• Title/Summary/Keyword: wave-energy

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Minimization of a CW CO2 Laser Output Ripple by using High Frequency Resonance Phenomena (고주파 공진현상을 이용한 CW CO2 레이저의 출력리플 최소화)

  • Sikander, Sakura;Kwon, Min-Jae;Kim, Hee-Je;Lee, Dong-Gil;Xu, Guo-Cheng
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.62 no.6
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    • pp.798-802
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    • 2013
  • In a conventional DC power supply used for CO2 laser, the circuit elements such as a rectifier bridge, a current-limiting resistor, a high voltage switch, energy storage capacitors ans a high-voltage isolation transformer using high turn ratio are necessary. Consequently, those supplies are expensive and require a large space. Thus, laser resonator and power supply should be optimally designed. In this paper, we propose a new power supply using high frequency resonance phenomena for CW(Continuous wave) CO2 laser (maximum output of 23W with discharge length of 450mm). It consists of a transformer including leakage inductance, magnetizing inductance and half-bridge converter, a three-stage Cockcroft-Walton and PFC(Power factor correction) circuit. The output ripple voltage can be controlled the minimum of 0.24% under the high frequency switching of 231kHz. Furthermore, the output efficiency was improved to 16.4% and the laser output stability of about 5.6% was obtained in this laser system.

A Node-Grouping MAC Protocol in Delay-Tolerant Underwater Acoustic Sensor Networks (지연 허용적인 수중 센서 네트워크에서 노드 그룹핑을 이용한 매체 접속 제어 프로토콜)

  • Cheon, Jin-Yong;Son, Kweon;Jang, Youn-Seon;Cho, Ho-Shin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.10B
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    • pp.1200-1209
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    • 2011
  • In this paper, we propose a novel energy efficient MAC protocol which is based on orthogonal frequency division multiple access (OFDMA) and exploits the physical characteristic that propagation loss of acoustic wave depends on the distance. In the proposed scheme, sensor nodes are grouped according to the distance to sink node. Then, each group uses a different frequency band. The proposed scheme not only enables all sensor nodes to maintain the signal-to-noise ratio above a certain required level (Accepted Minimum SNR, AMS), but also reduces overall transmission power consumption. In addition, the dynamic sub-channel allocation is employed in order to improve data transmission rate. Simulations show that proposed MAC protocol has better performance in a delay-tolerant underwater acoustic sensor networks.

Surface Electronic Structures and Magnetism of a Full-Heusler Alloy Co2CrGa(001): A First-principles Study

  • Jin, Ying-Jiu;Lee, Jae-Il
    • Journal of Magnetics
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    • v.12 no.3
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    • pp.97-102
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    • 2007
  • We have investigated the electronic structures and magnetism of a full Heusler alloy $Co_2CrGa(001)$ surface by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). We considered two types of different terminations: the Co-terminated (Co-Term) and the CrGa-terminated (CrGa-Term) surfaces. From the calculated layer-projected density of states (LDOS), we found that the surface of the CrGa-Term shows nearly half-metallic character while that of the Co-Term is far from the half-metallic. For the Co-Term, the surface Co atom moves down to the bulk region by $0.05{\AA}A$, while the subsurface Cr and Ga atoms move up to the surface layer by 0.05 and $0.01{\AA}$, respectively. For the CrGa-Term, there is a large inward relaxation of the surface Ga atom $(0.07{\AA})$, but the relaxation of the surface Cr atom is very small $(0.01{\AA})$. The relaxations affect not much to the overall shapes of DOS for both terminations, but make the surface states of the surface Cr and Ga atoms for the CrGa-Term shift to higher energy that enhances the nearly half-metallic character of the CrGa-Term. The magnetic moments of the surface $Cr(2.98{\mu}_B)$ in the CrGa-Term and the surface $Co(1.17{\mu}_B)$ in the Co-Term were much increased compared to those of the inner-layers $(1.79\;and\;0.77{\mu}_B)$, respectively, while that of the subsurface Cr atom in the Co-Term was decreased to $1.19{\mu}_B$.

A First-principles Study on the Electronic Structures and Magnetism of Antiperovskite Ti0.96Co0.02Fe0.02O2 (페로브스카이트 구조를 가지는 Ti0.96Co0.02Fe0.02O2의 전자구조와 자성)

  • Song, Ki-Myung;Bialek, B.;Lee, Jae-Il
    • Journal of the Korean Magnetics Society
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    • v.18 no.3
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    • pp.85-88
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    • 2008
  • We calculated the electronic structures of substituted cobalt nitrides, that is $FeCo_3N$ and $NiCo_3Ni$, by using the all electron fullpotential linearized augmented plane-wave (FLAPW) energy band method, and investigated the influence on the magnetic properties of $Co_4N$ due to the substitution of Co atom located at corner sites by iron and nickel atoms. We found that the magnetic moments of CoII atoms located at the face-center positions in these compounds are almost same to that of $Co_4N$. The magnetic moments of Fe and Ni atoms in $FeCo_3N$ and $NiCo_3Ni$ are 3.086 and $0.795\;{\mu}_B$, and they have the localized nature of magnetism.

Design of an Infrared Multi-touch Screen Controller using Stereo Vision (스테레오 비전을 이용한 저전력 적외선 멀티 터치스크린 컨트롤러의 설계)

  • Jung, Sung-Wan;Kwon, Oh-Jun;Jeong, Yong-Jin
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.47 no.2
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    • pp.68-76
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    • 2010
  • Touch-enabled technology is increasingly being accepted as a main communication interface between human and computers. However, conventional touchscreen technologies, such as resistive overlay, capacitive overlay, and SAW(Surface Acoustic Wave), are not cost-effective for large screens. As an alternative to the conventional methods, we introduce a newly emerging method, an optical imaging touchscreen which is much simpler and more cost-effective. Despite its attractive benefits, optical imaging touchscreen has to overcome some problems, such as heavy computational complexity, intermittent ghost points, and over-sensitivity, to be commercially used. Therefore, we designed a hardware controller for signal processing and multi-coordinate computation, and proposed Infrared-blocked DA(Dark Area) manipulation as a solution. While the entire optical touch control took 34ms with a 32-bit microprocessor, the designed hardware controller can manage 2 valid coordinates at 200fps and also reduce energy consumption of infrared diodes from 1.8Wh to 0.0072Wh.

Infinite Element for the Analysis of Harbor Resonances (항만 부진동 해석을 위한 무한요소)

  • Park, Woo-Sun;Chun, In-Sik;Jeong, Weon-Mu
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.6 no.2
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    • pp.139-149
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    • 1994
  • In this paper, a finite element technique is applied to the prediction of the wave resonance phenomena in harbors. The mild-slope equation is used with a partial reflection boundary condition introduced to model the energy dissipating effects on the solid boundary. For an efficient modeling of the radiation condition at infinity, a new infinite element is developed. The shape function of the infinite element is derived from the asymptotic behavior of the first kind of the Hankel's function in the analytical boundary series solutions. For the computational efficiency, the system matrices of the element are constructed by performing the relevant integrations in the infinite direction analytically. Comparisons with the results from experiments and other solution methods show that the present model gives fairly good results. Numerical experiments are also carried out to determine the proper distance to the infinite elements from the mouth of the halter, which directly affect the accuracy and efficiency of the solution.

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Observation of long-term disappearance and reappearance of the outer radiation belt

  • Lee, Dae-Young;Shin, Dae-Kyu;Kim, Kyung-Chan;Kim, Jin-Hee;Cho, Jung-Hee;Park, Mi Young;Angelopoulos, Vassilis;Hwang, Junga;Lee, Yonghee;Kim, Thomas
    • The Bulletin of The Korean Astronomical Society
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    • v.37 no.2
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    • pp.115.2-115.2
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    • 2012
  • In this study we have used the data of various instruments onboard the THEMIS spacecraft to study the characteristics of the outer radiation belt during the ascending phase of solar cycle 24. The most astonishing result is that we discovered four long-term (a month or so) periods during which the belt has nearly disappeared. The first disappearance started late 2008, followed by reappearance in ~a month, and three more similar events repeated until early 2010 when the belt has reappeared. This is well revealed at 719 keV electrons, which is the currently available uppermost energy channel from the THEMIS SST observation, but also seen at even lower energies. Overall consistent features were confirmed using the NOAA-POES observations. The vanished belt periods are associated with extremely weak solar wind conditions, low geomagnetic disturbances (in terms of Kp and AE/AL), greatly suppressed wave (ULF and chorus) activities, greatly reduced storm and substorm activities (little source particle supply), and expanded plasmapause locations. The direct observations of such events shed light on the fundamental question of the origin of the radiation belt, which is the main focus of our presentation.

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Pipe Leak Detection System using Wireless Acoustic Sensor Module and Deep Auto-Encoder

  • Yeo, Doyeob;Lee, Giyoung;Lee, Jae-Cheol
    • Journal of the Korea Society of Computer and Information
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    • v.25 no.2
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    • pp.59-66
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    • 2020
  • In this paper, we propose a pipe leak detection system through data collection using low-power wireless acoustic sensor modules and data analysis using deep auto-encoder. Based on the Fourier transform, we propose a low-power wireless acoustic sensor module that reduces data traffic by reducing the amount of acoustic sensor data to about 1/800, and we design the system that is robust to noise generated in the audible frequency band using only 20kHz~100kHz frequency signals. In addition, the proposed system is designed using a deep auto-encoder to accurately detect pipe leaks even with a reduced amount of data. Numerical experiments show that the proposed pipe leak detection system has a high accuracy of 99.94% and Type-II error of 0% even in the environment where high frequency band noise is mixed.

Assessment of the Counter-Flow Thrust Vector Control in a Three-Dimensional Rectangular Nozzle (3차원 직사각형 노즐에서 역유동 추력벡터 제어 평가)

  • Wu, Kexin;Kim, Tae Ho;Kochupulickal, James Jintu;Kim, Heuy Dong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.24 no.1
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    • pp.34-46
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    • 2020
  • Computational assessment of gas-dynamic characteristics is explored for a three-dimensional counter-flow thrust vector control system in a rectangular supersonic nozzle. This convergent-divergent nozzle is designed by Method of Characteristics and its design Mach number is specially set as 2.5. Performance variations of the counter-flow vector system are illustrated by varying the gap height of the secondary flow duct. Key parameters are quantitatively analyzed, such as static pressure distribution along the centerline of the upper suction collar, deflection angle, secondary mass flow ratio, and resultant thrust coefficient. Additionally, the streamline on the symmetry plane, three-dimensional iso-Mach number surface contour, and three-dimensional turbulent kinetic energy contour are presented to reveal overall flow-field characteristics in detail.

Effect of Airborne Noise from Ship Machinery on Underwater Noise (선박의 장비 공기소음이 수중소음에 미치는 영향)

  • Kim, Hyun-Sil;Kim, Jae-Seung;Kim, Bong-Ki;Kim, Sang-Ryul;Lee, Seong-Hyun
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.6
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    • pp.569-574
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    • 2011
  • In research vessels or naval ships, airborne noise from machineries such as diesel engine is the major source of underwater noise at low speed. In this paper, effect of engine noise on underwater noise is studied by considering two paths; sound radiation from hull plate and direct airborne noise transmission through hull plate. SEA (Statistical energy analysis) is used to predict hull plate vibration induced by engine noise, where SEA model consists of only two subsystems; engine room air space and hull plate. The pressure level in water is calculated from sound radiation by plate. Engine noise transmission through hull plate is obtained by assuming plane wave propagation in air-limp plate-water system. Two effects are combined and compared to the measurement, where speaker is used as a source in engine room and sound pressure levels in engine room and water are measured. The hydrophone is located 1 m away from the hull plate. It is found below 1000 Hz, prediction overestimates underwater sound pressure level by 5 to 12 dB.