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The swirling motion of blood flow is a widespread physiological flow phenomenon in the human body. The probability of cardiovascular and cerebrovascular diseases could be effectively reduced by swirling blood flow. In this study, first we proposed a new integrated vascular model with spiral folds on the inner wall. Based on the model, fluid-solid coupling simulation analyses of blood and blood vessels were performed. The results indicate that the spiral folds cause the swirling flow. This model provides new insights that may be of use for developing methods to generate swirling flow. Second, we discussed the specific effects of different fold parameters' characteristics on swirling flow. We found that increasing the pitch or cross-sectional area enhanced the swirling flow, specifically increasing cross-sectional diameter by 0.2 mm, wall shear stress by about 2 mm Hg, and deformation by about 0.2 µm. Finally, we proposed a new method to prepare an integrated artificial blood vessel based on the heteromorphic channel co-extrusion method; the inner wall of this blood vessel had a spiral fold structure and was micron scale in width. This study offers important guidance for the design of interventional treatments involving swirling flow. [ABSTRACT FROM AUTHOR]

A new type of cylindrical gas film seal (CGFS) with a flexible support is proposed according to the working characteristics of the fluid dynamic seal in high-rotational-speed fluid machinery, such as aero-engines and centrifuges. Compared with the CGFS without a flexible support, the CGFS with flexible support presents stronger radial floating characteristics since it absorbs vibration and reduces thermal deformation of the rotor system. Combined with the structural characteristics of a film seal, an analytical model of CGFS with a flexible wave foil is established. Based on the fluid-structure coupling analysis method, the three-dimensional flow field of a straight-groove CGFS model is simulated to study the effects of operating and structural parameters on the steady-state characteristics and the effects of gas film thickness, eccentricity, and the number of wave foils on the equivalent stress of the flexible support. Simulation results show that the film stiffness increases significantly when the depth of groove increases. When the gas film thickness increases, the average equivalent stress of the flexible support first decreases and then stabilizes. Furthermore, the number of wave foils affects the average foils thickness. Therefore, when selecting the number of wave foils, the support stiffness and buffer capacity should be considered simultaneously.

Taking a centralized drive electric vehicle power train as study object,considering the influence of coolant and lubricating oil,the fluid- structure model is established. The modal and vibration response of the model is researched. First,the fluid- structure model is proved to be correct by comparing its simulation result with the experimental result. Then,other two kinds of fluid- structure model,each one of which involved one kind of fluid,are established. The different influence degree of these two kinds of fluid on the model natural frequency is analyzed through modal simulation. At last,the power train vibration response under electromagnetic excitation is obtained by simulation,and it is compared with the result of the original model. The result indicates,that various dynamics phenomenon are showed by the model which considering the fluid- structure model with coolant,lubricating oil and mechanical components and the foundation for the subsequent optimization design is provided.

A fast mesh deformation method for propeller flow is developed based on the elastic solid method. The flow field of a propeller is assumed to be fulfilled with a kind of pseudo elastic solid which does not influence the flow. The vibration equation for the propeller blade-pseudo elastic solid system is derived. During fluid-structure coupling, the nodal displacement for the blade and the flow mesh is computed by modal superposition of the first several modes. Fluid-structure coupling is performed for a highly skewed propeller. The computing time for the dynamic mesh by the present method is about 0.017% of the computing time by the existing elastic solid method. The computing time for the fluid-structure coupling using the present method is 52% less than the computing time by the existing elastic solid method. [ABSTRACT FROM AUTHOR]

We study the time-harmonic resonance of a finite-length elastic plate in a fluid in uniform flow confined in a duct. Although the resonance frequencies are usually real, the combined effects of plate elasticity and of a flow can create complex frequencies, different from the usual so-called scattering frequencies, corresponding to instabilities. We study theoretically the existence of instabilities versus several problem parameters, notably the flow velocity and the ratio of densities and of sound speeds between the plate and the fluid. A three dimensional volume in the parameters space is defined, in which no instability can develop. In particular it corresponds to a low enough velocity or a light enough plate. The theoretical estimates are validated numerically. [ABSTRACT FROM AUTHOR]

Highlights • A new type of PDMS check valve is presented in a supporting piezoelectric pump. • The flow rate of improved check valve is significantly increased. • Solves a series of problems that exist with regular PDMS bridge check valve design. • The modular pump design that allows the adjustment of the pump performance. Abstract A technique of check valve improvement for high frequency and high flow rate piezoelectric pumps is presented. By adding in a blocking edge over polydimethylsiloxane (PDMS) film check valve to modify their deformation pattern, 40%–300% flow rate enhancement and 5–6 kPa output pressure increment were achieved on a bench top testing platform. Experimental results show that the new valve is benefits to design a high efficiency and high outflow piezoelectric pump. [ABSTRACT FROM AUTHOR]

The multiple scattering of sound waves and the fluid-structure interaction should be taken into account to calculate the acoustic scattering of underwater elastic corner reflectors. The scattering acoustic field of underwater elastic corner reflectors in far field is simulated by using structure finite element method(FEM)/fluid indirect coupled boundary element method(IBEM). The influences of plate material and thickness, incident angle and the type of corner reflector on target strength and the scattering mechanism are analyzed when the incident wave frequency varies from 5.0 k Hz to 20.0 kHz. The results show that the scattering acoustic field of underwater elastic corner reflectors has a strong frequency characteristic. It varies with plate material and thickness, and incident wave frequency. The multiple scattering of sound waves has important contributions to the backscattering acoustic field of corner reflectors. The simulated results are in good agreement with the experimental results. The structure design and optimization method of corner reflectors are presented. [ABSTRACT FROM AUTHOR]

Abstract A coupled fluid-structure-fracture approach was presented to study the dynamic fracture of pre-flawed elbow pipes subjected to internal hydrogen-oxygen detonation. The initial flaw is located at the extrados, crown and intrados of the elbow, respectively. The hydrogen-oxygen detonation was modeled by a user-programed burn method based on the CJ theory. The fracture of elbow pipe was simulated by a validated bivariate failure criterion which was deduced based on the adiabatic shear failure mechanism of materials at high strain rates. Results demonstrate that the presented approach can capture the detonation wave propagation and the complex crack extension and branching effectively. It is found the peak pressure at extrados is 2.9 times larger than that at intrados, but the hoop stresses and effective strains at the three initial flaw positions are comparable with each other, even the average amplitude of hoop stress at intrados is higher than those at extrados and crown. The increase of detonation pressure can lead to crack branching and makes more cracks propagate simultaneously. The crack initiating at crown tends to turn and run to the intrados when passing the transition sections of elbow, while the crack initiating at intrados is expected to branch here. The average crack speeds for forward cracks are 100–300 m/s, while the speeds are 70%–90% of the above for backward cracks. The branch crack speeds are generally less than 40% of those before branching. Furthermore, the elbow pipes with initial flaw at intrados generally have the largest total crack length, while elbow pipes with initial flaw at crown have the strongest resistance against crack propagation. It is also suggested that local bucking is an important feature that takes place in dynamic fracture processes of elbow pipes. Highlights • Increase of detonation pressure can lead to earlier branching of cracks. • The forward crack speed is 100–300 m/s and backward crack speed is 0.7–0.9 of above. • Cracks running axially at crown tend to turn to the intrados at transition sections. • Elbow pipe with flaw at crown has strongest resistance against dynamic fracture. • Local buckling is an important feature in the dynamic fracture of elbow pipe. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesters (PEHs) from fluid energy sources, particularly vortex shedding–induced vibrations, have received considerable attention in recent years. However, there still exists a common problem with these harvesters: the current optimum position of a vortex shedding–induced PEH located in the wake of a bluff body is commonly obtained through a series of experiments. This study proposes a theoretical model to determine the best position and demonstrate this mechanism. This theoretical model, which consists of fluid–structure and electromechanical couplings, is derived from the proposed PEH with a flapping sheet structure. The equivalent harmonic force in the fluid–structure coupling part caused by the vortexes on the flapping sheet is expressed by Bernoulli’s law and Lamb–Oseen vortex model. The system equations in the electro–mechanical coupling part are then obtained utilizing Euler–Bernoulli beam theory and an equivalent circuit model. This model was validated initially through the published data in the reference and then through the experimental results from a proposed PEH prototype. The optimum position of the PEH in the flow field is revealed by the analytical solution in numerical results and examined in experimental results. Moreover, the balanced match of fluid velocity and bluff body diameter can also contribute to the high–level system performance under the optimal load resistance. [ABSTRACT FROM AUTHOR]

A fast dynamic mesh technology by our research group has been applied in the time synchronized fluid-structure coupling. It is found that flow mesh update after the convergent calculation of the flow will induce excessive iterations in the computation of flow increasing the computing time of fluid-structure coupling. To reduce the computing time, a time-space synchronized fluid-structure coupling algorithm was developed in this paper based on the pre-existing time synchronized method and the fast dynamic mesh technology. The wing vibration and flow mesh deformation were computed using the fast dynamic mesh technology after each iteration in the calculation of the flow. Namely, the flow and the wing vibration were solved in space synchronization. The calculating convergence of the flow and the wing vibration were both achieved through iterations every time step. Namely, the flow and the wing vibration were solved in time synchronization. Thus, the flow and the wing vibration are coupled both in time and space synchronization. The flutter boundary of wing 445.6 was predicted using the present algorithm. The calculated results compare well with the experimental data and the computing time was almost reduced by 75%. [ABSTRACT FROM AUTHOR]

Microcracks caused by perforating operations in a cement sheath body and interface have the potential to further expand or even cause crossflow during hydraulic fracturing. Currently, there are few quantitative studies on the propagation of initial cement-body microcracks. In this paper, a three-dimensional finite element model for the propagation of initial microcracks of the cement sheath body along the axial and circumferential directions during hydraulic fracturing was proposed based on the combination of coupling method of fluid−solid in porous media and the Cohesive Zone Method. The influence of reservoir geological conditions, the mechanical properties of a casing-cement sheath-formation system, and fracturing constructions in the propagation of initial axial microcracks of a cement sheath body was quantitatively analyzed. It can be concluded that the axial extension length of microcracks increased with the increase of elastic modulus of the cement sheath and formation, the flow rate of fracturing fluid, and casing internal pressure, and decreased with the increase of the cement sheath tensile strength and ground stress. The elastic modulus of the cement sheath had a greater influence on the expansion of axial cracks than the formation elastic modulus and casing internal pressure. The effect of fracturing fluid viscosity on the crack expansion was negligible. In order to effectively slow the expansion of the cement sheath body crack, the elastic modulus of the cement sheath can be appropriately reduced to enhance its toughness under the premise of ensuring sufficient strength of the cement sheath.

To have a safe structural design, an analysis of the dynamic behavior of a Francis turbine runner with consideration of the added mass effects of surrounding water is necessary during design phase. Both in design and at off-design operations, large-scale forms of attached cavitation may appear on runner blades and can change the added mass effects of the surrounding fluid in relation to a single water domain. Consequently, a numerical investigation of the modal response of a Francis runner has been carried out by reproducing the presence of various sizes of leading edge cavitation (LEC) and trailing edge cavitation (TEC). The fluid−structure interaction problem has been solved by means of an acoustic-structural coupling method. The calculated added mass effects with cavitation have been compared with those corresponding to the pure water condition without cavitation. Firstly, a single blade has been investigated to evaluate the level of significance for the proposed cavity shapes and dimensions. Afterwards, based on the results obtained, the complete runner structure has been considered, factoring in similar cavity shapes and locations. The results prove that significant added mass effects are induced on the entire runner by the attached cavitation that increase the natural frequencies of the first modes. Moreover, the added mass effects increase with cavity size and amplitude of blade deformation below the cavity.

It is difficult to conduct the ground separation test of large-scale rocket fairings under vacuum condition. To predict the fairing separation during extra-atmospheric flight, the established finite element (FE) model should be corrected by using the ground separation test data. The ground separation test of a large-scale flexible fairing is simulated by the coupled Eulerian-Lagrangian method. The motion characteristics and breathing deformation data of fairing separating under air resistance are obtained and agree well with the test data, which verifies the correctness of the model and the method. The separation of rocket fairing during extra-atmosphere flight is simulated with the same FE model, and the effects of air resistance and axial overload on fairing separation and deformation characteristics are analyzed. The results show that the air resistance attenuates the velocity and breathing vibration frequency of rocket fairing, but increases the amplitude of the breathing motion; the amplitude of breathing motion increases with the increasing in axial overload, meanwhile, the breathing motion of fairing is related to the first-order vibration mode. [ABSTRACT FROM AUTHOR]

Summary: Cavitation erosion is caused in solids exposed to strong pressure waves developing in an adjacent fluid field. The knowledge of the transient distribution of stresses in the solid is important to understand the cause of damaging by comparisons with breaking points of the material. The modeling of this problem requires the coupling of the models for the fluid and the solid. For this purpose, we use a strategy based on the solution of coupled Riemann problems that has been originally developed for the coupling of 2 fluids. This concept is exemplified for the coupling of a linear elastic structure with an ideal gas. The coupling procedure relies on the solution of a nonlinear equation. Existence and uniqueness of the solution is proven. The coupling conditions are validated by means of quasi‐1D problems for which an explicit solution can be determined. For a more realistic scenario, a 2D application is considered where in a compressible single fluid, a hot gas bubble at low pressure collapses in a cold gas at high pressure near an adjacent structure. [ABSTRACT FROM AUTHOR]

As a form of passive control, padding rubber layers onto the most heavily deformed zones of a system can improve the dynamic behavior and the acoustic comfort of a vehicle system. This paper proposes an extensive hybrid modal synthesis method in order to study coupled fluid-structure systems, in retaining a few degrees of freedom. Modal criteria, corresponding to noise transmission paths between substructures in the system, have been derived to characterize the dynamic phenomenon from a modal view. These criteria were then substituted by Kriging interpolation models to avoid prohibitive simulation steps during optimization of the complex system. Once the mathematical models of the investigated modal criteria were established and the multi-objective functions for rubber characteristics defined, an approximate optimal solution leading to superior dynamic performance could be obtained based on a genetic algorithm. The analytical results and numerical experiments conducted have also justified the efficiency of our proposed strategy. [ABSTRACT FROM AUTHOR]

We propose a new high-order accurate numerical boundary treatment for solving hyperbolic systems of conservation laws and Euler equations using a Lagrange-remap approach on Cartesian grids in cases of physical boundaries not aligned with the mesh. The method is an adaptation of the Inverse Lax–Wendroff procedure [34–38] to the Lagrange-remap approach, which considerably alleviates the algebra. High-order accurate ghost values of conservative variables are imposed using Taylor expansions whose coefficients are found by inverting a (linear or non-linear) system which is well posed in all our examples. For 2D problems, a least-square procedure is added to prevent extrapolation instabilities. The Lagrange-remap formalism also provides a simpler fluid–structure coupling which is also described. Numerical examples are given for the linear case and Euler equations in 1D and 2D. [ABSTRACT FROM AUTHOR]

Nonlinear vibrations that occur in such bundle structures caused collisions between tubes and cross flows of the surrounding fluid. This paper presents modeling techniques for simulating the FSI dynamics of bundle tubes vibrating and colliding in fluids. A typical configuration of a three-dimensional tube bundles submerged in fluid of a cylindrical container is studied. Coupling conditions of displacement, velocity and forces are considered on the fluid-structure coupling interfaces. Contacts boundary between tubes and topological domain changes of the fluid are also considered on the fluid-structure coupling interface. Modeling techniques and algorithm are then established for flow-induced vibrations of the tubes, and collisions between tubes in fluids. The examples are presented to demonstrate the effectiveness of the proposed techniques. It has confirmed that our code produces the correct physics of the FSI problem, and capable of revealing the complex nonlinear mechanism with solid-solid contacts together with fluid-solid interactions. [ABSTRACT FROM AUTHOR]

Nomex honeycomb has very low relative density, thus there is a lot of the air entrapped within the cells of Nomex honeycomb sandwich structures. The air has a significant effect on the mechanical response under flatwise compression, and it was investigated herein. Firstly, experiments of the honeycomb with and without facesheets were performed to study the entrapped air effect. Secondly, the unit cell model and multi-cell model of the honeycomb were proposed, in which, two methods of modeling the entrapped air using commercial software LS-DYNA were developed. In the first method, six cell walls and two facesheets as well as the air entrapped by them are simulated as an air-filled cavity using Airbag tools. In the second method, the entrapped air is simulated by ALE (Arbitrary Lagrangian Eulerian) elements, which realize the grid deformation and material flow. Interaction between the entrapped air and cell walls under compression is analyzed using fluid-structure coupling algorithm. It is found in this paper that energy absorption capacity of Nomex honeycomb sandwich can be enhanced through the effect of the entrapped air on the cell walls folding process. The ALE method is superior to the airbag method in the unit cell models as regard to the energy absorption capacity and the energy absorbing process. [ABSTRACT FROM AUTHOR]

To better understand the dynamic characteristics of a hydrostatic spindle in fluid-structure coupling, the impact of oil film slip on the 4 dynamic stiffness and damping coefficients of the spindle is studied. On the basis of modified Reynolds equation, which considers the microscale velocity slip effect, rotation error of the spindle is calculated. To solve the rotor axis orbit under the existence of eccentric quality, 4 dynamic stiffness and damping coefficients of the oil film, which describe the dynamics of a rotor axis orbit, are calculated by using load increment method and the pressure perturbation method. The research results show that velocity slip caused a certain impact on dynamics of bearing stiffness and damping performance. The experiment of the measuring path of the shaft verifies the correct and effect of the orbit of shaft center model. [ABSTRACT FROM AUTHOR]

This paper addresses a co-simulation method for fluid power driven machinery equipment, i.e. oil hydraulic machinery. In these types of machinery, the fluid-structure interaction affects the end-product performance to a large extent, hence an efficient co-simulation method is of high importance. The proposed method is based on a 1D system model representing the fluid components of the hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies. This means that the fluid system simulation will get a more accurate structural response, and that the structural simulation will get more correct fluid loads at every time step, compared to decoupled analysis. Global system parameters such as fluid flow, performance and efficiency can be evaluated from the 1D system model simulation results. From the 3D FE-models, it is possible to evaluate displacements, stresses and strains to be used in stress analysis, fatigue evaluation, acoustic analysis, etc. The method has been implemented using two well-known simulation tools for fluid power system simulations and FE-simulations, respectively, where the interface between the tools is realised by use of the Functional Mock-up Interface standard. A simple but relevant model is used to validate the method. [ABSTRACT FROM AUTHOR]

In this paper, a graphical processing unit (GPU) implementation of adaptive particle refinement (APR) in the Smoothed Particle Hydrodynamics (SPH) framework is used to simulate the multi-phase flow and fluid-structure coupling problems. The multi-phase flow and fluid-structure coupling SPH models based on the Riemann solver are presented and the local particle refinement technique based on the axis-aligned square refinement pattern is adopted to split particles. A particle shifting technique constructing virtual fine particles (VFP-PST) is proposed to regularize the particle distribution for numrical accuracy and stability. To facilitate the device memory throughput efficiently, a dynamic resource management algorithm is used to implement GPU-accelerated adaptive particle refinement. Precision analysis shows the effect of the smooth length ratio of fine and coarse particles on numerical accuracy. Different tests have demonstrated that the proposed GPU-accelerated IAPR is accurate and stable and provides a promising approach to simulate the multi-phase flow and fluid-structure problems with low computational cost and comparable precision when compared with uniform particles. In order to improve numerical accuracy and save computation time in the applications of the SPH in large-scale or multi-scale problems, a GPU-accelerated adaptive particle refinement for multi-phase flow and fluid-structure coupling SPH is proposed in this paper. The novelty points are summarized as follows: • The multi-phase flow and fluid-structure coupling SPH model is developed with GPU-based adaptive particle refinement. • A particle shifting technique constructing virtual fine particles is proposed to regularize the particle distribution. • The dynamic resource management algorithm is proposed to implement the GPU-accelerated adaptive particle refinement. • Accuracy and stability of algorithm are analysed in detail using several multi-phase flow and fluid-structure coupling cases. [ABSTRACT FROM AUTHOR]

Operational shock (op-shock) analysis has been developed to consider the dynamics of components of a hard disk drive (HDD). Op-shock simulation uses simplified models. However, the dynamics of the components affect the head–disk interface (HDI) response, especially the disk curvature and ramp–disk contact. This paper investigated the effect of the dynamics of HDD components on the HDI response. As the HDD is more sensitive to external shock and vibration, the effects of the dynamics of HDD components need to be considered for accurate op-shock analysis. The ramp–disk contact is an important factor in an op-shock simulation, because ramp–disk contact and disk deformation occur during the shock. Therefore, this op-shock simulation modeled the ramp–disk contact and considered the disk curvature. To obtain an accurate result, a two-way coupled method was used to investigate the HDD dynamic response during op-shock. Using the op-shock model, the fluid-structure coupling effect was investigated and compared with a decoupled model that used linear springs to replace the air bearing. Then, we investigated the effect of the ramp–disk contact and disk curvature on the HDI response during a shock. [ABSTRACT FROM AUTHOR]

This article presents a novel calculation method for the bearing performance of the aerostatic thrust bearing. This method is provided while taking the fluid-structure coupling effect into account. High pressure air film leads to the structure deformation, thus the bearing clearance after deformation is utilized to estimate the real bearing performance. Furthermore, the influencing factors on the bearing performance, the thrust plate’s thickness, and the orifices’ location, are investigated on the basis of the fluid-structure coupling effect. The calculation method of the best gas film thickness is deduced and presented. Experimental results for validation highlight the reliability of this method. [ABSTRACT FROM AUTHOR]

For the analysis of dynamic characteristics of fluid-conveying pipes with piecewise linear support, a fluid-structure coupling dynamic model based on the finite element method is proposed. A user-defined pipe element based on Euler-Bernoulli beam is developed for modeling the pipes, considering the dynamic flow conditions. A nonlinear spring element is utilized to model the clamp between the pipe and the base. The dynamic responses of the system are obtained through the direct time integration. The stiffness of the clamp support is investigated by the analytical method and the experimental method, in which it is found that the clamp stiffness is piecewise linear. For different pipe geometries the user-defined element model, analytical model and measurement data are compared. The results show high quality of the element developed in this paper. Finally, the dynamic characteristics of the pipe system with piecewise linear support subjected to base harmonic excitation are calculated and the effects of the system parameters on pipe behaviors have also been studied. As a consequence, the model proposed in this paper can represent the piecewise linear nonlinearity of the clamp support and be used conveniently to investigate the effects of the fluid-structure coupling on the system behaviors. [ABSTRACT FROM AUTHOR]

Due to the advantages of good fracture performance and the application of carbon capture and storage (CCS), supercritical carbon dioxide (SC-CO2) is considered a promising alternative for hydraulic fracturing. However, the fracture initiation mechanism and its propagation under pressurized SC-CO2 jet are still unknown. To address these problems, a fluid–structure interaction (FSI)-based numerical simulation model along with a user-defined code was used to investigate the fracture initiation in an inhomogeneous shale rock. The mechanism of fracturing under the effect of SC-CO2 jet was explored, and the effects of various influencing factors were analyzed and discussed. The results indicated that higher velocity jets of SC-CO2 not only caused hydraulic-fracturing ring, but also resulted in the increase of stress in the shale rock. It was found that, with the increase of perforation pressure, more cracks initiated at the tip. In contrast, the length of cracks at the root decreased. The length-to-diameter ratio and the aperture ratio distinctly affected the pressurization of SC-CO2 jet, and contributed to the non-linear distribution and various maximum values of the stress in shale rock. The results proved that Weibull probability distribution was appropriate for analysis of the fracture initiation. The studied parameters explain the distribution of weak elements, and they affect the stress field in shale rock.

The high-speed impact of liquid droplets on blades in wet steam region seriously affects the safe operation of steam turbine. For blade stability and response characteristics, most studies utilized ideal gas as working medium and few studies focused on the role of droplets in the flow field. In this study, both the distribution information of droplet particles in the flow field and the impact of droplet particles on blades were comprehensively considered. First, the droplet distribution at the last stage inlet was calculated, and then the droplet-wall interaction model was determined and loaded into calculation process. The pressure distribution on blade surface, blade force variation, mechanical properties, and further dynamic response characteristics of blade were analyzed with ideal gas and wet steam models, respectively, by using one-/two-way fluid-structure interaction. Results show that the blade displacement of leading and trailing edges under wet steam model reaches the maximum at near 80% blade height, and there is a low frequency amplitude corresponding to 460 Hz–470 Hz with the peak value in the range of 22Pa–26Pa. The variations of the maximum displacement and maximum equivalent stress of the blade with time are more intense under wet steam model compared with those under ideal gas model. • The non-uniform incidence of droplets is considered at the inlet of the last stage of the steam turbine. • The process of droplet -wall interaction in the last stage is introduced. • Two way fluid-structure interaction is applied to study blade response characteristics. • The influence of droplet particles on the unsteady characteristics of the flow field in the last stage is studied. • The effect of droplet particles on the mechanical properties of the last stage rotor blade is studied. [ABSTRACT FROM AUTHOR]

Hydrodynamic forces from moving fluids can be utilized to remove contaminants which is an ideal fouling-release strategy for underwater surfaces. However, the hydrodynamic forces in the viscous sublayer are greatly reduced owing to the no-slip condition, which restricts their practical applications. Here, inspired by sweeper tentacles of corals, an active self-cleaning surface with flexible filament-like sweepers are reported. The sweepers can penetrate the viscous sublayer by utilizing energy from outer turbulent flows and remove contaminants with adhesion strength of >30 kPa. Under an oscillating flow, the removal rate of the single sweeper can reach up to 99.5% due to dynamic buckling movements. In addition, the sweepers array can completely clean its coverage area within 10 s through coordinated movements as symplectic waves. The active self-cleaning surface depends on the fluid-structure coupling between sweepers and flows, which breaks the concept of conventional self-cleaning., (© 2023 Wiley-VCH GmbH.)

A coupled Smoothed Particle Hydrodynamics-Finite Element Method (SPH-FEM) method was presented to simulate the dynamic fracture of cylindrical shell subjected to internal explosion. The movement of detonation products was modeled by SPH, and the fracture response of cylindrical shell was modeled by FEM, where they were coupled together by a penalty-based coupling approach. A rate-dependent failure criterion which was proposed and verified in our previous work was employed in the simulation to account for the adiabatic shear failure of the cylindrical shell. Also, the decoupled simulation was conducted to make a comparison with the coupled SPH-FEM simulation above. Results showed the interaction between blast wave and cylindrical shell, the dynamic crack propagation behavior and the leakage of detonation products. It is found that the coupled SPH-FEM method can well handle the fluid-structure interaction (FSI) problem which involves local topology changes and ruptures. Compared with decoupled simulation, the coupled SPH-FEM simulation gives a more reliable prediction of the final fracture morphology of cylindrical shell. The decoupled simulation tends to present a result with severer bulging deformation but smaller fracture size compared with the real situation. [ABSTRACT FROM AUTHOR]

Dynamic response of concrete lining structure in high pressure diversion tunnel under seismic load is of great importance for engineering design and safety assessment. In light of the basic idea of static damage constitutive in strain space, a dynamic damage and cracking model of concrete suitable for programming is established. Based on the explicit finite element method for analyzing the dynamic response of single-phase solid and fluid medium, combining with the boundary conditions at coupling interface, a dynamic explicit finite element solving format considering the coupling interaction of lining and inner water is presented. This method can directly integrate, solve without simultaneous equations, and greatly simplify the calculation process. Moreover, it can be easily used to analyze wave propagation problems with a variety of mediums. According to the damage evolution properties of concrete lining under seismic load, a calculation method of permeability coefficient considering the effect of damage and cracking is put forward, and the inner water exosmosis process with lining cracks is analyzed. The calculation results of engineering example can reasonably reflect the seismic response characteristics of concrete lining structure in high pressure diversion tunnel, and an effective analysis method is provided for the aseismic design of hydraulic tunnel. [ABSTRACT FROM AUTHOR]

It is computation-intensive and time-consuming to conduct the direct numerical simulation of the fluid and structure interaction of an entire blade row. This paper presents a reduced-order model (ROM) that significantly improves the efficiency of turbomachinery flutter analysis. This ROM is constructed with the system identification technique and under the modal theory through a single implementation of unsteady flow computation of several blade passages. The ROM for uncoupled flutter analysis can obtain the aerodynamic damping coefficients of all the Inter-Blade Phase Angles (IBPA) and structural nature frequencies. The ROM for coupled flutter analysis is to solve the eigenvalues of aeroelastic equations established by coupling the ROM with the structural dynamic equations of the whole annular blade row in state-space form. This ROM method is validated by its application to two test cases—an axial-flow cascade (Standand Test Configuration 4, STCF4) and a transonic axial-flow fan rotor (NASA Rotor 67). The results verify the capability of the proposed ROM method to compute the flutter characteristics of turbomachinery blades accurately and efficiently. Compared with the direct unsteady computational fluid dynamic (CFD) method (the direct unsteady Navier–Stokes method and fluid–structure coupling method), the computational efficiency of the ROM method is improved by more than 10 times. The comparison shows that the damping coefficients and vibration frequencies of coupled flutter calculation are close to uncoupled results when mass ratio increases. This ROM approach is highly suitable for the parametric, mistuning, and multi-mode coupling analysis at the early stage of turbomachinery blade design. [ABSTRACT FROM AUTHOR]

Two methods are generally used for the aeroelastic analysis of bladed-disc assemblies. The first, often referred to as the energy method, assumes that the fluid does not modify invacuum structural dynamic behavior. On the other hand, the second, based on an eigenvalue approach, considers the feedback effect of the fluid on the structure. In this paper, these methods are compared using different test cases, in order to highlight the limitations of the energy method. Within this comparison, the effect of material modifications on the coupled behavior of the assembly is examined.

This paper presents a numerical method to simulate the dynamic interaction between the structural deformation and the aerodynamic characteristics of flexible flapping wing for micro air vehicle (MAV). A fluid-structure coupling solver is developed based on the Navier-Stokes equations and the structural dynamic equations. In addition, the interface data exchange method based on the radial basis function and the moving mesh generation method based on the infinite interpolation are applied, which play an important role in the coupling research. The preceding method is validated by comparison with the wind tunnel experimental results. For the research scope of this article (R=5 × 104), the flexible deformation impacts of flapping wing on aerodynamic performance are presented. The simulation results proved that the structural deformation has a significant effect on the aerodynamic forces, especially on the thrust, and the structural deformation is determined by aerodynamic and inertial forces together, but with different impact ratio as the change of flapping frequency. Moreover, the flow details are further investigated to discuss the influence of flexible deformation on the aerodynamics. [ABSTRACT FROM AUTHOR]

This study focuses on the dynamic characteristics of the containers with fuel consumption. With fuel consumption, the fuel container system vibrates with decreasing mass, which is a typical variable mass system. In order to investigate the influences of the time-varying liquid on vibration of the containers, this fluid–structure coupling system with time-varying mass is modeled combining finite element method, used to model the structure, and virtual mass method representing the fluid. The dynamic responses and time–frequency analysis of the time-varying mass system are presented based on the numerical simulations. From the results, it is shown that decrease of the mass results in increase of the vibration frequencies of the system and induces an additional negative damping. The additional negative damping is proportional to the rate of mass change and causes the vibration to decay slowly. The results also suggest that the time–frequency analysis possess appealing advantages in processing nonstationary signals and thus are able to provide reliable time–frequency domain information for time-varying mass systems. [ABSTRACT FROM AUTHOR]

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• Mechanism of rippling deformation of pipe was explained. • Wave-pipe interaction and interference of flexural waves were analyzed. • Theoretical solution predicting the axial locations of ripples was derived. • The ripple closest to the end wall can be caused by two factors together. The unique rippling deformation of pipe due to internal detonation and reflected shock was studied. Numerical model incorporating thermo-viscoplastic constitutive model and considering the fluid-structure coupling between detonation wave and pipe was developed. Two pipes made of 304 L steel and 6061-T6 aluminum with different diameter-to-thickness ratios were analyzed. The computed pressure histories, strain response and residual plastic strain patterns were in reasonably good agreements with experiments. Through detailed analysis of wave-pipe interaction and the propagation of incident and reflected flexural waves along the pipe, it is revealed that the rippling deformation is caused by two factors: 1) Plastic bugling deformation near the end wall due to reflected maximum peak pressure; 2) Interference between incident and reflected flexural waves. An analytical solution predicting the axial locations of the ripples was also derived. The ripple closest the reflecting end can be caused by only the reflected maximum pressure or together with the interference effect, which depends on the specific material parameter and diameter-to-thickness ratio of the pipe. The resulting plastic deformation was severer if the above two factors act together. The conclusions provide insights to this unique phenomenon. [ABSTRACT FROM AUTHOR]

Pressure vessel-pipe-safety valve (PVPSV) is a commonly used combination in the industrial pressure systems. For the design optimization purpose, an in-depth investigation on the working mechanism of such a combination is essential. To this end, experimental and numerical analysis were performed in this paper. For measuring, an experimental test rig is specially designed and built, thereby dynamic tests were performed. The results indicate that the set-pressure of the safety valve and the valve spring stiffness have significant influence on the dynamics of the PVPSV. Upon certain operating conditions, the safety valve responds in unstable manners, e.g., flutter or chatter. To compensate the tests, a high-fidelity 2-D axis-symmetric system-level Computational Fluid Dynamics (CFD) model is used. The simulation results show that both the damping coefficient and the connecting pipe length have great influence on the dynamics of the PVPSV system. A PVPSV system with a small damping coefficient and/or a long connecting pipe is more likely to exhibit dynamic instability. Finally, combining the results of experiments and numerical simulations, a large enough net disc force coupled with insufficient kinetic energy loss of valve moving parts are considered to be the root cause of unstable operations of the PVPSV system. • An test rig containing a vessel, pipe and a valve is developed, thereby FSI of the PVPSV system can be studied in depth. • The FSI has a non-negligible influence on the dynamic response of the pressure vessel-pipe-safety valve system. • A better combination of the disc force and damping could avoid undesirable vibrations of the safety valve/PVPSV system. [ABSTRACT FROM AUTHOR]