• Title/Summary/Keyword: Added Mass Effect

검색결과 310건 처리시간 0.022초

확대촬영법 및 Mie 산란광법을 이용한 다성분연료의 분무구조에 관한 실험적 해명 (An Experimental Analysis on the Spray Structure of Multi-component Fuels Using Magnification Photograph and Mie Scattering Images)

  • 명광재;윤준규
    • Journal of Advanced Marine Engineering and Technology
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    • 제32권5호
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    • pp.707-716
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    • 2008
  • The objective of this study was to analyze the effect of mixed fuel composition and mass fraction on spray inner structure in evaporating transient spray under the variant ambient conditions. Spray structure and spatial distribution of liquid phase concentration were investigated using a thin laser sheet illumination technique on the three component mixed fuels. A pulsed Nd:YAG laser was used as a light source. The experiments were conducted in a constant volume vessel with optical access. Fuel was injected into the vessel with electronically controlled common rail injector. Used fuel contains i-octane($C_8H_{18}$), n-dodecane($C_{12}H_{26}$) and n-hexadecane($C_{16}H_{34}$) that were selected as low-, middle- and high-boiling point fuel, respectively. Experimental conditions are 42 MPa, 72 MPa and 112 MPa in injection pressure, $5\;kg/m^3$, $15kg/m^3$ and $30kg/m^3$ in ambient gas density, 300 K, 500 K, 600 K and 700 K in ambient gas temperature, 300 K and 368 K in fuel temperature and different fuel mass fraction. Experimental results indicated that the multi-component fuels made two phase region mixed vapor and liquid so that it would are helpful to improve combustion, for the fuels of high boiling point component could accelerate evaporation very much according as low boiling point fuel was added to high boiling point fuel.

신뢰성 보정된 발사체 개발비용 추정방안 연구 (Studies for Reliability-corrected Cost Estimation Methodology of Launch Vehicle Development)

  • 김홍래;유동서;장영근
    • 한국항공우주학회지
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    • 제40권4호
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    • pp.364-374
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    • 2012
  • 본 연구에서는 발사체의 개념설계 단계 동안 성능 변수뿐만 아니라 신뢰성에 따른 개발비용 추정방안을 분석하고자 하였다. 과거에는 발사체의 개발비용을 예측하기 위해서 주로 발사체의 성능과 건조 질량 등을 독립변수로 하는 추정 방법이 많이 이용되었다. 이러한 접근 방법은 비교적 근사하였지만 신뢰성 수준에 따른 비용 변화를 반영할 수 없기 때문에 원하는 신뢰성을 가진 발사체의 개발비용을 근접하게 예측하기는 쉽지 않았다. 본 논문에서는 이러한 비용추정 방법의 한계를 개선하기 위해 성능과 질량을 기반으로 한 비용 모델인 TRANSCOST에 신뢰성 개념을 도입하여 발사체 비용을 추정할 수 있는 방법론을 제시하였다. 이를 기반으로 신뢰성에 따른 한국형발사체(KSLV- II)의 개발비용을 추정했다.

Analysis of the Influence of Atmospheric Turbulence on the Ground Calibration of a Star Sensor

  • Xian Ren;Lingyun Wang;Guangxi Li;Bo Cui
    • Current Optics and Photonics
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    • 제8권1호
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    • pp.38-44
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    • 2024
  • Under the influence of atmospheric turbulence, a star's point image will shake back and forth erratically, and after exposure the originally small star point will spread into a huge spot, which will affect the ground calibration of the star sensor. To analyze the impact of atmospheric turbulence on the positioning accuracy of the star's center of mass, this paper simulates the atmospheric turbulence phase screen using a method based on a sparse spectrum. It is added to the static-star-simulation device to study the transmission characteristics of atmospheric turbulence in star-point simulation, and to analyze the changes in star points under different atmospheric refractive-index structural constants. The simulation results show that the structure function of the atmospheric turbulence phase screen simulated by the sparse spectral method has an average error of 6.8% compared to the theoretical value, while the classical Fourier-transform method can have an error of up to 23% at low frequencies. By including a simulation in which the phase screen would cause errors in the center-of-mass position of the star point, 100 consecutive images are selected and the average drift variance is obtained for each turbulence scenario; The stronger the turbulence, the larger the drift variance. This study can provide a basis for subsequent improvement of the ground-calibration accuracy of a star sensitizer, and for analyzing and evaluating the effect of atmospheric turbulence on the beam.

The effect of zinc, iron and manganese content on gamma shielding properties of magnesium-based alloys produced using the powder metallurgy

  • Mesut Ramazan Ekici;Emre Tabar;Gamze Hosgor;Emrah Bulut ;Ahmet Atasoy
    • Nuclear Engineering and Technology
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    • 제56권9호
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    • pp.3872-3883
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    • 2024
  • This study investigates the effects of Zinc (Zn), Manganese (Mn), and Iron (Fe) additions on the microstructure, corrosion behaviour, biocompatibility, mechanical, and gamma-ray shielding properties of Magnesium (Mg) alloys prepared in various compositions using powder metallurgy (PM). The microstructure and mechanical properties of these alloys were analyzed using electron microscopes (SEM and FE-SEM) and X-ray diffraction (XRD) methods. The results showed positive changes in the material's structure when the percentage of zinc added to pure magnesium increased. It was observed that the material became ductile, and the ductile fracture increased when the zinc ratio increased. The gamma-ray shielding properties of newly produced Mg-based alloys have also been discussed since they have a high potential for use in space technologies. Radiation shielding measurements have been performed using a 3" × 3" NaI(Tl) scintillation detector NaI (Tl) gamma-ray spectrometer. The gamma-ray shielding parameters such as the linear attenuation coefficients (μl), mass attenuation coefficient (μm), effective atomic number (Zeff), half-value layer (HVL), and tenth-value layer (TVL) have been determined experimentally at photon energies of 0.511 MeV (emitted from a22Na radioactive point source) and 1.173 MeV and 1.332 MeV (emitting from a60Co radioactive point source). The obtained parameters have been compared to the theoretical results of the XCOM software, and a satisfactory agreement has been found. It can be said from the results that the Mg30Zn alloy has the best shielding properties among the produced materials.

On the Period Change of the Contact Binary GW Cephei

  • Kim, Chun-Hwey;Song, Mi-Hwa;Yoon, Joh-Na;Jeong, Jang-Hae;Jeoung, Taek-Soo;Kim, Young-Jae;Kim, Jung-Yeb
    • Journal of Astronomy and Space Sciences
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    • 제27권2호
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    • pp.89-96
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    • 2010
  • BVR CCD observations of GW Cep were made on 15 nights in November through December 2008 with a 1-m reflector at the Jincheon station of the Chungbuk National University Observatory. Nineteen new times of minimum lights for GW Cep were determined and added to a collection of all other times of minima available to us. These data were then intensively analyzed, by reference to an O-C diagram, to deduce the general form of period variation for GW Cep. It was found that the O-C diagram could be interpreted as presenting two different forms of period change: an exclusively quasi-sinusoidal change with a period of 32.6 years and an eccentricity of 0.10; and a quasi-sinusoidal change with a period of 46.2 years and an eccentricity of 0.36 superposed on an upward parabola. Although a final conclusion is somewhat premature at present, the latter seems more plausible because late-type contact binaries allow an inter-exchange of both energy and mass between the component stars. The quasi-sinusoidal characteristics were interpreted in terms of a light-time effect due to an unseen tertiary component. The minimum masses of the tertiary component for both cases were calculated to be nearly the same as the $0.23-0.26M\;{\odot}$-ranges which is hardly detectable in a light curve synthesis. The upward parabolic O-C diagram corresponding to a secular period increase of about $4.12{\times}10^{-8}\;d/yr$ was interpreted as mass being transferred from the lesser to more massive component. The transfer rate for a conservative case was calculated to be about $2.66\;{\times}\;10^{-8}\;M_{\odot}/yr$ which is compatible with other W UMa-type contact binaries.

U-health system 활용이 남녀노인의 대사증후군 관리에 미치는 영향 (The effect of applying u-health system on metabolic syndrome management of elderly)

  • 정진욱;성순창
    • 디지털융복합연구
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    • 제11권11호
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    • pp.553-560
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    • 2013
  • 본 연구는 u-health system을 활용하여 대사증후군을 관리하고 위험인자, 신체구성, 체력의 변화를 검증하는데 그 목적이 있다. 남녀 노인 46명(남 24명; 여 22명)을 대상으로, 재택 개별 운동군과 u-health system 활용군으로 분류하였으며, 실험군과 대조군은 대사증후군 위험인자, 신체구성, 체력 검사를 실시한 후, 각각의 중재방법을 실시하고 12주 후에 같은 검사를 실시하였다. 대사증후군 지표는 남성과 여성 모두 혈당과 허리둘레에서 유의한 상호작용이 나타났다. 신체구성은 남성에서는 체중, 근육량, 체지방량, 체지방율, BMI에서 유의한 상호작용이 나타났으며, 여성의 경우 남성과 달리 근육량에서만 상호작용이 나타났다. 체력에서는 남성의 경우, 3m 왕복걷기, 기능적 팔뻗기, 보행속도에서 상호작용효과가 나타났으며, 여성의 경우 앉았다 일어나기, 6분 걷기, 악력에서 유의한 차이가 나타나 남성 그룹과는 차이를 보였다. 결론적으로 u-health system 통한 혈압, 혈당, 운동량의 수시 체크와 피드백은 대사증후군을 보다 지속적으로 관리하는데 효과가 있는 것으로 보인다. 그러나 운동 시 정확한 동작이나 방법에 대한 피드백을 제공하는 것은 아직도 부족한 부분이 많은 것으로 생각되어 이에 대한 정확한 정보를 제공할 수 있도록 개선이 필요하다.

모멘텀 슬래밍을 고려한 선체 운동 및 파랑하중 해석 (Numerical Analysis of Ship Motions and Wave Loads Including Momentum Slamming)

  • 황지희;박인규;구원철
    • 대한조선학회논문집
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    • 제49권2호
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    • pp.109-115
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    • 2012
  • Slamming phenomenon may occur when a ship navigates a high sea region, where the response of ship can be expected as elastic behaviour and the resultant wave loads may increase. In this paper, numerical analysis of ship motions and wave loads including momentum slamming was performed using the strip theory with regular waves. In order to analyze the effect of slamming force on the global ship motions, time histories of each mode of displacement and forces were simulated by using Newmark-beta time integration scheme. The added mass and damping coefficients calculated by Lewis form method were compared with the results of given references. For verification of numerical results, the motion RAOs of a S175 containership were calculated as an example of application and time histories of respective displacement and vertical bending moment were compared with the results of ITTC workshop benchmark test.

다점 계류된 원유 저장선에 대한 저주파수 운동 해석 (Slow Drift Motion Analyses for a FPSO with Spread Mooring Systems)

  • 이호영;박종환;곽영기
    • 한국해안해양공학회지
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    • 제13권3호
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    • pp.195-201
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    • 2001
  • 본 논문은 파랑중에 다전 계류된 원유저장선에 대한 저주파수 운동을 수치 모사하였다. 시간영역에서의 운동방정식은 충격응답함수를 포함하여 수평면상의 운동 즉 전후, 좌우 및 선수 운동을 고려하였다. 시간영역의 운동방정식에 나타난 부가질량, 파랑감쇠계수, 1차항 파랑 강제력 그리고 2차항 파랑 강제력을 주파수 영역의 특이점 분포법을 사용하여 계산하였고, 다점 계류된 계류삭은 체인이 해저면에 닿은 운동 효과를 포함하여 준 정적 현수선 이론으로 산정되었다. 계산 예로서 장파정 불규칙 파랑 중에 놓인 바아지식 원유저장선에 대한 시간 영역 해석을 수행하였다.

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물에 잠긴 다공 직사각평판의 실험적 모드 해석 (Experimental Modal Analysis of Perforated Rectangular Plates Submerged in Water)

  • 유계형;이명규;정경훈;이성철
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2002년도 추계학술대회논문집
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    • pp.416-421
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    • 2002
  • This paper dealt with an experimental study on the hydro-elastic vibration of clamped perforated rectangular plates submerged in water. The penetration of holes in the plates had a triangular pattern with P/D (pitch to diameter) 1.750, 2.125, 2.500, 3.000 and 3.750. The natural frequencies of the perforated plates in air were obtained by the analytical method based n the relation between the reference kinetic and maximum potential energy and compared with the experimental results. Good agreement between the results was found for the natural frequencies of the perforated plates in air. It was empirically found that the natural frequencies of the perforated plate in air increase with an increase of P/D, on the other hand, the natural frequencies of the perforated plate in contact with water decrease with an increase of P/D. Additionally, the effect of the submerged depth on the natural frequency was investigated.

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COMBUSTION CHARACTERISTICS OF INHOMOGENEOUS METHANE-AIR MIXTURE IN A CONSTANT VOLUME COMBUSTION CHAMBER

  • Choi, S.H.;Jeon, C.H.;Chang, Y.J.
    • International Journal of Automotive Technology
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    • 제5권3호
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    • pp.181-188
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    • 2004
  • A cylindrical constant-volume combustion chamber was used to investigate the flow characteristics at the spark electrode gap and the combustion characteristics of an inhomogeneous charge methane-air mixture under several parameters such as stratified pattern, initial charge pressure, ignition time and the excess air ratio of the initial charge mixture. Flow characteristics including mean velocity and turbulence intensity were analyzed by a hot-wire anemometer. The combustion pressure development, measured by a piezo-electric pressure transducer, was used to investigate the effect of initial charge pressure, excess air ratio and ignition times on combustion pressure and combustion duration. It was found that the mean velocity and turbulence intensity had the maximum value around 200-300 ms and then decreased gradually to near-zero value at 3000 ms. For the stratified patterns, the combustion rate under the rich injection (RI) condition was the fastest. Under the initial charge conditions, the second mixture was accompanied by an increase in the combustion rate, and that the higher the mass which is added in the second stage injection, the faster the combustion rate.