• Title, Summary, Keyword: 공진소멸

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A study on the identification of underwater propeller singing phenomenon (수중 프로펠러 명음 현상의 규명에 관한 연구)

  • Kim, Taehyung;Lee, Hyoungsuk
    • The Journal of the Acoustical Society of Korea
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    • v.37 no.2
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    • pp.92-98
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    • 2018
  • This paper is a study on the generation mechanism of propeller singing based on the cavitation tunnel test, underwater impact test, finite element analysis and computational flow analysis for the model propeller. A wire screen mesh, a propeller and a rudder were installed to simulate ship stern flow, and occurrence and disappearance of propeller singing phenomenon were measured by hydrophone and accelerometer. The natural frequencies of propeller blades were predicted through finite element analysis and verified by contact and non-contact impact tests. The flow velocity and effective angle of attack for each section of the propeller blades were calculated using RANS (Reynolds Averaged Navier-Stokes) equation-based computational fluid analysis. Using the high resolution analysis based on detached eddy simulation, the vortex shedding frequency calculation was performed. The numerical predicted vortex shedding frequency was confirmed to be consistent with the singing frequency and blade natural frequency measured by the model test.

How does Man and Non-human beings meet? (인간과 비인간 존재는 어떻게 만나는가?)

  • Sim, Gui-yeon
    • Journal of Korean Philosophical Society
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    • v.147
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    • pp.239-260
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    • 2018
  • Is an artificial intelligence robot, a non-human beings newly emerging in the age of technology, a threat to human beings, or a mutual cooperation or ensemble with human beings? The desire to control nature through the use of the power of science and technology is manifested in the fear that humans can annihilate themselves. This study attempts to identify the problems of Cartesian epistemology underlying these questions and fears and to answer these questions based on Merleau - Ponty 's ontological ontology using the Ontology and Latour' s ontology and technological philosophy. The cogito derived from the Cartesian philosophy became the basis of the structure of dichotomous epistemology of 'subjectivity and objectivity' based on human - reason. In the human-centered world, all non-human beings were tools or controls for humans. The problem of the modern people is not only to get help from the natural scientific methods to control the nature including man, but also to think that scientific method is the only way to understand the world. In criticizing this, Merleau-Ponty shows that the body mediates between human beings and non-human beings, and provides a possible ontological basis for the ontology. Merleau - Ponty 's phenomenological methodology and ontology are newly developed by Simondon under the influence of phenomenological philosopher and phenomenology. The relationship between human beings and nonhuman beings by Simondon appears as an ensemble of human and technical objects or a mutual co - operation of human and technical objects. In particular, Latour goes a step further in Simondon and defines all the bodies living in the world as actor-network theory, denying the core concept of modernity. Merleau - Ponty 's phenomenological view can be a new possible basis for the philosophical discussion of the technological age. We will see that the problem itself can be solved by shifting modern fear to a phenomenological attitude.

Estimation of Cavitation Bubble Distribution Using Multi-Frequency Acoustic Signals (다중 주파수를 이용한 캐비테이션 기포의 분포량 추정)

  • Kim, Dae-Uk;La, Hyoung-Sul;Choi, Jee-Woong;Na, Jung-Yul;Kang, Don-Hyug
    • The Journal of the Acoustical Society of Korea
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    • v.28 no.3
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    • pp.198-207
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    • 2009
  • Distribution of cavitation bubbles relative to change of the sound speed and attenuation in the water was estimated using acoustic signal from 20 to 300 kHz in two cases that cavitation bubbles exist and do not exist. To study generation and extinction property of cavitation bubble, bubble distribution was estimated in three cases: change of rotation speed (3000-4000 rpm), surface area of blade ($32-98\;mm^2$) and elapsed time (30-120 sec). As a result, the radii of the generated bubbles ranged from 10 to $60{\mu}m$, and bubble radius of $10-20{\mu}m$ and $20-30{\mu}m$ was accounted for 45 and 25% of the total number of cavitation bubbles, respectively. And generation bubble population correlated closely with the rotating speed of the blades but did not correlate with the surface area of blade. It was observed that 80% of total bubble population disappeared within 2 minutes. Finally, acoustic data of bubble distribution was compared with optical data.

Active optical coupler using the side polished single mode fiber and thermo-optic polymer multimode planar waveguide (측면 연마된 단일모드 광섬유와 열 광학 다중모드 평면도파로를 이용한 능동형 광 결합기)

  • 김광택;유호종;김성국;이소영;송재원;이상재;김시홍;강신원
    • Korean Journal of Optics and Photonics
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    • v.10 no.3
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    • pp.248-253
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    • 1999
  • In this paper, we have investigated a fiber type active coupler which utilizes the mode coupling between the side polished single mode optical fiber and the active multimode planar waveguide. The proposed device can be used for not only tunable wavelength filter or optical intensity modulator but also a tool for measuring optical properties of guiding material such as refractive index, birefringence, electro-optic coefficient, and thermo-optic coefficient. We gave designed and optimized a coupler structure using the BPM and fabricated the device using thermo-optic polymer as active planar waveguide overlay. The device showed that insertion loss was less then 0.5 dB, extinction ratio was -13 dB at the resonance wavelength, and the wavelength tunablity due to thermo-optic effect was -1.5 nm/$^{\circ}C$. The active coupler using thermo-optic effect can be used as a wavelength tunable filer, an optical intensity modulator and an optical sensor. pulses that are subsequently compressed by a dispersive optical fiber. Experimental results show that $sech^2$ shape pulses with a pulse width of ~14 ps and a time bandwidth product of ~0.34 are successfully generated at 10 GHz repetition rate. In contrast to other methods, such as higher order soliton compression, this approach does not depend on the optical power and thus shows promise for application to low-power lasers.

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Polymer Optical Microring Resonator Using Nanoimprint Technique (나노 임프린트 기술을 이용한 폴리머 링 광공진기)

  • Kim, Do-Hwan;Im, Jung-Gyu;Lee, Sang-Shin;Ahn, Seh-Won;Lee, Ki-Dong
    • Korean Journal of Optics and Photonics
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    • v.16 no.4
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    • pp.384-391
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    • 2005
  • A polymer optical microring resonator, which is laterally coupled to a straight bus waveguide, has been proposed and demonstrated using a nanoimprint technique. The propagation loss of the ring waveguide and the optical power coupling between the ring and bus waveguides was calculated by using a beam propagation method, then the dependence of the device performance on them was investigated using a transfer matrix method. We have especially introduced an imprint stamp incorporating a smoothing buffer layer made of a silicon nitride thin film. This layer played an efficient role in improving the sidewall roughness of the waveguide pattern engraved on the stamp and thus reducing the scattering loss. As a result the overall Q factor of the resonator was greatly increased. Also it reduced the gap between the ring and bus waveguides effectively to enhance the coupling between them, without relying on the direct writing method based on an e-beam writer. As for the achieved device performance at the wavelength of 1550 nm, the quality factor, the extinction ratio, and the free spectral range were ~103800, ~11 dB, and 1.16 m, respectively.