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Analysis of residual stresses in arterial wall
Novák, Kamil ; Fuis, Vladimír (referee) ; Burša, Jiří (advisor)
This thesis deals with computational modeling of the influence of residual stresses in idealized geometry of blood vessels and subsequent application of acquired knowledge to abdominal aortic aneurysm. In the terms of quality of the computational model, we reduced the uncertainties that are included in the computational model without considering the influence of residual stresses. The basic assumption of homogenization significant peaks of the stress between inner and outer vessel wall was met for each level of the computational model Methods that have been used are: deformation method (opening angle method), inverse mechanics of large deformations, fictitious temperature – for linear elastic material and hyperelastic material defined by the constitutive model. Numerical verification was carried out using program ANSYS.
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Stress-strain analysis of anastomosis between artery and artificial vascular graft
Hrubanová, Anna ; Švancara, Pavel (referee) ; Burša, Jiří (advisor)
This bachelor’s thesis deals with anatomy and pathology of arteries and possibilities of their replacement with vascular grafts. The first part of the thesis describes structure and mechanical properties of arterial wall. Furthemore, the biological and mechanical properties of vascular grafts and their influence of healing process are described. The second part of this thesis starts with non-linear calculation of deformation of arterial wall using generalized Hooke’s law. The analytical calculation of connection of artery and vascular graft using cylindrical momentum shell theory was made at the end of this thesis. Description of limitations of this method is also included.
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Analysis of Influence of Collagen Organization on Mechanical Properties of Arteries
Novák, Kamil ; Daniel, Matej (referee) ; Vimmr, Jan (referee) ; Burša, Jiří (advisor)
This dissertation thesis concerns with Analysis of Influence of Collagen Organization on Mechanical Properties of Arteries and it is divided into three main parts. Motivation for this dissertation thesis was in a study reviewing effect of material model upon resulting stresses in AAA. The effect was calculated in 70 patient-specific geometries of AAA, which exceeds the number of geometries in other scientific papers by one order. Within this study, two material models were used, i.e. real one and 100× stiffer, and obtained stresses were mutually compared. It was quantified that peak stress difference can be higher than 20 % in 10% of patients and therefore the real material model should be preferred over the artificial one although operation with this model is more demanding. The second part of this thesis deals with an identification of structural parameters (orientation and dispersion of collagen fibres) of porcine aortic tissue by using adjusted Fast Fourier Transform based algorithm. The extracted structural parameters were inserted into two-layer structure-motivated constitutive model Martufi-Gasser. This model was validated and its predictive capabilities were also tested with fine results. The most important information obtained from the digital image processing of ~9000 micrographs is existence of only one family of dispersed collagen fibres which breaks the current dogma present in many scientific papers about two families of collagen fibres. The third part concerns with a proposal of an automated phase-correlation based algorithm for obtaining collagen fibre direction from polarized light microscopy images. The proposed algorithm was verified and validated and it yields histograms of collagen fibre directions with overall number of measured points larger than it would be possible to get from any manual measurement. The limitation of the original proposed algorithm is in 90° period of polarized light intensity, thus the method results in angles in the range of 0°–90. Therefore the end of the thesis is dedicated resolving this problem and obtaining real angles in a span of 0°–180°. To this end, the microscope set-up was changed and the algorithm was adjusted accordingly. The original and the adjusted algorithms are collagen-specific, fast and an operator independent. Despite all the author´s effort put into collagen fibre waviness quantification directly from the histograms, the waviness has not been quantified yet in this way and it remains at the stage of research.
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Analysis of possibilities of analytical approaches suitable for evaluating of stress-strain states of idealized aortic shapes
Turčanová, Michaela ; Burša, Jiří (referee) ; Novák, Kamil (advisor)
The bachelor's thesis deals with possibilities of analytical solution of stress-strain states of arteries. The first part of the thesis gives an information about cardiovascular system and continuum mechanics. The calculation was performed analytically and also numerically using ANSYS program. The analytical calculation was carried out considering non-linear theory of thin and thick-walled vessels involving the residual stress and fictitious temperature approach. Furthermore, the analysis of solutions of abdominal aortic aneurysms was done based on linear theory. Description of other methods of linear theory and techniques of calculating with residual stress are briefly summarized.
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Analysis of impact of direction distribution of collagen fibres in arterial wall on its mechanical properties
Fischer, Jiří ; Návrat, Tomáš (referee) ; Burša, Jiří (advisor)
The aim of this thesis is to analyse literature with focusing on literature about directional distribution of collagen fibres. This knowledge is very important for computational modelling and FEM analysis of arterial wall. Comparison of suitability of different models of directional distribution of collagen fibres is made by fitting of different types of probability density functions. Impact assessment of different collagen fibres distribution on mechanical properties of the arterial wall and impact assessment of wall anisotropy is solved with finite element method. FEM analysis is done on three loading types – uniaxial tension, equibiaxial tension and inflation of artery by internal pressure. Output of this thesis is evaluation of results for various types of collagen fibres arrangement in arterial wall.
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Analysis of impact of direction distribution of collagen fibres in arterial wall on its mechanical properties
Fischer, Jiří ; Návrat, Tomáš (referee) ; Burša, Jiří (advisor)
The aim of this thesis is to analyse literature with focusing on literature about directional distribution of collagen fibres. This knowledge is very important for computational modelling and FEM analysis of arterial wall. Comparison of suitability of different models of directional distribution of collagen fibres is made by fitting of different types of probability density functions. Impact assessment of different collagen fibres distribution on mechanical properties of the arterial wall and impact assessment of wall anisotropy is solved with finite element method. FEM analysis is done on three loading types – uniaxial tension, equibiaxial tension and inflation of artery by internal pressure. Output of this thesis is evaluation of results for various types of collagen fibres arrangement in arterial wall.
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Stress-strain analysis of anastomosis between artery and artificial vascular graft
Hrubanová, Anna ; Švancara, Pavel (referee) ; Burša, Jiří (advisor)
This bachelor’s thesis deals with anatomy and pathology of arteries and possibilities of their replacement with vascular grafts. The first part of the thesis describes structure and mechanical properties of arterial wall. Furthemore, the biological and mechanical properties of vascular grafts and their influence of healing process are described. The second part of this thesis starts with non-linear calculation of deformation of arterial wall using generalized Hooke’s law. The analytical calculation of connection of artery and vascular graft using cylindrical momentum shell theory was made at the end of this thesis. Description of limitations of this method is also included.
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Analysis of Influence of Collagen Organization on Mechanical Properties of Arteries
Novák, Kamil ; Daniel, Matej (referee) ; Vimmr, Jan (referee) ; Burša, Jiří (advisor)
This dissertation thesis concerns with Analysis of Influence of Collagen Organization on Mechanical Properties of Arteries and it is divided into three main parts. Motivation for this dissertation thesis was in a study reviewing effect of material model upon resulting stresses in AAA. The effect was calculated in 70 patient-specific geometries of AAA, which exceeds the number of geometries in other scientific papers by one order. Within this study, two material models were used, i.e. real one and 100× stiffer, and obtained stresses were mutually compared. It was quantified that peak stress difference can be higher than 20 % in 10% of patients and therefore the real material model should be preferred over the artificial one although operation with this model is more demanding. The second part of this thesis deals with an identification of structural parameters (orientation and dispersion of collagen fibres) of porcine aortic tissue by using adjusted Fast Fourier Transform based algorithm. The extracted structural parameters were inserted into two-layer structure-motivated constitutive model Martufi-Gasser. This model was validated and its predictive capabilities were also tested with fine results. The most important information obtained from the digital image processing of ~9000 micrographs is existence of only one family of dispersed collagen fibres which breaks the current dogma present in many scientific papers about two families of collagen fibres. The third part concerns with a proposal of an automated phase-correlation based algorithm for obtaining collagen fibre direction from polarized light microscopy images. The proposed algorithm was verified and validated and it yields histograms of collagen fibre directions with overall number of measured points larger than it would be possible to get from any manual measurement. The limitation of the original proposed algorithm is in 90° period of polarized light intensity, thus the method results in angles in the range of 0°–90. Therefore the end of the thesis is dedicated resolving this problem and obtaining real angles in a span of 0°–180°. To this end, the microscope set-up was changed and the algorithm was adjusted accordingly. The original and the adjusted algorithms are collagen-specific, fast and an operator independent. Despite all the author´s effort put into collagen fibre waviness quantification directly from the histograms, the waviness has not been quantified yet in this way and it remains at the stage of research.
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|
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Analysis of possibilities of analytical approaches suitable for evaluating of stress-strain states of idealized aortic shapes
Turčanová, Michaela ; Burša, Jiří (referee) ; Novák, Kamil (advisor)
The bachelor's thesis deals with possibilities of analytical solution of stress-strain states of arteries. The first part of the thesis gives an information about cardiovascular system and continuum mechanics. The calculation was performed analytically and also numerically using ANSYS program. The analytical calculation was carried out considering non-linear theory of thin and thick-walled vessels involving the residual stress and fictitious temperature approach. Furthermore, the analysis of solutions of abdominal aortic aneurysms was done based on linear theory. Description of other methods of linear theory and techniques of calculating with residual stress are briefly summarized.
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