This paper studies path-breaking economic developments in Poland following the start of the systemic transformation in 1989. Three groups of countries are used for comparative analysis: those economically most advanced, those less developed but striving to catch up during the last 30–40 years, and as a subgroup of the latter, the transition economies. The paper has three objectives. The first is to show that many opinions regarding major aspects of the Polish transformation are at variance with the plain statistical facts. The second is to evaluate the pace and the extent of the progress so far in the effort to narrow the income and wealth gaps between Poland and most developed countries, particularly pre-2004 members of the European Union. The third consists of a discussion of factors which are likely to impede the pace of Poland’s economic development in the years to come.
The scope of the paper refers to long- and medium-run trends of labour supply in Poland. The main purpose is to determine current trends in the labour supply and its projections till the year 2050. In the theoretical part of the paper determinants of labour supply are considered. The projections are based on the population forecasts till 2050 made by the Central Statistical Office of Poland (CSO) and by the authors’ own simulations. Several variants of upper limit of working age and activity rates are taken into account. The population forecasts by the CSO indicate it will occur big decrease of working age population till 2050. The biggest decrease will refer to the group of working age 18–59/64 years and the lowest decrease in the age group 18–66 years. The analysis shows that the declines in labour supply in the years 2020–2050 will occur in all variants of working age population, the biggest decline in the variant assuming the age group 18–59/64 and the smallest decline – in the group 15–74 years. Retirement age is of big importance for the size of labour supply. This is why it is recommended to encourage older people to prolong their economic activity. It is also necessary to increase activity rates in the working age population.
The main topic of this study is the experimental measurement and mathematical modelling of global gas hold-up and bubble size distribution in an aerated stirred vessel using the population balance method. The air-water system consisted of a mixing tank of diameter T = 0.29 m, which was equipped with a six-bladed Rushton turbine. Calculations were performed with CFD software CFX 14.5. Turbulent quantities were predicted using the standard k-ε turbulence model. Coalescence and breakup of bubbles were modelled using the homogeneous MUSIG method with 24 bubble size groups. To achieve a better prediction of the turbulent quantities, simulations were performed with much finer meshes than those that have been adopted so far for bubble size distribution modelling. Several different drag coefficient correlations were implemented in the solver, and their influence on the results was studied. Turbulent drag correction to reduce the bubble slip velocity proved to be essential to achieve agreement of the simulated gas distribution with experiments. To model the disintegration of bubbles, the widely adopted breakup model by Luo & Svendsen was used. However, its applicability was questioned.
There exist cases where precise simulations of contact forces do not allow modeling the gears as rigid bodies but a fully elastic description is needed. In this paper, a modally reduced elastic multibody system including gear contact based on a floating frame of reference formulation is proposed that allows very precise simulations of fully elastic gears with appropriately meshed gears in reasonable time even for many rotations. One advantage of this approach is that there is no assumption about the geometry of the gears and, therefore, it allows precise investigations of contacts between gears with almost arbitrary non-standard tooth geometries including flank profile corrections.
This study presents simulation results that show how this modal approach can be used to efficiently investigate the interaction between elastic deformations and flank profile corrections as well as their influence on the contact forces. It is shown that the elastic approach is able to describe important phenomena like early addendum contact for insufficiently corrected profiles in dependence of the transmitted load. Furthermore, it is shown how this approach can be used for precise and efficient simulations of beveloid gears.