Acoustics of thermoviscous fluids: The Kirchhoff-Helmholtz representation in generalized form.

The Kirchhoff-Helmholtz representation of linear acoustics is generalized to thermoviscous fluids, by deriving separate bounded-region equations for the acoustic, entropy, and vorticity modes in a uniform fluid at rest. For the acoustic and entropy modes we introduce modal variables in terms of pressure and entropy perturbations, and develop asymptotic approximations to the mode equations that are valid to specified orders in two thermoviscous parameters. The introduction of spatial windowing for the mode variables leads to surface source and dipole distributions as a way of representing boundary conditions for each mode.

The effect of reverberation on the damping of bubbles.

The measurement of an acoustic emission, or scatter, from a bubble is not difficult. However, an accurate interpretation of that signal in terms of the bubble dynamics may require careful consideration. The study presented here is at first sight relatively simple: comparison of the predicted and measured quality factors of injected bubbles.

Weak nonlinear propagation of sound in a finite exponential horn.

This article presents an approximate solution for weak nonlinear standing waves in the interior of an exponential acoustic horn. An analytical approach is chosen assuming one-dimensional plane-wave propagation in a lossless fluid within an exponential horn. The model developed for the propagation of finite-amplitude waves includes linear reflections at the throat and at the mouth of the horn, and neglects boundary layer effects.

Simulation of acute subdural hematoma and diffuse axonal injury in coronal head impact.

Coronal head impacts were simulated in a physical model, based on the hypothesis that acute subdural hematoma (ASDH) is related to cerebral vertex displacement and diffuse axonal injury (DAI) to local Green-Lagrange strain. The geometry of the 2D model was based on anatomical measurements taken from the MRI scans of 10 adult males. Silicone gel modelled the cerebrum, paraffin the CSF and elastic membranes the trabeculae of the sulci.

Modelling the Brain for Rotational Loading: Shear Effects and Other Complications.

This study considers modelling the brain due to rotation of the skull where, at lower frequencies, the shear property of the material is important. Investigations reported here cover the effect of elastic and viscoelastic (lossy) cerebral material, the effect of the Falx protruding into the brain, the gap around the Falx and the brain filled with non viscous fluid in addition to different models of the Falx with bending or membrane stiffness. Analytical benchmark formulations are also described for the simple 2D plane strain in a cylinder produced by a half-sine rotation on the outer periphery which allows numerical (Finite Element) models to be validated.