Predicting Fly-Height Modulation and Contact Forces in Ultra-Low Flying Head-Disk Interfaces Using a Tri-State Switching Dynamic Contact Model

2001 ◽  
Author(s):  
Sung-Chang Lee ◽  
Andreas A. Polycarpou
Keyword(s):  
Contact Force ◽  
Contact Stiffness ◽  
Dynamic Contact ◽  
Design Guidelines ◽  
Contact Forces ◽  
Contact Dynamics ◽  
Contact Model ◽  
Flying Height ◽  
Disk Contact ◽  
Fly Height

Abstract In order to achieve higher recording densities up to 1 Tbit/In2 using conventional recording technologies, the recording slider will need to “fly” within 5 nm or less from the rotating disk. In such ultra-low flying height regimes, intermittent head/disk contact is unavoidable. Head/disk contact can cause large vibrations of the recording slider in the normal and lateral (off-track) directions as well as damage the disk due to large dynamic contact forces. This paper describes a simple continuum mechanics-based model that includes the dynamics of a flying head/disk interface (HDI) as well as the contact dynamics. Specifically, a lumped parameter one degree-of-freedom, three state nonlinear dynamic model representing the normal dynamics of the HDI and an asperity-based contact model are developed. The effects of realistic (dynamic microwaviness) and harmonic input excitations, contact stiffness (surface roughness) and air-bearing force during contact on fly-height modulation (FHM) and contact force are investigated. Based on the tri-state model predictions, design guidelines for reduced FHM and dynamic contact force are suggested.

Evaluation of vehicular contact force on bridge joints by vibration responses and object detection

2021 ◽  
Author(s):  
Di Su ◽  
Yuichiro Tanaka ◽  
Tomonori Nagayama
Keyword(s):  
Object Detection ◽  
Contact Force ◽  
Dynamic Contact ◽  
Contact Forces ◽  
Expansion Joints ◽  
Cyclic Movements ◽  
Bridge Joints ◽  
Vibration Responses ◽  
On The Road ◽  
Board System

<p>Expansion joints on bridges should accommodate cyclic movements to minimize imposition of secondary stresses in the structure. However, these joints are highly susceptible to severe and repeated vehicular impact that results their inherent discontinuity. In this paper, a portable on- board system including accelerometers and a drive recorder to evaluate the vehicular contact force on bridge joints is proposed. First, from the acceleration responses of the vehicle, the contact force exerted on the road surface is estimated from a half-car model by Kalman Filter. Next, extraction of the expansion joints is performed by object detection from videos taken by the drive recorder. Finally, a relative comparison of the contact forces acting on joints is performed, with location identification on the map. The proposed system benefits to utilize the dynamic contact forces results from on-board system to detect the potential risky joints more precisely and efficiently.</p>

Intra-Articular Knee Contact Force Estimation During Walking Using Force-Reaction Elements and Subject-Specific Joint Model2

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Yihwan Jung ◽  
Cong-Bo Phan ◽  
Seungbum Koo
Keyword(s):  
Contact Force ◽  
Inverse Dynamics ◽  
Reaction Force ◽  
Muscle Tension ◽  
Contact Forces ◽  
Contact Model ◽  
Grand Challenge ◽  
Subject Specific ◽  
Mean Square Errors

Joint contact forces measured with instrumented knee implants have not only revealed general patterns of joint loading but also showed individual variations that could be due to differences in anatomy and joint kinematics. Musculoskeletal human models for dynamic simulation have been utilized to understand body kinetics including joint moments, muscle tension, and knee contact forces. The objectives of this study were to develop a knee contact model which can predict knee contact forces using an inverse dynamics-based optimization solver and to investigate the effect of joint constraints on knee contact force prediction. A knee contact model was developed to include 32 reaction force elements on the surface of a tibial insert of a total knee replacement (TKR), which was embedded in a full-body musculoskeletal model. Various external measurements including motion data and external force data during walking trials of a subject with an instrumented knee implant were provided from the Sixth Grand Challenge Competition to Predict in vivo Knee Loads. Knee contact forces in the medial and lateral portions of the instrumented knee implant were also provided for the same walking trials. A knee contact model with a hinge joint and normal alignment could predict knee contact forces with root mean square errors (RMSEs) of 165 N and 288 N for the medial and lateral portions of the knee, respectively, and coefficients of determination (R2) of 0.70 and −0.63. When the degrees-of-freedom (DOF) of the knee and locations of leg markers were adjusted to account for the valgus lower-limb alignment of the subject, RMSE values improved to 144 N and 179 N, and R2 values improved to 0.77 and 0.37, respectively. The proposed knee contact model with subject-specific joint model could predict in vivo knee contact forces with reasonable accuracy. This model may contribute to the development and improvement of knee arthroplasty.

A Contact Model for Nonlinear Forced Response Prediction of Turbine Blades: Calculation Techniques and Experimental Comparison

2008 ◽  
Author(s):  
Christian M. Firrone ◽  
Marco Allara ◽  
Muzio M. Gola
Keyword(s):  
Normal Load ◽  
Contact Stiffness ◽  
Turbine Blades ◽  
Harmonic Balance Method ◽  
Forced Response ◽  
Contact Forces ◽  
Contact Model ◽  
Experimental Comparison ◽  
Normal Contact ◽  
Contact Models

Dry friction damping produced by sliding surfaces is commonly used to reduce vibration amplitude of blade arrays in turbo-machinery. The dynamic behavior of turbine components is significantly affected by the forces acting at their contact interfaces. In order to perform accurate dynamic analysis of these components, contact models must be included in the numerical solvers. This paper presents a novel approach to compute the contact stiffness of cylindrical contacts, analytical and based on the continuous contact mechanics. This is done in order to overcome the known difficulties in simultaneously adjusting the values of both tangential and normal contact stiffness experimentally. Monotonic loading curves and hysteresis cycles of contact forces vs. relative displacement are evaluated as a function of the main contact parameters (i.e. the contact geometry, the material properties and the contact normal load). The new contact model is compared with other contact models already presented in literature in order to show advantages and limitations. The contact model is integrated in a numerical solver, based on the Harmonic Balance Method (HBM), for the calculation of the forced response of turbine components with friction contacts, in particular underplatform dampers. Results from the nonlinear numerical simulations are compared with those from validation experiments.

Numerical Simulations of Slider Interaction With Multiple Asperity Using Hertzian Contact Model

1995 ◽  
Vol 117 (4) ◽  
pp. 575-579 ◽  
Author(s):  
Ellis Cha ◽  
D. B. Bogy
Keyword(s):  
Disk Drive ◽  
Contact Model ◽  
Hertzian Contact ◽  
Flying Height ◽  
Radius Of Curvature ◽  
Asperity Contact ◽  
Disk Contact ◽  
Suspension Dynamics ◽  
Magnetic Hard Disk ◽  
Hertzian Contact Model

A numerical simulation of slider-disk contact in a magnetic hard disk drive is studied using the Hertzian contact model. The slider-disk contact is caused by flying height fluctuation due to disk runout for very low flying sliders. The rough disk topography is generated numerically by combining a sinusoidal waviness and a Gaussian roughness. For each asperity contact, the radius of curvature is calculated from the disk topography, and the radius is used to calculate the contact force using the Hertzian contact model. The slider’s response to a single asperity calculated using the Hertzian contact model agrees well with the result obtained using the impulse-momentum based contact model. The simulation results of slider-disk contact including suspension dynamics are calculated with and without friction for a “nano-slider.”

Rough Surface Contact of Curved Conformal Surfaces: An Application to Rotor–Stator Rub

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Philip Varney ◽  
Itzhak Green
Keyword(s):  
Rough Surface ◽  
Contact Force ◽  
Contact Stiffness ◽  
Point Contact ◽  
Contact Model ◽  
Industrial Society ◽  
Real Surface ◽  
Linear Elastic ◽  
Surface Contact ◽  
Rough Surface Contact

Rotating machines and associated triboelements are ubiquitous in industrial society, playing a central role in power generation, transportation, and manufacturing. Unfortunately, these systems are susceptible to undesirable contact (i.e., rub) between the rotor and stator, which is both costly and dangerous. These adverse effects can be alleviated by properly applying accurate real-time diagnostics. The first step toward accurate diagnostics is developing rotor–stator rub models which appropriately emulate reality. Previous rotor–stator rub models disavow the contact physics by reducing the problem to a single esoteric linear contact stiffness occurring only at the point of maximum rotor radial deflection. Further, the contact stiffness is typically chosen arbitrarily, and as such provides no additional insight into the contacting surfaces. Here, a novel rotor–stator rub model is developed by treating the strongly conformal curved surfaces according to their actual nature: a collection of stochastically distributed asperities. Such an approach is advantageous in that it relies on real surface measurements to quantify the contact force rather than a heuristic choice of linear contact stiffness. Specifically, the elastoplastic Jackson–Green (JG) rough surface contact model is used to obtain the quasistatic contact force versus rotor radial deflection; differences and similarities in contact force between the linear elastic contact model (LECM) and JG model are discussed. Furthermore, the linear elastic model's point contact assumption is assessed and found to be inaccurate for systems with small clearances. Finally, to aid in computational efficiency in future rotordynamic simulation, a simple exponential curve fit is proposed to approximate the JG force–displacement relationship.

Nonlinear Thermal Protrusion and Slider Disk Contact Forces

2007 ◽  
Author(s):  
Bernhard Knigge ◽  
Andreas Moser ◽  
Jia-Yang Juang ◽  
Peter Baumgart
Keyword(s):  
Contact Force ◽  
New Technology ◽  
Hard Disk Drives ◽  
Contact Forces ◽  
Flying Height ◽  
Air Bearing ◽  
Thermal Protrusion ◽  
Trade Offs ◽  
Bearing Design ◽  
Heater Coil

Some of the recently shipped hard disk drives have a new technology to actively control the flying height between slider and disk. The slider to disk spacing is controlled by thermal protrusion actuation using a small heater coil which is located close to the read write element at the trailing end of the slider. By applying an electric current to the heater coil, the slider’s trailing end protrudes towards the disk and can be driven into contact with sufficiently high heating power. The contact force and the thermal protrusion efficiency is mainly controlled by air bearing design. In this paper we want to discuss the trade offs in air bearing design to achieve low contact force and high thermal actuation efficiency. We have done both numerical simulation and experimental measurements to investigate contact force and air bearing stiffness. Typically a softer air bearings will produce less contact force but usually exhibit worse flying height tolerances. We have found a nonlinear clearance change with applied heater power. At closer spacings, the pressure peak increases dramatically leading to reduced actuation efficiency. The actuation efficiency may also vary at different skew angles. For calibration purpose slider to disk touchdown requires contact. Due to different actuation efficiencies at different radii different contact forces are estimated.

Wheel–Rail Impact at Crossings: Relating Dynamic Frictional Contact to Degradation

2017 ◽  
Vol 12 (4) ◽  
Author(s):  
Zilong Wei ◽  
Chen Shen ◽  
Zili Li ◽  
Rolf Dollevoet
Keyword(s):  
Plastic Deformation ◽  
Contact Force ◽  
Frictional Contact ◽  
Point Contact ◽  
Strain Analysis ◽  
Dynamic Contact ◽  
Contact Forces ◽  
Fe Method ◽  
Normal Contact ◽  
The Impact

Irregularities in the geometry and flexibility of railway crossings cause large impact forces, leading to rapid degradation of crossings. Precise stress and strain analysis is essential for understanding the behavior of dynamic frictional contact and the related failures at crossings. In this research, the wear and plastic deformation because of wheel–rail impact at railway crossings was investigated using the finite-element (FE) method. The simulated dynamic response was verified through comparisons with in situ axle box acceleration (ABA) measurements. Our focus was on the contact solution, taking account not only of the dynamic contact force but also the adhesion–slip regions, shear traction, and microslip. The contact solution was then used to calculate the plastic deformation and frictional work. The results suggest that the normal and tangential contact forces on the wing rail and crossing nose are out-of-sync during the impact, and that the maximum values of both the plastic deformation and frictional work at the crossing nose occur during two-point contact stage rather than, as widely believed, at the moment of maximum normal contact force. These findings could contribute to the analysis of nonproportional loading in the materials and lead to a deeper understanding of the damage mechanisms. The model provides a tool for both damage analysis and structure optimization of crossings.

scholarly journals A continuous contact force model of planar revolute joint based on fitting method

2017 ◽  
Vol 9 (2) ◽  
pp. 168781401769047
Author(s):  
Yuntao Li ◽  
Qiquan Quan ◽  
Dewei Tang ◽  
Zhonghong Li ◽  
Zongquan Deng
Keyword(s):  
Contact Force ◽  
Contact Stiffness ◽  
Elastic Force ◽  
Contact Model ◽  
Force Model ◽  
Damping Force ◽  
Revolute Joint ◽  
Continuous Contact ◽  
Contact Force Model ◽  
Fitting Method

Both the process of eliminating the clearance in joints and the contact–impact process involve movement of a clearance mechanism, which may reduce transmission accuracy and lengthen the response time. An appropriate continuous contact force model is able to describe the contact phenomena of a joint with clearance in a facile manner. However, two main problems still should be solved in building the continuous contact force model. First, the elastic force parts in previous continuous contact force models for a revolute joint were established by amending the force exponent of the Hertz spherical contact model or by the modified Winkler contact model. Nevertheless, the force exponent is usually given by experience, and the thickness of the elastic layer in the Winkler theory is difficult to determine. Second, for the previous damping force parts of a revolute joint, the hysteretic damping coefficients were obtained by substituting the stiffness coefficient with the contact stiffness of revolute joint directly instead of using the energy conservation method for the complicated form of elastic force model. A feasible continuous contact force model based on a fitting method was proposed to avoid these problems. According to the experimental results, the continuous contact force model can be used to predict the contact characteristics of a planar revolute joint in a facile manner.

A Study of Subambient Pressure Tri-Pad Sliders Using Acoustic Emission

1998 ◽  
Vol 120 (1) ◽  
pp. 54-59 ◽  
Author(s):  
A. G. Khurshudov ◽  
F. E. Talke
Keyword(s):  
Acoustic Emission ◽  
Contact Force ◽  
Contact Forces ◽  
Constant Speed ◽  
Flying Height ◽  
Contact Behavior ◽  
Disk Interface

Acoustic emission is used to study the contact behavior of subambient pressure tri-pad sliders during start/stop and constant speed operation. The contact force at the slider/disk interface is determined as a function of velocity and the dependence of contact force on flying height is investigated. The results indicate that contact forces for typical subambient pressure tri-pad sliders are on the order of a few mN.

Evaluation of Friction Damping in Dovetail Root Joints Based on Dissipation Energy on Contact Surfaces

2009 ◽  
Author(s):  
Kunio Asai ◽  
Shigeo Sakurai ◽  
Takeshi Kudo ◽  
Norihiko Ozawa ◽  
Taizo Ikeda
Keyword(s):  
Contact Force ◽  
Contact Stiffness ◽  
Relative Displacement ◽  
Contact Angles ◽  
Forced Response ◽  
Contact Forces ◽  
Friction Damping ◽  
Normal Contact ◽  
Tangential Contact ◽  
Contact Surfaces

It is necessary to increase and estimate friction damping at contact interfaces to reduce vibratory stresses in turbines. The hysteresis behavior between tangential contact force and relative displacement should be precisely estimated to improve the accuracy of fiction-damping estimates. There is a difficulty in establishing a general model of hysteresis because tangential contact stiffness depends on many parameters, such as normal contact force, contact geometry, surface roughness, and wear status. We discuss a procedure to empirically calculate friction damping in dovetail root joints using the tangential contact stiffness estimated from measured natural frequencies and the micro-slip model whose coefficients were experimentally obtained from special fretting tests. Instead of the multi-harmonic balance methods, we calculated the friction damping on the basis of the energy dissipation at contact surfaces to discuss the effects of the tangential contact stiffness on several physical values, i.e., tangential and normal contact forces, natural frequency, and micro-slip. In our model, the linear forced response analysis was conducted by taking into consideration the non-linearity between the tangential contact force and the relative displacement by defining the actual and imaginary tangential contact stiffness. We confirmed that the numerically calculated damping ratios are quantitatively in very good agreement with the measured ones under different contact angles, input gravity levels, and contact forces. This indicates that if the tangential contact stiffness is accurately estimated, friction damping with our method can be precisely estimated under different test conditions. We also showed that the estimated tangential contact stiffness for dovetail root joints are smaller than those obtained by the fretting tests at high input gravity. This is probably because the contact interface partially separates during a cyclic loading in the former case; this results in the decrease of the contact area and contact stiffness.

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