Ruth Arís

Alya: Multiphysics engineering simulation toward exascale

Alya is a multi-physics simulation code developed at Barcelona Supercomputing Center (BSC). From its inception Alya code is designed using advanced High Performance Computing programming techniques to solve coupled problems on supercomputers efficiently. The target domain is engineering, with all its particular features: complex geometries and unstructured meshes, coupled multi-physics with exotic coupling schemes and physical models, ill-posed problems, flexibility needs for rapidly including new models, etc. Since its beginnings in 2004, Alya has scaled well in an increasing number of processors when solving single-physics problems such as fluid mechanics, solid mechanics, acoustics, etc. Over time, we have made a concerted effort to maintain and even improve scalability for multi-physics problems. This poses challenges on multiple fronts, including: numerical models, parallel implementation, physical coupling models, algorithms and solution schemes, meshing process, etc. In this paper, we introduce Alyas main features and focus particularly on its solvers. We present Alyas performance up to 100.000 processors in Blue Waters, the NCSA supercomputer with selected multi-physics tests that are representative of the engineering world. The tests are incompressible flow in a human respiratory system, low Mach combustion problem in a kiln furnace, and coupled electro-mechanical contraction of the heart. We show scalability plots for all cases and discuss all aspects of such simulations, including solver convergence.

What a difference in biomechanics cardiac fiber makes

Computational simulations of the heart are a powerful tool for a comprehensive understanding of cardiac function and its intrinsic relationship with its muscular architecture. Cardiac biomechanical models require a vector field representing the orientation of cardiac fibers. A wrong orientation of the fibers can lead to a non-realistic simulation of the heart functionality. In this paper we explore the impact of the fiber information on the simulated biomechanics of cardiac muscular anatomy. We have used the John Hopkins database to perform a biomechanical simulation using both a synthetic benchmark fiber distribution and the data obtained experimentally from DTI. Results illustrate how differences in fiber orientation affect heart deformation along cardiac cycle.

Alya Red CCM: HPC-Based Cardiac Computational Modelling

This paper describes Alya Red CCM, a cardiac computational modelling tool for supercomputers. It is based on Alya, a parallel simulation code for multiphysics and multiscale problems, which can deal with all the complexity of biological systems simulations. The final goal is to simulate the pumping action of the heart: the model includes the electrical propagation, the mechanical contraction and relaxation and the blood flow in the heart cavities and main vessels. All sub-problems are treated as fully transient and solved in a staggered fashion. Electrophysiology and mechanical deformation are solved on the same mesh, with no interpolation. Fluid flow is simulated on a moving mesh using an Arbitrary Lagrangian-Eulerian (ALE) strategy, being the mesh deformation computed through an anisotropic Laplacian equation. The parallel strategy is based on an automatic mesh partition using Metis and MPI tasks. When required and in order to take profit of multicore clusters, an additional OpenMP parallelization layer is added. The paper describes the tool and its different parts. Alya’s flexibility allows to easily program a large variety of physiological models for each of the sub-problems, including the mutual coupling. This flexibility, added to the parallel efficiency to solve multiphysics problems in complex geometries render Alya Red CCM a well suited tool for cardiac biomedical research at either industrial or academic environments.

Influence of fiber connectivity in simulations of cardiac biomechanics

PurposePersonalized computational simulations of the heart could open up new improved approaches to diagnosis and surgery assistance systems. While it is fully recognized that myocardial fiber orientation is central for the construction of realistic computational models of cardiac electromechanics, the role of its overall architecture and connectivity remains unclear. Morphological studies show that the distribution of cardiac muscular fibers at the basal ring connects epicardium and endocardium. However, computational models simplify their distribution and disregard the basal loop. This work explores the influence in computational simulations of fiber distribution at different short-axis cuts.MethodsWe have used a highly parallelized computational solver to test different fiber models of ventricular muscular connectivity. We have considered two rule-based mathematical models and an own-designed method preserving basal connectivity as observed in experimental data. Simulated cardiac functional scores (rotation, torsion and longitudinal shortening) were compared to experimental healthy ranges using generalized models (rotation) and Mahalanobis distances (shortening, torsion).ResultsThe probability of rotation was significantly lower for ruled-based models [95% CI (0.13, 0.20)] in comparison with experimental data [95% CI (0.23, 0.31)]. The Mahalanobis distance for experimental data was in the edge of the region enclosing 99% of the healthy population.ConclusionsCardiac electromechanical simulations of the heart with fibers extracted from experimental data produce functional scores closer to healthy ranges than rule-based models disregarding architecture connectivity.