Composite materials are being used more frequently for marine applications due to the advantages of a higher stiffness- and strength-to-weight ratio, and better corrosion resistance compared to metallic alloys. Many e...
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Composite materials are being used more frequently for marine applications due to the advantages of a higher stiffness- and strength-to-weight ratio, and better corrosion resistance compared to metallic alloys. Many examples consist of cantilevered structures, such as hydrofoils, propeller and turbine blades, keels, and rudders. A wide range of analytical and numerical tools exist for the free vibration analysis of composite structures in air due to their applicability to design problems in the aerospace industry, such as airplane wings, turbofan and propeller blades, and flight control surfaces. For these aerospace structures the inertial effects of the fluid are typically neglected due to the low relative density of air compared to the structure. Contrarily, for marine structures, fluid inertial (added mass) effects cannot be neglected, especially for composites with much higher fluid-to-solid density ratios. The objective of this work is to investigate the effects of material anisotropy and added mass on the free vibration response of rectangular, cantilevered composite plates/beams via combined analytical and numerical modeling. The results show that the natural frequencies of the composite plate are 50-70% lower in water than in air due to large added mass effects. The added mass is found to vary considerably with material orientation due to the bend-twist coupling of anisotropic composites, which affects the mode shapes and, consequently, the fluid inertial loads. The analytical method is found to yield accurate results for beam geometries and offers significant savings in computational cost compared to the finite element method. (c) 2012 Elsevier Ltd. All rights reserved.
The two-dimensional water entry and exit of a body whose shape varies in time in a prescribed way is investigated through analytical and numerical modelling. For this purpose, an analytical model has been developed wh...
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The two-dimensional water entry and exit of a body whose shape varies in time in a prescribed way is investigated through analytical and numerical modelling. For this purpose, an analytical model has been developed which extends the modified Logvinovich model of water impact to bodies with time-varying shape. A modified von Karman approach has been developed to describe the exit stage, and a rational derivation of the water exit model which is in use in offshore engineering is presented. CFD simulations are used to assess the accuracy of the analytical model. Several case studies of water entry and exit are presented. The analytical model provides very good force predictions during the entry stage in all cases, but the accuracy of the model in the exit stage depends on the maximum penetration depth. In particular, the appearance of high fluid forces on the body directed downward in both the entry and exit stages is remarkable. (C) 2013 Elsevier Ltd. All rights reserved.
An approximate boundary condition is developed in this paper to model fluid shear viscosity at boundaries of coupled fluid-structure system. The effect of shear viscosity is approximated by a correction term to the in...
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An approximate boundary condition is developed in this paper to model fluid shear viscosity at boundaries of coupled fluid-structure system. The effect of shear viscosity is approximated by a correction term to the inviscid boundary condition, written in terms of second order in-plane derivatives of pressure. Both thin and thick viscous boundary layer approximations are formulated;the latter subsumes the former. These approximations are used to develop a variational formation, upon which a viscous finite element method (FEM) model is based, requiring only minor modifications to the boundary integral contributions of an existing inviscid FEM model. Since this FEM formulation has only one degree of freedom for pressure, it holds a great computational advantage over the conventional viscous FEM formulation which requires discretization of the full set of linearized Navier-Stokes equations. The results from thick viscous boundary layer approximation are found to be in good agreement with the prediction from a Navier-Stokes model. When applicable, thin viscous boundary layer approximation also gives accurate results with computational simplicity compared to the thick boundary layer formulation. Direct comparison of simulation results using the boundary layer approximations and a full, linearized Navier-Stokes model are made and used to evaluate the accuracy of the approximate technique. Guidelines are given for the parameter ranges over which the accurate application of the thick and thin boundary approximations can be used for a fluid-structure interaction problem. (C) 2013 Elsevier Inc. All rights reserved.
An Air Film Damper (AFD) made with a highly damping material called Metal Rubber (MR) as the outer ring is a novel damping structure that aims to reduce the remarkable vibrations produced by a flexible rotor system. T...
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An Air Film Damper (AFD) made with a highly damping material called Metal Rubber (MR) as the outer ring is a novel damping structure that aims to reduce the remarkable vibrations produced by a flexible rotor system. The mechanism of an AFD is firstly put forward and the mechanical model describing the fluidstructureinteraction is constructed. Taking into consideration the complex whirl of the rotor and the precession of the floating ring, the Reynolds equation of AFDs is derived and the air film pressure is obtained. Based on these calculations, the selection of MR stiffness is introduced and the adaptive properties of AFD are analyzed. Then the effects of AFD on the rotordynamics are studied based on the characterization of the parameters of a rotor system in the steady state. The mechanism and the effects of AFD on a rotor system are verified through rotating experimental tests. The theoretical and experimental results both show that AFD can adjust the air film clearance adaptively according to the vibration of the rotor: this can not only decrease the friction between the journal and the floating ring, but can also provide additional stiffness and damping to the rotor system, thus yielding additional vibration control. (c) 2013 Elsevier Ltd. All rights reserved.
An approach for modeling the radiation damping of an infinite acoustic waveguide is the high-order absorbing boundary condition. This approach is employed in this study as a basis for analysis of an infinite water cha...
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An approach for modeling the radiation damping of an infinite acoustic waveguide is the high-order absorbing boundary condition. This approach is employed in this study as a basis for analysis of an infinite water channel. In order to achieve an accurate and efficient approach for this purpose, the imposed boundary condition should have two features: (a) the reservoir's bottom absorption which highly affects the pressure distribution inside the reservoir should be included in the formulation of the ABC;(b) the far-field base excitation, which is a significant factor during the vertical excitation should also be considered in the analysis. By separating the overall hydrodynamic pressure into scattered and incident pressure and involving the scattered term in the formulation of the ABC, an accurate and versatile boundary condition is obtained. This boundary condition is then applied in the analysis of several benchmark examples and the obtained results demonstrate the efficiency of the proposed technique. (C) 2013 Elsevier Ltd. All rights reserved.
In this paper the vibration behavior of a flexible cylinder subjected to an axial flow is investigated numerically. Therefore a methodology is constructed, which relies entirely on fluid-structure interaction calculat...
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In this paper the vibration behavior of a flexible cylinder subjected to an axial flow is investigated numerically. Therefore a methodology is constructed, which relies entirely on fluid-structure interaction calculations. Consequently, no force coefficients are necessary for the numerical simulations. Two different cases are studied. The first case is a brass cylinder vibrating in an axial water flow. This calculation is compared to experiments in literature and the results agree well. The second case is a hollow steel tube, subjected to liquid lead-bismuth flow. Different flow boundary conditions are tested on this case. Each type of boundary conditions leads to a different confinement and results in different eigenfrequencies and modal damping ratios. Wherever appropriate, a comparison has been made with an existing theory. Generally, this linear theory and the simulations in this paper agree well on the frequency of a mode. With respect to damping, the agreement is highly dependent on the correlation used for the normal friction coefficients in the linear theory. (C) 2013 Elsevier Ltd. All rights reserved.
A numerical technique for fluid-structure interaction, which is based on the finite element method (FEM) and computational fluid dynamics (CFD), was developed for application to an industrial chimney equipped with a p...
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A numerical technique for fluid-structure interaction, which is based on the finite element method (FEM) and computational fluid dynamics (CFD), was developed for application to an industrial chimney equipped with a pendulum tuned mass damper (TMD). In order to solve the structural problem, a one-dimensional beam model (Navier-Bernoulli) was considered and, for the dynamical problem, the standard second-order Newmark method was used. Navier-Stokes equations for incompressible flow are solved in several horizontal planes to determine the pressure in the boundary of the corresponding cross-section of the chimney. Forces per unit length were obtained by integrating the pressure and are introduced in the structure using standard FEM interpolation techniques. For the fluid problem, a fractional step scheme based on a second order pressure splitting has been used. In each fluid plane, the displacements have been taken into account considering an Arbitrary Lagrangian Eulerian approach. The stabilization of convection and diffusion terms is achieved by means of quasi-static orthogonal subscales. For each period of time, the fluid problem was solved and the geometry of the mesh of each fluid plane is updated according to the structure displacements. Using this technique, along-wind and across-wind effects have been properly explained. The method was applied to an industrial chimney in three scenarios (with or without TMD and for different damping values) and for two wind speeds, showing different responses.
This paper outlines the development and adaptation of a coupling strategy for transient temperature analysis in a solid via a conjugate heat transfer method. This study proposes a quasi-dynamic coupling procedure to b...
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This paper outlines the development and adaptation of a coupling strategy for transient temperature analysis in a solid via a conjugate heat transfer method. This study proposes a quasi-dynamic coupling procedure to bridge the temporal disparities between the fluid and the solid. In this approach, dynamic thermal modeling in the solid is coupled with a sequence of steady states in the fluid. This quasi-dynamic algorithm has been applied to the problem of convective heat transfer over, and transient conduction heat transfer within, a flat plate using the severe thermal conditions of a solid propellant rocket. Two different coupled thermal computations have been performed. In the first onereferred to as the reference computationthe coupling period is equal to the smallest solid time constant. In the second one, a very large coupling period is used. The results show that the procedure can predict accurate transient temperature fields at a reasonable computational cost. The simulation CPU time is approximately reduced by up to 90%, while maintaining a very good accuracy. All the details of the numerical test case are given in the paper. This application illustrates the capabilities and the overall efficiency of this coupled approach in a solid transient problem using long term simulations of time dependent flows. Copyright (c) 2013 John Wiley & Sons, Ltd.
An analytical method is proposed to determine the dynamic response of 3-D rectangular fluid containers with four flexible walls, subjected to seismic ground motion. By applying Rayleigh-Ritz method using the vibration...
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An analytical method is proposed to determine the dynamic response of 3-D rectangular fluid containers with four flexible walls, subjected to seismic ground motion. By applying Rayleigh-Ritz method using the vibration modes of flexible plates, fluid-structure interaction effects on the dynamic responses of fluid containers are considered. A mechanical model, which takes into account the deformability of the tank wall, is developed. The maximum seismic loading of the base at the tank and a section immediately above it can be predicted by this model. Accordingly, a 2-D simplified model is proposed to evaluate pressure distribution on the flexible tank wall. (C) 2013 Elsevier Ltd. All rights reserved.
The aeroelastic response of rocket nozzles subjected to combined axial thrust and side loads is investigated using a particular computational technique. The technique uses two-way "loose" coupling between an...
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The aeroelastic response of rocket nozzles subjected to combined axial thrust and side loads is investigated using a particular computational technique. The technique uses two-way "loose" coupling between an accurate flow solver and an accurate structural-dynamics solver to accurately capture the behavior of the internal flow, the behavior of the nozzle wall, and the interactions between the fluid-dynamic and structural-dynamic phenomena. It is shown that the technique captures the fluid-dynamic phenomena that are known to contribute to nozzle side loads, including the asymmetry in the propagation of the initial blast wave, the asymmetry in the separation lines, the pressure pulsations at the separation lines, the transition of separated flow patterns, and various flow instabilities. It is also shown that the computational technique couples the fluid-dynamic and the structural-dynamic solutions with an accuracy and a resolution that are sufficient for accurate prediction of the aeroelastic response modes in the system. The fluid-dynamics solver is validated for shock-induced flow separations in a sub-scale J-2S nozzle, while the structural-dynamic solver is validated for a typical dynamic response in a rocket nozzle. The two-way loose coupling methodology is validated for the flutter of a flat plate in supersonic flow, and the validation results are discussed and assessed with respect to the fitness of the computational technique for the prediction of the aeroelastic response of typical actual nozzle configurations. Finally, the side loads are computed for a J-2S nozzle with rigid walls and with flexible walls, and the results for the two types of walls are analyzed and compared. It is found that allowing aeroelastic coupling significantly affects the response of the nozzle and the predicted side loads. It is speculated that the computational technique investigated in this work combines all the elements required to accurately predict and simulate the aeroelastic res
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