Amplitude-frequency Characteristics Research Articles

Ensuring Safety of Gas Field Infrastructure Using ALARP and a Systematic Approach

Introduction. A significant part of the global and state economy is the production and supply of hydrocarbon raw materials. The issues of safety in this area will remain important in the coming decades. The problem is actively discussed in the professional and scientific community. Theoretical and applied works are published. Local, point-based methods are calculated and implemented, which allow predicting and preventing emergencies in certain units of the considered objects. At the same time, there are no sufficiently justified and reproducible system solutions that can take into account the state of, for example, oil or gas field as a single complex and act as indicators not only of ordinary local accidents, but also of systemic accidents — catastrophes. Such a scientifically and experimentally based solution is described in this article. The approach is proposed as part of the formation of a comprehensive scientific and technical program (CSTP) to ensure the safety of natural and technogenic objects (NTO). The aim of this work was to describe the practice of its application in the conditions of specific gas fields and to justify the refusal to focus on solutions that took into account only the minimum practically acceptable risk, that is, built on the ALARP principle (as low as reasonably practicable). Materials and Methods. The article was based on the results of field tests of natural and technogenic objects (NTO) of the oil and gas complex — the Yuzhno-Russkoye field of OJSC Severneftegazprom (SNGP), LLC Gazprom Dobycha Yamburg (GDYA) and the gas pumping station (GPS) Orlovka-2 (Ukraine), conducted with the authors’ participation. Significant results were obtained and evidence-based physically interpreted during acceptance tests of an explosion-proof certified, created under the guidance of the authors of a prototype of a disaster response system (DRS) at the integrated gas treatment plant (IGTP) in LLC GDYA in 2006. At the same time, for the first time in the world practice, the fact of early detection and parrying without consequences by means of DRS on the UKPG-2 of the development of a large-scale general industrial disaster was confirmed. In the form of graphs, the revealed patterns of NTO have been visualized, which made it possible to form harbingers of the development of accidents and catastrophes at the NTO of LLC "GDYA", SNGP and GPS "Orlovka-2". Information on the high experimental reproducibility of the obtained results was presented. The technology has been developed of early detection and parrying of all types of potentially dangerous self-exciting systemic phenomena on real NTO infrastructure — self-oscillations. Three cases of their excitation in real gas fields were presented. Results. The paper shows the fragmentary nature and locality of emergency protection systems based on the ALARP principle. The consequence of this was its complete unsuitability for early detection and counteraction to the most large-scale and costly system accidents — catastrophes that were multifactorial processes, in which none of the factors was decisive. The alternative complex solution of the problem proposed by the authors and brought to working condition was based on a system approach adapted to the NTO of the oil and gas complex. The measured parameters of various NTO infrastructure — fields of LLC "GDYA" and SNGP were processed and analyzed at the moments of development of self-oscillating modes on them, due to self-sustaining nonlinear mechanisms of interaction of NTO elements with constant (non-oscillatory) sources of energy replenishment. Three such modes of self-excitation were illustrated. The most informative in this case were the transient modes of operation of the equipment. According to the technologies experimentally developed by the authors, the areas of critical operating modes of equipment with pronounced potentially dangerous bifurcation points were analyzed. The result of superimposing treatments of the measured parameters of eight full-scale tests of NTO — graphs of dimensionless amplitude-frequency characteristics of the interconnections of a real dynamic system was presented: "input — gas cooling housing" → "output — pipe casing" at the frequency of self-oscillations. Discussion and Conclusion. The capabilities of ALARP did not meet the tasks of system monitoring of the occurrence and development of dangerous incidents in gas fields. This conclusion can be attributed to all standard sizes of NTO infrastructure in Russia. Fundamentally different solutions should be used to ensure comprehensive observability, controllability, and safety of NTO. A comprehensive scientific and technical program is recommended: "Innovative hardware and software tools and technologies to ensure the observability, controllability, and safety of the NTO infrastructure of Russia".

Open-loop flow control design guided by the amplitude-frequency characteristics of the reduced-order model

Unsteady separated flow is a common flow condition causing many detrimental effects in aerospace and other fields. Open-loop control is a potential means to eliminate these drawbacks. At present, the unsatisfactory performance of open-loop control mainly attributes to the high-dimensional parameter optimization procedure and the lack of efficient knowledge-guided control law design methods. This paper proposes a method managing to directly obtain the anti-resonant frequency from the input and output amplitude-frequency characteristic curves of the reduced-order model of the flow-control coupled system. Simultaneously, a negative gain criterion is proposed to judge whether the target control effect can be achieved under the current parameter combination. For the control of low Reynolds number flow around a cylinder, the simulation results show that the optimal open-loop control frequency is 1.268 times the natural frequency of the flow, which is consistent with the anti-resonant frequency, and 26.8% of the lift fluctuation is suppressed. This paper also studies the influence of parameters such as flow frequency change, control start time, jet mass flow rate, and so on. Furthermore, control position is the key parameter affecting the amplitude-frequency characteristics. The anti-resonance points on the curves corresponding to different control positions can also guide the design of the optimal control frequency, and the negative gain criterion is still applicable. This method greatly reduces the time consumption in parameter optimization and improves the engineering application prospect of the open-loop control in unsteady separated flow control.

Amplitude–Frequency Characteristics and Stability Regions of a Two-Layer Liquid under the Angular Vibrations of a Solid Body

Amplitude–Frequency Characteristics and Stability Regions of a Two-Layer Liquid under the Angular Vibrations of a Solid Body

Establishing the nature of kinetic effects of the high-temperature oxidation (combustion) process of some liquid organic matters by acoustic radiation

In this article, the results of the study on the physicochemical characteristics of some liquid organic matters on the kinetics of their high-temperature oxidation (combustion) were presented for the first time. These results were obtained by the method of acoustic emission spectrum from heat source. The research results of the amplitude-time characteristics (until cessation of combustion completely) and the frequency response functions (in a given frequency range) of oxidation (combustion) process of liquid organic matters showed that there are following unambiguous dependences: 1) the dependences of the number of the amplitude maximum of the frequency and time spectrum in a given frequency range, as well as of the fractal dimension of the received acoustic signal on the number of carbon atoms in the carbon frame of organic matters and their molar mass; and 2) the dependences of the time of beginning of the combustion (ignition) of primary cloud of organic matters vapors and the final combustion time of the primary cloud of organic matters vapors on the number of carbon atoms in the carbon frame of the organic matters and their partial vapor pressures. The practical aspect of using the results obtained is dictated by the need to develop standard samples of amplitude-time and amplitude-frequency characteristics, depending on the physicochemical and combustible properties of the organic matters. This is necessary for the data bank of the acoustic emission monitoring system to establish a fire hazardous state and make anti-crisis decisions at critical infrastructure facilities.

Analysis of vibration characteristics of face gear powering-split transmission system

A nonlinear dynamic model of the face gear powering-split transmission system was established, and the nonlinear dynamic characteristics of the face gear powering-split transmission system were studied by considering various factors such as support stiffness, time-varying meshing stiffness, lateral clearance of teeth, comprehensive transmission error and bearing stiffness. The Runge–Kutta integral method is used to solve the differential dynamics of the system. The nonlinear behavior of the system is described by the phase plane diagram, time history diagram, frequency domain diagram, and Poincare section diagram. The influence of external excitation frequency on the nonlinear behavior of the system is described by the bifurcation diagram. In addition, the multi-scale method is used to analyze the superharmonic resonance of the system and determine the stability conditions of the superharmonic resonance of the system. The influence of meshing damping, time-varying meshing stiffness, and time-delay control parameters on the amplitude-frequency characteristics of the system is studied by numerical analysis of the superharmonic resonance. The results show that the system will show periodic chaotic alternating motion characteristics under external excitation. Selecting meshing damping, meshing stiffness, and time delay control parameters in a reasonable range can effectively reduce the superharmonic co-amplitude and keep the system in a stable state.

A DFT-Based Method for Extraction Effective High Density Electromagnetic Signal from Pseudo-random Code

Pseudo-random signal, also known as pseudo-random code, which has statistical properties similar to random signal and can be repeatedly generated, so it is widely used in the field of signal transmission. Pseudo-random code is used as the carrier of an improved high-density electromagnetic system to improve the reliability and stability of the measurement. However, how to effectively extract the effective signal in the pseudo-random code is very important.In this paper, a method based on Discrete Fourier Transform (DFT) is proposed to extract effective signal from pseudo-random code. By analyzing the amplitude-frequency characteristics of the discrete spectrum of pseudo-random code, the search range of frequency bands can be narrowed. Find the maximum of a one-dimensional array to obtain the best estimate of the target frequency and its magnitude in the limited range of frequency bands. Simulation experiments and measured data show that the frequency data extracted by the method in this paper is highly consistent with the preset frequency, with little amplitude loss and less alias. Therefore, the method can extract the response information of the specified frequency contained in the pseudo-random code effectively with high efficiency.

Dynamic Response of Layered Media to Impact Loading (on the Example of Highways)

Introduction. The main way to assess the load-bearing capacity of road structures (which are layered media consisting of materials of different stiffness) is through impact testing. The analysis of the results of these tests is reduced to the consideration of only peak values of vertical displacements without taking into account the change of these parameters in the frequency and time range. At the same time, it is the study of amplitude-frequency characteristics of displacements that can allow solving a number of urgent problems related, for example, to bringing the actual values of vertical displacements to the values under the design modes of operation of the structure.The purpose of the study is to analyze the dynamic response of layered media (road structures) of automobile roads to impact loading, aimed at bringing the actual parameters of the dynamic response to the design values regulated by the requirements of domestic regulatory documents on road design.Materials and Methods. Modern shock loading facilities allow to reproduce the load with a pulse time of 0.03 s, while the design values of elastic moduli are calculated for 0.1 s. To overcome this contradiction, the authors realized an exact solution of the dynamic Lame equation for a multilayered half-space and constructed a series of amplitude-frequency characteristics of displacements, from the processing of which a simplified functional dependence was derived.Results. The methodology of construction of amplitude-frequency characteristics of displacements on the surface of road pavement under impact impact has been developed, which finds its practical application. On the basis of the exact solution of the dynamic Lame equation by means of statistical processing, a simplified regression dependence for vertical displacements is established. An example of calculation of the elastic moduli of the road structure layers taking into account their reduction depending on the time of load application is presented.Discussion and Conclusion. Within the framework of the study, for the first time, a methodology for bringing the actual values of vertical displacements to the values under the design modes of operation of a road structure, based entirely on the computational analysis of its dynamic VAT, in particular, the amplitude-frequency characteristic of deformation under unsteady impact, has been obtained. The developed approach is able to significantly increase the reliability of diagnostics of highway condition, as well as to ensure the unity of measurements and results obtained during the design and diagnostics of roads.

Electromechanical coupling dynamics for a novel non-resonant harmonic piezoelectric motor

Most of the traditional piezoelectric motors are driven by the resonance of piezoelectric ceramics and can achieve a large output torque. However, these motors also have the defects of high speed and difficulty to adjusting the speed when working. To overcome these issues, a novel non-resonant harmonic rotary piezoelectric motor operating at low speed is presented. Electromechanically coupled vibration has a great influence on the dynamic performance of the piezoelectric motor, which may lead to instability of the output performance of the motor. Therefore, the electromechanical coupling dynamic characteristics of the proposed non-resonant piezoelectric motor are studied in this paper. The working principle of the motor is illustrated, and the electromechanical dynamic model and nonlinear dynamic equations are established. Utilizing the dynamic equations, the coupled natural frequencies, amplitude-frequency characteristics, and dynamic responses of the motor are developed. Meanwhile, the influence of parameters on natural frequency and nonlinear response is analyzed. What's more, the natural frequencies of the system are tested by building an experimental platform. Results show the minimum coupled natural frequency of the motor is 11231 rad/s. The length of the piezoelectric stack, the length, and mass block of the harmonic rod have an important influence on the natural frequency of the proposed non-resonant harmonic piezoelectric motor. The nonlinear piezoelectric effect has a larger effect on the forced response amplitude when the excitation frequency is far away from resonance, but a smaller effect on the forced response amplitude when the excitation frequency is near resonance. What's more, the maximum error between the theoretical natural frequencies and the test frequencies is 3%, which verifies the correctness of the theoretical model.

Method of creation a digital twin of a vibration protection process

Various approaches to building digital twins are considered. The data-based approach has a big disadvantage due to need of the huge amount of information. The system-based ap-proach can not be used in some cases due to the lack of a mathematically justified method. One of such cases is a ball vibration absorber but they can be really useful for the vibration protection of high-rise flexible objects. The purpose of the research is to develop an algorithmic method of creating digital twins of the vibration protection process, which will provide the possibility of determining the optimal control parameters of the ball vibration absorber. The paper examines small steady oscillations of the dynamic system "supporting body - ball vibration absorber". Under the condition of small forced oscillations, the equation of the amplitude-frequency characteristic of the linear anti-vibration system was obtained. In view of the use in construction, the input and output parameters of the method of building a digital twin of a flexible structure were described and analyzed, as well as the methods of obtaining them. As a result of the evaluation of the speed of the method, a modification of the search way for the optimal parameters of the digital twin was proposed. The comparative analysis showed the high efficiency of the proposed anti-vibration sys-tem with optimally adjusted parameters of the digital twin. The proposed method allows to reduce the maximum value of the amplitude by approximately four times. Modifications of the method made it possible to speed it up by an average of three times, reduce the load on the processor and handle cases when finding the optimal parameters of a digital twin is a rather difficult analytical problem. The input and output parameters of the method and ways of obtaining them were de-scribed and analyzed. A comparative numerical analysis showed the high efficiency of the functioning of such a vibration protection system with optimally adjusted parameters of the ball vibration absorber.

A Frequency-Weighting Digital Filter in Sound Level Meter Based on Neural Computing Method

Frequency weighting networks are a critical component of a sound level meter (SLM), and their error characteristics directly determine the performances of SLM. For reducing the high-frequency error of the [Formula: see text] frequency-weighting filters with the bilinear transformation method (BTM), a design method for [Formula: see text] frequency-weighting filters based on neural computing method (NCM) is proposed. A detailed algorithm for solving the filter coefficients is provided, and the amplitude-frequency characteristics of the [Formula: see text] frequency-weighting filters with BTM and NCM are compared in detail. The experimental results show that the amplitude-frequency characteristics of the [Formula: see text] frequency-weighting filters in SLM with NCM are significantly better than those of BTM. The filter meets the requirements of the first class SLM defined by IEC61672, which demonstrates the effectiveness of this proposed method.

Development of the theory of root crop head cleaner movement in the longitudinal-vertical plane mounted behind a wheeled tractor

The relevance of developing analytical methods for studying the stability of root crop cleaners on tractors is determined by the need to improve the efficiency and quality of root crop head cleaning, as this affects the quality of the final product and its marketable properties. The research aims to increase the stability of the cleaner movement by constructing a mathematical model of its oscillatory motion in the longitudinal-vertical plane and its numerical solution to determine the influence of parameters in response to external disturbances. To achieve this goal, a new theory of the movement of a root crop head cleaner in the longitudinal-vertical plane, mounted behind a wheeled tractor, under the influence of the disturbing effect of irregularities in the longitudinal profile of the soil surface on the amplitude and phase frequency characteristics of its angular oscillations was developed. Using numerical calculations carried out on a personal computer, the conditions were found under which the stability of the cleaner’s movement in the specified plane will increase when the stiffness coefficient of the pneumatic tyres of the doubler wheels is 315 kN×m–1. This result is achieved when the pressure in the pneumatic wheel tyres is 135 kPa. As for the damping characteristics of the doubler wheel tyres, which are determined by the coefficient μ, it was found that when it changes from 350 N×s×m–1 to 1350 N×s×m–1, there is an invariance of the delay in the reaction of the cleaner to the disturbing effect when its frequencies change from 0 to 24 s–1. It was also found that the influence of the geometric dimensions of the cleaner is insignificant in the range of frequencies of oscillations of the ordinates of the longitudinal profile of soil surface irregularities from 0 to 24 s–1. This follows from the nature of changes in the obtained amplitude-frequency and phase-frequency characteristics. The methodology for constructing a mathematical model of the plane-parallel oscillatory motion of the cleaner can be used in similar analytical studies of other agricultural machines mounted on a wheeled aggregating tractor

Вторичный магнитоупругий резонанс в структуре: тонкая магнитная пленка – толстая упругая подложка

The task about excitation of connected magnetic and elastic vibrations in flat-parallel structure consisted of normal magnetized thin magnetic film applied on thick nonmagnetic substrate is considered. As a result of estimated task solution the amplitude-frequency characteristics of magnetic and elastic vibrations are found. It is shown that in conditions when the ferromagnetic resonance frequency is higher then own elastic vibration of the structure on the amplitude-frequency characteristics of magnetic vibrations applied the equidistance net of elastic resonances of structure. For the interpretation of observed resonance net it is proposed the model of phase synchronization between initial excitation and elastic wave which experience two passages along the thickness of structure. It is shown that the frequency of maximum elastic vibrations rounding exceeds frequency of maximum magnetization characteristic. The existence of own rounding elastic vibrations characteristic is named the second elastic system resonance. It is investigated the dependence of maximum second resonance characteristic from value of magnetoelastic interaction constant. It is shown that by increasing of this constant the frequency distance between both characteristic maxima increases. As a hypothesis of this increasing it is proposed the analogy with splitting of amplitude-frequency characteristic of system consisted of two connected resonators. It is investigated the amplitude-frequency characteristics magnetic and elastic vibrations in wide frequency region. On the equidistance elastic resonances net amplitude-frequency characteristic it is found the narrow equidistance disposed resonance depressions which are correspond to decreasing of amplitude more then two orders of value. It is shown that the frequency interval between neighbouring depressions is back proportional to distance between point of elastic vibrations registration and surface of substrate opposite to magnetic film. For the interpretation of depressions formation it is proposed the model which takes into account the phase opposition in registration point between wave which goes out of the excitation point and wave which is reflected from the opposite end of structure. Briefly noted some physical analogies of investigated phenomena.

Amplitude-Frequency Characteristics and Stability Regions of a Two-Layer Liquid Under Angular Vibrations of a Solid Body

The article considers the problem of nonlinear oscillations of the motion of liquids completely filling an axisymmetric cylindrical vessel moving around a horizontal axis \(O{\kern 1pt} *{\kern 1pt} Y\). The motion of each fluid is assumed to be potential and formulated in a cylindrical coordinate system. The influence of nonlinear coefficients on the characteristics of dynamic processes during finite rotational movements of the vessel is estimated and the case of forced angular oscillations of a vessel with liquids relative to a fixed axis is considered. The main nonlinear effects associated with the rotation of the diameter of the interface of liquids are also revealed. An approximate solution of the obtained non-linear equations, found by the Bubnov-Galerkin method, was used in the article. As a result of the transformation, the amplitude-frequency characteristics and stability regions of a two-layer liquid are constructed under forced angular oscillations of a round cylindrical vessel.

Упругие резонансы в структуре: тонкая магнитная пленка – толстая упругая подложка

The task about excitation of connected magnetic and elastic vibrations in flat-parallel-structure consisted of thin magnetic film applied on thick nonmagnetic substrate is considered. For the solution of this task the model of propagation periodic boundary regime is proposed. This solution allowed to build the amplitude-frequency characteristics of magnetic and elastic vibrations. In this case the characteristic of magnetic vibrations has the view as wide bell-like maximum on which is put by equidistance net of narrow elastic resonances which divided one to another on the frequency elastic resonance along the substrate thickness. It is executed the model presentation of superposition elastic resonances on magnetic using the system of two connected oscillators which frequencies differs in some orders. It is supposed the mechanism of superposition elastic resonances on magnetic characteristic which consist of coincidence wave phase after two-path wave passage through the substrate thickness and phase of initial excitation. It is investigated the influence of elastic wave dissipation on the structure of amplitude-frequency characteristics of magnetization and elastic displacement. It is found the critical value of elastic dissipation parameter. It is shown that below of this value the elastic vibrations have resonance character and higher become non-periodical. It is found the inversion value of dissipation parameter which determined the transition from symmetrical distribution of elastic resonances on magnetic characteristic to anti-symmetrical. It is shown that the inversion value of dissipation parameter more (on two-three orders) smaller that critical value. It is found the phenomenon of second elastic resonance which is consist of exceeding frequency maximum rounding of elastic resonance net over the frequency of maximum magnetization characteristic. It is found the connected with dissipation second resonance splitting which take place near the neighbouring of inversion value dissipation parameter.

CONFIGURATIONS OF ULTRASONIC EMITTER RESONANCE MODES FOR UNILATERAL ACCESS TO AN OBJECT

Link for citation: Azin A.V., Bogdanov E.P., Vasilyev A.V., Ponomarev S.A., Ponomarev S.V., Rikkonen S.V. Configurations of ultrasonic emitter resonance modes for unilateral access to an object. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 199-209. In Rus. Relevance. To prepare high-viscosity oil for transport, a number of methods are used in practice: thermal, chemical and the method of physical influences. Ultrasonic exposure of hydrocarbon raw materials is one of the physical methods. It is necessary to develop an effective method for tuning an ultrasonic emitter for maximum energy transfer into a multilayer technological medium. Aim: to study resonant operating modes of an ultrasonic emitter in a multilayer system with unilateral access to the object with simplified design of a resonance type ultrasonic emitter. Objects: oscillating system of an ultrasonic resonant type emitter, multilayer system, physical model of a system «ultrasonic emitter – multilayer system». Methods: mathematical modeling of linear oscillating system to determine the properties of oscillating system influence and technological factors on the form of vibration oscillations and on the amplitude-frequency characteristics of the system; experimental research on the basis of the physical model «ultrasonic emitter – multilayer system». Results. The authors have revealed a physical feature of the oscillatory system operation, which consists in the fact that at resonance the form of oscillations of the force signals of a multilayer piezoactor and vibration acceleration signals are purely harmonic in nature. This effect extends to operation of a resonant-type ultrasonic emitter in a short-circuit mode on a multilayer system. It was found that force and vibration acceleration amplitude-frequency characteristics of a multilayer piezoactor are similar to each other. Based on the analysis of theoretical and experimental data, the authors developed the method for adjusting the resonant operating modes of an ultrasonic emitter with unilateral access to an object. This allows simplification and reduction in the emitter design cost. The method for setting up oscillatory systems is applicable for laboratory and industrial installations. Conclusion. The research results show that in practice, harmonic shape of acceleration and force signals, as well as force amplitude of a multilayer piezoactor can be used as criteria for determining and adjusting the resonance of an oscillatory system. The oscillatory system of a resonant-type ultrasonic emitter can be tuned to resonance according to the shape and amplitude of the signal from the force sensor of the multilayer piezoactor. The force sensor is located in series with the multilayer piezoactor and does not require additional structural elements for its fastening. The ultrasonic emitter design is greatly simplified due to the absence of a vibration acceleration sensor. The method of adjusting the resonance of an oscillatory system using only a force sensor is also applied when operating a resonant-type ultrasonic emitter to a multilayer mechanical system. The developed design and technique for tuning the oscillatory system of a resonant-type ultrasonic emitter can be conveniently used when influencing process fluids through the walls of tanks and storage tanks.

Manifestations of catastrophic Turkish earthquakes February 6, 2023 in Kryvbas

We analyzed the impact of powerful Turkish earthquakes that occurred on February 6, 2023, including a magnitude 7.8 Mw earthquake at 01:17:36 (UTC) in Kahramanmarash—Gaziantep, a magnitude 6.7/6.3 Mw earthquake at 01:28:21 (UTC), and a magnitude 7.5 Mw earthquake at 10:24:50 in Ekinoz—Kahramanmarash, on the territory of Ukraine, particularly in the city of Kryvyi Rih.The study involved the examination of algorithms for processing data recorded at seismic stations belonging to the S.I. Subbotin Institute of Geophysics of the National Academy of Sciences of Ukraine and the Main Center for Special Control of t he State Space Agency of Ukraine. The analysis of digital records from these Turkish earthquakes provided ground shaking intensity parameters at the recording points: Odesa and KryvyiRih had intensity levels below 3, Kremenchuk recorded 2, and Poltava and Kyiv registered 1. The resulting isoseismal map illustrates that the attenuation of wave intensity from the Turkish earthquakes depended on the geotectonic structure of the Ukrainian territory through which the seismic vibrations propagated.
 The monitoring of the water level in a deep well recorded changes in geodynamic (hydrodeformation) processes following the powerful Turkish earthquakes on February 6, 2023. We found the level of fault-fracture groundwater in the territory of Kryvbaswas affected bythe earthquakes. The calculation of the propagation velocity in the upper part of the lithosphere of the rock deformation front showed a value of ≈19.0 km/min (0.5 km/min).Concurrently, a decrease in the groundwater level by 2—3 cm was recorded, making it possible to conclude that after the earthquake, short-period stretchings of the earth’s crust occurred, both in the zone of the Kryvyi Rih—Kremenchutsky fault and over the Ukrainian Shield, in in general.
 The calculated amplitude-frequency characteristics for the geological environment on the territory of Kryvyi Rih revealed that the maximum acceleration of seismic vibrations on the free-soil surface increases relative to bedrock by about 4 times in the frequency range from 1.2 Hz to 1.75 Hz.

Nonlinear vibration characteristics and bifurcation control of a class of piecewise constrained systems with dynamic clearances

Considering the mass block system under Piecewise nonlinear constraint, the vibration dynamic model of the system is established according to the generalized dissipative Lagrange principle, and the average method is used to solve the amplitude-frequency response of the vibration system. The influence of system parameters on vibration characteristics is analyzed with amplitude-frequency characteristics, phase plane characteristics, frequency characteristics, bifurcation characteristics ,and so on. The results show that: 1) the reverse of the rate of change of Piecewise nonlinear elastic force will destroy the stability of the system and obtain the relationship of the constraint parameters that need to be satisfied when the system is stable at the piecewise critical point. 2) With the increase in the number of nonlinear constraints, the vibration displacement of the system tends to be chaotic, and the frequency composition becomes more complex and variable, prone to resonance behavior. 3) As the static gap decreases and the dynamic gap amplitude and frequency increase, the unstable frequency range of the system will increase, and the vibration behavior will become chaotic and difficult to predict. 4) The design of a differential sliding mode controller can effectively control the bifurcation behavior of the system.

Some features of taking damping into account in calculating harmonic oscillations of linear systems

The problem of calculating harmonic oscillations of a linear damped system with inhomogeneous damping is considered. Along with the solution available in literature, which 
 requires the inversion of the matrix that determines the eigenvalues of the undamped system, the authors propose a new solution that does not require the inversion of the above mentioned matrix, but requires the inversion of the system damping matrix. The cases of hysteretic, viscous and mixed damping are considered. It is shown that the known solution gives an error near the resonance. At the resonance point, the result is not defined at all, and near the resonance it may be incorrect. An example of building the amplitude-frequency characteristic of a system with two mass tuned dynamic dampers and three peaks in the amplitude-frequency characteristic is given. The proposed formulas for calculating displacements are convenient for constructing the amplitude-frequency characteristics of damped systems with viscous, hysteretic and mixed types of damping.

Sonar echo detection based on two-dimensional matched filtering and convolutional neural network

In underwater acoustics, the performance of sonar echo detection is limited when the echo-to-noise ratio or echo-to-reverberation ratio is low. As an attempt to improve the echo detection rate and maintain a low false alarm rate, a method based on two-dimensional matched filtering (2-D-MF) and convolutional neural network (CNN) is proposed. The 2-D-MF divides the replica signal into multiple sub-replicas, each with different frequency components, and utilizes the sub-replicas to perform the matched filtering individually, obtaining 2-D-MF features that better represent the amplitude-frequency characteristics of the echo signal. The CNN is utilized as an echo detector to extract echo information from the 2-D-MF features and determine the presence of an echo. The proposed method is tested using data collected in the South China Sea, 2021. During the experiment, a transducer transmitted linear frequency modulation (LFM) signals, and a transponder, acting as an analog target, forwarded the LFM signals as echoes. The detection results demonstrate that this method can improve the echo detection rate by approximately 7% while maintaining a constant false alarm rate of 1‰.

Using the stm32f407vg microcontroller to study the amplitude-frequency characteristics of biological tissues

The electrical properties of biological tissues of a plant origin are studied using the microcontroller STM32f407vg. The formulation of the problem of identifying informative signs of the viability of biological tissues when using the method of impedance measurement is given. It is shown that since currently in medical diagnostic practice there is no instrument base that would allow in an operational setting to diagnose the ability of biological tissue to self-heal after injury and damage as a result of thermal exposure, a gunshot wound or prolonged compression, the development of methods and means of instrumental diagnostics in this area of knowledge is an important modern task.
 The results of experimental measurements of impedance characteristics in the frequency range of 20 Hz – 2.0 MHz are presented. The frequency dependences of the stress modulus of a biological tissue of a plant origin are analyzed in its intact state, as well as after exposure of samples of a biological tissue in a freezer.
 A comparative analysis of the obtained frequency dependences is carried out. A significant difference between the frequency dependences of the stress modulus on a biological tissue and the frequency dependence of the stress modulus on an isotonic solution is shown. The idea was proposed that the degree of difference in the frequency distribution of the impedance module of the biological tissue from the impedance module of the isotonic solution can serve as a criterion for assessing the degree of damage to the biological tissue.