1. A nonlinear probabilistic pitting corrosion model of Ni–Ti alloy immersed in shallow seawaterŠpiro Ivošević, Gyöngyi Vastag, Nataša Kovač, Peter Majerič, Rebeka Rudolf, 2022, izvirni znanstveni članek Opis: The degradation of metal materials in a marine environment represents the consequence
of the electrochemical corrosion of metals under the influence of the environment. The application
of new materials in the maritime industry requires experimental, real-world research on the form
of corrosive damage and the intensity of the corrosion. This paper analyses the pitting corrosion of
a rod-shaped nickel–titanium (Ni–Ti) alloy that was produced by means of the continuous casting
method. In total, three samples were posted in a real seawater environment and analysed after 6,
12, and 18 months. Pits were detected on the Ni–Ti alloy after 18 months of exposure to the marine
environment. The database on pitting corrosion was created by measuring depth in mm, which was
performed by means of a nonlinear method, and by the generation of an artificial database of a total
of 120, gauged in critical pit areas. The data were obtained by the application of a nonlinear model,
and under the assumption that corrosion starts after 12 months of exposure in the corrosive marine
environment. The EDX analysis of the Ni–Ti alloy composition inside the pits and on the edges of the
pits indicated that the corrosion process in the hole of the pit occurs due to the degradation of the Ni.
Ključne besede: Ni–Ti alloy, pitting corrosion, seawater, EDX analysis, nonlinear, probabilistic
Objavljeno v DKUM: 24.03.2025; Ogledov: 0; Prenosov: 5
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2. Nonlinear semi-numeric and finite element analysis of three-point bending tests of notched polymer fiber-reinforced concrete prismsŽiga Unuk, Milan Kuhta, 2024, izvirni znanstveni članek Opis: 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.
Ključne besede: 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
Objavljeno v DKUM: 19.02.2024; Ogledov: 350; Prenosov: 29
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3. The dynamics of a duopoly Stackelberg game with marginal costs among heterogeneous playersAtefeh Ahmadi, Sourav Roy, Mahtab Mehrabbeik, Dibakar Ghosh, Sajad Jafari, Matjaž Perc, 2023, izvirni znanstveni članek Opis: One of the famous economic models in game theory is the duopoly Stackelberg model, in which a leader and a follower firm manufacture a single product in the market. Their goal is to obtain the maximum profit while competing with each other. The desired dynamics for a firm in a market is the convergence to its Nash equilibrium, but the dynamics of real-world markets are not always steady and can result in unpredictable market changes that exhibit chaotic behaviors. On the other hand, to approach reality more, the two firms in the market can be considered heterogeneous. The leader firm is bounded rationale, and the follower firm is adaptable. Modifying the cost function that affects the firms' profit by adding the marginal cost term is another step toward reality. We propose a Stackelberg model with heterogeneous players and marginal costs, which exhibits chaotic behavior. This model's equilibrium points, including the Nash equilibrium, are calculated by the backward induction method, and their stability analyses are obtained. The influence of changing each model parameter on the consequent dynamics is investigated through one-dimensional and two-dimensional bifurcation diagrams, Lyapunov exponents spectra, and Kaplan-Yorke dimension. Eventually, using a combination of state feedback and parameter adjustment methods, the chaotic solutions of the model are successfully tamed, and the model converges to its Nash equilibrium.
Ključne besede: nonlinear dynamics, game theory, stability analysis, public goods
Objavljeno v DKUM: 02.08.2023; Ogledov: 459; Prenosov: 49
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4. A comparison of linear and nonlinear seismic tunnel-ground interaction analysesElefterija Zlatanović, Marina Trajković-Milenković, Dragan Lukić, Stanko Brčić, Vlatko Šešov, 2016, izvirni znanstveni članek Opis: In order to study the effects of a seismically induced tunnel–ground interaction, two-dimensional numerical analyses are performed using the sofware ANSYS. The study employs a coupled beam–spring model subjected to earthquake loading that is simulated under pure shear conditions and determined by a free-field ground-response analysis using the code EERA. The properties of the soil material are considered as both linear and nonlinear. The results obtained by linear dynamic analyses are compared with state-of-practice analytical elastic solutions. A comparison of the results of both linear and nonlinear analyses is also performed, and significant differences, as well as important factors influencing the tunnel–ground interaction for both cases, are evaluated.
Ključne besede: circular tunnel, linear/nonlinear soil behaviour, beam–spring model, plane-strain conditions, simplified dynamic FE analysis, soil–structure interaction
Objavljeno v DKUM: 18.06.2018; Ogledov: 1339; Prenosov: 82
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5. A 3D nonlinear dynamic analysis of a rock-fill dam based on IZIIS softwareVioleta Mircevska, Vladimir Bickovski, Mihail Garevski, 2007, izvirni znanstveni članek Opis: This paper treats the 3D nonlinear dynamic behavior of a rock-fill dam based on the Mohr-Coulomb failure criterion. The dam is situated in a steep, narrow, “V-shaped” rigid canyon. The concept of a massless rock foundation is treated, for which a certain part of the rock is included in the model. The dam-rock interface was modeled by contact elements, which allowed certain relative displacements between the two media of different stiffnesses. The generation of the 3D mathematical model was related to the topology of the terrain, and the nonlinear dynamic response was based on the "step-by-step" linear-acceleration direct-integration method, making use of the Wilson-θ method. The convergence process was in accordance with the Newton-Raphson method. First, the initial static effective stresses existing in the conditions of the established stationary filtration through the clayey core were defined. The analysis was based on an original FE program for the static and dynamic analyses of rock-fill dams, as well as a FE program for the solution of the stationary filtration process through the clayey core. The dynamic response of the 3D model of the dam was defined for the effect of harmonic excitations. Dynamic analyses in the linear and nonlinear domains were performed for the purpose of comparing the results. The time histories of the linear and nonlinear responses were defined for selected sections and nodes of the model, the tension cut-off zones, the plastic deformations, and the stress-shear strain relationships. The coefficient against the sliding of the potential sliding surfaces was also defined. It can be concluded that 3D analyses as well as a nonlinear material treatment of the soils built in the dam are imperative for a proper assessment of the stability of rock-fill dams situated in narrow canyons.
Ključne besede: automatic generation of 3D model, rock-fill dam, nonlinear dynamic analysis, elastic perfectly plastic criterion, tension cutoff, cracking zones, plastic deformations, stability
Objavljeno v DKUM: 18.05.2018; Ogledov: 1591; Prenosov: 183
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