• Korean Journal of Materials Research
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• v.15 no.3
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• pp.149-154
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• 2005

Teflon like fluorocarbon thin films have been deposited on silicon and oxide molds as an antistiction layer for the hot embossing process by an inductively coupled plasma (ICP) chemical vapor deposition (CVD) method. The process was performed at $C_4F_8$ gas flow rate of 2 sccm and 30 W of plasma power as a function of substrate temperature. The thickness of film was measured by a spectroscopic ellipsometry. These films were left in a vacuum oven of 100, 200 and $300^{\circ}C$ for a week. The change of film thickness, contact angle and adhesion and friction force was measured before and after the thermal test. No degradation of film was observed when films were treated at $100^{\circ}C$. The heat treatment of films at 200 and $300^{\circ}C$ caused the reduction of contact angles and film thickness in both silicon and oxide samples. Higher adhesion and friction forces of films were also measured on films treated at higher temperatures than $100^{\circ}C$. No differences on film properties were found when films were deposited on either silicon or oxide. A 100 nm silicon template with 1 to $500\;{\mu}m$ patterns was used for the hot embossing process on $4.5\;{\mu}m$ thick PMMA spun coated silicon wafers. The antistiction layer of 10 nm was deposited on the silicon mold. No stiction or damages were found on PMMA surfaces even after 30 times of hot embossing at $200^{\circ}C$ and 10 kN.

• Journal of Korea Water Resources Association
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• v.43 no.10
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• pp.921-932
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• 2010

In this study, the adjustment processes of the disturbed channels by sand or gravel mining were investigated by a two dimensional numerical model in the generalized coordinate system. As a numerical scheme, the CIP (cubic interpolated pseudoparticle method) method was used to calculate the advection term in the flow field and central difference method was used to the diffusion term in it. The pit of the channel was partially filled with sediment at the toe of the pit upstream. As time increased, the headcut erosion upstream in the pit was decreased due to the sediment inflow. The almost inflow sediment upstream was trapped into the pit and the sediment deposit wedge migrated downstream in the pit with the steep submerged angle of repose. The numerical model was reproduced well the evolution processes of the channel. The mining pit migrated with speed as the channel was steep, and the numerical results were in overall agreement with the experimental results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.12
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• pp.1087-1096
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• 2011

The purpose of current study is to develop and verify the newly developed solver for analyzing rotor flow using the open-source code. The algorithm of standard solver, OpenFOAM, is improved to analyze the rotor inflow with and without fuselage. For the calculation of the rotor thrust, the virtual blade method based on the blade element method is employed. The inflow velocities on the rotor disk used to specify the effective angle of attack, have been included in the solver. The results of the current rotor inflow analysis are verified by comparing with other experimental and numerical results. It was confirmed that the modified solver provides satisfactory results for rotor-fuselage interaction problem.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.158-163
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• 2005

Competitive electricity markets necessitate equitable methods for allocating transmission usage in order to set transmission usage charges and congestion charges in an unbiased and an open-accessed basis. So in competitive markets it is usually necessary to trace the contribution of each participant to line usage, congestion charges and transmission losses, and then to calculate charges based on these contributions. A UPFC offers flexible power system control, and has the powerful advantage of providing, simultaneously and independently, real-time control of voltage, impedance and phase angle, which are the basic power system parameters on which sys-tem performance depends. Therefore, UPFC can be used efficiently and flexibly to optimize line utilization and increase system capability and to enhance transmission stability and dampen system oscillations. In this paper, a mathematical approach to allocate the contributions of system users and UPFCs to transmission system usage is presented. The paper uses a dc-based load flow modeling of UPFC-inserted transmission lines in which the injection model of the UPFC is used. The relationships presented in the paper showed modified distribution factors that modeled impact of utilizing UPFCs on line flows and system usage. The derived relationships show how bus voltage angles are attributed to each of changes in generation, injections of UPFC, and changes in admittance matrix caused by inserting UPFCs in lines. The relationships derived are applied to two test systems. The results illustrate how transmission usage would be affected when UPFC is utilized. The relationships derived can be adopted for the purpose of allocating usage and payments to users of transmission network and owners of UPFCs used in the network. The relationships can be modified or extended for other control devices.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.11-14
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• 2009

The implementation of gelled propellants systems offers high performance, thrust-control, energy management of propulsion, storability, and high density impulse of solid propulsion. Present study focused on the spray behavior of liquid sheets formed by impinging jets of non-Newtonian liquids which are mixed by Carbopol 941 0.5%wt. The results are then compared with experiments conducted on spray images formed by impinging jets concerning with air-blast effect at center orifice. When gel propellants are injected by doublet impinging jets at low pressure, closed rim pattern shape appeared. As increasing air mass flow rate(decreasing GLR), spray breakup and atomization phenomenon better improved and spray structure instabilities for the effect of air-blast are also increased.

• Journal of Environmental Science International
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• v.18 no.3
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• pp.333-343
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• 2009

This study presents the analysis of an atmospheric flow around a single-doppler radar located in a pseudo-site. The use of a doppler radar in meteorological field of wind engineering has become widespread over the last several decades, but it has generally been recognized that the single-Doppler radar yields only one single velocity component - the radial velocity($V_r$) so that some additional hypotheses or simplifications must be necessary to get proper wind forecast. Therefore, in order to get an accurate radial velocity($V_r$) in this study, the existing methods such as VAD(Velocity Azimuth Display) and VARD(Velocity Area Display) are reformulated and applied to match the previous study(Waldteufel and Corbin), which have been an important indicator for retrieving a radar velocity. The results presented in this study include the results from different assessment methods in a peudo-site of different wind fields. Unless the existing method can consider the proper decomposition of radial velocity in the real site, then authors suggest an appropriate curve-fitting to decrease the uncertainty errors by changing a grid adaptation rate or applying a weighting function with respect to the wind angle. It is concluded that provided properly formulated fitting function are used, the wind retrieval from the Doppler radar using VAD and VARD methods can be a viable tool for use in wind engineering problems searching for the wind resources.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.6
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• pp.307-315
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• 2003

This paper proposes a novel simulation method of WPGS (Wind Power Generation System). The rotation speed control method of turbine under variable wind speed using the pitch control is proposed. Moreover, when wind speed exceeds the cut-out wind speed, the turbine will be stopped by controlling pitch angle to 90$^{\circ}$, otherwise it will be controlled to steady-state operation. For the purpose of effective simulation, the SWRW (Simulation method for WPGS using Real Weather condition) is used for the utility interactive WPGS simulation in this paper, in which those of three topics for the WPGS simulation: user-friendly method, applicability to grid-connection and the utilization of the real weather conditions, are satisfied. It is impossible to consider the real weather conditions in the WPGS simulation using the EMTP type of simulators and PSPICE, etc. External parameter of the real weather conditions is necessary to ensure the simulation accuracy. The simulation of the WPGS using the real weather conditions including components modeling of wind turbine system is achieved by introducing the interface method of a non-linear external parameter and FORTRAN using PSCAD/EMTDC in this paper. The simulation of long-term, short-term, over cut-out and under cut-out wind speeds will be peformed by the proposed simulation method effectively. The efficiency of wind power generator, power converter and flow of energy are analyzed by wind speed of the long-term simulation. The generator output and current supplied into utility can be obtained by the short-term simulation. Finally, transient-state of the WPGS can be analyzed by the simulation results of over cut-out and under cut-out wind speeds, respectively.

• Journal of The Korean Digital Architecture Interior Association
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• v.11 no.4
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• pp.5-11
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• 2011

The present study investigated the actual conditions of physical therapy rooms at long-term hospitals in Korea and conducted a comparative analysis to develop an efficient floor plan and facility improvement measures. 1. At hospitals surveyed, physical therapy services were used at a high frequency but they did not have enough space for rehab treatment and long paths of patient flow were found to make patient management inconvenient. Therefore, physical therapy units should be conveniently located both in terms of distance and direction so as to be accessible from patient rooms or wards. The space should be organized in a concentrated layout for efficiency of physical therapy, and floor planning for therapy units should ensure the best possible viewing angle to therapists. 2. With regard to the disease characteristics of patients, many physical therapy rooms were in difficult circumstances because of poor facilities, so they need to secure skilled personnel, supplement apparatuses and equipment and have rooms for functional recovery, hydrotherapy and operation treatment. In addition, each of the curtained or partitioned areas for treatment should be set up with consideration for the amount of space taken up by medical equipment. The area under each bed should be designed for patient convenience so that it can be used as storage space for patient's belongings and shoes. 3. Patients complained about the lack of physical therapy space, resting places or exercise areas and demanded the expansion of rehab programs and facilities. Physical therapy facilities need to be improved for patient privacy and effective natural ventilation. 4. At most of the long-term hospitals surveyed, physical therapy units were found to have small areas and treatment equipment and devices were insufficient compared to the number of patients. Therefore, it is required to secure more space (at least 138.24 sq. meters per 100 beds) and improve facilities for better physical therapy services.

• Journal of Ocean Engineering and Technology
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• v.24 no.4
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• pp.23-31
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• 2010

The flow around a remotely-operated vehicle (ROV) has been investigated numerically to improve the resistant performance by modifying the hull form of the ROV. In the case of the base hull form considered in this study, form drag rather than friction drag was the dominant component of total drag. Subsequently, the surfaces that were most susceptible to local pressure effects were modified to give them a more streamlined shape. Eleven different hull forms were chosen to undergo surface modification for drag reduction. In addition, four different boat-tail appendages with different slant angles were installed at the stern to reduce the wake vortices that are induced by the local regions of very low pressure. Consequently, a total of 11 different hull forms for drag reduction were considered. The final hull form, which combined the hull for which surface modification resulted in the lowest drag with a boat-tail appendage with a 15-degree slant angle, resulted in a drag reduction of 20%.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.9
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• pp.799-804
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• 2007

The behavior of spray emanating from an injector to be employed in a liquid-propellant thrust chamber is investigated by optical measurement techniques. The injector has eight holes, each of which has 30 cant angle from the center-axis with the diameter of 0.406 mm. In order to examine an atomization process according to the spray-generation conditions and the evolution along spray downstream, variational features in the velocity and size of droplets obtained through Dual-mode Phase Doppler An 799emometry (DPDA) are delineated and discussed together with instantaneous plane images captured by using Nd:Yag laser sheet beam. A categorization of spray-flow regime representing the atomization and turbulent nature is made through evaluating the non-dimensional parameters, i.e., Reynolds number and Weber number based upon the theoretical injection velocity. These qualitative and quantitative data of spray breakup will be a firm basis for the design of brand-new thruster