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Three-dimensional cfd analysis to study the thrust and efficiency of a biologically-inspired marine propulsor

Three-dimensional cfd analysis to study the thrust and efficiency of a biologically-inspired marine propulsor

Aquatic animals, which are the result of many millions of years of evolutionary optimization, are very quick, efficient, robust, and versatile. Accordingly, biologically-inspired mechanisms which emulate the movement of animals have recently become very popular. For the efficient design of a propulsion system it is very important to analyze the fluid flow in detail. CFD (Computational Fluid Dynamics) has become a powerful technique to understand the phenomena because it gives extensive information about the fluid flow characteristics.

In the present work, a propulsion system consisting of an undulating fin which emulates the fish swimming was built. In order to optimize the mechanism, several undulating configurations were studied using a 3D turbulent CFD model. The thrust, drag, efficiency and hydrodynamic characteristics were analyzed. Furthermore, it was shown that the efficiency and thrust depend strongly on the oscillation frequency, amplitude and wavelength.

In order to validate this CFD model, the numerically obtained thrust was successfully compared with experimental results from the laboratory mechanism.

Open access
New type of ponds? Changing of quantity and function of water bodies in rural built-up areas (Pilsen Region, Czechia)

Abstract

This study is focused on the changing of areas of water bodies in selected villages of the Pilsen Region (Czechia). We researched several different types of rural settlements and three time horizons with the help of old maps, orthophoto maps and GIS tools. To capture the influence of their location within the urban system, we chose 15 places from four categories (inner suburban area, outside suburban area, rural area, periphery rural area) depending on their distance to the core of the Pilsen agglomeration. There is no significant change in the amount of water bodies between the first reference period (1838-1839) and the second period (1957-1963) in the selected settlements. However, the third period (2013-2015) is characterized by the emergence of a large number of small water bodies - swimming pools and garden ponds. Based on the results of our research we identified the declining importance of public water bodies in some of the settlements. However, we have identified a notable prevalence of garden ponds which have a more positive ecological impact than pools. The proportion of private water bodies (covered and uncovered pools and garden ponds) in the total area of water bodies in the rural settlements in most cases is less than 20%, in the suburban settlements up to 100%. Peripheral settlements have a below-average share of these water bodies. The difference between the number of pools in different settlements is related to the proportion of newly built houses there. Although there are relatively fewer pools in rural settlements, the difference compared to the situation in suburban settlements is not pronounced due to the change in lifestyle in rural areas and the change in functions of some villages to recreational areas. Influence of pools on water consumption is dependent on the individual exchange technology of water in swimming pools. Filling of the pool before the season can overload the capacity of the local water supply.

Open access