• Journal of Power System Engineering
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• v.18 no.1
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• pp.63-68
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• 2014

The numerical analysis of fluid flow in the tube cleaning system is examined. The working flow used in this study is seawater, and the temperature change is not considered as the temperature change of seawater in the tube cleaning system is negligible. Also, the analysis is performed under the assumption of steady state. The screens of complicated morphologies are simplified for the analysis, and only one fourth of the tube cleaning system is modeled as the system has a symmetrical shape. The velocity inlet boundary condition is employed for the seawater inlet, whereas the outflow boundary condition is employed for two seawater outlets. In applying the outflow boundary condition for the system with more than two outlets, the flow rate can be arbitrarily assigned. In the analysis, the finite-volume method based numerical analysis tool, the pressure based solver, the standard k-$\varepsilon$ model are utilized, and the under relaxation factor is modified appropriately. From the analysis, the distribution of velocity vectors, pressure and path lines are obtained, and the physical characteristics of fluid flow in the tube cleaning system is well-examined.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.3
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• pp.524-530
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• 2011

This paper analyzes fault tolerance under a stator turn fault, according to the winding configuration. Improvement of torque characteristics and fault tolerance can be achieved by winding configuration without additional methods. And, torque characteristics and fault tolerance according to the winding configuration can be usually analyzed by analytical method. But, when the stator turn fault generates, compare to the steady-state, analysis of torque characteristics and fault tolerance using the analytical method is not accurate because it does not reflect influence in mutual inductance and magnetic non-linearity. Therefore, analysis of torque characteristics and fault tolerance has to be performed by using the numerical method under fault condition. This paper develops fault characteristics according to the winding configuration using the FEM-base model considered magnetic non-linearity. And, this paper suggests fault tolerance improvement according to the winding configuration, by the comparison of 8/12 and 10/12 models, under fault condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.493-500
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• 2014

Nonlinear characteristics of cellular counterflow diffusion flame near the radiative extinction limit at large Damk$\ddot{o}$hler number are numerically investigated. Lewis number is assumed to be 0.5 and flame evolution is calculated by imposing an infinitesimal disturbance to a one-dimensional(1-D) steady state flame. The early stage of nonlinear development is very similar to that predicted in a linear stability analysis. The disturbance with the wavenumber of the fastest growing mode emerges and grows gradually. Eventual, an alternating pattern of reacting and quenching stripes is developed. The cellular flame temperature is higher than that of 1-D flame because of the gain of the total enthalpy. As the Damk$\ddot{o}$hler number is further increased, the shape of the cell becomes circular to increase the surface area per unit reacting volume. The cellular flames do not extinguish but survive even above the 1-D steady state extinction condition.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.11
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• pp.874-882
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• 2003

The condition assessment of engineering systems has increased in importance because the manpower needed to operate and supervise various plants has been reduced. Especially, induction motors are at the core of most engineering processes, and there is an indispensable need to monitor their health and performance. So detection and diagnosis of motor faults is a base to improve efficiency of the industrial plant. In this paper, a model-based fault detection system is developed for induction motors, using steady state vibration signals. Early various fault detection systems using vibration signals are a trivial method and those methods are prone to have missed fault or false alarms. The suggested motor fault detection system was developed using a model-based reference value. The stationary signal had been extracted from the non-stationary signal using a data segmentation method. The signal processing method applied in this research is FFT. A reference model with spectra signal is developed and then the residuals of the vibration signal are generated. The ratio of RMS values of vibration residuals is proposed as a fault indicator for detecting faults. The developed fault detection system is tested on 800 hp motor and it is shown to be effective for detecting faults in the air-gap eccentricities and broken rotor bars. The suggested system is shown to be effective for reducing missed faults and false alarms. Moreover, the suggested system has advantages in the automation of fault detection algorithms in a random signal system, and the reference model is not complicated.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.5
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• pp.97-106
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• 2009

An objective of this study is to give practical information that could be used for calculating pollutant emission factors and fuel economy from Korean Inspection & Maintenance program, which has been using steady state acceleration simulation mode. Concentration results from I/M test is adequately converted to mass emission factors and fuel efficiency data, which have unit of g/km and km/L, respectively. Exhaust volume flow(EVF), which is for converting emission result from concentration to mass, is measured by tracer method in various vehicle speed - power condition. It is found that there is an apparent second order relationship between EVF and vehicle inertia weight. EVF is expressed in function of vehicle inertia weight in order to estimate EVF in I/M site without measuring device. Converted mass emission results from measured EVF and raw emission analyzer show a satisfactory agreement with those from conventional CVS-bag type measurement system. Mass emission factors and fuel efficiency from measured EVF and estimated EVF also show good agreement to each other. Considering that an I/M program has great advantages to recruit-based emission test in terms of the number of test vehicle, the information in this study can be used for developing an alternative procedure to collect more various data to establish national database of mobile emission factors and fuel economy, even though the driving cycle in I/M program is steady state cycle rather than transient cycle.

• Journal of Environmental Science International
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• v.1 no.2
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• pp.125-136
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• 1992

Digestion of a municipal wastewater sludge by the anaerobic sequencing batch reactor (ASBR) was investigated to evaluate the performance of the ASBR process at a critical condition of high-solids-content fined. The reactors were operated at an HRT of 10 days with an equivalent loading rate of 0.8-1.5 gVS/L/d at 35$^{\circ}C$ The main conclusions drawn from this study were as follows: 1. Digestion of a municipal wastewater sludge was possible using the ASBR in spite of high concentration of settleable solids in the sludge. The ASBRS with 3- and 4-day cycle period showed almost identical high digestion performances. 2. No adverse effect on digestion stability was observed In the ASBRS in spite of withdrawal and replenishment of 30% or 40% of liquid contents. A conventional anaerobic digester could be easily converted to the ASBR without any stability problem. 3. Flotation thickening occurred in thicken step of the ASBRS throughout steady state, and floating bed volume at the end of thicken period occupied about 70% of the working volume of the reactor Efficiency of flotation thickening in the ASBRS could be comparable to that of additional gravity thickening of a completely mixed digester. 4. Solids were accumulated rapidly in the ASBR during start-up period. Solids concentrations in the ASBRS were 2.6 times higher than that in the completely mixed control reactor at steady state. Dehydrogenase activity had a strong correlation with the solids concentration. Dehydrogenase activity of the digested flu형e in the ASBR was 2.9 times higher than that of the flu형e in the control reactor, and about 25 times higher than that of the subnatant in the ASBR. 5. Remarkable increase in equivalent gas production of 52% was observed at the ASBRS compared with the control reactor in spite of similar quality of clarified effluent from the ASBRS and control reactor. The increase in gas production from the ASBRS was believed to be combined results of accumulation of microorganisms, higher driving force applied, and additional long-term degradation of organics continuously accumulated.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.2
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• pp.61-70
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• 2000

The performance simulation program on the turboprop engine(PT6A-62), which is a main engine of the first trainer KT-1 in republic of Korea, was developed. Characteristics of engine components were required for the steady-state performance analysis including on and off design point analysis. In most cases, these were substituted for what scaled from well known engine components characteristics with the scaling law. The developed program was compared with CASTURB program which is well known for the simulation performance analysis, such as analysis results of mass flow rate, compressor pressure ratio, fuel flow rate, power, specific fuel consumption ratio and turbine inlet temperature in the following four cases, to evaluate whether the developed program is acceptable or not. The first case was the sea level static standard condition and other cases were considered with various flight Mach numbers, altitudes. After verifying the developed program, the partload performance analysis was carried out. Transient performance analysis for various fuel schedules were performed. When the fuel step increase of 0.1sec was performed, the overshoot of the compressor turbine inlet temperature occurred. However, the fuel ramp increase for longer than 0.1sec time was performed, the overshoot could be eliminated.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.104-111
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• 2013

Deterioration is accelerated due to additional intrusion of chloride ion in crack width in cracked concrete. In this paper, modeling on equivalent diffusion coefficient in cracked concrete is performed for 1-D (Anisotropic) and 2-D (Isotropic) diffusion based on steady state condition. In the previous research, rectangular shape of crack was considered but the shape was modified to wedge shape with torturity. For verification of the proposed model, crack is induced in concrete sample and migration test in steady state is performed for 1-D diffusion. For 2-D diffusion, previous test results are adopted for verification. Through considering wedge shape of crack with torturity, diffusion coefficients in 1-D and 2-D diffusion are reduced, and the more reasonable prediction is obtained. The results from the proposed model with torturity of 0.10~0.15 are shown to be in the best agreement with the test results.

• Journal of Korea Water Resources Association
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• v.31 no.4
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• pp.439-448
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• 1998

There are many methods to calculate steady-state flowrate in a large water distribution system. Linear method which analyzes continuity equations and energy equations simultaneously is most widely used. Though it is theoretically simple, when it is applied to a practical water distribution system, it produces a very sparse coefficient matrix and most of its diagonal elements are to be zero. This sparsity characteristic of coefficient matrix makes it difficult to analyze pipe flow using the linear method. In this study, a graph theory is introduced to water distribution system analysis in order to prevent from producing ill-conditioned coefficient matrix and the technique is developed to produce positive-definite matrix. To test applicability of developed method, this method is applied to 22 pipes and 142 pipes system located nearby Taegu city. The results obtained from these applications show that the method can calculate flowrate effectively without failure in converage. Thus it is expected that the method can analyze steady state flowrate and pressure in pipe network systems efficiently. Keywords : pipe flow analysis, graph theory, linear method.

• Nuclear Engineering and Technology
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• v.41 no.6
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• pp.831-840
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• 2009

In order to evaluate the start-up behavior and to identify, through abnormal operation occurrences, the transient behaviors of the Sulfur Iodine(SI) process, which is a nuclear hydrogen process that is coupled to a Very High Temperature Gas Cooled Reactor (VHTR) through an Intermediate Heat Exchanger (IHX), a dynamic simulation of the process is necessary. Perturbation of the flow rate or temperature in the inlet streams may result in various transient states. An understanding of the dynamic behavior due to these factors is able to support the conceptual design of the secondary helium loop system associated with a hydrogen production plant. Based on the mass and energy balance sheets of an electrodialysis-embedded SI process equivalent to a 200 $MW_{th}$ VHTR and a considerable thermal pathway between the SI process and the VHTR system, a dynamic simulation of the SI process was carried out for a sulfuric acid decomposition process (Second Section) that is composed of a sulfuric acid vaporizer, a sulfuric acid decomposer, and a sulfur trioxide decomposer. The dynamic behaviors of these integrated reactors according to several anticipated scenarios are evaluated and the dominant and mild factors are observed. As for the results of the simulation, all the reactors in the sulfuric acid decomposition process approach a steady state at the same time. Temperature control of the inlet helium is strictly required rather than the flow rate control of the inlet helium to keep the steady state condition in the Second Section. On the other hand, it was revealed that the changes of the inlet helium operation conditions make a great impact on the performances of $SO_3$ and $H_2SO_4$ decomposers, but no effect on the performance of the $H_2SO_4$ vaporizer.