3D Fluid-structure Interaction Research Articles

Real-time prediction of the deformation of microcapsules using Proper Orthogonal Decomposition

Microcapsules are liquid droplets enclosed by a thin elastic membrane. Being suspended in an external fluid, they undergo large deformations when flowing. Their deformation can be solved numerically, but the resolution of the fluid–structure interactions (FSI) requires extremely long computation times. This is a major constraint for instance when identifying the membrane mechanical properties from experimentations of microcapsules flowing in a microfluidic channel of similar size (Hu et al. PFE 2013). We propose to apply Model Order Reduction (MOR) to predict in real time the steady-state capsule deformed shape, needed to determine the membrane elasticity. A database of the capsule deformed shapes was obtained numerically by solving the three-dimensional (3D) FSI through a finite element-boundary integral method coupling, and by varying systematically the two non-dimensionalized parameters of the problem: the capillary number, ratio of the viscous to the elastic forces, and the capsule-to-tube size ratio. Among the MOR techniques, we chose to apply Proper Orthogonal Decomposition (POD) onto the database, which provides a vector basis of principal components, defining a multi-dimensional vector space. The advantage is that, when all the capsule shapes of the database are mapped into this new vector space, they form a manifold (smooth hypersurface) that represents all the admissible solutions of the problem. We show that POD with a manifold walking technique can be successfully applied to 3D microcapsule data sets, whether they are Lagrangian (e.g. known position vector fields) or Eulerian (i.e. when data is acquired experimentally or numerically using methods like level sets). In both cases, the problem dimensionality is reduced, the predicted capsule shapes are obtained within computation times of milliseconds, and they accurately fit the full FSI simulations. This paves the way to real-time computations for capsules in flow, while retaining all the physical ingredients of the FSI problem.

3D design and numerical simulation of a check-valve micropump for lab-on-a-chip applications

In this paper, we concentrated on designing and simulation of check-valve micropump for on-chip applications. A series of simulations were carried out by using 3D two-way fully-coupled fluid structure interaction analysis in combination with Arbitrary Lagrangian-Eulerian (ALE) method to understand pumping chamber and inlet/outlet micro check-valves. After extraction of characteristic equations of each component, micropump main equation is solved to find time-domain pumping chamber pressure. Then, Effects of actuation amplitude and frequency on micropump’s flow rate were studied for different chamber sizes from 2 mm to 4 mm. In addition, the effect of backpressure on micropumps’ flow rate was evaluated. Using this method of simulation helps the researchers to estimate performance of micropump before initiating fabrication process.

Evaluating the Impact of Calcification on Plaque Vulnerability from the Aspect of Mechanical Interaction Between Blood Flow and Artery Based on MRI.

Acute cerebral ischemic events and thrombosis are associated with the rupture/erosion of carotid atherosclerotic plaques. The aim of the present study was to determine the impact of calcification deposition on the wall shear stress (WSS) and stresses within the plaques using 3D fluid-structure interaction (FSI) models. Six patients with calcified carotid atherosclerosis underwent multisequence magnetic resonance imaging (MRI) and were divided into three groups according to the calcification volume. To evaluate the role of the calcification deposition on the stresses, the calcification content was replaced by lipids and arterial tissue, respectively. By comparing the results from the simulation with calcification, and when changing it to lipids there was a significant increment in the stresses at the fibrous cap (p = 0.004). Instead, by changing it to arterial tissue, there was no significant difference (p = 0.07). The calcification shapes that presented the highest stresses were thin concave arc-shaped (AS1) and thin convex arc-shaped (AS3), with mean stress values of 107 ± 54.2and 99.6 ± 23.4kPa, respectively. It was also observed that, the calcification shape has more influence on the level of stress than its distance to the lumen. Higher WSS values were associated with the presence of calcification. Calcification shape plays an important role in producing high stresses in the plaque. This work further clarifies the impact of calcification on plaque vulnerability.

Hemodynamics of a stenosed aortic valve: Effects of the geometry of the sinuses and the positions of the coronary ostia

Aortic valve stenosis is one of the most prevalent cardiovascular disease among adults worldwide. Stenosis of the aortic valve changes the hemodynamic parameters inside the aortic root which perpetuates aortic valve calcification and has been associated with the development of coronary artery atherosclerosis. Invasive studies have revealed that the geometry of the sinuses, as well as the locations of the coronary artery ostia, impact coronary blood flow hemodynamics, which has been associated with the development of coronary artery disease. The aim of this study is to elucidate this observed phenomenon, in which geometrical variations inside the aortic root and malfunctioning of the aortic valve because of the calcification not only affect the progression of the calcification but also lead to initiation of coronary artery atherosclerosis. A 2D fluid structure interaction model of the aortic valve was developed and simulated in ANSYS Fluent based on available echocardiography images in the literature. The model incorporates fluid structure interaction and employs the k − ω Menter's Shear Stress Transport (SST) turbulence model for the turbulent flow downstream of the leaflets. The effects of various diameters of the sinuses 25, 20.8, and 17.6 mm and positions of the coronary artery ostia (proximal, middle, and distal) on aortic root hemodynamics were investigated and parameters including transvalvular pressure gradient, valve orifice diameters, maximum jet velocity along the valve orifice area, and wall shear stresses on leaflets calculated. Results demonstrate that a severely calcified valve with the proximal coronary artery ostia witnesses a much higher transvalvular pressure gradient (approximately 10 times larger) compared to that for a healthy case. Moreover, the presence of the proximal coronary artery ostia for valves with diameters of the sinus 25 and 20.8 mm results in the reduction of the coronary blood flow and increase of the probability of coronary artery atherosclerosis.

Fluid structure interaction study of stenosed carotid artery considering the effects of blood pressure

Atherosclerosis is the most common cardiovascular disease (CVD) causing increased morbidity. Although atherosclerosis is a general disease involving several factors, it preferentially affects the wall of the vessel bifurcations. The use of advanced Computational Fluid Dynamics (CFD) techniques has the potential to shed more light in the further understanding of the causes of the disease and perhaps in its early diagnosis. In this work, a three-dimensional (3D) Fluid Structure Interaction (FSI) study was carried out for a patient specific carotid artery. By considering physiological conditions, first the normal and then with hypertension disease, haemodynamic parameters were evaluated to better understand the genesis and progression of atherosclerotic plaques in the carotid artery bifurcation. Two-way FSI was performed by applying a fully implicit second-order backward Euler differencing scheme using commercial software ANSYS and ANSYS CFX (version 19.0). Arbitrary Lagrangian–Eulerian (ALE) formulation was employed to calculate the arterial response by using the temporal blood response. Due to arterial bifurcation, obvious velocity reduction and backflow formation were observed which decreased shear stress and made it oscillatory at the starting point of the internal carotid artery near the carotid sinus, which resulted in low shear stress. Oscillatory Shear Index (OSI) signifies oscillatory behaviour of artery wall shear stress. By using anatomically realistic 3D geometry and representative physiological conditions, the results obtained for shear stress are more acceptable. Comparison of the results of this study with those in the published literature shows that the regions with low wall shear stress and with OSI value greater than 0.3 pose potential risk to the development of plaques. It was observed that haemodynamics of the carotid artery was very much affected by the geometry and flow conditions. Furthermore, regions of relatively low wall shear stress were observed post stenosis, which is a known cause of plaque development and progression.

A special numerical method for fluid-structure interaction problems subjected to explosion and impact loading

A three-dimensional (3D) embedded Eulerian-Lagrangian method is proposed to simulate the 3D fluid-structure interaction (FSI) problems subjected to explosion and impact loading. This method achieves a high-quality calculation of fluid and structure deformation by adding Lagrangian particles to Eulerian grids. The overall computational domain is solved by the Eulerian method, and the Lagrangian particles with specified volume and influence domains are used to track structural deformations. The bidirectional mapping of physical quantities is achieved using the weighted average of the influence domain, which are based on the topological relationship between Eulerian grids and Lagrangian particles. Then, the data dependence solution and parallel algorithm realization are presented for the large-scale numerical calculations of explosion and impact problems. Additionally, the corresponding parallel program is developed based on the message passing interface (MPI) standard, and the parallel efficiency of parallel hydrocode are tested. The numerical results of typical explosion and impact problems are compared with corresponding experimental data to verify the effectiveness of the method. These comparisons show that the embedded Eulerian-Lagrangian method successfully combine the advantages of both the Eulerian and Lagrangian methods to efficiently calculate the processes of large deformation and dynamic damage to the materials. The results presented in this work provide a useful reference point for further research on explosion and impact problems.

Fluid–structure interaction simulation based on immersed boundary-lattice Boltzmann flux solver and absolute nodal coordinate formula

Large deformation fluid–structure interaction (FSI) is a typical nonlinear problem in aero elastics. Engineering applications can be found in aviation, marine engineering, and bio-fluid mechanics. A three-dimensional (3D) parallel FSI solver based on an immersed boundary-lattice Boltzmann flux solver (IB-LBFS) and absolute nodal coordinate formula (ANCF) is established. The computational efficiency of the parallel IB-LBFS with moving boundaries is improved by several acceleration techniques, including Euler–Lagrangian interpolation matrix parallel assembling and sparse matrix solving methods. Structure dynamics simulation discretized in high-order ANCF elements distinctly reduces the number of finite elements compared with the standard finite element method. A multiple body dynamics (MBD) solver including a rigid body, ANCF cable elements, and ANCF plate elements is developed. The IB-LBFS, MBD solver, and coupled FSI solver are tested by the corresponding validation examples. A framework of solving 3D FSI problems of complex multiple flexible structures with large deformation in incompressible flow is presented. An implicit boundary condition enforced method is applied to achieve a strong coupling approach. For application demonstration, the inflation process of several types of parachute systems is simulated in which different Young’s moduli of the parachute canopy are considered. The interaction between dynamic deformation and an unsteady vortex is obtained and discussed.

Local Hemodynamic Analysis of the C-Pulse Device By 3D fluid-structure Interaction Simulation

Background: C-Pulse is a new, nonblood contacting device based on the concept of counter-pulsation that is designed for long-term implantation. However, there is a lack of comprehensive investigation of the pressure and velocity fields under the action of C-Pulse. Aim: In this paper, we aim to conduct a numerical simulation of the underlying mechanism of the device in order to analyze its performance and related undesirable issues. Materials & methods: A 3D finite element model is utilized to simulate the mechanism of the blood pumping. Results & conclusion: The simulation well reproduced the essential characteristics of the C-Pulse. Preliminary results were in a reasonable range while a couple of irregular flow patterns were identified.

Open-source immersogeometric analysis of fluid–structure interaction using FEniCS and tIGAr

We recently developed the open-source library tIGAr, which extends the FEniCS finite element automation framework to isogeometric analysis. The present contribution demonstrates the utility of tIGAr in complex problems by applying it to immersogeometric fluid–structure interaction (FSI) analysis. This application is implemented as the new open-source library CouDALFISh (Coupling, via Dynamic Augmented Lagrangian, of Fluids with Immersed Shells, pronounced “cuttlefish”), which uses the dynamic augmented Lagrangian (DAL) method to couple fluid and shell structure subproblems. The DAL method was introduced previously, over a series of papers largely focused on heart valve FSI, but an open-source implementation making extensive use of automation to compile numerical routines from high-level mathematical descriptions brings newfound transparency and reproducibility to these earlier developments on immersogeometric FSI analysis. The portions of CouDALFISh that do not use code generation also illustrate how a framework like FEniCS remains useful even when some functionality is outside the scope of its standard workflow. This paper summarizes the workings of CouDALFISh and documents a variety of benchmarks demonstrating its accuracy. Although the implementation emphasizes transparency and extensibility over performance, it is nonetheless demonstrated to be sufficient to simulate 3D FSI of an idealized aortic heart valve. Source code will be maintained at https://github.com/david-kamensky/CouDALFISh.

Experimental and numerical study of slamming problem for a trimaran hull

ABSTRACT The dynamic load from slamming is an important issue for the structure integrity of a trimaran hull. The slamming loads on a typical trimaran section, based on both experimental measurements and numerical simulations, are reported in this paper. The impact pressure at crucial positions in both space and time domain, the vertical acceleration of the specimen and the detailed motion of the flow field were monitored in the experiments. The trimaran slamming phenomenon also was simulated by using a modified MPS [Sun Z, Djidjeli K, Xing JT, Cheng F. 2015. Modified MPS method for the 2D fluid structure interaction problem with free surface. Comput Fluids. 122:47–65] method proposed by the author. A thorough comparison of various results with experiment were conducted to validate the numerical model. In the end, the flow field obtained from both high-speed camera images and numerical simulations were used to analyse the extreme values and distributions of the slamming load on the hull.

Verification of the coupled‐momentum method with Womersley's Deformable Wall analytical solution

In this paper, we perform a verification study of the Coupled-Momentum Method (CMM), a 3D fluid-structure interaction (FSI) model which uses a thin linear elastic membrane and linear kinematics to describe the mechanical behavior of the vessel wall. The verification of this model is done using Womersley's deformable wall analytical solution for pulsatile flow in a semi-infinite cylindrical vessel. This solution is, under certain premises, the analytical solution of the CMM and can thus be used for model verification. For the numerical solution, we employ an impedance boundary condition to define a reflection-free outflow boundary condition and thus mimic the physics of the analytical solution, which is defined on a semi-infinite domain. We first provide a rigorous derivation of Womersley's deformable wall theory via scale analysis. We then illustrate different characteristics of the analytical solution such as space-time wave periodicity and attenuation. Finally, we present the verification tests comparing the CMM with Womersley's theory.

An Eulerian-Lagrangian-Lagrangian method for 2D fluid-structure interaction problem with a thin flexible structure immersed in fluids

In this paper, the Eulerian-Lagrangian-Lagrangian (ELL) method is extended to solve fluid–structure interaction (FSI) problem with a very thin flexible structure immersed in the fluid. Such a new approach overcomes the failure of the immersed finite element method (IFEM) in handling the FSI problem when a reduced solid model is used for the thin structure. In this work, a continuum-based (CB) beam theory is adopted to model the 2D flexible thin structure that undergoes large deformation. In the ELL approach, the solid meshes can always coincide with the Lagrangian fluid meshes in a so-called “composite solid” domain that allows the accurate imposing of the changing interface boundary conditions in the FSI zone. The proposed approach is verified using three benchmarking problems of flow over a flexible vertical beam, flow over a cylinder beam system and 2D flapping flag in the uniform flow. The results are compared with those from the open literature. Other numerical examples are also computed to demonstrate the effectiveness of the ELL method.

A Reduced-Order Flow Model for Fluid-Structure Interaction Simulation of Vocal Fold Vibration.

We present a novel reduced-order glottal airflow model that can be coupled with the three-dimensional (3D) solid mechanics model of the vocal fold tissue to simulate the fluid-structure interaction (FSI) during voice production. This type of hybrid FSI models have potential applications in the estimation of the tissue properties that are unknown due to patient variations and/or neuromuscular activities. In this work, the flow is simplified to a one-dimensional (1D) momentum equation-based model incorporating the entrance effect and energy loss in the glottis. The performance of the flow model is assessed using a simplified yet 3D vocal fold configuration. We use the immersed-boundary method-based 3D FSI simulation as a benchmark to evaluate the momentum-based model as well as the Bernoulli-based 1D flow models. The results show that the new model has significantly better performance than the Bernoulli models in terms of prediction about the vocal fold vibration frequency, amplitude, and phase delay. Furthermore, the comparison results are consistent for different medial thicknesses of the vocal fold, subglottal pressures, and tissue material behaviors, indicating that the new model has better robustness than previous reduced-order models.

Microfluidic Passive Flow Regulatory Device with an Integrated Check Valve for Enhanced Flow Control.

A passive microvalve has appealing advantages in cost-effective and miniaturized microfluidic applications. In this work, we present a passive flow regulatory device for enhanced flow control in a microfluidic environment. The device was integrated with two functional elements, including a flow regulating valve and a flow check valve. Importantly, the flow regulating valve could maintain a stable flow rate over a threshold liquid pressure, and the flow check valve enabled effective liquid on/off control, thus accurate forward flow without any backward leakage was achieved. The flow performance of the flow regulating valve was analyzed through 3D FSI (Fluid-Structure Interaction) simulation, and several key parameters (i.e., fluidic channel height and width, control channel length, and Young’s modulus) were found to influence valve flow rate directly. To examine the flow characteristics of the device, we fabricated a prototype using 3D printing and UV laser cutting technologies, and the flow rates of the prototype under varied test pressures were measured in forward and reverse modes, respectively. Experimental results showed that nearly a constant flow rate of 0.42 ± 0.02 mL s−1 was achieved in the forward mode at an inlet pressure range of 70 kPa to 130 kPa, and liquid flow was totally stopped in the reverse mode at a maximum pressure of 200 kPa. The proposed microfluidic flow regulatory device could be employed for accurate flow control in low-cost and portable Lab-on-a-Chip (LoC) applications.

The role of porosity and 3D cross-stent configuration of multiple overlapping uncovered stents in the management of complex aortic aneurysms – Insights from haemodynamics

BackgroundMultiple overlapping uncovered stents (MOUS) have been introduced to manage complex aortic aneurysms with vital branches involvement. It has been shown that the porosity is a key determinant of the treatment outcome. However, the role of 3D cross-stent configuration remains unclear. MethodsOne patient with a complex aortic aneurysm judged not suitable for open surgery nor endovascular repair was invited to participate this study. In total, four bare metal stents were deployed. 3D lesion geometry was reconstructed based on pre- and post-operative CTA, and the zero-pressure configuration was recovered using an inverse procedure. Local haemodynamic parameters, including wall shear stress (WSS), oscillatory shear index (OSI), and particle relative resident time (RRT), as well as the vessel structural stress (VSS), were quantified using one-way fluid-structure interaction (FSI) analysis. In comparison to MOUS, a corresponding compact model was reconstructed by projecting inner layer stents to the most outer layer to form a single layer to eliminate the 3D cross-stent configuration and one-way FSI analysis was performed. ResultsResults obtained showed that the porosity decreased linearly with the number of stents. When the 1st stent was deployed, the mean velocity decreased 36.4% and further reduction of 49.3%, 59.8%, and 62.8% were observed when the 2nd, 3rd and 4th stents were deployed. WSS also decreased with the number of stents deployed, and both OSI and RRT increased, but the increase was very minor with the 4th stent. MOUS deployment induced high VSS concentration in the landing zone while the VSS and pressure in the sac remained nearly unchanged. The compact model yielded a small difference in the value of flow-related parameters and 10%–20% reduction in VSS. ConclusionCompared with porosity, the 3D cross-stent of MOUS configuration plays a minor role in the modulation of local haemodynamics. A compact model does not reduce high VSS concentration in the diseased region significantly.

A Multimodality Image-Based Fluid-Structure Interaction Modeling Approach for Prediction of Coronary Plaque Progression Using IVUS and Optical Coherence Tomography Data With Follow-Up.

Medical image resolution has been a serious limitation in plaque progression research. A modeling approach combining intravascular ultrasound (IVUS) and optical coherence tomography (OCT) was introduced and patient follow-up IVUS and OCT data were acquired to construct three-dimensional (3D) coronary models for plaque progression investigations. Baseline and follow-up in vivo IVUS and OCT coronary plaque data were acquired from one patient with 105 matched slices selected for model construction. 3D fluid-structure interaction (FSI) models based on IVUS and OCT data (denoted as IVUS + OCT model) were constructed to obtain stress/strain and wall shear stress (WSS) for plaque progression prediction. IVUS-based IVUS50 and IVUS200 models were constructed for comparison with cap thickness set as 50 and 200 μm, respectively. Lumen area increase (LAI), plaque area increase (PAI), and plaque burden increase (PBI) were chosen to measure plaque progression. The least squares support vector machine (LS-SVM) method was employed for plaque progression prediction using 19 risk factors. For IVUS + OCT model with LAI, PAI, and PBI, the best single predictor was plaque strain, local plaque stress, and minimal cap thickness, with prediction accuracy as 0.766, 0.838, and 0.890, respectively; the prediction accuracy using best combinations of 19 factors was 0.911, 0.881, and 0.905, respectively. Compared to IVUS + OCT model, IVUS50, and IVUS200 models had errors ranging from 1% to 66.5% in quantifying cap thickness, stress, strain and prediction accuracies. WSS showed relatively lower prediction accuracy compared to other predictors in all nine prediction studies.

Computational simulation of an artery narrowed by plaque using 3D FSI method: influence of the plaque angle, non-Newtonian properties of the blood flow and the hyperelastic artery models

Currently, cardiovascular diseases related to atherosclerosis are among the universal primary reasons for mortality. Artery stenosis is the narrowing of the artery, due to the formation of atheromatous plaque in the arterial tunica intima, a region of the blood vessel located between the endothelium and the tunica media. In the present paper, the blood flow is modeled in a stenosed artery, and the dynamic behavior of the atherosclerosis phenomenon is studied using computational analyses. To accomplish this aim, 3D finite element method (FEM) for modeling structural sections (including plaque and artery) and computational fluid dynamics (CFD) for modeling fluid part (blood flow) are coupled through a fluid-structure interaction (FSI). It is shown that the results of present FSI analysis are in good agreement with the available data in the literature. The influences of plaque geometry, in particular, plaque angle and percentage of stenosis, are investigated. Also, the effects of Newtonian and non-Newtonian properties of the blood flow and different hyperelastic artery models, including Ogden and Polynomial, are analyzed. The simulations show that with an increasing angle of the plaque, the stress of the artery increases, while the velocity of the blood flow decreases.

Verifications for Large-Scale Parallel Simulations of 3D Fluid–Structure Interaction Using Moving Particle Simulation (MPS) and Finite Element Method (FEM)

Fluid–Structure Interaction (FSI) is an important phenomenon in many fields. In this study, the Moving Particle Simulation (MPS) along with Finite Element Method (FEM) are coupled together. MPS-FEM coupled method is used as the numerical simulators to estimate the effects for structures by the fluid pressure of the tsunami. This simulator consists of two solvers: fluid analysis and structure analysis. The fluid analysis is based on MPS and the structural part is analyzed by using FEM. In this paper, for verification of the MPS-FEM coupled method, the problem of hydrostatic pressure on a structure is calculated. The results are compared with the theoretical values and the results obtained by the original FEM analysis. We confirmed that the MPS-FEM coupling method can achieve adequate accuracy. Furthermore, the MPS-FEM coupled simulation for the turbine building of Fukushima Dai-ichi Nuclear Power Station Unit 1 has been done.

A computational framework to investigate retinal haemodynamics and tissue stress

The process of vision begins in the retina, yet the role of biomechanical forces in the retina is relatively unknown and only recently being explored. This contribution describes a computational framework involving 3D fluid-structure interaction simulations derived from fundus images that work towards creating unique data on retinal biomechanics. We developed methods to convert 2D fundus photographs into 3D geometries that follow the curvature of the retina. Retina arterioles are embedded into a six-layer representation of the retinal tissue with varying material properties throughout the retinal tissue. Using three different human retinas (healthy, glaucoma, diabetic retinopathy) and by varying our simulation approaches, we report the effects of transient versus steady flow, viscosity assumptions (Newtonian, non-Newtonian and Fåhræus-Lindqvist effect) and rigid versus compliant retinal tissue, on resulting wall shear stress (WSS) and von Mises stress. In the retinal arterioles, the choice of viscosity model is important and WSS obtained from models with the Fåhræus-Lindqvist effect is markedly different from Newtonian and non-Newtonian models. We found little difference in WSS between steady-state and pulsatile simulations (< 5%) and show that WSS varies by about 7% between rigid and deformable models. Comparing the three geometries, we found notably different WSS in the healthy (3.3 ± 1.3Pa), glaucoma (5.7 ± 1.6Pa) and diabetic retinopathy cases (4.3 ± 1.1Pa). Conversely, von Mises stress was similar in each case. We have reported a novel biomechanical framework to explore the stresses in the retina. Despite current limitations and lack of complete subject-specific physiological inputs, we believe our framework is the first of its kind and with further improvements could be useful to better understand the biomechanics of the retina.

In Vivo Intravascular Ultrasound-Based 3D Thin-Walled Model for Human Coronary Plaque Progression Study: Transforming Research to Potential Commercialization

Cardiovascular disease (CVD) is the leading cause of death in the world. Considerable research has been done linking various mechanical risk factors to plaque progression and rupture. However, methods transforming research results to clinical implementation are limited by time-consuming processes. In this study, a 3D thin-wall (TW) model was developed to approximate the 3D fluid–structure interaction (FSI) model to save time for clinical implementations. Results from one patient data (100 TW models) indicated that the relative errors of the average plaque wall stress (APWS) and strain were less than 7%, meanwhile the correlation results of the TW models were similar with that of the FSI models.