• Title, Summary, Keyword: Power density

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Power Density Maximization of the Brushless DC Generator by Controlling the Optimal Current Waveform (최적 전류파형제어를 통한 브러시리스 DC 발전기의 출력밀도 최대화에 관한 연구)

  • 이형우
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.53 no.7
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    • pp.430-436
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    • 2004
  • This paper presents an advanced control technique for power density maximization of the Brushless DC (BLDC) generator by using the linear tracking method. In a generator of given rating, the weight and size of the system affect the fuel consumption directly. Therefore, power density is one of the most important issues in a stand-alone generator. BLDC generator has high power density in the machine point of view and additional increases of power density by control means can be expected. Conventional rectification methods cannot achieve the maximum power possible because of hon-optimal current waveforms. The optimal current waveform to maximize power density and minimize machine size and weight in a nonsinusoidal power supply system has been derived, incorporated in a control system, and verified by simulation and experimental work. A new simple algebraic method has been proposed to accomplish the proposed control without an FFT which is time consuming and complicated.

The Bandwidth from the Density Power Divergence

  • Pak, Ro Jin
    • Communications for Statistical Applications and Methods
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    • v.21 no.5
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    • pp.435-444
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    • 2014
  • The most widely used optimal bandwidth is known to minimize the mean integrated squared error(MISE) of a kernel density estimator from a true density. In this article proposes, we propose a bandwidth which asymptotically minimizes the mean integrated density power divergence(MIDPD) between a true density and a corresponding kernel density estimator. An approximated form of the mean integrated density power divergence is derived and a bandwidth is obtained as a product of minimization based on the approximated form. The resulting bandwidth resembles the optimal bandwidth by Parzen (1962), but it reflects the nature of a model density more than the existing optimal bandwidths. We have one more choice of an optimal bandwidth with a firm theoretical background; in addition, an empirical study we show that the bandwidth from the mean integrated density power divergence can produce a density estimator fitting a sample better than the bandwidth from the mean integrated squared error.

THREE-DIMENSIONAL CORE DESIGN OF A SUPER FAST REACTOR WITH A HIGH POWER DENSITY

  • Cao, Liangzhi;Oka, Yoshiaki;Ishiwatari, Yuki;Ikejiri, Satoshi;Ju, Haitao
    • Nuclear Engineering and Technology
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    • v.42 no.1
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    • pp.47-54
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    • 2010
  • The SuperCritical Water-cooled Reactor (SCWR) pursues high power density to reduce its capital cost. The fast spectrum SCWR, called a super fast reactor, can be designed with a higher power density than thermal spectrum SCWR. The mechanism of increasing the average power density of the super fast reactor is studied theoretically and numerically. Some key parameters affecting the average power density, including fuel pin outer diameter, fuel pitch, power peaking factor, and the fraction of seed assemblies, are analyzed and optimized to achieve a more compact core. Based on those sensitivity analyses, a compact super fast reactor is successfully designed with an average power density of 294.8 W/$cm^3$. The core characteristics are analyzed by using three-dimensional neutronics/thermal-hydraulics coupling method. Numerical results show that all of the design criteria and goals are satisfied.

Estimation of the Nuclear Power Peaking Factor Using In-core Sensor Signals

  • Na, Man-Gyun;Jung, Dong-Won;Shin, Sun-Ho;Lee, Ki-Bog;Lee, Yoon-Joon
    • Nuclear Engineering and Technology
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    • v.36 no.5
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    • pp.420-429
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    • 2004
  • The local power density should be estimated accurately to prevent fuel rod melting. The local power density at the hottest part of a hot fuel rod, which is described by the power peaking factor, is more important information than the local power density at any other position in a reactor core. Therefore, in this work, the power peaking factor, which is defined as the highest local power density to the average power density in a reactor core, is estimated by fuzzy neural networks using numerous measured signals of the reactor coolant system. The fuzzy neural networks are trained using a training data set and are verified with another test data set. They are then applied to the first fuel cycle of Yonggwang nuclear power plant unit 3. The estimation accuracy of the power peaking factor is 0.45% based on the relative $2_{\sigma}$ error by using the fuzzy neural networks without the in-core neutron flux sensors signals input. A value of 0.23% is obtained with the in-core neutron flux sensors signals, which is sufficiently accurate for use in local power density monitoring.

A Unified Analysis of Low-Power and High-Power Density Laser Welding Processes with Evolution of Free Surface (자유표면변형을 고려한 저에너지밀도 및 고에너지밀도 레이저 용접공정 통합 해석)

  • Ha Eung-Ji;Kim Woo-Seung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.10
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    • pp.1111-1118
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    • 2005
  • In this study, a unified numerical investigation has been performed on the evolution of weld pool and key-hole geometry during low-power and high-power density laser welding. Unsteady phase-change heat transfer and fluid flow with the surface tension are examined. The one-dimensional vaporization model is introduced to model the overheated surface temperature and recoil pressure during high-power density laser welding. It is shown that Marangoni convection in the weld pool is dominant at low-power density laser welding, and the keyhole with thin liquid layer and the hump are visible at high-power density laser welding. It is also shown that the transition from conduction welding to penetration welding fur iron plate exists when the laser power density is about $10^6W/Cm^2$.

Power density of various light curing units through resin inlays with modified layer thickness

  • Hong, Sung-Ok;Oh, Yong-Hui;Min, Jeong-Bum;Kim, Jin-Woo;Lee, Bin-Na;Hwang, Yun-Chan;Hwang, In-Nam;Oh, Won-Mann;Chang, Hoon-Sang
    • Restorative Dentistry and Endodontics
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    • v.37 no.3
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    • pp.130-135
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    • 2012
  • Objectives: The purpose of this study was to enhance curing light penetration through resin inlays by modifying the thicknesses of the dentin, enamel, and translucent layers. Materials and Methods: To investigate the layer dominantly affecting the power density of light curing units, resin wafers of each layer with 0.5 mm thickness were prepared and power density through resin wafers was measured with a dental radiometer (Cure Rite, Kerr). The dentin layer, which had the dominant effect on power density reduction, was decreased in thickness from 0.5 to 0.1 mm while thickness of the enamel layer was kept unchanged at 0.5 mm and thickness of the translucent layer was increased from 0.5 to 0.9 mm and vice versa, in order to maintain the total thickness of 1.5 mm of the resin inlay. Power density of various light curing units through resin inlays was measured. Results: Power density measured through 0.5 mm resin wafers decreased more significantly with the dentin layer than with the enamel and translucent layers (p < 0.05). Power density through 1.5 mm resin inlays increased when the dentin layer thickness was reduced and the enamel or translucent layer thickness was increased. The highest power density was recorded with dentin layer thickness of 0.1 mm and increased translucent layer thickness in all light curing units. Conclusions: To enhance the power density through resin inlays, reducing the dentin layer thickness and increasing the translucent layer thickness would be recommendable when fabricating resin inlays.

Density distributions and Power spectra of outflow-driven turbulence

  • Kim, Jongsoo;Moraghan, Anthony
    • The Bulletin of The Korean Astronomical Society
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    • v.39 no.1
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    • pp.57.2-57.2
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    • 2014
  • Protostellar jets and outflows are signatures of star formation and promising mechanisms for driving supersonic turbulence in molecular clouds. We quantify outflow-driven turbulence through three-dimensional numerical simulations using an isothermal version of the total variation diminishing code. We drive turbulence in real space using a simplified spherical outflow model, analyze the data through density probability distribution functions (PDFs), and investigate density and velocity power spectra. The real-space turbulence-driving method produces a negatively skewed density PDF possessing an enhanced tail on the low-density side. It deviates from the log-normal distributions typically obtained from Fourier-space turbulence driving at low densities, but can provide a good fit at high densities, particularly in terms of mass-weighted rather than volume-weighted density PDF. We find shallow density power-spectra of -1.2. It is attributed to spherical shocks of outflows themselves or shocks formed by the interaction of outflows. The total velocity power-spectrum is found to be -2.0, representative of the shock dominated Burger's turbulence model. Our density weighted velocity power spectrum is measured as -1.6, slightly less that the Kolmogorov scaling values found in previous works.

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The Design of PC-based Power Spectral Density Analyzer of Heart Rate Variability (PC-기반의 심박변동 팍워스픽트럼밀도 분석기 설계)

  • 김낙환;이응혁;민홍기;홍승홍
    • The Transactions of the Korean Institute of Electrical Engineers D
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    • v.52 no.9
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    • pp.547-553
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    • 2003
  • In this paper, we designed the PC-based analyzer of the power spectral density that could estimate the heart rate variability from time series data of R-R interval. The power spectral density estimated that it applied the autoregressive model to the measured electrocardiogram during a short period. Also, the characteristics of the designed analyzer are that it could process of the signal filtering, the generation and recomposition of time series and the feature extraction at the same time. Especially the analyzer reconstructed which applied the lowpass filter of the time series composed by the linear interpolation so as to enhance the signal-to-noise feature. We could estimate the power spectral density that confirmed a variety of power peak with low frequency range and high frequency rang of autonomic nerve by the heart rate variability.

A Study on the Improvement of Power Density for IPMSM (IPM 모터의 출력밀도 향상에 관한 연구)

  • Jin, Chang-Sung
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.64 no.5
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    • pp.701-707
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    • 2015
  • Recently, it has to design the motor to raise power density because of many necessary application, such as home appliances and hybrid electric vehicles. Power of motor is made up of the torque and speed. So, if the motor which is the same size and shape is designed to raise speed, power and power density are increase.