• 한국전산응용수학회:학술대회논문집
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• 한국전산응용수학회 2003년도 KSCAM 학술발표회 프로그램 및 초록집
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• pp.1-1
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• 2003

In this talk, a reduced-order modeling methodology based on centroidal Voronoi tessellations (CVT's)is introduced. CVT's are special Voronoi tessellations for which the generators of the Voronoi diagram are also the centers of mass (means) of the corresponding Voronoi cells. The discrete data sets, CVT's are closely related to the h-means clustering techniques. Even with the use of good mesh generators, discretization schemes, and solution algorithms, the computational simulation of complex, turbulent, or chaotic systems still remains a formidable endeavor. For example, typical finite element codes may require many thousands of degrees of freedom for the accurate simulation of fluid flows. The situation is even worse for optimization problems for which multiple solutions of the complex state system are usually required or in feedback control problems for which real-time solutions of the complex state system are needed. There hava been many studies devoted to the development, testing, and use of reduced-order models for complex systems such as unsteady fluid flows. The types of reduced-ordered models that we study are those attempt to determine accurate approximate solutions of a complex system using very few degrees of freedom. To do so, such models have to use basis functions that are in some way intimately connected to the problem being approximated. Once a very low-dimensional reduced basis has been determined, one can employ it to solve the complex system by applying, e.g., a Galerkin method. In general, reduced bases are globally supported so that the discrete systems are dense; however, if the reduced basis is of very low dimension, one does not care about the lack of sparsity in the discrete system. A discussion of reduced-ordering modeling for complex systems such as fluid flows is given to provide a context for the application of reduced-order bases. Then, detailed descriptions of CVT-based reduced-order bases and how they can be constructed of complex systems are given. Subsequently, some concrete incompressible flow examples are used to illustrate the construction and use of CVT-based reduced-order bases. The CVT-based reduced-order modeling methodology is shown to be effective for these examples and is also shown to be inexpensive to apply compared to other reduced-order methods.

• 한국정보통신학회논문지
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• 제16권12호
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• pp.2601-2606
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• 2012

본 논문에서는 2대 이상의 소형 발전기를 사용하는 환경에서 부하의 전력 소비량을 이용하여 에너지를 절약하는 전력 관리 시스템을 제안하고 개발하였다. 고속의 하드웨어 플로팅 포인트 연산처리가 가능한 TI사의 TMS320C6713 DSP 칩을 사용하여 하드웨어를 구성하였으며, 시리얼 통신을 이용하여 모니터링 PC와 통신하게 하였다. 모니터링 PC에서 수동제어가 가능하도록 하였으며, DSP main board에서 CT/PT센서로 수집한 데이터를 이용하여 자동적으로 발전기를 on/off 할 수 있도록 구현하였다. 실험 결과 본 논문에서 제안한 전력 관리 시스템이 이상 없이 동작하는 것을 확인할 수 있었으며, 부하의 전력사용량을 이용하여 에너지를 절약하는 알고리즘을 적용하였을 경우 소형 발전기 2대를 지속적으로 사용할 때 보다 더욱 오래 전력을 공급하는 것을 알 수 있었다.

• 한국도로학회논문집
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• 제7권4호
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• pp.125-140
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• 2005

본 연구에서는 콘크리트 포장에서 발생하는 소음을 저감시키기 위한 최적의 임의간격 횡방향 타이닝 설계 간격을 제안하였다. 기존 문헌조사를 바탕으로 소음 발생에 대한 원인을 규명하였고, LCG(linear congruential generators) 알고리즘 이론을 이용하여 특정 주파수에 집중되는 에너지를 효과적으로 분산시킬 수 있는 타이닝의 간격을 설계하였다. 실내 시뮬레이션 결과를 대구-포항 고속국도 현장에 적용하였고 기존 국내외에 적용된 임의간격 횡방향 타이닝 시공도 병행하여 실내 외 소음 및 교통소음을 비교하였다. 실내 외 소음 측정 결과, 피치 소음으로 인한 소음을 감소시킴으로써 임의간격 횡방향 타이닝 구간이 일반구간 보다 낮은 소음도를 보였으나, 그 효과가 크지 않았다. 교통 소음 측정에서도 전체적으로 일반 타이닝 구간에 비해 임의 간격 횡방향 타이닝 구간에서 더 큰 소음저감 효과를 확인할 수 있었으나, pass-by 소음 측정과는 다소 차이를 보였다.

• Journal of Power Electronics
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• 제11권5호
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• pp.759-766
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• 2011

This paper focuses on monitoring and predicting the short circuit faults of the rotor windings of large turbo-generator systems. For the purpose of increasing efficiency and decreasing maintenance cost, a method that combines the HHT (Hilbert Huang Transform) with a wavelet has been studied. This method is based on analyzing a classical Albright detecting coil. Due to the Empirical Mode Decomposition (EMD) and the Intrinsic Mode Functions (IMF) of the HHT the exact location of a short circuit of rotor windings may be given. However, a part of the useful information is eliminated by the unreasonable decomposing scale of the wavelet. Based on the thermodynamics modeling method, this study was illustrated with a 50MW turbo-generator system that is installed in Northern China. The analysis results, which have very good agreement with those of a previous study, show that the method of combining the HHT with a wavelet is an effective way to analyze and predict the short circuit faults of the rotor windings of large generators, such as supercritical turbo-generator systems and wind turbo-generator systems. This work can offer a useful reference for analyzing smart grids by improving the power quality of a distribution network that is supplied by a turbo-generator system.

• 대한수학회지
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• 제58권3호
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• pp.643-702
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• 2021

Fix ℤ/2 is the prime field of two elements and write 𝒜₂ for the mod 2 Steenrod algebra. Denote by GL_d := GL(d, ℤ/2) the general linear group of rank d over ℤ/2 and by ${\mathfrak{P}}_d$ the polynomial algebra ℤ/2[x₁, x₂, …, x_d] as a connected unstable 𝒜₂-module on d generators of degree one. We study the Peterson "hit problem" of finding the minimal set of 𝒜₂-generators for ${\mathfrak{P}}_d$. Equivalently, we need to determine a basis for the ℤ/2-vector space $$Q{\mathfrak{P}}_d:={\mathbb{Z}}/2{\otimes}_{\mathcal{A}_2}\;{\mathfrak{P}}_d{\sim_=}{\mathfrak{P}}_d/{\mathcal{A}}^+_2{\mathfrak{P}}_d$$ in each degree n ≥ 1. Note that this space is a representation of GL_d over ℤ/2. The problem for d = 5 is not yet completely solved, and unknown in general. In this work, we give an explicit solution to the hit problem of five variables in the generic degree n = r(2^t - 1) + 2^ts with r = d = 5, s = 8 and t an arbitrary non-negative integer. An application of this study to the cases t = 0 and t = 1 shows that the Singer algebraic transfer of rank 5 is an isomorphism in the bidegrees (5, 5 + (13.2⁰ - 5)) and (5, 5 + (13.2¹ - 5)). Moreover, the result when t ≥ 2 was also discussed. Here, the Singer transfer of rank d is a ℤ/2-algebra homomorphism from GL_d-coinvariants of certain subspaces of $Q{\mathfrak{P}}_d$ to the cohomology groups of the Steenrod algebra, $Ext^{d,d+*}_{\mathcal{A}_2}$ (ℤ/2, ℤ/2). It is one of the useful tools for studying these mysterious Ext groups.

• 생물환경조절학회지
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• 제23권2호
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• pp.83-87
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• 2014

본 연구는 저온기 시설참외 재배 시 탄산가스 발생제(탄산솔)의 사용효과를 구명하기 위하여 수행하였다. $600m^2$ 크기 하우스에 탄산가스 발생제(100g/1봉)를 10, 20 및 30봉을 각각 매달아 무처리와 비교하였다. 그 결과 무처리구에 비해 처리구에서 탄산가스 농도가 3.0~3.2배정도 높았다. 그리고 무처리구에 비해 처리구에서 과중이 20.2~22.0g 더 무겁고, 태좌부 당도가 $1.5{\sim}2.1^{\circ}Brix$ 더 높았으며, 색도(a값)도 우수하였다. 또한 탄산가스 발생제 처리한 것이 무처리에 비해 발효과율 및 기형과율이 각각 2.9~3.9%, 5.4~7.3% 감소하였고, 상품과율은 8.7~10.3% 증가하였다. 10a당 상품과 수량은 무처리구의 385.8kg에 비하여 탄산가스 발생제 10, 20 및 30봉 처리한 것이 각각 10.3%, 14.8%, 16.2% 증가하였다. 이상의 결과를 보아, 저온기 참외 시설재배시 탄산가스 발생제를 시용함으로써 탄산가스 농도가 높아져 광합성이 촉진되어 품질이 향상되고 수량이 증가한 것으로 판단되었다.

• 한국전기전자재료학회논문지
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• 제24권5호
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• pp.416-421
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• 2011

Nowadays, the increasing demands upon mobile devices such as wireless sensor networks and the recent advent of low power electrical devices such as MEMS make such renewable power sources attractive. A vibration-driven MEMS lead zirconate titanate $Pb(Zr,Ti)O_3$ (PZT) cantilever device is developed for energy harvesting application. This paper presents a piezoelectric based energy harvester which is suitable for power generating from conventional vibration and has in providing energy for low power electron ic devices. The PZT cantilever is used d33 mode to get the electrical power. The PZT cantilever based energy harvester with the dimension of 7 mm${\times}$3 mm${\times}$0.03 mm is fabricated using micromachining technologies. This PZT cantilever has the mechanical resonance frequency with a 900 Hz. With these conditions, we get experimentally the 37 uW output power from this device with the application of 1g acceleration using the 900 Hz vibration. From this study, we show the feasibility of one of energy harvesting candidates using PZT based structure. This PZT energy harvester could be used for various applications such a batteryless micro sensors and micro power generators.

• 전기학회논문지
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• 제64권1호
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• pp.16-22
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• 2015

As the development of Battery Energy Storage System(BESS) and the increasing of intermittent energy sources like wind power and photovoltaic, the application of BESS in load frequency control is considered as an effective method. To evaluate the effectiveness of BESS application in frequency control, we defined a governor free model of BESS to conduct dynamic simulation. Using the BESS dynamic model, we implemented the power system dynamic model including steam, gas and hydro turbine generators. In this paper we study the control performance of BESS in primary frequency control. The effect of BESS speed regulation rate and response time on governor free operation is investigated. In addition, we compared BESS from steam turbine generator in view point of frequency regulation.

• Journal of Advanced Marine Engineering and Technology
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• 제36권7호
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• pp.935-941
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• 2012

This paper describes a study of conventional electrical rig and simulated application of Flywheel Energy Storage system on the power system of the offshore plants with dynamic positioning system with the following aims: improve fuel consumption on engines, prevent blackout and mitigate voltage sags due to pulsed load and fault. Fuel consumption has been analyzed for the generators of the typical drilling rigs compared with the power plant with Flywheel Storage Unit which has an important aid in avoiding power interruption during DP (Dynamic Positioning) operation. The FES (Fly wheel Energy storage System) releases energy very quickly and efficiently to ensure continuity of the power supply to essential consumers such as auxiliary machinery and thrusters upon main power failure. It will run until the standby diesel generator can start and supply the electric power to the facilities to keep the vessel in correct position under DP operation. The proposed backup method to utilize the quick and large energy storage Flywheel system can be optimized in any power system design on offshore plant.

• 조명전기설비학회논문지
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• 제23권7호
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• pp.57-66
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• 2009

Microturbines system (MTS) are currently being deployed as small scale on-site distributed generators for microgrids and smart grids. In order to fully exploit DG potentialities, advanced integrated controls that include power electronics facilities, communication technologies and advanced modeling are required. Significant expectations are posed on gas microturbines that can be easily installed in large commercial and public buildings. Modeling, control, simulation of microturbine generator based distributed generation system in smart grid application of buildings for both grid-connected and islanding conditions are presented. It also incorporates modeling and simulation of MT with a speed control system of the MT-permanent magnet synchronous generator to keep the speed constant with load variation. Model and simulations are performed using MATLAB, Simulink and SimPowerSystem software package. The model is built from the dynamics of each part with their interconnections. This simplified model is a useful tool for studying the various operational aspects of MT and is also applicable with building cooling, heating and power (BCHP) systems