The vibration of micro resonators is strongly influenced by the hydrodynamics of the surrounding fluid in the vicinity of a rigid wall. While most prior efforts to model this hydrodynamic loading have focused on squee...
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The vibration of micro resonators is strongly influenced by the hydrodynamics of the surrounding fluid in the vicinity of a rigid wall. While most prior efforts to model this hydrodynamic loading have focused on squeeze film damping with very narrow gaps, in many practical applications, the resonators vibrate close to a surface with a moderate distance. Two recently developed models which deal with this problem are reviewed. Experiments by using a micro bridge resonator with a big range of gaps are performed at controlled gas pressures, and are compared with predictions from these theoretical models. The unsteady Navier-Stokes model yields the best agreement with experiments.
In this paper, we provide a brief overview of the development of stabilized and multiscale methods in fluid dynamics. We mainly focus on recent developments and new directions in the variational multiscale (VMS) metho...
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In this paper, we provide a brief overview of the development of stabilized and multiscale methods in fluid dynamics. We mainly focus on recent developments and new directions in the variational multiscale (VMS) methods. We also discuss applications of the VMS techniques to fluid dynamics problems involving computational challenges associated with high-Reynolds-number flows, wall-bounded turbulent flows, flows with moving domains including subdomains in relative motion, and free-surface flows.
The interaction between a fluid and a solid surface in relative motion represents a dynamical process that is central to the problem of laminar-to-turbulent transition (and consequent drag increase) for air, sea and l...
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The interaction between a fluid and a solid surface in relative motion represents a dynamical process that is central to the problem of laminar-to-turbulent transition (and consequent drag increase) for air, sea and land vehicles, as well as long-range pipelines. This problem may in principle be alleviated via a control stimulus designed to impede the generation and growth of instabilities inherent in the flow. Here, we show that phonon motion underneath a surface may be tuned to passively generate a spatio-temporal elastic deformation profile at the surface that counters these instabilities. We theoretically demonstrate this phenomenon and the underlying mechanism of frequency-dependent destructive interference of the unstable flow waves. The converse process of flow destabilization is illustrated as well. This approach provides a condensed-matter physics treatment to fluid-structure interaction and a new paradigm for flow control.
The response of aluminium sandwich panels with three thicknesses' core subjected to different underwater loading levels has been studied in the fluid-structure interaction (FSI) experiments. The transient response...
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The response of aluminium sandwich panels with three thicknesses' core subjected to different underwater loading levels has been studied in the fluid-structure interaction (FSI) experiments. The transient response of the panels is measured using a three-dimensional (3D) Digital Image Correlation (DIC) system, along with high-speed photography. The full-field shape and displacement profiles of dry face sheets were recorded in real time compared with those of monolithic plate. The out-of-plane deflection and in-plane strain were quantified and analyzed. Three typical deformation modes of sandwich panel were identified. The results show that the core structure is crushed resulting in an initial large circular shape of deformation in the center area of panels. From this moment on, the panel is starting to act as a free vibration beam with initial velocities. The deformation modes consisted of homogeneous large deformation for both face sheets, obvious deformation border on wet face sheet, core node imprinting, remarkable wrinkled skin of deformation border, and a partial delamination and partial tear failure of the dry face. The blast-resistance of sandwich panel can be highly efficiently improved by increasing the thickness of core structure.
In the present study, a finite element formulation is presented to investigate vibration response of elastic plates in contact with a fluid medium. The fluid is assumed to be incompressible and inviscid, and the imper...
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In the present study, a finite element formulation is presented to investigate vibration response of elastic plates in contact with a fluid medium. The fluid is assumed to be incompressible and inviscid, and the impermeability condition of the plate is taken into account. The classical plate theory (CPT), first-order shear deformation plate theory (FSDT), and Reddy third-order shear deformation plate theory (RSDT) are considered for the kinematic description of the solid medium and the simplified Navier-Stokes equations are used as the governing equations for the fluid medium. For each plate theory, a coupled set of finite element equations is derived. The effect of the fluid pressure is considered as an added mass and its effect on natural frequencies and mode shapes is investigated through several numerical simulations by varying the boundary conditions.
We are interested in the mathematical modeling of the deformation of the human lung tissue, called the lung parenchyma, during the respiration process. The parenchyma is a foam-like elastic material containing million...
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We are interested in the mathematical modeling of the deformation of the human lung tissue, called the lung parenchyma, during the respiration process. The parenchyma is a foam-like elastic material containing millions of air-filled alveoli connected by a tree-shaped network of airways. In this study, the parenchyma is governed by the linearized elasticity equations and the air movement in the tree by the Poiseuille law in each airway. The geometric arrangement of the alveoli is assumed to be periodic with a small period epsilon > 0. We use the two-scale convergence theory to study the asymptotic behavior as epsilon goes to zero. The effect of the network of airways is described by a nonlocal operator and we propose a simple geometrical setting for which we show that this operator converges as e goes to zero. We identify in the limit the equations modeling the homogenized behavior under an abstract convergence condition on this nonlocal operator. We derive some mechanical properties of the limit material by studying the homogenized equations: the limit model is nonlocal both in space and time if the parenchyma material is considered compressible, but only in space if it is incompressible. Finally, we propose a numerical method to solve the homogenized equations and we study numerically a few properties of the homogenized parenchyma model.
The use of a membrane to mitigate the extreme pressure loads on the roof of a surface-mounted prism is investigated. The fluid-structure interaction problem is solved by coupling the unsteady Navier-Stokes equation wi...
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The use of a membrane to mitigate the extreme pressure loads on the roof of a surface-mounted prism is investigated. The fluid-structure interaction problem is solved by coupling the unsteady Navier-Stokes equation with the membrane equation. The minimum number of membrane modes required for the solution is determined through a convergence study. The results show that this passive control technique can be used to reduce the extreme pressure coefficients by approximately 25%. This reduction is explained by investigating the effects of the membrane on the flow field. (C) 2014 American Society of Civil Engineers.
A lot of work has gone into the study of valveless micropumps for various applications. However, the complex fluid-structure interactional physics and associated phenomena such as cavitation affects the characterizati...
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A lot of work has gone into the study of valveless micropumps for various applications. However, the complex fluid-structure interactional physics and associated phenomena such as cavitation affects the characterization of valveless micropumps, for applying them reliably in any real-time applications. This paper presents a method of characterization of valveless micropump performance through dynamic measurement of chamber pressure. Experimental investigation has been carried out to study the micropump behavior through pressure measurement under both cavitation and non-cavitation conditions, and the results show that this technique is useful for the characterization of micropump.
In this paper, the applicability of the homotopy perturbation method (HPM) in analyzing the flutter of geometrically nonlinear cross-ply rectangular laminated plates resting on nonlinear elastic foundation is investig...
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In this paper, the applicability of the homotopy perturbation method (HPM) in analyzing the flutter of geometrically nonlinear cross-ply rectangular laminated plates resting on nonlinear elastic foundation is investigated. The piston theory is employed to evaluate the aerodynamic pressure acting on the plate. The von Karman geometric nonlinear theory is used to construct the governing equations of the system. The Galerkin's method is used to reduce the nonlinear partial differential equations to a nonlinear second-order ordinary differential equation, and the HPM is employed to study the effect of initial deflection, aspect ratio and stacking sequence on the flutter pressure of cross-ply laminated plates. The results show that the first approximation of the HPM leads to highly accurate solutions for the geometrically nonlinear flutter of cross-ply rectangular laminated plates subjected to the aerodynamic pressure.
A semi-implicit coupling strategy under the arbitrary Lagrangian-Eulerian description is presented for the incompressible fluid flow past a geometrically nonlinear solid in this paper. The incompressible fluid is solv...
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A semi-implicit coupling strategy under the arbitrary Lagrangian-Eulerian description is presented for the incompressible fluid flow past a geometrically nonlinear solid in this paper. The incompressible fluid is solved by means of the characteristic-based split (CBS) finite element method while the cell-based smoothed finite element method is employed to settle the governing equation of the geometrically nonlinear solid. Because of the CBS fluid solver, the present coupling strategy is performed in a semi-implicit fashion. In particular, the first step of the CBS scheme is explicitly treated whereas the others are implicitly coupled with the structural motion. The computational cost is hence reduced because no subiterations are included in the explicit coupling step and the fluid mesh is frozen in the implicit coupling step. A classic cantilever problem is dealt with to validate the structural solver, and then flow-induced vibrations of a restrictor flap in a uniform channel flow is analyzed in detail. The obtained results agree well with the existing data.
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