Computational Fluid-structure Interaction Research Articles

Multi-objective optimization design method of marine propeller based on fluid-structure interaction

To improve the quality and efficiency of propeller design and obtain the best design scheme of the propeller, an integrated automatic optimization design method of propeller is proposed by combining Fluid-Structure Interaction (FSI), Design of Experiment (DoE), and Non-dominated Sorting Genetic Algorithm II (NSGA-II). FSI calculation method instead of hydrodynamic calculation can make the propeller performance calculation more accurate. Sobol algorithm is used for DoE, the correlation between propeller parameters and the objective function is analyzed to obtain propeller sensitive parameters. The sensitive parameters are optimized by NSGA-II to obtain the best design scheme. Under the requirements of ensuring the thrust coefficient and structural strength of the propeller, the radial distribution of the skew, chord length, pitch, and camber is optimized, and finally, a design scheme with higher efficiency, larger thrust, and safer structure is obtained. Take the KP505 propeller as an example. The results show that the design method has higher efficiency and a wider solution set range, which is more suitable for practical engineering applications.

Effect of Incident Angle of Wear-Ring Clearance on Pressure Pulsation and Vibration Performance of Centrifugal Pump

A wear-ring is an important part of the centrifugal pump. The leakage flow in the wear-ring clearance and main flow at the impeller inlet form crossed mixed flows perpendicular to each other. Large eddies and shocks are produced at the intersection of the two flows due to great velocity difference and different directions, resulting in flow losses, unsteady flow, and even flow-induced vibration. Consequently, the pump performance, pressure pulsation and vibration, and other characteristics will be greatly affected. In this paper, 5 incident angles between the incident section of the wear-ring clearance and the circumferential direction of impeller inlet, i.e., the original angle (90°), 75°, 60°, 45°, and 30°, were formed with a low-specific-speed centrifugal pump as the study object. Unsteady flow calculation and fluid–structure interaction calculation were performed on centrifugal pumps with different wear-ring clearances; the effect of the incident angle of the wear-ring clearance on the distribution of pressure pulsation and vibration performance of centrifugal pump was analyzed. The results showed that the improved efflux angle of the wear-ring clearance could effectively weaken the impact disturbance of the leakage flow in the wear-ring clearance to the main flow at the inlet. Accordingly, the flow status at the inlet of the centrifugal pump was improved, flow losses were reduced, the efficiency of the centrifugal pump was improved, and the vibration amplitude and vibration energy of the pump were also reduced.

A Comparison Between Experimental Life Road Simulation and Computational Fluid Dynamics and Fluid Structure Interaction for Sedan Car

The flow around road vehicle is characterized by regions of separation that affect the aerodynamics and performance of the vehicle due to the variations in the negative pressure zones. In this work, Computational fluid dynamics and Fluid-structure interaction models are developed to simulate the aerodynamic performance of a sedan car. An experimental live road simulation is conducted to validate the performance and the accuracy of the presented models. The experimental setup was organized on a sedan car using tufts and digital cameras for flow visualization. Four cruise speeds of 40, 60, 80, and 100 km/hr are used. At low cruise speed the FSI simulation can attain the required result for indicating the negative pressure zones, created behind the car tail and mostly close to the car body. The experimental results appear to visualize the movement of the tufts that attained a certain angle corresponding to the flow speed, which matches the distribution of negative pressure and wake area. At high cruise speed the CFD simulation elucidated the separation area where the negative pressure created behind the car tail matched the movement of the tufts which attained an approximate straight angle corresponding to the flow speed having a swirling movement.

Hydrokinetic power scavenging from galloping phenomenon with two juxtaposed bluff bodies

A numerical investigation is performed on the flow-induced vibrations (FIVs) of two coupled cylinders with various cross-sections and their performance on power scavenging. The shear stress transport (SST) k - ω turbulence model is employed to study the turbulent conditions. The center distance ratio (l*) values of cylinders are divided into four cases (1.5D, 2D, 2.5D, and 3D) for comparative analysis. The results demonstrate that the reduced velocity and Reynolds number play key roles in the wake motion and dynamic responses of the coupled system. It has also been proven that the square-based cylinder system exhibits galloping without the presence of any vortex-induced vibration through four benchmarks of computational fluid-structure interaction (FSI) models. Considering the coupled square and circular cylinder system, the results indicate that depending on the distance between the two connected cylinders, the Reynolds number and the reduced velocity have a significant influence on the dynamics and efficiency of the system. Additionally, galloping dominants for all considered distances between the square and circular cylinders.

Fluid–structure interaction with ALE formulation and skeleton-based structural models

This paper presents a fluid–structure interaction (FSI) framework that combines an Arbitrary Lagrangian–Eulerian (ALE) formulation with skeleton-based structural models consisting of force-based frame elements. For the first time in literature, a methodology is proposed to enable coupling between fluid and force-based frame elements through an ALE formulation. In the proposed methodology, communication between the fluid and skeleton-based domains is performed through a geometric model of the physical fluid–structure interface. With the use of force-based frame elements, the intent is to perform accurate FSI calculations in cases where axial, flexure, and shear motions dominate the structural responses. The proposed framework is evaluated against FSI problems involving steady and unsteady incompressible laminar flows and different structural models representing horizontal (beam) and vertical (column) solid members.

Investigation on runner resonance and fatigue life of a high–head pump–turbine

The structural stability and fatigue of the runner of a high-head pump-turbine was explored by conducting a numerical simulation of the entire flow passage under different working conditions. A two-way fluid-structure interaction calculation method was used, which captured the values for 5.75 fn, 9 fn, 13 fn, 18 fn, and 20 fn ( fn is rotational frequency) in pressure fluctuation. The resonance of the runner was compared with the results of the modal analysis. The rain flow and damage accumulation methods were used to predict the fatigue life. The study found that the 13 fn pressure fluctuation of the fluid in the flow passage of the pump-turbine is the primary cause of the resonance of the runner blade. The main frequency of vibration is the third natural frequency of the runner. The vibration form is up and down along the Z–axis, and there are some high-order resonances. The most vulnerable part of the entire runner is located at the T-shaped connection between the blade inlet edge and the runner crown and bottom ring. The excitation force under the small flow condition is more complicated than that under the large flow condition, which is more likely to cause fatigue damage to the runner. In addition, the damage extent of the high-stress amplitude to the runner is obviously greater than the influence of the number of stress cycles, accounting for approximately 60% of the total damage. The research results can provide a reference for the operational stability and life prediction of a high-head pump-turbine runner.

Computational Investigation of a Novel Box-Wing Aircraft Concept

With regard to the current needs for greener aviation, this study focuses on a novel concept of Box-Wing Aircraft (BWA). Labelled SmartLiner (BWA/SL), this conceptual aircraft comes as a triplane comprising backward and forward swept wings. The aerodynamic performance and structural characteristics of this BWA/SL aircraft are here explored through numerical simulation, using Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI). The computational approach is first validated using NASA’s Common Research Model (CRM) aircraft, which is then taken as a reference solution against which to compare the aero-structural merits of the BWA/SL concept. Results show that, although its design is still preliminary and lacks optimization, the BWA/SL aircraft exhibits very decent aerodynamic performance, with higher lifting capacities and a reasonable lift-to-drag ratio. Moreover, thanks to the closed frame of its peculiar planform, it demonstrates superior structural characteristics, including under extreme loading scenarios. Based on this preliminary analysis and considering the room left for its further optimization, this conceptual aircraft thus appears as a potentially promising alternative for the development of more environmentally friendly airliners.

Laplacian-perturbed Lagrange-multiplier formulation for fluid-structure interaction

This paper presents a stabilized Lagrange-multiplier formulation for Euler-Lagrange type fluid-structure interaction (FSI) computations. The formulation adds a Laplacian perturbation term to the multiplier equation to relax over-constraint condition caused by the multimer formulation. The over-constraint occurs when the Euler mesh for fluid computation is finer than Lagrange meshes for structures around the FSI interfaces. We show a two-dimensional computation that demonstrates relaxation effect of the proposed method.

Abstract 12166: Biomechanical Impact of Valve Sparing Procedure Onto the Native Aorta, a Multi-Patient in silico Study

Introduction: Ascending thoracic aortic aneurysms (TAA) provide a nidus for dissection, which can be prevented by surgical prosthetic graft replacement. Grafts eliminate risk in resected regions, but are stiffer than native aortic tissue and can thus alter downstream hemodynamics. This study used computational modeling of fluid structure interaction (FSI) to study biomechanical impact of proximal aortic graft replacement on the descending aorta. Methods: TAA pts undergoing cardiac MRI (CMR) prior to and after valve sparing proximal aortic graft replacement (VSR) surgery were studied via FSI. Patient-specific anatomy was reconstructed by segmentation of 3D MR angiography. 4D flow was used to prescribe velocity at the inlet of the model and to define three-elements Windkessel parameters used to impose outlet boundary conditions. Results: FSI models were constructed in 5 male patients (61±10.6 years old) who underwent CMR pre (1.7±1.5 weeks) and post (28.5±2.3 weeks) proximal aortic graft replacement. Qualitative and quantitative comparison of numerical results with 4D-flow data confirmed FSI model’s ability to reproduce patients’ fluid-dynamics (mean RRMSE 0.244±0.059). Regarding post-operative hemodynamics, a post-operative oscillatory shear index (OSI) increment (Pt1: p-value < 0.05) and systolic peak wall shear stress (WSS) variation (Pt1: p-value <0.001, Pt3: <0.01, Pt5: <0.0001) were observed, particularly in proximal descending aorta ( Fig 1 ). Furthermore, from 9 to 63% post-operative distensibility increment was detected. Finally, a mean 4% principal strain intensification was noticed at graft’s suture site if compared to the native portion of the ascending aorta ( Fig 1 ). Conclusion: Computational FSI modeling analysis demonstrates VSR technique to alter downstream biomechanics, including wall shear stress variation and increased strain immediately distal to grafted territories.

Computational NX Fluid Structure Interaction (FSI) analysis on naval three way ball valve

This article represents the continuation of a study that was presented in another paper using the NX Siemens CAD program and FSI (fluid structure interaction analysis) for a complex valve encountered in the naval domain, a ball valve known as (three way ball valve -TWB). In designing of this valve presented in the previous work, some drawings (sketches) of the component parts presented in engineering guidelines were used, all dimensions being determined by the author. In the FSI analysis the same NX Siemens program was used to discretize the solid bodies of the valve coming into contact with the fluid, materials were chosen for these bodies, boundary conditions were set and the pressure field exerted by the fluid on the solid bodies was imported. Finally a series of conclusions were drawn about the speeds, pressures of the fluid and how they are distributed on the walls of the valve, determining the so-called structural analysis “fluid structure interaction”.

Dense flow field interpolations from PTV data in the presence of generic solid boundaries

Three-dimensional flow measurements by Particle Tracking Velocimetry (PTV) provide scattered flow information, that often needs to be interpolated onto a regular grid. Therefore, the use of experimental data assimilation approaches such as VIC+ (Schneiders and Scarano, 2016) were proposed to enhance the instantaneously available spatial resolution limits beyond that of the PTV measurements. Nevertheless, there exists no prior attempt to perform the data assimilation when the flow is in direct contact with physical objects. Thus, in order to handle generic solid body intrusions within the flow fields of VIC+ application, the utilization of Arbitrary Lagrangian-Eulerian and immersed boundary treatment approaches of the computational fluid-structure interaction (FSI) frameworks are proposed. The introduced variants over the standard VIC+ are assessed with a high fidelity numerical test case of flow over periodic hills. The accuracy superiority of the flow field reconstructions with the proposed approaches are denoted especially in close proximity of the interaction surface. An experimental application of the introduced methods is demonstrated to compute the pressure distribution over an unsteadily moving elastic membrane surface, revealing the time-resolved interaction between the flow structures and the membrane deformations.

Study on Fluid-Structure Interaction of Flexible Membrane Structures in Wind-Induced Vibration

A strongly coupled monolithic method was previously proposed for the computation of wind-induced fluid-structure interaction of flexible membranous structures by the authors. How to obtain the accurate solution is a key issue for the strongly coupled monolithic method. Projection methods are among the commonly used methods for the coupled solution. In the work here, to impose initial pressure boundary conditions implicitly defined in the original momentum equations in classical projection methods when dealing with large-displacement of membranous structures, a modified factor is introduced in corrector step of classical projection methods and a new modified projection method is obtained. The solution procedures of the modified projection method aimed at strongly coupled monolithic equations are given, and the related equations are derived. The proposed method is applied to the computation of a two-dimensional fluid-structure interaction benchmark case and wind-induced fluid-structure interaction of a three-dimensional flexible membranous structure. The performance and efficiency of the modified projection method are evaluated. The results show that the modified projection methods are valid in the computation of wind-induced fluid-structure interaction of flexible membranous structures, with higher accuracy and efficiency compared with traditional methods. The modified value has little effects on the computation results whereas iteration times has significant effects. Computation accuracy can be improved greatly by increasing iteration times with less increase in computation time and little effects on stability with the modified projection method.

Neuromechanical wave resonance in jellyfish swimming

For organisms to have robust locomotion, their neuromuscular organization must adapt to constantly changing environments. In jellyfish, swimming robustness emerges when marginal pacemakers fire action potentials throughout the bell's motor nerve net, which signals the musculature to contract. The speed of the muscle activation wave is dictated by the passage times of the action potentials. However, passive elastic material properties also influence the emergent kinematics, with time scales independent of neuromuscular organization. In this multimodal study, we examine the interplay between these two time scales during turning. A three-dimensional computational fluid-structure interaction model of a jellyfish was developed to determine the resulting emergent kinematics, using bidirectional muscular activation waves to actuate the bell rim. Activation wave speeds near the material wave speed yielded successful turns, with a 76-fold difference in turning rate between the best and worst performers. Hyperextension of the margin occurred only at activation wave speeds near the material wave speed, suggesting resonance. This hyperextension resulted in a 34-fold asymmetry in the circulation of the vortex ring between the inside and outside of the turn. Experimental recording of the activation speed confirmed that jellyfish actuate within this range, and flow visualization using particle image velocimetry validated the corresponding fluid dynamics of the numerical model. This suggests that neuromechanical wave resonance plays an important role in the robustness of an organism's locomotory system and presents an undiscovered constraint on the evolution of flexible organisms. Understanding these dynamics is essential for developing actuators in soft body robotics and bioengineered pumps.

Fluid-Structure Interaction Analyses of Biological Systems Using Smoothed-Particle Hydrodynamics.

Simple SummaryComputational simulations of biological systems are an intrinsic element of engineering in medicine, allowing physicians the ability to visualize the pathophysiology behind a disease. Many biomedical applications require fluid–structure interaction analyses. This paper provides a review of fluid–structure interaction methods using smoothed-particle hydrodynamics to analyze the dynamics of biological processes.Due to the inherent complexity of biological applications that more often than not include fluids and structures interacting together, the development of computational fluid–structure interaction models is necessary to achieve a quantitative understanding of their structure and function in both health and disease. The functions of biological structures usually include their interactions with the surrounding fluids. Hence, we contend that the use of fluid–structure interaction models in computational studies of biological systems is practical, if not necessary. The ultimate goal is to develop computational models to predict human biological processes. These models are meant to guide us through the multitude of possible diseases affecting our organs and lead to more effective methods for disease diagnosis, risk stratification, and therapy. This review paper summarizes computational models that use smoothed-particle hydrodynamics to simulate the fluid–structure interactions in complex biological systems.

Reprint of: Fluid-structure interaction modeling of blood flow in the pulmonary arteries using the unified continuum and variational multiscale formulation

In this work, we present a computational fluid-structure interaction (FSI) study for a healthy patient-specific pulmonary arterial tree using the unified continuum and variational multiscale (VMS) formulation we previously developed. The unified framework is particularly well-suited for FSI, as the fluid and solid sub-problems are addressed in essentially the same manner and can thus be uniformly integrated in time with the generalized-α method. In addition, the VMS formulation provides a mechanism for large-eddy simulation in the fluid sub-problem and pressure stabilization in the solid sub-problem. The FSI problem is solved in a quasi-direct approach, in which the pressure and velocity in the unified continuum body are first solved, and the solid displacement is then obtained via a segregated algorithm and prescribed as a boundary condition for the mesh motion. Results of the pulmonary arterial FSI simulation are presented and compared against those of a rigid wall simulation.

Computational fluid-structure interaction of a restrained ogive-cylindrical body with a blunt elliptical base at a high incidence

The fluid-structure interaction of an elastically restrained inclined tangent ogive-cylindrical body with a blunt elliptical base is investigated numerically. The flow is three-dimensional, compressible, and laminar, and the slender body is allowed to yaw at high incidence. The resulting response exhibits an intricate bifurcation structure that includes bistable periodic (finite amplitude) and nonstationary (small amplitude) limit cycles for moderate angles of attack, and nonstationary (finite amplitude) oscillations for high angles of attack.

Computational investigation of left ventricular hemodynamics following bioprosthetic aortic and mitral valve replacement

The left ventricle of the heart is a fundamental structure in the human cardiac system that pumps oxygenated blood into the systemic circulation. Several valvular conditions can cause the aortic and mitral valves associated with the left ventricle to become severely diseased and require replacement. However, the clinical outcomes of such operations, specifically the postoperative ventricular hemodynamics of replacing both valves, are not well understood. This work uses computational fluid–structure interaction (FSI) to develop an improved understanding of this effect by modeling a left ventricle with the aortic and mitral valves replaced with bioprostheses. We use a hybrid Arbitrary Lagrangian–Eulerian/immersogeometric framework to accommodate the analysis of cardiac hemodynamics and heart valve structural mechanics in a moving fluid domain. The motion of the endocardium is obtained from a cardiac biomechanics simulation and provided as an input to the proposed numerical framework. The results from the simulations in this work indicate that the replacement of the native mitral valve with a tri-radially symmetric bioprosthesis dramatically changes the ventricular hemodynamics. Most significantly, the vortical motion in the left ventricle is found to reverse direction after mitral valve replacement. This study demonstrates that the proposed computational FSI framework is capable of simulating complex multiphysics problems and can provide an in-depth understanding of the cardiac mechanics.

Bioprosthetic aortic valve diameter and thickness are directly related to leaflet fluttering: Results from a combined experimental and computational modeling study

ObjectiveBioprosthetic heart valves (BHVs) are commonly used in surgical and percutaneous valve replacement. The durability of percutaneous valve replacement is unknown, but surgical valves have been shown to require reintervention after 10 to 15 years. Further, smaller-diameter surgical BHVs generally experience higher rates of prosthesis–patient mismatch, which leads to higher rates of failure. Bioprosthetic aortic valves can flutter in systole, and fluttering is associated with fatigue and failure in flexible structures. The determinants of flutter in BHVs have not been well characterized, despite their potential to influence durability. MethodsWe use an experimental pulse duplicator and a computational fluid-structure interaction model of this system to study the role of device geometry on BHV dynamics. The experimental system mimics physiological conditions, and the computational model enables precise control of leaflet biomechanics and flow conditions to isolate the effects of variations in BHV geometry on leaflet dynamics. ResultsBoth experimental and computational models demonstrate that smaller-diameter BHVs yield markedly higher leaflet fluttering frequencies across a range of conditions. The computational model also predicts that fluttering frequency is directly related to leaflet thickness. A scaling model is introduced that rationalizes these findings. ConclusionsWe systematically characterize the influence of BHV diameter and leaflet thickness on fluttering dynamics. Although this study does not determine how flutter influences device durability, increased flutter in smaller-diameter BHVs may explain how prosthesis–patient mismatch could induce BHV leaflet fatigue and failure. Ultimately, understanding the effects of device geometry on leaflet kinematics may lead to more durable valve replacements.

A partitioned scheme for adjoint shape sensitivity analysis of fluid–structure interactions involving non-matching meshes

This work presents a partitioned solution procedure to compute shape gradients in fluid–structure interaction (FSI) using black-box adjoint solvers. Special attention is paid to project the gradients onto the undeformed configuration due to the mixed Lagrangian–Eulerian formulation of large-deformation FSI in this work. The adjoint FSI problem is partitioned as an assembly of well-known adjoint fluid and structural problems. The sub-adjoint problems are coupled with each other by augmenting the target functions with auxiliary functions, independent of the concrete choice of the underlying adjoint formulations. The auxiliary functions are linear force-based or displacement-based functionals which are readily available in well-established single-disciplinary adjoint solvers. Adjoint structural displacements, adjoint fluid displacements, and domain-based adjoint sensitivities of the fluid are the coupling fields to be exchanged between the adjoint solvers. A reduced formulation is also derived for the case of boundary-based adjoint shape sensitivity analysis for fluids. Numerical studies show that the complete formulation computes accurate shape gradients whereas inaccuracies appear in the reduced gradients. Mapping techniques including nearest element interpolation and the mortar method are studied in computational adjoint FSI. It is numerically shown that the mortar method does not introduce spurious oscillations in primal and sensitivity fields along non-matching interfaces.

Thinner biological tissues induce leaflet flutter in aortic heart valve replacements

Valvular heart disease has recently become an increasing public health concern due to the high prevalence of valve degeneration in aging populations. For patients with severely impacted aortic valves that require replacement, catheter-based bioprosthetic valve deployment offers a minimally invasive treatment option that eliminates many of the risks associated with surgical valve replacement. Although recent percutaneous device advancements have incorporated thinner, more flexible biological tissues to streamline safer deployment through catheters, the impact of such tissues in the complex, mechanically demanding, and highly dynamic valvular system remains poorly understood. The present work utilized a validated computational fluid-structure interaction approach to isolate the behavior of thinner, more compliant aortic valve tissues in a physiologically realistic system. This computational study identified and quantified significant leaflet flutter induced by the use of thinner tissues that initiated blood flow disturbances and oscillatory leaflet strains. The aortic flow and valvular dynamics associated with these thinner valvular tissues have not been previously identified and provide essential information that can significantly advance fundamental knowledge about the cardiac system and support future medical device innovation. Considering the risks associated with such observed flutter phenomena, including blood damage and accelerated leaflet deterioration, this study demonstrates the potentially serious impact of introducing thinner, more flexible tissues into the cardiac system.