High Vibration Amplitudes Research Articles

Hand-arm vibration transmissibility measurement from the petrol driven motorboat engine

Petrol driven motorboat engine consisted of direct handle-engine mounting mechanism which exposed the operators to the high level of vibration and can lead to the Hand-arm Vibration syndrome (HAVs). The transmitted vibration from the engine to the handle with natural frequency excitation making the transmitted vibration worsen. This study is focusing on the vibration analysis of the 3.3 HP motorboat engine and the transmitted vibration to the operator handle in specific directions and frequency ranges. A lab-scale experimental rig with motorboat engine is set-up to represent the actual operation of the motorboat engine. Experimental Modal Analysis (EMA) is conducted at the motorboat handle to obtain the natural frequencies in y and z axis directions. Two levels of engine speed (Speed 1: Low and Speed 2: High) are taken into consideration for the vibration measurement of both engine and handle in x, y and z axis directions. From this study, the natural frequencies of the handle are determined within 75 – 80 Hz. For the vibration spectral measurement, the engine has produced high vibration in x and y axis directions, whereby the transmitted vibration to the handle is worst in y axis direction. At Speed 1, the engine excited the vibration within frequency range of 45 – 50 Hz while by increasing the engine to Speed 2, the vibration peak shifted to 95 – 100 Hz with higher vibration amplitude. In overall, the vibration transmissibility at the handle are significant between the frequency range of 0 – 100 Hz (above 1) which can result the HAVs among the operators if no necessary action been taken.

Нестационарное запаздывание установления нелинейных колебаний в системе двух связанных осцилляторов. Часть 1. Общие положения. Формирование упрощенной системы.

Нестационарное запаздывание установления нелинейных колебаний в системе двух связанных осцилляторов. Часть 1. Общие положения. Формирование упрощенной системы.

On the energy losses due to tracks vibrations in rubber track crawler vehicles

In spite of an increasing number of rubber-tracked vehicles, there are no engineering models for predicting and optimizing the energy consumption of vehicles of this type. To formulate those models, the models of the phenomena resulting in the internal losses of rubber-track systems need to be developed. This article presents a model describing the losses caused by the transverse vibrations of rubber tracks. The predictions made using the model are discussed against the background of the preliminary experimental tests on a sample rubber track for heavy off-road vehicles. The model predictions and the experimental tests suggest that the losses caused by the 1st mode vibration of rubber tracks are marginal in relation to the total internal resistance of rubber-track systems. However, according to the model predictions, a significant increase in the rubber-tracked undercarriage internal resistance is expected as a result of the high-amplitude track vibrations corresponding to the higher-order modes. To make the model applicable in practice, a method for determining the essential parameters of the model, including the bending stiffness and the decrement of oscillation damping, is demonstrated. The accuracy of the method is confirmed by the computations, where the sag and the frequency of the 1st mode free vibration of a sample track are predicted with an error of 10% and 1.8%, respectively. The parameter values obtained by this method are suitable for modeling a wide variety of off-road vehicles. The method can be applied to many other types of reinforced rubber belts, e.g., conveyor belts.

Two-dimensional nonlinear energy sink for effective passive seismic mitigation

Structures and machines are often exposed to sudden high-amplitude vibrations that may cause local or extended structural failure. This calls for effective and reliable methodologies for vibration mitigation, one of which is the use of linear or nonlinear dynamic vibration absorbers. Current studies in this area have focused mainly on uni-directional vibration absorbers, thus limiting their applicability in practical applications where the excitation is applied in the plane. For example, real-life structures are subjected to a multitude of multi-directional seismic excitations, so uni-directional devices for mitigating such effects would have limited effectiveness. Accordingly, in this work we propose a two-dimensional nonlinear passive absorber, which we term two-dimensional nonlinear energy sink (2D-NES), and investigate its efficacy to robustly suppress seismic excitations in arbitrary directions on the plane. First, a numerical optimization process is formulated to optimize the 2D-NES for the especially severe Kobe seismic excitation through a set of quantitative measures related to the seismic response of the primary structure. Then, its robustness is confirmed by applying two additional historic earthquakes with different frequency and energy contents. The results demonstrate that the optimized 2D-NES is capable of effectively and rapidly suppressing seismic, multi directional excitations. This work is one of the first studies of 2D nonlinear vibration absorbers capable of robust passive mitigation of seismic loads applied in arbitrary planar directions. This design can be suitable for broad applications ranging from the nano/micro- to the macro-scale.

Hybrid Numerical-Experimental Model Update Based on Correlation Approach for Turbine Components

Abstract Bladed-disks in turbomachines experience high cycle fatigue failures due to high vibration amplitudes. Therefore, it is important to accurately predict their dynamic characteristics including the mechanical joints at blade-disk interfaces. Before the experimental identification of these joints, it is of paramount importance to accurately measure the interface degrees-of-freedom (DoF). However, they are largely inaccessible for the measurements. For this reason, expansion techniques can be used in order to update the single components. But the expansion can be affected adversely if the measurements are not properly correlated with the updated model. Therefore, a frequency domain expansion method called System Equivalent Model Mixing (SEMM) is used to expand a limited set of measurements to a larger set of numerical DoF. Different measured models—termed the overlay models—are taken from an impact testing campaign of a blade and a disk and coupled to the numerical model according to the SEMM. The expanded models—termed the hybrid models—are then correlated with the validation channels in a round-robin way by means of Frequency Response Assurance Criteria (FRAC). The global correlations depict whether or not a measurement and the respective expansion is properly correlated. By this approach, the least correlated channels can be eliminated from the measurements to have a better updated hybrid model. The method is tested on both the structures (the blade and the disk) and it is successfully shown that removing the uncorrelated channels does improve the quality of the hybrid models.

Control of Very Lightweight 2-DOF Single-Link Flexible Robots Robust to Strain Gauge Sensor Disturbances: A Fractional-Order Approach

This article deals with the control of two degrees of freedom manipulators that have a flexible and very lightweight link. These robots have a single low-frequency and high-amplitude vibration mode. Their actuators have high friction, and their vibration sensors are often strain gauges that have offset and high-frequency noise. These problems reduce the robot precision and produce noisy control signals that saturate actuators. An efficient control system is proposed to overcome these drawbacks. Actuator friction effect is nearly removed by closing a high gain position control loop around the actuator. It causes the separation of the robot dynamics into the controlled actuator fast subsystem and the link dynamics slow subsystem. Based on that, an innovative control system is designed to remove vibrations using the singular perturbation theory combined with the input-state linearization technique. This control system includes fractional-order controllers that nearly remove unknown sensor offset and sensor ramp disturbances while reducing the high-frequency component of the control signal caused by sensor noise. Simulated and experimental results show the superior performance of these controllers over other standard integer-order controllers of similar complexity and nominal behavior.

Nonlinear vibrations of beams with bilinear hysteresis at supports: interpretation of experimental results

Experimental vibration responses of beams with nonlinear boundary conditions were interpreted using a bilinear spring model. Two systems of beams were considered: one is a single rod and the second one is a cluster of parallel rods linked together. The boundary conditions at the beam ends, for both systems, were provided by spacer grids, which are specific supports used in nuclear industry. The experiments were conducted with the beams immersed in still water. The nonlinear boundary conditions imposed to the beams by the spacer grids were experimentally characterized. The boundary conditions changed from having a rotational linear stiffness at low vibration amplitudes to bilinear with hysteresis at higher vibration amplitudes. The bilinear stiffness was found to be of the softening type. A bilinear stiffness model with viscous damping was used to interpret the forced vibration response of the beams. The stiffness and damping ratio used in the model were identified at any excitation level by minimizing, in the frequency domain, the weighted distance between the set of experimental points and the corresponding numerical results. The equivalent viscous damping of the system grew with the vibration amplitude. Very good agreement between numerical and experimental results was obtained for both the beam systems studied in the frequency and force-displacement domains. The model was further refined by using a piecewise linear stiffness function with additional switching points and introducing nonlinear damping. The identified model was capable of reproducing the experimental results with accuracy and without the requirement to adjust the parameters at different excitation levels.

Effect of Strain Measurement Layout on Damage Detection and Localization in a Free Falling Compliant Cylinder Impacting a Water Surface

The need for effective and reliable damage detection and localization systems is growing in several engineering fields, in particular in water impact problems characterized by impulsive loading conditions, high amplitude vibrations and large local deformations. In this paper, we further develop the approach presented in previous works to detect damage of water-impacting structures. Specifically, we provide a set of experimental tests on a flexible plastic cylinder impacting the water after a 50 cm free fall. The cylindrical specimen is artificially damaged in a known position. Strain measurements are performed through a set of nine fiber Bragg gratings distributed along the circumference of a cylinder section. We show that strain sensors can be used as reference sensors, for structure displacements reconstruction, and control sensors, for damage detection purposes, and the computation of the difference between measured and expected deformation may allow damage detection. Moreover, we investigate how exchanging control and reference sensors in the same sensor arrangement affect damage detection and localization.

Energy harvesting from flow-induced vibration of a low-mass square cylinder with different incidence angles

This numerical study investigates the flow-induced vibration responses and energy harvesting characteristics of a low-mass square oscillator. We first test three typical incidence angles of α = 0°, 22.5°, and 45° with reduced velocities Ur ranging from 3.8 to 26. The most interesting phenomenon is that large-amplitude vibrations can be generated at high reduced velocities, regardless of the angle α. We show that this is because of the following mechanisms: (i) For α = 0°, galloping occurs, resulting in high-amplitude and low-frequency vibrations; (ii) for α = 45°, the cylinder undergoes vortex-induced vibrations (VIVs) without the high-amplitude galloping instability. The unsteady vortex shedding effects are enhanced by a very low mass ratio, leading to “VIV forever” in the tested range of Ur with high-level amplitudes; and (iii) for α = 22.5°, the oscillations in the high-Ur range include both VIV and galloping components. Thus, the large amplitude is caused by the galloping instability and enhanced vortex-shedding effects. Due to the existence of large-amplitude vibrations, the low-mass square cylinder demonstrates the potential and necessary robustness for energy harvesting applications. Overall, α = 45° is the most suitable arrangement for the conversion of power. To further improve the efficiency, we test a 45° cylinder under damping ratios ζ ranging from 0.01 to 0.7. The results indicate that the energy harvesting characteristics are sensitive to the damping ratio when ζ < 0.3. Of all the tested cases, ζ = 0.7 provides the highest average efficiency.

Effects of the crack location on the dynamic response of multi-storey frame subjected to the passage of a high-speed train

The high-speed railways require more viaduct than a conventional railway. When the viaduct is subjected to high-amplitude vibrations for a long time, the fatigue-induced crack formation can occur . The presence of a crack changes the stiffness of the structure. Depending on the location of the crack, the reduction effect in stiffness varies. In this study, the presence of a single crack in a multi-storey frame structure, which is considered as a viaduct model, has been investigated. Effects of crack location on the dynamic response are investigated via 3D velocity-crack location-dynamic magnification factor (or maximum displacement) graphs. The train is modelled as a four-axle two-bogie multi-body system with 10 DOF and moving at a constant speed. The finite element method, based on Euler–Bernoulli beam theory, is used to simulate the vibrations of the coupled vehicle-structure system. Wilson-theta time integration scheme is used to solve the equation of motion. It has been determined that when the crack is located at the midpoint of the top beam, the highest effect on the dynamic response is observed.

Effect of material on fluid elastic instability of parallel triangular tube array subjected to water cross

The effect of tube material and structure on fluid elastic instability is examined experimentally using a parallel triangular finned tube array with a P/D ratio of 1.78. Flow-induced vibration is a common cause of failure in shell and tube heat exchangers, and it may result in substantial harm to the heat exchanger as well as significant financial loss. There are different mechanisms responsible for flow induced vibration out of which fluid elastic instability and vortex shedding are the most severe due to their sudden occurrence and high amplitude of vibration. Different parameters affect the tube vibration when the tube array is subjected to water crossflow. In this paper effect of tube material and fin are examined for fluid elastic instability. Experimentation was performed to measure demanding velocity at fluid elastic instability for plain and finned tubes for steel, aluminum and copper material. A fully flexible tube array with a cantilever end condition and with a constant pitch ratio subjected to water cross flow was considered. Testing was done with a gradually increasing water flow rate from 5 m3/hr and increases up to 75 m3/hr to obtain fluid elastic instability. The relationship between the critical velocity at fluid elastic instability and the mass damping parameter was investigated using Connor's equation. The amplitude response of vibration concerning the change in velocity shows that the addition of fins, as well as the material change, greatly affects the fluid elastic instability. A small peak before the occurrence of fluid elastic instability was observed. This is maybe due to vortex shedding which further required to be verified using the Strouhal number.

The Motion of Strawberry Leaves in an Air-Assisted Spray Field and its Influence on Droplet Deposition

HighlightsA visualization method for the motion of strawberry leaves in an air-assisted spray field is proposed.Strawberry leaves showed two motion states in different critical velocity ranges of the sprayer airflow.The airflow instability and the turbulence effect are considered important factors for the leaf vibrations.A strawberry leaf azimuth angle in the range of 90° to 270° can provide good deposition with smaller droplets.Abstract. The reasonable motion of crop plants in an air-assisted spray field can improve droplet deposition. Therefore, this study focuses on the motion of strawberry leaves and the droplet deposition mechanism in an air-assisted spray field. First, this study proposes a descriptive method for strawberry leaf motion in an air-assisted spray field and clarifies the important influence of strawberry leaf motion on droplet deposition. Second, an experiment was performed on the motion and droplet capture of single strawberry leaves in multi-position postures in an air-assisted spray field. The results showed that the leaves had two motion states (i.e., low amplitude with low frequency and high amplitude with high frequency) at different airflow velocities and inclination angles, and the critical airflow velocity corresponding to the two motion states was determined to be 8.7 m s-1. When the azimuth angle of the strawberry leaves is in the range of 90° to 270°, a reasonable inclination angle of the airflow and the high frequency and high amplitude vibration state of the leaves driven by the airflow will provide good deposition and canopy penetration of droplets with smaller diameters. Keywords: Air-assisted spray field, Droplet deposition, Motion, Spray, Strawberry leaves.

Dynamic analysis of elliptical vibrating screen based on disc motor

ABSTRACT According to the requirements of the current drilling fluid vibrating screen for high efficiency, high reliability and low energy consumption, an elliptical vibrating screen based on disk motor is proposed. The dynamic analysis model of the vibrating screen of the three-excited motor is established, and the dynamic characteristics of the whole system and key structures are studied by multi-body dynamics and finite element method. The dynamic stress response characteristics of the rigid flexible coupling system of screen box are mainly analysed. Based on the deformation and stress of the flexible body damage node analysis results, through the fatigue cumulative damage theory and rain-flow counting method against casing load surface fatigue life prediction, verifying the reliability of fatigue life of screen box. The result shows that: Three Eccentric Rotors elliptical vibrating screen can achieve balanced elliptical vibration track, meeting the requirements of high stable amplitude vibration, and its natural frequency, structural strength and fatigue life all meet the engineering requirements, verifying the feasibility and effectiveness of the design scheme.

Simultaneously achieving self-toughening and self-reinforcing of polyethylene on an industrial scale using volume-pulsation injection molding

It is critical and difficult for production of large polymer parts using injection molding method to simultaneously achieve both good flowability and mechanical properties. Volume-Pulsation Injection Molding (VPIM) technology, exerting a high-amplitude vibration force field during the entire injection molding process, can be exploited to address this challenge, on an industrial scale. Through orientation of macromolecules with vibration forces during injection molding, mechanical properties of polymers can be improved at low cost without sacrificing flowability. In this study, employing VPIM technology, self-toughening and self-reinforcing of high-density polyethylene (HDPE) were realized while maintaining satisfactory flowability. Comparing with those of the convention injection molding (CIM) samples @ 210 °C, impact and yield strengths of the VPIM samples @ 0.7 Hz-210 °C were increased by 782.93% and 14.25%, respectively. According to crystal morphologies, shish-kebabs were formed in intermediate layer, leading to a remarkable enhancement in mechanical properties. Injection temperature and processing frequency had an influence on the shish-kebab structure and the intermediate layer thickness, thereby determining mechanical properties. These analysis results were supported by the evidence from impact-fractured surface morphology, 2D-SAXS, 2D-WAXD, and DSC. The response law of crystal structure and morphology to the vibration flow field was proposed to uncover the influence of processing conditions on material properties.

Piezoelectric energy enhancement strategy for active fuzzy harvester with time-varying and intermittent switching

This study aims to increase the amount of electrical energy harvested from a piezoelectric vibration energy harvester under unloaded and high-load resistance conditions. Although increased piezoelectric charge due to the synchronized switch harvesting on inductor (SSHI) strategy damps mechanical vibrations, the mechanical vibration amplitude of a mechanical element in a harvester is assumed to be constant for most discussions regarding the active harvester with SSHI strategy. However, this assumption is not valid under excessive switching actions, in which case the performance of the harvester deteriorates. This problem is known as the vibration suppression effect. To address this problem, in this study, two switching strategies for the charge inversion circuit—namely, switching considering vibration suppression-threshold (SCVS-t) and adaptive SCVS-t (ASCVS-t)—are proposed through intermittent switching actions. During the harvesting process, intermittent switching using these strategies is performed based on the output voltage threshold, thus maintaining high mechanical vibration amplitude and excellent harvesting performance by avoiding excess switching. The ASCVS-t adopts a tuning algorithm for the time-varying threshold and can achieve appropriate intermittent switching and effective harvesting under various vibration conditions without pre-tuning. Experimental comparisons with conventional strategies confirm that the proposed strategies achieve 2.9 times and 2.0 times greater harvested energy storages than a standard harvester and conventional switching strategy, respectively.

Phonon-driven ultrafast symmetry lowering in a Bi2Se3 crystal

Selective excitation of coherent high-amplitude vibrations of atoms in a solid can induce exotic nonequilibrium states, in which the character of interactions between electronic, magnetic and lattice degrees of freedom is considerably altered and the underlying symmetries are broken. Here we use intense single-cycle terahertz pulses to drive coherently the dipole-active $E_u^1$ phonon mode of a Bi$_2$Se$_3$ crystal. As a result, several Raman-active modes are simultaneously excited in a nonlinear process, while one of them, having the $E_g^2$ symmetry, experiences dynamical splitting during the first two picoseconds after excitation. The corresponding angular scattering pattern is modified indicating coexistence of two phonon modes characteristic of a nonequilibrium state with a lower crystal symmetry. We observe also a short-lived frequency splitting of the original $E_g^2$ mode that immediately after excitation amounts to $\sim 25\%$ of the unperturbed value. This transient state relaxes with a characteristic time of $\sim$ 1 ps, that is close to the decay time of the squared amplitude of the resonantly excited infrared-active $E_u^1$ mode. We discuss possible mechanisms of the dynamical splitting: nonlinear lattice deformation caused by the intense $E_u^1$ vibrations and excitation of anisotropic electronic distribution due to nonlinear electron-phonon interaction. Our data also contain an evidence in favor of the sum-frequency Raman mechanism of generation of the coherent $E_g^2$ phonons in Bi$_2$Se$_3$ excited by terahertz pulses.

Monitoring dynamic characteristics of 600 m+ Shanghai Tower during two consecutive typhoons

Though the dynamic performance of high-rise buildings under wind has been widely investigated, there have been relatively limited studies focusing on the wind effects on 600 m+ super high-rise buildings based on real measured data during typhoons. This paper presents the field measurement results of structural dynamic characteristics and wind-induced responses of the Shanghai Tower with a height of 632 m during two successive typhoons, from August 12 to 18, 2018. Additionally, based on the analytical mode decomposition method, a modified discrete-time Fourier transformation method combined with moving window technology in time domain is developed to analyze the time-varying characteristics of natural frequencies. The relationship between the mean wind speed and acceleration amplitudes is investigated as well. A numerical experiment is carried out to verify the effectiveness of the random decrement technique, by using which the time-varying average damping ratios of the first mode associated with the Shanghai Tower are identified. In addition, the damping ratios do not exhibit an increasing trend with the increase of vibration amplitudes without the contribution of the tuned mass damper. It recommends that the critical damping ratios under high vibration amplitude are 2.5%–3.0% when the damper is active and 0.5%–1.0% when the damper is inactive. The analytical results can provide useful information for the dynamic characteristics as well as the wind-resistant design for 600 m+ super high-rise buildings.

A 3D model to solve U-tube steam generator secondary side thermal-hydraulics with coupled primary-to-secondary side heat transfer

The U-tubes of steam generators (SG) are concerned by vibration issues. The vibration behavior is driven by the local secondary flow (velocity, void fraction, two-phase pattern). Fluid-elastic instability (FEI) can be considered as the most severe vibration phenomenon, since it features high vibration amplitudes and tube-to-tube contacts, which can rapidly cause tube rupture. In order to predict if the fluid forces exerted along the tube bundle can trigger a FEI, numerical tools able to calculate the secondary side of a SG are needed. In the frame of its mission of assessing methods adopted by utilities for demonstrating the safe operation of nuclear facilities, the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN) has developed such a numerical model. The model is based on a 3D homogeneous drift-flux formulation of the SG steam-water mixture, together with a porous media approach to account for the tube bundle. The model is implemented in the ANSYS Fluent CFD code. The SG primary side is solved using a dedicated meshing. The secondary side and the primary side meshes communicate through heat transfer, which is fundamental to obtain consistent numerical results. The details of the numerical approach are described in the first part of this paper. Then, numerical versus experimental results comparisons in terms of heat transfer are provided for a SG test facility: numerical and experimental results are in good agreement. The model was then applied to a real SG: numerical results are in good agreement with nominal operating parameters.

Performance analysis of a quasi-zero stiffness vibration isolation system with scissor-like structures

To isolate low-frequency vibration, a novel single-degree-of-freedom vibration isolation system with quasi-zero stiffness (QZS) and nonlinear damping using geometric nonlinearity is proposed in this study. One of the remarkable features of this system is the use of scissor-like structures (SLSs) to achieve the nonlinear stiffness and damping. The length difference between the connecting rods in SLS is considered. First, both the stiffness and damping characteristics are derived and analyzed in detail. Then, the frequency response and force transmissibility are obtained using the harmonic balance method. Finally, the effects of structural parameters on the isolation performance are investigated. Theoretical results show that the proposed QZS vibration system can not only isolate low-frequency vibration but also suppress the high-amplitude vibration in the resonant region. Besides, increasing nonlinear damping has little influence on the isolation performance in high frequencies. The proposed QZS vibration system can outperform a classical counterpart.

COGNITIVE REACTION TIME PERFORMANCE AND SUBJECTIVE DROWSINESS: A CRITICAL EVALUATION OF THE EFFECT OF WHOLE-BODY VIBRATIONS

It is believed that exposure to whole-body vibration (WBV) may increase seated occupant drowsiness, and seated occupant drowsiness may contribute to vehicular accidents. Previous studies on driver comfort have indicated that long-term exposure to WBV may have an adverse effect on musculoskeletal disorders. However, the effects of WBV on seated occupants’ drowsiness have been less rigorously studied. Thus, this study aims to investigate the association between exposure to WBV and drowsiness level. Laboratory experiments were designed and involved eighteen healthy male volunteers. Volunteers were exposed to random gaussian vibration for 20-minutes with the frequency between 1-15Hz. The transmitted vibration magnitude was adjusted for each volunteer to become 0.2ms-2 for low vibration magnitude and 0.4ms2 for medium vibration magnitude. Volunteers’ vigilance was measured by the Psychomotor Vigilance Task (PVT) before and after the vibration exposure. The analyses revealed a substantial drop in volunteers’ vigilance level after exposure to vibration and the effect was more pronounced in high vibration amplitude 0.4 ms-2. These findings suggested that exposure to vibration even as low as 20-minutes may attribute to the reduction of alertness level.