Comparison of multiphase SPH and LBM approaches for the simulation of intermittent flows

Smoothed Particle Hydrodynamics (SPH) and Lattice Boltzmann Method (LBM) are increasingly popular and attractive methods that propose efficient multiphase formulations, each one with its own strengths and weaknesses. In this context, when it comes to study a given multi-fluid problem, it is helpful to rely on a quantitative comparison to decide which approach should be used and in which context. In particular, the simulation of intermittent two-phase flows in pipes such as slug flows is a complex problem involving moving and intersecting interfaces for which both SPH and LBM could be considered. It is a problem of interest in petroleum applications since the formation of slug flows that can occur in submarine pipelines connecting the wells to the production facility can cause undesired behaviors with hazardous consequences. In this work, we compare SPH and LBM multiphase formulations where surface tension effects are modeled respectively using the continuum surface force and the color gradient approaches on a collection of standard test cases, and on the simulation of intermittent flows in 2D. This paper aims to highlight the contributions and limitations of SPH and LBM when applied to these problems. First, we compare our implementations on static bubble problems with different density and viscosity ratios. Then, we focus on gravity driven simulations of slug flows in pipes for several Reynolds numbers. Finally, we conclude with simulations of slug flows with inlet/outlet boundary conditions. According to the results presented in this study, we confirm that the SPH approach is more robust and versatile whereas the LBM formulation is more accurate and faster

Lithospheric electrical conductivity structure across Southern Scotland and Northern England

Magnetotelluric soundings in the range (100-0.01Hz. ) have been carried out along a 140 km. profile across S.Scotland and N.England. Following discussion of the steps taken to reduce cultural noise in the response functions, the results for 13 stations along the traverse are presented. Since the study of dimensionality parameters supports 1-D modelling, rotationally invariant resistivity-depth data have been subjected to two 1-D inversion schemes and the different parameters of the model derived have been examined using the Most squares approach. Two dimensional numerical modelling has also been carried out considering both the present data and those of earlier induction studies along the profile.The resulting geoelectrical model confirms the existence of a crustal conducting layer (10-50 Ohm.m.) as found in earlier induction studies. Results of this study show additionally that- a) the conductor rises to a depth of nearly 3.5 km. about 20km. south of the SUF i.e., near the axis of the Eskdalemuir magnetic variation anomaly b) the conductor is at a depth of about 8-10 km. in region of the Weardale granite in N. England, c) there is a marked resistivity-depth variation below S.Scotland and d) the surface resistivity along the profile decreases from NW to SE and corresponds well to the Ordovician, the Silurian and the Carboniferous sediments. The geophysical interpretation of the model has been discussed in association with the results of earlier induction studies, seismic and gravity studies and the various tectonic models of the Iapetus suture zone. Based on the present study and comparison with electric structures of other tectonic regions, a hypothetical tectonic model has been proposed for this study region. It comprises a resistive triangular wedge surrounded by a conducting layer which is incorporated as a signature for the presence of a subducting plate in an island arc environment.In addition to these field investigations, several computational analyses have also been undertaken. The main studies were - a) procedures to reduce noise from the recorded data using digital filtering techniques and b) determination of the distortion of telluric field measurements due to a conducting hill using a conformal mapping method. Digital filters have been discussed with special reference to persistent noise signals, eg. power lines, electrical fences etc. Delay line filtering, notch filtering and the maximum entropy method have been applied to both synthetic and field data and the results are discussed. The effect of a two-dimensional conducting hill on the telluric fields measured on a horizontal surface has been studied using the Schwartz-Christoffel conformal transformation technique. The results indicated that the distortion depends strongly on the inclination, height of the hill and depth to the basement. The distortion of apparent resistivity values computed from MT field measurements has also been discussed.In addition, some consideration has been given to - a) the processing of the data in the time domain using adaptive filters, b) the application of joint inversion of DC-AMT data to resolve shallow structures in N.England and c) the distortion effects of near surface inhomogeneities in N.England.These various studies are presented in 7 chapters with 3 Appendices and the results are discussed in chapter-8, where the conclusions and suggestions for further work are also presented

Digital Signal Processing Research Program

Contains table of contents for Section 2, an introduction, reports on twenty-one research projects and a list of publications.U.S. Navy - Office of Naval Research Grant N00014-93-1-0686Lockheed Sanders, Inc. Contract P.O. BY5561U.S. Air Force - Office of Scientific Research Grant AFOSR 91-0034National Science Foundation Grant MIP 95-02885U.S. Navy - Office of Naval Research Grant N00014-95-1-0834MIT-WHOI Joint Graduate Program in Oceanographic EngineeringAT&T Laboratories Doctoral Support ProgramDefense Advanced Research Projects Agency/U.S. Navy - Office of Naval Research Grant N00014-89-J-1489Lockheed Sanders/U.S. Navy - Office of Naval Research Grant N00014-91-C-0125U.S. Navy - Office of Naval Research Grant N00014-89-J-1489National Science Foundation Grant MIP 95-02885Defense Advanced Research Projects Agency/U.S. Navy Contract DAAH04-95-1-0473U.S. Navy - Office of Naval Research Grant N00014-91-J-1628University of California/Scripps Institute of Oceanography Contract 1003-73-5

A coupled thermo-hydro-mechanical model of jointed hard rock for compressed air energy storage

Renewable energy resources such as wind and solar are intermittent, which causes instability when being connected to utility grid of electricity. Compressed air energy storage (CAES) provides an economic and technical viable solution to this problem by utilizing subsurface rock cavern to store the electricity generated by renewable energy in the form of compressed air. Though CAES has been used for over three decades, it is only restricted to salt rock or aquifers for air tightness reason. In this paper, the technical feasibility of utilizing hard rock for CAES is investigated by using a coupled thermo-hydro-mechanical (THM) modelling of nonisothermal gas flow. Governing equations are derived from the rules of energy balance, mass balance, and static equilibrium. Cyclic volumetric mass source and heat source models are applied to simulate the gas injection and production. Evaluation is carried out for intact rock and rock with discrete crack, respectively. In both cases, the heat and pressure losses using air mass control and supplementary air injection are compared

Towards a solution of the closure problem for convective atmospheric boundary-layer turbulence

We consider the closure problem for turbulence in the dry convective atmospheric boundary layer (CBL). Transport in the CBL is carried by small scale eddies near the surface and large plumes in the well mixed middle part up to the inversion that separates the CBL from the stably stratified air above. An analytically tractable model based on a multivariate Delta-PDF approach is developed. It is an extension of the model of Gryanik and Hartmann [1] (GH02) that additionally includes a term for background turbulence. Thus an exact solution is derived and all higher order moments (HOMs) are explained by second order moments, correlation coefficients and the skewness. The solution provides a proof of the extended universality hypothesis of GH02 which is the refinement of the Millionshchikov hypothesis (quasi- normality of FOM). This refined hypothesis states that CBL turbulence can be considered as result of a linear interpolation between the Gaussian and the very skewed turbulence regimes. Although the extended universality hypothesis was confirmed by results of field measurements, LES and DNS simulations (see e.g. [2-4]), several questions remained unexplained. These are now answered by the new model including the reasons of the universality of the functional form of the HOMs, the significant scatter of the values of the coefficients and the source of the magic of the linear interpolation. Finally, the closures 61 predicted by the model are tested against measurements and LES data. Some of the other issues of CBL turbulence, e.g. familiar kurtosis-skewness relationships and relation of area coverage parameters of plumes (so called filling factors) with HOM will be discussed also