Computation of Far-Field Sound Generation in a Fluid-Structure Interaction Problem

1985 ◽  
Vol 107 (2) ◽  
pp. 210-215 ◽  
Author(s):  
A. T. Conlisk
Keyword(s):  
Asymptotic Methods ◽  
Inviscid Flow ◽  
Physical Situation ◽  
Point Dipole ◽  
Time Step ◽  
Single Vortex ◽  
Mechanical Spring ◽  
Surface Protrusion ◽  
Unsteady Loading ◽  
Moving Media

The problem of generation of sound in moving media has become an important problem in recent years. Accordingly, in this paper we examine the inviscid flow past a bump on a plane wall in which vorticity disturbances initially placed upstream convect downstream and interact with the bump. The physical situation of interest is that of a flow in which vortices are formed far upstream and then impinge on a surface protrusion. The bump in the wall is assumed to be cylindrical in shape and mounted on a mechanical spring. It may undergo nonlinear transverse oscillations as a result of the unsteady loading caused by the vortices. The flow field and the structure are then fully coupled and solutions for the vortex paths and consequent structure position must be obtained interactively and numerically at each time step. The relevant acoustic variables such as pressure, and potential may then be obtained in the limit as the Mach number M → 0 by asymptotic methods for any number of vortices. An acoustic point dipole is generated by impingement of an isolated vortex on the structure but a much more complicated behavior of the acoustic pressure is generated for more complex vortex arrays. Results for a single vortex and two vortices are presented.

Direct Simulation of Electrorheological Suspensions Subjected to Spatially Nonuniform Electric Field

2002 ◽  
Author(s):  
J. Kadaksham ◽  
P. Singh ◽  
N. Aubry
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Lagrange Multiplier ◽  
Dipole Approximation ◽  
Nonuniform Electric Field ◽  
Lagrange Multiplier Method ◽  
Body Motion ◽  
Multiplier Method ◽  
Point Dipole ◽  
Time Step

A numerical method based on the distributed Lagrange Multiplier method (DLM) [2,8] is developed for direct simulations of electrorheological (ER) liquids subjected to spatially varying electric fields. The flow inside particle boundaries is constrained to be rigid body motion by the distributed Lagrange multiplier method. The point-dipole approximation [6] is used to model the electrostatic forces acting on the polarized particles. The code is verified by performing a convergence study that shows that the results are independent of mesh and time step sizes. In a spatially nonuniform electric field the particles move to the regions where the magnitude of electric field is locally maximum when the particle permittivity is greater than that of the liquid. On the other hand, when the particle permittivity is smaller than that of the liquid the particles move to the regions of local minimum of electric field.

Analysis of Fluid-Structure Interaction by Means of Dynamic Unstructured Meshes

1998 ◽  
Vol 120 (4) ◽  
pp. 792-798 ◽  
Author(s):  
F. J. Blom ◽  
P. Leyland
Keyword(s):  
Euler Equations ◽  
Fluid Structure Interaction ◽  
Fluid Motion ◽  
Inviscid Flow ◽  
Euler Method ◽  
Time Step ◽  
Fluid Structure ◽  
Large Rotation ◽  
Structure Interaction ◽  
Naca0012 Airfoil

This paper presents a computational analysis on forced vibration and fluid-structure interaction in compressible flow regimes. A so-called staggered approach is pursued where the fluid and structure are integrated in time by distinct solvers. Their interaction is then taken into account by a coupling algorithm. The unsteady fluid motion is simulated by means of an explicit time-accurate solver. For the fluid-structure interaction problems which are considered here the effects due to the viscosity can be neglected. The fluid is hence modeled by the Euler equations for compressible inviscid flow. Unstructured grids are used to discretise the fluid domain. These grids are particularly suited to simulate unsteady flows over complex geometries by their capacity of being dynamically refined and unrefined. Dynamic mesh adaptation is used to enhance the computational precision with minimal CPU and memory constraints. Fluid-structure interaction involves moving boundaries. Therefore the Arbitrary Lagrange Euler method (ALE-method) is adopted to solve the Euler equations on a moving domain. The deformation of the mesh is controlled by means of a spring analogy in conjunction with a boundary correction to circumvent the principle of Saint Venant. To take advantage of the differences between fluid and structure time scales, the fluid calculation is subcycled within the structural time step. Numerical results are presented for large rotation, pitching oscillation and aeroelastic motion of the NACA0012 airfoil. The boundary deformation is validated by comparing the numerical solution for a flat plate under supersonic flow with the analytical solution.

Numerical Simulation of Vortex Shedding in Normal Triangular Tube Arrays

2006 ◽  
Author(s):  
Bjo¨rn Selent ◽  
Craig Meskell
Keyword(s):  
Vortex Shedding ◽  
Vortex Method ◽  
Reynolds Numbers ◽  
Normal Velocity ◽  
Time Step ◽  
Single Vortex ◽  
Time Stepping ◽  
Tube Arrays ◽  
Flow Through ◽  
Particle Velocities

The unsteady flow through normal triangular tube arrays is simulated applying the Cloud-in-Element method. The scheme realizes time-stepping via a Langrangian vortex method using random-walk to model diffusion in the flow. The vortex particle velocities are computed on a fixed unstructured grid at each time step. Zero normal velocity on solid boundaries is enforced by a source panel method and zero slip is achieved by introducing vorticity into the flow at each time step. Simulations have been carried out for normal triangular tube arryas with pitch ratios of 1.32, 1.61, 2.08, 2.63 at Reynolds numbers of 1000, 3000, 5000 and 10000. Single vortex shedding frequencies have been observed for the smaller pitch ratios while two Strouhal numbers are obtained for the sparse arrays. This is consistent with experimental data in the literature. Also the overall flow structures were captured successfully.

Viscoelastic shear flow over a wavy surface

2016 ◽  
Vol 801 ◽  
pp. 392-429 ◽  
Author(s):  
Jacob Page ◽  
Tamer A. Zaki
Keyword(s):  
Polymer Chains ◽  
Critical Layer ◽  
Lower Wall ◽  
Fourier Synthesis ◽  
Channel Depth ◽  
Single Vortex ◽  
Flow Response ◽  
Finite Extensibility ◽  
Surface Protrusion ◽  
Sinusoidal Surface

A small-amplitude sinusoidal surface undulation on the lower wall of Couette flow induces a vorticity perturbation. Using linear analysis, this vorticity field is examined when the fluid is viscoelastic and contrasted to the Newtonian configuration. For strongly elastic Oldroyd-B fluids, the penetration of induced vorticity into the bulk can be classified using two dimensionless quantities: the ratios of (i) the channel depth and of (ii) the shear-waves’ critical layer depth to the wavelength of the surface roughness. In the shallow-elastic regime, where the roughness wavelength is larger than the channel depth and the critical layer is outside of the domain, the bulk flow response is a distortion of the tensioned streamlines to match the surface topography, and a constant perturbation vorticity fills the channel. This vorticity is significantly amplified in a thin solvent boundary layer at the upper wall. In the deep-elastic case, the critical layer is far from the wall and the perturbation vorticity decays exponentially with height. In the third, transcritical regime, the critical layer height is within a wavelength of the lower wall and a kinematic amplification mechanism generates vorticity in its vicinity. The analysis is extended to localized, Gaussian wall bumps using Fourier synthesis. The Newtonian flow response consists of a single vortex above the bump. In the shallow-elastic flow, a second vortex with opposite circulation is established upstream of the surface protrusion and is induced by the vorticity layer on the upper wall. In the deep transcritical case, the perturbation field consists of a pair of counter-rotating vortices centred on the large vorticity around the critical layer. The more realistic FENE-P model, which accounts for the finite extensibility of the polymer chains, shows the same qualitative behaviour.

Dynamics of Electrorheological Suspensions Subjected to Spatially Nonuniform Electric Fields

2004 ◽  
Vol 126 (2) ◽  
pp. 170-179 ◽  
Author(s):  
J. Kadaksham ◽  
P. Singh ◽  
N. Aubry
Keyword(s):  
Electric Field ◽  
Pressure Gradient ◽  
Lagrange Multiplier ◽  
Critical Value ◽  
Nonuniform Electric Field ◽  
Lagrange Multiplier Method ◽  
Multiplier Method ◽  
Point Dipole ◽  
Time Duration ◽  
Time Step

A numerical method based on the distributed Lagrange multiplier method (DLM) is developed for the direct simulation of electrorheological (ER) liquids subjected to spatially nonuniform electric field. The flow inside particle boundaries is constrained to be rigid body motion by the distributed Lagrange multiplier method and the electrostatic forces acting on the particles are obtained using the point-dipole approximation. The numerical scheme is verified by performing a convergence study which shows that the results are independent of mesh and time step sizes. The dynamical behavior of ER suspensions subjected to nonuniform electric field depends on the solids fraction, the ratio of the domain size and particle radius, and four additional dimensionless parameters which respectively determine the importance of inertia, viscous, electrostatic particle-particle interaction and dielectrophoretic forces. For inertia less flows a parameter defined by the ratio of the dielectrophoretic and viscous forces, determines the time duration in which the particles collect near either the local maximums or local minimums of the electric field magnitude, depending on the sign of the real part of the Clausius-Mossotti factor. In a channel subjected to a given nonuniform electric field, when the applied pressure gradient is smaller than a critical value, the flow assists in the collection of particles at the electrodes, but when the pressure gradient is above this critical value the particles are swept away by the flow.

Toward a neuroscope: An application of high-performance computing for real-time evaluation of brain function using MRI

1994 ◽  
Vol 52 ◽  
pp. 922-923
Author(s):  
C. S. Potter ◽  
C. D. Gregory ◽  
H. D. Morris ◽  
Z.-P. Liang ◽  
P. C. Lauterbur
Keyword(s):  
Human Brain ◽  
Brain Function ◽  
High Performance ◽  
Complex Signal ◽  
Time Step ◽  
Brain Organization ◽  
Cognitive Studies ◽  
Positron Emission ◽  
Imaging And Spectroscopy ◽  
3D Anatomy

Over the past few years, several laboratories have demonstrated that changes in local neuronal activity associated with human brain function can be detected by magnetic resonance imaging and spectroscopy. Using these methods, the effects of sensory and motor stimulation have been observed and cognitive studies have begun. These new methods promise to make possible even more rapid and extensive studies of brain organization and responses than those now in use, such as positron emission tomography.Human brain studies are enormously complex. Signal changes on the order of a few percent must be detected against the background of the complex 3D anatomy of the human brain. Today, most functional MR experiments are performed using several 2D slice images acquired at each time step or stimulation condition of the experimental protocol. It is generally believed that true 3D experiments must be performed for many cognitive experiments. To provide adequate resolution, this requires that data must be acquired faster and/or more efficiently to support 3D functional analysis.

From Finite Sample to Asymptotic Methods in Statistics

2009 ◽  
Author(s):  
Pranab K. Sen ◽  
Julio M. Singer ◽  
Antonio C. Pedroso de Lima
Keyword(s):  
Asymptotic Methods ◽  
Finite Sample
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