Hydrogenerator system identification using a simple geneticalgorithm

This paper investigates an identification procedure for a hydrogenerator plant using an adaptive technique. The procedure operates on field data consisting of sampled gate position and electrical frequency. The field data was recorded while the plant was operating under various load conditions. The procedure adapted to ongoing plant changes by continuously updating the identification results. It is shown that the adaptive technique, in this case genetic algorithm based, was capable of identifying the hydrogenerator system and following plant parameter changes while the plant operated under conditions of sufficient frequency excursions. These conditions include offline and isolated network operation where effective control is critical     

Simulation of combustion process of a single biomass pellet based on heterogeneous-dimension discretization

Abstract

In this paper, one-dimensional intra-pellet solid model combined with multi-dimensional extra-pellet environment model were used to simulate the combustion processes of a biomass pellet in a furnace. The combustion processes of the solid phase were calculated using a self-written MATLAB code, and the processes of the extra-pellet fluid environment were calculated using the commercial CFD code. The two codes were coupled together by exchanging the data of source terms and boundary conditions in real-time. Experiments on combustion of a single corn-stover pellet in a tube furnace were implemented to validate the calculation method and acceptable agreements were obtained, and the main errors are within 10%. The heterogeneous-dimension discretization method made the updating and debugging of the physical and chemical mechanism of the solid phase very easy. Compared with constant environment conditions, the average error of coupling calculation method is decreased by about 5%. The calculation method can be extended to deal with many other problems.     

A Finite-Volume-Based Approach for Dynamic Fluid-Structure Interaction

It is common to adopt finite-element methods to solve solid mechanics problems and finite-volume methods for fluid dynamics computations. The use of different methods causes complication of the solution procedure for problems involving both fluids and solids. In this study, a partitioned approach based on the finite-volume method for dynamic fluid–structure interaction is presented. The method is formulated in a way suitable for an unstructured mesh with arbitrary grid geometry. The variables for the fluid are stored at the centroids of grid cells, whereas those for the solid at the grid nodes. The latter arrangement makes it more suitable for large structure deformation. After spatial discretization for the solid using the finite-volume approach, the resulting system of ordinary differential equations is solved implicitly using the dual-time-stepping scheme. As for the fluid calculation, a pressure-based algorithm is employed and the time step is advanced in a prediction-correction manner. The finite-volume method for the solid is assessed by calculating the deformation and dynamics of a cantilever under various loads. Good agreement with analytical solutions is obtained. Then, the solution procedure is applied to two cases with coupled fluid flow and structure dynamics. One is the flow over a vertical plate with one end fixed on the floor in a channel. The other is the flow over a cylinder with a plate attached to it on the lee side.     

On upgrading the numerics in combustion chemistry codes

A method of updating and reusing legacy FORTRAN codes for combustion simulations is presented using the DAEPACK software package. The procedure is demonstrated on two codes that come with the CHEMKIN-II package, CONP and SENKIN, for the constant-pressure batch reactor simulation. Using DAEPACK generated code, analytical derivative calculations, sparsity pattern information, and hidden discontinuity information can be obtained for the models of interest. This information can be easily integrated with different solvers giving the modeler great flexibility in selecting the best solution procedure. Using the generated code, the CONP code was connected to three different solvers, and the SENKIN code was connected to two different solvers. The effect of model formulation, analytical derivatives, sparsity, and sensitivity equation solution method were analyzed for three large kinetic mechanisms for methane, acetylene, and n-heptane. For the n-heptane model, with 544 species and 2446 reactions, a factor of 10-speed improvement over the original solution procedure was found using analytical derivatives and sparse linear algebra. For sensitivity calculations, for a small number of parameters, a factor of 55 improvement over the original solution procedure was found for the n-heptane problem. Upon closer examination of results, no one method is found to always be superior to other methods, and selection of the appropriate solution procedure requires an examination of the specific kinetic mechanism, which is easily conducted using DAEPACK generated code.     

PARALLEL COMPUTATION OF TURBULENT COMBUSTION AND FLAME SPREAD IN FIRES

A parallel procedure based on a single-program, multiple-data (SPMD) algorithm is presented for parallel computing of turbulent combustion and flame spread in fires. The computation is based on modeling of radiative turbulent reacting flow and pyrolysis of solid fuel. With angular domain decomposition applied to the parallel computing of radiation and spatial domain decomposition to the computation of nonradiative turbulent reacting flow and solid fuel pyrolysis, the whole computation is distributed among a group of concurrent tasks, which communicate with each other through a message-passing interface library. Using this procedure, a self-developed computational combustion code has been parallelized on both a multiprocessor PC and a symmetric multiprocessor (SMP) system, SGI Origin 2000. The parallelization was verified by comparing the parallel results with sequential results. The performance of the parallel procedure was evaluated using various test cases. As expected, the efficiency of parallelism varies with both computer architecture and case scenario. In general, good efficiency was obtained.     

PARALLEL COMPUTATION OF TURBULENT COMBUSTION AND FLAME SPREAD IN FIRES

A parallel procedure based on a single-program, multiple-data (SPMD) algorithm is presented for parallel computing of turbulent combustion and flame spread in fires. The computation is based on modeling of radiative turbulent reacting flow and pyrolysis of solid fuel. With angular domain decomposition applied to the parallel computing of radiation and spatial domain decomposition to the computation of nonradiative turbulent reacting flow and solid fuel pyrolysis, the whole computation is distributed among a group of concurrent tasks, which communicate with each other through a message-passing interface library. Using this procedure, a self-developed computational combustion code has been parallelized on both a multiprocessor PC and a symmetric multiprocessor (SMP) system, SGI Origin 2000. The parallelization was verified by comparing the parallel results with sequential results. The performance of the parallel procedure was evaluated using various test cases. As expected, the efficiency of parallelism varies with both computer architecture and case scenario. In general, good efficiency was obtained.     

A BLOCKED-OFF-REGION STRATEGY TO COMPUTE FIRE-SPREAD SCENARIOS INVOLVING INTERNAL FLAMMABLE TARGETS

ABSTRACT

A finite-volume blocked-off-region procedure is developed to represent internal flammable targets in fire-spread scenarios. In this procedure, the computational domain includes both gas and solid regions. The standard numerical scheme is modified to render hydrodynamically inactive the solid regions and to match the interface conditions at the burning solid surface correctly. A two-grid refinement procedure is used to solve the conjugate heat and mass transfer problem accurately. The first large-scale scenario concerns the flame spread over a vertical panel exposed to a burner flame. Second, the procedure is used to simulate cone calorimeter tests of particle board. For the latter application, the predicted mass loss rates are in qualitative agreement with experimental data.     

Optimizing conditions for obtaining a solid solution of tungsten carbide in titanium carbide by preparing it in a precisely controlled gas medium

A new ecologically acceptable procedure is proposed of preparing a solid solution of titanium carbide–tungsten carbide (TiC–WC) in hydrogen which contains an equilibrium amount of methane. The procedure allows the carbon content of TiC–WC to be obtained with the required precision. The use of the methane–hydrogen medium allows a solid solution to be obtained with no carbon black present. This prevents the detrimental impurities to enter into the solid solution from the carbon black, thus improving properties of carbides and reducing environmental pollution.     

Lattice Boltzmann Simulation of Incompressible Transport Phenomena in Macroscopic Solidification Processes

A lattice Boltzmann (LB) simulation strategy is proposed for the incompressible transport phenomena occurring during macroscopic solidification of pure substances. The proposed model is derived by coupling a passive scalar-based thermal LB model with the classical enthalpy–porosity technique for solid–liquid phase-transition problems. The underlying hydrodynamics are monitored by a conventional single-particle density distribution function (DF) through a kinetic equation, whereas the thermal field is obtained from another kinetic equation which is governed by a separate temperature DF. The phase-changing aspects are incorporated into the LB model by inserting appropriate source terms in the respective kinetic equations through the most formal technique following the extended Boltzmann equations along with an appropriate enthalpy updating scheme. The proposed model is validated extensively with one- and two-dimensional solidification problems for which analytical and numerical results are available in the literature, and finally, it is used for solving a benchmark problem, the Bridgman crystal growth in a square crucible.     

Monte Carlo solution of anisotropic heat conduction

Based on the fixed-step random walk procedure a Monte Carlo algorithm for the solution of anisotropic heat conduction is presented. It is shown that the Monte Carlo solution is attainable only for a specified range of solid thermal conductivities. It is also illustrated that by following two simple clues considerable reduction in computation time may be achieved. Finally, steady-state temperature distribution, obtained by the Monte Carlo calculations, is presented for a two-dimensional anisotropic solid having simple geometry and boundary conditions.     

On estimating thermal diffusivity using analytical inverse solution for unsteady one-dimensional heat conduction

A modified procedure for calculating the thermal diffusivity of solids based on temperature measurements at two points and the semi-infinite boundary condition is presented. The method makes use of a solution to the unsteady one-dimensional inverse heat conduction problem for the semi-infinite solid. The procedure gives accurate results based on temperature changes produced by an arbitrary fluctuating heat flux source at the boundary.     

A simple theoretical model for condensed-phase equilibria based on a hard-sphere equation-of-state and its applications

Detailed knowledge of solid–liquid phase transitions is not only of academic interest but is also important for industrial-process applications, such as the use of high-pressure crystallization as a separation method. In previous reports, we have studied solid–liquid phase equilibria of several binary-systems containing aromatic compounds, using our unified solid–liquid–vapor equation-of-state (EOS), and demonstrated that our EOS method can be successfully applied to such systems. However, the procedure of analyses is rather complicated and not necessarily straightforward. In this report, we develop a much simpler model for condensed-phase behaviors. The model is based on our previously reported hard-sphere EOS. Successful applications to real compound systems are demonstrated.     

Laminar natural convection in differentially heated rectangular enclosures with vertical diffusive walls

Real enclosures have diffusive walls. A procedure is developed to evaluate the natural convection effective global Nusselt number for rectangular enclosures with vertical diffusive walls. The effective Nusselt number is evaluated using the temperature difference imposed over the exterior faces of the enclosure, the usual correlations for rectangular enclosures without diffusive walls, and the diffusive properties of the solid vertical walls, which are concentrated on a single dimensionless parameter. The proposed procedure is tested by comparing the obtained results with those achieved from the complete two-dimensional numerical simulation of the conjugated heat transfer problem occurring in the complete enclosure, with diffusive walls. The result is a helpful tool that promptly helps the thermal engineer when dealing with enclosures with diffusive walls.     

FINITE-ELEMENT ANALYSIS OF HEAT CONDUCTION PROBLEMS WITH IRREGULAR REGION BOUNDARY USING MULTILEVEL TECHNIQUES

The main goal of this article is to introduce a numerical procedure for the calculation of solidification and melting using the PISO algorithm. Since coupling among velocity, pressure, temperature, and liquid fraction is important in phase-change problems, an improved PISO algorithm is required to couple these variables properly. To achieve this goal, the present study proposes the use of the enthalpy method for the inner iterations of the matrix solver, in order to predict more accurate temperature and liquid fraction that satisfy the energy balance criterion simultaneously. Another difference of the present method from other conventional coupling methods is in updating the permeability term of the momentum equation with liquid fractions predicted in the first correction step. This may couple the velocities with the liquid fractions more closely. A comparison of the proposed method with a standard iterative method is made for three different cases, showing that improved predictions are obtained in terms of computing speed and solution robustness.     

Coupling conjugate heat transfer with in-cylinder combustion modeling for engine simulation

A conjugate formulation to predict heat conduction in the solid domain and spray combustion in the fluid domain was developed for multidimensional engine simulation. Heat transfer through the wall affects the combustion process in the cylinder and the thermal loading on the combustion chamber surface. To account for the temporal and spatial variations of temperature on the chamber surface, a fully coupled numerical procedure was developed to simulate in-cylinder flow and solid heat conduction simultaneously. Temperature fields in both the fluid and the solid domains were coupled by imposing equal heat flux and equal temperature at the fluid–solid interface. The formulation was first validated against analytical solutions. The formulation was then applied to simulate the in-cylinder combustion process and the solid heat conduction in a diesel engine under different operating conditions. Results show that the present model is able to predict unsteady and non-uniform temperature distributions on the chamber surface, which can fluctuate by nearly 100 K during combustion. The highest temperature on the piston surface occurs at the bowl edge along the spray axis. Predicted global engine parameters agree well with the experimental data. The present approach can be used to improve engine design for optimal combustion and reduced thermal loading.     

Enthalpy porosity model for melting and solidification of pure-substances with large difference in phase specific heats

A modified enthalpy porosity formulation is introduced to capture melting and solidification of pure substances. When melting and solidification of pure substances are addressed by the fixed grid based volume averaging technique, it is possible to obtain two equivalent and interchangeable mathematical formulations of the energy conservation equation if the governing equation is expressed in terms of temperature as the primary dependent variable. Between these two formulations, only one form is shown to provide physically consistent numerical solutions when very large difference in specific heats for liquid and solid phases is involved. A modified enthalpy updating scheme is proposed to predict the solid/liquid fraction during melting and solidification process of pure substances having large difference in phase specific heats. The results from the proposed scheme are validated with the existing results from literature involving numerical prediction of freezing of water. The physical consistency of the simulation results obtained by solving two interchangeable forms of energy conservation equation is tested and compared considering a case study involving melting of ice. While one of the conservation forms fails to predict the melting process, the other conservation form successfully predicts physically consistent result. The proposed formulation is capable of predicting melting and solidification of all pure substances including those with large difference in phase specific heats such as water and paraffin wax.     

活塞CAD／CAM一体化技术

本文介绍了活塞CAD／CAM技术内容和发展现状,在三维有限元的基础上,采用面向对象的技术和专家知识型的数据库建立活塞的实体模型,并在进行有限元的剖分和边界条件的确立后对分析结果优化设计,最后将设计好的实体通过在计算要上自动生成NC程序,开发建立起一套在三维实体建模基础上的活塞CAD／CAM一体化系统。     

Analysis of close-contact melting heat transfer

The foremost characteristic of close-contact melting is that the source and the solid are continuously separated by a very thin melt film in which the flow is predominantly in one direction (i.e. along the thin film channel). This fact is used to formulate a mathematical model and develop a marching integration solution procedure for the model equations. As an example, the problem of melting under a descending, horizontal, cylindrical source at constant surface heat flux is solved. The results indicate that the heat transfer from the source to the solid is dominated by conduction across the thin melt layer. For this configuration, the effects of Stefan number and the relative density of the source on its velocity are investigated and reported. The predicted heat source velocity and its dependence on its relative density is in good agreement with the experiments.     

Self-discharge in solid state cells

The contribution of self discharge processes to solid state battery behaviour is often assessed using the Wagner polarisation technique, which yields a value for electronic conductivity. The validity of this procedure, is, in principle, suspect because of the different natures of the Wagner cell and the working battery. Results are presented for room temperature silver and copper solid state batteries, for which it appears that, in fact, results for Wagner cells can yield useful data pertinent to self discharge.