Time‐domain boundary conditions for outdoor ground surfaces

2003 ◽  
Vol 114 (4) ◽  
pp. 2441-2441
Author(s):  
Sandra L. Collier ◽  
Vladimir E. Ostashev ◽  
D. Keith Wilson ◽  
David H. Marlin
Keyword(s):  
Boundary Conditions ◽  
Time Domain ◽  
Domain Boundary

scholarly journals Time‐domain boundary conditions in atmospheric acoustics

2007 ◽  
Vol 121 (5) ◽  
pp. 3064-3064
Author(s):  
Vladimir E. Ostashev ◽  
Sandra L. Collier ◽  
David H. Marlin ◽  
D. Keith Wilson ◽  
David F. Aldridge ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Time Domain ◽  
Domain Boundary ◽  
Atmospheric Acoustics

scholarly journals Nonlinear Modal Analysis of a One-Dimensional Bar Undergoing Unilateral Contact via the Time-Domain Boundary Element Method

2017 ◽  
Author(s):  
Jayantheeswar Venkatesh ◽  
Anders Thorin ◽  
Mathias Legrand
Keyword(s):  
Boundary Element Method ◽  
Boundary Conditions ◽  
Boundary Element ◽  
Time Domain ◽  
Domain Boundary ◽  
Unilateral Contact ◽  
Dimensional System ◽  
One Dimensional ◽  
The Time Domain ◽  
Element Method

Finite elements in space with time-stepping numerical schemes, even though versatile, face theoretical and numerical difficulties when dealing with unilateral contact conditions. In most cases, an impact law has to be introduced to ensure the uniqueness of the solution: total energy is either not preserved or spurious high-frequency oscillations arise. In this work, the Time Domain Boundary Element Method (TD-BEM) is shown to overcome these issues on a one-dimensional system undergoing a unilateral Signorini contact condition. Unilateral contact is implemented by switching between free boundary conditions (open gap) and fixed boundary conditions (closed gap). The solution method does not numerically dissipate energy unlike the Finite Element Method and properly captures wave fronts, allowing for the search of periodic solutions. Indeed, TD-BEM relies on fundamental solutions which are travelling Heaviside functions in the considered one-dimensional setting. The proposed formulation is capable of capturing main, subharmonic as well as internal resonance backbone curves useful to the vibration analyst. For the system of interest, the nonlinear modeshapes are piecewise-linear unseparated functions of space and time, as opposed to the linear modeshapes that are separated half sine waves in space and full sine waves in time.

Padé approximation in time-domain boundary conditions of porous surfaces

2007 ◽  
Vol 122 (1) ◽  
pp. 107-112 ◽  
Author(s):  
Vladimir E. Ostashev ◽  
Sandra L. Collier ◽  
D. Keith Wilson ◽  
David F. Aldridge ◽  
Neill P. Symons ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Time Domain ◽  
Domain Boundary ◽  
Padé Approximation ◽  
Pade Approximation ◽  
Porous Surfaces

Application and Verification of Time-Domain Impedance Boundary Conditions in CAA Simulations

2021 ◽  
Author(s):  
Ang Li ◽  
Jun Chen
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Frequency Domain ◽  
Time Domain ◽  
Fluid Dynamic ◽  
Domain Boundary ◽  
Impedance Boundary Condition ◽  
Wall Region ◽  
Impedance Boundary ◽  
Acoustic Resistance

Abstract In computational fluid dynamic (CFD) and computational aeroacoustics (CAA) simulations, the wall surface is normally treated as a purely reflective wall. However, some surface treatments are usually applied in experiments. Thus, the simulation results cannot be validated by experimental results. In aeroacoustics analysis, impedance is a quantity to characterize reflectivity and absorption of an acoustically treated surface. One of the major numerical challenges in CAA simulations is to define acoustically well-posed boundary conditions. The impedance boundary condition is a frequency-domain boundary condition. However, CFD and CAA simulations are time-domain computations, which means the frequency-domain impedance boundary condition cannot be adopted directly. Several methods, including the three-parameter model, the z-transform method and the reflection coefficient model, were developed. In the present study, a coupling method that combines the time-domain impedance boundary condition and Large Eddy Simulations (LES) is proposed. A channel flow with wall impedance is simulated at different acoustic resistance and reactance. The approach is verified by the case with purely reflective wall impedance. For the flow with wall impedance. The effects of acoustic resistance and reactance are investigated. It is found that the wall impedance contributes to the noise reduction in the near-wall region, and with the decrease of the resistance or reactance, the sound pressure level is decreased. The method developed in this study is expected to be applied to a variety of noise-control problems.

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