含微生物气泡高饱和砂土循环三轴剪切CFD-DEM模拟          下载免费PDF全文

蒋明镜  沈振义  刘俊  杨涛  谭亚飞鸥 《地震工程学报》2021,43(2):353-360

为探究砂土液化的微观机理,根据室内试验中微生物反硝化反应气泡的生成速率,建立数值模拟的时效性关系,分别制取微生物处理0天、2天、3天和5天的高饱和砂土试样,采用CFD-DEM耦合方法模拟不同工况下砂土试样的循环三轴不排水剪切试验。依据砂土试样的力链分布、抗液化振次、孔压比、轴向应变和力学配位数在加载过程中的变化情况,从宏微观角度分析砂土试样的抗液化能力。模拟结果表明:含微生物气泡高饱和砂土的抗液化强度较饱和砂土有所提升;随着微生物处理时间的增加,砂土试样的饱和度降低,孔压比和轴向应变的累积变慢,抗液化能力增强。  相似文献   

Viscosity of magmas containing highly deformable bubbles     

M. Manga  M. Loewenberg 《Journal of Volcanology and Geothermal Research》2001,105(1-2)

The shear viscosity of a suspension of deformable bubbles dispersed within a Newtonian fluid is calculated as a function of the shear rate and strain. The relative importance of bubble deformation in the suspension is characterized by the capillary number (Ca), which represents the ratio of viscous and surface tension stresses. For small Ca, bubbles remain nearly spherical, and for sufficiently large strains the viscosity of suspension is greater than that of the suspending fluid, i.e. the relative viscosity is greater than 1. If Ca>O(1) the relative viscosity is less than one. In the limit that Ca→∞ (surface tension is dynamically negligible), numerical calculations for a suspension of spherical bubbles agree well with the experimental measurements of Lejeune et al. (1999, Rheology of bubble-bearing magmas. Earth Planet. Sci. Lett., vol. 166, pp. 71–84). In general, bubbles have a modest effect on the relative viscosity, with viscosity changing by less than a factor of about 3 for volume fractions up to 50%.  相似文献   

电场产生的赤道扩展F的时空演变          下载免费PDF全文

黄朝松 Kell.  MC 《地球物理学报》1996,39(3):296-305

利用计算机模拟研究了非均匀电场产生的赤道扩展Ｆ的时空演变。非均匀电场能在赤道电离层Ｆ区底部触发Ｒａｙｌｅｉｇｈ－Ｔａｙｌｏｒ不稳定性，导致等离子体泡形态。计算中非均匀电场的幅度取为０．２５－１．００ｍＶ／ｍ，所产生的等离子体泡在２０００ｓ以内就能穿过Ｆ峰达到５４０ｋｍ的高度。所得结果阐明了非均匀电场在赤道扩展Ｆ中的作用，指出了产生等离子体泡一种可能的扰动源。由于Ｅ区和Ｆ区电场是相互影响的，从而揭示了Ｅ区和Ｆ区扰动的相互联系。  相似文献   

CCD images and long-slit spectroscopy of the ring nebula around θ Mus     

Carlos Guillermo Giménez de Castro  & Virpi S. Niemela 《Monthly notices of the Royal Astronomical Society》1998,297(4):1060-1066

We present the first digital CCD images and long-slit spectroscopy of the optical ring nebula around the Wolf–Rayet star θ Mus. The CCD images obtained through narrow-band filters centred at [O  iii ] and Hα show that the nebula has a filamentary structure, similar to supernova remnants, mainly seen in [O  iii ]. A spatial detachment between [O  iii ] and Hα images suggests excitation stratification, or multiple rings. An analysis of the physical conditions in the nebula was performed by means of long-slit CCD spectra. The spectral images show that the nebula is of low density and medium excitation. By means of quotients of recombination and collisional spectral line fluxes we determine that the principal excitation mechanism is photoionization. We have determined the electronic temperature and density, and chemical abundances for the oxygen at different sites within the nebula. Nebular chemical abundances are found to be similar to the Galactic ISM, indicating that the nebula is mainly composed of swept up material.  相似文献   

Sound scattering by hydrodynamic wakes of sea animals     

Selivanovsky  Dmitry A.; Ezersky  Alexander B. 《ICES Journal of Marine Science》1996,53(2):377-381

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Extensive gas bubble release in Norwegian spring-spawning herring (Clupea harengus) during predator avoidance     

Nottestad  L. 《ICES Journal of Marine Science》1998,55(6):1133-1140

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Experimental investigation on the motion of bubbles in the moonpool with a sonar model inside     

《Applied Ocean Research》2019

Bubbles are becoming a threat to the measurement of equipment and human activities in the moonpool, while little is known about the characteristics of bubbles in the moonpool. We aim to investigate the motion patterns and characteristic of bubbles in the moonpool. To support the investigation, experiments were conducted in a water tunnel. Images of bubbles in and under the moonpool were captured by two high-speed cameras. The software Tema and program PolyParticleTracker were used to track the bubbles in the moonpool. We obtain information of bubbles in the moonpool, including movement patterns of bubbles, generation of bubbles, relationship between amount of bubbles and the freesurface, temporal and spatial distribution of bubbles, the size and the velocities of bubbles.  相似文献   

The orientations of molecular clouds in the outer Galaxy: evidence for the scale of the turbulence driver?     

Sami Dib  C. Jakob Walcher  Mark Heyer  Edouard Audit  Laurent Loinard 《Monthly notices of the Royal Astronomical Society》2009,398(3):1201-1206

Supernova (SN) explosions inject a considerable amount of energy into the interstellar medium (ISM) in regions with high-to-moderate star formation rates. In order to assess whether the driving of turbulence by supernovae is also important in the outer Galactic disc, where the star formation rates are lower, we study the spatial distribution of molecular cloud (MC) inclinations with respect to the Galactic plane. The latter contains important information on the nature of the mechanism of energy injection into the ISM. We analyse the spatial correlations between the position angles (PAs) of a selected sample of MCs (the largest clouds in the catalogue of the outer Galaxy published by Heyer et al). Our results show that when the PAs of the clouds are all mapped to values into the  [0°, 90°]  interval, there is a significant degree of spatial correlation between the PAs on spatial scales in the range of 100–800 pc. These scales are of the order of the sizes of individual SN shells in low-density environments such as those prevailing in the outer Galaxy and where the metallicity of the ambient gas is of the order of the solar value or smaller. These findings suggest that individual SN explosions, occurring in the outer regions of the Galaxy and in likewise spiral galaxies, albeit at lower rates, continue to play an important role in shaping the structure and dynamics of the ISM in those regions. The SN explosions we postulate here are likely associated with the existence of young stellar clusters in the far outer regions of the Galaxy and the ultraviolet emission and low levels of star formation observed with the Galaxy Evolution Explorer (GALEX) satellite in the outer regions of local galaxies.  相似文献   

Three-dimensional numerical model of the Omega Nebula (M17): simulated thermal X-ray emission     

J. Reyes-Iturbide  P. F. Velázquez  M. Rosado  A. Rodríguez-González  R. F. González  A. Esquivel 《Monthly notices of the Royal Astronomical Society》2009,394(2):1009-1015

We present 3D hydrodynamical simulations of the superbubble M17, also known as the Omega Nebula, carried out with the adaptive grid code yguazú-a , which includes radiative cooling. The superbubble is modelled considering the winds of 11 individual stars from the open cluster inside the nebula (NGC 6618), for which there are estimates of the mass-loss rates and terminal velocities based on their spectral types. These stars are located inside a dense interstellar medium, and they are bounded by two dense molecular clouds. We carried out three numerical models of this scenario, considering different line-of-sight positions of the stars (the position in the plane of the sky is known, thus fixed). Synthetic thermal X-ray emission maps are calculated from the numerical models and compared with ROSAT observations of this astrophysical object. Our models successfully reproduce both the observed X-ray morphology and the total X-ray luminosity, without taking into account the thermal conduction effects.  相似文献   

Hydrodynamical simulations of Galactic fountains – II. Evolution of multiple fountains     

C. Melioli  F. Brighenti  A. D'Ercole  E. M. de Gouveia Dal Pino 《Monthly notices of the Royal Astronomical Society》2009,399(3):1089-1105

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