182 research outputs found
Experimental evidence of random shock-wave intermittency
We report the experimental observation of intermittency in a regime dominated
by random shock waves on the surface of a fluid. We achieved such a
nondispersive surface-wave field using a magnetic fluid subjected to a high
external magnetic field. We found that the small-scale intermittency of the
wave-amplitude fluctuations is due to shock waves, leading to much more intense
intermittency than previously reported in three-dimensional hydrodynamics
turbulence or in wave turbulence. The statistical properties of intermittency
are found to be in good agreement with the predictions of a Burgerslike
intermittency model. Such experimental evidence of random shock-wave
intermittency could lead to applications in various fields
HPC compact quasi-Newton algorithm for interface problems
In this work we present a robust interface coupling algorithm called Compact
Interface quasi-Newton (CIQN). It is designed for computationally intensive
applications using an MPI multi-code partitioned scheme. The algorithm allows
to reuse information from previous time steps, feature that has been previously
proposed to accelerate convergence. Through algebraic manipulation, an
efficient usage of the computational resources is achieved by: avoiding
construction of dense matrices and reduce every multiplication to a
matrix-vector product and reusing the computationally expensive loops. This
leads to a compact version of the original quasi-Newton algorithm. Altogether
with an efficient communication, in this paper we show an efficient scalability
up to 4800 cores. Three examples with qualitatively different dynamics are
shown to prove that the algorithm can efficiently deal with added mass
instability and two-field coupled problems. We also show how reusing histories
and filtering does not necessarily makes a more robust scheme and, finally, we
prove the necessity of this HPC version of the algorithm. The novelty of this
article lies in the HPC focused implementation of the algorithm, detailing how
to fuse and combine the composing blocks to obtain an scalable MPI
implementation. Such an implementation is mandatory in large scale cases, for
which the contact surface cannot be stored in a single computational node, or
the number of contact nodes is not negligible compared with the size of the
domain. \c{opyright} Elsevier. This manuscript version is made available
under the CC-BY-NC-ND 4.0 license
http://creativecommons.org/licenses/by-nc-nd/4.0/Comment: 33 pages: 23 manuscript, 10 appendix. 16 figures: 4 manuscript, 12
appendix. 10 Tables: 3 manuscript, 7 appendi
Three-dimensional direct numerical simulation of free-surface magnetohydrodynamic wave turbulence
We report on three-dimensional direct numerical simulation of wave turbulence
on the free surface of a magnetic fluid subjected to an external horizontal
magnetic field. A transition from capillarywave turbulence to anisotropic
magneto-capillary wave turbulence is observed for an increasing field. At high
enough field, wave turbulence becomes highly anisotropic, cascading mainly
perpendicularly to the field direction, in good agreement with the prediction
of a phenomenological model, and with anisotropic Alfv{\'e}n wave turbulence.
Although surface waves on a magnetic fluid are different from Alfv{\'e}n waves
in plasma, a strong analogy is found with similar wave spectrum scalings and
similar magnetic-field dependent dispersionless wave velocities.Comment: in press in Phys. Rev E (Letter). For Supplemental Material, see
http://www.msc.univ-paris-diderot.fr/~falcon/PRE\_Letter22/PRE2022andSuppMat.pd
Parallel SFC-based mesh partitioning and load balancing
Modern supercomputers allow the simulation of complex phenomena with
increased accuracy. Eventually, this requires finer geometric discretizations
with larger numbers of mesh elements. In this context, and extrapolating to the
Exascale paradigm, meshing operations such as generation, adaptation or
partition, become a critical bottleneck within the simulation workflow. In this
paper, we focus on mesh partitioning. In particular, we present some
improvements carried out on an in-house parallel mesh partitioner based on the
Hilbert Space-Filling Curve.
Additionally, taking advantage of its performance, we present the application
of the SFC-based partitioning for dynamic load balancing. This method is based
on the direct monitoring of the imbalance at runtime and the subsequent
re-partitioning of the mesh. The target weights for the optimized partitions
are evaluated using a least-squares approximation considering all measurements
from previous iterations. In this way, the final partition corresponds to the
average performance of the computing devices engaged.Comment: 10 pages, 9 figures. arXiv admin note: text overlap with
arXiv:2005.0589
Extension of the parallel Sparse Matrix Vector Product (SpMV) for the implicit coupling of PDEs on non-matching meshes
The Sparse Matrix Vector Product (SpMV) is one of the main operations of iterative solvers, and, in a parallel context, it is also the siege of point-to-point communications between the neighboring MPI processes. The parallel SpMV is built in such a way that it gives, up to round off errors, the same result as its sequential counterpart. In this regards, nodes on the interfaces (or halo nodes if halo are considered) are duplicated nodes of the same original mesh. It is therefore limited to matching meshes. In this work, we generalize the parallel SpMV to glue the solution of non-matching (non-conforming) meshes through the introduction of transmission matrices. This extension of the SpMV thus enables the implicit and parallel solution of partial differential equations on non-matching meshes, as well as the implicit coupling of multiphysics problems, such as fluid-structure interactions. The proposed method is developed similarly to classical parallelization techniques and can therefore be implemented by modifying few subroutines of an already MPI-based code. According to the proposed framework, the classical parallelization technique appears as a particular case of this general setup.Peer ReviewedPostprint (author's final draft
BittyBuzz: A Swarm Robotics Runtime for Tiny Systems
Swarm robotics is an emerging field of research which is increasingly
attracting attention thanks to the advances in robotics and its potential
applications. However, despite the enthusiasm surrounding this area of
research, software development for swarm robotics is still a tedious task. That
fact is partly due to the lack of dedicated solutions, in particular for
low-cost systems to be produced in large numbers and that can have important
resource constraints. To address this issue, we introduce BittyBuzz, a novel
runtime platform: it allows Buzz, a domain-specific language, to run on
microcontrollers while maintaining dynamic memory management. BittyBuzz is
designed to fit a flash memory as small as 32 kB (with usable space for
scripts) and work with as little as 2 kB of RAM. In this work, we introduce the
BittyBuzz implementation, its differences from the original Buzz virtual
machine, and its advantages for swarm robotics systems. We show that BittyBuzz
is successfully integrated with three robotic platforms with minimal memory
footprint and conduct experiments to show computation performance of BittyBuzz.
Results show that BittyBuzz can be effectively used to implement common swarm
behaviors on microcontroller-based systems.Comment: 6 page
HPC-enabling technologies for high-fidelity combustion simulations
With the increase in computational power in the last decade and the forthcoming Exascale supercomputers, a new horizon in computational modelling and simulation is envisioned in combustion science. Considering the multiscale and multiphysics characteristics of turbulent reacting flows, combustion simulations are considered as one of the most computationally demanding applications running on cutting-edge supercomputers. Exascale computing opens new frontiers for the simulation of combustion systems as more realistic conditions can be achieved with high-fidelity methods. However, an efficient use of these computing architectures requires methodologies that can exploit all levels of parallelism. The efficient utilization of the next generation of supercomputers needs to be considered from a global perspective, that is, involving physical modelling and numerical methods with methodologies based on High-Performance Computing (HPC) and hardware architectures. This review introduces recent developments in numerical methods for large-eddy simulations (LES) and direct-numerical simulations (DNS) to simulate combustion systems, with focus on the computational performance and algorithmic capabilities. Due to the broad scope, a first section is devoted to describe the fundamentals of turbulent combustion, which is followed by a general description of state-of-the-art computational strategies for solving these problems. These applications require advanced HPC approaches to exploit modern supercomputers, which is addressed in the third section. The increasing complexity of new computing architectures, with tightly coupled CPUs and GPUs, as well as high levels of parallelism, requires new parallel models and algorithms exposing the required level of concurrency. Advances in terms of dynamic load balancing, vectorization, GPU acceleration and mesh adaptation have permitted to achieve highly-efficient combustion simulations with data-driven methods in HPC environments. Therefore, dedicated sections covering the use of high-order methods for reacting flows, integration of detailed chemistry and two-phase flows are addressed. Final remarks and directions of future work are given at the end.
}The research leading to these results has received funding from the European Union’s Horizon 2020 Programme under the CoEC project, grant agreement No. 952181 and the CoE RAISE project grant agreement no. 951733.Peer ReviewedPostprint (published version
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