A semi-analytical method is developed to consider free vibrations of a functionally graded elastic plate resting on Winkler elastic foundation and in contact with a quiescent fluid. Material properties are assumed to ...
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A semi-analytical method is developed to consider free vibrations of a functionally graded elastic plate resting on Winkler elastic foundation and in contact with a quiescent fluid. Material properties are assumed to be graded distribution along the thickness direction according to a power-law in terms of the volume fractions of the constituents. The fluid is considered to be incompressible and inviscid. In the analysis, the effect of an in-plane force in the plate due to the weight of the fluid is taken into account. By satisfying the compatibility conditions along the interface of fluid and plate, the fluid-structure interaction is taken into account and natural frequencies and mode shapes of the coupled system are acquired by employing energy methods. The results obtained from the present approach are verified by those from a finite element analysis. Besides, the effects of volume fractions of functionally graded materials, Winkler foundation stiffness and in-plane forces on the dynamic of plate are elucidated.
The 3D piezoelasticity theory and the spatial state-space approach are used to study the steady-state non-axisymmetric sound radiation and scattering characteristics of an infinitely long, arbitrarily thick, orthotrop...
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The 3D piezoelasticity theory and the spatial state-space approach are used to study the steady-state non-axisymmetric sound radiation and scattering characteristics of an infinitely long, arbitrarily thick, orthotropic functionally graded hollow circular cylinder, coupled with an inner (actuator) layer of functionally graded piezoceramic material. The method of stationary phase is employed for evaluation of the radiated far-field pressure integral. Numerical simulations include water-submerged air-filled steel-PZT4 composite cylinders driven by harmonic electromechanical loads or insonified by an obliquely incident plane sound wave. Also, when the actuator layer is operating in the active vibration mode, the effects of the number of control modes on the input voltage required for partial or complete cancellation of the far-field and internal radiated pressures as well as on the backscattering form function and noise reduction amplitudes are examined. Limiting cases are considered and validity of formulation is established by comparison with available data as well as with the aid of a commercial finite element package.
This research aims to enhance the knowledge on stress-strain states of a coiled pipe used for hydraulic transient experiments. The membrane theory of shells of revolution has been applied for the description of axial ...
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This research aims to enhance the knowledge on stress-strain states of a coiled pipe used for hydraulic transient experiments. The membrane theory of shells of revolution has been applied for the description of axial and circumferential strains while an inverse method has been used to analyse bending effects. The developed stress-strain model has been successfully validated for dynamic loading. Finally, a simplified version of the stress-strain equations is presented with the goal to facilitate fluid-structure interaction FSI implementation in the hydraulic transient model. The fluid wave speed formula for coiled pipes has been presented. (C) 2014 Elsevier Ltd. All rights reserved.
The development of an adaptive free surface, mesh cutting, methodology, in order to analytically integrate pressures on varying wet parts of partially submerged surfaces in the presence of waves, is presented. Given a...
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The development of an adaptive free surface, mesh cutting, methodology, in order to analytically integrate pressures on varying wet parts of partially submerged surfaces in the presence of waves, is presented. Given a function of free-surface elevation, the algorithm checks for the intersection of the body with the free surface and, based on user-defined parameters, modifies the initial mesh, by subdividing the elements where necessary and eliminating others, via a quadtree approach. Redundant sub-divisions, generated in the quad-division process, are partially eliminated, but the quadrilateral nature of the elements is always kept. The free-surface function must be single-valued and its definition domain simply connected. Hydrostatic and Froude-Krylov forces are computed exactly on each panel by means of analytical formulations, which are derived and presented, based on the theory of linear gravity waves and from applying Green's theorem. Copyright (c) 2014 John Wiley & Sons, Ltd.
The cavitation aspect of the transient interaction of a vessel hull with extreme breaking waves is considered. The authors show that the elastic deformation of thin hull elements by a short water-wave pressure pulse c...
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The cavitation aspect of the transient interaction of a vessel hull with extreme breaking waves is considered. The authors show that the elastic deformation of thin hull elements by a short water-wave pressure pulse can be accompanied by hull cavitation. The effect of this cavitation is important if the duration of loading by the water pressure is less than the period of the fundamental frequency of the hull element oscillation, and is shown to increase the magnitude of the loading. (C) 2014 Elsevier Ltd. All rights reserved.
Bubble load in a noncontact underwater explosion can cause the ship hull global response and local response. In current literature, the ship hull is usually simplified as a hull girder to analyze its global response. ...
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Bubble load in a noncontact underwater explosion can cause the ship hull global response and local response. In current literature, the ship hull is usually simplified as a hull girder to analyze its global response. However, literature dealt with the local response of a 3-D surface ship hull subjected to an underwater bubble were limited. This investigation develops a procedure which couples the finite element method with doubly asymptotic approximation (DAA) method to study the problem of transient responses of a ship hull structure subjected to an underwater explosion bubble. Using a 3-D ship model as examples, the global and local responses of the ship model in vertical, transverse and longitudinal directions are performed in detail. The acceleration, velocity and displacement time histories are presented. The characteristics of both the global and local responses of the ship model are discussed. The numerical results show that besides global whipping response, the ship hull also sustains severe local responses in different directions subjected to underwater explosion bubble jetting, which should be taken into consideration. (C) 2013 Elsevier Ltd. All rights reserved.
A numerical approach is proposed to simulate the interaction between flow and flexible nets in steady current. The numerical approach is based on the joint use of the porous-media model and the lumped-mass model. The ...
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A numerical approach is proposed to simulate the interaction between flow and flexible nets in steady current. The numerical approach is based on the joint use of the porous-media model and the lumped-mass model. The configuration of flexible nets can be simulated using the lumped-mass model and the flow field around fishing nets can be simulated using the porous-media model. Using an appropriate iterative scheme, the fluid-structure interaction problem can be solved and the steady flow field around flexible nets can be obtained. In order to validate the numerical models, the numerical results were compared with the data obtained from corresponding physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. Using the proposed numerical approach, this paper presents the flow field around a single flexible net and two flexible nets with a spacing distance. Both the configuration of the flexible nets and the flow velocity results are in accordance with those of the corresponding physical model tests. (C) 2013 Elsevier Ltd. All rights reserved.
Three-dimensional numerical modeling using Detached Eddy Simulation (DES) based on unsteady Reynolds-Averaged Navier-Stokes (RANS) with the k-omega SST (Shear-Stress Transport) turbulence model has been carried out to...
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Three-dimensional numerical modeling using Detached Eddy Simulation (DES) based on unsteady Reynolds-Averaged Navier-Stokes (RANS) with the k-omega SST (Shear-Stress Transport) turbulence model has been carried out to evaluate the characteristics of a shallow wake flow. The shallow wake is generated by inserting a sharp-edged bluff body in the open channel flow. A horseshoe vortex is captured in front of the body, which stretches downstream and envelops the vortices that form part of the shear layers. The mean and instantaneous flow field characteristics in the wake are examined and compared at different downstream locations to evaluate the three-dimensional features in the flow. Streamwise positive directed velocity is observed in the wake centerline at horizontal planes close to the bed. Flow features hitherto not captured in experimental studies can be identified in sections parallel to the bed and body. A typical signature of three-dimensionality, upward ejection of fluid elements from the bed towards the free surface, is also observed in the wake. (C) 2013 Elsevier Ltd. All rights reserved.
Laboratory-scale fluidstructureinteraction (FSI) experiments and finite element (FE) simulations are performed to examine the one-dimensional blast response of double-walled hulls, consisting of two skins sandwichin...
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Laboratory-scale fluidstructureinteraction (FSI) experiments and finite element (FE) simulations are performed to examine the one-dimensional blast response of double-walled hulls, consisting of two skins sandwiching a layer of water. Both monolithic and sandwich designs are considered for the outer skin. Experiments are conducted in a transparent shock tube which allows measurements of water cavitation and hull response by high-speed photography. Experiments and FE predictions are found in good agreement and allow concluding that the impulse imparted to double hulls by underwater explosions can be dramatically reduced by employing the sandwich construction of the outer skin;such reductions are scarcely sensitive to the thickness of the water layer. (C) 2013 Published by Elsevier Ltd.
Physiologically relevant simulations of blood flow require models that allow for wall deformation. Normally a fluid-structure interaction (FSI) approach is used;however, this method relies on several assumptions and p...
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Physiologically relevant simulations of blood flow require models that allow for wall deformation. Normally a fluid-structure interaction (FSI) approach is used;however, this method relies on several assumptions and patient-specific material parameters that are difficult or impossible to measure in vivo. In order to circumvent the assumptions inherent in FSI models, aortic wall motion was measured with MRI and prescribed directly in a numerical solver. In this way is not only the displacement of the vessel accounted for, but also the interaction with the beating heart and surrounding organs. In order to highlight the effect of wall motion, comparisons with standard rigid wall models was performed in a healthy human aorta. The additional computational cost associated with prescribing the wall motion was low (17%). Standard hemodynamic parameters such as time-averaged wall shear stress and oscillatory shear index seemed largely unaffected by the wall motion, as a consequence of the smoothing effect inherent in time-averaging. Conversely, instantaneous wall shear stress was greatly affected by the wall motion;the wall dynamics seemed to produce a lower wall shear stress magnitude compared to a rigid wall model. In addition, it was found that if wall motion was taken into account the computed flow field agreed better with in vivo measurements. This article shows that it is feasible to include measured subject-specific wall motion into numerical simulations, and that the wall motion greatly affects the flow field. This approach to incorporate measured motion should be considered in future studies of arterial blood flow simulations.
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