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This work explores the use of an embedded Computational Fluid Dynamics method to study the type B Aortic Dissection. The use of the proposed technique makes it possible to easily test different Intimal Flap configurations without any need of remeshing. To validate the presented methodology we take as reference test case an in vitro experiment present in the literature. This experiment, which considers several Intimal Flap tear configurations (number, size and location), mimics the blood flow in a real type B Aortic Dissection. We prove the correctness and suitability of the presented approach by comparing the pressure values and waveform. The obtained results exhibit a remarkable similarity with the experimental reference data.Complementary, we present a feasible surgical application of the presented computer method. The aim is to help the clinicians in the decision-making before the type B Aortic Dissection surgical fenestration. The capabilities of the proposed technique are exploited to efficiently create artificial re-entry tear configurations . We highlight that only the radius and center of the re-entry tear need to be specified by the clinicians, without any need to modify neither the model geometry nor the mesh.The obtained computational surgical fenestration results are in line with the medical observations in similar clinical studies.
This work describes a novel formulation for the simulation of incompressible Navier–Stokes problems involving nonconforming discretizations of membrane‐like bodies. The new proposal relies on the use of a modified finite element space within the elements intersected by the embedded geometry, which is represented by a discontinuous (or element‐by‐element) level set function. This is combined with a Nitsche‐based imposition of the general Navier‐slip boundary condition, to be intended as a wall law model. Thanks to the use of an alternative finite element space, the formulation is capable of reproducing exactly discontinuities across the embedded interface, while preserving the structure of the graph of the discrete matrix. The performance, accuracy and convergence of the new proposal is compared with analytical solutions as well as with a body fitted reference technique. Moreover, the proposal is tested against another similar embedded approach. Finally, a realistic application showcasing the possibilities of the method is also presented.
This work derives an incompressible variational multiscales time-averagedNavier-Stokes (NS) formulation that aims at obtaining accurate steady state solutions. Rather than using the standard time instantaneous velocity and pressure, the new formulation devises a time averaging procedure based on rewriting and solving the NS equations in terms of the newly defined time-averaged velocity and pressure. Hence, the method could be understood as a convenient change of variable so that the problem is rewritten directly in terms of the steady state quantities. The important advantage of such a point of view is that it can in principle be applied to any other formulation. Such time averaging procedure is complemented by two time step modification strategies in order to accelerate the convergence to the steady state. The guidelines of an integrated framework are presented in the article, starting with the description of the proposed numerical technique applied to general incompressible flows. The explanation is enhanced with a one-dimensional (1D) nonlinear oscillator example. Several results are presented concerning analytical benchmarks, simulation of flows in laminar, transitional and turbulent regimes with and without an inherently steady solution.
K E Y W O R D Scomputational fluid dynamics, finite element method, Navier-Stokes, steady state, time-averaged, variational multiscale method This project was conducted in cooperation with International Centre for Numerical Methods in Engineering (CIMNE).This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
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