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1.
The phenomena of natural convection caused by a concentration gradient usually creates currents as a result of buoyancy forces. These forces are formed from the combined effect of a fluid density gradient and the body force (gravitational force). The above phenomenon was studied experimentally in a circular glass column of 0.08 m diameter and 1 m length. This column was erected vertically and filled with distilled water with a salt bag placed on top of it and partially immersed in water. The dissolution mechanism was then modelled and a finite difference method was used to solve the formulated equations by using the implicit scheme of MacCormack (Anderson et al., 1984). The experimental results and the numerical predictions are represented graphically and give compatible agreement. 相似文献
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从分析某高架桥中异形板板底裂缝的特点及成因着手 ,对设计与施工工艺诸方面提出防止裂缝的对策和对裂缝进行加固的全过程。 相似文献
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Kenichi Asakawa Kensuke Watari Hidetoshi Ohuchi Masahiko Nakamura Tadahiro Hyakudome Yasuhisa Ishihara 《Advanced Robotics》2016,30(1):41-49
A buoyancy engine with a swashplate-type axial piston pump was developed. Its oil extrusion and drawing properties under high hydraulic pressure were evaluated. This buoyancy engine is now installed in an underwater glider that will achieve long-term monitoring of ocean environments up to 2100 m depth in a designated area with lower operational costs. This bidirectionally functioning pump can control the amount of oil in extrusion and draw operations. When drawing oil under high pressure, the hydraulic pump and the electric motor, respectively, act as a hydraulic motor and an electric generator. The generated electric power is absorbed by a damping resistor. The oil-drawing and extrusion properties were measured using a large hyperbaric chamber that is able to produce an almost identical environment to that of actual operations. Results confirmed stable oil extrusion operations up to 21 MPa. Regarding oil-drawing properties, although it was measured only up to 10 MPa in the hyperbaric chamber, it can be inferred that the system can draw the oil and can control the buoyancy precisely up to 21 MPa by replacing the two-way ball valve with an electromagnetic latching solenoid valve. 相似文献
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在空间微重力环境的地面模拟技术中,中性浮力法利用水的浮力使实验体处于漂浮状态,可以提供六自由度运动模拟,并且可进行长时间的与空间十分相似的自由运动。因此可以采用该方法实现空间飞行器空间任务的地面模拟演示和功能验证。姿态控制作为空间任务的基本操作之一,其在中性浮力实验环境下的控制模拟非常重要,需要针对复杂的水下环境进行设计。目前针对水下航行器的研究非常广泛,但是专门针对中性浮力环境下空间任务模拟的研究并不多,缺少理论验证与仿真。本文针对中性浮力环境下实验体姿态机动模拟控制律设计问题进行研究。首先根据流体力学和动量矩定理推导出实验体的姿态动力学方程,根据四元数与角速度的关系得到实验体的姿态运动学方程;然后在理想状态下基于动力学方程,使用Lyapunov方法设计实验体的姿态机动模拟控制律,并证明了闭环系统的渐进稳定性;最后通过仿真验证了控制算法的性能,为中性浮力环境下实验体姿态机动模拟提供理论基础。 相似文献
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运用CLSVOF方法数值模拟了三维单气泡在液体中的上升和变形过程,分别考察了液体的表面张力和浮力对上升气泡变形的影响。计算结果表明:CLSVOF方法能比较精确地跟踪三维单气泡在液体中的上升过程;在相同密度比和粘度比情况下,随着液体表面张力的减小和液体浮力的增大,气泡底部形成的射流使得气泡下缘凹陷变得明显,变形幅度加大,射流穿透气泡的时间提前。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(5):330-341
We describe the numerical simulation results of bubble motion under gravity by the lattice Boltzmann method(LBM), which assumes that a fluid consists of mesoscopic fluid particles repeating collision and translation and a multiphase interface is reproduced in a self-organizing way by repulsive interaction between different kinds of particles. The purposes in this study are to examine the applicability of LBM to the numerical analysis of bubble motions, and to develop a three-dimensional version of the binary fluid model that introduces a free energy function. We included the buoyancy terms due to the density difference in the lattice Boltzmann equations, and simulated single- and two-bubble motions, setting flow conditions according to the Eötvös and Morton numbers. The two-dimensional results by LBM agree with those by the Volume of Fluid method based on the Navier-Stokes equations. The three-dimensional model possesses the surface tension satisfying the Laplace's law, and reproduces the motion of single bubble and the two- bubble interaction of their approach and coalescence in circular tube. These results prove that the buoyancy terms and the 3D model proposed here are suitable, and that LBM is useful for the numerical analysis of bubble motion under gravity. 相似文献
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