Efficient Lagrangian particle tracking algorithms for distributed-memory architectures

This paper focuses on the solution of the dispersed phase of Eulerian–Lagrangian one-way coupled particle laden flows. An efficient two-constraint domain partitioning for 2D and 3D unstructured hybrid meshes is proposed and implemented in distributed memory architectures. A preliminary simulation, using a set of representative particles, is performed first to suitably tag the cells with a weight proportional to the probability of being crossed by a particle. In addition, an innovative parallel ray-tracing location algorithm is presented. A global identifier is assigned to each particle resulting in a significant reduction of the overall communication among processes. The proposed approaches are verified against two steady reference cases for ice accretion simulation: a NACA 0012 profile and a NACA 64A008 swept horizontal tail. Furthermore, a cloud droplet impact test case starting from an unsteady flow around a 3D cylinder is performed to evaluate the code performances on unsteady problems

A robust 3D particle tracking solver for in-flight ice accretion using arbitrary precision arithmetic

A particle tracking code is presented to compute droplet trajectories within a known Eulerian flow field for in-flight ice accretion simulations. The implementation allows for hybrid or unstructured meshes used by common CFD solvers. A known vicinity algorithm was devised to identify particles inside the mesh by computing the intersection between the particle trajectory and the faces of the mesh elements. Arbitrary precision arithmetic is used in the intersection evaluation in order to avoid errors when selecting the exit face if the intersection point is close to or coincident with a vertex or an edge. State-of- the-art wall interaction models are used to take into account droplet rebound, splash and spread at the walls. Non planar surface elements are assumed to improve the accuracy in evaluating the trajectory of secondary re-emitted particles. The software exhibits almost linear scaling when running in parallel on a distributed memory system. The particle tracking code is assessed against the experimental results regarding the impingement of Supercooled Large Droplets over a wing

A scalable Lagrangian particle tracking method

Particle tracking within an underlying flow field is routinely used to analyse both industrial processes and natural phenomena. In a computer code running on a distributed-memory architecture, the different behaviour of fluid-particle systems must be taken into account to properly balance element-particle subdivision among processes. In unsteady simulations, the parallel efficiency is even more critical because it changes over time. Another challenging aspect of a scalable implementation is the initial particle location due to the arbitrary shapes of each subdomain. In this work, an innovative parallel ray tracing particle location algorithm and a two-constrained domain subdivision are presented. The former takes advantage of a global identifier for each particle, resulting in a significant reduction of the overall communication among processes. The latter is designed to mitigate the load unbalance in the particles evolution while maintaining an equal element distribution. A preliminary particle simulation is performed to tag the cells and compute a weight proportional to the probability to be crossed. The algorithm is implemented using MPI distribute memory environment. A cloud droplet impact test case starting from an unsteady flow around a 3D cylinder has been simulated to evaluate the code performances. The tagging technique results in a computational time reduction of up to 78% and a speed up factor improvement of 44% with respect to the common flow based domain subdivision. The overall scalability is equal to 1.55 doubling the number of cores

Insight from an Italian Delphi Consensus on EVAR feasibility outside the instruction for use: the SAFE EVAR Study

BACKGROUND: The SAfety and FEasibility of standard EVAR outside the instruction for use (SAFE-EVAR) Study was designed to define the attitude of Italian vascular surgeons towards the use of standard endovascular repair (EVAR) for infrarenal abdominal aortic aneurysm (AAA) outside the instruction for use (IFU) through a Delphi consensus endorsed by the Italian Society of Vascular and Endovascular Surgery (Societa Italiana di Chirurgia Vascolare ed Endovascolare - SICVE). METHODS: A questionnaire consisting of 26 statements was developed, validated by an 18 -member Advisory Board, and then sent to 600 Italian vascular surgeons. The Delphi process was structured in three subsequent rounds which took place between April and June 2023. In the first two rounds, respondents could indicate one of the following five degrees of agreement: 1) strongly agree; 2) partially agree; 3) neither agree nor disagree; 4) partially disagree; 5) strongly disagree; while in the third round only three different choices were proposed: 1) agree; 2) neither agree nor disagree; 3) disagree. We considered the consensus reached when >70% of respondents agreed on one of the options. After the conclusion of each round, a report describing the percentage distribution of the answers was sent to all the participants. RESULTS: Two -hundred -forty-four (40.6%) Italian Vascular Surgeons agreed to participate the first round of the Delphi Consensus; the second and the third rounds of the Delphi collected 230 responders (94.3% of the first -round responders). Four statements (15.4%) reached a consensus in the first rounds. Among the 22 remaining statements, one more consensus (3.8%) was achieved in the second round. Finally, seven more statements (26.9%) reached a consensus in the simplified last round. Globally, a consensus was reached for almost half of the proposed statements (46.1%). CONCLUSIONS: The relatively low consensus rate obtained in this Delphi seems to confirm the discrepancy between Guideline recommendations and daily clinical practice. The data collected could represent the source for a possible guidelines' revision and the proposal of specific Good Practice Points in all those aspects with only little evidence available

Efficient radial basis function mesh deformation methods for aircraft icing

This paper presents an approach to update the moving ice boundary resulting from aircraft icing simulations using radial basis function mesh deformation techniques. State-of-the-art surface and volume point reduction schemes are used to reduce the computational cost of the mesh deformation. The data reduction schemes which are utilised include multi-level greedy surface point selection and volume point reduction. The multi-level greedy surface point selection reduces the number of control points to increase the efficiency of the interpolation operation. While the volume point reduction improves the computational cost of the volume mesh update operation which is important for large data sets. The paper assesses the capabilities of radial basis function mesh deformation for both two and three-dimensional problems. Furthermore, the effectiveness of the deformation technique is assessed for both local, non-smooth deformations and global, smooth deformations. The convergence history of the multi-level greedy point selection is assessed in terms of number of control points and computational cost. The location of the selected control points near the ice accretion illustrates the efficacy of the method for localised deformations. The results show that the radial basis function mesh deformation performs well for both the two and three-dimensional problems. The data-reduction schemes utilised in this work represent a significant improvement to standard radial basis function mesh deformation for aircraft icing problems comprising of large data-sets typical of three-dimensional problems

Efficient radial basis function mesh deformation methods for aircraft icing

This paper presents an approach to update the moving ice boundary resulting from aircraft icing simulations using radial basis function mesh deformation techniques. State-of-the-art surface and volume point reduction schemes are used to reduce the computational cost of the mesh deformation. The data reduction schemes which are utilised include multi-level greedy surface point selection and volume point reduction. The multi-level greedy surface point selection reduces the number of control points to increase the efficiency of the interpolation operation. While the volume point reduction improves the computational cost of the volume mesh update operation which is important for large data sets. The paper assesses the capabilities of radial basis function mesh deformation for both two and three-dimensional problems. Furthermore, the effectiveness of the deformation technique is assessed for both local, non-smooth deformations and global, smooth deformations. The convergence history of the multi-level greedy point selection is assessed in terms of number of control points and computational cost. The location of the selected control points near the ice accretion illustrates the efficacy of the method for localised deformations. The results show that the radial basis function mesh deformation performs well for both the two and three-dimensional problems. The data-reduction schemes utilised in this work represent a significant improvement to standard radial basis function mesh deformation for aircraft icing problems comprising of large data-sets typical of three-dimensional problems

A robust 3D particle tracking solver for in-flight ice accretion using arbitrary precision arithmetic

A particle tracking code is presented to compute droplet trajectories within a known Eulerian flow field for in-flight ice accretion simulations. The implementation allows for hybrid or unstructured meshes used by common CFD solvers. A known vicinity algorithm was devised to identify particles inside the mesh by computing the intersection between the particle trajectory and the faces of the mesh elements. Arbitrary precision arithmetic is used in the intersection evaluation in order to avoid errors when selecting the exit face if the intersection point is close to or coincident with a vertex or an edge. State-of- the-art wall interaction models are used to take into account droplet rebound, splash and spread at the walls. Non planar surface elements are assumed to improve the accuracy in evaluating the trajectory of secondary re-emitted particles. The software exhibits almost linear scaling when running in parallel on a distributed memory system. The particle tracking code is assessed against the experimental results regarding the impingement of Supercooled Large Droplets over a wing

A scalable Lagrangian particle tracking method

Particle tracking within an underlying flow field is routinely used to analyse both industrial processes and natural phenomena. In a computer code running on a distributed-memory architecture, the different behaviour of fluid-particle systems must be taken into account to properly balance element-particle subdivision among processes. In unsteady simulations, the parallel efficiency is even more critical because it changes over time. Another challenging aspect of a scalable implementation is the initial particle location due to the arbitrary shapes of each subdomain. In this work, an innovative parallel ray tracing particle location algorithm and a two-constrained domain subdivision are presented. The former takes advantage of a global identifier for each particle, resulting in a significant reduction of the overall communication among processes. The latter is designed to mitigate the load unbalance in the particles evolution while maintaining an equal element distribution. A preliminary particle simulation is performed to tag the cells and compute a weight proportional to the probability to be crossed. The algorithm is implemented using MPI distribute memory environment. A cloud droplet impact test case starting from an unsteady flow around a 3D cylinder has been simulated to evaluate the code performances. The tagging technique results in a computational time reduction of up to 78% and a speed up factor improvement of 44% with respect to the common flow-based domain subdivision. The overall scalability is equal to 1.55 doubling the number of cores