油气藏储层流体渗流理论表征新参数——流度梯度的实验研究

渗流理论是流体在储层中的动态描述，流动能力大小直接影响油气开采、油田产量、最终采收率以及经济效益等。如何有效准确地表征储层流体的渗流特征，一直是油气开发学家们探讨的问题。目前能够表征油气渗流的参数很多，但每一种方法都有其优缺点。在长期的科研实践中，首次提出了油气渗流理论的表征新参数——流度梯度，该参数能够比较全面、真实、准确地表征油气渗流能力大小、黏度场分布情况。计算方法简便，在实际应用中取得比较好的效果，能够为油气田高效开发提供一定的理论指导，也对深入了’解油气藏开发动态和提高采收率具有重要的现实意义。

Analysis of a Wenzhou-Hitting Exceptionally Strong Rainstorm Associated with a Typhoon Inverted Trough in September,1999

Using T106 numerical products, MM5 simulations in conjunction of Q-vector scheme-computed NCEP results, observations and satellite cloud images, study is undertaken for an exceptionally intense rainstorm event afflicting the Wenzhou region of Zhejiang province far away from the tropical storm center happening early on the morning of September 4, 1999 （TS9909 hereinafter）. Evidence suggests that, like previously-studied typhoons landing in autumn south of Xiamen to the eastern part of Guangdong, TS9909 has an inverted trough in the central south of the coastal belt of Zhejiang province that produces the rainstorm from the meso convective complex （MCC） on the warm, moist shear inside; the time and order of the magnitude of the rainfall are bound up with the development of the pattern of strong Q-vector divergence gradients during the event for the study area; the NE - SW coastline and the unique topography of the Yandang mountains inside the region are favorable for air lifting are the major contributors to the torrential rains.

Convection and Phase-Separation Behavior of Binary Mixture under Microwave Irradiation

When the temperature of a thin layer of a solution is vertically controlled, Rayleigh-Bemard convection is observed. When a binary isobutyric acid aqueous solution is used as the binary mixture, phase separation is simultaneously induced at the approximate critical solution temperature. In this study, these behaviors of phase separation and convection were observed under microwave irradiation. When the microwave power was higher, coalescence of fine droplets after the initial phase separation was accelerated and the coalescence size decreased. However, the solution became more unsteady because of smaller interfacial tension or greater heat generated by the radiation. Finally, in cases of higher microwave power, a steady convection pattern could not exist for a prolonged period because the water-rich phase was more active toward microwave irradiation, and the vertical temperature gradient became disordered.

Typhoon-dominated Influence on Wood Debris Distribution and Transportation in a High Gradient Headwater Catchment

Wood debris is an important component of mountain streams. It causes serious damage and renders difficulty of water resource management in Taiwan. In this study, the quantity of wood debris and variation of migratory wood debris during flood events were examined. The downstream of Gaoshan Creek and Qijiawan Creek, located at Central Taiwan, was selected as the study area. The distribution and dynamic of wood debris in a high gradient headwater catchment were quantified using field surveys. A formula of critical depth for wood debris entrainment was used to evaluate the wood debris migration during three flooding events. In the study area, wood abundance and unit volume increased downstream, and wood density decreased downstream within a channel network. The channel morphology, riparian vegetation, and wood debris characteristics were found to influence the wood storage. As a result, the wood debris has an irregular accumulative distribution in the steep stream, and it migrates easily in the stream because of a high flow discharge. Strong relationships between the channel width and wood debris variables are discovered. Moreover, wood debris has a tendency to accumulate at sites with low stream power and wood debris dams, topographical notches, and unique geological structures. Our findings assist in the understanding of the effects of channel characteristics on distributions of wood debris in steep stream systems.

Pressure Variation in the Fluid inside a Tesla Turbine

The recent technological developments being applied to Tesla like turbines for converting fluid energy into mechanical （axis） energy often lead to non-frequently used models. Given a disk shaped machine rotating around its own symmetry axis, part of the machine energy is transferred to the fluid itself, pushing it to the disk periphery. This way the farther the exhaust orifice is from the disk outside contour, the larger will be the pressure loss experienced by the system. This work studies the overall energy balance and momentum exchange between fluid and machine. Simple calculation shows that for total pressure gradients above two bar the machines become inefficient for having tangential velocity whose intensity is 50% higher than the intensity of the jet velocity prior to the interaction. For values of the pressure gradient above 5.7 bar, the machine peripheral velocity is equal to the incident jet velocity. In this case it is not possible to deliver power under permanent regime. Finally it is shown that when the feeding pressure of an impulse turbine is enough for more than one stage, then one should use this option to obtain thermal efficiencies similar to those of reaction machines. The jet of fluid to move a Tesla like turbine should enter the unit as close as possible to the direction tangential to the movement, （i.e., normal to the radius at the considered position）. This fluid should leave the machine right after interacting with it. Any permanence of the fluid after transferring its momentum to the machine can be extremely prejudicial to the system behavior.

Research on the Correlation of the Fluctuating Density Gradient of the Compressible Flows

This work is to study a role of the fluctuating density gradient in the compressible flows tbr the computational fluid dynamics （CFD）. A new anisotropy tensor with the fluctuating density gradient is introduced, and is used for an invariant modeling technique to model the turbulent density gradient correlation equation derived from the continuity equation. The modeling equation is decomposed into three groups proportional to the mean velocity, proportional to the mean strain rate, and proportional to the mean density. The characteristics of the correlation in a wake are extracted from the results by the two dimensional direct simulation, and shows the strong correlation with the vortices in the wake near the body. Thus, it can be concluded that the correlation of the density gradient is a significant parameter to describe the quick generation of the turbulent property in the compressible flows.

Investigation of Barree-Conway non-Darcy flow effects on coalbed methane production

Coalbed gas non-Darcy flow has been observed in high permeable fracture systems,and some mathematical and numerical models have been proposed to study the effects of non-Darcy flow using Forchheimer non-Darcy model.However,experimental results show that the assumption of a constant Forchheimer factor may cause some limitations in using Forchheimer model to describe non-Darcy flow in porous media.In order to investigate the effects of non-Darcy flow on coalbed methane production,this work presents a more general coalbed gas non-Darcy flow model according to Barree-Conway equation,which could describe the entire range of relationships between flow velocity and pressure gradient from low to high flow velocity.An expanded mixed finite element method is introduced to solve the coalbed gas non-Darcy flow model,in which the gas pressure and velocity can be approximated simultaneously.Error estimate results indicate that pressure and velocity could achieve first-order convergence rate.Non-Darcy simulation results indicate that the non-Darcy effect is significant in the zone near the wellbore,and with the distance from the wellbore increasing,the non-Darcy effect becomes weak gradually.From simulation results,we have also found that the non-Darcy effect is more significant at a lower bottom-hole pressure,and the gas production from non-Darcy flow is lower than the production from Darcy flow under the same permeable condition.

Steady thermal-solutal capillary convection in a shallow annular pool with the radial temperature and concentration gradients

Using asymptotical analysis,we investigate the characteristics of the coupled thermal and solutal capillary convection with the radial temperature and solute concentration gradients in a shallow annular pool with the free surface.The pool is heated from the outer cylinder with high solutal concentration and cooled at the inner cylinder with low solutal concentration.The asymptotic solution is obtained in the core region in the limit as the aspect ratio,which is defined as the ratio of the depth to the width of the pool,goes to zero.The comparison with the previous work certifies that the asymptotic solution is right and believable.The influences of the solutal capillary force,the buoyant force,the Soret effect and the geometric parameters on the fluid flow are analyzed.

Decadal change of East Asian summer tropospheric temperature meridional gradient around the early 1990s

During 1979–2004, the East Asian summer precipitation has experienced another significant decadal shift around the early 1990 s. Based on three radiosonde temperature datasets and four reanalysis datasets, this paper examines the decadal change of the East Asian summer tropospheric temperature around the early 1990 s. The results show that the meridional gradient of layer mean upper tropospheric temperature for 200–500 h Pa(here after UTT, UTT is upper tropospheric temperature) also underwent an obvious decadal decrease around 1992. The tropospheric temperature south to 35°N becomes decadal cooling, centered along the Yangtze River Valley, while the tropospheric temperature north to 35°N shows a decadal warming, centered in Northwest China-Mongolia. JRA-25 reanalysis is better than the other reanalysis datasets in revealing this decadal change. This decadal shift of East Asian summer UTT may be ascribed to the decadal change of the ENSO period from low-frequency oscillation(4–6 yr) to quasi-biennial oscillation since 1992. It behaves as an increase of ENSO developing events and a reduction of ENSO decaying events. It leads to stronger forcing of ENSO developing summer and weaker forcing of ENSO decaying summer, leading to the dominant role of monopole cooling mode of East Asian UTT after 1992, in contrast to the dominant role of dipole mode of East Asia UTT before 1992. The summer UTT difference between 1993–2004 and 1979–1992 shows a "South cooling-North Warming" pattern, and thereby contributes to the interdecadal decrease of East Asian summer UTT meridional gradient around 1992.

Experimental demonstration of the coupling effect of vertical velocity on latent heat flux

According to the cross coupling theorem of atmospheric turbulence, latent heat flux comprises two components, a vertical humidity gradient flux and a coupling flux of vertical velocity. In this paper, observational data are employed to demonstrate and analyze the coupling effect of vertical velocity on latent heat flux. The results highlight the presence of a coupling zero-effect height. When the observational level exceeds or underlies the coupling zero-effect height, the coupling effect suppresses or enhances the latent heat flux, respectively. Above the heterogeneous terrain in the experimental region, the overall difference between the estimated and the observed latent heat fluxes decreases from 27% to 2% (for ascending flow) and from 47% to 28% (for descending flow), after compensating for gradient flux. The coupling theorem of atmospheric turbulence is well validated by our analysis, supporting a role for experimental datasets in unraveling the mysteries of atmospheric turbulence.

Effect of surface roughness element on near wall turbulence with zero-pressure gradient

In the present paper,we present an investigation on the effect of roughness elements onto near-wall kinematics of a zeropressure-gradient turbulent boundary layer.An array of spanwisely-aligned cylindrical roughness elements was attached to the wall surface to regulate the near-wall low-speed streaky structures.With both qualitative visualization and quantitative measurement,we found that the regularization only occurs in the region below the height of the roughness elements.Statistical analysis on the probability distribution of the streak spanwise spacing showed that the mean spanwise streak spacing is dominated by the roughness elements;however,the latter's effect is in competition with the intrinsic streak generation mechanisms of smooth wall turbulence.Below the top of the roughness elements,local streamwise turbulent fluctuation intensity can be reduced by about 10%.We used POD analysis to depict such regularization effect in terms of near-wall structure modulation.We further found that if the spanwise spacing of roughness elements increased to be larger than the mean streak spacing in the smooth wall turbulence,there is no streak-regularization effect in the buffer region,so that the near-wall streamwise turbulent fluctuation intensity doesn't reduce.

Nonlinear size-dependent dynamic instability and local bifurcation of FG nanotubes transporting oscillatory fluids

Oscillation of fluid flow may cause the dynamic instability of nanotubes,which should be valued in the design of hanoelectromechanical systems.Nonlinear dynamic instability of the fluid-conveying nanotube transporting the pulsating harmonic flow is studied.The nanotube is composed of two surface layers made of functionally graded materials and a viscoelastic interlayer.The nonlocal strain gradient model coupled with surface effect is established based on Gurtin-Murdoch's surface elasticity theory and nonlocal strain gradient theory.Also,the size-dependence of the nanofluid is established.by the slip flow model.The stability boundary is obtained by the two-step perturbation-Galerkin truncation-Incremental harmonic balance(IHB)method·and compared with the linear solutions by using Bolotin's method.Further,the Runge-Kutta method is utilized to plot the amplitudefrequency bifurcation curves inside/outside the region.Results reveal the influence of nonlocal stress,strain gradient,surface elasticity and slip flow on the response.Results also suggest that the stability boundary obtained by the IHB method represents two bifurcation points when sweeping from high frequency to low frequency.Differently,when sweeping to high.frequency,there exists a hysteresis boundary where amplitude jump will occur.

Heat transfer analysis of viscoelastic fluid flow due to metachronal wave of cilia

This study describes ciliary motion on the transport of fluids in human body with heat transfer. The mathematical model of the flow of a Jeffrey fluid in a tube of finite length is considered due to metachronal wave of cilia motion. Flow equations have been modeled and simplified using similarity variables. Exact solutions of the formulated problem have been obtained for velocity, temperature and pressure gradient and graphs for velocity, pressure rise pressure gradient and temperature profile have been plotted and studied for different values of specific physical parameters. Trapping phenomena and isotherms are presented at the end of the paper.

Spatially adaptive long-term semi-Lagrangian method for accurate velocity advection

We introduce a new advection scheme for fluid animation.Our main contribution is the use of long-term temporal changes in pressure to extend the commonly used semi-Lagrangian scheme further back along the time axis.Our algorithm starts by tracing sample points along a trajectory following the velocity field backwards in time for many steps.During this backtracing process,the pressure gradient along the path is integrated to correct the velocity of the current time step.We show that our method effectively suppresses numerical diffusion,retains small-scale vorticity,and provides better long-term kinetic energy preservation.