• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11A
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• pp.1053-1062
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• 2008

This paper provides a general and compact expression for the probability density function (pdf) and the moment-generating function (MGF) of the maximal ratio combiner output over Rayleigh fading channels. It is then used to derive closed form expression bit error rate (BER) for M-PSK, M-PAM and M-QAM, respectively. A variety of simulations is performed and shows that they match exactly with analytic ones.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.235-241
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• 2004

Computations were performed to investigate the effects of air staging on combustion in three stage heavy-oil fired combustion burner. The burner was designed for 3 MW. Different amounts of air are introduced into each 3 three stages by means of each dampers. The goal of the study is to understand combustion phenomena according to each air stage mass ratios through CFD. Air flow rates at three inlets are adjusted by dampers inside a burner. Here, injection conditions of liquid fuel are kept constant throughout all simulations. This assumption is made in order to limit the complexity of oil combustion though it may cause some disagreement. In case of cold flows, only longitudinal velocities arc considered, On the other hand, flow, temperature and NOx generations are taken into account for reactive flows. Simple parametric study was conducted by setting 1'st air stage mass ratio as a parameter. And an optimal operation condition was found. The computational study is based on k-e model, P-1 radiation model(WSGGM) and PDF, and is implemented on a commercial code, FLUENT.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.58-65
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• 2009

The paper identifies noise characteristics of a nonliner image sensor model which reflects a saturation effect of each detector pixel and extends the result to estimate an image SNR (Signla-to-Noise Ratio) distribution over all the pixels in a detector. In particular, nonlinearity of a pixel is studied from two perspectives of including asymmetry of a noise PDF (Probability Distribution Function) and enhancing a pixel SNR value, in comparison to a linear model. It is noted that the proposed image SNR distribution function is useful to effectively select new optimal operation parameter values: an integration time and an pixel-summing number, even after a launch campaign, assuming sensor gain degradation in orbit or inevitable modification of some operation parameter values due to space contingency.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.209-214
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• 2002

Computations were performed to investigate the flow, temperature and pollutants in two stage heavy-oil combustion burner. The burner geometry and flow conditions were provided by a burner company. The goal of the study is to understand combustion phenomena according to each air inlet's velocity, excessive air ratio and air temperature through CFD. Air flow rates at two inlets are adjusted by a damper inside a burner. Here, injection conditions of liquid fuel are kept constant throughout all simulations. This assumption is made in order to limit the complexity of oil combustion though it may cause some disagreement. The final goal of this research is to design a Low-NOx heavy oil combustion burner through comparison between computational study and experimental ones. Besides experiments, simulation works can give us insights into heavy oil combustion and help us design a Low NOx burner while saving time and cost. The computational study is based on k-e model, P-1 radiation model(WSGGM) and PDF, and is implemented on a commercial code, FLUENT.

• Journal of the Korean Society of Combustion
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• v.4 no.2
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• pp.35-41
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• 1999

The purpose of this study is to establish the flame structure and NOx emission characteristics of the swirl flow coaxial diffusion combustion in the model gas turbine combustor. The mean temperature, ion currents and NOx emission measurement technique showed the effect of equivalence ratio into flame length and flame stability. As a result of this study, NOx emission was increased by increasing the equivalence ratio, and the peak value of the NOx was appeared near the flame front.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.539-542
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• 2011

In this paper, we have implemented a performance analysis of $2{\times}1$ Alamouti scheme suggested by Alamouti, composed of the transmit space-time code and the simple linear decoding processing, in perfectly time-varying and spatially correlated channels. In addition, we derived the closed-form probability density function (PDF) of the output signal-to-noise ratio (SNR) and the outage probability of the Alamouti scheme as a function of the spatial correlation coefficient in the consideration of no correlation in time. As a result, it was found that the performance of the Alamouti scheme could be significantly degraded particularly in the case that the channels are time-varying and spatially correlated.

• 한국연소학회:학술대회논문집
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• 1999.10a
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• pp.139-148
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• 1999

In oder to analyze the effect of operating conditions on pulverized coal combustion, a numerical study is conducted at the pulverized coal combustor. Eulerian approach is used for the gas phase, whereas Lagrangian approach is used for the particle phase. Turbulence is modeled using standard ${\kappa}-{\varepsilon}$ model. The description of species transport and combustion chemistry is based on the mixture fraction/probability density function(PDF) approach. Radiation is modeled using P-l model. The turbulent dispersion of particles is modeled using discrete random walk model. Swirl number of secondary air affects the flame front, particle residence time and carbon conversion. Primary/Secondary air mass ratio also affects the flame front but little affects the carbon conversion and particle residence time. Air-fuel ratio only affects the flame front due to lack of oxygen. Radiation strongly affects the flame front and gas temperature distribution because pulverized coal flame of high temperature is considered.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.338-341
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• 1993

A EEG(ElectroEncephaloGram) compression scheme based on subband coding techniques is presented in this paper. Considering the frequency characteristics of EEG, the raw signal was decomposed into different frequency bands. After decomposition, optimal bit allocation was done by adapting to the standard deviation in each frequency bands, and decomposed signals were quantized using pdf(probability density function)-optimized nonuniform quantizer. Based on the above mentioned coding scheme, coding results of various multichannel EEG signal were shown with compression ratio and SNR(signal-to-noise ratio).

• Journal of the Korean Institute of Telematics and Electronics
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• v.16 no.5
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• pp.12-17
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• 1979

This paper presents the investigation of the theoretical symbol error performances of an M-ary differential phase-shift-keyed(DPSK) system in an interference environment. A simple method is transmitted over a nondistroting channel, but additively corrupted by Gaussian noise and cochannel interference. Computed DPSK symbol error performance results for M=2, 4, and 8 are compared with the corresponding curves for coherent phase-shift-Keyed(CPSK) system as a function of carrier-to-noise power ratio(CNR) with carrier-to-interferer power ratio(CIR) as a parameter. Comparisons between DPSK systems reveal, as we might expect, that DPSK system suffers more degradation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.274-277
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• 2012

Large eddy simulation is applied to the turbulent flow and heat transfer in straight cooling passages with varying aspect ratio. The turbulent statistics of the flow and thermal quantities are calculated and the characteristics of Nusselt number are investigated. To scrutinize near-wall streamwise vortices, a conditional sampling technique is adopted. Clockwise and counter-clockwise rotating streamwise vortices are sampled and the probability density function of the vortex circulation Reynolds number and wall Nusselt number are calculated.