Vibration Amplitude Research Articles

A Low-Frequency Vibration Sensor Based on Ball Triboelectric Nanogenerator for Marine Pipeline Condition Monitoring.

Marine pipeline vibration condition monitoring is a critical and challenging issue, on account of the complex marine environment, while powering the required monitoring sensors remains problematic. This study introduces a vibration sensor based on a ball triboelectric nanogenerator (B-TENG) for marine pipelines condition monitoring. The B-TENG consists of an acrylic cube, polyester rope, aluminum electrodes, and PTFE ball, which converts vibration signals into electrical signals without the need for an external energy supply. The experimental results show that B-TENG can accurately monitor the frequency, amplitude, and direction of vibration in the range of 1-5 Hz with a small error of 0.67%, 4.4%, and 5%, and an accuracy of 0.1 Hz, 0.97 V/mm, and 1.5°, respectively. The hermetically sealed B-TENG can monitor vibration in underwater environments. Therefore, the B-TENG can be used as a cost-effective, self-powered, highly accurate vibration sensor for marine pipeline monitoring.

Helicopter vibration control employing superelastic pitch link with shape memory alloy

One of the main applications of shape memory alloy (SMA) concerns vibration control, especially superelastic SMA (SMA-SE), which presents a significant stress hysteresis and can work as a damper while adding minimal weight to the structure. In helicopters, vibration is a phenomenon inherent to their operation, and although cannot be eliminated, must be minimized to acceptable levels of safety and comfort. In this context, this paper aims to present the design, testing, and dynamic behavior of a new device entitled smart pitch link, a device with superelastic material for passive vibration control. The paper depicts the design process, assembly, and device testing using a whirl tower that simulates a helicopter rotor in hover. The approach adopts a comparative analysis of the dynamic response on the prototype in reference condition, with a stiff pitch link, with the modified prototype, and with the superelastic pitch link installation. In addition, beyond hover tests, cyclic commands and an asymmetrical lateral gust were employed to observe the output response of the device under transient loadings. Contrary to the literature data about the low time response of SMA, the device presents satisfactory time response and attenuation in frequencies close to main rotor frequencies, with signal attenuations between 2 to 4 dB without any external energy consumption, which, in a comparative analysis, may exceed more than 50% of vibrational amplitude attenuation.

Comprehensive analysis of ultrasonically atomized 316L stainless steel powder using adjusted additive manufacturing suitability factor

This study focuses on the 316L stainless steel powder produced by using an innovative ultrasonic atomization (UA) method. The production process was optimized at electrical currents with 120 A and vibration amplitude with 80% proving the most effective for maximizing productivity. The study extensively evaluated particle size and shape, bulk and tapped densities, Hausner's ratio, and Carr index, finding the UA steel powder to possess high sphericity, minimal satellite particles, and excellent flowability, qualities crucial for additive manufacturing (AM). A new approach for calculating the additive manufacturing suitability factor was developed, incorporating custom weighting factors for rheological parameters to reduce the influence of parameters with high uncertainty or statistical insignificance, thus improving accuracy. When compared using this method, the UA powder demonstrated superiority over its commercial counterparts by approximately 1% and 10%, underscoring its promise for AM applications.

Harnessing flow-induced vibrations for energy harvesting: Experimental and numerical insights using piezoelectric transducer.

Flow-induced vibrations (FIV) were considered as unwanted vibrations analogous to noise. However, in a recent trend, the energy of these vibrations can be harvested and converted to electrical power. In this study, the potential of FIV as a source of renewable energy is highlighted through experimental and numerical analyses. The experimental study was conducted on an elastically mounted circular cylinder using helical and leaf springs in the wind tunnel. The Reynolds number (Re) varied between 2300-16000. The motion of the cylinder was restricted in all directions except the transverse direction. The micro-electromechanical system (MEMS) was mounted on the leaf spring to harvest the mechanical energy. Numerical simulations were also performed with SST k-ω turbulence model to supplement the experiments and were found to be in good agreement with the experimental results. The flow separation and vortex shedding induce aerodynamic forces in the cylinder causing it to vibrate. 2S vortex shedding pattern was observed in all of the cases in this study. The maximum dimensionless amplitude of vibration (A/D) obtained was 0.084 and 0.068 experimentally and numerically, respectively. The results showed that the region of interest is the lock-in region where maximum amplitude of vibration is observed and, therefore, the maximum power output. The piezoelectric voltage and power output were recorded for different reduced velocities (Ur = 1-10) at different resistance values in the circuit. It was observed that as the amplitude of oscillation of the cylinder increases, the voltage and power output of the MEMS increases due to high strain in piezoelectric transducer. The maximum output voltage of 0.6V was observed at Ur = 4.95 for an open circuit, i.e., for a circuit with the resistance value of infinity. As the resistance value reduced, a drop in voltage output was observed. Maximum power of 10.5μW was recorded at Ur = 4.95 for a circuit resistance of 100Ω.

A high-speed gear reshaping method for electric vehicles combining the effects of input torque and speed variation.

In this study, we introduce an optimization method for high-speed gear trimming in electric vehicles, focusing on variations in input torque and speed. This approach is designed to aid in vibration suppression in electric vehicle gears. We initially use Tooth Contact Analysis (TCA) and Loaded Tooth Contact Analysis (LTCA) to investigate meshing point localization, considering changes in gear tooth surface and deformations due to load. Based on impact mechanics theory, we then derive a formula for the maximum impact force. A 12-degree-of-freedom bending-torsion-axis coupled dynamic model for the helical gear drive in the gearbox's input stage is developed using the centralized mass method, allowing for an extensive examination of high-speed gear vibration characteristics. Through a genetic algorithm, we optimize the tooth profile and tooth flank parabolic modification coefficients, resulting in optimal vibration-suppressing tooth surfaces. Experimental results under various input torques and speeds demonstrate that the overall vibration amplitude is stable and lower than that of conventional gear shaping methods. Specifically, the root mean square of vibration acceleration along the meshing line under different conditions is 58.02 m/s2 and 20.33 m/s2, respectively. The vibration acceleration in the direction of the meshing line is 20.33 m/s2 and 20.02 m/s2 under varying torques and speeds, with 20.33 m/s2 being the lowest. Furthermore, the average magnitude of the meshing impact force is significantly reduced to 5015.2. This high-speed gear reshaping method not only enhances gear dynamics and reliability by considering changes in input torque and speed but also effectively reduces vibration in electric vehicle gear systems. The study provides valuable insights and methodologies for the design and optimization of electric vehicle gears, focusing on comprehensive improvement in dynamic performance.

Extraction and evaluation of cable forces of a cable-stayed bridge based on amplitude and phase estimation method

In order to identify the time-varying frequency and amplitude of structural vibration based on the bridge structural health monitoring data and obtain the cable force of cable-stayed bridges in real time, a spectrum analysis method based on amplitude and phase estimation (APES) was proposed in this study. The amplitude spectrum of the acceleration data is first calculated by the APES method, the real-time spectrogram of the cable is obtained by the sliding window method. Then the modal frequency and amplitude are automatically extracted from the real-time spectrum by using a frequency extrusion post-processing technique, which can be regarded as the average value of the instantaneous frequency and amplitude respectively. Next, the fundamental frequency of the cable is extracted by using an automatic identification method, and the performance of the proposed method is verified. Finally, real-time scoring of cable forces and structural condition assessment is achieved with consideration of the moderation index model as well as the material strength. The results show that the APES method can use shorter calculation samples than the traditional Fast Fourier Transform (FFT) to obtain higher resolution and more accurate amplitude, which provides a theoretical basis for the real-time identification of fundamental frequency based on short-term monitoring data. The frequency extrusion post-processing-algorithm can reduce the spectrum recognition delay and improve timeliness of the cable force evaluation. The time-varying cable force with an interval of 10 s can be used to reflect the health status of the cable in time. The research results can provide technical support for the real-time extraction of cable force of long-span cable-stayed bridges, and can also provide an effective basis for component condition evaluation and bridge maintenance decision-making.

Experimental Research Into Aeroelastic Phenomena in Turbine Rotor Blades Inside ARIAS EU Project

Abstract This paper describes an aeroelastic experimental campaign on a low-pressure turbine-bladed rotor in a rotating wind tunnel that took place as a part of the Advanced Research Into Aeromechanical Solutions (ARIAS) EU project. The campaign can be considered a continuation of the free-flutter test that was performed as part of the FUTURE EU project, where the saturation of asynchronous vibrations due to dry friction was characterized. This new campaign studied new aspects of the physics behind saturated flutter, including the non-linear interaction between synchronous excitation and asynchronous vibration, the effectiveness of different mistuning patterns to suppress flutter, and the viability of under-platform dampers as a technology to control the amplitude of asynchronous vibrations. Furthermore, the campaign explored various operation conditions for the turbine rotor, including near-stall. In general, there was a good agreement between the theoretical predictions regarding all these different aspects of turbine flutter and the test results.

Impacts of hot electron diffusion, electron–phonon coupling, and surface atoms on metal surface dynamics revealed by reflection ultrafast electron diffraction

Metals exhibit nonequilibrium electron and lattice subsystems at transient times following femtosecond laser excitation. In the past four decades, various optical spectroscopy and time-resolved diffraction methods have been used to study electron–phonon coupling and the effects of underlying dynamical processes. Here, we take advantage of the surface specificity of reflection ultrafast electron diffraction (UED) to examine the structural dynamics of photoexcited metal surfaces, which are apparently slower in recovery than predicted by thermal diffusion from the profile of absorbed energy. Fast diffusion of hot electrons is found to critically reduce surface excitation and affect the temporal dependence of the increased atomic motions on not only the ultrashort but also sub-nanosecond times. Whereas the two-temperature model with the accepted physical constants of platinum can reproduce the observed surface lattice dynamics, gold is found to exhibit appreciably larger-than-expected dynamic vibrational amplitudes of surface atoms while keeping the commonly used electron–phonon coupling constant. Such surface behavioral difference at transient times can be understood in the context of the different strengths of binding to surface atoms for the two metals. In addition, with the quantitative agreements between diffraction and theoretical results, we provide convincing evidence that surface structural dynamics can be reliably obtained by reflection UED even in the presence of laser-induced transient electric fields.

Light-Weighting and Comparative Simulation Analysis of the Forearm of Welding Robots

The light-weighting of a robotic arm is an important aspect of robot research. In the operation of existing welding robots, excessive vibrations in the welding actuators have been observed, which lead to reduced welding precision and work efficiency. The direct connection between the forearm and the welding actuator is a key component that affects vibrations. Based on this, a study on light-weighting the forearm is proposed. Using the theory of topology optimization with variable density structure, the structural dimensions, shapes, and geometric parameters of the forearm are optimized. The material removal methods of “hole cutting” and “local hollowing” are employed to reconstruct the forearm structure model. Static, modal, and transient simulations were performed on the forearm model pre-optimization and post-optimization. The optimization results show that the mass of the forearm is reduced by 19.8%. The static simulation comparative analysis shows that, under the same constraints and load conditions, the maximum total deformation of the optimized forearm is reduced by 3.6%, the maximum stress is reduced by 3.2%, and the maximum equivalent elastic strain is reduced by 5.7%. The optimized forearm structure is more reasonable and exhibits better mechanical performance. Modal simulation comparative analysis shows that the first and second natural frequencies of the optimized forearm are increased by 9.8% and 7.0%, respectively. Transient simulation comparative analysis demonstrates that, under the maximum operating condition, the vibration frequency and amplitude of the optimized welding robot forearm are reduced by 19.4% and 26.9%, respectively. The maximum amplitudes of the maximum equivalent stress curve and maximum equivalent elastic strain curve are reduced by 51.0% and 46.0%, respectively. This study provides a guarantee for reducing vibrations in welding actuators, improving welding precision, and enhancing the work efficiency of the welding robot.

Dynamics and Wake Interference Mechanism of Long Flexible Circular Cylinders in Side-by-Side Arrangements

The vortex-induced vibrations of two side-by-side flexible cylinders in a uniform flow were studied using a three-dimensional direct numerical simulation at Reynolds number Re = 350 with an aspect ratio of 100, and a center-to-center spacing ratio of 2.5. A mixture of standing-traveling wave pattern was induced in the in-line (IL) vibration, while the cross-flow (CF) vibration displayed a standing-wave characteristic. The ninth vibration mode prominently occurred in both IL and CF directions, along with competition between multiple modes. Proximity effects from the neighboring cylinder caused the primary frequency to be consistent between IL and CF vibrations for each cylinder, deviating from the IL to CF ratio of 2:1 in isolated cylinder conditions. Repulsive mean lift coefficients were observed in both stationary and vibrating conditions for the two cylinders due to asymmetrical vortex shedding in this small gap. Comparatively, lift and drag coefficients were notably increased in the vibrating condition, albeit with a lower vortex shedding frequency. Positive energy transfer was predominantly excited along the span via vortex shedding from the cylinder itself and the neighboring one, leading to increasing lower-mode vibration amplitudes. The flip-flopping (FF) wake pattern was excited in the stationary and vibrating cylinders, causing spanwise vortex dislocations and wake transition over time, with the FF pattern being more regular in the stationary cylinder case.

Numerical Investigation of the Excitation Characteristics of Contaminated Nozzle Rings

The deposition of combustion residues in the nozzle ring (NR) of a turbocharger turbine stage changes the NR geometry significantly in a random manner. The resultant complex and highly asymmetric geometry induces low engine order (LEO) excitation, which may lead to resonance excitation of rotor blades and high cycle fatigue (HCF) failure. Therefore, a suitable prediction workflow is of great importance for the design and validation phases. The prediction of LEO excitation is, however, computationally expensive as high-fidelity, full annulus CFD models are required. Previous investigations showed that a steady-state computational model consisting of the volute, the NR, and a radial extension is suitable to reduce the computational costs massively and to qualitatively predict the level of LEO forced response. In the current paper, the aerodynamic excitation of 69 real contaminated NRs is analyzed using this simplified approach. The results obtained by the simplified simulation model are used to select 13 contaminated NR geometries, which are then simulated with a model of the entire turbine stage, including the rotor, in a transient time-marching manner to provide high-fidelity simulation results for the verification of the simplified approach. Furthermore, two contamination patterns are analyzed in a more detailed manner regarding their aerodynamic excitation. It is found that the simplified model can be used to identify and classify contamination patterns that lead to high blade vibration amplitudes. In cases where transient effects occurring in the rotor alter the harmonic pressure field significantly, the ability of the simplified approach to predict the LEO excitation is not sufficient.

Extraction of high activity bacterial urease and its application to biomineralization of soil

Biomineralization based on bacterial enzyme induced carbonate precipitation (BEICP) process is a promising alternative to cement-based ground treatment technology. The bacterial urease used in BEICP process is usually ultrasonic extracted from urease-producing bacteria. To efficiently extract urease with relatively higher activity from bacterial cells, the ultrasonic extraction parameters of urease were optimized in this study. Next, a series of bacterial urease extraction tests and sand column treatment tests were conducted to investigate the effects of vibration amplitude, upper temperature limit, and cooling method on the urease extraction process and biomineralization of sand. The results show that the upper temperature limit is an important factor affecting the extraction efficiency and the activity of the extracted urease solution, and the optimum upper temperature limit is 50 °C. The results indicate that increasing vibration amplitude could improve the extraction efficiency, but it hardly affects the urease activity (UA) under the optimal temperature. Continuous cooling could effectively simplify the operation and further improve the efficiency of urease extraction. Under the same urease activity of biotreatment solution, there is no marked difference in calcium carbonate content (CCC) and unconfined compressive strength of biomineralized sand columns prepared by urease solution extracted with different vibration amplitudes and upper temperature limits. The results of this study could provide a reference for application of BEICP technology of urease extraction to large-scale soil treatment.

Machinability of elliptical ultrasonic vibration milling γ-TiAl: Chip formation, edge breakage, and subsurface layer deformation

Superior strength and high-temperature performance make γ-TiAl vital for lightweight aero-engines. However, its inherent brittleness poses machining problems. This study employed Elliptical Ultrasonic Vibration Milling (EUVM) to address these problems. Considering the influence of machining parameters on vibration patterns of EUVM, a separation time model was established to analyze the vibration evolutionary process, thereby instructing the cutting mechanism. On this basis, deep discussions regarding chip formation, cutting force, edge breakage, and subsurface layer deformation were conducted for EUVM and Conventional Milling (CM). Chip morphology showed the chip formation was rooted in the periodic brittle fracture. Local dimples proved that the thermal effect of high-speed cutting improved the plasticity of γ-TiAl. EUVM achieved a maximum 18.17% reduction in cutting force compared with CM. The force variation mechanism differed with changes in the cutting speed or the vibration amplitude, and its correlation with thermal softening, strain hardening, and vibratory cutting effects was analyzed. EUVM attained desirable edge breakage by achieving smaller fracture lengths. The fracture mechanisms of different phases were distinct, causing a surge in edge fracture size of γ-TiAl under microstructural differences. In terms of subsurface deformation, EUVM also showed strengthening effects. Noteworthy, the lamellar deformation patterns under the cutting removal state differed from the quasi-static, which was categorized by the orientation angles. Additionally, the electron backscattering diffraction provided details of the influence of microstructural difference on the orientation and the deformation of grains in the subsurface layer. The results demonstrate that EUVM is a promising machining method for γ-TiAl and guide further research and development of EUVM γ-TiAl.

Splitter-plate proximity-induced transitions in flow-induced vibration of a triangular prism

The effect of a splitter-plate downstream of an elastically mounted equilateral triangular prism on flow-induced vibration is numerically investigated at Reynolds number Re = 100, mass ratio m* = 10, damping ratio ζ = 0.005, cylinder-plate gap G* = 0.3, and various angle of attacks α = 0°–60°. The α = 0° and 60° correspond to vertex and edge of the cylinder facing the free stream. Under the effect of the splitter plate, a single transition from vortex-induced vibration (VIV) to proximity-induced galloping (PIG) in the vibrational response for an axisymmetric circular cylinder is reported, whereas, for the present non-axisymmetric triangular prisms, the varying α exhibits four proximity-induced transitions: VIV to modified VIV at smaller α = 0° and 25°, VIV to PIG at α = 35°, distinct VIV-galloping to combined PIG-galloping at α = 40°, and asymmetric to symmetric-galloping at larger α = 60°. The plate results in more symmetric vibration for high α ≥ 35°, while a reduction is observed for α ≤ 25°. The gap-flow leads to onset (α = 35°) and enhancement (α = 40°) of afterbody re-attachment on the prism, which significantly enhances the galloping instability and vibrational amplitude. A reduction in galloping instability leading to a slight reduction in amplitude is found for α = 60° prism. The study shows that the presence of the splitter-plate downstream influences near-wake structure and far-wake vortex shedding modes, which lead to stabilizing and destabilizing near-wake flow and distinct vibrational characteristics—depending on the angle of attack (α).

Effect of runner radial installation deviation on the flow characteristics of the 1000MW turbine

Abstract The flow simulation of a hydraulic turbine is not limited to calculations and analyses under ideal conditions and simplified models, but it should also consider the existence of radial installation deviations in actual operating conditions and their influence on the flow of the turbine. Therefore, this study focuses on a 1000MW unit and analyzes the internal flow characteristics under actual operating conditions while considering the radial installation deviations of the turbine wheel. The results show that the absolute value of pressure increases with the increase of radial deviation, but the difference value remains almost constant. And it also indicates that the magnitude of the radial forces increases with the increase in radial installation deviations. There are two linear relationship curves, one before 0.5mm and one after 0.5mm, with the latter growing at a faster rate. Furthermore, taking the crown as an example, the influence of the wall velocity-generated dynamic pressure on the clearance is different. Lastly, considering the magnitude of the combined forces and vibration amplitude, the crown is the most critical part that should be given attention. The research findings can guide the high-quality installation of 1000MW units during major overhauls and provide valuable technical references for similar units. The research outcomes can also guide the initial installation and major overhaul stages of 1000MW units and offer beneficial technical references for other similar units.

Design and Testing of 3D Textile Materials with Vibro-Insulating Properties, Applicable in the Construction of Vibroisolating Seats for Machine and Device Operators

Abstract In this article, the author describes the problem with low frequency vibrations in the range of 0–100 Hz and how exposure to these vibrations could affect human health when working in dangerous environments. For this research, vibrations in the range of 0–30 Hz were studied as this frequency range has the largest impact on human health and such vibrations usually occur when operating excavators, forklifts or Melex vehicles. Workers who are exposed to these vibrations usually work in a seated position for many hours. Over time, exposure to dangerous vibrations in the working environment will cause damage to the human spine, resulting in a great deal of discomfort for the worker. In order to alleviate the pain, the worker will tend to shift their seating position away from the correct position, which further compounds the issue. The author proposes the use of a 3D knitted seat mat in order to reduce the amplitude of any harmful vibrations. This will provide better ergonomic conditions for the user and will reduce the effects of low frequency vibrations.

Nonlinear dynamic behavior of single-layered black phosphorus with an attached mass

The investigation of black phosphorus-based (BP)-based mass sensors provides theoretical support for the development of mass-detection devices. This study examines the non-linear dynamic behavior of a rectangular single-layered BP (SLBP) with an attached mass through the utilization of molecular dynamics (MD) simulations and a nonlinear orthotropic plate model (NOPM) with a concentrated mass. The results indicate that significant deformation of an SLBP with an attached mass necessitates consideration of geometric nonlinearity, although the attached mass does not affect the deformation. Additionally, this paper discusses the impact of the attachment mass and the amplitude of harmonic force on the non-linear forced vibration of the SLBP. It is observed that as the attachment mass increases, the nonlinear vibration resonance frequency decreases, while the peak amplitude increases. Furthermore, the thermal nonlinear vibration of SLBP with an attached mass has been investigated, revealing that an increase in the attached mass leads to a decrease in the nonlinear vibration frequency but an increase in the amplitude of the nonlinear vibration of SLBP with an attached mass. Overall, comparison with MD simulation results, this investigation suggests that NOPM with a concentrated mass effectively describes the nonlinear vibration behavior of an SLBP with an attached mass, providing theoretical support for designing such devices to detect attached masses.

Segregation on small rubble bodies due to impact-induced seismic shaking

We present a framework to study regolith segregation on rubble-pile asteroids—self-gravitating granular aggregates—due to seismic shaking induced by impacts sustained during their lifetimes. We first relate the amplitude and frequency of surface vibrations to the location and severity of an impact, and the rubble body’s geometry and bulk properties. For illustration, the body is taken to be an ellipsoid with size and spin close to that of Itokawa, although more complex asteroid shapes may be incorporated. We then model the body’s collisional history stochastically given the variability in the impact activity on an asteroid. Finally, we use discrete element simulations to investigate the regolith’s response to impacts. In these simulations, in any sample collisional history, every time an impact occurs, a bin filled with a grain mixture and located at the region of interest on the asteroid is vibrated at that impact’s associated amplitude and frequency. Using this framework, we find that impact-driven seismicity is sufficient to drive size segregation on small rubble-piles, but the segregation quality depends on several aspects, e.g. total impact energy supplied, placement of the region of interest, bulk wave speed and seismic diffusivity.

Ударное возбуждение магнитоупругой системы периодической последовательностью сверхкоротких импульсов поля

The nonlinear magnetization precession in normal magnetized ferrite film which has magnetic, elastic and magnetoelastic properties is investigated. The excitation field is presented as a vibration on resonance frequency which is modulated by short pulses which frequency is more lower than resonance frequency. It is proposed the formation procedure of periodic succession of ultra-short pulses by the involution to even degree of modulation signal sine. It is found two different cases of excitation: first when modulate pulse duration is larger than initial signal period and second when modulate pulse duration is smaller than initial signal period. In the first case the modulated signal has the form of main frequency vibrations tandem and in the second case the modulated signal has the form of unit sign-variation pulse. It is investigated the time development of magnetic and elastic vibrations whish are firmed by excitation field. It is shown that in the first case the magnetization vibrations at first hat sharp jump to upward and after this decreases by exponent. In this case the elastic vibrations after the same jump at first increases and then decreases by exponent. The elastic vibrations behaviour is interpret as energy pump from magnetic system to elastic system. In the second case the initial jump both vibrations is absent. It is investigated the degree modulation index influence to excited vibrations. It is shown that by increasing of this index the amplitude of magnetic and elastic vibrations decreases. It is investigated the magnetization excited vibrations character by different degree of magnetoelastic connection. It is introduced the coefficient multiple of magnetoelastic constant which is equal to ratio of considered constant to value of magnetoelastic constant of yttrium iron garnet. It is shown that by increasing of multiple coefficient the magnetization vibrations period is increased. It is found the sharp increasing the period by determined value of multiple coefficient which has a threshold character. It is investigated the excitation of magnetization in large time interval when the multiple coefficient is above the threshold value. It is found the principle difference between two cases when pulse duration is large or smaller as alternating field period. It is shown that in the first case the magnetization vibrations has the character of equilibrium position precession in conditions of orientational transition. In the second case the magnetization vibrations has the form of periodic re-orientational jumps from one equilibrium position to another. It is mentioned some properties of observed phenomena and proposed some recommendations for further investigations.

Study on partial load vortex and pressure pulsation characteristics of Francis turbine

Abstract Under partial load condition of the Francis turbine, problems such as hydraulic vibration, noise, and high amplitude pressure pulsation that endanger the safe and efficient operation of the unit are inevitable during the transient process. Based on dynamic grid technology and CFD technology, unsteady numerical simulation was conducted for the closing process of the active guide vane from 54% opening to 38% opening, and the evolution characteristics of internal vortex and pressure pulsation were analyzed. The results show that there is always a vortex structure at the crown of the runner during the transition process of variable load. Because of the vortex structure, a “banded” low-pressure zone appears on the suction surface of the blade, which gradually approaches the lower ring of the runner as the vortex structure develops. The analysis of the pressure signal in the runner region shows that the pressure coefficient on the suction surface fluctuates greatly due to the influence of the distribution position of the vortex structure, and the evolution of the vortex structure from continuous to local fracture will lead to a sudden increase of the pressure coefficient. In addition, the frequency components within the runner domain include the frequency of the movable guide vanes passing through the blade and the low-frequency components caused by the evolution of eddy currents within the runner.