High Natural Frequency Research Articles

Ultra-high-sensitivity micro-accelerometer achieved by pure axial deformation of piezoresistive beams

Microfabricated piezoresistive accelerometers with purely axially deformed piezoresistive beams have demonstrated high performance. However, the conventional design of such accelerometers requires complex theoretical calculations and specific dimensional conditions to achieve purely axial deformation, which inevitably increases the difficulty and cost of the design and manufacturing. We propose an innovative structure that can simply realize pure axial deformation of piezoresistive beams by eliminating the transverse displacement at both ends without tedious calculations. An accelerometer based on the structure was fabricated; both static and dynamic performances were tested. The results showed that the accelerometer had high sensitivity (2.44 mV g−1 with 5 V bias, without circuit amplification), low cross-axis sensitivity (1.56% and 0.49 %, respectively), and high natural frequency (11.4 kHz), with a measurement range of 0–100 g. This design method provides an easy approach for designing high-performance piezoresistive sensors.

Dynamic characteristics and response analysis of a new type of prefabricated fly ash foam concrete structure

Traditional structural dynamics methods for calculating the natural vibration period and mode shape of a structure are not ideal for structures with high natural frequencies. In particular, when buildings are subjected to seismic waves of predominant periods, they will resonate and cause more severe damage. This phenomenon disregards the effect of damping on a structure. The major parameter that considers energy dissipation in structures is the damping ratio. However, no good method for directly calculating the damping ratio is currently available. To address this issue, this study proposes a calculation method for natural vibration period and mode (damping method) that considers damping. It calculates the structural damping ratio by using an energy method and then applies structural dynamics and ABAQUS to verify the results. Finally, ABAQUS is used to study the dynamic response of the new prefabricated fly ash foam concrete structure under the action of two natural waves, and one artificial wave at different fortification intensities. The results show that the influence of damping on the natural vibration period and shape value of the structure is within 9.0%. The damping ratio of this structure is 0.059. The maximum interlayer displacement of the structure under the action of bidirectional seismic waves is 25.3 mm. The maximum interlayer displacement angle is 1/493, the torsional displacement ratio is 1.28, and the minimum interlayer shear force is 609 kN. All the calculation results meet the design requirements of “no collapse under strong earthquakes.”

Pengaruh Pengerolan Alur Pelat Heksagonal Terhadap Frekuensi Pribadinya Dalam Kondisi Bebas-Bebas

Public interest in pick-up cars as a means of transportation for transporting goods has continued to increase lately because they are considered more flexible for transporting raw materials, workshop products and agricultural products and are capable of being operated on urban and rural roads that have different road roughness, as well as in very high traffic conditions. Plate panels that must be used in pick-up vehicles need to be designed as thin as possible but have high stiffness and natural frequency so that they are more efficient in fuel use and able to withstand vibrations that occur during driving. This study aims to determine the natural frequency that occurs in the plate panel profile for vehicle bodies resulting from the cold rolling process. The galvanized steel plates used are 0.6 and 0.8 mm thick. The natural frequency test method is used with free boundary conditions, where the conditioning plate is suspended by a rope. The natural frequency test tool used is the vibroport 80 at an existential pressure of 10 grams, with the hammer hitting the centre of the panel and the sensors being positioned at 0 and 90 degrees. Based on the test results that have been carried out, the panel specimen with a thickness of 0.8 mm obtained the highest natural frequency value of 922.5 Hz, while for a plate thickness of 0.6 mm, the highest value was only 816.25 Hz. However, the two groups of specimens with plate panel thicknesses of 0.6 and 0.8 mm because of rolling experienced an average increase in natural frequency, reaching 2.3 – 2.5 times when compared to the flat plates without the rolling process. The conclusion is that as the natural frequency value increases, the plate panel stiffness also increases.

Development of a High-Performance Microaccelerometer With Position Independent Pure-Axial Stressed Piezoresistive Beams

It has been demonstrated that piezoresistive beams in a purely axial deformation state significantly enhance the performance of piezoresistive accelerometer. Current solution to realize purely axial deformation of piezoresistive beams for high performance micro-accelerometer relies heavily on beam positions, which limits its design flexibility and the error tolerance in the fabrication process. In this paper, a novel structure with position independent pure axially deformed piezoresistive beams is proposed. By controlling synchronous displacements at both ends of piezoresistive beams, the pure axially stress states of the piezoresistive beams can be easily realized at any beam position without tedious theoretical calculations. The theoretical model was developed to understand the relationship between the displacement and the axial stress of the piezoresistive beams, as well as the natural frequency of the whole structure. Then, the correctness of the theoretical model was verified by finite element simulation and experiments. The results demonstrated that the accelerometer had an extremely high sensitivity of 2.44 mV/g/5 V (without circuit amplification), and a high natural frequency of 11.4 kHz.

Dynamic analysis of thick plates reinforced with agglomerated GNPs

In this work, the quasi-3D hyperbolic shear deformation theory (quasi-3D HSDT) is utilized to examine the dynamics of thick rectangular plates reinforced with rectangular nanofillers known as graphene nanoplatelets (GNPs). Agglomeration of the GNPs is incorporated and the mechanical characteristics like shear, elastic, and bulk moduli, Poisson's ratio, and density are analysed according to the mixture along with the Eshelby-Mori-Tanaka approach. Hamilton's principle is hired to derive the solving equations, the Navier approach is hired to present an analytical solution in the spatial domain, and the Newmark method is hired to provide an approximate solution in the time domain. The relevance of the dynamic response and the natural frequencies of the plate on several parameters are explored such as dispersion pattern and the GNPs percentage and agglomeration parameters. It is discovered that for a specific GNPs percentage, growth in the amount of agglomerated GNPs leads to lower natural frequencies and higher dynamic deflection. Meanwhile, for a specific mass fraction of the agglomerated GNPs, growth in the volume of clusters brings about higher natural frequencies and lower dynamic deflection.

Investigation of GFRP/AA7075-T6 Scarf Joint as a Robot Arm for High Natural Frequency and Damping Ratio

Investigation of GFRP/AA7075-T6 Scarf Joint as a Robot Arm for High Natural Frequency and Damping Ratio

A Rayleigh-Ritz solution for high order natural frequencies and eigenmodes of monopile supported offshore wind turbines considering tapered towers and soil pile interactions

Offshore wind turbines may be exposed to extreme or accidental loads during the service life, such as extreme water slamming, ship collisions, earthquakes, extreme winds, ice loads, etc. Under the action of such loads, they will respond not only in the primary eigenmode, but also high order modes. This paper presents a Rayleigh-Ritz solution for high order natural frequencies and eigenmodes of monopile supported offshore turbines. The model considers explicitly tapered wind turbine towers and soil-pile interactions. Different soil conditions are considered using equivalent cross coupled springs at the mudline. The proposed Rayleigh-Ritz solution is applied to the DTU 10 MW wind turbine mounted on a monopile foundation. The predicted natural frequencies and eigenmodes are compared with nonlinear finite element simulations using USFOS. The results show excellent agreement for the first 3 eigenmodes. Even higher eigenmodes than the 3rd order are also calculated but are not presented. They can be readily obtained if needed.High order natural frequencies and eigenmodes using the proposed Rayleigh-Ritz solution can, together with the Duhamel's integral, be well utilized in the buckling and collapse analysis and design of monopile supported offshore wind turbines in Ultimate Limit States (ULS) and Accidental Limit States (ALS). In addition, the high accuracy of the predicted primary natural frequency makes it a useful design tool to help avoid undesired resonance from external excitation loads and to reduce resonance related fatigue effects in Fatigue Limit States (FLS).

A Nonlinear Impact-Driven Triboelectric Vibration Energy Harvester for Frequency Up-Conversion.

Energy harvesting effectively powers micro-sensors and wireless applications. However, higher frequency oscillations do not overlap with ambient vibrations, and low power can be harvested. This paper utilizes vibro-impact triboelectric energy harvesting for frequency up-conversion. Two magnetically coupled cantilever beams with low and high natural frequencies are used. The two beams have identical tip magnets at the same polarity. A triboelectric energy harvester is integrated with the high-frequency beam to generate an electrical signal via contact-separation impact motion between the triboelectric layers. An electrical signal is generated at the low-frequency beam range achieving frequency up-converter. The two degrees of freedom (2DOF) lumped-parameter model system is used to investigate the system's dynamic behavior and the corresponding voltage signal. The static analysis of the system revealed a threshold distance of 15 mm that divides the system into monostable and bistable regimes. In the monostable and bistable regimes, softening and hardening behaviors were observed at low frequencies. Additionally, the threshold voltage generated was increased by 1117% in comparison with the monostable regime. The simulation findings were experimentally validated. The study demonstrates the potential of using triboelectric energy harvesting in frequency up-converting applications.

The manufacture and reliability analysis of the all-rigid Fabry–Perot resonator for fiber-optic acoustic sensors

By the continuous development of aerospace, petroleum exploration, and other industrial fields, the fiber-optic acoustic sensor (FOAS) with high reliability is a desideration sensor, which can be used for noise monitoring in the extremely harsh environment. The FOAS based on the all-rigid Fabry–Perot resonator (FPR) relies on the new acoustic sensitive principle, where the change in the air refractive index is induced by sound waves and gets rid of the distortion caused by the mechanical characteristics of the acoustic sensor based on the movable parts. So, the FPR-based FOAS is very suitable for acoustic sensing in the harsh environment. In this paper, the reliability of this kind of FOASs is simulated and analyzed. The modal and anti-vibration simulation results of FPR with different sizes show that the FPR has a high natural frequency, and the external vibration environment does not affect the acoustic sensitivity of the FPR. The micro and small-batch all-rigid FPR can be manufactured by the optical contact. Moreover, the FPR can withstand the high temperature of 500°C that is verified by rapid heat treatment equipment. In order to improve the reliability of the FOAS, the metal packing shell is designed and fabricated. Moreover, the vibration and high-temperature tests of the packaged sensor are carried out. The two groups of tests show that the sensor can work normally under 10 g of acceleration vibration and 200°C high temperature, respectively. Therefore, the FOAS based on the FPR has high reliability and is very suitable for noise monitoring in the extreme harsh environment of various industrial fields. Furthermore, the research results of this paper will enhance the competitiveness and influence of the commercialized FOAS.

Compressive forces influence on the vibrations of double beams

Abstract The influence of compressive forces on the lower and upper natural frequencies of the double beams has been studied in this article. Euler–Bernoulli’s hypotheses have been used to derive the natural frequency equations. Two asymmetric beams were assumed in this work, and four different boundary conditions were applied in these equations: Pinned–Pinned, Clamped–Clamped, Clamped–Free, and Clamped–Pinned. When the axial compressive force is increased about 18 times, it is observed that the lower natural frequencies decreased by 19% for PP beam, 8% for CC beam, 81% for CF beam, and 12% for CP beam. However, the greatest effect of the axial force on the higher frequencies is by reducing it in the CC beam by a ratio that does not exceed 2%. A rise in the values of axial compressive force causes a reduction in the lower natural frequencies, mostly for the CF beam, while it has a little effect on the higher natural frequencies. Similarly, when the compressive forces on the upper and lower beams fluctuate simultaneously, their effect is doubled on the frequencies when the axial compressive force on one of the two beams changes only.

The Numerical Assembly Technique for arbitrary planar beam structures based on an improved homogeneous solution

AbstractThe Numerical Assembly Technique (NAT) is extended to investigate arbitrary planar frame structures with a focus on the computation of natural frequencies. This allows us to obtain highly accurate results without resorting to spatial discretization. To this end, we systematically introduce a frame structure as a set of nodes, beams, bearings, springs, and external loads and formulate the corresponding boundary and coupling conditions. As the underlying homogeneous solution of the governing equations, we use a novel approach recently presented in the literature. This greatly improves the numerical stability and allows the stable computation of very high natural frequencies accurately. We show this improvement by investigating the condition number of the system matrix and also by the use of variable precision arithmetic.

Accurate Cutting-Force Measurement with Smart Tool Holder in Lathe.

Cutting force in lathe work is closely related to tool wear and affects the turning quality. Direct measurement of the cutting force by measuring the strain of the tool holder is challenging because the tool holder design aims to be highly rigid in order to undertake large cutting forces. Accordingly, the most popular dynamometer designs modify the standard tool holder by decreasing the structural rigidity of the holder, which reduces the machining precision and is not widely accepted. In order to solve the issue of the low stiffness of the dynamometer reducing the machining precision, in this paper, the ultra-low strain on the tool holder was successfully detected by the highly sensitive semiconductor strain gauges (SCSG) adjacent to the blade cutting insert. However, the cutting process would generate much heat, which increases the force measuring area temperature of the tool holder by about 30 °C. As a result, the readout drifted significantly with the temperature changes due to the high temperature coefficient of SCSG. To solve this problem, the temperature on the tool holder was monitored and a BP neural network was proposed to compensate for temperature drift errors. Our methods improved the sensitivity (1.14 × 10-2 mV/N) and the average relative error of the BP neural network prediction (≤1.48%) while maintaining the original stiffness of the tool holder. The smart tool holder developed possesses high natural frequency (≥6 kHz), it is very suitable for dynamic cutting-force measurement. The cutting experiment data in the lathe work show comparable performance with the traditional dynamometers and the resolution of the smart tool holder is 2 N (0.25% of total range).

Impact of stacking sequence on vibration damping and viscoelastic behavior of woven jute sustainable composite

The potential adoption of sustainable materials as replacements for traditional technological materials, whose production depends on the consumption of non-renewable resources like oil, coal, or natural gas, presents a global issue. Natural resources provide an appealing foundation for reconsidering and, in certain instances, optimising modern manufacturing while also making it sustainable. This study focuses on the impact of the number of layers on the viscoelastic behaviour and vibration damping of a sustainable jute-woven reinforced composite. Five types of samples were prepared using compression moulding technique i.e., Neat Resin (NRC), 2 layer(2WJPC),3 layer(3WJPC), 4 layer(4WJPC) and 5 layers (5WJPC). The findings showed that the 4-layer woven jute-polyester composite has the highest natural frequency (4WJPC) and it is about 40% higher than that of matrix material. The lowest measured damping ratio in the DMA test was found in the 5-layer woven jute polyester composite (5WJPC) at 5 Hz frequency. The woven jute mat composite can be employed as a sustainable damping material for low-cost structures, according to the aforementioned results.

Analytical solutions for vibration of Bi-directional functionally graded nonlocal nanobeams

This article provides analytical solutions for the vibration of bidirectional functionally graded (BDFG) nanobeams. The material characteristics of BDFG nanobeams vary along the axial and the thickness directions. The nonlocal elasticity theory of Eringen is followed to model the small-scale effects. The nanobeam's vibrational behavior is formulated by Euler-Bernoulli and Timoshenko beam theories. Hamilton's principle is used to derive the governing equations of motion. Using the Laplace transform, analytical solutions to the governing equations are established, and sets of closed-form frequency equations for four boundary conditions of nonlocal nanobeams are presented. The effects of material constants in both the axial and the thickness directions are investigated. The accuracy of the presented frequency equations is demonstrated by comparisons with a few numerical results available in the literature. It is discovered that when the material parameter along the axis increases, clamped nanobeams have a higher natural frequency, but simply supported, cantilevered, and propped cantilevered nanobeams have a lower. Nonetheless, a rising material parameter along the thickness direction exhibited identical decreasing patterns in natural frequency for all boundary conditions.

Stability Analysis and Distortion Compensation of Robot Structure Dynamics for a Hybrid Simulator

AbstractThe space docking process must be simulated on the ground to guarantee the success of the space docking task. By synthesizing a physical simulation and a numerical simulation, a hybrid simulator can simulate the complicated contact process of space docking. A hybrid simulator consists of a robot (i.e., lower platform), upper platform, docking mechanisms, contact force and torque measurement system, and numerical simulation system. To ensure the simulation accuracy, the robot is expected to have a high structure stiffness, high structure natural frequency, and high bandwidth frequency response. However, these performances are always limited in implementation. In this paper, how the structural dynamics of the robot affect the hybrid simulation accuracy is studied. Due to the structural dynamics of the robot, the divergence and convergence of the hybrid simulation are both possible. The stability conditions are given. A distortion compensation method for the structure dynamics of the robot is proposed. The stability analysis after the compensation is given. The software emulations and experiments are used to verify the analysis and the distortion compensation method. Experiments on real docking mechanisms are given to show the applications.

Comparative Analysis of Four Cylinder Engine Camshaft Material

One of the main concerns of engineers in the field of internal combustion engines is to extend the service life of the components. Also, automotive manufacturer continually increase power train parameters, e.g. the output power and torque together with weight reduction, but this often leads to higher noise and vibration. The aim of this paper is to suggesting a better material for camshaft by comprising 2 different materials such as Grey C.I. and SAE 52100 on the basis of natural frequency, stress and deflection, wear and friction, bending strength, so it minimize vibration problem and increase service life of camshaft. From the frequency, stress and deflection obtained it is observed that the material SAE52100 gives highest natural frequency, less stress and deflection, high bending strengths than currently used material (Grey C.I.). But it is observed that specific wear rate and coefficient of friction of SAE 52100 and Grey C.I .same in all conditions, which is does not adversely affect on fuel economy. So the SAE 52100 material is most suitable material for camshaft amongst the selected materials for analysis.

An Integrated GNSS/MEMS Accelerometer System for Dynamic Structural Response Monitoring under Thunder Loading

Dynamic response monitoring is of great significance for large engineering structural anomaly diagnosis and early warning. Although the global navigation satellite system (GNSS) has been widely used to measure the dynamic structural response, it has the limitation of a relatively low sampling rate. The micro-electro-mechanical system (MEMS) accelerometer has a high sampling frequency, but it belongs to the approaches of acceleration measurements as the absolute position is unavailable. Hence, in this paper, an integrated vibration monitoring system that includes a GNSS receiver and 3-axis MEMS accelerometers was developed to obtain the dynamic responses under the thunder loading. First, a new denoising algorithm for thunderstorm-induced vibration data was proposed based on variational mode decomposition (VMD) and the characteristics of white noise, and the low-frequency disturbance was separated from the GNSS displacement time series. Then, a power spectral density (PSD) analysis using data collected by the integrated system was carried out to extract low/high natural frequencies. Finally, field monitoring data collected at Huanghuacheng, Hefangkou, and Qilianguan in Beijing’s Huairou District were used to validate the effectiveness of the integrated system and processing scheme. According to the results, the proposed integrated GNSS/MEMS accelerometer system can not only be used to detect thunder loading events, but also completely extract the natural frequency based on PSD analysis. The high natural frequencies detected from the accelerometer data of the four Great Wall monitoring stations excited by the thunderstorms are 42.12 Hz, 12.94 Hz, 12.58 Hz, and 5.95 Hz, respectively, while the low natural frequencies detected from the GNSS are 0.02 Hz, 0.019 Hz, 0.016 Hz, and 0.014 Hz, respectively. Moreover, thunderstorms can cause the Great Wall to vibrate with a maximum displacement of 14.3 cm.

A simplified approach for fatigue life prediction of aquaculture nets under waves and currents

With increasing trends to move fish farms to more exposed locations engineers need quick and accurate tools for creating initial design proposals. In this paper, a simplified analytical model for estimating the axial force in the ropes supporting the fish net is presented. Hydrodynamic loads acting on the net are calculated using a state of the art screen model. The simplified analytical model is a quasi-static solution based on the principle of virtual displacements. The assumed mode shape in the calculations is a simplification of the actual quasi-static displacement shape under combined wave and current loading in view of the high natural frequencies of pre-tensioned ropes compared to wave frequencies. The results from the simplified calculations are compared to numerical simulations performed in RIFLEX. The simplified method is extremely efficient with regard to computation time compared to the numerical simulations and is well suited for preliminary design of fish nets.

Dynamic Characteristics and Frequency Reliability Analysis of an Optimized Compliant Stroke Amplification Mechanism

Abstract To rapidly analyze the dynamic characteristics of a compliant stroke amplification mechanism (CSAM) with completely distributed compliance, an analytical model based on the dynamic stiffness matrix with consideration of the damping effect is proposed. The natural frequency of the CSAM is optimized without attenuation of the amplification ratio based on this model. The optimized CSAM exhibits an approximately 112% higher natural frequency than the original mechanism along the main motion direction. The optimization result is verified through finite element simulation, with less than a 7% difference being observed. Moreover, the effects of frequency on the amplification ratio and input stiffness of the optimized CSAM are also discussed. The structural resonance is defined as the failure criterion of the optimized CSAM, and the sensitivity of the failure probability to manufacturing errors at different positions is analyzed. The findings show that the failure probability of the CSAM is more sensitive to parameters associated with the coordinates of the output stage and vertex.

Theoretical, numerical, and experimental investigation on the compliance and natural frequency of sinusoidal flexure hinges

AbstractTo design a flexure hinge with high precision and high natural frequency, the sinusoidal flexure hinge is proposed in this article. First, the formulae for the compliance and precision factors of the hinge were derived based on the Euler–Bernoulli beam theory and the Gauss–Legendre quadrature formula. The natural frequency was also investigated based on the transfer matrix method. Compared with the simulation results of ANSYS Workbench, the results show that the modeling error is less than 6.7%. Second, the influence of structural parameters on compliance, precision factor, compliance precision ratio, and natural frequency was analyzed. The results show that compliance and precision are often contradictory, and the minimum thickness significantly influences the hinge's performance. Compared with conic flexure hinges in terms of compliance, precision, compliance precision ratios, and natural frequency, the sinusoidal flexure hinges have a better comprehensive performance. Finally, a flexure hinge was manufactured, and compliance was measured. The experimental results show that the error between the experimental value and the modeling value is 7.8%. Both simulation and experimental results verify the effectiveness of the sinusoidal flexure hinge model.