共查询到19条相似文献,搜索用时 322 毫秒
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为获取不同风场下TNT爆炸烟云扩散时空分布规律与高度变化模型,本文理论描述了爆炸烟云扩散过程与机理,开展了不同水平风速下烟云扩散的计算流体力学(computational fluid dynamics, CFD)仿真和外场时空分布实验,建立了不同水平风速下烟云高度随时间变化模型及烟云最终高度计算模型,分析了烟云扩散过程中形态、温度、密度、速度变化规律。研究结果显示:CFD方法仿真烟云分布结果与实验结果基本一致,大气稳定且无风条件下烟云高度随时间呈指数0.5的幂函数关系,最终高度与爆炸当量可拟合为指数0.47的幂函数模型;水平风会加快烟云与空气混合的速度,导致幂函数模型中指数参数随风速变大而呈线性减小规律,风速越大烟云上升速度衰减越快、上升时间越短、最终高度越低。 相似文献
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将震源矩张量中的各分量作为权重因子,利用基本Green函数的线性组合可以对地震波场进行描述,本文利用水平分层模型下的广义反射-透射系数方法的地震波场正演公式,反演了苏联东哈萨克斯坦地下核试验场的7次地下核爆炸、3次震中位置相近的天然地震的震源矩张量,反演结果表明地下核爆炸震源明显含有爆炸源成分,同时包含双力偶成分(DC)和线性偶极补偿源成分(CLVD),且CLVD成分比重大,CLVD的存在可用层裂机制来解释;天然地震震源矩张量的反演结果表明,DC源为主要成分,符合剪切位错震源模式。 相似文献
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地下爆炸与介质的能量耦合和介质中的波传播机制是理解地下爆炸源物理的重要基础。为研究地下爆炸辐射地震波能量的传播衰减规律,分析了黏弹性介质中地下爆炸地震波能量的组成。基于无限介质中黏弹性球面波理论,给出了速度、位移、应力、应变等物理量Laplace域的理论解。利用Laplace数值逆求解方法,建立了黏弹性介质中地下爆炸辐射地震波场的计算方法。以干黄土作为典型黏弹性材料,计算给出了地震波能量的传播特征,分析了地下爆炸辐射能量的传播衰减规律。结果表明:(1)在黏弹性介质中,某球面处流入的能量随半径增加而逐渐降低。在理想弹性介质中,某球面处流入的能量在几倍弹性半径外即可稳定到某一定值;(2)在某一固定的有限观测区域内,当观测时间足够长时,势能和耗散能均趋于某一定值,辐射动能趋于零;(3)当有限的观测区域能容纳一个完整波长的地震波时,地震波辐射动能的稳态值随波传播距离的增大而减小,总体上可以用指数函数和幂函数进行分段拟合。 相似文献
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区域分层介质模型下, 可以将地震波场描述为矩张量各分量作为权重的基本格林函数的线性组合,利用该理论地震波场可以反演实际天然地震或地下核爆炸的震源机制,反演结果中不同震源机制成分的比重,可以用来识别地下核爆炸,该系统方法越来越受到关注。给出了基于广义反射-透射系数方法的水平分层介质模型的地震波场正演公式,并对基于该公式的单台反演结果的准确性、稳定性、可靠性进行了理论分析,为利用该公式对实际地下核爆炸进行反演提供了理论基础,该方法对利用区域少量甚至是单站记录数据检测、识别地下核爆炸具有重要参考意义。 相似文献
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运用速度传感器和拾振器,对40 kg TNT当量爆炸塔在15、20、25和40 kg TNT炸药爆炸加载下爆炸塔旁侧实验室所在地面、屋顶以及塔顶的振动速度进行监测分析。测试结果表明:在本实验条件下实验室地面质点振动速度峰值均小于5 cm/s,振动持续时间为5~10 s,振动频率一般高于10 Hz;屋顶的竖向振动峰值是水平向的6~7倍,即存在显著的竖向振动放大效应。小波包分析表明:地面竖向振动携带的能量是水平向振动携带能量的2.5~4.0倍,质点振动信号中95%以上的能量处于0~160 Hz频带,而竖向振动中90%以上的能量集中在10~40 Hz范围。研究结果提示:6 m深隔振沟的隔振效果十分有限,在超过5 kg TNT当量的加载条件下,欲取得理想的隔振效果,应选择独立地基和隔振支座的减振设计方式。 相似文献
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基于球形发散波实验技术及圆环型电磁粒子速度测试技术,采用0.125 g TNT当量的微型炸药作为爆炸源,对填实爆炸下有机玻璃中球形波的传播规律进行了实验研究,并基于粒子速度波形进行了分析。结果表明:粒子速度峰值及粒子位移峰值符合指数衰减规律,粒子速度、位移峰值的衰减指数分别为1.34和1.28;负向粒子速度峰值随比距离的增加有先增大后减小的趋势;基于强间断假设得到的低压(小于1 GPa)下径向压力峰值-粒子速度峰值关系与一维应变下得到的σ-v Hugoniot曲线吻合较好;采用变模量模型假设,结合粒子速度数据反演的有机玻璃弹性模量E=(6.40±0.64)GPa、体积模量K=(7.12±0.71)GPa、剪切模量G=(2.37±0.24)GPa。 相似文献
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The coupling influence of airflow and temperature on the two-dimensional distribution of the film resulted from fuel spray impinging on a horizontal flat wall was studied with experiments. The horizontal airflow direction was perpendicular to the vertical axis of the injection spray. The results show that, as air velocity increases, the film shape turns from a circle to an oblong. As wall temperature increases, the film area shrinks. Film thickness decreases as wall temperature or air velocity increases. The boiling point of the fuel is an important temperature to affect the film area and the film thickness. Film center moves more far away in the downstream direction as air velocity increases. For a certain air velocity, film center moves less far away as wall temperature increases. 相似文献
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An Eulerian/Lagrangian numerical simulation is performed on mixed sand transport. Volume averaged Navier–Stokes equations are solved to calculate gas motion, and particle motion is calculated using Newton's equation, involving a hard sphere model to describe particle-to-particle and particle-to-wall collisions. The influence of wall characteristics, size distribution of sand particles and boundary layer depth on vertical distribution of sand mass flux and particle mean horizontal velocity is analyzed, suggesting that all these three factors affect sand transport at different levels. In all cases, for small size groups, sand mass flux first increases with height and then decreases while for large size groups, it decreases exponentially with height and for middle size groups the behavior is in-between. The mean horizontal velocity for all size groups well fits experimental data, that is, increasing logarithmically with height in the middle height region. Wall characteristics greatly affects particle to wall collision and makes the flat bed similar to a Gobi surface and the rough bed similar to a sandy surface. Particle size distribution largely affects the sand mass flux and the highest heights they can reach especially for larger particles. 相似文献
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Alexander R. Horner-Devine 《Experiments in fluids》2006,41(4):559-571
A technique is presented for measuring velocity, density and scalar transport in a buoyant rotating gravity current. Existing methods for combined PIV and PLIF are modified for use in a stratified flow on a rotating table and strategies for beam alignment, index of refraction matching, surface tension matching and photobleaching correction are presented. In addition, the PIV–PLIF technique is modified to resolve the velocity and density fields in a cross-section of the current perpendicular to the mean flow direction, allowing the transport in this direction to be computed. This is done by rotating the plane of the laser sheet 15° to the horizontal. This sheet angle is high enough that the entire cross-section of the current is contained in the viewing area, but low enough that horizontal PIV particle displacements are resolved. The technique is used successfully to measure the transport of buoyant fluid in a non-rotating channel to within 5% of the prescribed flow. Results from a rotating gravity current experiment are then presented and compared with previous experiments. 相似文献
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O. S. Sentemova 《Moscow University Mechanics Bulletin》2011,66(6):138-140
The problem of motion of a homogeneous ball on a horizontal plane is considered. It is assumed that the contact patch is of
spherical shape, whereas the pressure center does not coincide with the center of the contact patch and is displaced in the
sliding direction of the ball. The friction force has two components that are parallel and perpendicular to the sliding velocity;
the friction force moment has a vertical component and two horizontal components being parallel and perpendicular to the sliding
velocity. 相似文献
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Modelling of gas–solid turbulent channel flow with non-spherical particles with large Stokes numbers
This paper describes a complete framework to predict the behaviour of interacting non-spherical particles with large Stokes numbers in a turbulent flow. A summary of the rigid body dynamics of particles and particle collisions is presented in the framework of Quaternions. A particle-rough wall interaction model to describe the collisions between non-spherical particles and a rough wall is put forward as well. The framework is coupled with a DNS-LES approach to simulate the behaviour of horizontal turbulent channel flow with 5 differently shaped particles: a sphere, two types of ellipsoids, a disc, and a fibre. The drag and lift forces and the torque on the particles are computed from correlations which are derived using true DNS.The simulation results show that non-spherical particles tend to locally maximise the drag force, by aligning their longest axis perpendicular to the local flow direction. This phenomenon is further explained by performing resolved direct numerical simulations of an ellipsoid in a flow. These simulations show that the high pressure region on the acute sides of a non-spherical particle result in a torque if an axis of the non-spherical particle is not aligned with the flow. This torque is only zero if the axis of the particle is perpendicular to the local direction of the flow. Moreover, the particle is most stable when the longest axis is aligned perpendicular to the flow.The alignment of the longest axis of a non-spherical particle perpendicular to the local flow leads to non-spherical particles having a larger average velocity compared to spherical particles with the same equivalent diameter. It is also shown that disc-shaped particles flow in a more steady trajectory compared to elongated particles, such as elongated ellipsoids and fibres. This is related to the magnitude of the pressure gradient on the acute side of the non-spherical particles. Finally, it is shown that the effect of wall roughness affects non-spherical particles differently than spherical particles. Particularly, a collision of a non-spherical particle with a rough wall induces a significant amount of rotational energy, whereas a corresponding collision with a spherical particle results in mostly a change in translational motion. 相似文献
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《European Journal of Mechanics - B/Fluids》2003,22(4):369-377
The knowledge of the conditions in which particles denser than fluid settle is important in many areas of engineering, environmental sciences, meteorology, etc.For particle flows influenced by vortices, research mainly related to steady horizontal vortices has been undertaken. In this paper we determine the influence of the inclination of the vortex axis in the gravitational settling of particles.The results obtained, in relation to the trajectories, are qualitatively similar to previous ones for horizontal vortices. The main difference is this: in a horizontal vortex particles always remain in a plane perpendicular to the vortex axis and in an inclined vortex (angle θ) particles do not remain on that plane because there is a component vtcosθ that takes them out.The average fall velocity 〈vz〉 has an asymptote to the dimensionless terminal velocity vt; this tendency is faster as the Stokes Number St increases and as vt decreases. A fundamental result is the following: as θ decreases, vt is reached faster because the component of the velocity u of the Rankine vortex over the Oz direction is small and because the vt component that tries to keep the particles in a plane perpendicular to the vortex axis is small, so the vortex takes action over the particles for a small period of time. 相似文献
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