Optimizing numerical Aneurism growth predications.

University essay from KTH/Hållfasthetslära (Inst.)

Author: Gustav Thorén; [2015]

Keywords: ;

Abstract:

Abdominal Aortic aneurysm (AAA) is a localized dilation of the abdominal aorta exceeding the normal diameter by more than 50 %. A common complication is rupture of the vessel wall, which in most cases is life-threatening. In order to prohibit loss of life, efforts in trying create computational models to predict failure of the vessel wall has been made. Current non-linear finite element models for biomechanical rupture risk assessment (BRRA) are very computational demanding and require very long computational times.

A BRRA using an automatic time-step scheme is presented in order to speed up the computational time of the very demanding Finite Element Analysis (FEA) models available. The numerical scheme is governed by the collagen dynamics and two numerical approaches are presented. One in which the time step depends only on the maximum incremental change of collagen in one of all directions, and a second in which the time step is governed by the total incremental change of collagen in all directions and the incremental change of the undulations stretches. Simulations were carried out both without and with contact conditions with the spine.

Early results show a 50-75 % speed up in computational time at the cost of a small relative error. The results showed similar failure stress as previous studies, which implies that the constitutive model is sound and that the time-stepping approach has potential.

Further research should include in vitro validation and optimization to the geometry and constitutive model of the aorta. Also, validation of the second time-stepping approach is needed. Furthermore, linking the growth of the intra-luminal thrombos (ILT) to the blood flow in the vessel is needed since the ILT adds structural integrity to the AAA.

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