• 제목/요약/키워드: mass ratio

검색결과 3,969건 처리시간 0.033초

SURFACE BRIGHTNESS AND MASS DISTRIBUTION OF THE LATE TYPE SPIRAL GALAXY NGC 2403

  • Lee, Yoo-Mi;Chun, Mun-Suk
    • 천문학회지
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    • 제22권1호
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    • pp.31-41
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    • 1989
  • Luminosity profile of the late type spiral galaxy NGC 2403 was obtained using the PDS scan of the plate. Some physical parameters (scale length, total magnitude, central brightness, disk to bulge ratio and concentric indices) were calculated from the brightness distribution. Total mass and the mass to luminosity ratio were estimated from the fitting of various mass models.

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라이다 관측자료를 이용한 미세먼지 농도 산정 (Estimation of Particle Mass Concentration from Lidar Measurement)

  • 김만해;여희동;;임한철;이철규;허복행;유영석;손병주;윤순창;김상우
    • 대기
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    • 제25권1호
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    • pp.169-177
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    • 2015
  • Vertical distribution of particle mass concentrations was estimated from 8-year elastic-backscatter lidar and sky radiometer data, and from ground-level PM10 concentrations measured in Seoul. Lidar ratio and mass extinction efficiency were determined from aerosol optical depth (AOD) and ground-level PM10 concentrations, which were used as constraints to estimate particle mass concentration. The mean lidar ratio (with standard deviation) and mass extinction efficiency for the entire 8-year study period were $60.44{\pm}23.17$ sr and $3.69{\pm}3.00m^2g^{-1}$, respectively. The lidar ratio did not vary significantly with the ${\AA}ngstr{\ddot{o}}m$ exponent (less than ${\pm}10%$); however, the mass extinction efficiency decreases to $1.82{\pm}1.67m^2g^{-1}$ (51% less than the mean value) when the ${\AA}ngstr{\ddot{o}}m$ exponent is less than 0.5. This result implies that the particle mass concentration from lidar measurements can be underestimated for dust events. Seasonal variation of the particle mass concentration estimated from lidar measurements for the boundary layer, was quite different from ground-level PM10 measurements. This can be attributable to an inhomogeneous vertical distribution of aerosol in the boundary layer.

Impact of cable sag on the efficiency of an inertial mass damper in controlling stay cable vibrations

  • Wang, Zhi-hao;Gao, Hui;Xu, Yan-wei;Chen, Zheng-qing;Wang, Hao
    • Smart Structures and Systems
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    • 제24권1호
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    • pp.83-94
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    • 2019
  • Passive negative stiffness dampers (NSDs) that possess superior energy dissipation abilities, have been proved to be more efficient than commonly adopted passive viscous dampers in controlling stay cable vibrations. Recently, inertial mass dampers (IMDs) have attracted extensive attentions since their properties are similar to NSDs. It has been theoretically predicted that superior supplemental damping can be generated for a taut cable with an IMD. This paper aims to theoretically investigate the impact of the cable sag on the efficiency of an IMD in controlling stay cable vibrations, and experimentally validate superior vibration mitigation performance of the IMD. Both the numerical and asymptotic solutions were obtained for an inclined sag cable with an IMD installed close to the cable end. Based on the asymptotic solution, the cable attainable maximum modal damping ratio and the corresponding optimal damping coefficient of the IMD were derived for a given inertial mass. An electromagnetic IMD (EIMD) with adjustable inertial mass was developed to investigate the effects of inertial mass and cable sag on the vibration mitigation performance of two model cables with different sags through series of first modal free vibration tests. The results show that the sag generally reduces the attainable first modal damping ratio of the cable with a passive viscous damper, while tends to increase the cable maximum attainable modal damping ratio provided by the IMD. The cable sag also decreases the optimum damping coefficient of the IMD when the inertial mass is less than its optimal value. The theoretically predicted first modal damping ratio of the cable with an IMD, taking into account the sag generally, agrees well with that identified from experimental results, while it will be significantly overestimated with a taut-cable model, especially for the cable with large sag.

집중 질량및 관성 모멘트를 갖는 회전하는 티모센코 보의 면외굽힘 진동 (Flapwise Bending Vibration of Rotating Timpshenko Beams with Concentrated Mass and Mass Moment of Inertia)

  • 박정훈;유홍희
    • 소음진동
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    • 제8권2호
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    • pp.353-360
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    • 1998
  • In this paper, a modeling method for the bending vibration analysis of rotating Timoshenko beams with concentrated mass and mass moment of inertia is presented. The shear and rotary inertia effects become critical for the accurate estimation of the natural frequencies and mode shapes as the slenderness ratio decreases. The natural frequencies obtained by using the Timoshenko beam theory are lower than those by using the Euler beam theory. The critical angular speed, which does not exist only with the concentrated mass, exists with the concentrated mass moment of inertia.

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THE EVOLUTION OF BARYONIC MASS OF ELLIPTICAL GALAXIES IN THE SLOAN DIGITAL SKY SURVEY

  • PENG, TING-HUNG;KOY, CHUNG-MING;TIAN, YONG;CHEN, CHEN-HUNG
    • 천문학논총
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    • 제30권2호
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    • pp.385-387
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    • 2015
  • Stellar mass is an important parameter of galaxies. We estimate the dynamical mass of an elliptical galaxy by its velocity dispersion and effective radius using the Hernquist model in the framework of MOdified Newtonian Dynamics (MOND). MOND is an alternative theory to the dark matter paradigm. In MOND the dynamical mass is the same as the baryonic mass or luminous mass, and in elliptical galaxies most of the baryons reside in stars. We select elliptical galaxies between redshift 0.05 and 0.5 from the main galaxy sample and the luminous red galaxy sample in the Sloan Digital Sky Survey. We find that the stellar mass-to-light ratio at different redshift epochs can be fitted by a gamma distribution, and its mean is smaller at smaller redshifts.

Reduced ion mass effects and parametric study of electron flat-top distribution formation

  • 홍진희;이은상;;민경욱
    • 천문학회보
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    • 제37권2호
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    • pp.118.2-118.2
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    • 2012
  • In particle-in-cell (PIC) simulation studies related to ion-ion two-stream instability, a reduced ion-to-electron mass ratio is often employed to save computation time. But it was not clearly verified how electrons dynamics are coupled with the slower evolution of ion-ion interactions under the external electric field. We have studied the ion beam driven instability using a 1D electrostatic PIC code by comparing different rescaling of parameter with real ion mass from the reference simulation with reduced ion mass. As the external electric field is stronger, the excited unstable mode range was more sensitively affected by the system size with the real mass ratio than the reduced ion mass. The results show that the reduced mass ratio should be used cautiously in PIC code as the electron dynamics can modify the ion instabilities. Additionally we found the formation of electron flat-top distribution in the final saturation stage. Simulation results show that in the early phase electrostatic solitary waves are quasi-periodically formed, but later they are fully dissipated resulting in heated, flat-top distributions. New electron beam components are occasionally formed. These are a consequence of the interaction with solitary wave structures. We parametrically investigate the development of electron phase space distributions for various drift speeds of ion beams and temperature ratios between ions and electrons

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High performance active tuned mass damper inerter for structures under the ground acceleration

  • Li, Chunxiang;Cao, Liyuan
    • Earthquakes and Structures
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    • 제16권2호
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    • pp.149-163
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    • 2019
  • By integrating an active tuned mass damper (ATMD) and an inerter, the ATMDI has been proposed to attenuate undesirable oscillations of structures under the ground acceleration. Employing the mode generalized system, the dynamic magnification factors (DMF) of the structure-ATMDI system are formulated. The criterion can then be defined as the minimization of maximum values of the DMF of the controlled structure for optimum searching. By resorting to the defined criterion and the particle swarm optimization (PSO), the effects of varying the crucial parameters on the performance of ATMDI have been scrutinized in order to probe into its superiority. Furthermore, the results of both ATMD and tuned mass dampers inerter (TMDI) are included into consideration for comparing. Results corroborate that the ATMDI outperforms both ATMD and TMDI in terms of the effectiveness and robustness. Especially, the ATMDI may greatly reduce the demand on both the mass ratio and inerter mass ratio, thus being capable of further miniaturizing both the ATMD and TMDI. Likewise the miniaturized ATMDI still keeps nearly the same stroke as the TMDI with a larger mass ratio. Hence, the ATMDI is deemed to be a high performance control device with the miniaturization and suitable for super-tall buildings.

기체연료엔진의 제어시스템 설계를 위한 엔진 모델링 및 검증 (Engine Modeling and Validation for Control System Design of a Gaseous-fuel Engine)

  • 심한섭;선우명호
    • 한국자동차공학회논문집
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    • 제11권1호
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    • pp.7-17
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    • 2003
  • Highly accurate control of an air-fuel ratio is very important to reduce exhaust gas emissions of gaseous-fuel engines. In order to achieve this purpose, a precise engine model is required to estimate engine performance from the engine design process which is applied to the design of an engine controller. Engine dynamics are considered to develop a dynamic engine model of a gaseous-fuel engine. An effective air mass ratio is proposed to study variations of the engine dynamics according to the water vapor and the gaseous-fuel in the mixture. The dynamic engine model is validated with the LPG engine under steady and transient operating conditions. The experimental results in the LPG gaseous-fuel engine show that the estimation of the air flow and the air-fuel ratio based upon the effective air mass ratio is more accurate than that of a normal engine model.

A CFD ANALYSIS ON THE INFLUENCE OF OPERATING CONDITIONS AND EJECTOR CONFIGURATION ON THE HYDRODYNAMICS AND MASS TRANSFER CHARACTERISTICS OF GAS-LIQUID EJECTOR

  • Utomo, Tony;Jin, Zen-Hua;Yi, Chung-Seub;Jeong, Hyo-Min;Chung, Han-Shik
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2007년도 춘계학술대회B
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    • pp.2817-2822
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    • 2007
  • The purpose of this paper is to study the influence of operating condition and ejector geometries on the hydrodynamics and on the mass transfer characteristic of ejector. The CFD results were validated with available experimental data. Flow field analyses and predictions of ejector performance were also carried out. Variation on the operating conditions was made by varying the gas-liquid flow rate ratio in the range of 0.2 to 1.2. The ejector configuration was also varied on the length to diameter ratio of mixing tube ($L_M/D_M$) in the range of 4 to 10. CFD studies show that at $L_M/D_M$ 5.5, the volumetric mass transfer coefficient increases with respect to gas flow rates. Meanwhile, at $L_M/D_M$ 4, the plot of volumetric mass transfer coefficient to gas-liquid flow rates ratio reach maximum at gas-liquid flow rates ratio of 0.6. This study also shows that volumetric mass transfer coefficient decrease with respect to the increase of mixing tube length.

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공급 질량비 변화에 따른 2유체 노즐의 액주분열특성에 관한 실험적 연구 (An Experimental Study on the Break-up Characteristics of Twin-Fluid Nozze According to tile Variations of Feeding Mass-ratio)

  • 강신재;오제하;노병준
    • 한국분무공학회지
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    • 제1권1호
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    • pp.63-75
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    • 1996
  • The purpose of this study is to investigate the break-up characteristics by taking advantage of a two-phase coaxial nozzle. Air and water are utilized as working fluids and the mass ratio air/water has been controlled to characterize the atomization, diffusion and development of mixing process. By way of a photographic technique, conventional developing structures and diffusion angles have been analyzed systematically with variations of mass ratios. The turbulent flow components of the atomized particles were measured by a two channel LDV system and the data were treated by an on-lined measurement equipment. According to the photographic results the spreading angles decreased because the axial inertia moment was relatively higher than the lateral one with respect to the increase of mass ratio. It is found the jet flow diffuses linearly in a certain limit region while the atomizing characteristics, in terms of the distributions of particle diameters did not show particular differences. It may be expected that these fundamental results can be used as reference data in studying the atomization, breakup and diffusions.

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