Structure vibration under the influence of unsteady hydrodynamic forces caused by the flow around their surfaces can adversely affect durability and rupture life. Reducing the adverse effects of hydrodynamic forces is currently possible with the help of linked CFD and vibration calculations. However, for an adequate description of the associated processes one should use calculation models and approaches specific to the hydro-vibration problem. To justify and validate such approaches, an experimental model was developed and a series of structure excitation tests in water flow was carried out.

The model comprises two cylinders installed sequentially in water crossflow. Vibration levels, pressure and velocity fluctuations were measured in the tests as a functions of the flow velocity. The application of different non-intrusive measurement techniques was possible due to relatively simple test model construction which may be used for cross-validation and experimental uncertainty quantification.

Flow-structure interaction, caused by synchronization effect of the flow separation frequency (or it’s spectral components) and eigenfrequency of cylinder, was analyzed based on simultaneously measured data. The tests performed gave the information about dynamical characteristics of the flow and vibration parameters of cantilevered cylinders. The experimental results are used for identification of required accuracy of hydrodynamic forces calculation by CFD and validation of oneand two-way linked methods for flow excitation frequency calculation.

Mirror antenna systems are widely used in satellite and space communication systems and radio astronomy. Development of these areas requires new efficient antenna systems' design. Possible technical solution for creating an effective mirror antenna is a “hybrid” scheme, when an adaptive phased antenna array is used as an irradiator. This paper is devoted to the development of an out-of-focus irradiator based on a phased antenna array for a space communications' parabolic reflector antenna. The aim of the work is to develop an optimal design of the irradiator with the choice of the structural element of the antenna array and experimental studies of the selected structural element.

The wavefront recovery method was used as a tool for selecting the irradiator configuration. The idea of this method use is to reproduce the electromagnetic field of an incident plane wave with an irradiator in order to uniformly illuminate the aperture of the antenna mirror.

In order to select the structural element of the irradiator several antennas were considered: a patch antenna, a flat spiral antenna, a conical spiral antenna. The requirements for the phased antenna array element were defined. The irradiator based on the above mentioned was simulated and the irradiator geometry was optimized according to the maximum gain criterion.

The maximum gain was achieved for the irradiator based on conical spiral antennas and amounted to 30.8 dB, which for the considered mirror aperture of 2.4 m is close to traditional focal schemes. The results obtained make it possible to create an adaptive antenna system able to compensate for the deviations of the mirror's shape from the theoretical profile, as well as phase distortions in the atmosphere by changing the lattice weights coefficients.

Due to the development of automation and control systems, methods and devices for measuring of electric current large values are of great interest. The aim of the work was to develop a schematic diagram of a distributed current strength sensor based on the Brillouin optical frequency domain analysis; to create a mathematical model of the sensor to demonstrate its work and to calculate the basic parameters of the sensor. To provide the measurement optical fiber with conductive coating is used. Between the current bus, where current is measured, and conductive coating the Ampere force arises. Strain occurs in optical fiber due to this force. Stimulated Brillouin scattering has the strain dependent characteristic frequency. Shift of the characteristic frequency allows to measure current in the bus. To measure the characteristic frequency and the location of its shift Brillouin optical frequency domain analysis is used.

The mathematical model of sensor operation based on tree-wave model of stimulated Brillouin scattering is demonstrated. This model allows calculating intensity of optical signal in the fiber in dependence of characteristic frequency shift. Brillouin optical frequency domain analysis uses inverse Fourier transform to obtain pulse response.

A schematic diagram of a distributed current sensor based on the method of Brillouin optical frequency domain analysis is presented. An a priori estimate of parameters of the measuring system was carried out on the basis of the mathematical model of stimulated Brillouing scattering in an optical fiber. The spatial resolution of the sensor when determining the length and location of fiber sections was 0.06 m. The resolution of the sensor was 0.22 kA, the maximum value of the current strength was 25 kA. Dependence of the sensor operation at different powers of the laser used was investigated. The refractive index change influence on the result of measurements was estimated.

Controlling of parameters of manufactured transistors and interoperational controlling during their production are necessary conditions for production of competitive products of electronic industry. Traditionally for controlling of bipolar transistors the direct current measurements and registration of capacity-voltage characteristics are used. Carrying out measurements on alternating current in a wide interval of frequencies (20 Hz–30 MHz) will allow to obtain additional information on parameters of bipolar transistors. The purpose of the work is to show the possibilities of the method of impedance spectroscopy for controlling of differential resistance of p–n-junctions of the bipolar p–n–p-transistor in active mode.

The KT814G p–n–p-transistor manufactured by JSC “INTEGRAL” was studied by the method of impedance spectroscopy. The values of differential electrical resistance and capacitance for base–emitter and base–collector p–n-junctions are defi at direct currents in base from 0.8 to 46 µA.

The results of the work can be applied to elaboration of techniques of fi checking of discrete bipolar semiconductor devices.

Improving the wear resistance of the surface of metal parts used in various industries is one of the relevant areas of materials science. The aim of this work was a comparative study of the wear resistance of a sample of an aluminum alloy (EN AW-2024, an aluminum alloy of the Al-Cu-Mg system) modified with ultrafine particles of minerals using the sclerometry method, which makes it possible to measure the physicomechanical properties of the material at the microscale, as well as determining some tribological parameters (hardness and elastic modulus) of a duralumin sample with a mineral coating.

Wear resistance was measured using a NanoScan-4D scanning hardness tester using the multi-cycle friction method using a sapphire sphere with control of the pressing force and the deepening of the tip into the sample. The use of such a measurement system is especially important when testing thin modified layers, when the layer thickness is comparable with the surface roughness parameters and the influence of the substrate is excluded.

The measurement results showed that the wear resistance of the surface of an aluminum alloy sample modified with ultrafine mineral particles increased by more than 12 times compared to the wear resistance of an aluminum alloy surface without modification. Also, measurements of the hardness and elastic modulus of the surface of the modified sample were performed taking into account the features of measuring the mechanical parameters of thin layers.

The obtained parameters of the modified surface of the aluminum alloy can be further used to build models of the processes of friction and wear of the surface modified by ultrafine particles of minerals. The lack of an acceptable explanation of the nature of the special properties of the surface modified by particles of minerals of natural origin does not exclude the use of the observed effects to significantly increase the resource of various parts and mechanisms.

At the present stage of development of digital information technologies intensive digitalization (computerization) of both direct and indirect measurement methods is taking place. The direct consequence of the computerization of measurements was, firstly, the emergence of a new class of measuring instruments – Processor measuring instruments (PRIS), secondly, increasing the level of formalization of measuring procedures, thirdly, the creation of a new, revolutionary technology –Virtual Instrument (VI). The purpose of the article is to analyze the development of digital technologies for measuring spectra, identifying the problems that arise in this case and formulating priority scientific and applied problems for their resolution.

Theoretical and applied research has established that digital spectrum measurement technologies, in addition to significant advantages, have certain disadvantages. It has been shown that the disadvantages of digital technologies for measuring spectra arise both from the nature of digital methods and from the analytical and stochastic properties of the bases of the applied transformations in measuring the spectra. An analysis of digital methods for measuring spectra showed that methods based on Discrete Fourier Transform (DFT) retain their leading role and are effective in almost all subject areas. However, there are also problems of digitalization of measurements of the spectra of signals based on the DFT, which are associated, first of all, with the manifestation of a number of negative effects that are absent with analog methods for measuring spectra based on the Fourier transform. This is the periodization effect of the measuring signal and its spectrum, the stockade effect, as well as the aliasing effect. As the analysis showed, existing methods of dealing with the negative effects of digitalization of spectrum measurements solve the problems of introducing digital technologies only partially. To combat the negative effects of digitalization of spectral measurements, a generalization of the DFT in the form of a parametric DFT (DFT-P) (Parametric Discrete Fourier Transform – DFT-P) is proposed.

The main scientific and applied problems of computerization of signal spectrum measurements are formulated: the development of the theory of digital methods for measuring signal spectra, the creation of new and improvement of existing digital methods for measuring signal spectra, the development of algorithmic, software and metrological software for PRIS and VI for the implementation of DFT-P.

Presence of anisotropy of the ferromagnetic materials' properties determines the need for its research and control, since it has a significant impact on the basic physicomechanical characteristics of details, products and constructions. The aim of the work was to experimentally investigate the possibility of using the magnetic noise method for non-destructive testing of mechanical properties of ferromagnetic materials particularly value of the coefficient of normal anisotropy Rn of sheet metal, mechanical stresses under elastic deformation of electrical steel and the anisotropy of the physical and mechanical properties of ferromagnetic materials.

Since the mechanical anisotropy is related to the magnetic anisotropy, the magnetic method of the Barkhausen effect (MBE) was used in its study, the informative parameters of which belong to the group of magnetic anisotropy. Comparison of the results of anisotropy evaluation on a set of samples of stamped sheet steel using the MBE with values Rn measured by the manufacturer showed their close match. This revealed the possibility of Rn level evaluation using the MBE. Device for circular rotation of the Barkhausen transducer on the sample surface and device for forming of elastic bending stresses in the sample were constructed. To study the magnetic anisotropy in various materials and the impact of elastic tensile and compressive stresses by bending on it using the MBE.

It has been found that the elastic deformation in samples of electrical steel leads to dramatic change of the magnetic noise level and the shape of the circular diagrams, taking into account the sign of the stresses generated in the sample. It was established that as a result of cold rolling in the production process, electrical steel samples have a pronounced texture due to the direction of rolled sheet. The created elastic stresses in the considered range practically do not change the texture (induced crystallographic anisotropy) after the material rolling.

The results can be useful for studying, monitoring and testing of anisotropy, crystallographic texture, structural heterogeneity of ferromagnetic materials in the form of sheet metal, sheet steel and coil steel, sheet metal forming and for solving other problems using the magnetic noise method in aboratory and workshop conditions.