• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.309-313
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• 2004

Prediction of green water loads acting an the bow deck is an essential part for the design of bow structures against the green water impact. Proper technique of the green water simulation is highly required for the prediction of green water loads. In this paper, a new numerical method for green water simulation, which is based an predictor-corrector-upwind finite difference scheme of the 2nd kind, is introduced. Through the comparisons between computed' results and experimental measurements, it is verified that the present numerical tool is adequate as a practical calculation tool for the green water problem.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.2
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• pp.297-306
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• 2014

The paper presents the numerical analysis of wave run-up over rubble-mound breakwaters covered by antifer units using a technique integrating Computer-Aided Design (CAD) and Computational Fluid Dynamics (CFD) software. Direct application of Navier-Stokes equations within armour blocks, is used to provide a more reliable approach to simulate wave run-up over breakwaters. A well-tested Reynolds-averaged Navier-Stokes (RANS) Volume of Fluid (VOF) code (Flow-3D) was adopted for CFD computations. The computed results were compared with experimental data to check the validity of the model. Numerical results showed that the direct three dimensional (3D) simulation method can deliver accurate results for wave run-up over rubble mound breakwaters. The results showed that the placement pattern of antifer units had a great impact on values of wave run-up so that by changing the placement pattern from regular to double pyramid can reduce the wave run-up by approximately 30%. Analysis was done to investigate the influences of surface roughness, energy dissipation in the pores of the armour layer and reduced wave run-up due to inflow into the armour and stone layer.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.70-75
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• 2014

Programs of energy balance, mode analysis and transient analysis for a liquid rocket engine have been introduced. The analysis methods have been verified through comparison between the present results, and the results of the other program and experimental data. An energy balance analysis is used for engine system design at the early development phase. A mode analysis is used for decision of engine operation conditions and test conditions, and studying deviation of an engine performance. A transient analysis can predict a propellant flow rate, thrust, impulse at transient phase. It is essential to establish a startup/shut down sequence. The analysis programs will be used to develop the engines of KSLV-II.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.75-82
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• 2015

This paper presents a new technique for enhancing power quality by reducing harmonics in the neutral conductor. Three-Phase Four-Wire (3P4W) system is commonly used where single and three phase loads are connected to Point of Common Coupling (PCC). Due to unbalance loads, the 3P4W distribution system becomes unbalance and current flows in the neutral conductor. If loads are non-linear, then the harmonic content of current will flow in neutral conductor. The neutral current that may flow towards transformer neutral point is compensated by using a series active filter. In order to reduce the harmonic content, the series active filter is connected in series with the neutral conductor by which neutral and phase current harmonics are reduced significantly. In this paper, solar PV based inverter circuit is proposed for compensating neutral current harmonics. The simulation is carried out in MATLAB/SIMULINK and also an experimental setup is developed to verify the effectiveness of the proposed method.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.11
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• pp.85-92
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• 2003

In this paper, a multiple U-shaped slot antenna on 5㎓ band is designed, fabricated, and measured. The prototype consists of a U-shaped slot and two Invert U-shaped slot. To obtain wide bandwidth, the foam layer is inserted between ground plane and substrate. After various parameters, length, width, position of U-shaped slot horizontal, interval length between two invert U-shaped slot, feeding position and airgap width, optimized, a multiple U-shaped slot antenna is fabricated and measured. The measured results of the antenna are compared with its simulated results. A 2:1 VSWR impedance bandwidth of 20.4% is achiedved by employing this technique. The gain is about 5.5㏈i. The experimental far-field patterns are stable across the pass band.

• Computers and Concrete
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• v.20 no.2
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• pp.145-154
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• 2017

In geological engineering, grouting with Portland cement is a common technique for ground improvement, during which micro-fine cement is applied as a slurry, such that it intrudes into soil voids and decreases soil porosity. To determine the utility and behavior of cements with different Blaine values (index of cement particle fineness) for stabilization of fine sand, non-destructive and destructive tests were employed, such as laser-ray determination of grain size distribution, and sedimentation, permeability, and compressive strength tests. The results of the experimental study demonstrated a suitable mix design for the upper and lower regions of the cement-grading curve that are important for grouting and stabilization. Increasing the fineness of the cement decreased the permeability and increased the compressive strength of grouted sand samples considerably after two weeks. Moreover, relative to finer (higher Blaine value) or coarser (lower Blaine value) cements, cement with a Blaine value of $5,100cm^2/g$ was optimal for void reduction in a grouted soil mass. Overall, study results indicate that cement with an optimum Blaine value can be used to satisfy the designed geotechnical criteria.

• Journal of Power Electronics
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• v.17 no.2
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• pp.442-452
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• 2017

This paper deals with the input-output modeling of a vector controlled PMSM drive system and design of a simple multiple model adaptive control (MMAC) scheme with desired transient responses. We present a discrete-time modeling technique using closed-loop identification that can experimentally identify the equivalent models in the d-q coordinates. A bank of linear models for the equivalent plant of the current loop is first obtained by identifying them at several operating points of the current to account for nonlinearity. Based on these models, we suggest a simple q-axis MMAC combined with a fixed d-axis controller. After the current controller is designed, another equivalent model including the current controller in the speed control loop shall be similarly obtained, and then a fixed speed controller is synthesized. The proposed approach is demonstrated by experiments. The experimental set up consists of a surface mounted PMSM (5 KW, 220V, 8 poles) equipped with a flywheel load of 220kg and a digital controller using DSP (TMS320F28335).

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.326-334
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• 1986

The effects of flow interaction between adjacent sprays in twin-spray system on the spatial distribution of injected liquid (water) and drop size distribution in condensable (steam) environment were carefully observed through experiments. The spatial distribution of injected liquid in twin-spray system appears to be more uniform than the simple superposition of the spatial distributions of liquid obtained from each individual spray. Drop size distribution was obtained by using the immersion sampling technique. It was found that, in the twin-spray, the larger numbers of small drops are collected throughout the spraying region due to the increase of entrainment velocity of ambient steam compared with the case of simple superposition of each individual spray. Moreover, in the overlapped portion of the twin-spray, the drop size distribution was changed also due to the collision between large drops. As a result, the behavior of twin-spray system (and eventually multiple-spray system) can not be predicted precisely by simple superposition of the behaviors of each constituting spray. Hence, for the design of multiple spray system, the effect of flow interaction between sprays should be taken into account seriously.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.1 s.151
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• pp.26-31
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• 2007

Understanding viscoelastic properties of composite materials is essential for the design and analysis of composite structures. Specially, the loss factor and Young's modulus must be known to develop finite element codes for a composite structure with several damping materials. In this study, an advanced technique for obtaining accurate loss factor and Young's modulus of a composite structure is introduced based on the method of American Society for Testing and Materials (ASTM). The loss factor and Young's modulus of a composite structure are measured for different temperatures by performing the test in a vibration measurement room where temperature can be controllable from 5 to 45 Celsius.

• Journal of Korean Academy of Nursing
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• v.27 no.4
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• pp.857-870
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• 1997

The purposes of this study were to describe 12 years of patient-related oncology nursing research in Korea, identifying various nursing interventions, and assesing the effectiveness of the interventions, through analysis and synthesis of the accumulated research papers. One hundred and seventy-nine studies were selected for this study and these were mostly descriptive in design (69.2%). Of the 179 studies, 25 met the criteria for meta-analytic treatment. Twenty-five experimental studies were found in theses and dissertations (68%), 92% used convenience sample, and the median sample size was 40. Subjects were predominantly in treatment and rehabilitation (76%). Most studies(68%) were not derived from a theory base, with only 8% reporting use of a nursing theory. Results of the meta-analysis are as follows. The effect size of the nursing intervention type was found to be significantly effective. The standardized mean difference ranged from a high positive of 2.55 to a low negative of -0.22. Direct personal nursing intervention method was more effective than indirect group method. Two nursing intervention methods were more effective than one. The greatest effect size was thyxical intervention. The greatest mean effect size was scalp hypothermia technique. Teaching was a frequent intervention after 1990, although a wide range of treatments were studied. Effect size of intervention for symptom management was largest in relieving pain. Effective intervention method for relieving anxiety was exercise.