Change Of Vibration Amplitude Research Articles

Investigating the dissipative effects of liquid-filled particle dampers using coupled DEM–SPH methods

One of the main disadvantages of solid-particle-filled dampers, generally called particle dampers (PDs), is that their performance is sensitive to vibration amplitude changes. The efficiency of PDs seems to reduce drastically with low intensity driving acceleration, especially when the acceleration level falls below that of gravity. In this paper, a new approach is investigated, in which the damper is filled with a combination of both solid and liquid fillings, in order to reduce such undesirable PD short comings. In order to quantify and understand the influence of various dissipation mechanisms, simulations were performed. The liquid motion is modeled using the smoothed particle hydrodynamics (SPH) method and the discrete element method (DEM) is used to model the motion of solid particles. In order to validate the simulation models, also a laboratory experiment was set up. This experiment consists of a damper, in this case a cylindrical acrylic container filled with spherical particles in combination with distilled water, mounted on a vertical leaf spring. By analyzing the free oscillation behavior of the leaf spring, the corresponding damper performance is characterized. The insights gained during experiments were then utilized to identify and validate the DEM and SPH models, respectively. Initially, damping behavior of dampers with solid filling and liquid filling are analyzed independent of each other. Then, these two configurations are compared with dampers with a combination of both solid and liquid fillings. In order to model solid–liquid dampers a coupled SPH–DEM approach is used. Experimental and simulation results show that dampers with a mixture of solid and liquid filling perform better than purely solid-filled or purely liquid-filled dampers, especially under low intensity driving accelerations. The main reasons behind this effect are believed to be that the solid particles with the additional hydraulic forces due to an added liquid are more agile leading to more relative motion and thereby leading to more energy dissipation. Moreover, the violent sloshing motion of the liquid through the tiny gaps, created by solid particles, also leads to more energy dissipation.

A mass sensor based on 3-DOF mode localized coupled resonator under atmospheric pressure

In this paper, for the first time, the mass sensitivity of a 3-DoF mode localized electrostatically coupled resonator is investigated and characterized under atmospheric pressure. A reversible method is used in which nanoparticles are added on and removed from one resonator of the 3-DOF coupled resonator system. Furthermore, a comparison of three mass sensitivity characterization methods was carried out: resonance frequency shift, resonance vibration amplitude change and resonance vibration amplitude ratio. MATLAB/SIMULINK and COMSOL Multiphysics models for the 3-DoF coupled resonator system are presented. The simulation results and theoretical calculations are in good agreement with the experimental data. The results show that a 3-DOF mode localized coupled resonator has potential to be employed for biosensing applications.

Monitoring blood removal failure during haemodialysis

We examined the effectiveness of using a triaxial accelerometer to detect blood removal failure during haemodialysis. Monitoring actual extracorporeal blood flow during dialysis is crucial as duration and blood flow directly affect the efficiency of dialysis. However, a sudden decline in blood flow in the extracorporeal line can occur fairly easily, resulting in blood removal failure. The general method of assessing blood removal failure involves visual monitoring of the detector pillow, but dialysis circuits without a pillow are currently being used to prevent problems such as coagulation. Therefore, we measured changes in blood flow in the feeding circuit using a triaxial accelerometer connected to the arterial side drip chamber. We observed an increase in vibration amplitude of the circuit when the actual flow was lower than the ‘settings’ value for blood flow. Therefore, a triaxial accelerometer can be used to effectively and promptly detect a divergence between ‘settings’ flow and actual flow because it can measure changes in vibration amplitude due to an obstruction or a reduction in blood flow. Thus, establishing threshold values for this amplitude can result in the triaxial accelerometer replacing the currently used pillow device for monitoring blood flow for detecting blood removal failure.

Управляемая вибрация звеньев подвижности производственного механизма

Introduction. The work subject is investigating friction characteristics of the moving surfaces of the production mechanism (PM) links including executive mechanisms (EM), and work tools (WT) of technological machines (TM) in the low-speed zone of an asynchronous motor (AM) powered from an autonomous voltage inverter (AVI) in the “AVI - AM” system. The work objective is to find a technical solution to the reduction of the friction effect in the PM links on the frequency-controlled drive (FCD) mechanical characteristics in the low- and creep-speed zone, and also, to the validation of the rated vibration feasibility of the mobile links in the PM guides under the starting-braking AM modes. Materials and Methods. To solve the research problems, the concept of bimodal AVI control that provides the formation of quasi-sinusoidal voltage for AM power supply in the “AVI - AM” system with the harmonic coefficients K u u > 8% is used. The program control of the amplitudes of the fundamental 5th and 7th harmonics of the stator current is applied. These harmonics form the fluctuating torques on the AM shaft and cause the normalized vibration of the PM links. Research Results. The justification and experimental proof of the AVI control feasibility providing a project change in the AM shaft vibration amplitude and a decrease in the effective friction coefficient of the PM moving links aiming at the elimination of the seizure of the links under the PM operation conditions are obtained. Such an effect is possible under the AM rotor spinning in the low current frequency (0.5-20 Hz) zone which is typical for the slow-speed motion of PM under the starting-braking FCD modes. Discussion and Conclusions. The application domain of the developed technical solution covers many PMs with FCD for which the short-time operation modes (with CY of 40% and more) are considered basic. Thus, the use of the effect of vibration linearization of the friction coefficient in the PM links allows the following: to reduce the AM breakaway voltage and significantly extend the FCD speed control range, to increase the ride quality and improve the PM out put link kinematics on which the WT is fixed.

An experimental investigation of vibration characteristics of compression ignition engine running with neem methyl ester

Reduction of fossil fuel reserves, environmental deterioration, global warming, and rigorous emission norms have necessitated the need for alternate fuel such as biodiesels. Diesel engines produce a higher vibration which leads to a reduced engine life span. In the present study, the vibration of a compression ignition engine has been measured for both diesel and Neem methyl ester. The experiments were carried out at 0%, 25%, 50%, 75%, and 100% load when the engine runs at a constant speed of 1500 rpm and with a compression ratio of 16. Triaxial accelerometer is used for measuring engine vibration along vertical, lateral, and longitudinal directions. Data acquisition and analysis are obtained by NI LabVIEW. It has been observed that an engine running with NME produces lower combustion induced vibration acceleration compared to diesel fuel. It is also noticed that higher peak amplitudes are observed at the frequency of 25 Hz for both diesel and NME, within the range of 0–100 Hz and along three directions. Within the range of 100–3000 Hz, the highest peak amplitudes are observed for engine running with diesel compared to neem methyl ester. At a 100% load, the change in vibration amplitude is 64.94 %, 86.41%, and 17% along vertical, lateral, and longitudinal directions when fuel is changed from NME to diesel. Combustion characteristics such as maximum cylinder pressure, heat release rate, and rate of pressure rise are also measured for both diesel and NME in order to find the relationship between combustion and vibration. At full load conditions, the maximum combustion pressure and maximum rate of pressure rise are increased by 2.1% and 8.33% with pure diesel compared to neem methyl ester. The experimental work suggests that neem methyl ester can be directly used in diesel engines in view of a lesser engine vibration and higher engine life.

Pulsed laser ablation as a tool for in-situ balancing of rotating parts

The balancing of complex rotating systems is a challenging task as it may require repetitive (dis)assembly to enable mass adjustments; thus, developing methods for in-situ dynamic balancing of rotatives is regarded as a key technology enabler. In this context laser balancing with its high flexibility in adjusting its firing frequency (to match that of the rotating part) and pulse energy (to vary the material removal) could offer significant advantages from both precision and cost point of view.In this paper, a laser balancing system is developed to continuously remove material from a target part in a controlled and automated manner. The amount of material ablated can be controlled by an influence coefficient, which is related to the change in vibration amplitude for a predefined amount of pulses at a given operational balancing speed, material, and geometry of the rotative part. The proposed system features a three-layered case-driven programmatic approach to optimize single-plane balancing process duration in a fully automated system. This enables the use of prioritization to avoid misfire and therefore, structural damage to the targeted part. Furthermore, the application allows the component to be balanced to all common balancing grades as specified in the ISO 1940/1 standard. Thus, validation trials involved balancing an Inconel 718 rotative to a preliminarily specified balancing grade by extracting the acceleration signals using an IIR peak filter. A computer simulation encompassing the rotor bearing state space system, a model of the laser and the adapted peak detection algorithm, has been developed and used to validate the trials conducted. Henceforth, a maximum deviation from the desired correction position of less than 1mm has been recorded. Moreover, it has been shown that the detection and correction of imbalances can be reliably achieved by reducing the vibration level of a rotor from G 22.5 to G 19.5.

Self-Oscillation-Based Frequency Tracking for the Drive and Detection of Resonance Magnetometers.

This paper reports a drive and detection method for Micro-Electro-Mechanical System (MEMS)-based Lorentz-force resonance magnetometers. Based on the proposed MEMS magnetometer, a drive and detection method was developed by using self-oscillation to adjust the mismatch between the mechanical resonance frequency and the coil drive frequency as affected by temperature fluctuations and vibration amplitude changes. Not only was the signal-to-noise ratio enhanced by the proposed method compared to the traditional method, but the test system automatically reached resonance frequency very rapidly when powered on. Moreover, the linearity and the measurement range were improved by the magnetic feedback generated by the coil. Test results indicated that the sensitivity of the proposed magnetometer is 59.6 mV/μT and its noise level is 0.25 μT. When operating in ±65 μT, its nonlinearity is 2.5‰—only one-tenth of the former prototype. Its power consumption is only about 250 mW and its size is only 28 mm × 28 mm × 10 mm, or about one-eighth of the original sensor; further, unlike the former device, it can distinguish both positive and negative magnetic fields. The proposed method can also be applied in other MEMS sensors such as gyroscopes and micromirrors to enhance their frequency tracking ability.

Oil shale separation using a novel combined dry beneficiation process

Significant mineral impurities are produced during oil shale mining. However, inorganic minerals can be partially discarded, with an improvement in oil shale quality, through physical separation methods. Based on analysis of physical properties of oil shale, this paper firstly proposes a separation process combining compound dry cleaning and vibrated air dense medium fluidized bed (VADMFB) separation, for separation of oil shale across the full size range of 100–0mm. We systematically analyzed the effects of changes in vibration amplitude and frequency on separation results and oil ratios for both systems. When oil shale with a size range of 100–6mm was separated using compound dry cleaning, using optimal vibrational parameters of f=53Hz and A=3.6mm, yields of concentrate was 20.49%, respectively, with corresponding oil content of 11.20%, The probable error (E) was 0.155–0.21 with the largest oil content segregation degree. Oil shale with a size fraction of 6–0mm was separated in a VADMFB separator at optimal vibrational conditions (f=36Hz and A=2.5mm). Resultant yields of concentrate was 21.70%, respectively, with corresponding oil content of 10.1%. E was 0.16–0.185 with the largest oil ratio segregation intensity. This study thus confirms that the proposed combined dry beneficiation process can effectively separate oil shale along the full size range of 100–0mm.

Investigation on surface roughness in rotary ultrasonic side grinding of SiCp/Al composites

SiCp/Al composites are widely used in many fields because of their outstanding mechanical and physical characteristics; however, they are difficult to machine owing to the reinforced particles in the matrix. In this work, the rotary ultrasonic side grinding experiments of SiCp/Al composites reinforced with 45% volume SiC particles were carried out to investigate the effects of the spindle speed, feeding speed, cutting depth and ultrasonic vibration amplitude on the surface roughness. The values of surface roughness have different change regularities with spindle speed and cutting depth in various intervals. The Ra values show a rising trend with increased feed rate and it is in line with the change of Ra in machining of ordinary metal materials. The varying pattern of Ra with the change of vibration amplitude is similar to ultrasonic-assisted grinding of other hard and brittle materials.

Static and dynamic behavior of a selected cable‐stayed footbridge with respect to change of the cable tension

AbstractThe paper presents the theoretical analysis of the possibilities of using the authors' own method of actively reducing resonant vibration in cable‐stayed footbridges. The method of actively reducing vibration was earlier tested on a laboratory model of a steel footbridge, [1]. The method relies on changing the static tension in chosen cables. The term “active” refers to the fact that the tension changes would only be introduced when resonant vibration of the structure occurred. A change in the cable tensions should cause a change of the natural frequencies for which resonant vibration amplification appeared earlier. Eigenproblem sensitivity analysis, formulated for the structure according to the second order theory, is the basis for choosing the cables in which the tension should change. Apart from analyzing the effectiveness of the active method for reducing resonant vibration, the influence of cable tension change on other values was also studied. These values included the changes in vibration amplitudes, as well as changes of cross‐section forces, tensions, and static bend of the structure elements that are most sensitive to tension change. It was also established whether the tension changes in chosen cables, which were large enough to cause a practically significant reduction of resonant vibration, cause exceeding the levels of Serviceability Limit State (SLS) and Ultimate Limit State (ULS) for the structure as a whole or for some of its elements. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Detection and analysis of chatter occurrence in micro-milling process

An experimental study to understand the characteristics related to chatter occurrence in micro-milling operations is presented. Accelerometers are used to measure the vibration signals in the machining process. The acceleration signals are then analysed in the time domain and the frequency domain. Along with the onset of chatter, it is found that there is a characteristic shift of the dominant frequency components in addition to the change of vibration amplitude. A modulation of the spindle frequency around the chatter frequency is also found to be present in the vibration signal. A dimensionless chatter indicator based on revolution root-mean-square values is designed and used to evaluate the stability of the micro-milling process. It is shown that the proposed indicator provides a simple, but effective way to detect chatter onset.

Analysis on Vibratory Subsoiler Considering Slowly Varying Parameter

According to the analysis to the motion track of the subsoiler, the influence on the motion track caused by the vibration amplitude and vibratory frequency has been reached, the system model of the vibratory subsoiler with slowly varying parameters of the soil has been built , the asymptotic method is adopted to carry out solving and analyzing, and experimental study is done by using the vibratory subsoiler. Analysis shows that the change of soil stiffness, soil damping, and soil quality parameters makes the system resonance curve shift, and the change of vibration amplitude, vibration frequency can improve the efficiency of deep scarification of soil.

Damage-sensitive features from non-linear vibration response of reinforced concrete structures

Reinforced concrete structures respond in non-linear manner under dynamic loads even at low levels of vibration. This causes softening in concrete which may result in the unstable vibration. By considering the non-linearity, the effects of amplitude of vibration on the modal characteristics can be used to extract damage-sensitive features. In this article, investigations carried out on the phenomena associated with non-linear vibration, which were observed during the vibration tests on damaged reinforced concrete structures, are discussed. For effectively identifying the non-linear damage features in reinforced concrete structures from the frequency spectral information, an appropriate vibration testing procedure is formulated in this study. Damage features are evaluated from the changes in vibration amplitude with frequency at different damage levels under various types of excitations and their force levels. Damage indicators based on basic signal statistics and non-linearity in vibration responses are evaluated. Using the phase-plane information obtained from various damage scenarios, non-linear damage indices have been formulated. Another significant non-linear damage feature has been identified by the occurrence of higher harmonics observed by analysing the spectral density functions obtained from the frequency domain decomposition. The results obtained from this study would pave the way for identifying the damage in heterogeneous and non-linear structures such as reinforced concrete.

Vortex-induced vibrations of pipes conveying pulsating fluid

The vortex-induced vibrations of a long flexible pipe conveying fluctuating flows are investigated via a two-mode discretization of the governing differential equations. In the present work, the internal fluid velocity is assumed to have a harmonically varying component superposed on a steady mean velocity. Direct perturbation method of multiple scales (MMS) is adopted to transform the governing nonlinear partial differential equations (PDEs) into ordinary differential equations (ODEs), which are then analyzed numerically for the pipe with principal parametric resonances during lock-in for each of the first two modes. The results indicate that in the case of a pipe containing fluctuating flows, the peak of vibration amplitudes is larger than that of a pipe conveying steady flows. With the increase of detuning parameter for the frequency of pulsating flow, the variation range of vibration amplitudes of the pipe enlarges first and then narrows, with jumping phenomenon that the vibration amplitude changes from multi-value to single-value and then returns to multi-value between the two regions of multi-value responses, which has not been discovered yet. From the amplitude-frequency response curves one can see that the hysteresis may occur with small increments or decrements of the detuning parameter. It is also found that if the pipe system is in the lock-in condition for a certain mode, the pulsating component can have an obvious impact on the dynamics of the pipe only when the parametric resonance occurs in the same mode. In addition, the method of numerical simulations (MNS) is directly employed to verify our implementation of MMS.

Nonlinear dynamics of a bistable piezoelectric-composite energy harvester for broadband application

The continuing need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted renewed interest in recent years for energy harvesting technologies capable of capturing energy from ambient vibrations. A particular focus has been placed on piezoelectric materials and devices due to the simplicity of the mechanical to electrical energy conversion and their high strain energy densities compared to electrostatic and electromagnetic equivalents. In this paper an arrangement of piezoelectric layers attached to a bistable asymmetric laminate is investigated experimentally to understand the dynamic response of the structure and power generation characteristics. The inherent bistability of the underlying structure is exploited for energy harvesting since a transition from one stable configuration to another, or “snap-through”, is used to repeatedly strain the surface bonded piezoelectric and generate electrical energy. This approach has been shown to exhibit high levels of power extraction over a wide range of vibrational frequencies. Using high speed digital image correlation, a variety of dynamic modes of oscillation are identified in the harvester. The sensitivity of such modes to changes in vibration frequency and amplitude are investigated. Power outputs are measured for repeatable snap-through events of the device and are correlated with the measured modes of oscillation. The typical power generated is approximately 3.2 mW, comparing well with the needs of typical wireless senor node applications.

In situ testing on a new crashworthy device against ship-mitre gate collision

The mitre gate has been widely used in ship locks. However, apart from the normal operational loads, the gate is subjected to unexpected incidents, including sudden loads such as collision of the ship. Due to the fact that this kind ofstructure is widely used in a variety of ship locks and holds great promise for future applications, the safety of the structure has received widespread attention. Nowadays, traditional steel fenders are widely used as crashworthy devices in most mitre gates. In order to improve the crashworthiness of the structure, a new crashworthy device made from rubber composite against ship-mitre gate collision is developed instead of traditional steel fenders. In situ testing on this new fender is performed in order to investigate the crashworthiness of the fender. A real ship is used to crash against the gate in the ship lock to create a structural vibration in the test. The dynamic responses of the gate with steel and the new fender are detected so as to compare the effects of the different collision protection systems used in the gate. The test results show that the vibration amplitude changes greatly between gates with steel and the new fender. The structural maximal acceleration and strain responses all decrease when the gate installs the new fender. Based on the in situ vibration test conducted, the installation of a new fender as collision protection device is proven to be an effective method to make the gate in the ship lock safer.

Process Damping and Cutting Tool Geometry in Machining

Regenerative vibration, or chatter, limits the performance of machining processes. Consequences of chatter include tool wear and poor machined surface finish. Process damping by tool-workpiece contact can reduce chatter effects and improve productivity. Process damping occurs when the flank (also known as the relief face) of the cutting tool makes contact with waves on the workpiece surface, created by chatter motion. Tool edge features can act to increase the damping effect. This paper examines how a tool's edge condition combines with the relief angle to affect process damping. An analytical model of cutting with chatter leads to a two-section curve describing how process damped vibration amplitude changes with surface speed for radiussed tools. The tool edge dominates the process damping effect at the lowest surface speeds, with the flank dominating at higher speeds. A similar curve is then proposed regarding tools with worn edges. Experimental data supports the notion of the two-section curve. A rule of thumb is proposed which could be useful to machine operators, regarding tool wear and process damping. The question is addressed, should a tool of a given geometry, used for a given application, be considered as sharp, radiussed or worn regarding process damping.

Experimental Research on the Effect of Sinusoidal Excitation on Dynamic Wheel Load of Hydro-Pneumatic Suspension Vehicle

Based on the mathematical model of quarter car body model being put forward, the indoor platform experiment of quarter car body with hydro-pneumatic suspension system was done. During test, the parameters of dynamic wheel load along with the change of vibration amplitude and frequency were investigated. The results show that: the cycle of acceleration of sprung mass has half cycle lag than unsprung mass, and the main parameters of dynamic wheel load has increased significantly along with the increase of vibration amplitude and frequency. At the same time, through analysis the acceleration time responses of sprung and unsprung mass, it can be shown that hydro-pneumatic suspension has good anti-vibration performance.

Long-term monitoring of wind-induced responses of a large-span roof structure

A long-term monitoring of the wind acceleration responses of the World Cup Stadium's roof structure in Jeju-do, Korea was carried out. Modal properties were extracted from collected data using the system identification technique, and variations of modal properties associated with the change in temperature and vibration amplitude (wind speed) were examined. The investigation indicated that up to a 5% increase in the natural frequencies was accompanied by a 27.2 °C rise in temperature. It also indicated approximately 5% decreases in the natural frequencies and increases of more than twice the damping ratios with an increase in five times the vibration amplitude. In addition, the reliability of the natural frequency prediction for this type of structures using the current analytical technique was examined by comparing with measured natural frequencies. In the FE model, nonlinear effects caused by the geometric stiffness and stress stiffening were included. The analytical natural frequencies showed good agreement with the measured values within a difference of 5%. An analytical prediction of wind-induced responses of the structure was made based on the wind tunnel test results, the analytical natural frequencies and mode shapes, including the added mass effect. Predicted wind-induced responses showed reasonable match with the measured accelerations during typhoons and winter storms.

Control of Two-Dimensional Vibrating System

A strategy for control of a system of two electrical vibrators mounted onto the vibrating plate of a typical small table vibrator was discussed in the present paper. The aim of the considered control system is rapid positioning of counterbalances for ensuring achievement of the assumed directions of vibrations and loading forces (where , m is unbalanced mass, ω is angular velocity of the vibrator shaft, e is distance between the unbalanced mass and the vibrator rotary axis). The strategy of the control consists in setting of different directions of vibrator rotations together with controlled change of vibration frequency and amplitude. Numerical analysis was performed. The obtained results are presented in a graphical form.