• Journal of Coastal Disaster Prevention
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• v.4 no.1
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• pp.7-19
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• 2017

In this study, waves and currents observed by acoustic AWAC, VECTOR and Aquadopp Profiler in Anmok coastal waters were analysed to account for the variability of wave and current and to understand the mechanism of sediment transport generated by wave-induced current in the surf-zone. The monthly variation of wave and residual currents were analysed and processed with long-term observed AWAC data at station W1, located at the water depth of about 18m measured during from February 2015 to September 2016. Wave-induced currents were also analysed with intensive field measurements such as wave, current, suspended sediment, and bathymetry data observed at the surf-zone during in winter and summer. The statistical result of wave data shows that high waves coming from NNE and NE in winter (DEC-FEB) are dominant due to strong winds from NE. But in the other season waves coming from NE and ENE are prevalent due to the seasonal winds from E and SE. The residual currents with southeastern direction parallel to the shoreline are dominant throughout a year except in winter showing in opposite direction. The speed of ebb-dominant southeastern residual currents decreasing from surface to the bottom is strong in summer and fall but weak in winter and spring. By analysing wave-induced current, we found that cross-shore current were generated by swell waves mainly in winter with incoming wave direction about $45^{\circ}$ normal to the shoreline. Depending on the direction of incoming waves, longshore currents in the surf-zone were separated to southeastern and northwestern flows in winter and summer respectively. The variation of observed currents near crescentic bars in the surf-zone shows different direction of longshore and cross-shore currents depending on incoming waves implying to the reason of beach erosion generating the beach cusp and sandbar migration during high waves at Anmok.

• Journal of Astronomy and Space Sciences
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• v.39 no.4
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• pp.159-167
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• 2022

Because of the small number of spacecraft available in the Earth's magnetosphere at any given time, it is not possible to obtain direct measurements of the fundamental quantities, such as the magnetic field and plasma density, with a spatial coverage necessary for studying, global magnetospheric phenomena. In such cases, empirical as well as physics-based models are proven to be extremely valuable. This requires not only having high fidelity and high accuracy models, but also knowing the weakness and strength of such models. In this study, we assess the accuracy of the widely used Tsyganenko magnetic field models, T96, T01, and T04, by comparing the calculated magnetic field with the ones measured in-situ by the GOES satellites during geomagnetically disturbed times. We first set the baseline accuracy of the models from a data-model comparison during the intervals of geomagnetically quiet times. During quiet times, we find that all three models exhibit a systematic error of about 10% in the magnetic field magnitude, while the error in the field vector direction is on average less than 1%. We then assess the model accuracy by a data-model comparison during twelve geomagnetic storm events. We find that the errors in both the magnitude and the direction are well maintained at the quiet-time level throughout the storm phase, except during the main phase of the storms in which the largest error can reach 15% on average, and exceed well over 70% in the worst case. Interestingly, the largest error occurs not at the Dst minimum but 2-3 hours before the minimum. Finally, the T96 model has consistently underperformed compared to the other models, likely due to the lack of computation for the effects of ring current. However, the T96 and T01 models are accurate enough for most of the time except for highly disturbed periods.

• Journal of the Korean Society of Marine Environment & Safety
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• v.13 no.4
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• pp.21-26
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• 2007

A study on analysis and application of ocean currents information extracted from SAR (Synthetic Aperture Radar) satellite image. The current information extracted from SAR satellite image is not real vector information but scalar information in normal direction of orbital path. To correct current information extracted from satellite image, observation of currents in the field is carried out at the same time and area as those of satellite image. In the analysis, current information extracted from satellite image is corrected by using observed ones. By this correction, the speed and the direction of current can be estimated. The extract current information seem to agree well with the observed ones.

• Journal of the Korean Magnetics Society
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• v.6 no.2
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• pp.106-111
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• 1996

Electric machines such as motors which have rmving parts are designed for producing mechanical force or torque. The accurate calculations of electromagnetic force and torque are important in the design these machines. Electromagnetic force calculation method using the results of Finite Element Method(FEM) has been presented variously in 2-D problems. Typically the Maxwell's Stress Tensor method and the method of virtual work are used. The former calculates forces by integrating the surface force densities which can be expressed in terms of Maxwell Stress Tensor(MST), and the latter by differentiating the electromagnetic energy with respect to the virtual dis¬placement of rigid bodies of interest. In the problems including current source, magnetic vector potentials(MVP) have rmstly been used as unknown variables for field analysis by a numerical method; e. g. FEM. This paper, thus, introduces the two both methods using MVP in 3-D case. To verify the usefulness of presented methods, a solenoid model is chosen and analyzed by 3-D and axisymmetric FEM. It is found that the force calculation results are in good agreement for several mesh schemes.

• Geophysics and Geophysical Exploration
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• v.7 no.2
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• pp.136-147
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• 2004

In this study, the characteristics of magnetotelluric (MT) responses due to a three-dimensional (3-D) body are analyzed with 3-D numerical modeling. The first model for the analysis consists of a single isolated conductive body embedded in a resistive homogeneous half-space. The second model has an additional conductive overburden while the other conditions remain the same as the first one. The analysis of apparent resistivities shows well that the 3-D effects are dominant over some frequency range for the first model. Two mechanisms, current channeling and induction, for secondary electric fields due to the conductive body are analyzed at various frequencies: at high frequencies induction is more dominant than channeling, while at low frequencies channeling is more dominant than induction. Tippers have a strong relation to the position of anomalous body and the real and imaginary parts of induction vector also indicate the position of anomalous body. off-line conductive anomaly sometimes causes severe problem in 2-D interpretation. In such case, induction vector analysis can give information on the existence and location of the anomalous body. Each parameter of the second model shows similar responses as those of the first model. The only difference is that the magnitude of all parameters is decreased and that the domain showing the 3-D effects becomes narrower. As shown in this study, the analysis of 3-D effects provides a useful and effective means to understand the 3-D subsurface structure and to interpret MT survey data.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.30B no.10
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• pp.69-76
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• 1993

In this paper we propose a design of a digital neuron processor using the residue number system for efficient matrix.vector multiplication involved in neural processing. Since the residue number system needs no carry propagation for modulus operations, the neuron processor can perform multiplication considerably fast. We also propose a high speed algorithm for computing the sigmoid function using the specially designed look-up table. Our method can be implemented area-effectively using the current technology of digital VLSI and siumlation results positively demonstrate the feasibility of our method. The proposed method would expected to adopt for application field of digital neural network, because it could be realized to currently developed digital VLSI Technology.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.985-986
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• 2011

This paper deals with d-q axis equivalent circuit analysis of IPMSM(Interior Permanent Magnet Synchronous Motors) considering voltage harmonics. In the field weakening region, as the current vector angle increased, back-emf contains large harmonics, therefore, significant underestimation of voltage or overestimation of speed can be occurred from the conventional d-q axis equivalent circuit analysis. In order to consider the effects of voltage harmonics, a harmonic coefficient is introduced and verified by experiments.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.846-848
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• 2001

In this paper, electromagnetic fields of a linear induction motor with cage-type secondary are analyzed by the finite element method. Contact resistances between end-bars and secondary conductors are considered in the finite element analysis. The field quantify is a magnetic vector potential transformed into a phasor form. As a result, the sensitivities of a phase current thrust and normal force are presented according to the variation of the contact resistance.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.560-563
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• 1997

Sound intensity method is well known as a visualization technique of sound field and sound propagation in noise control. Sound intensity is a vector quantity that describes the magnitude and the direction of net flow of acoustic energy at a given position. The current measuring method is expensive and difficult to identify the noise source exactly. In this paper, we have studied the noise source identification and the characteristics of noise source of rotary compressor for air conditioner using complex sound intensity method. The new method for instantaneous sound intensity is also proposed and it is useful for transient state and steady state. The criteria of these states select auto correlation coefficient. The advantage, simplicity and economic attribution of this method are verified by analyzing the characteristics of noise source with instantaneous sound intensity compared to mean sound intensity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.836-839
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• 2003

A pneumatic servo valve which is widely applied in industrial field. And It is consist of force motor, spool ＆ sleeve and servo controller. In this study. we developed the force motor which is consume to low power for a pneumatic servo valve. We could reduce the number of turn of the solenoid by using ferromagnetic permanent magnet and took different direction of each other using one coil instead of two coil. we modeled a system consisting of various electro-mechanical subsystems. The appropriateness of the model was verified by simulation. The simulation model resolved the motion of spool, the winding current and the magnetic force. Also, we calculated the displacement and velocity of the spool, flux contour line, b vector. flux density. flux linkage, back EMF etc.