Supply Holes Research Articles

Simulation Research on the Influence of Oil Damping to the Effect of Assimilating Impulsion Based on Accumulator

The general function library and hydraulic control library of EASY5 software were used to establish the dynamic model of hydraulic system of a sudden load, which could assimilate impulsion based on accumulator. The system was simulated with different diameters of the oil supply hole of accumulator. The simulation results were compared and analyzed to research the influence of oil damping to the effect of assimilating impulsion based on accumulator. From the simulation results, a hydraulic circuit consists of a throttle valve controlled by pressure and an accumulator was put forward to improve the capacity of accumulator to assimilate impulsion by changing the oil damping of accumulator through throttle valve, which had certain of meaning in project.

The fluid–structure interaction between a tensioned elastica and a flotation guide

Fluid–structure interaction between a flotation-guide and a tensioned elastic beam was investigated theoretically and experimentally. The work is inspired by manufacturing of thin flexible materials such as paper, foils and tape, collectively known as web. The mechanics of the web was modeled as an elastica beam, and solved in a Eulerian reference system by using the finite element method. The fluid mechanics in the beam/flotation-guide interface was modeled with two different fluid mechanics approaches with and without height averaging of the flow variables. The fluid models were solved with a finite volume approach. A stacked, iterative coupling algorithm was used to obtain coupled solutions. Experiments were performed to verify the two FSI models. The experiments showed that the supply pressure inside the flotation-guide must be at least equal to the belt-wrap pressure of the web for flotation to occur, as expected. The effects of large web deformations and using the height-averaged fluid model were analyzed by varying design parameters such as web wrap angle, flotation-guide radius, supply pressure, and the distribution of the pressure supply holes. This work showed that the height-averaged fluid mechanics model fails to predict the two-dimensional flow near the exit regions, which develops for cases where the web-reverser clearance tends to have large diverging variations. It was also shown that in order to keep the applied web tension at a constant level, the arc length of the web between the supports must change.

Performance Comparison of Aerostatic Gas Bearings of Two Different Gas Supply Modes

In order to analyze the feature of high-load and high-stiffness gas bearing with tapered recess, the complete gas field consisting of supply hole and clearance is built up, and a laminar flow model and a sectional turbulent-laminar flow model are respectively applied to calculate the pressure distribution of centrally-fed gas bearing with tapered recess in different clearances. The theoretical results agree in general with the experimental. The experimental result demonstrates its high load, however its big gas cavity. On the above basis a circular ring gas supply bearing with tapered recess is presented, the calculation result shows that for this new type of ring inlet bearing the pressure drop in entrance area will be reduced effectively even with smaller tapered recess height, and compared with centrally-fed gas bearing with tapered recess, its gas recess volume decreased and stability increased, while the load capacity is basically the same.

Influence of pocket‐size on misaligned hole‐entry journal bearing

PurposeHole‐entry hybrid journal bearings are widely used in many applications owing to their favourable characteristics. Ever increasing technological developments demand much improved performance from these class of bearings operating under the most stringent, exact and precise conditions. Therefore, it becomes imperative that the hole‐entry journal bearings be designed on the basis of more accurately predicted bearing characteristics data. The purpose of this paper is to describe a theoretical study to demonstrate the combined influence of the effect of pocket size at the outlet of supply holes and the journal misalignment on the performance of an orifice compensated hole‐entry hybrid journal bearing system.Design/methodology/approachFinite element method is used to solve the Reynolds equation governing the flow of an incompressible lubricant in the clearance space between the journal and bearing together with equation of flow through an orifice. The journal misalignment has been accounted for by defining a pair of misalignment parameters sigma and delta. The effect of pocket size at the outlet of supply holes has been accounted by defining a non‐dimensional parameter which is function of diameter of pocket and journal diameter.FindingsThe results presented in this paper indicate that the effect of journal misalignment is, in general, to cause a reduction in bearing dynamic characteristics parameters whereas the effect of pocket size is to slightly compensate this loss. Performance of a two lobe four recessed journal bearing, a proper selection of bearing offset factor along with type of restrictor (capillary or orifice) is essential.Originality/valueThis paper presents valuable data relating to hole‐entry hybrid journal bearings useful for bearing designers.

Comparison between grooved and plane aerostatic thrust bearings: static performance

The demand of air bearings is increasing for those applications that require precision linear movements or high-speed rotations. In particular in this paper air pads for air motion technology are studied. The paper analyses the effect of a circumferential groove machined on the pad surface on pressure distribution, air flow consumption and stiffness. Two geometries are investigated and compared: one with three supply orifices and the other with a circumferential groove as well. The static characteristics of the pads are experimentally determined with also the pressure distributions under the pads along the radial and circumferential directions. The experimental pressure distributions are compared with the simulated ones, obtained with a numerical program at the purpose developed. The numerical model considers a general formulation of the supply holes discharge coefficient that can be used also in presence of a circumferential groove.

CFD Research on Aerostatic Bearing with Tangential Supply Holes

The radial aerostatic bearings with reversely tangential gas supply holes have been proved successfully in some applications to improve the dynamic stability. However, the concept lacks firm theoretical support. Aerostatic bearings with reversely tangential gas supply holes and radial gas supply holes were designed. The finite volume method (FVM) was used to solve the three-dimension flow field, the static characteristics of them were studied, and the following conclusions were drawn: The tangential gas supply holes can improve the pressure distributions in the working clearance, but they can’t effectively improve the load capacity and stiffness. The improvement of the characteristics of aerostatic bearings with tangential gas supply holes is at the expense of excessive gas consumption. For aerostatic bearings, when the eccentricity ( ) is large and the rotor speed ( ) is high, the dynamic effect can effectively improve the load capacity and stiffness.

Characteristics of Subsonic Velocity Field of Externally Pressurized Gas Thrust Bearings

The complete gas field including supply hole and clearance is built up, and a two-dimensional laminar flow model and local turbulent flow model are used to calculate the parameters of gas thrust bearing in different clearances. The calculation results basically agree with the experimental results. The numerical results illustrate the shock/boundary layer interaction and the shock train phenomenon. The analysis of velocity and pressure show that, with increase of both gas supply pressure and clearance thickness, the gas flows more quickly at the entrance of supply hole, which produces local back-flow, there is supersonic flow behind the throat, and pressure rise slowly with the dissipation effect at wall and oblique shock wave, the gas lowers down to subsonic velocity, gradually shows non-viscosity.

Performance of Externally Pressurized Grooved Thrust Bearings

Externally pressurized grooved gas thrust bearings for shaft systems were studied both numerically and experimentally. Three thrust bearings composed of a symmetric pair of rings facing a shaft collar were tested. The rings, with inner and outer diameters of 52 and 110 mm, respectively, are equipped with a polar array of eight holes, with a 0.35-mm diameter, distributed on a 65-mm-diameter circumference. The influence of a circumferential groove situated in correspondence with the supply holes is discussed. In particular, two thrust bearings have a rectangular cross-sectional groove of 0.7-mm width and 10- and 20-μm depth. A numerical model based on Reynolds' equation is used to study thrust-bearing performance in relation to geometry (diameter of supply holes, clearance, and groove dimensions). A test rig is used to monitor thrust-bearing axial load capacity and stiffness, and evaluate damping and stability at different supply pressure rates. Experimental and numerical results are compared and discussed.

A Study of the Steady-State Performance of a Pressurized Air Wave Bearing at Concentric Position

The steady-state performance of a pressurized air wave bearing in concentric position is predicted using a commercial computational fluid dynamics (CFD) code. This code solves the three-dimensional compressible Navier-Stokes equations in the turbulent regime, taking into account the real geometry of both the bearing fluid film and the supply regions. The code can provide detailed information about the flow (pressure, turbulent kinetic energy distributions, velocity profiles, etc.) in all bearing regions including the supply holes. This approach does not involve a correction of the flow rate with an empirical discharge coefficient. The predicted values of the supply flow rates are compared to the experimental values obtained with a dedicated wave bearing test rig located at NASA Glenn Research Center in Cleveland, Ohio.

Effect of base stocks on the automobile engine bearing

The government has required that engine oil viscosity be lowered and that highly refined base stocks be used in engine oils, with the aim of promoting low fuel consumption and developing long-life oils. To improve the reliability of automobile plain bearings by means of engine oils, we have developed a bearing test apparatus that uses a half-metal. Oil can be supplied through the oil supply port in the same way as in actual engines. In this apparatus, variable loads can be applied to the opposite side of the oil supply hole of the bearing by hydraulic pressure that is synchronized with the rotational speed of the shaft. The influence of the base stocks used for engine oils on the contact between the rotating shaft and the bearing metal, and on the bearing rotating torque generated by rotation of the shaft, were investigated. We found that the contact ratio and the bearing rotating torque varied with different types of base stock compositions, even if the base stocks had the same viscometric properties. Therefore, it is necessary to develop countermeasures to avoid adverse effects when lowering engine oil viscosity and using highly refined base stocks.

Externally pressurized gas bearings: A comparison between two supply holes configurations

Radial vibration of a vertical rotor with externally pressurized gas bearings is analyzed. The time-dependent Reynolds equation is solved together with the journal equation of motion to obtain the response characteristics of the bearing system. The bearings are supplied with either one or two sets of supply orifices. Stiffness and flow rate are compared for both cases. Stability maps are obtained at different supply pressures and with different supply orifice diameters. The mass range from orbital stability to instability is studied as a function of supply hole downstream pressure level.

EXPERIMENTAL AND CFD STUDY ON ONE NEW TYPE OF AEROSTATIC BEARING

The pressure depression is usually observed just after the gas supply hole. In order to improve the pressure distribution, a new type of aerostatic bearing (NT) is designed, which has a tapered chamber at the outlet of the gas supply hole. The Fluent software is used to simulate the working conditions of aerostatic bearings. The simulation results show the simulation method can effectively estimate the pressure depression and the pressure distribution of the NT is remarkably improved compared with the traditional annular orifice type (TT). It's found that the characteristics of the Mach Number (MN) distribution of the NT are different from those of the TT and the tapered chamber can effectively reduce the velocity at the bearing clearance entrance. A test rig is built. Thepressure distributions are tested and the simulation results of the NT agree well with the experimental results. The simulation method provides a good theoretical method to study the aerostatic bearings and the new design will be helpful to the development of high load capacity aerostatic bearings.

STUDY OF A GAS THRUST BEARING WITH SUPPLY GROOVES

Plane externally pressurized thrust gas bearings for high speed spindles are considered. The behavior of the rotor-bearing system is studied both numerically and experimentally. A numerical model based on Reynolds equation is used to simulate the static and dynamic behavior of the system. Flow rate equation through inlet orifices is coupled with Reynolds equation. The flow rate is calculated by considering an experimentally determined discharge coefficient, that is function of holes diameter and local clearance. To increase stiffness are studied thrust bearings presenting a circumferential groove situated at the same radius of the supply holes. The influence of the groove on stiffness and stability is discussed. Simulations are made to evaluate the influence of supply holes diameter and of axial clearance on bearing characteristics. Two thrust bearings are studied experimentally. They are composed by a symmetric couple of disks facing the rotor flange. The internal and external diameters of the disks are 52 mm and 110 mm and equipped with 8 holes of diameter 0.35 mm on a circumference of diameter 65 mm. A thrust bearing present a rectangular section circumferential groove, located at the same radius of the orifices, of width 0.7 mm and thickness 10Pm. Comparisons between simulated and experimental stiffness are presented.

Effect of Wear on the Performance of Non-Recessed Orifice Compensated Hybrid Journal Bearing

A bearing subjected to frequent start/stop operations is worn progressively due to rubbing. As a consequence, the geometry of the bearing changes and the performance is affected. This paper presents a theoretical study of the performance of an orifice compensated worn non-recessed hole-entry hybrid journal bearing system. The finite element method has been used to solve the Reynolds equation, governing the flow of the lubricant in the clearance space between the journal and the bearing, along with a restrictor flow equation. The global system equation with the orifice restrictor is nonlinear, which is solved by an iterative technique using the Newton-Raphson method. Two types of journal bearing configurations, having symmetrical and asymmetrical distribution of supply holes around the circumferential direction, have been investigated in the present study. The effect of the wear depth on the journal bearing performance characteristics have been presented for a wide range of restrictor design parameters and external loads. The study demonstrates that the wear affects the bearing performance parameters and the degree of variation is affected by the operating condition, the bearing configuration, and the type of restrictor used. The influence of wear can be reduced by a proper selection of the bearing configuration (symmetrical/asymmetrical), the restrictor, and its design parameter.

Study of supply cut‐off and bearing geometric parameters on design of hybrid journal bearing

PurposeHybrid bearings have found increasing applications in various machines owing to their large number of favorable characteristics like high load carrying capacity, increased minimum fluid film thickness, long life and increased damping making them attractive for various applications such as turbo machinery, machine tool spindles, precision grinder spindles, etc. A careful design of such bearing for optimum performance has always been among the key issues of the researchers. The present work has been carried out to study the effect of bearing geometric parameters on performance of hybrid journal bearing and supply cut‐off behavior has also been studied for the improved performance.Design/methodology/approachThe generalized Reynold's equation governing the fluid flow in the clearance space between bearing and journal has been solved using finite element method to determine the pressure distribution, subsequently performance of hole‐entry hybrid journal bearing are computed. The journal centre equilibrium position for the given load is computed and the formulation is explained. The geometric parameters include aspect ratio, land width ratio, number of rows and number of holes per row. Further, performance of the bearing is computed with increasing the load, which induces negative pressure or the backpressure at the supply holes subsequently those are plugged to support the higher load.FindingsThe obtained results are presented in graphical form and logical conclusions are drawn and the modified configurations with reduced number of holes are suggested for higher load. It is observed that the bearing configuration with aspect ratio = 1.0 and land width ratio = 0.2 is best for high load support for low power requirement as less lubricant is required to be pumped in the bearing yet it provides sufficient fluid film thickness and lower values of maximum pressure. The load carrying capacity of the bearing can be further increased by plugging the holes on which backpressure is obtained for same bearing configuration. A feedback control with hybrid bearing system will sustain the sudden increase of load by shutting off the supply of the lubricant through supply hole where negative pressure is encountered.Originality/valueThe paper addresses the performance of non recessed hybrid journal bearings with wide range of geometric parameter. The results are quite useful for the bearing designer. The supply cut‐off is another aspect of originality of the paper as it provides the better load support.

Discharge coefficients of orifice-type restrictor for aerostatic bearings

The paper describes an experimental study conducted in order to determine the supply hole discharge coefficients of externally pressurized gas bearings. Tests were carried out on annular orifices and simple orifices with feed pocket. Air consumption and pressure distributions were measured as a function of supply pressure and air gap height for several different orifice and pocket sizes. Discharge coefficients were approximated by an experimental formula based on the Reynolds number and feeding systems geometry.

Numerical Calculation of Pressure Distribution in the Bearing Clearance of Circular Aerostatic Thrust Bearings with a Single Air Supply Hole

This paper describes the pressure distribution in the bearing clearance of circular aerostatic thrust bearings with a single air supply hole. In case of high air supply pressure or large bearing clearance, it was reported that shock wave occurs and forms complex fluid structure in the bearing clearance. However, it is very difficult to obtain the information of flow structure in detail from flow visualization because of very narrow bearing clearance. Therefore, we calculated the flow field using computational fluid dynamics (CFD) instead of Reynolds equation and supersonic flow model. In addition, we measured pressure distributions in the bearing clearance. It was consequently found that shock wave does not occur near a feeding hole, and air flow changes from laminar to turbulent flow in some limited area in the radial direction where pressure recovery in relatively large.

721 熱硬化油膜法による静圧気体軸受すきま内流れの可視化(二酸化チタンに及ぼすオレイン酸の影響)(GS-11 軸受)

The heat curing oil film method using thermosetting property oil film is a new oil film method. The heat curing oil film method, in which not only the plane flow pattern in wall surface but also oil film thickness of the steady flow can be measured, is newly developed. The heat curing oil film method is a very useful method for visualization of an air flow in the clearance of an externally pressurized gas-lubricated circular thrust bearing with a central supply hole. The rheological characteristics and the effect of the oleic acid on the rheological characteristics of the heat curing oil without silicone oil and hardener are investigated in this paper.

Substrate distribution in fungus chambers in nests of Atta bisphaerica Forel, 1908 (Hym., Formicidae)

Abstract: Substrate distribution was studied in three adult colonies of the leaf‐cutting ant Atta bisphaerica Forel, 1908 using dye. Some supply holes were mapped using baits made from small plastic straws impregnated with citric pulp. Two holes, equidistant from one another, were then selected in each nest. The colonies were excavated completely 24 h after bait placement. During excavation, fungus chambers were checked for dye. We observed that the dyed baits were distributed in all sectors and at all depths regardless of where the baits had been placed. This supported the hypothesis that toxic baits placed in a single supply hole are uniformly distributed throughout the colony.

2610 単一給気孔をもつ円形空気静圧スラスト軸受のすきま内圧力分布の数値計算

2610 単一給気孔をもつ円形空気静圧スラスト軸受のすきま内圧力分布の数値計算