The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine,as one of the results of fluid and structure interactions in stirred vessels,was measured using a moment sensor equi...The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine,as one of the results of fluid and structure interactions in stirred vessels,was measured using a moment sensor equipped with digital telemetry.An analysis of the shaft bending moment amplitude shows that the amplitude distribution of the bending moment,which indicates the elasticity nature of shaft material against bending deformation,follows the Weibull distribution.The trends of amplitude mean,standard deviation and peak deviation characteristics manifest an "S" shape versus gas flow.The "S" trend of the relative mean bending moment over gas flow rate,depending on the flow regime in gas-liquid stirred vessels,resulted from the competition among the nonuniformity of bubbly flow around the impeller,the formation of gas cavities behind the blades,and the gas direct impact on the impeller when gas is introduced.A further analysis of the bending moment power spectral density shows that the rather low frequency and speed frequency are evident.The low-frequency contribution to bending moment fluctuation peaks in the complete dispersion regime.展开更多
Combined shear-compression tests and simulations were performed on a closed-cell aluminum foam over a wide range of loading angles in order to probe their yield behaviors under biaxial loading conditions.Combined shea...Combined shear-compression tests and simulations were performed on a closed-cell aluminum foam over a wide range of loading angles in order to probe their yield behaviors under biaxial loading conditions.Combined shear-compression tests were carried out by using a pair of cylindrical bars with beveled ends.The yield surfaces were experimentally measured and compared with various theoretical yield surface models.The cellular structures of closed-cell aluminum foams were modeled as tetrakaidecahedrons and their biaxial crushing behaviors were simulated by the finite element method.The results show that,yield initiates from the stress-concentrated corners in the specimens under combined shear-compression loading and the stress distribution is no longer uniform at the specimen/bar interfaces.In the range of cell sizes studied,the larger the foam cell size is,the higher the yield stress is.Aluminum foam density is found to be the dominant factor on its mechanical properties compared with the cell size and is much more significant in engineering practice.展开更多
The hydrodynamic behavior of multiple bubbles rising upward is a field of ongoing research since various aspects of their interaction require further analysis. Shape deformation, rise velocity, and drag coefficient ar...The hydrodynamic behavior of multiple bubbles rising upward is a field of ongoing research since various aspects of their interaction require further analysis. Shape deformation, rise velocity, and drag coefficient are some of the uncertainties to be determined in a bubble upward flow. For this study the predictions of the three-dimensional numerical simulations of the volume of fluid（VOF） CFD model were first compared with experimental results available in the literature, serving as benchmark cases. Next, 28 cases of pairs of equal and unequal-sized in-line pairs of bubbles moving upwards were simulated. The bubble size varied between 2.0–10 mm. Breakthrough of the present study is the small initial distance of 2.5 R between the center of the bubbles. To provide a more practical nature in this study material properties were selected to match methane gas and seawater properties at deepsea conditions of 15 MPa and 4 ℃, thus yielding a fluid-to-bubble density ratio λ = 7.45 and viscosity ratio n = 100.46. This is one of the few studies to report results of the coalescence procedure in this context. The hydrodynamic behavior of the leading and trailing bubbles was thoroughly studied. Simulation results of the evolution of the rise velocity and the shape deformation with time indicate that the assumption that the leading bubble is rising as a free rising single one is not valid for bubbles between 2.0–7.0 mm. Finally, results of the volume of the daughter bubble exhibited an oscillating nature.展开更多
Simulations of bubble entrainment into a stationary Gaussian vortex are performed by using the combined particle tracking method(PTM)and boundary element method(BEM).Before the bubble is captured by the vortex core,os...Simulations of bubble entrainment into a stationary Gaussian vortex are performed by using the combined particle tracking method(PTM)and boundary element method(BEM).Before the bubble is captured by the vortex core,oscillation and migration of the quasi-spherical nucleus are solved by using improved RP equation and the momentum theorem in the Lagrangian reference frame simultaneously,and the trajectory of the nucleus presents a kind of reduced helix shape.After captured by the vortex core,the bubble grows immediately and moves and deforms along the vortex core axis.The non-spherical evolution and deformation of the bubble is simulated by adopting a mixed Eulerian-Lagrangian method.The output of quasi-spherical stage is taken as the input of non-spherical stage,and all the behaviors of the entrained bubble can be simulated such as inception,motion,deformation and split.Numerical results agree well with published experimental data.On this basis,the influences of various factors such as viscosity,surface tension,buoyancy are studied systemically.Hopefully the results from this paper would provide some insight into the control on vortex bubble entrainment.展开更多
文摘The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine,as one of the results of fluid and structure interactions in stirred vessels,was measured using a moment sensor equipped with digital telemetry.An analysis of the shaft bending moment amplitude shows that the amplitude distribution of the bending moment,which indicates the elasticity nature of shaft material against bending deformation,follows the Weibull distribution.The trends of amplitude mean,standard deviation and peak deviation characteristics manifest an "S" shape versus gas flow.The "S" trend of the relative mean bending moment over gas flow rate,depending on the flow regime in gas-liquid stirred vessels,resulted from the competition among the nonuniformity of bubbly flow around the impeller,the formation of gas cavities behind the blades,and the gas direct impact on the impeller when gas is introduced.A further analysis of the bending moment power spectral density shows that the rather low frequency and speed frequency are evident.The low-frequency contribution to bending moment fluctuation peaks in the complete dispersion regime.
基金Project(2017JJ3359)supported by the Natural Science Foundation of Hunan Province,ChinaProject(KFJJ13-11M)supported by the Opening Project of State Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology),China.
文摘Combined shear-compression tests and simulations were performed on a closed-cell aluminum foam over a wide range of loading angles in order to probe their yield behaviors under biaxial loading conditions.Combined shear-compression tests were carried out by using a pair of cylindrical bars with beveled ends.The yield surfaces were experimentally measured and compared with various theoretical yield surface models.The cellular structures of closed-cell aluminum foams were modeled as tetrakaidecahedrons and their biaxial crushing behaviors were simulated by the finite element method.The results show that,yield initiates from the stress-concentrated corners in the specimens under combined shear-compression loading and the stress distribution is no longer uniform at the specimen/bar interfaces.In the range of cell sizes studied,the larger the foam cell size is,the higher the yield stress is.Aluminum foam density is found to be the dominant factor on its mechanical properties compared with the cell size and is much more significant in engineering practice.
文摘The hydrodynamic behavior of multiple bubbles rising upward is a field of ongoing research since various aspects of their interaction require further analysis. Shape deformation, rise velocity, and drag coefficient are some of the uncertainties to be determined in a bubble upward flow. For this study the predictions of the three-dimensional numerical simulations of the volume of fluid（VOF） CFD model were first compared with experimental results available in the literature, serving as benchmark cases. Next, 28 cases of pairs of equal and unequal-sized in-line pairs of bubbles moving upwards were simulated. The bubble size varied between 2.0–10 mm. Breakthrough of the present study is the small initial distance of 2.5 R between the center of the bubbles. To provide a more practical nature in this study material properties were selected to match methane gas and seawater properties at deepsea conditions of 15 MPa and 4 ℃, thus yielding a fluid-to-bubble density ratio λ = 7.45 and viscosity ratio n = 100.46. This is one of the few studies to report results of the coalescence procedure in this context. The hydrodynamic behavior of the leading and trailing bubbles was thoroughly studied. Simulation results of the evolution of the rise velocity and the shape deformation with time indicate that the assumption that the leading bubble is rising as a free rising single one is not valid for bubbles between 2.0–7.0 mm. Finally, results of the volume of the daughter bubble exhibited an oscillating nature.
基金supported by the Excellent Young Scientists Fund(Grant No.51222904)the national natural science foundation of China(Grant No.11302056)
文摘Simulations of bubble entrainment into a stationary Gaussian vortex are performed by using the combined particle tracking method(PTM)and boundary element method(BEM).Before the bubble is captured by the vortex core,oscillation and migration of the quasi-spherical nucleus are solved by using improved RP equation and the momentum theorem in the Lagrangian reference frame simultaneously,and the trajectory of the nucleus presents a kind of reduced helix shape.After captured by the vortex core,the bubble grows immediately and moves and deforms along the vortex core axis.The non-spherical evolution and deformation of the bubble is simulated by adopting a mixed Eulerian-Lagrangian method.The output of quasi-spherical stage is taken as the input of non-spherical stage,and all the behaviors of the entrained bubble can be simulated such as inception,motion,deformation and split.Numerical results agree well with published experimental data.On this basis,the influences of various factors such as viscosity,surface tension,buoyancy are studied systemically.Hopefully the results from this paper would provide some insight into the control on vortex bubble entrainment.
