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Multi-fragmental and multi-phase availability models of the safety-critical I&C systems with two-cascade redundancy

Kharchenko Vyacheslav, Ponochovnyi Yuriy, Babeshko Ievgen

International Journal of Electronics and Telecommunications

2024

Vol. 70, No. 1

211--218

Traditional availability, reliability, and safety models face the dimension problem due to a huge number of components in modern systems, motivating further research in this field. This paper focuses on multi-fragmental and multiphase models for availability and functional safety assessment of the information and control (I&C) systems with two-cascade redundancy considering design faults manifestation during operation. The methodology of the research is based on Markov and semi-Markov chains with the utilization of multi-phase modeling. Several multi-phase models are developed and investigated considering different conditions of operation and failures caused by version faults. The case study of the research is based on the analysis of safety-critical nuclear power plant I&C systems such as the reactor trip systems developed using the programmable platform RadICS.

Development of multi-phase models of blood flow for medium-sized vessels with stenosis

Kopernik Magdalena, Tokarczyk Paweł

Acta of Bioengineering and Biomechanics

2019

Vol. 21, no. 2

63--70

The purpose of the work was to develop two-phase non-Newtonian blood models for medium-sized vessels with stenosis using power law and Herschel–Bulkley models. Methods: The blood flow was simulated in 3D models of blood vessels with 60% stenosis. The Ansys Fluent software was applied to implement the two-phase non-Newtonian blood models. In the present paper, the mixture model was selected to model the two phases of blood: plasma and red blood cells. Results: Simulations were carried out for four blood models: a) single-phase non-Newtonian, b) two-phase non-Newtonian, c) two-phase Herschel–Bulkley with yield stress 0 mPa, and d) two-phase Herschel–Bulkley with yield stress 10 mPa for blood plasma, while flow took place in vessel with stenosis 60%. Presentation of results in this paper shows that stenosis can substantially affect blood flow in the artery, causing variations of velocity and wall shear stress. Thus, the results in the present paper are maximum values of blood velocity and wall shear stress, profiles and distributions of blood velocity and wall shear stress computed for single- and two-phase blood models for medium-sized vessels with stenosis. Conclusions: For the two-phase blood models the influence of initial velocity on blood flow in the stenosis zone is not observed, the velocity profiles are symmetric and parabolic. Contrary, for the single phase non-Newtonian blood model, the velocity profile is flat in the stenosis zone and distribution of velocity is disturbed just behind the stenosis zone. The shapes of wall shear stress profiles for twophase blood models are similar and symmetric in the center of stenosis. The biggest differences in maximum values of velocities and wall shear stress are observed between single phase non-Newtonian power law and Herschel–Bulkley blood models. The comparison of the obtained results with the literature indicates that the two-phase Herschel–Bulkley model is the most suitable for describing flow in medium-sized vessels with stenosis.