1. A novel data-driven surrogate approach for fast evaluation of the dynamics of soft ellipsoidal micro-particles in dilute viscous flowJana Wedel, Ivan Dominik Horvat, Nejc Vovk, Matjaž Hriberšek, Jure Ravnik, Paul Steinmann, 2026, original scientific article Abstract: We present a novel data-driven surrogate approach for fast evaluation of the deformation dynamics of soft particles, both initially spherical and ellipsoidal, suspended in external flows, specifically predicting the hydrodynamic tractions on the particle surface. The core of the approach relies on expressing the required force dyad as a linear combination of velocity gradient components, modulated by form coefficients. These coefficients scale shear, rotational, and extensional flow contributions to the velocity gradient. Two training strategies are proposed: one utilizing analytical data, which enables a computational speedup, and another based on data obtained with 3D direct numerical simulations (DNS) using the boundary element method (BEM), with the latter demonstrating the feasibility of this approach even in the absence of analytical solutions. Validation against established literature benchmarks confirms the model’s accuracy in three scenarios: (i) ellipsoidal particles in the quasi-rigid limit in pipe flow, (ii) initially spherical particles in shear flow, and (iii) initially ellipsoidal particles in shear flow. In all cases, the data-driven surrogate approach achieves excellent agreement with reference results. This work establishes a foundation for extending our data-driven approach to flow-induced deformations of soft particles of more complex particle shapes, such as superellipsoids and other non-ellipsoidal geometries, where no analytical traction expression is available.
Keywords: neural network, pseudo-rigid bodies, Barycenter and shape dynamics, Lagrangian particle tracking
Published in DKUM: 27.11.2025; Views: 0; Downloads: 2
 Full text (7,16 MB)
This document has many files! More... |
2. Ellipsoidal soft micro-particles suspended in dilute viscous flowJana Wedel, Matjaž Hriberšek, Jure Ravnik, Paul Steinmann, 2025, original scientific article Abstract: Soft particles in viscous flows are prevalent both in nature and in various industrial applications. Notable examples include biological cells such as blood cells and bacteria as well as hydrogels and vesicles. To model these intriguing particles, we present an extension of our recent, efficient, and versatile pseudo-rigid body approach, originally developed for initially spherical soft particles suspended in arbitrary macroscale viscous flows. The novel extension allows modeling the barycenter and shape dynamics of soft initially non-spherical, i.e. ellipsoidal particles by introducing a novel shape and orientation tensor. We consider soft, micrometer-sized, ellipsoidal particles deforming affinely. To this end, we combine affine deformations (as inherent to a pseudo-rigid body) and the Jeffery-Roscoe model to analytically determine the traction exerted on a soft ellipsoidal particle suspended locally in a creeping flow at the particle scale. Without loss of generality, we assume nonlinear hyperelastic material behavior for the particles considered. The novel extension of our recent numerical approach for soft particles demonstrates that the deformation and motion of the particles can be accurately reproduced also for ellipsoidal particles and captures results from the literature, however, at drastically reduced computational costs. Furthermore, we identify both the tumbling and trembling dynamic regime for soft ellipsoidal particles suspended in simple shear flow again capturing results from the literature. Our extended approach is first validated using experimental and numerical studies from the literature for quasi-rigid as well as soft particles, followed by a comparison of the effects of particle deformability for some well-known fluid flow cases, such as laminar pipe flow, lid-driven cavity flow, and a simplified bifurcation. We find that taking particle deformability into account leads to notable deviations in the particle trajectory compared to rigid particles, with increased deviations for higher initial particle aspect ratio. Furthermore, we demonstrate that our approach can track a statistically relevant number of soft particles in complex flow situations.
Keywords: soft particles, Lagrangian particle tracking, pseudo-rigid bodies, point-particle method
Published in DKUM: 19.05.2025; Views: 0; Downloads: 3
Full text (4,82 MB)
This document has many files! More... |
3. A novel pseudo-rigid body approach to the non-linear dynamics of soft micro-particles in dilute viscous flowJana Wedel, Matjaž Hriberšek, Jure Ravnik, Paul Steinmann, 2024, original scientific article Abstract: We propose a novel, demonstrably effective, utmost versatile and computationally highly efficient
pseudo-rigid body approach for tracking the barycenter and shape dynamics of soft, i.e. nonlinearly deformable micro-particles dilutely suspended in viscous flow. Pseudo-rigid bodies are
characterized by affine deformation and thus represent a first-order extension to the kinematics
of rigid bodies. Soft particles in viscous flow are ubiquitous in nature and sciences, prominent
examples, among others, are cells, vesicles or bacteria. Typically, soft particles deform severely
due to the mechanical loads exerted by the fluid flow. Since the shape dynamics of a soft particle -
a terminology that shall here also include its orientation dynamics - also affects its barycenter
dynamics, the resulting particle trajectory as a consequence is markedly altered as compared to
a rigid particle. Here, we consider soft micro-particles of initially spherical shape that affinely
deform into an ellipsoidal shape. These kinematic conditions are commensurate with i) the affine
deformation assumption inherent to a pseudo-rigid body and ii) the celebrated Jeffery-Roscoe
model for the traction exerted on an ellipsoidal particle due to creeping flow conditions around
the particle. Without loss of generality, we here focus on non-linear hyperelastic particles for the
sake of demonstration. Our novel numerical approach proves to accurately capture the particular
deformation pattern of soft particles in viscous flow, such as for example tank-treading, thereby
being completely general regarding the flow conditions at the macro-scale and, as an option, the
constitutive behavior of the particle. Moreover, our computational method is highly efficient and
allows straightforward integration into established Lagrangian tracking algorithms as employed
for the point-particle approach to track rigid particles in dilute viscous flow.
Keywords: soft particles, pseudo-rigid bodies, Barycenter and shape dynamics, Lagrangian particle tracking
Published in DKUM: 19.09.2024; Views: 0; Downloads: 20
Full text (2,18 MB)
This document has many files! More... |
4. Numerical simulations of the flow and aerosol dispersion in a violent expiratory event : Outcomes of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory eventsJordi Pallares, Alexandre Fabregat Tomas, Akim Lavrinenko, Hadifathul Akmal bin Norshamsudin, Gabor Janiga, David Frederick Fletcher, Kiao Inthavong, Marina Zasimova, Vladimir Ris, Nikolay Ivanov, Robert Castilla, Pedro Javier Gamez-Montero, Gustavo Raush, Hadrien Calmet, Daniel Mira, Jana Wedel, Mitja Štrakl, Jure Ravnik, Douglas Hector Fontes, Francisco José De Souza, Cristian Marchioli, Salvatore Cito, 2023, original scientific article Abstract: This paper presents and discusses the results of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events” aimed at assessing the ability of different computational codes and turbulence models to reproduce the flow generated by a rapid prototypical exhalation and the dispersion of the aerosol cloud it produces. Given a common flow configuration, a total of 7 research teams from different countries have performed a total of 11 numerical simulations of the flow dispersion by solving the Unsteady Reynolds Averaged Navier–Stokes (URANS) or using the Large-Eddy Simulations (LES) or hybrid (URANS-LES) techniques. The results of each team have been compared with each other and assessed against a Direct Numerical Simulation (DNS) of the exact same flow. The DNS results are used as reference solution to determine the deviation of each modeling approach. The dispersion of both evaporative and non-evaporative particle clouds has been considered in 12 simulations using URANS and LES. Most of the models predict reasonably well the shape and the horizontal and vertical ranges of the buoyant thermal cloud generated by the warm exhalation into an initially quiescent colder ambient. However, the vertical turbulent mixing is generally underpredicted, especially by the URANS-based simulations, independently of the specific turbulence model used (and only to a lesser extent by LES). In comparison to DNS, both approaches are found to overpredict the horizontal range covered by the small particle cloud that tends to remain afloat within the thermal cloud well after the flow injection has ceased.
Keywords: numerical simulations, computational fluid dynamics
Published in DKUM: 28.03.2024; Views: 456; Downloads: 476
Full text (8,63 MB)
This document has many files! More... |
5. A novel particle–particle and particle–wall collision model for superellipsoidal particlesJana Wedel, Mitja Štrakl, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2023, original scientific article Keywords: multiphase flow, Lagrangian particle tracking, superellipsoid, collision, friction
Published in DKUM: 28.03.2024; Views: 171; Downloads: 9
Full text (6,50 MB)
This document has many files! More... |
