• Ocean Systems Engineering
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• v.10 no.1
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• pp.87-110
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• 2020

Catamaran has recently been a choice to support a typical vertical axis turbine in floating tidal current energy conversion system. However, motion responses associated with the catamaran can reduce the turbines efficiency. The possibility to overcome this problem isto change the catamaran parameter by varying and simulating the demi-hull separations to have lower motion responses. This simulation was undertaken by Computational Fluid Dynamic (CFD) using potential flow analysis. Cases of demi-hull separation were considered, with ratios of demi-hull separation (S) to the breadth of demi-hull (B), ^S/_B of 3.45, 4.95, 6.45, 7.2 and 7.95. In order to compare to the previous works in the literature, the regular wave was set with wave height of 0.8 m. Furthermore, the analysis was carried out by irregular waves with significant wave height, H_s, of about 0.09 to 1.5 m and the wave period, T, of about 1.5 to 6 s or corresponding to the wave frequency, ω, of about 1.1 to 4.2 rad/s. The wave spectrum was derived from the equation of the International Towing Tank Conference (ITTC). For the case of turbines-loaded catamaran under consideration, the new finding is that the least significant amplitude response can be satisfied at the ratio ^S/_B of 7.2. This study indicates that selecting a right choice of demi-hull separation ratio could contribute in reducing motion responses of the tidal current turbines-loaded catamaran.

• Journal of Welding and Joining
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• v.20 no.1
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• pp.76-82
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• 2002

In these days, many advanced nations have enforced import restrictions against things emitting electromagnetic wave which has report that it is so harmful. In general, electromagnetic wave is composed of electric wave and magnetic wave. The reflection of electromagnetic wave is mainly reflected by conductive materials and the magnetism loss is generated by magnetic ferrite. The magnetism loss of ferrite is separated by eddy current loss, residual magnetism loss and hysteresis loss. Thermal sprayed coating is intended to manufacture because of simple processes and high efficient electromagnetic wave shielding. The high efficient thermal sprayed coatings were made from the magnetic ferrite materials that characterizes absorption of electromagnetic wave, and the electric conductive materials that characterize emitting of electromagnetic wave. This study was manufactured thermal sprayed coatings to improve absorption-efficiency, and measured the electromagnetic wave shielding efficiency. As the experimental results, high electromagnetic wave shield efficiency was obtained at wave frequency 2GHz to thermal sprayed ferrite coatings manufactured by size distribution range of spray powders, $38~88\mu\textrm{m}$.

• Journal of Korea Society of Industrial Information Systems
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• v.21 no.1
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• pp.7-15
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• 2016

Ocean wave parameters are important for safety and efficiency of operation and routing of marine traffic. In this paper, by using X-band marine radar, we try to develop an effective algorithm for collecting ocean surface information such as current velocity, wave parameters. Specifically, by exploiting iterative refinement flow instead of using fixed control schemes, an effective algorithm is designed in such a way that it can not only compute efficiently the optimized current velocity but also introduce new cost function in an optimized way. Experimental results show that the proposed algorithm is very effective in retrieving the wave information compared to the conventional algorithms.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.43 no.2
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• pp.101-115
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• 2007

The pound net fishery is very important one in Korean coastal fishery and it need to grasp the characteristics of the net affected by many factors. It is considered that the structure and the shape of the pound net can be changed by the direction and speed of current, wave height, depth and conditions of sea bed. However, most of all, the speed of current and wave height influence more upon the pound net than any other factors to deform and flutter. In this study, author carried out the experiments with a model of double one-side pound net made by the similarity law as 1:100 scales at a real experimental area, and additionally the model net experiments were conducted in the circulating water channel in Pukyong National University. The author analyzed the data of transformation of shape and tension of the model pound net to recognize the characteristics of the current and wave acting on it. Regardless of the direction of flow affecting on the fish court net or bag net, the deformed angle and depth to the side panel and bottom of box nets becomes bigger as the wave gets higher and the period of wave is faster. The tension in both upward or downward tends to be changed by the speed of wave. Those value of changes occurred similarly in either fish court net or bag net. Generally, when bag net is located at upward of flow, the value of tension was bigger 10% than any other location or nets. Regardless of the setting direction, the tension of the pound net is increased in proportion to flow speed, wave height and period of wave, and it becomes bigger about 15-30% at upward to flow than downward. Where the flow is upward in the court net, the tension in the wave increased to 37% compared to the one in the flow only in the condition of flow of 0.1-0.3m/s. Where the flow is upward in the bag net, the tension in the wave increased to 52% in the flow of 0.1m/s, and the tension increased to 48% in the flow of 0.2-0.3m/s.

• Journal of information and communication convergence engineering
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• v.15 no.3
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• pp.175-181
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• 2017

This paper describes the upgrade of an existing wave information retrieval algorithm by employing noise reduction in the pixel domain. Several algorithms for collecting wave information parameters from X-band radar image sequences including the wind field and current velocity have been developed over the past three decades. Using these algorithms, a band-pass filter (BPF) is applied to remove the non-wave contribution from the image spectra after the sea surface current velocity has been computed. However, such BPF designs have been both complex and insufficient in removing undesired components in X-band radar images. For this study, to improve the performance of wave information retrieval, an efficient noise reduction algorithm is incorporated into a regular wave information retrieval process. That is, the proposed algorithm was designed for operation in a more proper manner by effectively removing the undesired components in the pixel domain. Experiment results demonstrate that the proposed algorithm produces very close estimates to the buoy data records under undesirable noise conditions.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.4
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• pp.295-301
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• 2008

Recently, the demand on mm-wave (millimeter-wave) applications has increased dramatically. While circuits operating in the mm-wave frequency band have been traditionally implemented in III-V or SiGe technologies, recent advances in Si MOSFET operation speed enabled mm-wave circuits realized in a Si CMOS technology. In this work, a 58 GHz CMOS LC cross-coupled VCO (Voltage Controlled Oscillator) was fabricated in a $0.13-{\mu}m$ Si RF CMOS technology. In the course of the circuit design, active device models were modified for improved accuracy in the mm-wave range and EM (electromagnetic) simulation was heavily employed for passive device performance predicttion and interconnection parasitic extraction. The measured operating frequency ranged from 56.5 to 58.5 GHz with a tuning voltage swept from 0 to 2.3 V. The minimum phase noise of -96 dBc/Hz at 5 MHz offset was achieved. The output power varied around -20 dBm over the measured tuning range. The circuit drew current (including buffer current) of 10 mA from 1.5 V supply voltage. The FOM (Figure-Of-Merit) was estimated to be -165.5 dBc/Hz.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.2
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• pp.72-82
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• 1992

To accurately estimate nearshore current in shallow water regions. it is necessary to investigate the irregular wave transformation characteristics and radiation stress produced by random sea waves. This research is to investigate the application or the individual wave Analysis Method. the Component Wave Analysis Method and Representative Wave Analysis Method in the shallow water region. These methods were estimated by wave shallowing transformation when the waves propagate from deep water to shallow water region b)r generating regular waves, two component waves and irregular waves (Bretschneider-Mitsuyasu type). That is, the Indivisual Wave Analysis Method is to investigate from the viewpoint of shallow water transformation of wave statistical characteristics and their zero-down-crossing waves (wave height period and wave celerity). And the component Wave Analysis Method is to investigate from the view point of shallow water transformation of basic frequency component wave and their interference frequency component wave. In addition, this research is to compare the measured mean water level elevation with the calculated one from radiation stress of irreguar waves that is assumed in the three methods above.

• Journal of the Korean Vacuum Society
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• v.5 no.1
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• pp.85-92
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• 1996

The external electricla characteristics of helicon wave plasmas were measured over a wide range of RF power and magnetic filed. External parameters. such as antenna voltage , current, phase shift, and interanl parameter, electron density were measured at 7MHz, 1mTorr Ar discharge . The equivalent discharge resistance and reactance, and the power transfer efficiency were calculated through these measurements. There are a helicon mode which produces high density plasma by helicon wave and a lowmode which produces low density plasma by capaictive electric field. In case of the helicon mode, the anternna voltage and current were lower than those of the low-mode. The phase difference between voltage and current decreased suddenly at the transition point from the low-mode to the helicon mode. Equivalent resistance and power efficiency increased and reactance decreased suddenly at the transition point. These results mean that the power transperred to plasma and the nutual coupling between the antenna and plasma increase as the mode changes from the low-mode to the helicon mode.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.11
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• pp.1819-1828
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• 1989

In this paper, we determined the modulation index for minimization of speed ripple and position error using maximum speed ripple (SRF) and maximum position error(PEF) in current source TPWM inverter. Through computer simulation, we compared with total current harmonic distortion, SRF and PEF for square wave modulation method and TPWM method. As a result, it turns out that square wave modulation method is superior to TPWM method of 3 pulses per half cycle in speed ripple and position error contents. And TPWM is better than square wave method when pulse number is more than 5. Also, in these pulse numbers, moduladtion index of minimum speed ripple and munimum position error is 0.91.

• Journal of the Korea Fashion and Costume Design Association
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• v.16 no.2
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• pp.139-150
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• 2014

The purposes of this study are to analyze current situation of fashion market of Vietnam who is mainly influenced by Korean wave, analyze preferred fashion brand product and street fashion style of women in 10~20s interested in fashion so much, and develop the design suitable for Vietnamese consumers' preference so as to seek the methods domestic fashion industry can have competitive edge in emerging economic market. It's significant to suggest the direction of Korean new contents and seek the possibility of advancing new market by getting out of domestic market which is stagnated by preparing the foothold of fiber and fashion industry, beyond the first effects of Korean wave. Through this study, current situation of Korean wave which recently becomes new Korean wave based on the K-pop and futhermore, one of worldwide cultural situation could be recognized. Based on the preference of the Korean wave, current situation of Korean fashion industry spread gradually in Vietnam and design characteristics of fashion style preferred by Vietnamese consumers could be grasped. As the result, the design which can satisfy various needs of Vietnamese female consumers preferring fashion style was developed based on the characteristics by product's styles of Vietnamese fashion market. In addition, it intended to be helpful to plan the design of casual wear which is more professional so that Korean fashion industry can advance Vietnamese market through it.