Abstract: Flash calculations are a performance bottleneck of compositional flow simulations. Some work has demonstrated the feasibility of using sparse grid techniques to remove the bottleneck, but a complete realisation of the idea is still not available. Thus, this work fills the niche. By introducing a new concept of layer to sparse grid points, the sparse grid construction can become much efficient. As a result, a much easier data structure the array can be used to store the sparse grids. Compared with the popular data structures to store the sparse grids such as the hash table and the tree, the array can minimize the space size and the traversing time, and at the same time reduce the number of points in the sparse grids by removing the architecture ancestors in the tree, which in turn makes parallelization of flash calculations come true. All of them are not only contributions to flash calculations, but also contributions to existing sparse grid techniques. Moreover, both of the sparse grid construction and interpolation algorithms can be done in parallel. Different from the former parallel algorithms in sparse grid techniques, which have troubles in decomposing the domain equally and keeping load balance among the processors, our parallel algorithm can achieve load balance easily among the threads for any sparse grid configurations. Lastly, multicomponent experiments are also carried out to demonstrate the accuracy, correctness and efficiency of the algorithms.

Abstract: Displacement methane (CH4) by injection gases is regarded an effective way to exploit shale gas and sequestrate carbon dioxide (CO2). In this study, we use grand canonical Monte Carlo (GCMC) simulation to investigate the displacement CH4 by injection gases firstly. Then, molecular dynamics (MD) simulation is used to investigated the adsorption occurrence behavior of CH4 in different pore size. The shale model is constructed by organic and inorganic material, which is an original and comprehensive simplification for the real shale composition. The results show that both the displacement amount of CH4 and sequestration amount of CO2 see an upward trend with the increase of pore size. The CO2 molecules can replace the adsorbed CH4 from the adsorption sites directly. On the contrary, when N2 molecules are injected into the pores, these molecules can decrease the partial pressure of CH4. With the increase of the pores width, the adsorption oc-currence transfers from single adsorption layer to four adsorption layers. It is ex-pected that our work can reveal the mechanisms of adsorption and displacement of shale gas, which could provide a guidance and reference for displacement ex-ploitation of shale gas and sequestration of CO2.

Abstract: A coupled LBGK scheme, constituting of two independent distribution functions describing velocity and temperature respectively, is established in this paper. Chapman-Enskog expansion, a procedure to prove the consistency of this mesoscopic method with macroscopic conservation laws, is also conducted for both lattice scheme of velocity and temperature, as well as a simple introduction on the common used DnQb model. An efficient coding manner for Matlab is proposed in this paper, which improves the coding and calculation efficiency at the same time. The compact and efficient scheme is then applied in the simulation of Rayleigh-Benard convection, which is a natural heat convection problem common seen in modern industries. The results are interesting and reasonable, and meet the experimental data well. The stability of this scheme is also proved through different cases with a large range of Rayleigh number, until 2 million.

Abstract: Natural gas pipeline networks are the primary means of transporting natural gas, and safety is the priority in production operation. Investigating the vulnerability of natural gas pipeline networks can effectively identify weak links in the pipeline networks and is critical to the safe operation of pipeline networks. In this paper, based on network evaluation theory, a pipeline network topology-based natural gas pipeline network method to identify sources of vulnerability was developed. In this process, based on characteristics of actual flow in natural gas pipeline networks, network evaluation indices were improved to increase the accuracy of the identification of sources of vulnerability for natural gas pipeline networks. Based on the improved index, a topology-based identification process for sources of vulnerability for natural gas pipeline networks was created. Finally, the effec-tiveness of the proposed method was verified via pipeline network hydraulic simulation. The result shows that the proposed method is simple and can accu-rately identify sources of vulnerability in the nodes or links in natural gas pipeline networks.

Abstract: Due to complicated rheological behaviors and elastic effect of viscoelastic fluids, there are very few literatures reporting the large-eddy simulation (LES) studies on turbulent drag-reduction (DR) mechanism of viscoelastic fluids. In addition, these few studies are limited within the low Reynolds number situations. In this paper, LES approach is employed to further investigate the flow characteristics and DR mechanism of high Reynolds viscoelastic turbulent drag-reducing flow. To improve the accuracy of LES, an N-parallel FENE-P constitutive model based on multiple relaxation times and an improved mixed subgrid-scale (SGS) model are both utilized. DR rate and velocity fluctuations under different calculation conditions are analyzed. Contributions of different shear stresses on frictional resistance coefficient, and turbulent coherent structures which are closely related to turbulent burst events are investigated in details to further reveal the DR mechanism of high Reynolds viscoelastic turbulent drag-reducing flow. Especially, the different phenomena and results between high Reynolds and low Reynolds turbulent flows are addressed. This study is expected to provide beneficial guidance to the engineering application of turbulent DR technology.