Showing papers on "Added mass published in 2002"
TL;DR: A standard quasi-steady model of insect flight is modified to include rotational forces, translational forces and the added mass inertia, and the revised model predicts the time course of force generation for several different patterns of flapping kinematics more accurately than a model based solely on translational force coefficients.
Abstract: We used a dynamically scaled model insect to measure the rotational forces produced by a flapping insect wing. A steadily translating wing was rotated at a range of constant angular velocities, and the resulting aerodynamic forces were measured using a sensor attached to the base of the wing. These instantaneous forces were compared with quasi-steady estimates based on translational force coefficients. Because translational and rotational velocities were constant, the wing inertia was negligible, and any difference between measured forces and estimates based on translational force coefficients could be attributed to the aerodynamic effects of wing rotation. By factoring out the geometry and kinematics of the wings from the rotational forces, we determined rotational force coefficients for a range of angular velocities and different axes of rotation. The measured coefficients were compared with a mathematical model developed for two-dimensional motions in inviscid fluids, which we adapted to the three-dimensional case using blade element theory. As predicted by theory, the rotational coefficient varied linearly with the position of the rotational axis for all angular velocities measured. The coefficient also, however, varied with angular velocity, in contrast to theoretical predictions. Using the measured rotational coefficients, we modified a standard quasi-steady model of insect flight to include rotational forces, translational forces and the added mass inertia. The revised model predicts the time course of force generation for several different patterns of flapping kinematics more accurately than a model based solely on translational force coefficients. By subtracting the improved quasi-steady estimates from the measured forces, we isolated the aerodynamic forces due to wake capture.
746 citations
TL;DR: In this article, mesoscale structures (bubbles, clusters and streamers) in two-phase flows, especially in gas-solid fluidized beds significantly affect macroscopic hydrodynamic behavior.
222 citations
TL;DR: In this article, the authors present closures for the drag and virtual mass force terms appearing in a two-fluid model for flow of a mixture consisting of uniformly sized gas bubbles dispersed in a liquid.
Abstract: We present closures for the drag and virtual mass force terms appearing in a two-fluid model for flow of a mixture consisting of uniformly sized gas bubbles dispersed in a liquid. These closures were deduced through computational experiments performed using an implicit formulation of the lattice Boltzmann method with a BGK collision model. Unlike the explicit schemes described in the literature, this implicit implementation requires iterative calculations, which, however, are local in nature. While the computational cost per time step is modestly increased, the implicit scheme dramatically expands the parameter space in multiphase flow calculations which can be simulated economically. The closure relations obtained in our study are limited to a regular array of uniformly sized bubbles and were obtained by simulating the rise behaviour of a single bubble in a periodic box. The effect of volume fraction on the rise characteristics was probed by changing the size of the box relative to that of the bubble. While spherical bubbles exhibited the expected hindered rise behaviour, highly distorted bubbles tended to rise cooperatively. The closure for the drag force, obtained in our study through computational experiments, captured both hindered and cooperative rise. A simple model for the virtual mass coefficient, applicable to both spherical and distorted bubbles, was also obtained by fitting simulation results. The virtual mass coefficient for isolated bubbles could be correlated with the aspect ratio of the bubbles.
184 citations
TL;DR: In this article, the authors describe an extension and validation of the Euler/Lagrange approach for time-dependent calculations of the flow evolving in a bubble column. But they do not consider the effect of wake-generated turbulence by means of consistent Lagrangian-like terms.
174 citations
TL;DR: In this article, an iterative modal analysis approach is developed to determine the effect of transverse cracks on the dynamic behavior of simply supported undamped Bernoulli-Euler beams subject to a moving mass.
102 citations
TL;DR: In this paper, the apparent mass of a parafoil shape for motions along various axes is computed using potential flow analysis from this, the 6 x 6 apparent mass matrix about some reference point is computed Parametric forms for estimating the terms are given.
Abstract: For an arbitrarily shaped body, there may be more than one center of apparent mass The apparent mass of a parafoil shape for motions along various axes is computed using potential flow analysis From this, the 6 x 6 apparent mass matrix about some reference point is computed Parametric forms for estimating the terms are given The existence of multiple mass centers results in off-diagonal terms in this matrix that couple the translational and rotational motions It is shown how the nondiagonal 6 x 6 apparent inertia matrix about a certain reference point can be used to compute the corresponding apparent mass matrix at any other reference point Dynamic equations including nonlinear terms are presented
74 citations
TL;DR: In this article, a computer program DIVA has been developed to take into account a flowing fluid, a mean radial pressure and initial pre-stress in circular cylindrical shells.
71 citations
55 citations
TL;DR: In this paper, an analytical method is presented to find the eigenfrequencies of a rectangular plate carrying a uniformly distributed mass, using the standard Galerkin procedure, the equation of motion is reduced to a set of ordinary differential equations.
49 citations
TL;DR: In this paper, the authors studied the stability and mixing in bubble columns with liquid flow and showed that the transition from bubble flow to slug flow in a vertical pipe is driven by the deformation of the bubbles associated to drag and added mass.
34 citations
TL;DR: In this paper, the effect of steady viscous forces on vibrations of shells with internal and annular flow has been considered by using the time-mean Navier-Stokes equations, which has been validated by comparison with available results for shells with uniform constraints and added lumped masses.
01 Feb 2002
TL;DR: In this paper, the modal characteristics of rotating cantilever beams with a concentrated mass located in an arbitrary position are investigated by employing hybrid deformation variables, and the resulting equations are linear but capture the stiffening effect induced by the rotational motion of the beam.
Abstract: Modal characteristics of rotating cantilever beams with a concentrated mass located in an arbitrary position are investigated in this paper. Equations of motion are derived by employing hybrid deformation variables. The resulting equations are linear but capture the stiffening effect induced by the rotational motion of the beam. For modelling of the concentrated mass, use is made of the Dirac delta function, which avoids increasing the degrees of freedom of the system. The resulting equations of motion are transformed into dimensionless forms in which four dimensionless parameters are identie ed. The effects of the dimensionless parameters on the modal characteristics of the rotating beams are examined through numerical study. It is found that the magnitude and the location of the concentrated mass signie cantly ineuence the modal characteristics of the rotating beam.
TL;DR: In this article, a method based on the dynamic Green function has been proposed to determine the optimum values of masses and/or springs and their locations on a beam structure in order to confine the vibration at an arbitrary location.
TL;DR: In this article, a method of seismic analysis for a cylindrical liquid storage structure considering the effects of the interior fluid and exterior soil medium in the frequency domain is presented, which can be applied to the structure embedded in ground as well as on ground.
Abstract: This paper presents a method of seismic analysis for a cylindrical liquid storage structure considering the effects of the interior fluid and exterior soil medium in the frequency domain. The horizontal and rocking motions of the structure are included in this study. The fluid motion is expressed in terms of analytical velocity potential functions, which can be obtained by solving the boundary value problem including the deformed configuration of the structure as well as the sloshing behavior of the fluid. The effect of the fluid is included in the equation of motion as the impulsive added mass and the frequency-dependent convective added mass along the nodes on the wetted boundary of the structure. The structure and the near-field soil medium are represented using the axisymmetric finite elements, while the far-field soil is modeled using dynamic infinite elements. The present method can be applied to the structure embedded in ground as well as on ground, since it models both the soil medium and the structure directly. For the purpose of verification, earthquake response analyses are performed on several cases of liquid tanks on a rigid ground and on a homogeneous elastic half-space. Comparison of the present results with those by other methods shows good agreement. Finally, an application example of a reinforced concrete tank on a horizontally layered soil with a rigid bedrock is presented to demonstrate the importance of the soil-structure interaction effects in the seismic analysis for large liquid storage tanks.
TL;DR: In this article, the added mass and damping coefficients for a circular cylinder oscillating horizontally in a uniformly stratified fluid of limited depth and in a continuously stratified liquid with a smooth pycnocline were evaluated from Fourier transforms of the experimental records of impulse response functions.
Abstract: This paper presents the force coefficients (added mass and damping) for a circular cylinder oscillating horizontally in a uniformly stratified fluid of limited depth and in a continuously stratified fluid with a smooth pycnocline. The frequency-dependent added mass and damping are evaluated from Fourier transforms of the experimental records of impulse response functions. The stratification is shown to have a strong effect on the fluid–body interaction. It is found that, when the characteristic vertical extent of stratification (depth of uniformly stratified fluid or pycnocline thickness) decreases, the power radiated with internal waves is reduced and the maximum of the frequency spectrum of wave power shifts toward lower frequency. The results of experiments are compared with available theoretical predictions.
TL;DR: The method presented in this paper uses measurements of flexural vibration of a beam and of the same beam carrying a known additional concentrated mass to identify the beam’s structural parameters, such as mass and stiffness, from the eigenfrequencies of these two structures and from the analytical solutions of the dynamic response of both structures.
TL;DR: In this paper, a general integral equation is presented to calculate the forces exerted on a two-dimensional (2D) body of arbitrary shape immersed in unsteady, incompressible flows.
TL;DR: In this article, an eigenfunction expansion series was derived to circumvent convergence difficulties associated with the jump in the shear force due to the moving interaction force, an improved series expansion employing the static Green's function was derived.
Abstract: In this paper the problem of an oscillator traversing an elastically supported continuum is studied. The flexibility in the boundaries of the continuum is modeled by linear transverse springs. The response of the continuum and the dynamic interaction force between the moving oscillator and the continuum are evaluated by an eigenfunction expansion series. To circumvent convergence difficulties associated with the jump in the shear force due to the moving interaction force, an improved series expansion employing the static Green's function is derived. The coupled governing equations of motion are solved numerically and results are obtained to examine the effects of the boundary flexibility on the response, the dynamic interaction force, the shear force spatial and temporal distributions, as well as the convergence properties of the expansion series. It is found that high order modal terms contribute significantly to the shear force expansion series in the elastically supported model. The presence of large amplitude and high frequency components in the shear force is critical in understanding the cumulative fatigue failure of the structure. A useful and compact formula estimating the value of the support stiffness above which a boundary may be modeled as simply supported is also derived
TL;DR: In this article, the authors report the results of a recent MHI study in which three important aspects of fluidelastic instability were considered: (i) two-phase fluid damping and added mass under prototypical conditions, (ii) the nature of unsteady fluid forces leading to fluidastic instability, and finally (iii) the fluideastic instability mechanism itself.
TL;DR: In this paper, the dynamic stability of a spinning unconstrained beam subjected to a pulsating follower force P 0 + P 1 cos Ωt is analyzed, where a concentrated mass is located at an arbitrary location on the beam, and the stability of the beam is studied with the mass at various locations.
TL;DR: In this article, the local stability and period-doubling bifurcations of the response to a transverse harmonic excitation of a slender cantilever beam partially immersed in a fluid and carrying an intermediate lumped mass are analyzed and studied for the resonance responses of the first three modes of vibration, using two-term harmonic balance method.
TL;DR: In this paper, a simple formula is derived that gives a relation between the force coefficients for a body oscillating in homogeneous and uniformly stratified ideal fluids, which implies the existence of a universal nondimensional similitude criterion for a family of affinely similar bodies, namely, the bodies that can be transformed into each other by vertical dilation of the initial coordinate system.
Abstract: This paper presents a study on affine similitude for the force coefficients of an arbitrary body oscillating in a uniformly stratified fluid. A simple formula is derived that gives a relation between the force coefficients for a body oscillating in homogeneous and uniformly stratified ideal fluids. In particular, it implies the existence of a universal nondimensional similitude criterion for a family of affinely similar bodies, namely, the bodies that can be transformed into each other by vertical dilation of the initial coordinate system. Theoretical results are verified by experiments with a set of spheroids having different length-to-diameter ratios. The experimental technique for evaluation of the frequency-dependent force coefficients is based on Fourier analysis of the time-history of damped oscillation tests.
TL;DR: In this paper, an energy-based Lyapuniform globally asymptotically stable (UGAS) closed-loop control system for marine vessels with nonsymmetric system inertia matrices is presented.
TL;DR: In this paper, the shape analysis of the magnetic fluid under the external force was performed by solving the Navier-Stoke equation and the magnetic field energy equation simultaneously, and the final curvature of the fluid was determined under constraint of magnetic-fluid volume.
Abstract: In this paper, the method to obtain the shape of the magnetic fluid under the external force is derived. For the shape analysis of the magnetic fluid, Maxwell equation for the magnetic-field energy and Navier-Stoke equation for the mechanical energy of the fluid need to be solved simultaneously. The main idea of the method is that dynamic constant is the same value on the fluid surface because of the boundary equilibrium conditions. The final curvature of the fluid is determined under constraint of the magnetic-fluid volume. The effects of the gravitational force, centrifugal force, and external pressure on the shape of the magnetic fluid are analyzed and the computed results agreed well with photographic images.
TL;DR: In this paper, the dispersion equation for a fluid-loaded sandwich plate is derived and the convergence rate of an approximate solution based on the modal composition of the Green matrix is estimated.
01 Jan 2002
TL;DR: In this article, a cantilevered rigid cylinder was mounted on an elastic (leaf spring) two-degree-of-freedom device, which not only acts as an elastic support, but also acts as a special mechanical transducer to measure accelerations/forces/displacements in the stream-wise (x) and the cross-wise(y) directions.
Abstract: Vortex Induced Vibrations (VIV) of elastically mounted rigid cylinders, with low mass-damping parameter values, are strongly dependent on the added mass coefficient. This paper aims to contribute to the technical literature by presenting some results from experiments carried out at University of Sao Paulo – USP and at the Sao Paulo State Technological Research Institute – IPT. A cantilevered rigid cylinder was mounted on an elastic (leaf spring) two-degree-of-freedom device. The device is not only an elastic support, but acts also as a special mechanical transducer to measure accelerations/forces/displacements in the stream-wise (x) and the cross-wise (y) directions. A comprehensive experimental calibration of such a device was carried out, both “in air” and “in water”. The added mass coefficient in the cross-wise direction was indirectly determined from forces and acceleration measurements as a function of the reduced velocity. Results from time-domain and frequency-domain analyses are compared with those obtained by Vikestad et al. (2000) [1].Copyright © 2002 by ASME
TL;DR: In this article, a clamped-free flexible arm rotating in a horizontal plane and carrying a moving mass is modeled by the Euler-Bernoulli beam theory in which rotatory inertia and shear deformation effects are ignored.
TL;DR: An explicit set of ordinary differential equations that approximately describe the dynamics of many rigid bodies (without any hypothesis on their geometry) inside an ideal fluid is presented in this article, where two applications of these equations are made.
Abstract: An explicit set of ordinary differential equations that approximately describe the dynamics of many rigid bodies (without any hypothesis on their geometry) inside an ideal fluid is presented. Two applications of these equations are made. At first, it is shown how to use these equations to compute the added-mass tensor of a single body made up of simpler units (like spheres, cylinders, and ellipsoids). Then the hydrodynamic force and torque that a small-amplitude fast oscillating body induces on another body that can freely move in its vicinity is computed. The noticeable result is that if the free body is sufficiently far from the oscillating one then the averaged interaction force is attractive if and only if the density of the free body is larger than the density of the fluid. Finally, computations for a pendulum system are presented. It seems that the latter system is suitable for experimentation.
TL;DR: In this article, an analytical and numerical study of the dynamics of a beam-mass system is presented, with special attention on the phenomena arising due to the motion of the attached mass and modal interactions produced by the existence of multi-component parametric resonance under primary resonance.