A fast sparse block circulant matrix vector product

In the context of computed tomography (CT), iterative image reconstruction techniques are gaining attention because high-quality images are becoming computationally feasible. They involve the solution of large systems of equations, whose cost is dominated by the sparse matrix vector product (SpMV). Our work considers the case of the sparse matrices being block circulant, which arises when taking advantage of the rotational symmetry in the tomographic system. Besides the straightforward storage saving, we exploit the circulant structure to rewrite the poor-performance SpMVs into a high-performance product between sparse and dense matrices. This paper describes the implementations developed for multi-core CPUs and GPUs, and presents experimental results with typical CT matrices. The presented approach is up to ten times faster than without exploiting the circulant structure.Romero Alcalde, E.; Tomás Domínguez, AE.; Soriano Asensi, A.; Blanquer Espert, I. (2014). 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Aero-Thermo-Mechanical Modelling and Validation of Transient Effects in a High Pressure Turbine Internal Air System

Accurate prediction of metal temperatures, blade tip and seal clearances in high pressure compressor and turbine air systems leads to dramatic improvements in overall aero-engine efficiency and component life. Fast transients during an engine flight profile may introduce large changes in geometry between adjacent rotor and stator components. The changing dynamics in a few critical seals and interfaces can change the dynamics of the entire engine, compromising efficiency, integrity and long service life. In this paper we present results of a coupled aero-thermo-mechanical transient simulation of a high pressure turbine assembly throughout an engine flight cycle. The fluid and solid model geometry is approximated as 2D axisymmetric. The problem, formulated as a four field coupled multiphysics system of equations, is simplified using a quasi-steady state assumption: the transient thermal solid problem is coupled to a sequence of steady fluid problems and static structural problems. The predicted results compare well with the experimental measurements over the entire fluid-solid interface. We show improvement in transient predictions isolating the effects of the solid domain deformation. The remaining transient error is linked to temporal uncertainties in the fluid model inlet boundary conditions which were taken as a spatial average of the main annulus flow conditions

Nonlinear acceleration of coupled fluid-structure transient thermalproblems by Anderson mixing

Conjugate heat-transfer problems are typically solved using partitioned methods where fluid and solid subdomains are evaluated separately by dedicated solvers coupled through a common boundary. Strongly coupled schemes for transient analysis require fluid and solid problems to be solved many times each time step until convergence to a steady state. In many practical situations, a fairly simple and frequently employed fixed-point iteration process is rather ineffective; it leads to a large number of iterations per time step and consequently to long simulation times. In this article, Anderson mixing is proposed as a fixed-point convergence acceleration technique to reduce computational cost of thermal coupled fluid–solid problems. A number of other recently published methods with applications to similar fluid–structure interaction problems are also reviewed and analyzed. Numerical experiments are presented to illustrate relative performance of these methods on a test problem of rotating pre-swirl cavity air flow interacting with a turbine disk. It is observed that performance of Anderson mixing method is superior to that of other algorithms in terms of total iteration counts. Additional computational savings are demonstrated by reusing information from previously solved time steps

Coupled Fluid-Structure Transient Thermal Analysis of a Gas Turbine Internal Air System With Multiple Cavities

This paper presents the transient aerothermal analysis of a gas turbine internal air system through an engine flight cycle featuring multiple fluid cavities that surround a HP turbine disk and the adjacent structures. Strongly coupled fluid-structure thermal interaction problems require significant computational effort to resolve nonlinearities on the interface for each time step. Simulation times may grow impractical if multiple fluid domains are included in the analysis. A new strategy is employed to decrease the cost of coupled aerothermal analysis. Significantly lower fluid domain solver invocation counts are demonstrated as opposed to the traditional coupling approach formulated on the estimates of heat transfer coefficient. Numerical results are presented using 2D finite element conduction model combined with 2D flow calculation in five separate cavities interconnected through the inlet and outlet boundaries. The coupled solutions are discussed and validated against a nominal stand-alone model. Relative performance of both coupling techniques is evaluated