is compared with conventional noise model equation. In addition, for obtaining the intrinsic noise sources of devices, noise parameters(minimum noise figure $F_{min}$, equivalent noise resistance $R_n$ optimized source admittance $Y_{opt}=G_{opt}+B_{opt}$) in submicron MOSFETs is extracted. With this extraction method, the intrinsic noise parameters of MOSFET without effects of probe pad and extrinsic parasitic elements from RF noise measurements can be directly obtained.

• Progress in Superconductivity and Cryogenics
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• 제20권1호
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• pp.19-22
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• 2018

The thermal and electrical properties of the conductor are critical parametersfor the design and optimization of the superconducting magnet. This paper presents simulation code to analyze electrical and thermal stability characteristics of the second generation (2G) high-temperature superconductor (HTS) by varying copper stabilizer thickness. Two types of commercial 2G HTS coated conductor tapes, YBCO and GdBCO were used in this study. These samples were cooled by Liquid Nitrogen ($LN_2$) having boiling at 77.3 K and an equivalent electrical circuit model for them is choosen and analysed in details. Also, an over-current pulse test in which a current exceeding a critical current was performed. From the simulation results, the influences of the copper stabilizer thickness on the stability characteristics of these samples are presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제28권10호
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• pp.1155-1162
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• 2004

This paper is the forth paper of several companion papers which compare the method of Air-Fuel ratio determination. In the previous work, various AFR calculations were performed for various fuels and the results were compared with each other. The comparison, however, were limited to numerical value and estimation of each equation or method was insufficient. In this paper, the overall estimation of the methods was attempted. Also, the method of trouble shooting of instrumentation was presented. Through the estimation of methods, it is concluded that the Eltinge method contains inherently the most perfect thermal dissociation model as far as the exhaust composition is concerned; therefore, this might be regarded as the most general equation of AFR determination among the existing ones. The others might be considered as approximate form. In addition, the mal-distribution factor in Eltinge method is qualitatively equivalent to thermal dissociation chemical equilibrium constant K. Lastly, it is illustrated that all instrumentation error, including the sampling line leakage, can be easily detected through the analyzing the exhaust component on the Eltinge chart.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제21권3호
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• pp.457-472
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• 1997

We studied the temperature distribution and heat transfer characteristics of TEFC induction motor with thermal network program for more efficient design and better cooling performance of it. We knew the characteristics and the windage loss of outer cooling fan from fan test experiments. Frame axial and peripheral heat transfer coefficients and endwinding heat transfer coefficient were measured by various model experiments and then, compared with other experimental results. Frame was the main heat transfer surface, load-side and fan-side surface were not thermally symmetric from the heat flux distribution analysis. Steady and unsteady temperature distributions were measured by real motor experiments. From the results, we knew that rotor surface temperature was higher than coil temperature and the hottest spot in the coil was loadside endwinding outside surface. We compared the simulation results with those of real motor test and the two results showed a good agreement.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• 제14권1호
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• pp.21-30
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• 1985

One of the problems with the Boiling Water Reactor involves the flow and thermal mixings in the suppression water pool high pressure steam discharge into the pool in case of emergency core relief. Varioos heat sensitive devices and pumps for the reactor core cooling are installed in the middle of the suppression pool. Especially the pumps utilize pool water in order to cool the reactor core in emergency cases. In this case, the water temperature for the reactor cool ins should be below a certain temperature specified by the reactor design. In the present investigation, in other to determine the optimum locations of these pumping devices, numerical solutions have been obtained for the model to determine the f low mixing characteristics. Experimental investigations have also been carried out for the flow mixing and for the thermal mixing in the pool during the discharge. Considering that the discharge steam through the Quenching Device becomes hot water immediately in the water pool, the steam- equivalent hot water has been utilized. Examining these characteristices, it becomes possible to deform me the best locations for RCIC, LPCI , HPCI pumps in the suppression water pool for the emermency reactor core cooling.

• Structural Engineering and Mechanics
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• 제90권4호
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• pp.357-370
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• 2024

Due to the fact that the mechanism of the effects of temperature and initial geometric imperfection on low-velocity impact problem of axially moving plates is not yet clear, the present paper is to fill the gap. In the present paper, the nonlinear dynamic behavior of axially moving imperfect graphene platelet reinforced metal foams (GPLRMF) plates subjected to lowvelocity impact in thermal environment is analyzed. The equivalent physical parameters of GPLRMF plates are estimated based on the Halpin-Tsai equation and the mixing rule. Combining Kirchhoff plate theory and the modified nonlinear Hertz contact theory, the nonlinear governing equations of GPLRMF plates are derived. Under the condition of simply supported boundary, the nonlinear control equation is discretized with the help of Gallekin method. The correctness of the proposed model is verified by comparison with the existing results. Finally, the time history curves of contact force and transverse center displacement are obtained by using the fourth order Runge-Kutta method. Through detailed parameter research, the effects of graphene platelet (GPL) distribution mode, foam distribution mode, GPL weight fraction, foam coefficient, axial moving speed, prestressing force, temperature changes, damping coefficient, initial geometric defect, radius and initial velocity of the impactor on the nonlinear impact problem are explored. The results indicate that temperature changes and initial geometric imperfections have significant impacts.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제28권10호
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• pp.381-386
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• 2016

An optimization algorithm is developed based on a simulation case of a single family house model equipped with PV arrays. To increase the nationwide use of PV power generation facilities, a market-competitive electricity price needs to be introduced, which is determined based on the time of use. In this study, quadratic programming optimization was applied to minimize the electricity bill while maintaining the indoor temperature within allowable error bounds. For optimization, it is assumed that the weather and electricity demand are predicted. An EnergyPlus-based house model was approximated by using an equivalent RC circuit model for application as a linear constraint to the optimization. Based on the RC model, model predictive control was applied to the management of the cooling load and electricity for the first week of August. The result shows that more than 25% of electricity consumed for cooling can be saved by allowing excursions of temperature error within an affordable range. In addition, profit can be made by reselling electricity to the main grid energy supplier during peak hours.

• The Transactions of The Korean Institute of Electrical Engineers
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• 제59권9호
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• pp.1615-1620
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• 2010

A thin film thermoelectric cooler for COB direct assembly was proposed and the COB cooler structure was modeled by electrical equivalent circuit by using SPICE model of thermoelectric devices. The embedded cooler attached between the die chip and metal plate can offer the possibility of thin film active cooling for the COB direct assembly. We proposed a driving method of TEC by using pulse width modulation technique. The optimum power to the TEC is simulated by using a SPICE model of thermoelectric device and passive components representing thermal resistance and capacitance. The measured and simulated results offer the possibility of thin film active cooling for the COB direct assembly.