1. A computational study of artery curvature and endograft oversize influence on seal zone behavior in endovascular aortic repairŽiga Donik, Willa Li, Blessing Nnate, Joseph A. Pugar, Nhung Nguyen, Ross Milner, Enrique Cerda, Luka Pocivavsek, Janez Kramberger, 2024, original scientific article Abstract: Thoracic endovascular aortic repair (TEVAR) is a minimally invasive procedure involving the placement of
an endograft inside the dissection or an aneurysm to direct blood flow and prevent rupture. A significant
challenge in endovascular surgery is the geometrical mismatch between the endograft and the artery, which
can lead to endoleak formation, a condition where blood leaks between the endograft and the vessel wall. This
study uses computational modeling to investigate the effects of artery curvature and endograft oversizing,
the selection of an endograft with a larger diameter than the artery, on endoleak creation. Finite element
analysis is employed to simulate the deployment of endografts in arteries with varying curvature and diameter.
Numerical simulations are conducted to assess the seal zone and to quantify the potential endoleak volume
as a function of curvature and oversizing. A theoretical framework is developed to explain the mechanisms of
endoleak formation along with proof-of-concept experiments. Two main mechanisms of endoleak creation are
identified: local buckling due to diameter mismatch and global buckling due to centerline curvature mismatch.
Local buckling, characterized by excess graft material buckling and wrinkle formation, increases with higher
levels of oversizing, leading to a larger potential endoleak volume. Global buckling, where the endograft
bends or deforms to conform to the centerline curvature of the artery, is observed to require a certain degree
of oversizing to bridge the curvature mismatch. This study highlights the importance of considering both
curvature and diameter mismatch in the design and clinical use of endografts. Understanding the mechanisms
of endoleak formation can provide valuable insights for optimizing endograft design and surgical planning,
leading to improved clinical outcomes in endovascular aortic procedures.
Keywords: finite element analysis (FEA), endovascular aortic repair, endoleak, stent graft, TEVAR, EVAR
Published in DKUM: 29.07.2024; Views: 83; Downloads: 7
 Full text (2,83 MB)
This document has many files! More... |
2. |
3. Nonlinear semi-numeric and finite element analysis of three-point bending tests of notched polymer fiber-reinforced concrete prismsŽiga Unuk, Milan Kuhta, 2024, original scientific article Abstract: A nonlinear semi-numeric and finite element analysis of three-point bending tests of notched polymer fiber-reinforced concrete prisms was performed. The computational and experimental results were compared in terms of the load-displacement behavior. The vertical midspan displacement and the crack mouth opening displacement results were considered. The nonlinear semi-numeric computational procedure involved the moment-curvature relation, calculated by considering the constitutive material law from the fib Model Code for Concrete Structures 2010, and considered a plastic hinge mechanism to simulate the cracked region behavior. Two sets of tensile mechanical properties were considered for the constitutive material law: back-calculated (by an inverse analysis) tensile strength properties from the experimental results, and tensile strength properties calculated by simplified expressions from the fib Model Code for Concrete Structures 2010. Other mechanical properties were determined by additional compressive tests and standard relations for the dependency of various mechanical properties on the concrete compressive strength. The nonlinear finite element analysis incorporated the Menetrey-Willam material model to simulate the fiber-reinforced concrete behavior. The nonlinear semi-numeric analysis load-displacement results based on the back-calculated tensile strength properties relatively accurately matched with the experimental results, whereas the nonlinear semi-numeric analysis load-displacement results based on tensile strength properties calculated by simplified expressions from the fib Model Code for Concrete Structures 2010 and the nonlinear finite element analysis load-displacement results showed certain shortcomings.
Keywords: polymer fiber-reinforced concrete, moment-curvature relation, nonlinear plastic hinge, load-displacement relation, crack width, nonlinear analysis, finite element analysis, Menetrey-Willam material model, three-point bending test, compressive test
Published in DKUM: 19.02.2024; Views: 330; Downloads: 15
Full text (6,91 MB)
This document has many files! More... |
4. An alternative method of increasing the transmission performance of a conventional 110 kV cable lineDardan Klimenta, Dragan Tasić, Miroljub S. Jevtić, 2019, professional article Abstract: The purpose of this paper is to show that a significant increase in the ampacity of a 110 kV underground cable line is achievable, if a hydronic asphalt pavement system is applied along the entire line, and if the cable trench is completely filled with high thermal conductivity bedding in order to improve the conduction of heat between the line and the surface of the earth. In such a way, it would be possible to simultaneously collect and then store heat from the sun and cable line. The mutual thermal effects between the 110 kV cable line and the hydronic asphalt pavement, in the presence of solar radiation, wind-driven convection and heat emission along the earth surface, are simulated using FEM-based models for the most unfavourable summer conditions and the most common winter conditions. An adequate experimental background is also provided based on the existing measurements relevant to the thermal analysis performed. It was found that, compared to the associated base cases, the cable ampacity can be increased up to 92.3% for the most unfavourable summer conditions, and up to 60.3% for the most common winter conditions.
Keywords: ampacity, finite-element method, hydronic asphalt pavement, power cable, thermal analysis
Published in DKUM: 05.12.2023; Views: 357; Downloads: 5
Full text (921,99 KB)
This document has many files! More... |
5. Development of mathematical models in explicit form for design and analysis of axial flux permanent magnet synchronous machinesFranjo Pranjić, Peter Virtič, 2020, original scientific article Abstract: This article proposes a methodology for the design of double-sided coreless axial flux permanent magnet synchronous machines, which is based on a developed model for calculating the axial component of the magnetic flux density in the middle of the distance between opposite permanent magnets, which also represents the middle of the stator. Values for different geometric parameters represent the input data for the mathematical model in explicit form. The input data are calculated by using a simplified finite element method (FEM), which means that calculations of simplified 3D models are performed. The simplified model consists of two rotor disks with surfacemounted permanent magnets and air between them, instead of stator windings. Such a simplification is possible due to similar values of permeability of the air and copper. For each simplified model of the machine the axial component of the magnetic flux density is analyzed along a line passing through the center of opposite permanent magnets and both rotor disks. Values at the middle of the distance between the opposite permanent magnets are the lowest and are therefore selected for the input data at different stator, rotor disks and permanent magnets (PM) thicknesses. Such input data enable the model to consider the nonlinearity of materials.
Keywords: axial flux, analysis, coreless, development, design, explicit form, finite element method, mathematical models, permanent magnet, synchronous
Published in DKUM: 01.12.2023; Views: 491; Downloads: 15
Full text (2,70 MB)
This document has many files! More... |
6. Experimental and numerical analysis of fracture mechanics behavior of heterogeneous zones in S690QL1 grade high strength steel (HSS) welded jointDamir Tomerlin, Dražan Kozak, Luka Ferlič, Nenad Gubeljak, 2023, original scientific article Abstract: The heterogeneity of welded joints’ microstructure affects their mechanical properties, which can vary significantly in relation to specific weld zones. Given the dimensional limitations of the available test volumes of such material zones, the determination of mechanical properties presents a certain challenge. The paper investigates X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The experimental work is focused on tensile testing to obtain stress-strain properties, as well as fracture mechanics testing. Considering the aforementioned limitations of the material test volume, tensile testing is carried out with mini tensile specimens (MTS), determining stress-strain curves for each characteristic weld zone. Fracture mechanical testing is carried out to determine the fracture toughness using the characteristic parameters. The experimental investigation is carried out using the single edge notch bend (SENB) specimens located in several characteristic welded joint zones: base metal (BM), heat affected zone (HAZ), and weld metal (WM). Fractographic analysis provides deeper insight into crack behavior in relation to specific weld zones. The numerical simulations are carried out in order to describe the fracture behavior of SENB specimens. Damage initiation and evolution is simulated using the ductile damage material behavior. This paper demonstrates the possibility of experimental and numerical determination of fracture mechanics behavior of characteristic heterogeneous welded joint zones and their influence on crack path growth.
Keywords: heterogeneous welded joint, high strength steel, mechanical testing, damage, fracture, mechanical properties, finite element analysis
Published in DKUM: 30.11.2023; Views: 398; Downloads: 20
Full text (11,25 MB)
This document has many files! More... |
7. 3D coupled electromagneticthermal analysis of a hybrid electromagnetic system with magnetic flux modulationIvan Hadzhiev, Iosko Balabozov, Vultchan Gueorgiev, Ivan Yatchev, 2021, original scientific article Abstract: This paper presents a study of the electromagnetic and thermal field of a new construction of a hybrid electromagnetic system with magnetic flux modulation. The numerical studies were realised using the finite element method. The coupled problem electromagnetic field-electric circuit-thermal field was solved. A computer model of the hybrid electromagnetic system was developed for the purpose of the study using the software programme COMSOL. Results for the distribution of the electromagnetic and thermal field in the hybrid electromagnetic system with magnetic modulation were obtained at different supply voltages.
Keywords: Coupled problems, finite element analysis, hybrid electromagnetic system, magnetic flux modulation, permanent magnets
Published in DKUM: 13.11.2023; Views: 251; Downloads: 4
Full text (1,45 MB)
This document has many files! More... |
8. CALIBRATION OF A NEW METHOD FOR CREATING IMPERFECTIONS ON SLENDER STRUCTURES : magistrsko deloSimon Hudales, 2022, master's thesis Abstract: For the design of slender structures consisting of plates and tubes, such as supporting structures at cranes, buckling is beside stress and fatigue often the governing failure criteria. Stability analysis of such structures is usually performed using the GMNIA method according to DIN EN 1993. For this purpose, a suitable geometric equivalent imperfection must be applied to the structure. Buckling inherent shapes are determined for this purpose and scaled according to applicable safety concepts. Including imperfections in stability analysis can generally be relevant for the load-bearing behavior of a structure. Within this master thesis work, the influence of the initial geometric imperfection on stability behaviour is investigated.
This study examines the influence, that imperfections imposed on members subjected to tensile stress have on stability behaviour. Tensile members of structures are identified and initial geometric imperfection is imposed on them in addition to critical members, that are subjected to compression stress. It is shown, that including imperfections on tensile members in stability analysis, has only a minor influence on stability behaviour and stiffness of the structure, both reducing it just slightly.
Further on, investigation on boom model, that is supporting structure of the crawler crane, is made. Boom model consist of main chord members and diagonals connecting them. At the joint connection of boom and two diagonal members, one subjected to tension and one subjected to compression stress, appears area of high shear stresses. Influence of the direction, that imperfection is imposed on the diagonal member, and what is the influence on the stability behaviour and structural strength is presented in this work. Most severe case of the two chosen direction is pointed out and discussed.
Keywords: stability analysis, initial geometric imperfections, thin-walled structures, finite element method
Published in DKUM: 06.07.2022; Views: 574; Downloads: 57
Full text (5,14 MB) |
9. 3D response of an excavation adjacent to buildings supported by inclined strutsZahra Sabzi, Ali Fakher, 2017, original scientific article Abstract: The presented study focuses on field observations and a 3D numerical analysis of open-cut excavations adjacent to a building supported by inclined struts. The performance of the struts in carrying the building loads and decreasing the deflections is investigated. Struts reduce the amount of deformations and also create a corner effect similar to the diaphragm walls corner. The influence of the distance between the struts is studied and the optimum struts interval is proposed. The most effective configuration of struts installation in reducing the deflections and building damage is proposed. A displacement-based design guideline is also presented based on the results of numerical studies.
Keywords: measurement, 3D finite-element analysis, displacement-based design
Published in DKUM: 18.06.2018; Views: 1152; Downloads: 180
Full text (2,85 MB)
This document has many files! More... |
10. Numerical analysis of circular footings on natural clay stabilized with a granular fillMurat Ornek, Mustafa Laman, Ahmet Demir, Abdulazim Yildiz, 2012, original scientific article Abstract: In this study, numerical predictions of the scale effect for circular footings supported by partially replaced, compacted, layers on natural clay deposits are presented. The scale- effect phenomenon was analyzed according to the footing sizes. Numerical analyses were carried out using an axisymmetric, two-dimensional, finite-element program. Before conducting the analysis, the validity of the constitutive model was validated using field tests performed by authors with seven different footing diameters up to 0.90 m and with three different partial replacement thicknesses. It is shown that the behavior of the circular footings on natural clay soil and the partial replacement system can be reasonably well represented by the Mohr Coulomb model. The Mohr-Coulomb model parameters were derived from the results of conventional laboratory and field tests. After achieving a good consistency between the results of the test and the numerical analysis, the numerical analyses were continued by increasing the footing diameter up to 25 m, considering the partial replacement thickness up to two times the footing diameter. The results of this parametric study showed that the stabilization had a considerable effect on the bearing capacity of the circular footings and for a given value of H/D the magnitude of the ultimate bearing capacity increases in a nonlinear manner with the footing diameter. The Bearing Capacity Ratio (BCR) was defined to evaluate the improved performance of the reinforced system. It was found, based on numerical and field-test results that the BCR of the partially replaced, natural clay deposits increased with an increase in the footing diameter and there was no significant scale effect of the circular footing resting on natural clay deposits.
Keywords: scale effect, circular footing, field test, finite-element analysis, natural clay, granular fill
Published in DKUM: 13.06.2018; Views: 1224; Downloads: 154
Full text (554,10 KB)
This document has many files! More... |
