Pocket Pressure Research Articles

Analytical Research on Characteristics of Deep-shallow Journal Bearings with Orifice Restrictors

Hydrodynamic-static hybrid journal bearing with orifice restrictor is a kind of bearing that the throttling effect is realized by orifice restrictor and the second throttling effect is realized by shallow recess. There is a shortage of the existing theory that can not study the load characteristics which are affected by the recess structure parameters and operation parameters in analytical method. It is inconvenient for engineers to use the computational fluid dynamics software, due to the disadvantage of long period of calculation. On the assumption of subsection linearization of pocket pressure, a method is proposed to analyze the deep-shallow bearing characteristics, such as load capacity, bearing stiffness, flow rate and temperature ascending relationship. The analytical method is used to study bearing characteristics with the different structure parameters and working parameters, such as supply pressure, spindle speed, oil inlet aperture, shallow depth and initial oil film thickness. It is demonstrated that stiffness is close to the biggest value and temperature rising is close to the lowest one, when the shallow depth is thicker than the initial oil film by twice or three times, in the conditions that all other structural parameters and operating parameters are unchanged. The reliability of the analytical method has been verified by comparing experimental results with the analytical values.

Experimental Research Regarding the Influence of Pocket Pressure Values on the Stiffness of Hydrostatic Guideways

A very important parameter which must be considered when designing a hydrostatic guideway of high stiffness is the pressure from the hydrostatic pockets. Modifications of this parameter during functioning are caused by variations of flow and supply pressure and also by the defective geometry of the hydrostatic pockets. The pocket pressure has a major importance for achieving the hydraulic sustentation, because it determines the load capacity, which thenceforth determines the film thickness and the flow. The latter is used for determining the hydraulic resistance of lands and also for deciding the geometry of the hydrostatic guideway as a whole. Based on these considerations, the analysis of the pocket pressure variations represents an important criterion which should be taken into account when designing a hydrostatic guideway with a very high stiffness. The present paper contains a new method for analysing the hydrostatic guideway behaviour with regard to its stiffness, for different pocket pressure values. The experimental research was carried out on a closed hydrostatic guideway, with the moving element having the dimensions of 500x260 [m and the pocket dimensions of 150x88 [m.

Oil pocket’s bearing capacity analysis of liquid hydrostatic worktable in Gantry Moving Milling Center

Durning the design process of hydrostatic rotary worktable, the processing and assembly tolerance, (the offset of worktable and the gap of the oil film’s thickness) is ignored. But it will cause that the real bearing of oil pocket deviates from the initial design value, and then the performance of rotary worktable will be reduced significantly. Up to now, no effort is found toward the research of influence of the processing and assembly tolerance on the performance of the rotary worktable. So the hydrostatic oil film is assumed as the elastomer in this paper, and then the bearing capacity of the oil pocket is studied with and without the mass offset of the worktable by taking an expression between the bearing capacity and the oil film’s thickness of the oil pocket as the deform compatibility equation. The influence of the processing tolerance of the oil sealing belt’s gap on the bearing capacity of the oil pocket is analyzed. In the light of the liquid hydrostatic worktable of Gantry Moving Milling Center using on the scene, the oil pocket’s pressure of the worktable is tested using Rotary Worktable Test System under the circumstance of the mass offset of the worktable and the gap tolerance of the oil sealing belt, and then the equivalent offset of worktable, the average pressure of the oil pocket and the actual thickness of the oil film are analyzed respectively. The test results show that the bearing capacity component of the oil pocket caused by G is consistent, and the component caused by M is relative to the position of the oil pocket. When the oil sealing belt’s gap is larger than the theoretical value, the bearing capacity of the oil pocket is smaller than the others; whereas the bearing capacity of the oil pocket is larger than the others. The maximum and minimum equivalent offsets are 0.256 4 mm and 0.047 5 mm, respectively, and the average oil pocket pressure varies from 0.345 MPa to 0.460 MPa, the maximum and minimum value of the actual oil film thickness are 109.976 μm (No. 7 oil pocket) and 93.467 μm (No. 10 oil pocket), respectively. The research results can be used to detect the offset of the worktable and the actual thickness of the oil film under processing and assembly tolerance, and provides a basis way for detecting the processing and assembly tolerance of rotary worktable signing reasonably of Gantry Moving Milling Center.

Performance of hydrostatic tilted thrust pad bearings of various recess shapes operating with non-Newtonian lubricant

Hydrostatic thrust bearings are an integral part of hydroelectric power stations. These bearings are usually designed to work under parallel operation, but tilt is inevitable due to manufacturing errors, assembly errors, structural vibrations and structural deformations. Owing to the advent of latest advancements in manufacturing techniques, any geometric shape of recess can be easily manufactured and the designer has a greater flexibility. The geometric shape of recess significantly affects the performance of a bearing. Therefore, the present study is aimed to numerically analyze the influence of the tilt and recess shape on the static and dynamic performance characteristics of the hydrostatic thrust pad bearing system having Rabinowitsch fluid model lubricant. The lubricant obeying Rabinowitsch fluid model with tilt makes the Reynolds equation highly non-linear therefore, finite element method is used to analyze. Three different types of recess shapes of equal area A¯b/A¯oc=4 have been analyzed to model hydrostatic thrust pad compensated by orifice compensator. The numerically simulated results indicate that the tilt angle significantly affects the dynamic and static characteristic parameters. The value of pocket pressure and fluid film reaction of a hydrostatic thrust pad bearing has been found to significantly decrease with tilt whereas the value of lubricant flow, fluid film stiffness coefficient and fluid damping coefficient increase with tilt.

Closure to “Pressure Surges Following Sudden Air Pocket Entrapment in Storm-Water Tunnels” by Jose G. Vasconcelos and Gabriel M. Leite

Closure to “Pressure Surges Following Sudden Air Pocket Entrapment in Storm-Water Tunnels” by Jose G. Vasconcelos and Gabriel M. Leite

Influence Factor Analysis for Gas Fluctuation of Aerostatic Guideway

For the problem of the gas fluctuation of the aerostation, the structure of gas pocket, the diameter parameters of the orifice, and the supply pressure of the guideway impact on the gas film cyclone and fluctuation is researched, The cyclone phenomenon is close relationship with the gas fluctuation by comparing the simulation data. From the simulation results we obtained the factors affecting the gas fluctuation are: The orifice diameter, the structure shape of the gas pocket and gas pressure size. The pressure size in the above factors affects the gas fluctuation greatly, this was verified by experiment, and the law of the vibration is good agreement with the simulation results. This provides a theoretical basis to inhibit the gas film fluctuation of the aerostatic guideway from the structure and process parameters, and to improve the stability and machining accuracy.

Performance of hydrostatic circular thrust pad bearing operating with Rabinowitsch fluid model

Polymer-based additives such as poly isobutylene are blended with lubricating oil to enhance the lubricating performance of the base oil. The Rabinowitsch fluid model effectively describes the influence of polymer additives on the lubricating performance of a non-Newtonian (pseudoplastic) lubricant. This article deals with the analysis of a capillary compensated hydrostatic circular thrust pad bearing using Rabinowitsch fluid model. For a circular recess hydrostatic thrust bearing operating with pseudoplastic lubricant, the closed form expressions for load-carrying capacity, lubricant flow rate, fluid film stiffness coefficient and damping coefficient have been obtained using a small perturbation method. The close form solutions for different performance characteristic parameters have been compared with the results obtained from finite element method formulation. The numerically simulated results indicate that pseudoplastic parameter significantly affects the parameters of the bearing performance characteristics such as pocket pressure, lubricant flow rate, fluid film stiffness coefficient and damping coefficient. The value of the fluid film stiffness coefficient gets substantially increased with the pseudoplastic parameter whereas the value of damping coefficient gets reduced. The analytical results presented in this study can be used to obtain an optimum performance of a hydrostatic circular thrust pad bearing.

Multidisciplinary design optimization of tool head for heavy duty CNC vertical turning mill

Purpose – The purpose of this paper is to introduce a new method to carry out the design optimization of the tool head system in the heavy‐duty machine tool where closed hydrostatic guideways with multiple pockets are employed.Design/methodology/approach – A more accurate method of pressure calculation for closed hydrostatic guideways is introduced. Then, a multidisciplinary design optimization (MDO) model is formulated for design of a tool head system, which minimizes the highest pocket pressure under some constraints from machining accuracy and vibration resistance requirements as well as constraints from ballscrew design specifications. Finally, a metamodel‐based design space alternation (DSA) strategy is proposed to solve the optimization problem.Findings – The results show that the maximum pocket pressure in a tool head system can be reduced over 47 percent with a proper design while all the constraints are satisfied. As a consequence, the tool head system can safely work under the maximum output pre...

A Dynamic Analysis of Hydrodynamic Wave Journal Bearings

The purpose of this paper is to study the dynamic behavior of a three-wave journal bearing using a transient approach. The transient analysis permits the determination of the rotor behavior after the fractional frequency whirl appears. The journal trajectory is determined by solving a set of nonlinear equations of motion using the Runge-Katta method. The fluid film forces are computed by integrating the transient Reynolds equation at each time step location of the shaft with respect to the bearing. Because of the large values of the rotational speeds, turbulent effects were included in the computations. The influence of the temperature on the viscosity was also considered. Numerical results were compared to experimental results obtained at the NASA Glenn Research Center. Comparisons of the theoretical results with experimental data were found to be in good agreement. The numerical and experimental results showed that the fluid film of a three-wave journal bearing having a diameter of 30 mm, a length of 27 mm, and a wave amplitude ratio greater than 0.15 is stable even at rotational speeds of 60,000 RPM. For lower wave amplitude ratios, the threshold speed at which the fluid film becomes unstable depends on the wave amplitude and on the supply pocket pressure. Even if the fluid film is unstable, the wave bearing maintains the whirl orbit inside the bearing clearance.

Transient Flow in a Rapidly Filling Horizontal Pipe Containing Trapped Air

The pressure within a trapped air pocket in a rapidly filling horizontal pipe is investigated both experimentally and analytically. The downstream end of the pipe is either sealed to form a dead end or outfitted with an orifice to study the effects of air leakage on the pressure. Three types of pressure oscillation patterns are observed, depending on the size of the orifice. When no air is released or orifice sizes are small, the cushioning effects of the air pocket prevents the water column from impacting on the pipe end and from generating high water hammer pressures. However, the maximum pressure experienced may still be several times the upstream driving pressure. When the orifice size is very large, the air cushioning effect vanishes and the water hammer pressure is dominant. For intermediate orifice sizes, the pressure oscillation pattern consists of both long-period oscillations (while the air pocket persists) followed by short-period pressure oscillations (once water hammer pressures dominate). Air leakage is observed to play a significant role in increasing the magnitude of the observed pressures during rapid filling, resulting in peak pressures up to 15 times the upstream head. An analytical model, capable of calculating the air pocket pressure and the peak pressure when the water column slams into the end of the pipe, is developed and results are compared with those of experiments. The model was successful in determining the amplitude of the peak pressure for the entire orifice range and was able to simulate the pressure oscillation pattern for the case of a negligible water hammer impact effect. Although the model was unable to simulate the pressure oscillation pattern for substantial air release, it was able to predict the type of pressure oscillation behavior and the peak pressure.

Characteristics of hydrostatic bearing/seal parts for water hydraulic pumps and motors. Part 2: On eccentric loading and power losses

In this paper, the load-carrying capacity, power losses and stiffness of disk-type hydrostatic thrust bearings including the case of eccentric loading are discussed theoretically. The numerical analysis method is established based on a two-dimensional elastohydrostatic problem with an elastic deformation model, which is extended to adapt it for a non-axisymmetric load acting on the thrust bearing. The bearing is made of a combination of stainless steel/stainless steel and stainless steel/plastics. For the elastic materials, the maximum stiffness derived from, i.e., minimum film thickness is, larger than that of the rigid material in the range of a large ratio of pocket pressure and a hydrostatic balance ratio of over unity, which is defined as the ratio of the load to the maximum hydrostatic load-carrying capacity. The maximum load-carrying capacity and minimum power loss can exist in the domain of the hydrostatic balance ratio over unity for the case of the bearing consisting of elastic/rigid materials, in comparison with that composed of the same rigid materials. For the case of water, the power loss due to leakage flow is slightly larger but that due to frictional torque is much smaller than that in the case of hydraulic oil. Then, the total power loss is much smaller than that of hydraulic oil.

Characteristics of hydrostatic bearing/seal parts for water hydraulic pumps and motors. Part 1: Experiment and theory

In this study, the characteristics of disk-type hydrostatic thrust bearings supporting concentric loads, simulating the major bearing/seal parts of water hydraulic pumps and motors, are presented. The bearing is made up of a combination of stainless steel/stainless steel and stainless steel/plastics. The characteristics are evaluated by studying the relationships among the load-carrying capacity, pocket pressure, film thickness, and leakage flow rate. For the elastic material, Young’s modulus is a nonlinear relationship between stress acting on the seal surface and compressive strain. The load-carrying capacity expressed by the ratio of hydrostatic balance is not only dependent on the supply pressure (with the same restrictor) but also on the elastic modulus of materials. The calculated results coincide well with the experimental results.

Paradoxical hypotony after laser in situ keratomileusis

We present a case of paradoxically low (0 to 2 mm Hg) intraocular pressure (IOP) measured by Goldmann applanation and Tono-Pen tonometry in an eye with corticosteroid-induced high IOP after laser in situ keratomileusis. The patient complained of blurred vision and ocular pain in both eyes. The eyes were firm by palpation, and the IOP measured by Schiotz indentation tonometry was 38 mm Hg. An interface fluid pocket was identified by slitlamp examination, and the corneal surface became steeper. These findings resolved after flap relifting, interface irrigation, and addition of antiglaucoma medications. We postulate that the paradoxically low reading by applanation tonometry was due to fluid accumulation within the flap–bed interface. The applanation tonometry reflected the interface fluid pocket pressure rather than the real high IOP. An exceedingly low IOP should be verified by palpation or by Shiotz indentation tonometry, and interface fluid should be identified.

CHARACTERISTICS OF THE BEARING/SEAL PARTS OF PISTON PUMPS AND MOTOR FOR WATER HYDRAULIC SYSTEMS

In this paper the characteristics of disk type hydrostatic thrust bearings supporting concentric loads, simulating the major bearing/seal parts of water hydraulic pumps and motors, are presented. The bearing is made up by combination of stainless steel/stainless steel and stainless steel/plastics. The characteristics are evaluated by the relationship among the load capacity, pocket pressure, film thickness, and leakage flow rate. The main results are as follows: 1) the load capacity expressed by the ratio of hydrostatic balance is not only dependent of the supply pressure (with the same restrictor) but also of the elastic modulus of materials, 2) effects of inlet pressure drop into the bearing land are much smaller than those of elastic deformation, especially in plastics, 3) the calculated results coincide well with the experimental results.

Geometry and Pressure in a Trochoidal-Type Machine Without Apex Seal

In a trochoidal-type machine, the friction and wear due to the apex seal is a major problem. In order to increase the efficiency and reliability of this type of machine, we propose to replace the apex seals by tight running clearances. A peritrochoid with its special conjugate envelope is a good candidate for a trochoidal-type machine without apex seal. This paper presents its geometry attributes and pressure processes inside the pockets. First, the coordinates of contact point and pocket volumes at any shaft angle are derived. Then, the pressure processes inside the pockets are simulated with simplified valves. Finally, the effect of clearance on pocket pressure at different speeds is studied. The results indicate that a trochoidal-type machine without apex seal is worthy of further research and development.

Uncertainty and Sensitivity Analysis Results Obtained in a Preliminary Performance Assessment for the Waste Isolation Pilot Plant

Uncertainty and sensitivity analysis results obtained in a preliminary performance assessment for the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico are presented. The most appropriate conceptual model for performance assessment at the WIPP is believed to include gas generation due to corrosion and microbial action in the repository and a dual-porosity (matrix and fracture porosity) representation for solute transport in the Culebra Dolomite Member of the Rustler Formation. Under these assumptions, complementary cumulative distribution functions (CCDFs) summarizing radionuclide releases to the accessible environment due to both cuttings removal and groundwater transport fall substantially below the release limits promulgated by the U.S. Environmental Protection Agency (EPA). This is the case even when the current estimates of the uncertainty in analysis inputs are included. Performance assessment results are dominated by cuttings removal. The releases to the accessible environment due to groundwater transport make very small contributions to the total release. The variability in the distribution of CCDFs that must be considered in comparisons with the EPA release limits is dominated by the rate constant in the Poisson model for drilling intrusions. The variability in releases to the accessible environment due to cuttings removal is dominated by drill bit diameter. For a single borehole, whether or not a release due to groundwater transport from the repository to the Culebra occurs is controlled by Salado halite permeability, with no releases for small values (i.e., <5 × 10−21 m2). Further, releases that do reach the Culebra for larger values of halite permeability are small and usually do not reach the accessible environment. A potentially important scenario for the WIPP involves two or more boreholes through the same waste panel, of which at least one penetrates a pressurized brine pocket and at least one does not. For these scenarios, the uncertainty in release to the Culebra due to groundwater transport is dominated by borehole permeability, brine pocket pressure, and the solubilities for individual elements (i.e., americium, neptunium, plutonium, thorium, uranium). Once a release reaches the Culebra, matrix distribution coefficients for the individual elements are important, with releases to the Culebra often failing to reach the accessible environment over the 10 000-yr period specified in the EPA regulations.

油圧機器しゅう動部の最適設計に関する研究 第１報 基礎方程式および最適条件

Reasonable design methods of the optimum dimensions of the bearing/seal parts of hydraulic equipment are presented. The minimum power loss, minimum dimensions (maximum load carrying capacity), and maximum moment-stiffness, as well as the maximum stiffness, are established as the optimum conditions. In this study, we have used circular hydrostatic bearings as the bearing/seal parts. The basic equations considering the effects of the dynamic supply pressure, eccentric dynamic load, and elastic deformation are derived. The representative design parameters are the radius of the bearing/seal parts, pocket radius ratio, and aspect ratio of the restrictor. In this report, we discuss the optimum analytical solutions for the hydrostatic thrust bearings with the capillary restrictor under steady concentric loads. The conditions of the minimum power loss, maximum load carrying capacity, and maximum stiffness correspond to that the ratio of power losses of leakage to friction is 1/3, the pocket radius is equal to the equivalent radius of load-area, and the pocket pressure ratio is 2/3, respectively. The optimum design methods based on the minimum power loss and minimum dimensions considering the degree of freedom of design are presented. From the maximum moment-stiffness, it shows that the optimum pocket pressure ratio is given by 5/6, and this is a favorable design method for a miniaturization of the bearing/seal parts.

Load capacity of multi-recess hydrostatic journal bearings at high eccentricities

A finite element program has been set up to evaluate the pocket pressure, load capacity and the rate of flow of the lubricant in a four pocket hydrostatic journal bearing under stationary as well as steady speed conditions. Numerical calculations have been extended to the extreme journal position which represents the eccentricity ratio close to unity. Also experimental measurements have been carried out for the particular case of a stationary journal and the results thus obtained have been compared with those numerically obtained. While confirming the previously predicted load capacity at low eccentricity ratios, the present numerical and experimental results show a higher load capacity at high eccentricity ratios close to unity.

Elastohydrostatic lubrication of capillary compensated circular pad thrust bearings

The effect of elastic deformation of the circular thrust pad was considered in determining the performance characteristics of a capillary compensated hydrostatic circular thrust bearing. The matched solution of the elastohydrostatic problem was obtained by using the finite element method and an iterative procedure. For the convenience of bearing designers a nondimensional deformation coefficient C ̄ d is defined in terms of p s , E, t h and h f . The performance characteristics of circular pocket thrust bearings are presented in terms of pocket pressure, load capacity, bearing flow, fluid film stiffness and damping coefficients for various values of the restrictor design parameter C ̄ s2 and the deformation coefficient C ̄ d . The values of the damping coefficients C ̄ are compared for circular and annular pocket bearings.

DETERMINATION OF OPTIMUM CONDITIONS OF CAPILLARY COMPENSATED HYDROSTATIC SLIDEWAYS*

Abstract This paper presents the determination of the greatest stiffness and least power consumption of capillary compensated hydrostatic slideways, prestressed and non-prestressed, respectively. Design equations for determining the optimum values of supply pressure, pocket pressure, length of free-periphery of slideways rim, thickness of land of slideways rim, viscosity, capillary-discharge coefficient and power consumption are determined, other variables held constant. The paper determines the operative conditions which correspond strictly or approximately to the conditions assumed in the equations. Diagrams show the effect of discrepancy between optimum and actual conditions on the stiffness of slideways.