Bouncing Vibration Research Articles

Scale Models to Verify the Effectiveness of the Methods to Reducing the Vertical Bending Vibration of the Railway Vehicles Carbody: Applications and Design Elements

The purpose of this paper is to present applications and design elements of scale models of the carbody of railway vehicles integrated in experimental laboratory systems to verify the effectiveness of the methods to reduce vertical bending vibration of the carbody. In the first part of the paper, some applications of such experimental systems are presented, which include different scale models of the railway vehicle carbody. In the second part of the paper, the structure and dimensioning elements of a new demonstrative experimental system, specially designed by the authors of the present paper for testing the functionality of an original method of reducing the vertical bending vibrations of the carbody of railway vehicles, are presented. This method is based on an innovative approach that involves the use of a passive system consisting of two bars rigidly mounted on the longitudinal beams of the carbody underframe, having the role of opposing the bending of the carbody. The main element of the demonstrative experimental system is the scale model of the vehicle carbody, reduced to a beam, on which the two bars, called anti-bending bars, are mounted. For the dimensioning of the experimental model of the carbody and the anti-bending bars, original methodologies are developed in which several conditions are involved. In the case of the dimensioning of the experimental model of the carbody, the conditions refer to the convenient adoption of the scaling factor of the dimensions of the real carbody from the perspective of the practical realization of the experimental model of the carbody, ensuring the buckling stability of the demonstrative experimental system, achieving natural frequency of the vertical bending of the real carbody and avoiding the interference of the bounce vibration with the vertical bending vibration of the demonstrative experimental model of the carbody. The dimensions of the anti-bending bars are established from the condition that the vertical bending frequency of the experimental model of the carbody is outside the range of sensitivity of the human body to vertical vibration. Additionally, the natural frequency of the vertical bending vibration of the anti-bending bars must be chosen to avoid interference with the vertical bending vibration of the experimental model of the carbody. The effectiveness of the anti-bending bars in reducing the vertical bending vibration of the experimental model of the carbody is investigated with the help of numerical simulation results developed based on an original theoretical model of the experimental model of the carbody with anti-bending bars.

Investigation into the Trampoline Dynamic Characteristics and Analysis of Double Bounce Vibrations.

Double bounce is an unusual and potentially very hazardous phenomenon that most trampoline users may have experienced, yet few would have really understood how and why it occurs. This paper provides an in-depth investigation into the double bounce. Firstly, the static and dynamic characteristics of a recreational trampoline are analysed theoretically and verified through experiments. Then, based on the developed trampoline dynamic model, double bounce simulation is conducted with two medicine balls released with different time delays. Through simulation, the process of double bounce is presented in detail, which comprehensively reveals how energy is transferred between users during double bounce. Furthermore, the effect of release time delay on double bounce is also presented. Finally, we conducted an experiment which produced similar results to the simulation and validated the reliability of the trampoline dynamic model and double bounce theoretical analysis.

Smoothed Particle Hydrodynamics Simulation of Liquid Drop Impinging Hypoelastic Surfaces

The phenomenon of liquid drops impact on elastic surfaces widely exists in nature and industry. Theoretical description of this phenomenon is relatively difficult, due to its transient and fluid–structure interaction nature. In this study, a numerical model is proposed based on the smoothed particle hydrodynamics (SPH) method to simulate a liquid drop impact on hypoelastic solid surfaces. A key feature of the proposed model is that the surface tension effect is modeled by reconstructing the free surface of the droplet. We simulate water drops impact on super-hydrophobic cantilever beams. Interesting phenomena of droplet bouncing and beam vibration are reproduced by the model. The predicted behavior qualitatively agrees with the experimental observation. These analyses may be beneficial to engineering new materials and new devices in such areas as fabrics, agriculture, petroleum, and micro/nano technology.

Global sensitivity analysis of hydraulic system parameters to hydraulically interconnected suspension dynamic response

This paper aims to provide the parameter sensitivities of a half-car fitted with a hydraulically interconnected suspension system using a global sensitivity analysis method. The impedance matrix of hydraulic subsystem and mechanical and hydraulic coupled system dynamic equations are derived in the frequency domain. The frequency response functions and a road surface model are set up to achieve response such as bounce acceleration power spectrum density and roll acceleration power spectrum density. By using Sobol global sensitivity analysis method, the level of sensitivity of hydraulic parameter to bounce response and roll response is calculated. The obtained results indicate that valves connected to hydraulic chambers have a large impact on bounce vibration model and accumulator and the valves connected to it make a large impact on roll vibration model. All this work provides a theoretical basis for car ride estimate and further parameter optimisation of the hydraulically interconnected suspension.

Study of Wheel-Rail Vibration in Railways

Together with the rapid development of high-speed railways, extensive research into railway technologies is compulsory, especially on the aspect of dynamic interactions between vehicle and railway line, in order to guarantee the operational security of vehicles at high speed and improve the passengers comfort. The increase in the severity of the dynamic interaction between wheel and rail arises from the increasing speed of trains. As a result, it is necessary to analyze for the characteristics of wheel-rail vibration. The curve is an important component of a railway line and is usually the very source of wheel-rail vibration, especially at the time when a vehicle rapidly passes through a railway line, and will seriously affect the safety and comfort of the vehicle. At present, the usual practice is to only take some limit values to design the vertical section of railway lines, such as the maximum slope and the minimum slope length, according to the grade of a certain right line. Moreover, the existing studies on the vertical curve focused more on the vertical section parameters without considering the influence of these parameters on the dynamic interaction between the vehicle and line. The aforementioned studies involve either static or quasi-static analysis. There is little literature available on using a systematic method based on dynamics to study wheel-rail vibration, and some related issues are mainly the assessment making for a certain line. Based on the multi-body dynamics and the existing achievements, this paper aims to systematically investigate the influence of vertical section parameters on the characteristics of wheel-rail vibration and discuss the relationship between the acting region of wheel-rail vibration and these parameters. Furthermore, the characteristics of wheel-rail vibration at different velocities are investigated. The evaluation of the vibrations behavior in a railway vehicle is one of the matters taken into consideration even from the design stage. The decrease of vibrations to an acceptable level in terms of running behavior, safety, passengers comfort and track fatigue is required by regulations at European level for vehicle homologation and their admission into traffic.The vibrations of railway vehicles are mainly produced by the interaction between the track and the rail. Regarding a track with irregularities or deviations from the ideal geometry it creates vibrations of vehicles, which are developed both vertically and horizontally. These two types of vibrations are decoupled, though, due to the construction symmetries (inertial, elastic, plastic, linear and geometric). As for the vertical vibrations, the bounce and pitch vibrations are the main reasons of the vehicles dynamic behavior. They can be studied on simple models, one or two degrees of freedom, based on the hypothesis of excitation symmetry, by considering only one mobile base as if the wheel-sets had identical motions . This is the reason why the results with these models can be overestimated.This paper presents the influence of vehicle wheel bases and of the steel tire in running conditions, depending on some geometric characteristics. The influence will be further reflected by the vehicles response to the crossing over the rolling track random irregularities and in the magnitude of the vertical accelerations. This is the reason why the complete model of a passenger vehicle has been accounted for, including the car body bending vibrations. The movement equations have been treated in an original manner and brought to a form that points out the symmetrical and anti-symmetrical decoupled movements of vehicle and their excitation modes.

Identification of contact bouncing vibrations using TFC active slider and adaptive fuzzy control for advanced active slider design

The recent advance of magnetic storage technology includes the active thermal fly-height control (TFC) technique that is able to reduce the clearance between read/write heads and disk surface to be of few nanometers. However, it has been estimated that TFC technique alone cannot provide the even smaller clearances necessary to achieve Tbit/in2 recording densities due to the presence of bouncing vibrations and instability. In this work we investigate hybrid active slider technique with both thermal and piezoelectric actuators to achieve extremely high-density recording. The nonlinear system dynamics of thermal actuated slider is established by test-based identification. We propose an adaptive fuzzy control hybrid active slider design in which piezoelectric actuation is added to the existing thermal actuated slider design, so as to fully eliminate the high frequency bouncing vibrations. It can yield more than Tbit/in2 recording density with sub-nanometer level clearance, while using the state-of-the-art and matured manufacturing techniques for active piezoelectric slider and TFC slider.

Characteristic analysis of pitch-resistant hydraulically interconnected suspensions for two-axle vehicles

This paper proposes a new method to investigate the characteristics of pitch-resistant hydraulically interconnected suspension (HIS) systems for two-axle vehicles in the pitch plane. The equations of motion for the mechanical and hydraulic coupled system are developed, in which the hydraulic strut forces are derived using the impedance transfer matrix method. The stiffness and damping matrices of the coupled systems are described in a manner similar to the generalized form of uncoupled conventional suspension (UCS) systems. The additional properties of HIS systems are explicitly described via hydraulic physical parameters. Based on the generalized form, (1) the accumulators of HIS systems can be functionally equivalent to a combined system with tandem bump and pitch-angular springs; (2) the direction damper valves (DDVs), which are located at the outlets of actuator cylinders, function like uncoupled tandem dampers; (3) the pitch damper valves (PDVs), which are fitted on the hose to connect the accumulators, alter the mode damping similar to the accumulators changing the mode stiffness; (4) the opposite installation corresponding to the schematic of front piston-rod-upward and rear piston-rod-downward produces higher mode stiffness and damping than the other installations. The dynamic responses are studied between the vehicles with HIS and UCS. Moreover, the damping coefficients are evaluated with the modal analysis method. The obtained results indicate that (1) the top and bottom DDVs mainly affect the vehicle body’s pitch motion and bounce vibration, respectively, (2) the PDVs are able to alter the load distribution among wheel stations, and (3) damping parameters can be designed to minimize the vehicle body’s pitch motion.

Feedforward stability control of active slider in sub-nanometer spacing regime

This paper proposes a feedforward control scheme to control the bouncing instability of active-head air-bearing slider. The principle of the scheme for stability control of bouncing slider is discussed. Simulation results show that the control scheme is proved to be able to substantially reduce the bouncing vibrations. Compared to other controllers, the proposed scheme is less computationally intensive and is thus suitable for real time implementation.

Stiffness Performance Simulation and Testing of a New Type Integrated Suspension Strut

The design scheme of a new type strut was put forward, whose stiffness characteristics can undertake linkage control. The structure and basic principle of this new suspension component were introduced. According to fluid mechanics and thermodynamics, a mathematical model for the stroke dependent stiffness characteristics of the strut was established, and the stiffness characteristics were analyzed by using software SIMULINK. Then the stiffness performance bench test of the strut specimen was carried out for verification. Results show that the test results agree well with the simulation results. It is verified that the established mathematical model is correct and the stiffness of this strut shows nonlinear changes vary with the displacement of piston. When the suspension is largely impacted, the stiffness of this strut increases quickly which could restrain the wheel bouncing, body roll and vertical vibration.

근 접촉 영역에서 부상중인 슬라이더의 Touch-Down특성의 실험적 해석

Head Disk Interface (HDI) in a Hard Disk Drive (HDD) has decreased to achieve high areal density. Thus, the contact between a slider and a disk becomes more important. The contact between the slider and the disk can cause severe wear and damage of both the slider and the disk. Especially, Touch Down (TD) that the contact occurs continuously and repeatedly is extremely dangerous. Therefore, it is necessary to analyze the unstable bouncing vibration of the slider in head-disk interface. In this paper, we investigate the characteristic and causes of the Touch Down.

Numerical Investigation of Bouncing Vibrations of an Air Bearing Slider in Near or Partial Contact

Near or partial contact sliders are designed for the areal recording density of 1 Tbit/in.2 or even higher in hard disk drives. The bouncing vibration of an air bearing-slider in near or partial contact with the disk is numerically analyzed using three different nonlinear slider dynamics models. In these three models, the air bearing with contact is modeled either by using the generalized Reynolds equation modified with the Fukui–Kaneko slip correction and a recent second order slip correction for the contact situation, or using nonlinear springs to represent the air bearing. The contact and adhesion between the slider and the disk are considered either through an elastic contact model and an improved intermolecular adhesion model, respectively, or using an Ono–Yamane multi-asperity contact and adhesion model (2007, “Improved Analysis of Unstable Bouncing Vibration and Stabilizing Design of Flying Head Slider in Near-Contact Region,” ASME J. Tribol., 129, pp. 65–74.). The contact friction is calculated by using Coulomb’s law and the contact force. The simulation results from all of these models show that the slider’s bouncing vibration occurs as a forced vibration caused by the moving microwaviness and roughness on the disk surface. The disk surface microwaviness and roughness, which move into the head disk interface as the disk rotates, excite the bouncing vibration of the partial contact slider. The contact, adhesion, and friction between the slider and the disk do not directly cause a bouncing vibration in the absence of disk microwaviness or roughness.

Dynamic Head-Disk Interface Instabilities With Friction for Light Contact (Surfing) Recording

Recent advances in hard-disk drive technology involve the use of a thermal fly-height control (TFC) pole tip protrusion to bring the read/write recording elements of the slider closer to the disk surface and thus achieve terabit per square inch recording densities. A dynamic, contact mechanics-based friction model of the head-disk interface (HDI) that includes roughness and accounts for the TFC geometry and its influence on the HDI dynamics is presented. The model is based on physical parameters and does not include any empirical coefficients. Experimental flyability/touchdown measurements were performed and used to examine in detail the HDI contact criterion in the presence of surface roughness and dynamic microwaviness. Using the model, a procedure is outlined that identifies the optimal clearance and light contact conditions, i.e., the amount of thermal actuation that minimizes, both, the clearance, as well as the flying height modulation. Through calculation of the time varying interfacial forces, mean pressure and shear stress at the HDI can be predicted and used to characterize the contact regime. Based on our results, a light contact regime with reduced bouncing vibrations and low stresses (thus, low wear) that would enable surfing recording is identified.

Suppression of Friction-Induced Vibration of a Glass Plate by a Dynamic Absorber

Friction-induced vibration often causes noise problems. When a plate-like object is rubbed by rubber, self-excited vibration is generated, which results in noise since plate vibration oscillates the air. For reducing vibration and noise, we investigate the characteristics of friction-induced vibration of a glass plate experimentally. Then, we study the effectiveness of a dynamic absorber mounted on the glass plate. The results demonstrate that the self-excited vibration is well suppressed by an absorber, and that absorbers with higher damping ratios are more effective than those with lower. The location of an absorber is also examined for reduction of vibration. Further, analytical study is performed to understand the mechanism of the vibration. We obtain an analytical model from observation and analyze the motion assuming bouncing vibration. Calculated results agree qualitatively with experimental ones.

Design optimisation of sub-5 nm Head-Disk Interfaces using a two-degree-of-freedom dynamic contact model with friction

The realisation of Tbit/in² areal densities will depend on the successful Head-Disk Interface (HDI) designs that will result in the smallest possible head media spacing. In this study, the effect of HDI roughness on flying/contact dynamics of sub-5 nm HDIs was investigated. Rough surface interfacial and dynamic contact models were used to predict time varying slider motion, from which output responses were generated through regression modelling. Provided that the input disk dynamic microwaviness is low, one could design the interface to have low roughness and area for fully flying or high roughness and area for mild, sustained contact and reduced Bouncing Vibrations (BVs).

Theoretical Study of Self-Excited and Forced Vibrations of Flying Head Slider in Near-Contact Region

After introducing our previous study of bouncing instability of a flying head slider, we numerically investigated slider dynamics in the near-contact region taking the root-mean-square value and frequency roll-off factor of the micro-waviness as parameters by using 2-degrees-of-freedom slider model, random micro-waviness model and lubricated rough-surface-contact characteristics model. We found that the slider exhibits self-excited bouncing vibration with a frequency close to the lower pitch frequency under small microwaviness but tends to exhibit forced vibration with a resonant frequency in the upper pitch mode as the amplitude of microwaviness increases. If the amount of microwaviness and destabilized sources are reduced sufficiently, there is a contact sliding condition without self-excited and forced bouncing vibration.

Dynamics of Partial Contact Head Disk Interface

A nonlinear dynamic model is developed to analyze the bouncing vibration of partial contact air bearing sliders, which are designed for the areal density of 1 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . In this model, the air bearing with contact is modeled using the generalized Reynolds equation modified with the Fukui-Kaneko slip correction and a recent slip correction for the contact situation. The adhesion, contact, and friction between the slider and the disk are also considered in this model. The adhesion force is calculated using a modified intermolecular force model; the contact force is obtained through an elastic quasi-static contact model that considers the slider and disk roughness. Realistic measured roughness of the slider and the disk are used in the simulation. It is found that minimizing the trailing pad size can reduce the slider's bouncing and crash likelihood. The surface roughness and adhesion have a strong effect on the slider's bouncing vibration, while the friction between the slider and disk is found to have less effect

Experimental and Theoretical Investigation of Bouncing Vibrations of a Flying Head Slider in the Near-Contact Region

We experimentally and theoretically investigated in detail bouncing vibrations of a flying head slider in the near-contact region between the head and disk surface. By changing the Z-height in the experiment, we evaluated the effect of the pitch static angle on the ambient pressure at which unstable bouncing vibration starts and stops. We found that the touch-down and take-off pressure hysteresis decreased as the pitch static angle increased even though the flying height at the trailing edge decreased slightly. From detailed measurement of the slider dynamics at the threshold of the bouncing vibration, we found that the trailing edge of the slider was first attracted to the disk. As the pitch static angle decreased, the magnitude of the first drop of the trailing edge increased and the bouncing vibration amplitude increased more rapidly. We also measured the mode of the bouncing vibration by using two laser Doppler vibrometers simultaneously. By using an improved two-degree-of-freedom slider model, in which the small micro-waviness and the shearing force of the lubricant were taken into account, we could analyze the touch-down/take-off hysteresis, mode, and destabilization process of the bouncing vibration similar to the experimental results. We also theoretically found that either self-excited bouncing vibration with lower pitch frequency or forced vibration with higher pitch frequency was generated, depending on the magnitudes of the micro-waviness and the disturbance.

Development of contact sliders with nanotextures by femtosecond laser processing

This paper describes the development of novel contact sliders with nanotextures by means of femtosecond laser processing. In order to achieve a magnetic recording density of more than 1 Tb/in2, it is necessary to create an ultralow head-disk interface (HDI) spacing, i.e., less than 2–3 nm. Thus far, various new concept HDI technologies have been proposed for developing such near-contact or contact recording HDI. In this paper, the authors propose the concept of a novel contact slider. This slider has nanotextures fabricated by femtosecond laser processing. Sliders with five DLC thin-film pads on the air bearing surfaces were used, and the pad diameter and thickness are 40 μm and 40 nm, respectively. The fabrication process of nanotextures on the DLC thin-film pads employed a femtosecond Ti:sapphire laser. The laser wavelength and pulse width are 800 nm and 120 fs, respectively. Contact slider experiments were also carried out, using (1) the fabricated contact sliders having nanotextures with different RMS heights and (2) a contact slider without nanotextures. The nanotribological characteristics of the contact HDI as well as the dynamics of the contact sliders were investigated. In addition, the behavior of the ultrathin liquid lubricant film was evaluated by using a surface reflectance analyzer (SRA) after the contact slider experiments. It was found that the nanotextures produced by femtosecond laser processing are very effective for next-generation contact sliders and the optimum RMS heights of the nanotextures can be obtained. These advancements will facilitate the development of contact HDI with lower friction, lower wear of the contact slider surfaces, smaller change in the lubricant film thickness and lower contact slider bouncing vibration.

Friction, Heat, and Slider Dynamics During Thermal Protrusion Touchdown

Thermal protrusion of the write head in a hard disk drive can be used to control the transition of the slider from flying to contact. Once in contact with the disk, the level of interference can be adjusted gradually by electrical power, making this a very convenient, fast, and high resolution approach for investigating the head disk interface (HDI) during the transition from flying to contact. In this paper we investigate the slider dynamics during the transition from flying to contact, as well as at controlled levels of contact interference. In particular, the touchdown-takeoff hysteresis is analyzed by monitoring friction, read element resistance, tribo-current, acoustic emission and laser Doppler vibrometer signal from the slider. A novel disk texture was developed that significantly improved the contact dynamics and hysteresis. On circumferentially smooth media we observe increased friction, heat, slider bouncing vibrations, and increased hysteresis

Improved Analysis of Unstable Bouncing Vibration and Stabilizing Design of Flying Head Slider in Near-Contact Region

This paper describes an improved analytical study of the bouncing vibration of a flying head slider in the near-contact region and gives quantitative designs guideline for realizing a stable flying head slider, based on the results of a parametric study. First, we numerically calculated the general characteristics of the contact and adhesion forces between a smooth contact pad and disk surface by considering asperity contact, the lubricant meniscus, and elastic bulk deformation. As a result, it was shown that the contact characteristics can be represented by a simple model with five independent parameters when the asperity density is large and the asperity height is small as in cases of current slider and disk surfaces. Then, we numerically computed the slider dynamics in a two degree of freedom slider model with nonlinear air-bearing springs by using the simplified contact characteristic model. As a result, we have obtained a self-excited bouncing vibration whose frequency, amplitude and touchdown/takeoff hysteresis characteristics agree much better with the experimental results compared with our previous analysis. From a parametric study for takeoff height, we could obtain design guidelines for realizing a stable head slider in a low flying height of 5nm or less.