• Journal of the Korea Society for Simulation
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• v.12 no.3
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• pp.31-40
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• 2003

This paper studies an optimal policy for a certain class of (s, S) inventory control systems, where the demands are characterized by the renewal arrival process. To minimize the average cost over a simulation period, we apply a stochastic optimization algorithm which uses the gradients of parameters, s and S. We obtain the gradients of objective function with respect to ordering amount S and reorder point s via a combined perturbation method. This method uses the infinitesimal perturbation analysis and the smoothed perturbation analysis alternatively according to occurrences of ordering event changes. The optimal estimates of s and S from our simulation results are quite accurate. We consider that this may be due to the estimated gradients of little noise from the regenerative system simulation, and their effect on search procedure when we apply the stochastic optimization algorithm. The directions for future study stemming from this research pertain to extension to the more general inventory system with regard to demand distribution, backlogging policy, lead time, and inter-arrival times of demands. Another direction involves the efficiency of stochastic optimization algorithm related to searching procedure for an improving point of (s, S).

• Journal of the Korean BIBLIA Society for library and Information Science
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• v.4 no.1
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• pp.129-142
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• 1980

The present paper discusses some problem areas in supplying information. As the world advances in civilization, we need exact and rapid information exchange, it may be said in this connection that we also feel keenly the necessity of the industrialization of the information. In accordance with the industrialization of the information, we can find the following phenomena: 1. Increase of present potentiality users. 2. Demand of high level information in accordance with the improvement of education level, 3. Increase of demand in the information materials in accordance with growth of research and development. 4. Contraction of the existing knowhow and degeneration of special field technique, 5. Increase of information concerned person for policy making in the government and in the industry. In the meantime, the information problem occurs for efficient management of information materials, in addition to numerical increase of various kinds, increase of users crate control and standardization problem, so it is needed to improve a mode of expression, structure, file and methods of usage. The librarian, as a information processor, should recognize that the information is national resources and improve the marketability of information industry. We need an administrative system of national level for the development of library in accordance with increase of an administrator who is engaged in information activities.

• Korean Journal of Social Welfare
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• v.44
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• pp.64-90
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• 2001

There has been a demand of changing service delivery system for social welfare services, and therefore changing is resource acquisition environment for community social welfare service organizations (CSWSOs). These phenomena are, however, not properly actualized through the CSWSOs. The discrepancy between environmental demand and organizational adaptation seems to result from our lack of understanding those organizations. Based on this understanding, several research problems have been formulated on resource acquisition behaviors of CSWSOs. Empirical data were gathered, and the final sample included 82 social welfare agencies of Pusan province and 122 top/high level agency administrators. The result of data analysis and their implications are as follows: (1) Most of CSWSOs prefer government grants to other financial resources, because government resources can give them more stability than others including private donations and user fees. (2) In order to induce changes in CSWSOs, their stability needs should be properly counted. (3) There is no enough evidence to prove that CSWSOs leaders' personal characteristics have contributed to the behavioral differences on financial resource acquisition among CSWSOs. Rather, there has been enough evidence to prove for influences by institutional environment factors. So, it is recommended that, in order to change behaviors of CSWSOs, the focus should be given to the proper control of those institutional environment factors.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.12
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• pp.2251-2261
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• 2016

The use of renewable energy sources and energy storage systems is increasing due to new policies in the energy industries. However, the increase in distributed generation hinders the reliability of power systems. In order to stabilize power systems, a virtual power plant has been proposed as a novel power grid management system. The virtual power plant plays includes different distributed energy resources and energy storage systems. We define a core virtual power plant technology related to demand response and ancillary service for the cases of Korea, America, and Europe. We also suggest applications of the proposed virtual power plant to the vehicle-to-grid market for restructuring national power industries in Korea.

• Earthquakes and Structures
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• v.14 no.6
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• pp.537-549
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• 2018

Using vertical links in eccentric braced frames is one of the best passive structural control approaches due to its effectiveness and practicality advantages. However, in spite of the subject importance there are limited studies which evaluate the seismic reliability and response reduction factor (R-factor) in this system. Therefore, the present study has been conducted to improve the current understanding about failure mechanism in the structural systems equipped with vertical links. For this purpose, following definition of demand and capacity response reduction factors, these parameters are computed for three different buildings (4, 8 and 12 stories) equipped with this system. In this regards, pushover and incremental dynamic analysis have been employed, and seismic reliability as well as multi-level response reduction factor according to the seismic demand and capacity of the frames have been derived. Based on the results, this system demonstrates high ductility and seismic energy dissipation capacity, and using the response reduction factor as high as 8 also provides acceptable reliability for the frame in the moderate and high earthquake intensities. This system can be used in original buildings as lateral load resisting system in addition to seismic rehabilitation of the existing buildings.

• Membrane and Water Treatment
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• v.7 no.1
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• pp.11-22
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• 2016

The characterization of treatment performance with respect to mixed liquor suspended solids (MLSS) concentration enables greater control over system performance and contaminant removal efficiency. Hybrid membrane bioreactors (HMBRs) have yet to be well characterized in this regard, particularly in the context of greywater treatment. The aim of this study, therefore, was to determine the optimal MLSS concentration for a decentralized HMBR greywater reclamation system under typical loading conditions. Treatment performance was measured at MLSS concentrations ranging from 1000 to 4000 mg/L. The treated effluent was characterized in terms of biochemical oxygen demand ($BOD_5$), chemical oxygen demand (COD), turbidity, ammonia ($NH_3$), total phosphorus (TP), total kjeldahl nitrogen (TKN), and total nitrogen (TN). An MLSS concentration ranging from 3000 to 4000 mg/L yielded optimal results, with $BOD_5$, COD, turbidity, $NH_3$, TP, TKN, and TN removals reaching 99.2%, 97.8%, 99.8%, 99.9%, 97.9%, 95.1%, and 44.8%, respectively. The corresponding food-to-microorganism ratio during these trials was approximately 0.23 to 0.28. Operation at an MLSS concentration of 1000 mg/L resulted in an irrecoverable loss of floc, and contaminant residuals exceeded typical guideline values for reuse in non-potable water applications. Therefore, it is suggested that operation at or below this threshold be avoided.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.10
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• pp.491-497
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• 2006

For high efficiency and easy speed control of brushless DC (BLDC) motor, the demand of BLDC motor is increasing. Especially demand of interior permanent magnet (IPM) BLDC with high efficiency and high power in electric motion vehicle is increasing. However, IPM BLDC basically has a high cogging torque that results from the interaction of permanent magnet magnetomotive force (MMF) harmonics and air-gap permeance harmonics due to slotting. This cogging torque generates vibration and acoustic noises during the driving of motor. Thus reduction of the cogging torque has to be considered in IPM BLDC motor design by analytical methods. This paper proposes the cogging torque reduction method for IPM BLDC motor. For reduction of cogging torque of IPM BLDC motor, this paper describes new technique of the flux barriers design. The proposed method uses sinusoidal form of flux density to reduce the cogging torque. To make the sinusoidal air-gap flux density, flux barriers are applied in the rotor and flux barriers that installed in the rotor produce the sinusoidal form of flux density. Changing the number of flux barrier, the cogging torque is analyzed by finite element method. Also characteristics of designed model by the proposed method are analyzed by finite element method.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.1
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• pp.1-8
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• 2006

Now a day, owing to high efficiency and easy speed control of brushless DC(BLDC) motor, the demand of BLDC motor that has high power and low noises are increasing. Especially demand of interior permanent magnet(IPM) BLOC with high efficiency and high power in electric motion vehicle is increasing. IPM BLDC motor has permanent magnets in the rotor. Because it has two different flux paths, magnetic reluctance differences are generated in d-axis and q-axis. As the result of the inductance differences that are generated by the saliency(magnetic reluctance differences) in the rotor, the motor has structure advantage that has the additional reluctance torque except a magnet torque and because magnet is situated inside the rotor, the mechanical structure is strong. Therefore IPM BLDC motor makes possible to have high speed and high power. This paper presents a design and characteristics analysis of IPM BLDC motor for electric vehicle. To design IPM BLDC motor, surface mounted permanent magnet(SPM) BLDC motor is used as the initial design model. According to the shape-ratio() of permanent magnet, the characteristic of IPM BLDC motor is analyzed by Finite element method (FEM). Characteristics analysis results of the designed motor are compared with the experimental results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.11
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• pp.102-108
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• 2020

The demand for lightweight materials and high-strength steel has rapidly increased to help reduce the weight of a vehicle body; it improves the fuel efficiency of automobiles and provides passenger safety. Additionally, as the material becomes thinner, the demand for its resistance against corrosion becomes higher. Hence, the application of the surface-treated steel sheet has surged rapidly. In this study, a weld bonding experiment using a delta spot welding machine is performed on a thin sheet of a different material (Al6061-T6/GA440). The thickness of the material was kept at 1 mm to reduce the weight of the automobile body parts. Additionally, the purpose of this study is to control the heat input by applying the welding conditions of a multi-stage pressure pattern to improve corrosion resistance shear strength. The analysis of nugget diameter measurement, shear tensile test, and salt spray test was performed to achieve the aim.

• Earthquakes and Structures
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• v.22 no.6
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• pp.585-595
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• 2022

Using the nonlinear static procedures has become very common in seismic codes to achieve the nonlinear response of the structure during an earthquake. The capacity spectrum method (CSM) adopted in ATC-40 is considered as one of the most known and useful procedures. For this procedure the seismic demand can be approximated from the maximum deformation of an equivalent linear elastic Single-Degree-of-Freedom system (SDOF) that has an equivalent damping ratio and period by using an iterative procedure. Data from the results of this procedure are plotted in acceleration- displacement response spectrum (ADRS) format. Different improvements have been made in order to have more accurate results compared to the Non Linear Time History Analysis (NL-THA). A new procedure is presented in this paper where the iteration process shall not be required. This will be done by estimation the ductility demand response spectrum (DDRS) and the corresponding effective damping of the bilinear system based on a new parameter of control, called normalized yield strength coefficient (η), while retaining the attraction of graphical implementation of the improved procedure of the FEMA-440. The proposed procedure accuracy should be verified with the NL-THA analysis results as a first implementation. The comparison shows that the new procedure provided a good estimation of the nonlinear response of the structure compared with those obtained when using the NL-THA analysis.