The phenomenon of high-amplitude inflation waves resulting from a sharp axial acceleration of the aorta, as may occur in road accidents, is investigated theoretically. The aorta is modeled as an axisymmetric tapered membranic shell (tube) made of an incompressible, nonlinear viscoelastic material with cylindrical orthotropy. It is filled with an inviscid, incompressible fluid whose flow is considered as quasi-one dimensional along the tube axis. The equations of motion of the tube and of the fluid are solved numerically, by using a two-step explicit scheme, for several axial acceleration profiles. The solutions shows that an inflation wave is generated and it propagates in opposite direction to that of the acceleration. The wall stresses, deformations and their time derivatives as well as fluid velocity and pressure are determined along the tube at different time intervals. Peak axial and circumferential stresses are high, with the latter far exceeding the former. These stresses may cause rupture of the aorta.

A mathematical model for large amplitude wave propagation in a thin walled distensible tube is developed. The tube wall is considered as a membranic shell made of an incompressible, non-linear viscoelastic material with cylindrical orthotropy. The fluid is regarded as incompressible and inviscid and the flow is quasi-one-dimensional. The case of a pressure step applied at one end of a uniform straight tube is solved as an example. The system of partial differential equations, describing the motions of the fluid and the wall, are integrated numerically by using a two-step explicit scheme. Flow and deformation variables as well as the wave velocity are determined in time and space.

One of the major contributing factors to the life of knee endoprostheses is wear resulting from sliding of the mating surfaces. Although this is not considered the primary cause for failure of the prosthesis, the importance of reducing wear becomes more pronounced with the increase of life expectancy of the patients. Sliding mechanisms are subjected to wear significantly more than rolling mechanisms. It was therefore suggested to develop a prosthetic knee joint in which the mating surfaces will roll one on top of the other. For this purpose an experimental study was carried out aimed at the investigation of the natural knee centrodes. Rolling of the natural centrodes on each other is bound to retain the natural kinematics of the knee elements and that of the soft tissues. Since the natural centrodes were found mechanically inadequate for reproduction, synthetic surfaces were postulated and examined. The various surfaces were subjected to kinematic optimization and the optimal surfaces from structural and kinematic reproduction aspects were selected. Finally, a conceptual configuration of the joint is suggested taking into account the necessary constraints for the performance of the rolling function.