• Solar Energy
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• v.9 no.1
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• pp.43-52
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• 1989

Heat transfer rate and heat flux from the condenser with internally triangular fins rotating heat pipe has been numerically studied by finite element method. The results of numerical and P.J. Martos' experimental showed good agreement and it was able to predict to the performance of a rotating heat pipe. By increasing fin half angle or fin height, heat transfer rate from condenser was increased slightly but heat flux was decreased. By increasing condenser radius or r.p.m. of rotating heat pipe, heat transfer rate and heat flux was increased rapidly. Heat transfer rate was rapidly increased with increasing fin numbers in case of few fm numbers but slowly increased at many fin numbers. So the optimum fin numbers were a half of maximum fin numbers which was able to install in the condenser of a rotating heat pipe.

• Journal of the Korean Society of Combustion
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• v.3 no.2
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• pp.41-50
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• 1998

Numerical simulations of nonpremixed $CH_4/C_2HCl_3$(Trichloroethylene, TCE)/Air flames are conducted at atmospheric pressure in order to understand the effect of hydrocabon bound chlorine on methane/air flames. A chemical kinetic mechanism is employed, the adopted scheme involving 48 gas-phase species and 445 elementray reaction steps containing 223 backward reactions. The calculated temperature, velocity, and critical strain rate are compared with the experiments for the flame (16.1% TCE by Vol.) estabilished at a strain rate of $175s^{-1}$. Whereas there is overall good agreement between predictions and the measurements, it appears that the critical strain rate is higher than measured, and some areas of further refinement in the kinetic mechanism are required.

• Journal of Radiation Protection and Research
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• v.12 no.1
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• pp.54-60
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• 1987

The quasi-exposure rate and the quasi-effective energy of the natural radiation in the field at 47 monitoring points around nuclear power plants have been studied with the pair filter thermoluminescence dosimeter system. The results of the six years observation showed that the relationship between the quasi-exposure rate $X_q$, and quasi-effective energy $E_q$ can be represented as a hyperbolic function: $X_q=A+C/(E_q-B)$, where the constants A and B correspond to the quasi-exposure rate of cosmic-rays and the minimum quasi-effective energy of natural radiation, respectively. Furthermore, the constant A is in close agreement with the values obtained by using ionization chambers and scintillation detectors. The constant B is approximately 0.68 MeV, closely corresponding to the mean energy of the photons emitted from natural uranium.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.139-141
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• 2007

Compression tests were carried out to investigate morphologies of compressed specimen, deformation microstructure and stress-strain relation in high-nitrogen austenite stainless steel. Tests were performed under a wide range of temperature and, with true strain rates up to $\dot{\varepsilon}$ =0.05, 0.1, 0.5 and $1.0s^{-1}$. The activation energy of loading force was equal to plastic deformation energy within the temperature range of $900^{\circ}C$ to $1250^{\circ}C$. Dynamically recrystallized grain size decreased with an increasing strain rate and temperature. Flow stresses and deformation microstructures, were used to quantify the critical strain rate and recrystallized grain size. The grain size versus strain rate-temperature map obtained in the study was in good agreement with the deformation microstructures of compressed specimens.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.4
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• pp.490-497
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• 1998

An elast-biscoplastic finite element analysis is performed to investigate detailed growth behavior of creep cracks and the numerical results are compared with experimental results. The results of mesh translation method are compared with those of node release method. Load line displancement curve obtained from the crack growth analysis by mesh translation shows the improved results than that obtained from the crack growth by node release method when the secondary creep rate is only used as creep material property. The results of accounting for primary creep rate and instantaneous plasticity shows a good agreement with the experimental result.

• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.115-123
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• 1994

Under variable amplitude loading conditions, retardation or accelerated condition of fatigue crack growth occurs with every cycle, Because fatigue crack growth behavior varied depend on load time history. The modeling of stress amplitude with storm loading acted to ships and offshore structures applied this paper. The crack closure behavior examine by recording the variation in load-strain relationship. By taking process mentioned above, fatigue crack growth rate, crack length, stress intensity factor, and crack closure stress intensity factor were obtained from the stress cycles of each type of storm ; A(6m), B(7m), C(8m), D(9m), E(11m) and F(15m) which was wave height. It showed that the good agreement with between the experiment results and simulation of storm loads. So this estimated method of crack propagtion rate gives a good criterion for the safe design of vessels and marine structure.

• Journal of Ocean Engineering and Technology
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• v.35 no.2
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• pp.99-112
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• 2021

The prediction of maneuverability is very important in the design process of an underwater vehicle. In this study, we predicted the steady turning ability of a symmetrical underwater vehicle while considering interactions between the yaw rate and drift/rudder angle through a simulation-based methodology. First, the hydrodynamic force and moment, including coupled derivatives, were obtained by computational fluid dynamics (CFD) simulations. The feasibility of CFD results were verified by comparing static drift/rudder simulations to vertical planar motion mechanism (VPMM) tests. Turning motion simulations were then performed by solving 2-degree-of-freedom (DOF) equations with CFD data. The turning radius, drift angle, advance, and tactical diameter were calculated. The results show good agreement with sea trial data and the effects on the turning characteristics of coupled interaction terms, especially between the yaw rate and drift angle.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2659-2665
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• 2024

This study proposes an algorithm that combines a Kalman Filter method with effective decay constant correction to improve the accuracy of predicting radiation dose rate distribution during emergencies. The algorithm addresses the limitations of relying solely on measurement data by incorporating calculation data and refining the estimations. The effectiveness of algorithm was assessed using hypothetical test scenarios, which demonstrated a significant improvement in the accuracy of dose rate prediction compared to the model predictions. The estimates generated by the algorithm showed a good agreement with the measured data, and the discrepancies tend to decrease over time. Furthermore, the application of the effective decay constant correction accelerated the reduction of prediction errors. In conclusion, it was confirmed that the combined use of the Kalman filter method and effective decay constant correction is an effective approach to improve the accuracy of dose rate prediction.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.411-416
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• 1999

The measurement of unsteady flow rate is of vital importance to clarify and improve the dynamic characteristics in pipeline, hydraulic components and system. There is also demand for a real time flow sensor of ability to measure unsteady flow rate with high accuracy and fast response to realize feedback control of flow rate in fluid power systems. In this paper, we propose an approach for estimating unsteady flow rate through a pipeline and components under high pressure condition. In the method, unsteady flow rate is estimated by using hydraulic pipeline dynamics and the measured pressure values at two distant points along the pipeline. The distributed parameter model of hydraulic pipeline is applied with consideration of frequency dependent viscosity friction and unsteady velocity distribution at a cross section of a pipeline. By using the self-checking functions of the method, the validity is investigated by comparison with the measured and estimated pressure waveforms at the halfway section on the pipeline. The results show good agreement between the estimated flow rate waveforms and theroetical those under unsteady laminar flow conditions. the method proposed here is useful in estimating unsteady flow rate through an arbitray cross section in hydraulic pipeline and components without installing an instantaneous flowmeter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.7
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• pp.468-473
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• 2010

This paper deals with approximate integral solutions to the one-dimensional model describing the charging process of stratified thermal storage tanks. Temperature is assumed to be the form of Fermi-Dirac distribution function, which can be separated to two sets of cubic polynomials for each hot and cold side of thermal boundary layers. Proposed approximate integral solutions are compared to the previous works of the approximate analytic solutions and show reasonable agreement. The approach, however, has benefits in mathematical difficulties, complicated solution form and unstable convergence of series solution founded in the previous analytic solutions. Solutions for a semi-infinite region, which have simple closed form solutions, give close agreement to those for a finite region. Thermocline thickness is obtained in closed form and shows proportional behavior to the square root of time and inverse proportional behavior to the square root of flow rate.