arXiv subjects

Robinson Perić

Publications and source records attributed to Robinson Perić.

4 recordsLinked to original sources

arXiv2021

Optimizing wave-generation and wave-damping in 3D-flow simulations with implicit relaxation-zones

In finite-volume-based flow-simulations with free-surface waves, wave reflections at the domain boundaries can cause substantial errors in the results and must therefore be minimized. This can be achieved via `implicit relaxation zones', but only if the relaxation zone's case-dependent parameters are optimized. This work proposes an analytical approach for optimizing these parameters. The analytical predictions are compared against results from 2D-flow simulations for different water depths, flow solvers, and relaxation functions, and against results from 3D-flow simulations with strongly wave-reflecting bodies subjected to nonlinear free-surface waves. The present results demonstrate that the proposed approach satisfactorily predicts both the optimum parameter settings and the upper-limit for the corresponding reflection coefficients $C_{\mathrm{R}}$. Simulation results for $C_{\mathrm{R}}$ were mostly below or equal to the analytical predictions, but never more than $3.4\%$ larger. Therefore, the proposed approach can be recommended for engineering practice. Furthermore, it is shown that implicit relaxation zones can be considered as a special-case of forcing zones, a family of approaches which includes among others absorbing layers, damping zones and sponge layers. The commonalities and differences between these approaches are discussed, including to what extend the present findings are applicable to these other approaches and vice versa.

physics.flu-dyn↗

arXiv2020

Analytical and numerical investigation of the airflow in face masks used for protection against COVID-19 virus -- implications for mask design and usage

The use of face masks for the general public has been suggested in literature as a means to decrease virus transmission during the global COVID-19 pandemic. However, literature findings indicate that most mask designs do not provide reliable protection. This paper investigates the hypothesis that the impaired protection is mainly due to imperfect fitting of the masks, so that airflow, which contains virus-transporting droplets, can leak through gaps into or out of the mask. The fluid dynamics of face masks are investigated via analytical and numerical computations. The results demonstrate that the flow can be satisfactorily predicted by simplified analytical 1D-flow models, by efficient 2D-flow simulations and by 3D-flow simulations. The present results show that already gap heights larger than 0.1mm can result in the mask not fulfilling FFP2 or FFP3 standards, and for gap heights of ca. 1mm most of the airflow and droplets may pass through the gap. The implications of these findings are discussed and improvements to existing mask designs are suggested.

physics.med-ph↗

arXiv2017

Analytical Prediction of Reflection Coefficients for Wave Absorbing Layers

In finite-volume-based flow simulations, absorbing layers are widely used to reduce pressure wave reflections at boundaries of the computational domain. A disadvantage of absorbing layers is that they contain case-dependent parameters; thus the question is how to optimally tune these parameters, so that a desired reduction of reflections can be obtained? As a step towards the answer of these questions, this article presents a theory which predicts reflection coefficients for absorbing layers. The theory is given for 1D-wave propagation and is then extended to 2D and 3D to cover waves of oblique incidence. The theory is validated via flow simulations of regular and irregular pressure waves in air and water, based on Navier-Stokes-type equations and the finite-volume method. Theory predictions and simulation results show good agreement. It is demonstrated how the theory can be used to optimally tune the absorbing layer parameters to minimize undesired wave reflection. Thus the theory has benefits for a wide range of applications of finite-volume-based flow simulations in industrial practice.

physics.flu-dyn↗

arXiv2017

Analytical Prediction of Reflection Coefficients for Wave Absorbing Layers in Flow Simulations of Regular Free-Surface Waves

Undesired wave reflections, which occur at domain boundaries in flow simulations with free-surface waves, can be minimized by applying source terms in the vicinity of the boundary to damp the waves. Examples of such approaches are absorbing layers, damping zones, forcing zones, relaxation zones and sponge layers. A problem with these approaches is that the effectivity of the wave damping depends on the parameters in the source term functions, which are case-dependent and must be adjusted to the wave. The present paper presents a theory which analytically predicts the reflection coefficients and which can be used to optimally select the source term parameters before running the simulation. The theory is given in a general form so that it is applicable to many existing implementations. It is validated against results from finite-volume-based flow simulations of regular free-surface waves and found to be of satisfactory accuracy for practical purposes.

physics.flu-dyn↗