Fluid-structure Interaction Results Research Articles

Prediction of performance parameters of a hermetic reciprocating compressor applying an artificial neural network

The efficiency of the compressor's thermodynamic, mechanical, and electric motors can be increased by minimizing their losses. Based on the design characteristics of the compressor, the current study proposes an artificial neural network (ANN) model to forecast the mass flow rate, cooling capacity, compression power, and discharge line loss of the hermetic reciprocating compressor as outputs. This study uses experimental and numerical results obtained by the fluid–structure interaction (FSI) method, and the whole findings are used as inputs for the machine learning method. Using 36 numerical and 3 experimental data sets, a multilayer network is created with input parameters defining mass flow rate, cooling capacity, compression power, and discharge line energy loss. The input parameters for the network model are the compressor's design parameters, which include the compressor speed, discharge valve thickness, and discharge valve length. When comparing the experimental and FSI methods for compressor speeds of 1300, 2100, and 3000 rpm, the FSI study's mass flow rate and cooling capacity parameters converged at 11.9%, 9.1%, and 9.3%, respectively, to their actual values. The convergence rate to experimental compression power data was −0.3%, 2.6%, and 11%. The numerical-experimental deviation for discharge line energy losses is 14.9%, −3.6%, and 7.8%, respectively, for 1300, 2100, and 3000 rpm. With the Levenberg–Marquardt (LM) ANN model, which is used in this study, the average squared error value is calculated as 1.75E-02 and the R2 value is calculated as 0.99976. ANN model can predict outputs with average deviation rates of less than 0.88%. It is seen that results obtained with the ANN method provide high convergence on the experimental and FSI results, while the results obtained with the regression model deviate from the compressor exhaust line results by more than ±20%, and the ANN method is more successful than regression.

Geometric deformation prediction of a centrifugal impeller considering welding distortion and fluid-structure interaction

An impeller serves in a centrifugal fan, pushes the surrounding air and in turn reacts on itself. The fluid-to-structure response and part welding distortion during the fabrication and working processes will cause the impeller to deform and reduce fan performance. This work develops a numerical simulation approach and focuses on two essential factors: welding distortion and distortion induced by fluid to structure interaction. The research target was an impeller comprising five thin-plate curved fillet joints, and its total distortion was predicted using the proposed approach. First, the structure of the impeller was modeled with solid elements, and each welded local joint's welding distortion was measured with a modified inherent strain method. A one-way fluid-structure coupling analysis carefully examined the distortion induced by Fluid-Structure Interaction (FSI) from the fluid medium and coupling surfaces. Then, an interpolation method was conducted to compute the welding and FSI distortion contours using a simple structural analysis. To determine the inherent strain in a curved and non-curved fillet joint, a detailed transient analysis by the Thermal Elastic Plastic (TEP) Finite Element Method (FEM) and their welding distortion, plastic strain distribution, and inherent deformation are discussed. The welding and flow field tests both agree with the simulation results, confirming the modified inherent strain method and relevant FSI results. Thus, the developed approach can provide a suitable reference for controlling distortion in welded fans and related fluid machinery.

Influence of Rigid-Elastic Artery Wall of Carotid and Coronary Stenosis on Hemodynamics.

Cardiovascular system abnormalities can result in serious health complications. By using the fluid-structure interaction (FSI) procedure, a comprehensive realistic approach can be employed to accurately investigate blood flow coupled with arterial wall response. The hemodynamics was investigated in both the coronary and carotid arteries based on the arterial wall response. The hemodynamics was estimated based on the numerical simulation of a comprehensive three-dimensional non-Newtonian blood flow model in elastic and rigid arteries. For stenotic right coronary artery (RCA), it was found that the maximum value of wall shear stress (WSS) for the FSI case is higher than the rigid wall. On the other hand, for the stenotic carotid artery (CA), it was found that the maximum value of WSS for the FSI case is lower than the rigid wall. Moreover, at the peak systole of the cardiac cycle (0.38 s), the maximum percentage of arterial wall deformation was found to be 1.9%. On the other hand, for the stenotic carotid artery, the maximum percentage of arterial wall deformation was found to be 0.46%. A comparison between FSI results and those obtained by rigid wall arteries is carried out. Findings indicate slight differences in results for large-diameter arteries such as the carotid artery. Accordingly, the rigid wall assumption is plausible in flow modeling for relatively large diameters such as the carotid artery. Additionally, the FSI approach is essential in flow modeling in small diameters.

Fluid–structure interaction of human nasal valves under sniff conditions and transport of inhaled aerosols: A numerical study

The nasal valve is the narrowest part of the nasal airway which is responsible for the largest part of the nasal resistance. Even little changes in the aperture can affect the flow downstream through the nose significantly. Its principal function is to limit airflow for example during a rapid and short inhalation, also called a sniff. Coupling Computational Fluid Dynamics (CFD) with Fluid–Structure Interaction (FSI) allows solving and exchanging force and displacement between the solid and fluid domains and offers a more accurate representation of the physical system in confined flow cases. Furthermore, particle transport and deposition are performed in this study to reveal the effect of the complex coupling on the nasal cavity deposition of inhaled aerosols. Two different configurations are used to model the nasal valve and differences in magnitudes in deformations are observed during the sniff. A comparison between FSI results and the in-vivo evaluation of the deformation shows an acceptable agreement as to the first step of validation. In addition, the results demonstrated that FSI increases significantly the particle deposition in the nasal cavity and the micro-particle diameter is the critical range parameter to enhance deposition with nasal valve deformation during a sniff.

Numerical study on gust energy harvesting with an efficient modal based fluid-structure interaction method

Gust disturbance during flight causes elastic vibrations and rigid body motions of an aircraft. A macro fiber composite (MFC)-based energy harvester can be used to obtain energy from gust-induced vibrations. This paper aims to present an efficient fluid-structure interaction (FSI) method for fast and accurate calculation of gust response and harvested energy of a fly wing aircraft half model. In this method, computational fluid dynamics (CFD) and computational structural dynamics (CSD) are coupled by embedding a modal-superposition-based structural solver into the CFD solver. Parallel data exchange and interpolation strategy on the fluid-structure interface is introduced to improve the computational efficiency. MFC harvester is modeled by a piezoelectric beam model, and the displacement of the piezoelectric beam is obtained by interpolation from FSI results. The numerical results of gust response and MFC voltage output are in good accordance with wind tunnel test results, while the calculation time is only 1/8 of the time consuming of a direct CFD/CSD coupling method. The influences of gust frequency, gust amplitude, freestream velocity, and the number of retained modes on energy harvesting are investigated. Results indicate that the accuracy of the calculation can be guaranteed by the superposition of several retained modes, and the additional suction provided by leading-edge vortices causes a nonlinear increase in energy harvesting near the stalling angle of attack.

Theoretical modeling and experimental investigation of a V-Shaped traveling wave piezoelectric transducer for ultrasonic cavitation Peening: Part B

In industrial applications, the highly stressed axial components are easily damaged by cyclic loads if their surfaces are not enhanced, since cracks and stress concentrations occur on the cylindrical components after turning. By the peening processes, the residual tensile stress can be removed and the surface hardness can be increased, thereby increasing the tool life. Compared to other peening processes, ultrasonic cavitation peening is a potential method to achieve surface processing of metal specimens and attracted much attention, since fewer polluting effluents are produced, with the exception of metal oxide powder that can be easily collected and recycled. Additionally, this method is cheap to perform and there are no thermal effects. In this project, we proposed a V-shaped traveling wave piezoelectric vibrating system for the ultrasonic cavitation peening to achieve an even performance on a cylindrical surface upon single treatment. The transfer matrix modeling and the cavitation field have already been investigated. In the investigations of the ultrasonic cavitation field, only the radial vibration in the inner surface of the ring sonotrode was considered and studied. However, the effects of the tangential vibration on the cavitation intensity and distribution as well as the mechanical properties of the workpiece surfaces are important to evaluate the performances of the proposed V-shaped transducer. In this paper, the numerical simulation of fluid–structure interaction (FSI) was investigated by first using the finite element method, considering liquid pressure, liquid flow velocity and vapor volume fraction. Then, the liquid flow velocity was measured using the color tracer method to validate the FSI results. Finally, the treatments for cylindrical workpieces using ultrasonic cavitation peening were conducted, and the performances of the treatments were evaluated by means of micro-hardness and surface roughness. The results show that the roughness of the cylindrical workpiece surfaces did not increase significantly, but micro hardness increased by as high as 54%.

Using Autoregressive with Exogenous Input Models to Study Pulsatile Flows

The content of this paper shows the first outcomes of a supplementary method to simulate the behavior of a simple design formed by two rectangular leaflets under a pulsatile flow condition. These problems are commonly handled by using Fluid-Structure Interaction (FSI) simulations; however, one of its main limitations are the high computational cost required to conduct short time simulations and the vast number of parameter adjustments to simulate different scenarios. In order to overcome these disadvantages, we propose a system identification method with hereditary computation—AutoRegressive with eXogenous (ARX) input method—to train a model with FSI simulation outcomes and then use this model to simulate the outputs that are commonly measured from this kind of simulation, such as the pressure difference and the opening area of the leaflets. Numerical results of the presented methodology show that our model is able to follow the trend with significant agreement with the FSI results, with an average correlation coefficient R of Rtr=90.14% and Rtr=92.27% in training; whereas for validation, the average R is Rval=93.31% and Rval=83.08% for opening area and pressure difference, respectively. The system identification model is efficiently capable of estimating the outputs of the FSI approach; however, it is not intended to substitute FSI simulations, but to complement them when the requirement is to conduct many repetitions of the phenomena with similar conditions.

Fluid structure interaction studies of human airways

Study of flow characteristics of human airways using Fluid-Structure Interaction (FSI) analysis is very important in the context of prognosis, diagnostic and treatment of respiratory diseases. The present study is focused on effect of elasticity on the respiratory wall during inhalation. Airflow in Computed Tomography (CT) scan model with rigid and compliant airway walls is studied. FSI technique is used to simulate the airflow in the model. The comparison for the two different respiratory models (rigid and compliant) shows that FSI technique brings out more realistic results as compared to Computational Fluid Dynamics (CFD) analysis. It is found that respiratory wall elasticity affects the different flow parameters (pressure, wall shear stress, etc.) at different location of the model. Wall shear stress (WSS) and airway pressure were decreased due to flexibility effect of the airway wall. This will help medical practitioners to correlate the clinical assessment with this FSI results.

Experimental and numerical analysis of a multilayer composite ocean current turbine blade

Ocean environmental corrosion and mechanical load vibration introduce considerable negative effects caused by the fluid-structure-environment interaction. A new design scheme for a blade with salinity corrosion resistance and mechanical fatigue resistance is proposed, based on numerical simulation and fatigue tests. The one-way fluid-structure interaction (FSI) model for an ocean current turbine blade was established and calculated by a computational fluid dynamics (CFD) solver and finite element method (FEM) solver. According to the FSI results, the maximum equivalent stress and deformation in extreme operating conditions are found to be within material and structural limits. On this basis, an aluminum alloy/nano particles reinforced polypropylene multilayer composite blade was designed and fatigue tested. The results show that an obvious crack-resistance effect exists within a certain stress range, and there is basically no change in the fatigue crack growth rates of NPRP in the four environmental fatigue tests. The multilayer composite blades with immersion pretreatment can stand 1 × 107 cycles of fatigue tensile loads and torque loads without failure. The results provide specific theoretical guidance for the optimization of the structural design of ocean current turbine blade in ocean environment.

Evaluation of 4D flow MRI-based non-invasive pressure assessment in aortic coarctations

Severity of aortic coarctation (CoA) is currently assessed by estimating trans-coarctation pressure drops through cardiac catheterization or echocardiography. In principle, more detailed information could be obtained non-invasively based on space- and time-resolved magnetic resonance imaging (4D flow) data. Yet the limitations of this imaging technique require testing the accuracy of 4D flow-derived hemodynamic quantities against other methodologies.With the objective of assessing the feasibility and accuracy of this non-invasive method to support the clinical diagnosis of CoA, we developed an algorithm (4DF-FEPPE) to obtain relative pressure distributions from 4D flow data by solving the Poisson pressure equation. 4DF-FEPPE was tested against results from a patient-specific fluid-structure interaction (FSI) simulation, whose patient-specific boundary conditions were prescribed based on 4D flow data. Since numerical simulations provide noise-free pressure fields on fine spatial and temporal scales, our analysis allowed to assess the uncertainties related to 4D flow noise and limited resolution.4DF-FEPPE and FSI results were compared on a series of cross-sections along the aorta. Bland-Altman analysis revealed very good agreement between the two methodologies in terms of instantaneous data at peak systole, end-diastole and time-averaged values: biases (means of differences) were +0.4 mmHg, −1.1 mmHg and +0.6 mmHg, respectively. Limits of agreement (2 SD) were ±0.978 mmHg, ±1.06 mmHg and ±1.97 mmHg, respectively. Peak-to-peak and maximum trans-coarctation pressure drops obtained with 4DF-FEPPE differed from FSI results by 0.75 mmHg and −1.34 mmHg respectively. The present study considers important validation aspects of non-invasive pressure difference estimation based on 4D flow MRI, showing the potential of this technology to be more broadly applied to the clinical practice.

Multi-fidelity fluid–structure interaction analysis of a membrane blade concept in non-rotating, uniform flow condition

Abstract. In order to study the aerodynamic performance of a semi-flexible membrane blade, fluid–structure interaction simulations have been performed for a non-rotating blade under steady inflow condition. The studied concept blade has a length of about 5 m. It consists of a rigid mast at the leading edge, ribs along the blade, tensioned edge cables at the trailing edge and membranes forming the upper and lower surface of the blade. Equilibrium shape of membrane structures in the absence of external loading depends on the location of the supports and the prestresses in the membranes and the supporting edge cables. Form-finding analysis is used to find the equilibrium shape. The exact form of a membrane structure for the service conditions depends on the internal forces and also on the external loads, which in turn depend on the actual shape. As a result, two-way coupled fluid–structure interaction (FSI) analysis is necessary to study this class of structures. The fluid problem has been modelled using two different approaches, which are the vortex panel method and the numerical solution of the Navier–Stokes equations. Nonlinear analysis of the structural problem is performed using the finite-element method. The goal of the current study is twofold: first, to make a comparison between the converged FSI results obtained from the two different methods to solve the fluid problem. This investigation is a prerequisite for the development of an efficient and accurate multi-fidelity simulation concept for different design stages of the flexible blade. The second goal is to study the aerodynamic performance of the membrane blade in terms of lift and drag coefficient as well as lift-to-drag ratio and to compare them with those of the equivalent conventional rigid blade. The blade configuration from the NASA-Ames Phase VI rotor is taken as the baseline rigid-blade configuration. The studied membrane blade shows a higher lift curve slope and higher lift-to-drag ratio compared with the rigid blade.

A beam-membrane structure micromachined differential pressure flow sensor

A beam-membrane structure micromachined flow sensor is designed, depending on the principle of differential pressure caused by the mass flow, which is directly proportional to the square flow rate. The FSI (fluid structure interaction) characteristics of the differential pressure flow sensor are investigated via numerical analysis and analog simulation. The working mechanism of the flow sensor is analyzed depending on the FSI results. Then, the flow sensor is fabricated and calibrated. The calibration results show that the beam-membrane structure differential pressure flow sensor achieves ideal static characteristics and works well in the practical applications.

Design and fluid–structure interaction analysis of a micromachined cantilever‐based differential pressure flow sensor

A micromachined cantilever-based flow sensor is designed based on differential pressure. Numerical analysis and analogue simulation are used to investigate the FSI (fluid–structure interaction) characteristics of the differential pressure flow sensor. The FSI model is created using the hydromechanics and elastic mechanics, and a systematic theory is established to complete the numerical analysis. Then the working mechanism of the flow sensor is analysed depending on the FSI results. The analogue simulation is undertaken by the commercial software FLUENT and ANSYS. The result of the numerical analysis is similar to that of the analogue simulation. Considering the results of the numerical analysis and the analogue simulation, the shape and size of the flow sensor are optimised. Moreover, the optimised flow sensor is fabricated and calibrated. The calibration results show that the cantilever-based differential pressure flow sensor achieves ideal static characteristics and works well in practical applications.

Effects of wall distensibility in hemodynamic simulations of an arteriovenous fistula

Arteriovenous fistulae are created surgically to provide adequate access for dialysis patients suffering from end-stage renal disease. It has long been hypothesized that the rapid blood vessel remodeling occurring after fistula creation is in part a process to restore the mechanical stresses to some preferred level, i.e., mechanical homeostasis. The current study presents fluid-structure interaction (FSI) simulations of a patient-specific model of a mature arteriovenous fistula reconstructed from 3D ultrasound scans. The FSI results are compared with previously published data of the same model but with rigid walls. Ultrasound-derived wall motion measurements are also used to validate the FSI simulations of the wall motion. Very large time-averaged shear stresses, 10-15 Pa, are calculated at the fistula anastomosis in the FSI simulations, values which are much larger than what is typically thought to be the normal homeostatic shear stress in the peripheral vasculature. Although this result is systematically lower by as much as 50% compared to the analogous rigid-walled simulations, the inclusion of distensible vessel walls in hemodynamic simulations does not reduce the high anastomotic shear stresses to "normal" values. Therefore, rigid-walled analyses may be acceptable for identifying high shear regions of arteriovenous fistulae.

Design and In Vitro Assessment of an Improved, Low-Resistance Compliant Thoracic Artificial Lung

Current thoracic artificial lungs (TALs) have blood flow impedances greater than the natural lungs, which can result in abnormal pulmonary hemodynamics. This study investigated the impedance and gas transfer performance of a compliant TAL (cTAL). Fluid-structure interaction analysis was performed using ADINA (ADINA R&D Inc., Watertown, MA) to examine the effect of the inlet and outlet expansion angle, θ, on device impedance and blood flow patterns. Based on the results, the θ = 45° model was chosen for prototyping and in vitro testing. Glycerol was pumped through this cTAL at 2, 4, and 6 L/min at 80 and 100 beats/min, and the zeroth and first harmonic impedance moduli, Z(0) and Z(1), were calculated. Gas transfer testing was conducted at blood flow rates of 3, 5, and 7 L/min. Fluid-structure interaction results indicated that the 45° model had an ideal combination of low impedance and even blood flow patterns and was thus chosen for prototyping. In vitro, Z(0) = 0.53 ± 0.06 mm Hg/(L/min) and Z(1) = 0.86 ± 0.08 mm Hg/(L/min) at 4 L/min and 100 beats/min. Outlet PO(2) and SO(2) values were above 200 mm Hg and 99.5%, respectively, at each flow rate. Thus, the cTAL had lower impedance than hard shell TALs and excellent gas transfer.

Investigation of unsteady flow-induced impeller oscillations of a single-blade pump under off-design conditions

The periodically unsteady flow-induced impeller oscillations for a single-blade pump are investigated both numerically and experimentally under off-design conditions. A partitioned strategy with load transfer method is selected for achieving successful fluid–structure interaction (FSI) simulations with strong two-way coupling. Three-dimensional, unsteady Reynolds-averaged Navier–Stokes equations are solved with a shear stress transport turbulence model for the fluid side, while a transient structure dynamic analysis with the finite element method is employed for the structure side. Radial deflections of the pump impeller are successfully measured using proximity sensors to validate the FSI results. The comparison of the deflection results focuses on both phase and amplitude aspects under different operational conditions. The FSI calculation results are confirmed by the experiment, but deviations are still observed for about half of an impeller rotation. Therefore, a rigorous analysis of the comparison between the angles of the obtained x and y components is carried out to understand the cause of the deviation. Meanwhile, the transient pressure measured at the casing by both computational fluid dynamics and experimental methods is qualitatively analyzed. Furthermore, hydrodynamic forces are also analyzed considering a strong FSI effect in both the rotating and stationary coordinate frame under off-design conditions to understand the behavior of the transient excitation forces, which directly lead to the rotor deflection.