Doctoral Thesis

Operational Safety and Reliability Enhancement of Large-Scale Hydrostatic Bearings

Final Thesis 2.34 MB

Author of thesis: Ing. Jan Foltýn, Ph.D.

Acad. year: 2025/2026

Supervisor: doc. Ing. Petr Svoboda, Ph.D.

Reviewers: Jean Bouyer, PhD, HDR, dr hab. inż. Wodtke Michał

Abstract:

This dissertation investigates the operational safety of large-scale hydrostatic bearings, in which load capacity is provided by an externally pressurized lubricating film separating sliding surfaces. Although hydrostatic lubrication enables negligible wear and very low friction even at zero speed, bearings of large diameter exhibit reduced safety margins. Segmentation of pads and tracks, assembly inaccuracies, structural compliance, thermal effects, and hydraulic disturbances can locally reduce film thickness and move the system toward contact-prone conditions. The dissertation therefore adopts a safety-oriented perspective in which the minimum lubricating film thickness and its distribution are treated as the key parameters governing reliability in rigid, segmented hydrostatic bearings. The main aim of this dissertation is to investigate, through analysis and experimental validation, how geometric deviations, hydraulic instabilities, and operating conditions affect the minimum lubricating film thickness in large-scale hydrostatic bearings, and to assess lubricating film thickness and its distribution as safety-relevant indicators of proximity to surface contact in rigid segmented bearing arrangements. The work is structured as three peer-reviewed journal papers. The first paper develops a contactless optical point tracking method for measuring lubricating film thickness without permanently installed sensors and validates it experimentally. The second paper examines pad alignment as a direct safety factor by comparing mechanical leveling, pressure-based alignment, and optical coordinate measurement method, demonstrating that optical alignment provides the most uniform film thickness distribution. The third paper applies the methodology to the hydrostatic bearing system of the Very Large Telescope, where contactless measurements reveal film-thickness variations caused by segmentation and simulated restrictor faults. Overall, this dissertation provides experimentally validated diagnostic tools and supports a preventive, film-thickness-based safety strategy for large hydrostatic bearings.

Keywords:

Tribology, Hydrostatic lubrication, Lubricating film thickness, Bearing safety, Lubricating film distribution

Date of defence

22.06.2026

Result of the defence

Defended (thesis was successfully defended)

znamkaPznamka

Process of defence

The dissertation meets the requirements arising from Section 47 of Act No. 111/1998 Coll., on Higher Education Institutions and on Amendments adn Supplements to Other Acts, and from Article 40 of the Study and Examination Regulations of Brno University of Technology. It contains original results published, among others, in three articles in an impact-factor journal.

Language of thesis

English

Faculty

Fakulta strojního inženýrství

Department

Institute of Machine and Industrial Design

Study programme

Design and Process Engineering (D-KPI-P)

Composition of Committee

doc. Ing. Daniel Koutný, Ph.D. (předseda)
doc. Ing. David Nečas, Ph.D. (místopředseda)
doc. Ing. Milan Klapka, Ph.D. (člen)
dr hab. inż. Wodtke Michał (člen)
Jean Bouyer, PhD, HDR (člen)

Supervisor’s report
doc. Ing. Petr Svoboda, Ph.D.

Assessment of the supervision process - Very good

The supervision process followed the pre-set rules for PhD study. The process was based meetings and on-demand discussions with supervisor, co-supervisor and colleagues from a Hydrostatic Research Group. The candidate was always well prepared to discuss the issue of the dissertation including reflection of critical comments. The final PhD thesis and research papers were prepared in time and in sufficient quality. The output of the dissertation was three main Jimp research papers (Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Journal of tribology-transactions of the ASME, Machines) supplemented by a conference paper from 2024 ISIEA conference (Latest Advancements in Mechanical Engineering. ISIEA 2024. Lecture Notes in Networks and Systems). The teaching activities of candidate were focused especially on tutorials of courses of 3CD - CAD and 4KC - Design and CAD. The candidate attended two international conferences where he presented partial results of his research: 7th World Tribology Congress 2022, Lyon, France and 9th International Tribology Conference 2023, Fukuoka, Japan.

Assessment of the candidate's ability to work independently - Very good

The candidate worked independently, based on the discussion with me and my colleagues from the lab and other experts from universities and companies in the field of mechanical engineering. I would like to highlight his cooperation with foreign experts in the field of HSL: Dr. Michal Wodtke (Gdansk University of Technology) and prof. Traian Cicone (Universitae Politehnica Bucharest). The candidate independently designed a methodology of experiments based on the state of the art, performed experiments, and, according to the results analyses, he formulated conclusions. All publications in which the candidate is listed as the main author were prepared independently based on original research findings. The candidate also supervised two bachelor theses, one diploma thesis and significantly participated in the other research projects of our small Hydrostatic Research Group with Bosch Rexroth company. The candidate also participated in work and study abroad internships (Free University of Bozen-Bolzano, Gdańsk University of Technology, European Southern Observatory in Chile).

Assessment of the contribution that the research makes to knowledge in the field - Very good

The PhD thesis is composed from three main research papers in the journals with impact factor (Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Journal of tribology-transactions of the ASME, Machines) supplemented by the state of the art. However, the candidate is also author and co-author of other publications in the field of tribology in journals with impact factor (see 8. List of main publications). He also participated in applied research outcomes (utility model and two functional samples). The main scientific output of this thesis is the safety of large-scale hydrostatic bearings by addressing critical aspects of lubricating film integrity under realistic operating, assembly, and fault conditions. The developed optical point tracking method demonstrated that non-contact optical techniques can provide film thickness measurements with accuracy and repeatability comparable to proximity sensors, while exhibiting reduced measurement dispersion. Alignment accuracy has a direct and measurable impact on film uniformity. The results confirm that addressing assembly inaccuracies through precise geometric alignment, rather than compensating them through elastic deformation, is essential for maintaining both safety and precision in rigid, segmented hydrostatic bearings. These findings are missing in current methodologies for the design of HSB. This work helps to find answers to some of the questions regarding the HSB design. I believe that the obtained scientific findings will suite the future development of HSB for better design and safety.

Conclusion

This PhD thesis is an independent scientific work that presents a novel solution to a significant problem in the research area and demonstrates the candidate’s ability to conduct independent research.

Grade proposed by supervisor: A

Reviewer’s report
Jean Bouyer, PhD, HDR

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Reviewer’s report
dr hab. inż. Wodtke Michał

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Posudek oponenta [.pdf] 201,66 kB

Responsibility: Mgr. et Mgr. Hana Odstrčilová