• Transactions of Materials Processing
• /
• v.13 no.2
• /
• pp.174-179
• /
• 2004

The effect of grain refinement on the plastic deformation behaviour of nanocrystalline metallic materials is investigated. A phase mixture model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. For the grain interior phase two concurrent mechanisms are considered: dislocation glide and mass transfer by diffusion. The proposed constitutive model was implemented into a finite element code (DEFORM) using a semicoupled approach. The finite element method was applied to simulating room temperature tensile deformation of Cu down to the nanoscale grain size in order to investigate the pre- and post-necking behaviour.

• Journal of the Korean Society of Safety
• /
• v.35 no.4
• /
• pp.84-91
• /
• 2020

The Korean nuclear industry developed the SPACE (Safety and Performance Analysis Code for nuclear power plants) code and this code adpots two-phase flows, two-fluid, three-field models which are comprised of gas, continuous liquid and droplet fields and has a capability to simulate three-dimensional model. According to the revised law by the Nuclear Safety and Security Commission (NSSC) in Korea, the multiple failure accidents that must be considered for accident management plan of nuclear power plant was determined based on the lessons learned from the Fukushima accident. Generally, to improve the reliability of the calculation results of a safety analysis code, verification work for separate and integral effect experiments is required. In this reason, the goal of this work is to verify calculation capability of SPACE code for multiple failure accident. For this purpose, it was selected the experiment which was conducted to simulate a Multiple Steam Generator Tube Rupture(MSGTR) accident with Passive Auxiliary Feedwater System(PAFS) operation by Korea Atomic Energy Research Institute (KAERI) and focused that the comparison between the experiment results and code calculation results to verify the performance of the SPACE code. The MSGR accident has a unique feature of the penetration of the barrier between the Reactor Coolant System (RCS) and the secondary system resulting from multiple failure of steam generator U-tubes. The PAFS is one of the advanced safety features with passive cooling system to replace a conventional active auxiliary feedwater system. This system is passively capable of condensing steam generated in steam generator and feeding the condensed water to the steam generator by gravity. As the results of overall system transient response using SPACE code showed similar trends with the experimental results such as the system pressure, mass flow rate, and collapsed water level in component. In conclusion, it could be concluded that the SPACE code has sufficient capability to simulate a MSGTR accident.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38A no.5
• /
• pp.416-425
• /
• 2013

A hybrid PN code phase acquisition system based on a least-mean-square adaptive filter, interpreted as a channel estimator is proposed and analyzed for direct-sequence spread-spectrum systems under frequency selective Rayleigh fading channels. Closed form expressions are derived for the filter tap weights and detection/false alarm probabilities. Compared to previously proposed systems, the proposed system achieves smaller mean acquisition times, is more robust to the operating signal-to-noise ratio and allows for multiplication free tap weight updates.

• 한국전산유체공학회:학술대회논문집
• /
• 2009.11a
• /
• pp.177-184
• /
• 2009

Cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has focused on the simulation of cavitating flow past cylinders with strong side flows. The governing equation is the Navier-Stokes equation based on the homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved liquid and vapor phase, separately. An implicit dual time and preconditioning method are employed for computational analysis. For the code validation, the results from the present solver have been compared with experiments and other numerical results. A fairly good agreement with the experimental data and other numerical results have been obtained. After the code validation, the strong side flow was applied to include the wake flow effects of the submarine or ocean tide.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.3 no.4
• /
• pp.723-736
• /
• 1999

Code optimization phase in a compiler are very important because the phase reduces the running time and the storage size of machine codes. I developed flow analyzers and optimizers on intermediate codes. The flow analyzers generate control-flow and data-flow information. The optimizers transform the intermediate codes into the improved codes using this information. This paper describes the development of flow analyzers and optimizers. I also examined the execution performance, the cost and the dependency of each optimization.

• Journal of the Korean Graphic Arts Communication Society
• /
• v.13 no.1
• /
• pp.93-104
• /
• 1995

Liquid crystal-polymer composite(LCPC) films promising new materials for both projection displays and vision product. LCPC films consist of a continous liquid crystal phase embedded in a three- dimensional network of polymer matrix. The liquid crystal in these LC phases can be elecrtrically switched giving rise to an opaque scattering off-stats and a transparent, non-scatting on- stats. In this work. a premixture is composed of LC, UV-curable monomer and photonitiator. LCPC films are formed by photopolymerization induced phase separation from this premixture. In conclusion, structure and electro-optical properties of LCPC films strongly depends on the selection of monomer, LC content and curing rate.

• Journal of Institute of Control, Robotics and Systems
• /
• v.18 no.11
• /
• pp.1034-1039
• /
• 2012

In this paper, a structure of precise positioning based on satellite navigation system is proposed. The proposed system is consisted with three parts, range domain filter, navigation filter and position domain filter. The range domain filter generates carrier phase-smoothed-Doppler and Doppler-smoothed-code measurements. And the navigation filter calculates position and velocity using double-differenced code/carrier phase/Doppler measurements. Finally, position domain filter smooth position error, and it means enhancement of positioning performance. The proposed positioning method is evaluated by trajectory analysis using precise map date. As a result, the position error occurred by multipath or cycle slip was reduced and the calculated trajectory was in true lane.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03a
• /
• pp.327-333
• /
• 2008

The cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has developed a base code for simulating cavitating flows past cylinders and hydrofoils. The governing equation is the Navier-Stokes equation based on homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved in liquid and vapor phase, separately. The solver employs an implicit preconditioning algorithm in curvilinear coordinates. The computations have been carried out for the cylinders with spherical, 1- and 0-caliber forebody and hydrofoil of ALE and NACA cross-section and, then, compared with experiments and other numerical results. Fairly good agreements with experiments and numerical results have been achieved. The present base code has shown the feasibility to solve the cavitating flow past supercavitating torpedo after the improvement for compressibility effects and interactions with hot exhaust gas of propulsive rocket.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.10a
• /
• pp.327-333
• /
• 2008

The cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has developed a base code for simulating cavitating flows past cylinders and hydrofoils. The governing equation is the Navier-Stokes equation based on homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved in liquid and vapor phase, separately. The solver employs an implicit preconditioning algorithm in curvilinear coordinates. The computations have been carried out for the cylinders with spherical, 1- and 0-caliber forebody and hydrofoil of ALE and NACA cross-section and, then, compared with experiments and other numerical results. Fairly good agreements with experiments and numerical results have been achieved. The present base code has shown the feasibility to solve the cavitating flow past supercavitating torpedo after the improvement for compressibility effects and interactions with hot exhaust gas of propulsive rocket.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.10 no.6
• /
• pp.951-958
• /
• 1999

Multicarrier modulation or orthogonal frequency division multiplexing(OFDM) is a promising technique for mobile communications systems, since it has a strong immunity to multipath fading without employing complicated adaptive equalization. In this paper, performance of MC DS-CDMA/MPSK(multi-carrier direct sequence-code division multiple access/mary phase shift keying) and DS-CDMA/MPSK(direct sequence-code division multiple access/mary phase shift keying) with coherent detection for a CDMA system over Nakagami fading channel analysis. For a given bandwidth, it is shown that MC DS-CDMA/MPSK eventually outperforms DS-CDMA MPSK with random sequences.