https://scidar.kg.ac.rs/handle/123456789/1 University of Kragujevac. Serbia Wed, 06 May 2026 03:52:07 GMT 2026-05-06T03:52:07Z https://scidar.kg.ac.rs/handle/123456789/23128 Title: Analytical Methodology for Gear Tooth Number Synthesis in a Ravigneaux Planetary Gear with Seven Kinematic Links and Two Degrees of Freedom Authors: Čukić, Stefan; Miladinovic, Slavica; Gajević, Sandra; Milovanović, Filip; Ivanović, Lozica; Stojanovic, Blaza Abstract: Existing methods for selecting the number of teeth in complex planetary gear systems are often methodologically demanding. They do not always ensure all conditions required for proper operation and assembly. This paper presents an analytical methodology for determining gear tooth numbers. The method is demonstrated on a Ravigneaux planetary gear set with seven kinematic links and two degrees of freedom. It ensures the simultaneous satisfaction of all meshing and assembly conditions. Starting from the known transmission ratios, the number of teeth of one central gear, and the selected angular displacement of the outer planet gear, analytical relationships are derived. These allow the determination of the tooth numbers of all remaining gear elements. The procedure is implemented in Python 3.13. This enables a systematic evaluation of predefined input ranges and an automatic verification of geometric constraints, including interference and undercutting conditions. The proposed method yields six feasible configurations. Compared with the Borg-Warner M85 automatic transmission, deviations in individual gear ratios reach up to 10%. Significantly lower tooth numbers are achieved for several gears. These results suggest that the proposed methodology can achieve comparable kinematic performance while offering more compact gear designs and a potential weight reduction. The developed model also provides a basis for extension to more complex configurations and integration with optimisation and dynamic criteria in planetary gear synthesis. Thu, 01 Jan 2026 00:00:00 GMT https://scidar.kg.ac.rs/handle/123456789/23128 2026-01-01T00:00:00Z https://scidar.kg.ac.rs/handle/123456789/23127 Title: Environmental Assessment of Cruise Ships and Superyachts with Multi-Criteria Evaluation of Marine Fuels Authors: Marković, Saša; Petrović, Nikola; Marinković, Dragan; Nikolic, Boban; Komatina, Nikola Abstract: Cruise ships and superyachts have experienced significant global expansion throughout the 21st century. Although the growth in cruise passenger numbers was temporarily disrupted by the COVID-19 pandemic, occupancy rates have since rebounded and even exceeded pre-pandemic levels. This study highlights the significant environmental impact of cruise ships and luxury yachts, particularly in terms of air emissions and marine pollution. Emission levels associated with different fuel types and marine engines are analysed, including the average emissions generated by the Norwegian Cruise Line fleet while docked in ports, as well as the estimated emission reductions achievable through the implementation of onshore power supply systems. To identify environmentally preferable fuel options, a hybrid ANN/MCDM framework is applied. The weighting coefficients of eight evaluation criteria are determined using the Artificial Neural Network/Extreme Learning Machine (ANN/ELM) model, ensuring an objective and data-driven assessment of their relative importance. The ANN/ELM model was trained using emission and fuel-related data collected from the literature and industry reports, and its performance was validated using standard validation procedures, achieving satisfactory predictive accuracy for determining the weighting coefficients. The final ranking of eight fuel alternatives is subsequently performed using the Ranking Alternatives by Weighting of Evaluated Criteria (RAWEC) method. The considered alternatives include conventional and emerging marine fuels currently used in practice or under technological development (A1–A8), while the optimization criteria (C1–C8) encompass major air pollutants (CO2, NOx, SOx, CO, PM, CH4), the fuel cost-to-consumption ratio, and the potential impact on water pollution. The water pollution criterion is assessed qualitatively using the Saaty scale. The integrated ANN/ELM–RAWEC approach enables a systematic comparison of marine fuels and supports the identification of options with the lowest overall environmental impact. Thu, 01 Jan 2026 00:00:00 GMT https://scidar.kg.ac.rs/handle/123456789/23127 2026-01-01T00:00:00Z https://scidar.kg.ac.rs/handle/123456789/23126 Title: Development of a systematic instrumentation methodology for continuous torque measurement in high-capacity shafts Authors: Bižić, Milan; Petrović, Dragan Abstract: This paper presents the development of a systematic instrumentation methodology for continuous torque measurement in high-capacity shafts, based on the application of strain gauges. Within the proposed methodology, systematically derived solutions to the most important challenges in the development of instrumented shafts for torque measurement are presented, including the determination of optimal strain gauge locations, their arrangement and number, as well as the configuration of their connection into Wheatstone bridges. The main objective of the proposed methodology is to achieve high sensitivity and accuracy of torque measurement while simultaneously neutralizing parasitic effects in the output signal of the Wheatstone bridge. In addition, the model-based calibration procedure of the measurement system and an inverse torque determination algorithm based on the output signal of the Wheatstone bridge are presented. The developed methodology was tested on a finite element method (FEM) model of a high-capacity wind turbine shaft under various loading conditions, considering the combined effects of torque (to be measured), bending moments, as well as axial and transverse forces. The obtained results demonstrate that the developed methodology enables high numerical consistency in torque determination, with deviations between the prescribed torque in the FEM model and the torque obtained by inverse determination being less than 0.04%. Thus, it is confirmed that the proposed methodology can be successfully applied in the development of high-capacity instrumented shafts intended for continuous torque measurement. Thu, 01 Jan 2026 00:00:00 GMT https://scidar.kg.ac.rs/handle/123456789/23126 2026-01-01T00:00:00Z https://scidar.kg.ac.rs/handle/123456789/23125 Title: Experimental Determination of Combustion Process Parameters of Biodiesel Fuel Made from Waste Grape Seeds Authors: Djuric, Zeljko; Grujic, Ivan; Glišović, Jasna; Gordić, Dušan; Milasinovic, Aleksandar; Stojanovic, Nadica Abstract: Biodiesel fuel produced through transesterification is mainly used in blends with conven-tional diesel fuel (D100). The analysis of the combustion process parameters for each spe-cific biodiesel fuel represents the basis for a rational approach to the utilization of availa-ble motor fuel quantities. In this study, the differential and cumulative heat release laws during the combustion of D100 and blends of biodiesel fuel made from waste grape seed oil and D100 were analyzed. In addition, the engine efficiency and economy for the cases of using the aforementioned fuels were analyzed. The tests were conducted on a single-cylinder, air-cooled diesel engine with direct fuel injection. The engine testing was con-ducted for two engine loads; that for which the brake was a mean effective pressure of 4.2 bar, and for the full load, that for the brake was a mean effective pressure of 5.6 bar at engine speeds of 1635 rpm, 1937 rpm, and 2239 rpm. All experimental work was con-ducted for conventional diesel fuel D100 and for biodiesel diesel blends B7 and B14. The combustion rates of D100, a blend containing 7% of biodiesel by volume (B7), and a blend containing 14% of biodiesel by volume (B14) were examined. However, the higher com-bustion rate of the B14 blend, particularly during the combustion of the first 50% of the fuel mass per cycle, could have a positive impact on the fuel economy of the working cycle and the brake thermal efficiency (BTE). The maximum heat release rates for D100, B7, and B14 at full load and an engine speed of 2239 rpm are 115.65 J/deg, 148.01 J/deg, and 152.99 J/deg, respectively. At full load and engine speeds of 1635 rpm and 2239 rpm, the brake thermal efficiencies (BTEs) for D100, B7, and B14 were 0.301, 0.285, and 0.296 and 0.281, 0.273, and 0.277, respectively. Under other tests, the highest BTE was observed for the B14 blend. Therefore, from the perspective of brake thermal efficiency (BTE), the most favora-ble blend for application is B14. Thu, 01 Jan 2026 00:00:00 GMT https://scidar.kg.ac.rs/handle/123456789/23125 2026-01-01T00:00:00Z