• Journal of Korean Society of Industrial and Systems Engineering
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• v.39 no.1
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• pp.25-30
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• 2016

It is critical to forecast the maximum daily and monthly demand for power with as little error as possible for our industry and national economy. In general, long-term forecasting of power demand has been studied from both the consumer's perspective and an econometrics model in the form of a generalized linear model with predictors. Time series techniques are used for short-term forecasting with no predictors as predictors must be predicted prior to forecasting response variables and containing estimation errors during this process is inevitable. In previous researches, seasonal exponential smoothing method, SARMA (Seasonal Auto Regressive Moving Average) with consideration to weekly pattern Neuron-Fuzzy model, SVR (Support Vector Regression) model with predictors explored through machine learning, and K-means clustering technique in the various approaches have been applied to short-term power supply forecasting. In this paper, SARMA and intervention model are fitted to forecast the maximum power load daily, weekly, and monthly by using the empirical data from 2011 through 2013. $ARMA(2,\;1,\;2)(1,\;1,\;1)_7$ and $ARMA(0,\;1,\;1)(1,\;1,\;0)_{12}$ are fitted respectively to the daily and monthly power demand, but the weekly power demand is not fitted by AREA because of unit root series. In our fitted intervention model, the factors of long holidays, summer and winter are significant in the form of indicator function. The SARMA with MAPE (Mean Absolute Percentage Error) of 2.45% and intervention model with MAPE of 2.44% are more efficient than the present seasonal exponential smoothing with MAPE of about 4%. Although the dynamic repression model with the predictors of humidity, temperature, and seasonal dummies was applied to foretaste the daily power demand, it lead to a high MAPE of 3.5% even though it has estimation error of predictors.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.11
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• pp.1236-1244
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• 2012

A equivalent stiffness modeling has been performed for extracting the equivalent stiffness properties which are orthotropic elastic model from a large scale wind turbine rotor blade so that structure model can be constructed more simply for the three dimensional static aeroelastic analysis. In order to present the procedure of equivalent stiffness modeling, NREL 5MW class wind turbine rotor having the three stiffness information which are flapewise, edgewise and torsional stiffness was chosen. This method is based on applying unit moment at the tip of the blade as well as fixing all degree of freedom at the blade root and calculating the displacement from the load analysis to obtain the elastic modulus corresponding to equivalent stiffness referred to the NREL reports on blade divided into 5 sections respectively. In addition, one section was divided into 3 parts and the trend functions were used to make the equivalent stiffness model more correctly and quickly. Through the comparison of stiffness between the reference values and calculated values from equivalent stiffness model, the investigation of the accuracy on the stiffness values and the efficiency for constructing the model was conducted.

• Journal of Power System Engineering
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• v.12 no.4
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• pp.5-11
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• 2008

The RI gasoline engine haying a sub-chamber had a high cycle variation due to the difficulty of the residual gas scavenge in the sub-chamber. To solve this problem and improve the combustion performance of RI engine, we devised a method to inject directly CNG fuel into the sub-chamber. A DI diesel engine of single cylinder was converted into a RI-CNG engine and an electronic control unit for the engine was manufactured. In this study, the combustion characteristics of the RI-CNG engine were investigated with the injection timings and air excess ratios at the load conditions of 50% throttle open rate and 1700rpm. As the results from this study, the RI-CNG engine worked reliably under the condition of the ignitable lean limit of $\lambda=1.7$ by showing the $COV_{imep}$ below about 5%. And the highest thermal efficiency could be obtained in the injection timing that produced the high imep and the low $COV_{imep}$ at the same time. The CO emission concentration indicated very low values and the THC and $NO_x$ showed an opposite pattern. With a view to improving the thermal efficiency and reducing the harmful emissions, the proper control region of the ignition timing and the mixture ratio were nearly ATDC $20^{\circ}\sim50^{\circ}$ and $\lambda=1.4$ respectively.

• Geotechnical Engineering
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• v.12 no.5
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• pp.127-136
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• 1996

Recently, EPS which has unit weight of only 20~30kg/m3, is used for acquiring the safety of settlement and bearing capacity, In Korea, EPS was first used in 1993 as backfill material for abutment that was constructed on soft ground in Inchon. Since then EPS has been used increasingly as backfill material. However, adequate modelling has not yet been proposed for the prediction of the behavior of EPS. Only it's design strength was proposed as the results of unconfined strength and creep test. Accordingly this paper executed triaxial compression test on EPS with various density and confining pressure. Through the analysis of test data the behavior of EPS for strainstress, tangential modulus and poisson's ratio can be expressed in functions with parameters of density and confining pressure of EPS. From these results, this paper proposed a nonliner model describing the behavior of EPS.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.223-233
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• 2003

Sand compaction pile (SCP) is one of the ground improvement techniques which are being used for not only accelerating consolidation but also increasing bearing capacity of loose sands or soft clay grounds. In this study, laboratory model tests and 3-D finite element analyses were performed to investigate the interaction between sand compaction piles and surrounding soft soils. Based on the results obtained, as the area replacement ratio increases, the stress concentration ratio increases at the pile point, the settlement decreases, and the relative displacement between column and soil also decreases. It is also found that numerical study is illustrated by good comparison with model test results, and the numerical analysis revealed slip effects which could not be specifically identified in the model tests.

• Journal of Korea Game Society
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• v.8 no.3
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• pp.61-68
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• 2008

Quadtree-based terrain visualization methods have been used in a lot of applications. However, because most procedures are performed on the CPU, the rendering speed is slow in comparison to methods using GPU. In this paper, we present a quadtree-based terrain visualization method working on the GPU with specially designed data structure, error-texture and LOD-texture, and block-based acceleration method. In preprocessing step, we calculate errors in world space and store them to error-texture. In rendering step, we examine projected errors of error-texture and choose the detail level, then store the projected errors to LOD-texture. View frustum culling is performed as block unit using the values of error-texture and LOD-texture. This method reduces CPU load and performs time consuming jobs such as LOD selection and view frustum culling.

• Journal of Korea Multimedia Society
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• v.13 no.1
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• pp.38-46
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• 2010

A stable game managing system is absolutely needed to accept simultaneous interlacing of many users for on- line game system. The proposed P2P on-line game system in this paper is able to get stable and real-time game managing within limited time stamp utilizing through reorganizing peers according to synchronous time which can be avoid congestion on one region, it is possible to synchronize for game nodes within limited time stamp utilizing. Reorganizing M-tree which leads 10 distribute loads. The system manages each region unit, and it is execute no matter how big game sizes are. Thus to ensure such as the problems of expand server and stabilization or message transmission. Also, prove efficiency of the suggested system through the simulation.

• Journal of Broadcast Engineering
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• v.16 no.2
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• pp.258-273
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• 2011

This paper designs and implements a multi-view 3D video player system which is operated faster than existing video player systems. The structure for obtaining the near optimum speed in a multi-processor environment by parallelizing the component modules is proposed to process large volumes of multi-view image data at high speed. In order to use the concurrency of bottleneck, we designed image decoding, synthesis and rendering modules in a pipeline structure. For load balancing, the decoder module is divided into the unit of viewpoint, and the image synthesis module is geometrically divided based on synthesized images. As a result of this experiment, multi-view images were correctly synthesized and the 3D sense could be felt when watching the images on the multi-view autostereoscopic display. The proposed application processing structure could be used to process large volumes of multi-view image data at high speed, using the multi-processors to their maximum capacity.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.4
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• pp.127-134
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• 2017

A rotary table is a positioning device used in metalworking for the multiple axes of machine tools, and the utilization trend is increasing with machining efficiency. In the construction of a rotary table, the core technology is a power transfer unit that drives the table, typically a gear type and a roller gear cam type. As the rollers installed on the turret column have rolling movement on the contact surface of the roller gear cam, the roller gear cam type has the advantage of low wear, high load, and fast driving. Therefore, it is currently being replaced by a roller gear cam type. In this study, we researched a 5-axis machining method for the roller gear cam on a rotary table and a new method of applying double roller gear cam curve to reduce the noise and shock between the roller and the cam surface. We implemented the 5-axis machining process in this study using software to generate NC-code and machined the roller gear cams using a Mazak Integrex-200IV. We found that the roller gear cam and turret were able to identify mutual touch status and the noise from the operation of the roller gear cam was substantially reduced.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.9
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• pp.1669-1673
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• 2008

A new cycle ergometer using a Magneto-Rheological (MR) rotary brake system has been developed for rehabilitation of hemiplegia patients to reduce uneven pedaling characteristics. For this purpose, a control method to adjust the resistance of the MR rotary brake in real time based on the magnitude of the muscular force exerted by the subject has been devised so that the mechanical resistance to the pedaling can be minimized when the affected leg was engaged for pedaling. A series of experiments were carried out with and without the engagement of this real-time control mode of MR rotary brake at different pedaling rate to find out the effect of the real-time control mode. The characteristics of the pedaling for these specific conditions were analyzed based on the variations in angular velocities of the pedal unit. The results showed that the variations in the angular velocities were decreased by 42.9% with the control mode. The asymmetry of pedaling between dominant and non-dominant leg was 19.63% in non-control mode and 1.97% in the control mode. The characteristics of electromyography(EMG) in the lower limbs were also measured. The observation showed that Integrated EMG(IEMG) reduced with the control mode. Therefore, the new bicycle system using MR brake with the real time control of mechanical resistance was found to be effective in recovering the normal pedaling pattern by reducing unbalanced pedaling characteristics caused by disparity of muscular strength between affected and unaffected leg.