Increasing Excitation Frequency Research Articles

Advancements in electrohydraulic fatigue testing: Innovations in variable resonance frequency control and comprehensive characterization

This study addresses the challenge in electro-hydraulic fatigue testing machines where increasing excitation frequency leads to reduced output load amplitude, making it difficult to optimize both frequency and amplitude simultaneously. A new approach is introduced with the variable resonance fatigue testing machine controlled with 2D excitation valves. This technique involves adjusting the system’s intrinsic frequency by altering its mass, aligning the excitation frequency with the intrinsic frequency, and leveraging resonance energy to enhance excitation amplitude for broad-range resonance near the resonance point. The relationship between the system’s intrinsic frequency, the equivalent mass of the upper connector, and the upper fixture is explored, yielding analytical solutions. Experimental research validates these simulations, in the resonance condition, the fatigue testing machine energy efficiency can reach 94 %, to further verify the fatigue testing machine in the resonance condition to realize the High energy efficiency. Demonstrating that the system’s intrinsic frequency decreases with increasing mass, allowing for a broad frequency resonance between 200 and 300 Hz. Operating in a broadband resonance region, the output load force is increased by 60 %–95 % and the system flow is reduced by 20 %–30 %. This mass-adjustment technique effectively alters the system’s intrinsic frequency, expanding the electro-hydraulic fatigue testing machine’s application scope.

Strain clamp condition monitoring for transmission lines based on acoustic emission signals

Abstract To ensure the reliability and safety of the power supply in the electric system, it is significant to realize the strain clamp condition monitoring for transmission lines. A strain clamp vibration test rig was designed and built to collect acoustic emission (AE) signals generated by strain clamps with an excitation frequency of 30, 50, 70, 90, and 110 Hz, respectively. The characteristics of the collected AE signals are then analyzed in the time domain and time-frequency domain. The results of the signal analysis in the time domain show that, the increasing excitation frequency leads to a higher amplitude of the AE signal, and the signal period is consistent with that of the excitation. Meanwhile, both the root-mean-square (RMS) and the average signal level (ASL) of the AE signal increase continuously with the excitation frequency, of which the growth trends are different. Additionally, the results of the signal analysis in the time-frequency domain also show that the signal spectrum is mainly concentrated in the range of 30 kHz to 200 kHz at different excitation frequencies and the increasing excitation frequency significantly leads to more high-frequency components in the AE signal.

Friction modulation through normal vibrations in an inchworm-inspired robot

The inchworm′s locomotion strategy has significantly influenced bionic robotics research, guiding efforts to mimic its structural and movement characteristics. This study introduces an innovative method to modulate horizontal friction in an inchworm-inspired robot using normal vibrations. By harnessing the dynamics between friction forces, self-deformation, and normal excitations, the robot can mimic crawling motion. A simplified mechanical model is established to reveal the robot′s movement. And the numerical simulations are conducted to analyze the influence of excitation and friction coefficients on the robot′s movement. The findings reveal that the robot′s velocity initially increases and then decreases as the excitation frequency increases, signifying the feasibility of achieving precise control through normal excitations. This study contributes to tribology and robotic locomotion paradigms.

Lift-Off Effect of Koch and Circular Differential Pickup Eddy Current Probes

A flexible or planar eddy current probe with a differential structure can suppress the lift-off noise during the inspection of defects. However, the extent of the lift-off effect on differential probes, including different coil structures, varies. In this study, two planar eddy current probes with differential pickup structures and the same size, Koch and circular probes, were used to compare lift-off effects. The eddy current distributions of the probes perturbed by 0° and 90° cracks were obtained by finite element analysis. The analysis results show that the 90° crack can impede the eddy current induced by the Koch probe even further at relatively low lift-off distance. The peak-to-peak values of the signal output from the two probes were compared at different lift-off distances using finite element analysis and experimental methods. In addition, the effects of different frequencies on the lift-off were studied experimentally. The results show that the signal peak-to-peak value of the Koch probe for the inspection of cracks in 90° orientation is larger than that of the circular probe when the lift-off distance is smaller than 1.2 mm. In addition, the influence of the lift-off distance on the peak-to-peak signal value of the two probes was studied via normalization. This indicates that the influence becomes more evident with an increase in excitation frequency. This research discloses the lift-off effect of differential planar eddy current probes with different coil shapes and proves the detection merit of the Koch probe for 90° cracks at low lift-off distances.

Research on the vibration isolation performance of a metal rubber-disc spring shock isolation device

In view of the fact that the vibration response of the laser-emitting telescope in the combination of artillery and light equipment cannot meet the target design requirements, this paper designs a new metal rubber-disc spring shock isolation device and conducts experimental research on its vibration isolation performance. The research is conducted from the frequency sweep test and the fixed frequency test. Through the vibration isolation performance test, it is found that the natural frequency of the metal rubber-disc spring shock isolation device is lower than that of the steel wire rope vibration isolator, and the frequency domain where vibration isolation occurs is wider, with better vibration isolation performance. In the fixed frequency test, the acceleration transfer rate of the metal rubber-disc spring composite vibration isolator is significantly better than that of the steel wire rope vibration isolator in the low-frequency range. As the excitation frequency increases, the difference between the acceleration transfer rate of the steel wire rope vibration isolator and the metal rubber-disc spring composite vibration isolator gradually shrinks, and finally converges.

Coupled dynamic instability of graphene platelet-reinforced dielectric porous arches under electromechanical loading

Graphene platelet-reinforced dielectric porous (GPLRDP) arches are a kind of multifunctional structures, which can be used to design various dielectric resonators and soft robotic components. This work studies the coupled dynamic instability of GPLRDP arches under electromechanical loading. It is assumed that the presence of voids is uniformly distributed in the arch structure, while graphene platelets (GPLs) are uniformly dispersed inside the skeleton of such voids. The effective medium theory (EMT) is used to determine the effective dielectric permittivity and Young's modulus of such structures. Based on the Hamilton principle, the governing equations of this problem are formulated. The differential quadrature method (DQM) and the Bolotin method are then used for solving the arch system to identify the coupled dynamic instability region. In this study, we observe the coupling effect of parametric and forced resonance phenomena. A series of numerical experiments are also carried out to examine the influence of porosities, GPL weight fractions, boundary conditions, and electrical voltage levels on the critical excitation frequency and coupled dynamic instability behavior of GPLRDP arches. It is found that the coupled dynamic instability region becomes wider and shifts to low frequency as the effect of porosity increases. When the signal amplitude of AC frequency is within a certain range, there is an abrupt increase of the critical excitation frequency under a high level of DC voltage. The numerical results of this work demonstrate that the location and size of the coupled dynamic instability region can be actively controlled by adjusting the material and structural parameters.

Dynamic response of Camellia oleifera fruit-branch based on mathematical model and high-speed photography

In order to study the motion law and shedding characteristics of fruits during the vibration harvesting process of Camellia oleifera fruit. The dynamic equation of fruit-branch picking was established, the vibration output solution and picking inertial force of Camellia oleifera fruit forced vibration were solved by mathematical methods, and the spectral curve between picking force and frequency when forced vibration of Camellia oleifera fruit was analysed by MATLAB. The three-dimensional model of fruit-branch was established, and the modal analysis and harmonious response analysis were carried out, and the optimal excitation frequency range was 4–8 Hz, and the optimal excitation load of fruit-branch was 50N. The self-made canopy camellia fruit picker was used to continuously vibrate the side branches of Camellia oleifera, and the high-speed camera was used to record the movement process of Camellia oleifera fruit at different vibration frequencies, and the results showed that the movement trajectory of Camellia oleifera fruit was complex and the result of a combination of multiple movements. With the increase of excitation frequency, the speed and acceleration of fruit and flower buds also increased, but the average shedding force of fruits and buds did not change much, and the average shedding force of flower buds was greater than that of fruits. The results of this experiment are basically consistent with the results of the simulation analysis. The results of this study can provide a theoretical basis for the design, selection and research and development of mechanical harvesting equipment.

Research on nonlinear dynamic characteristics of high-speed gear in two-speed transmission system

The working performance and service life of the two-speed transmission system directly affects the performance and service life of helicopters and other equipment. One of the main tasks of the two-speed transmission system research is to improve its dynamic characteristics. For the two-speed transmission system in high-speed gear, a purely torsional nonlinear dynamic differential equation set considering the number of planetary gears, backlash, and clutch dynamic load is established by using the lumped parameter method, and the equations are dimensionless. Then the dimensionless differential equation set is solved by using the variable step-size fourth-order Runge–Kutta method, and the phase diagram and Poincare diagram of high-speed gear are obtained. By changing the dynamic friction coefficient of the friction clutch and the backlash of the gear pair, the influence of parameter change on the nonlinear dynamic characteristics of the system is analyzed. The results show that, with the increase of excitation frequency, the system has experienced single cycle, quasi-cycle, chaos, and double cycle, then changed from double cycle to chaotic motion, and then changed from chaotic motion to double cycle and single cycle motion in turn, and found the path to chaos. In the low-frequency band, reducing the friction coefficient of the friction clutch can reduce vibration amplitude; In the middle-frequency band, reducing the friction coefficient will make the system tend to unstable vibration. In the high-frequency band, it is a single-cycle movement, which is not affected by friction coefficient.

Noise Prediction and Plasma-Based Control of Cavity Flows at a High Mach Number

Cavity flows are a prevalent phenomenon in aerospace engineering, known for their intricate structures and substantial pressure fluctuations arising from interactions among vortices. The primary objective of this research is to predict noise levels in high-speed cavity flows at Mach 4 for a rectangular cavity characterized by an aspect ratio of L/D = 7. Moreover, this study delves into the influence of the plasma actuator on noise control within the cavity flow regime. To comprehensively analyze acoustic characteristics and explore effective noise reduction strategies, a computational fluid dynamics technique with the combination of a delayed detached eddy simulation (DDES) and plasma phenomenological model is established. Remarkably, the calculated overall sound pressure level (OASPL) and plasma-induced velocity closely align with the experimental data, validating the reliability of the proposed approach. The results show that the dielectric barrier discharge (DBD) plasma actuator changes the movement range of a dominating vortex in the cavity to affect the OASPL at the point with the maximum noise level. The control of excitation voltage can reduce the cavity noise by 2.27 dB at most, while control of the excitation frequency can only reduce the cavity noise by 0.336 dB at most. Additionally, the increase in excitation frequency may result in high-frequency sound pressure, but the influence is weakened with the increase in the excitation frequency. The findings highlight the potential of the plasma actuator in reducing high-Mach-number cavity noise.

Analysis of influencing factors on vibration characteristics of electro-hydraulic vibration cutting system

The cutting process of the cantilever tunneling machine mainly generates excitation through the cutting motor or the hydraulic cylinder driven by the hydraulic system. Regardless of the driving method, the frequency width of the excitation system is limited, difficult to control, and the excitation effect is poor. Therefore, in order to improve excavation efficiency, the excitation system parallel to the original cutting and rotating system is designed. Based on the excitation characteristics caused by alternating fluid flow, the core component of the excitation system, hydraulic exciter, is designed, and the dynamics and dynamic characteristics of the excitation system are analyzed. Based on AMESim software, analyze the impact of factors such as pump displacement, excitation frequency, and pipeline parameters on the operational performance of the electro-hydraulic vibration cutting system, and conduct experimental verification by building a cutting test bench. The experimental results show that as the inner diameter of the pipeline increases, the fluctuation at the acceleration turning point decreases in each cycle and approaches the peak faster. As the excitation frequency increases, the cutting acceleration of the electro-hydraulic excitation cutting system decreases first and then increases, verifying the accuracy of the simulation results. In the experiment, it was found that the acceleration transformation range of the cutting head of the excitation system is the smallest and most stable when the excitation frequency is 30 Hz. In order to verify that the excitation frequency of 30 Hz is the optimal frequency, further contact force tests were conducted on the cutting teeth. It was found that when the hydraulic excitation system adds a 30 Hz excitation frequency, the contact force on the cutting teeth is the smallest. It is more conducive to reducing the damage and wear of the cutting head, and the cutting effect of the cutting head is more obvious. The research results are beneficial for improving the cutting performance of the electro-hydraulic excitation cutting system, providing theoretical support for the selection of cutting parameters for excavation machinery and hydraulic excitation, and improving the existing theoretical system for active excitation cutting vibration analysis of excavation machines.

A hybrid piezoelectric-electromagnetic energy harvester used for harvesting and detecting on the road

At present, some piezoelectric energy harvesters (PEH) have been widely used in various small wireless electronic devices and micro intelligent sensing devices for self-power supply, but PEH still needs to be further improved in the effective acquisition of road vibration energy at low frequency (<10 Hz), especially at ultra-low frequency (<5 Hz) and broadening the capture energy band. Based on this, this paper proposes a hybrid piezo-electromagnetic road vibration energy harvesting device -TPEH (Triple piezoelectric energy harvester) suitable for road deceleration belts. Spring is introduced as the key to improve the efficiency of energy harvesting. Firstly, the vibration environment of the deceleration belts is surveyed, and then the influence of different K, frequencies, vehicle types and impedance on the energy capture effect is observed in the experiment. The experimental results show that: first of all, K = 20 N/kg main spring has the best resilience; Secondly, with the increase of excitation frequency from 0 Hz to 10 Hz, the maximum peak voltage of TPEH increases from 5.7V to 31.2V, and reaches the full bandwidth in the low frequency range of 0–10 Hz, especially the frequency band widening in the range of 0–1 Hz has ma de a breakthrough. Then, the total output power of TPEH reaches a maximum of 10.29 mW under the optimal load condition of 10 kΩ. Finally, TPEH is applied to the speed strip of a local road section. Through reasonable distribution of vibration signals, TPEH could accurately wireless communication module.

Effects of piezoelectric synthetic jet actuator parameters on synthetic jet formation process and actuator performance

Aiming at the problem that the non-linearity between the piezoelectric vibrator deflection and the excitation amplitude of the piezoelectric synthetic jet actuator (SJA) causes it difficult to obtain the variation laws of the synthetic jet (SJ) velocity accurately, a theoretical model of the whole flow field of the piezoelectric SJA is established and four important parameters (half period jet mean velocity, Reynolds number, effective jet length and energy) for evaluating the performance of the SJ are proposed. Then a two-dimensional axisymmetric numerical simulation is carried out with k-ω turbulence model to study the SJ formation process and the velocity characteristics of the SJ at the orifice. The results show that the fluid pressure in the cavity is the main reason causing the non-linearity between the piezoelectric vibrator deflection and the excitation amplitude, the influence of which decreases with the increase of the orifice diameter. The SJ velocity increases first and then decreases slowly with the increase of excitation frequency. The extreme point occurs at the first resonant frequency of the piezoelectric vibrator and the position of the maximum velocity occurs at 0.5 mm outside the orifice. Other conditions being constant, both the piezoelectric vibrator deflection and jet velocity have a maximum value when the radius ratio of the piezoelectric layer to the elastic layer is 0.75. Smaller piezoelectric layer thickness leads to larger lateral displacement of the piezoelectric vibrator, and the optimum thickness ratio is 0.25. The results of this study have important guiding significance for accurately obtaining the variation laws of the SJ velocity as well as rationally designing the piezoelectric SJA.

Experimental investigation of three-dimensional free-surface and interfacial sloshing in a vertical cylindrical tank

In the present study, hundreds of experiments have been conducted on the three-dimensional free-surface and interfacial sloshing in a vertical cylindrical tank containing two immiscible liquids. The bounds of different free-surface and interfacial wave regimes are determined by maintaining fixed excitation amplitude and slowly increasing excitation frequency until another type of wave regime began to appear. In general, three types of the free-surface wave regimes are observed when the excitation frequency is in the neighborhood of the lowest natural frequency of the free surface, i.e., planar gravity wave, chaotic gravity wave, and swirling gravity wave. Similarly, when the excitation frequency is near the lowest natural frequency of the internal interface, three types of interfacial wave regimes, i.e., planar gravity wave, chaotic gravity-capillary wave, and swirling gravity-capillary wave, are generated. Besides, it is worth pointing out that when the excitation frequency is near the lowest natural frequency of the internal interface as well as very close to a third of the lowest natural frequency of the free surface, large-amplitude rotating wave motion occurs at both the free surface and the internal interface. This is due to even though the excitation frequency is far away from the natural frequency of the free surface, the secondary resonance can still become dominant and lead to large-amplitude motion of the free-surface rotating wave and subsequently influences the internal interface. This paper reveals that the sloshing behaviors of two-layer liquid in the vertical cylindrical tank are much more complicated than those of single-layer liquid.

Dynamical characterization of a Duffing–Holmes system containing nonlinear damping under constant excitation

A Duffing-Holmes system containing nonlinear damping is used to investigate some dynamical properties of the system under the combined action of constant excitation and simple harmonic excitation. The harmonic balance method is used to find the main vibration equation of the system and obtain the amplitude-frequency response relationship. In the analysis of the global characteristics of the system, the Melnikov method is applied to analyze the necessary, insufficient conditions for the analysis of the system chaos, and the correctness of the analytical solution is verified by numerical calculations; the effect of the constant excitation amplitude on the global characteristics of the system is analyzed by the cell mapping method. The paper shows: gradually increasing the constant excitation amplitude causes the system amplitude-frequency response to appear rigidly asymptotic phenomenon; the boundary curve of the system generating chaos in the sense of Smale's horseshoe, with the increase of excitation frequency ω, the curve first decreases, then rises, finally tends to infinity, and the possibility of chaos occurs most near the resonance frequency of the system; with the change of the constant excitation amplitude, The number of attractor domains and attractors in the global attraction domain of the system changes substantially with the change of the constant excitation amplitude, and the attractor domains are entangled with each other.

Experimental study on characteristics of liquid dynamics in a cylindrical water tank under harmonic excitation

AbstractAs the offshore engineering industry continued to develop, issues such as damage to storage structures due to liquid shaking became increasingly prevalent. This paper explored the dynamic response of liquid within a rigid cylindrical water tank subjected to harmonic excitation through vibration table tests, analyses, and numerical simulations. Using the Laplace equation and the Bessel function of the first kind, the analytical formula of liquid dynamic response was derived. A numerical model was established by ANSYS software to verify the accuracy of the analytical solution. At the same time, the response characteristics of hydrodynamic pressure and liquid level wave height were studied by vibration table tests. In this experiment, a rigid cylindrical water tank with varying depths of liquid was subjected to harmonic excitations utilizing a vibration table. In most cases, the experimental results agreed well with the analytical formula. However, under conditions of relatively severe liquid sloshing, there was a discrepancy in peak values between the experiment and the analytical formula. The experimental data indicated that both the hydrodynamic pressure and liquid level wave height increase with an increase in harmonic excitation frequency and amplitude.

Nonlinear dynamics and control of connected hydro-pneumatic suspension with fractional order

This paper develops a four-degree-of-freedom dynamics model with fractional order based on an anti-roll connected hydro-pneumatic suspension of a four-axle vehicle. A comprehensive evaluation function determines the optimal order. The effects of the excitation parameters and the suspension’s internal parameters on the system’s nonlinear dynamics are investigated under sinusoidal superimposed white noise excitation. According to the simulation analysis, the system gradually stabilizes as the excitation amplitude and frequency increase. The flow coefficient variation does not affect the system. The initial pressure shows the system’s chaotic and transient periodic motion in the study interval. By establishing a double power convergence sliding film variable structure controller to control the suspension, the chaos is effectively suppressed by comparing the before and after control.

Effect of excitation vibration on mechanical property and stress corrosion resistance of cast steel

Cast steel parts can realize rapid prototyping effectively, which is suitable for complex structural design. However, due to the large residual stress, the problem of mechanical property degradation is more obvious. In order to solve this problem, a high temperature excitation vibration treatment scheme is proposed in this paper. By applying different excitation frequencies and impact forces, the effects of mechanical properties and stress corrosion properties are studied and verified. Based on the finite element software ANSYS, the modal shape and resonant frequency of the cast steel parts are obtained, and verified by the sweep frequency module in the excitation vibration system. According to the characteristics of modal shape, five typical detection paths are set, and stress sensors are arranged every 200 mm. In order to obtain the specific effects of excitation frequency and impact force amplitude on mechanical properties, nine parts samples were prepared on the same production line according to the matching requirements of test parameters. In addition, the main external parameters that remain unchanged during vibration excitation are set as initial 750 ℃ and vibration excitation time of 60 s, which can fully affect the effect of austenite transformation. Keeping the synchronization of test parameters in different samples, the distribution rules of residual stress under different excitation frequencies and forces are obtained and analyzed. In the aspect of mechanical properties, the microstructure, hardness, yield strength and tensile strength of the specimens subjected to vibration were compared and analyzed. In the aspect of stress corrosion performance research, stress corrosion cracking test was carried out in weak acid environment to obtain the tensile stress curve and fracture morphology of the specimen. The results show that the excitation vibration at high temperature can effectively eliminate the residual stress of cast steel parts, but the increase of excitation frequency does not correspond to the effect of residual stress elimination. When the exciting force exceeds a certain value, the stress relief effect cannot be further improved. Excitation vibration can reduce the internal hardness of cast steel parts to a certain extent, and improve the yield strength and tensile strength. At the same time, it has a positive role in promoting the improvement of stress corrosion resistance.

Effect of Pipe Bends on the Low-Frequency Torsional Guided Wave Propagation

Wave motion in pipe bends is much more complicated than that in straight pipes, thereby changing considerably the propagation characteristics of guided waves in pipes with bends. Therefore, a better understanding of how guided waves propagate in pipe bends is essential for inspecting pipelines with bends. The interaction between a pipe bend and the most used non-dispersive torsional mode at low frequency in a small-bore pipe is studied in this paper. Experiments are conducted on a magnetostrictive system, and it is observed that T(0,1) bend reflections and mode conversions from T(0,1) to F(1,1) and F(2,1) occur in the pipe bend. The magnitude of the T(0,1) bend reflections increases with increasing propagation distance and excitation frequency. The amplitude of the mode-converted signals also increases with increasing propagation distance, but it decreases with increasing excitation frequency. Because of their longer bent path, the test signals for a pipe bend with a bending angle of 180X are much more complicated than those for one with a bending angle of 90X. Therefore, it is even more difficult to scan a bent pipe with a large bending angle. The present findings provide some insights into how guided waves behave in pipe bends, and they generalize the application of guided-wave inspection in pipelines.

Dynamic characterization of 3D printed bolted joints

The paper deals with the effect of different parameters on the frictional energy dissipated by 3D-printed bolted joints of different configurations. A test rig is developed using the accelerometers and shaker to perform this task. The shaker provides the force that induces a relative displacement between plates. The induced relative displacement is measured using the accelerometer. The bolted plate samples are 3D printed with polylactic acid (PLA) fibre using fused deposition modelling (FDM) and joined together using a metal bolt. The four different configurations of bolted joints are developed. A single bolt flat contact, a double bolt flat contact (90°orientation), a single bolt slanted contact (1°angle on both surfaces), and a single bolt flat and curved contact. The effect of bolt preload, excitation frequency, and excitation amplitude on the experimental frictional energy dissipation of the bolted joint is studied. The energy dissipation increases with the increase in excitation amplitude and the bolt preload. However, with increasing excitation frequency, the energy dissipation decreases. The type of contact between bolted plates also seems to affect the frictional energy dissipation.

Improving energy harvesting from low-frequency excitations by a hybrid tri-stable piezoelectric energy harvester

This paper presents the design of a novel hybrid tri-stable piezoelectric energy harvester (HTPEH) that improves the energy harvesting efficiency of piezoelectric energy harvesters operating at low frequencies. The proposed HTPEH is an extension of a conventional tri-stable cantilever piezoelectric energy harvester with an elastic base (TPEH + EB), and it incorporates vertical and rotational elastic amplifiers that are installed between the mass block at the left end of a cantilever beam and the left side of a U-shaped frame to enhance the system's nonlinear characteristics. By utilizing Hamilton's principle, a HTPEH's nonlinear electromechanical equation is formulated, and the harmonic balance method is used to obtain analytical solutions for the displacement amplitude, voltage amplitude, and power amplitude. The study investigates the effects of various parameters, including the elastic amplifier-to-base stiffness ratio and elastic amplifier-to-piezoelectric cantilever beam mass ratio on the energy harvesting performance of the HTPEH. The results indicate that the displacement and voltage amplitude of the HTPEH exhibit two peaks as the external excitation frequency increases, and adjusting the relative mass and stiffness between the elastic amplifier and the piezoelectric cantilever beam can alter the frequency band interval where the two response peaks of the system are located. This allows the HTPEH to enter inter-well motion at low-level external excitation, resulting in high output power. The HTPEH outperforms the TPEH + EB in terms of energy harvesting efficiency under low-frequency environmental excitation.