• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.181-188
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• 2004

Structural analysis for materials containing regularly spaced in-homogeneities is usually executed by using averaged material properties. For the homogenization process, a unit cell is defined and loaded somehow, and its response is investigated to evaluate the properties. The imposed loading conditions should accord to the behavior of unit cell immersed in the macroscopic structure in order to guarantee the accuracy of the effective properties. Each unit cell shows periodic variation of strain if the material is loaded uniformly, and in this study, direct implementation of this characteristic behavior is attempted on FE models of unit cell. Conventional finite element analysis tool can be used without any modification, and the boundary of unit cell is constrained in a way that the periodicity is satisfied. The proposed method is applicable to skew arrayed in-homogeneity problems. The flexibility matrix relating tonsorial stress and strain components in skewed rectilinear coordinate system is transformed so that the required engineering constants can be evaluated. Effective properties are computed for the materials with square and skew arrayed circular holes, and its accuracy is examined.

• Journal of KSNVE
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• v.7 no.1
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• pp.99-106
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• 1997

Centrigugal fans are widely used due to their ability to achieve relatively high pressure ratios in a short axial distance compared to axial fans. Because of their widespread use, the noise generated by these machines causes one of serious problems. In general, centrigugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the periodic flow discharged radially from the impeller and the stator blades or the cutoff. But in vacuum cleaner fan the noise is dominated by not only the discrete tones of BPF but also broadband frequencies. In this study we investigate the mechanism of broadband noise and predict for the unsteady flow field and the acoustic pressure field associated with the centrifugal fan. DVM(discrete vortex method) is used to calculates the flow field and the Lowson's method is used to predict the acoustic pressures. From the results we find that the broadband noise of a circular casing centrifugal fan is due to the unsteady force fluctuation around the impeller blades related to the vortex shedding. The unsteady forces associated with the shed vortices at impeller and related to the interactions to the diffuser and the exit.

• IE interfaces
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• v.13 no.3
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• pp.424-430
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• 2000

Supply chain management (SCM) is an area that has recently received a great deal of attention in the business community. While SCM is relatively new, the idea of coordinated planning is not. During the last decades, many researchers have investigated multi-stage inventory problems. However, only a few papers address the problem of cost-optimal coordination of multi-stage inventory control with respect to service measures. Even published approaches have a shortcoming in dealing with a delivery lead time consisted of a shipping time and a waiting time. Assumed that there is no waiting time, or that the delivery lead time is implicitly compounded of a shipping time and a waiting time, the problem is often simplified into a multi-stage buffer allocation and a single-stage stochastic buffer sizing problem at all installations. This paper presents a simulation-based heuristic algorithm and a comparison with others for the problem that cannot be decomposed into a multi-stage buffer allocation and a single-stage stochastic buffer sizing problem because the waiting time ties together all stages. The comparison shows that the simulation-based heuristic algorithm performs better than other approaches in saving average inventory cost for both Poisson and Normal demands.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.3
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• pp.96-101
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• 2013

Automotive brake system is an essential element for the safety. The system is powered by the circulation of brake oil. A braker hose is used for the circulation of the oil in this system. Layout of the hose changes according to the steering and stress occur in the hose. A lot of the durability tests are performed in order to prevent serious problems such as hose bursting by the accumulation of the stress before setting an optimized hose layout on automobile. The test is conducted for the layout which is same such as set in automobile. In the test, brake hose layout shall exercise the same mode of thousands of times under the high temperature and periodic pressure condition and then the damage of the tested hose is inspected. This test, however, has a disadvantage of heavy consumption of time and money. In order to compensate for these drawbacks, the finite element method(FEM) study was performed to predict the changes in the layout of the brake hose. In this study, the FEM results and the test results were compared and the validity was verified. The radius of curvature of the FEM and test at the same positions were especially investigated for the validation. Also, this study will be used as the basis of research on the life prediction of brake hose.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.42 no.4
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• pp.116-125
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• 2019

The Dynamic Vehicle Routing Problem (DVRP) involves a combinatorial optimization problem where new customer demands become known over time, and old routes must be reconfigured to generate new routes while executing the current solution. We consider the high level of dynamism problem. An application of highly dynamic DVRP is the ambulance service where a patient contacts the service center, followed by an evaluation of case severity, and a visit by a practitioner/ ambulance is scheduled accordingly. This paper considers a variant of the DVRP and proposes a decentralized algorithm in which collaborators (Depot and Vehicle), both have only partial information about the entire system. The DVRP is modeled as a periodic re optimization of VRP using the proposed decentralized algorithm where collaborators exchange local information to achieve the best global objective for the current state of the system. We assume the existence of a dispatcher e.g., headquarter of the company who can communicate to vehicles in order to gather information and assigns the new visits to them. The effectiveness of the proposed decentralized coordination algorithm is further evaluated using benchmark data given in literature. The results show that the proposed method performed better than the compared algorithms which utilize the centralized coordination in 12 out of 21 benchmark problems.

• The Journal of Engineering Research
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• v.8 no.1
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• pp.107-118
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• 2006

The difficulties to build a 3-dimensional water quality model for the coastal water quality improvement and the environmental recovery estimation are the lack of periodic observed data and the many problems to observe continuously. I observed the rainfall and non-point pollutants outflow patterns in Jinhae-Masan basin as mid-step researches for the water quality simulation and management method development in a coastal area. I applied Landsat image system and Geographic Information System to analyze the runoff and non-point pollutants outflow patterns. A water quality simulation model (SWMM) applied to Jinhae-Masan basin with results of the land use distribution, non-point pollution loads, and watershed informations from GIS(IDRISI used). I proposed some improved survey and GIS application methods reflect upon the pollutant characteristics from the observed non-point pollutant outflow patterns.

• International Commerce and Information Review
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• v.15 no.2
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• pp.189-206
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• 2013

In this paper, we investigate if the new merchant fee system has problems. The fee was fixed by government policies and there were no processes of listening to market participants. Therefore, we suggest improvements as follows. First, large-sized stores take burdens for the rest of stores so credit card companies and the government should try to minimize the increasing rate for large-sized stores. Second, credit card firms need to give VAN companies roles of stabilizing authorizing processes. Third, periodic update requires because of credibility. Fourth, contents of merchant fee should be disclosed to merchants. Fifth, there needs discussions for merchant fees of debit cards.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2004.11a
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• pp.117-124
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• 2004

Dynamic and fragmented characteristics ale two of the most significant factors that distinguish the construction industry from other industries. Previous forecasting techniques have failed to solve the problems derived from the above characteristics and do not provide considerable support. This paper deals with providing a more precise forecasting by applying Case-based Reasoning (CBR). The newly developed model in this study enables project managers to forecast monthly expenditures with less time and effort by retrieving and referring only projects of a similar nature, while filtering out irrelevant cases included in database. For the purpose of accurate forecasting. the choice of the numbers of referring projects was investigated. it is concluded that selecting similar projects at $5\~6\;\%$ out of the whole database will produce a more precise forecasting. The new forecasting model. which suggests the predicted values based on previous projects, is more than just a forecasting methodology it provides a bridge that enables current data collection techniques to be used within the context of the accumulated information. This will eventually help all the participants in the construction industry to build up the know ledge derived from invaluable experience.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.230-231
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• 2005

As environmental problems are important, automotive industries are developing various techniques to prevent air pollution. One of these is Positive Crankcase Ventilation (PCV) system. It removes blowby gas which includes about 30% hydrocarbon of total generated quantity. In this system, a PCV valve is attached in a manifold suction tube to control the flow rate of blowby gas which generates differently according to various operating conditions of an automotive engine. As this valve is very important, designers are feeling to design it because of both small size and high velocity. For this reason, we numerically investigated to understand both spool dynamic motion and internal fluid flow characteristics. As the results, spool dynamic characteristics, i.e. displacement, velocity, acting force, increase in direct proportion to the magnitude of differential pressure and indicate periodic oscillating motions. And, the velocity at the orifice region decreases according to the increase of differential pressure because of energy loss which is caused by the sudden decrease of flow area at the orifice region and the increase of flow volume in the front of spool head. Finally, the mass flow rate at the outlet decreases with the increase of spool displacement. We expect that PCV valve designers can easily understand fluid flow inside a PCV valve with our visual information for their help.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.4
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• pp.27-33
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• 2003

Circular Distributed-feedback (DFB) guiding structures can be incorporated in most of the semiconductor laser devices because of the frequency-selective property applicable as an optical filter in optical communications. In this paper, we present a novel and simple modal transmission-line theory (MTLT) using Floquet-Babinet's principle to analyze the optical filtering characteristics of Bragg gratings with cylindrical profile. The numerical results reveal that this method offers a simple and convenient algorithm to analyze the filtering characteristics of circular DFB configurations as well as is extended conveniently to evaluate the guiding problems of circular multi-layered periodic structures.