• Laser Solutions
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• v.18 no.3
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• pp.1-5
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• 2015

A 3D printer based on laser powder deposition (LPD), also known as DED (direct energy deposition), has been developed for fabricating metal parts. The printer uses a ytterbium fiber laser (1070nm, 1kW) and is equipped with an Ar purge chamber, a three-dimensional translation stage and a powder feeding system composed of a powder chamber and delivery nozzles. To demonstrate the performance of the printer, a tapered cylinder of 320mm in height has been fabricated successfully using Ti-6Al-4V powders. The process parameters including the laser output power, the scan speed, and the powder feeding rate have been optimized. A 3D printed test specimen shows mechanical properties (yield strength, ultimate tensile strength, and elongation) exceeding the criteria to employed in a variety of Ti alloy applications.

• International Journal of Automotive Technology
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• v.2 no.1
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• pp.9-16
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• 2001

The lifetime of power train components can be improved dramatically by finding crack initiation points with suitable software tools and optimization of the critical areas. With increasing capacities of computers the prediction of the lifetime for components by numerical methods gets more and more important. This paper discusses some applications of the outstanding fatigue simulation program FEMFAT supporting the assessment of uniaxially and multiaxially loaded components (as well as welding seams and spot joints). The theory applied in FEMFAT differs in some aspects from classical approaches like the nominal stress concept or the local one and can be characterized by the term "influence parameter method". The specimen S/N-curve is locally modified by different influence parameters as stress-gradient to take into account notch effects, mean-stress influence which is quantified by means of a Haigh-diagram, surface roughness and treatments, temperature, technological size, etc. It is possible to consider plastic deformations resulting in mean-stress rearrangements. The dynamic loading of power train components is very often multiaxial, e.g. the stress state at each time is not proportional to one single stress state. Hence, the directions of the principal axes vary with time. We will present the way how such complex load situations can be handled with FEMFAT by the examples of a crank case and a gear box.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.4
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• pp.392-400
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• 2016

In this paper, a study based on engine operating conditions versus hybrid excavator engines was conducted about the engine performance and fuel consumption via the 1-D engine simulation model. First of all, engine operating points with performance and emission were determined by driving patterns. The 1-D HFEM(High Frequency Engine Model) was developed for deep insight into engine combustion and the energy conversion phenomena. In accordance with changing operating points, especially High Idle and Rated output conditions, engine parameters and systems such as turbocharger(Waste Gate Turbocharger and Variable Geometry Turbocharger) injection strategies and EGR(Exhaust Gas Recirculation) should be considered. Therefore, various configurations and parametric analysis with optimization methods in hybrid excavator were simulated and optimized by NLPQL(Non-linear Programming by Quadratic Lagrangian algorithm) in 1-D HFEM. As a result, the fuel consumption with the developed hybrid electric excavator engine could be significantly decreased and bsfc(Brake Specific Fuel Consumption) was also reduced about 5 % to 7 % without any performance degradation.

• Analytical Science and Technology
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• v.33 no.2
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• pp.76-85
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• 2020

A stainless-steel needle (Hamilton 90022, 22 gauge, 718-㎛ o.d., 413-㎛ i.d., 51-mm length, bevel tip) with an electrochemically coated polyaniline layer having a microbore tunnel was newly prepared as a device for headspace in-needle microextraction. For designing the needle, the polyaniline layer length was optimized, and to evaluate the extraction efficiency for polycyclic aromatic hydrocarbons, numerous cyclic voltammetry scans were conducted. In addition, the optimization of the analytical conditions (including the adsorption and desorption parameters) and the validation of the analytical method were conducted. The optimized adsorption and desorption conditions were 40 ℃ for 30 min and 230 ℃ for 60 s, respectively. Finally, in this study, a polyaniline layer was electrochemically deposited on the in-needle surface, and it exhibited good thermal stability. The needle with the polyaniline layer was repeatedly used more than 200 times during this study. This method has some advantages in terms of the extraction time, extraction efficiency, and analysis cost.

• Food Science of Animal Resources
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• v.32 no.3
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• pp.274-284
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• 2012

In this study, the effects of physical parameters (30-270 MPa of pressure, 3-57 min of time, and 1-$49^{\circ}C$ of temperature) on pork quality were investigated. Response surface methodology was used in order to monitor and model the changes in pork quality under varied pressure conditions. As quality characteristics, shear force, water holding capacity (WHC) and the CIE color of pork were measured, and optimum pressure conditions were evaluated by statistical modeling. Pressure improved the WHC of pork at relatively low temperature ($<25^{\circ}C$); however, the opposite occurred with increasing temperature. Although pressure and temperature affected the tenderness of the meat, interaction effects among variations were not observed. At pressure levels higher than 200 MPa, the color of pork differed markedly from that of the untreated controls. In particular, differential scanning calorimetry (DSC) revealed marked evidence of myosin denaturation. The present study demonstrates that pork quality varies depending on pressure conditions.

• Korean Journal of Food Science and Technology
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• v.22 no.3
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• pp.234-240
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• 1990

Attempts have been made to optimize the hydrolysis conditions of the oyster and the mussel by the commercial proteolytic enzymes. Raw materials were digested with seven different commercial enzymes, and their quality parameters measured in terms of degree of hydrolysis and content of free amino nitrogen, nucleic acid-related substances. and free amino acids as well as sensory evaluation of optimization of their hydrolysis conditions. As a result, following enzymes have been disclosed as effective for enzymatic digestion: MKC-HT proteolytic, alcalase 0.6L and thermease for the oyster whereas MKC-acid fungal protease and thermoase for the mussel, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.9A
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• pp.2221-2229
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• 1998

Handoff is an important parameter for system performance and capacity analysis in CDMA cell planning. In this paper, simulation tool for analyzing the effects of soft handoff on cell planning of CDMA network is developed by studying propagation model in 1.9GHz frequency specrum, soft hadnoff algorithm given by IS-95, and several parameters for CDMA cell planning. By using the tool, soft handoff gain and effects of soft handoff on cDMA system performance and capacity are analyzed. Research results and simulation tool developed in this paper can be used for optimal CDMA cell planning for PCS and IMT-2000 in 1.9GHz frequency spectrum such as locating base station and parameter optimization.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1770-1776
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• 1998

This paper presents a waveguide-to-mircostrip transition at Ka-band using antipodal finlines. Critical design parameters were identified with the help of theoretical analysis. Experimental optimization was performed together with 3-D FEM analysis in an effort to find optimum dimensions of the transition. In addition to the conventional antipodal finline transition, a new dielectric impedance transformer was introduced to further reduce the insertion loss. Optimized waveguide-to-microstrip transition showed an insertion loss of 0.3~0.4dB/transition at Ka-band. This transition provides superior reproducibility and better performance than conventional coaxcable-to-microstrip transition.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.51 no.2
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• pp.69-75
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• 2002

AVR parameter tuning for voltage control of power system generators has generally been performed with the analytic methods and the simulation methods, which mostly depend on off-line linear mathematical models of excitation control system. However, due to the nonlinear nature of excitation control system, excitation control system performance of the tuned Parameters using the above conventional tuning methods may not be appropriate for some operating conditions. This paper presents an AVR parameter tuning method using actual on-line data of the excitation control system with the parameter optimization technique. As this method utilizes on-line operating data of the target excitation control system not the mathematical model of the system, it can overcome the limitation of model uncertainty Problems in conventional method, and it can tune the AVR parameter set which gives desired performance at the operating conditions. For the verification of proposed tuning method, two case studies with scaled excitation systems and the real-time power system simulator are presented.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.10
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• pp.447-450
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• 2003

This paper presents a process optimization of antireflection (AR) coating on crystalline Si solar cells. Theoretical and experimental investigations were performed on a double-layer AR (DLAR) coating of MgF$_2$/CeO$_2$. We investigated CeO$_2$ films as an AR layer because they have a proper refractive index of 2.46 and demonstrate the same lattice constant as Si substrate. RF sputter grown CeO$_2$ film showed strong dependence on a deposition temperature. The CeO$_2$ deposited at 40$0^{\circ}C$ exhibited a strong (111) preferred orientation and the lowest surface roughness of 6.87 $\AA$. Refractive index of MgF$_2$ film was measured as 1.386 for the most of growth temperature. An optimized DLAR coating showed a reflectance as low as 2.04% in the wavelengths ranged from 0.4${\mu}{\textrm}{m}$ to 1.1${\mu}{\textrm}{m}$. We achieved the efficiencies of solar cells greater than 15% with 3.12% improvement with DLAR coatings. Further details on MgF$_2$, CeO$_2$ films, and cell fabrication parameters are presented in this paper.