Vaclav Kopecky

Measurement of piezoelectric transformer vibrations by digital holography

A method for the measurements of the out-of-plane displacement on the surface of vibrating object is presented herein. This method is based on frequency-shifted time-averaged digital holographic interferometry, employing the principle of phase shifting. This approach allows for significant noise reduction, which results in high sensitivity of measurements. This method makes it possible to measure vibrations with amplitudes in the nanometer range over the whole measured surface. This method was applied to the visualization of the out-of-plane vibration modes of piezoelectric transformers. The amplitude and modal shapes were measured with a very high resolution. Furthermore, aspects influencing the measurement errors are discussed and the measurement results by holographic method were compared with the well-established single-point laser interferometry measurement method.

The methodic for study of smart surfaces using PIV technique

This article introduces the methodic for the study of smart surfaces using PIV method. The problem of investigation of super- and ultrahydrophobic- surfaces deals with the quantifying description of the fluid flow behavior in the near-wall region. The objective is to realize comparative study of commercial smart surfaces and their interaction of fluid flow according to the assessment of contact angle. The article interprets the results of measurement of fluid behavior over the whole testing chamber and the synchronized near-wall measurement with optimized dynamic range. The results are shown in the correlation of measured contact angle before and after testing and there are explained changes in the flow behavior.

A digital holographic method for the measurement of piezoelectric transformer vibrations

Method for the measurements of the out-of-plane displacement on the surface of vibrating object is presented. The method is based on the frequency-shifted time average digital holographic interferometry employing the principle of phase shifting. This approach allows for a significant noise reduction, which results in the high sensitivity of measurements. The method makes it possible to measure the vibrations with amplitudes in the nanometer range over the whole measured surface. The method was applied to the visualization of the out-of-plane vibration modes of piezoelectric transformers. The amplitude and modal shapes were measured with a very high resolution. Results of measurement were used to judge the influence of mounting on the electrical properties of piezoelectric transformers in operation.

Experimental setup for laser-induced breakdown in aqueous media

This article presents the visualization of the cavitation bubble generated with laser-induced breakdown. The cavitation bubble is generated with 532nm Nd: YAG laser beam, 10ns short with two different optical setups. Here, we use direct optical way focusing the laser beam, and reverse way base on the focusing mirror. We are using different laser light power and visualize the laser probe in correlation of bubble characteristics. The visualization is set on long-distance microscopy and shadowgraph lightening method. The main goal of the research is to set the optical setup for the laserinduced breakdown and to create the calibration relation curve for the bubble size dependence on the input energy of the laser beam. This calibration curve is related to the lifespan of each bubble, or the group of bubbles.

Time resolved PIV measurement of fluid dynamics in agitated vessels

Here we present the results obtained by TR PIV measurements focused on detailed flow analysis in the selected region. The investigated area was placed 3mm above the blades axis and 5mm far from the blade edge. The captured images were firstly analysed on the mean velocity distribution and the intensity of turbulence {UV} statistics. Here we used the time resolved technique for the experimental study of the flow field in the agitated vessel. The results of the application POD and ODP algorithm on the captured datasets uncovered the existence of unsteady structures in the area that was assumed to be stable. The existence of these structures is bringing a novel view on the mixing process.

The interaction between fluid flow and ultra-hydrophobic surface in mini channel

Interaction of liquid with ultra-hydrophobic surface is accompanied by creation of layer of air. The effect of the air film has a potential of use in industry in many applications. The quality of the surface is influenced by matrix roughness, the character of physical or chemical cover. There was developed a method for analysis of the liquid flow and the air film using the lighting in volume, visualization with CCD camera and long distance microscope, and optical filters. There were prepared four stainless steel samples of inner channel of dimensions (80 × 8 × 8) mm and initial surface roughness Ra 0.33, Ra 1.0, Ra 2.0, and Ra 2.2. The inner channel was treated with plasma and commercial hydrophobic coating Greblon (WEILBURGER Coatings GmbH). There was realized study focused on the liquid flow velocity profile close to the air film. There are present results for laminar, transient and turbulent flows. The study also estimated the air film thickness depending on the Re number. The knowledge of the air film behaviour helps applied suitable degree of processing and cover for the target application.

An effect of entrance length on development of velocity profile in channel of millimeter dimensions

Here we used modified PIV technique completed with long distance microscope probe for experimental investigation of the flow velocity profile in a rectangular duct. We came from the analytical and numerical prediction of the entrance length for fully developed velocity profile. The results of measurement completed knowledge about the flow stability and velocity profile shape in the channel of 0.00375 hydraulic diameters. There was marked a range of entrance length constant for the transient flow area. The presents of the fluctuating velocities in the transition flow is explained with POD snapshot and modes projection. The minimal entrance length for the laminar, transition, and turbulent flow is set.

Visualization and measurement of the air film close ultra-hydrophobic surfaces

The ultra-hydrophobic surfaces have the prospect of great importance in industry, both in applications demanding easy cleaning, and they are presumed to reduce loss when the active parts of hydraulic machines are treated. Interaction of fluids with ultra-hydrophobic surface is accompanied by creation of layer of air, so called air film, which depends on the quality of the surface. The quality of the surface is influenced by the matrix roughness, the character of physical or chemical cover. This properties lead to monolithic air layer presented as air film, or lead to plurality of bubbles of various sizes seated upon the surface. The air film can be observed visually at sufficient magnification and the dynamic interaction between fluid flow and air film can be studied with Global Imaging methods, particularly Particle Image Velocimetry (PIV). There is the velocity profile in the vicinity of the air film in the main interest of the research. Here we present the visualization of air film depending on Reynolds number of flowing liquid.

Drop movement analysis on inclined surface for the adhesion coefficient determination

This article brings the description and the method for the object detection and analysis of the sliding drop on the inclined surface. This experimental work is essential for the knowledge on the adhesive coefficient determination. The investigation method was tested directly on selected surfaces - one ultra hydrophobic. The set of measurements proved the idea of the linear dependence of the inclination angle and set the adhesive coefficient to hydrophobic materials.

Measurement of vibration mode structure for adaptive vibration suppression system by digital holography

This paper describes method for the measurement of vibration modes structure based on frequency modulated digital holography used in adaptive system for vibration suppression.