In multiphase pumps transporting gas-liquid two-phase flows,the high-speed rotation of the impeller induces complex deformations in bubble shapes within the flow domain,making the prediction of gasliquid two-phase dra...In multiphase pumps transporting gas-liquid two-phase flows,the high-speed rotation of the impeller induces complex deformations in bubble shapes within the flow domain,making the prediction of gasliquid two-phase drag forces highly challenging in numerical simulations.To achieve precise prediction of the drag forces on irregular bubbles within multiphase pumps,this study modifies the existing bubble drag force model and applies the revised model to the prediction of gas-liquid two-phase flow within multiphase pumps.The research findings indicate that the modified drag force model significantly enhances the accuracy of predicting flow characteristics within the pump,particularly under high gas volume fraction conditions.The simulation results for gas phase distribution and vorticity exhibit strong agreement with experimental data.The modified drag model better captures the accumulation of the gas phase at the suction side of the impeller outlet.It also accurately predicts the vortex characteristics induced by bubble backflow from the trailing edges of the diffuser.Additionally,the adjustment of the drag coefficient enhances the model’s ability to represent local flow field characteristics,thereby optimizing the performance simulation methods of multiphase pumps.Compared to traditional drag force models,the modified model reduces prediction errors in head and efficiency by 36.4%and 27.5%,respectively.These results provide important theoretical foundations and model support for improving the accuracy of gas-liquid two-phase flow simulations and optimizing the design of multiphase pumps under high gas volume fraction conditions.展开更多
This paper presents the results of a numerical investigation of micro-sized particle removal by droplet impact. Computational fluid dynamics simulation is used to calculate the flow distribution of droplet impact on a...This paper presents the results of a numerical investigation of micro-sized particle removal by droplet impact. Computational fluid dynamics simulation is used to calculate the flow distribution of droplet impact on a flat surface. The hydrodynamic forces exerted on the particle are then computed. Key factors controlling particle removal are discussed. Both hydrophilic and hydrophobic surfaces are considered. The flow distributions,especially the front edge expanding upon impact at microscale,strongly depend on surface wettability. The associated hydrodynamic forces on the particles vary accordingly. In addition, the impact on a dry surface can produce higher removal efficiency than that on a wet surface. Under the same impact conditions, the drag force exerted on a particle residing on a dry surface can be three orders of magnitudes larger than on a wet surface. Improving droplet impact velocity is more effective than improving droplet size.展开更多
The fixed-gas drag force from a model calculation method that stabilizes the agitation capabilities of different gas ratios was used to explore the influence of temperature and hydrogen concentration on fluidizing dur...The fixed-gas drag force from a model calculation method that stabilizes the agitation capabilities of different gas ratios was used to explore the influence of temperature and hydrogen concentration on fluidizing duration, metallization ratio, utilization rate of reduction gas, and sticking behavior. Different hydrogen concentrations from 5vol%to 100vol%at 1073 and 1273 K were used while the drag force with the flow of N2 and H2 （N2：2 L·min^-1;H2：2 L·min^-1） at 1073 K was chosen as the standard drag force. The metallization ratio, mean reduc-tion rate, and utilization rate of reduction gas were observed to generally increase with increasing hydrogen concentration. Faster reduction rates and higher metallization ratios were obtained when the reduction temperature decreased from 1273 to 1073 K. A numerical relation among particle diameter, particle drag force, and fluidization state was plotted in a diagram by this model.展开更多
In the present paper, based on the two-phase model (Eulerian model), the two dimensional fluid flow liz air-stirred water systems is simulated, and the effect of interphase lift force on the fluid flow is specially d...In the present paper, based on the two-phase model (Eulerian model), the two dimensional fluid flow liz air-stirred water systems is simulated, and the effect of interphase lift force on the fluid flow is specially discussed. In the Eulerian two-phase model, gas and liquid phase are considered to be two different continuous fluids interacting with each other through the finite inter-phase areas. The exchange between the phases is represented by source terms in conversation equations. Turbulence is assumed to be a property of the liquid phase, k - ε model is used to describe the behavior of the liquid phase. The dispersion of phases due to turbulence is represented by introducing a diffusion term in mass consecrvation equation. The contribution of bubble movement to the turbulent energy and its dissipation rate is taken into accounted by adding extra volumetric source terms to the equations of turbulent enemy and its dissipation rate. The comparison between the mathematical simulation and experiment data indicates that the interphase lift force has a big effect on the flow behavior, and considering both drug force and lift force as interphase forces is important to accurately simulate the gas-water two-phase fluid flow in air-stirred systems. The interphase lift force makes bubbles move away from the centerline, the gas concentration is decreased near the centerline, and increased near the wall. The lift force is smaller than drug force at the same place, especially far away from the centerline.展开更多
Micromotors are widely used in cell operation,drug delivery and environmental decontamination due to their small size,low energy consumption and large propelling power.Compared to traditional Janus micromotor,the shel...Micromotors are widely used in cell operation,drug delivery and environmental decontamination due to their small size,low energy consumption and large propelling power.Compared to traditional Janus micromotor,the shell Janusmicromotor has better motion performance.However,the structural optimization of itsmotion performance is still unclear.The main factor restricting the motion performance of shell Janus micromotors is the drag forces.In the current work,theoretical analysis and numerical simulation were applied to analyze the drag forces of shell Janus micromotors.This study aims to design the optimum structure of shell Janus micromotors with minimum drag forces and obtain the magnitude of drag forces considering both the internal and external fluids of the shell Janus micromotors.Moreover,the influence of the motor geometry and Reynolds number on the drag coefficient was analyzed using numerical simulations.The results provide guidance for the optimum flow velocity,opening diameter and shell thickness to achieve minimum drag force.展开更多
The occurrence of blockages of trash intercepting net in nuclear power plant due to marine biofouling has become increasingly frequent,leading to significant changes in the mechanical state.This paper establishes a CF...The occurrence of blockages of trash intercepting net in nuclear power plant due to marine biofouling has become increasingly frequent,leading to significant changes in the mechanical state.This paper establishes a CFD(Computational Fluid Dynamics)model to simulate the hydrodynamic forces of trash intercepting net under the action of regular waves.The porous media model is used to calculate the hydrodynamic forces,and the maximum mooring load is also evaluated.The simplified calculation method considering the different curved shape based on the flat nets are proposed,and the influences of wave parameters,solidity,and curved shape are investigated.The results indicate that under the regular wave conditions,as the solidity increases,the phenomenon of secondary wave peaks becomes more pronounced.The horizontal wave force reduction coefficient follows a three-piecewise linear relationship with the non-dimensional deformation level of curved shape.The trash intercepting net exhibits more potent scattering effects on short-wave conditions,displaying significant non-linear characteristics.The deformation level of the trash intercepting net is a significant factor influencing the mooring load.展开更多
A control scheme named the variable-lateral-force cavitator, which is focused on the control of lift force, drag force and lateral forces for underwater supercavity vehicles was proposed, and the supercavitating flow ...A control scheme named the variable-lateral-force cavitator, which is focused on the control of lift force, drag force and lateral forces for underwater supercavity vehicles was proposed, and the supercavitating flow around the cavitator was investigated numerically using the mixture multiphase flow model. It is verified that the forces of pitching, yawing, drag and lift, as well as the supercavity size of the underwater vehicle can be effectively regulated through the movements of the control element of the variable-lateral-force cavitator in the radial and circumferential directions. In addition, if the control element on either side protrudes to a height of 5% of the diameter of the front cavitator, an amount of forces of pitching and yawing equivalent to 30% of the drag force will be produced, and the supercavity section appears concave inwards simultaneously. It is also found that both the drag force and lift force of the variable-lateral-force cavitator decline as the angle of attack increases.展开更多
Response spectra of fixed offshore structures impacted by extreme waves are investigated based on the higher order components of the nonlinear drag force. In this way, steel jacket platforms are simplified as a mass a...Response spectra of fixed offshore structures impacted by extreme waves are investigated based on the higher order components of the nonlinear drag force. In this way, steel jacket platforms are simplified as a mass attached to a light cantilever cylinder and their corresponding deformation response spectra are estimated by utilizing a generalized single degree of freedom system. Based on the wave data recorded in the Persian Gulf region, extreme wave loading conditions corresponding to different return periods are exerted on the offshore structures. Accordingly, the effect of the higher order components of the drag force is considered and compared to the linearized state for different sea surface levels. When the fundamental period of the offshore structure is about one third of the main period of wave loading, the results indicate the linearized drag term is not capable of achieving a reliable deformation response spectrum.展开更多
The spectral properties of nonlinear drag forces of random waves on vertical circular cylinders are analyzed in this paper by means of nonlinear spectral analysis. The analysis provides basic parameters for estimation...The spectral properties of nonlinear drag forces of random waves on vertical circular cylinders are analyzed in this paper by means of nonlinear spectral analysis. The analysis provides basic parameters for estimation of the characteristic drag forces. Numerical computation is also performed for the investigation of the effects of nonlinearity of the drag forces. The results indicate that the wave drag forces calculated by linear wave theory are larger than those calculated by the third order Stokes wave theory for given waves. The difference between them increases with wave height. The wave drag forces calculated by use of linear approximation are about 5% smaller than their actual values when measured in the peak values of spectral densities. This will result in a safety problem for the design of offshore structures. Therefore, the nonlinear effect of wave drag forces should be taken into consideration in design and application of important offshore structures.展开更多
We introduce a corrected sinusoidal-wave drag force method （SDFM） into optical tweezers to calibrate the trapping stiffness of the optical trap and conversion factor （CF） of photodetectors. First, the theoretical ...We introduce a corrected sinusoidal-wave drag force method （SDFM） into optical tweezers to calibrate the trapping stiffness of the optical trap and conversion factor （CF） of photodetectors. First, the theoretical analysis and experimental result demonstrate that the correction of SDFM is necessary, especially the error of no correction is up to 11.25% for a bead of 5μm in diameter. Second, the simulation results demonstrate that the SDFM has a better performance in the calibration of optical tweezers than the triangular-wave drag force method （TDFM） and power spectrum density method （PSDM） at the same signal-to-noise ratio or trapping stiffness. Third, in experiments, the experimental standard deviations of calibration of trapping stiffness and CF with the SDFM are about less than 50% of TDFM and PSDM especially at low laser power. Finally, the experiments of stretching DNA verify that the in situ calibration with the SDFM improves the measurement stability and accuracy.展开更多
To study drag force on a moving heavy quark through a plasma,we use a deformed AdS spacetime,in which deformation parameter c describes non-conformality in AdS/QCD.In this case,the quark is mapped to a probe string in...To study drag force on a moving heavy quark through a plasma,we use a deformed AdS spacetime,in which deformation parameter c describes non-conformality in AdS/QCD.In this case,the quark is mapped to a probe string in the AdS space.Considering the probable contribution of the deformation parameter in the probe string,we apply a general form of c-dependent string ansatz in the drag force computation.Then,we find the acceptable value of this parameter as it satisfies QCD calculations.Using this result,we also discuss the diffusion constant which is in agreement with the phenomenological result for the non-relativistic limit.Also,we show that while in absence of a deformation parameter,the probe string is a strictly increasing function of radial coordinate,the c-dependent probe string has a maximum value versus z.展开更多
A formulation of the skin-friction drag related to the Reynolds shear stress in a turbulent channel flow is derived. A direct numerical simulation （DNS） of the turbulent control is performed by imposing the spatiall...A formulation of the skin-friction drag related to the Reynolds shear stress in a turbulent channel flow is derived. A direct numerical simulation （DNS） of the turbulent control is performed by imposing the spatially oscillating spanwise Lorentz force. Under the action of the Lorentz force with several proper control parameters, only the periodi- cally well-organized streamwise vortices are finally observed in the near-wall region. The Reynolds shear stress decreases dramatically, especially in the near-wall area, resulting in a drag reduction.展开更多
Cylindrical cross sections are critical components in offshore structures, including jacket platform legs, pipelines, mooring lines, and risers. Thesecylindrical structures are subjected to vortex-induced vibrations (...Cylindrical cross sections are critical components in offshore structures, including jacket platform legs, pipelines, mooring lines, and risers. Thesecylindrical structures are subjected to vortex-induced vibrations (VIV) due to strong ocean currents, where vortices generated during fluid flowresult in significant vibrations in crossflow and in-flow directions. Such vibrations can lead to severe damage to platforms, cables, and risersystems. Consequently, mitigating VIV caused by vortex-induced forces is important. This study investigates the hydrodynamic performance offive strake models relative to a bare cylinder at moderate Reynolds numbers. The models encompass one conventional continuous helical strake(HS) and four helical discrete strake (HDS) with varying segment spacing between the fins. The hydrodynamic performance, specifically liftand drag force coefficients, was computed using a Reynolds averaged Navier –Stokes-based CFD solver and validated with experimentalmeasurements. The conventional HS suppresses 95% of the lift force but increases the drag force by up to a maximum of 48% in measurements.The HDS suppress the lift force by 70%–88% and increase the drag force by 15%–30%, which is less than the increase observed with the HS.Flow visualization showed that HS and HDS cylinders mitigate vortex-induced forces by altering the vortex-shedding pattern along the length ofthe cylinder. The HDS achieves a reduction in drag compared with the conventional continuous HS. The segment spacing is found to significantlyimpact the reduction in vortex-induced forces.展开更多
Drag force is a key parameter in the numerical modeling of gas-particle flow in circulating fluidized beds. The reliability of current drag force correlations over the regime of fast fluidization has, however, not bee...Drag force is a key parameter in the numerical modeling of gas-particle flow in circulating fluidized beds. The reliability of current drag force correlations over the regime of fast fluidization has, however, not been thoroughly investigated. In this article, a drag force correlation accounting for the clustering effects for Geldart A particles is used to simulate the behaviors typical of fast fluidization, including dynamic evolution of clusters as well as time- averaged axial and lateral voidage profiles. Diverse images of clusters are captured and the time-averaged profiles of voidage are shown to be in quantitative agreement with the present empirical correlation. The results based on different constitutive correlations of drag force show the importance of the choice of drag force in modeling fast-fluidized beds. This drag force correlation, based on a simple averaging assumption, could give some basic insights about the magnitude of the drag reduction.展开更多
This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vege...This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vegetation are considered as the drag force item. The secondary currents are also taken into account in the governing equations, and the preliminary estimation of the secondary current intensity coefficient K is discussed. The predicted results for the straight channels and the apex cross-section of meandering channels agree well with experimental data, which shows that the analytical model presented here can be applied to predict the flow in compound channels with vegetated floodplains.展开更多
The variations of drag force acting on the windbreak and the bulk drag coefficients for different windbreak widths were studied experimentally in the Eiffel-type non-circulating wind tunnel at the Hydraulic Engineerin...The variations of drag force acting on the windbreak and the bulk drag coefficients for different windbreak widths were studied experimentally in the Eiffel-type non-circulating wind tunnel at the Hydraulic Engineering Laboratory, Saitama University, Japan, to elucidate the effects of windbreak width in the wind direction on wind velocity reduction behind a windbreak. The variations of flow field for different windbreak widths were studied numerically by using the two-dimensional Reynolds-averaged Navier-Stokes （RANS） equation with a k-c turbulence closure model. Results show that the total drag force to wind increased with increasing windbreak width, but the bulk drag coefficient decreased slightly. The relationship between the bulk drag coefficient Cd and the windbreak width W and height H can be presented by the equation of Ca= kd （W/H）^-b （kd, b： constants）. The result of the numerical simulation shows that the windbreak width greatly affects the location and the value of the minimum wind velocity. The wind velocity decreased by 15%-22% as the windbreak width increased.展开更多
The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the un...The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the unit volume where the effect of the vegetation on the flow is considered as a drag force item, The compound channel is divided into 3 sub-regions in the transverse direction, and the coefficients in every region＇s differential equations were solved simultaneously. Thus, the analytical solution of the transverse distribution of the depth-averaged velocity for uniform flow in a partially vegetated compound channel was obtained. The results can be used to predict the transverse distribution of bed shear stress, which has an important effect on the transportation of sediment. By comparing the analytical results with the measured data, the analytical solution in this paper is shown to be sufficiently accurate to predict most hydraulic features for engineering design purposes.展开更多
The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream c...The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream control cylinder （d） varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder （G） ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio （G/D） and the diameter ratio between the two cylinders （d/D） have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.展开更多
An analytical solution for predicting the vertical distribution of streamwise mean velocity in an open channel flow with submerged flexible vegetation is proposed when large bending occurs. The flow regime is separate...An analytical solution for predicting the vertical distribution of streamwise mean velocity in an open channel flow with submerged flexible vegetation is proposed when large bending occurs. The flow regime is separated into two horizontal layers： a vegetation layer and a free water layer. In the vegetation layer, a mechanical analysis for the flexible vegetation is conducted, and an approximately linear relationship between the drag force of bending vegetation and the streamwise mean flow velocity is observed in the case of large deflection, which differes significantly from the case of rigid upright vegetation. Based on the theoretical analysis, a linear streamwise drag force-mean flow velocity expression in the momentum equation is derived, and an analytical solution is obtained. For the free water layer, a new expression is presented, replacing the traditional logarithmic velocity distribution, to obtain a zero velocity gradient at the water surface. Finally, the analytical predictions are compared with published experimental data, and the good agreement demonstrates that this model is effective for the open channel flow through the large deflection flexible vegetation.展开更多
The dynamic response of offshore platforms is more serious in hostile sea environment than in shallow sea. In this paper, a hybrid solution combined with analytical and numerical method is proposed to compute the stoc...The dynamic response of offshore platforms is more serious in hostile sea environment than in shallow sea. In this paper, a hybrid solution combined with analytical and numerical method is proposed to compute the stochastic response of fixed offshore platforms to random waves, considering wave-structure interaction and non-linear drag force. The simulation program includes two steps: the first step is the eigenanalysis aspects associated the structure and the second step is response estimation based on spectral equations. The eigenanalysis could be done through conventional finite element method conveniently and its natural frequency and mode shapes obtained. In the second part of the process, the solution of the offshore structural response is obtained by iteration of a series of coupled spectral equations. Considering the third-order term in the drag force, the evaluation of the three-fold convolution should be demanded for nonlinear stochastic response analysis. To demonstrate this method, a numerical analysis is carried out for both linear and non-linear platform motions. The final response spectra have the typical two peaks in agreement with reality, indicating that the hybrid method is effective and can be applied to offshore engineering.展开更多
基金funded by Sichuan Natural Science Foundation Outstanding Youth Science Foundation(No.2024NSFJQ0012)Key project of Regional Innovation and Development Joint Fund of National Natural Science Foundation(No.U23A20669)Sichuan Science and Technology Program(2022ZDZX0041).
文摘In multiphase pumps transporting gas-liquid two-phase flows,the high-speed rotation of the impeller induces complex deformations in bubble shapes within the flow domain,making the prediction of gasliquid two-phase drag forces highly challenging in numerical simulations.To achieve precise prediction of the drag forces on irregular bubbles within multiphase pumps,this study modifies the existing bubble drag force model and applies the revised model to the prediction of gas-liquid two-phase flow within multiphase pumps.The research findings indicate that the modified drag force model significantly enhances the accuracy of predicting flow characteristics within the pump,particularly under high gas volume fraction conditions.The simulation results for gas phase distribution and vorticity exhibit strong agreement with experimental data.The modified drag model better captures the accumulation of the gas phase at the suction side of the impeller outlet.It also accurately predicts the vortex characteristics induced by bubble backflow from the trailing edges of the diffuser.Additionally,the adjustment of the drag coefficient enhances the model’s ability to represent local flow field characteristics,thereby optimizing the performance simulation methods of multiphase pumps.Compared to traditional drag force models,the modified model reduces prediction errors in head and efficiency by 36.4%and 27.5%,respectively.These results provide important theoretical foundations and model support for improving the accuracy of gas-liquid two-phase flow simulations and optimizing the design of multiphase pumps under high gas volume fraction conditions.
文摘This paper presents the results of a numerical investigation of micro-sized particle removal by droplet impact. Computational fluid dynamics simulation is used to calculate the flow distribution of droplet impact on a flat surface. The hydrodynamic forces exerted on the particle are then computed. Key factors controlling particle removal are discussed. Both hydrophilic and hydrophobic surfaces are considered. The flow distributions,especially the front edge expanding upon impact at microscale,strongly depend on surface wettability. The associated hydrodynamic forces on the particles vary accordingly. In addition, the impact on a dry surface can produce higher removal efficiency than that on a wet surface. Under the same impact conditions, the drag force exerted on a particle residing on a dry surface can be three orders of magnitudes larger than on a wet surface. Improving droplet impact velocity is more effective than improving droplet size.
基金supported by the National Natural Science Foundation of China(No.51234001)the Major State Basic Research Development Program of China(No.2012CB720401)
文摘The fixed-gas drag force from a model calculation method that stabilizes the agitation capabilities of different gas ratios was used to explore the influence of temperature and hydrogen concentration on fluidizing duration, metallization ratio, utilization rate of reduction gas, and sticking behavior. Different hydrogen concentrations from 5vol%to 100vol%at 1073 and 1273 K were used while the drag force with the flow of N2 and H2 （N2：2 L·min^-1;H2：2 L·min^-1） at 1073 K was chosen as the standard drag force. The metallization ratio, mean reduc-tion rate, and utilization rate of reduction gas were observed to generally increase with increasing hydrogen concentration. Faster reduction rates and higher metallization ratios were obtained when the reduction temperature decreased from 1273 to 1073 K. A numerical relation among particle diameter, particle drag force, and fluidization state was plotted in a diagram by this model.
文摘In the present paper, based on the two-phase model (Eulerian model), the two dimensional fluid flow liz air-stirred water systems is simulated, and the effect of interphase lift force on the fluid flow is specially discussed. In the Eulerian two-phase model, gas and liquid phase are considered to be two different continuous fluids interacting with each other through the finite inter-phase areas. The exchange between the phases is represented by source terms in conversation equations. Turbulence is assumed to be a property of the liquid phase, k - ε model is used to describe the behavior of the liquid phase. The dispersion of phases due to turbulence is represented by introducing a diffusion term in mass consecrvation equation. The contribution of bubble movement to the turbulent energy and its dissipation rate is taken into accounted by adding extra volumetric source terms to the equations of turbulent enemy and its dissipation rate. The comparison between the mathematical simulation and experiment data indicates that the interphase lift force has a big effect on the flow behavior, and considering both drug force and lift force as interphase forces is important to accurately simulate the gas-water two-phase fluid flow in air-stirred systems. The interphase lift force makes bubbles move away from the centerline, the gas concentration is decreased near the centerline, and increased near the wall. The lift force is smaller than drug force at the same place, especially far away from the centerline.
基金the Fundamental Research Funds for the Central Universities(WUT:2019III075GX)the Open Foundation of Hubei Key Laboratory of Theory and Application of Advanced Materials Mechanics(Grant No.TAM201813).
文摘Micromotors are widely used in cell operation,drug delivery and environmental decontamination due to their small size,low energy consumption and large propelling power.Compared to traditional Janus micromotor,the shell Janusmicromotor has better motion performance.However,the structural optimization of itsmotion performance is still unclear.The main factor restricting the motion performance of shell Janus micromotors is the drag forces.In the current work,theoretical analysis and numerical simulation were applied to analyze the drag forces of shell Janus micromotors.This study aims to design the optimum structure of shell Janus micromotors with minimum drag forces and obtain the magnitude of drag forces considering both the internal and external fluids of the shell Janus micromotors.Moreover,the influence of the motor geometry and Reynolds number on the drag coefficient was analyzed using numerical simulations.The results provide guidance for the optimum flow velocity,opening diameter and shell thickness to achieve minimum drag force.
基金financially supported by National Natural Science Foundation of China(Grant No.52201311)Fundamental Research Funds for the Central Universities.
文摘The occurrence of blockages of trash intercepting net in nuclear power plant due to marine biofouling has become increasingly frequent,leading to significant changes in the mechanical state.This paper establishes a CFD(Computational Fluid Dynamics)model to simulate the hydrodynamic forces of trash intercepting net under the action of regular waves.The porous media model is used to calculate the hydrodynamic forces,and the maximum mooring load is also evaluated.The simplified calculation method considering the different curved shape based on the flat nets are proposed,and the influences of wave parameters,solidity,and curved shape are investigated.The results indicate that under the regular wave conditions,as the solidity increases,the phenomenon of secondary wave peaks becomes more pronounced.The horizontal wave force reduction coefficient follows a three-piecewise linear relationship with the non-dimensional deformation level of curved shape.The trash intercepting net exhibits more potent scattering effects on short-wave conditions,displaying significant non-linear characteristics.The deformation level of the trash intercepting net is a significant factor influencing the mooring load.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51379108 and 51609125)the Open Foundation of Engineering Research Center of Eco-environment in Three Gorges Reservoir Region,Ministry of Education(Grant No.2015KF-03)the University Scientific Research and Application Project of Yichang(Grant No.A16-302-a13)
文摘A control scheme named the variable-lateral-force cavitator, which is focused on the control of lift force, drag force and lateral forces for underwater supercavity vehicles was proposed, and the supercavitating flow around the cavitator was investigated numerically using the mixture multiphase flow model. It is verified that the forces of pitching, yawing, drag and lift, as well as the supercavity size of the underwater vehicle can be effectively regulated through the movements of the control element of the variable-lateral-force cavitator in the radial and circumferential directions. In addition, if the control element on either side protrudes to a height of 5% of the diameter of the front cavitator, an amount of forces of pitching and yawing equivalent to 30% of the drag force will be produced, and the supercavity section appears concave inwards simultaneously. It is also found that both the drag force and lift force of the variable-lateral-force cavitator decline as the angle of attack increases.
文摘Response spectra of fixed offshore structures impacted by extreme waves are investigated based on the higher order components of the nonlinear drag force. In this way, steel jacket platforms are simplified as a mass attached to a light cantilever cylinder and their corresponding deformation response spectra are estimated by utilizing a generalized single degree of freedom system. Based on the wave data recorded in the Persian Gulf region, extreme wave loading conditions corresponding to different return periods are exerted on the offshore structures. Accordingly, the effect of the higher order components of the drag force is considered and compared to the linearized state for different sea surface levels. When the fundamental period of the offshore structure is about one third of the main period of wave loading, the results indicate the linearized drag term is not capable of achieving a reliable deformation response spectrum.
文摘The spectral properties of nonlinear drag forces of random waves on vertical circular cylinders are analyzed in this paper by means of nonlinear spectral analysis. The analysis provides basic parameters for estimation of the characteristic drag forces. Numerical computation is also performed for the investigation of the effects of nonlinearity of the drag forces. The results indicate that the wave drag forces calculated by linear wave theory are larger than those calculated by the third order Stokes wave theory for given waves. The difference between them increases with wave height. The wave drag forces calculated by use of linear approximation are about 5% smaller than their actual values when measured in the peak values of spectral densities. This will result in a safety problem for the design of offshore structures. Therefore, the nonlinear effect of wave drag forces should be taken into consideration in design and application of important offshore structures.
基金supported by the National Natural Science Foundation of China(Grant Nos.11302220,11374292,and 31100555)the National Basic Research Program of China(Grant No.2011CB910402)
文摘We introduce a corrected sinusoidal-wave drag force method （SDFM） into optical tweezers to calibrate the trapping stiffness of the optical trap and conversion factor （CF） of photodetectors. First, the theoretical analysis and experimental result demonstrate that the correction of SDFM is necessary, especially the error of no correction is up to 11.25% for a bead of 5μm in diameter. Second, the simulation results demonstrate that the SDFM has a better performance in the calibration of optical tweezers than the triangular-wave drag force method （TDFM） and power spectrum density method （PSDM） at the same signal-to-noise ratio or trapping stiffness. Third, in experiments, the experimental standard deviations of calibration of trapping stiffness and CF with the SDFM are about less than 50% of TDFM and PSDM especially at low laser power. Finally, the experiments of stretching DNA verify that the in situ calibration with the SDFM improves the measurement stability and accuracy.
基金supported by Strategic Priority Research Program of Chinese Academy of Sciences(XDB34030301)supported by the PIFI(2021PM0065)。
文摘To study drag force on a moving heavy quark through a plasma,we use a deformed AdS spacetime,in which deformation parameter c describes non-conformality in AdS/QCD.In this case,the quark is mapped to a probe string in the AdS space.Considering the probable contribution of the deformation parameter in the probe string,we apply a general form of c-dependent string ansatz in the drag force computation.Then,we find the acceptable value of this parameter as it satisfies QCD calculations.Using this result,we also discuss the diffusion constant which is in agreement with the phenomenological result for the non-relativistic limit.Also,we show that while in absence of a deformation parameter,the probe string is a strictly increasing function of radial coordinate,the c-dependent probe string has a maximum value versus z.
基金Supported by the National Natural Science Foundation of China(Nos.11172140 and 11372356)the Open Project of State Key Laboratory of Explosion Science and Technology in Beijing Institute of Technology(No.KFJJ13-3M)
文摘A formulation of the skin-friction drag related to the Reynolds shear stress in a turbulent channel flow is derived. A direct numerical simulation （DNS） of the turbulent control is performed by imposing the spatially oscillating spanwise Lorentz force. Under the action of the Lorentz force with several proper control parameters, only the periodi- cally well-organized streamwise vortices are finally observed in the near-wall region. The Reynolds shear stress decreases dramatically, especially in the near-wall area, resulting in a drag reduction.
文摘Cylindrical cross sections are critical components in offshore structures, including jacket platform legs, pipelines, mooring lines, and risers. Thesecylindrical structures are subjected to vortex-induced vibrations (VIV) due to strong ocean currents, where vortices generated during fluid flowresult in significant vibrations in crossflow and in-flow directions. Such vibrations can lead to severe damage to platforms, cables, and risersystems. Consequently, mitigating VIV caused by vortex-induced forces is important. This study investigates the hydrodynamic performance offive strake models relative to a bare cylinder at moderate Reynolds numbers. The models encompass one conventional continuous helical strake(HS) and four helical discrete strake (HDS) with varying segment spacing between the fins. The hydrodynamic performance, specifically liftand drag force coefficients, was computed using a Reynolds averaged Navier –Stokes-based CFD solver and validated with experimentalmeasurements. The conventional HS suppresses 95% of the lift force but increases the drag force by up to a maximum of 48% in measurements.The HDS suppress the lift force by 70%–88% and increase the drag force by 15%–30%, which is less than the increase observed with the HS.Flow visualization showed that HS and HDS cylinders mitigate vortex-induced forces by altering the vortex-shedding pattern along the length ofthe cylinder. The HDS achieves a reduction in drag compared with the conventional continuous HS. The segment spacing is found to significantlyimpact the reduction in vortex-induced forces.
基金the National Key Technologies R&D Program (2001BA401A03-10).
文摘Drag force is a key parameter in the numerical modeling of gas-particle flow in circulating fluidized beds. The reliability of current drag force correlations over the regime of fast fluidization has, however, not been thoroughly investigated. In this article, a drag force correlation accounting for the clustering effects for Geldart A particles is used to simulate the behaviors typical of fast fluidization, including dynamic evolution of clusters as well as time- averaged axial and lateral voidage profiles. Diverse images of clusters are captured and the time-averaged profiles of voidage are shown to be in quantitative agreement with the present empirical correlation. The results based on different constitutive correlations of drag force show the importance of the choice of drag force in modeling fast-fluidized beds. This drag force correlation, based on a simple averaging assumption, could give some basic insights about the magnitude of the drag reduction.
基金supported by the National Natural Science Foundation of China (Nos. 50679061, 50709025,and 50749031)
文摘This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vegetation are considered as the drag force item. The secondary currents are also taken into account in the governing equations, and the preliminary estimation of the secondary current intensity coefficient K is discussed. The predicted results for the straight channels and the apex cross-section of meandering channels agree well with experimental data, which shows that the analytical model presented here can be applied to predict the flow in compound channels with vegetated floodplains.
文摘The variations of drag force acting on the windbreak and the bulk drag coefficients for different windbreak widths were studied experimentally in the Eiffel-type non-circulating wind tunnel at the Hydraulic Engineering Laboratory, Saitama University, Japan, to elucidate the effects of windbreak width in the wind direction on wind velocity reduction behind a windbreak. The variations of flow field for different windbreak widths were studied numerically by using the two-dimensional Reynolds-averaged Navier-Stokes （RANS） equation with a k-c turbulence closure model. Results show that the total drag force to wind increased with increasing windbreak width, but the bulk drag coefficient decreased slightly. The relationship between the bulk drag coefficient Cd and the windbreak width W and height H can be presented by the equation of Ca= kd （W/H）^-b （kd, b： constants）. The result of the numerical simulation shows that the windbreak width greatly affects the location and the value of the minimum wind velocity. The wind velocity decreased by 15%-22% as the windbreak width increased.
基金the National Natural Science Foundation of China(Nos.50679061,50709025and50749031)
文摘The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the unit volume where the effect of the vegetation on the flow is considered as a drag force item, The compound channel is divided into 3 sub-regions in the transverse direction, and the coefficients in every region＇s differential equations were solved simultaneously. Thus, the analytical solution of the transverse distribution of the depth-averaged velocity for uniform flow in a partially vegetated compound channel was obtained. The results can be used to predict the transverse distribution of bed shear stress, which has an important effect on the transportation of sediment. By comparing the analytical results with the measured data, the analytical solution in this paper is shown to be sufficiently accurate to predict most hydraulic features for engineering design purposes.
基金supported by the National Natural Science Foundation of China(Grant No.40871050)
文摘The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream control cylinder （d） varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder （G） ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio （G/D） and the diameter ratio between the two cylinders （d/D） have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.
基金Project supported by the National Natural Science Foundation of China(Nos.11372232 and 51479007)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20130141110016)the State Water Pollution Control and Management of Major Special Science and Technology(No.2012ZX07205-005-03)
文摘An analytical solution for predicting the vertical distribution of streamwise mean velocity in an open channel flow with submerged flexible vegetation is proposed when large bending occurs. The flow regime is separated into two horizontal layers： a vegetation layer and a free water layer. In the vegetation layer, a mechanical analysis for the flexible vegetation is conducted, and an approximately linear relationship between the drag force of bending vegetation and the streamwise mean flow velocity is observed in the case of large deflection, which differes significantly from the case of rigid upright vegetation. Based on the theoretical analysis, a linear streamwise drag force-mean flow velocity expression in the momentum equation is derived, and an analytical solution is obtained. For the free water layer, a new expression is presented, replacing the traditional logarithmic velocity distribution, to obtain a zero velocity gradient at the water surface. Finally, the analytical predictions are compared with published experimental data, and the good agreement demonstrates that this model is effective for the open channel flow through the large deflection flexible vegetation.
基金National Natural Science Foundation of China(Grant No.59895410,59779002)
文摘The dynamic response of offshore platforms is more serious in hostile sea environment than in shallow sea. In this paper, a hybrid solution combined with analytical and numerical method is proposed to compute the stochastic response of fixed offshore platforms to random waves, considering wave-structure interaction and non-linear drag force. The simulation program includes two steps: the first step is the eigenanalysis aspects associated the structure and the second step is response estimation based on spectral equations. The eigenanalysis could be done through conventional finite element method conveniently and its natural frequency and mode shapes obtained. In the second part of the process, the solution of the offshore structural response is obtained by iteration of a series of coupled spectral equations. Considering the third-order term in the drag force, the evaluation of the three-fold convolution should be demanded for nonlinear stochastic response analysis. To demonstrate this method, a numerical analysis is carried out for both linear and non-linear platform motions. The final response spectra have the typical two peaks in agreement with reality, indicating that the hybrid method is effective and can be applied to offshore engineering.
