Subjects: Mechanics >> Hydromechanics submitted time 2024-06-17 Cooperative journals: 《应用力学学报》
Abstract：
The scattering characteristics of a two-dimensional cavity under the incidence of elastic waves in a double-porous fluid-saturated medium are studied by the indirect boundary integral equation method(IBIEM)in this article,which is based on the plane wave potential function. The dynamic Green’s function of two-dimensional line source in a saturated full space with double pores is derived,and the displacement field and stress field of each scattered wave are given. Based on the verification of numerical accuracy,the problem of seismic wave scattering under the incidence of plane P and SV waves is solved by taking a cavity in the two-dimensional saturated full space with double pores as an example. Numerical results show that the displacement amplitude,hoop stress amplitude,and pore pressure’s changing regulation in dual-porous media are closely related to different incident waveforms,incident frequency,porosity,and boundary drainage conditions. The displacement amplitude peak appears at low frequency(dimensionless frequency η≤2)incidence.Compared with dry soil conditions,the hoop stress amplitude is more complicated. The existence of matrix pore pressure and crack pore pressure increases the energy effect of the double pore-saturated site,where the overall vibration trend is greater than that of the site under dry soil conditions,and the magnification can reach 62%.
Subjects: Mechanics >> Hydromechanics submitted time 2024-06-17 Cooperative journals: 《应用力学学报》
Abstract：
The hydrodynamics of air-liquid compound droplet impact on the super-hydrophobic surface was experimentally studied. We investigated the critical conditions of cavity rupture,the maximum spreading coefficient,and the temporal evolution of the spreading coefficient during impact. The difference between the compound and single-phase droplet impact was analyzed. The experimental results show that the critical threshold of cavity rupture increases with the increase of liquid viscosity and the decrease of air-liquid diameter ratio. The maximum spreading coefficient of compound droplets decreases with the increase of both liquid viscosity and cavity size. We derived the theoretical formula for the critical condition of cavity rupture,and the theoretical model of maximum spreading coefficient for the air-liquid compound droplet impact. In addition,we also studied the contact time of compound droplets after impact,which is smaller than that of the single-phase droplet under three kinds of air-liquid diameter ratio. A theoretical formula of dimensionless contact time with diameter ratio is proposed.
Subjects: Mechanics >> Hydromechanics submitted time 2024-06-17 Cooperative journals: 《应用力学学报》
Abstract：
Based on numerical simulation,the dynamic characteristics of double localized traveling wave(DLTW)convection in a cavity with separation ratio ψ=-0.4and an aspect ratio Γ=40 are studied.The results show that convective roll is generated at the two end wall,propagates to the center and disappears at a certain location.The traveling wave convection region near the two ends of the rectangular cavity coexists with the conduction region without convection in the middle,forming a DLTW convection.Traveling waves propagate from both ends of the cavity to the middle of the DLTW convection.Temperature and vertical velocity distributions in the midheight of the cavity are harmonic structures with smooth waveforms.Concentration distribution is a platform structure.With the development of time,the maximum vertical velocity stabilizes at a certain value and changes periodically.The Nusselt number of the lower wall is basically stable at a certain value.The maximum vertical velocity and Nusselt number on the lower wall and the time for them to reach stability increase with the increase of reduced Rayleigh number.DLTW convection is stable in the range of reduced Rayleigh number r∈{1.52,1.57 .The length of convective zone of DLTW increases with the increase of reduced Rayleigh number.The fitting formula for the length of convective zone of DLTW varying with the reduced Rayleigh number is given.
Subjects: Mechanics >> Hydromechanics submitted time 2024-06-17 Cooperative journals: 《应用力学学报》
Abstract：
The control rod falling law and falling time of passive shutdown in sodium cooled fast reactor are important parameters for control rod design,and they are typical hydrodynamic problems.In order to explain the swing and impact phenomena of control rod assembly in sodium cooled fast reactor during rod drop test,the falling process of control rod is simulated and studied by using the dynamic grid method of simulation software,the factors influencing the falling law of control rod are analyzed,and the method of buffering the falling speed of control rod is proposed.The error between the test results and the numerical simulation results is 2.44%.The main conclusions are as follows:the simulation results show that there are shaking and eccentricity phenomena in the process of control rod falling,and the shaking amplitude can be reduced by reducing the center of gravity of the control rod.The initial eccentricity and falling eccentricity of control rod have little effect on the overall falling time.The small hole at the bottom of the buffer cup does not affect the buffer effect,and the serrated groove structure on the surface of the buffer cup can effectively improve the buffer effect.The cushioning effect of serrated groove is 47.2% higher than that of rectangular groove.
Subjects: Mechanics >> Hydromechanics submitted time 2024-04-19 Cooperative journals: 《应用力学学报》
Abstract：
When the pressure gate valve is closed in the large-span inverted siphon pipeline,it is usually accompanied by the phenomenon of water hammer.At the same time,the coupling effect of the fluid and the solid exists.In order to study the pressure wave under different valve closing time and the dynamic response of the structure with considering the coupling effect,the overall hydraulic calculation is carried out with taking the large-span inverted siphon pipeline and the arch bridge structure as the research objects.Based on the fluid-structure coupling analysis theory,the water hammer pressure wave calculated by the overall hydraulic model is used as the loading condition of the fluid part,and the two-way fluid-structure coupling analysis is carried out on the workbench platform to solve the displacement,internal force,and stress of the bridge structure.The results show that under different valve closing time conditions,the change trend of the water hammer pressure wave curve is roughly the same,and the displacement time history curve of each monitoring point of the structure is basically consistent with the law of the water hammer pressure wave curve.When the valve is closed at a constant speed,increasing the closing time of the gate valve can be an effective measure to reduce the water hammer pressure; the water hammer force has the greatest effect on the bridge pipe,followed by the cover beam,and the arch ring is the smallest,and the dynamic response of the structure mainly occurs along the bridge direction.
Subjects: Mechanics >> Hydromechanics submitted time 2023-06-21 Cooperative journals: 《应用力学学报》
Abstract：
This work discusses the dynamics and structure of(atmospheric)turbulent vortices.Restricted by Taylor-Proudman theorem,the strong vorticity can be rigidly shifted in disturbance,thus possessing a strong vorticity viscosity to involve the viscous forces in the actual equilibrium; then Sullivan vortex solution can be formed if Geostrophic force can be separated.The constraint conditions required by the theorem make the vortex solution often exist only in high eddy regions,and appears as a vortex band due to the phenomenon of the rigid preserving area in the disturbance.The actual structure of vortex is quantitatively related to two parameters and restricted by the criterion function.Some structures in turbulence and electromagnetic wave can be explained qualitatively and quantitatively by it.
Subjects: Mechanics >> Hydromechanics submitted time 2023-06-21 Cooperative journals: 《应用力学学报》
Abstract：
Based on the commercial software Fluent,the large eddy simulation(LES)method is used to numerically study the three-dimensional flow around three circular cylinders in a staggered arrangement at Re=3 900.In order to verify the correctness of the numerical method,a case involved in the single cylinder is selected to verify the relevant parameters.Subsequently,the key parameter of the spacing ratio(L/D)is analyzed on the influence of the flow characteristics of the staggered three-cylinder array.Within the range of the small spacing ratio(1.5≤L/D≤2.0),the time-averaged drag coefficient of the middle and downstream cylinders is smaller than that of single cylinder; when the spacing ratio is 3.0,the time-averaged pressure coefficient distribution of the upstream cylinders is quite different from the results of other cases; the formation of skewed flow in the wake of the three cylinder array can found at L/D=1.5; the distribution characteristics of the boundary vortex flux of the three-cylinder array are given.It shows that the streamwise vortex is mainly generated on the surface of the midstream cylinder and enters the flow field with deforming and stretching.
Subjects: Mechanics >> Hydromechanics submitted time 2022-11-01 Cooperative journals: 《应用力学学报》
Abstract： Large-span roof structure has become one of the main forms of building structure,and the retractable roof structure is a new structure form in recent years.The research on large span retractable roof by numerical simulation in China is still in its infancy stage.This paper establishes four roof models with different opening and closing states,analyzes the wind pressure characteristics of the roof surface under different opening and closing states,different wind angles,and different wind speeds,and conducts the analysis when the roof is fully opened.The partition then calculates the partition size coefficient and gives a reasonable suggested value for the partition,which provides an effective reference for future actual projects.The results show that the wind direction angle has a great influence on the distribution of wind pressure on the roof surface; especially the 30° and 60° wind direction angles have a prominent influence on the distribution of wind pressure coefficient.The opening and closing of the roof also significantly affects the wind pressure distribution,but has little influence on the wind pressure coefficient value.
Subjects: Mechanics >> Hydromechanics submitted time 2022-11-01 Cooperative journals: 《应用力学学报》
Abstract： To study the characteristics of the wellbore pressure changes of thermal recovery of heavy oil in carbonate reservoirs,considering the effect of temperature on viscosity of oil and stress sensitivity of reservoirs,the triple permeability mathematical model in triple media has been constructed.The mathematical model is of nonlinear partial differential equations with variable coefficients.The difference equations have been discretized by the fully implicit finite difference scheme.Newton-Raphson method has been used for solving nonlinear difference equations.The Jacobi matrices of the difference equations are tridiagonal matrix.Using the properties of tridiagonal matrix,the iteration speed is improved.According to the calculation results,the typical well test curves have been plotted.Sensitivity of parameters has been analyzed.There are eight stages of pressure response.The sensitivities of viscosity depend on temperature are different in different reservoirs.The higher the sensitivities of viscosity depend on temperature,the greater the values of pressure in reservoirs.When the cross flow stages are earlier,the time of the cross flow between the fractures and vugs is shortened and the strength is weakened,causing the earlier decrease in the pressure derivative.
Subjects: Mechanics >> Hydromechanics submitted time 2022-11-01 Cooperative journals: 《应用力学学报》
Abstract： Based on standard k-ε,the two-dimensional flow around a circular cylinder with different surface roughness is numerically simulated at a subcritical Reynolds number of 3 900.The effects of surface roughness on the lift coefficient,drag coefficient,vorticity field and surface pressure distribution are analyzed.The results show that with the increase of surface roughness,the number of peak frequencies of drag coefficient fluctuation decreases,the dominant frequencies of lift and drag coefficient changes irregularly,and the average drag coefficient and root-mean-squared lift coefficient decrease.The regularity of wake vortex arrangement and the strength of vortex shedding decreases.The flow separation point moves towards the rear of the cylinder as the roughness increases.At the back of the cylinder,lower pressure coefficients correspond to higher roughness.The results of this paper are helpful to the research of cylindrical flow control technology.
Subjects: Mechanics >> Hydromechanics Subjects: Mine Engineering Technology >> Development Engineering of Oil and Gas Well submitted time 2022-05-12
Abstract：
Almost all the oil or gas reservoirs have sharp interfaces. The key to establish the corresponding mathematical flow model is to find the reasonable phase pressures and velocities connection conditions at the sharp interfaces. In the existing seepage mechanics theory, it is generally recognized that the velocity and pressure of each phase of fluid are continuous at the sharp interface (named CPVCM). However, we can find that CPVCM contradicts some other multiphase seepage phenomena or theories: (1) The saturation distribution of fluid in the real world does not always obey the fluids distribution rules that CPVCM required；(2) Near the flood front, CPVCM conflicts with Rankine-Hugoniot Interface Conditions;（3）It has been proved that the formula of phase fluxes across the sharp interface which are derived from CPVCM, harmonic average of transmissibility, possible give non-physical results in some cases, so that they have been replace by single points upstream weighting method(SPU) and other high order method, such as TVD,ENO,WENO et al. . Therefore, we retraced the way that how to derive the CPVCM based on the mass conservation law in the early lectures, and find that the two particles on both sides of the interface which mentioned in the interface condition has been misplaced on the same interface, therefore, the proof process is essentially equivalent to preset the continuity of velocity and pressures of each phase and prove they are continuous. Such proof is invalid self-proof. Then, taking the incompressible two-phase fluids flow in the porous media as an example, the interface condition with discontinuous velocity and pressure of each phase (JPVCM) is obtained according to the same laws of mass conservation and two-phase Darcy’s law. Finally, it is suggested that, as for the incompressible two-phase flow in porous media, the jump conditions should be (1) total velocity of the two phases are equal, (2) the velocity of each phase at the sharp interface adopt the upstream ones.
Peer Review Status:
Awaiting Review
Subjects: Mine Engineering Technology >> Development Engineering of Oil and Gas Well Subjects: Mechanics >> Hydromechanics submitted time 2021-01-06
Abstract： Jump interface in porous media exists widely in oil and gas reservoirs during development. The traditional seepage theory holds that the pressure and Darcy velocity are continuous at the discontinuous interface, and we have falsified them in previous studies. In this paper, taking gas-water phase as an example and considering the compressibility of the fluids, the connection conditions of phase pressures and Darcy velocities at the immovable jump interface are established. The results show that :(1) the total pressure is always continuous, but the phase pressure of each phase can be discontinuous;(2) The total Darcy velocity at the both sides are equal, but the phase Darcy velocity probably discontinuous;(3) The connection conditions of fixed jump interface do not comfort to Rankine - Hugoniot conditions, which are different from mobile jump interface, i.e. flood front.
Peer Review Status:Awaiting Review
Subjects: Mine Engineering Technology >> Development Engineering of Oil and Gas Well Subjects: Mechanics >> Hydromechanics submitted time 2020-12-25
Abstract： Gas-liquid two-phase displacement are widely observed in oil and gas reservoir. The traditional seepage theory holds that the phase pressures and Darcy velocities must be continuous at the jump interface, and we have falsified them in previous studies. In this paper, the jump interface condition of two-phase seepage is extended from incompressible fluids to compressible. Taking gas-water displacement as an example, the new connection conditions of phase pressures and Darcy velocities at the gas-water displacement front in porous media were built. The results show that at the flood front, the global pressure is continuous, but not the fluid pressure are. (2) The total Darcy velocity can be discontinuous with a specific functional relationship;(3) The phase Darcy velocity of each phase of the fluid is discontinuous.
Peer Review Status:Awaiting Review
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