Periodica Polytechnica (Budapest University of Technology and Economics)
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Numerical Investigation of Wave Induced Scour Depth Around Slender and Grouped Monopile
Get PDFWave-induced scour around monopile foundations poses a critical challenge for offshore wind turbine design, affecting stability, serviceability, and maintenance costs. Despite extensive experimental studies, high-fidelity numerical tools are still needed to capture complex interactions between wave kinematics, sediment transport, and pile geometry. This study presents a numerical investigation of scour depth around slender monopiles under regular wave conditions. A validated three-dimensional CFD model (FLOW-3D) employing the Volume of Fluid method and RNG k–ε turbulence closure was used to simulate wave–structure–seabed interaction. Sediment transport was modeled using the Meyer–Peter and Müller bedload formulation and an advection–diffusion equation for suspended load. The influence of the Keulegan–Carpenter (KC) number was examined for KC = 8.8–24, covering inertia- and drag-dominated regimes. Results showed that higher KC values intensified vortex-induced sediment transport and scour, while lower KC values led to gradual development. A marked increase occurred beyond KC ≈ 14, indicating a regime shift in flow–sediment interaction. Grouped-cylinder cases at G/D = 1 and 2 showed that narrow spacing produced mutual sheltering and reduced scour, whereas wider spacing caused deeper localized erosion. Single monopile predictions matched experimental data and empirical formulas, demonstrating the model's predictive capability. These findings emphasize the strong KC dependence of scour and suggest that spacing ratios above G/D = 1.5 may help mitigate adverse group effects in array layouts under oscillatory wave forcing
Determinate Chloride Diffusion Coefficient and Corrosion Initiation on Self-consolidating Concrete: Experimental and Numerical Approaches
Get PDFThe use of supplementary cementitious materials (SCMs) such as silica fume (SF), metakaolin (MK), fly ash (FA), and slag (SL) can significantly extend concrete life, especially for those exposed to coastal environments. An essential part of estimating the service life of the reinforced concrete (RC) structures is estimating the time when the corrosion begins. The diffusion coefficient that leads to the concentration of chloride ions in concrete is one of the most important parameters for evaluating the corrosion initiation time. This study determined the chloride diffusion coefficient by preparing samples containing different admixtures based on the Nord-test accelerated migration test. The samples are placed in two environmental conditions, submerged and dry and wet cycles for 180 days. The Charged System Search (CSS) meta-exploration algorithm based on the Hesofer-Lind-Rakowitz-Fissler (HL-RF) method evaluated corrosion and chloride diffusion coefficient initiation time. Test results and numerical models showed that in a sample with admixture, its corrosion resistance was almost two times that of the ordinary concrete and the initial corrosion time. If several types of admixture are used, the corrosion time becomes twice as long as when only one admixture is utilized. The best performance for the durability of concrete belonged to the samples with three admixtures. Using additives, MK, SF, and SL, with concrete results in the probability of corrosion to decrease by about 40% after 25 years, and at 50 years, this value becomes about 50%
Critical Buckling Investigation of Composite Beams Under Poisson's Effect Using Nonlocal and Higher-order Shear Deformation Theories
Get PDFThis investigation addresses the study of the buckling of composite material beams with different stacking sequences using nonlocal theory. A rotational field was introduced along the width of the beam, considering Poisson's effect and higher-order transverse shear deformation theories with a new warping shape function. The equilibrium equations are derived analytically using the energy principle, and the numerical solution of these equations is based on energy minimization using the Ritz method. A comparative study with different higher-order deformation theories was conducted to calculate the dimensionless critical buckling of a symmetrically and asymmetrically cross-ply laminated composite beam for two types of materials. To examine the influence of the nonlocal effect on critical buckling, another study was carried out on an isotropic material beam using nonlocal theory for different slenderness ratios. The dimensionless critical buckling results show perfect agreement with and without nonlocal theory compared to previously available works in the literature. A detailed investigation of Poisson’s effect on critical buckling demonstrated its significant influence in the case of short beams made of unidirectional composites and laminated composites with different fiber orientations
A tanulási élmény tervezésének módszertani lehetőségei
No full textThe rapidly evolving technological environment is a challenge for members of society. In the work environment and in everyday life, new tools are emerging that need to be learned and new skills developed to meet the demands of the labour market. In Hungary, the Eger library training institution has been using the makerspace for several years and nowadays they have a well-developed methodology. The 3D printer, the laser cutter and the smart home solutions are among the most popular services and can be effectively integrated into the methodological solutions for the design of the learning experience.Az erősödő technológiai környezetben átalakulnak az emberi képességek, ezért az alfa generáció a hagyományostól eltérő oktatási módszereket igényel. Új és ígéretes irányként megjelennek a tanulási élmény tervezésére fókuszáló megoldások, amelyek célja, hogy biztosítsák a tanuló számára a célorientált, ugyanakkor emberközpontú tanulást. A módszer jól alkalmazható a könyvtárakban megindult digitális módszertani képzések továbbfejlesztéseként. A tanulmányunkban azokat a tanulási élmény tervezését támogató módszertani megoldásokat ismertetjük, amelyek az Eszterházy Károly Katolikus Egyetem hallgatóinak, valamint a Bródy Sándor Könyvtár látogatóinak tartott képzéseken már gyakorlatban is alkalmazásra kerültek
Stability Analysis of Slopes under Surcharge Loading Using FE Stress Deviator Increasing Method-proposal of Stability Charts
Get PDFGiven the well-known shortcomings of the traditional limit equilibrium methods (LEMs) in addressing slope stability issues, there has been a growing interest towards employing finite element analysis as a viable alternative in recent years. However, due to the inherent limitations in the conventional finite element analysis, the application of finite element method (FEM) as a strength reduction method (SRM) or as finite element limit analysis (FELA) does not consistently yield successful results. To improve the efficiency of finite element analysis for addressing slope stability problems, a new methodology called 'Stress Deviator Increasing Method' (SDIM) has been recently proposed. It involves gradual expansion of the mobilized stress Mohr's circles until the soil failure takes place according to a predefined non-convergence criterion. In this paper an attempt is made to analyze the effects of surcharge loading on both factor of safety (FOS) value and location of the slip line using the finite element by SDIM by carrying out a restricted parametric study. Specifically, the effects of surcharge loading magnitude, the proximity of the surcharge with respect to the slope edge and the load distribution span were thoroughly analyzed and documented in the light of FOS values and plastic strain regions. The paper ends by proposing design stability charts in which, for a given surcharge magnitude and a geometric configuration, the user is able to determine the FOS for a combination of soil strength parameters
Optimal Power Flow Solution of Hybrid AC–DC Network Using Particle Swarm Method
Get PDFIn this article, we have tackled the multi-objective optimization problem of hybrid AC-DC networks using a metaheuristic method called particle swarm optimization (PSO). The approach of our work answers the following questions: how to model and integrate a direct current (DC) system, including VSC lines and converter stations, into the power optimization computation (OPF) process. To do this, the entire DC system (lines and VSC stations) is converted into a notional AC equivalent system using appropriate modeling, enabling the application of traditional AC OPF methods. Within the framework of multi-objective optimization, the Pareto technique is used to select the optimal solution from among those satisfying the defined objectives. The algorithm developed was implemented in the Matlab environment and tested on a modified IEEE-30 bus test network. The results obtained were compared with those of similar work published previously. The contribution of our research in the field of AC-DC hybrid power system optimization lies in the modeling of VSC stations integrated in an AC network, aiming to perform multi-objective optimization using tools developed for AC networks
Mechanical Behavior of Layered Composite Structures of Aluminum Foam Partially Filled with Polyamide
Get PDFIn this study, the mechanical properties of layered composite structures were investigated. We achieved the layered structure by hot-pressing 1 mm, 3 mm, or 5 mm thick polyamide 6 (PA) sheets into the pores on the top and bottom sides of an open-cell metal foam at 240 °C and 15 MPa (150 bar). The PA-infiltrated depths varied with the thickness of the hot-pressed PA sheets. According to the bending and post-impact bending tests, flexural strengths improved as the infiltration depth of PA increased. Compared to the metal foam, a maximum of 15% increase in flexural strength and a 400% increase in residual flexural strength were measured. However, using a 1 mm thick PA sheet lowered the flexural strength of the open-cell metal foam. We found that the 1 mm thick PA sheet failed to fully infiltrate the foam pores, resulting in residual voids at the metal-PA interface, which caused premature fracture during bending
Effect of Temperature on the Compressibility Behavior of Glass Fiber-bentonite Mixture
Get PDFIn line with the global need for energy, various renewable and clean energy sources have become increasingly popular. Heat piles, buried high-voltage cables, and high-level nuclear waste (HLW) storage areas are examples of energy structures. Since these energy structures emit high temperatures and increase the temperature of the surrounding soil, investigating and improving the thermo-hydro-mechanical behavior of soils under high temperatures has become essential. Bentonite is a clay with high montmorillonite content, which is preferred as a buffer material due to its high swelling capacity, low hydraulic conductivity and chemical resistance.In the present study, a series of laboratory experiments were conducted to investigate the volumetric deformation behavior of bentonite at 80 °C. Tests were performed on the samples kept at 80 °C to observe the effect of high temperature on the volumetric deformation of bentonite in short and long (6 months and 1 year) terms. Glass fiber (GF) was added to bentonite due to its favorable engineering properties at high temperatures. The results have shown that high temperature increased the compressibility of bentonite mixtures while decreasing swelling deformation. The compressibility of the mixtures after curing decreased. Compared to room temperature (RT), the compression strain increased by 22.8% at 80 °C. With 6-months curing at 80 °C, it further increased by up to 33.2%. However, after 1-year curing, a slight decrease of 4.9% was observed. GF significantly increased the swelling behavior of bentonite at RT. However, this effect decreased at high temperature
RETRACTED: Enhancing Decision-making in Uncertain Domains through Optimized Fuzzy Logic Systems
No full textThis article has been retracted at the request of the Editor since Authors submitted this paper twice to the journal