Tuncay Karaçay

In this study, the Reynolds equation derived in spherical coordinates for compressible fluids has been solved using a hybrid approach combining the differential transformation method (DTM) and the finite difference method (FDM). To accelerate convergence, the classical successive over-relaxation (SOR) method has been enhanced by adding a slope parameter ( β ). The effects of the relaxation parameter ( α ) and the slope parameter ( β ) on pressure distribution, load-carrying capacity, iteration count, and total solution time have been investigated for different eccentricity ratios. The results show that increasing α significantly reduces the iteration count, while the addition of β provides a further reduction in computation time, especially when α is already optimized. For fixed α and β values, the accelerated scheme introduces a practical speed deviation trade-off in the load-carrying-capacity results under the adopted stopping criterion. The shortest solution time is obtained with α = 3 and β = 0 . 1 , approximately 50 s, compared with 145 s for the baseline case ( α , β ) = (1, 0). To recover the baseline solution while retaining the computational benefit of acceleration, an adaptive strategy is introduced in which α and β are gradually reduced to 1 and 0, respectively, as convergence is approached. The findings demonstrate that the developed SOR approach can significantly accelerate the numerical solution of the Reynolds equation in spherical coordinates, thereby enhancing computational efficiency in engineering applications. Experimental validation is performed by measuring the shaft lift at different supply pressures, and the corresponding eccentricity ratios showed reasonable agreement with the simulation results.

The dynamic behavior of a polymer ball bearing system is mostly dependent on the contact characteristics among the ball and the races of the bearing. Although the well-known Hertz contact theory is widely used to model contacts in conventional bearings, it cannot be directly applied to polymer bearings due to the viscoelastic characteristics of the polymer structures. In this study, contacts in the polymer hybrid ball bearing are modeled using elastoplastic characteristics. The contact between inner/outer raceways and the ball is solved in elastic, elastoplastic, and plastic characteristics regions depending on the polymer structure and the loads. Then, two-degree of freedom rigid rotor-bearing system is simulated under different rotational speeds as well as different rotor weights. In order to investigate the nonlinear nature of the dynamic response, results are analyzed with different methods such as waterfalls, bifurcation diagrams, phase diagrams and Poincaré sections. The characteristic changes in the contact form elastic to elastoplastic regions are observed as a new peak in the time history that may lead to chaotic motion. A similar response is also seen when a single ball-race contact is in the elastoplastic region. The results are helpful to understand the cause and result of contact in a viscoelastic contact condition.

Polymer-bearing usage has been increasing recently, especially in sectors where hygiene is important. These bearings have advantages due to their resistance to corrosion, even with most chemicals. Besides, they do not require additional lubrication. Contrary to the expectation, polymer bearings are generally more expensive than conventional steel bearings. 3D printing of polymer bearings could be a solution to specific requirements; however, additive manufacturing processes have their own problems. Since the materials used in production with the 3D method are polymer-based, whether the bearings produced with this method can be used instead of the original polymer bearings has become a new research topic. Therefore, in this study, in order to examine the distinctive behavior throughout its service life, a new hybrid polymer bearing was developed using steel balls taken from the original polymer bearing, both inner and outer bearings of which were produced with a 3D printer, to create hybrid polymer bearings, using the Fused Deposition Method (FDM) has been obtained. Bearings are tested under load, and vibration data are acquired in order to investigate their fatigue behavior during their service life. The results indicate that Additive Manufacturing offers a workable way to create a polymer hybrid ball bearing. However, when the values obtained for both bearings are examined, it is seen from the test results that the strength of the bearings produced by the FDM method could be better.

This study suggests a 3D printed aerostatic bearing concept. The design has a high number of orifices distributed around the bearing to obtain smoother pressure distribution for performance. Inner channels are formed to connect and feed air to each orifice using the advantage of additive manufacturing. The concept is investigated numerically to determine the performance gain of the high number of orifices by calculating bearing stiffness and load carrying capacity. In order to validate the simulation and performance gain an experimental study is conducted by testing Stereolithography (SLA) type 3D printed bearings with various orifice numbers. The bearing stiffnesses and mass flow rates of the specimens are measured, and results are discussed in terms of performance by comparing numerical results. The 3D printed bearings concept has shown promising results in terms of performance while keeping air consumption limited compared to conventional air bearings.

Metamaterials have superior properties compared to materials found in nature and allow the tailoring of static and dynamic characteristics of the cell structures. In this study, the vibration characteristics of the sandwich plate systems composed of lattice beam structures are investigated and their behavior under various loading conditions is determined. In this context, a matrix-based solution method is developed to calculate the natural frequencies of the structure by assuming lattice elements as individual Euler–Bernoulli beams. The same structures are also analyzed with a commercial finite-element solver (ANSYS) to compare the results. In order to verify the results and determine the applicability of the proposed approach, an experimental study is conducted. Unit cell structures are additively manufactured with Stereolithography (SLA) and experimental modal analysis is performed using impact testing. Also, the amount of deflections on the structures under various loading conditions is determined experimentally by performing three-point bending tests on the plates. It has been concluded that approximate vibration characteristics of lattice-type metamaterial structures with various unit cell geometries can be determined in a short time by utilizing the matrix-based method without the need for any commercial software or performing complex experiments.