Study of Slider Dynamics Over Very Smooth Magnetic Disks

1996 ◽  
Vol 118 (2) ◽  
pp. 382-387 ◽  
Author(s):  
Shoji Suzuki ◽  
Henry Nishihira
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
Laser Doppler Vibrometer ◽  
Low Frequency ◽  
Surface Characteristics ◽  
Disk Surface ◽  
Low Frequencies ◽  
Smooth Disk ◽  
Ae Signal ◽  
Fly Height

Flying characteristics of 50 percent negative pressure sliders on aluminum, glass, and silicon disks with different surface characteristics are described. By using an AE (acoustic emission) and LDV (Laser Doppler Vibrometer) we were able to study the effect of surface roughness and disk materials on the dynamics of the slider. In the regime where the slider flies below the glide height (30 nm) and contact with the disk surface can occur, the AE signal consisted of low frequencies related to air bearing resonance (around 100 kHz), and high frequency related to slider body vibrations (735 kHz). Interestingly, in the high speed regime the AE signal contained low frequency signals. The signal increased as the fly height of the slider increased when flying on the smooth surfaces except on the silicon disk. LDV measurements revealed that the excitation from the silicon disk surface was smaller than on the aluminum disk or the glass disk by 10 dB, which contributed to suppress the vibration of the slider. For a given excitation from the disk, the surface roughness played a key role in determining the slider vibration. We also determined that a fly height fluctuation occurred due to the surface roughness, but the effect was found to be very small. The difference between the textured and smooth surface was from the damping effect on the slider vibration. The slider was made to collide with a protrusion fabricated on a disk surface to study the damping characteristics of the slider. The textured disk surface gave more damping than on the smooth disk surface by up to 20 percent.

Measurement of Dynamic Strain

1943 ◽  
Vol 10 (2) ◽  
pp. A85-A92
Author(s):  
C. O. Dohrenwend ◽  
W. R. Mehaffey
Keyword(s):  
High Speed ◽  
Shock Loading ◽  
Low Frequency ◽  
Dynamic Strain ◽  
Time Axis ◽  
Low Frequencies ◽  
Strain Measurements ◽  
Moving Vehicles ◽  
Machine Parts ◽  
Dynamic Strains

Abstract The measurement of dynamic strains of both high and low frequency give rise to a variety of problems in instrumentation. Two types of equipment and circuits designed and used by the authors are discussed in detail. The first type based on the amplitude-modulated method is for low frequencies from zero to about 15 per cent of the carrier frequency of 1025 cycles per sec. The equipment has application to strain measurements varying from static values to those produced in moving vehicles, various machine parts, structures such as crane bridges, in fact all strain measurements where the frequency is 150 cycles per sec or less. The second type of equipment discussed is a potentiometer type and is for high-frequency strain measurements from 100 cycles per sec to 8000 cycles per sec. This high-speed equipment is conveniently used for impact strain, such as produced in hammer blows, shock loading, forging equipment, and impact-factor determination. Both units are designed to be used with a cathode-ray oscillograph which lends itself to a variety of recording methods. The methods discussed include both the type where the time axis is obtained by sweeping the oscilloscope beam on a stationary film and where the time axis is obtained mechanically.

scholarly journals Superluminal Motion in CTA 102

1989 ◽  
Vol 134 ◽  
pp. 529-530
Author(s):  
Ann E. Wehrle
Keyword(s):  
Flux Density ◽  
High Speed ◽  
Low Frequency ◽  
Precise Determination ◽  
Flux Variation ◽  
Low Frequencies ◽  
Superluminal Motion ◽  
Low Frequency Variability ◽  
Expansion Speed

Sholomitskii (1965) discovered that the flux density of the quasar CTA 102 varies at low frequencies on a timescale of a few months. Low-frequency variability can be explained by “superluminal flux variation” (Romney et al. 1984): If the intrinsic brightness of a component moving in a relativistically beamed source varies by only a few percent, the observer sees its flux density change by a much larger factor δ3-α when the optically thin blob moves almost directly toward the observer. Such a relativistically beamed source is likely to exhibit superluminal motion if studied with sufficient resolution and sensitivity. Superluminal motion in CTA 102 was discovered by Bååth (1987) who concluded on the basis of maps made at three epochs at a frequency of 932 MHz that two components were separating at a rate of 0.65 milliarcseconds (mas) per year. Using a redshift z = 1.037 and H0 = 100 km s−1 Mpc−1, q0 = 0.5, this expansion speed corresponds to (18 ± 4)h−1c. The extraordinarily high speed led us to make VLBI images of the source at a higher frequency in order to increase the resolution and make a more precise determination of the speed.

Simultaneous TR-PIV and CH* Chemiluminescence During Combustion-Instability Triggered Flame-Flashback in a Backward Facing Step Combustor

2019 ◽  
Author(s):  
Pankaj Pancharia ◽  
Vikram Ramanan ◽  
Baladandayuthapani Nagarajan ◽  
S. R. Chakravarthy
Keyword(s):  
Turbulence Intensity ◽  
High Speed ◽  
Combustion Instability ◽  
Low Frequency ◽  
High Amplitude ◽  
Static Stability ◽  
Low Frequencies ◽  
High Speed Data Acquisition ◽  
Flame Imaging ◽  
Flame Flashback

Abstract The present study is an experimental investigation of the nature of acoustically induced flashback in a lab-scale dump combustor. The control parameters varied include the inlet Reynolds number (Re) and the inlet turbulence intensity. The primary bifurcation plots of the combustor from stable to the unstable condition are seen to be significantly altered by the inlet turbulence intensity, with the latter delaying the onset of combustion instability to higher Re. The analysis of multivariate high-speed data acquisition and processing (viz. unsteady pressure, flame imaging and velocity field by means of PIV) reveals the role of low-frequency high amplitude acoustics in modulating the flame. It is seen that high amplitude oscillations are sustained by two mechanisms 1. Modulation of the flame by coherent structures shedding at the step and 2. The bulk flame motion in-and-out at the edge of the step. It is seen that flow reversal at sufficiently low frequencies provide enough duration for the hot products to ignite fresh reactants upstream of the duct, which in-turn reinforces the coherent unsteadiness in the system, thereby increasing the propensity of the mixture to be ignited more upstream with every cycle. This ultimately leads to the flame flashing back till the point of premixing. This work thus addresses and reforms the occurrence of flashback being an example of loss of static stability, whereby the overriding presence of dynamic combustion instability results in a flashback to behave in a dynamic manner.

Vibration Control of a Rigid and Flexible High-Speed Railway Vehicle

2020 ◽  
Author(s):  
Semiha Türkay ◽  
Aslı S. Leblebici
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Railway Vehicle ◽  
Allowable Limit ◽  
Low Frequencies ◽  
Railway Line ◽  
Power Spectral ◽  
Spectral Density Functions ◽  
The Right ◽  
Euler Bernoulli Beam

Abstract In this paper, the vertical carbody dynamics of the railway vehicle excited by random track inputs are investigated. The multi-objective ℋ∞ controllers for carbody weight of the actual, heavy and a mass confined in a polytopic range have been designed with the aim of reducing the wheel forces, heave, pitch and roll body accelerations of the vehicle. Later, the carbody mass is modelled as a free-free Euler Bernoulli beam and the low frequency flexural vibrations of the train body are examined. An omnibus ℋ∞ controller is synthesized to suppress both the rigid and low frequencies flexible modes of the railway vehicle. The performances of the ℋ∞ controllers are verified by using the passive and active suspension responses on the right and left rail track disturbances that are represented by the power spectral density functions authenticated for the stochastic real track data collected from the Qinhuangdao-Shenyang passenger railway line in China. Simulation results showed that all controllers exhibit a very good performance by effectively reducing the car-body accelerations in vicinity of the resonanat frequencies while keeping the wheel-rail forces in the allowable limit.

scholarly journals Spectra of Low-Frequency Ground Vibrations Generated by High-Speed Trains on Layered Ground

1997 ◽  
Vol 16 (4) ◽  
pp. 257-270 ◽  
Author(s):  
V.V. Krylov
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Ground Vibration ◽  
Ground Vibrations ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
High Speed Trains ◽  
Frequency Components ◽  
Noticeable Reduction ◽  
Layered Ground

Increase in speeds of modern railway trains is usually accompanied by higher levels of generated ground vibrations. In the author's earlier paper [V.V. Krylov, Applied Acoustics, 44, 149–164 (1995)], it has been shown that especially large increase in vibration level may occur if train speeds v exceed the velocity of Rayleigh surface waves in the ground cR., i.e., v > cR. Such a situation might arise, for example, with French TGV trains for which speeds over 515 km/h have been achieved. The present paper investigates the effect of geological layered structure of the ground on ground vibrations generated by high-speed trains. It is shown that, since Rayleigh wave velocities in layered ground are dispersive and normally increase at lower frequencies associated with deeper penetration of surface wave energy into the ground, the trans-Rayleigh condition v > cR may not hold at very low frequencies. This will cause a noticeable reduction in low-frequency components of generated ground vibration spectra. Theoretical results are illustrated by numerically calculated frequency spectra of ground vibrations generated by single axle loads travelling at different speeds and by TGV or Eurostar high-speed trains.

Spacing Modulation of Magnetic Head Due to Topographical Feature of Disk Surface

1998 ◽  
Vol 120 (3) ◽  
pp. 542-548 ◽  
Author(s):  
Shoji Suzuki
Keyword(s):  
High Resolution ◽  
Smooth Surface ◽  
Disk Surface ◽  
Magnetic Head ◽  
Signal Modulation ◽  
Height Range ◽  
Smooth Disk ◽  
Topographical Feature ◽  
Fly Height ◽  
Ramp Load

To achieve high recording density, the combination of low flying head and smooth disk surface is very desirable. Although high stiction associated with the smooth surface can be avoided by zone texturing or ramp load, stable flying condition must be assured by a smooth disk surface. Disk topography is an important factor in the flying stability of the head. In this work, read back signal modulation analysis was incorporated to characterize the disk topography. By increasing the writing frequency up to 25 MHz, high resolution was demonstrated in the fly height range between 15 nm to 50 nm. This resolution is sufficient to evaluate today’s low flying heads. A subambient pressure design which is typical for an MR head and a proximity head design for an inductive head were evaluated over very smooth aluminum disks. The effect of various disk clamping forces was also investigated. Relationship between disk waviness and flying stability of heads was studied.

Cluster Analysis on Vibration Characteristic in High Speed Ball-End Milling Hardened Steel

2011 ◽  
Vol 188 ◽  
pp. 145-149
Author(s):  
Bin Jiang ◽  
S.C. Yang ◽  
Yin Jin Yang ◽  
Min Li Zheng ◽  
P. Sun
Keyword(s):  
Surface Roughness ◽  
High Frequency ◽  
High Speed ◽  
End Milling ◽  
Low Frequency ◽  
Hardened Steel ◽  
High Speed Milling ◽  
Ball End Milling ◽  
Vibration Behavior ◽  
Low Frequency Vibration

Aim at the uncertainty of vibration behavior in high speed ball-end milling hardened steel, carried out the experiment of high speed milling hardened steel and modal analysis of cutter, studied vibration behavior of cutter and workpiece, and established vibration behavior sequence of high speed milling hardened steel. Using gray system theory, did gray cluster analysis of vibration characteristics, explored the correlation among cutter vibration, workpiece vibration and surface roughness characteristics, put forward the method of characterizing vibration characteristics in high speed ball-end milling hardened steel. The results show that high frequency vibrations of cutter and workpiece are caused by the interaction of centrifugal and dynamic cutting force, the increase of cutter overhang enhances high frequency vibration of cutter, the characteristic of cutter vibration changes from low frequency vibration to interaction of low frequency vibration and high frequency vibration. Using cutters with different overhang, surface roughness of high speed milling hardened steel has similar characteristics, surface roughness in row spacing direction can characterize low frequency vibration of cutter, and surface roughness in feed can characterize resonance characteristic of cutter caused by high frequency vibrations of cutter and workpiece.

Evaluation of Surface Roughness in High-Speed Shaping of Ni-P

2012 ◽  
Vol 516 ◽  
pp. 125-129
Author(s):  
Daisuke Kono ◽  
Sho Nakade ◽  
Atsushi Matsubara
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
Natural Vibration ◽  
Cutting Speed ◽  
Laser Doppler Vibrometer ◽  
Work Piece ◽  
Velocity Change ◽  
Tool Motion ◽  
Chip Removal ◽  
Cutting Speeds

A flat surface was machined by shaping to investigate the influence of the cutting speed on surface finish. When the cutting speed was 10-30 m/min, the surface roughness deteriorated because fine valleys with a depth of 40-200 nm were caused. Because the pitch of the valleys was almost equal at different cutting speeds, it was concluded that the valleys were not caused by the natural vibration of the machine tool. The velocity of the tool tip was measured by a laser Doppler vibrometer to compare the tool motion and the work piece profile. The periodical velocity change of the tool corresponded to the pitch of valleys. When a work piece with higher phosphorus content was machined, the valleys were not caused at a cutting speed of less than 30 m/min. It is estimated that the smoothness of chip removal has an influence on the emergence of valleys.

A Study of Machining Characteristics of YG8 in High Speed Grinding

2011 ◽  
Vol 487 ◽  
pp. 108-112 ◽  
Author(s):  
Jian Wu Yu ◽  
M. Cheng ◽  
Shao Hui Yin ◽  
G.Z. Xie ◽  
X.L. Zhou
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
Surface Characteristics ◽  
Grinding Force ◽  
Good Surface ◽  
High Speed Grinding ◽  
Grinding Conditions ◽  
Good Surface Roughness ◽  
Material Removal Mode ◽  
Machining Characteristics

The machining characteristics of cemented carbide YG8 under high speed grinding conditions are reported in this paper. The experimental investigation focused on the grinding force, surface roughness and surface characteristics influenced by various wheel speeds, feed rates and depths of cut. Surface roughness was slightly improved by increasing of wheel speed, and the increase in hmax generated bigger grinding force and decreased specific energy, which could be explained by material removal mode and SEM micrographs of surface. The results revealed that high machining efficiency was achieved and relatively good surface roughness was obtained simultaneously.

Gravity-Assisted, Passive Cancellation of Disturbances for Inertial Sensors

2013 ◽  
Author(s):  
Taras Karpachevskyy ◽  
Swavik Spiewak
Keyword(s):  
High Speed ◽  
Vibration Isolation ◽  
Inertial Sensors ◽  
Inertial Sensor ◽  
Broad Class ◽  
Signal Transmission ◽  
Low Frequency ◽  
Cost Ratio ◽  
Low Frequencies ◽  
Digital Circuitry

Continuing enhancements in Microsystem Technologies facilitate the development of inertial sensors — accelerometers and gyroscopes — of unprecedented performance to cost ratio and broaden the frontiers of their application. Of particular interest, because of their immunity to ambient disturbances, are sensors equipped with high resolution Electro-Mechanical ΣΔ converters and with a high speed, digital serial signal transmission. The digital circuitry of these sensors reaches the accuracy of 0.02 parts-per-million (ppm). However, the analogue transducers of measured physical quantities into electrical signals inside of the even best inertial sensors are prone to inherent imperfections of analog systems such as nonlinearity, cross-sensitivity, or noise. The best accuracy of these transducers is about two orders of magnitude worse than that of the electrical circuitry. The overall accuracy can be greatly improved by using corrective filters that cancel the effects of imperfections in the analogue transducers. The effectiveness of these filters hinges upon the accuracy of identifying comprehensive models of the analogue transducers. Ambient disturbances, in particular mechanical vibrations, greatly deteriorate the accuracy of identification. Their impact can be attenuated to some extent by using vibration isolation platforms. The effectiveness of attenuation is usually good at the frequencies above 5–10 Hz, however it is poor at low frequencies. This poor attenuation is a significant disadvantage since the low frequency phenomena in inertial sensors have pronounced impact on their suitability for a broad class of applications (e.g., navigation). The presented research focuses on the design of a passive vibration isolation device in which horizontal movement is coupled to tilt in a way that a component of the gravity perceived by the tested inertial sensor effectively cancels out the horizontal acceleration coming from the ambient vibrations.

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