BLIADZE, G. Optimalizace tvaru mazací mezery hydrodynamického olejového radiálního ložiska [online]. Brno: Vysoké učení technické v Brně. Fakulta strojního inženýrství. 2024.

Posudek vedoucího

Novotný, Pavel

Student performed some form of optimization of the lubrication gap dimensions in order to minimize frictional losses in the lubrication layer. The work includes 57 pages (45 pages excluding the introductory part and the list of references). The student completed the final thesis several months late. During the thesis production, the student came frequently for consultations and consulted intensively on some issues. It can be appreciated the fact that even though he did not have appropriate courses in the subject matter in his previous studies, he was able to complete the thesis. Unfortunately, the final version was not provided to the supervisor well in advance of submission. The current state research is of a lower standard both in terms of information found and in terms of processing. Especially the introductory general sections on turbochargers are redundant. Other sections lack a deeper analysis of the state of the art. A considerable amount of literature can be found on the subject. The proposed calculation models are basically correct and can describe the bearing parameters with some simplification. The optimization algorithm used is very specific, basically it involves generating a large number of input parameter variations and selecting the best variation with the lowest value of the objective function. Due to the speed of expression of the objective function and according to the constraints on the input parameter values, this approach is possible. The presented results suggest (not prove) that the optimization was done appropriately, but they show some uncertainties: - The oil temperature at the outlet of the default bearing variant is over 900°C (Figs. 27, 28), which is obviously unrealistic. - The results in Figures 24-30 do not indicate for which operating conditions they were determined. It should be added that several operating conditions were used in the optimization. - The results do not represent the bearing performance for all operating conditions. - The thermal model is probably not included correctly in the calculation, high oil temperature will significantly reduce the viscosity and this will reduce the friction torque. The graphical presentation is rather below average, all the relationships, derivations and figures are taken from the literature. After an overall evaluation, it can be concluded that the graduate has met the minimum requirements for a thesis.

Posudek oponenta

Kocman, František

Mr. Bliadze's 65-page thesis can be divided into a research part containing 29 pages and a part including the student's own contribution to the problem, containing 16 pages. The thesis is rather difficult to read because the student lacks sufficient knowledge of English. As a result, some sentences do not make sense (e.g. page 24 - ... most desirable for sliding bearings in automatic turbochargers; it can be assumed that the student meant automotive turbochargers). There are also a lot of typos. It is therefore a shame that the student did not send his work for proofreading or at least have it read by someone with a better level of English. The situation is similar for technical terms (e.g. "Turbo Single"). There are also a lot of pofidery statements (page 14 - "As we can see one of the main causes of the turbo lag is friction in the bearings."; page 27 - "CFD models take the analysis a step further by solving the Navier-Stokes equations directly.") as a result of which one can doubt the student's knowledge of the subject. Although the title suggests that this is a thesis focused on bearing optimization, the student devotes a substantial part of the research to turbochargers. The section on bearing optimization is only less than 4 pages long. At the same time, the thesis is full of stylistic errors such as confusion of upper and lower case letters, nonsensical references (page 14 - "...most commonly acknowledged. Fig. The main causes..."), inconsistent labelling of figures, a table which is a figure, lack of spaces between sentences, commas, periods, etc. The citations are all apparently inserted manually (wrong numbering) and sometimes in the wrong place. In addition, the student occasionally provides details that are not supported by citations. The sources used are of good quality, mostly scientific papers and technical literature, with a good representation of publications published in the last 10 years. The student often repeats himself in the text. He also fails to properly justify the choice of the optimisation algorithm, especially the choice of the genetic algorithm. Due to the use of MATLAB, I miss a more detailed description of the genetic algorithm settings, or whether he used the default settings, where he only changed the four parameters mentioned above. There is no justification as to why the population size was set to 50. As a result, convergence to the real minimum is not guaranteed. Furthermore, there is a lack of evaluation or at least a superficial comparison of the global and local optimization algorithms available to the student with respect to the hydrodynamic bearing problem. In his thesis, the student states that the optimization process took 15-20 seconds, but he does not mention the parameters of the device on which the calculation was performed. Considering the initial inlet oil temperature of 80 °C (Table 2), it is striking that the student's initial design oil outlet temperature of approximately 940 °C (Figure 27) seems to be alright to him. Although the student calculated the oil warming, there is no indication whether he considered the dependence of the viscosity on the oil temperature, as a result of which the correctness of the friction torque can be doubted, and he would probably have noticed the above mentioned error. Despite this, the student has met the minimum requirements for his thesis.

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