arXiv subjects

Marin Lauber

Publications and source records attributed to Marin Lauber.

6 recordsLinked to original sources

arXiv2026

Scaling WaterLily.jl with MPI and an improved geometric multigrid solver

We present recent performance-oriented developments in WaterLily, a scale-resolving incompressible flow solver written in pure Julia that runs seamlessly on CPUs and GPUs of any vendor. Supported by the newly added MPI-based parallelism, strong-scalability tests display a near-ideal linear trend, and weak-scaling efficiency is kept above 85% before node memory-concurrency contention dominates parallel performance. Inter-node weak scalability is sustained above 96% with grid size up to 1 billion cells. We further benchmark improvements to the geometric multigrid Poisson solver enabled by an adaptive under-relaxed red-black Gauss-Seidel smoother together with anisotropic coarsening operators.

physics.comp-ph↗

arXiv2026

Stability of Kirigami parachutes in effectively infinite numerical domains

Kirigami, the art of cutting flat sheets into deployable 3D structures, has recently inspired a new class of parachutes which can deploy into a naturally stable inverted canopy. However, the dynamic mechanism, fluid forces, and geometrical parameters that grant this stability have not yet been clearly identified. In this paper, we use a novel Biot-Savart far-field boundary condition to perform prescribed acceleration and free-falling simulations in effectively infinite domains, tracking the descent of a parameterized kirigami parachute. The far-field velocity is reconstructed from the interior vorticity, resulting in less than 0.1% variation in the predicted dynamics as the domain size is doubled. We first show the linear forces drop 2-5 times as the parachute is deployed due to increased permeability, whereas the moments increase due the counterbalancing effect of the increased lever-arm. Next, we find that the kirigami parachute achieves stable flight for deployment heights as small as half its radius, quickly damping out applied perturbations. For smaller deployments, the parachute tumbles due to side-slip and rotational coupling, as in falling disks. These effectively unbounded simulations identify that deployments approximately equal to the radius offer high drag forces with strong dynamic stability, providing a simple design rule for deployable parachutes.

physics.flu-dyn↗

arXiv2026

The mechanics of the $\textit{Less In More Out}$ artificial heart: modeling fabric-based soft robotic devices

Recently, the Less In More Out device, a fluidically actuated soft total artificial heart was proposed. This device uses arrays of pouch motors to achieve a positive fluidic lever when pneumatically actuated against physiological hemodynamic conditions. Extensive experimental characterization demonstrated its potential; however, experiments alone cannot resolve the internal mechanical fields that govern device durability and performance. Here, we develop a computational framework to investigate intrinsic device mechanics, such as stress concentrations, strain paths, and fatigue life, and to explore targeted design modifications that improve durability and efficiency. We show that our model reproduces the nonlinear deformation and pressure-volume relationships measured experimentally under varying hemodynamic conditions. Across designs, devices with fewer pouches deliver higher stroke volumes but exhibit up to 50% higher peak von Mises stresses, which reduces their fatigue life. Our simulations further identify heat-sealed seams and buckling regions as durability-limiting features. As a proof of concept, we vary the valve support aspect ratio and relative endocardial-epicardial pouch fabric compliance, reducing the peak von Mises stress by ~10% while maintaining identical physiological outputs and improving mechanical efficiency. Overall, our framework enables detailed evaluation of stress hotspots, buckling, and fatigue life, and offers a foundation for optimizing artificial hearts and other fluidically actuated fabric-based soft robotic devices.

q-bio.TO↗

arXiv2025

Using Biot-Savart boundary conditions for unbounded external flow on Eulerian meshes

We introduce a novel boundary condition for incompressible Eulerian simulations formulated using a Biot-Savart vorticity integral that maintains high-accuracy results even when the domain boundary is within a body-length of immersed solid boundaries. The key prerequisite to accurately couple the Biot-Savart condition to the Eulerian velocity and pressure fields is including the influence of the vorticity generated at the immersed boundaries during the incompressible-flow projection step. While the resulting linear operator for the pressure is non-local, it can be efficiently solved by partitioning it into the standard local Poisson operator and the Biot-Savart update. We use oct-tree clustering for the Fast Multi-level Method (FM$\ell$M) to reduce the computational cost of the evaluation of the Biot-Savart integral on the boundaries of a 3D simulation with $N$ points from $O(N^{5/3})$ to $O(N)$ and show that this has bounded errors. We show that the new method captures the analytical added-mass force of accelerating 2D and 3D plates exactly and matches experimentally measured wake development even when the entire domain only extends 1/2 diameter from the plate. The new method also predicts accurate time-varying forces for a 2D circle and 3D sphere regardless of domain size, while classical boundary conditions require a domain more than 100 times larger in 2D to converge on the new method's result. Finally, we study the highly sensitive 2D deflected wakes produced by high frequency flapping foils to the new boundary conditions and show that truncating the deflected wake within four cord-lengths of the body changes the body force amplitudes by 10-40%. Doubling the wake size recovers the asymptotic results to within 5%.

physics.flu-dyn↗

arXiv2023

Immersed-Boundary Fluid-Structure Interaction of Membranes and Shells

This paper presents a general and robust method for the fluid-structure interaction of membranes and shells undergoing large displacement and large added-mass effects by coupling an immersed-boundary method with a shell finite-element model. The immersed boundary method can accurately simulate the fluid velocity and pressure induced by dynamic bodies undergoing large displacements using a computationally efficient pressure projection finite volume solver. The structural solver can be applied to bending and membrane-related problems, making our partitioned solver very general. We use a strongly-coupled algorithm that avoids the expensive computation of the inverse Jacobian within the root-finding iterations by constructing it from input-output pairs of the coupling variables from the previous time steps. Using two examples with large deformations and added mass contributions, we demonstrate that the resulting quasi-Newton scheme is stable, accurate, and computationally efficient.

physics.flu-dyn↗

arXiv2021

Immersed Boundary Simulations of Flows Driven by Moving Thin Membranes

Immersed boundary methods are extensively used for simulations of dynamic solid objects interacting with fluids due to their computational efficiency and modelling flexibility compared to body-fitted grid methods. However, thin geometries, such as shells and membranes, cause a violation of the boundary conditions across the surface for many immersed boundary projection algorithms. Using a one-dimensional analytical derivation and multi-dimensional numerical simulations, this manuscript shows that adjustment of the Poisson matrix itself is require to avoid large velocity, pressure, and force prediction errors when the pressure jump across the interface is substantial and that these errors increase with Reynolds number. A new minimal thickness modification is developed for the Boundary Data Immersion Method (BDIM-σ),which avoids these issues while still enabling the use of efficient projection algorithms for high-speed immersed surface simulations.

physics.flu-dyn↗