Applications of the conjugate gradient FFT method in scattering and radiation including simulations with impedance boundary conditions

The theoretical and computational aspects related to the application of the Conjugate Gradient FFT (CGFFT) method in computational electromagnetics are examined. The advantages of applying the CGFFT method to a class of large scale scattering and radiation problems are outlined. The main advantages of the method stem from its iterative nature which eliminates a need to form the system matrix (thus reducing the computer memory allocation requirements) and guarantees convergence to the true solution in a finite number of steps. Results are presented for various radiators and scatterers including thin cylindrical dipole antennas, thin conductive and resistive strips and plates, as well as dielectric cylinders. Solutions of integral equations derived on the basis of generalized impedance boundary conditions (GIBC) are also examined. The boundary conditions can be used to replace the profile of a material coating by an impedance sheet or insert, thus, eliminating the need to introduce unknown polarization currents within the volume of the layer. A general full wave analysis of 2-D and 3-D rectangular grooves and cavities is presented which will also serve as a reference for future work

The design and implementation of a purely digital stereo-photogrammetric system on the IBM 3090 multi-user mainframe computer

This thesis is concerned with an investigation into the possibilities of implementing various aspects of a purely digital stereo-photogrammetric (DSP) system on the IBM 3090 150E mainframe multi-user computer. The main aspects discussed within the context of this thesis are:-i) Mathematical modelling of the process of formation of digital images in the space and frequency domains.ii) Experiments on improving the pictorial quality of digital aerial photos using Inverse and Wiener filters.iii) Devising and implementing an approach for the automatic sub-pixel measurement of cross-type fiducial marks for the inner orientation, using the Gradient operator and image modelling least squares (IML) approach.iv) Devising and implementing a method for the digital rectification of overlapping aerial photos and the formation of the stereo-model.v) Design and implementation of a digital stereo-photogrammetric system (DSP) and the generation of a DTM using visual measurement.vi) Investigating the feasibility of stereo-viewing of binary images and the possibility of performing measurements on such images.vii) Implementing a method for the automatic generation of a DTM using a one-dimensional image correlation along epipolar lines and experimentally optimizing the size of the correlation window.viii) Assessment of the accuracy of the DTM data generated both by the DSP and the automatic correlation method.ix) Vectorization of the rectification and correlation programs to achieve higher speed-up factors in the computational process

Structural Tailoring of Advanced Turboprops (STAT)

This interim report describes the progress achieved in the structural Tailoring of Advanced Turboprops (STAT) program which was developed to perform numerical optimizations on highly swept propfan blades. The optimization procedure seeks to minimize an objective function, defined as either direct operating cost or aeroelastic differences between a blade and its scaled model, by tuning internal and external geometry variables that must satisfy realistic blade design constraints. This report provides a detailed description of the input, optimization procedures, approximate analyses and refined analyses, as well as validation test cases for the STAT program. In addition, conclusions and recommendations are summarized

CHARMM: The biomolecular simulation program

CHARMM (Chemistry at HARvard Molecular Mechanics) is a highly versatile and widely used molecular simulation program. It has been developed over the last three decades with a primary focus on molecules of biological interest, including proteins, peptides, lipids, nucleic acids, carbohydrates, and small molecule ligands, as they occur in solution, crystals, and membrane environments. For the study of such systems, the program provides a large suite of computational tools that include numerous conformational and path sampling methods, free energy estimators, molecular minimization, dynamics, and analysis techniques, and model-building capabilities. The CHARMM program is applicable to problems involving a much broader class of many-particle systems. Calculations with CHARMM can be performed using a number of different energy functions and models, from mixed quantum mechanical-molecular mechanical force fields, to all-atom classical potential energy functions with explicit solvent and various boundary conditions, to implicit solvent and membrane models. The program has been ported to numerous platforms in both serial and parallel architectures. This article provides an overview of the program as it exists today with an emphasis on developments since the publication of the original CHARMM article in 1983. © 2009 Wiley Periodicals, Inc.J Comput Chem, 2009.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63074/1/21287_ftp.pd

The NAS parallel benchmarks

A new set of benchmarks was developed for the performance evaluation of highly parallel supercomputers. These benchmarks consist of a set of kernels, the 'Parallel Kernels,' and a simulated application benchmark. Together they mimic the computation and data movement characteristics of large scale computational fluid dynamics (CFD) applications. The principal distinguishing feature of these benchmarks is their 'pencil and paper' specification - all details of these benchmarks are specified only algorithmically. In this way many of the difficulties associated with conventional benchmarking approaches on highly parallel systems are avoided

Architecture independent environment for developing engineering software on MIMD computers

Engineers are constantly faced with solving problems of increasing complexity and detail. Multiple Instruction stream Multiple Data stream (MIMD) computers have been developed to overcome the performance limitations of serial computers. The hardware architectures of MIMD computers vary considerably and are much more sophisticated than serial computers. Developing large scale software for a variety of MIMD computers is difficult and expensive. There is a need to provide tools that facilitate programming these machines. First, the issues that must be considered to develop those tools are examined. The two main areas of concern were architecture independence and data management. Architecture independent software facilitates software portability and improves the longevity and utility of the software product. It provides some form of insurance for the investment of time and effort that goes into developing the software. The management of data is a crucial aspect of solving large engineering problems. It must be considered in light of the new hardware organizations that are available. Second, the functional design and implementation of a software environment that facilitates developing architecture independent software for large engineering applications are described. The topics of discussion include: a description of the model that supports the development of architecture independent software; identifying and exploiting concurrency within the application program; data coherence; engineering data base and memory management

Sparse Equation-Eigen Solvers for Symmetric/Unsymmetric Positive-Negative-Indefinite Matrices with Finite Element and Linear Programming Applications

Vectorized sparse solvers for direct solutions of positive-negative-indefinite symmetric systems of linear equations and eigen-equations are developed. Sparse storage schemes, re-ordering, symbolic factorization and numerical factorization algorithms are discussed. Loop unrolling techniques are also incorporated in the coding to enhance the vector speed. In the indefinite solver, which employs various pivoting strategies, a simple rotation matrix is introduced to simplify the computer implementation. Efficient usage of the incore memory is accomplished by the proposed restart memory management schemes. A sparse version of the Interior Point Method, IPM, has also been implemented that incorporates the developed indefinite sparse solver for linear programming applications. Numerical performance of the developed software is conducted by performing the static analysis and eigen-analysis of several practical finite elements models, such as the EXXON Offshore Structure, the High Speed Civil Transport (HSCT) Aircraft, and the Space Shuttle Solid Rocket Booster (SRB). The results have been compared to benchmark results provided by the Computational Structural Branch at NASA Langley Research Center. Small to medium-scale linear programming examples have also been used to demonstrate the robustness of the proposed sparse IPM

Large-eddy simulation of turbulent flows with heat transfer in simple and complex geometries

Some basic aspects of turbulence, transition to turbulence, and turbulence modelling, are summarized in Chapter 1 (Introduction). Emphasis is put on the increasing understanding of turbulent phenomena made possible by recent advances in the theory of dynamical systems; on the concept of "coherent structure"; and on the parallel evolution of computing power and computational fluid dynamics. Chapter 2 is a survey of the turbulence modelling technique known as Large Eddy Simulation (LES). The equations governing fluid flow and scalar transport are introduced; the direct simulation of turbulent flows and its limitations are briefly outlined; and the concept of LES, with the related topics of decomposition, filtering and subgrid modelling, is discussed. The state of the art in LES is reviewed in the last three sections, under the separate headings of proposed subgrid models; wall boundary conditions; and applications presented in the literature. An attempt is made to give the most complete and updated possible account of the subject; work carried out from the early 'Seventies up to now is considered. Emphasis is put more on physical models and corresponding performances than on numerical methods and computational details. In Chapter 3, the finite-volume numerical techniques used in the present work are presented and discussed. Emphasis is put on those aspects and options which bear more relevance for the accuracy and quality of the results, such as the pressure-velocity coupling algorithm, the discretization of advective terms and the treatment of centred (co-located), body-fitted grids. The architecture and the basic features of the computer code Harwell-FL0W3D, Release 2, are outlined, while the modifications introduced in order to implement the Smagorinsky subgrid model and the appropriate boundary conditions for LES are described in detail. In Chapters 4-6 results are presented and discussed for the basic geometries studied. Chapter 4 deals with the flow between indefinite parallel plates (plane channel), one of which heated with a uniform heat flux. For this basic geometry, a detailed study is presented on the influence of numerical options (grid size, time step and time-stepping method, pressure-velocity coupling, discretization of the advective terms); model parameters (Smagorinsky constant, subgrid Prandtl number, near-wall damping); Reynolds number; and alternative wall boundary conditions. The issues of initial conditions, numerical transients and statistical processing of the results are also discussed with some depth. In Chapter 5, computations are presented for a plane channel having one of the walls roughened by transverse square ribs. An extensive literature review of experimental and numerical studies on this geometry is included. The parametrical study is limited here to the influence of grid size and Reynolds number; LES results are presented in detail for a reference case, and are compared with experimental flow and heat transfer data. Chapter 6 is dedicated to the geometry of cross-corrugated ducts, representative of storage-type air preheaters for fossil-fuelled power stations. Flow and heat transfer predictions from direct simulation and LES are presented; they are compared with experimental results and with numerical predictions obtained by a standard and a low-Reynolds number version of the k-s turbulence model. Finally, Chapter 7 summarizes the main conclusions which can be drawn from the above studies. Emphasis is put on the basic issue of LES applicability to engineering problems of practical interest, and of its feasibility using a commercial, general-purpose (though highly sophisticated) computer code. A critical comparison with more conventional turbulence modelling approaches is outlined, and 'weak spots', or issues requiring further clarifications, are pointed out for future studies. The work includes an extensive bibliography with almost 400 references, and an appendix on the tensorial formulation of the governing equations of fluid dynamics in general domains

An Adaptive Differencing Scheme for Elliptic Flows.

This thesis deals with the formulation of a computationally efficient multiple-grid adaptive differencing (MAD) scheme for two-dimensional elliptic flow and heat transfer problems. This algorithm equidistributes a measure of the error by using higher order differencing schemes locally in adaptively determined high error-estimate regions. The third-order accurate QUICK scheme is used in regions of high error estimate which are dynamically flagged on the basis of a preliminary first order upwind solution. Boundary conditions for the flagged regions are taken from the preliminary upwind solution. Multigrid type calculations are performed. Three multiple-grid schemes are developed. In the first scheme, MAD1-WFDS, the entire domain and flagged subdomains are solved at each multiple-grid iteration. The second scheme, MAD2-WDS, solves the entire domain at each iteration, employing the QUICK form of the discretized equations in the flagged regions and the original upwind formulation elsewhere. The third algorithm, MAD3-FDS, is similar to the first, except the entire domain is not solved after the subdomain solution. Instead, only the unflagged portion of the problem domain is solved, using the improved values obtained in the flagged regions as boundary conditions. The three MAD algorithms are applied to two convection-diffusion and two flow problems. The results are compared to the exact solution (if available), the upwind and QUICK solutions, and to each other. MAD1-WFDS shows the best improvement to the upwind scheme but requires the most additional computing time. MAD2-WDS requires the least additional computing time, but shows the least improvement over the upwind solution. The code for MAD1-WFDS is parallelized to reduce the real computation time required for problem solutions. The upwind and QUICK schemes are also parallelized for comparison. Several program levels or granularities were parallelized to determine an optimal level of parallelization. Parallelizing on the subdomain level and parallelizing the solution of the general variable equation yielded good results. A real time savings of 26.4% was achieved in one case (in spite of the fact that the solution was not computed on a dedicated machine) at a cost of a 7.8% increase in cpu time required by the parallel run over the serial run