Wyniki wyszukiwania - BazTech

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Rotors of vertical-axial wind turbines assembled in bearings and aerodynamic characteristics of a blade with unclosed wing profile

Panda Anton, Rozhkova Lyudmila, Kuznetsov Eduard, Nahornyi Volodymyr

Management Systems in Production Engineering

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2022

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nr 4 (30)

298--303

EN

In world practice, traditional blades used in high-speed wind turbines, both horizontal-axial and vertical-axial, have a wing-shaped profile. However, for horizontal-axial wind turbines, blades with such a profile have a fairly narrow range of operating values of the angle of attack of the incoming air flow and a low value of the moment of pulling from place. As for vertical-axial wind turbines, the self-starting of the rotor with wing blades is completely absent and additional devices are needed to start the rotor into operation. In order to ensure the selfstarting of the rotor and the operation of the wind turbine at high and low wind speeds, a new shape of the blade profile was developed, called non-closed wing profile. The concept of the development is that the blade should have a configuration in which the pulling force is involved at the beginning of the movement, and then, with the establishing of the movement, a lifting force would arise, which acquires a prevailing character in the operating mode. The article presents the results of experimental studies of the aerodynamic characteristics of the developed non-closed wing blades. One of the results obtained is to determine the effect of the thickness of the blade profile on the range of values of subcritical angles of attack of the incoming air flow and the differences between the nature and range of changes in the coefficients of lifting force and pulling force in a traditional wing blade and a blade with a non-closed wing profile. Studies of the rotor model of a vertical-axial wind turbine with non-closed wing blades have confirmed the presence of its self-starting and operability even at low wind speeds.

2

Roughness effects of textured surfaces in hydrodynamic lubrication

Bahi Youssef, El Gadari Mhammed, Rahmoune Miloud

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 3

9--21

EN

Several studies have been conducted to improve and model the lubricated contact between surfaces. The main subjects were defining the hydrodynamic parameters to reduce energy losses and protect the environment. Some of the proposed models have studied the effect of textures in hydrodynamic lubrication and have proved that adapted shapes and geometries can improve the performance of lubricated contacts. A hydrodynamic model was developed by assuming the roughness of the textured surface and considering the cavitation in a steady-state regime. The proposed model was validated and compared with the analytical model of Fowell et al. [1]. Three different textures shapes were considered. The results showed that the rough-textured thrust affects the hydrodynamic performance significantly. Thus, by increasing the arithmetic roughness of textured surfaces, the hydrodynamic pressure, and the lifting force increase depending on the texture shape. A rougher surface slightly increases the friction force for the three considered textures.

3

The non-unicity of the film thickness in the hydrodynamic lubrication: novel approach generating equivalent micro-grooves and roughness

El Gadari M., Hajjam M.

International Journal of Applied Mechanics and Engineering

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2021

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Vol. 26, no. 3

44--61

EN

Since the 1960s, all studies have assumed that a film thickness “h” provides a unique pressure field “p” by resolving the Reynolds equation. However, it is relevant to investigate the film thickness unicity under a given hydrodynamic pressure within the inverse theory. This paper presents a new approach to deduce from an initial film thickness a widespread number of thicknesses providing the same hydrodynamic pressure under a specific condition of gradient pressure. For this purpose, three steps were presented: 1) computing the hydrodynamic pressure from an initial film thickness by resolving the Reynolds equation with Gümbel’s cavitation model, 2) using a new algorithm to generate a second film thickness, 3) comparing and validating the hydrodynamic pressure produced by both thicknesses with the modified Reynolds equation. Throughout three surface finishes: the macro-shaped, micro-textured, and rough surfaces, it has been demonstrated that under a specific hydrodynamic pressure gradient, several film thicknesses could generate the same pressure field with a slight difference by considering cavitation. Besides, this paper confirms also that with different ratios of the averaged film thickness to the root mean square (RMS) similar hydrodynamic pressure could be generated, thereby the deficiency of this ratio to define the lubrication regime as commonly known from Patir and Cheng theory.

4

Assessment of the technical level of magnetic fishing tools

Romanyshyn Taras, Romanyshyn Liubomyr, Bembenek Michał, Mokhnii Ihor

Management Systems in Production Engineering

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2020

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nr 2 (28)

78--83

EN

A variety of magnetic fishing tools poses the task of the optimal choice of tool for eliminating accidents during the construction, operation and repair of wells. Existing criteria for assessing the quality of fishing magnets are characterized by the complexity of the determination and the ambiguity of the results. Therefore, the aim of research is development of a new approach to determining the technical level of fishing tools of various types and designs. A complex criterion has been developed that allows to evaluate the technical level of magnetic systems by correlating the actual and theoretical values of the total and specific lifting forces. Also it has been carried out a qualimetric analysis of magnetic tools, which are currently offered by world manufacturers. As a result, mathematical models are found that describe the average and modern world level of devices with specific lifting force. Technical decisions are proposed, the implementation of which in the design of magnetic systems of fishing tools will allow to achieve high values of lifting force. Application of the proposed complex criterion along with the results of qualimetric analysis will make it possible to objectively assess the technical level of magnetic fishing tools both at the design stage and during serial production.

5

Performance comparison of different aerodynamic shapes for autonomous underwater vehicles

Khalin Anatoliy, Kizilova Nataliya

Archive of Mechanical Engineering

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2019

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Vol. LXVI, nr 2

171--189

EN

A brief review of the existing autonomous underwater vehicles, their types, design, movement abilities and missions is presented. It is shown, the shape optimization design and enhancement of their efficiency is the main problem for further development of multipurpose glider technologies. A comparative study of aerodynamic performance of three different shape designs (the airfoil NACA0022 based (I), flattened ellipsoidal (II) and cigar-type (III) bodies of the same volumes) has been carried out. Geometrical modelling, meshing and computational fluid dynamics (CFD) simulations have been carried out with AnSys15.0. The pathlines and wall shear stress distributions have been computed to understand the advantages and disadvantages of each shape. The lift and drag coefficients, aerodynamic quality, power index and pitching moment have been computed. The higher efficiency of the shape I/shape II at higher/lower angles of attack (greater than 20o and less than 20o) has been found. The shape III develops high speeds at the same angles of attack and has higher manoeuvrability at relatively low aerodynamic quality. The comparative analysis of the flow capabilities of studied autonomous undersea vehicles proposes some design improvement for increasing their energy efficiency and flow stability.