Fluid-structure Interaction Analysis Research Articles

A novel cost-efficient deep learning framework for static fluid–structure interaction analysis of hydrofoil in tidal turbine morphing blade

A tidal turbine can benefit from exquisitely designed morphing blades with a flexible trailing edge by mitigating up to 90% of the load fluctuation in harsh ocean environments, which reduces the overall cost of tidal energy. However, existing fluid–structure interaction (FSI) methods of resolving flow-induced deformation of the blades is computationally expensive, which poses an important challenge to effective morphing blade design. This paper presents a novel static FSI tool based on deep learning to cost-efficiently analyze the fluid–structure coupling of a hydrofoil. Specifically, adopting a convolutional neural network (CNN) to predict the fluid force and finite element method (FEM) to solve the solid structure response, a new CNN-FEM framework with an iterative scheme for solving the FSI problem is developed to achieve equilibrium between the fluid and structural forces. The new framework is used to predict the elastic deformation of the flexible blade section of the hydrofoil to demonstrate its effectiveness in the FSI evaluation. Comparison of the results to those produced by commercially developed software (i.e., Ansys Workbench) shows that this method yields extremely close prediction results of average equivalent stress and an accuracy of more than 92%. Moreover, it is 100 times more computationally efficient than the commercial Ansys Workbench software, requiring less than 3s for one-way FSI calculation. Taking advantage of this cost-effectiveness, the CNN-FEM can be used to achieve the accurate prediction of the deformation characteristics of the flexible hydrofoil under various flow scenarios that lay a foundation for advanced morphing blade design in the future.

The added mass of a closed-type cushion in uniform flow

Ethylene-Tetra-Fluoro-Ethylene (ETFE) cushions are popularly used in modern civil engineering structures. When a cushion vibrates in uniform flow, the surrounding fluid will be driven to move along with it. The inertia of fluid then produces an action on the cushion, which is known as the effect of added mass. This effect is usually very significant due to the light weight of these cushions. This paper proposes a new method to estimate the added mass on a close-type ETFE cushion vibrating in uniform flow with an improved accuracy compared with methods in the literature. The aerodynamic force is assumed to consist of pressures from uniform flow and potential flow induced by perturbation of the vibrating cushion. An analytical expression for the added mass on the cushion is then proposed based on the Laplace equation and Bernoulli equation, in which the velocity of the potential fluid above the vibrating cushion is assumed to vary along the z-direction in the form of a quartic function, and the non-uniform distribution of the added mass over the enveloping membrane is also considered. The proposed method is verified by comparing the dynamic responses of the cushion considering the added mass from the Computational Structural Dynamics (CSD) module of ADINA with those in the literature and those obtained from the fluid–structure interaction (FSI) analysis. The effects of different influencing factors on the accuracy of the method, e.g., side length of the cushion, initial inner pressure, wind velocity and wind direction angle, are further studied. Results show that: (a) the proposed method to estimate the added mass is more accurate than those in the literature with results closer to those from the FSI analysis; (b) an increase in the side length of the cushion will lead to a more non-uniform distribution of the added mass; (c) the side length of the cushion and wind velocity have a slight effect on the accuracy of the proposed method with the maximum error within 5%; and (d) an increase in the initial inner pressure can improve the accuracy of the proposed method while the wind direction angle seems to have little influence.

GRS contributions to flow-induced vibrations related activities in Europe

Abstract Flow-induced vibrations in nuclear power plants may lead to material fatigue, fretting wear, and eventually to loss of component integrity. The consequences might be substantial costs due to long unplanned outages or a fault that requires safety provisions to perform as intended. To avoid these, Fluid-Structure Interaction analyses are performed to understand and predict the complex thermal-hydraulic and structural mechanics phenomena. To further advance the knowledge of solving FSI problems with the help of numerical tools, in the beginning of 2020, the joint industry VIKING project was established in Europe. Further, OECD/NEA initiated in 2021 an FSI Benchmark on FIV that should be finished by the end of 2022 and the final synthesis report should be published in 2023. This paper provides a short overview of the GRS contributions within these two international activities on the prediction of FIV in nuclear power reactors. The content of this article was initially presented at the 33rd German CFD Network of Competence Meeting, held on March 22–23 at GRS in Garching, Germany.

Fluid-structure interaction analysis of airflow, structural mechanics and aerosol dynamics in a four-generation acinar model

Elucidating the aerosol dynamics in the pulmonary acinar region is imperative for both health risk assessment and inhalation therapy, especially nowadays with the occurrence of the global COVID-19 pandemic. During respiration, the chest's outward elastic recoil and the lungs' inward elastic recoil lead to a change of transmural pressure, which drives the lungs to expand and contract to inhale and expel airflow and aerosol. In contrast to research using predefined wall motion, we developed a four-generation acinar model and applied an oscillatory pressure on the model outface to generate structure deformation and airflow. With such tools at hand, we performed a computational simulation that addressed both the airflow characteristic, structural mechanics, and aerosol dynamics in the human pulmonary acinar region. Our results showed that there is no recirculating flow in the sac. The structural displacement and stress were found to be positively related to the change of model volume and peaked at the end of inspiration. It was noteworthy that the stress distribution on the acinar wall was significantly heterogeneous, and obvious concentrations of stress were found at the junction of the alveoli and the ducts or the junction of the alveoli and alveoli in the sac. Our result demonstrated the effect of breathing cycles and aerosol diameter on deposition fraction and location of aerosols in the size range of 0.1–5 μm. Multiple respiratory cycles were found necessary for adequate deposition or escape of submicron particles while having a negligible influence on the transport of large particles, which were dominated by gravity. Our study can provide new insights into the further investigation of airflow, structural mechanics, and aerosol dynamics in the acinar depth.

Design and Development of Flapping Wing UAV

Flapping wing air vehicles are unmanned miniature aircraft’s that draw inspiration from birds, bats and insects. They utilize continuous flapping wing motion to generate aerodynamic forces and moments. The fluid structure interaction analysis of biological and artificial flapping flyers is extremely complicated thus an efficient unsteady aerodynamic model is required in such time consuming problems as optimal flapping wing simulation. This project deals with designing a flapping wing air vehicle which includes applying inertial impulsive force to UAV in such a way that the flapping wing air vehicle reaches almost constant flight speed after removing the initial impulsive forces. The flow dynamics are different of the flapping wing air vehicles with that of the fixed wing UAV and this project deals with the utilization of the flapping wing in the UAV to overcome the challenges faced by a fixed wing UAV like maneuverability in remote areas, sound produced and identification during mission. Structural and aerodynamic characteristics of a bird in flight offer benefits over typical propeller or rotor driven unmanned air vehicle (UAV). Hence this study deals with the designing of an flapping wing UAV to overcome these drawbacks of fixed wing UAV.

Effect of coronary artery dynamics on the wall shear stress vector field topological skeleton in fluid–structure interaction analyses

AbstractIn this paper, we investigate the impact of coronary artery dynamics on the wall shear stress (WSS) vector field topology by comparing fluid–structure interaction (FSI) and computational fluid dynamics (CFD) techniques. As one of the most common causes of death globally, coronary artery disease (CAD) is a significant economic burden; however, novel approaches are still needed to improve our ability to predict its progression. FSI can include the unique dynamical factors present in the coronary vasculature. To investigate the impact of these dynamical factors, we study an idealized artery model with sequential stenosis. The transient simulations made use of the hyperelastic artery and lipid constitutive equations, non‐Newtonian blood viscosity, and the characteristic out‐of‐phase pressure and velocity distribution of the left anterior descending coronary artery. We compare changes to established metrics of time‐averaged WSS (TAWSS) and the oscillatory shear index (OSI) to changes in the emerging WSS divergence, calculated here in a modified version to handle the deforming mesh of FSI simulations. Results suggest that the motion of the artery can impact downstream patterns in both divergence and OSI. WSS magnitude is also decreased by up to 57% due to motion in some regions. WSS divergence patterns varied most significantly between simulations over the systolic period, the time of the largest displacements. This investigation highlights that coronary dynamics could impact markers of potential CAD progression and warrants further detailed investigations in more diverse geometries and patient cases.

Durability Analysis of Wind Turbine Blade Coating under Random Aeolian Sand

Wind turbine has a poor working environment and suffered from Aeolian sand and rain for a long time, which results in serious damage to blade coating and greatly affects the later maintenance, the safe and stable operation of wind turbine. In this regard, this paper intends to use numerical simulation method to simulate the erosion process of blade coating under random Aeolian sand, and then study its durability in Aeolian environment. Taking Inner Mongolia as an example, the Weibull distribution wind speed model is established by using the measured wind speed data, and then the dynamic pressure, the impact load and the stress response of blade coating are obtained by FSI (Fluid Structure Interaction) analysis, finally, the fatigue life of blade coating is analyzed by nCode (nCode software). The results show that the dynamic pressure, the impact load and the stress response of blade coating is between20-140 Pa, 0.4-7.9 N and 0.4-2.79 MPa respectively. The maximum damage of blade coating is located near the leading edge of blade tip and its side, and the fatigue life of blade coating is 2.0×108 s.

Frequency dependency of dynamic force coefficients for hermetic squeeze film dampers utilizing fluid-bounding flexible structures

The following paper focuses on the dynamic behavior of hermetic squeeze film dampers (HSFD) that utilize fluid-bounding flexible members as a part of the support structure. More specifically, the current paper advances an engineering design modification to the existing HSFD concept, which is aimed at rendering the dynamic force coefficients frequency independent. The paper introduces analytical models, which are used to explain the frequency dependency of force coefficients observed in past experimental testing of HSFD. Furthermore, the insights gained from the analytical models are used to conceive a new frequency independent damper architecture. The analytical study leverages commercially available finite element analysis (FEA) and computational fluid dynamics (CFD) software to conduct several fluid-structure-interaction (FSI) simulations of various damper architectures. In addition to the FSI analysis a more computationally efficient reduced order model (ROM) was developed, coupling structural flexibility with the fluid dynamics in the damper. Ultimately, these design tools were used to identify critical design features and configurations needed for constant linear frequency independent force coefficients. The results show a damper configuration with minimal frequency dependency of the stiffness and damping coefficients when incorporating pass through channels in combination with accumulator volumes.

Numerical simulation and analysis of fluid-structure interaction on 3D MHKF-180 and NACA4418 cavitating hydrofoils

A numerical investigation of structural and hydrodynamic performance of 3D stainless steel MHKF-180 and NACA4418 cavitating hydrofoils has been carried out using one-way fluid-structure interaction (FSI). Under the application of hydrodynamic load, the structural performance of MHKF-180 is compared with NACA4418 in terms of natural frequency, maximum tip deformation, and von Mises stress, whereas hydrodynamic performance is compared in terms of lift coefficient, drag coefficient, lift to drag ratio, pressure coefficient, and Strouhal number. The simulation is performed at a chord-based Reynolds number, Re = 750000, for different cavitation numbers and angles of attack using ANSYS software. The present result is validated by comparing the natural frequency and pressure coefficient curve of the non-cavitating NACA66 hydrofoil and lift coefficient and drag coefficient of cavitating NACA4412 hydrofoil with the available experimental data. The fluid flow is simulated using the unsteady-Reynolds-averaged-Navier-Stokes (URANS) equations and Realizable k −ε turbulence model. The cavitation effect on the hydrofoil is studied using the Zwart-Gerber-Belamri cavitation model. Comparing the maximum tip deformation under cavitation, the MHKF-180 shows larger tip deformation than NACA4418 hydrofoil. However, the hydrodynamic performance, assessed in terms of lift coefficient, MHKF-180 gives a better than NACA4418 under the cavitating condition at different angles of attack and for different cavitation numbers.

Analysis of fluid-structure interaction in a directional permeability membrane in pressure-driven flow

Finite volume and finite element analysis of fluid-structure interaction is performed to understand the behavior of a directional permeability membrane in pressure-driven flow. The membrane is comprised of two flexible porous sheets separated by a spacer. The porous sheets each have a different thickness with pores that are offset from each other. The design allows flow when the thicker sheet is on the high pressure side, but prevents flow if the pressure gradient is reversed. Flow through the membrane is studied for a pressure range of 0.01–0.1 m H2O in forward flow to understand the complex fluid motion and dependence of membrane deformation on sheet thickness, downstream pore diameter, and initial gap between the sheets. In forward flow, maximum mass flow rate of 0.2 g s−1 (or flow rate of 12.024 ml min−1) can be obtained at 0.1 m H2O pressure head. Reverse flow conditions are modeled to study the effect of design parameters on the required closing pressure, indicating that as little as 0.0325 m H2O of pressure head is required for closing.

Computational fluid–structure interaction analysis of flapping uvula on aerodynamics and pharyngeal vibration in a pediatric airway

The uvula flapping is one of the most distinctive features of snoring and is critical in affecting airway aerodynamics and vibrations. This study aimed to elucidate the mechanism of pharyngeal vibration and pressure fluctuation due to uvula flapping employing fluid–structure interaction simulations. The followings are the methodology part: we constructed an anatomically accurate pediatric pharynx model and put attention on the oropharynx region where the greatest level of upper airway compliance was reported to occur. The uvula was assumed to be a rigid body with specific flapping frequencies to guarantee proper boundary conditions with as little complexity as possible. The airway tissue was considered to have a uniform thickness. It was found that the flapping frequency had a more significant effect on the airway vibration than the flapping amplitude, as the flapping uvula influenced the pharyngeal aerodynamics by altering the jet flow from the mouth. Breathing only through the mouth could amplify the effect of flapping uvula on aerodynamic changes and result in more significant oropharynx vibration.

Analyses for simulation-based solution of fluid-structure interaction in percutaneous coronary intervention

Fluid-structure interaction (FSI) analysis is of great significance for the clinical practice of percutaneous coronary intervention (PCI). In this study the finite element method (FEM) model of Y-shaped coronary artery is established and the solution methodology of FSI analysis is presented in detail, and then the FSI analyses are performed to get quantities of interest by analyzing the three main effect factors of PCI, thereby to get preferred intervention pattern. The formula to calculate the coefficient of fluctuation δ, is proposed and employed to characterize the oscillation properties of the guide wire (GW) structure. A total of 48 different working condition cases have been simulated numerically using the established method, and a comprehensive analysis on the comparison of variables with different effect factors has been presented. It has been shown that the oscillation phenomena of blood flow force and displacement are found; and, for vascular stenosis, the phenomenon of recirculation is also found for all of the cases at the bifurcation owing to the existence of plaque. For initial observations, the main branch (MB) entry means seems to be one good means, which can be used for initial detection of vascular stenosis or obstruction. For vascular stenosis, three comparisons are made and discussed, and the variation laws can be used to give application guidance. In addition, a trial test has also been performed to indirectly verify the reliability of the simulation results. This work can provide insights useful for the control and setting of catheter/GW operation in PCI, especially for surgical assisted robot.

Hydrodynamic considerations for improving the design/evaluation of over-topped bridge decks during extreme floods

Flow over an Iranian bridge deck is studied under an actual extreme flood event happening similarly nowadays in many countries due to climate change. Rigorous transient fluid-structure interaction analyses using the realizable k-ε turbulence model and the VOF Method are conducted. Geotechnical and abutments damages are neglected. Water surface profiles, velocity vectors, and hydrodynamic coefficients are determined. Based on the latest hydrological regime, particularly in supercritical flows, the results are partially compared against the latest advanced design codes, to evaluate the performance of their hydrodynamic and hydraulic provisions in similar incidents. It was acknowledged that the flood loads recommended by the Federal Highway Administration (FHWA) are fairly acceptable, Eurocode-1 predicts them rather accurately but not in extreme cases, and the Australian Standard (AS-5100.2) is less effective due to over-estimation of the hydrodynamic loads. Instead, the latter offers comprehensive user-defined hydraulic conditions. Furthermore, upon gradual rise of the water level to thrice the deck height, bridge stability is found to be at risk due to highly turbulent states. It is recommended that due to such threats, re-evaluation of flood regime, as well as its distinct hydrodynamic properties have to be accounted for, when evaluating existing bridges or designing new ones.

Parametric model order reduction by machine learning for fluid–structure interaction analysis

An improved nonintrusive parametric model order reduction (pMOR) approach is proposed for the flow field interpolation regarding fluid–structure interaction (FSI) objects. Flow field computation using computational fluid dynamics (CFD) requires excessive computational time and memory. Nonintrusive and data-driven MOR schemes have been proposed to overcome such limitations. The present methodology is implemented by both proper orthogonal decomposition (POD) and a modified Nouveau variational autoencoder (mNVAE). POD attempts to reduce the number of degrees of freedom (DOFs) on the precomputed series of the full-order model parametric result. The reduced DOF yields parametrically independent reduced bases and dependent coefficients. Then, mNVAE is employed for the interpolation of POD coefficients, which will be combined with POD modes for parametrically interpolated flow field generation. The present approach is assessed on the benchmark problem of a two-dimensional plunging airfoil and the highly nonlinear FSI phenomenon of the limit cycle oscillation. The comparison was executed against other POD-based generative neural network approaches. The proposed methodology demonstrates applicability on highly nonlinear FSI objects with improved accuracy and efficiency.

Fluid-structure interaction characteristics of inflatable reentry aeroshell at subsonic speed

Inflatable aeroshells, made of flexible membranes and pressurized inflatable torus, experience significant aerodynamic loads during atmospheric entry. The aerodynamic forces deform the lightweight, flexible membrane, and such deformation changes the flow field, changing the aerodynamic characteristics and increasing the deformation even further. Thus, fluid-structure coupled modeling of these problems is crucial for the reliable performance prediction of such reentry vehicles. This study provides wind tunnel experimental results on subsonic fluid-structure interaction (FSI), focusing on the aeroshell deformation and oscillatory behavior designed to validate coupled simulations. Wind tunnel experiments were conducted using a scaled membrane aeroshell model for subsonic speed. Aerodynamic coefficients, pressures at the rear of the model, and structural vibrations were measured for freestream Mach number of 0.3. A two-way coupled FSI model was set up in a partitioned manner for analyzing detailed distributions of the flow field properties, which was validated by the experimental data. The model was based on the open-source fluid solver OpenFOAM, computational structural solver CalculiX and coupling library preCICE. The present FSI analysis model well reproduced fundamental features such as swing motion, membrane deformation, and the wake in the flow field simulation, which were observed in the experiment. The results indicated that the membrane surface deforms elastically by aerodynamic force caused by the large pressure difference between the front and rear sides of the vehicle. The continuous generation and shedding of the wake vortex caused unsteady behavior in the flow field, followed by the small amplitude oscillation of the aeroshell. An external aerodynamic force caused the oscillation because the frequency of this oscillation did not correspond to that of natural frequencies.

Investigation of the effect of adaptive characteristics on non-cavitating noise for flexible propeller in non-uniform flow via the fluid-structure interaction model

When constructing a low-noise submarine, it is crucial to consider the non-cavitating noise from the propeller. Non-cavitating noise reduction is crucial for submarine stealth and survivability. Recently, several studies have been conducted on the use of flexible propellers as a means of reducing non-cavitating noise. However, there are no studies on the use of flexible propellers with adaptive characteristics to reduce noise in wake fields. Thus, this study investigated the noise reduction effect of adaptive characteristics on non-cavitating noise for the flexible propeller in the wake field. Numerical investigations on the main propeller variables were conducted based on the proposed procedure using fluid-structure interaction and acoustic analysis models. The results were compared with those of rigid propellers to determine the possible reasons for noise reduction. Finally, the acoustic analysis results of the flexible propeller were compared with those of the rigid propeller to reveal the effectiveness of the adaptive characteristics.

Fluid-structure interaction and band gap analysis of periodic composite liquid-filled pipe

This paper studies the vibration band gap characteristics of a liquid-filled composite pipeline. The transfer matrix method is used to create a one-dimensional fluid–structure interaction model of the composite pipeline from the constitutive equation, physical equations, and boundary conditions of the anisotropic material. A phononic crystal pipeline is designed with a periodic arrangement on the axial pipe wall. The method used to analyze the fluid–structure interaction of liquid-filled composite and phononic crystal pipelines is verified by comparing responses with finite-element method results. The results’ agreement demonstrates the method’s and calculation code’s correctness. Furthermore, the band gaps for an empty composite phononic crystal pipe, water hammer, and a liquid-filled pipe are calculated by Bloch vector theory, and the effects of fluid–structure interaction and the composite parameters on the three band gap characteristics are analyzed. The numerical results show that Poisson’s coupling affects the band gap at some frequency points, while the laying angle and fiber volume fraction in the composite pipe influence the band gap length and amplitude change. The research results of this paper provide a reference for the design and vibration control of liquid-filled composite pipelines.

Effect of stresses acting on impeller blades

This paper examines the impact of temperature, pressure, and blade thickness on the stresses experienced by impeller blades during operation. The impeller is subject to a range of stresses arising from thermal, fluid, and mechanical factors that can cause deformation if they exceed certain thresholds. The study focuses on an impeller supplied by HAUS Centrifuge Technologies, which suffered damage while operating at 33000 rpm. Six blade thickness offsets, ranging from 0.05 mm to 0.15 mm, were analyzed structurally, and the Von-Mises stresses were compared to the impeller material yield strength. The impeller with the lowest stress, at 197.43 MPa, was chosen for fluid-structure interaction analysis. The impeller was then manufactured and tested for performance using ISO 5389 standard in HAUS test facility. The CFD results indicated that the polytropic efficiency of the thickened impeller increased to 86.57%, compared to the original impeller polytropic efficiency of 75.8%. However, the volumetric flow decreased from 4211.3 m3 per hour to 3658.3 m3 per hour when using ?the thicker impeller?. The data collected supports the conclusion that an increase in blade thick-ness can help to reduce the stresses acting on the blade.

流体－構造連成解析によるバイブレーションルアーの水中運動再現および構造最適設計

Lure fishing is a well-known type of fishing that uses artificial lures instead of traditional live baits. Vibratory lure is a kind of lures performs greater vibration behavior than other kinds of lures. In common, more excellent vibration behavior of vibrating lure can attract carnivorous fish more efficiently. Up to now, lure design is generally based on the intuition of the designer, and there is little academic research on vibrating lure. In this study, we build the finite element model of a commercial vibration lure using a 3D scanner at first. Then, fluid–structure interaction (FSI) analysis is carried out to reproduce underwater motion of the vibration lure, where we can calculate the frequency of the flow induced vibration (FIV). Finally, in order to obtain the best FIV behavior of the vibration lure, based on the simulation results of FSI analysis, we perform structural design optimization of the vibration lure using the Box-Behnken design method, which belongs to the response surface methodology. In the structural design optimization, we set three design variables, which are the positions (x and z) of the weight placed in the lower part of the lure, and the eye position (i.e., the knot position between fishing line and lure) along the lure body. According to optimal results, the highest frequency of the FIV can reach 6.95Hz. However, the present work is still in the early stage of the academic research on lure design, we aim to develop more optimization method for lure design that make lure fishing more interesting for both beginners and anglers.

Fluid-Structure Interaction Analysis of Carotid Artery Blood Flow with Machine Learning Algorithm and OpenFOAM

In this study, a patient-specific carotid artery model was analyzed with an open source program foam-extend. The research includes the effect of arterial wall deformation by fluid-structure analysis. Pulsatile velocity cycle is trained for 144 patients with different hemodynamic parameters, by machine learning algorithm using blood flow velocity measured from 337 points of the carotid artery. Data used for training is obtained from an open source in the literature. Here, the machine learning algorithm was created by the help of an open source code Phyton. Then, using trained values of machine learning, and the known systole and diastole blood pressures for a specific chosen patient, the patient-specific pulsatile velocity cycle was estimated. The estimated pulsatile velocity cycle was then fitted to Fourier series. This pulsatile velocity cycle is used as the input boundary condition for the model analyzed in foam-extend. The outlet boundary condition, pulsatile pressure cycle is found by 4-Element Windkessel algorithm. Wall shear stresses and time averaged wall shear stresses were obtained for both the rigid and fluid structure interaction models, and variation of displacement throughout the pulsatile cycle was found for the FSI model. Wall shear stresses, velocity, and displacements were obtained high at peak systole, consistent with pulsatile cycles. Like the wall shear stresses, the time averaged wall shear stresses for the FSI model were also found lower than the rigid model. The wall shear stresses showed an increase towards the exit of internal and external carotid artery.