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fluid-structure interaction analysis of the thromboembolic risk in the left atrial appendage under atrial fibrillation: Effect of hemodynamics and morphological features

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COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2024年 246卷 108056-108056页

作者： Musotto, Giulio Monteleone, Alessandra Vella, Danila Zuccarello, Bernardo Cannova, Ruggero Cook, Andrew Bosi, Giorgia Maria Burriesci, Gaetano Ri MED Fdn Bioengn Grp Palermo Italy Univ Palermo Dept Engn Palermo Italy UCL Inst Cardiovasc Sci Inst Cardiovasc Sci London England Great Ormond St Hosp Sick Children London England UCL UCL Mech Engn Torrington Pl London WC1E 7JE England

Background: Complications of atrial fibrillation (AF) include ischemic events originating within the left atrial appendage (LAA), a protrusion of the left atrium with variable morphological characteristics. The role of the patient specific morphology and pathological haemodynamics on the risk of ischemia remains unclear. Methods: This work performs a comparative assessment of the hemodynamic parameters among patient-specific LAA morphologies through fluid-structure interaction computational analyses. Three LAA models per each of the four commons patient-specific morphological families (chicken wing, cactus, windsock, and cauliflower) were analysed. Mechanical properties of the tissue were based on experimental uniaxial tests on a young pig's heart. Boundary conditions were imposed based on clinical assessments of filling and emptying volumes. Sinus rhythm and atrial fibrillation operative conditions were simulated and analysed. Results: For each model, the effect of morphological and functional parameters, such as the number of trabeculae and LAA stroke volume, over the hemodynamics established into the appendage was analysed. Comparison between results obtained in healthy and diseased conditions suggested the introduction of a new parameter to quantify the risk of thrombosis, here called blood stasis factor (BSF). This is defined as the LAA surface area which permanently experiences levels of shear strain rate inferior to a threshold value, set to 5 s-1 (BSF5). Conclusions: This work suggests that the current morphological classification is unsuitable to evaluate the probability of thrombus formation. However, hemodynamic parameters easy to determine from clinical examinations, such as normalised stroke volume, LAA orifice flow rate and presence of extensive trabeculations can identify departures from healthy hemodynamics in AF and support a more systematic stratification of the thromboembolic risk.

关键词： Atrial fibrillation Left atrial appendage fluid-structure interaction Cardiovascular engineering Patient-specific numerical models

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fluid-structure interaction simulations for a temperature-sensitive functionally graded hydrogel-based micro-channel

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JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND structureS 2021年第6期32卷 661-677页

作者： Ghasemkhani, Amir Mazaheri, Hashem Amiri, Arya Bu Ali Sina Univ Fac Engn Dept Mech Engn Hamadan *** Hamadan Iran Univ Tehran Coll Engn Sch Mech Engn Tehran Iran

The behavior of a temperature-sensitive micro-channel have been investigated in this study which mainly includes a functionally graded (FG) hydrogel as a sensor or an actuator. In order to achieve this goal, both fluid-structure interaction (FSI) and non-FSI simulations are conducted for hydrogel with homogeneous property distribution as well as FG hydrogels with different number of layers (2-16 layers). Moreover, this study investigates the FG hydrogel cross-linking density that obeys a general exponential form. In addition to all mentioned, the FG hydrogels are considered in both ascending and descending states with vertically and horizontally functionally graded property distributions (VFG and HFG hydrogels). Subsequently, the importance of the difference between the FG and homogenous hydrogels has been highlighted in the findings of the study. Besides, the FSI influence has a vital role in these structures especially once an FG material is utilized. According to the findings, the ascending and descending distributions of the hydrogel properties may significantly affect the micro-channel behavior, especially in horizontally graded type. This process can be done in a way that for descending distribution of HFG there exist no closing state for the micro-channel.

关键词： fluid-structure interaction numerical simulations functionally garaged hydrogel temperature-sensitive hydrogel

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Nonlinear vibration analysis of a generally orthotropic cracked micro-plate with variable thickness considering fiber effects and fluid-structure interaction

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART G-JOURNAL OF AEROSPACE ENGINEERING 2025年

作者： Chandrakar, Bhupesh Kumar Jain, Nitin Kumar Gupta, Ankur Natl Inst Technol Dept Mech Engn Raipur 492010 India

This research investigates the nonlinear vibration response of partially cracked, generally orthotropic, rectangular micro-plates featuring non-uniform thicknesses coupled with a fluid medium. The traditional classical plate theory (CPT) in conjunction with a modified couple stress theory (MCST) is used to derive the governing equation of a generally orthotropic rectangular plate of varying thickness. The presence of a partial crack at the plate's center is modeled using a simplified line spring model (LSM), and in-plane forces and bending moment resulting from a partial crack are incorporated into the equation. Furthermore, the interaction with a fluid medium is considered, with the introduction of virtual added mass via the velocity potential function and Bernoulli's equations, considering both horizontal and vertical plate immersion scenarios. The study also explores thickness variations in one and two dimensions along the X and Y axes. The methodology employs Galerkin's approach to convert governing equations into time-dependent modal coordinates, and Berger's method introduces nonlinearity into these coordinates. The approximation solution, a method of multiple scales, is utilised to solve the plate's nonlinear governing equations. Various parameters are considered in the analysis, including crack length, size effect, thickness variations, fiber orientations, fluid levels, and immersion depth. The study explores the impact of these factors on the vibration behaviour of submerged partially cracked, generally, orthotropic non-uniform thickness micro-plates under two different boundary conditions, presenting novel findings. Additionally, an illustration is provided to visually depict the bending-hardening and bending-softening phenomenon concerning the taper constant and depth of submergence.

关键词： Vibration micro-plate crack varying thickness fluid-structure interaction

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An enhanced moving particle semi-implicit method for simulation of incompressible fluid flow and fluid-structure interaction

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COMPUTERS & MATHEMATICS WITH APPLICATIONS 2023年第1期145卷 41-57页

作者： Cai, Qinghang Chen, Ronghua Guo, Kailun Tian, Wenxi Qiu, Suizheng Su, G. H. Xi An Jiao Tong Univ Sch Nucl Sci & Technol Shaanxi Key Lab Adv Nucl Energy & Technol State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

An enhanced moving particle semi-implicit method for simulation of incompressible fluid flow and FSI (fluid -structure interaction) is developed in the present paper. Based on the recent studies on LSMPS (Least Square Moving Particle Semi-implicit) method [1,2], the fluid models for FSI are improved, and the elastic structure models and fluid-structure coupling schemes are developed. Many strategies are developed to reduce the influence of mechanical vibration of elastomers on fluid calculation. The models are validated step by step. The improved fluid models with different Dirichlet and Neumann boundary are validated through hydrostatic pool problem, connecting tube problem and dam break problem. The elastic structure models under the velocity boundary and the loading boundary are validated through free oscillation cantilever problem and pressurized ring problem respectively. The fluid-structure coupling schemes are validated by the violent sloshing problem without considering the elastic deformation and the problem of dam break with an elastic gate. The results show a good performance of the developed method on the simulation of incompressible fluid flow and fluid-structure interaction.

关键词： Particle method Least squares MPS method Elastic structure fluid-structure interaction

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Onset and nature of flow-induced vibrations in cerebral aneurysms via fluid-structure interaction simulations

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BIOMECHANICS AND MODELING IN MECHANOBIOLOGY 2023年第3期22卷 761-771页

作者： Bruneau, David A. Valen-Sendstad, Kristian Steinman, David A. Univ Toronto Dept Mech & Ind Engn Toronto ON Canada Simula Res Lab Dept Computat Physiol Oslo Norway

Clinical, experimental, and recent computational studies have demonstrated the presence of wall vibrations in cerebral aneurysms, thought to be induced by blood flow instability. These vibrations could induce irregular, high-rate deformation of the aneurysm wall, and potentially disrupt regular cell behavior and promote deleterious wall remodeling. In order to elucidate, for the first time, the onset and nature of such flow-induced vibrations, in this study we imposed a linearly increasing flow rate on high-fidelity fluid-structure interaction models of three anatomically realistic aneurysm geometries. Prominent narrow-band vibrations in the range of 100-500 Hz were found in two out of the three aneurysm geometries tested, while the case that did not exhibit flow instability did not vibrate. Aneurysm vibrations consisted mostly of fundamental modes of the entire aneurysm sac, with the vibrations exhibiting more frequency content at higher frequencies than the flow instabilities driving those vibrations. The largest vibrations occurred in the case which exhibited strongly banded fluid frequency content, and the vibration amplitude was highest when the strongest fluid frequency band was an integer multiple of one of the natural frequencies of the aneurysm sac. Lower levels of vibration occurred in the case which exhibited turbulent-like flow with no distinct frequency bands. The current study provides a plausible mechanistic explanation for the high-frequency sounds observed in cerebral aneurysms, and suggests that narrow-band (vortex-shedding type) flow might stimulate the wall more, or at least at lower flow rates, than broad-band, turbulent-like flow.

关键词： Aneurysm Biological vibration High-frequency wall motion fluid-structure interaction Flow instability Spectral analysis Hemodynamics

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Validation of a partitioned fluid-structure interaction simulation for turbo machine rotors

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SHIPS AND OFFSHORE structureS 2023年第6期18卷 775-786页

作者： Lund, Jorrid Gonzalez, Daniel Ferreira Neitzel-Petersen, Jan Clemens Radtke, Lars Abdel-Maksoud, Moustafa Duester, Alexander Hamburg Univ Technol TUHH Numer Struct Anal Applicat Ship Technol M 10 Schwarzenberg Campus 4 C D-21073 Hamburg Germany Hamburg Univ Technol TUHH Inst Fluid Dynam & Ship Theory M 8 Hamburg Germany

A partitioned solution approach for the fluid-structure interaction (FSI) simulations of turbo machine rotors is presented. The in-house developed boundary element method solver panMARE is used for the fluid simulation, while the structural side is treated with the commercial finite element method solver ANSYS. The generic in-house multiphysics coupling library comana is used for the management of the implicit coupling procedure. As the first example, the KRISO container ship propeller is considered. The simulation is validated for open water test conditions assuming a rigid propeller based on the thrust and torque coefficients. Simulation results for a flexible propeller in open water are also presented. In the second example, the validation of the FSI simulation is conducted for a multilayered flexible submersible mixer based on thrust and torque coefficients and local strains. The results show a good agreement between the simulations and the experimental data for both examples.

关键词： Propeller submersible mixer fluid-structure interaction finite element method boundary element method validation

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A semi-implicit finite element formulation of the partitioned method for fluid-structure interaction based on a flux boundary condition of pressure equation

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JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY 2023年第5期37卷 2417-2424页

作者： Ha, Sang Truong Choi, Hyoung Gwon Long, Ngo Cu Lee, Sang-Wook Le Quy Don Tech Univ Dept Mech Engn Hanoi Vietnam Seoul Natl Univ Sci & Technol Dept Mech & Automot Engn Seoul 01811 South Korea Univ Ulsan Sch Mech Engn Ulsan 44610 South Korea

A semi-implicit algorithm of the partitioned method is newly proposed for fluid-structure interaction using the finite element method. In particular, an incompressible fluid flow is solved by a splitting method, and the solid domain of a reference configuration is solved by a total Lagrangian approach. While the viscous traction of the fluid flow is explicitly estimated in a coupling algorithm, the pressure traction from the fluid flow is implicitly coupled with the solid motion through iterative computations separately performed on the fluid and then the solid domain. By employing a weak formulation of the pressure Poisson equation based on a flux (fluid velocity) boundary condition, solid motion is successfully coupled with the pressure equation during the iterative computation. The proposed method has been found to be more efficient compared with not only a fully-implicit scheme of the partitioned method, but also a monolithic formulation in terms of CPU time and memory usage. Lastly, the parallel implementation of the proposed method is very attractive due to the fluid-solid coupling through a simple pressure Poisson equation.

关键词： Finite element method fluid-structure interaction Flux boundary condition Partitioned method Semi-implicit algorithm

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fluid-structure interaction with Kelvin-Voigt Damping and Quantized State Integration Methods

Fluid-Structure Interaction with Kelvin-Voigt Damping and Qu...

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作者： Mahawattege, Rasika Lasantha The University of Memphis

学位级别：Ph.D., Doctor of Philosophy

The class of fluid-structure interaction models in the physical dimension d = 2,3 has been the object of intense mathematical studies in the past several years. In the case of static interface, justified to be appropriate for small, rapid oscillations of the structure, the typical configuration considers a structure – modeled by a d-dimensional wave-type equation –surrounded by a fluid –modeled by the d-dimensional dynamic Stokes equation involving pressure. Coupling takes place at the common interface of the two media where the individual equations evolve and is given by differential operators. Thus, the overall system provides a physical illustration of hyperbolic- parabolic coupling. The present dissertation represents a key distinctive novelty over past literature whereby the structure equation includes a (strong) Kelvin-Voigt damping. Two specific cases of structure are analyzed, both with physically significant interface conditions: (1) a wave with Kelvin-Voigt damping (d = 2, 3), and (2) a plate with Kelvin-Voigt damping (d = 2). In both cases, this dissertation provides the following main results: (i) analyticity of the s.c. contraction semigroup (on a natural physical space), describing the overall coupled dynamics; (ii) a detailed (and surprising) spectral analysis of its generator; (iii) uniform stability of such semigroup, either on the entire space or, when this is not true, on a natural subspace of codimension one, obtained by factoring out the one dimensional eigenspace corresponding to the zero eigenvalue. The final chapter includes the original work done during a summer 2021 NSF-MSGI Internship at the Oak Ridge National Laboratory, under the sponsorship of senior scientist Dr. J. Nutaro. It introduces a novel quantized state integration method that is analogous to the explicit, second order Runge-Kutta technique. For a single differential equation over an interval where the solution is monotonic, such method exhibits an error proportional to the squ

关键词： Kelvin-Voigt damping fluid-structure interaction Runge-Kutta

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fluid-structure interaction in phaco-emulsification based cataract surgery

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INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES 2024年 267卷

作者： Wang, Zhaokun Wang, Chenglei Zhao, Fuwang Ren, Feng Luo, Xiaoyu Tang, Hui Hong Kong Polytech Univ Dept Mech Engn Kowloon Hong Kong Peoples R China Hong Kong Polytech Univ Sch Fash & Text Hong Kong Peoples R China Northwestern Polytech Univ Sch Marine Sci & Technol Xian Shanxi Peoples R China Univ Glasgow Sch Math & Stat Glasgow City G12 8QQ Scotland

Cataract scatters the light as it enters the eye, blurs images and severely interferes people's daily activities. The only effective therapy is cataract surgery, in which the clouded lens is phacoemulsified and removed. However, an aberrant iris distortion, namely intra-operative floppy iris syndrome (IFIS), is not uncommon in the phacoemulsification process, and it greatly degrades the surgical outcomes. Despite its great impact, the mechanism of IFIS has seldom been explored from the mechanics viewpoint. This study constitutes the first exploration into IFIS mechanism within the torsional-irrigation/aspiration (T -I/A) combined mode, from the perspective of fluidstructure coupling, employing our newly developed fluid-structure interaction (FSI) simulation framework. The impacts of several factors, including probe type and position, irrigation and aspiration (I/A), iris stiffness and lens presence, are evaluated in two different torsional-irrigation/aspiration (T -I/A) combined configurations, corresponding to the scenarios of coaxial and bimanual I/A operations. Results reveal that by altering the probe's location in anterior chamber, three distinct modes of iris dynamics are recognized and defined as repulsion (RP), attraction (AT), and adhesion (AH) modes according to the relative iris-probe location. Among them, RP mode, where the iris is repelled by the probe, is preferred to ensure the safety of the iris. Furthermore, IFIS could be alleviated by stiffening iris, reducing I/A strength and choosing coaxial I/A device. These interventions result in the contraction of the damaging AH zone towards the iris root, occurring at approximately one-fourth (coaxial case), one-fifth (coaxial case), and one-fourth of the iris length, achieved by quadrupling iris stiffness, ceasing I/A flow, and utilizing coaxial I/A device, respectively. However, the risk of IFIS is only marginally impacted by the lens presence. Our findings gain a deeper insight into the iris dynamics in

关键词： Cataract Phacoemulsification Intra-operative floppy iris syndrome fluid-structure interaction Irrigation/aspiration Iris dynamics

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fluid-structure interaction Analysis of Ascendable Horizontal-Bar Wastewater Screen for Enhanced Trapping Performance

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WATER 2024年第24期16卷 3671-3671页

作者： Memon, Safi Ahmed Akhtar, Shehnaz Chae, Hyeon-Bae Choi, Du-Whan Das, Raj Park, Cheol-Woo Kyungpook Natl Univ Sch Mech Engn 80 Daehakro Bukgu 41566 Daegu South Korea Univ Ulsan Sch Mech Engn Ulsan 44610 South Korea I ENTEC Co Ltd 18 Gil 33 Seongseogongdanbukro Daegu 42712 South Korea RMIT Univ Sch Engn 124 Trobe St Melbourne Vic 3000 Australia

Wastewater accumulates debris as it moves through sewage systems and must undergo purification at treatment plants, where insoluble debris is screened at the inlet. Previous studies have focused on screening mechanisms using rotating or ascendible sub-screens with vertical bars, and the effects of horizontal bars on structural integrity and fluid flow have not yet been explored. The present study addresses this gap by proposing a novel screening mechanism with horizontal bars and providing insights into flow behaviour and structural performance. The proposed mechanism consists of a main screen, an ascendible sub-screen and a rake system, and its effects on the flow distribution inside the channel and the resulting deformations and stress affecting the mechanism are computationally analysed. The problem is modelled as a fluid-structure interaction and solved using the arbitrary Lagrangian-Eulerian approach. Velocity distribution, structural deformation and stress are analysed for the various inlet flow velocities and critical configurations of the screening mechanism. The sub-screen in the proposed mechanism exhibited reduced deformation (0.9 mm for vertical bars and 0.2 mm for horizontal bars versus 2.2 mm in previous vertical-only designs). The maximum von Mises stress values were well below the 250 MPa yield strength, with peak stresses of 3.8 MPa in the sub-screen and 0.23 MPa in the main screen. Key operating conditions causing flow separation and velocity fluctuations are identified, and design improvements are suggested. The study provides guidelines for manufacturing and operating wastewater-screening mechanisms whilst mitigating undesirable performance and minimising deformation and stress in the mechanism.

关键词： wastewater-screening mechanism fluid-structure interaction flow separation deformation von Mises stress

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