排序方式： 共有10条查询结果，搜索用时 15 毫秒
1
1.
2.
We present advances in compositional modeling of two-phase multi-component flow through highly complex porous media. Higher-order methods are used to approximate both mass transport and the velocity and pressure fields. We employ the Mixed Hybrid Finite Element (MHFE) method to simultaneously solve, to the same order, the pressure equation and Darcy's law for the velocity. The species balance equation is approximated by the discontinuous Galerkin (DG) approach, combined with a slope limiter. In this work we present an improved DG scheme where phase splitting is analyzed at all element vertices in the two-phase regions, rather than only as element averages. This approximation is higher-order than the commonly employed finite volume method and earlier DG approximations. The method reduces numerical dispersion, allowing for an accurate capture of shock fronts and lower dependence on mesh quality and orientation. Further new features are the extension to unstructured grids and support for arbitrary permeability tensors (allowing for both scalar heterogeneity, and shear anisotropy). The most important advancement in this work is the self-consistent modeling of two-phase multi-component Fickian diffusion. We present several numerical examples to illustrate the powerful features of our combined MHFE–dg method with respect to lower-order calculations, ranging from simple two component fluids to more challenging real problems regarding CO2 injection into a vertical domain saturated with a multi-component petroleum fluid. 相似文献
3.
Contrast in capillary pressure of heterogeneous permeable media can have a significant effect on the flow path in two-phase immiscible flow. Very little work has appeared on the subject of capillary heterogeneity despite the fact that in certain cases it may be as important as permeability heterogeneity. The discontinuity in saturation as a result of capillary continuity, and in some cases capillary discontinuity may arise from contrast in capillary pressure functions in heterogeneous permeable media leading to complications in numerical modeling. There are also other challenges for accurate numerical modeling due to distorted unstructured grids because of the grid orientation and numerical dispersion effects. Limited attempts have been made in the literature to assess the accuracy of fluid flow modeling in heterogeneous permeable media with capillarity heterogeneity. The basic mixed finite element (MFE) framework is a superior method for accurate flux calculation in heterogeneous media in comparison to the conventional finite difference and finite volume approaches. However, a deficiency in the MFE from the direct use of fractional flow formulation has been recognized lately in application to flow in permeable media with capillary heterogeneity. In this work, we propose a new consistent formulation in 3D in which the total velocity is expressed in terms of the wetting-phase potential gradient and the capillary potential gradient. In our formulation, the coefficient of the wetting potential gradient is in terms of the total mobility which is smoother than the wetting mobility. We combine the MFE and discontinuous Galerkin (DG) methods to solve the pressure equation and the saturation equation, respectively. Our numerical model is verified with 1D analytical solutions in homogeneous and heterogeneous media. We also present 2D examples to demonstrate the significance of capillary heterogeneity in flow, and a 3D example to demonstrate the negligible effect of distorted meshes on the numerical solution in our proposed algorithm. 相似文献
4.
胡伟标 《CT理论与应用研究》1996,5(1):32-34
本文叙述了ＣＴＸ线质量控制，对控制部件光束限位器、准值器、以及射线校正器等工作原理进行了系统的分析，并对各故障部件的控制进行改进讨论。 相似文献
5.
不同TVD 格式对内孤立波数值模拟结果影响研究 总被引：1，自引：0，他引：1
为了研究不同TVD格式对内孤立波模拟结果的影响,利用改进后的SUNTANS三维非静压海洋模型,通过理想算例和南海东北部海域内孤立波的模拟,比较分析了求解温盐方程TVD格式的4种经典通量限制函数(superbee, minmod, van Leer和MUSCL)对计算结果的影响。综合理想算例和南海东北部海域模拟结果,在所讨论的4种通量限制函数中,利用MUSCL限制函数所得模拟结果最优,建议在南海东北部海域内孤立波模拟中采用MUSCL限制函数。 相似文献
6.
针对复杂流体运动中物质输运方程的数值求解面临地形复杂、数值阻尼过大以及数值振荡等难题,建立了Godunov格式下求解二维水流-输运方程的高精度耦合数学模型,提出了集成输运对流项的HLLC (Harten-Lax-van Leer-Contact)型近似黎曼算子,可同时计算水流通量及输运通量,不仅有效模拟了复杂地形上水流运动,而且解决了输运方程中对流项产生的数值阻尼过大和不稳定振荡等难题。采用水深-水位加权重构技术和Minmod限制器,提高了模型处理复杂混合流态的能力,同时结合Hancock预测-校正方法,使模型具有时空二阶精度。算例结果表明,模型精度高、稳定性好,能有效抑制数值阻尼,适合模拟实际复杂流体运动中物质的输运过程,具有较好的推广应用价值。 相似文献
7.
Numerical investigations on one-dimensional nonlinear acoustic wave with third and fourth order nonlinearities are presented
using high-order finite-difference (HFD) operators with a simple flux-limiter (SFL) algorithm. As shown by our numerical tests,
the HFDSFL method is able to produce more stable, accurate and conservative solutions to the nonlinear acoustic waves than
those computed by finite-difference combined with the flux-corrected-transport algorithm. Unlike the linear acoustic waves,
the nonlinear acoustic waves have variable phase velocity and waveform both in time-space (t-x) domain and frequency-wavenumber (f-k) domain; of our special interest is the behaviour during the propagation of nonlinear acoustic waves: the waveforms are strongly
linked to the type of medium nonlinearities, generation of harmonics, frequency and wavenumber peak shifts. In seismic sense,
these characteristics of nonlinear wave will introduce new issues during such seismic processing as Normal Moveout and f-k filter. Moreover, as shown by our numerical experiment for a four-layer model, the nonlinearities of media will introduce
extra velocity errors in seismic velocity inversion. 相似文献
8.
在求解Euler方程时,带TVB限制器的Runge-Kutta间断有限元(RKDG)方法是一种高精度、高并行效率的方法,而浸入边界方法是一种较新颖且对网格要求较低的方法,适用于处理复杂几何外形的边界.尝试了将上述2种方法结合起来求解Euler方程在笛卡尔网格上具有复杂几何外形的物体绕流问题,数个经典算例的数值结果验证了该方法的有效性. 相似文献
9.
In most TVD schemes, the r-factors were proposed according to the cell-centered (CC) finite volume method (FVM) framework for the numerical approximation to the convective term. However, it is questionable whether those r-factors would be appropriate and effective for the vertex-centered (VC) FVM. In the paper, we collected five kinds of r-factor formulae and found out that only three of those, respectively by Bruner (1996), Darwish and Moukalled (2003) and Cassuli and Zanolli (2005) can be formally extended to a context of the VC FVM. Numerical tests indicate that the TVD schemes and r-factors, after being extended and introduced to a context of the VC FVM, maintained their similar characteristics as in a context of the CC FVM. However, when the gradient-based r-factors and the SUPERBEE scheme were applied simultaneously, non-physical oscillations near the sharp step would appear. In the transient case, the oscillations were weaker in a context of the VC FVM than those in a context of the CC FVM, while the effect was reversed in the steady case. To eliminate disadvantages in the gradient-based r-factor formula, a new modification method by limiting values on the virtual node, namely in the paper, was validated by the tests to effectively dissipate spurious oscillations. 相似文献
10.
In this paper, we develop a two-scale operator-splitting method for the classical two-phase flow model, which handles advective and diffusive processes on different grids. The aim is to reduce computational complexity without loss of accuracy by using the numerical flexibility of operator-splitting techniques. To enhance the stability and the robustness with regards to sharp fronts, an additional slope limiter is introduced as a local post-processing step. For simplicity of notation, we provide the method in one dimension first and then generalize it to higher dimensions. Numerical examples illustrate the effect of the slope-limiting step and show the performance and flexibility of the proposed two-scale method. 相似文献
1