A Generalized Variational Principle for Dissipative Hydrodynamics and its Application to Biot's Theory for the Description of a Fluid Shear Relaxation
Abstract:A generalization of Hamilton's and Onsager's variational principles for dissipative hydrodynamical systems is represented in terms of the mechanical and heat displacement fields. A system of equations for these fields is derived from the extreme condition case using a Lagrangian formulation for the difference between the kinetic and the free energies and for the time integral of the dissipation function. The generalized hydrodynamic equation system is then evaluated using the generalized variational principle. At low frequencies this system corresponds to the traditional Navier-Stokes equations and in the high frequency limit it describes propagation of acoustical and heat modes with finite propagation velocities.
Based on the generalized variational principle a system of Biot-type equations is derived that takes into account the fluid shear viscosity relaxation. This leads to the existence of two shear propagation modes in addition to two longitudinal modes as found in the original Biot approach. One of the two shear modes is an acoustical wave, while the other is a low-frequency diffusive wave. The phase velocity and attenuation factor for the second shear mode depend linearly on the frequency. This behavior is different from that of the diffusive longitudinal mode which depends on the square root of the frequency.
Document Type: Research Article
Publication date: March 1, 2010
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- Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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