• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.50.1-50.1
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• 2015

We present a new hydrodynamic simulation based on the unstructured moving mesh scheme. The simulation utilizes the Voronoi tessellation technique that produces polygonal cells composed of, on average, 13 surfaces each in 3D. We devise the incremental expanding method (IEM) and hybrid-neighbor searching algorithm and achieve the CPU time just proportional to the number of particles, i.e., O(N). We show the results of requisite tests for hydrodynamic simulations and demonstrate superiority of our code over the conventional codes using the stationary meshes. The applications in the context of cosmological and galactic simulations are also discussed.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.32.1-32.1
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• 2013

We use numerical simulations to investigate the evolution of both the star formation rate (SFR) and the observable properties of equal-mass disk merger remnants for 18 different orbital configurations. In our analysis, the photometric properties of the remnants have been constructed by considering dust reddening effect in order to facilitate the comparison with observational data of large surveys such as the Sloan Digital Sky Survey (SDSS). First, we found that the detailed evolutions of merging galaxies are different between the merging characteristics such as merging time scale, SFR history, and burst efficiency. Around $70{\pm}5$ percent of gas turns into stars until the merger-induced starburst ends regardless of merger types. Our study also suggests that merger features involve a small fraction of stars. Merger features last roughly 3 times the final coalescence time of galaxy mergers. For a shallower surface brightness limit, the features seem to survive in a shorter time, which is the reason why detecting merger features by using shallow surveys were difficult in the past.

• Journal of Ocean Engineering and Technology
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• v.31 no.1
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• pp.36-46
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• 2017

Most of the studies on the hydraulic characteristics of wave-current interaction have used 2-D hydraulic experiments or 2-D numerical simulations. However, it is difficult to understand the wave-current interaction found in actual estuaries using these. Therefore, a numerical water tank was constructed in this study to perform simulations involving a 3-D river mouth. The result showed a change in the water surface at the river mouth from the wave-current interaction. With an increase in the ratio ($V_c/C_i$) between the river current and wave celerity, the wave height and mean water level of the river increased at the wave and current meeting point. A higher $V_c/C_i$ caused a stronger wave-current interaction and increased the turbulence kinetic energy. Thus, the wave height attenuation became larger by the wave-current interaction with a higher $V_c/C_i$. In addition, it was possible to understand the flow characteristics in the vicinity of the river mouth as a result of the wave-current interaction using the mean flow and mean time-averaged velocity at the mid-cross section of river.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.1
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• pp.40-47
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• 2005

This paper concerns on Filtered-x least mean square (FXLMS) algorithm for adaptive estimation of feedforward control parameters. The conditions for convergence in ensemble mean of the FXLMS algorithm are derived and the directional convergence properties are discussed from a new geometric vector analysis. The convergence and its directionality are verified along with some computer simulations.

• Journal of the Korean Society for Marine Environment & Energy
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• v.1 no.2
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• pp.82-95
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• 1998

In this paper, two series of numerical simulations are performed using LS/DYNA3D: The first series of numerical simulations are collision events between a 310,000 DWT double hull VLCC (struck ship) and two 35,000 and 105,000 DWT tankers (striking ships). Collisions are assumed to occur at the middle of the VLCC with the striking ships moving at right angle to the YLCC centerline. The second ones, grounding accidents of two 40,000 DWT Conventional and Advanced Double Hull lanker bottom structures, CONV/PD328 and ADH/PD328 models. The overall objective of this study is to understand the structural failure and energy absorbing mechanisms during collision and grounding events for double hull tanker side and bottom structures, which lead to the initiation of inner shell rupture and cause the kinetic energy dissipation to bring the ship to a stop. These numerical simulations will contribute to the estimation of damage extents of collision and grounding accidents and the future improvements in lanker safety at the design stage.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.21-29
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• 2001

In order to detect the precise port/starboard direction of arrival of target signal in real noisy ocean environments, Inverse beamforming (IBF) algorithm is surveyed theoretically and the detection performances of IBF are analyzed with simulations. Cardioid Inverse beamforming algorithm was proposed for port/starboard discrimination and the performance was studied with simulations. It is shown that IBF has a 3dB array gain advantage over Conventional beamforming (CBF) under ideal conditions. This 3 dB advantage is proven theoretically and illustrated with simulations. The fact that the IBF beamwidth is narrower than the CBF beamwidth by a factor of 0.68 proves the performance of defection and spatial resolution improvement. Comparing the simulation results of Cardioid Inverse beamforming and Conventional Cardioid beamforming, it is shown that Cardioid Inverse beamformer has enhanced performance in minimum detection level, detection accuracy and resolution. Due to the results of moving target bearing detection test in endfire, it is shown that Cardioid Inverse beamformer has better performance, comparing the Conventional Cardioid beamformer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.80-82
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• 2016

In this letter, we evaluate the performances of both GOOK and GFSK de/modulation techniques which are candidates for ULP communications in WPAN systems. For the performance evaluation, we define the system model for each of GOOK and GFSK de/modulations and perform computer simulations based on the proposed models. From the computer simulations, we show that GOOK de/modulation technique has 15 dB out-of-band emission gain and is robust over frequency offsets in terms of BER compared to GFSK de/modulation technique.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.1208-1211
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• 1996

In this paper, an efficient and robust robot path planning technique is discussed. Concentric Ripple Edge Evaluation and Progression( CREEP ) algorithm[1] has been elaborated and expanded to carry out 3-D path planning. Like the 2-D case, robot can always find a path, if one exists, in a densely cluttered, unknown and unstructured 3-D obstacle environment. 3-D space in which the robot is expected to navigate is modeled by stacking cubic cells. The generated path is resolution optimal once the terrain is fully explored by the robot or all the information about the terrain is given. Path planning times are significantly reduced by local path update. Accuracy and efficiency of wave propagation in CREEP algorithm are achieved by virtual concentric sphere wave propagation. Simulations in 2-D and 3-D spaces are performed and excellent results are demonstrated.

• Journal of the military operations research society of Korea
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• v.31 no.1
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• pp.42-57
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• 2005

Korea DM&S(Defence Modeling & Simulation) development plan includes construction of a distributed simulation model which enables us to construct, operate, integrate and connect war game simulations. US DoD and IEEE set the HLA/RTI as the standard of distributed simulation model. HLA/RTI models each simulator as a Federate and group of them as a Federation. Simulation with the model shows interoperability and finally executes a war game simulation. Because of different resolutions and features, it is not satisfied 'interoperability' and 'reusability' of simulation perfectly MRM (Multi Resolution Modeling) has been introduced, and many developed countries including the United States have studied the technology to simulate the model with different resolutions. This thesis proposes the need for introduction of MRM and analyzes both technical and operational validity when we apply MRM model to army war game simulations. For these purposes, we 1) find MRM main issues with the study about MRM basic concepts and case studies of MRM's applications, 2) present the need of MRM and its relation with DM&S development plan, and 3) analyze its technical and operational validity when we apply MRM to an example, CHANG-JO21 and JEON-TOO21.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.661-673
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• 2020

The quarter-core simulation of BEAVRS Cycle 2 depletion benchmark has been conducted using the MCS/CTF coupling system. MCS/CTF is a cycle-wise Picard iteration based inner-coupling code system, which couples sub-channel T/H (thermal/hydraulic) code CTF as a T/H solver in Monte Carlo neutron transport code MCS. This coupling code system has been previously applied in the BEAVRS benchmark Cycle 1 full-core simulation. The Cycle 2 depletion has been performed with T/H feedback based on the spent fuel materials composition pre-generated by the Cycle 1 depletion simulation using refueling capability of MCS code. Meanwhile, the MCS internal one-dimension T/H solver (MCS/TH1D) has been also applied in the simulation as the reference. In this paper, an analysis of the detailed criticality boron concentration and the axially integrated assembly-wise detector signals will be presented and compared with measured data based on the real operating physical conditions. Moreover, the MCS/CTF simulated results for neutronics and T/H parameters will be also compared to MCS/TH1D to figure out their difference, which proves the practical application of MCS into the BEAVRS benchmark two-cycle depletion simulations.