Effect Of Fluid Loading Research Articles

A vibration analysis of stiffened plates under heavy fluid loading by an energy finite element analysis formulation

An energy finite element analysis (EFEA) formulation for high frequency vibration analysis of stiffened plates under heavy fluid loading is presented. The added mass effect and the radiation damping effect due to the fluid loading are incorporated in the derivation of the EFEA governing differential equations. In addition, the fluid loading effect and the presence of a stiffener are accounted when computing the power transfer coefficients through plate/stiffener junctions. The effect of the fluid on power transfer coefficients of a plate/stiffener junction is analyzed and discussed. The new formulation is validated by comparing EFEA results to solutions by very dense finite element models for several plate/stiffener assemblies, which include two coplanar plates connected by a stiffener, two plates connected at a 45° angle by a stiffener, and a section of a typical naval structure. All plates are considered in contact with dense fluid from one side. The energy ratios between the receiving sections of the plates and the excited sections of the plates are computed and good correlations are observed between the EFEA and the very dense FEA results.

Acoustic radiation force due to incident plane-progressive waves on coated spheres immersed in ideal fluids

In this study, the acoustic radiation force resulting from the interaction of a plane progressive wave with a coated sphere was examined. The linear acoustic scattering problem was obtained first by solving the classical boundary conditions to obtain the required coefficients. The radiation force was then determined by averaging the momentum flux tensor expressed in terms of the total scattering pressure or velocity potential in an ideal fluid. Numerical calculations of the radiation force function Yp , which is the radiation force per unit energy density and unit cross-section, were displayed versus the dimensionless size parameter x=k1 b (k1 is the wave number in the exterior fluid and b the radius of the uncoated sphere) over a large range of frequencies. Particular emphasis has been focused on the coating thickness and the absorption of sound inside the outer covering layer. The fluid-loading effect on the radiation force function curves was also analysed.

What effect of vasoactive drugs on passive leg raising response in critically ill patients?

Passive leg raising (PLR) mimics the hemodynamic effects of rapid fluid loading (FL) by shifting venous blood from the legs towards the intrathoracic compartment and by increasing right and left ventricular preloads.

Does fluid loading influence measurements of intestinal permeability?

IntroductionUrinary recovery of enterally administered probes is used as a clinical test of intestinal mucosal permeability. Recently, evidence has been provided that the recovery of some but not all sugar probes is dependent on the amount of diuresis and renal function. The aim of this study was to assess the effect of fluid loading on the urinary recovery of sugar probes in healthy volunteers.MethodsIn a cross-over study, 10 healthy volunteers ingested 100 ml of a solution containing 0.2 g of 3-O-methyl-D-glucose (3-OMG), 0.5 g of D-xylose, 1.0 g of L-rhamnose, and 5.0 g of lactulose on two different days. The volunteers were randomized to receive either 2 litres of Ringer acetate or no fluid during the following 3 hours. The sugar concentrations were measured in 5-hour urine samples period.ResultsFluid loading increased urine production and urinary recovery of xylose. Fluid loading did not influence the urinary recovery of 3-OMG, L-rhamnose, or lactulose. Neither the lactulose/rhamnose ratio nor the 3-OMG/rhamnose ratio changed.ConclusionFluid loading increases mediated carbohydrate transport but not the lactulose/rhamnose ratio, after oral sugar administration in healthy volunteers. It remains to be determined whether sugar probes are handled differently in response to fluids in patients with organ dysfunctions.

A numerical method for the calculation of dynamic response and acoustic radiation from an underwater structure

An approach combining finite element with boundary element methods is proposed to calculate the elastic vibration and acoustic field radiated from an underwater structure. The FEM software NASTRAN is employed for computation of the structural vibration. An uncoupled boundary element method, based on the potential decomposition technique, is described to determine the acoustic added mass and damping coefficients that result due to fluid loading effects. The acoustic matrices of added mass and damping coefficients are then added to the structural mass and damping matrices, respectively, by the DMAP modules of NASTRAN. Numerical results are shown to be in good agreement with experimental data. The complex eigenvalue analyses of underwater structure are obtained by NASTRAN solution sequence SOL107. Results obtained from this study suggest that the natural frequencies of underwater structures are only weakly dependent on the acoustic frequency if the acoustic wavelength is roughly twice as large as the maximum structural dimension.

Analytical-numerical matching for fluid-loaded structures with discontinuities

The method of analytical-numerical matching (ANM) is applied to several example problems involving the radiation and vibration of a fluid-loaded cylindrical shell with structural discontinuities. These problems are used to verify the accuracy of the method compared to a purely numerical approach, and to demonstrate the usefulness of ANM for solving problems involving nonaxisymmetric forcing and constraints on structures that are otherwise axisymmetric. The principal advantage of the ANM method for this application is its ability to employ a spectral method (modal decomposition in azimuth) in the solution of a problem that is nonaxisymmetric. ANM divides the original problem into local and global subproblems that are solved separately. The discontinuity is handled using a high-resolution local finite-element model. Smooth forces are derived from solving an analytical matching problem on the local domain, and these smooth forces are then applied to a low-resolution numerical global problem. The superposition of solutions to the subproblems is equivalent to the solution of the original problem. For fluid loading, the local high-resolution model is solved in vacuo, and the effects of fluid loading are included completely by the low-resolution global problem.

Lamb Waves Propagating in an LiNbO3 Plate under the Mechanical and Dielectric Loadings of a Fluid

This research is focused on exploring the fluid loading effects on the dispersion spectra of Lamb modes propagating in a piezoelectric (X-LiNbO3) plate. Theoretical calculations based on a partial wave analysis are used to characterize the shifting behaviors of dispersion spectra caused by the loading fluid with mechanical/dielectric properties. On the other hand, the fluid loading effects are experimentally investigated by measuring the dispersion spectra of an X-LiNbO3 plate with free and immersed boundary conditions. Results of the theoretical calculations are supported by the measurement. It is also found that, for the case of water as a common immersion fluid for an X-LiNbO3 plate, the dielectric loading effect dominates the shifting of the dispersion spectra, while the mechanical density loading effect can be neglected.

Analysis of wave propagation in sandwich plates with and without heavy fluid loading

The paper addresses wave motions in an unbounded sandwich plate with and without heavy fluid loading in a plane problem formulation. A sandwich plate is composed of two identical isotropic skin plies and an isotropic core ply. Several alternative theories for stationary dynamics of such a plate or a beam are derived, including a formulation in the framework of a theory of elasticity applied for a core ply. ‘In-phase’ and ‘anti-phase’ wave motions (with respect to transverse deflections of skins) of a sandwich beam are analyzed independently of each other. Dispersion curves obtained by the use of ‘elementary’ theories are compared with those obtained by the use of an ‘exact’ theory (which involves the theory of elasticity in a description of wave motion in a core ply) for a plate without fluid loading. It is shown that these simplified models are capable of giving a complete and accurate description of all propagating waves in not too high-frequency range, which is sufficient in practical naval and aerospace engineering. In the case of heavy fluid loading, similar analysis is performed for ‘anti-phase’ wave motions of a beam. Two simplified theories as well as an ‘exact’ one are extended to capture fluid loading effects. A good agreement between results obtained in ‘elementary’ and ‘exact’ problem formulations is demonstrated. The role of fluid's compressibility in the generation of propagating waves in a sandwich plate is explored. It is shown that, whereas analysis of wave motions in the case of an incompressible fluid predicts an existence of two propagating waves, only one such wave exists when a fluid is sufficiently compressible. The threshold magnitude of the ratio of a sound speed in an acoustic medium to a sound speed in a skin's material is found, which separates these two regimes of wave motions for a given set of parameters of sandwich plate composition.

High-frequency vibration analysis of thin elastic plates under heavy fluid loading by an energy finite element formulation

An energy finite element analysis (EFEA) formulation for computing the high frequency behavior of plate structures in contact with a dense fluid is presented. The heavy fluid loading effect is incorporated in the derivation of the EFEA governing differential equations and in the computation of the power transfer coefficients between plate members. The new formulation is validated through comparison of EFEA results to classical techniques such as statistical energy analysis (SEA) method and the modal decomposition method for bodies of revolution. Good correlations are observed and the advantages of the EFEA formulation are identified.

Noise radiated from a rotating submerged elastic cylindrical thin shell

Although the aeroacoustics of high Reynolds number boundary layers is reasonably well understood, less is known about the hydroacoustics of such flows, and the effect of fluid loading. The noise generated by the turbulent boundary layer around an elastic, thin-walled and cylindrical shell rotating in quiescent water was studied in the Georgia Tech. Underwater Acoustic Tank for Reynolds numbers up to 200<th>000. The steel shell, which is filled with air, has a diameter D of 0.625 m, a wall thickness of 0.004D, and an aspect ratio of unity; the tank dimensions are 19D by 12D by 11D. Extraneous noise sources (e.g., bearing and motor vibration) were isolated from the net signal to estimate flow noise. Radiated noise power was calculated from hydrophone data under a diffuse field assumption. To our knowledge, these results are unique in both their structural acoustics and fluid mechanics scaling.

Silencing using flexible plate in a duct

A flexible plate interacting with air in a duct can provide passive means for low frequency broadband transmission loss. The sensitivity of the system to various parameters including unintentionally applied tension, effect of external fluid loading, lateral plate cross modes, structural and acoustic boundary condition are analyzed through experimental measurements and theoretical predictions. In order to avoid breakout noise, a backing cavity can be introduced below the plate. This introduces differences in filtering characteristics. Compared to plate in a single duct, the two-duct system will have higher plate resonance frequencies due to cavity loading on the plate. Means to achieve low frequency broadband transmission loss using two-duct silencers will be discussed. Significance of three dimensionality of the problem will be brought out by comparing the results of three-dimensional finite-element analysis with experimental data. Successful designs and experiments for low frequency attenuation will be presented. [Work supported by NSF and ONR.]

Flow noise predictions of a submerged cylinder under turbulent boundary layer excitations

The unsteady fluctuated pressure underneath turbulent boundary layers (TBL) is one of major noise sources in moving vehicles. Recently, discretized TBL forcing functions have been applied to planar structures in air [Y. F. Hwang and S. A. Hambric, Noise-Con, 2000; M. Allen and N. Vlahopoulos, Computers and Structures, 2000; M. Allen and N. Vlahopoulos, Finite Elements in Analysis and Design, 2001; M. Allen, R. Sbragio, and N. Vlahopoulos, AIAA J. 2001]. This paper discusses prediction of the flow-induced radiated noise and surface responses of a submerged hemisphere-capped cylindrical shell (L/D=11). The FEM/IFEM (infinite finite element method) approach is used to calculate structural acoustic transfer functions and to accurately account for the fluid loading effects. The effect on TBL due to the curvature of a cylinder is captured by utilizing the potential flow—boundary layer theory to determine key boundary layer parameters. Predictions of the surface intensity and far field responses are developed through stochastic analysis due to the natural of the TBL excitations. A MATLAB script is generated to determine the power spectral density of the responses. [Work supported by ONR Code 334.]

The effect of fluid loading on radiation efficiency.

The metric "radiation efficiency," used to estimate a panel's radiated acoustic power from a measure of its normal velocity, is typically derived under the condition of very light fluid loading. This paper shows that efficiencies calculated in this manner can significantly overestimate the radiated power when the condition of light fluid loading is not met, as can be the case for steel plates in water. It is also shown that, when fluid loading is not light, a baffled semi-infinite plate is not a good model for an interior support. Numerical results are presented for radiation efficiencies calculated for steel plates in water, and are compared to those calculated under the assumption of vanishing fluid loading.

An energy finite element formulation for high-frequency vibration analysis of plate structures subjected to heavy fluid loading

An energy finite element formulation for computing the high-frequency behavior of plate structures in contact with a dense fluid is presented. The heavy fluid loading effect is incorporated in the derivation of the governing differential equations and in the computation of the power transfer coefficients between plate members. The validity of the new formulation is demonstrated through comparison to an analytical solution and to results computed by conventional finite element models comprised by a large number of elements. The influence of the heavy fluid on the dynamic response of two marine structures is identified by comparing results computed with and without the effect of fluid loading. The impact of the heavy fluid loading on the computation of the power transfer coefficients is also identified. [Research supported by the Michigan Seagrant.]

Insight into the diagnosis of conductive hearing loss using wideband acoustic reflectance measurements of surgically modified human temporal bones

There is mounting evidence to suggest that wideband acoustic impedance/reflectance measurements will aid in the clinical diagnosis of various middle ear pathologies. In preparation for clinical trials, wideband pressure reflectance measurements (100 Hz to 8 kHz) were made looking into the ear canals of three human temporal bones which were surgically modified to simulate five possible pathological conditions [unpublished data of J. Allen, G. Ball, S. Nishihara, and R. Goode]. The experimental procedure, data, and analysis are presented for the different modifications. The unmodified, air-filled tympanic cavity data characterize the baseline losses for the entire system. A fluid-filled typanic cavity characterizes the effect of fluid loading on the tympanic membrane, simulating the condition of acute and chronic otitis media (middle ear infection). The fixed stapes condition simulates the effect of otosclerosis (calcification of the stapes footplate). Disarticulated stapes and the severed stapedius tendon conditions are both symptoms associated with chronic otitis media or cholesteatoma (middle ear cysts). Finally, the fixed malleus condition can be a warning sign of otitis media, but can easily be misdiagnosed as otosclerosis. It is hoped that this work will provide a physical basis for the interpretation of wideband pressure reflectance data collected in future clinical trials.

The effect of aminophylline on right heart function in young pigs after ligation of the right coronary artery.

An experimental model of right heart failure was developed to determine the effects of fluid loading and aminophylline on right heart function. We hypothesised that aminophylline would specifically improve right heart function through a decrease in pulmonary vascular resistance and, possibly, an increase in cardiac contractility. Right heart infarct was induced in ten experimental pigs and seven control pigs by ligating branches of the right coronary artery. The effect of fluid loading with a colloid solution and subsequent bolus doses of aminophylline on haemodynamics was observed. Fluid loading improved haemodynamics as expected. Aminophylline transiently improved cardiac index and pulmonary vascular resistance, but simultaneously caused an increase in heart rate and a decrease in stroke volume. Although aminophylline may reduce right heart afterload, it did not improve overall cardiac function in this experimental model of right heart infarction.

Increased lactulose/rhamnose ratio during fluid load is caused by increased urinary lactulose excretion.

Noninvasive assessment of intestinal permeability in vivo is based on the measurement of urinary excretion of orally administered sugar probes. It is expressed as a ratio, usually lactulose/rhamnose or 3-O-methyl-D-glucose (3-OMG)/rhamnose. In both endotoxemic and control rats that were receiving fluid, we observed an increase in the recovery of lactulose and 3-OMG but not rhamnose in both groups, suggesting an enhancement of intestinal permeability. In the measurement of intestinal permeability, all pre- and postmucosal factors are considered equal for all sugars. We hypothesized that postmucosal factors and not changes in intestinal permeability caused the increased urinary lactulose and 3-OMG recoveries observed during fluid loading. Therefore, the effects of fluid loading on urinary excretion of the sugar probes were studied in healthy rats receiving the sugars intravenously. After intravenous injection, fluid loading increased urinary lactulose recovery threefold but not that of 3-OMG and rhamnose. In conclusion, fluid loading increases the lactulose/rhamnose ratio independent of changes in intestinal permeability. The 3-OMG/rhamnose ratio is not influenced by fluid loading.

Magnetic excitation and acoustical detection of torsional and quasi-flexural modes of spherical shells in water

A simple electromagnetic acoustic wave transducer (EMAT) based on a wire coil was used to excite the resonant modes of a stainless steel spherical shell without direct mechanical contact. The coupling produced by this EMAT was examined first for shells in air and then for shells immersed in water to examine the effects of fluid loading on the shell’s spectrum. It was found that the torsional modes were excited using this method and these modes radiated sound into the surrounding water contrary to expectations. This excitation is shown to depend on the presence of a permanent magnetization in the shell itself or on the presence of a static external field applied at right angles to the axis of the coil. Possible mechanisms for the excitation and the acoustic radiation of the torsional modes are considered. The excitation of quasi-flexural shell modes is also discussed for shells in air and in water. The shell responds at the oscillation frequency of the applied field and at twice the frequency. Some potential applications of this method of measuring modes are noted.

Wavenumber-Harmonic Analysis of a Periodically Supported Beam Under the Action of a Convected Loading

The vibro-acoustic response of an infinite, fluid-loaded and periodically supported Timoshenko beam under a convected harmonic loading has been obtained in a mathematical form. Instead of considering the dynamics of a single substructure alone, an essentially different technique named as wavenumber-harmonic method for the analysis of periodic structures is presented. The method involves the use of Fourier transform, then the associated wavenumber response is expressed in a series form that represents wave components of the flexural motion. This approach differs from the space-harmonic analysis which describes the beam motion in spatial domain. With this approach the periodic boundary conditions and the phase relation between two substructures are not required. Furthermore, incorporating the heavy fluid loading effect is easy. This method can be used conveniently to calculate the sound power radiated from a fluid-loaded infinite beam, which is subject to either a moving point or distributed loading. The influence of periodic supports on the sound radiation has also been examined for different speeds of convected loading. [S0739-3717(00)01002-3]

Midfrequency acoustical modeling of a coated plate

A steel plate with an attached thick viscoelastic layer exhibits ‘‘midfrequency’’ characteristics at relatively low frequencies, certainly below 1 kHz for a 1-in. steel plate with thicker coating. The low-shear stiffness of the coating leads to a cut-on frequency associated with a shear thickness resonance. Classical plate theory or composite plate theory cannot capture this phenomenon. Although it is not difficult to compute the exact dispersion and modal properties of this system, an approximate plate theory is required in order to examine how the coated plate interacts dynamically with uncoated regions (reflection, transmission), and for modeling scattering from structure incorporating these elements. A hybrid plate theory is presented, based on a classical Kirchhoff assumption for the steel, and a Timoshenko/Mindlin model for the coating. This leads to a three degrees of freedom model, which exhibits the same dispersive properties as the exact theory. Comparisons and differences are discussed. The effects of fluid loading are also presented. [Work supported by ONR.]