• Journal of Welding and Joining
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• v.26 no.4
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• pp.61-65
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• 2008

The static force balance model (SFBM) has been used to analyze drop transfer in gas metal arc welding. Although the SFBM is capable of predicting the detaching drop size in the globular mode with reasonable accuracy, discrepancy between the calculated and experimental results increases with current. In order to reduce discrepancy, the SFBM is modified by considering the momentum of the molten metal flow, which is generated by the pinch pressure. The momentum increases with smaller drop size and becomes compatible to the electromagnetic force. The modified force balance model (MFBM) predicts the experimental results more accurately, and extends its application to the projected mode.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.1-8
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• 2002

When a body enters waters, its original kinetic energy or momentum is distributed among the body and surrounding water in the form of added mass. Due to the transfer of the energy or momentum, the bode is subjected to the hydrodynamic impact forces and acceleration. This impact behavior can be an important criterion of submersible vehicle launched to the air. In this paper, based on Life-boat model, an approximate method is proposed for the evaluation of the forces and responses of cylindrical rigid bode by water entry impact. The impact forces are calculated by yon Karman's momentum theory and motion responses the body, especially acceleration, are calculated by a numerical integration of the motion equations derived by hydrodynamic force equilibrium. The proposed method is expected to be a simple but efficient tool lot the preliminary design or motion analysis of a body subjected to water entry impact.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.193-200
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• 2011

The external disturbance torque acting on a low earth orbit spacecraft was analyzed. For the Earth pointing attitude, the maximum torque to the spacecraft is about $8.3{\times}10^{-4}$ Nms and the momentum accumulated for an orbit is about 1.4 Nms and for the Sun pointing attitude, the maximum torque to the spacecraft is about $1.6{\times}10^{-3}$ Nms and the momentum is accumulated about 3.0 Nms in the spacecraft body reference frame. The analysis results confirm that the size of magnetic torquer selected previously for the satellite is sufficient to manage the accumulated momentum by considering the dumping capacity for an orbit.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.492-492
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• 2009

Nowadays in Republic of Korea, there is no distinct reference for the related design technology of rotor blade of wind turbine. Therefore the optimum design and evaluation of performance is carried out with foreign commercial code softwares. This paper shows in-house code software that evaluates the aerodynamic design of wind turbine rotor blade using blade element-momentum theory (BEMT) and processes that is applied through various aerodynamics theories such as momentum theory, blade element theory, prandtl's tip loss theory and strip theory. This paper presents the results of the numerical analysis such as distribution of aerodynamic properties and performance curves using in-house code POSEIDON.

• Journal of the Korean Society of Industry Convergence
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• v.3 no.4
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• pp.361-367
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• 2000

This paper proposes an efficient feature extraction of the image data using nonlinear principal component analysis neural networks of a new learning algorithm. The proposed method is a learning algorithm with momentum for reflecting the past trends. It is to get the better performance by restraining an oscillation due to converge the global optimum. The proposed algorithm has been applied to the cancer image of $256{\times}256$ pixels and the coin image of $128{\times}128$ pixels respectively. The simulation results show that the proposed algorithm has better performances of the convergence and the nonlinear feature extraction, in comparison with those using the backpropagation and the conventional nonlinear PCA neural networks.

• The Journal of Asian Finance, Economics and Business
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• v.8 no.3
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• pp.361-372
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• 2021

This research aimed to analyze the momentum strategy of foreign investors with the smallest trading transactions in the Indonesian stock market. This study applied a quantitative method approach using intraday transaction data of companies listed on the LQ-45 Index for March, April, and May 2017, obtained from the Indonesia Capital Market Institute (TICMI) which is a subsidiary of the Indonesia Stock Exchange (IDX). The number of companies with available data is 35 companies, consisting of 23 non-government stocks and 12 government stocks. The number of observations from the 35 companies was 8,686,030 observations where the government companies recorded 2,751, 545 and the non-government companies 1,387,016 observations. All data was then squeezed and grouped into small, medium, and large trade transaction orders. The data analysis method used was paired t-test with SPSS to analyze cumulative abnormal returns in the formulation and test periods. This study found that small foreign investors carried out momentum strategies on stocks listed on the LQ-45 Index. However, re-testing was done by separating government and non-government shares. It turned out that small foreign investors performed a momentum strategy on non-government and a contrarian strategy on government.

• Nuclear Engineering and Technology
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• v.54 no.4
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• pp.1495-1507
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• 2022

The improvement of thermal-hydraulic analysis techniques is essential to ensure the safety and reliability of nuclear power plants. The one-dimensional two-fluid model has been adopted in state-of-the-art thermal-hydraulic system codes. Current constitutive equations used in the system codes reach a mature level. Some exceptions are the partition method of wall friction in the momentum equation of the two-fluid model and the interfacial drag force model for a horizontal two-phase flow. This study is focused on deriving the partition method of wall friction in the momentum equation of the two-fluid model and modeling the interfacial drag force model for a horizontal bubbly flow. The one-dimensional momentum equation in the two-fluid model is derived from the local momentum equation. The derived one-dimensional momentum equation demonstrates that total wall friction should be apportioned to gas and liquid phases based on the phasic volume fraction, which is the same as that used in the SPACE code. The constitutive equations for the interfacial drag force are also identified. Based on the assessments, the Rassame-Hibiki correlation, Hibiki-Ishii correlation, Ishii-Zuber correlation, and Rassame-Hibiki correlation are recommended for computing the distribution parameter, interfacial area concentration, drag coefficient, and relative velocity covariance of a horizontal bubbly flow, respectively.

• The KIPS Transactions:PartB
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• v.9B no.5
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• pp.643-652
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• 2002

This paper proposes an efficient hybrid fixed-point (FP) algorithm for improving performances of the independent component analysis (ICA) based on neural networks. The proposed algorithm is the FP algorithm based on secant method and momentum for ICA. Secant method is applied to improve the separation performance by simplifying the computation process for estimating the root of objective function, which is to minimize the mutual informations of the independent components. The momentum is applied for high-speed convergence by restraining the oscillation if the process of converging to the optimal solution. It can simultaneously achieve a superior properties of the secant method and the momentum. The proposed algorithm has been applied to the composite fingerprints and the images generated by random mixing matrix in the 8 fingerprints of $256\times{256}$-pixel and the 10 images of $512\times{512}$-pixel, respectively. The simulation results show that the proposed algorithm has better performances of the separation speed and rate than those using the FP algorithm based on Newton and secant method. Especially, the secant FP algorithm can be solved the separating performances depending on initial points settings and the nonrealistic learning time for separating the large size images by using the Newton FP algorithm.

• The Korean Journal of Financial Management
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• v.23 no.2
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• pp.1-25
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• 2006

This paper studied the performance of momentum strategy and contrarian strategy based or past stock return ratio of Korean stock market. The comparative study shows that the volatility of stock markets that can be found the performance of momentum strategy is smaller than that of emerging stock market. Accordingly, This paper examines that the performances of momentum strategy and contrarian strategy are affected by the larger volatility in Korean stock market. Further analysis using the 6 years sub-portfolios reveals that the momentum strategy is significant only during 1980 to 1986 time period when it had the least market volatility. Additionally, we investigate whether firm-level volatility as well as market volatility influence on the performance of contrarian strategy, and figure out that the momentum strategy is significant for the portfolio composed of firms with smaller volatility for previous period, while not significant for the portfolio composed of firms with larger volatility.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.2
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• pp.113-120
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• 2009

To numerically simulate aerodynamics of rotor-airframe interaction in a rigorous manner, we need to solve the Navier-Stokes system for a rotor-airframe combination in a single computational domain. This imposes a computational burden since rotating blades and a stationary body have to be simultaneously dealt with. An efficient alternative is a momentum source method in which the action of rotor is approximated as momentum source in a stationary mesh system built around the airframe. This makes the simulation much easier. The magnitude of the momentum source is usually evaluated by the blade element theory, which often results in a poor accuracy. In the present work, we evaluate the momentum source from the simulation data by using the Navier-Stokes equations only for a rotor system. Using this data, we simulated the time-averaged steady rotor-airfame interaction and developed the unsteady rotor-airframe interaction. Computations were carried out for the simplified rotor-airframe model (the Georgia Tech configuration) and the results were compared with experimental data. The results were in good agreement with experimental data, suggesting that the present approach is a usefull method for rotor-airframe interaction analysis.