Elastically-nonlinear model for the dynamics of the human back
In the present investigation, a comprehensive set of reliable data for the human spine has been established, and a useful aggregation and analysis of the data has also been carried out. Data obtained has been presented in tabulated and graphical forms to allow easy comparison with other researchers' data. The new accurate data obtained has been used in the construction of a kidney-shaped model of a functional spinal unit which has been subjected to finite element testing that resulted in very good agreement with the results of other published models. A computer-based formulation for the dynamic analysis of an' inertia-variant spatial human body system has also been developed. The human body system is modelled as a multi-body system consisting of interconnected rigid, elastic and visco-elastic components. Each of these components is allowed to undergo large angular rotations. A linear visco-elastic Kelvin-Viogt model is employed whereby stress is assumed to be proportional to the time rate of strain. The focus in this work is placed on the analysis and diagnosis of lumbar and lumbo-sacral back problems associated with lifting activities. All human links are treated as rigid, while the entire lumbar spine is considered to be elastic. Flexibility of the lumbar spine is introduced into the mathematical model using a set of short and stubby finite elements which describe the behavior of the vertebrae and discs at the lumbar region and which accounts for both geometric and inertia nonlinearities. The implementation of the model and analysis of results has been limited to the two-dimensional case in the sagittal plane in recognition of the well known difficulties encountered in solving human body systems. Health and safety issues in material handling are currently receiving the concern of many researchers as well as manufacturing companies. Therefore, two case studies were carried to establish the importance, accuracy and validity of the model developed in this thesis. A two dimensional lifting task with a flexible lumbar spine formed the first case study whilst the second was a pushing task.