• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.2
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• pp.85-91
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• 2002

A novel multi-section power divider configuration is Proposed to obtain wide-band frequency performance up to microwave frequency region. Design procedures for the proposed microwave broadband power divider are composed of a Planar multi-section three-Ports hybrid and a waveguide transformer design procedures. The multi∼section power divider is based on design theory of the optimum quarter- wave transformer Furthermore, in order to obtain the broadband isolation performance between the two adjacent output ports, the odd mode equivalent circuit should be matched by using the lossy element such as resistor. The derived design formula for calculating these odd mode∼matching elements is based on the singly terminated filter design theory. The waveguide transformer section is designed to suppress the propagation of the higher order modes such as waveguide modes due to employing the metallic electric wall. Simulation and experiment show excellent performance of multi section power divider.

• Journal of Navigation and Port Research
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• v.29 no.7
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• pp.627-634
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• 2005

Gunsan-Janghang Harbor is located at the mouth of Gum River, on the central west coast of Korea The harbor and coastal boundaries are protected from the effects of the open ocean by natural coastal islands and shoals due to depositions from the river, and two breakwaters. The navigation channel commences at the gap formed by the outer breakwater and extends through a bay via a long channel formed by an isolated jetty. For better understanding and analysis of wave transformation process where a wide coastline changes appear due to on-going reclamation works, we applied the spectral wave model including wind effect to the related site, together with the energy balance models. This paper summarizes comparisons of coastal responses predicted by several numerical wave predictions obtained at the coastal waters near Gunsan-Janghang Harbor. Field and numerical model investigations were initially conducted for the original navigation channel management project. We hope to contribute from this study that coastal engineers are able to use safety the numerical models in the area of port and navigational channel design.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.303-308
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• 2004

The failure at the head section of rubble mound breakwaters is more important than other failure modes. because this initial failures will occur the failure of the trunk section and lead to the instability of the structure. The three-dimensional failure modes are discussed using the experimental data with multi-directional waves considering the failure modes. It was occurred by the topographical characteristics around the head of rubble mound breakwater. The spacial characteristics of failure mode around the rubble-mound structures can be summarized as follows: 1) It was clarified that the failure modes at the round head of a detached breakwater are classified as failure by plunging breaker on the slope, failure by direct incident wave force and failure at the rubble mound breakwaters. 2) The failure mode was found in the lower wave height than the design wave by the breaker depth effects and topography around structures. It is clarified that the structure was monitored safely designed for the design wave but the failure was occurred by the reason of breaker waves.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.447-449
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• 2004

The purpose of this study is measured surface acoustic wave(SAW) characteristics to confirm utilization possibility as SAW sensor using new Pb(Mg$_{1}$3/Nb$_{2}$3/) $O_3$-PbTiO$_3$ (PMN-PT) piezoelectric substrate. We have tried to see if the material can be practically available as a new surface acoustic wave (SAW) biosensor to detect protein. The experimental results clarified that the frequency filtering of the central frequency of the PMN-PT substrate is a superior result to that of the LiTaO$_3$ (LT) substrate, but the result was not completely satisfactory. We know there is a problem in the design of inter-digital transducer (IDT) pattern. The waves transferred through the input terminal forms SAW which is sure to be transferred to the direction of the output terminal and the backward direction of the input terminal. This reflected wave is reiterated with SAW, which is transferred to the output direction, and so the frequency filtering gives a not good result. The electromechanical coupling coefficient of the PMN-PT substrate is excellent, and we can use it as a SAW sensor, in the near future, provided that there will be a new IDT design to increase the frequency filtering.

• Journal of electromagnetic engineering and science
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• v.1 no.1
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• pp.95-99
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• 2001

According to the progress of the electronic industy and radio communication technologies, mankind might enjoy its abundant life On the other hand, many social problems such as EMI, and unnecessary electromagnetic wave occur due to the increased use of electromagnetic wave. Therefore, the organiztions such as CISPR, FCC, ANSl,etc. have provided the standard of electromagnetic wave enviroment for the countermeasure of the EMC. It had been required that the absorbing ability of an electromagnetic wave absorber is more than 20 dB, the bandwidth of which is required through 30 MHz to 1,000 MHz for satisfying the international standard about an anechoic chamber for EMI/EMS measurment. From November of 1998, however, the CISPRll has accepted the extended frequency band from 1 GHz to 18 GHz additionally in the bandwidth of EMI measurementent$^{[1]}$ . In this paper, we proposed a new type absorber satisfying the above requirements and carried out broadband design using the equivalent material constants method. Futheremore, the experiments were carried out over the frequency band from 30 MHz to 2 GHz, and hence, the validity of the proposed design theory was confirmed.

• Fashion & Textile Research Journal
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• v.11 no.1
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• pp.156-165
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• 2009

The purpose of this study was to compare men's hair style preference by gender according to occassion. Data were collected through a survey of 149 males and 175 females and analyzed by SPSS packages. The results of this study were as follows : 1) Male prefers to short, straight and black hair while female prefers to shot, nature wave and black hair. 2) Both male and female don't prefer to permanent and hair dyeing. 3) On the occasion of job interview, both male and female prefer to short, straight and black hair. On the occasion of blind date, male prefers to short, straight and black hair while female prefers to short, natural wave and natural brown hair. On the occasion of matchmaker meeting for marriage, male prefers to short, straight and black hair while female prefers to short, natural wave and dark brown hair. On the occasion of club party, male prefers to middle length, straight and black hair while female prefers middle length, natural wave and natural brown hair. On the occasion of leasure time, male prefers to short, straight and black hair while female prefers to short, natural wave and natural brown hair. And both male and female prefer to use hats for skin protection during outdoor leasure time.

• Journal of Drive and Control
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• v.11 no.3
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• pp.31-40
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• 2014

This paper proposes a multi absorbing wave energy converter design, in which a hydrostatic transmission is used to transfer wave energy to electric energy. The most important feature of this system is its combination of the pressure coupling principle with the use of a hydraulic accumulator to eliminate the effects of wave power fluctuation; this maintains a constant speed of the hydraulic motor. Tilt motion of a floating buoy was employed as the power take-off mechanism. Furthermore, a PID controller was designed to carry out the speed control of the hydraulic motor. The design offers some advantages such as extending the life of the hydraulic components, increasing the amount of energy harvested, and stabilizing the output speed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.283-296
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• 2020

A numerical model is established to investigate the run-up of a solitary wave after propagating over a triangular saw-tooth-shaped submerged breakwater. A rectangular-shaped submerged breakwater is simulated for comparison. Several factors, including the submerged depth, the lagoon length and the beach slope, are selected as independent variables. The free surface motions and velocity fields of the solitary wave interacting with the submerged breakwater are discussed. The results show that the submerged depth and lagoon length play significant roles in reducing the run-up. The influence of the beach slope is not significant. At the same submerged depth, the triangular saw-tooth-shaped submerged breakwater has only a slightly better effect than the rectangular-shaped submerged breakwater on the run-up reduction. However, a calmer reflected wave profile could be obtained with the rougher surface of the saw-tooth-shaped submerged breakwater. The study conclusions are expected to be useful for the conceptual design of saw-tooth-shaped submerged breakwaters.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3540-3550
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• 2022

The supercritical carbon dioxide (S-CO₂) Brayton cycle is an important energy conversion technology for the fourth generation of nuclear energy. Since the printed circuit heat exchanger (PCHE) used in the S-CO₂ Brayton cycle has narrow channels, Rayleigh-Bénard (RB) convection is likely to exist in the tiny channels. However, there are very few studies on RB convection in supercritical fluids. Current research on RB convection mainly focuses on conventional fluids such as water and air that meet the Boussinesq assumption. It is necessary to study non-Boussinesq fluids. PRB convection refers to RB convection that is affected by horizontal incoming flow. In this paper, the computational fluid dynamics simulation method is used to study the PRB convection phenomenon of non-Boussinesq fluid-supercritical carbon dioxide. The result shows that the inlet Reynolds number (Re) of the horizontal incoming flow significantly affects the PRB convection. When the inlet Re remains unchanged, with the increase of Rayleigh number (Ra), the steady-state convective pattern of the fluid layer is shown in order: horizontal flow, local traveling wave, traveling wave convection. If Ra remains unchanged, as the inlet Re increases, three convection patterns of traveling wave convection, local traveling wave, and horizontal flow will appear in sequence. To characterize the relationship between traveling wave convection and horizontal incoming flow, this paper proposes the relationship between critical Reynolds number and relative Rayleigh number (r).

• New & Renewable Energy
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• v.20 no.2
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• pp.26-34
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• 2024

Floating offshore wind turbines (FOWTs) have been developed to overcome large water depths and leverage the abundant wind resource in deep seas. However, wind-wave misalignment can occur depending on the weather conditions, and most megawatt (MW)-class turbines are horizontal-axis wind turbines subjected to yaw errors. Therefore, the power performance and dynamic response of super-large FOWTs exposed simultaneously to these external conditions must be analyzed. In this study, several scenarios combining wind-wave misalignment and yaw error were considered. The IEA 15 MW reference FOWT (v1.1.2) and OpenFAST (v3.4.1) were used to perform numerical simulations. The results show that the power performance was affected more significantly by the yaw error; therefore, the generator power reduction and variability increased significantly. However, the dynamic response was affected more significantly by the wind-wave misalignment increased; thus, the change in the platform 6-DOF and tower loads (top and base) increased significantly. These results can be facilitate improvements to the power performance and structural integrity of FOWTs during the design process.