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Coronary obstruction is a complication that may affect patients receiving Transcatheter Aortic Valve Replacement (TAVR), with catastrophic consequences and long-term negative effects. To enable healthy coronary perfusion, it is fundamental to appropriately position the device with respect to the coronary ostia. Nonetheless, most TAVR delivery systems do not control commissural alignment to do so. Moreover, no in silico study has directly assessed the effect of commissural alignment on coronary perfusion. This work aims to evaluate the effect of TAVR commissural alignment on coronary perfusion and device performance. A two-way computational fluid-structure interaction model is used to predict coronary perfusion at different commissural alignments. Moreover, in each scenario, hemodynamic biomarkers are evaluated to assess device performance. Commissural misalignment is shown to reduce the total coronary perfusion by − 3.2 % and the flow rate to a single coronary branch by − 6.8 %. It is also observed to impair valvular function by reducing the systolic geometric orifice area by − 2.5 % and increasing the systolic transvalvular pressure gradients by + 5.3 % and the diastolic leaflet stresses by + 16.0 %. The present TAVR patient model indicates that coronary perfusion, hemodynamic and structural performance are minimized when the prosthesis commissures are fully misaligned with the native ones. These results support the importance of enabling axial control in new TAVR delivery catheter systems and defining recommended values of commissural alignment in upcoming clinical treatment guidelines. • A fluid-structure interaction model of TAVRs was used to analyze the effect of commissural alignment on coronary perfusion. • Commissural misalignment reduced total coronary perfusion by -3.2% and up to -6.8% in a single coronary outlet. • No significant effects of commissural alignment on thrombogenic risk were observed. • Misalignment reduced the systolic orifice area by -2.5% and increased transvalvular pressure gradients by +5.3%. • Results support the importance of enabling axial control in novel TAVR catheter delivery systems. [ABSTRACT FROM AUTHOR]

We present a new overlapping Dirichlet/Robin Domain Decomposition method. The method uses Dirichlet and Robin transmission conditions on the interfaces of an overlapping partitioning of the computational domain. We derive interface equations to study the convergence of the method and show its properties through four numerical examples. The mathematical framework is general and can be applied to derive overlapping versions of all the classical nonoverlapping methods. [Copyright &y& Elsevier]

We present a Chimera method for the numerical solution of incompressible flows past objects in relative motion. The Chimera method is implemented as an iteration-by-subdomain method based on Dirichlet/Neumann(Robin) coupling. The DD method we propose is not only geometric but also algorithmic, for the solution on each subdomain is obtained on separate processes and the exchange of information between the subdomains is carried out by a master code. This strategy is very flexible as it requires almost no modification to the original numerical code. Therefore, only the master code has to be adapted to the numerical codes and the strategies used on each subdomain. As a basic flow solver, we a use stabilized finite element method. [Copyright &y& Elsevier]

Communities around the world are increasingly interested in nature-based solutions to the mitigation of coastal risks by coastal forests, but it remains unclear how much protective benefits vegetation provides, particularly in the limit of highly energetic flows after tsunami impact. The current study, using a three-dimensional incompressible computational fluid dynamics model with a fluid–structure interaction approach, aims to quantify how energy reflection and dissipation vary with different degrees of rigidity and vegetation density of a coastal forest. We represent tree trunks as cylinders and use the elastic modulus of hardwood trees such as pine or oak to characterize the rigidity of these cylinders. The numerical results show that energy reflection increases with rigidity only for a single cylinder. In the presence of multiple cylinders, the difference in energy reflection created by varying rigidity diminishes as the number of cylinders increases. Instead of rigidity, we find that the blockage area created by the presence of multiple tree trunks dominates energy reflection. As tree trunks are deformed by the hydrodynamic forces, they alter the flow field around them, causing turbulent kinetic energy generation in the wake region. As a consequence, trees dissipate flow energy, highlighting coastal forests reducing the onshore energy flux of tsunamis by means of both reflection and dissipation. • The number of tree trunks and the spacing between them are more important for tsunami-risk mitigation than the species-specific properties. • Deflection of tree trunks alters the flow field around them, causing turbulent kinetic energy generation in the wake region. • Coastal forests reduces the onshore energy flux of tsunamis by means of both reflection and dissipation. [ABSTRACT FROM AUTHOR]

This paper introduces a preconditioned variational multiscale stabilization (P-VMS) method for compressible flows. In this introductory paper we focus on inviscid flow and steady state problems. The Euler equations are solved on fully unstructured grids and discretized using the finite element method. The P-VMS method can be decomposed into three parts. First, a local preconditioner is applied to the continuous equations to reduce the stiffness while covering a wide range of Mach numbers. Then, the resulting preconditioned system is discretized in space using finite elements and stabilized with a variational multiscale stabilization method adapted for the preconditioned equations. In this paper, the solution is advanced in time using a fully explicit time discretization, although P-VMS is general and can be applied to fully implicit solvers. The proposed method is assessed by comparing convergence and accuracy of the solutions between the non-preconditioned and preconditioned cases, in particular for van Leer–Lee–Roe ’s (1991) and Choi-Merkle ’s (1993) preconditioners, in some selected examples covering a large range of Mach numbers. [ABSTRACT FROM AUTHOR]

• A radiation transport solver describing neutronic transport is introduced. • The model is used to reproduce shielding benchmarks included in SINBAD database. • The solver is included as a module into the high-performance computational mechanics code ALYA. • The results obtained achieved good accuracy over extended domains. • This implementation in Alya will allow coupling of radiation transport with thermo-mechanical solutions in large domains. We present significant improvements and validations of a deterministic neutron transport code (NEUTRO) dedicated to solving the Boltzmann Transport Equation. The code is integrated as a module in the Alya software package developed by the Barcelona Supercomputing Center which uses the Discrete Ordinates Method on angular coordinates, multi-group for energy discretization and FEM on unstructured meshes to treat special complex domains. The anisotropy of the scattering medium is introduced into the scattering kernel using real base expressions for spherical harmonics. In order to build the total cross-section and the respective group matrix for the elastic cross-section, we use the NJOY code. We test the solver using different geometries, orders of integration for the angular discretization and number of energy groups. Finally, we compare our results against benchmarks obtained from an NEA database that reported measurements of leakage spectra of several materials. [ABSTRACT FROM AUTHOR]

• The Integral Length Scale Approximation Subfilter Scale Model is applied to separated flows. • A procedure to determine the model constant is proposed. • A low-dissipation finite-element method is used. • The model accounts for interactions between numerical error and turbulence modelling errors. • Flows over a sphere and an Ahmed body are computed, and good agreement with the data is obtained. A new model for the unresolved stresses in large-eddy simulations was recently proposed by Piomelli et al. [J Fluid Mech 2015; 766:499–527] and Rouhi et al., [Phys Rev Fluids 2016; 1(4):0444011], in which the length scale is not related to the grid size, but determined based on turbulence properties. This model, the Integral Length-Scale Approximation (ILSA), has a single parameter, s τ , which represents the contribution of the unresolved scales to the momentum transport, and is assigned by the user. We test ILSA in complex geometries using a low-dissipation finite-element method, and propose a rational method to determine s τ on the basis of a grid-convergence study. The interaction of the model with the numerical method and grid topology is studied first; then, two cases are considered: the subcritical flow around a sphere, and the flow over the Ahmed body, a simplified car model. In each case calculations are performed using three grids and varying s τ. With a consistent combination of grid size and s τ the statistical results are in very good agreement with DNS data and experimental measurements. The eddy viscosity is insensitive to sudden variation of the mesh size, and the model adjusts to the different dissipation and diffusion characteristics associated with different grid topologies and numerical techniques. [ABSTRACT FROM AUTHOR]

Highlights • Presentation of Alya computational mechanics code in the fusion field. • Including a neutronics module within an HPC multiphysics framework. • First benchmark results of the neutron transport module. Abstract Integrated modelling is an important element of tokamak fusion research. It contributes to the interpretation and planning of experiments, validation of theory against experimental results, development of plasma control techniques as well as the design of next step devices. Large efforts continue to be devoted to the integrated modelling of plasma physics effects in a fusion reactor core and have led to significant progress in physics understanding, while tools to model multiphysics phenomena taking place in fusion reactor components such as tritium breeding blankets have not yet reached a similar level of detail and completeness. We are developing a new high performance computing tool for simulating the latter effects. It is based a parallel computational mechanics code Alya which is specially designed for running with high efficiency standards in large scale supercomputers and is capable of solving different physics problems in a coupled way. As first step towards multiphysics simulations of fusion reactor components, we are developing a new neutron transport module based on the deterministic approach for coupling with the existing, implemented physics modules in Alya. This module, together with existing physics implemented in Alya will allow to solve future high fidelity multiphysics and multiscale problems. We present the capabilities of the Alya system and the latest version of the new neutron transport module currently under development. [ABSTRACT FROM AUTHOR]

Targeted nasal drug delivery can provide improved efficacy for drug formulations to be delivered at high efficacy rates. Some parameters that influence drug delivery have a dependency on the patient's technique of administration and the spray device itself. When the different parameters, each having a specific range of values are combined, the combinatory permutations for studying its effects on particle deposition become large. In this study, we combine six input spray parameters (the spray half-cone angle, the mean spray exit velocity, the breakup length from the nozzle exit, the diameter of the nozzle spray device, the particle size, and the sagittal angle of the spray) with a range of values to produce 384 combinations of spray characteristics. This was repeated for three inhalation flow rates of 20, 40, and 60 L/min. To reduce the computational costs of a full transient Large Eddy Simulation flow field, we create a time-averaged frozen field and perform the time integration of particle trajectories through the flow field to determine the particle deposition in four anatomical regions of the nasal cavity (anterior, middle, olfactory and posterior) for each of the 384 spray field. A sensitivity analysis determined the significance of each input variable on the deposition. It was found the particle size distribution significantly affected deposition in the olfactory and posterior regions, while the spray device insertion angle was significant for deposition in the anterior and middle regions. Five machine learning models were evaluated based on 384 cases and it was found that despite the small sample dataset the simulation data was sufficient to provide accurate machine-learning predictions. [Display omitted] [ABSTRACT FROM AUTHOR]

Validating numerical models against experimental models of nasal spray deposition is challenging since many aspects must be considered. That being said, it is a critical step in the product development process of nasal spray devices. This work presents the validation process of a nasal deposition model, which demonstrates a high degree of consistency of the numerical model with experimental data when the nasal cavity is segmented into two regions but not into three. Furthermore, by modelling the flow as stationary, the computational cost is drastically reduced while maintaining quality of particle deposition results. Thanks to this reduction, a sensitivity analysis of the numerical model could be performed, consisting of 96 simulations. The objective was to quantify the impact of four inputs: the spray half cone angle, mean spray exit velocity, breakup length from the nozzle exit and the diameter of the nozzle spray device, on the three quantities of interest: the percentage of the accumulated number of particles deposited on the anterior, middle and posterior sections of the nasal cavity. The results of the sensitivity analysis demonstrated that the deposition on anterior and middle sections are sensitive to injection angle and breakup length, and the deposition on posterior section is only, but highly, sensitive to the injection velocity. [Display omitted] [ABSTRACT FROM AUTHOR]

Validating numerical models against experimental models of nasal spray deposition is challenging since many aspects must be considered. That being said, it is a critical step in the product development process of nasal spray devices. This work presents the validation process of a nasal deposition model, which demonstrates a high degree of consistency of the numerical model with experimental data when the nasal cavity is segmented into two regions but not into three. Furthermore, by modelling the flow as stationary, the computational cost is drastically reduced while maintaining quality of particle deposition results. Thanks to this reduction, a sensitivity analysis of the numerical model could be performed, consisting of 96 simulations. The objective was to quantify the impact of four inputs: the spray half cone angle, mean spray exit velocity, breakup length from the nozzle exit and the diameter of the nozzle spray device, on the three quantities of interest: the percentage of the accumulated number of particles deposited on the anterior, middle and posterior sections of the nasal cavity. The results of the sensitivity analysis demonstrated that the deposition on anterior and middle sections are sensitive to injection angle and breakup length, and the deposition on posterior section is only, but highly, sensitive to the injection velocity. [Display omitted] [ABSTRACT FROM AUTHOR]

The nasal valve is the narrowest part of the nasal airway which is responsible for the largest part of the nasal resistance. Even little changes in the aperture can affect the flow downstream through the nose significantly. Its principal function is to limit airflow for example during a rapid and short inhalation, also called a sniff. Coupling Computational Fluid Dynamics (CFD) with Fluid–Structure Interaction (FSI) allows solving and exchanging force and displacement between the solid and fluid domains and offers a more accurate representation of the physical system in confined flow cases. Furthermore, particle transport and deposition are performed in this study to reveal the effect of the complex coupling on the nasal cavity deposition of inhaled aerosols. Two different configurations are used to model the nasal valve and differences in magnitudes in deformations are observed during the sniff. A comparison between FSI results and the in-vivo evaluation of the deformation shows an acceptable agreement as to the first step of validation. In addition, the results demonstrated that FSI increases significantly the particle deposition in the nasal cavity and the micro-particle diameter is the critical range parameter to enhance deposition with nasal valve deformation during a sniff. • The results demonstrated that FSI increases significantly the particle deposition in the nasal cavity. • The micro-particle diameter is the critical range parameter to enhance deposition with nasal valve deformation during a sniff. • The Comparison between FSI results and the in-vivo evaluation of the deformation shows an acceptable agreement as first step of validation. [ABSTRACT FROM AUTHOR]

The results of a Fourier stability analysis of the preconditioned variational multiscale stabilization (P-VMS) method introduced in Moragues et al. (2015) are presented in this paper. P-VMS combines a variational multiscale stabilized finite elements discretization together with local preconditioning. In this work, we deal with the P-VMS method using van Leer–Lee–Roe ’s (vanLeer et al., 1991) and Choi–Merkle ’s (Choi and Merkle, 1993) local preconditioners. We solve the Euler equations of compressible flow for steady problems. We concentrate on explicit time integration schemes. The stability analysis is performed on a two dimensional simplified problem with a structured mesh and its conclusions are applied to two and three dimensional general problems with unstructured meshes. As a result of this analysis a local Courant–Friedrichs–Lewy number is defined for the computation of the time step. The convergence rate is evaluated, and compared with the traditional constant Courant–Friedrichs–Lewy number for various test cases spanning a large range of Mach numbers. [ABSTRACT FROM AUTHOR]

Because of their widely generalized use in many industries, composites are the subject of many research campaigns. More particularly, the development of both accurate and flexible numerical models able to capture their intrinsically multiscale modes of failure is still a challenge. The standard finite element method typically requires intensive remeshing to adequately capture the geometry of the cracks and high accuracy is thus often sacrificed in favor of scalability, and vice versa. In an effort to preserve both properties, we present here an extended finite element method (XFEM) for large scale composite fracture simulations. In this formulation, the standard FEM formulation is partially enriched by use of shifted Heaviside functions with special attention paid to the scalability of the scheme. This enrichment technique offers several benefits since the interpolation property of the standard shape function still holds at the nodes. Those benefits include (i) no extra boundary condition for the enrichment degree of freedom, and (ii) no need for transition/blending regions; both of which contribute to maintaining the scalability of the code. Two different cohesive zone models (CZM) are then adopted to capture the physics of the crack propagation mechanisms. At the intralaminar level, an extrinsic CZM embedded in the XFEM formulation is used. At the interlaminar level, an intrinsic CZM is adopted for predicting the failure. The overall framework is implemented in ALYA, a mechanics code specifically developed for large scale, massively parallel simulations of coupled multi-physics problems. The implementation of both intrinsic and extrinsic CZM models within the code is such that it conserves the extremely efficient scalability of ALYA while providing accurate physical simulations of computationally expensive phenomena. The strong scalability provided by the proposed implementation is demonstrated. The model is ultimately validated against a full experimental campaign of loading tests and X-ray tomography analyzes. [ABSTRACT FROM AUTHOR]

In view of the ongoing COVID-19 pandemic and its effects on global health, understanding and accurately modelling the propagation of human biological aerosols has become crucial. Worldwide, health professionals have been one of the most affected demographics, representing approximately 20% of all cases in Spain, 10% in Italy and 4% in China and US. Methods to contain and remove potentially infected aerosols during Aerosol Generating Procedures (AGPs) near source offer advantages in reducing the contamination of protective clothing and the surrounding theatre equipment and space. In this work we describe the application of computational fluid dynamics in assessing the performance of a prototype extraction hood as a means to contain a high speed aerosol jet. Whilst the particular prototype device is intended to be used during tracheotomies, which are increasingly common in the wake of COVID-19, the underlying physics can be adapted to design similar machines for other AGPs. Computational modelling aspect of this study was largely carried out by Barcelona Supercomputing Center using the high performance computational mechanics code Alya. Based on the high fidelity LES coupled with Lagrangian frameworks the results demonstrate high containment efficiency of generated particles is feasible with achievable air extraction rates. • Evaluation of a new device to reduce the risk of infection during Aerosol Generating Procedures for use in COVID-19 surgical tracheotomy. • High fidelity LES coupled with Lagrangian frameworks is used as results to demonstrate the efficiency. • Accurate numerical modelling of the propagation of human biological aerosols. [ABSTRACT FROM AUTHOR]

Accurate prediction of deformation and collapse of the upper airway during breathing is required for effective and personalised treatment of obstructive sleep apnoea (OSA). While numerical modelling techniques such as fluid–structure interaction (FSI) are promising, an outstanding challenge is to accurately predict the deformation of the airway during breathing and thus the occurrence of OSA. These difficulties arise because the effective stiffness of the soft tissue in the human upper airway varies due to neuromuscular effects on the stiffness of the underlying muscles. In addition, both the elasticity and anisotropy of the soft tissues along the upper airway are poorly characterised. Finally, gravitational effects on anatomic features are yet to be considered. In this study, a validated FSI technique is introduced that allows prediction of the extent and position of the major deformation in the upper airway. This technique is used to analyse the behaviour of the upper airway in the two most common sleeping positions and for a range of effective tissue stiffnesses. The results demonstrate that sleeping position, gravity and soft tissue stiffness (used here as a proxy for neuromuscular effects) are the main factors that affect upper airway collapse. Therefore, this study provides new insights into the mechanisms of OSA and a new methodology that significantly advances the patient-specific treatment of OSA. [ABSTRACT FROM AUTHOR]