Amplitude Frequency Research Articles

Weight Effects on Vertical Transverse Vibration of a Beam with a Nonlinear Energy Sink

Reductions in the vibration of a continuum system via a nonlinear energy sink have been widely investigated. It is usually assumed that weight effects can be ignored if the vibration is measured from the static equilibrium configuration. The present investigation reveals the dynamic effects of weight on the vertical transverse vibrations of a Euler–Bernoulli beam coupled with a nonlinear energy sink. The governing equations considering and neglecting weights were derived. The equations were discretized with some numerical support. The discretized equations were analytically solved via the harmonic balance method. The harmonic balance solutions were compared with the numerical solution via the Runge–Kutta method. Finite element simulations were performed via ANSYS software (version number:2.2.1). Free and forced vibrations, predicted by equations considering or neglecting the weights, were compared with the finite element solutions. For the forced vibrations, the amplitude–frequency responses determined by the harmonic balance method agree well with those calculated by the Runge–Kutta method. The free and forced vibration responses predicted by the equations considering the weights are closer to those computed by the finite element method than the responses predicted by the equation neglecting the weights. The assumption that weights can be balanced by static deflections leads to errors in the analysis of the vertical transverse vibrations of a Euler–Bernoulli beam with a nonlinear energy sink.

Steady‐state free precession NMR without Fourier transform: Redefining the capabilities of 19F NMR as a discovery tool

The 2024 Zurich perfluorinated compounds (PFCs) summit reiterated the urgent need for non‐selective analytical approaches for PFC detection. 19F NMR holds great potential, however, sensitivity limitations lead to long analysis times and/or the possibility of not detecting low concentration species. Steady State Free Precession (SSFP) NMR collects the signal in a steady state regime, allowing 100’s of acquisitions in the timespan of a single traditional NMR scan. Unfortunately, data truncation from SSFP leads to artifacts and spectral broadening on Fourier transform, hindering interpretation. When non‐Fourier based time‐domain analysis is used, namely, complete reduction to amplitude frequency tables (CRAFT), limitations of SSFP are eliminated while sensitivity gains are retained. This work introduces the combined approach, then applies it for the measurement of PFCs in environmental and biological samples. In all cases, the approach reduces analysis time from many hours to minutes and/or greatly increases the range of compounds detected. For example, when PFOA was spiked into human blood, the detection limit improved ~50‐fold vs standard NMR, while in a standard mixture, the approach detected compounds missed by LC‐MS/MS. The technique can be adapted to any nucleus providing a facile approach to reduce experiment time and improve sensitivity of NMR in general.

Steady-state free precession NMR without Fourier transform: Redefining the capabilities of 19F NMR as a discovery tool.

The 2024 Zurich perfluorinated compounds (PFCs) summit reiterated the urgent need for non-selective analytical approaches for PFC detection. 19F NMR holds great potential, however, sensitivity limitations lead to long analysis times and/or the possibility of not detecting low concentration species. Steady State Free Precession (SSFP) NMR collects the signal in a steady state regime, allowing 100's of acquisitions in the timespan of a single traditional NMR scan. Unfortunately, data truncation from SSFP leads to artifacts and spectral broadening on Fourier transform, hindering interpretation. When non-Fourier based time-domain analysis is used, namely, complete reduction to amplitude frequency tables (CRAFT), limitations of SSFP are eliminated while sensitivity gains are retained. This work introduces the combined approach, then applies it for the measurement of PFCs in environmental and biological samples. In all cases, the approach reduces analysis time from many hours to minutes and/or greatly increases the range of compounds detected. For example, when PFOA was spiked into human blood, the detection limit improved ~50-fold vs standard NMR, while in a standard mixture, the approach detected compounds missed by LC-MS/MS. The technique can be adapted to any nucleus providing a facile approach to reduce experiment time and improve sensitivity of NMR in general.

Numerical and Experimental Investigations of a Double‐Suction Pump With a Middle Spacer and a Staggered Impeller

ABSTRACTDouble‐suction pumps are among the most commonly used mechanical devices in irrigation and drainage. To investigate the effects of the impeller configuration with a spacer and staggered arrangement on the internal flow field and radial force characteristics of a double‐suction centrifugal pump, a comparison investigation was conducted using the same type of pump with three different impeller configurations: a symmetrically arranged impeller without a spacer, a symmetrically arranged impeller with a spacer and a staggered 25° arrangement impeller with a spacer. This study employed a combination of experimental and numerical simulation methods to analyse changes in the head, efficiency, transient radial force and internal flow field under three typical operating conditions. The results indicate that the staggered 25° arrangement impeller with a spacer results in a higher head and efficiency than both the symmetrically arranged impellers without a spacer and those with a spacer across most working conditions. Furthermore, the efficiency improvement is most significant at low flow rates for the staggered 25° arrangement impeller with a spacer compared with the other configurations. In terms of the internal flow field, the addition of a spacer and staggered 25° arrangement impeller effectively reduces the high‐velocity flow, making the pressure distribution gradient more reasonable and the turbulent kinetic energy distribution more uniform. Additionally, adding spacers and employing staggered arrangements effectively reduces the steady‐state radial forces as well as the main frequency amplitude of the radial force fluctuations on the impeller. This improves both the high‐velocity flow structure attenuation rate and outlet flow stability for double‐suction impellers. By comparing and analysing the external characteristics, internal flow field and radial force characteristics of different impeller configurations, this study proposes an improved impeller scheme based on a spacer and staggered arrangement, which provides a new optimization idea for improving the efficiency and stability of double‐suction centrifugal pumps in irrigation systems.

Age predicts peak gamma frequency and N1 amplitude of visual evoked potential

The current study investigated whether the age of healthy adults could predict the peak gamma frequency and the peak amplitudes of VEP components (N1, P2). 49 healthy participants (aged between 19 and 52 years) underwent EEG recordings during a visual task eliciting clear gamma frequency oscillations and VEP activities. After eliminating noisy and outlier data, data from 41 participants were analysed using simple linear regression. The results indicated that age was a significant predictor of peak gamma frequency and the peak amplitude of VEP-N1 but not the peak amplitude of VEP-P2. Age was negatively associated with peak gamma frequency and the peak amplitude of VEP-N1. These findings support previous research indicating that ageing is associated with decreased cortical inhibition, highlighting the importance of GABA in maintaining cortical E-I balance.

Collective modes in terahertz field response of disordered superconductors

We consider a problem of nonlinear response to an external electromagnetic radiation in conventional disordered superconductors which contain a small amount of weak magnetic impurities. We focus on the diffusive limit and use Usadel equation to analyze the excitation energy and dispersion relation of the collective modes. We determine the resonant frequency and dispersion of both amplitude (Schmidt-Higgs) and phase (Carlson-Goldman) modes for moderate strength of magnetic scattering. We find that the minimum energy required for the excitation of the both of these modes decreases with an increase in spin-flip scattering. Surprisingly we also find that as a result the Carlson-Goldman mode becomes gapless and as a consequence can only be excited at some finite value of the threshold momentum. We thus discover yet another physical realization of a state with gapped momentum dispersion of one of its collective modes. The value of the threshold momentum is determined by the distance between the two consecutive spin-flip scattering events which, in turn, is proportional to the scattering time between two consecutive scattering events. The amplitude mode is diffusive and becomes strongly suppressed with the increase in spin-flip scattering. Possible ways to experimentally verify our results are also discussed.

Search for high-frequency gravitational waves with Rydberg atoms

We propose high-frequency gravitational wave (GW) detectors with Rydberg atoms. Rydberg atoms are ultra-sensitive detectors of electric fields. By setting up a constant magnetic field, a weak electric field is generated upon the arrival of GWs. The weak electric field signal is then detected by an electromagnetically induced transparency (EIT) in the system of the Rydberg atoms. Recently, the minimum detectable electric field with the Rydberg atoms is further improved by employing superheterodyne detection method. Hence, even the weak signal generated by GWs turns out to be detectable. We calculate the amplitude of Rabi frequency of the Rydberg atoms induced by the GWs and show that the sensitivity of the Rydberg atoms becomes maximum when the size of the Rydberg atoms is close to the wavelength of GWs. We evaluate the minimum detectable amplitude of GWs with Rubidium Rydberg atoms and find that the detector can probe GWs with a frequency f=4.2GHz and an amplitude around 10-20.

The improvement in the quality of 6–0 mm low-grade high-sulfur lignite via a compound dry separation bed

ABSTRACT The drastic decline in high-quality coal leads to the extensive development and utilization of low-rank coal in China. This study employs a compound dry separation bed to desulfurize and reduce the ash content of lignite. It focuses on the influence of multistage separation trough angles (θ), vibration frequency (f) and vibration amplitude (A) on the spatial distribution of the sulfur content and systematically analyses the particles migration behavior. The results indicate considerable differences in the sulfur content spatial distribution when θ = 45°, f = 26 hz, and A = 3.2 mm, and the degree of sulfur desorption reaches its maximum value (S sulfur = 1.18–1.21) meanwhile. Separation and quality enhancement tests conducted under optimal parameters achieved a clean coal yield of 70.29%, a sulfur content of 0.74%, an ash content of 7.29% and a probable error (E p ) of 0.08 g/cm3, demonstrating high-precision dry desulfurization and quality enhancement of lignite.

Design and study of moving-iron torque motor for two-dimensional proportional servo valve

This paper proposes a novel moving-iron torque motor designed for two-dimensional (2D) valves. The torque motor features a strap spring in place of the traditional return spring, effectively reducing the overall number of springs. The unique design allows the torque motor to return to its circumferential neutral position through the return torque generated by the strap spring. In order to analyze the torque-displacement characteristics of the torque motor, an analytical model is established, and a simulation model is constructed based on the equivalent magnetic circuit method, which takes into account the magnetic leakage at the control coil and the working air gap. In order to select a strap spring that matches the stiffness of the magnetic spring of the torque motor, the structural parameters of the spring are optimized using the response surface method with multi-objective optimization, and finally three springs with different stiffnesses are manufactured according to the optimization results. The experimental results show that the maximum step-up time of the torque motor is 20.6 ms, the maximum step-down time is 21.6 ms, the maximum hysteresis loop is 12.5%, and the maximum linearity is 20%. In order to improve the −3dB cut-off frequency of the torque motor, this paper adopts the current closed-loop control method, and increases the maximum cut-off frequency not exceeding 25 Hz in the open-loop mode to 110 Hz.The hysteresis loop and linearity of the torque motor decrease with the increase of the spring stiffness. The amplitude frequency −3dB cutoff frequency increases with increasing spring stiffness.

An Analysis of the Effect of Cavitation on Rotor–Stator Interaction in a Bidirectional Bulb Tubular Pump

This study delves into rotor–stator interaction within a bidirectional bulb tubular pump under cavitation conditions. Using pressure pulsation tests on a model pump and numerical simulations performed with ANSYS CFX software, we analyzed pressure pulsation and flow field data across three distinct flow rates and multiple cavitation numbers. Both time-domain and frequency-domain analyses were conducted to examine the patterns of pressure pulsation influenced by flow rates and cavitation numbers at various monitoring locations. A numerical flow field analysis further validated the findings. The results reveal that rotor–stator interaction manifests in the vaneless spaces of the pump during cavitation. The onset of cavitation alters the amplitudes of dominant frequencies at different flow rates. Near the guide vane and impeller, the dominant frequencies shift toward the impeller frequency and guide vane frequency, respectively. Under low-flow conditions, the rotor–stator interaction effect is more conspicuous due to the deteriorated flow pattern. Pressure pulsations are more strongly influenced in the front vaneless space (FVP) than in the rear vaneless space (RVP). This difference arises because the front guide vane destabilizes rather than stabilizes the flow pattern, worsening the rotor–stator interaction. Additionally, the FVP is less affected by the impeller than the RVP, further amplifying the influence of rotor–stator interaction on pressure pulsation. These findings provide a theoretical foundation for mitigating the effects of rotor–stator interaction on the operational stability and efficiency of bidirectional bulb tubular pumps.

Experimental study of dynamic properties of CMC flat plates in oxidative environment

Accelerated failure of CMC (Ceramic Matrix Composites) structural components in aero engines occurs under oxidative vibrational environments. This study investigates the failure mechanisms of CMCs under high-temperature oxidative vibrational conditions. Experiments were conducted to measure the vibrational response of CMC plates at 1200°C in oxygenated, non-oxygenated, and non-vibrational environments. Combined with techniques such as Energy-Dispersive X-ray Spectroscopy (EDS) and thermogravimetric analysis, the failure mechanisms of CMCs in oxidative vibrational environments were elucidated. The research results indicate that oxidation leads to a decline in the mass and mechanical properties of CMCs, resulting in a reduction in the natural frequency and response amplitude of CMC structures. The presence of vibrational loads causes the opening of matrix cracks, accelerating the oxidation of fibers within the CMC, thereby leading to a more significant decline in CMC plates’ performance and dynamic response.

Acoustic Emission Analysis of the Cracking Behavior in ECC-LWSCC Composites

Acoustic emission (AE) analysis was utilized to assess the cracking behavior of six lightweight self-consolidating concrete (LWSCC)–engineering cementitious composite (ECC) beams under flexural loading. Two control beams were fully cast with ECC containing either polyvinyl alcohol (PVA) fibers or steel fibers (SF). The remaining four beams were ECC-LWSCC composite beams, with the ECC layer containing PVA fibers or SF placed on either the tension or compression side. The results showed that the control beams had the highest ultimate load capacity, followed by beams repaired in tension, and then beams repaired in compression. PVA fibers exhibited higher performance compared to steel fibers at the first crack load, while steel fibers enhanced the beam’s performance at the ultimate load stage. During the flexural testing, AE parameters such as the number of hits, signal amplitude, and cumulative signal strength (CSS) were collected until failure. The analysis of these AE parameters was effective in detecting the first crack and evaluating cracking propagation in all beams. Changing the type of fibers (PVA and SF) in the ECC layer showed a significant effect on AE parameters. Moreover, adding a new ECC layer to an existing LWSCC layer resulted in variations in the signal amplitude. Finally, the flexural failure mode was confirmed with the aid of the rise time/maximum amplitude vs. average frequency analysis.

Conflicting Evidence for a Motor Timing Theory of Stuttering: Choral Speech Changes the Rhythm of Both Neurotypical and Stuttering Talkers, but in Opposite Directions.

Talking in unison with a partner, otherwise known as choral speech, reliably induces fluency in people who stutter (PWS). This effect may arise because choral speech addresses a hypothesized motor timing deficit by giving PWS an external rhythm to align with and scaffold their utterances onto. This study tested this theory by comparing the choral speech rhythm of people who do and do not stutter to assess whether both groups change their rhythm in similar ways when talking chorally. Twenty adults who stutter and 20 neurotypical controls read a passage on their own and then a second passage chorally with a neurotypical partner. Their speech rhythm was evaluated using Envelope Modulation Spectrum (EMS) analysis to derive peak frequency, a measure of the dominant rate of modulation in the sound envelope, as well as peak amplitude (the amplitude of the peak frequency), across several octave bands associated with different features of speech. The two groups displayed opposing patterns of rhythmic change during choral reading. People with a stutter increased their EMS peak frequency when they read chorally, while neurotypical talkers' choral speech was characterized by reduced peak frequency compared to solo reading. Our findings show that the choral speech rhythm of PWS differs from that of neurotypical talkers. This indicates limited support for the hypothesis that choral speech addresses a motor timing deficit by giving PWS a rhythmic cue with which to align.

Effect of amplitude on resonance and propulsive characteristics of a pitching flexible panel

We present the effect of amplitude on resonance and propulsive characteristics of a pitching flexible panel in quiescent water. The first mode of the resonant frequency (fn1) of the fluid-panel system is determined based on the measured peak lateral excursion of the trailing-edge of the flexible panel at various input frequencies and pitch amplitudes. Both the resonant frequency and peak amplitude ratio a∗ are found to decrease with an increase in the pitch angle. The propulsive force ratio T∗ and power ratio P∗ are defined as the ratio of the mean propulsive force generated and the propulsive power required for the flexible panel to the rigid panel, respectively. The variation of T∗ and P∗ as a function of the frequency ratio f∗=f/fn1 shows that both the propulsive force and the required power are strongly interlinked to the peak lateral excursion of the trailing-edge of the flexible panel. The characteristic flapping velocity of the trailing edge governs the propulsive performance such that propulsive force generation and power required are found to increase with an increase in the characteristic flapping velocity. Moreover, the pitch amplitude can be considered as an input parameter to manipulate the resonance characteristics of a flexible panel, thereby achieving better propulsive performance for various cruise speeds.

Experimental Investigation and Modeling of Surface Roughness in BTA Deep Hole Drilling with Vibration Assisted.

The surface roughness of hole machining greatly influences the mechanical properties of parts, such as early fatigue failure and corrosion resistance. The boring and trepanning association (BTA) deep hole drilling with axial vibration assistance is a compound machining process of the tool cutting and the guide block extrusion. At the same time, the surface of the hole wall is also ironed by the axial large amplitude and low-frequency vibration of the guide block. The surface-forming mechanism is very complicated, making it difficult to obtain an effective theoretical analytical model of the surface roughness of the hole wall through kinematic analysis. In order to achieve accurate prediction of the surface quality of the hole wall, the chip-breaking mechanism and the hole wall formation mode of BTA deep hole vibration drilling were analyzed. The influence of drilling spindle speed, feed, amplitude, and vibration frequency on the surface roughness of the hole wall during BTA deep hole vibration drilling was illustrated by a single-factor experiment. A four-factor and three-level test scheme was designed by using the Box-Behnken design (BBD) experimental design method. A surface roughness prediction model for hole wall machining was established based on the response surface methodology. The accuracy of the prediction model was analyzed through ANOVA, and the complex correlation coefficient of the model was 0.9948, indicating that the prediction model can better reflect the mapping relationship between vibration drilling parameters and surface roughness. After optimization analysis and experimental verification, the obtained vibration drilling parameters can achieve smaller surface roughness. The error between the predicted value of the model and the experimental measurement value is 8.65%. The established prediction model is reliable and can accurately predict the surface roughness of the hole wall of BTA deep hole axial vibration drilling, providing a theoretical basis for the surface quality control of the machining hole wall. It can be applied to process optimization in practical production.

Study on the Relationship Between Vibration Signals in CFRP Grinding and Grinding Mechanism

AbstractIn the process of grinding carbon fiber reinforced polymer (CFRP), the changing state of acceleration vibration signal is closely related to the grinding surface quality. Therefore, the time domain and frequency domain signal changes in acceleration can be used to monitor and control the grinding process to improve machining quality and efficiency. In this paper, changes in acceleration frequency domain signals under different grinding angles are studied, and the relationship between the vibration forms of acceleration frequency domain signals at the beginning, middle and end of grinding as well as the surface morphology and quality of the corresponding grinding position is studied. Combined with the micro-morphology of the grinding area, it can be seen that, a high frequency and low amplitude vibration can improve the grinding surface quality, but a high amplitude will have a negative impact on the grinding quality. The acceleration vibration during grinding is more stable and the corresponding surface quality is better. With an increase in grinding angle, the maximum amplitude of acceleration first increases and then decreases. The length of the surface fiber also initially decreases and then increases. Lastly, the resin residue first increases and then decreases. The purpose of this study is to provide a theoretical basis for the subsequent grinding state adjustment.

AIoT-Driven Leak Detection in Real Water Networks Using Hydrophones

AbstractAcoustic sensing technology is a familiar approach to detect leakage in urban water networks. Critical issues like false alarms, difficult leak locations, missed leaks, unknown site conditions, and high repair costs are still prevalent. The situation warrants developing a more sophisticated and efficient leak detection approach in real water networks. Hydrophone based acoustic technology has a strong promise for high precision detection of leaks. However, AIoT approach using hydroacoustic data for real water leak detection are rarely reported. The current study, therefore, proposes an integrated signal analysis and machine learning-based ensemble model for leak detection using a hydrophone-based smart IoT system. The results show that the most significant features are peak frequency and maximum amplitude. Random forest is the most robust classifier for cost effective long-term monitoring, and the proposed voting ensemble classifies leaks and no leaks with high accuracy on both unseen data and new sites. Specifically, proposed models have very few alarms and missed leaks are reported, a significant problem in models developed using accelerometers and noise loggers. The study shows a significant contribution to the domain of leak detection for real urban water networks.

Wake Detection and Positioning for Autonomous Underwater Vehicles Based on Cilium-Inspired Wake Sensor.

This paper proposes a method for passive detection of autonomous underwater vehicle (AUV) wakes using a cilium-inspired wake sensor (CIWS), which can be used for the detection and tracking of AUVs. First, the characteristics of the CIWS and its working principle for detecting underwater flow fields are introduced. Then, a flow velocity sensor is used to measure the flow velocities of the "TS MINI" AUV's wake at different positions, and a velocity field model of the "TS MINI" AUV's wake is established. Finally, the wake field of the "TS MINI" AUV was measured at various positions using the CIWS. By analyzing the data, the characteristic frequency of the AUV's propeller is identified, which is correlated with the AUV's rotation speed and the number of blades. Through further analysis, a mapping model is established between the spectral amplitude of the characteristic frequency at different positions and the corresponding wake velocity. By substituting this mapping model into the AUV's wake velocity field model, the possible position range of the sensor relative to the AUV propeller can be estimated. The research provides a technical foundation for underwater detection and tracking missions based on wake detection.

Fatigue-induced changes in electromyographic activity after repeated racing turns: a pilot study.

Alpine skiing races are physically demanding events characterized by numerous repeated near-maximal activations of the lower limb muscles. Although this type of task is known to induce neuromuscular fatigue, electromyographic activity (EMG) adaptations after repeated maximal-intensity skiing have not been previously investigated. Six skiers completed a 6-turns section with (FAT) and without performing 30 giant slalom (GS) turns (CONT). Isometric knee extensors maximal force (Fmax) was measured before and immediately after both conditions. On-snow EMG activity of VM, VL, RF, BF, SMST and GM muscles were compared between conditions for both the outside (OL) and inside (IL) legs using turn-averaged EMG amplitude (RMSOL and RMSIL) and EMG mean power frequency (MPFOL and MPFIL). EMG time-frequency maps were also computed and compared between conditions using statistical parametric mapping (SPM) analysis. Fmax was significantly lower after FAT (-20.1%, p < 0.001), but did not change after CONT. RMSOL was lower in FAT for BF (-26.8%, p = 0.020). RMSIL was lower in FAT for VM (-24.7%, p = 0.036) and GM (-27.3%, p = 0.021). MPFOL was lower in FAT for VM (-8.2%, p = 0.028), VL (-11.3%, p = 0.025), RF (-13.1%, p = 0.007), SMST (-9.3%, p = 0.004) and GM (-7.4%, p = 0.034). MPFIL was lower in FAT for VM (-13.0%, p = 0.016) and RF (-11.1%, p = 0.034). SPM analysis indicated that the initiation phase of the turn was specifically affected. Thirty GS turns led to a substantial decrease in Fmax and altered motor command, as indicated by reduced EMG frequency content, specifically in the initiation phase of the turn. The present pilot data highlight the importance of characterizing neuromuscular fatigue in competitive GS skiing.

Design a chaotic circuit using tunable and power efficient memristor emulator circuit for image encryption

Abstract In a non-linear dynamic system, chaos is a deterministic phenomenon that arises when the state vector trajectories become highly sensitive to the initial conditions, given certain criteria and periodic. The memristor, being the fourth essential component of a two-terminal device, has the potential to overcome the barrier for secure communication against eavesdroppers and manufacturing of duplicate chaotic transrecivers by the untrusted foundaries.It can close a gap among secure manufacturing and reliable communication because its resistance can be programmed by the designer not by the foundary. This property makes the communication system more efficient, reliable secure, and provides more security. In this study, the memristor and analog design of a chaotic transreviver is designed. The memristor model is designed using a Current mirror operational transconductance amplifier (OTA) and an analog multiplier with sinusoidal input having amplitude (V_m) and input frequency (f). Variations in input frequency, and amplitude have an impact on conductance and resistance state and the OTA parameter g_m Also affects the V-I response. The research focuses on memristor tunability with a variation of the hysteresis curve using factors such as temperature, amplitude, load resistance, frequency, and incremental and decremental behavior and secure communication using a Chaotic circuit using memristor. The maximum operational frequency that exhibits a pintch hystresis curve is 100 kilohertz, and a power dissipation of 3.1 µW with noise 56nV/Hz^(1/2). The results also show the chaotic system are sensitive with their secret key or starting conditions of integrator which is uses for the encryption approach.