• Journal of the Korean Society for Precision Engineering
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• v.33 no.3
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• pp.235-242
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• 2016

The purpose of this study is an attempt to improve the functionality of a conventional Fused Deposition Modeling (FDM) process using the Automatic Tool Changer (ATC) to perform multimaterial production and post-processing. Hybrid-FDM means a fusion of an Additive Manufacturing process and grinding process using the ATC system. In order to enhance the potentiality of production capacity for multi-material fabrication and surface roughness improvement, two extrusion tools and one grinding tool system are suggested. A pneumatic chuck is attached on a moving platform in the XY axes plane and an extrusion head and grinding head are placed in a docking station, allowing for a quick changeover with each other. Therefore, the manufacturing lead time can be reduced efficiently for the fabrication of a product.

• Journal of Internet Computing and Services
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• v.5 no.4
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• pp.23-33
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• 2004

In this paper, we propose a novel traffic measurement based detection of network attack symptoms on high speed Internet backbone links. In order to do so, we characterize the traffic patterns from the normal and the network attacks appeared on Internet backbone links, and we derive two efficient measures for representing the network attack symptoms at aggregate traffic level. The two measures are the power spectrum and the ratio of packet counts to traffic volume of the aggregate traffic. And, we propose a new methodology to detect networks attack symptoms by measuring those traffic measures. Experimental results show that the proposed scheme can detect the network attack symptoms very exactly and quickly. Unlike existing methods based on Individual packets or flows, since the proposed method is operated on the aggregate traffic level. the computational complexity can be significantly reduced and applicable to high speed Internet backbone links.

• Journal of the Korean Applied Science and Technology
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• v.30 no.3
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• pp.540-550
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• 2013

Various efforts have been explored to save the cost in many industrial fields. In order to recover the residual thermal energy from the flue gas, an extreme high efficiency heat exchanger is planning to install at a power plant. The gas temperature will be reduced to $40^{\circ}C$ from $115^{\circ}C$. Thus gas buoyancy decreases, and dispersion of nitrogen oxides is expected to deteriorate as increasing relative humidity. In this study, the conversion of nitrogen monoxide to nitrogen dioxide and dispersion regime are investigated through computational modeling. Nitrogen dioxide which indicates 0.1 ppm at 85 m from the ground could be propagated to 620 m at $115^{\circ}C$ of the flue gas, whilst when cooled down to $40^{\circ}C$, it expands up to 750 m. The ground level influence area showed more expansion of dispersion, approximately to 930 m.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.1199-1205
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• 1993

It has been well known that the assumption of full state availability is one of the most important restrictions to the practical realization of VSCS. And several attempts to alleviate the assumption had been made. However, it is not easy to find a positive scheme among them. Recently, an output feedback variable structure control system(OFVSCS) was proposed and the effectiveness of the scheme was validated for the disturbance free systems. The purpose of this study is to propose a robust OFVSCS that have the robust properties against process parameter variations and external distrubances by extending the basic OFVSCS and to evaluate its control performances through power system stabilizer design example. The ROFVSCS is composed of dynamic switching function and output feedback switching control inputs that are constructed by the use of the unknown vector modeling technique. With the proposed scheme, existence of sliding mode is guaranteed and any nonzero bias can be suppressed in the face of disturbances and process parameter variations as far as well-known matching condition is satisfied. Due to the fact that the ROFVSCS is driven by small number of measured informations, the practical application of VSCS for the systems with unmeasurable states and for high order systems that conventional schemes cannot be applied, is possible with the proposed scheme. It is noticeable that the implementation cost of VSCS can be considerably reduced without sacrifice of control performances by adopting ROFVSCS since there is no need measure the states with high measurement cost.

• Advances in materials Research
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• v.9 no.3
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• pp.189-202
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• 2020

The objective of the present work is to investigate the effect of cutting parameters (Vc, fz and ap) on tool life and the level of vibrations velocity in the machined part during face milling operation of hardened AISI 52100 steel. Dry-face milling has been achieved in the annealed (28 HRc) and quenched (55 HRc) conditions using multi-layer coating micro-grain carbide inserts. Statistical analysis based on the Response surface methodology (RSM) and ANOVA analysis have been conducted through a plan of experiments methodology using a reduced Taguchi table (L9) in order to obtain engineering models for tool life and vibration velocity in the workpiece for both heat treatment conditions. The results show that the cutting speed has a dominant influence on tool life for both soft and hard part. Cutting speed and feed per tooth is the most significant parameters for vibration levels. Comparing the experimental values with those predicted by the developed engineering models of tool life and levels of vibrations velocity, a good correlation has been obtained (between 97% and 99%) in annealed and hard conditions.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.10a
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• pp.73-73
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• 2011

In fact, asynchronous motors are used widely. Asynchronous motors which have large power (compared to the source supplies) is needed to start them in various methods. The theory of application reduced voltage to motor's stator or variable resistor fed rotor for the purpose of altering the motor's torque and power consumption characteristics is an idea that has existed for many years. These concepts have flourished mainly due to the need to limit torque and limited generator/power distribution capabilities. However, how can know exactly the time of switching steps with different types of motors as well as load characteristics is very difficult. This paper focuses on the design and development mathematical models of motor[1][2], load, ACB, asynchronous machine and then is implemented in SIMULINK in order to calculate this time, special on ships where power generation station is limited. The simulation results are both compared and discussed in detail so that it can apply to conclude the most suitable and applicable starting time for new system with various motors and load.

• Journal of information and communication convergence engineering
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• v.13 no.4
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• pp.235-240
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• 2015

A decimation chain for multi-standard reconfigurable radios is presented for 900-MHz and 1,900-MHz dual-band cellular standards with a data interpolator based on the Lagrange method for adjusting the variable data rate to a fixed data rate appropriate for each standard. The two proposed configurations are analyzed and compared to provide insight into aliasing and the signal bandwidth by means of a newly introduced measure called interpolation error. The average interpolation error is reduced as the ratio of the sampling frequency to the signal BW is increased. The decimation chain and the multi-rate analog-to-digital converter are simulated to compute the interpolation error and the output signal-to-noise ratio. Further, a method to operate the above-mentioned chain under a compressed mode of operation is proposed in order to guarantee continuous packet connectivity for inter-radio-access technologies. The presented decimation chain can be applied to LTE, WCDMA, GSM multi-mode multi-band digital front-end which will ultimately lead to the software-defined radio.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.115-122
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• 2014

Injection pressure is one of factors that influence part quality. In this paper, injection pressure was minimized by optimizing valve gate locations. In order to perform design optimization, MAPS-3DTM (Mold Analysis and Plastic Solution-3D) was used for injection mold analysis and PIAnOTM (Process Integration, Automation and Optimization) was used as process integration and design optimization. Also we adapted meta models based on design of experiments for efficiency. By using introduced methodology, we were able to obtain a result so that maximum injection pressure reduced by 28% compared to the initial design. And the validity of the proposed method could also be demonstrated.

• Journal of Biosystems Engineering
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• v.37 no.5
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• pp.327-334
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• 2012

Purpose: The color changes in red pepper during far infrared drying were studied in order to establish a color change model. Methods: The far infrared drying experiments of red pepper were conducted at two temperature levels of 60, $70^{\circ}C$ and two air velocity levels of 0.6 and 0.8 m/s. The results were compared with the hot-air drying method. The surface color changes parameters of red pepper were measured qualitatively based on L (lightness), a (redness), b (yellowness) and total color changes (${\Delta}E$). The goodness of fit of model was estimated using the coefficient of determination ($R^2$), the root mean square error (RMSE), the mean relative percent error (P) and the reduced chi-square (${\chi}^2$). Results: The results show that an increase in drying temperature and air velocity resulted in a decrease in drying time, the values of L (lightness) and a (redness) decreased with drying time during far infrared drying. The developed model showed higher $R^2$ values and lower RMSE, P and ${\chi}^2$ values. Conclusions: The model in this study could be beneficial to describe the color changes of red pepper by far infrared drying.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.12
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• pp.1208-1216
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• 2007

Turbomachinery such as turbines, pumps and compressors, which are installed in transportation systems, including aircrafts, ships, and space vehicles, etc., often perform crucial missions and are exposed to potential dangerous impact environments such as base-transferred shock forces. To protect turbomachinery from excessive shock forces, it may be needed to accurately analyze transient responses of their rotors, considering the dynamics of mount designs to be applied. In this study a generalized FE transient response analysis model, introducing relative displacements, is proposed to accurately predict transient responses of a flexible rotor-bearing system with mount systems to base-transferred shock forces. In the transient analyses the state-space Newmark method of a direct time integration scheme is utilized, which is based on the average velocity concept. Results show that for the identical mount systems considered, the proposed FE-based detailed flexible rotor model yields more reduced transient vibration responses to the same shocks than a conventional simple model, obtained by treating a rotor as concentrated lumped mass, equivalent spring and a damper or Jeffcott rotor model. Hence, in order to design a rotor-bearing system with a more compact light-weighted mount system, preparing against any potential excessive shock, the proposed FE transient response analysis model herein is recommended.