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Chernov V.M.,National Research Nuclear University MEPhI | Leont'eva-Smirnova M.V.,National Research Nuclear University MEPhI | Potapenko M.M.,HIGH-TECH | Polekhina N.A.,Tomsk State University | And 4 more authors.
Technical Physics | Year: 2016

The thermophysical properties (specific heat, thermal diffusivity, thermal conductivity, linear thermal expansion coefficient, density) of 12% chromium ferritic–martensitic steels EK-181 (RUSFER-EK-181) and ChS-139 and the structure–phase transformations that occur in them upon heating and cooling in the temperature range 20–1100°C are studied. The temperatures of the start and finish of the α → γ and γ → α transformations in these steels and the Curie temperature are determined by differential scanning calorimetry. Peaks in the temperature dependence of the specific heat and jumplike changes in the linear thermal expansion coefficient and the density and the minimum of thermal diffusivity are detected in the α → γ transformation range. Specific heat peaks, thermal conductivity minima, and inflection points in thermal diffusivity curves are also observed near the Curie temperature. © 2016, Pleiades Publishing, Ltd.


Bazulin E.G.,Scientific and Production Center
Russian Journal of Nondestructive Testing | Year: 2015

To reduce the structural-noise level during ultrasonic testing using antenna arrays, an attempt was undertaken to implement a method for whitening echo signals with the further reconstruction of reflector images using the correlation or C-SAFT method. It is proposed to use the maximum-entropy (ME) method for reconstructing reflector images from measured echo signals. When performing numerical experiments for calculating the ultrasonic field in a medium with regions that were formed according to the principle of Voronoi diagrams, the finite-difference method in the time domain (FDTD) was used to numerically solve the vector wave equation. The attempt to use the echosignal whitening algorithm failed because of the poor conditionality of the system of linear algebraic equations, whereas the application of the ME method allowed the structural-noise level to be reduced by more than 6 dB. © 2015, Pleiades Publishing, Ltd.


Bazulin E.G.,Scientific and Production Center
Russian Journal of Nondestructive Testing | Year: 2014

A method that is proposed for calibrating an antenna array that is installed on a wedge provides refinement of the coordinates of the centers of piezoelectric elements. Precise knowledge of the coordinates will make it possible to obtain images in which reflections from reflectors will coincide with their actual positions with an accuracy no worse than a half wavelength. The calibration principle involves the minimization of the objective function that describes the difference between the antenna-array-measured echo signals from a 2-mm-diameter side drilled hole (SDH) at a depth of 12 mm and the calculated echo signals from the same hole. The algorithm operation was tested for echo signals calculated in the CIVA program. The calibration results for several antenna arrays on wedges and images of an SDH are presented, which were obtained using the method for digital antenna-array focusing (DAAF) for various acoustic systems. © 2014 Pleiades Publishing, Ltd.


Bazulin E.G.,Scientific and Production Center
Russian Journal of Nondestructive Testing | Year: 2015

To reduce the time of recording echo signals by an antenna array that operates in the double-scanning mode, it was proposed to use a set of pseudo-orthogonal coding signals. As the coding signals, it is possible to use frequency-modulated signals or phase-manipulated signals according to the Kasami code by analogy to the FDMA or CDMA techniques for multichannel communication. The use of the maximum-entropy method for decoding echo signals made it possible to reduce the noise level and increase the longitudinal resolution of reflector images in comparison to the case of using matched filtering. If an image is formed as the coherent sum of several partial images that are reconstructed using the C-SAFT method for various positions of the antenna array, it is proposed to use several sets of Kasami codes in order to additionally reduce the noise level by more than 6 dB. Numerical experiments show the efficiency of the proposed approach. © 2015, Pleiades Publishing, Ltd.


Bazulin E.G.,Scientific and Production Center
Russian Journal of Nondestructive Testing | Year: 2015

A modification of the combined SAFT (C-SAFT) method for reconstructing reflector images in a test object, which consists of several regions with different acoustic properties, in particular, anisotropy properties, is proposed. A method for the direct construction of a family of rays, which exit from the point where a transmitter is positioned, is used to calculate the ray trajectories with consideration for the anisotropy. After the family of rays is constructed, it is possible to analyze their attribution to a certain acoustic scheme and to approximate the calculated delays on the spatial grid of the region of iterest (ROI). This will allow one to calculate the pulse travel time from a transmitter to any point of the ROI and back to the receiver and to use the C-SAFT method for reconstructing reflector images. During processing of echo signals that were calculated in the CIVA program, the efficiency of the proposed method was demonstrated. Accounting for the anisotropy in a model experiment increased the focusing quality when reconstructing images of side-drilled holes in a specimen with a repair weld. © 2015, Pleiades Publishing, Ltd.


Bazulin E.G.,Scientific and Production Center
Russian Journal of Nondestructive Testing | Year: 2015

It is proposed to use the inverse C-SAFT (invC-SAFT) method to provide spatial-sensitivity equalization (SSE), which takes not only the delay times of the arrival of echo signals but also their amplitudes and phase nonuniformities into account. The invC-SAFT method reconstructs images of reflectors with a uniform scattering indicatrix in the form of reflections whose amplitudes change within ±2 dB; thus, the invC-SAFT method possesses the property of “inborn” spatial-sensitivity leveling. Numerical and model experiments at longitudinal and transverse waves confirm the efficiency of the proposed SSE method for nondirectional reflectors. © 2015, Pleiades Publishing, Ltd.


Kumenko A.I.,Scientific and Production Center | Kostyukov V.N.,Scientific and Production Center | Kuz'minykh N.Y.,Scientific and Production Center
Thermal Engineering | Year: 2016

To visualize the physical processes that occur in the journal bearings of the shafting of power generating turbosets, a technique for preliminary calculation of a set of characteristics of the journal bearings in the domain of possible movements (DPM) of the rotor journals is proposed. The technique is based on interpolation of the oil film characteristics and is designed for use in real-time diagnostic system COMPACS®. According to this technique, for each journal bearing, the domain of possible movement of the shaft journal is computed, then triangulation of the area is performed, and the corresponding mesh is constructed. At each node of the mesh, all characteristics of the journal bearing required by the diagnostic system are calculated. Via shaft-position sensors, the system measures—in the online mode—the instantaneous location of the shaft journal in the bearing and determines the averaged static position of the journals (the pivoting vector). Afterwards, continuous interpolation in the triangulation domain is performed, which allows the real-time calculation of the static and dynamic forces that act on the rotor journal, the flow rate and the temperature of the lubricant, and power friction losses. Use of the proposed method on a running turboset enables diagnosing the technical condition of the shafting support system and promptly identifying the defects that determine the vibrational state and the overall reliability of the turboset. The authors report a number of examples of constructing the DPM and computing the basic static characteristics for elliptical journal bearings typical of large-scale power turbosets. To illustrate the interpolation method, the traditional approach to calculation of bearing properties is applied. This approach is based on a Reynolds two-dimensional isothermal equation that accounts for the mobility of the boundary of the oil film continuity. © 2016, Pleiades Publishing, Inc.

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