scholarly journals A note on applicability of locally-reacting boundary conditions for Delany-Bazley type porous material layer backed by rigid wall

2015 ◽  
Vol 36 (5) ◽  
pp. 459-462 ◽  
Author(s):  
Yosuke Yasuda ◽  
Satoki Ueno ◽  
Hidehisa Sekine
Keyword(s):  
Porous Material ◽  
Boundary Conditions ◽  
Rigid Wall ◽  
Material Layer

Hydroelastic Vibration of Rectangular Plates

1996 ◽  
Vol 63 (1) ◽  
pp. 110-115 ◽  
Author(s):  
Moon K. Kwak
Keyword(s):  
Boundary Conditions ◽  
Approximate Formula ◽  
Natural Frequencies ◽  
Mass Matrix ◽  
Ritz Method ◽  
Plate Boundary ◽  
Rigid Wall ◽  
Mode Shapes ◽  
Rectangular Plates ◽  
Virtual Mass

This paper is concerned with the virtual mass effect on the natural frequencies and mode shapes of rectangular plates due to the presence of the water on one side of the plate. The approximate formula, which mainly depends on the so-called nondimensionalized added virtual mass incremental factor, can be used to estimate natural frequencies in water from natural frequencies in vacuo. However, the approximate formula is valid only when the wet mode shapes are almost the same as the one in vacuo. Moreover, the nondimensionalized added virtual mass incremental factor is in general a function of geometry, material properties of the plate and mostly boundary conditions of the plate and water domain. In this paper, the added virtual mass incremental factors for rectangular plates are obtained using the Rayleigh-Ritz method combined with the Green function method. Two cases of interfacing boundary conditions, which are free-surface and rigid-wall conditions, and two cases of plate boundary conditions, simply supported and clamped cases, are considered in this paper. It is found that the theoretical results match the experimental results. To investigate the validity of the approximate formula, the exact natural frequencies and mode shapes in water are calculated by means of the virtual added mass matrix. It is found that the approximate formula predicts lower natural frequencies in water with a very good accuracy.

Study on the influence of boundary conditions on the airflow resistivity measurement of porous material

2020 ◽  
Vol 161 ◽  
pp. 107181
Author(s):  
Xinzhong Xiong ◽  
Xuewen Liu ◽  
Liang Wu ◽  
Jinxiang Pang ◽  
Hewei Zhang
Keyword(s):  
Porous Material ◽  
Boundary Conditions ◽  
Resistivity Measurement

A model for the boundary condition of a porous material. Part 2

1971 ◽  
Vol 49 (2) ◽  
pp. 327-336 ◽  
Author(s):  
S. Richardson
Keyword(s):  
Boundary Condition ◽  
Porous Material ◽  
Boundary Conditions ◽  
Material Part

The present paper contains an analysis of the model of a porous material proposed in part 1, and carries out calculations which allow comparison between theory and the experiments described therein. The relevant boundary conditions to be applied at an interface between a fluid and such a material are considered.

scholarly journals Sound absorption of a micro-perforated plate backed by a porous material under high sound excitation: measurement and prediction

2013 ◽  
Vol 2 (4) ◽  
pp. 281 ◽  
Author(s):  
Rostand Boumda Tayong ◽  
Thomas Dupont ◽  
Philippe Leclaire
Keyword(s):  
Porous Material ◽  
Sound Absorption ◽  
Perforated Plate ◽  
Rigid Wall ◽  
Experimental Results ◽  
Mean Flow ◽  
Sound Levels ◽  
Specific Impedance ◽  
Air Flow Resistivity ◽  
High Sound

The sound absorption coefficient of perforated facings backed by porous materials is studied under high sound intensities in the absence of mean flow. The theoretical considerations are based on the equivalent fluid following the Johnson-Champoux-Allard approach and the use of the transfer matrix method. To take into account the high sound levels effects, the air flow resistivity of each layer is modified following the Forchheimer law. Two specimens of perforated plate are built and tested when backed by a polymeric foam and a fibrous material. A specific impedance tube setup is developed for the measurement of the surface acoustic impedance for sound pressure levels ranging from 90 dB to 150 dB at the surface of the perforated facing. To corroborate the validity of the presented method, two considerations are particularly depicted in the experimental results: first, the case where the perforated facing and the porous material are both directly backed by a rigid wall and the case where there is an air cavity between the porous material and the rigid wall. Good agreement is observed between the simulation and the experimental results.

Linear and nonlinear baroclinic instability with rigid sidewalls

1995 ◽  
Vol 291 ◽  
pp. 109-138 ◽  
Author(s):  
Michael D. Mundt ◽  
Nicholas H. Brummell ◽  
John E. Hart
Keyword(s):  
Boundary Conditions ◽  
Baroclinic Instability ◽  
Rigid Wall ◽  
Bottom Friction ◽  
Stable Region ◽  
External Control ◽  
Weakly Nonlinear ◽  
Slip Boundary ◽  
Highly Nonlinear ◽  
Parameter Values

The behaviour of baroclinic waves growing from instability in a two-layer channel flow with rigid (no-slip) sidewalls is described and contrasted with that for the more traditional free-slip boundary conditions. The linear theory for the onset of small-amplitude disturbances shows that the change in lateral boundary conditions has only a modest effect for typical laboratory parameter values, although the no-slip case is slightly more unstable at very small values of bottom friction. On the other hand, the nonlinear evolution of no-slip modes is completely different. While the free-slip case becomes aperiodic only at large values of the supercriticality (F–Fc)/Fc, the rigid wall case can be subcritically chaotic. Aperiodic, highly nonlinear wave motions are possible for external control values set in the linearly stable region of parameter space. Weakly nonlinear analysis shows that the no-slip case has a negative Landau constant for moderately small values of bottom friction, and it is in this regime that high-resolution numerical simulations exhibit subcritical chaos. At larger values of bottom friction, the rigid-wall simulations undergo a supercritical quasi-periodic transition to chaos at modest, order one, supercriticality, which is substantially smaller than that required for chaos in the free-slip case.

scholarly journals Nonlinear stability of the one-domain approach to modelling convection in superposed fluid and porous layers

2010 ◽  
Vol 466 (2121) ◽  
pp. 2695-2705 ◽  
Author(s):  
Antony A. Hill ◽  
Magda Carr
Keyword(s):  
Porous Material ◽  
Boundary Conditions ◽  
Nonlinear Stability ◽  
Navier Stokes ◽  
Governing Equations ◽  
Porous Layers ◽  
Stability Bound ◽  
Interfacial Boundary ◽  
The One ◽  
Modelling Approach

Studies of the nonlinear stability of fluid/porous systems have been developed very recently. A two-domain modelling approach has been adopted in previous works, but was restricted to specific configurations. The extension to the more general case of a Navier–Stokes modelled fluid over a porous material was not achieved for the two-domain approach owing to the difficulties associated with handling the interfacial boundary conditions. This paper addresses this issue by adopting a one-domain approach, where the governing equations for both regions are combined into a unique set of equations that are valid for the entire domain. It is shown that the nonlinear stability bound, in the one-domain approach, is very sharp and hence excludes the possibility of subcritical instabilities. Moreover, the one-domain approach is compared with an equivalent two-domain approach, and excellent agreement is found between the two.

Heat Conduction of a Porous Material

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Koji Miyazaki ◽  
Saburo Tanaka ◽  
Daisuke Nagai
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Porous Material ◽  
Boundary Conditions ◽  
Periodic Boundary ◽  
Phonon Dispersion ◽  
Bulk Material ◽  
Periodic Boundary Conditions ◽  
Boltzmann Transport ◽  
Time Space

In this study, we introduce our numerical and experimental works for the thermal conductivity reduction by using a porous material. Recently thermal conductivity reduction has been one of the key technologies to enhance the figure of merit (ZT) of a thermoelectric material. We carry out numerical calculations of heat conduction in porous materials, such as phonon Boltzmann transport (BTE) and molecular dynamics (MD) simulations, in order to investigate the mechanism of the thermal conductivity reduction of a porous material. In the BTE, we applied the periodic boundary conditions with constant heat flux to calculate the effective thermal conductivity of porous materials.In the MD simulation, we calculated the phonon properties of Si by using the Stillinger–Weber potential at constant temperature with periodic boundary conditions in the x, y, and z directions. Phonon dispersion curves of single crystal of Si calculated from MD results by time-space 2D FFT are agreed well with reference data. Moreover, the effects of nanoporous structures on both the phonon group velocity and the phonon density of states (DOS) are discussed. At last, we made a porous p-type Bi2Te3 by nanoparticles prepared by a beads milling method. The thermal conductivity is one-fifth of that of a bulk material as well as keeping the same Seebeck coefficient as the bulk value. However, electrical conductivity was much reduced, and the ZT was only 0.048.

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