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Abstract: This study presents the influence of the type of weave and relative fabric density on surface roughness and the coefficient of friction in raw cotton woven fabrics. Relative fabric density, which represents how full a fabric is compared to the maximum packing density allowed by its weave, provides a more accurate basis for comparison than absolute fabric density. Analysis revealed that both the type of weave and relative fabric density have a statistically significant effect on surface roughness, while neither factor significantly impacts the coefficient of friction. Notably, increasing relative fabric density consistently reduces surface roughness in plain, 2/2 twill, and, to some extent, 5-end satin fabrics, with plain fabrics showing the highest roughness overall. At high densities, 2/2 twill fabrics exhibit greater structural stability, yielding smoother surfaces than 5-end satin fabrics, reversing trends detected at lower densities. Furthermore, the relationship between surface roughness and friction was decoupled in plain and 2/2 twill fabrics—specifically, increased density leads to smoother surfaces and higher friction. 5-end satin fabrics were unique in showing a simultaneous reduction in both surface-mechanical properties as fabric density increased. These findings highlight that relative fabric density is a critical parameter for engineering fabrics with tailored performance properties.
Keywords: fabric engineering, woven fabric geometry, type of weave, relative fabric density, surface roughness, coefficient of friction, cotton woven fabrics
Published in DKUM: 04.12.2025; Views: 0; Downloads: 2
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Abstract: Introduction. The integration of Renewable Energy Sources (RESs), particularly Wind Energy Conversion Systems (WECS), is vital for reducing reliance on fossil fuels and addressing climate change. However, this transition poses challenges, including ensuring grid stability in the face of intermittent RESs. Compliance with grid codes is crucial, with a focus on Low Voltage Ride Through (LVRT) capability. Problem. The intermittent nature of RESs, specifically in Permanent Magnet Synchronous Generator (PMSG) based WECS, presents challenges to grid stability during voltage dips. Goal. To enhance voltage stability and LVRT capability in PMSG-based WECS by integrating a Dynamic Voltage Restorer (DVR) with an energy storage device. This involves regulating the input DC voltage to the DVR using a type 2 fuzzy controller, adapting intelligently to changing conditions. Methodology. DVR, powered by an energy storage device, is strategically integrated with WECS. A type 2 fuzzy controller regulates the DC voltage to DVR. The rectified WECS output undergoes processing through an isolated flyback converter. A 31-level Cascaded H-Bridge Multilevel Inverter (CHBMLI) with PI control ensures high-quality AC output. Results. The validation of developed system is executed using MATLAB/Simulink revealing a reduced Total Harmonic Distortion (THD) value of 1.8 %, ensuring significance in LVRT capability. Originality. The strategic integration of DVR with PMSG-based WECS, addresses the LVRT challenges. The use of type 2 fuzzy controller for intelligent voltage regulation and a sophisticated multilevel inverter contributes to the uniqueness of proposed solution. Practical value. The developed system provides benefits by ensuring reliable LVRT capability in PMSG-based WECS with reduced THD of 1.8 % indicating improved grid compatibility. References 26, tables 5, figures 20.
Keywords: permanent magnet synchronous generator, wind energy conversion systems, low voltage ride through, type 2 fuzzy controller, isolated flyback converter, 31-level cascaded H-bridge multilevel inverter, PI controller
Published in DKUM: 06.11.2025; Views: 0; Downloads: 2
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Abstract: The distribution of the consecutive level-spacing ratio is now widely used as a tool to distinguish integrable from chaotic quantum spectra, mostly due to its avoidance of the numerical spectral unfolding. Like the use of the Rosenzweig-Porter approach to obtain the Berry-Robnik distribution of level spacings in mixed-type systems, in this paper, we extend this approach to analytically derive the distribution of spacing ratios for random matrices comprised of independent integrable blocks and chaotic blocks. We have numerically confirmed this analytical result using random matrix theory in paradigmatic models such as the quantum kicked rotor and the Hénon-Heiles system.
Keywords: level-spacing ratios, mixed-type systems, distribution of spacing ratios, paradigmatic models
Published in DKUM: 03.11.2025; Views: 0; Downloads: 1
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Abstract: This paper presents an experimental and numerical analysis of the mechanical behaviour of orthopaedic implants with crack-type defects, considering the principles and advantages of the modern X-FEM method, which was used due to limitations of traditional FEM in terms of crack growth simulation, especially for complex geometries. In X-FEM, the finite element space is enriched with discontinuity functions and asymptotic functions at the crack tip, which are integrated into the standard finite element approximation using the unity division property. Though rare, femoral component failures are well-documented complications that can occur after hip prosthetic implantation. Most stem fractures happen in the first third of the implant due to the loosening of the proximal stem and fixation of the distal stem, leading to bending and eventual fatigue failure. The main goal of this paper was to obtain accurate and representative models of such failures. Experimental analyses of the mechanical behaviour of implants subjected to physiological loads, according to relevant standards, using a new combined approach, including both experiments and numerical simulations was presented. The goal was to verify the numerical results and obtain a novel, effective methodology for assessing the remaining fatigue life of hip implants. For this purpose, the analysis of the influence of Paris coefficients on the total number of cycles was also considered. Hence, this simulation involved defining loads to closely mimic real-life scenarios, including a combination of activities such as ascending stairs, stumbling, and descending stairs. The tensile properties of the titanium alloy were experimentally determined, along with the Paris law coefficients C and m. The finite element software ANSYS 2022R2 version was used to develop and calculate the three-dimensional model with a crack, and the resulting stresses, stress intensity factors, and the number of cycles presented in the figures, tables, and diagrams. The results for the fatigue life of a partial hip implant subjected to various load cases indicated significant differences in behaviour, and this underscores the importance of analysing each case individually, as these loads are heavily influenced by each patient’s specific activities. It was concluded that the use of numerical methods enabled the preliminary analyses of the mechanical behaviour of implants under fatigue loading for several different load cases, and these findings can be effectively used to predict the possibility of Ti-6Al-4V implant failure under variable cyclic loads.
Keywords: structural integrity, fatigue fracture, extended finite element method (XFEM), experimental testing, DIC, numerical simulations, stress intensity factor, orthopaedic implants, crack-type defect
Published in DKUM: 21.03.2025; Views: 0; Downloads: 8
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Abstract: Purpose: Regular exercise reduces obesity and the risk of cardiovascular disease. However, health-promoting benefits of physical activity are commonly associated with increased inflammation and oxidative stress. Here, we tested whether constant moderate exercise is able to prevent or attenuate the oxidative/nitrosative stress, inflammation, and serum lipids in lean and obese rats. Methods: Four-month-old female Sprague Dawley rats received standard or a high-fat diet. Animals were subjected to a physical activity protocol, consisting of 30 min forced treadmill exercise for 5 consecutive days per week during 10 months. Baseline and sedentary (non-exercised) rats were used as controls. Lipids, oxidized low-density lipoprotein cholesterol, nitric oxide metabolites, and pro- and anti-inflammatory markers were measured in blood collected upon euthanasia. Results: At variance to young baseline control rats, 14-month-old animals fed normal diet had increased plasma lipid levels, including total cholesterol and triglycerides, which were further elevated in rats that consumed a high-fat diet. While treadmill exercise did not lower the amount of serum lipids in standard diet group, forced physical activity reduced non-high-density lipoprotein cholesterol in response to high-fat diet feeding. Exercised rats fed standard diet or high-fat diet had lower abundancy of nitric oxide metabolites, which coincided with increased levels of oxidized low-density lipoprotein cholesterol. Accordingly, the amount of nitric oxide metabolites correlated inversely with oxidized low-density lipoprotein cholesterol and homo-arginine. Exercise significantly reduced inflammatory cytokines in high-fat diet fed rats only. Conclusion: Our study suggests that regular exercise alters the equilibrium between oxidative and anti-oxidative compounds and reduces pro-inflammatory cytokines.
Keywords: long-term moderate exercise, nitric oxide, nitric oxide synthase, oxidized LDL, Sprague Dawley rats, western-type diet
Published in DKUM: 10.12.2024; Views: 0; Downloads: 55
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