Recess Pressure Research Articles

Theoretical and Experimental Comparisons for Rotordynamic Coefficients of a High-Speed, High-Pressure, Orifice-Compensated Hybrid Bearing

Comparisons are presented between measurements and predictions for a 76.2 mm diameter, high-speed (24,600 rpm), high-pressure (7.0 MPa), hybrid bearings using warm (54°C) water as a test fluid. “Hybrid” refers to combined hydrostatic and hydrodynamic action. Test results are presented for an orifice-fed, square-recess configuration with five recesses. Data are provided for rotordynamic coefficients including direct and cross-coupled stiffness, direct damping, direct added-mass coefficients, and the whirl-frequency ratio. Experimental results are compared to predictions from an analysis by San Andres (1990a), which accounts for both temporal and convective acceleration terms in the fluid film. San Andres’ development uses an orifice discharge coefficient to model the pressure drop from supply pressure to recess pressure. With experimentally determined discharge-coefficient values as input, good agreement is obtained between theory and experiment. However, predictions are sensitive to changes in the orifice discharge coefficients.

Numerical Analysis on Steady Characteristics of Hydrostatic Cryogenic Journal Bearing.

Steady characteristics of a hydrostatic cryogenic journal bearing used for the liquid hydrogen turbopump of rocket engines are numerically analyzed. The bearing has many recesses arranged in two rows in a staggered manner. The turbulent lubrication equation is solved under the assumption that the temperature change in the bearing is negligible in accordance with the experimental results. Effects of the rotational speed, the shaft eccentricity and the pressure drop at the recess edge are considered in the analysis. Their effects on the film pressure distribution, the recess pressures, the total lubricant flow rate and the load carrying capacity are clarified. Moreover, effects of the distance between two recess rows, the orifice parameter, number of recesses and the radial clearance on these characteristics are investigated.

Performance of an externally pressurized rectangular gas bearing under constant effective recess pressure

The present study predicts the performance of an externally pressurized rectangular recessed gas bearing under different operating conditions. The analysis makes use of simplifying assumptions and an empirical formula which relates the recess pressure to the bearing supply pressure. A comparison between the theoretical results obtained and available experimental data shows qualitative agreement. There are some deviations in pressure distribution and load-carrying capacity especially at greater film thickness and supply pressures. The reasons for these deviations are discussed.

TEAM WORKING AT BRITISH ALCAN

Describes major changes to working practices made at British Alean Primary & Recycling Ltd. which were part of wide‐ranging cultural changes implemented by the firm in an attempt to counteract its history of strike action and the pressures of sector recession Outlines the new process of team working in which each production area aims to have multi‐skilled, interchangeable team members able to work in all roles and on all equipment in their department, and in which ownership of output is entrusted to the team. Suggests that such innovation has greatly improved the company′s performance.

Experimental Versus Theoretical Characteristics of a High-Speed Hybrid (Combination Hydrostatic and Hydrodynamic) Bearing

The high-speed test facility designed and installed at Texas A&M to study water lubricated journal bearings has been successfully used to test statically an orifice compensated five-recess-hybrid (combination hydrostatic and hydrodynamic) bearing for two radial clearance configurations. Measurements of relative-bearing position, torque, recess pressure, flow rate, and temperature were made at speeds from 10,000 to 25,000 rpm and supply pressures of 6.89 MPa (1,000 psi), 5.52 MPa (800 psi), and 4.14 MPa (600 psi). For speeds of 10,000 and 17,500 rpm, the bearing load capacity was also investigated. A pitching instability of the bearing limited the number of test cases. A 2-dimensional, bulk-flow, Navier-Stokes numerical analysis program was used for all theoretical performance predictions. Orifice discharge coefficients used in the program were calculated from measured flow and pressure data. Reynolds numbers for flow within the bearing lands due to shaft rotation and recess pressurization ranged from 6700 to 16,500. Predictions sensitivity to ±10 percent changes in the input parameters was investigated. Results showed that performance prediction sensitivities are high for changes in discharge coefficients and negligible for changes in relative roughness. The numerical predictions of relative bearing position, recess pressure, flowrate, and torque are very accurate, provided the selected orifice discharge coefficients are correct.

How to Profit from Premium‐priced Brands or ″Pile It High, Sell It Cheap″ – and Go Bankrupt!

Too much emphasis has been given in recent years to competition on price and not enough to building customer loyalty through strong branding based on well‐promoted product quality. While this is understandable under the pressures of recession, continuous price cutting and the consequent squeeze on margins leads to the replacement of distinctive brands by undifferentiated, minimalist, low‐margin commodities which lack marketing support. A better understanding of business, retailer and consumer needs and perceptions of value for money can lead to the more profitable strategy of “charge high and give more”.

Approximate Analysis of Turbulent Hybrid Bearings. Static and Dynamic Performance for Centered Operation

An analytical study for the flow and dynamic force response in turbulent hybrid journal bearings is presented. Fluid inertia effects at the recess edges and film lands are included. For small amplitude motions about the centered position, the equations for the flow on the film lands and recesses are solved in close form by invoking the thin-land assumption. Predictions from the present simplified analytical theory agree well with full numerical predictions. The effect of recess pressure on the dynamic force response of a L02 hybrid bearing is discussed in detail.

The Declining Guestworker Population in West German Cities: the Case of Nuremberg

The foreign guestworker population of West Germany has declined considerably since 1981, as a result of economic recession and government-induced pressures. The paper assesses the significance of these national economic and demographic trends in a major city, Nuremberg. An analysis of the spatial outcomes of the main processes involved in population contraction suggests that, within the inner city in particular, these are far from simple. Moreover, the increasing numbers of ethnic German refugees from Eastern Europe in recent years, together with considerable numbers of Third World refugees, have created additional complications in the urban scene.

Hybrid Journal Bearings: Theoretical and Experimental Results

The analysis of actual lubrication problems needs to take into account particularities in the flow coming from kinematic conditions and contact geometry. For hybrid journal bearings lubricated by low dynamic viscosity fluid, turbulence and pressure drops due to inertia forces in the recess outlets are phenomena which must be taken into account to compute their working characteristics. A global method of study of lubricated contacts in isothermal laminar or not laminar flow by finite element method is presented. It can solve a great number of lubrication problems. A new type of approximation element for lubrication (Hermitian type) is used because it offers the following advantages: The nonlinearities in lubrication which come from turbulence phenomena, geometrical discontinuities (pressure drops) or boundary conditions (recess pressure) require the derivation of unknown functions. Added interpolations are not necessary to determine these values because the nodal unknowns are the values of the function and its derivatives in the two directions. As the modified Reynolds equation is in Cartesian coordinates, in the case of closed geometries such as journal bearings, joining is done just by nodal identification which guarantees continuity of the pressure and of its derivatives. The validity of this numerical model is realized with an experimental study done with a three recess hybrid journal bearing for different kinematic and geometric configurations. In a general way, experimental and theoretical results are in good agreement.

Experimental investigation of hybrid journal bearings

Experimental pressure distribution measurements in hybrid journal bearings are presented and the influence of inertia forces in the recess outlets and pressure generation in the pockets for high rotating speeds are shown. These results are in good agreement with the theoretical results given by an established model.

Characteristics of a hybrid journal bearing with one recess: Part 1: Dynamic considerations

A fluid film hybrid journal bearing with one recess, as used in tandem cold rolling mills, is studied theoretically in two ways. The dynamic response of the hybrid bearing, under isothermal conditions due to the decrease in hydrostatic pressure, is considered and presented in Part 1 of the study, while the thermal effects on the load capacity, temperature distribution, etc of the bearing will be dealt with and described in Part 2. In this paper, the dynamic behaviour of the journal due to the decrease in hydrostatic pressure is presented in the form of transient orbits and squeezed-film speeds, which are shown to be dependent on the initial equilibrium conditions. In the analysis, when the recess pressure is dropped below the hydrodynamic pressure generated by the fluid film, it is found to be difficult to obtain a convergent solution. The dynamic response of the bearing, due to the shut-off of external pressure is, therefore, simulated by the dynamic behaviour of the journal due to a series of pressure drops in arbitrary time intervals. The results show that the journal is quite stable in such conditions.

Making Ends Meet: How Families Cope with Inflation and Recession

A survey of almost 2000 families in 1976 found that 59 percent had fallen behind rising prices and almost as many, 52 percent, were hurting because of inflation. The families most affected by inflation and recession were the less privileged ones, those of low income, the retired, the semiskilled and unskilled, and members of minority groups, the Blacks and Spanish speaking. A variety of coping mechanisms were identified, ranging from income-raising strategies such as taking second jobs, having additional family members go to work, and working more overtime, to lowering consumption, greater self-reliance, bargain hunting, and sharing with others. Lowering consumption was almost the universal response to inflation as families in all walks of life reported cutting back on food, clothing, and entertainment expenditures. About one third of the respondents reported that financial pressures from inflation and recession were causing problems for their marriages, and more than one fourth said that financial pressures had damaged their mental health. The pressures of inflation and recession generated considerable hostility toward government and politicians, who were blamed for the economic ills. Confidence in government was virtually nonexistent among those hard hit by inflation and recession.

Strategy and the “business portfolio”

In this article the author goes on to develop the conclusion reached in his previous article which appeared in the December edition of Long Range Planning. These conclusions concerned the requirements for strategic success for an individual business, here they are developed into their implications for strategy development in the typical multibusiness company. It is argued that relative competitive position and growth are the two fundamental parameters which must be considered in determining the strategy that an individual business should follow when viewed within the context of the company's overall ‘business portfolio’. The likely patterns of business strategy which will lead to overall corporate success are discussed and contrasted with those which can lead to disaster. The key is that strategies should be made to differ widely from business to business, as a function of the growth and relative competitive position of each business and the company's overall resource position particularly with respect to cash. The ‘across the board’ defensive measures which many companies have adopted in recent years as their response to the pressures of inflation and recession are therefore argued to be singularly inappropriate for the long term. The ‘business portfolio’ concept provides a superior approach for developing the differentiated strategic business objectives which are necessary for any company to make the most of its opportunities.

A fundamental approach to strategy development

The problem of developing sound business strategy is probably more difficult now than it has been at any time since the war. In the midst of conflicting pressures of inflation, recession, unemployment, business failures, and social and political upheaval, today's businessman faces an environment which is both unfamiliar and uncertain. The lack of predictability concerning economic affairs can make it seem impossible to plan effectively for the future. Yet without sound strategy today, corporate survival itself may be called into question. What should be done? In this, the first of two articles, the author suggests that the key to strategy development now is to focus more than ever before on ‘fundamentals’. For the individual business, market share appears to be paramount, as is shown by the ‘experience curve effect’, a concept developed by the Boston Consulting Group in the course of its international work in advising companies on corporate strategy problems. Relative competitive position thus becomes the required simple but fundamental strategic goal. However, the quest for a superior market share must take place within the confines of an appropriately defined strategic business segment. In a further article in the February 1977 issue of LRP the author will go on to expand these conclusions concerning individual businesses, considering their implications for the sound development of strategy for the multi-business company.

The influences of the fluid capacitance in the oil feed line system on the transient response of hydrostatic guideways

A machine tool table supported by externally pressurized guideways can be frequently found to exhibit an underdamped response to squeeze loads when the supply pressure for the hydrostatic guideways is changed by means of the restrictor or the pressure regulator in the pressurized oil feed line in order to obtain suitable bearing characteristics. It is known that the resulting overshoot is largely affected by the oil feed line between the restrictor and the recess, because the oil feed line has some fluid capacitance induced by the compressibility of the pressurized oil, the elastic deformation of the pipe and the intermixing of air into the overall system. To clarify the influences of the fluid capacitance in the oil feed line on the dynamic characteristics of the hydrostatic guideway, the overshoots resulting from step loads have been investigated. Experiments were carried out with a simple model hydrostatic guideway system having a pipe line with large fluid capacitance and the changes of oil film thickness have been measured. From the experimental results, it is shown that the overshoot ratio which is defined as the ratio of the overshoot to the steady displacement of table increases with increasing fluid capacitance in the pipe line and shows a maximum value when the oil film stiffness is a maximum. In the case of constant bearing load condition, the maximum oil film stiffness can be found when the value of pressure ratio p r / p s is not equal to 2 3 but 1 3 , where p r is the recess pressure and p s is supply pressure. To confirm these experimental results, the motion of a table supported on an externally pressurized oil film has been studied theoretically. The results are in good agreement with the experimental results and show that the overshoot rate is governed by a dimensionless characteristic T c which is the ratio of static oil film stiffness K s to compressibility stiffness K c defined as K c = A 2 e / C a and dimensionless static oil film stiffness K s is defined as K s = K s/(W/h) , (where, C a is the fluid capacitance in the pipe line between the recess and the restrictor, A e is the effective area of the pad, W is the bearing load and h is the oil film thickness). The term T c determines the overshoot rate and the overshoot appears in the case when T c > 1. Furthermore, in order to indicate that the optimum pressure ratio p r / p s is equal to 1 3 in the case of constant load, the relationship between the oil film stiffness K s and the pressure ratio p r / p s considering the various bearing conditions have been calculated and it is shown that there are four optimum conditions.

Characteristics of Externally Pressurized Journal Bearings with Membrane-Type Variable-Flow Restrictors as Compensating Elements

The characteristics of externally pressurized journal bearings with four recesses and with membrane-type variable-flow restrictors as compensating elements are analytically investigated by using the bearing model of Raimondi and Boyd. The effects of the ratio of the recess pressure at zero eccentricity to the supply pressure (pressure ratio), the eccentricity ratio, the compliance of the membrane and the shaft rotation on the lubricant flow rate, the load capacity and the stiffness of these bearings are presented for a given aspect ratio and inter-recess*** land width-to-diameter ratio. For a non-rotating shaft, it is shown that when the bearing operates at zero eccentricity there is a pressure ratio that gives an optimum bearing stiffness. This pressure ratio is a function of the aspect ratio of the bearing only. Using this pressure ratio, data for the load capacity and stiffness of the bearing are presented for an eccentricity ratio that varies from 0 to 0·1. For these data, the membrane compliances used are those that would give an infinite bearing stiffness if the bearing were operating at zero eccentricity.

A General Analysis of Multi-Recess Hydrostatic Journal Bearings

A number of assumptions enable the effects of both pressure and velocity induced flow between adjacent recesses to be included in an analysis of multi-recess hydrostatic journal bearings. Consideration of the rate of energy dissipation within a bearing enables an optimum speed variable to be defined which relates the speed of shaft rotation to the other describing parameters involved. The behaviour of a particular orifice compensated bearing of high aspect ratio was investigated at large values of eccentricity ratio and it was revealed that considerable interaction occurred between the recesses. The performance of the bearing was found to be determined jointly by its pressure ratio, speed variable and, significantly, the direction of loading. Considerable variations inload capacity occurred with changes in these parameters and it is shown that the range of operation of multi-recess bearings may be limited as some recess pressures may drop to the ambient pressure. The application of these results to practical designs is suggested.

Research on Controlled Hydrostatic Bearing

For controlled hydrostatic bearings having variable restrictions, it is possible to make their static stiffness increase greatly by means of the automatic regulation of recess pressure; namely the recess pressure controlled by a spool valve rises rapidly according to the displacement of journal or shaft, thus the bearings possess very high load capacity at steady state. However, it may be considered that the dynamic behavior of these controlled bearings is inferior to an ordinary bearing employed conventional fixed restriction of flow. For practical use of these therefore, the investigations of the static and dynamic characteristics are riquired. This paper bearings, presents experimental results obtained by a testing device, which is made to examine the procedure of practical design and refers to theoretical research on a controlled hydrostatic journal bearing having a variable restriction by means of the spool valve and four rectangular recess around the shaft. The static and dynamic characteristics of the controlled hydrostatic bearing are discussed.

The effect of lubricant inertia in hydrostatic thrust-bearing lubrication

The customarily neglected effect on the load capacity of hydrostatic thrust-bearings of the lubricant inertia is examined here for both liquid and gaseous lubricants. It is found that for liquid lubricants load capacities calculated by neglecting inertia can be significantly in error even at normal operating speeds. For gaseous lubricants the effect is the same for low recess pressures but tends to lessen at higher recess pressures.