• 한국전산유체공학회지
• /
• 제2권1호
• /
• pp.8-12
• /
• 1997

The three-dimensional Euler equations are solved numerically for the analysis of contraction flows in wind or water tunnels. A second-order finite difference method is used for the spatial discretization on the nonstaggered grid system and the 4-stage Runge-Kutta scheme for the numerical integration in time. In order to speed up the convergence, the local time stepping and the implicit residual-averaging schemes are introduced. The pressure field is obtained by solving the pressure-Poisson equation with the Neumann boundary condition. For the evaluation of the present Euler solver, numerical computations are carried out for three contraction geometries, one of which was adopted in the Large Cavitation Channel for the U.S. Navy. The comparison of the computational results with the available experimental data shows good agreement.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
• /
• pp.34-39
• /
• 1999

If the on-line cutting conditions (e.g. speed, feedrate, radial and axal depth of cuts) can be identified in an end milling process, much information about cutting forces will be estimated from the cutting force model. Therefore, those estimated conditions can be applied to monitoring and control areas. In this paper, a real-time estimation algorithm for radial and axial depth of cuts is studied in end milling using the averaging cutting forces per tooth. The analytical estimation models of depth of cuts are derived from the geometric cutting force model. The validity of the estimation models is verified on a horizontal machining center through the experiments in various cutting conditions.

• 대한의용생체공학회:의공학회지
• /
• 제8권2호
• /
• pp.117-117
• /
• 1987

The medical image processing system is intended for a diverse set of users in the medical Imaging Parts. This system consists of a 640 Kbyte IBM-PC/AT with 30 Mbyte hard disk, special purpose image processor with video input devices and display monitor. Image may be recorded and processed in real time at sampling rate up to 10 MHz. This system provides a wide range of image enhancement processing facilities via a menu-driven software packages. These facilities include point by point processing, image averaging, convolution filter and subtraction.

• ETRI Journal
• /
• 제33권6호
• /
• pp.841-848
• /
• 2011

A signal-to-noise ratio (SNR) enhancement algorithm using multiple chirp symbols with clock drift is proposed for accurate ranging. Improvement of the ranging performance can be achieved by using the multiple chirp symbols according to Cramer-Rao lower bound; however, distortion caused by clock drift is inevitable practically. The distortion induced by the clock drift is approximated as a linear phase term, caused by carrier frequency offset, sampling time offset, and symbol time offset. SNR of the averaged chirp symbol obtained from the proposed algorithm based on the phase derotation and the symbol averaging is enhanced. Hence, the ranging performance is improved. The mathematical analysis of the SNR enhancement agrees with the simulations.

• 한국소음진동공학회논문집
• /
• 제22권10호
• /
• pp.917-924
• /
• 2012

Noise power of large machineries, such as textile looms, winders, and twisting machines, is often measured in a reverberant space because they cannot be installed and operated in an anechoic chamber due to their size, weight, and operating conditions. Factors affecting the measurement error of an in-situ noise power measurement include the nonuniform reverberation time and the direction of sound intensity vector which is usually regarded as normal to the measurement surface. In this study errors due to these factors are estimated with the aid of numerical simulation based on the ray-tracing technique. The averaging of reverberation times measured at several points on the measurement surface is suggested to reduce the errors from nonuniform absorption. Also the direction cosine of each surface element is taken into account, which as a whole is represented as a solid angle of the measurement surface.

• 천문학회보
• /
• 제45권1호
• /
• pp.55.1-55.1
• /
• 2020

In an attempt to investigate the nonlinear dynamics such as shock, shear, and turbulence associated with ultra-relativistic jets, we develop a new relativistic hydrodynamics (RHD) code based on the weighted essentially non-oscillatory (WENO) scheme. It is a 5th-order accurate, finite-difference scheme, which has been widely used for solving hyperbolic systems of conservation equations. The code is parallelized with MPI and OpenMP. Through an extensive set of tests, the accuracy and efficiency of different WENO reconstructions, and different time discretizations are assessed. Different implementations of the equation of state (EOS) for relativistic fluid are incorporated, As the fiducial setup for simulations of ultra-relativistic jets, we adopt the EOS in Ryu et al. (2006) to treat arbitrary adiabatic index of relativistic fluid, the WENO-Z reconstructions to minimize numerical dissipation without loss of stability, and the strong stability preserving Runge-Kutta (SSPRK) method to achieve stable time stepping with large CFL numbers. In addition, the code includes a high-order flux averaging along the transverse directions for multi-dimensional problems, and the modified eigenvalues for the acoustic modes to effectively control the carbuncle instability. We find that the new code performs satisfactorily simulations of ultra-relativistic jets.

• Current Optics and Photonics
• /
• 제7권6호
• /
• pp.708-713
• /
• 2023

A robust all-fiber nonlinear amplifying loop-mirror-based mode-locked femtosecond laser is demonstrated. Power-dependent nonlinear phase shift in a Sagnac loop enables stable and power-efficient mode-locking working as an artificial saturable absorber. The pump power is adjusted to achieve the lowest intensity noise for stable long-term operation. The minimum pump power for mode-locking is 180 mW, and the optimal pump power is 300 mW. The lowest integrated root-mean-square relative intensity noise of a free-running mode-locked laser is 0.009% [integration bandwidth: 1 Hz-10 MHz]. The long-term repetition-rate instability of a free-running mode-locked laser is 10^-7 over 1,000 s averaging time. The repetition-rate phase noise scaled at 10-GHz carrier is -122 dBc/Hz at 10 kHz Fourier frequency. The demonstrated method can be applied as a seed source in high-precision real-time mid-infrared molecular spectroscopy.

• 한국인터넷방송통신학회논문지
• /
• 제11권2호
• /
• pp.231-236
• /
• 2011

근래에 위치 정보를 이용하는 위치기반서비스는 많은 분야에서 이용되고 있다. 그에 따라 위치인식 기법들에 대해 많은 연구가 이루어지고 있다. 다양한 위치인식 시스템 중 TOA(Time of Arrival)이나 TDOA(Time Difference of Arrival)와 같은 시간 기반 위치인식 알고리즘을 사용하는 위치인식 시스템에서는 AWGN(Additive White Gaussian Noise)와 다중경로에 의한 왜곡이 위치인식 성능의 저하를 발생시킨다. 본 논문에서는 이런 성능 저하를 극복하기 위해서 여러 개의 펄스를 평균하는 방법으로 잡음을 제거한다. 그리고 임계값 설정을 통해 직선 경로 신호를 검출함으로써 위치인식 성능을 향상시키는 기법에 대해 연구하였다.

• 대한기계학회논문집B
• /
• 제21권3호
• /
• pp.427-435
• /
• 1997

Conditional sampling techniques are utilized to investigate the relation between the wall skin-friction and stream wise velocity fluctuations in a turbulent boundary layer. Conditionally averaged results using a peak detection and the VITA (variable-interval time-averaging) technique show that a high skin friction is associated with high frequency components of the wall skin-friction fluctuations. The conditionally averaged wall skin-friction fluctuations obtained by using the VITA technique have a positively-skewed characteristics compared with the conditionally averaged stream wise velocity fluctuations. It is confirmed that there exists a phase shift between the wall skin-friction and stream wise velocity fluctuations, which was also found from the long-time averaged space-time correlations. The amount of phase shift between the wall skin-friction and stream wise velocity fluctuations is the same as that from the long-time averaged space-time correlations and does not change despite the variation of the detection threshold.

• 한국지능시스템학회논문지
• /
• 제10권2호
• /
• pp.113-121
• /
• 2000

이 논문에서는 병렬구조 퍼지시스템(PSFS)에 기초한 카오스 시계열 데이터의 예측 알고리즘에 대해 연구하였다 병렬구조 퍼지시스템은 병렬로 연결된 여러개의 퍼지시스템에 의하여 구성되어있다. 병렬구조 퍼지시스템을 구성하고 있는 각 퍼지시스템은 다른 임베딩 차원과 시간지연을 가지고 과거의 데이터를 이용하여 동일한 데이터를 독립적으로 예측한다 퍼지시스템은 입출력 데이터를 클러스터링하여 모델링되는 MISO Sugeno 퍼지규칙에 의하여 특징지어진다. 각 퍼지시스템에 대한 최적 임베딩차원은 주어진 시간지연값에 대해서 최적의 성능을 갖도록 선정된다. 병렬구조 퍼지시스템은 각 구성요소 퍼지스템들의 예측값중에서 최대값과 최소값을 가지는 예측결과를 제외하고 나머지 값들을 평균하여 최종 예측 결과를 얻는다.