Fluid rigid body interaction is commonly occurring phenomenon and this phenomenon is of high importance in many engineering applications. The main objective of the present paper is to analyse vibrations due to fluid-rigid body interactions by inclining the frontal area of flat plate to flow. As understood from the existing research, the main challenge is the understanding of non-stationary fluid body interactions. Interaction analysis, optimization and synthesis tasks include space-time programming methods and approximate analytical methods. This article discusses an approximate analytical method in which the object's interaction with fluid flow is divided into two parts in the fluid body interaction space. The first part is the frontal pressure side that arise as a result of change of momentum in the system that can be conveniently represented in a differential form. The second part includes the idea of describing the interaction behind the plate as a certain thin (vacuum) side was accepted. This thin vacuum side also depends on the frontal area flow interaction. The use and precision of the approximate analytical method was verified by experiments in the wind tunnel. The method was used for good analysing of varying frontal area (until flattening) of flat plate in fluid flow. The main parameters for motion excitation are the changes in plate-flow interaction area, velocity and angle of inclination of the flat square plate to the fluid flow. Experiments were performed at 10 m•s-1 keeping in view the wind speeds that were observed in the past in Riga, Latvia.
The paper presents a theory of body collision with pit corner. The theory can be successfully applied in approaching tasks coping with the orientation of details in technological processes and control systems, the motion of elements in mechanisms having a gap, collisions in motion of different sport objects, the analysis of car accidents etc. The applied theory deals with car motion after collision with a specific obstacle i.e. pit corner. The study is based on linear and angular momentum theorems and two restitution coefficients of normal impulse from both sides of the obstacle. The obtained results can be used for assessing road accidents in case of car collision with one or more obstacles. The object of contact may involve hitting a plane foundation, the ditch and edging of a highway or a rock in the field.
Abstract. The HPGe detector assembly of gamma-ray spectrometer cooled by Stirling cycle cryocooler is under consideration. Modal analysis based on the compiled dynamic model was carried out. The natural frequencies and modes shapes for HPGe detector with relative efficiency 15 % mounted by supports made from composite G-Etronax and CESTILENE HD 1000 were calculated by Solidworks simulation. The frequencies of the axial mode are in range of 200-600 Hz where electrical interferences caused by mechanical vibrations (so-called microphone noise) has a large impact on the resolution of spectrometer. It is shown that for cryostat cap the lowest natural frequencies determined by the thickness of input window lay in higher frequency range. The validity of the adopted model was confirmed by the experiments. The calculated natural frequencies of the detector assembly are compared to the harmonics of cryocooler's vibration. The results obtained are useful to identify the interferences source in electrical circuits of spectrometer at its adjusting.
An approximate method for the analysis of interaction between wind flow and rigid flat blades is considered. The method allows synthesis and optimization of wind energy conversion systems without using space-time-programming procedures. By this method, the action of wind flow on the blade is subdivided on frontal pressure and vacuum (depression) on leeward side. The method was tested by computer simulation and experiments in wind tunnel. Examples of optimization tasks are solved in application to blades with simple shape. New wind energetic device with controlled orientation of flat blades to air flow is developed. Theoretical and experimental analysis of blade's interaction with airflow is performed. Aerodynamic coefficients for blade's drag and lifting forces are determined experimentally in wind tunnel. Optimization of system parameters is made. To increase the efficiency of energy transformation, it is proposed to change, by special law, the orientation of blade's working surface relative to airflow during rotation of the rotor. It is shown that the optimal angular rotation frequency ratio between rotor and blade is equal to two. Serviceability and main advantages of the proposed method are confirmed by experiments with physical model of airflow device.
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