The flow of a solid-water mixture through an upward-facing step in a channel is numerically investigated. The effect of expansion ratio, mean solids volume fraction and particle diameter on the velocity field, pressure distribution and solid volume fraction field is studied. Expansion ratios of 0.50 and 0.67, particle diameter of 125 µm and 440 µm and mean solid volume fraction between 0.05 and 0.20 are considered. Particle density is 2465 kg m-3 . An Eulerian twofluid model is used to simulate the flow. Due to the lack of experimental data, the model was validated by comparison to other numerical investigations and to experimental data about the horizontal pipe case. Afterwards, it is studied the effect of the above mentioned parameters upon the degree of coupling between the phases and the extension of the disturbance region in the pressure and solid volume fraction fields downstream the step. Parameters of engineering interest, such as the reattachment length and the pressure recovery downstream the enlargement, are investigated.
One of vital and challenging tasks is to improve double suction pump performance in conditions when essential changes of their parameters are required without playing with their dimension in case of adapting their capacity to seasonality or flow-rtae change for a long time interval or for pipelines at various stage of their development. In this paper a few design options of flow parts executed for the same casing have been examined:
- Nominal mode: Semi-volute suction chamber, double suction impeller and double volute discharge chamber;
- Suboptimal mode: replaceable impellers and diffusers are used (same suction and discharge chambers)
Numerical analysis results of the flow parts are presented in this article. Double suction pumps with projected diffuser for replaceable rotor with 0.6 Qn flow-rate and with perspective diffusers engineered within ANSYS CFX-12.0. The latter (perspective diffusers) have been analyzed to find final ways to reduce hydraulic losses. Q-H, power consumption and performance curves are also given. Numerical experiment is an effective method for predicting patterns of characteristic curves even for such sophisticated flow parts as double suction pumps with a combined discharge chamber. and Obsahuje seznam literatury
A mathematical model of the roadway automobile motion is numerically analyzed. This model is intended to describe the roadway automobile stability. A previous paper [6] described the model in detail and the general method of qualitative analysis. In the present paper, we continue the discussion of stability by numerical simulations and the specific question we attempted to answer is: which parameter(s) of automobile geometry and quality of the roadway can serve as a reliable predictors) for car crash? Data from Daimler-Chrysler AG and Ford Motor Company Limited were used for that purpose, considering three car types - Mercedes-Benz E 320 (T-modelle), Ford Focus and Mercedes-Benz Sprinter (1). Hence, one can consider the present work as a natural continuation of [6]., Obsahuje seznam literatury, and Článek doplňuje Appendix na str. 294-295
Central European lowland wet meadows are habitats of great conservation interest, however, their phytosociological status has been to a large extent dependent on specific phytosociological traditions in different countries. In order to bridge the gaps between different national schemes of vegetation classification, a statistical analysis of variation in species composition of these meadows in the Czech Republic, E Austria, Slovakia, Hungary and NE Croatia was performed, using a data set of 387 geographically stratified vegetation relevés sampled at altitudes < 350 m. Principal coordinates analysiswas used to identify and partial out the noise component in the variation in this data set. The relevés were classified by cluster analysis. A new method for identifying the optimal number of clusters was developed, based on species fidelity to particular clusters. This method suggested the optimum level of classification with three clusters and secondary optimum levels with five and nine clusters. Classification based on three clusters separated the traditional phytosociological alliances of Calthion palustris and Molinion caeruleae, both with a suboceanic phytogeographical affinity, and a group of flooded meadows of large river alluvia, with a continental affinity. The latter group included the traditional alliances of Agrostion albae, Alopecurion pratensis, Cnidion venosi, Deschampsion cespitosae and Veronico longifoliae-Lysimachion vulgaris; however, the internal heterogeneity of this group did not reflect putative boundaries between these alliances as proposed in the phytosociological literature. Therefore we suggest to unite these alliances in a single alliance Deschampsion cespitosae Horvatić 1930 (the oldest valid name). Classification with nine clusters was interpreted at the level of broad phytosociological associations. Particular clusters were characterized by statistically defined groups of diagnostic species and related to macroclimatic variables.