Mechanical Vibration Research Articles

Experimental analysis on Self Compacting Concrete by using Nano - Silica Gel

Abstract: Self-Compacting Concrete (SCC) has gained widespread recognition in modern construction due to its ability to flow under its weight, eliminating the need for mechanical vibration. Despite its numerous advantages, challenges such as maintaining stability, durability, and achieving optimal mechanical performance persist. Incorporating nano-silica gel, a material known for its high pozzolanic activity and micro-filling capability, offers a promising solution to address these challenges. This experimental study evaluates the impact of nano-silica gel on the fresh, mechanical, and durability properties of SCC. The research involves preparing SCC mixes with varying nano-silica gel dosages (0.5%, 1%, 1.5%, and 2% by weight of cement) and analyzing their performance through a series of standardized tests. Fresh properties such as slump flow, T500 flow time, and V-funnel tests are used to assess workability and flow characteristics. Hardened properties, including compressive strength, split tensile strength, and flexural strength, are evaluated at different curing ages. Durability is analyzed through Rapid Chloride Penetration and Sulfate Resistance tests to assess the resistance to chemical attacks. Results indicate that the inclusion of nano-silica gel significantly enhances the flowability, compressive strength, and durability of SCC. The optimal performance is observed at 1% nano-silica gel dosage, beyond which a reduction in workability and strength occurs due to increased particle agglomeration. This study demonstrates that nano-silica gel can substantially improve SCC properties, making it a viable material for high-performance and sustainable construction practices. These findings contribute to the ongoing development of advanced concrete technologies, paving the way for future research in optimizing SCC mixes with nano-materials.

Theoretical and experimental study on optical polarization states in overhead optical cables under complex weather conditions such as real lightning

Abstract By analyzing the changes in three Stokes vectors, the trajectory of polarization state on the Poincaré sphere, and the polarization change rate, both theoretical and practical aspects of polarization state variations in signal light within optical fiber composite overhead power ground wires (OPGWs) during real thunderstorm conditions, were examined. Our findings reveal that lightning and mechanical vibrations both impact the polarization state of the signal light in OPGW. Theoretical models demonstrate that lightning induces polarization changes through the Faraday magneto-optic effect and exhibits nonlinear electro-optic effects, leading to a maximum polarization change rate of Mrad s−1. In contrast, mechanical vibrations cause long-term, low-intensity polarization rate changes, with a maximum polarization rate of Krad s−1, highlighting a significant optical birefringence effect. Digital signal processing algorithms for coherent receivers with over 100G polarization multiplexing provide valuable guidance for recovering polarization states.

Bioinspired Magnetized String with Tension-Dependent Eigenfrequencies for Wearable Human-Machine Interactions.

Flexible and wearable devices have exhibited potential for applications in the fields of human-machine interactions (HMIs) and Internet of Things. However, challenges remain in the improvement of the communication storage capacity with a simplified architecture. Inspired by tension regulation in natural tendons, a single-channel wearable HMI strategy is proposed using the eigenfrequency of magnetized strings as a sensing solution. Based on electromagnetic induction, mechanical vibration of the magnetized string can electrically induce periodical damping signals in the coil that are associated with the intrinsic eigenfrequency property of the string. Using a theoretical vibration model, nonoverlapping eigenfrequencies are precisely customized by designing the dimension/modulus or tension status of the string to broaden the eigenfrequency library. By integrating strings with different eigenfrequencies, multiple commands can be realized with a single communication channel. Moreover, identifiable commands can be flexibly tuned with only one magnetized string by customizing the tensile length (string tension) for eigenfrequency regulation. Demonstrations such as tactile addressing, authentication systems, and robotic control indicate the potential of the interface for multifunctional HMI applications. We expect that this strategy will provide a valuable reference for the future design of wearable HMI interfaces with high storage capacity and controllability in an accessible architecture.

Femtosecond Laser Introduced Cantilever Beam on Optical Fiber for Vibration Sensing

An all-fiber vibration sensor based on the Fabry-Perot interferometer (FPI) is proposed and experimentally evaluated in this study. The sensor is fabricated by introducing a Fabry-Perot cavity to the single-mode fiber using femtosecond laser ablation. The cavity and the tail act together as a cantilever beam, which can be used as a vibration receiver. When mechanical vibrations are applied, the cavity length of the Fabry-Perot interferometer changes accordingly, altering the interference fringes. Due to the low moment of inertia of the fiber optic cantilever beam, the sensor can achieve broadband frequency responses and high vibration sensitivity without an external vibration receiver structure. The frequency range of sensor detection is 70 Hz–110 kHz, and the sensitivity of the sensor is 60 mV/V. The sensor’s signal-to-noise ratio (SNR) can reach 56 dB. The influence of the sensor parameters (cavity depth and fiber tail length) on the sensing performance are also investigated in this study. The sensor has the advantages of compact structure, high sensitivity, and wideband frequency response, which could be a promising candidate for vibration sensing.

Study on the Vibration Mechanism of the Core Components of an HVDC Filter Capacitor

Study on the Vibration Mechanism of the Core Components of an HVDC Filter Capacitor

A Five-Axis Toolpath Corner-Smoothing Method Based on the Space of Master–Slave Movement

The smoothing of linear toolpaths plays is critical in improving machining quality and efficiency in five-axis CNC machining. Existing corner-smoothing methods often overlook the impact of spline curvature fluctuations, which may lead to acceleration variations, hindering surface quality improvements. The paper presents a five-axis toolpath corner-smoothing method based on the space of master–slave movement (SMM), aiming to minimize curvature fluctuations in five-axis machining and improve surface quality. The concept of movement space in master–slave cooperative motion is introduced, where the tool tip position and tool orientation are decoupled into a main motion trajectory and two master–slave movement space trajectories. By deriving the curvature monotony conditions of a dual Bézier spline, a G2-continuous tool tip corner-smoothing curve with minimal curvature fluctuations is constructed in real-time. Subsequently, using the SMM and the asymmetric dual Bézier spline, a high-order continuous synchronization relationship between the tool tip position and tool orientation is established. Simulation tests and machining experiments show that with our smoothing algorithm, maximum acceleration values for each axis were reduced by 21.05%, while jerk was lowered by 22.31%. These results indicate that trajectory smoothing significantly reduces mechanical vibrations and improves surface quality.

Strong Interference Elimination in Seismic Data Using Multivariate Variational Mode Extraction.

Seismic data acquired in the presence of mechanical vibrations or power facilities may be contaminated by strong interferences, significantly decreasing the data signal-to-noise ratio (S/N). Conventional methods, such as the notch filter and time-frequency transform method, are usually inadequate for suppressing non-stationary interference noises, and may distort effective signals if overprocessing. In this study, we propose a method for eliminating mechanical vibration interferences in seismic data. In our method, we extended the variational mode extraction (VME) technique to a multivariate form, called multivariate variational mode extraction (MVME), for synchronous analysis of multitrace seismic data. The interference frequencies are determined via synchrosqueezing-based time-frequency analysis of process recordings; their corresponding modes are extracted and removed from seismic data using MVME with optimal balancing factors. We used synthetic data to investigate the effectiveness of the method and the influence of tuning parameters on processing results, and then applied the method to field datasets. The results have demonstrated that, compared with the conventional methods, the proposed method could effectively suppress the mechanical vibration interferences, improve the S/Ns and enhance polarization analysis of seismic signals.

Computer Vision-Based Research on the Mechanism of Stick–Slip Vibration Suppression and Wear Reduction in Water-Lubricated Rubber Bearing by Surface Texture

Water-lubricated rubber bearings are a critical component of the propulsion systems in underwater vehicles. Particularly under conditions of low speed and high load, friction-induced vibration and wear often occur. Surface texturing technology has been proven to improve lubrication performance and reduce friction and wear; however, research on how different texture parameters affect friction-induced vibration and wear mechanisms remains insufficient. In this study, various texture patterns with different area ratios and aspect ratios were designed on the surface of water-lubricated rubber bearings. By combining these designs with an in situ observation system based on computer vision technology, the effects of texture parameters on bearing friction, vibration, and wear were thoroughly investigated. The experimental results show that surface textures play a critical role in improving hydrodynamic effects and stabilizing the lubrication film at the friction interface. Specifically, textures with a high area ratio (15%) and aspect ratio (3:1) exhibited the best vibration suppression effect, primarily due to the reduction in actual contact area. However, excessively high area ratios may lead to increased surface wear. This study concludes that a reasonable selection of texture area and aspect ratios can significantly reduce frictional force fluctuations and vibration amplitude, minimize surface wear, and extend bearing life.

Research on Measurement Algorithm of Thermocouple Time Constant Under Multiple Incentive Experimental Conditions

ABSTRACTThe time constant is often an important indicator parameter to evaluate the response speed of thermocouples. However, in practical applications, the output signal suffers from interference and deformation due to the excitation signal not satisfying the desired step size, data transmission delay, and the effect of mechanical vibrations, which do not match the output response of the system of the same order. In addition, the measurement results are not reproducible due to the subjective influence of the manual measurement method. In this paper, we propose a method to compute the time constant. The output signal is modified by filtering and fitting to enable the automatic calculation of the time constant, and the parameters of the algorithm are discussed. We developed a thermocouple time constant measurement device using a water bath and laser excitation conditions, obtaining response signals from thermocouples with different wire diameters and laser powers. The results demonstrate the effectiveness of the proposed time constant calculation methods in accurately capturing the changing trend of thermocouples with different wire diameters and laser powers. These methods successfully meet the requirements for processing the dynamic response signals of thermocouples under various excitation conditions.

Long-Tune Natural Logarithmic Wavelength Modulation Spectroscopy for Gas Sensing.

This article presents a gas sensing method based on long-tune natural logarithmic wavelength modulation spectroscopy (long-tune ln-WMS) and explores means to improve its accuracy. The long-tune spectrum can detect multiple gases with high precision. In ln-WMS, due to the natural logarithm algorithm, the harmonic magnitude which is related to gas concentration would not be affected by the light intensity fluctuations. However, the background signal of the harmonic will become strong and nonlinear in the long-tune spectrum. Three CO2 absorption lines and one H2O line near 2004 nm are applied to verify the proposed theory. The effects of light intensity, modulation depth, gas concentration, and phase shift on the harmonics are tested separately through both simulations and experiments. The results reveal that our proposed method can always keep the harmonics at their maximum which ensures high measurement precision. Moreover, the background signal only varies with the modulation depth, not the concentration and light intensity. Even the mechanical vibrations cannot disturb the harmonics, which enables the proposed method to be suitable for gas detection in harsh environments, especially for heavy dust and severe mechanical vibrations. The CO2 concentration detection results indicate that when the background is eliminated, the accuracy can be achieved with a relative error of below 0.5%, while the error would be greater than 5% with background presence. The proposed long-tune ln-WMS method is effective for trace gas detection (weak absorption) or over-modulation conditions and has potential applications in field inspection.

Effect of Variations in Aggregate Ratios on the Fresh, Hardened, and Durability Properties of Self-Compacting Concrete.

Self-compacting concrete (SCC) is a type of concrete that can be poured into complex geometries and dense reinforcement areas without the need for mechanical vibration, exhibiting excellent segregation resistance and flowability. Its adoption in the construction industry has surged in recent years due to its environmental, technical, and economic advantages, including reduced construction time and minimized occupational hazards. The performance of SCC is significantly influenced by the properties of the aggregates used. This study investigates the effects of variations in the coarse-to-fine aggregate ratio and water/binder (w/b) ratio on the fresh, hardened, and durability properties of SCC. A total of eight different SCC mixtures were prepared, utilizing two distinct s/b ratios and four varying fine-to-coarse aggregate ratios. The results indicated that increasing the s/b ratio enhanced fresh state performance but adversely affected mechanical strength and shrinkage behavior. Furthermore, the need for admixture and flow times improved with increasing coarse aggregate content, attributed to the reduction in cohesiveness and viscosity. However, this change did not significantly impact mechanical properties, while high-temperature resistance and shrinkage exhibited an upward trend.

Vibration-Based Diagnostics of Non-Ceramic Insulators: Characterization of Signals

This paper presents an experimental method for testing composite insulators based on vibration testing. The method used investigated the propagation, signal shape, and distortion of excited mechanical waves under the influence of defects. The aim of the method was to identify defects in the core of a composite insulator that cannot be economically detected by currently available diagnostic methods in field conditions. Therefore, this experiment aimed to distinguish between the mechanical waves’ characteristics of damaged and intact insulators using inexpensive tools. This article seeks to provide a basis for mechanical vibration diagnostics of composite insulators by demonstrating that damage to the core can result in a perceptible difference in the characteristics of mechanical waves when testing within the frequency range of audible sound.

Nonlinear Vibrations of Low Pressure Turbine Bladed Disks: Tests and Simulations

One of the most effective methods to limit the mechanical vibrations of bladed disks is the use of friction damping at mechanical joint interfaces. Unfortunately, dedicated tests to assess the impact of mistuning and the effectiveness of friction dampers are uncommon. This paper presents an original design of an academic demonstrator to perform an experimental analysis of the dynamic response of a tip-free bladed disk with under-platform dampers (UPDs), including an identification of intrinsic and contact mistuning introduced by the UPDs. The 48-blade disk was tested in a vacuum spinning rig by using permanent magnets. Vibration measurements were performed with the Blade Tip-Timing system. Tests were simulated using the Policontact tool, which predicted the average experimental nonlinear response in the presence of UPD, confirming the tool’s ability to capture the general nonlinear dynamic behavior of the mistuned bladed disk. This study presents a novel approach combining experimental Blade Tip Timing (BTT) with numerical simulations using Policontact (ver. 3.0) software and a model update based on experimental evidence to validate nonlinear dynamic responses. It distinguishes between intrinsic and contact mistuning effects, providing new insights into their impact on bladed disk vibrations. Additionally, a comparison of aluminum and steel UPDs reveals that steel offers a 26% greater damping efficiency due to its higher density and preload, significantly improving vibration reduction.

Research on the effect of grinding force on the axial ultrasonic vibration-assisted grinding of Ti-6Al-4V with multi-grain conical grinding head

A multi-grain conical grinding head capable of performing both peripheral and end-face grinding was created in Abaqus to simulate conventional grinding (CG) and axial ultrasonic-assisted vibration grinding (AUVAG) on Ti-6Al-4V alloy. A comparative analysis was conducted to examine the effects of key grinding parameters on the fluctuation amplitude and mean value of grinding forces in CG and AUVAG. The mechanism of ultrasonic vibration’s influence on grinding forces was analyzed, and a theoretical model for normal and tangential grinding forces in peripheral grinding of Ti-6Al-4V was established. Additionally, the surface morphology of CG and AUVAG was analyzed. The study found that the fluctuation amplitude of grinding forces in both AUVAG and CG increases with the axial grinding depth, feed rate, ultrasonic amplitude, and ultrasonic frequency, while it decreases with increasing spindle speed. However, the fluctuation amplitude in AUVAG is greater than that in CG. The average grinding forces in both CG and AUVAG increase with the grinding depth and feed rate, and decrease with the spindle speed. Compared to CG, the mean F x ([Formula: see text]) and F y ([Formula: see text]) are lower in AUVAG, while the mean F z ([Formula: see text]) is higher. Under different axial grinding depths, the maximum reduction in [Formula: see text] and [Formula: see text] for AUVAG is 4.70% and 5.18%, respectively, while the maximum increase in [Formula: see text] is 77.48%. At different feed rates, the maximum reduction in [Formula: see text] and [Formula: see text] for AUVAG is 3.02% and 21.01%, respectively, while the maximum increase in [Formula: see text] is 81.67%. Under different spindle speeds, the maximum reduction in [Formula: see text] and [Formula: see text] is 7.20% and 17.82%, respectively, and the maximum increase in [Formula: see text] is 281%. As the ultrasonic amplitude and frequency increase, [Formula: see text] significantly rises, but the effect on [Formula: see text] and [Formula: see text] is weak. AUVAG improves the surface quality of the specimen.

All time-scale decomposition method and its application in gear fault diagnosis

Adaptive signal decomposition methods, especially without parameters, have become a popular way of diagnosing mechanical faults due to their capability to process mechanical vibration signals adaptively. Empirical mode decomposition (EMD), local mean decomposition (LMD), and local characteristic-scale decomposition (LCD) are typical parameterless adaptive signal decomposition methods currently applied to mechanical fault diagnosis. All of these methods use extreme points to construct baselines, and the mono-component signals are decomposed from an original signal by multiple sift. However, since these methods define time-scale parameters only through extreme points, they are prone to lose the local feature information of an original signal and lead to mode mixing. Aiming at the above problems, the time-scale parameters is defined by using extreme points and zero crossing points simultaneously in this paper. Therefore, we propose a new adaptive signal decomposition method called all time-scale decomposition (ATD). A complex signal can be adaptively decomposed into multiple independent all time-scale components by the ATD method. The baselines of ATD are constructed jointly by extreme points and zero crossing points, so ATD can extract more local feature information of a signal to suppress the mode mixing. First, the principle of ATD is proposed and the method of determining zero crossing points is introduced in this paper. Then, an empirical formula for compensation factor used to determine zero crossing points is deduced. Finally, ATD is verified by the simulation signals and gear signals, respectively. The results indicate that ATD has stronger mode mixing suppression capability and decomposition performance than EMD, LMD, and LCD, and it can be effectively used for gear fault diagnosis.

Exploring dynamics, stability, and bifurcation in a coupled damped oscillator with piezoelectric energy harvester

In this work, we analyze and investigate the mathematical modeling of a dynamical system connected to a piezoelectric device. Piezoelectric transducers are established as highly effective energy harvesting (EH) devices, often employed in real-world mechanical systems. The structure of the dynamical model contains a damped Duffing oscillator acting as the major component, which is connected to an unstretched pendulum and simultaneously to the piezoelectric harvester. To derive the governing equations of motion (EOM), Lagrange’s equations are applied based on the system’s generalized coordinates, in which they are analytically solved using the multiple scales (MS) perturbation method up to the second approximation. Moreover, the solutions achieved are compared with numerical ones to increase transparency and demonstrate the accuracy of the approximate solutions. In addition, comprehensive graphical representations have been produced to investigate the nonlinear stability of the modulation equations. Phase portraits, bifurcation diagrams, and Lyapunov spectra are displayed to depict various system behaviors, alongside Poincaré maps for deeper understanding. The various stability ranges are also explored and discussed. In conclusion, mechanical vibrations are transformed into electricity by the piezoelectric transducer connected to the dynamic model, which has widespread applications and includes crystal oscillators, medical ultrasound, gas igniters, and displacement transducers.

Mechanical properties and vibration characteristics of multiaxial carbon/glass hybrid fiber composites

AbstractIn this paper, the mechanical properties and vibration characteristics of Carbon‐Glass Hybrid Fiber Composites (CGHFC) are experimentally investigated with varying axial directions and blending ratios. The experimental results demonstrate a significant increase in the tensile strength of the CGHFC with an increasing content of carbon fibers. The biaxially CGHFC exhibits a maximum static tensile strength of 413.27 MPa in the 0° direction and 466.33 MPa in the 90° direction, surpassing both the quadratic and uniaxial directions. Notably, compared to biaxially oriented glass fiber material, the tensile strength of CGHFC is enhanced by 44.36%, thereby significantly improving its overall performance, making them particularly suitable for blade structures subjected to simultaneous tensile and vibratory loads. By optimizing the fiber orientation and blend ratio, the CGHFC provides good vibration control and fatigue resistance while ensuring high strength, thus maximizing the overall performance and service life of the blades. The results of this paper provide important data and theoretical support for the selection and design of wind turbine blade materials and help to promote the development of composite materials in wind turbine blade structure and design.Highlights CGHFCs show enhanced tensile strength with more carbon fibers. Biaxial CGHFCs have max tensile strength at 0° and 90° directions. CGHFCs' strength improves by 44.36% over glass fiber materials. Optimized CGHFCs offer superior vibration control and fatigue resistance. Research supports wind turbine blade material innovation.

Effects of nanodiamonds on the mechanical properties, acoustic properties, vibration damping, and flame retardancy of ramie-fiber epoxy composite panels used for indoor applications

This research aims to systematically analyze the impact of nanodiamonds (NDs) in ramie fiber-reinforced epoxy resin acoustic panels used for indoor applications. The panels (four variants) are fabricated using six layers of ramie fiber with various weight percentages of NDs (0.0, 0.2, 0.4, and 0.6) in epoxy resin by the vacuum resin infusion process (VRIP). Mechanical characterization (tensile and flexural strength) was carried out using Instron 8801 universal testing machine. The impedance tube-based sound absorption coefficient (SAC) test was performed at low frequency and higher frequency, respectively. The void content in the panel is evaluated using a micro-x-ray computed tomography (CT) scanner. The dispersion of nanoparticles is studied using scanning electron microscopy (SEM) images. The vertical flame-retardant test and the horizontal flame-retardant test were conducted according to the UL-94 standard. The 0.4 wt.% NDs sample showed good tensile strength (59.178 MPa) and flexural strength (69.134 MPa) compared with other panels. The panels showed differences in SAC values for different weight percentages of NDs, both at lower and higher frequencies. The 0.6 wt.% NDs sample attained the maximum SAC of 0.906 at 6000 Hz in the high-frequency and 0.34 at 1112 Hz in the low-frequency. The SEM reveals an even distribution of NDs in both the 0.2 and 0.4 wt.% NDs panels, while agglomerates form in the 0.6 wt.% panels. The CT scan result shows void content both internally and externally in the panels. There are no voids in the panels where NDs are uniformly distributed. The synergistic effect of NDs in epoxy resin forms a char over the burnt surfaces of samples, enhancing the flame-retardant properties of the panels. According to this study, adding NDs to ramie fiber epoxy composites has improved the panels’ necessary qualities, making them suitable for use as indoor acoustic conditioning materials.

Dynamic regulation of the photothermal conversion performances of nano-enhanced phase change material composited with ceramic foam subjected to external fields

This study aims to comparatively analyze the melting characteristics of magnetic Fe3O4 nano-enhanced phase change materials (NEPCM) assisted by optimum filling strategies of Al2O3 foam ceramics, ultrasonic field and magnetic field under solar radiation. A visualization experimental platform consisting of an ultrasonic field, a magnetic field, and infrared thermography is constructed and used to evaluate in detail the evolution of the melting front, the temperature distribution, and the heat transfer mechanism under different experimental conditions in a square cavity. The results show that the 1 wt% NEPCM using an ultrasonic field has the highest solar energy conversion efficiency of 39.99 % among the 18 experimental groups. This suggests that the cavitation effect and acoustic flow effect induced by ultrasound with a power of 40 W periodic ultrasonic mechanical vibration improve the uniformity of the distribution of magnetic nanoparticles, resulting in improved heat transfer properties. In the experimental group where a magnetic field is applied, the downward movement of the melting interface is accelerated due to the force of the magnetic field on the Fe3O4 nanoparticle. Under the effect of localized porous filling, the solar conversion efficiency of 1 wt% NEPCM is 31.57 % and the total energy storage is as high as 14.39 kJ. With the increase of concentration, the solar conversion efficiency and total energy storage decrease gradually. However, under the simultaneous effect of magnetic field and localized porous filling, the solar conversion efficiency and energy storage show an opposite trend. From a comprehensive point of view, the application of periodic ultrasound with a power of 40 W can effectively improve the photothermal conversion capacity of the PCM.

Effects of mechanical interfaces on magnetic levitation systems and analysis of self-excited vibration mechanisms in coupled systems

Effects of mechanical interfaces on magnetic levitation systems and analysis of self-excited vibration mechanisms in coupled systems