• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.143-146
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• 2001

The evolution of dynamic recrystallization (DRX) was studied with torsion test for AISI 304 stainless steel in the temperature range of $900-1000^{\circ}C$ and strain rate range of 0.05-5/sec. The evolution of DRX was investigated with microstructural analysis and change of flow stress curve slope. The investigation of serrated grain boundaries using electron back scattered diffraction (EBSD) analysis indicated that the nucleated new DRX grain size was similar to the size of bulging part. Before the steady state, the dynamically recrystallizing grains do not remain a constant size and gradually grow to the size of fully DRX grain at steady state. The calculation of grain size was based on $X_{DRX}$ and the assumption, which the nucleated DRX grains are growing to the steady state, continuously. It was found that the calculated results agreed with the microstructure of the alloy.

• International Journal of Control, Automation, and Systems
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• v.6 no.3
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• pp.378-385
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• 2008

This paper aims to present a polynomial approach to the steady-state optimal filtering for delayed systems. The design of the steady-state filter involves solving one polynomial equation and one spectral factorization. The key problem in this paper is the derivation of spectral factorization for systems with delayed measurement, which is more difficult than the standard systems without delays. To get the spectral factorization, we apply the reorganized innovation approach. The calculation of spectral factorization comes down to two Riccati equations with the same dimension as the original systems.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.130-134
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• 2001

In the re-entry control system, errors apt to induce because the time derivative of drag acceleration is analytically estimated. Still more, the difficulty of estimation of the exact drag coefficient in hypersonic velocity and the nun-reality of the scale height cause a steady-state drag error. This paper proposes the additional method of the disturbance observer. This reduces the steady-state drag error according to the following series. First, this method estimates a error in drag acceleration time derivative by the analytic calculation and then creates the new drag acceleration time derivative using the estimated error. The performance of the re-entry control system is verified about 32 reference trajectories.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.248-251
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• 2004

Stability of truck and trailer are the most significance in Thai automotive industry. This paper presents the mathematical model of a six-degree-of-freedom semi-trailer vehicle. Search method was implemented to obtain the optimum design variables of the trailer which are the distance from the fifth wheel to the centroid of the trailer and the distance from the centroid of the trailer to the trailer axel. The objective function is to minimize the steady side slip velocity, steady-state yawing velocity and steady-state angle between the tractor and the trailer. From the calculation , the optimum distance from the fifth wheel to the centroid of the trailer and the optimum distance from the centroid of the trailer to the trailer axle are 5.50 and 3.25 meters respectively. The stability of the optimal semi-trailer vehicle was also examined in steady state. The steady side slip velocity, yawing velocity and the angle between tractor and trailer are also obtained using linearization technique under unit step disturbance of the tractor front wheel steering angle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.5
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• pp.746-755
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• 1997

This paper addresses the systematic procedure using sequential approach for the analysis of the coupled thermo-mechanical behavior of a steady rolling tire. Not only the knowledge of mechanical stresses but also of the temperature loading in a rolling tire are very important because material damage and material properties are significantly affected by the temperature. In general, the thermo-mechanical behavior of a pneumatic tire is highly complex transient phenomenon that requires the solution of a dynamic nonlinear coupled themoviscoelasticity problem with heat source resulting from internal dissipation and friction. In this paper, a sequential approach, with effective calculation schemes, to modeling this system is presented in order to predict the temperature distribution with reasonable sccuracies in a steady state rolling tire. This approach has the three major analysis modules-deformation, dissipation, and thermal modules. In the dissipation module, an analytic method for the calculation of the heat source in a rolling tire is established using viscoelastic theory. For the verification of the calculated temperature profiles and rolling resistance at different velocities, they were compared with the measured ones.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2230-2245
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• 2023

KANT (KAIST Advanced Nuclear Tachygraphy) is a PWR core simulator recently developed at Korea Advance Institute of Science and Technology, which solves three-dimensional steady-state and transient multigroup neutron diffusion equations under Cartesian geometries alongside the incorporation of thermal-hydraulics feedback effect for multi-physics calculation. It utilizes the standard Nodal Expansion Method (NEM) accelerated with various Coarse Mesh Finite Difference (CMFD) methods for neutronics calculation. For thermal-hydraulics (TH) calculation, a single-phase flow model and a one-dimensional cylindrical fuel rod heat conduction model are employed. The time-dependent neutronics and TH calculations are numerically solved through an implicit Euler scheme, where a detailed coupling strategy is presented in this paper alongside a description of nodal equivalence, macroscopic depletion, and pin power reconstruction. For validation of the steady, transient, and depletion calculation with pin power reconstruction capacity of KANT, solutions for various benchmark problems are presented. The IAEA 3-D PWR and 4-group KOEBERG problems were considered for the steady-state reactor benchmark problem. For transient calculations, LMW (Lagenbuch, Maurer and Werner) LWR and NEACRP 3-D PWR benchmarks were solved, where the latter problem includes thermal-hydraulics feedback. For macroscopic depletion with pin power reconstruction, a small PWR problem modified with KAIST benchmark model was solved. For validation of the multi-physics analysis capability of KANT concerning large-sized PWRs, the BEAVRS Cycle1 benchmark has been considered. It was found that KANT solutions are accurate and consistent compared to other published works.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.2
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• pp.140-149
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• 1999

This study is on the development of the computer program that calculates a 3-D hull temperadistribution and analyzes BOR(Boil off rate) to be important to the heat design of a membrane type LNG carrier. The quarter of a tank is taken as an calculation model. And the thermal conductivity of insulation is assumed to be the function of a temperature. In the present steady state calculation, the temperature of LNG in a cargo tank is assumed to be -$162^{\circ}C$ and the air temperature of a cofferdam, to be +$5^{\circ}C$. The lowest air temperature in compartments is calculated as $21.39^{\circ}C$ under the USCG condition ($T_{air}=-18^{\circ}C,\;T_{sw}=O^{\circ}C)$ and B.O.R value is O.0977%/day under the maximum boil-off condition, IMO IGC ($T_{air}=45^{\circ}C,\;T_{sw}=32^{\circ}C$), which satisfies the requirement by KOGAS. The calculated temperature distribution over tank panels at each condition is maximum 3% less than GTT's results. From the results of this study, it can be concluded that the present design of LNG cargo tank satisfies the requirement by KOGAS.

• Journal of Navigation and Port Research
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• v.31 no.7
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• pp.579-587
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• 2007

Samchunpo(Sin Hyang) Harbor is located in the bay of Sa Chun, the central south coast of Korean peninsula. The harbor and coastal boundaries have been protecting by natural coastal islands and shoals. Currently, The Sin Hyang harbor needs maintenance and renovation of the sheltered structures against the weather deterioration and typhoon damages. Consequently to support this, the calculation of accurate design wave through the typhoon wave attack is necessary. In this study, calculation of incident wave condition is simulated using steady state spectrum energy wave model(wide area wave model) from 50 years return wave condition. And this simulation results in wide offshore area were used for the input of the extended mild slope wave model at the narrow coastal area. Finally, the calculation of design wave at Sin Hyang harbor entrance was induced by Boussinesq wave model(detail area wave model) simulation. The numerical model system was able to simulate wave transformations from generation scale to shoreline or harbor impact. We hope these results will be helpful to the engineers doing placement, design, orientation, and evaluation of a wide range of potential solutions in this area.

• Journal of Information Processing Systems
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• v.15 no.2
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• pp.331-343
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• 2019

Dynamic thermal rating of the overhead transmission lines is affected by many uncertain factors. The ambient temperature, wind speed and wind direction are the main sources of uncertainty. Measurement uncertainty is an important parameter to evaluate the reliability of measurement results. This paper presents the uncertainty analysis based on Monte Carlo. On the basis of establishing the mathematical model and setting the probability density function of the input parameter value, the probability density function of the output value is determined by probability distribution random sampling. Through the calculation and analysis of the transient thermal balance equation and the steady- state thermal balance equation, the steady-state current carrying capacity, the transient current carrying capacity, the standard uncertainty and the probability distribution of the minimum and maximum values of the conductor under 95% confidence interval are obtained. The simulation results indicate that Monte Carlo method can decrease the computational complexity, speed up the calculation, and increase the validity and reliability of the uncertainty evaluation.

• Proceedings of the KIEE Conference
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• 1997.07a
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• pp.124-126
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• 1997

A number of electromagnetic devices periodically driven by solid-state switches have been analyzed with time-stepping finite element method, which requires much time to reach a steady state. The sensitivity analysis which have been used for the shape design is employed for an efficient calculation of linear magnetodynamics with nonsinusoidal driving sources. The high-order frequency sensitivity from the harmonic finite element formulation is used along with Fourier transform and Taylor series expansion. The algorithm is validated through a numerical example of a single-phase transformer driven by a trapezoidal voltage source.