Volume 59 (2022): Edizione 5 (October 2022)

The paper presents a simulation model developed for a special optical coupler intended for coupling radiation from signal and pump sources used for the realization of cladding-pumped doped fibre amplifiers. The model is developed in COMSOL Multiphysics and used to assess the pumping efficiency for different side pumping angles and different numbers of electromagnetic modes. The obtained results show that the highest pumping efficiency, above 75 %, is achieved for 5–14 modes when two fibres representing the pump source and the signal source form a 10-degree angle between their central axes. The search for the optimal number of modes corresponds to the development trend in optical coupler technology where the multimode pumping by light-emitting diode (LED) replaces the classical scheme with a single-mode pumping by a laser diode (LD).

The research is devoted to the elaboration of the wear part contact estimation using 3D surface texture parameters defined in the standard ISO 25178-2:2012 for contact (it is known that elastic contact gives less wear rate) area, friction, and wear rate determination. In our research, the sphere and random flat surface model was used, where the height of surface asperities h(x, y) had a normal probability distribution. As a result of research, the equations for estimation of the elastic contact area were derived and, we obtained conditions at which it was possible to use equations for flat random surfaces. The results of this study could have wide practical application, for example, in design, choosing the geometrical and physical-mechanical parameters of the parts, calculation of real stresses, wear rate and life time of contact parts, etc.

This review article covers the topics of evaluation and experimental determination of oxygen mass transfer coefficients (k_La) for their application in characterising bioreactors and fermentations processes. The article provides a comparison of different experimental approaches for determining k_La in bioreactors. Additionally, the influence of bioreactor design and fermentation parameters on k_La is discussed. The aim of the article is to provide useful information regarding the approaches for selecting bioreactors and their working regimes to achieve optimal fermentation results.

With an emphasis on the visual appearance of buildings, surface and internal gas pipelines are being built into structures and walls, which can affect system serviceability and occupant safety. When placing gas pipelines in a closed room (shafts, ducts, facade structures, etc.) there is a risk that in case of leakage, natural gas will accumulate in the room, which together with the ambient air, within the specified concentration limits, forms an explosive mixture. The present paper analyses the built-in internal gas pipeline systems, their installation norms, operation and maintenance problems in different types of buildings. It is shown that requirements do not cover all possible gas pipeline installation options. The analysis of the gas supply system operator shows that non-compliance with the applicable norms has been identified in every third of the 400,000 gas consumers in Latvia in the surface and internal gas pipeline system. To improve and develop safety requirements, it is planned to perform an experiment that is described in detail in this paper. Pre-experimental calculations are made to set reference points in the study and find the main influencing parameters on gas leakage process.

The paper analyses the constraints related to optical tracking of an HMD with a single commercial binocular stereoscopic optical tracking system and offers an overview of different factors affecting the best active fiducial set-up and marker geometries for reliable tracking with a focus on the rotational accuracy of a marker.

Two IR diode models with different emission characteristics were tested as active fiducials and the results were compared to localization accuracy of passive fiducials. In terms of preferable marker geometry, it was found that the area enclosed by the fiducials should be maximized. Thus, due to geometrical constraints, very small marker geometries may not be stable or feasible entirely. Rotational accuracy was analysed for cases when the marker was not directly facing the tracking device and it was found that rotation about one axis introduced errors to the determined orientation in space related to the other axes as well.

Surface potential decay (SPD) of a corona charged polymeric material is a powerful tool to characterise electrical properties such as charge transport, trapping/detrapping and recombination. Over the years, various predictive simulation techniques have been proposed to describe charge transport within the material. Despite recent progress, it appears that there have been a few attempts to theoretically interpret the nature of the charge migration on the insulation surface. The aim of the present paper is to introduce a new technique with differential evolution algorithm (DEA) to reveal the steady state surface potential decay experimental results. Experimental measurement was carried on a thin film of polyethylene terephthalate (thickness: 0.5 mm; surface: 50 mm × 50 mm). The domains of variation of the factors used were respectively: 1000 V to 1800 V; 25 to 55 °C; 50 % to 80 %. The simulation results show that computational modelling and optimization approaches may improve the effectiveness to characterise electrical properties of polymers. More importantly, these studies demonstrate that DEA is effective and performs better than the experimental design method.