Fluid-structure Interaction Study Research Articles

Effects of external ventricular drainage decompression of intracranial hypertension on rebleeding of brain aneurysms: A fluid structure interaction study

ObjectivesThe treatment of hydrocephalus using external ventricular drainage (EVD) seems to favour rebleeding of an untreated ruptured aneurysm. FSI studies are valuable to study this environment. Patients and methodsFrom December 2014 to December 2017, 61 patients with SAH required EVD due to hydrocephalus, 6 patients had aneurysm rebleeding after the procedure. Two controls for each case was included. DSA studies were used for fluid–structure interaction simulations using two scenarios high ICP (5332 Pa) and low ICP (133 Pa). ResultsMaximum displacement of the wall in HICP was 0.34 mm and 0.26 mm in rebleeding and no rebleeding cases respectively, after EVD (LICP), it was 0.36 mm and 0.27 mm. The difference after implantation of EVD (HICP-LICP) had an average of 0.01567 mm and 0.00683 mm in rebleeding and no rebleeding cases (p = 0.05). This measure in low shear areas of the aneurysm was 0.026 and 0.0065 mm in rebleeding and no rebleeding cases (p = 0.01).Effective stress in the HICP was 4.77 MPa and 3.26 MPa in rebleeding and no rebleeding cases (p = 0.25). In LICP condition, this measure was 2.28 MPa and 1.42 MPa respectively (p = 0.33). TAWSS had no significant differences in the conditions of HICP and LICP. ConclusionChanges after EVD placement includes an increase in the wall displacement with greater differences over low shear areas, this had a strong association with rebleeding.

Experimental investigation on the influence of gap vortex streets on fluid-structure interactions in hexagonal bundle geometries

Gap vortex streets characterise many industrial applications involving rod bundle flows, such as heat exchangers and nuclear reactors. These structures, known as gap vortex streets, may excite the structural components of the bundle to resonance, leading to fretting and fatigue. This work aims to measure these coherent structures and the resulting displacement and oscillation frequency of the neighbouring rod, to provide unique data for fluid-structure interaction studies and to develop a general correlation for estimating the coherent structure’s wavelength. A water loop was built to host a hexagonal rod bundle. Fluorinated Ethylene Prophylene (FEP), a refractive index matching (RIM) material, was used to have undisturbed optical access in the area around the central rod. The flow was measured with Laser Doppler Anemometry (LDA) to detect coherent structures, while the vibrations were measured with a high speed camera. A new correlation for estimating the wavelength of the coherent structures is derived with dimensional analysis based on experimental evidence. The correlation is tested on different geometries: rectangular channels with single or half-rods, and two rod bundles, within the pitch-to-diameter ratio (P/D) range 1.02–1.2. Moreover fluctuations in the flow, given by the detected coherent structures, govern the structural response of the rod. The rod is excited to resonance if these fluctuations match twice the natural frequency of the rod.

Indirect Traumatic Optic Neuropathy Induced by Primary Blast: A Fluid-Structure Interaction Study.

Current knowledge of traumatic ocular injury is still limited as most studies have focused on the ocular injuries that happened at the anterior part of the eye, whereas the damage to the optic nerve known as traumatic optic neuropathy (TON) is poorly understood. The goal of this study is to understand the mechanism of the TON following the primary blast through a fluid-structure interaction model. An axisymmetric three-dimensional (3D) eye model with detailed orbital components was developed to capture the dynamics of the eye under the blast wave. Our numerical results demonstrated a transient pressure elevation in both vitreous and cerebrospinal fluid (CSF). A high strain rate over 100 s-1 was observed throughout the optic nerve during the blast with the most vulnerable part located at the intracanalicular region. The optic nerve deforming at such a high strain rate may account for the axonal damage and vision loss in patients subjected to the primary blast. The results from this work would enhance the understanding of indirect TON and provide guidance in the design of protective eyewear against such injury.

Experimental study of fluid structure interaction on fuel assemblies on the ICARE experimental facility

Accurate knowledge of the mechanical behaviour of the reactor core is needed to estimate the effects of a seismic excitation on a nuclear power plant. Experimental works are needed in order to validate models and to have a better understanding of involved phenomena. The fuel assemblies, in the reactor core, are subjected to an axial water flow which modifies their dynamical behaviour. In this framework a new experimental facility, ICARE, is designed in order to investigate fluid structure interaction phenomena on half scale fuel assemblies. The design of the ICARE experimental facility allows to emphasise the effects of the coupling between different fuel assemblies due to the presence of the water flow. In this paper a brief review of previous experimental facilities is presented and the new ICARE experimental facility is illustrated. ICARE facility consists in 4 half scale fuel assemblies (2×2 lattice) in a vertical channel submitted to axial flow; one of the assemblies is excited by an hydraulic jack. The aim of this paper is to discuss the experimental results obtained during four experimental campaigns on the ICARE set-up. First, the mechanical behaviour of a single fuel assembly is analysed, and the effect of different experimental parameters is assessed. Added mass, added damping and added stiffness effects due to the water flow are estimated. Later, the coupling between different assemblies is investigated. The presence of the flow induces hydrodynamic effects on non excited fuel assemblies, both on excitation direction and transversal one. Furthermore the increase of the water flow causes the increase of the coupling forces and gives rise to a static coupling between the assemblies.

Influence of arterial mechanical properties on carotid blood flow: Comparison of CFD and FSI studies

Carotid artery blood flow is studied to compare models with rigid and elastic walls. Considering a patient-specific geometry and transient boundary conditions. In the case of rigid walls, only the fluid (blood) behavior is considered, in a typical Computational Fluid Dynamics study. With the elastic walls, the reciprocal influence of both fluid and solid (blood and artery) are taken into account, constituting a Fluid-Structure Interaction study. Furthermore, the study of the influence of mechanical properties of the artery, which become stiffer with the progression of atherosclerosis, on blood flow is also presented, an innovative approach relative to the work done in this field. Results show that the carotid sinus is the preferential zone to develop atherosclerosis, given its low values of Time-Averaged Wall Shear Stress. Additionally, it is fundamental to consider the arterial wall as elastic bodies, given that the rigid model overestimates the flow velocity and Wall Shear Stress. On the different mechanical properties of the vessel, its influence is minimal in the Time-Averaged Wall Shear Stress profiles. However, given the results of the displacement and velocity profiles, their inclusion in blood flow simulations in stenosed arteries should be considered.

A combined digital image correlation/particle image velocimetry study of water-backed impact

Several aeronautical and naval structures are routinely exposed to impulsive loading conditions that elicit complex fluid-structure interactions. An archetypal problem that has attracted considerable attention is the impact on a compliant plate, fixed on a water surface. Despite significant progress in mathematical modeling of the impact, several technical questions remain open due to the lack of a simultaneous experimental characterization of the structural response and fluid flow. Here, we seek to fill this gap of knowledge through the integration of digital image correlation (DIC) and particle image velocimetry (PIV). We employ DIC to measure the apparent in-plane displacement of the plate, from which we reconstruct its out-of-plane deflection. On the other hand, PIV is utilized to measure the velocity field of the water, from which we infer the pressure field in the fluid and the hydrodynamic loading on the plate. We examine a number of aggregated measures, including the mid-span deflection, strain energy stored in bending and stretching of the plate, modal contribution factors, hydrodynamic loading, and added mass coefficient. Just as our approach constitutes a significant methodological step forward in the study of unsteady fluid-structure interactions, our experimental results contribute new evidence for an improved understanding of water-backed impact.

A stabilized ALE method for computational fluid–structure interaction analysis of passive morphing in turbomachinery

Computational fluid–structure interaction (FSI) and flow analysis now have a significant role in design and performance evaluation of turbomachinery systems, such as wind turbines, fans, and turbochargers. With increasing scope and fidelity, computational analysis can help improve the design and performance. For example, it can help add a passive morphing attachment (MA) to the blades of an axial fan for the purpose of controlling the blade load and section stall. We present a stabilized Arbitrary Lagrangian–Eulerian (ALE) method for computational FSI analysis of passive morphing in turbomachinery. The main components of the method are the Streamline-Upwind/Petrov–Galerkin (SUPG) and Pressure-Stabilizing/Petrov–Galerkin (PSPG) stabilizations in the ALE framework, mesh moving with Jacobian-based stiffening, and block-iterative FSI coupling. The turbulent-flow nature of the analysis is handled with a Reynolds-Averaged Navier–Stokes (RANS) model and SUPG/PSPG stabilization, supplemented with the “DRDJ” stabilization. As the structure moves, the fluid mechanics mesh moves with the Jacobian-based stiffening method, which reduces the deformation of the smaller elements placed near the solid surfaces. The FSI coupling between the blocks of the fully-discretized equation system representing the fluid mechanics, structural mechanics, and mesh moving equations is handled with the block-iterative coupling method. We present two-dimensional (2D) and three-dimensional (3D) computational FSI studies for an MA added to an axial-fan blade. The results from the 2D study are used in determining the spanwise length of the MA in the 3D study.

Enhancing wind energy harvesting performance of vertical axis wind turbines with a new hybrid design: A fluid-structure interaction study

Vertical axis wind turbines (VAWTs) provide promising solutions for wind energy harvesting in complex flow environment. However, it is challenging to guarantee satisfactory self-starting capability and high power efficiency simultaneously in a VAWT design. To address this challenge, a new hybrid Darrieus-Modifed-Savonius (HDMS) VAWT is designed and numerically tested using a fluid-structure interaction approach based on high fidelity computational fluid dynamics. A systematic study is conducted to analyze the effects of the moment of inertia, turbine structure, and external load on the self-starting capability and power efficiency. It is found that compared with the Darrieus VAWT, the HDMS design has better self-starting capability due to the torque provided by the MS rotor at small tip speed ratios (TSRs). The larger the MS rotor is, the better the self-starting capability is. However, there is penalty on power efficiency when the size of the MS rotor increases. With an appropriately sized MS rotor, the HDMS design can maintain high power efficiency comparable with the Darrieus VAWT at large TSRs. The key flow physics is that the HDMS design can keep accelerating at small TSRs due to the inner MS rotor, and can suppress dynamic stall on the Darrieus rotor at large TSRs.

Computational Study of Fluid-Structure Interaction on Flapping Wing under Passive Pitching Motion

AbstractDuring the past few decades, various fluid–structure interaction (FSI) analysis approaches have been developed and applied to understand the physical processes related to a flexible flappin...

Biomechanics of Acute Subdural Hematoma in the Elderly: A Fluid-Structure Interaction Study.

Acute subdural hematoma (ASDH) caused by bridging vein (BV) rupture is a frequent and lethal brain injury, especially in the elderly. Brain atrophy has been hypothesized to be a primary pathogenesis associated with the increased risk of ASDH in the elderly. Although decades of biomechanical endeavors have been made to elucidate the potential mechanisms, a thorough explanation for this hypothesis appears lacking. Therefore, a recently improved finite element head model, in which the brain-skull interface was modeled using a fluid-structure interaction (FSI) approach with special treatment of the cerebrospinal fluid as arbitrary Lagrangian-Eulerian fluid formulation, is used to partially address this understanding gap. Models with various degrees of atrophied brains and thereby different subarachnoid thicknesses are generated and subsequently exposed to experimentally determined loadings known to cause ASDH or not. The results show significant increases in the cortical relative motion and BV strain in the atrophied brain, which consequently exacerbates the ASDH risk in the elderly. Results of this study are suggested to be considered when developing age-adapted protecting strategies for the elderly in the future.

The effect of endothelial nitric oxide synthase on the hemodynamics and wall mechanics in murine arteriovenous fistulas

Creation of a hemodialysis arteriovenous fistula (AVF) causes aberrant vascular mechanics at and near the AVF anastomosis. When inadequately regulated, these aberrant mechanical factors may impede AVF lumen expansion to cause AVF maturation failure, a significant clinical problem with no effective treatments. The endothelial nitric oxide synthase (NOS3) system is crucial for vascular health and function, but its effect on AVF maturation has not been fully characterized. We hypothesize that NOS3 promotes AVF maturation by regulating local vascular mechanics following AVF creation. Here we report the first MRI-based fluid-structure interaction (FSI) study in a murine AVF model using three mouse strains: NOS3 overexpression (NOS3 OE) and knockout (NOS3−/−) on C57BL/6 background, with C57BL/6 as the wild-type control (NOS3+/+). When compared to NOS3+/+ and NOS3−/−, AVFs in the OE mice had larger lumen area. AVFs in the OE mice also had smoother blood flow streamlines, as well as lower blood shear stress at the wall, blood vorticity, inner wall circumferential stretch, and radial wall thinning at the anastomosis. Our results demonstrate that overexpression of NOS3 resulted in distinct hemodynamic and wall mechanical profiles associated with favorable AVF remodeling. Enhancing NOS3 expression may be a potential therapeutic approach for promoting AVF maturation.

Finite Element Predictions of Sutured and Coupled Microarterial Anastomoses

Simulation using computational methods is well-established for investigating mechanical and haemodynamic properties of blood vessels, however few groups have applied this technology to microvascular anastomoses. This study, for the first time, employs analytic and numeric models of sutured and coupled mi-croarterial anastomoses to evaluate the elastic and failure properties of these techniques in realistic geometries using measured arterial waveforms. Computational geometries were created of pristine microvessels and mi-croarterial anastomoses, performed using sutures and a coupling device. Vessel wall displacement, stress, and strain distributions were predicted for each anastomotic technique using finite element analysis (FEA) software in both static and transient simulations. This study focussed on mechanical properties of the anastomosis im- mediately after surgery, as failure is most likely in the early post-operative period. Comparisons were also drawn between stress distributions seen in analogous non-compliant simulations. The maximum principal strain in a sutured anastomosis was found to be 84% greater than in a pristine vessel, whereas a mechanically coupled anastomosis reduced arterial strain predictions by approximately 55%. Stress distributions in the su-tured anastomoses simulated here differed to those in reported literature. This result is attributed to the use of bonded connections in existing studies, to represent healed surgical sites. This has been confirmed by our study using FEA, and we believe this boundary condition significantly alters the stress distribution, and is less representative of the clinical picture following surgery. We have demonstrated that the inertial effects due to motion of the vessel during pulsatile flow are minimal, since the differences between the transient and static strain cal- culations range from around 0.6–7% dependent on the geometry. This implies that static structural analyses are likely sufficient to predict anastomotic strains in these simulations. Furthermore, approximations of the shear strain rate (SSR) were calculated and compared to analogous rigid-walled simulations, revealing that wall compliance had little influence on their overall magnitude. It is important to highlight, however, that SSR variations here are taken in isolation, and that changing pressure gradients are likely to produce much greater variation in vessel wall strain values than the influence of fluid flow alone. Hence, a formal fluid-structure interaction (FSI) study would be necessary to ascertain the true relationship.

Fluid-structure interaction study of spider’s hair flow-sensing system

In the present work we study the spider’s hair flow-sensing system by using fluid-structure interaction (FSI) numerical simulations. We observe experimentally the morphology of Theraphosa stirmi’s hairs and characterize their mechanical properties through nanotensile tests. We then use the obtained information as input for the computational model. We study the effect of a varying air velocity and a varying hair spacing on the mechanical stresses and displacements. Our results can be of interest for the design of novel bio-inspired systems and structures for smart sensors and robotics.© 2018 Elsevier Ltd. All rights reserved.Selection and Peer-review under responsibility of 1st International Conference on Materials, Mimicking, Manufacturing from and for Bio Application (BioM&M).

Numerical analysis on stability of nuclear fuel plates with inlet support comb

Many nuclear research reactors use or are planned with cores containing flat-plate-type fuel elements. One of the problems of this fuel element design is the mechanical stability of the fuel plates. High-velocity coolant flowing through the narrow channels that separate the plates can cause large deflections of these plates leading to local overheating, structural failure or plate collapse. In particular, in real fuel elements and experimental tests, flow-induced deflections at the leading edge and along the length of the plates have been detected. Some authors have indicated that the use of a support comb removes the leading-edge static divergence, but it has been also suggested that, even with the comb, there are significant deflections away from the inlet.In this work, a fluid-structure interaction study is conducted to examine the effectiveness of using an inlet comb on the mechanical stability of fuel plates. The system consists of two fuel plates bounded by three-equal coolant channels. The pressure loadings caused by the fluid flow are calculated using a CFD model and the structural response of the plates and the support comb are determined by means of an FEA model. The two-way fluid-structure interaction method was employed for coupling the fluid and solid solvers.The results presented here show that the static divergence at the inlet end is effectively eliminated with the installation of a support comb. Nevertheless, the main contribution of this work is the detection of deformation of the plates along their length and that it was an increasing function of the fluid velocity in the channels. As a consequence, the flow channels could be constricted or completely closed, thus affecting the safe operation of the nuclear reactor. To the best of our knowledge, this is the first numerical analysis reported in the literature that models the fluid-structure interaction phenomenon of adjacent plates with the support comb located at the midpoint of their inlet end.

Application of SPH-FE method for fluid-structure interaction using immersed boundary method

PurposeThis paper aims to propose a new smoothed particle hydrodynamics (SPH)-finite element (FE) algorithm to study fluid–structure interaction (FSI) problems.Design/methodology/approachThe fluid domain is discretized based on the theory of SPH), and solid part is solved through FE method, similar to other SPH-FE methods in the previous studies. Instead of master-slave technique, the interpolating (kernel) functions of immersed boundary method are implemented to couple fluid and solid domains. The procedure of modeling completely follows the classic IB framework where forces and velocities are transferred between interacting parts. Three benchmark FSI problems are simulated and the results are compared with those of similar numerical and experimental works.FindingsThe proposed SPH-FE algorithm with promising and acceptable results can be utilized as a reliable method to simulate FSI problems.Originality/valueContrary to most SPH-FE algorithms, the calculation of contact force is not required at interacting boundaries and no iterative process is proposed to calculate forces, velocities and positions at new time step.

A fluid–structure interaction study of soft robotic swimmer using a fictitious domain/active-strain method

Biological swimmers often exhibit rich physics due to the hydrodynamic coupling between the fluid flow and the immersed deforming body. Complexity and nonlinearity of their behaviors have imposed significant challenges in design and analysis of robots that mimick biological swimming motions. Inspired by the recent experimental studies of soft robotic swimmers, we develop a fictitious domain/active strain method to numerically study the swimming motion of thin, light-weight robots composed of smart materials that can actively undergo reversible large deformations (e.g., liquid crystal elastomer). We assume the elastic material to be neo-Hookean, and behave like an artificial “muscle” which, when stimulated, generates a principal stretch of contraction. We adopt an active strain approach to impose contractive strains to drive elastic deformation following a multiplicative decomposition of the deformation gradient tensor. The hydrodynamic coupling between the fluid and the solid is then resolved by using the fictitious domain method where the induced flow field is virtually extended into the solid domain. Pseudo body forces are employed to enforce the interior fictitious fluid motion to be the same as the solid structure dynamics. Using the fictitious domain/active strain method, we perform a series of numerical explorations for soft robotic swimmers with both 2D and 3D geometries. We demonstrate that these robot prototypes can effectively perform undulatory swimming and jet-propulsion when active strains are appropriately distributed on the elastica.

Control design in cyber-physical fluid–structure interaction experiments

Cyber-physical fluid dynamics is a hybrid experimental–computational approach to study fluid–structure interaction (FSI). It enables on-the-fly changes to structure inertia, damping, stiffness, and even kinematic constraints by replacing traditional elastically-mounted structures with actuators and a controller. The control design plays a central role in matching the closed-loop dynamics of the cyber-physical structure (CPS) to those of the desired structure. Control designs based on traditional proportional–integral–derivative (PID) and post-modern H∞ control are presented. The controllers are synthesized to match the linearized desired structural dynamics (or the input–output response) but no assumption of linearity is levied on the fluid behavior. To quantify the matching of input–output response, a CPS deviation index is defined based on H∞ norms. To evaluate and compare the performance of the control designs, two well-known FSI instabilities are considered, galloping and aeroelastic flutter. These FSI instabilities represent convenient test cases because they can be analyzed with linear aerodynamic models. Comparing the critical instability flow velocity and oscillation frequency of the CPS with different control designs and the desired mechanical structure demonstrates that the internal structure of the controller is crucial to fully matching the response of the desired structure. H∞ model-matching control with admittance causality is found to be the most adept control design for the CPS.

A fluid-structure interaction study on vulnerability of different coronary plaques to blood flow increase during physical exercise

Pathological studies have shown that coronary atherosclerotic plaques are more prone to rupture under physical exercise. In this paper, using a fully coupled fluid-structure interaction (FSI) analysis based on arbitrary Lagrangian-Eulerian (ALE) finite element method, the effect of the coronary blood flow rate increase during physical exercise on the plaque rupture risk is investigated for different plaque types. It is proved that the increase in coronary blood flow rate during physical exercise considerably increases the maximum stress in the plaque fibrous cap which can potentially lead to the plaque rupture. The issue is investigated for different plaque shapes and their vulnerability to exercise condition is compared. It is observed that the diffused plaque type which experiences the maximum stress of 187.9 kPa at rest and 544 kPa at exercise is the most critical plaque type. Because it is subjected to the highest stress in both of these conditions. However, the descending plaque type exhibits the highest susceptibility to physical activity, since its maximum stress increases from 68.9 kPa at rest to 280.5 kPa at exercise which means an increase of about 308%.

Fluid-structure interaction study of a mixed-flow pump impeller during startup

PurposeThe purpose of this paper is to experimentally and numerically study the transient hydraulic impact and overall performance during startup accelerating process of mixed-flow pump.Design/methodology/approachIn this study, the impeller rotor vibration characteristics during the starting period under the action of fluid–structure interaction was investigated, which is based on the bidirectional synchronization cooperative solving method for the flow field and impeller structural response of the mixed-flow pump. Experimental transient external characteristic and the transient dimensionless head results were compared with the numerical calculation results, to validate the accuracy of numerical calculation method. Besides, the deformation and dynamic stress distribution of the blade under the stable rotating speed and accelerating condition were studied based on the bidirectional fluid–structure interaction.FindingsThe results show that the combined action of complex hydrodynamic environment and impeller centrifugal force in the startup accelerating process makes the deformation and dynamic stress of blade have the rising trend of reciprocating oscillation. At the end of acceleration, the stress and strain appear as transient peak values and the transient effect is nonignorable. The starting acceleration has a great impact on the deformation and dynamic stress of blade, and the maximum deformation near the rim of impeller outlet edge increases 5 per cent above the stable condition. The maximum stress value increases by about 68.7 per cent more than the steady-state condition at the impeller outlet edge near the hub. The quick change of rotating speed makes the vibration problem around the blade tip area more serious, and then it takes the excessive stress concentration and destruction at the blade root.Originality/valueThis study provides basis and reference for the safety operation of pumps during starting period

Fluid Structure Interaction Study of High Pressure Stage Gas Turbine Blade Having Grooved Cooling Channels

Gas turbines are broadly used in propulsion of aircraft and in the generation of electric power. Conserving of gas turbine blades is a foremost importance since high pressure stage blades will be exposed to high temperature operational surroundings. Numerous techniques have been incorporated for the cooling of high pressure stage blades and one such technique is to incorporate innovative helicoidal cooling ducts near the leading edge and cooling channels having differently shaped grooves to pass high velocity cooling air along the blade span. By incorporating helicoidal duct and cooling channels having different shaped grooves, there is a potential to deliver additional surface area which facilitates cooling. Since fluid structure interaction is the main aim of this study, the loading of the blade analogous to the static pressure in addition to thermal field on the surfaces of the blade are attained using computational fluid dynamics run. The study brings out deformation due to temperature, centrifugal and pressure load of the high pressure phase blade having grooved cooling channels in the vicinity of trailing edge region. A parametric methodology will be considered for changing the cooling fluid channel geometry to enhance the process of cooling near the trailing edge region. It is found from the fluid structure interaction analysis that cooling channels having buttress shaped grooved configuration near the trailing edge result in improved cooling properties resulting in improved operationalstability of the blade