Vibro-acoustics response of a simplified glass window excited by the turbulent wake of a quarter-spherocylinder body.

Inside vehicle cabins, an important part of interior noise is generated from cabin window vibration. The vibration is stimulated by surface pressure fluctuations that are produced by exterior flows and flow-induced noise. To numerically investigate the cabin noise, both exterior flows and noise must be resolved in simulations. This requirement motivates us to utilize advanced computational fluid dynamics (CFD) and computational aeroacoustics (CAA) based on a quarter-spherocylinder body, which is a general model for vehicle mirrors. The blunt body is mounted upstream of a rectangular window of a cuboid cavity. The turbulent flow is simulated using compressible large eddy simulation, compressible detached eddy simulation, and incompressible detached eddy simulation (I-DES). The exterior noise is either predicted by coupling the I-DES with an acoustic wave modeling method, or directly solved using compressible CFD methods. Given surface pressure fluctuations on the window from the CFD and CAA methods, the window vibration and interior noise are simulated with a finite element method. The effects of compressibility, turbulence modeling methods, and grid topology (polyhedral and trimmed elements) are discussed. The computational efficiency of the numerical methods is addressed. The contributions of hydrodynamic and acoustic pressure fluctuations to the interior noise are clarified.

Deformation of dorsal root ganglion due to pressure transients of venous blood and cerebrospinal fluid in the cervical vertebral canal.

The dorsal root ganglion (DRG) that is embedded in the foramen of the cervical vertebra can be injured during a whiplash motion. A potential cause is that whilst the neck bends in the whiplash motion, the changes of spinal canal volume induce impulsive pressure transients in the venous blood outside the dura mater (DM) and in the cerebrospinal fluid (CSF) inside the DM. The fluids can dynamically interact with the DRG and DM, which are deformable. In this work, the interaction is investigated numerically using a strong-coupling partitioned method that synchronize the computations of the fluid and structure. It is found that the interaction includes two basic processes, i.e., the pulling and pressing processes. In the pulling process, the DRG is stretched towards the spinal canal, and the venous blood is driven into the canal via the foramen. This process results from negative pressure in the fluids. In contrast, the pressing process is caused by positive pressure that leads to compression of the DRG and the outflow of the venous blood from the canal. The largest pressure gradient is observed at the foramen, where the DRG is located at. The DRG is subject to prominent von Mises stress near its end, which is fixed without motions. The negative internal pressure is more efficient to deform the DRG than the positive internal pressure. This indicates that the most hazardous condition for the DRG is the pulling process.

Transient pressure changes in the vertebral canal during whiplash motion--A hydrodynamic modeling approach.

In vehicle collisions, the occupant's torso is accelerated in a given direction while the unsupported head tends to lag behind. This mechanism results in whiplash motion to the neck. In whiplash experiments conducted for animals, pressure transients have been recorded in the spinal canal. It was hypothesized that the transients caused dorsal root ganglion dysfunction. Neck motion introduces volume changes inside the vertebral canal. The changes require an adaptation which is likely achieved by redistribution of blood volume in the internal vertebral venous plexus (IVVP). Pressure transients then arise from the rapid redistribution. The present study aimed to explore the hypothesis theoretically and analytically. Further, the objectives were to quantify the effect of the neck motion on the pressure generation and to identify the physical factors involved. We developed a hydrodynamic system of tubes that represent the IVVP and its lateral intervertebral vein connections. An analytical model was developed for an anatomical geometrical relation that the venous blood volume changes with respect to the vertebral angular displacement. This model was adopted in the hydrodynamic tube system so that the system can predict the pressure transients on the basis of the neck vertebral motion data from a whiplash experiment. The predicted pressure transients were in good agreement with the earlier experimental data. A parametric study was conducted and showed that the system can be used to assess the influences of anatomical geometrical properties and vehicle collision severity on the pressure generation.