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We present a numerical method specifically designed for simulating three-dimensional fluid–structure interaction (FSI) problems based on the reference map technique (RMT). The RMT is a fully Eulerian FSI numerical method that allows fluids and large-deformation elastic solids to be represented on a single fixed computational grid. This eliminates the need for meshing complex geometries typical in other FSI approaches and greatly simplifies the coupling between fluid and solids. We develop a three-dimensional implementation of the RMT, parallelized using the distributed memory paradigm, to simulate incompressible FSI with neo-Hookean solids. As part of our method, we develop a field extrapolation scheme that works efficiently in parallel. Through representative examples, we demonstrate the method’s suitability in investigating many-body and active systems, as well as its accuracy and convergence. The examples include settling of a mixture of heavy and buoyant soft ellipsoids, lid-driven cavity flow containing a soft sphere, and swimmers actuated via active stress.

We previously introduced and verified the reduced unified continuum formulation for vascular fluid–structure interaction (FSI) against Womersley’s deformable wall theory. Our present work seeks to investigate its performance in a patient-specific aortic setting in which assumptions of idealized geometries and velocity profiles are invalid. Specifically, we leveraged 2D magnetic resonance imaging (MRI) and 4D-flow MRI to extract high-resolution anatomical and hemodynamic information from an in vitro flow circuit embedding a compliant 3D-printed aortic phantom. To accurately reflect experimental conditions, we numerically implemented viscoelastic external tissue support, vascular tissue prestressing, and skew boundary conditions enabling in-plane vascular motion at each inlet and outlet. Validation of our formulation is achieved through close quantitative agreement in pressures, lumen area changes, pulse wave velocity, and early systolic velocities, as well as qualitative agreement in late systolic flow structures. Our validated suite of FSI techniques offers a computationally efficient approach for numerical simulation of vascular hemodynamics. This study is among the first to validate a cardiovascular FSI formulation against an in vitro flow circuit involving a compliant vascular phantom of complex patient-specific anatomy.

Background Understanding the hemodynamics of an abdominal aortic aneurysm (AAA) is crucial for risk assessment and treatment planning. This study introduces a low-cost, patient-specific in vitro AAA model to investigate hemodynamics using particle image velocimetry (PIV) and flow-simulating circuit, validated through fluid–structure interaction (FSI) simulations. Methods In this study, 3D printing was employed to manufacture a flexible patient-specific AAA phantom using a lost-core casting technique. A pulsatile flow circuit was constructed using off-the-shelf components. A particle image velocimetry (PIV) setup was built using an affordable laser source and global shutter camera, and finally, the flow field inside the AAA was analyzed using open-source software. Fluid–structure interaction (FSI) simulations were performed to enhance our understanding of the flow field, and the results were validated by PIV analysis. Both steady-state and transient flow conditions were investigated. Results Our experimental setup replicated physiological conditions, analyzing arterial wall deformations and flow characteristics within the aneurysm. Under constant flow, peak wall deformations and flow velocities showed deviations within − 12% to + 27% and − 7% to + 5%, respectively, compared to FSI simulations. Pulsatile flow conditions further demonstrated a strong correlation (Pearson coefficient 0.85) in flow velocities and vectors throughout the cardiac cycle. Transient phenomena, particularly the formation and progression of vortex structures during systole, were consistently depicted between experimental and numerical models. Conclusions By bridging high-fidelity experimental observations with comprehensive computational analyses, this study underscores the potential of integrated methodologies in enhancing our understanding of AAA pathophysiology. The convergence of realistic AAA phantoms, precise PIV measurements at affordable cost point, and validated FSI models heralds a new paradigm in vascular research, with significant implications for personalized medicine and bioengineering innovations.

Elevated intraocular pressure (IOP) appears to have a broader impact on increased resistance to aqueous humor (AH) outflow through the conventional aqueous outflow system (AOS). However, it is still unknown how AH drainage resistance is produced or why it becomes increased in glaucoma. It is hard to accurately obtain hydrodynamic parameters of AH within the trabecular meshwork (TM) outflow pathway tissues based on current technology. In this study, we reconstructed the rat AOS model with high-resolution two-photon imaging, and simulated the AH outflow process. The resolution of the two-photon imaging system can be up to 0.5 μm for imaging the AOS tissues. Quite a few morphological parameters of rat TM in conditions of normal and elevated IOP were determined using the experiment integrated with the simulation method. We determined that the TM thickness is 49.51 ± 6.07 μm with an IOP of 5.32 kPa, which significantly differed from the TM thickness of 66.4 ± 5.14 μm in the normal IOP group. Furthermore, 3D reconstruction of local aqueous drainage channels from two-photon microscopy images revealed detailed structures of the AOS and permitted the identification of 3D relationships of Schlemm’s canal, collector channel, and trabecular drainage channels. An algorithm of finite element micro-modeling of the rat TM outflow pathways reveals the importance of TM for mechanical performance, with the potential to assist clinical therapies for glaucoma that seek to steer clear of an abnormal TM. Graphical abstract

This work addresses research questions arising from the application of geometrically exact beam theory in the context of fluid-structure interaction (FSI). Geometrically exact beam theory has proven to be a computationally efficient way to model the behavior of slender structures while leading to rather well-posed problem descriptions. In particular, we propose a mixed-dimensional embedded finite element approach for the coupling of one-dimensional geometrically exact beam equations to a three-dimensional background fluid mesh, referred to as fluid–beam interaction (FBI) in analogy to the well-established notion of FSI. Here, the fluid is described by the incompressible isothermal Navier–Stokes equations for Newtonian fluids. In particular, we present algorithmic aspects regarding the solution of the resulting one-way coupling schemes and, through selected numerical examples, analyze their spatial convergence behavior as well as their suitability not only as stand-alone methods but also for an extension to a full two-way coupling scheme.

Transport and mixing in the gastric duct occur via peristaltic flow. In vivo data are hard to collect and require strict ethical approval. In contrast, both in vitro and in silico studies allow detailed investigation and can be constructed to answer specific questions. Therefore, the aim of this study was to design a new elastic thermoplastic polyurethane (TPU) intestine model and to compare the flow patterns observed experimentally with those predicted by a Fluid Structure Interaction (FSI) simulation. Here, we present complementary studies that allow feedback to improve both techniques and provide mutual validation. The experimental work provides direct measurement of mixing, and the simulation allows the experimental setup to be studied to determine the impacts of various parameters. We conclude by highlighting the utility of this approach.

Seals are well‐known for their remarkable hydrodynamic trail‐following capabilities made possible by undulating flow‐sensing whiskers that enable the seals to detect fish swimming as far as 180 m away. In this work, the form‐function relationship in the undulating whiskers of two different phocid seal species, viz. harbor and gray seals, is studied. The geometry and material properties of excised harbor and grey seal whiskers are systematically characterized using blue light 3D scanning, optical and scanning electron microscopy, and nanoindentation. The effect of the undulating geometry on the whiskers’ vibration in uniform water flow is studied using both experimental (piezoelectric MEMS and 3D‐printed piezoresistive sensors developed in‐house) and numerical (finite element method) techniques. The results indicate that the dimensionless ratio of undulation wavelength to mean whisker diameter (λ/Dm) in phocid seals may have evolved to be in the optimal range of 4.4–4.6, enabling an order‐of‐magnitude reduction in vortex‐induced vibrations (compared to a similarly‐shaped circular cylinder) and, consequently, an enhanced flow sensing capability with minimal self‐induced noise. The results highlight the importance of the dimensionless λ/Dm ratio in the biomimetic design of seal whisker‐inspired vibration‐resistant structures, such as marine risers and wake detection sensors for submarines. Phocid seal whiskers possess a unique undulating geometry that reduces vortex‐induced vibrations (VIV) and helps the seal track its prey. In this work, the form‐function relationships in harbor and grey seal whiskers are studied. The results indicate that the wavelength‐to‐mean diameter ratio (λ/Dm) of the undulating whiskers may have evolved to possess an optimal value of 4.5 to minimize VIV.

The in-line monitoring of liquid properties, such as density and viscosity, is a key process in many industrial areas such as agro-food, automotive or biotechnology, requiring real-time automation, low-cost and miniaturization, while maintaining a level of accuracy and resolution comparable to benchtop instruments. In this paper, 3D-printed cuboid-shaped liquid cells featuring a rectangular vibrating plate in one of the sides, actuated by PZT piezoelectric layers, were designed, fabricated and tested. The device was resonantly excited in the 3rd-order roof tile-shaped vibration mode of the plate and validated as a density-viscosity sensor. Furthermore, conditioning circuits were designed to adapt the impedance of the resonator and to cancel parasitic effects. This allowed us to implement a phase-locked loop-based oscillator circuit whose oscillation frequency and voltage amplitude could be calibrated against density and viscosity of the liquid flowing through the cell. To demonstrate the performance, the sensor was calibrated with a set of artificial model solutions of grape must, representing stages of a wine fermentation process. Our results demonstrate the high potential of the low-cost sensor to detect the decrease in sugar and the increase in ethanol concentrations during a grape must fermentation, with a resolution of 10 µg/mL and 3 µPa·s as upper limits for the density and viscosity, respectively.

This paper reports on the study of a piezoelectric actuated micropump with integrated elastomeric check valves that can transport small amounts of fluid in a highly controllable manner. The proposed micropump consists of a piezoelectric actuated fluid chamber with two integrated elastomeric check valves for regulating input and output flow direction, while restricting backflows. The actuation, fluid dynamic response and fluid–structure interactions at various working cycles are studied through a fully coupled multiphysics simulation (solid mechanics, electrostatic and fluid flow). The pump bodies are manufactured by micromachining of PMMA sheets, while the middle elastomeric membrane and diaphragm are fabricated by spin-coating PDMS. The experimental results confirm that the micropump can provide sufficiently low-velocity outflow for biomedical applications between 3.4 – 41.8 µl/min. The performance of the micropump is improved significantly through a convenient geometric modification of an off-the-shelf piezoelectric brass disc. Furthermore, the combination of this micropump with the 3D cell-culture microfluidic chip realizes the dynamic culture of cells encapsulated in 3D hydrogels with a continuous flowing medium, which offers the potential for changing the traditional mode of 3D cell culture with a static supply of nutrition and factors.

The geometry of the arteries at or near arterial bifurcation influences the blood flow field, which is an important factor affecting arteriogenesis. The blood can act sometimes as a non-Newtonian fluid. However, many studies have argued that for large and medium arteries, the blood flow can be considered to be Newtonian. In this work a comprehensive investigation of non-Newtonian effects on the blood fluid dynamic behavior in an aorta-iliac bifurcation is presented. The aorta-iliac geometry is reconstructed with references to the values reported in Shah et al. (1978); the 3D geometrical model consists of three filleted cylinders of different diameters. Governing equations with the appropriate boundary conditions are solved with a finite-element code. Different rheological models are used for the blood flow through the lumen and detailed comparisons are presented for the aorta-iliac bifurcation. Results are presented in terms of the velocity profiles in the bifurcation zone and Wall Shear Stress (WSS) for different sides of the bifurcation both for male and female geometries, showing that the Newtonian fluid assumption can be made without any particular loss in terms of accuracy with respect to the other more complex rheological models.