The vibrations of a shaft in rotary mechanical systems supported by angular contact ball bearings are investigated theoretically and experimentally for various preloads in this paper. In the theoretical part of the study, a dynamic bearing model is presented, a rigid shaft supported by EHL angular contact bearing has been modelled as 5 DoF. Non-linear equations of motion are solved numerically by the Runge–Kutta method. In the second part of the study, an experimental setup that enables performing different operating cases has been designed to validate the theoretical results. Theoretical and experimental data are investigated and compared in both time and frequency domains and the results are compared. It is observed from both the theoretical and experimental studies that preload has a significant effect on the vibration behaviour. Results show that the increase in preload reduces the amplitude of the variable compliance frequencies of bearing, the natural frequency of system is shifted to a higher value, and using signal processing with an envelope spectrum gives better results in spectral analysis; small deviations occur between the theoretical and the experimental data due to modulation and noise from machine elements such as gear, motor, misalignment, waviness, etc. Therefore, the presented dynamic bearing model can be used with a reasonable accuracy to examine effect of preload on the vibration of shaft-bearing system.

Predicting oil film thickness at ball–raceway contacts under elastohydrodynamic lubrication (EHL) conditions remains a complex tribological challenge. This complexity arises from dynamic variations in contact load, rotational speed, hydrodynamic effects, and the nonlinear load–deformation characteristics of the contacting surfaces. This study presents a numerical investigation of oil film thickness variations corresponding lubricant properties in rolling bearings using a 5-degree-of-freedom (5-DoF) shaft–bearing model. The model incorporates isothermal EHL and a rigid shaft supported by a pair of angular contact ball bearings. The governing nonlinear equations of motion are solved iteratively via a quasi-static approach, coupling oil film thickness and contact force calculations. Results indicate that oil film thickness increases proportionally with both lubricant viscosity and shaft speed. A twofold increase in shaft speed results in approximately 57% enhancement in film thickness. Similarly, increasing viscosity elevates film thickness proportionally, while the pressure–viscosity coefficient significantly enhances film formation. Notably, the outer raceway exhibits a 13% thicker film than the inner raceway, owing to its higher surface conformity. Furthermore, low-speed operation under heavy loads induces mixed lubrication regimes, compromising film integrity. Results provides insight for lubricant selection and bearing design to mitigate starvation in industrial applications.

Sustainability studies aiming to reduce CO2e emissions is increasing gradually. Generally energy-based approaches is being used in these studies. In this paper, the carbon footprint calculations of energy-consuming systems in the OSTIM Technical University building is examined, focusing on the use of solar energy for emission reduction. An Exergy-based approach, generally ignored in CO2e calculations, is adopted. The carbon emissions calculation is carried out according to the ISO14064 by monitoring the University’s energy consumption. In order to reduce CO2e, use of solar energy PV panels for the University building is evaluated. Calculations showed that intended PV panels could meet 16% of the annual electricity demand, leading to an 18% reduction in CO2e emissions compared to grid reliance. For Exergy analysis, general electricity generation sources (fossil fuel, renewable, etc.) are considered in obtaining the CO2e caused by using grid electricity. It is concluded that using electricity generated from PV panels instead of grid electricity resulted in less exergy destruction and approximately 61% low in carbon emissions. The planned PV panel installation’s payback period calculated as 5.1 years. The obtained results suggest that calculating CO2e emissions using the Exergy method provides a more realistic view, due to not only considering consumption but also taking into account energy generation, transmission, and distribution lines.

Landing gears, which are designed to absorb impact energy in order to provide support to the aircraft during landing, take-off and ground operations, are important components of the structure. Shimmy, which is one of the causes of aircraft failures, is a vibration that occurs as a result of the interaction of tire and landing gear dynamics and can cause an accident. In this study, the shimmy behavior of a helicopter used for civil, military and air ambulance purposes are investigated at different load and taxiing velocities. A landing gear single degree of freedom mathematical model is obtained and a Von Schlippe stressed spring tire model is included. The eigenvalues of the equations of motion are analyzed and stability maps of the system for different operating conditions are obtained. Runge-Kutta method (MATLAB ode45) is used to solve the equations of motion and a viscous damper is proposed. To obtain the damping, versions of the non-Newtonian silicone oil in the damper with different kinematic viscosities were evaluated. Apparent viscosities were obtained using the rheological values of the silicone oil and the analysis was repeated. As a result of the shimmy analysis at the initial velocities and maximum loading values required for the helicopter to taxiing, it was seen that damping was achieved in all conditions by using versions of the silicone oil with higher kinematic viscosities.