共查询到20条相似文献,搜索用时 312 毫秒
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讨论了作平面运动的薄板上一个质点在不同条件下的旋轮线轨迹,并讨论了这些不同形状的旋轮线是怎样由圆轮的纯滚动形成的. 相似文献
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北京大学力学系《小问题》组 《力学与实践》1987,9(1):63-64
133.一轮半径为R,重量为P,在其铅垂直径的上端B点处作用水平力Q。轮与水平面间的滚动摩阻系数为δ。问水平力Q使轮子只滚动而不滑动吋,轮与 ... 相似文献
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本刊1987第2期上《小问题》栏133题的解答读后,似感不妥.不揣冒昧,愿与原作者商榷.为方便计,现将原题及解答抄录如下:133.一轮半径为 R,重量为 P,在其铅垂直径的上端 B 点处作用水平力 Q.轮与水平面间的滚动摩阻系数为δ.问水平力 Q 使轮子只滚动而不滑动时,轮与水平面间的摩擦系数(?)需要满足什么条件?答133.轮子滚动的条件为 相似文献
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滚而不滑非静力学问题 总被引:3,自引:0,他引:3
黄克智;余寿文;程莉 《力学与实践》1989,11(2):76-63
本刊1987第2期上《小问题》栏133题的解答读后,似感不妥.不揣冒昧,愿与原作者商榷.为方便计,现将原题及解答抄录如下:133.一轮半径为 R,重量为 P,在其铅垂直径的上端 B 点处作用水平力 Q.轮与水平面间的滚动摩阻系数为δ.问水平力 Q 使轮子只滚动而不滑动时,轮与水平面间的摩擦系数(?)需要满足什么条件?答133.轮子滚动的条件为 ... 相似文献
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文献[1]研究了平面接触机构的两构件作无相对滑动的滚动的运动分析.本文则研究两构件在接触处有相对滑动时的加速度分析. 相似文献
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Finite-sized inertial spherical particles are fully-resolved with the immersed boundary projection method(IBPM) in the turbulent open-channel flow by direct numerical simulation(DNS). The accuracy of the particle surface force models is investigated in comparison with the total force obtained via the fully-resolved method. The results show that the steady-state resistance only performs well in the streamwise direction, while the fluid acceleration force, the added-mass force, and the shear-induced Saffman lift can effectively compensate for the large-amplitude and high-frequency characteristics of the particle surface forces, especially for the wall-normal and spanwise components. The modified steady-state resistance with the correction effects of the acceleration and the fluid shear can better represent the overall forces imposed on the particles, and it is a preferable choice of the surface force model in the Lagrangian point-particle method. 相似文献
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Shusaku Harada Yosuke KobayashiTakanori Sawano Emi Noguchi 《International Journal of Multiphase Flow》2011
For real-time measurement of the fluid force acting on a particle which moves freely in liquid, we have made a “sensor particle” with a built-in wireless sensor. The sensor particle contains a 3-axis acceleration sensor, 3-axis magnetometer, microcomputer, wireless module and cells. The MEMS acceleration sensor detects the gravitational acceleration in addition to the dynamic acceleration of particle. In order to remove the gravity from acceleration signals, we applied the external magnetic field which is oriented in the same direction as the gravity field. The 3-axis magnetometer detects the direction of external magnetic field and consequently we can remove gravitational acceleration from the sensor signals with arbitrary attitude of particle. A preliminary experiment was performed for checking the accuracy of the measurement system. Firstly we measured the force acting on a settling particle toward a solid wall in liquid. The obtained signals of acceleration (force divided by mass) agrees well with the theoretical prediction of particle motion in liquid for each instant of time. The sensor particle also detects the lubrication force which is exerted on particle for a very short time when it comes close to the wall. Moreover, we applied our system to the gravitational settling of the particle assemblage and detected the fluid force acting on a particle in multi-particle system. 相似文献
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Analysis of the flow in inhomogeneous particle beds using the spatially averaged two-fluid equations
The drag force term appearing in two-fluid models for fluid–particle flows is commonly closed by expressing it as a function of the local quantities, such as the local particle volume fraction, the local slip velocity between the particle and fluid phases, and the local mean-squared fluctuating velocity of the particles. The adequacy of such closures for inhomogeneous suspensions has been debated in the literature and some researchers have suggested the need for additional terms involving spatial gradients in these quantities. To test this proposition, simulations of flow in inhomogeneous steady beds of particles have been performed using the lattice-Boltzmann method. The particle beds consisted of disordered assemblies with a density profile on a scale much larger than the particle radius. Inhomogeneous beds with a controlled density profile were generated in three different ways, (i) by inhomogeneous stretching of the particle bed in one direction, (ii) by applying an inhomogeneous force to the particle phase during random motion of the particles, and (iii) by taking snapshots of a direct simulation of a traveling wave in a fluidization simulation. The global structure of the three beds was comparable, while assessment of the radial distribution functions showed that the three beds exhibited clearly different microscopic structures. 相似文献
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Basset力研究进展与应用分析 总被引:5,自引:0,他引:5
Basset力为两相流中颗粒与流体存在相对加速度时所产生的一种非恒定气动力 ,以往对其进行了大量的实验研究、理论分析和数值模拟。本文通过对Basset力研究文献的综述 ,分析并归纳了各种不同两相流动问题中该力的影响情况 ,得到的结论是 :对于气泡在液体内的流动问题 ,当气泡运动的脉动频率很大或很小时可以忽略Basset力对其运动的影响 ;对于固体或液体颗粒在气体中的运动问题可以忽略Basset力的影响 ;而其它两相流动问题则需要根据具体问题的特点来决定是否考虑Basset力的影响 ,其中需要考察 :流体与颗粒密度差别 ,颗粒尺寸 ,流动特征时间和颗粒运动弛豫时间 ,相对加速度 (或减速度 )等因素。本文还探讨了Basset力研究的发展方向。 相似文献
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Droplet motion/departure, which is governed by external force acceleration coefficient, droplet radius and surface wettability on solid surfaces under external forces such as gravitational force, play a significant role in characterizing condensation heat transfer, especially when high fractional non-condensable gases (NCG) present. However, due to the challenge in visualizing the vapor/steam velocity field imposed by droplet motion/departure, the detailed mechanism of droplet motion/departure on condensing surfaces has not been completely investigated experimentally. In this study, droplet motion/departures on solid surfaces under external forces and their interactions with steam flow are simulated using two dimensional (2D) multiphase lattice Boltzmann method (LBM). Large external force acceleration coefficient, droplet radius and contact angle, lead to large droplet deformation and high motion/departure velocity, which significantly shortens the droplet residual time on the solid surface. Our simulation shows that steam vortices (lateral velocity) induced by droplet motion/departure can greatly disturb the vapor flow and would be intensified by increasing external force acceleration coefficient, droplet radius, and contact angle. In addition, the location of vortex center shifts in the ascending direction with increase of these factors. The average lateral velocities induced by droplet motion/departure at various conditions are obtained. The mass transfer resistance is substantially reduced owing to the droplet motion/departure, leading to an enhanced heat flux. The experimental results are compared to validate the influence of droplet motion/departure on condensation heat transfer performance, especially for steam–air mixture with the presence of high fractional NCG. 相似文献
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In this paper, we compute the location of the imminent hinges and the minimum thickness, t, of a circular masonry arch with mid-thickness radius, R, and embracing angle, β, which can just sustain its own weight together with a given level of a horizontal ground acceleration, ε g. Motivated from the recent growing interest in identifying the limit equilibrium states of historic structures in earthquake prone areas, this paper shows that the value of the minimum horizontal acceleration that is needed to convert an arch with slenderness (t/R, β) into a four-hinge mechanism depends on the direction of the rupture at the imminent hinge locations. This result is obtained with a variational formulation and the application of the principle of stationary potential energy, and it is shown that a circular arch becomes a mechanism with vertical ruptures when subjected to a horizontal ground acceleration that is slightly lower than the horizontal acceleration needed to create a mechanism with radial ruptures. The paper explains that the multiplicity on the solution for the minimum uplift acceleration is a direct consequence of the multiple possible ways that a masonry arch with finite thickness may rupture at a given location. The paper further confirms that the results obtained with commercially available distinct element software are in very good agreement with the rigorous solution. 相似文献
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Fuel migration in a water flowing through a porous medium generally occurs parallel to porous strata, which may not be horizontal. In this case, gravity tends to cause vertical segregation of fluids, depending on their densities. This phenomenon can exert a strong effect on fuel migration. The gravitational force creates the buoyancy force which acts upon the fuel, and may be either parallel or anti-parallel to the water flow direction.In this study, the above effects are investigated using the one-dimensional model of Pistineret al. We go beyond the latter investigation in describing the influence of the gravitational forces upon the movement of fuel saturation fronts in a vertical porous layer against and along the water flow direction.It is found that when the directions of the buoyancy force and of the water flow are anti-parallel, fuel migrates in the direction of the buoyancy force, provided the latter is strong enough. However, in the case of a weak buoyancy force, the direction of migration of the fuel depends on its mass. Small fuel masses move mainly in the direction of the water flow. However, big fuel slugs possessing large masses will move mainly in the direction of the buoyancy force. Slugs, characterized by intermediate masses, have no preferable moving direction and are almost stagnant. 相似文献
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《Particuology》2022
The motion of a projectile impact onto a granular target results in both the resistance force exerted on the projectile and rheology of granular media. A horizontal arrangement of cylinder quasistatically and dynamically intruding into granular media under different velocities and angles is simulated using discrete element method. Three distinguished drag force regimes are exhibited, including hydrostatic-like force independent of velocity, viscous force related to velocity, and inertial drag force proportional to the square of velocity. Meanwhile, the influence of penetration angles on drag force is examined for these three regimes, and a force model, which is related to penetration depth and angle, is proposed for quasi-static penetration. Then, flow characteristics of the granular media, such as velocity field, pressure field, packing fraction etc., are traced, and a rheology model of packing fraction and inertial number is established. 相似文献