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Performance and stability comparison of hydrostatic bearing pad geometry optimization approaches
(Springer Nature, 2025-04-30) Michalec, Michal; Foltýn, Jan; Svoboda, Petr; Křupka, Ivan; Hartl, Martin
Hydrostatic bearings are commonly used across a range of applications, yet their reliance on externally pressurized lubricants presents significant energy consumption challenges. This research aims to experimentally assess various approaches for optimizing the geometry of hydrostatic bearing pads. Utilizing a two-pad hydrostatic tester equipped with online diagnostics, we analyzed optimized multi-recess pads developed through both analytical methods and computational fluid dynamics (CFD). Our results demonstrate that the CFD method achieves a substantially greater film thickness recess pressure compared to the analytical method under similar experimental conditions. Additionally, the CFD approach reduces pumping power losses by 14%. However, this improvement in performance is accompanied by a reduction in film stiffness and an increased sensitivity to eccentric overload or misalignment, as highlighted in our findings. While the adoption of CFD-optimized geometries offers significant potential for lowering energy consumption, maintaining precise alignment especially in large-scale applications remains essential. In summary, our study suggests that employing CFD optimization can effectively reduce the service costs associated with hydrostatic bearings, but optimal outcomes necessitate careful alignment considerations.
Uncertainty analysis of hydrostatic bearing working conditions with experimental, CFD, and analytical approach
(SPRINGER HEIDELBERG, 2025-05-02) Foltýn, Jan; Maccioni, Lorenzo; Michalec, Michal; Concli, Franco; Svoboda, Petr
The design and real-time control of hydrostatic bearings (HS) require precise models capable of accurately predicting bearing behaviour under diverse operational conditions. Traditional analytical models have been found to be inadequate to simultaneously estimating critical parameters, including carrying capacity, recess pressure, film thickness, and flow rate. To overcome these limitations, Computational Fluid Dynamics (CFD) has emerged as a powerful tool in recent years. However, the accuracy of operational data used to calibrate the numerical and analytical models significantly influences the propagation of uncertainty. This study focusses on an experimental campaign and the development of a CFD model within the OpenFOAM® environment. Numerical and analytical models were calibrated using various input parameters, such as flow rate and recess pressure, to replicate experimental conditions while accounting for extreme operational scenarios and the inherent uncertainties in the experimental data. The results indicate that although average CFD predictions exhibit consistent errors in estimating operational parameters, the uncertainty ranges of the experimental and numerical data overlap under the conditions examined. On the contrary, analytical predictions show notable discrepancies, even when measurement uncertainties are considered. In particular, recess pressure emerged as the most effective input parameter to accurately estimating carrying capacity. These findings highlight the critical importance of incorporating measurement uncertainties into the calibration of numerical and analytical models for HS bearings, offering valuable information for their precise design and effective real-time control. Moreover, this paper demonstrates how CFD enables the consideration of misalignments measured during experimentation, a factor that is not accounted for in current analytical models.
On the Friction and Lubrication of 3D Printed Ti6Al4V Hip Joint Replacement
(Springer Nature, 2025-04-28) Rebenda, David; Odehnal, Lukáš; Uhrová, Simona; Nečas, David; Vrbka, Martin
The present study investigates the tribological performance of 3D printed Ti6Al4V total hip replacements (THR) compared to conventionally produced THRs from CoCrMo and FeNiCr alloys. The objective was to evaluate the suitability of 3D printed titanium alloy, with and without DLC coating, for THR rubbing surfaces and to investigate the potential benefits of 3D printing technology for friction and lubrication. A pendulum hip joint simulator was employed to replicate the swinging motion of a hip joint, thereby enabling the measurements of coefficient of friction (COF) and the observation of lubricant film formation under realistic conditions between the metal femoral head and acetabular cup. The experiments demonstrated that additive manufacturing enables the creation of specific surface topographies that can enhance protein adsorption, but also introduce surface imperfections negatively affecting tribological properties. The elevated surface roughness of additively manufactured femoral heads did not inevitably result in an increase in COF and was comparable to that of conventionally manufactured femoral heads. The additively manufactured Ti6Al4V head without DLC coating also exhibited a more rapid increase in lubricant film thickness during dynamic motion. In conclusion, the findings indicate that while 3D printing offers promising advancements in implant customization and material properties, its application requires careful consideration of surface finishing and coating methods to achieve optimal tribological performance.
Wheel Squeal Mitigation Under Water Lubrication
(Faculty of Engineering, University of Kragujevac, Serbia, 2024-09-15) Navrátil, Václav; Galas, Radovan; Klapka, Milan; Kvarda, Daniel; Omasta, Milan
This study investigates the potential of applying water to the wheel-rail contact to reduce squealing noise. For this purpose, a twin-disc device with a single tram wheel and real wheel suspension stiffnesses was devel-oped. Three types of tests were performed. During the tests, adhesion coefficient, sound pressure level and wheel axial vibration were meas-ured. The tests under dry conditions were carried out to describe the frequency spectrum of wheel vibration and to establish reference values for further measurements. The tests under wet conditions were carried out to investigate the ability of water to reduce adhesion and noise. Finally, tests with varying amounts of water in contact were carried out because of the low adhesion risk. The experimental results showed that the twin-disc device was able to reproduce both the adhesion and noise properties of the contact. Tests with different amounts of water showed that the application of water can be a promising way to reduce squealing noise from wheel-rail contact.
Current state-of-the art review of footwear-ground friction
(Springer, 2024-08-14) Rebenda, David; Sáha, Tomáš
The most important role of footwear is to ensure safe, functional walking, and foot protection. For the proper functionality of not only the work shoes, the anti-slip behavior of the shoe under various conditions and environments plays an important role in the prevention of slips, trips, falls, and consequent injuries. This article is intended to review the current understanding of the frictional mechanisms between shoe outsoles and various counterfaces that impact the evaluation of outsole slipperiness. Current research focuses on the mechanisms driving outsole friction on different ground surfaces or the definition and description of parameters that influence outsole friction. Subsequently, the review discusses the effect of various surface contaminants on footwear friction. Lastly, challenges and outlooks in the field of footwear outsoles are briefly mentioned.

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