Fluid-structure Interaction Simulations Research Articles

An experimentally-verified approach for enhancing fluid drag force simulation in vertical oilwell drill strings

ABSTRACT The oilwell drilling fluid flows cause viscous and hydrodynamic forces on drill strings. This effect is ignored or treated as a constant in most drill string models. The present study introduces mathematical models for lateral vibration damping and axial drag forces that are employable in lumped segment drill string models. First, the variables to which drilling fluid-generated forces are most sensitive were identified and the Response Surface Method was applied to design the experiment matrix. The lateral vibration-damping experiments, which were validated using a scaled-down physical model, and the axial drag experiments were done using Fluid-Structure Interaction simulations. The results were statistically analysed to acquire the models and were implemented in a 3D lumped segment bond graph developed using the Newton-Euler formulation and body-fixed coordinates. The results indicate a considerable effect of the extended treatment of damping and axial drag on bending moment fluctuation, wellbore interactions, and weight on bit.

Effects of core air gaps and steel inserts on thermal response of GFRP-balsa sandwich panels subjected to fire

Sandwich systems composed of combustible glass fiber-reinforced polymer (GFRP) face sheets and balsa cores must fulfill fire resistance requirements if used, for instance, in bridge or building construction. Air gaps and steel inserts in the balsa core, the latter to suspend external pipes below bridge decks for example, may therefore present critical zones where heat ingress is facilitated, and fire resistance is therefore reduced. The thermal responses of such GFRP-balsa sandwich panels comprising through-thickness air gaps or steel inserts, and subjected to a one-sided external fire, were thus investigated by furnace experiments and fluid-structure interaction simulations. Through-thickness air gaps and steel inserts between the face sheets cooled the surrounding zones close to the hot face and heated those located towards the cold face. In T-shape steel inserts penetrating the bottom face sheet, the fire-exposed flange collected the heat and the whole section around the insert was significantly heated. The results revealed that the remaining cross section might be considerably reduced by char formation around the air gaps and steel inserts. Although the effect is quite local, it may be significant if slabs are unidirectional or if it occurs at critical locations, e.g., in the vicinity of supports.

Multiple limit cycle amplitudes in high-fidelity predictions of standstill wind turbine blade vibrations

Abstract. In this study, vortex-induced vibrations (VIVs) on the IEA 10 MW blade are investigated using two methodologies in order to assess strengths and weaknesses of the two simulation types. Both fully coupled fluid–structure interaction (FSI) simulations and computational fluid dynamics (CFD) with forced motion of the blade are used and compared. It is found that for the studied cases with high inclination angles, the forced-motion simulations succeed in capturing the power injection by the aerodynamics, despite the motion being simplified. From the fully coupled simulations, a dependency on initial conditions of the vibrations was found, showing that cases which are stable if unperturbed might go into large VIVs if provoked initially by, for instance, inflow turbulence or turbine operations. Depending on the initial vibration amplitudes, multiple limit cycle levels can be triggered, for the same flow case, due to the non-linearity of the aerodynamics. By fitting a simple damping model for the specific blade and mode shape from FSI simulations, it is also demonstrated that the equilibrium limit cycle amplitudes between power injection and dissipation can be estimated using forced-motion simulations, even for the multiple stable vibration cases, with good agreement with fully coupled simulations. Finally, a time series generation from forced-motion simulations and the simple damping model is presented, concluding that CFD amplitude sweeps can estimate not only the final limit cycle oscillation amplitude, but also the vibration build-up time series.

Fluid-structure interaction analysis of oblique ship-bridge collisions

The hydrodynamic effect in ship-bridge collisions is usually considered by the constant added mass (CAM) method in current studies. However, no research to date has examined its applicability, particularly for oblique collisions. To this end, high-fidelity physics-based finite-element (FE) models are developed in this study to investigate the fluid-structure interaction (FSI) behavior during ship-bridge collisions with different impact angles. The FSI modeling method based on the LS-DYNA code is examined and verified by the potential flow solver WADAM. The hydrodynamic effect predicted by the developed FSI model is consistent with the WADAM result. The verified FSI models are used to assess the influences of several key parameters (e.g., impact angles, impact positions, ship drafts and impact velocities) on the hydrodynamic effect for different ship-bridge collision scenarios. It is found that the ship-bridge collision process obtained from the FSI simulation is different from that of the CAM method for oblique collision scenarios. The CAM method is unsuitable for oblique collisions because it is unable to capture the hydrodynamic effect properly. Also, the FSI simulations indicate that the current design specifications underestimate the impact force and the dissipated energy in oblique collisions. An analytical formula is improved to estimate the energy absorbed by either the ship or the bridge in oblique collisions. Good agreements are achieved between the FSI analysis results and the improved formula.

High-fidelity fluid structure interaction simulations of turbulent-like aneurysm flows reveals high-frequency narrowband wall vibrations: A stimulus of mechanobiological relevance?

Recent high-fidelity/resolution computational fluid dynamics simulations of intracranial aneurysm hemodynamics have revealed turbulent-like flows. We hypothesized that the associated high-frequency pressure fluctuations could promote aneurysm wall vibrations. We performed fully coupled high-fidelity transient fluid structure interaction simulations between the blood flow and compliant aneurysm sac wall taking 5,000 time steps per second using a 3D patient-specific model previously shown to harbour turbulent-like flow. Our results show that the flow velocity contained fluctuations with a smooth and continuously decaying energy up to ∼160Hz, and fluctuating pressures with characteristic frequency peaks at approximately 30, 130 and 210Hz. There was a strong two-way coupling between the pressure and the wall deformation, for which the frequency spectrum showed similar characteristics, but with a narrow band peak at ∼120Hz with large regional differences in amplitude up to 80μm. The physics of the flow is broadly consistent with clinical reports of turbulent-like flows, while the physics of the wall is consistent with reports of spectral peaks in aneurysm patients. As many aneurysms are known to harbour turbulent-like flows, wall vibrations could be a widespread phenomenon. Finally, since aneurysms are vascular pathologies by definition and many/most aneurysms do not have endothelial cells but still display a focal remodeling, we hypothesize that vibrations and stresses within the wall itself might play a role in the mechanobiological processes of vessel wall pathology.

Computational Fluid–Structure Interaction Analysis of Piston Pin Multiphase Elastohydrodynamic Lubrication With Unsteady Flow Channel Variation

Abstract This research focuses on the multiphase oil film tribology between the piston pin and the connecting rod in an internal combustion engine and establishes a new computational approach for thin-film lubrication with unsteady flow channel variation. First, the pin and the connecting rod are considered as rigid bodies, and 3D numerical analysis of the cavitating lubricating oil flow is performed when combustion load is applied to the pin. We find that dynamic pressure does not increase around the connecting rod edge and that pressure is potentially insufficient to support the load. In the second numerical analysis, the pin and the connecting rod are considered to be elastically deformable structures, and coupled 3D multiphase fluid–structure interaction simulation is performed. The boundary lubrication area is detected using a statistical Greenwood–Tripp model as unevenness of the contacted metal surface. The results show that pressure distribution spreads more widely than in the result for rigid bodies and that the film was thicker as well. Also, the pin deformed like a bow, but the deformation of the connecting rod was quite small, suggesting a potential mechanical contact at the edge of the connecting rod with the pin. By comparison with an actual operationally used piston pin, we find that the fluid–structure coupled analysis qualitatively predicted the seizure location.

Bullseye focusing of cylindrical waves at a liquid–solid interface

Two pairs of converging and superimposing shock and Rayleigh waves are generated on a glass substrate by focusing laser pulses on two concentric rings in a bullseye configuration (67 and 96 μm radii). We experimentally study the threshold for the substrate damage as a function of the number of repetitions and the delay (0–20 ns). The bullseye focusing experiments are compared to a single focusing ring. Additionally, fluid–structure interaction simulations using a volume-of-fluid framework are utilized to estimate the stresses. The lowest number of repetitions to attain surface damage is found for constructive superposition of the Rayleigh waves, i.e., here for a delay of 10 ns. The observed damage is consistent with the simulations where the largest positive stresses (∼5.6 GPa) are achieved for bullseye focusing with Δt=10 ns followed by Δt=20 ns, which corresponds to a simultaneous shock wave focusing. In all these cases, the positive stresses are followed (a few nanoseconds later) by the negative stresses that can reach ∼−6.4 GPa.

SILICOFCM platform, multiscale modeling of left ventricle from echocardiographic images and drug influence for cardiomyopathy disease

Background and objectiveIn silico clinical trials are the future of medicine and virtual testing and simulation are the future of medical engineering. The use of a computational platform can reduce costs and time required for developing new models of medical devices and drugs. The computational platform, which is one of the main results of the SILICOFCM project, was developed using state-of-the-art finite element modeling for macro simulation of fluid-structure interaction with micro modeling at the molecular level for drug interaction with the cardiac cells. SILICOFCM platform is using for risk prediction and optimal drug therapy of familial cardiomyopathy in a specific patient. MethodsIn order to obtain 3D image reconstruction, the U-net architecture was used to determine geometric parameters for the left ventricle which were extracted from the echocardiographic apical and M-mode views. A micro-mechanics cellular model which includes three kinetic processes of sarcomeric proteins interactions was developed. It allows simulation of the drugs which are divided into three major groups defined by the principal action of each drug. Fluid-solid coupling for the left ventricle was presented. A nonlinear material model of the heart wall that was developed by using constitutive curves which include the stress-strain relationship was used. ResultsThe results obtained with the parametric model of the left ventricle where pressure-volume (PV) diagrams depend on the change of Ca2+ were presented. It directly affects the ejection fraction. The presented approach with the variation of the left ventricle (LV) geometry and simulations which include the influence of different parameters on the PV diagrams are directly interlinked with drug effects on the heart function. It includes different drugs such as Entresto and Digoxin that directly affect the cardiac PV diagrams and ejection fraction. ConclusionsComputational platforms such as the SILICOFCM platform are novel tools for risk prediction of cardiac disease in a specific patient that will certainly open a new avenue for in silico clinical trials in the future.

Fluid-Structure Interaction Study of The Effect of Stent on Local Hemodynamics Parameters at The Stented Carotid Artery Bifurcation

Previous fluid-structure interaction (FSI) studies on carotid bifurcation focused on the effect of wall compliance on the predicted hemodynamic features in normal or atherosclerotic carotid arteries. However, FSI study on patient-specific post-stent carotid model is still lacking, and to the authors knowledge no such a study has been reported so far. This study attempts to simulate the full-scale patient-specific post- stent carotid bifurcation geometry with the hope to understand the effect of wall compliance on hemodynamic quantities. The FSI model was based on patient-specific geometry consisting of three components i.e., the carotid artery wall and stent as the solid domain, and blood in the fluid domain. Full FSI simulations incorporating patient-specific boundary conditions at the inlet and outlets, and realistic homogenous incompressible carotid wall and stent were completed to evaluate the flow patterns and wall shear stress. The FSI simulation results were compared with the corresponding rigid-wall model. The quantitative difference in time-averaged wall shear stress (TAWSS) distribution between the FSI and rigid-wall models shows that FSI model predicted 8% less of the area in the low TAWSS band (<0.4%) compared 0.4 - 1.2 Pa. The results suggest that although the effect of wall compliance on flow patterns in the patient-specific post-stent carotid model is negligible, its quantitative effect on wall shear stress may not be trivial and should be considered in future studies

Design and Fabrication of Untethered Light-Actuated Microbots in Fluid for Biomedical Applications

Untethered mobile robots at the micro-scale have the ability to improve biomedical research by performing specialized tasks inside complex physiological environments. Light-controlled wireless microbots are becoming the center of interest thanks to their accuracy in navigation and potential to carry out operations in a non-invasive manner inside living environments. The pioneering light-engineered microbots are currently in the early stage of animal trials. There is a long way ahead before they can be employed in humans for therapeutic applications such as targeted drug delivery, cancer cell diagnosis, tissue engineering, etc. The design of light-actuated microbots is one of the challenging parts along with the biocompatibility and precision control for in vivo applications. Recent progress in light-activated microbots has revealed a few innovative design concepts. In this study, we presented a framework on the different aspects with a comparative analysis of potential designs for the next generation of light-controlled microbots. Utilizing numerical simulations of fluid-structure interactions, limiting design elements of the microbots are addressed. We envision that this study will eventually facilitate the integration of robotic applications into the real world owing to the described design considerations.

The pathogenesis of superior mesenteric artery dissection: An in-depth study based on fluid–structure interaction and histology analysis

ObjectiveTo explore the role of hemodynamic factors in the occurrence of superior mesenteric artery (SMA) dissection (SMAD) using a fluid–structure interaction (FSI) simulation method, and to identify histopathologic changes occurring in the wall of the SMA. MethodsA total of 122 consecutive patients diagnosed with SMAD and 122 controls were included in this study. Hemodynamic factors were calculated using a FSI simulation method. Additionally, SMA specimens obtained from 12 cadavers were stained for histological quantitative analysis. ResultsThe mean aortomesenteric angle (59.7° ± 21.4° vs 48.2° ± 16.8°; p < .001) and SMA maximum curvature (0.084 ± 0.078 mm-1 vs 0.032 ± 0.023 mm−1; p < .001) were higher in SMAD patients than the controls. Larger aortomesenteric angles and SMA curvatures were associated with higher and more concentrated wall shear stress at anterior wall of the SMA curve segment, co-located with the dissection origins. The mean thickness of media (325.18 ± 44.87 µm vs 556.92 ± 138.32 µm; p = .003) was thinner in the anterior wall of the SMA curve than in the posterior wall. The area fractions of elastin (17.96% ± 3.36% vs 27.06% ± 4.18%; p = .002) and collagen (45.43% ± 6.89% vs 55.57% ± 7.57%; p = .036) were lower in anterior wall of the SMA curve than in posterior wall. ConclusionIncreased aortomesenteric angle and SMA curvature are risk factors for SMAD. Both of these factors can cause local hemodynamic abnormalities, which can lead to histopathologic changes in anterior wall of SMA.

Advancements and Opportunities in Characterizing Patient-Specific Wall Shear Stress Imposed by Coronary Artery Stenting

The success of drug-eluting stents (DES) is limited by restenosis and, to a lesser extent, late stent thrombosis. Mechanical stimuli have been implicated in these outcomes, with indices of wall shear stress (WSS) determined from computational simulations being reported most frequently. The current work summarizes state-of-the-art computational approaches applicable to patient-specific models aimed at further understanding changes in WSS indexes imposed by stent implantation. We begin with a review of best practices involved in the process and then summarize the literature related to stent-induced WSS alterations. Image-based reconstruction methods are also discussed, along with the latest generation boundary conditions that replicate cardiac physiology and downstream vasculature in the setting of coronary artery disease. The influence of existing material property data on WSS results obtained with geometries reconstructed from finite element modeling and fluid structure interaction (FSI) simulations is reviewed, along with the novel approaches being used to provide coronary artery plaque data that are currently missing from the literature. We also consider the use of machine learning tools that have the potential for impact when assessing the role of adverse stent-induced WSS in suboptimal clinical outcomes. We conclude by focusing on challenging cases that involve DES implantation, which may benefit from recent advancements in patient-specific computational modeling.

Semi-Automated Construction of Patient-Specific Aortic Valves from Computed Tomography Images.

This paper presents a semi-automatic method for the construction of volumetric models of the aortic valve using computed tomography angiography images. Although the aortic valve typically cannot be segmented directly from a computed tomography angiography image, the method described herein uses manually selected samples of an aortic segmentation derived from this image to inform the construction. These samples capture certain physiologic landmarks and are used to construct a volumetric valve model. As a demonstration of the capabilities of this method, valve models for 25 pediatric patients are created. A selected valve anatomy is used to perform fluid-structure interaction simulations using the immersed finite element/difference method with physiologic driving and loading conditions. Simulation results demonstrate this method creates a functional valve that opens and closes normally and generates pressure and flow waveforms that are similar to those observed clinically.

Influence of blood pressure and rheology on oscillatory shear index and wall shear stress in the carotid artery

Atherosclerosis is a localized complication dependent on both the rheology and the arterial response to blood pressure. Fluid–structure interaction (FSI) study can be effectively used to understand the local haemodynamics and study the development and progression of atherosclerosis. Although numerical investigations of atherosclerosis are well documented, research on the influence of blood pressure as a result of the response to physio–social factors like anxiety, mental stress, and exercise is scarce. In this work, a three-dimensional (3D) Fluid–Structure Interaction (FSI) study was carried out for normal and stenosed patient-specific carotid artery models. Haemodynamic parameters such as Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI) are evaluated for normal and hypertension conditions. The Carreau–Yasuda blood viscosity model was used in the FSI simulations, and the results are compared with the Newtonian model. The results reveal that high blood pressure increases the peripheral resistance, thereby reducing the WSS. Higher OSI occurs in the region with high flow recirculation. Variation of WSS due to changes in blood pressure and blood viscosity is important in understanding the haemodynamics of carotid arteries. This study demonstrates the potential of FSI to understand the causes of atherosclerosis due to altered blood pressures.

A detailed methodology to model the Non Contact Tonometry: a Fluid Structure Interaction study.

Understanding the corneal mechanical properties has great importance in the study of corneal pathologies and the prediction of refractive surgery outcomes. Non-Contact Tonometry (NCT) is a non-invasive diagnostic tool intended to characterize the corneal tissue response in vivo by applying a defined air-pulse. The biomarkers inferred from this test can only be considered as indicators of the global biomechanical behaviour rather than the intrinsic biomechanical properties of the corneal tissue. A possibility to isolate the mechanical response of the corneal tissue is the use of an inverse finite element method, which is based on accurate and reliable modelling. Since a detailed methodology is still missing in the literature, this paper aims to construct a high-fidelity finite-element model of an idealized 3D eye for in silico NCT. A fluid-structure interaction (FSI) simulation is developed to virtually apply a defined air-pulse to a 3D idealized eye model comprising cornea, limbus, sclera, lens and humors. Then, a sensitivity analysis is performed to examine the influence of the intraocular pressure (IOP) and the structural material parameters on three biomarkers associated with corneal deformation. The analysis reveals the requirements for the in silico study linked to the correct reproduction of three main aspects: the air pressure over the cornea, the biomechanical properties of the tissues, and the IOP. The adoption of an FSI simulation is crucial to capture the correct air pressure profile over the cornea as a consequence of the air-jet. Regarding the parts of the eye, an anisotropic material should be used for the cornea. An important component is the sclera: the stiffer the sclera, the lower the corneal deformation due to the air-puff. Finally, the fluid-like behavior of the humors should be considered in order to account for the correct variation of the IOP during the test which will, otherwise, remain constant. The development of a strong FSI tool amenable to model coupled structures and fluids provides the basis to find the biomechanical properties of the corneal tissue in vivo.

Aerodynamic analysis for a bat-like robot with a deformable flexible wing

AbstractDue to the efficient and flexible flight ability of bats, bat-like robots have become the focus of research in the field of bionic robots. Aerodynamic calculation is an important part of the research field of bat-like robot, which is the basis of the structure design and flight controller design of bat-like robot. However, due to the complex flight mechanism of bats, there is no mature theoretical method to calculate the flight aerodynamic force of bat-like robots. To solve this problem, this paper takes the membrane of a bat-like robot as the research object and analyzes in detail the effects of wing folding and unfolding and flexible deformation of the membrane on the chord length, passive torsion angle and relative velocity. Based on quasi-steady state model and blade element method, a set of aerodynamic calculation method for flexible deformed wing is established. In order to verify the effectiveness of the proposed method, the theoretical calculation results and the results of the fluid-structure interaction simulation are compared and analyzed under various working conditions. The two results are in good agreement under each working condition, and the errors are all within reasonable range, which proves the effectiveness of the method. This study can provide a theoretical basis for rational structure design and precise flight control of bat-like robot.

Simultaneous measurement of pressure and temperature in a supersonic ejector using FBG sensors

In this work, we have demonstrated the use of fiber Bragg grating (FBG) sensors for simultaneous measurement of wall static pressure and temperature in a supersonic ejector. Supersonic ejectors are ground-based high-speed aerodynamic test facilities characterized by harsh conditions, such as high pressure and temperature gradients. An FBG-based sensor setup was developed consisting of a pressure measuring bare FBG and a specially designed pressure-insensitive FBG temperature probe that can be mounted on the wall of the supersonic ejector. The FBG temperature probe was used for temperature measurement as well as temperature compensation of the pressure measuring FBG sensor. Wall static pressure measurements in the supersonic ejector were carried out at different tank pressures and Mach number flows. The FBG pressure measurements were validated with those of standard piezoresistive-based sensor measurements. Both responses were found to match closely, with FBG sensors having a faster response time and higher pressure resolution. Fluid structure interaction simulation was carried out in Comsol Multiphysics to understand the interaction of high-speed turbulent flow with FBG sensor. The FBG strain profile due to flow-induced stress and its dependence on flow pressure was studied. A detailed analysis of the effect of preceding fiber length on FBG pressure measurement was carried out. FBG sensors, due to their miniature size, ability to withstand harsh environments and multi-parameter sensing capability, can be used in ground-based aerodynamic test facilities with minimal intrusion into the flow.

Performance analysis of composite laminates wing skin with the aid of fluid structure interaction of aerodynamic loading-structural analysis

Advances in today’s technology have led to the use of composite materials with their advantages of significant high strength with lightweight structure in aircraft design worldwide. With the aid of simulation, ANSYS, two main common problems in designing the aircraft composite wing, which is the aerodynamic loading on the wing and composite modeling; whereby both can be coupled to solve the aforementioned problems. The paper addresses with the use of fluid Structure Interaction (FSI) simulation and developed a standard numerical approach by integrating the aerodynamic loading from fluid domain with Finite Element (FE) analysis from structural domain in the application of hybrid composite laminates of aircraft wing structure. In this study, the Computational Fluid Dynamics (CFD) is conducted on the selected wing model of Selig 1223 in order to obtain the pressure loading from fluid domain before transferring it as an input to FE composite of structural domain. The FSI simulation was performed for two parametric conditions, namely Composite Wing Skin without Honeycomb (CWS) and Composite Wing skin with Honeycomb (CWSwH). From the result, CWSwH has lower total deformation with 3.06% percentage difference compared to CWS. However, the shear stress and strain values of CWSwH showed higher value than those of CWS due to the effect of the elasticity of honeycomb core. Therefore, the numerical approach of FSI with the application composite material has proven to be feasible and significant of current research on the behavior of fluid flow and structural for the wing skin, which replicates the real conditions of the aircraft wing during take-off or cruise.

Flow-induced vibration of flexible cylinders covered by fixed fairings with different chord-thickness ratios

Fairings are important vortex-induced vibration (VIV) suppression devices in the offshore and marine engineering applications. For circular cylinders in the marine structures, both their mean deflection in the in-line direction and the oscillation amplitude in the cross-flow direction can be effectively reduced when the fairings work properly. However, plenty recent investigations report that when the rotational elements of fairings fail to function, the VIV suppression functions may be deprived and severe galloping oscillations may occur. However, very few studies discussed the galloping oscillation mechanism for slender flexible cylinders. We perform a numerical study on the fluid–structure interaction of flexible cylinders covered by fixed fairings with different chord-thickness ratios (c/t) using a self-developed fluid–structure interaction simulation code. The Reynolds number is 1.68×104, which is based on the incoming velocity and the diameter of the cylinder. It is found that large amplitude, low frequency and low order galloping responses are prominent in the cases where the flexible cylinder is covered by fairings with large c/t. The large added mass and the low fluid force oscillation frequency in galloping are found to induce the low vibration frequency and the low order ‘lock-in’ modes in flexible cylinder responses.

Reliability study on the fatigue life of film cooling blades in advanced aero-engine turbines: Neglected crystal orientation uncertainty in casting

The orientation uncertainty of single-crystal turbine blades is a neglected practical engineering problem, and previous research has paid little attention to it. The work innovatively presents the random distribution regularity of the spatial orientation formed in the casting of single crystal blades and its influence on the structural reliability, which establish a foundation for the orientation design of blades. In this work, the uncertain characteristics of the spatial orientation for single crystal cast blades are mathematically quantified. Meanwhile, based on the classical material constitutive and life equations, the elastic-plastic theoretical and fatigue life evaluation models related to orientation are deduced and firstly applied to turbine blade engineering analysis. The elastic-plastic stress distributions of single-crystal turbine blades considering thermal effects are obtained by the fluid-structure interaction simulation. The spatial orientation distribution characteristics is presented from analyzing hundreds of samples. Finally, the influence of the uncertain orientation on the low cycle fatigue life reliability and structural failure probability of single-crystal turbine blades are clarified for the first time by using the BP neural network and stepwise response method. Our results demonstrate that crystal orientation uncertainty, especially in long-life design, can cause a serious failure probability, proving the necessity of orientation control for single crystal turbine blades clearly.