Impulsive Vibration Research Articles

Damage Evaluation by Impulsive Response in Structure Filled with Liquid

A double-walled liquid mercury target vessel, which consists of outer and inner walls, is being globally developed for MW-class spallation neutron sources. When proton beams bombard a mercury target, pressure waves are generated due to the rapid thermal heat deposition. These pressure waves trigger impulsive vibrations in the mercury vessel, and cause cavitation damage to the inner wall of the vessel. In this study, the dependency of the vibration behavior of the mercury vessel on the damage is systematically investigated through numerical simulations and experiments, for inner wall damage characterized by hole diameters of 1, 5, 10, 20, and 40 mm. A method referred to as wavelet differential analysis is developed, and a parameter referred to as average intensity is derived for a quantitative damage evaluation. Both the numerical simulation and experimental results show that the average intensity is damage-sensitive and depends on the damage feature size. The critical damage hole diameter is estimated to be 10 mm during damage evaluation.

Failure of a pressure vessel for rail transport of fluid carbon dioxide

In 1976, a pressure vessel of a tank wagon burst during gravity shunting. The pressure vessel was filled with cold fluid carbon dioxide and failed by cleavage fracture explosively. Big parts of the vessel were flung up to 300m, a building was destroyed, and rails as well as the superstructure of the gravity shunting yard were damaged.The initiation sites of the fracture and the orientations of crack propagation were determined by means of the patterns on the fracture surfaces of the broken parts. The initiation sites were located in the heat-affected zone (HAZ) of welds, close to transitions of cross-sections and the starting and end points, respectively, of the welds. The primary initiation of crack propagation was almost certainly on the left side, close to the weld of the fixed bearing connecting the vessel with the carriage.The results of metallographic investigations indicated the development of cold weld cracks during welding. Mechanical behavior assessments on specimens extracted from the failed vessel indicated sufficient strength and ductility in tensile loading. The values of the notched-bar impact energy or toughness were within the limits according to industry rules and standards, except for one metal sheet of the vessel that was welded to the left fixed bearing.During shunting, two tank wagons were inappropriately braked, and began to roll too quickly. One rail brake used for deceleration of the wagons caused impulsive noises and vibrations, resulting in high impulsive loading of the first wagon. The cold weld cracks in the heat-affected zones near the fixed bearing of the pressure vessel were initiation points for unstable crack growth. As the result of very low notched-bar impact toughness, crack propagation was not arrested and unstable cleavage fracture occurred.Due to a second similar accident, happened one year before, a program was started to assess characteristic values of pressure vessel materials and the influence of weld parameters by the manufacturer, the inspecting authority, and BAM. The scientific findings led to modifications of industry rules and standards with regard to using ISO-V specimens and to higher required values for notched-bar impact energy for fine grain structural steels.

Impulse vibration transmissibility characteristics in the presence of localized surface defects in deep groove ball bearing systems

The present study analyzes the impulse vibration transmission through the deep groove ball bearing systems caused by a localized surface defect on the bearing raceways. The analysis is performed to understand the use of vibration signal in rotating machines for condition monitoring and diagnostics. A new dynamic model of a deep groove ball bearing system that accounts for the contact stiffness between the outer race and housing, and includes the effect of a localized defect on raceways is formulated in this study. This model is applied to examine the effect of housing materials on the contact stiffness between the outer race and housing, and the vibration transmission characteristics through the ball bearing systems. A series of parametric studies is also performed to understand the relationships between the material properties, the outer race–housing contact stiffness, and ball bearing vibration response, and as well as the vibration transmission characteristics of the impulse caused by the defects with different sizes. The numerical results demonstrate that the proposed model provides a way for simulating vibration transmissibility characteristics through the ball bearing systems, which was previously not possible. An experimental investigation is also presented to validate the proposed model.

A novel sensing method of fault in moving machine

Fault in rotating parts of a machine such as bearings and gears often causes periodic impulses and they are transmitted to adjacent parts while it is moving with a constant speed. It has been an issue, therefore, to find a best means that can tell us the existence of periodic impulse and the period as early as possible. Previous researches mainly use accelerometers since it can easily measure the vibration due to impulse. They normally require considerable measurement time and inconvenience, especially if we have to use them for many different machines. This is straightforward consequence because the sensor is to be removed from and attached to the machine elements as many time as required. This paper proposes a novel method to sense the periodic impulse of moving machinery, by using a non-contact sensor such as a microphone. The method uses the periodic impulsive sound radiated by the fault instead of the impulsive vibration. It is not only more convenient than using the accelerometers, but it can also promptly test a lot of machines; they only have to pass by the microphone during the measurement. However, because the machine under test is moving, the measured impulsive signal is not periodic due to Doppler effect. This makes it difficult to estimate the period of impulses as well as to find the existence of fault. In order to solve this, we firstly model and analyze the characteristics of the moving periodic impulsive sound. Based on this, a method to sense the existence of fault is introduced by utilizing characteristics of moving periodic impulsive sound. The performance is tested by theory and simulation with respect to the signal to noise ratio.

Lift-over crossings as a solution to tram-generated ground-borne vibration and re-radiated noise

The operation of trams close to sensitive buildings can lead to concerns over ground-borne vibration and re-radiated noise. Vibration generated at the wheel/rail interface propagates through the track structure, through the ground and into buildings, where it may cause disturbance as perceptible vibration and/or re-radiated noise. This paper presents work undertaken to solve a re-radiated noise problem within the auditorium of the Royal Concert Hall, Nottingham, UK. The hall is situated alongside a crossover between two tracks of Nottingham’s Express Transit tramway. Initial measurements established the dominance of re-radiated noise over airborne noise. Simultaneous noise and vibration measurements were then used to establish the relative significance of the impulsive vibration generated at the various rail discontinuities of the crossover, compared with the essentially continuous vibration due to wheel/rail roughness. The results led to the selection of a new ‘lift-over’ crossing, together with an improved design of switch, as the basis for solving the problem. The paper includes descriptions of the experimental methods, together with a summary of the results. The new crossover design is described and the results of the commissioning measurements are presented as a final demonstration of the new lift-over crossing’s performance.

A theoretical and experimental study of surface generation under spindle vibration in ultra-precision raster milling

In ultra-precision raster milling (UPRM), the impulse spindle vibration induced by the impulse-like cutting forces is intrinsic and special mechanism majorly influencing surface topography. It is fundamentally distinctive with the step spindle vibration induced by the step-like cutting forces in turning. However, no work has been conducted to study surface generation under the impulse spindle vibration in UPRM in depth. Consequently, this paper theoretically and experimentally elaborates that in UPRM, (i) the impulse spindle vibration includes the axial, radial and coupled-tilting spindle vibration with damping; (ii) the excitation frequency of the impulse-like cutting forces, i.e. spindle speed, determines the spindle vibration characteristics, i.e. synchronous or asynchronous spindle vibration; (iii) the coupled-tilting spindle vibration is a predominant factor influencing surface generation; and (iv) the irregular spindle-vibration waves induced by the impulse spindle vibration produce one of the irregular, lattice-like and stripe patterns or their hybrids at a milled surface.

Correlation analysis of bone vibration frequency and its mass:volume ratio

Background: Vibration analysis is a well-established technique in industry to analyse materials physical properties. The application to bone’s physical properties is unclear. This study investigated the relationship between bone vibration frequency and mass:volume ratio (ρ). Methods: We used eight turkey bones (tibio tursus). Following soft tissue removal, a 12 cm diaphyseal section was isolated, marrow removed using a water jet and the bones dried at 25 °C for 1 week. Bone volume was determined by water displacement, and mass by weighing. Bones were held in a vice at one end in a consistent manner and vibrated either using a miniature vibration motor (continuous vibration approach) or a miniature electronic hammer (impulse vibration approach). Vibration signals were recorded using CM-01B sensor. For the impulse approach, the highest peak in the magnitude frequency spectrum of the vibration signal (F) was used to determine the bone vibration frequency. For the continuous vibration approach, the difference (FD) between the motor vibration frequency and the bone vibration frequency (obtained from the highest peak in the magnitude frequency spectrum) was used. Results: The impulse approach correlated more strongly with ρ than did the continuous approach (correlation of F with ρ 0.57 vs 0.38 respectively). Summary: This study suggests that vibration analysis may be a valuable technique in assessing bone mass/volume properties. This was a preliminary study and we are currently conducting a larger study to explore the findings further.

The effects of spindle vibration on surface generation in ultra-precision raster milling

Spindle vibration has a significant influence on surface quality of ultra-precision-machined components. However, relatively few studies on the particular spindle vibration under the excitation of intermittent cutting forces in ultra-precision raster milling (UPRM) have been reported. In this study, a specialized model for an aerostatic bearing spindle under the impulsive excitation from intermittent cutting forces of UPRM is developed and its derived mathematical solutions reveal that the spindle vibration is impulsive response. The theoretical and experimental results signify that the impulsive spindle vibration produces inhomogeneous scallops forming ribbon-stripe patterns and irregular patterns like run-out on a surface of UPRM. The potential benefits for UPRM are the theoretical supports for optimization and prediction of surface generation through the optimal selection of spindle speed.

Solvability of a class of impulsive damped vibration problems

In this paper, a class of impulsive damped vibration problems are considered. Existence results are obtained by using variational method and critical point theorem. The obtained results are also valid and new even if the impulsive damped vibration problem is reduced to impulsive Hamiltonian system and Hamiltonian system. Examples are presented to illustrate the feasibility and effectiveness of the results. Copyright © 2013 John Wiley & Sons, Ltd.

Dynamic simulation of planetary gear with tooth root crack in ring gear

Planetary gear is widely used in different areas due to its advantages such as compactness, large torque-to-weight ratio, large transmission ratios, reduced noise and vibrations. However, the tooth faults like cracks are seldom concentrated. In this paper, a mesh stiffness model of internal gear pair with a tooth root crack in the ring gear is derived based on the potential energy principle. The mesh stiffness model is incorporated into the dynamic model of a one-stage planetary gear set with 21-degree-of-freedom (DOF) to investigate the effect of the internal gear tooth root crack. The crack cases with different dimensions are designed in this paper to demonstrate their influences on the mesh stiffness and the dynamic performance of the planetary gear set. The simulated results show that bigger reduction in mesh stiffness is caused by the growth in the crack size. And the impulsive vibrations and sidebands can be observed in the dynamic response of the planetary gear set in time and frequency domains, respectively. Both their amplitudes increase as the crack propagation which supply the possibility for them to be the indicators in the condition monitoring and fault diagnosis of planetary gear system.

Study on an Active Controlled Caster for Carts with Low Crash and Vibration

In recent years, it has been increasingly necessary that patients, medicines and small precision parts should be carried smoothly and quietly by carts with advanced casters. This paper presents experimental and simulational results of a cart with an active controlled caster to reduce cart's crashes and vibrations. First, the active controlled caster is introduced, which has a mechanical low-crash structure based on the idea of center of percussion. Next, the dynamical model of the cart with the caster is derived to study the caster control of the low crashes and vibrations. This model also includes the road model with a bump and the actuator model for the control. Then we show some experimental results of the cart with the controlled caster, compared to the simulation results. The proposed control is verified to effectively reduce the impulsive crashes and vibrations of the cart. Finally, we in brief discuss the control effect from the view point of the transfer functions and Bode gain diagrams of the cart model.

Optimal sinusoidal modelling of gear mesh vibration signals for gear diagnosis and prognosis

In this paper, the synchronous signal average of gear mesh vibration signals is modelled with the multiple modulated sinusoidal representations. The signal model parameters are optimised against the measured signal averages by using the batch learning of the least squares technique. With the optimal signal model, all components of a gear mesh vibration signal, including the amplitude modulations, the phase modulations and the impulse vibration component induced by gear tooth cracking, are identified and analysed with insight of the gear tooth crack development and propagation. In particular, the energy distribution of the impulse vibration signal, extracted from the optimal signal model, provides sufficient information for monitoring and diagnosing the evolution of the tooth cracking process, leading to the prognosis of gear tooth cracking. The new methodologies for gear mesh signal modelling and the diagnosis of the gear tooth fault development and propagation are validated with a set of rig test data, which has shown excellent performance.

Damage detection of RC beams based on experiment and analysis of nonlinear dynamic characteristics

The experimental and analytical investigation on damage detection of reinforced concrete (RC) beams has been carried out using a testing RC beam. The correlations between the damage extent and the nonlinear dynamic characteristics (NDC) of the testing beam are presented in this paper. The NDC of the RC beam were obtained by means of time–frequency analysis (TFA) of displacement responses from the impulsive and harmonic vibration tests. The correlation between the displacement amplitude and the excitation frequency in the case of forced vibration was obtained. Combining the results from the TFA with the relationship of displacement amplitude and corresponding natural vibration frequency (DA-CNVF) from the harmonic vibration tests, a reasonable window width for TFA was suggested. It is observed that the window width of seven times of the fundamental period of the testing structure is a suitable option in the time–frequency analysis. Using the TFA with this appropriate moving window width, the relationship between DA-CNVF at different damage levels in the case of free vibration was used to depict and analyze the NDC of the damaged RC beam. The feasibility of using NDC of a damaged RC beam from either forced harmonic or free vibration tests to detect damage level is discussed. The NDC of the reinforced concrete beam can be used to detect its damage levels if the apparent damage is not significant. Therefore, this damage detection method may be suitable for structures with small damage invisible or hard to be found by naked eyes.

Vehicle Design Influences Whole Body Vibration Exposures: Effect of the Location of the Front Axle Relative to the Cab

Using a repeated measure design, this study compared differences in whole body vibration (WBV) exposures among 13 drivers who drove a truck with the cab over the front axle (cab-over design) and a truck with the cab situated behind the front axle (non-cab-over design). The drivers drove both trucks over a standardized route that comprised three distinct segments: a freeway segment, a city street segment with stop-and-go driving (traffic lights), and a city street segment without traffic lights. A portable WBV data acquisition system collected tri-axial time-weighted and raw WBV data per ISO 2631-1 and 2631-5 standards. Simultaneous global positioning system (GPS) data were also collected to compare vehicle speeds. The GPS data indicated that there were no speed differences between the two vehicles. However, average and impulsive z-axis vibration levels were significantly higher for the cab-over design than for the non-cab-over design. In addition, significant WBV exposure differences between road types were found, with the freeway segments having the lowest exposures and the city street segments without traffic lights having the highest exposures. Vehicle type and the associated WBV exposures should be considered when purchasing vehicles to be used by full-time professional vehicle operators.

Fault Detection of Water Hydraulic Motor by Demodulated Vibration Signal Analysis with the Hilbert Transform and Genetic Algorithm

Abstract The vibration signals analysis from the water hydraulic motor is the most modern technique for fault detection of water hydraulic motor. The machine’s residual life is estimated by the detection of the fault presence and type at an earlier stage for the adequate plan of maintenance. The most important components in the impulsive vibration signal spectra are the rotational frequency and its harmonics as well as sidebands due to modulation phenomena. This paper studied the fault detection of fluid machines by the demodulated frequency components of the periodic impulse vibration signal. We apply the Hilbert transform to demodulate the characteristic envelope of the periodic impulsive signal to show the fundamental frequencies. The adaptive spectrogram is optimized to get the optimal parameters to show the characteristic frequencies of the Hilbert transform-based envelope of the vibration signals. The results show that it is applicable and effective to fault detection of water hydraulic motor by analyzing the demodulated frequency components of the periodic impulsive signal.

Denoising in Steel Structural Impulsive Vibration Signal Based on Independent Component Analysis

The analysis of structure vibration signals is influenced by noise mixed in the signals. Independent component analysis (ICA) method is introduced to denoise the vibration signals in this paper. The representative algorithms: FastICA and JADE are told in detail. The algorithms are applied to separate steel structural vibration signals. The denoising performances in impulsive vibration signals generated by steel structure demonstrate the effectiveness and good robustness of ICA method.

Faults diagnosis of rolling element bearings based on modified morphological method

In order to effectively smooth noise and extract the impulse components in the vibration signals of defective rolling element bearings, a new modified morphology analytical method has been proposed. In this method, average of the closing and opening operator has been used as the morphology operator. Being the flat and zero adopted as the shape and the height of structure element (SE), respectively, the optimized length of SE is defined by a new proposed criterion (called SNR criterion). The effect of the new method is validated by both simulated impulsive signal and vibration signal of three defective rolling bearings with an outer, an inner and a rolling element faults and compared with Nikolaou’s method. The result shows that the proposed method has the superior performance in extracting impulsive characteristics of vibration signals, especially for the high level noise signals, and can implement better in diagnosis of defective rolling element bearing.

Parametrization of all Three Impulse Zero Vibration Input Shapers

Input shaping has been demonstrated to be a simple method of reducing vibration in many types of controlled machines. The method is implemented by convolving a command signal with an impulse sequence of input shaper to produce a shaped input that is then used to command the system. Designing the input shaper involves determining the amplitudes and timing of the impulses such that the resulting shaped commands lead to desired levels of vibration reduction. Up to now, to the best knowledge of the authors, it is known only few special types of input shapers (ZV, ZVD, ZVDk, EI, SI,...). This paper presents two general approaches for parametrization of all three impulse zero vibration input shapers.

Study on detecting lumber damage using acoustic radiation

The method using the sound caused by knocking the lumber to detect its damages has applied for a long time, but it mostly depends on the people’s experience and the subjective elements which could cause great errors to the judgment of damage. This paper analyzed the relationship between the lumber vibration impulse response and acoustic radiation properties. The analysis results showed that lumber acoustic radiation time-domain and frequency-domain signal characteristics depend on the structural characteristics of lumber. By testing the lumber acoustic radiation properties, it was known that the differences of damage and its location could change the main vibration frequency, energy of the lumber and waveform of time-domain. Based on these characteristics, it is effective to identify the damage of the lumber and its location.

Experimental studies of the impulsive ultrasonic machining by a tool with an intermediate striker

Some experimental data on the process of impulsive ultrasonic machining are presented. Also given are the data on variations in the impulsive vibration frequency of a workpiece and a tool.