| 1. |
- Gasser, T. Christian, et al.
(författare)
-
Spatial orientation of collagen fibers in the abdominal aortic aneurysm's wall and its relation to wall mechanics
- 2012
-
Ingår i: Acta Biomaterialia. - : Elsevier BV. - 1742-7061 .- 1878-7568. ; 8:8, s. 3091-3103
-
Tidskriftsartikel (refereegranskat)abstract
- Collagen is the most abundant protein in mammals and provides the abdominal aortic aneurysm (AAA) wall with mechanical strength, stiffness and toughness. Specifically, the spatial orientation of collagen fibers in the wall has a major impact on its mechanical properties. Apart from valuable microhistological information, this data can be integrated by histomechanical constitutive models thought to improve biomechanical simulations, i.e. to improve the biomechanical rupture risk assessment of AAAs. Tissue samples (n = 24) from the AAA wall were harvested during elective AAA repair, fixated, embedded, sectioned and investigated by polarized light microscopy. The birefringent properties of collagen were reinforced by picrosirius red staining and the three-dimensional collagen fiber orientations were identified with a universal rotary stage. Two constitutive models for collagen fibers were used to integrate the identified structural information in a macroscopic AAA wall model. The collagen fiber orientation in the AM wall was widely dispersed and could be captured by a Bingham distribution function (kappa(1) = 11.6, kappa(2) = 9.7). The dispersion was much larger in the tangential plane than in the cross-sectional plane, and no significant difference between the medial and adventitial layers could be identified. The layered directional organization of collagen in normal aortas was not evident in the AAA. The collagen organization identified, combined with constitutive descriptions of collagen fibers that depend on its orientation, explain the anisotropic (orthotropic) mechanical properties of the AAA wall. The mechanical properties of collagen fibers depend largely on their undulation, which is an important structural parameter that requires further experimental investigation.
|
|
| 2. |
- Ghulam, M. M., et al.
(författare)
-
Characterization of Non-reacting Swirling Flow in a Gas Turbine Fuel Injector
- 2021
-
Ingår i: AIAA Scitech 2021 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics (AIAA). ; , s. 1-22
-
Konferensbidrag (refereegranskat)abstract
- The current work investigates the swirling flow of a gas fuel injector utilized in the Lean Direct Injection (LDI) combustion system. Planer particle image velocimetry (PIV) measurements and large eddy simulation (LES) numerical analysis are conducted to have a profound understanding of the swirling flow characteristics. Specifically, the impacts of the level of confinement with a rectangular cross-section and different Reynolds number are examined. Increasing the Reynolds number increases the strength of swirling jets and reverse flow region. More significant changes occurred on the mean flowfield due to the confinement effect such as increasing the width of the reverse flow region and increasing/decreasing the size of the recirculation zones which in turn effects the inlet jet penetration. The inlet jet spreads at a larger angle as the size of the outer recirculation zone (ORZ) increases with the confinement ratio. The shape of the inner recirculation zone (IRZ) vortex structure on the unconfined flow is characterized to be a thin and short vortex and located on top of the nozzle exit, and it becomes thicker and longer vortex located further downstream from the nozzle exit upon confinement. The increased size of the IRZ vortex structure in confined cases is an indication of the increased thickness of the inner shear layer (ISL) that increases linearly as the confinement ratio increases. LES results reveled there is a connection channel between the reverse flow region and the ORZ of the swirling flow emanating from the multiple-jet LDI nozzle. Higher level of turbulence is associated with the location of the IRZ vortex structure. Proper orthogonal decomposition (POD) analysis is preformed to extract coherent fluctuating flow features. The swirling flow of the LDI nozzle exhibits the single-helical and double-helical precessing vortex core (PVC) modes, with the first one being the most energetic mode. The general flow structure of the coherent single-helix PVC mode on the unconfined flow consists of four vortices: two corner vortices rotating in opposite of each other, and a tiny vortex on top of the nozzle exit followed by a huge central vortex rotating in a different direction. Upon confinement the outer vortices attached to the wall of the combustor and the central vortex becomes about twice bigger. The preexistence of the outer vortices on the unconfined flow suggests that the formation of the ORZ is not caused by the confinement, but rather it is a part of the natural behavior of a highly turbulent swirling flow which magnified in the case of confined environment. The single-helix PVC mode gains higher energy value and becomes less-sensitive to the increase of the Reynolds number as the confinement ratio decreases. This is linked to the asymmetry mode shapes, and energy content linearity between the axial and radial components associated with the single-helix PVC mode.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Ashvinkumar, Vikrant, et al.
(författare)
-
Local Routing in Sparse and Lightweight Geometric Graphs
- 2019
-
Ingår i: LIPICS. - : Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik. ; 149, s. 1-30
-
Konferensbidrag (refereegranskat)abstract
- Online routing in a planar embedded graph is central to a number of fields and has been studied extensively in the literature. For most planar graphs no O(1)-competitive online routing algorithm exists. A notable exception is the Delaunay triangulation for which Bose and Morin showed that there exists an online routing algorithm that is O(1)-competitive. However, a Delaunay triangulation can have Omega(n) vertex degree and a total weight that is a linear factor greater than the weight of a minimum spanning tree. We show a simple construction, given a set V of n points in the Euclidean plane, of a planar geometric graph on V that has small weight (within a constant factor of the weight of a minimum spanning tree on V), constant degree, and that admits a local routing strategy that is O(1)-competitive. Moreover, the technique used to bound the weight works generally for any planar geometric graph whilst preserving the admission of an O(1)-competitive routing strategy.
|
|
| 10. |
- Ashvinkumar, Vikrant, et al.
(författare)
-
Local Routing in Sparse and Lightweight Geometric Graphs
- 2022
-
Ingår i: Algorithmica. - : Springer. - 0178-4617 .- 1432-0541. ; 84, s. 1316-1340
-
Tidskriftsartikel (refereegranskat)abstract
- Online routing in a planar embedded graph is central to a number of fields and has been studied extensively in the literature. For most planar graphs no O (1)-competitive online routing algorithm exists. A notable exception is the Delaunay triangulation for which Bose and Morin (SIAM J Comput 33(4):937-951, 2004) showed that there exists an online routing algorithm that is O(1)-competitive. However, a Delaunay triangulation can have Omega (n) vertex degree and a total weight that is a linear factor greater than the weight of a minimum spanning tree. We show a simple construction, given a set V of n points in the Euclidean plane, of a planar geometric graph on V that has small weight (within a constant factor of the weight of a minimum spanning tree on V), constant degree, and that admits a local routing strategy that is O (1)-competitive. Moreover, the technique used to bound the weight works generally for any planar geometric graph whilst preserving the admission of an O (1)-competitive routing strategy.
|
|
