Research in Mechanical Engineering

BIOMECHANICS

Staff Involved: A.D. Lucey, I.M. Howard

Project Description(s):

Dynamics of the upper airway

This research seeks to understand the interaction of the (time-varying) human inspiratory airflow and the deformable tissue that characterises both the soft palate and the walls of the pharynx. Motivation for this study comes from the condition of sleep apnoea in which airway blockage occurs during sleep leading to dangerous levels of daytime drowsiness. Both low and high Reynolds number models of the fluid flow are being developed. In the former, an in-house finite-element flow solution has been developed. This has been fully coupled to a finite-difference representation of the soft-palate dynamics. Both flutter and divergence types of instabilities have been simulated. For high Reynolds numbers, potential flow is assumed although viscous effects are implicitly included through the imposition of the Kutta condition at the trailing edge of the soft palate. The wake downstream of this point is modelled by discrete shed vortices. Although at present focused on a particular application, the methods and phenomena being uncovered have much wider relevance being representative of any thin plate-like structure flapping in a fluid flow.

Pressure-pulse propagation in the human spine

This project, carried out in collaboration with Warwick University, serves to elucidate the pathogenesis of syringomyelia, a condition caused by cerebro-spinal fluid entering the spinal cord to create syrinxes (fluid cavities), thereby swelling and damaging the nerves within the cord. A model of pressure-pulse propagation in a closed system comprising two fluids separated by flexible membrane has been developed as a simple analogue. It has been shown, both theoretically (using linear and weakly nonlinear analyses) and numerically (using the method of characteristics) that disturbance steepening can occur leading to shock-like conditions - or an elastic jump - that propagates along the spine. The reflection of such a pulse at an end obstruction is then shown to yield large a transmural pressure difference that may explain the migration of fluid into the spine.

Biodynamic responses in off-road equipment operators

Prolonged exposure to vehicular vibration and shocks has been related to discomfort, reduced work efficiency and various health and safety risks, especially for off-road vehicle drivers. As a consequence of whole-body vibration and shock exposure, some operators suffer from lumbar spine disorders and lower back pain. This research study attempts to evaluate the potential health hazards and factors which may cause degenerative disorders of the lumbar spine and discs of a seated human exposed to whole-body vibration and repeated mechanical shocks.

It was observed that in the field, all the operators/drivers were exposed to pitching motions or rocking movements continuously during the working period. Pitch motion, jerk and rocking movements were observed to contain more horizontal excitation than vertical vibration. The jerk or rocking movement was observed to cause changes to the body posture. The body posture has been shown in this study to influence directly the forces acting both in the pelvis and in the spine. The results of experimental modelling show that all factors including the vibration, seating posture and fore-and-aft rocking movement, directly increased the forces acting on the pelvis.

A dynamic simulation model has been produced using the Working Model 2D software which has clearly revealed that the type, magnitude of vibration and also the seat suspension influences the seat-buttocks and lumbar spine force. Both compressive and shear force estimates were consistent with material properties and geometry. The next phase of the research would involve the simulation of the lumbar spine forces under field type excitation conditions.

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