• Journal of Korean Society on Water Environment
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• v.20 no.3
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• pp.197-205
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• 2004

Batch test methods have developed for a long time to measure kinetic and stoichiometric parameters which are required to perform steady state design and mathematical modelling of activated sludge processes. However, at various So/Xo ratios, abnormal behaviors of ordinary heterotrophic organism in batch tests have been reported in many researches. Thus, in this research, abnormal behaviors of heterotrophs in batch tests were investigated at various So/Xo conditions by measuring and interpreting oxygen utilization rate. As So/Xo ratio increased, the calculated values of maximum specific growth rates, ${\mu}_{H,max}$ and $K_{MP,max}$, increased. However, at a certain point of So/Xo (around 10mgCOD/mgMLAVSS), ${\mu}_{H,max}$ and $K_{MP,max}$ values started to decrease. According to this observation, three prominent behaviours of heterotrophs were identified at various So/Xo conditions. (1) At low So/Xo region (below 5 mgCOD/mgMLAVSS), the oxygen utilization rate of heterotrophs in batch tests were almost stable and consequently yielded lower maximum specific growth rate. (2) At high So/Xo region (up to 5~10 mgCOD/mgMLAVSS), oxygen utilization rate incresed sharply with time and indicated more upward curvature than the predicted OUR with conventional activated sludge model, which consists of single hetetrotrophs group. Thus, in this region, competition model of two organisms, fast-grower and slow-grower, seemed to be appropriate. (3) At extremely high So/Xo region (over 10mgCOD/mgMLAVSS), significant oxygen utilization rate was still observed even after depletion of readily biodegradable COD. This might be caused by retarded utilization of intermediates which were generated by self inhibition mechanism in the process of RBCOD uptake.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.4
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• pp.1-13
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• 2003

For spatial free vibration of non-symmetric thin-walled curved beams with shear deformation, an improved formulation is proposed in the present study. The elastic strain and the kinetic energies are first derived by considering constant curvature and shear deformation effects due to shear forces and restrained warping torsion. Next equilibrium equations and force-deformation relations are obtained using a stationary condition of total potential energy. And the finite element procedures are developed by using isoparametric curved beam element with arbitray thin-walled sections. Particularly not only shear deformation and thickness-curvature effects on vibration behaviors of curved beams but also mode transition and crossover phenomena with change in curvatures of beams are parametrically investigated. In order to illustrate the accuracy and the reliability of this study, various numerical solutions for spatial free vibration are compared with results by available references and ABAQUS's shell element.

• Korean Journal of Chemical Engineering
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• v.35 no.12
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• pp.2327-2335
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• 2018

Fluid catalytic cracking (FCC) is an important chemical process that is widely used to produce valuable petrochemical products by cracking heavier components. However, many difficulties exist in modeling the FCC process due to its complexity. In this study, a dynamic process model of a FCC process is suggested and its structural observability is analyzed. In the process modeling, yield function for the kinetic model of the riser reactor was applied to explain the product distribution. Hydrodynamics, mass balance and energy balance equations of the riser reactor and the regenerator were used to complete the modeling. The process model was tested in steady-state simulation and dynamic simulation, which gives dynamic responses to the change of process variables. The result was compared with the measured data from operating plaint. In the structural analysis, the system was analyzed using the process model and the process design to identify the structural observability of the system. The reactor and regenerator unit in the system were divided into six nodes based on their functions and modeling relationship equations were built based on nodes and edges of the directed graph of the system. Output-set assignment algorithm was demonstrated on the occurrence matrix to find observable nodes and variables. Optimal locations for minimal addition of measurements could be found by completing the whole output-set assignment algorithm of the system. The result of this study can help predict the state more accurately and improve observability of a complex chemical process with minimal cost.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2720-2727
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• 2022

The Generation IV Lead-cooled fast reactor (LFR) take the liquid lead or lead-bismuth eutectic alloy (LBE) as the coolant of the primary cooling circuit. Combined with the natural characteristics of lead alloy and the design features of LFR, the system is the simplest and the number of equipment is the least, which reflects the inherent safety characteristics of LFR. The nuclear main coolant pump (MCP) is the only power component and the only rotating component in the primary circuit of the reactor, so the various operating characteristics of the MCP are directly related to the safety of the nuclear reactor. In this paper, various working conditions that may occur in the normal rotation (positive rotating) of the MCP and the corresponding internal flow characteristics are analyzed and studied, including the normal pump condition, the positive-flow braking condition and the negative-flow braking condition. Since the corrosiveness of LBE is proportional to the fluid velocity, the distribution of flow velocity in the pump channel will be the focus of this study. It is found that under the normal pump condition and positive-flow braking conditions, the high velocity region of the impeller domain appears at the inlet and outlet of the blade. At the same radius, the pressure surface is lower than the back surface, and with the increase of flow rate, the flow separation phenomenon is obvious, and the turbulent kinetic energy distribution in impeller and diffuser domain shows obvious near-wall property. Under the negative-flow braking condition, there is obvious flow separation in the impeller channel.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.3
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• pp.139-143
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• 2022

In this study, Among the electromagnetic induction power generation (EMG) techniques, the design specifications of the RFPM were set, and a suitable test prototype was manufactured through finite element analysis (FEM, 2D) required for characteristic calculation. In addition, a dedicated testing device (Dynamo-Tester) was designed and manufactured to measure and analyze the test prototype. The test product was measured with a test device and the result is analyzed to suggest a method that can be applied by generating as much output power as possible to charge the battery of the wearable IT device using actual kinetic energy of the human body. As a result of the test, the output power was 1.679W and the efficiency was 79.31% under the conditions of rotation speed of 780.9rpm, torque of 0.264kgf/cm, and load current of 73.6~73.9mA. Therefore, it was analyzed that it was possible to charge the wearable device with the output of the ultra-small RFPM pendulum generator.

• Advances in aircraft and spacecraft science
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• v.10 no.2
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• pp.107-125
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• 2023

Drag reduction is significant research in aircraft design due to its effect on the cost of operation and carbon footprint reduction. Aircraft currently use conventional solid winglets to reduce the induced drag, adding extra structural weight. Fluidic on-demand winglets can effectively reduce drag for low-speed flight regimes without adding any extra weight. These utilize the spanwise airflow from the wingtips using hydraulic actuators to create jets that negate tip vortices. This study develops a computational model to investigate fluidic on-demand winglets. The well-validated computational model is applied to investigate the effect of injection velocity and angle on the aerodynamic coefficients of a rectangular wing. Further, the turbulence parameters such as turbulent kinetic energy (TKE) and turbulent dissipation rate are studied in detail at various velocity injections and at an angle of 30°. The results show that the increase in injection velocity shifted the vortex core away from the wing tip and the increase in injection angle shifted the vortex core in the vertical direction. Further, it was found that a 30° injection is efficient among all injection velocities and highly efficient at a velocity ratio of 3. This technology can be adopted in any aircraft, effectively working at various angles of attack. The culmination of this study is that the implementation of fluidic winglets leads to a significant reduction in drag at low speeds for low aspect ratio wings.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.77-77
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• 2016

Thin films synthesized by plasma processes have been widely applied in a variety of industrial sectors. The structure control of thin film is one of prime factor in most of these applications. It is well known that the structure of this film is closely associated with plasma parameters and species of plasma which are electrons, ions, radical and neutrals in plasma processes. However the precise control of structure by plasma process is still limited due to inherent complexity, reproducibility and control problems in practical implementation of plasma processing. Therefore the study on the fundamental physical properties that govern the plasmas becomes more crucial for molecular scale control of film structure and corresponding properties for new generation nano scale film materials development and application. The thin films are formed through nucleation and growth stages during thin film depostion. Such stages involve adsorption, surface diffusion, chemical binding and other atomic processes at surfaces. This requires identification, determination and quantification of the surface activity of the species in the plasma. Specifically, the ions and neutrals have kinetic energies ranging from ~ thermal up to tens of eV, which are generated by electron impact of the polyatomic precursor, gas phase reaction, and interactions with the substrate and reactor walls. The present work highlights these aspects for the controlled and low-temperature plasma enhanced chemical vapour disposition (PECVD) of Si-based films like crystalline Si (c-Si), Si-quantum dot, and sputtered crystalline C by the design and control of radicals, plasmas and the deposition energy. Additionally, there is growing demand on the low-temperature deposition process with low hydrogen content by PECVD. The deposition temperature can be reduced significantly by utilizing alternative plasma concepts to lower the reaction activation energy. Evolution in this area continues and has recently produced solutions by increasing the plasma excitation frequency from radio frequency to ultra high frequency (UHF) and in the range of microwave. In this sense, the necessity of dedicated experimental studies, diagnostics and computer modelling of process plasmas to quantify the effect of the unique chemistry and structure of the growing film by radical and plasma control is realized. Different low-temperature PECVD processes using RF, UHF, and RF/UHF hybrid plasmas along with magnetron sputtering plasmas are investigated using numerous diagnostics and film analysis tools. The broad outlook of this work also outlines some of the 'Grand Scientific Challenges' to which significant contributions from plasma nanoscience-related research can be foreseen.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.111-121
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• 2001

Rockfall protection fences are used for diminishing rockfall damage in roads side slopes. In order to install the fences in effective way, the conditions of rock slopes and total predicted impact energy of fa11ing rock should be considered. However, the fences have been constructed without any consideration for lithology, height and slope angle of rock slope in Korea. In addition, the information about the performance of the protection fences, which should be evaluated by in-situ test or laboratory test in order to check out the practical use in the field, is not available. Therefore, in design manual for the rockfall protection fence, the specific details for the installation of this type of fence are not provided yet. The full sized rockfall in situ test was carried out for the calculation of falling energy of rock and the evaluation of the maximum energy absorbing capacity of fence. For this test, the rock slopes whose heights are about 20 m and dip angle of 65 degree, have been chosen. This is because those geometries are mean height and slope angle of most road cut slopes along Korean national highway. Based on the preliminary simulation procedure, four different sizes of concrete ball (0.7, 1.3, 2.3 and 4.3 ton) were prepared and flour different types of protection fence were constructed. The results of this test provide information about the maximum energy absorbing capacity of the fence, kinetic energy of rockfall and restitution coefficient, and these results can be utilized in the establishment of rockfall fence design and construction manual.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.2
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• pp.79-85
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• 2012

In this study, Application of sequencing batch reactor (SBR) process for RO retentate treatment was performed. Efficiency of treatment by load and temperature variation was tested. The SBR process was operated two types as HRT per one cycle was 8 and 12 hours, respectively. Methanol was injected for an effective denitrificaion owing to low C/N ratio of the RO retentate. TN removal efficiency of the SBR process was relatively stable at the change of flow-rate and temperature. The optimum time cycle of SBR process was 2 cycle/day for TN removal, and in the case of 3 cycle/day, the effluent TN concentration was found under the effluent quality standard. In the result of assessment, the application of SBR process for RO retentate treatment was effective and could be utilized to design for the wastewater treatment plant. The specific nitrification rate (SNR) and specific denitrification rate (SDNR) were $0.043{\sim}0.066kg\;NH_3-N/kg\;MLVSS{\cdot}day$ and $0.096{\sim}0.287kg\;NH_3^--N/kg\;MLVSS{\cdot}day$, respectively. The derived kinetic could be applied for design to the aerobic and anoxic tank in the RO retentate treatment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.649-656
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• 2011

A model for the numerical simulation of lithium-ion batteries (LIBs) is developed for use in battery cell design, with a view to improving the performances of such batteries. The model uses Newman-type electrochemical and transfer $theories^{(1,2)}$ to describe the behavior of the lithium-ion cell, together with the Levenberg-Marquardt optimization scheme to estimate the performance or design parameters in nonlinear problems. The mathematical model can provide an insight into the mechanism of LIB behavior during the charging/discharging process, and can therefore help to predict cell performance. Furthermore, by means of least-squares fitting to experimental discharge curves measured at room temperature, we were able to obtain the values of transport and kinetic parameters that are usually difficult to measure. By comparing the calculated data with the life-test discharge curves (SB LiMotive cell), we found that the capacity fade is strongly dependent on the decrease in the reaction area of active materials in the anode and cathode, as well as on the electrolyte diffusivity.