Non-equilibrium interphase heat and mass transfer during two-phase flow in porous media—Theoretical considerations and modeling

Mass and heat transfer occurring across phase-interfaces in multi-phase flow in porous media are mostly approximated using equilibrium relationships or empirical kinetic models. However, when the characteristic time of flow is smaller than that of mass or heat transfer, non-equilibrium situations may arise. Commonly, empirical approaches are used in such cases. There are only few works in the literature that use physically-based models for these transfer terms. In fact, one would expect physical approaches to modeling kinetic interphase mass and heat transfer to contain the interfacial area between the phases as a variable. Recently, a two-phase flow and solute transport model was developed that included interfacial area as a state variable [36]. In that model, interphase mass transfer was modeled as a kinetic process.     

Lattice-Boltzmann simulations of the capillary pressure–saturation–interfacial area relationship for porous media

Hysteresis in the relationship between capillary pressure (P_c), wetting phase saturation (S_w) and nonwetting–wetting interfacial area per volume (a_nw) is investigated using multiphase lattice-Boltzmann simulations of drainage and imbibition in a glass bead porous system. In order to validate the simulations, the P_c–S_w and a_nw–S_w main hysteresis loops were compared to experimental data reported by Culligan et al. [Culligan KA, Wildenschild D, Christensen BS, Gray WG, Rivers ML, Tompson AB. Interfacial area measurements for unsaturated flow through porous media. Water Resour Res 2004;40:W12413]. In general, the comparison shows that the simulations are reliable and capture the important physical processes in the experimental system. P_c–S_w curves, a_nw–S_w curves and phase distributions (within the pores) show good agreement during drainage, but less satisfactory agreement during imbibition. Drainage and imbibition scanning curves were simulated in order to construct P_c–S_w–a_nw surfaces. The root mean squared error (RMSE) and mean absolute error (MAE) between drainage and imbibition surfaces was 0.10 mm⁻¹ and 0.03 mm⁻¹, respectively. This small difference indicates that hysteresis is virtually nonexistent in the P_c–S_w–a_nw relationship for the multiphase system studied here. Additionally, a surface was fit to the main loop (excluding scanning curves) of the drainage and imbibition P_c–S_w–a_nw data and compared to the surface fit to all of the data. The differences between these two surfaces were small (RMSE = 0.05 mm⁻¹ and MAE = 0.01 mm⁻¹) indicating that the P_c–S_w–a_nw surface is adequately represented without the need for the scanning curve data, which greatly reduces the amount of data required to construct the non-hysteretic P_c–S_w–a_nw surface for this data.     

Water wave interaction with an array of bottom-mounted surface-piercing porous cylinders

The interaction of water waves with arrays of bottom-mounted, surface-piercing circular cylinders is investigated theoretically. The sidewall of each cylinder is porous and thin. Under the assumptions of potential flow and linear wave theory, a semi-analytical solution is obtained by an eigenfunction expansion approach first proposed for impermeable cylinders by Spring and Monkmeyer (1974), and later simplified by Linton and Evans (1990). Analytical expressions are developed for the wave motion in the exterior and all interior fluid regions. Numerical results are presented which illustrate the effects of various wave and structural parameters on the hydrodynamic loads and the diffracted wave field. It is found that the porosity of the structures may result in a significant reduction in both the hydrodynamic loads experienced by the cylinders and the associated wave runup.     

Water wave interaction with a floating porous cylinder

The interaction of water waves with a freely floating circular cylinder possessing a side-wall that is porous over a portion of its draft is investigated theoretically. The porous side-wall region is bounded top and bottom by impermeable end caps thereby resulting in an enclosed fluid region within the structure. The problem is formulated based on potential flow and linear wave theory and assuming small-amplitude structural oscillations. An eigenfunction expansion approach is then used to obtain semi-analytical expressions for the hydrodynamic excitation and reaction loads on the structure. Numerical results are presented which illustrate the effects of the various wave and structural parameters on these quantities. It is found that the permeability, size and location of the porous region may have a significant influence on the horizontal components of the hydrodynamic excitation and reaction loads, while its influence on the vertical components in most cases is relatively minor.     

基于电力线载波通信技术的油田井下设备通信系统

传统的油田井下设备通信系统难以满足油田井下工况恶劣、电磁干扰强、通信距离长等特殊使用环境要求,通信不可靠.基于新型通信技术——电力线载波通信技术,建立油田井下设备电力线模型并分析特性,选择合适载波频率确定通信系统的硬件设计方案,利用软硬件结合方式进行抗干扰设计,研制一种基于电力线载波通信的井下设备通信系统.实验结果表明:该系统通信距离达到3km,准确率为100%,可以满足油田井下及其他恶劣工况环境下设备使用要求,具有一定的应用前景.     

GNSS接收机测量强震地震波的精度分析

在分析强震地震波信号幅频特性的基础上,采用GNSS信号模拟器,设计具有强震地震波特点的正弦轨迹,从载波相位原始量测数据和定位结果两个层面分别评估两款GNSS接收机（Trimble Net-R9和NovAtel OEM628）高频（50 Hz）观测的测量性能。结果表明,在地震波高频动态条件下,两款接收机的载波相位和定位结果都出现了明显误差,测量精度随正弦运动频率的增加而恶化,Trimble Net-R9接收机尤甚。     

渗流场反分析及其在多孔介质中的应用

本文讨论了复杂地质环境中渗流场的反分析问题，利用地下水流数值模拟结合最优化技术，通过对地下渗流场的模拟和寻优，求得描述地下含水介质非稳定渗流场的重要参位──渗透系数和给水度的模型解，并应用于各向同性的多孔介质渗流场反分析实例中。     

地理系统与地理信息系统

人类认识自己住居的星球是漫长的,然而是加速度的。学科的分化和交叉是多层次的。统一地理学一再遭受过冲击,但它的合理的内核——地理综合体是客观存在的。地图和遥感作为信息载体证实了这一观点。地理系统的概念反映当代科学技术进步和社会需求;而地理信息系统为地理学发挥区域性与综合性的优势提供了一种现代化的高技术手段。     

关于波浪作用下粉土质海床中共振现象的解释

本文详细讨论了粉土质床在波浪作用下所呈现共振现象的力学机制。利用有限深海床下波浪载荷对土层响应的研究，系统地比较了理论计算结果和实验结果。提出在波浪作用下粉土质土层中存在着一硬土层，从而引发Ｂｒａｇｇ共振。     

Inertial instability of large Rossby number horizontal shear flows in a thin homogeneous layer

A horizontal shear flow having a Rossby number, Ro, greater than unity on a rotating plane can become unstable when its shear value is less than −f, the Coriolis frequency. In this paper, this instability is investigated for an O(10 km) submesoscale, sinusoidal shear flow in a thin homogeneous fluid layer as in an oceanic mixed layer or a shallow sea. The most unstable mode is shown by a linear analysis to occur in a narrow localized region centered around the maximum anticyclonic current shear. However, nonlinear numerical calculations show that the instability can grow to encompass both unstable and stable regions of the current. A consequence of this finite-amplitude evolution is the formation of surface convergence/shear fronts. The possibility that inertial instability mechanism is a source of some surface convergence/shear features seen in remote sensing images of the sea surface is discussed. A comparison is made with the shear-flow instability that can occur concurrently in a sinusoidal shear current, and inertial instability is shown to be the dominant instability mechanism in the immediate range above Ro=2.