On the assessment of the potential for extracting information on defects in the main pipeline by the method of radar analysis of natural oscillation frequency

The paper deals with the issue of diagnostics of main pipelines by the vibration method, exploring the influence of the formation of cracks in the walls of the pipeline on the change in the frequency characteristics of the pipeline. By analyzing the difference in the natural oscillation frequency of a pipe with a crack and without it, it is possible to assess the location of the defect with a certain accuracy. The issue of the possibility of reading the natural oscillations of the main pipeline from the surface of the soil located above the pipeline is also being studied.

Approximate Calculation of the Natural Oscillation Frequency of the Vibrating Table in Inter-Resonance Operation Mode

The first natural frequency of oscillations of the vibrations of a discrete-continuous interresonant vibrating table plate was found using the functions of the Krylov-Duncan. The continuous member, presented in a plate hinged at four points, is used as a reactive mass with distributed parameters to create an inter-resonance vibrating table with an electromagnetic drive. For this purpose, the plate was considered as a rod on hinged supports. The justification of this approach is confirmed by simulation in the Ansys software. The results were confirmed using the approximate Rayleigh-Ritz method. The geometric shape of the plate is reduced to a section of a hyperboloidal surface. The results of simulation of the first natural frequency were verified experimentally.

Analysis of the natural oscillation frequency of the long-span trusses with flanged connections

Приводится анализ частоты собственных колебаний большепролетной фермы с фланцевыми соединениями. Выполнен расчет фланцевого соединения с различными случаями исключения болтов из работы соединения. Анализ результата расчета показал, что возникновение повреждений и дефектов конструкций здания в локальных зонах, величина которых несущественно снижает общую жесткость каркаса, практически не влияет на динамические характеристики каркаса. The analysis of the natural vibration frequency of a large-span truss with flanged connections is given. The calculation of the flange connection with various cases of exclusion of bolts from the connection operation is performed. Analysis of the calculation results showed that the occurrence of damage and defects in the building structures in local areas, the value of which significantly reduces the overall rigidity of the frame, practically does not affect the dynamic characteristics of the frame.

EXPERIMENTAL INVESTIGATION OF TRANSITIONAL PROCESSES OF THE INERTIVE DRIVE VIBRATION MACHINE

Purpose: to study the transients in the vibrating machine that accompany the start from rest and run out.The studies were performed on a laboratory vibrating screen. The screen is driven by an adjustable drive - a single-shaft inertial vibrator, which has imbalances with variable mass. The screen has a resonant setting, ie h natural oscillation frequency is less than the frequency of the forcing force of the drive.The GY-521 module with the MPU6050 chip is used to measure the kinematic characteristics. This module allows you to measure linear acceleration and angular velocity.The graphs show typical graphs of changes in the acceleration points of the vibrating screen box at full cycle: from start to complete stop.The graphs show the run-out (stop) areas of the screen. There is an increase in the amplitude of the oscillation of the acceleration of the screen box during the passage of the resonant frequency. This phenomenon is characteristic of the vibrating machine with a resonant setting.

Experimental study of a lock-in phenomenon in the case of a mechanical oscillator flowmeter

Oscillatory flowmeters are susceptible to pulsatile flow and mechanical oscillator flowmeters are no exception. The experimental study was conducted to determine possible measurement errors for specific pulsation amplitude thresholds. The study verified that no frequency lock-in takes place for pulsation frequencies which are subharmonics of the natural oscillation frequency, nor for harmonics higher than the 2nd.

A Two-Mass Gyro-Particle as a Tool for Supersonic Aeroelasticity Analysis

When a flying vehicle reaches a high supersonic speed, plasma occurs in the flow, hampering the application of the traditional piston theory and its modifications to solve the aeroelasticity problem. This work considers flow modelling using a system of two-mass gas gyro-particles capable of dividing into two charges and ionizing the flow. The two-mass gas gyro-particle has two elements and two pairs of multiple frequencies. As the gyro-particle interacts with the surface of an elastic body, it starts to rotate and pulsate, and the multiple frequencies split. As the pulsation frequency of the gas gyro-particle reaches the natural oscillation frequency of the elastic structure, resonance occurs and the structure flutters. It is assumed that the supersonic character of the flow is determined not by the velocity of the flying vehicle, but by the rotational frequency of the gas gyro-particle. The higher the particle’s rotational frequency, the higher the aerodynamic drag. If the rotational frequency is high enough, then the screening effect takes place: the vehicle decelerates and turns upside down. This is called divergence, and the plasma is not taken into account. In this work, a 2D model is used to interpret the flutter and the divergence effects.

INFLUENCING OF THIN PROTECTIVE COATINGS ON NATURAL FREQUENCIES OF RADIAL OSCILLATIONS OF CLADDINGS OF FUEL RODS OF NUCLEAR REACTORS

The natural frequencies and the modes of the radial oscillations are computed by using the method of grids for the cylindrical claddings made with the thin protective coatings for the fuel rods of the nuclear reactors. It is received the values more than 150 kHz for first natural frequencies of the radial oscillations of the claddings of fuel rods of the WWER-1000 nuclear reactors. It is shown that the thin protective coatings lead to noticeable increasing of first natural oscillation frequency, but have negligible influencing on the second and higher natural frequencies as well as on the modes of the radial oscillations of the claddings of fuel rods.

Objective assessment of stiffness in the gastrocnemius muscle in patients with symptomatic Achilles tendons

ObjectivesTo establish quantitative values of stiffness for the gastrocnemius muscle in patients diagnosed with Achilles tendinopathy.DesignCase–control study with a single (cross sectional) time point of patients diagnosed with unilateral Achilles tendinopathy and an asymptomatic group.MethodsSample of 50 participants: 25 participants with symptomatic unilateral Achilles tendinopathy (symptomatic group) with the asymptomatic side of this group used as a control (control group 1). A third group of 25 participants with asymptomatic Achilles tendons (control group 2). Mechanical stiffness parameters, including natural oscillation frequency (F), dynamic stiffness (S), mechanical stress relaxation time (R), logarithmic decrement (D) and creep (C), were assessed using the MyotonPRO. Measurements at the medial and lateral gastrocnemii were taken as non-weight bearing (NWB) and weight bearing (WB).ResultsSignificant (p<0.05) differences were observed between the mean symptomatic group and control groups 1 and 2 in the WB and NWB conditions for natural oscillation frequency (F), dynamic stiffness (S), and creep (C). There was a significant reduction in S WB and conversely a significant increase in S of the symptomatic group NWB. Creep (C) and mechanical stress relaxation time (R) were significantly (p<0.05) less in the symptomatic group NWB. Significant differences were observed between the NWB and WB data sets for logarithmic decrement (D). NWB D demonstrated significantly (p<0.05) higher scores than the WB condition.ConclusionThis study demonstrated that there was a significant reduction in stiffness of the gastrocnemius muscle in participants with Achilles tendinopathy compared with the two control groups. The WB MyotonPRO measures for the symptomatic groups of F and S were significantly lower, indicating a decrease in the tonal properties (F) and dynamic stiffness (S) of the muscle. The application of MyotonPRO technology to measure changes in stiffness in the gastrocnemius muscle may be useful to measure as part of a rehabilitation programme where specific attention could be placed to increase the tonal properties of the muscle. Further studies are required to develop a robust clinical application of this technology, particularly with regard to Achilles tendinopathy.

Experience of diagnostics of engineering structures by the method of small impacts

The problems of diagnostics of engineering structures during their service life are considered. As one of the promising methods, the method of vibration diagnostics for changing dynamic parameters (natural frequencies and decrements of oscillations, amplitudes and forms of oscillations) was chosen. The results of various studies in the field of vibration diagnostics of bridge structures are analyzed. The results of the study of the influence of various damages on the dynamic parameters of structures using finite element models are presented. Summarized data of long-term studies of the Siberian transport University to evaluate the technical state of structures based on measurement of natural oscillation frequency. The limitation of the method of vibration diagnostics for lower forms of vibration is associated with low sensitivity and significant influence of various factors on the results. However, in some cases, vibration diagnostics of structures under excitation of oscillations by small pulse effects can be effective. Examples of vibrodiagnostics of the state of structures are given. Vibrodiagnostics is particularly relevant in the study of the actual dynamic work of pedestrian bridges. Regular fixation of «digital dynamic portraits» allows you to track changes in technical condition. It is advisable to use methods of vibration diagnostics and in assessing the effectiveness of strengthening structures. In conclusion, it is noted that using the methods considered, it is possible to organize a system of periodic or continuous automated monitoring of the technical condition of bridges. This is especially important to prevent sudden failures of technically complex and unique structures, as well as in the case of serious damage to the load-bearing structures.