Despite the proliferation of cellular fused filament fabrication (FFF) polymer components for a variety of industrial applications, few studies have investigated their fluid-structure interaction (FSI) behavior during...
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Despite the proliferation of cellular fused filament fabrication (FFF) polymer components for a variety of industrial applications, few studies have investigated their fluid-structure interaction (FSI) behavior during loading, particularly under dynamic impact conditions. Furthermore, the extent to which residual stresses from the FFF build process affect the dynamic load bearing characteristics has not been addressed. In this work, simulations and experiments are conducted for cylindrical nylon specimens fabricated with two different internal closed-cell cavity structures to assess the influence of the entrapped fluid and the FFF residual stresses on the state of stress during high strain-rate impact. The demonstrated 2-stage computational approach includes a thermomechanical model of the FFF build to calculate residual stress and distortion, which forms the initial state for a subsequently executed dynamic impact model using smoothed particle hydrodynamics (SPH) to capture the effects of air within the internal cavities. Dynamic displacement boundary conditions for the FSI simulations are identified using digital image correlation (DIC), obtained from impact experiments on the FFF specimens performed using split Hopkinson pressure bar (SHPB) tests. Findings reveal that FFF residual stresses significantly influence the stress-strain response during dynamic impact, even at strain rates of 500-600 s(-1). In addition, while the influences of both FFF residual stress and FSI vary with internal cellular structure, the study reveals that their coupled effects must be considered to accurately characterize the impact behavior. Validity of the 2-stage numerical approach, as well as significance of FFF residual stress and the influence of FSI, are justified by comparing numerical predictions with experimental measurements, and observing root-mean-square stress errors within 12.77% and 11.87%, and peak stress errors within 1.93% and 1.34% for the two specimens.
We construct an exact solution for a stationary fluid flow through a channel with upper wall attached to an elastic spring. The position of the upper wall is determined from the interaction between the fluid and the w...
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We construct an exact solution for a stationary fluid flow through a channel with upper wall attached to an elastic spring. The position of the upper wall is determined from the interaction between the fluid and the wall. It is displacement computed from a quartic equation that can be solved by radicals and the solution is proved to be physically reasonable.
This paper presents a novel coupled formulation for fluid-structure interaction (FSI) problems involving free-surface fluid flows, fracture phenomena, solid mutual contact and large displacements. The numerical formul...
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This paper presents a novel coupled formulation for fluid-structure interaction (FSI) problems involving free-surface fluid flows, fracture phenomena, solid mutual contact and large displacements. The numerical formulation combines three different Lagrangian computational methods. The Particle Finite Element Method (PFEM) is used to solve the free-surface fluid flow, a Finite Element Method (FEM) with smoothed isotropic damage model is employed for the solution of solid structures and debris, finally, the Discrete Element Method (DEM) is used to manage the contact interaction between different solid boundaries, including the new ones generated by propagating cracks. The proposed method has a high potential for the prediction of the structural damages on civil constructions caused by natural hazards, such as floods, tsunami waves or landslides. Its application field can also be extended to fracture phenomena in structures and soils/rocks arising from explosions or hydraulic fracking processes. Several numerical examples are presented to show the validity and accuracy of the numerical technique proposed. (C) 2021 Elsevier Ltd. All rights reserved.
The axial vibration of the liquid-filled pipes can be represented with a four-equation fluid-structure interaction (FSI) model. When distributed friction was neglected, this model could be solved with an exact solutio...
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The axial vibration of the liquid-filled pipes can be represented with a four-equation fluid-structure interaction (FSI) model. When distributed friction was neglected, this model could be solved with an exact solution without computational grid, while the only weakness was the high time cost. A fast meshless solution (FMS) developed earlier used the time-line interpolation rather than the recursive algorithm, to speed the calculation. For the purpose of practical applications, the FMS for supports at pipe end and middle position is proposed, and series connection is also studied in this paper. The support is described by the complex constraint including elastic, damping and inertial effects. A numerical case of the double-pipe water hammer is employed to validate the series connection and end supports. The FMS for the middle support is validated by an existing experiment, where the support can be described by the dry friction. Both numerical and experimental cases indicate the effectiveness and the efficiency of the proposed solution method. (C) 2021 Elsevier Ltd. All rights reserved.
The spent fuel of a nuclear power plant is generally stored in a wet storage pool. In case of a seismic event, one has to ensure the integrity of the spent fuel and structures holding them called spent fuel racks. In ...
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The spent fuel of a nuclear power plant is generally stored in a wet storage pool. In case of a seismic event, one has to ensure the integrity of the spent fuel and structures holding them called spent fuel racks. In this study, a simple model accounting for 12 racks is proposed and compared with experimental results involving reduced scale racks. fluid-structure interactions are modeled in terms of added coupling mass and damping, and free surface effects are accounted for. Comparison between simulations and experimental results showed good agreement. In spite of the simplicity of the model, simulations succeed to give a reasonable estimation of racks accelerations and were able to reproduce the effect of excitation amplitude and water level.
Accuracies of ultrasonic methods for estimation of motion/deformation should be evaluated, but such evaluation in real experiments is not easy because it is difficult to know the true distribution of motion/deformatio...
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Accuracies of ultrasonic methods for estimation of motion/deformation should be evaluated, but such evaluation in real experiments is not easy because it is difficult to know the true distribution of motion/deformation in complex geometry, such as an atherosclerotic plaque model. In the present study, numerical simulation was performed to obtain ultrasonic echo signals from a deforming plaque model. The accuracies of our phase-sensitive 2D motion estimator in estimation of velocity and strain rate were evaluated to be 22.8% and 27.6%, respectively, and the spatial features of the estimated velocity and strain rate distributions were well corresponded to the true distributions.
The water impact of an inclined flat plate and at high horizontal velocity is experimentally investigated with focus on the fluid-structure interaction aspects. Several test conditions have been examined by varying th...
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The water impact of an inclined flat plate and at high horizontal velocity is experimentally investigated with focus on the fluid-structure interaction aspects. Several test conditions have been examined by varying the vertical to horizontal velocity ratio, the pitch angle and the plate thickness. Measurements are performed in terms of strains, loads and local pressure. The study highlights the significant changes in the strains and, more in general, in the structural behaviour when varying the plate stiffness and the test conditions. For some of the test presented, permanent deformations are also found. The strong fluid-structure interaction is analysed by com-paring the simultaneous measurements of strains and pressures, and it is shown that the deformation of the plate leads to a reduction of the pressure peak and to a corresponding pressure rise behind it. The variation in the shape of the spray root caused by the structural deformation are discussed based on both pressure measurements and underwater images. Despite the reduction of the pressure peak intensity, it is shown that the structural deformation leads to an increase in the total loading up to 50% for the test conditions examined in this study. It is also observed that in presence of large structural deformations the hydrodynamic loads do not obey the scaling that works in the case of the thick plates, and some practical conclusions about the scaling of tests in presence of a strong fluid-structure interaction are provided.
In this work, we present a new optimal control approach to fluid-structure interaction parameter estimation problems. The goal is to obtain the desired deformation by controlling the solid material properties, such as...
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In this work, we present a new optimal control approach to fluid-structure interaction parameter estimation problems. The goal is to obtain the desired deformation by controlling the solid material properties, such as the Young modulus. We consider a stationary monolithic FSI problem where solid and liquid forces at the interface are automatically balanced. We consider inequality constraints in order to bound the Young modulus control admissible set. For the optimization, we adopt the Lagrange multiplier method with adjoint variables and obtain the optimality system which minimizes the augmented Lagrangian functional. We implement a projected gradient-based algorithm in a multigrid finite element code suitable for the study of large solid displacements. In order to support the proposed approach, we perform numerical tests with different objectives and control constraints. (C) 2021 Elsevier Ltd. All rights reserved.
A flapping motion is an important fluid-structure interaction (FSI) phenomenon. Although it has been extensively studied, there are still many unknowns. Because there are numerous parameters in the kinematics and morp...
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A flapping motion is an important fluid-structure interaction (FSI) phenomenon. Although it has been extensively studied, there are still many unknowns. Because there are numerous parameters in the kinematics and morphology for flapping motions, it is difficult to experimentally determine parameter values that enhance flapping aerodynamics because of the associated time, cost, and space constraints. Therefore, a simulation-based study is a promising approach for investigating flapping motions. In our previous work, we developed an interface-tracking-based three-dimensional (3D) parallel FSI analysis system by the partitioned iterative method. However, this system failed in some cases during parametric calculations for various flapping motions. This seems because of 3D large movements and complex twisting motions of a deformable flapping wing. Because the distortion of a fluid mesh often leads to failure in the FSI analysis, the selection of a mesh control scheme greatly influences the robustness. Improving the robustness of the analysis is essentially important for the parametric analyses with a wide range of parameter sets to be tested. In the present study, we incorporate the solid-extension mesh moving technique (SEMMT) together with a specialized mesh design surrounding the flapping wing into our analysis system to improve the robustness. Furthermore, we quantitatively demonstrate the effectiveness of the above mesh control technique in 3D flapping problems by measuring the degree of mesh distortion. Using the improved FSI analysis method, we have succeeded in conducting wide range parametric studies of flapping motions to compare active and passive pitch motions and investigate lead-lag motions. We found that passive pitch caused due to appropriate Young's modulus in an elastic portion was able to produces a high lift coefficient which was almost equivalent to active pitch cases. We also confirmed that some lead-lag motions enhance the lift force.
Coastal bridges serve as lifelines in evacuation and rescue after coastal natural hazards. It is thus vital to reveal the spatial failure mechanism for coastal bridges under extreme waves. In this study, a high-effici...
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Coastal bridges serve as lifelines in evacuation and rescue after coastal natural hazards. It is thus vital to reveal the spatial failure mechanism for coastal bridges under extreme waves. In this study, a high-efficient pseudofluid-structure interaction (PFSI) solution scheme is proposed to investigate the spatial failure mechanism of coastal bridges under extreme waves. A series of laboratory experiments and numerical simulations are conducted to verify the proposed solution scheme. The results solved by the proposed solution scheme are acceptable and reliable under the small rotation of the deck, which could be used to efficiently assess the deck failure, and the calculation process is high-efficient. The spatial failure mechanism of the typical coastal bridge is investigated by using the proposed solution scheme in this study. The properties of wave forces on the deck are discussed based on numerous experimental measurements considering various wave parameter combinations and inundation conditions firstly. Subsequently, the failure thresholds of bearing vertical and horizontal reaction forces are obtained by parametric analysis considering various wave parameter combinations using the proposed solution scheme. Additionally, two typical failure modes (i.e., fall-beam failure and overturning failure) are analyzed by considering time-varying restraining stiffnesses in vertical and horizontal directions. The obtained results can be served as a robust reference for the design and management of coastal bridges under extreme waves.
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