Abstract: In this paper, we study a dynamic fluid-structure interaction (FSI) problem involving a rotational elastic turbine, which is modeled by the incompressible fluid model in the fluid domain with the arbitrary Lagrangian-Eulerian (ALE) description and by the St. Venant-Kirchhoff structure model in the structure domain with the Lagrangian description, and the application to a hemodynamic FSI problem involving an artificial heart pump with a rotating rotor. A linearized rotational and deformable structure model is developed for the rotating rotor and a monolithic mixed ALE finite element method is developed for the hemodynamic FSI system. Numerical simulations are carried out for a hemodynamic FSI model with an artificial heart pump, and are validated by comparing with a commercial CFD package for a simplified artificial heart pump.

Abstract: In this paper, the influence of depth from the free surface of the fish and turning motion will be clarified by numerical simulation. We used Moving-Grid Finite volume method and Moving Computational Domain Method with free surface height function for numerical simulation schemes. Numerical analysis is performed by changing the radius at a certain depth, and the influence of the difference in radius is clarified. Next, analyze the fish that changes its depth and performs rotational motion at the same rotation radius, and clarify the influence of the difference in depth. In any cases, the drag coefficient was a positive value, the side force coefficient was a negative value and the lift coefficient was a smaller value than drag. Analysis was performed with the radius of rotation changed at a certain depth. The depth was changed and the rotational motion at the same rotation radius was analyzed. As a result, it was found the following. The smaller radius of rotation, the greater the lift and side force coefficients. The deeper the fish from free surface, the greater the lift coefficient. It is possible to clarify the influence of depth and radius of rotation from the free surface of submerged fish that is in turning motion on the flow.

Abstract: The full paper describes a three-part numerical investigation of fluid flow and heat transfer in a bend situation that has not been studied in the past. The investigation is motivated by interest in how downstream fluid-flow and heat transfer processes are affected by upstream flow disturbances. The investigated physical situation is a 90o pipe bend fitted with a wall-adjacent obstruction that partially blocks the flow cross section. The first phase of the work consisted of comparing results of numerical simulations with experimental data. The second phase of the paper is focused on determining the impact of the inlet flow distribution on the pressure drop in the bend proper and in the attached pipe. Heat transfer in a straight pipe situated downstream of the bend exit is the focus of the third and the most significant section of the paper. The heat transfer results are reported in terms of the circumferentially averaged Nusselt number displayed as a function of position along the pipe for Reynolds numbers ranging from 100 to 10,000. Each set of simulations consisted of cases with two different bend radii, each being simulated for six different Reynolds numbers between 100 and 10,000. There were four different sets, ranging from no blockage to as high as 60% blockage, all created using an orifice situated at the same position right before the start of the bend. It was found that the disturbances caused by the blockage significantly enhance the Nusselt number values. As expected for Nusselt numbers in the section of pipe after the bend, the numbers are higher for higher Reynolds number flows. Nusselt numbers increase non-monotonically with increase in blockage upstream of the flow, possibly due to jet-like flow patterns that develop as a result of increased blockage. A rather unsuspected result is that Nusselt numbers are seemingly more affected by the sharpness of the bends than the blockage ratio such that increasing the sharpness of the pipe bend increases the Nusselt number right after the bend more than increasing the blockage ratio does. Another interesting phenomenon demonstrated in these numerical investigations is the existence of plateaus in what was expected to be monotonic decrease in Nusselt numbers along the straight sections of pipes after the bend, specifically in high Reynolds number flows. Given that this cannot be explained by existing understanding of heat transfer in pipe bends, experimental verification of this phenomenon would be the logical next step in understanding heat transfer in pipe bends.

Abstract: The modified Buckley-Leverett (MBL) equation describes two-phase flow in porous media, and it is a prototype for modeling the underground oil recovery process. In this paper, we extend the second and third order classical central schemes for the hyperbolic conservation laws to solve the MBL equation which is of pseudo-parabolic type. The MBL equation differs from the classical Buckley-Leverett (BL) equation by including a balanced diffusive-dispersive combination. The classical BL equation gives a monotone water saturation profile for any Riemann problem; on the contrast, when the dispersive parameter is large enough, the MBL equation delivers non-monotone water saturation profiles for certain Riemann problems as suggested by the experimental observations. Numerical results in this paper confirm the existence of non-monotone water saturation profiles consisting of constant states separated by shocks.

Abstract: A stable gas-kinetic scheme based on circular function is proposed for simu-lation of viscous compressible flows in this paper. The main idea of this scheme is to simplify the integral domain of Maxwellian distribution func-tion over the phase velocity and phase energy to modified Maxwellian func-tion, which will integrate over the phase velocity only. Then the modified Maxwellian function can be degenerated to a circular function with the as-sumption that all particles are distributed on a circle. Firstly, the RAE2822 airfoil is simulated to validate the accuracy of this scheme. Then the nose part of an aerospace plane model is studied to prove the potential of this scheme in industrial application. Simulation results show that the method presented in this paper has a good computational accuracy and stability.

Abstract: We study a new edge stabilization method for the finite element discretization of the convection-dominated diffusion-convection equations. In addition to the stabilization of the jump of the normal derivatives of the solution across the inter-element-faces, we additionally introduce a SUPG/GaLS-like stabilization term but on the domain boundary other than in the interior of the domain. New stabilization parameters are also designed. Stability and error bounds are obtained. Numerical results are presented. Theoretically and numerically, the new method is much better than other edge stabilization methods and is comparable to the SUPG method, and generally, the new method is more stable than the SUPG method.

Abstract: The behavior prediction of the transport system of a region and optimization of such a system in connection with the data networks, especially for large-scale areas, seems very necessary and quite challenging problem and attracts an attention of many researchers [1]. Due to extensive expansion of cities, increase of the number of vehicles on the roads and constant grow of the transportation lines with increased complexity, this task is up-to-date and hard to solve with the methods presented at the moment. Empirical correlations or data obtained during observations of some crucial areas of interest are not always enough to predict parameters of that networks at different states, critical situations or moments of time, therefore numerical simulation seems to be a good choice to predict traffic flow behavior. It should be mentioned that numerical methods used earlier are not always capable to deal with the large-scale problems due to dependence on the extensive computational resources or inability to resolve local features of the transport flow and data networks [2]. Existing mathematical models can be divided into two classes: a) local microscopic models which are working on car-by-car basis [3] and b) continuum-like models which are dealing with the entire traffic flow and operating with the averaged quantities [4]. The first class is capable to resolve interaction between different vehicles, data transfer between cars or between a car and a road infrastructure, thus providing detailed information in critical areas (crossroads, joints, etc.), but requires significant amount of computational resources as simulated domain grows. The continuum approach, on the other hand, is much less resource demanding and suitable to simulate large-scale road elements (long parts of the roads, for example), but unable to resolve complex parts of the transportation system without some additional knowledge about traffic flow in that regions obtained “a-priori”. Presented work is focused on the overcoming of two deficiencies of both classes by the proposal of a hybrid modeling approach. This approach utilizes both types of methods at different scales. For the local (small) scale the microscopic models are used to obtain distribution of traffic parameters at particular road elements and provide network data distribution between road users. The integration procedure is performed for car parameters such as density and velocity and averaged values is substituted into the continuum-like model based on the hydrodynamic approach. That part of the algorithm performs the simulation of the entire transport network at macro scales without detailed description of local elements, and output values obtained at that step are used as input values for the microscopic model. Therefore, an iterative technique is performed to obtain developed transport flow for the entire region. In parallel, the traffic flow information will be used to predict the load of the data networks which are used for communication purposes between vehicles and road infrastructure and evaluation of data payload optimization will be conducted to provide sufficient throughput and reliability of such networks. The algorithm is implemented on the basis of high level programming language and initial simulations for the purpose of the testing and validation will be conducted. These simulations will be compared along with the experimental data obtained by the means of the experimental apparatus initially prepared by the research group from SPbSPU. The paper is presented within the framework of the project No. 18-07-00430 which is supported by the Russian Foundation for Basic Research. 1. Xinkai Wu, Henry X. Liu, Using high-resolution event-based data for traffic modeling and control: An overview, Transportation Research Part C, 2014, Vol. 42, P. 28–43. 2. M. Kontorinaki, A. Spiliopoulou, C. Roncoli, M. Papageorgiou, First-order traffic flow models incorporating capacity drop: Overview and real-data validation, Transportation Research Part B, 2017, Vol. 106, P. 52-75. 3. Nagel K., Schreckenberg M. A cellular automaton model for freeway traffic. Phys. I France, 1992, Vol. 2, P. 2221–9. 4. C. Wagner, A Navier-Stokes-like traffic model, Physica A, 1997, Vol. 245, P. 124-38.

Abstract: An conservative remapping scheme often requires intersections between two mesh and a reconstruction scheme on the old cells (Lagrangian mesh). Computing the exact overlaps is complicated even in the simplest case. In this paper, We propose method to calculate intersections of two dismissable general quadrilateral mesh of the same logically structure in a planar domain. The quadrilateral polygon intersection problem is reduced to a problem that how an edge in a new mesh intersects with a local frame which consists at most 7 connected edges in the old mesh. As such, locality of the method is persevered. The alternative direction technique is applied to reduce the dimension of the searching space, We call the method as a symmetric sweep algorithm. It reduces more than 256 possible intersections between a new cell with the old mesh to 34 (17 when considering symmetry) programmable intersections between an edge and an local frame whenever the intersection between the old and new cell does not degenerate. Besides, we shall show how the computational amount depends on the underlying problem in term of singular intersection points. A simple and detailed classification on the type of overlaps is presented. According to classification, degeneracy of an intersection can be easily identified.

Abstract: This paper presents a finite element solver for linear poroelasticity problems on quadrilateral meshes based on the displacement-pressure two-field model. This new solver combines the Bernardi-Raugel element for linear elasticity and a weak Galerkin element for Darcy flow through the implicit Euler temporal discretization. The solver does not use any penalty factor and has less degrees of freedom compared to other existing methods. The solver is free of nonphysical pressure oscillations, as demonstrated by numerical experiments on two widely tested benchmarks. Extension to other types of meshes in 2-dim and 3-dim is also discussed.

Abstract: In this paper, we improve the preprocessing phase of the ALT algorithm through parallelization. ALT is a preprocessing-based, goal-directed speed-up technique that uses A* (A star), Landmarks and Triangle inequality which allows fast computations of shortest paths (SP) in large-scale networks. Although faster techniques such as arc-flags, SHARC, Contraction Hierarchies and Highway Hierarchies already exist, ALT is usually combined with these faster algorithms to take advantage of its goal-directed search to further reduce the SP search calculation time and its search space. However, ALT relies on landmarks and optimally choosing these landmarks is NP-hard, hence, no effective solution exists. Since landmark selection relies on constructive heuristics and the current SP search speed-up is inversely proportional to landmark generation time, we propose a parallelization technique which cuts the landmark generation time significantly while increasing its effectiveness.

Abstract: In this talk, we discuss our recent efforts on developing efficient open-access computational tools for poroelasticity. In particular, we examine (1) the newly added Matlab modules to our code package DarcyLite; (2) our new efforts on C++ modules for deal.II package. Several new finite element solvers have been implemented. These include utilizing the novel Arbogast-Correa elements within the weak Galerkin framework to solve Darcy, elasticity, and poroelasticity problems. Numerical simulations will be presented.

Abstract: In this paper, we study linearly first and second order in time, uniquely solvable and unconditionally energy stable numerical schemes to approximate the phase field model of solid-state dewetting problems based on the novel approach SAV (scalar auxiliary variable), a new developed efficient and accurate method for a large class of gradient flows. The schemes are based on the first order Euler method and the second order backward differential formulas(BDF2) for time discretization, and finite element methods for space discretization. It is shown that the schemes are unconditionally stable and the discrete equations are uniquely solvable for all time steps. we present some numerical experiments to validate the stability and accuracy of the proposed schemes.

Abstract: A novel numerical scheme including time and spatial discretization is presented for the coupled Cahn-Hilliard and Navier-Stokes equations in this paper. Variable densities and viscosities are considered in the numerical scheme. By introducing an intermediate velocity in both Cahn-Hilliard equation and the momentum equation, the scheme can keep the discrete energy law. A splitting method based on the pressure stabilization is implemented to solve the Navier-Stokes equation, while the stabilization approach or convex splitting method is used for the Cahn-Hilliard equation. This novel scheme is totally decoupled, linear, unconditionally energy stable for two-phase incompressible flow diffuse interface model. Numerical results demonstrate the validation, accuracy, robustness and discrete energy law of the proposed scheme in this paper.

Abstract: In this paper, we firstly study numerical methods for gas flow simulation in dual-continuum porous media. Typical methods for oil flow simulation in dual-continuum porous media cannot be used straightforward to this kind of simula-tion due to the artificial mass loss caused by the compressibility and the non-robustness caused by the non-linear source term. To avoid these two problems, corrected numerical methods are proposed using mass balance equations and lo-cal linearization of the non-linear source term. The improved numerical methods are successful for the computation of gas flow in the double-porosity double-permeability porous media. After this improvement, temporal advancement for each time step includes three fractional steps: i) advance matrix pressure and frac-ture pressure using the typical computation; ii) solve the mass balance equation system for mean pressures; iii) correct pressures in i) by mean pressures in ii). Numerical results show that mass conservation of gas for the whole domain is guaranteed while the numerical computation is robust.

Abstract: We study the numerical approximation of the incompressible miscible displacement equations on general quadrilateral grids in two dimensions. The flow equation is discretized by multipoint flux mixed finite element method and the transport equation is approximated by discontinuous Galerkin method. First-order convergence for velocity in $L^{\infty}(L^2)$ and concentration in $L^2(H^1)$ is derived. A numerical example is presented to support the theoretical analysis.

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.