• 제어로봇시스템학회:학술대회논문집
• /
• 2001.10a
• /
• pp.167.5-167
• /
• 2001

Single point attitude determination method provides an optimal attitude minimizing the Wahba loss function. However, for the insufficient number of measurement vectors, the conventional single point methods has no unique solution. Thus, we introduce the sequential method to and an optimal attitude minimizing the windowed loss function. In this paper, this function is de ned as the sum of square errors for all measurement vectors within the axed sliding window. For simple implementation, the proposed algorithm is rewritten as a recursive form. Moreover, the covariance matrix is derived and expressed as a recursive form. Finally, we apply this algorithm to the attitude determination system with three LOS measurement sensors.

• Journal of the Korean Data and Information Science Society
• /
• v.22 no.6
• /
• pp.1251-1256
• /
• 2011

Consider a p-variate ($p{\geq}4$) normal distribution with mean ${\theta}$ and identity covariance matrix. Using a simple property of noncentral chi square distribution, the generalized Bayes estimators dominating the Lindley estimator under quadratic loss are given based on the methods of Brown, Brewster and Zidek for estimating a normal variance. This result can be extended the cases where covariance matrix is completely unknown or ${\Sigma}={\sigma}^2I$ for an unknown scalar ${\sigma}^2$.

• Journal of Korea Water Resources Association
• /
• v.49 no.12
• /
• pp.1015-1025
• /
• 2016

In general, manholes installed as urban drainage facilities are a variety forms such as straight path manholes, 90 degree bend manhole, three-way combining manhole, and four-way combining manhole. In particular, the surcharged flow at a four-way manholes installed in the downstream of urban sewer system is the main cause of the urban inundation caused by the energy loss. Therefore, it is necessary to analyze the flow characteristics and estimate the head loss coefficients at surcharged four-way combining manholes. The hydraulic experimental apparatus which can change the manhole shapes (square, circle) and flow ratios were installed to estimate the head loss coefficients. In the experiments, two inflows ($Q_m$, $Q_{lat}$) were varied from 0 to $4.8{\ell}/sec$ and 24 combinations were tested in total. The flow ratios $Q_{lat}/Q_{out}$ were varied from 0 to 1 for a total flow $Q_{out}$ ($Q_{out}=Q_m+2Q_{lat}$) of 2, 3, 4, and $4.8{\ell}/sec$, respectively. The variation of head losses were strongly influenced by the lateral inflow because the head loss coefficient increases as the flow ratios $Q_{lat}/Q_{out}$ increases. It was estimated head loss coefficients of the circular manhole is slightly lower than those of the square manhole. However, there was no significant difference of head loss as discharges change. The range of head loss coefficients at four-way combining manhole according to the change of the lateral inflow ratio was estimated to be 0.4 to 0.8. Also, the relation equations between the head loss coefficients (K) and the lateral inflow ratios ($Q_{lat}/Q_{out}$) were suggested in this paper.

• Proceedings of the KIEE Conference
• /
• 1999.07a
• /
• pp.259-261
• /
• 1999

In this paper, we investigated the frequency dependences of AC loss and the magnetic properties of a superconductor using magnetization method. We used the YBCO bulk superconductor sample which has a square-shaped cross sectional area of $6mm{\times}6mm$. and 43mm-long in axial direction. The applied AC magnetic field was parallel to the direction of sample axis. It is observed that YBCO bulk has the diamagnetic properties. AC loss calculation of YBCO bulk superconductor was performed by evaluating the total area of magnetization traces. We performed two cases of experiments, one for $B_m<B_p$ and the other for $B_m<B_p$. The experiments showed that the AC loss dependences on frequency were different in each mode, as was indicated in other publications.

• Journal of Power System Engineering
• /
• v.12 no.3
• /
• pp.26-31
• /
• 2008

This experimental study investigates the local heat transfer enhancement characteristics and the associated frictional head loss in the rectangular channel with a single inclined baffle. Four different types of the baffle are used. The inclined baffles have the width of 19.8 cm, the square diamond of $2.55cm{\times}2.55cm$, and the inclination angle of 5o, and number of holes of up to 9. Reynolds number is varied between 23,000 and 57,000. Results show that the heat transfer and friction factor depend significantly on the number of baffle holes and Reynolds number. The friction factor decreases with increasing Reynolds number and the number of holes on the baffle. It is found that the heat transfer performance of baffle type II(3 hole baffle) has the best values.

• 한국전산유체공학회:학술대회논문집
• /
• 2010.05a
• /
• pp.305-307
• /
• 2010

In this study, we develop a method to achieve heat transfer enhancement inside a square duct with high aspect ratio without changing any inner structures. Especially, a method to lower the possible maximum temperature is suggested if constant heat flux is provided to single surface of square duct. Knowing the fact that heat transfer rate is inversely proportional to flow area, we proposed tapered channel concept which uses narrower gap toward the flow exit where the maximum temperature is expected. To maintain equivalent power consumption, inlet section has been enlarged. To verify the proposed concept, experimental tests have been performed.

• Journal of electromagnetic engineering and science
• /
• v.4 no.1
• /
• pp.43-49
• /
• 2004

A low-frequency coaxial reflectometer(LCR) with a thin-wire inner conductor is designed and constructed to measure nondestructively the absorbing performance of electromagnetic absorbers in the frequency range of 10 MHz to 200 MHz. The LCR consists of a square coaxial transmission line and a network analyzer with a time-domain measurement capability. Inherent characteristics of a square coaxial line with a thin-wire inner conductor which deteriorate the impedance matching of the input port of the LCR are addressed. And the characteristics are improved by employing a multiwire inner conductor. Measured and calculated reflection losses of a flat ferrite tile absorber are presented.

• Knowledge Management Research
• /
• v.21 no.1
• /
• pp.27-40
• /
• 2020

Response surface methodology (RSM) empirically studies the relationship between a response variable and input variables in the product or process development phase. The ultimate goal of RSM is to find an optimal condition of the input variables that optimizes (maximizes or minimizes) the response variable. RSM can be seen as a knowledge management tool in terms of creating and utilizing data, information, and knowledge about a product production and service operations. In the field of product or process development, most real-world problems often involve a simultaneous consideration of multiple response variables. This is called a multiple response surface (MRS) problem. Various approaches have been proposed for MRS optimization, which can be classified into loss function approach, priority-based approach, desirability function approach, process capability approach, and probability-based approach. In particular, the loss function approach is divided into univariate and multivariate approaches at large. This paper focuses on the univariate approach. The univariate approach first obtains the mean square error (MSE) for individual response variables. Then, it aggregates the MSE's into a single objective function. It is common to employ the weighted sum or the Tchebycheff metric for aggregation. Finally, it finds an optimal condition of the input variables that minimizes the objective function. When aggregating, the relative weights on the MSE's should be taken into account. However, there are few studies on how to determine the weights systematically. In this study, we propose an interactive procedure to determine the weights through considering a decision maker's preference. The proposed method is illustrated by the 'colloidal gas aphrons' problem, which is a typical MRS problem. We also discuss the extension of the proposed method to the weighted MSE (WMSE).

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.14 no.4
• /
• pp.247-256
• /
• 2021

In this paper, we propose a packet loss concealment (PLC) algorithm using pitch harmonic motion prediction and adaptive signal amplitude prediction and. The spectral motion prediction method divides the spectral motion of the previous usable frame into predetermined sub-bands to predict and restore the motion of the lost signal. In the proposed algorithm, the speech signal is classified into voiced and unvoiced sounds. In the case of voiced sounds, it is further divided into pitch harmonics using the pitch frequency to predict and restore the pitch harmonic motion of the lost frame, and for the unvoiced sound, the lost frame is restored using the spectral motion prediction method. When the continuous loss of speech frames occurs, a method of adjusting the gain using the least mean square (LMS) predictor is proposed. The performance of the proposed algorithm was evaluated through the objective evaluation method, PESQ (Perceptual Evaluation of Speech Quality) and was showed MOS 0.1 improvement over the conventional method.

• Proceedings of the IEEK Conference
• /
• 2002.07a
• /
• pp.654-657
• /
• 2002

This paper introduces the design and implementation of 40-㎓-band low noise amplifier (LNA) with ultra low gain flatness for wide-band wireless multimedia and satellite communication systems. The 40-㎓-band 4-stage LNA MMIC (Monolithic Microwave Integrated Circuit) demonstrates a small signal gain of more than 20 ㏈, an input return loss of 10.3 ㏈, and an output return loss of 16.3 ㏈ for 37$\square$42 ㎓. The gain flatness of the 40-㎓-band 4-stage LNA MMIC was 0.1 ㏈ for 37$\square$42 ㎓. The noise figure of the 40 ㎓-band LNA was simulated to be less than 2.7 dB for 37~42 ㎓. The chip size of the 4-stage LNA MMIC was 3.7${\times}$1.7 $\textrm{mm}^2$.