原子力プラントのライフサイクル情報管理に基づく廃炉シミュレーションに関する研究

Tohoku University博士（情報科学）thesi

Workshop on Grid Generation and Related Areas

A collection of papers given at the Workshop on Grid Generation and Related Areas is presented. The purpose of this workshop was to assemble engineers and scientists who are currently working on grid generation for computational fluid dynamics (CFD), surface modeling, and related areas. The objectives were to provide an informal forum on grid generation and related topics, to assess user experience, to identify needs, and to help promote synergy among engineers and scientists working in this area. The workshop consisted of four sessions representative of grid generation and surface modeling research and application within NASA LeRC. Each session contained presentations and an open discussion period

Proceedings for the ICASE Workshop on Heterogeneous Boundary Conditions

Domain Decomposition is a complex problem with many interesting aspects. The choice of decomposition can be made based on many different criteria, and the choice of interface of internal boundary conditions are numerous. The various regions under study may have different dynamical balances, indicating that different physical processes are dominating the flow in these regions. This conference was called in recognition of the need to more clearly define the nature of these complex problems. This proceedings is a collection of the presentations and the discussion groups

Semiannual report, 1 October 1990 - 31 March 1991

Research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics, numerical analysis, and computer science is summarized

Simulation of Conformal Spiral Slot Antennas on Composite Platforms

During the course of the grant, we wrote and distributed about 12 reports and an equal number of journal papers supported fully or in part by this grant. The list of reports (title & abstract) and papers are given in Appendices A and B. This grant has indeed been instrumental in developing a robust hybrid finite element method for the analysis of complex broadband antennas on doubly curved platforms. Previous to the grant, our capability was limited to simple printed patch antennas on mostly planar platforms. More specifically: (1) mixed element formulations were developed and new edge-based prisms were introduced; (2) these elements were important in permitting flexibility in geometry gridding for most antennas of interest; (3) new perfectly matched absorbers were introduced for mesh truncations associated with highly curved surfaces; (4) fast integral algorithms were introduced for boundary integral truncations reducing CPU time from O(N-2) down to O(N-1.5) or less; (5) frequency extrapolation schemes were developed for efficient broadband performance evaluations. This activity has been successfully continued by NASA researchers; (6) computer codes were developed and extensively tested for several broadband configurations. These include FEMA-CYL, FEMA-PRISM and FEMA-TETRA written by L. Kempel, T. Ozdemir and J. Gong, respectively; (7) a new infinite balun feed was designed nearly constant impedance over the 800-3000 MHz operational band; (8) a complete slot spiral antenna was developed, fabricated and tested at NASA Langley. This new design is a culmination of the projects goals and integrates the computational and experimental efforts. this antenna design resulted in a U.S. patent and was revised three times to achieve the desired bandwidth and gain requirements from 800-3000 MHz

Low-Rank Iterative Solvers for Large-Scale Stochastic Galerkin Linear Systems

Otto-von-Guericke-Universität Magdeburg, Fakultät für Mathematik, Dissertation, 2016von Dr. rer. pol. Akwum Agwu OnwuntaLiteraturverzeichnis: Seite 135-14

Multiblock modeling of flow in porous media and applications

We investigate modeling flow in porous media in multiblock domain. Mixed finite element methods are used for subdomain discretizations. Physically meaningful boundary conditions are imposed on the non-matching interfaces via mortar finite element spaces. We investigate the pollution effect of nonmatching grids error on the numerical solution away from interfaces. We prove that most of the error in the velocity occurs along the interfaces, and that high accuracy is preserved in the interior of the subdomains. In case of discontinuous coefficients, the pollution from the singularity affects the accuracy in the whole domain. We investigate the upscaling error resulting when fine resolution data is approximated on a very coarse scale. Extending work of Wheeler and Yotov, we incorporate this upscaling error in an a posteriori error estimator for the pressure, velocity and mortar pressure. We employ a non-overlapping domain decomposition method reducing the global system to one that is solved iteratively via a preconditioned conjugate gradient method. This approach is suitable for parallel implementation. The balancing domain decomposition method for mixed finite elements following Cowsar, Mandel, and Wheeler is extended to the case of mortar mixed finite elements on non-matching multiblock grids. The algorithm involves solution of a mortar interface problem with one local Dirichlet solve and one local Neumann solve on each iteration. A coarse solve is used to guarantee consistency and to provide global exchange of information. Quasi-optimal condition number bounds independent of the jump in coefficients are derived. We finally consider multiscale mortar mixed finite element discretizations for single and two phase flows. We show optimal convergence and some superconvergence in the fine scale for the solution and its flux. We also derive efficient and reliable a posteriori error estimators suitable for adaptive mesh refinement. We have incorporated the above methods into a parallel multiblock simulator on unstructured prismatic meshes employing a non-overlapping domain decomposition algorithm and mortar spaces. Numerical experiments are presented confirming all theoretical results

Modelling In-situ Upgrading (ISU) of heavy oil using dimensionless analysis and operator splitting method

The In-Situ Upgrading (ISU) of bitumen and oil shale is a very challenging process to model numerically because a large number of components need to be modelled using a system of equations that are both highly non-linear and strongly coupled. In addition to the transport of heat by conduction and convection, and the change of properties with varying pressure and temperature, these processes involve transport of mass by convection, evaporation, condensation and pyrolysis chemical reactions. The behaviours of these systems are difficult to predict as relatively small changes in the material composition can significantly change the thermophysical properties. Accurate prediction is further complicated by the fact that many of the inputs needed to describe these processes are uncertain, e.g. the reaction constants and the temperature dependence of the material properties. The large number of components and chemical reactions involves a non-linear system that is often too large for full field simulation using the Fully Implicit Method (FIM). Operator splitting (OS) methods are one way of potentially improving computational performance. Each numerical operator in a process is modelled separately, allowing the best solution method to be used for the given numerical operator. A significant drawback to the approach is that decoupling the governing equations introduces an additional source of numerical error, known as splitting error. Obviously the best splitting method for modelling a given process is the one that minimises the splitting error whilst improving computational performance over that obtained from using a fully implicit approach. Although operator splitting has been widely used for the modelling of reactive-transport problems, it has not yet been applied to models that involve the coupling of mass transport, heat transfer and chemical reactions. One reason is that it is not clear which operator splitting technique to use. Numerous such techniques are described in the literature and each leads to a different splitting error, which depends significantly on the relative importance of the mechanisms involved in the system. While this error has been extensively analysed for linear operators for a wide range of methods, the results observed cannot be extended to general non-linear systems. It is therefore not clear which of these techniques is most appropriate for the modelling of ISU. Analysis using dimensionless numbers can provide a useful insight into the relative importance of different parameters and processes. Scaling reduces the number of parameters in the problem statement and quantifies the relative importance of the various dimensional parameters such as permeability, thermal conduction and reaction constants. Combined with Design of Experiments (DOE), which allows quantification of the impact of the parameters with a minimal number of numerical experiments, dimensionless analysis enables experimental programmes to be focused on acquiring the relevant data with the appropriate accuracy by ranking the different parameters controlling the process. It can also help us design a better splitting method by identifying the couplings that need to be conserved and the ones that can be relaxed. This work has three main objectives: (1) to quantify the main interactions between the heat conduction, the heat and mass convection and the chemical reactions, (2) to identify the primary parameters for the efficiency of the process and (3) to design a numerical method that reduces the CPU time of the simulations with limited loss in accuracy. We first consider a simplified model of the ISU process in which a solid reactant decomposes into non-reactive gas. This model allows us to draw a parallel between the in-situ conversion of kerogen and the thermal decomposition of polymer composite when used as heat-shield. The model is later extended to include a liquid phase and several reactions. We demonstrate that a ISU model with nf fluid components, ns solid components and k chemical reactions depends on 9+k*(3+nf+ns-2)+8nf+2ns dimensionless numbers. The sensitivity analysis shows that (1) the heat conduction is the primary operator controlling the time scale of the process and (2) the chemical reactions control the efficiency of the process through the extended Damköhler numbers, which quantify the ratio of chemical rate to heat conduction rate at the heater temperature for each reaction in the model. In the absence of heat loss and gravity effects, we show that the ISU process is most efficient at a heater temperature for which the minimum of the extended Damköhler numbers of all reactions included in the model was between 10 and 20. For the numerical method, the standard Iterative Split Operator (ISO) does not perform well due to many convergence failures, whereas the standard Sequential Split Operator (SSO) and the Strang-Marchuk Split Operator (SMSO) give large discretization errors. We develop a new method, called SSO-CKA, which has smaller discretization error. This method simply applies SSO with three decoupled operators: the heat conduction (operator $C$), the chemical reactions (operator $K$) and the heat and mass convection (operator $A$), applied in this order. When we apply SSO-CKA with the second-order trapezoidal rule (TR) for solving the chemical reaction operator, we obtain a method which generally gives smaller discretization errors than FIM. We design an algorithm, called SSO-CKA-TR-AIM, which is faster and generally more accurate than FIM for simulations with a kinetic model including a large number of components that could be regrouped into a small number of chemical classes for the advection and heat conduction operator. SSO-CKA works best for ISU models with small reaction enthalpies and no other reaction than pyrolysis reactions, but can give a large discretization method for ISU models with non-equilibrium reactions.Open Acces

Phase behaviour studies related to biodiesel production using supercritical methanol

Biodiesel is a promising renewable and sustainable fuel that can replace fossil fuels. Among the different techniques used to produce biodiesel, the transesterification process is currently the preferred method. The conventional transesterification process is based on acid-base catalysis, but this technique has many drawbacks including a requirement for high-purity feedstocks, and costly pre-treatment and downstream processes. A recent alternative process, using a supercritical alcohol (preferably methanol) without a catalyst, may offer some advantages. This process can utilise a wide range of potential feedstocks (especially wastes), shows high production efficiency, and requires only simple post-processing. However, this technique requires conditions of high temperature and high pressure which increase the utility costs and may restrict the economic feasibility and sustainability of the process. In order to fully explore these issues and to optimise the process conditions, better understanding of the phase behaviour of the mixtures involved in the biodiesel process is required. The components of interest include fatty acids, esters alcohols and co-solvent such as carbon dioxide and the conditions include high pressures and wide ranges of temperature. Phase equilibrium studies on systems relevant to biodiesel production with supercritical methanol available in the literature are very limited. The principal focus of this project is the experimental investigation of the phase behaviour of representative mixtures with small molecular chains, which exist during biodiesel production, over wide ranges of temperatures and pressures. In addition to the experimental work, the research will include both modelling works on the mixtures of interest supported by a simulation for the process using gPROMS, a simulation tool developed by Process Systems Enterprise (PSE) company. In this project, new fluid-phase equilibrium measurements have been carried out on two relevant representative binary systems: (methyl propanoate + carbon dioxide) and (butanoic acid + carbon dioxide) using a high-pressure quasi-static analytical apparatus with compositional analysis using a gas chromatography. The measurements for the (methyl propanoate + carbon dioxide) mixture were made along six isotherms at temperatures from (298.15 to 423.15) K and at pressures up to near the mixture critical pressure at each temperature while for the mixture (butanoic acid + carbon dioxide) the measurements were made along eight isotherms at temperatures from (323.13 to 423.2) K and pressures up to the mixture critical pressures. Vapour-liquid equilibrium (VLE) data obtained for the mixtures have been compared with the predictions of SAFT- Mie model, a group-contribution version of the Statistical Associating Fluid Theory (SAFT). The group interaction parameters in SAFT- Mie reported in literature have been revised by fitting to the new experimental VLE data. After parameters optimisation, the model was found to be in a good agreement with the measured VLE data for both bubble and dew points. The experimental data were also compared with the description of Peng Robinson equation of state (PR EoS) combined with the classical one-fluid mixing rules integrating one temperature-independent binary interaction parameter for (methyl propanoate + carbon dioxide) system and two temperature-independent binary interaction parameters for (butanoic acid + carbon dioxide) system. The results after tuning show that the PR EoS can also predict well the system measured data, except in the critical regions in which PR EoS shows overprediction. Furthermore, the phase equilibria of (methyl propanoate + propionic acid + carbon dioxide), (tert-butanol + water + carbon dioxide) and (toluene + water + carbon dioxide) ternary systems were studied by the means of the high-pressure quasi-static analytical apparatus. Compositions of present phases coexisting in vapour-liquid equilibrium (VLE) for (methyl propanoate + propionic acid + carbon dioxide) mixture were measured along six isotherms at temperatures from (323.12 to 423.11) K and pressures from (1 to 20) MPa at equal feed molar ratio of (methyl propanoate + propionic acid). Phase behaviour measurements were also collected at different compositions of the mixture (methyl propanoate + propionic acid) at fixed temperatures and pressures. Compositions of coexisting phases of the ternary system (tert-butanol + carbon dioxide + water) have been obtained along five isotherms at temperatures of (283.2, 298.18, 323.13, 373.10 and 423.17) K and at pressures of (4.0, 8.0, 12.0 and 18.0) MPa with different known feed compositions of (tert-butanol + water) while the phase behaviour of the system (toluene + water + carbon dioxide) was investigated along four isotherms at temperatures from (338.15 to 413.15) K and pressures up to the upper critical end point (UCEP). The data obtained for the ternary mixtures have been compared with the descriptions of SAFT- Mie and PR equation of states. Other cross interactions available in biodiesel systems such as (COOH - CH3OH), (OH_Gl - CH3OH), (CO2 - CH=), (CH3OH - CH=), (COOH - CH=) and (H2O - CH=) were estimated in this work by regression to fluid-phase behaviour data published in literature. The comparison between the predictions of SAFT- Mie reported in literature and those of SAFT- Mie after refining the parameters were shown. Preliminary designs of one-step process (transesterification) and two-step processes (hydrolysis and esterification) for biodiesel production under supercritical conditions were suggested and simulated using gPROMS ProcessBuilder software. The CO2 co-solvent effect on the one-step process based on literature data was also examined by a process flowsheet. The research including new phase behaviour measurements, modelling and gPROMS simulation is expected to contribute to optimisation of biodiesel production processes.Open Acces