High Vibration Amplitudes Research Articles

Analysis of Deformation in an Aluminium Hull Impacting Water Free Surface

Water impacts provide a challenge for a wide range of applications, from aerospace, to marine, mechanical and civil engineering, due to the complexity conveyed by the coexistence of impulsive loads, large local deformations and high-amplitude vibrations. Thus, the need for reliable structural health monitoring (SHM) systems is emerging in the industrial field of fluid-structure interaction (FSI) applications. In this paper, we leverage the previous work on strain and displacement fields reconstruction to analyse a scale aluminium model subject to water vertical and oblique impacts. Fibre Bragg grating (FBG) sensors were installed on the hull ribs and used both as reconstruction sensors (to reconstruct the structure mechanical behaviour characteristics) and as control sensors, by using their signals to compare the real and reconstructed structural parameters, at the sensors locations. Finally, the effectiveness of different reconstruction layouts was investigated referring to the strain signal reconstruction quality in case of both vertical and oblique impacts. Results show the potential of the described method for the reconstruction of strain signal through a proper choice of the reconstruction sensors positions both in case of vertical and oblique impacts.

Vortex- and Wake-Induced Vibrations of a Circular Cylinder Placed in the Proximity of Two Fixed Cylinders

PurposeThis study aims to understand the vibratory response of a circular cylinder placed in proximity to other fixed bodies.MethodsA circular cylinder model was placed in a circulating water channel and was supported elastically to vibrate in the water. Another two circular cylinders were fixed upstream of the vibrating cylinder. The temporal displacement variations of the vibrating cylinder were measured and processed by a frequency analysis.ResultsWhen the inline spacings were small, two amplitude peaks appeared in the reduced velocity range 3.0–13.0. When the inline spacings were large, the amplitude response showed a single peak.ConclusionFor small inline spacings, the first peak was attributed to high-amplitude vibrations forced by Karman vortex streets shed from the upstream cylinders. The second peak arose from interactions of the wakes of the upstream cylinder with the vibrating cylinder. When the inline spacing increased, the vortex-induced vibrations resembled those of an isolated cylinder.

Calculation of the steady-state roughness and the size of the hardened layer during vibration finishing and hardening processing with high amplitudes

The results of studies of the method of vibration hardening and finishing processing with high vibration amplitudes are presented. Theoretical models of such processing with classical (traditional) amplitudes are presented, which allow evaluating the surface roughness and depth of the hardened layer. Correction factors are proposed that take into account the effect of high amplitudes on the parameters of the treated surface. Based on the results of experimental studies with high amplitudes, the values of the parameters of the treated surface are determined. The dependence of the steady-state roughness of the surface and the depth of the hardened layer on the value of high vibration amplitudes is established.

Design and Modeling of Viscoelastic Layers for Locomotive Wheel Damping

Rail–wheel interaction is one of the most significant and studied aspects of rail vehicle dynamics. The vibrations caused by rail–wheel interaction can become critical when the radial, lateral and longitudinal loads of the vehicle, cargo and passengers are experienced while the vehicle is in motion along winding railroad paths. This mainly causes an excessive production of vibrations that may lead to discomfort for the passengers and shortening of the life span of the vehicle’s body parts. The use of harmonic response analysis (HRA) shows that the wheel experiences high vibrational amplitudes from both radial and lateral excitation. The present study describes a numerical and experimental design procedure that allows mitigation of the locomotive wheel resonance during radial and lateral excitations through viscoelastic layers. It is proven that these high frequencies can be reduced through the proper design of damping layer mechanisms. In particular, three parametric viscoelastic damping layer arrangements were analyzed (on the web of both wheel sides, under the rim of both wheel sides and on the web and under the rim of both wheel sides). The results demonstrate that the correct design and dimensions of these viscoelastic damping layers reduce the high-amplitude resonance peaks of the wheel successfully during both radial and lateral excitation.

Fractional Control of a Lightweight Single Link Flexible Robot Robust to Strain Gauge Sensor Disturbances and Payload Changes

In this paper, a method to control one degree of freedom lightweight flexible manipulators is investigated. These robots have a single low-frequency and high amplitude vibration mode. They hold actuators with high friction, and sensors which are often strain gauges with offset and high-frequency noise. These problems reduce the motion’s performance and the precision of the robot tip positioning. Moreover, since the carried payload changes in the different tasks, that vibration frequency also changes producing underdamped or even unstable time responses of the closed-loop control system. The actuator friction effect is removed by using a robust two degrees of freedom PID control system which feeds back the actuator position. This is called the inner loop. After, an outer loop is closed that removes the link vibrations and is designed based on the combination of the singular perturbation theory and the input-state linearization technique. A new controller is proposed for this outer loop that: (1) removes the strain gauge offset effects, (2) reduces the risk of saturating the actuator due to the high-frequency noise of strain gauges and (3) achieves high robustness to a change in the payload mass. This last feature prompted us to use a fractional-order PD controller. A procedure for tuning this controller is also proposed. Simulated and experimental results are presented that show that its performance overcomes those of PD controllers, which are the controllers usually employed in the input-state linearization of second-order systems.

Study on heat pipe heat dissipation of high-power ultrasonic transducer

In order to solve the problems of frequency shift, efficiency decline and life shortening caused by temperature rise in the working process of high-power ultrasonic transducer, the technology of heat pipe is employed for enhancing heat dissipation of the ultrasonic transducer. A new type of high-power transducer with heat pipe heat dissipation (HPUT) is proposed in this study. The heat pipe radiator adopts the form of a copper–water-composite wick, and installs straight fins on the condensation section to enhance heat dissipation. Six heat pipe radiators are embedded in the front cover plate of the transducer close to the piezoelectric ceramic and evenly arranged along the circumference of the transducer. The vibration characteristics, radiated sound field characteristics and heat dissipation characteristics of the HPUT are compared with those of traditional Langevin ultrasonic transducer (TLUT) through simulations and experiments. Results manifest that compared with the TLUT, the HPUT has much lower operation temperature (reduced by 60% in this study), much smaller resonant frequency shift (reduced by 75% in this study) and the higher vibration amplitude (increased by 25% in this study). This study will contribute to the development of high-power ultrasonic transducer which has potential application value in many industrial fields.

Experimental study on designing optimal vibration amplitude in ultrasonic assisted incremental forming of AA6061-T6

Superimposing ultrasonic vibration with metal working process has been proven as effective auxiliary method for improving the quality characteristics. Since, the incremental forming is a state-of-the-art sheet metal working process, number of researches which applied ultrasonic vibration to this process are limited and further studies are still required to basically understand its influence on performance measures. In the present study, an experimental attempt was made to understand how the vibration amplitude influences the forming force, thickness distribution and dimensional accuracy of the samples formed by incremental forming process. In order to do so, series of single factor experiments were designed by variation of vibration amplitude (0, 5, 10 and 15 µm) as main parameter and other parameters were kept constant. The obtained results revealed that increasing the vibration amplitude up to a certain value results in reduction of forming force and dimensional deviation, as well it results in thinning in critical region. At the end of the work, an optimization framework was designed to find interaction effect of process factors with achieving regarding minimized process time as well desired sample quality. It is found from optimization results that superimposing high vibration amplitude provides condition for obtaining minimum process time as well desired quality characteristic of workpiece.

A novel technique for automating stiffness measurement and emphasizing the main wave: Coherent-wave auto-selection (CHASE)

This study aims to develop and assess a new automated processing technique in MR elastography (MRE), namely coherent-wave auto-selection (CHASE). CHASE enables automatic selection of the region of interest (ROI) for stiffness measurement by extraction of the coherent wave region (CHASE ROI), and it improves the reconstruction of stiffness by a directional filter oriented along the main wave in each pixel (CHASE filtering). In this study, MRE of a phantom and of the liver of four healthy volunteers was performed. To investigate the potential of CHASE, this study assessed the CHASE according to three indices through the phantom study: 1) agreement on the ROI settings between CHASE and expert observers, 2) noise dependency, and 3) effect of the CHASE on stiffness variability within the CHASE ROI. The agreements on the ROI settings were analyzed by Cohen's kappa coefficient (κ). The noise dependency was analyzed by the mean absolute percentage errors (MAPEs) within the ROI between low (20%–80% amplitudes) and high vibration amplitudes (100% amplitude). The stiffness variability was assessed by standard deviation (SD) within the ROI. In the volunteer study, agreements on the ROI settings (or stiffness value) and stiffness variability within the CHASE ROI were assessed using κ-value (or intraclass correlation coefficient: ICC) and coefficient of variation, respectively. The results showed close agreement on the ROI settings and stiffness (κ-value: greater than 0.61 in both the phantom and volunteer studies, ICC: 0.97 in the volunteer study). The MAPEs within the CHASE ROI were much smaller than those in the whole region of the phantom (CHASE ROI vs. the whole region at 20% amplitude: 10.3% vs. 50.8%). Moreover, in both the phantom and volunteer studies, the stiffness variation within the CHASE ROI was smaller in the elastogram processed with CHASE filtering than in the unprocessed one. Our results demonstrated that the CHASE has high robustness against noise and the potential to provide ROI settings for stiffness measurement comparable to expert observers, as well as improve the reconstruction of stiffness.

Experimental investigations on post-flutter performance of a bridge deck sectional model using a novel testing device

This paper studies the flutter performances of a streamlined bridge deck sectional model using a recently developed testing device for large-amplitude free vibration test. The reported torsional vibration amplitude of the sectional model exceeds 15°, and higher vibration amplitudes can be achieved if desired. The flutter performances at various initial angles of attack α0, the hysteresis behavior, and the energy budget property of the flutter response are analyzed. Experimental results show that the sectional model exhibits divergent vibrations right after the critical flutter velocities for α0 = 0°, −3°, and −5°, while it performs limit cycle oscillations (LCO) after the critical flutter velocities for α0 = +3° and +5°. Hysteresis phenomena are observed for all tested angles of attack. Both the critical flutter velocity and the vibration amplitudes around the critical velocity may be affected by the initial impulse excitation exerted on the bridge deck. The vertical-to-torsional amplitude ratio decreases with increasing the vibration amplitude for a coupled LCO, while the opposite rule is observed for a divergent vibration. The energy dissipated by the mechanical damping accumulates continuously while the total mechanical energy varies non-monotonously with increasing time. This study is expected to deepen the understanding of the flutter responses of a bridge deck in the presence of nonlinear aerodynamic effects. The experimental results can also serve as a database for validating computational fluid dynamics procedures and nonlinear self-excited force models.

New controller (NPDCVF) outcome of FG cylindrical shell structure

This paper presents a new active controller technique effect of functionally graded (FG) cylindrical shell structure model within joint harmonic and parametric excitations. The new active controller involves Nonlinear Proportional-Derivative (NPD) plus Negative Cubic Velocity Feedback (NCVF) as a new nonlinear control method (NPDCVF). The motivation of this study is the well-known observation that NPDCVF control method can offer a means to improve the performance of plant systems. The coupled nonlinear differential equations with two modes have been derived applying the von Kármán nonlinear theory, Galerkin’s process, and the static condensation technique. Static condensation is the process of decreasing the number of free displacements or degrees of freedom. We have added other three different controller methods over the structure to select the best controller. The three applied controller methods to the considered structure are: Integral Resonant Control (IRC), Positive Position Feedback (PPF), and Nonlinear Integral Positive Position Feedback (NIPPF) which are applied to the considered structure. We establish that the best one for dipping the high vibration amplitudes is the NPDCVF as a new controller. The perturbation technique is useful to solve the present model including quadratic and cubic nonlinearities subjected to mixed harmonic and parametric forces within the simultaneous primary resonance case (Ω=ω1,Ω=ω2) as the worst resonance case of the system. All numerical outcomes have been completed with the help of MATLAB Ra 18.0 program software over the investigated model. The obtained results have proved that this new controller is excellent for improving the structure by reducing the risky vibrations caused during primary resonances. Frequency response equations have helped in observing the stability examination of the obtained numerical solutions. The actions of several factors performed on the controlled model have been examined and described. Some comparisons have also been prepared with the available recent published papers of a similar model.

Laser induced surface analysis of acoustic materials for noise reduction

Every material has its own surface configuration and the surface gets modified when it is treated using some surfactants. The action of surfactants on the material creates a number of elastic skeletal structures which enable the material to be used as acoustic material for absorption of sound. The sensitivity of the material to high intensity of sound has great importance in different technological applications. A laboratory designed noncontact laser based sensor has shown its credential by sensing the surface roughness, which is an essential and sufficient condition for measurement of the sound absorption coefficient. The sensitivity is measured from speckle contrast which provides the suitability of the material for sensing sound intensity. The estimation of surface roughness and the presence of porosity are well recognized by the speckle contrast which helps measure the efficiency of the sound absorption coefficient. The incident of a laser beam in the presence of sound intensity significantly enhances the sound absorption followed by the loss of kinetic energy due to high amplitude vibrations within the pores present on the surface of the material medium exposed under the high intensity of laser light.

Numerical and experimental analysis of pressure fluctuations in the draft-tube of a Francis turbine using the swirl number

Pressure fluctuations in the draft-tubes of hydraulic turbines are the most dominant issues that may cause damages to a hydraulic power plant. When the frequency of the fluctuations coincides with one natural frequencies of the plant, resonance with high amplitude vibrations and pressure pulsations occurs, dramatically impacting the integrity of the plant. This research focuses on the part-load behaviour of a medium specific-speed Francis turbine (with specific speed 184 m.kW), designed by the authors in the framework of an industrial project. This paper combines the results of model tests with CFD simulation to investigate the part-load behaviour of the turbine. To do so, performance of the turbine is numerically simulated at one operating condition by solving the RANS equations via the commercial code ANSYS CFX 19.0. The k-ω SST turbulence model is used to predict the turbine performance. In addition, model tests are conducted in the range of 20% to 110% guide vane opening. To capture pressure fluctuations in the draft-tube, 12 static pressure sensors are installed in 4 different sections of the draft-tube. The no-swirl and other iso-swirl lines of the draft tube flow are first determined by using CFD results. Furthermore, pressure signals from model tests are analysed by performing cross spectral density analysis. Two transitions in the behaviour of the precessing vortex under part-load conditions occurring at given values of swirl number are observed. Finally, it is observed that linear correlations between the Strouhal number of the vortex rope frequency and the swirl number can be established within the 2nd and 3rd part-load regimes, independently of the values of the speed coefficient.

Image processing technology in high frequency vibration direction and amplitude measurement

In recent years, with the development of computer software and hardware and artificial intelligence technology, photoelectric imaging equipment has gradually developed in the direction of digitization and intelligence. This paper mainly studies the application of image processing technology in the measurement of high-frequency vibration direction and amplitude. According to the corresponding relationship between the vibration blur image and the still image in the frequency spectrum, the image is preprocessed. This article adopts the traditional camera calibration method, which uses a special standard template to calibrate the internal and external parameters of the camera. The three-dimensional search algorithm is used to analyze and compare the recognition images of the left and right cameras in each state, and finally calculate the internal and external parameters of the camera. The data shows that the fundamental frequency is about 4.9 Hz, and the fundamental frequency order basically fluctuates around 16. The calculated amplitudes are 0.89, 0.93 and 0.99μm, respectively. The results show that the image processing technology can restore image edge details to a certain extent, suppress noise, and effectively shorten the matching time between feature points.

Nonlinear friction behavior in ultrasonic welding of aluminum alloy to carbon fiber reinforced PA6 composite

Accurate prediction of the friction-mediated interaction between workpieces in ultrasonic welding requires nonlinear multi-physical models. Local contact points that are in slip receive a heat flux from friction, which raises the local temperature and therefore, changes the local material stiffness and local stresses. These local changes affect the contact status and the overall dynamics. The effects of vibration amplitude and clamping force on the nonlinear friction behavior in ultrasonic welding of aluminum alloy to carbon fiber reinforced thermoplastic (CFRTP) are particularly important process parameters that can be controlled. Their effect is investigated through a multiphysics coupled model with consideration of the nonlinear contact, nonlinear structural dynamics, and the transient heat conduction. Solutions are obtained by combining the harmonic balance method with the finite element method. Intuitively, large amplitudes promote sliding and higher heating, while large clamping forces can promote sticking and lower heating. Unexpectedly however, results show that the amplitude has a limited influence on the process, while the clamping force has a significant influence. That is because optimal heating results from a balanced manifestation of sticking, sliding and temperature at the interface. In particular, results suggest that a low clamping force with a high vibration amplitude is desirable for the ultrasonic welding of aluminum alloys to CFRTP composites.

Acoustic Resonance in an Axial Multistage Compressor Leading to Non-Synchronous Blade Vibration

Abstract Significant non-synchronous blade vibrations (NSVs) have been observed in an experimental three-stage high-speed compressor at part-speed conditions. High-amplitude acoustic modes, propagating around the circumference and originating in the highly loaded stage-3, have been observed in coherence with the structural vibration mode. In order to understand the occurring phenomena, a detailed numerical study has been carried out to reproduce the mechanism. Unsteady full-annulus Reynolds-averaged Navier–Stokes simulations of the whole setup have been performed using the solver elsA. The results revealed the development of propagating acoustic modes which are partially trapped in the annulus and are in resonance with an aerodynamic disturbance in rotor-3. The aerodynamic disturbance is identified as an unsteady separation of the blade boundary layer in rotor-3. The results indicate that the frequency and phase of the separation adapt to match those of the acoustic wave and are therefore governed by acoustic propagation conditions. Furthermore, the simulations clearly show the modulation of the propagating wave with the rotor blades, leading to a change of circumferential wave numbers while passing the blade row. To analyze if the effect is self-induced by the blade vibration, a non-coherent structural mode has been imposed in the simulations. Even at high vibration amplitude, the formerly observed acoustic mode did not change its circumferential wave number. This phenomenon is highly relevant to modern compressor designs, since the appearance of the axially propagating acoustic waves can excite blade vibrations if they coincide with a structural eigenmode, as observed in the presented experiments.

High-Performance Face Milling of 42CrMo4 Steel: Influence of Entering Angle on the Measured Surface Roughness, Cutting Force and Vibration Amplitude

High feed Milling is a new milling method, which allows to apply high feed rates and increase machining efficiency. The method utilizes face cutters with a very small entering angle, of about 10°–20°. Thus, the cut layer cross-section is different than in traditional milling. In order to examine the high feed milling (HFM), experimental tests were conducted, preceded by an analysis of cutting zones when milling with an HF face cutter. The face milling tests of 42CrMo4 steel with the use of an HF cutter characterized by an entering angle, dependent on axial depth of cut ap and insert radius r values, as well as with a conventional face cutter with the entering angle of 45° were performed. The study focused on analyzing the vibration amplitude, cutting force components in the workpiece coordinate system, and surface roughness. The experimental tests proved, that when milling with constant cut layer thickness, the high feed cutter allowed to obtain twice the cutting volume in comparison with the conventional face cutter. However, higher machining efficiency resulted in an increase in cutting force components. Furthermore, the results indicate significantly higher surface roughness and higher vibration amplitudes when milling with the HF cutter.

Analysis on ground surface in ultrasonic face grinding of silicon carbide (SiC) ceramic with minor vibration amplitude

Compared to conventional grinding, ultrasonic face grinding of SiC ceramic with vibration amplitude more than 3 μm has been proved to improve the machining efficiency but usually face the problem of reducing the workpiece surface quality. The material removal mechanism and ground surface quality by ultrasonic face grinding using minor vibration amplitude (less than 1 μm) still remains uncertain and needs to be further investigated. In the present work, experiments of ultrasonic face grinding of SiC ceramic are carried out to study the influence of processing parameters (e.g. depth of cut, wheel speed and ultrasonic vibration amplitude) on the surface finish. The results show that both the grinding forces and ground surface roughness increase significantly with the increase of depth of cut and the decrease of wheel speed. However, with the increase of ultrasonic vibration amplitude, the grinding forces decrease rapidly first and then keep steady, and the ground surface roughness shows three variation stages: dropping, climbing and stabilizing, which achieves the smallest value of 0.04 μm at the amplitude of 0.216 μm. From the analysis of acquired workpiece surface morphology and image processing result, the proportion of chunks and pits on the workpiece surface is reduced due to ductile removal in case of ultrasonic vibration amplitude less than 0.2 μm, but increases when the amplitude is more than 0.2 μm because the material is removed in brittle domain. Finally, a sample machined at relatively high wheel speed and minor vibration amplitude is provided to support the findings. The proposed investigation provides a new approach to achieve mirror surface of SiC ceramic using ultrasonic face grinding.

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.