• Advances in nano research
• /
• 제3권3호
• /
• pp.143-168
• /
• 2015

Initiation of crack and its growth simulation requires accurate model of traction - separation law. Accurate modeling of traction-separation law remains always a great challenge. Atomistic simulations based prediction has great potential in arriving at accurate traction-separation law. The present paper is aimed at establishing a method to address the above problem. A method for traction-separation law prediction via utilizing atomistic simulations data has been proposed. In this direction, firstly, a simpler approach of common neighbor analysis (CNA) for the prediction of crack growth has been proposed and results have been compared with previously used approach of threshold potential energy. Next, a scheme for prediction of crack speed has been demonstrated based on the stable crack growth criteria. Also, an algorithm has been proposed that utilizes a variable relaxation time period for the computation of crack growth, accurate stress behavior, and traction-separation atomistic law. An understanding has been established for the generation of smoother traction-separation law (including the effect of free surface) from a huge amount of raw atomistic data. A new curve fit has also been proposed for predicting traction-separation data generated from the molecular dynamics simulations. The proposed traction-separation law has also been compared with the polynomial and exponential model used earlier for the prediction of traction-separation law for the bulk materials.

• 한국도로학회논문집
• /
• 제15권4호
• /
• pp.21-29
• /
• 2013

PURPOSES : The objective of this study is to provide for the overall SPL (Sound Pressure Level) prediction model by using the NCPX (Noble Close Proximity) measurement method in terms of regression equations. METHODS: Many methods can be used to measure the traffic noise. However, NCPX measurement can powerfully measure the friction noise originated somewhere between tire and pavement by attaching the microphone at the proximity location of tire. The overall SPL(Sound Pressure Level) calculated by NCPX method depends on the vehicle speed, and the basic equation form of the prediction model for overall SPL was used, according to the previous studies (Bloemhof, 1986; Cho and Mun, 2008a; Cho and Mun, 2008b; Cho and Mun, 2008c). RESULTS : After developing the prediction model, the prediction model was verified by the correlation analysis and RMSE (Root Mean Squared Error). Furthermore, the correlation was resulted in good agreement. CONCLUSIONS: If the polynomial overall SPL prediction model can be used, the special cautions are required in terms of considering the interpolation points between vehicle speeds as well as overall SPLs.

• ETRI Journal
• /
• 제38권5호
• /
• pp.807-817
• /
• 2016

A novel fast algorithm is suggested for a coding unit (CU) mode decision using pseudo rate-distortion based on a separated encoding structure in High Efficiency Video Coding (HEVC). A conventional HEVC encoder requires a large computational time for a CU mode prediction because prediction and transformation procedures are applied to obtain a rate-distortion cost. Hence, for the practical application of HEVC encoding, it is necessary to significantly reduce the computational time of CU mode prediction. As described in this paper, under the proposed separated encoder structure, it is possible to decide the CU prediction mode without a full processing of the prediction and transformation to obtain a rate-distortion cost based on a suitable condition. Furthermore, to construct a suitable condition to improve the encoding speed, we employ a pseudo rate-distortion estimation based on a Hadamard transformation and a simple quantization. The experimental results show that the proposed method achieves a 38.68% reduction in the total encoding time with a similar coding performance to that of the HEVC reference model.

• 한국가시화정보학회지
• /
• 제21권1호
• /
• pp.18-25
• /
• 2023

In these days, high dimensional data prediction technology based on neural network shows compelling results in many different kind of field including engineering. Especially, a lot of variants of convolution neural network are widely utilized to develop pixel level prediction model for high dimensional data such as picture, or physical field value from the sensors. In this study, velocity vector field of ideal flow on ship surface is estimated on pixel level by Unet. First, potential flow analysis was conducted for the set of hull form data which are generated by hull form transformation method. Thereafter, four different neural network with a U-shape structure were conFig.d to train velocity vectors at the node position of pre-processed hull form data. As a result, for the test hull forms, it was confirmed that the network with short skip-connection gives the most accurate prediction results of streamlines and velocity magnitude. And the results also have a good agreement with potential flow analysis results. However, in some cases which don't have nothing in common with training data in terms of speed or shape, the network has relatively high error at the region of large curvature.

• 한국ITS학회 논문지
• /
• 제12권4호
• /
• pp.44-55
• /
• 2013

지능형교통체계(ITS: Intelligent Transportation System)의 발전은 과거에 비해 보다 신뢰성 있고 폭넓은 교통자료 및 기상자료 등의 취득을 가능하도록 하였다. 이러한 첨단 시스템의 발전에 따라 수집된 자료를 이용하여 교통상황과 기상상황에 대한 다양한 연구가 활발히 진행되고 있다. 본 연구에서는 도로 기상정보 시스템(RWIS: Road Weather Information System)자료와 검지기 자료를 이용하여 강우량에 따른 속도 감소 패턴을 분석하고, 강우량에 따른 속도감소량 산출 결과를 통해 강우수준을 분류하는 기준을 제시하였다. 인공신경망을 이용하여 강우수준별 통행속도를 예측하였으며, 예측 결과를 비교하여 강우수준별 통행속도 예측 특성을 분석하였다. 분석결과, 강우수준 분류 기준은 0.4mm/5min, 0.8mm/5min으로 나타났으며, 강우수준별 속도와 교통량에 대한 분산분석 결과 강우수준별로 차이를 보이는 것으로 나타났다. 인공신경망을 통한 5분 단위의 통행속도 예측결과, 비강우인 경우에는 과거 5개 자료, 즉, 25분 동안의 속도자료를 사용하여 분석하는 것이 예측력이 높게 나타났으며, 강우가 발생하는 경우에는 과거 2~3개 자료, 즉, 10~15분 동안의 속도자료를 사용하는 것이 예측력이 높게 나타났다. 본 연구에서는 기상조건에 관계없이 신뢰성 있는 교통정보를 제공하기 위한 통행시간 예측 방법론을 제시함으로써 통행시간 정보 등의 교통정보 제공 시 보다 정확한 정보를 제공하여 교통상황 예측정보의 신뢰도 향상 및 교통상황 예측정보의 활용도를 증대시킬 수 있을 것으로 기대된다.

• 한국항해항만학회지
• /
• 제38권6호
• /
• pp.593-600
• /
• 2014

실시간 해수유동 정보를 중심으로 신조선 선박의 실선시운전에서 활용될 수 있는 정보 제공 시스템을 개발하였다. 본 시스템에서는 실선시운전 지원 정보로서 특정시간 해수유동의 공간분포를 예측하여 제공하며, 특정지점 해수유동의 시계열 변동을 예측하여 제공한다. 또한 본 시스템은 실선시운전에 있어 시험선박 운항경로에서의 해수유동 정보 및 선속 손실정보를 제공하기 위하여 GPS와 연결할 수 있는 기능을 가지고 있으며, 이러한 기능을 이용하여 실선시운전시 자동으로 운항경로상의 해수유동 실시간 정보 및 해수유동에 의한 선속손실을 계산하여 제공한다. 실선시운전 중의 정보 제공 이외에, 본 시스템에서는 특정한 시험시간과 시험경로에 대해 선속손실을 예측하여 제공함으로써 최적의 시험시간 및 시험경로를 계획할 수 있도록 지원하는 기능도 가지고 있다. 본 연구에서 개발된 실선시운전을 위한 실시간 해수유동 예측시스템은 효율적인 시험계획과 정확한 해역특성 파악을 지원할 뿐 아니라, 실선에 탑재되어 시험 중에 요구되는 다양한 정보를 제공한다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제53권3호
• /
• pp.143-151
• /
• 2004

High-speed permanent magnet machines are likely to be a key technology for electric drives and motion control systems for many applications, since they are conductive to high efficiency, high power density, small size and low weight. In high-speed machines, the permanent magnets are often contained within a retaining sleeve. However, the sleeve and the magnets are exposed to high order flux harmonics, which cause parasitic eddy current losses. Rotor losses of high-speed machines are of great importance especially in high-speed applications, because losses heat the rotor, which is often very compact construction and thereby difficult to cool. This causes a danger of demagnetization of the NdFeB permanent magnets. Therefore, special attention should be paid to the prediction of the rotor losses. This paper is concerned with the rotor losses in permanent magnet high-speed machines that are caused by permeance variation due to stator slotting. First, the flux harmonics are determined by double Fourier analysis of the normal flux density data over the rotor surface. And then, the rectilinear model was used to calculate rotor losses in permanent magnet machines. Finally, Poynting vector have been used to investigate the rotor eddy current losses of high-speed Permanent magnet machine.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 춘계학술대회 논문집
• /
• pp.425-431
• /
• 2013

Nowadays, high speed train has settled down as a fast and convenient environment-friendly transportation and it's need is gradually increasing. However increased train speed leads to increased aerodynamic noise, which causes critically affects comfortability of passengers. Especially, the pantograph of high speed train is protruded out of train body, which is the main factor for increased aerodynamic noise. Since aerodynamic noise caused pantograph should be measured in high speed, it is difficult to measure it and to analysis aerodynamic noise characteristics due to the various types of pantograph. In this research, aerodynamic noise of pantograph is predicted by CFD (Computational Fluid Dynamic) and FW-H (Ffowcs Williams-Hawkings) equation. Also, Wind tunnel test results and numerical simulation results were compared. As a result, Simulation results predicting sound pressure level is very similar with wind tunnel test result. To analyze contribution of the pantograph to the noise of high-speed train, simulation results compared with measurement results of exterior noise. The simulation reuslts found that pantograph is a dominant noise source of high-speed trains's exterior noise in low frequency section. This dominant noise was come out from vortex shedding of the panhead in the pantograph. This research will be utilized for reduce sound pressure level of pantograph.

• 한국자동차공학회논문집
• /
• 제19권5호
• /
• pp.82-91
• /
• 2011

In this paper, a planar model for mechanics of a vehicle/pedestrian collision incorporating road gradient is derived to evaluate the pre-collision speed of vehicle. It takes into account a few physical variables and parameters of popular wrap and forward projection collisions, which include horizontal distance traveled between primary and secondary impacts with the vehicle, launch angle, center-of-gravity height at launch, distance from launch to rest, pedestrian-ground drag factor, the pre-collision vehicle speed and road gradient. The model including road gradient is derived analytically for reconstruction of pedestrian collision accidents, and evaluates the vehicle speed from the pedestrian throw distance. The model coefficients have physical interpretations and are determined through direct calculation. This work shows that the road gradient has a significant effect on the evaluation of the vehicle speed and must be considered in accident cases with inclined road. In additions, foreign/domestic empirical cases and multibody dynamic simulation results are used to construct a least-squares fitted model that has the same structure of the analytical one that provides an estimate of the vehicle speed based on the pedestrian throw distance and the band within which the vehicle speed would be expected to be in 95% of cases.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2003년도 ICCAS
• /
• pp.57-60
• /
• 2003

We have proposed the adaptive noise reduction algorithm using the MDFT. The algorithm proposed use the linear prediction coefficients of the AR method based on Sign algorithm that is the modified LMS instead of the least mean square(LMS). The signals with a random noise tracking performance are examined through computer simulations and confirmed that the high speed adaptive noise reduction processing system is realized with rapid convergence.