Narrow Results

This work investigates the free vibrations of innovative thermally loaded nanoplates constructed by integrating magneto-electro-elastic (MEE) layers with functionally-graded graphene platelet-reinforced composite cores (FG-GPLRC) and accounting for viscous fluid interactions. An advanced multiphysics model is developed using the Navier–Stokes equations to capture fluid structure coupling effects, Halpin–Tsai, and the rule of mixtures micromechanics to predict the non-uniform effective properties, third-order shear deformation plates theory (TSDPT) to incorporate thickness stretching, and the nonlocal strain gradient theory (NSGT) to characterize size dependencies. The Galerkin technique is used to solve the governing equations, which are derived from the Hamilton’s principle. Parametric analyses quantify the influences of fluid depth, temperature fluctuations, temperature profiles, nonlocal and strain gradient parameters, electric and magnetic potentials, graphene distribution patterns, graphene weight fractions, and boundary conditions on the vibration response. The outcomes of this study provide design guidelines and predictive tools enabling active vibration control systems for next-generation thermally-loaded nanocomposite structures with widespread applications from aerospace vehicles to nanoelectronics.

The vibrational characteristics in a submerged double-shell structure, which consists of two concentric cylindrical shells coupled by the entrained fluid, are investigated in this paper considering the acoustic-structure coupling. An analytical model is proposed based on the wave propagation approach and the Flügge thin-shell theory, and then a detailed analysis is conducted. The spectrum of the averaged quadratic velocity of total modal superposition is calculated to elucidate the vibrational transmission between inner and outer shells, while that of typical modes are separated to further clarifies the strong and weak coupling. Furthermore, the natural frequencies of the inner and outer shell are determined by the location of the resonance peak in the separated spectrum. The impact of variation of the governing parameters such as the length, the radius and the thickness on the natural frequencies of double-shell structure are investigated and some conclusions are outlined.

During the operation of a turbine, the water level drop can cause vibration and damage to the flow components, severely threatening its stability and reliability. Investigating the impact of operational parameters on the internal flow field and flow structures of tidal turbines under low flow conditions is crucial for peak shaving and deployment of tidal power stations. This paper takes a 24MW turbine as the research object, using numerical calculations to analyze the effects of tailwater height on the flow characteristics and structural properties of the unit under low flow conditions. It studies the hydraulic impact on the flow component walls under different operating parameters and verifies the reliability of numerical calculations through vibration and stress tests. The results show that the increase in tailwater level affects the turbine’s flow characteristics, forming large-scale, high-intensity vortices in the internal flow field and causing pressure pulsations near the wall surface. Modal analysis reveals that under different tailwater heights, the maximum modal effective mass exists along the axis of the impeller, with modal frequencies higher than the main frequencies of pressure pulsations. The impeller region corresponds to the turbine chamber wall bearing significant stress, which induces strain. The magnitude of stress and the degree of strain are positively correlated with the tailwater height. The research findings provide guidance for tailwater regulation and stable operation of tidal power stations.

As a flexible component in high-pressure vessels and pipeline systems, bellows experience significant fluid–structure interaction effects under high-speed internal fluids and external vibrations. Nevertheless, their dynamic response mechanisms coupled with fluid–structure interaction mentioned below have not yet been clarified so far. In this work, a novel pressure-balanced metal bellow (PBMB) for low-stiffness and high-pressure resistance is firstly proposed. Several fluid–structure interaction models were considered to study the dynamic response characteristics of the PBMB. An experimental platform associated with fluid–structure interaction was established to validate the effectiveness of its vibration attenuation performance. The results indicate that the PBMB has an obvious vibration attenuation effect in the range of 5–90Hz, and super-harmonic and sub-harmonic resonance phenomena occur in the range of 90–200Hz. Under constant fluid conditions, fluid density, viscosity, flow velocity, and pressure are positively correlated with the response amplitude of the PBMB. The response of the PBMB oscillates at the fluid entry point due to both pulsating flow velocity and pulsating pressure. After several cycles, the response caused by pulsating flow velocity gradually decays and stabilizes. Thus, the impact of pulsating frequency on the stability of the response of bellows is insignificant during the initial cycles.

This paper aims to study the aerodynamic and propulsive performance of a plunging airfoil using novel plunging waveform, that creates additional trailing edge vortices, that affects the flow field and, consequently, the aerodynamic loads on the airfoil. This waveform is generated by means of superpositioning of the regular sinusoidal wave with a faster one. This novel waveform not only allows to add another pair of trailing edge vortices but also to control their strength. It is found that as the weight of the faster wave increases, the thrust coefficient increases rapidly while the propulsive efficiency decreases slowly, allowing a window of high thrust with small efficiency reduction. Understanding the effect of generating additional trailing edge vortices within the regular flapping cycle on the propulsive performance is the main objective of this work.

In this paper, the lattice Boltzmann (LB) method is used in order to simulate non-Newtonian blood flows in deformable vessels. Casson's rheological model is adopted and a local correction to the relaxation time is implemented in order to modify the viscosity. The hyperelastic, hardening and anisotropic behavior of a flexible arterial wall is discussed and a closed-form solution is used to predict the deformed configuration of the vessel. A partitioned staggered-explicit strategy to couple the LB method and such analytical prediction is proposed.

This paper deals with the simulation of water entry problems using the lattice Boltzmann method (LBM). The dynamics of the free surface is treated through the mass and momentum fluxes across the interface cells. A bounce-back boundary condition is utilized to model the contact between the fluid and the moving object. The method is implemented for the analysis of a two-dimensional flow physics produced by a symmetric wedge entering vertically a weakly-compressible fluid at a constant velocity. The method is used to predict the wetted length, the height of water pile-up, the pressure distribution and the overall force on the wedge. The accuracy of the numerical results is demonstrated through comparisons with data reported in the literature.

In this paper, numerical analysis aiming at simulating biological organisms immersed in a fluid are carried out. The fluid domain is modeled through the lattice Boltzmann (LB) method, while the immersed boundary method is used to account for the position of the organisms idealized as rigid bodies. The time discontinuous Galerkin method is employed to compute body motion. An explicit coupling strategy to combine the adopted numerical methods is proposed. The vertical take-off of a couple of butterflies is numerically simulated in different scenarios, showing the mutual interaction that a butterfly exerts on the other one. Moreover, the effect of lateral wind is investigated. A critical threshold value of the lateral wind is defined, thus corresponding to an increasing arduous take-off.

Rupture of the abdominal aortic aneurysm (AAA) is the result of the relatively complex interaction of blood hemodynamics and material behavior of arterial walls. In the present study, the cumulative effects of physiological parameters such as the directional growth, arterial wall properties (isotropy and anisotropy), iliac bifurcation and arterial wall thickness on prediction of wall stress in fully coupled fluid-structure interaction (FSI) analysis of five idealized AAA models have been investigated. In particular, the numerical model considers the heterogeneity of arterial wall and the iliac bifurcation, which allows the study of the geometric asymmetry due to the growth of the aneurysm into different directions. Results demonstrate that the blood pulsatile nature is responsible for emerging a time-dependent recirculation zone inside the aneurysm, which directly affects the stress distribution in aneurismal wall. Therefore, aneurysm deviation from the arterial axis, especially, in the lateral direction increases the wall stress in a relatively nonlinear fashion. Among the models analyzed in this investigation, the anisotropic material model that considers the wall thickness variations, greatly affects the wall stress values, while the stress distributions are less affected as compared to the uniform wall thickness models. In this regard, it is confirmed that wall stress predictions are more influenced by the appropriate structural model than the geometrical considerations such as the level of asymmetry and its curvature, growth direction and its extent.

This paper studies the two-dimensional (2D) water-entry and exit of a rotating circular cylinder using the Sub-Particle Scale (SPS) turbulence model of a Lagrangian particle-based Smoothed-Particle Hydrodynamics (SPH) method. The full Navier–Stokes (NS) equations along with the continuity have been solved as the governing equations of the problem. The accuracy of the numerical code is verified using the case of water-entry and exit of a nonrotating circular cylinder. The numerical simulations of water-entry and exit of the rotating circular cylinder are performed at Froude numbers of 2, 5, 8, and specific gravities of 0.25, 0.5, 0.75, 1, 1.75, rotating at the dimensionless rates of 0, 0.25, 0.5, 0.75. The effect of governing parameters and vortex shedding behind the cylinder on the trajectory curves, velocity components in the flow field, and the deformation of free surface for both cases have been investigated in detail. It is seen that the rotation has a great effect on the curvature of the trajectory path and velocity components in water-entry and exit cases due to the interaction of imposed lift and drag forces with the inertia force.

Computational modeling plays an important role in biology and medicine to assess the effects of hemodynamic alterations in the onset and development of vascular pathologies. Synthetic analytic indices are of primary importance for a reliable and effective a priori identification of the risk. In this scenario, we propose a multiscale fluid-structure interaction (FSI) modeling approach of hemodynamic flows, extending the recently introduced three-band decomposition (TBD) analysis for moving domains. A quantitative comparison is performed with respect to the most common hemodynamic risk indicators in a systematic manner. We demonstrate the reliability of the TBD methodology also for deformable domains by assuming a hyperelastic formulation of the arterial wall and a Newtonian approximation of the blood flow. Numerical simulations are performed for physiologic and pathologic axially symmetric geometry models with particular attention to abdominal aortic aneurysms (AAAs). Risk assessment, limitations and perspectives are finally discussed.

In this paper, the flapping dynamics and wake flow characteristics in the nonlinear hysteresis region are investigated experimentally by immersing a cantilevered flexible plate in uniform airflow. The experimental results show that the flapping mode of a cantilevered flexible plate in hysteresis region will be transited from periodical traveling wave mode to limited cantilever-like mode with the variation of Reynolds number. The flapping mode will greatly influence the kinetic parameters of a flexible plate and also wake flow characteristics. The comparison of Strouhal number values between flapping flexible plate and animals further indicates that the fluid dynamics between passive flapping and active swimming is similar to the obtained optimal propulsive efficiency. Flow visualization reveals that the Karman vortex street appears, vanishes and coherent structures of turbulent flow arise behind the stable flexible plate with increasing Reynolds number. Meanwhile, the measurements of pressure distribution in wake flow provide a good physical understanding of the energy-saving mechanism and the optimal arrangement in fish school. Moreover, the fast Fourier transform (FFT) spectra of fluctuating velocity indicate that the characteristics of wake flow are closely related to the flapping mode of flexible plate. The wake flow will come into strong harmonic excitation state when flapping mode transits into a limited cantilever-like mode.

The objective of this project is to develop a numerical approach that simulates the behavior of sloshing water with linear free surface waves on a sloping beach inside a 2D rectangular tank. The current computational approach represents the first stage in the development of a precise modeling framework for wave energy converters (WEC). The 2D tank model was generated using the ANSYS FLUENT program, with the Navier–Stokes equations being discretized on a regular structured grid employing the finite volume method (FVM). The validity of the model has been shown for linear sloshing conditions. Moreover, an examination is conducted to analyze the impact of tank flexibility on the phenomenon of liquid sloshing. The simulation was conducted under seven different wave steepness conditions. The primary objective of this study was to investigate the phenomenon of fluid–structure interaction in the context of movable plates. The investigation of the flow domain encompasses a crucial study on the output power of the plate WEC, specifically focusing on scenarios where plate heights remain constant and the motion of fluid streamlines around the plate is considered. The primary objective of this study is to investigate the relationship between drag force and wave steepness. This observation illustrates a positive correlation between wave steepness and drag force. The revolutionary structure of the ocean buildings may provide a novel and exact method for estimating the wave strength. The usefulness of WEC lies in its capacity to interact with water waves and harness renewable energy from the ocean. This study introduces a novel computational fluid dynamics (CFD) methodology that effectively captures the dynamic interaction between a solid object and a two-phase flow. The examination of the impact of wave steepness on the dynamics of a movable thin plate in intermediate water is a fresh and noteworthy subject of inquiry. This study has substantial importance as a valuable resource for the development of practical systems and possesses direct relevance in the design of WEC for the purpose of harnessing oceanic energy.

Large eddy simulation is used to explore flow features and energy exchange physics between turbulent flow and structure vibration in the near-wall region with fluid–structure interaction (FSI). The statistical turbulence characteristics in the near-wall region of a vibrating wall, such as the skin frictional coefficient, velocity, pressure, vortices, and the coherent structures have been studied for an aerofoil blade passage of a true three-dimensional hydroturbine. The results show that (i) FSI greatly strengthens the turbulence in the inner region of y⁺ < 25; and (ii) the energy exchange mechanism between the flow and the vibration depends strongly on the vibration-induced vorticity in the inner region. The structural vibration provokes a frequent action between the low- and high-speed streaks to balance the energy deficit caused by the vibration. The velocity profile in the inner layer near the vibrating wall has a significant distinctness, and the viscosity effect of the fluid in the inner region decreases due to the vibration. The flow features in the inner layer are altered by a suitable wall vibration.

This work is concerned with modeling the interaction of fluid flow with flexible solid structures. An improving spring smooth analogy and an improved constant volume transfer (ICVT) are used to provide fluid mesh control and transfer the information on the interfaces between fluid and structure, respectively. The time integrating algorithm is based on the predictor multi-corrector algorithm (PMA).

An important aspect of this work is that we present a directly coupled approach, in which a large eddy simulation (LES) fluid solver and a structure solver have been coupled together to solve a hydroelasticity problem using the finite element method. To demonstrate the performance of the proposed approach, two working examples were used. One is the vibration of a beam immersed in incompressible fluid, another is the hydroelastic behavior of an ideal guide vane in a hydro turbine passage. The numerical results show the validity of the proposed approach.

To make an insight into the interaction characteristics of a flat plate rotating in laminar flows, the immersed boundary (IB)-lattice Boltzmann (LB) method combined with the multiple-relaxation-time (MRT) collision model in two dimensions is presented. Furthermore, an implicit velocity-correction IB method is proposed to deal with the interface of moving solid boundary interacting with fluid flows. Two valuable sub-issues are particularly highlighted in the research. One is the multiple-relaxation-time immersed boundary-lattice Boltzmann (MRT-IB-LB) implementation of the fluid-structure interface enforcing the nonslip boundary condition, and the other is the effects of rotating velocities associated with aspect ratios on the plate interacting with the flows. The model is validated with the benchmark case: the flow around a cylinder asymmetrically placed in a channel. Then the effects of different rotating velocities and aspect ratios are researched. With the increasing of aspect ratios, the vortex shedding frequency increases and the multiple dominant frequencies of the hydrodynamic force occur. The formed vortices are driven downstream and amalgamated into the dominant vortices in the biased flow. The average values of hydrodynamic forces can be enlarged by increasing aspect ratio. Additionally, the drag coefficient can be decreased but the lift coefficient is increased by increasing the rotating velocity.

This study aims to investigate the aeroelastic behaviors of cylindrical composite panels in a high-speed flow. A fluid-structure coupling program is applied to simulate the response of the interaction with the presence of both fluid and structural nonlinearities at $Ma=0.99$. The cylindrical composite panels with different layer orientations, cross-ply and angle-ply are modeled by an assemblage of triangular finite elements and the nonlinearity caused by large displacement is described by an updated tangent stiffness matrix. The inviscid unsteady equations are discretized by an AUSMpw+ flux splitting scheme. The static divergence, flutter characteristic and post-flutter response are computed and analyzed with the increase of the dynamic pressure. The results show that static and dynamic responses vary with the layer orientation. Particularly, the dynamic response of the cross-ply panel presents as high-frequency resonant oscillation; on the contrary, the dynamic response of the angle-ply panel appears as low-frequency single mode oscillation. Nonlinearities involved with aeroelastic response, such as the movement of the multiple-shock structure, and large displacement in structure, are discussed.

Coriolis mass flowmeter (CMF) is widely used in the industrial field. In mass flow measurement, there are many impurities in measured fluids that will adhere to the inner wall of the vibrating tube of CMF. The vibration characteristics of CMF would change due to the structural change, i.e., wall clung state, which will generate the wall clung state fault. In this paper, aiming at the wall clung state fault of CMF, the finite element model of CMF is established based on ANSYS. The velocity distribution of fluid in the vibrating tube of CMF is analyzed, considering the fluid–structure interaction. The location of the wall clung state in a vibrating tube is determined. Then, the fault model is established. The mechanism of the vibration transmission characteristics outwards of CMF caused by the wall clung state is analyzed by harmonic response analysis. Finally, the failure mode of CMF is investigated.

In this paper, an immersed membrane method (IMM) is proposed for the simulation of three-dimensional (3D) fluid-structure interaction phenomena in a mechanical heart valve (MHV).

Hull cavitation evolution induced by an underwater explosion (UNDEX) near a deformable steel structure is numerically investigated using a multiphase compressible fluid solver^1-3 coupled with an unsteady one-fluid cavitation model^4,5. A series of computations are conducted with varying structure surface curvature. Results suggest that structure surface curvature influence the peak pressures generated from the shock impact and cavitation collapse; a concave-designed surface not only causes local shock focus but also enhances the subsequent cavitation reload.