Fluid Structure Interaction Mechanism Research Articles

Fluid-structure interaction mechanism in shear thickening fluid/Foam composite for advanced protective structures

Fluid-structure interaction (FSI) between shear thickening fluid (STF) and soft materials is pivotal in designing advanced protective structures. This study delves into the FSI mechanisms within a composite structure known as STF/Foam, which features the infusion of STF into foam. Through comprehensive drop weight tests, the STF/Foam exhibited exceptional cushioning performance. In addition to analyzing FSI from the perspective of structural materials, this study also examines it from the STF standpoint, enabling a multi-faceted understanding of the energy absorption mechanism. To accurately characterize the rheological properties of STF, a novel decoupling method is proposed, accounting for both temporal and spatial inhomogeneities of STF. The research findings indicate that the viscosity variation of STF significantly enhances the energy absorption capabilities of the STF/Foam composite. This study reveals the intricate fluid-solid coupling mechanism between STF and foam. The STF demonstrates a unique combination of shear resistance akin to high-viscosity fluids and the easy flow characteristics of low-viscosity fluids. The modulation of STF viscosity optimizes the structural deformation pattern, thereby rationalizing the energy absorption mechanism of the composite. Consequently, STF/Foam showcases superior cushioning performance. Further investigation into various parameters associated with STF and foam highlights their influence on the structural cushioning performance. These insights lay a theoretical foundation and provide design guidelines for the future development of STF-based controllable protective structures.

Flow field characteristics and vibration responses of saddle-shaped membrane structures

Elastically mounted flexible membrane roofs exposed to flows are prone to vortex-induced vibrations and even aero-instability due to the strong fluid–structure interaction (FSI). This study is to investigate the FSI mechanism in the saddle-shaped membrane structure over a range of Reynolds numbers and wind directions in laminar flows, by bridging structural vibration responses and flow dynamics. The aeroelastic characteristics of membrane structures, including statistics of displacement responses, oscillation frequency, and oscillation damping ratios, were identified from the perspective of time and frequency domains. Simultaneously, the particle image velocimetry system was employed to visualize the flow features, including velocity vector, turbulence intensity, and vortex evolution in both space and time. The flow modes were further decomposed by proper orthogonal decomposition (POD) to capture the salient aspects of the flow. Three patterns of POD modes are identified, and the first mode plays the dominant role in POD modes. It showed that as the wind Reynolds number increases, the space between the shear layer and membrane surface would be narrowed, and resultantly the vortices turn out smaller in scale and closer in space. This trend leads to an increase in the frequency of vortex shedding and a stronger FSI effect. When the frequency of vortex shedding approaches the fundamental frequency of structures, the vibration of the membrane would be shifted from turbulent buffeting to vortex-induced resonance, featured with lock-in frequency, significant amplified displacement, and negative aerodynamic damping ratio.

Numerical Study on Hydrodynamic Performance of a Pitching Hydrofoil with Chordwise and Spanwise Deformation

The hydrofoil plays a crucial role in tidal current energy (TCE) devices, such as horizontal-axis turbines (HATs), vertical-axis turbines (VATs), and oscillating hydrofoils. This study delves into the numerical investigation of passive chordwise and spanwise deformations and the hydrodynamic performance of a deformable hydrofoil. Three-dimensional (3D) coupled fluid–structure interaction (FSI) simulations were conducted using the ANSYS Workbench platform, integrating computational fluid dynamics (CFD) and finite element analysis (FEA). The simulation involved a deformable hydrofoil undergoing pitching motion with varying elastic moduli. The study scrutinizes the impact of elastic modulus on hydrofoil deformation, pressure distribution, flow structure, and hydrodynamic performance. Coefficients of lift, drag, torque, as well as their hysteresis areas and intensities, were defined to assess the hydrodynamic performance. The analysis of the correlation between pressure distribution and deformation elucidates the FSI mechanism. Additionally, the study investigated the 3D effects based on the flow structure around the hydrofoil. Discrepancies in pressure distribution along the spanwise direction result from these 3D effects. Consequently, different chordwise deformations of cross-sections along the spanwise direction were observed, contributing to spanwise deformation. The pressure difference between upper and lower surfaces diminished with increasing deformation. Peak values and fluctuations of lift, drag, and torque decreased. This study provides insights for selecting an appropriate elastic modulus for hydrofoils used in TCE devices.

Experimental and numerical studies on a passively deformed coupled-pitching hydrofoil under the semi-activated mode

Flexibility is expected to positively affect the hydrodynamic and energy-harvesting performance of deformable hydrofoils, which have a simple structure and can be easily implemented in practical engineering applications. However, the characteristics of the fluid-structure interaction and power capturing are complicated. In this study, to reveal the fluid-structure interaction (FSI) mechanism and the effects of the passive deformation on the energy-harvesting performance, a flexible hydrofoil to conduct a coupled-pitching motion under the semi-activated mode was proposed and investigated experimentally and numerically. In the experimental study, a deformation-measuring technology based on a digital imaging algorithm was developed and employed for water channel tests. The effects of the hydrofoil profile and activated pitching amplitude on the deformation status, torque output, and energy-harvesting performance were studied experimentally. In the numerical study, a three-dimensional unsteady two-way FSI model was established and validated using experimental results. The influence mechanisms of the damping torque coefficient, activated pitching amplitude, and elasticity modulus on the passive deformation, its phase difference with the activated pitching angle, and the hydrodynamic and energy-harvesting performances were studied. Compared with the rigid hydrofoil, the energy-harvesting efficiency and power coefficient of the passively deformable hydrofoil could be increased by 4.8 % and 8.0 %, respectively, as the phase difference zone was close to 3π/4. In addition, positive and negative phase difference zones for performance enhancement were identified, which provides a future direction for optimizing flexible hydrofoils and control strategies.

Implosion mechanisms of underwater ring-stiffened metallic cylindrical shells

Underwater cylindrical shells are prone to implosion due to the surrounding high hydrostatic pressure, and introducing ring-rib is a promising approach to reduce the risk. However, the influences of the ring-rib on the deformation mode and the fluid-structure interaction mechanism are still unclear. This paper investigates the dynamic response of ring-stiffened cylindrical shells during the implosion process. The finite element model is firstly established and the numerical simulation is verified by the existing experiment. Then, the numerical method is used to simulate the implosion of ring-stiffened cylindrical shells with various geometrical parameters. The fluid motion, induced pressure and deformation features are investigated and the relationship between them is clarified. Finally, pure and ring-stiffened cylindrical shell implosions are compared and parametric analyses are performed by varying the number and thickness of ring-ribs. Results show that ring-stiffened cylindrical shells with higher collapse resistance deform asymmetrically and the flow field response changes depending on the deformation mode. Introduction of ring-ribs can significantly increase the critical pressure and reduce the percentage of induced pressure. As the number and thickness of ribs increased, the critical and peak implosion pressures of the ring-stiffened cylindrical shells increased by 153% and 146%, respectively.

Examining error-contaminated, long-span bridge buffeting vibration by Stochastic Differential Equations

This paper summarizes the development of an analytically-based and numerically-implemented algorithm for the analysis of uncertainty propagation in aeroelastic systems. The term “uncertainty” is utilized to describe either simplifications in the modeling of the fluid–structure interaction mechanism or the effect of experimental errors, for example emerging during wind-tunnel tests. The algorithm is applied to study the dynamic response of long-span bridges. This study provides, by theoretical derivations, estimation of the stationary joint-probability distribution of the generalized bridge response, accounting for perturbations in the buffeting loads. The formulation includes physical states, fluid–structure interaction states and a random variable, which quantifies the errors in the span-wise correlation of the buffeting deck load. A 1200m span bridge is used for illustration of the numerical algorithm.

Numerical study on the influence of fabric permeability on the inflation process and aerodynamic characteristics of disk-gap-band parachute

Supersonic parachute plays a crucial role in Mars exploration missions. The disk-gap-band (DGB) parachute he been used in all the successful Mars exploration missions. The parachute is fabricated from different porous fabric materials, and the fabric permeability is an important design and performance parameter, now it has been proved that the fabric permeability of porous canopy has important effects on the complicated flow fields around the parachute and in turn effects the nonlinear deformation and aerodynamic performances of the flexible canopy. However, till now, the influence mechanism of fabric permeability on the fluid-structure interaction mechanism and aerodynamic performance of supersonic flexible porous parachute in the inflation process still remain unknown. Therefore, in this study, a fluid-structure coupling method was used to numerically simulate the inflation process of disk-gap-band parachute with different fabric permeability (i.e., different fabric materials), and the effect of fabric permeability on the aerodynamic performance of disk-gap-band parachute was also analyzed. The results showed that the fabric permeability has a significant effect on the inflation process of DGB parachute with different fabric materials. During the inflation process, the oscillation angle and drag coefficients of the parachute both gradually decreased with the increase of fabric permeability, while the stability performance of the parachute became more complicated. Furthermore, it was also found that the influence of fabric permeability was different under subsonic and supersonic conditions. The K5836-3 fabric used as canopy material has better stability under subsonic conditions, and the 42105 fabric material has the best stability under supersonic conditions.

Computational fluid–structure interaction framework for passive feathering and cambering in flapping insect wings

AbstractIn flapping insect wings, veins support flexible wing membranes such that the wings form feathering and cambering motions passively from large elastic deformations. These motions are essentially important in unsteady aerodynamics of insect flapping flight. Hence, the underlying mechanism of this phenomenon is an important issue in studies on insect flight. Systematic parametric studies on strong coupling between a model wing describing these elastic deformations and the surrounding fluid, which is a direct formulation of this phenomenon, will be effective for solving this issue. The purpose of this study is to develop a robust numerical framework for these systematic parametric studies. The proposed framework consists of two novel numerical methods: (1) A fully parallelized solution method using both algebraic splitting and semi‐implicit scheme for monolithic fluid–structure interaction (FSI) equation systems, which is numerically stable for a wide range of properties such as solid‐to‐fluid mass ratios and large body motions, and large elastic deformations. (2) A structural mechanics model for insect flapping wings using pixel modeling (pixel model wing), which is combined with explicit node‐positioning to reduce computational costs significantly in controlling fluid meshes. The validity of the proposed framework is demonstrated for some benchmark problems and a dynamically scaled model incorporating actual insect data. Finally, from a parametric study for the pixel model wing flapped in fluid with a wide range of solid‐to‐fluid mass ratios, we find a FSI mechanism of feathering and cambering motions in flapping insect wings.

Investigation on Numerical Simulation of VIV of Deep-Sea Flexible Risers

The vortex-induced vibration (VIV) of flexible risers is a complex fluid–structure interaction (FSI) phenomenon. In this study, we conducted a numerical simulation method based on the slicing method to study the vortex-induced vibration (VIV) of deep-sea flexible risers with different slenderness ratios and uniform flow velocities. The method combines the finite element model of the riser structure with the two-dimensional flow field slices solved by the Fluent solver. The fluid–structure interaction was realized by a self-compiled UDF program and the overset mesh technique. The numerical results were validated by comparing them with experimental data. The VIV characteristics of the riser, such as the vibration track, vibration mode, vibration frequency and wake vortex shedding mode, were analyzed. The article reveals the nonlinear dynamic features of flexible riser vibration, such as multi-frequency vibration, wide-frequency vibration and multi-modal vibration. The article also provides insights into the fluid–structure interaction mechanism of VIV of deep-sea flexible risers.

The effect of spacing on the flow-induced vibration of one-fixed-one-free tandem cylinders with a rigid splitter plate

The fluid-structure interaction mechanism of an assembly system, including a fixed upstream cylinder and a transverse oscillating downstream cylinder with a rigid splitter plate, is numerically studied at a low Reynolds number Re = 150 and mass ratio m* = 10.0. The effect of different spacing ratios (G/D = 1.5, 3.0, 5.0, and 8.0) and reduced velocities (Ur = 1.0–40.0) on the dynamic responses, hydrodynamic characteristics, and wake patterns of the downstream cylinder-plate (DCP) are analyzed in detail. The results show that, depending on the spacing ratios and the reduced velocities, different response regimes can be identified: (a) For G/D = 1.5 and 3.0, the response of the DCP presents a steady flow at low Ur where the oscillation is completely suppressed. As Ur increases, the response regime shifts to vortex-induced vibration (VIV), which is characterized by a wider lock-in bandwidth and a larger peak vibration amplitude than those of the single cylinder-plate body. (b) For G/D = 5.0 and 8.0, the response regimes consist of VIV and galloping. For the former, the upstream vortex shedding leads to a significant increase in the lift force on the DCP, and its frequency is highly synchronized with the oscillation. By contrast, multiple harmonic components of the lift force are observed in the galloping-dominated Ur range. Two prominent peaks can be identified in the power spectra. The lower peak, produced by the reattachment of the separated shear layers, is the main contributor to the oscillation. The higher peak originating from the upstream vortex shedding frequency is out of phase with the oscillation, and its contribution to the oscillation is very small.

Flexible Impact-Resistant Composites with Bioinspired Three-Dimensional Solid–Liquid Lattice Designs

The ubiquitous solid-liquid systems in nature usually present an interesting mechanical property, the rate-dependent stiffness, which could be exploited for impact protection in flexible systems. Herein, a typical natural system, the durian peel, has been systematically characterized and studied, showing a solid-liquid dual-phase cellular structure. A bioinspired design of flexible impact-resistant composites is then proposed by combining 3D lattices and shear thickening fluids. The resulting dual-phase composites offer, simultaneously, low moduli (e.g., 71.9 kPa, lower than those of many reported soft composites) under quasi-static conditions and excellent energy absorption (e.g., 425.4 kJ/m3, which is close to those of metallic and glass-based lattices) upon dynamic impact. Numerical simulations based on finite element analyses were carried out to understand the enhanced buffering of the developed composites, unveiling a lattice-guided fluid-structure interaction mechanism. Such biomimetic lattice-based flexible impact-resistant composites hold promising potential for the development of next-generation flexible protection systems that can be used in wearable electronics and robotic systems.

Blood pressure-driven rupture of blood vessels

To develop better diagnosis and treatment techniques of cardiovascular disease such as aneurysm, further understandings of the biomechanical mechanisms and failure behaviors of blood vessels is urgent. Importantly, blood pressure, residual stress, loads from surrounding tissues, and fluid-structure interactions greatly influence the spatiotemporal evolution of deformation and damage of blood vessels. However, directly incorporating these effects into a fluid-structure interaction mechanism analysis of blood vessels remains challenging. Here, we proposed a novel virtual bar model for surrounding tissues and correlated residual stress and loads from the surrounding tissues with perivascular pressures of blood vessels based on a strategy of pressure decomposition. Meanwhile, we developed a pristine meshfree framework incorporating both the Fung-type hyperelasticity and the Casson's non-Newtonian fluid model for modeling the deformation and rupture of blood vessels. An essential physical phenomenon, blood pressure-induced spontaneous ruptures of blood vessels, are successfully captured using our method. It should be highlighted that the effects of material constitutive model, loads from surrounding tissues, the off-axis distance of aneurysm and outlet resistance can be systematically characterized using the proposed model. Another valuable finding is that surrounding tissues have significant effects on the deformation and damage behaviors of blood vessel, however, it was ignored in most of biomechanics simulations. Our work will provide a landmark computational framework for studying surrounding tissues and a potential numerical implementation for fluid-driven failure analysis in biological tissues.

Nonlinear transient response of elastoplastic sandwich beam in underwater blast and the fluid-structure interaction

This work focuses on a new theory on the transient response of elastoplastic sandwich beam in underwater blast, and two fully coupled fluid-structure interaction (FSI) models are proposed, to gain insight into the propagation and dissipation of underwater blast wave, and the optimal design for sandwich structure with excellent underwater blast resistance. Based on the nonlinear dynamic high-order sandwich panel theory (EHSAPT) according to the authors’ preceding work [1], the governing equation of motion is constructed and modified by integrating the rarefaction-wave-related term into the structural damping matrix. So, the underwater blast analysis is transformed into the dynamic response of sandwich structure with structural damping under the superposition of incident and reflected waves in vacuum. Furthermore, this governing equation is simplified to get the analytical solution of impulse transferred to the sandwich structure, by implementing displacement and core rigidity assumptions. Finite element simulation and two existing FSI models are used to validate the accuracy. Conclusions are drawn that, the key aspects dominating FSI mechanism and time-domain response include pressure signatures, fluid characteristics, front-face mass, core density, and core elastic modulus, and the quantitative relationships are provided. Moreover, the core elastic modulus dominates the impulse transmitted to the sandwich structure, and the core strength and strain hardening govern the pressure delivered to the supports.

Influence of FRP arrestors on the dynamic collapse and implosion of underwater pipelines

The dynamic collapse of pipelines in deep water can create pressure pulses that affect the performance of surrounding structures. In this study, the pipe implosion process was analysed using the Lagrangian–Eulerian method. The numerical model was calibrated using the experimental data, and the responses of the pipelines and surrounding fluid during pipeline collapse and buckle propagation were obtained. The fluid–structure interaction mechanism of the composite arrestors attenuating the pressure pulse was investigated. The simulation results showed that the implosion of a pipeline was a transient high-energy dynamic event. The fluid surrounding the pipe rushed towards the pipe surface at a high velocity during implosion and dynamic buckle propagation, which resulted in a spatial change in pressure distribution. Notably, the unidirectional fibre reinforced polymer (FRP) arrestor had a positive effect on reducing the peak pressure of the pulse wave. Furthermore, the effects of different arrestor spacings and materials on pipe buckling and implosion pressure were discussed, and the design of FRP arrestors was optimised.

Study on the Material Properties of Microconcrete by Dynamic Model Test.

As an important water conveying structure, the seismic safety of the hydraulic aqueduct has attracted considerable interest. Different from the general bridge structure, the seismic analysis of the aqueduct structure needs to consider its fluid–structure interaction. The existing numerical simulation methods cannot truly reflect the fluid–solid coupling mechanism. Therefore, scholars began to use shaking table tests to study the fluid–structure interaction mechanism. However, the research is immature, and it is mostly focused on the seismic response analysis, and there are few studies on the model test similarity ratio and model material properties. Based on this, in this paper, according to the requirements of the test similarity ratio, the orthogonal experiment was used to explore the influence of barite sand content, water–cement ratio, fine sand ratio, and lime ratio on the mechanical properties of microconcrete. The performance indicators of microconcrete under different mix ratios vary widely, with a minimum variation of 19% and a maximum of 102%. Barite sand has the most significant control effect on the density, and the water–cement ratio has the most significant control effect on the compressive strength and elastic modulus. The density variation range is 2.37–2.81 g/cm3, the cube compressive strength variation range is 18.37–36.94 MPa, and the elastic modulus variation range is 2.11 × 104–3.28 × 104 MPa. This study will provide certain evidence for the similarity ratio design and material selection of the scaled model test of the fluid–solid coupling structure.

Stability analysis for laminar separation flutter of an airfoil in the transitional flow regime

Laminar separation flutter (LSF) is a type of aeroelastic instability phenomenon characterized by small-amplitude low-frequency pitching oscillations of the airfoil. The present study aims to gain insight into the intrinsic dynamics of LSF via data-driven stability analysis. The proposed data-driven approach relies on the autoregressive with exogenous input (ARX) technique to design reduced-order models (ROMs) of unsteady aerodynamics in a state-space format. First, high-fidelity full-order numerical simulations of the LSF phenomenon are performed using the incompressible Unsteady Reynolds-Averaged Navier–Stokes equations and the Shear-Stress Transport k−ω turbulence model with Low-Reynolds-number correction. The calculated LSF responses show good agreement with previous experimental data in the literature. Then, linear stability analysis (LSA) of the aeroelastic system is carried out to reveal the underlying fluid-structure interaction mechanism. The LSA model is developed by coupling the ROM with the structure motion equation. LSA results indicate that the LSF phenomenon is primarily caused by the instability of the structure mode (SM), which is induced by the mutual repulsion effect between one static fluid mode (FM) and the SM. The presence of laminar separation near the trailing-edge of the airfoil can significantly reduce the stability of the static FM, which ultimately strengthens the fluid-structure coupling effect and leads to LSF. We would like to emphasize that LSF is essentially different from other flow-induced vibration phenomena, such as transonic buffeting of an airfoil and vortex-induced vibration of bluff bodies, for which the instabilities are triggered by the coupling between one dynamic FM and the SM. Finally, the effects of the mass ratio, structural damping ratio, and freestream turbulence intensity on the aeroelastic system are also investigated.

Suppression of vortex-induced vibration of a circular cylinder by a finite-span flexible splitter plate

We present experiment and analysis of the effectiveness of a flexible splitter plate in the suppression of vortex-induced vibration (VIV) of a circular cylinder. The important finding is that it is not necessary to suppress VIV by a full-span flexible splitter plate, while efficient control can be achieved by a finite-span one. The fluid-structure interaction and control mechanism are revealed by analysis of wake evolution and force characteristics.

Mass ratio effect on vortex-induced vibration for two tandem square cylinders at a low Reynolds number

A numerical simulation study is conducted to investigate the effect of the mass ratio (m* = 3, 10, and 20) on vortex-induced vibration (VIV) of two tandem square cylinders at Re = 150. In this study, we mainly focus on the mass ratio effect on the vibration response, force characteristics, wake mode pattern, and fluid–structure-interaction (FSI) mechanism. The results show that mass ratio plays an important role in the VIV response of the two cylinders. With increasing reduced velocity, both the upstream cylinder (UC) and downstream cylinder (DC) at m* = 3 exhibit the soft-lock-in phenomenon (at a lock-in frequency ratio of fy/fn < 1) instead of the typical lock-in phenomenon (at a lock-in frequency ratio of fy/fn ≈ 1). With increase in the mass ratio to m* = 10 and 20, the soft-lock-in phenomenon disappears, while the DC exhibits the typical lock-in phenomenon. The maximum amplitudes of the two cylinders notably decrease with increasing mass ratio. Furthermore, the mass ratio exerts a major impact on the distance between the two cylinders, which may change the flow pattern. The distance sharply decreases in the synchronization region at m* = 3 but remains almost constant at m* = 10 and 20. In addition, the wake mode and FSI mechanism are more diverse at a low mass ratio (m* = 3).

Lattice Boltzmann analysis of fluid structure interaction mechanism around a row of five side-by-side square cylinders

In this paper numerical investigations are performed to examine the effect of Reynolds numbers (Re) and spacing ratios (g) on flow around a row of five side-by-side square cylinders using the lattice Boltzmann method. The Reynolds number is varied in the range 75 ≤ Re ≤ 175, while spacing ratio is varied between 0.5 and 5. The flow structure mechanism around a row of five side-by-side square cylinders is studied in terms of vorticity contours visualization, time trace analysis of drag and lifts coefficients, and power spectrum analysis of lift coefficient. The effect of Re on force statistics like mean drag coefficient and Strouhal number is also analyzed. The present data are compared with the data of single square cylinder and good agreement is observed for large spacing ratio (g = 5). The flow behind five side-by-side square cylinders is classified into three different flow regimes and these regimes are further subdivided into seven different regimes. The observed flow regimes are compared with those of the other researchers published studies and found good agreement.

Mode interpretation of interference effects between tall buildings in tandem and side-by-side arrangement with POD and ICA

In this study, the effect of gap distance on the aerodynamic interference effect of two neighboring buildings has been systematically investigated. Firstly, the variation of aerodynamic features of principal building with different gap distances (from 1.5B to 6B) and wind directions (from 0°to 180°) are analyzed. Then, Proper Orthogonal Decomposition (POD) and Independent Component Analysis (ICA) methods are employed to further unveil the interference mechanism under tandem and side-by-side arrangement. The spatial-spectral feature of surface pressure field, including pressure pattern, modal coefficients and correlation are comprehensively compared to highlight the differences of POD and ICA. The results show that 3B is recognized as the critical gap whose pressure pattern is more similar to the small gap type than the large gap type. Moreover, two new phenomena, “mode competition” and “mode transition”, are respectively captured by POD and ICA in tandem arrangement, and quantitively interpreted by modal load component ratio. For side-by-side arrangement, the variation of channeling effect with gap distance is well reflected by both POD and ICA pressure patterns. Compared with POD, ICA provides a more variety of information on pressure patterns by capturing their variation with gap distance on all four side-surfaces. These conclusions can enhance understanding of fluid–structure interaction mechanism and provide reference for wind-induced responses control measures for interference buildings.