1,721,373 research outputs found
Assessment of a sponge layer non-reflecting boundary treatment for high-order CAA/CFD computations
No full textIn this work we carefully assess the effectiveness and flexibility of a sponge layer non-reflecting boundary treatment in the context of a very high-order space discretization by solving several different flow problems. We opted for this simple yet practical approach as it perfectly fits into an implicit accurate time discretization. A parametric study on the absorbing layer performance has been firstly performed on canonical computational aeroacoustics (CAA) test cases. These flow problems, modelled with the Linearized Euler Equations (LEE), suggested some guidelines for the choice of the sponge parameters. Thereafter we applied the same approach to other more complex flow models, i.e. the Navier–Stokes (N–S) and the Reynolds averaged Navier–Stokes (RANS) equations closed by the View the MathML sourcek-ω ̃ turbulence model. The results demonstrate that the use of a non-reflecting boundary treatment is mandatory for the correct prediction of some quantities and distributions, e.g. the sound directivity, otherwise spoiled by boundary conditions reflections. Finally, our numerical evidences suggest that the guidelines for the design of a near-optimal absorbing sponge layer, numerically obtained on LEE test cases, can be extended, with some confidence, to more complex flow models, i.e. N–S, RANS
An agglomeration-based discontinuous Galerkin method for compressible flows
Full text linkThis thesis investigates the flexibility associated to Discontinuous Galerkin (DG) discretization on very general meshes obtained by means of agglomeration techniques. The work begins with a brief overview of the main tools that have been extended or specifically developed to deal with arbitrarily shaped elements in the DG context. Then two different implementations of the BRMPS scheme introduced by Bassi, Rebay, Mariotti, Pedinotti and Savini in [16] for the DG discretization of the Laplace operator on arbitrarily shaped elements have been presented. The validation of the scheme on a Poisson problem shows that the discrete polynomial space preserves optimal convergence properties.
The discretization of the second order differential operator has been directly extended to the Navier-Stokes equations and the Reynolds Averaged Navier-Stokes (RANS) equations coupled with the k-w turbulence model of Wilcox [54]. In this regard, an implicit time integration strategy has been considered and assessed on classical validation test cases for the compressible f uid dynamics.
Then a simple alternative approach to high-order mesh generation is presented. Indeed, once a standard fine grid able to provide an accurate domain discretization has been produced by means of standard low-order grid generation tools, a computational mesh suitable for the desired accuracy and computationally affordable can be obtained via agglomeration while keeping the boundary resolution of the fine grid. The effectiveness of this approach in representing the geometry of the domain is numerically assessed both on a Poisson model problem and on challenging inviscid and viscous test cases.
Finally, the freedom in simply defining the topology of agglomerated meshes leads to a nonstandard approach to h-adaptivity that exploits adaptive agglomeration coarsening of a properly fine underlying grid. The effectiveness of this approach has been assessed on test cases involving both error-based and fl ow feature-based simple estimators
A mathematical framework for cooperative collision avoidance of human-driven vehicles at intersections
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Entropy conserving implicit time integration in a Discontinuous Galerkin solver in entropy variables
No full textThis article presents a fully discrete entropy conserving/stable method based on a Discontinuous Galerkin (DG) discretization in entropy variables coupled with a modified Crank-Nicolson scheme. The entropy conserving time integration is inspired by the work of LeFloch, originally developed in the context of a Finite Volume method in conservative variables. This entropy conserving time integrator is here adapted to a DG discretization in entropy variables also demonstrating the fulfilment of entropy conservation regardless of the time step size and the type of elements used (quadrangular or triangular elements, possibly with curved edges). The performance of the implicit method will be demonstrated by computing several inviscid flow problems, i.e., the convection of an isentropic vortex, the double shear layer, the Kelvin-Helmholtz instability, the shedding flow past a triangular wedge, the Sod shock tube, the receding flow and the Taylor-Green vortex
Discontinuity induced bifurcations of non-hyperbolic cycles in nonsmooth systems
No full textWe analyze three codimension-two bifurcations occurring in nonsmooth systems, when a nonhyperbolic cycle (fold, flip, and Neimark–Sacker cases, in both continuous and discrete time) interacts with one of the discontinuity boundaries characterizing the system's dynamics. Rather than aiming at a complete unfolding of the three cases, which would require specific assumptions on both the class of nonsmooth system and the geometry of the involved boundary, we concentrate on the geometric features that are common to all scenarios. We show that, at a generic intersection between the smooth and discontinuity induced bifurcation curves, a third curve generically emanates tangentially to the former. This is the discontinuity induced bifurcation curve of the secondary invariant set (the other cycle, the double-period cycle, or the torus, respectively) involved in the smooth bifurcation. The result can be explained intuitively, but its validity is proved here rigorously under very general conditions. Three examples from different fields of science and engineering are also reported
Improved estimation of elbow flexion angle from IMU measurements using anatomical constraints
No full textObjectives:
Inertial Measurement Units (IMUs) are a valid alternative to optical tracking systems for human motion capture, but they are subject to several disturbances that limit their accuracy. We aim to improve the accuracy of elbow joint angle estimation from IMU measurements by introducing a novel postprocessing algorithm that uses anatomical constraints and does not require any prior calibration or knowledge of anthropometric parameters.
Materials and Methods:
We propose a new error model that addresses sensor misalignment and fusion errors. We use an error state extended Kalman filter (ESEKF) with state constraints to integrate the anatomical constraints. We validate the proposed algorithm by testing it in different scenarios and comparing it with a state-of-the-art optical tracking system.
Results:
The research results highlight the superior performance of the proposed method compared with existing techniques. The study demonstrates a significant reduction in errors, particularly in complex arm movements and under strong external disturbances. The results obtained in the three different tested scenarios underscore the robustness and effectiveness of the developed algorithm, reaching half the error committed by the existing calibration-free correction algorithms proposed in the literature.
Conclusions:
The developed technique provides highly accurate estimates of joint angles in several challenging real-world scenarios
A fully-discrete entropy conserving/stable discretization for inviscid unsteady flows
No full textThe aim of this work is to contribute to the development of a high-order accurate discretization that is entropy conserving and entropy stable both in space and in time. To do this, the general framework is based on a high-order accurate discontinuous Galerkin (dG) method in space with entropy working variables, several entropy conservative and stable numerical fluxes and an entropy conserving modified Crank-Nicolson method. We present the first results, obtained with the discretizations here proposed, for two bi-dimensional unsteady viscous test-case: The Taylor-Green vortex and the double shear layer
Abstraction-based Safety Verification and Control of Cooperative Vehicles at Road Intersections
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