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1

Reversed Robin Hood syndrome in the light of nonlinear model of cerebral circulation

Piechna A., Cieslicki K.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 2

459--464

EN

The brain is supplied by the internal carotid and vertebro-basilar systems of vessels interconnected by arterial anastomoses and forming at the base of the brain a structure called the Circle of Willis (CoW). An active intrinsic ability of cerebral vascular bed maintains constant Cerebral Blood Flow (CBF) in a certain range of systemic pressure changes. This ability is called autoregulation and together with the redundant structure of the CoW guarantee maintaining CBF even in partial occlusion of supplying arteries. However, there are some situations when the combination of those two mechanisms causes an opposite effect called the Reversed Robin Hood Syndrome (RRHS). In this work we proposed a model of the CoW with autoregulation mechanism and investigated a RRHS which may occur in the case of Internal Carotid Artery (ICA) stenosis combined with hypercapnia. We showed and analyzed the mechanism of stealing the blood by the contralateral side of the brain. Our results were qualitatively compared with the clinical reports available in the literature.

2

Using ANSYS and SORCER Modeling Framework for the Optimization of the Design of a Flapping Wing Bionic Object

Abramowicz M., Kamieniecki K., Piechna A., Rubach P., Piechna J.

Machine Dynamics Research

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2015

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Vol. 39, No. 1

21-36

EN

Growing modeling software capabilities together with available computational resources enable the modeling of more and more complex multi-physical problems. At the same time, the preparation of such simulation requires a collaboration of both engineers and software. Multidisciplinary Design Optimization (MDO) platforms are used to integrate simulation tools and expert knowledge that represents various engineering disciplines. The presented study demonstrates an effective use of a specialized CFD program and an MDO platform the SORCER Modeling Framework (SMF) for the automation and optimization of the design of a flapping wing bionic object. The SMF realizes an optimization loop by using independent blocks prepared using ANSYS Workbench. An unsteady flow generated by the prescribed flapping wing trajectory is simulated. A number of geometrical and physical parameters is defined in the SMF model and then transferred to the slave blocks of the CFD program. An automated ANSYS workflow generates a geometry of computational domain, realizes it's proper meshing, initializes and performs the simulation, and finally passes the results to the SMF. The proposed system is an example of usage of the SMF that demonstrates the connection of specialized knowledge and a complex CFD simulation with simple and efficient control.

3

Ex vivo and in silico study of human Common Carotid Arteries pressure response in physiological and inverted state

Piechna A., Cieślicki K., Lombarski L., Ciszek B.

International Journal of Applied Mechanics and Engineering

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2015

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Vol. 20, no. 1

209--214

EN

Arterial walls are a multilayer structures with nonlinear material characteristics. Furthermore, residua stresses exist in unloaded state (zero-pressure condition) and they affect arterial behavior. To investigate these phenomena a number of theoretical and numerical studies were performed, however no experimental validation was proposed and realized yet. We cannot get rid of residual stresses without damaging the arterial segment. In this paper we propose a novel experiment to validate a numerical model of artery with residual stresses. The inspiration for our study originates from experiments made by Dobrin on dogs’ arteries (1999). We applied the idea of turning the artery inside out. After such an operation the sequence of layer is reversed and the residual stresses are re-ordered. We performed several pressure-inflation tests on human Common Carotid Arteries (CCA) in normal and inverted configurations. The nonlinear responses of arterial behavior were obtained and compared to the numerical model. Computer simulations were carried out using the commercial software which applied the finite element method (FEM). Then, these results were discussed.