共查询到20条相似文献,搜索用时 156 毫秒
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介绍了用恒流法自制仪器精确测定液体的黏度.该自制仪器,能有效地保证底部的密封性、液体水位恒定和可操作性.另外,还增设一个玻璃管连通器,并附加一根标尺和游标,可使液体水位的测量精确度提高.在接毛细管输出液体的量筒处加上光电计时,可使测量液体的流速的精确度提高.再将相关数据送入已编好程序的电子仪器进行计算并显示出黏度.另外该仪器可调换不同管径的毛细管,因此应用本方法能快速准确地测量多种液体的黏度. 相似文献
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指向性指数在评价电声换能器,特别是在声呐应用中,一直是一个重要的参量。但因为它包含三维图案的积分,所以精确地计算和测量这个参数是困难的。因此,在理论上和测量中都广泛使用了近似方法。本文报道中运用的三种近似方法是:1.利用理论近似计算公式计算指向性指数;2.实测波束宽度再作理论近似计算;3.方向性图案测量和图表积分。用这三种方法分别测量和计算了四种换能器的指向性指数。 相似文献
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建立了二端面转轴相对转动系统的非线性动力学方程.对于等力矩的动力学方程进行了定性分析,得到了方程的稳定性等性质.用平均方法求得方程在一定条件下的近似解.
关键词:
非线性动力学方程
稳定性
极限环
近似解 相似文献
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An efficient and inexpensive method that uses a glass plate mounted onto a motorized rotating stage as a beam-steering device for the generation of dynamic optical traps is reported.Force analysis reveals that there are drag and trapping forces imposed on the bead in the opposite directions,respectively,in a viscous medium.The trapped bead will be rotated following the beam’s motion before it reaches the critical escape velocity when the drag force is equal to the optical trapping force.The equilibrium condition facilitates the experimental measurement of the drag force with potential extensions to the determination of the viscosity of the medium or the refractive index of the bead.The proposed technique can easily be integrated into conventional optical microscopic systems with minimum modifications. 相似文献
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STEN SARMAN 《Molecular physics》2013,111(1):27-35
The lack of a centre of inversion in a cholesteric liquid crystal allows linear cross-couplings between thermodynamic forces and fluxes that are polar vectors and pseudo vectors respectively. This makes it possible for a temperature gradient parallel to the cholesteric axis to induce a torque which rotates the director. This phenomenon is known as the Lehmann effect. The converse is also possible: one can drive a heat current by rotating the director. In this work a recently developed non-equilibrium molecular dynamics simulation algorithm is applied to calculate the cross-coupling coefficient between the temperature gradient and the torque for a molecular model system based on the Gay-Berne fluid. According to the Onsager reciprocity relations this cross-coupling coefficient is equal to the coupling between the director angular velocity and the heat current. The cross-coupling coefficients are found to be very small but non-zero and the Onsager reciprocity relations are satisfied within the statistical uncertainty. 相似文献
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A. Steyerl T. Ebisawa K. -A. Steinhauser M. Utsuro 《Zeitschrift für Physik B Condensed Matter》1981,40(4):283-286
The viscosity coefficient of flux motion in lead films was determined using high resolution magnetooptical flux detection combined with measurements of the flux-flow voltage. A comparison with theoretical models shows, that eddy-current damping is the dominant mechanism for the viscous drag force. The experimental results indicate, that frictional forces due to pinning centers can be neglected in our specimens. The viscosity coefficient was determined by a measurement of the number and the size of flux tubes and their velocities during the flux-flow process.Supported by a grant from the Deutsche Forschungsgemeinschaft 相似文献
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Korean river design standards set general design standards for rivers and river-related projects in Korea, which systematize the technologies and methods involved in river-related projects. This includes measurement methods for parts necessary for river design, but does not include information on shear stress. Shear stress is one of the factors necessary for river design and operation. Shear stress is one of the most important hydraulic factors used in the fields of water, especially for artificial channel design. Shear stress is calculated from the frictional force caused by viscosity and fluctuating fluid velocity. Current methods are based on past calculations, but factors such as boundary shear stress or energy gradient are difficult to actually measure or estimate. The point velocity throughout the entire cross-section is needed to calculate the velocity gradient. In other words, the current Korean river design standards use tractive force and critical tractive force instead of shear stress because it is more difficult to calculate the shear stress in the current method. However, it is difficult to calculate the exact value due to the limitations of the formula to obtain the river factor called the tractive force. In addition, tractive force has limitations that use an empirically identified base value for use in practice. This paper focuses on the modeling of shear-stress distribution in open channel turbulent flow using entropy theory. In addition, this study suggests a shear stress distribution formula, which can easily be used in practice after calculating the river-specific factor T. The tractive force and critical tractive force in the Korean river design standards should be modified by the shear stress obtained by the proposed shear stress distribution method. The present study therefore focuses on the modeling of shear stress distribution in an open channel turbulent flow using entropy theory. The shear stress distribution model is tested using a wide range of forty-two experimental runs collected from the literature. Then, an error analysis is performed to further evaluate the accuracy of the proposed model. The results reveal a correlation coefficient of approximately 0.95–0.99, indicating that the proposed method can estimate shear-stress distribution accurately. Based on this, the results of the distribution of shear stress after calculating the river-specific factors show a correlation coefficient of about 0.86 to 0.98, which suggests that the equation can be applied in practice. 相似文献
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In this Letter, the influence of the "Coriolis drift" on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torque on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiments. 相似文献
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J. Nissen S. Gritsch G. Wiegand J.O. Rädler 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):335-344
We report on the wetting behavior of phospholipid membranes on solid surfaces immersed in aqueous solution. Using fluorescence
microscopy, the spreading velocity of fluid bilayers advancing from a lipid source is investigated. The kinetic spreading
coefficient was measured as a function of temperature for pure DMPC membranes and as a function of charge density and cholesterol
content for binary membranes. A theoretical model for the membrane flow is presented, which takes into account the liquid
crystalline bilayer architecture of the lipid membrane. The spreading power results from the membrane-solid VdW interaction
and is dissipated in hydrodynamic shear flow as well as by inter-monolayer friction within the bilayer. The frictional drag
causes a dynamic tension gradient in the spreading membrane, which is manifested by a single exponential decay of the fluorescence
intensity profile along the spreading direction. Obstacles are shown to act as pinning centers deforming the advancing line
interface. However, no depinning was observed, since the centers are circumflown without abrupt relaxation.
Received 6 November 1998 相似文献
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一种新型垂直轴风力机的CFD分析 总被引:1,自引:0,他引:1
Savonius风力机由于作用在叶片的凸面上的"负阻力"和来流不稳定性导致效率低,该"负阻力"造成一个负转矩降低了输出功率,并且在某些来流角度下导致原装的Savonius风力机启动困难。本文提出一种采用控制叶片数目和叶片不同弯曲度的控制来提高风能的利用率,并用CFD方法模拟不同转子结构的内流特征,为消除"负阻力",提出一种采用导叶或挡风板的结构实现引流,并数值分析了该结构的流动特征。模拟结果显示,新结构的多叶片Savonius风力机的转矩和启动特性有明显改善,且功率系数也比普通的Savonius风力机高。 相似文献
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N. K. Tanasheva T. O. Kunakbaev A. N. Dyusembaeva N. N. Shuyushbayeva S. K. Damekova 《Technical Physics》2017,62(11):1631-1633
We have reported the results of experiments on determining the drag coefficient and the thrust coefficient of a two-bladed wind-powered engine based on the Magnus effect with rotating rough cylinders in the range of air flow velocity of 4–10 m/s (Re = 26800–90000) for a constant rotation number of a cylindrical blade about its own axis. The results show that an increase in the Reynolds number reduces the drag coefficient and the thrust coefficient. The extent of the influence of the relative roughness on the aerodynamic characteristics of the two-bladed wind-powered engine has been experimentally established. 相似文献