Squeeze Film Effect Research Articles

Estimation of the squeeze film effect in a surface acoustic wave motor

This paper describes the air film characteristic in the interface between the slider and stator substrate of a surface acoustic wave (SAW) motor, and the difference of the squeeze film effect by the form of the slider. Because the vibration amplitude of the SAW motor is several 10 nm order, analysis of pressure was performed by using the molecular gas-film lubrication (MGL) equation. In the analysis, the MGL equation was split into advection phase and nonadvection phase, and calculation of advection and nonadvection phases was performed by using the cubic interpolated propagation (CIP) method and the finite difference method, respectively. From analysis results it was found that the time to steady pressure of air film depends on the radius of projection arranged on the contact surface of the slider. Also found was that the steady pressure in the interface does not depend on the radius and height of the projection, but it depends on the minimum spacing between the slider and the stator substrate.

Inactivation of Cryptosporidium parvum by Ultrasonic Irradiation

The inactivation of Cryptosporidium parvum was investigated by the use of three different sonicators utilizing the squeeze-film effect, which may occur when ultrasound is irradiated into an extremely thin space and generate intensified pressure in the sample suspension. To expand from the small-scale horn-type sonicator to large-scale cylindrical or cleaning bath sonicators, the inactivation effectwas improved. In the case of the cylindrical sonicator (26.6 kHz, 30 W), 97% of the initial concentration of 2260 oocysts mL(-1) was inactivated at33 mL min(-1) (residence time of approximately 5.2 min). Hundreds of cubic meters of water can be treated per day at several kW using this sonicator. In addition, the simultaneous use of sonication and chlorination showed a beneficial effect on inactivation for C. parvum based on the evaluation of infectivity testing and morphological observation.

Frictionless compression testing using load-applying platens made from porous graphite aerostatic bearings

In compression testing of soft materials at high strains, friction between a sample and the load-applying platens induces a differential lateral expansion that is visually evident as barreling. Barreling reduces the accuracy of the tests as a means of establishing accurate material properties. Current techniques for reducing friction, which involve liquid squeeze film lubrication, may not achieve true frictionless interfaces, are messy, and may adversely affect some samples. This article examines the use of porous graphite aerostatic bearings as a frictionless testing interface. The physics of a soft material under compressive loading by porous air bearings is investigated with simple finite element analysis and air flow models. An aerostatic bearing assembly is also constructed and compared to other friction reduction techniques. The results of these experiments indicate that there are benefits to using air bearings as they are clean, chemically inert, extremely stiff, reduce friction to levels comparable to existing methods, have negligible squeeze film effect, are repeatable, and allow for cyclic compression testing.

Modelling squeeze film effects in a MEMS accelerometer with a levitated proof mass

A triaxial accelerometer is presented which employs as its proof mass a mechanically free micromachined disc that is electrostatically levitated. Air damping plays a critical role in the operation of the accelerometer, providing stability to an inherently unstable system. Systems that operate beyond the cut-off frequency, however, suffer reduced gain due to the spring component of the squeeze film damping, resulting in decreased sensitivity. A finite-element model for extracting squeeze film damping coefficients for transverse and rotational motion of the disc, via an analogy to heat transfer theory, is presented. The use of the analogy enables a reduction of the problem from a complex three-dimensional computational fluid dynamics domain to a two-dimensional heat transfer domain. The model is used to evaluate the effect of including damping holes in the proof mass. The high-frequency oscillation and physical size of the proof mass dictate that the accelerometer is operated well beyond its cut-off frequency and so the inclusion of damping holes in the proof mass can result in an increase rather than decrease in the damping coefficient. The resulting system-level model, implemented in Matlab/Simulink, is then used to evaluate the effect of the squeeze film damping on the device performance.

Experimental Study of Collision Motion, Contact Force and Adhesion Force of Hemispherical Sliders with Stationary Magnetic Disks

In order to make clear the dynamic contact and adhesion forces of a magnetic head slider in near contact regime, we experimentally investigated the dynamic collision motion of hemispherical sliders on stationary magnetic disks. We used the hemispherical glass sliders of 1 and 2 mm in radius and the magnetic disks with different lubricant thickness of 0, 1, 2 and 3 nm with and without UV irradiation. As a result, we found that the dynamic adhesion forces of 1 and 2 mm radius sliders are almost equal to their static meniscus forces. In the case of 1 mm radius slider and 3 nm thick lubricant without UV, the dynamic adhesion force increases significantly because of a squeeze film effect. The 2 mm radius slider does not show a clear dynamic adhesion force at an impact velocity larger than 1.5 mm/s. We also found that contact force can be estimated by Hertz contact theory.

Resistive field bond graph models for hydrodynamically lubricated bearings

A lumped parameter model was developed for hydrodynamically lubricated bearings: elements that feature fully lubricated contact between surfaces in relative motion. The bearing models were represented as bond graphs. Currently, bond graphers view bearings as single-port resistance elements, which only account for losses associated with relative tangential motions between surfaces. Machine designers view bearings as devices that generate forces normal to surfaces in relative motion, to maintain position and alignment of shafts or surfaces. Both effects occur in real bearings, coupled together via physics. A lumped parameter model for hydrodynamically lubricated bearings is developed in this paper. The model includes the physical coupling between rotational degrees of freedom and orthogonal degrees of freedom associated with maintaining alignments. These lumped parameter models were synthesized from solutions of the Reynolds equation for various bearing geometries, and include normal motion and squeeze film effects. Since the forces, velocities and displacements pertaining to these orthogonal motions are physically coupled via viscous and constriction effects in the bearing's lubricant flow, the bond graph models involve resistive fields. Examples apply these concepts to thrust and journal bearings.

Force interactions between substrates and SPM cantilevers immersed in fluids

With the availability of equipment used in Scanning Probe Microscopy (SPM), researchers have been able to probe the local fluid–substrate force interactions with resolutions of pN using a variety of SPM cantilevers. When using such methods, it is essential to differentiate between contributions to the net force on the cantilever. Specifically, the interaction between the cantilever, substrate and fluid, quantified while generating force curves, are discussed and compared with theoretical models for squeeze-film effects and drag on the SPM cantilevers. In addition we have demonstrated a simple method for utilizing the system as a micro-viscometer, independently measuring the viscosity of the lubricant for each test.

A Study on Squeeze Films Between Porous Rubber Surface and Rigid Surface: Analysis Based on the Viscoelastic Continuum Model

The squeeze-film effect between a porous rubber surface and a rigid surface has been investigated as a problem of viscoelastic hydrodynamic lubrication (VEHL). An axisymmetric continuum model is introduced to estimate the surface deformation of a cylindrical porous rubber block based on a three-element viscoelastic model. The coefficients in the viscoelastic constitutive equation are experimentally determined and then the deformation of the porous rubber block is calculated by the FEM technique. The approximate solutions for the fluid pressures in the squeeze film are obtained from the equation of motion, which includes both local and convective inertia terms, and the continuity equation, using the perturbation method. Experimental data on the squeeze-film pressures and forces are also obtained under the sinusoidal squeezing motion of a rigid plate facing a cylindrical porous rubber block. It is found that the difference between the VEHL solutions and the EHL (elastohydrodynamic lubrication) solutions becomes more marked for a higher frequency of squeeze oscillation due to the effect of viscoelasticity of the porous rubber. The VEHL solutions hence correspond better to the measured results and yield a smaller surface deformation of the porous rubber block than the EHL solutions as the frequency of squeeze oscillation increases. The results also show that the fluid inertia effect due to the flow in the squeeze film becomes noticeable for a higher frequency of the squeezing motion as the effect of viscoelasticity of the porous rubber.

Theory of microfluidic squeeze-film dominated fluid ejection

We present a theory for predicting fluid ejection for microfluidic systems that utilize the squeeze-film effect as the dominant pressure generation mechanism. We derive the equations of motion for such systems taking into account both viscous and inertial effects. The dominant viscous term is due to the squeeze-film effect, in which a thin layer of incompressible viscous fluid is ‘squeezed’ between a moving piston and an orifice plate. We apply Reynolds lubrication theory and derive an analytical expression for the squeeze-film pressure distribution, taking into account both flow through the orifice and restricted flow around the piston. The dominant inertial effects are due to the acceleration of fluid between the piston and the orifice plate, through the orifice, and around the piston. We derive an analytical expression for an effective fluid mass that accounts for these effects. We use these expressions in the equations of motion and obtain a theoretical model for predicting the behaviour of squeeze-film dominated microfluidic fluid ejectors. We demonstrate the theory via application to a practical device.

Squeeze film damping effect on switching time of a MOEMS optical switch

This paper presents theoretical analysis for the effect of air squeeze film damping on a MOEMS optical switch with the slant lower electrode. Analytical formulae are derived for the squeeze film damping coefficient and the squeeze film damping torque on the cantilever beam of the optical switch. According to solving the dynamic equation, the effect of the air squeeze film damping on the switching time is analyzed. There are discrepancies of 0.15 ms and 0.80 ms for the switching time T off and T on , respectively, without considering the squeeze film damping. Therefore the effect of the air squeeze film damping on T on is more obvious than that on T off .

Inactivation of Escherichia coli by ultrasonic irradiation

Ultrasonic inactivation of Escherichia coli XL1-Blue has been investigated by high-intensity ultrasonic waves from horn type sonicator (27.5 kHz) utilizing the “squeeze-film effect”. The amplitude of the vibration face contacting the sample solution was used as an indication of the ultrasonic power intensity. The inactivation of the E. coli cells by ultrasonic irradiation shows pseudo first-order behavior. The inactivation rate constant gradually increased with increasing amplitude of the vibration face and showed rapid increase above 3 μm (p–p). In contrast, the H 2O 2 formation was not observed below 3 μm (p–p), indicating that the ultrasonic shock wave might be more important than indirect effect of OH radicals formed by ultrasonic cavitation in this system. The optimal thickness of the squeeze film was determined as 2 mm for the E. coli inactivation. More than 99% of E. coli cells was inactivated within 180-s sonication at the amplitude of 3 μm (p–p) and 2 mm of the thickness of the squeeze film.

スクイーズ膜効果による超音波キャビテーションを利用した海洋水保全技術

Recently, destruction of the ecological environment caused by plankton in ballast water on oceangoing ships is one of the most crucial topics for ocean environmental protection. The author has proposed a technique for water treatment using ultrasonic cavitation induced by the squeeze-film effect and has made a prototype of an ultrasonic sterilizer. This sterilizer can efficiently inactivate oosysts of Cryptospridium purvum which is pathogenic protozoan. In this paper, the effect of this ultrasonic water treatment on Heterocapsa circularisquama, which is phytoplankton and has sometimes caused red tide pollution, is experimentally investigated with the aim of applying to ballast water treatment. As a result, the number of killing H. circularisquama cells per unit input energy is almost constant independently of the thickness of the squeeze-film. The efficiency of inactivation of C. purvum oosysts are also rediscussed from the viewpoint of the number of inactivated oosysts per unit input energy.

Acceleration switch with extended holding time using squeeze film effect for side airbag systems

Bulk micromachined silicon mechanical acceleration switches have been designed, fabricated, and characterized for the purpose of crash sensing for side airbag systems in which high-speed response is required for triggering the airbag. In order to inflate the airbag, collision should be recognized by analyzing the output signals of the electrical accelerometer and the acceleration switch to prevent mis-operation caused by an electromagnetic noise. The ON-state duration of the acceleration switch is designed to convert to the acceleration magnitude, and for this purpose squeeze film effect is utilized. The acceleration switch consists of an electrical contact part suspended from the surrounding seismic mass which performs holding of the ON-state using the squeeze film effect. A reliable and sticking-free switching operation was realized by Au microspring contact. The contact resistance achieved was 600 mΩ. It responded quickly and held the ON-state up to 6 ms depending on the acceleration amplitude.

Static behavior and dynamic stability analysis of grooved rectangular aerostatic thrust bearings by modified resistance network method

This paper begins with the development of the resistance network method (RNM) for designing an aerostatic rectangular bearing with X-shaped grooves. The Newmark integration method and the modified RNM, which takes into account the equilibrium of the mass flow rate and the squeeze film effect, are used to analyze the time-dependent dynamic behaviors at each time step. Finally, the stability properties as well as impulse responses of this type of bearing, which simulates variation in film gap caused by imperfect guideway geometry, are demonstrated in the current paper.

A study on the behavior of the film thickness between piston shoe and swash plate using the squeeze film effect and the drag flow effect

The purpose of this study is to explain the loss mechanism between piston shoe and swash plate of axial piston units and to derive new presuppositions for developing a new unit or improving an existing one. The film thickness was measured at constant pressure to find out the correlation between speed and the drag flow effect. The behavior of the film thickness between piston shoe and swash plate in the real unit was described through combining a squeeze-film-effect with a drag flow effect.

Dynamic Analysis of the X-shaped Groove Aerostatic Bearings with Disk-Spring Compensator.

This paper describes the development of the modified resistance network method (RNM) for analyzing the dynamic behaviors of X-shaped grooves aerostatic bearing with a passive disk-spring compensator. The Newmark integration method and the modified RNM, which takes into account on the equilibrium of the mass flow rate and the squeeze film effect, are used to analyze the time-dependent dynamic behaviors. Results show that after impulse most of the vibrations are absorbed by the disk-spring compensator and the table can maintain a small vibration around the equilibrium position.

302 スクイーズ膜効果を用いた超音波水処理 : 超音波殺菌セルの直並列化による水処理システムの構築

The ultrasonic sterilizing method is environmentally safe because of using non-chemicals. We have made a prototype of an ultrasonic sterilizer which induces cavitation utilizing the squeeze-film effect. Our previous experimental results shows that the prototype called "the ultrasonic sterilizing cell" can efficiently inactivate Cryptosporidium oosysts. The ultrasonic sterilizing cell can treat only a small amount of water, but the cost of treatment is much lower than the cost of the conventional ultrasonic treatment of water. For the treatment of a large amount of water, the specifications of water treatment systems consisting of the cells in series and parallel are theoretically investigated from the view point of reaction kinetics. There is a probability that a few kilowatt system will be able to treat about 100m^3 per day of water contaminated by Cryptosporidium oosysts with high efficiency. The system is expected to treat filter backwash water.

Prediction of wet band brake dynamic engagement behaviour Part 1: Mathematical model development

A wet (oil-lubricated) band brake is a critical component in the operation of automatic transmission systems in automotive applications. Its engagement characteristics significantly affect the quality of automatic shifting. During the automatic transmission design process, it is important to characterize band engagement behaviour accurately under a wide range of operating conditions. This paper describes a mathematical model which predicts the dynamic engagement behaviour of the wet band brake. The space-time-dependent model includes the effects of squeeze film, asperity deformation, porous oil diffusion, heat transfer and loading pressure distribution caused by a self-energizing mechanism. The model can be readily implemented and efficiently executed on a computer as a standalone program or as a subroutine for automatic transmission shift simulations. Knowledge of band engagement obtained through the model is expected to lead to improved band design and automatic transmission shift calibration processes.

Direct evidence of lubrication in ceramic-on-ceramic total hip replacements

A study of surface contact and separation of ceramic-on-ceramic joints was undertaken in 25 per cent bovine serum using a hip simulator. An electrical resistivity technique was used to detect the extent of surface separation throughout a complete walking cycle. The femoral and acetabular components were coated in a thin conducting film of titanium nitride to allow application of the resistivity technique to non-conducting ceramic. Surface separation of the acetabular and femoral components was detected throughout each simulated walking cycle. Fluctuations in the applied voltage across the joint were observed which could not be attributed to elastohydrodynamic or squeeze-film lubrication effects. The probable cause of the voltage fluctuations was brief and occasional contact between the surfaces caused by a combination of asperity contact and subsequent detachment of the conductive coating.

Ultrasonic transmission and reception from bulk-micromachined transducers.

Acoustic transduction in air from two bulk-micromachined silicon structures is investigated. Both contain silicon diaphragms of the order of 2 mm2 in close proximity to a metallized substrate. One diaphragm is mass-loaded; the other is not. Their resonant frequencies (70 and 360 kHz) are dominated by squeeze film trapping of ambient air, and the Q of each device is about 8. The lower frequency (LF) device is characterized by electrical and acoustic measurements using a calibrated microphone. Novel diagnostic methods that exploit the non-linear nature of the transducer are described. The adequacy of calibration by reciprocity is confirmed at 70 kHz and applied to the high frequency device. An insertion loss of 19 dB is measured, which compares well with reports of other silicon-based transducers. Observed losses are accounted for by squeeze-film damping applied to the diaphragm-substrate gap. The ability to control the bandwidth by the squeeze film effect, the good efficiency, and the relatively standard method of construction could make such ultrasonic transducers useful in specialist applications.