scholarly journals Foil Bearing Design Guidelines for Improved Stability

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
J. Schiffmann ◽  
Z. S. Spakovszky
Keyword(s):  
Pressure Distribution ◽  
Mass Parameter ◽  
Critical Mass ◽  
Design Guidelines ◽  
Fluid Film ◽  
Structural Damping ◽  
Foil Bearing ◽  
Improved Stability ◽  
Bearing Design ◽  
The Impact

Experimental evidence in the literature suggests that foil bearing-supported rotors can suffer from subsynchronous vibration. While dry friction between top foil and bump foil is thought to provide structural damping, subsynchronous vibration is still an unresolved issue. The current paper aims to shed new light onto this matter and discusses the impact of various design variables on stable foil bearing-supported rotor operation. It is shown that, while a time domain integration of the equations of motion of the rotor coupled with the Reynolds equation for the fluid film is necessary to quantify the evolution of the rotor orbit, the underlying mechanism and the onset speed of instability can be predicted by coupling a reduced order foil bearing model with a rigid-body, linear, rotordynamic model. A sensitivity analysis suggests that structural damping has limited effect on stability. Further, it is shown that the location of the axial feed line of the top foil significantly influences the bearing load capacity and stability. The analysis indicates that the static fluid film pressure distribution governs rotordynamic stability. Therefore, selective shimming is introduced to tailor the unperturbed pressure distribution for improved stability. The required pattern is found via multiobjective optimization using the foil bearing-supported rotor model. A critical mass parameter is introduced as a measure for stability, and a criterion for whirl instability onset is proposed. It is shown that, with an optimally shimmed foil bearing, the critical mass parameter can be improved by more than two orders of magnitude. The optimum shim patterns are summarized for a variety of foil bearing geometries with different L/D ratios and different degrees of foil compliance in a first attempt to establish more general guidelines for stable foil bearing design. At low compressibility (Λ < 2), the optimum shim patterns vary little with bearing geometry; thus, a generalized shim pattern is proposed for low compressibility numbers.

scholarly journals Foil Bearing Design Guidelines for Improved Stability

2012 ◽  
Author(s):  
J. Schiffmann ◽  
Z. S. Spakovszky
Keyword(s):  
Pressure Distribution ◽  
Mass Parameter ◽  
Critical Mass ◽  
Design Guidelines ◽  
Fluid Film ◽  
Structural Damping ◽  
Foil Bearing ◽  
Improved Stability ◽  
Bearing Design ◽  
The Impact

Experimental evidence in the literature suggests that foil bearing supported rotors can suffer from sub-synchronous vibration. While dry-friction between top foil and bump foil is thought to provide structural damping, sub-synchronous vibration is still an unresolved issue and has been recently attributed to the non-linearity of the bump-foil support stiffness. A non-linear rotordynamic model corroborates this hypothesis, however a forcing is required to excite the system. The current paper aims to shed new light onto this matter and discusses the impact of various design variables on stable foil bearing supported rotor operation. It is shown that, while a time domain integration of the equations of motion of the rotor coupled with the Reynolds equation for the fluid film is necessary to quantify the evolution of the rotor orbit, the underlying mechanism and the onset speed of instability can be predicted by coupling a reduced order foil bearing model with a rigid-body, linear rotordynamic model. Using this model it is shown that the excitation source inducing sub-synchronous vibration is a classical aerodynamic instability resulting from bearing fluid film forces. A sensitivity analysis suggests that structural damping has limited effect on stability. It is shown that the location of the axial feed line of the top foil significantly influences the bearing load capacity and stability. The analysis further indicates that the static fluid film pressure distribution governs rotordynamic stability. Therefore selective shimming is introduced to tailor the unperturbed pressure distribution for improved stability. The required pattern is found via multi-objective optimization using the foil bearing supported rotor model. A critical mass parameter is introduced as a measure for stability, and a criterion for whirl instability onset is proposed. It is shown that with an optimally shimmed foil bearing, the critical mass parameter can be improved by more than two orders of magnitude. The optimum shim patterns are summarized for a variety of foil bearing geometries with different L/D ratios and different degrees of foil compliance in a first attempt to establish more general guidelines for stable foil bearing design. At low compressibility (Λ < 2) the optimum shim patterns vary little with bearing geometry, thus a generalized shim pattern is proposed for low compressibility numbers.

Enhanced Groove Geometry for Herringbone Grooved Journal Bearings

2013 ◽  
Author(s):  
J. Schiffmann
Keyword(s):  
Cross Section ◽  
Mass Parameter ◽  
Critical Mass ◽  
Stability Margin ◽  
Design Guidelines ◽  
Journal Bearings ◽  
Diameter Ratio ◽  
Width Ratio ◽  
Constant Pitch ◽  
Order Of Magnitude

Although gas lubricated Herringbone Grooved Journal Bearings (HGJB) are known for high rotordynamic stability thresholds, small clearance to diameter ratios are required for stable rotor operation. Tight clearances not only increase bearing losses but also yield challenging manufacturing and assembly tolerances, which ultimately translate into cost. Traditionally, the grooves of HGJB are of helical nature with constant cross-section and pitch. The current paper aims at increasing the clearance to diameter ratio and the stability threshold of grooved bearings by introducing enhanced groove geometries. The axial evolution of groove width, depth and local pitch are described by individual 3rd order polynomials with four interpolation points. The expression for the smooth pressure distribution resulting from the narrow groove theory is modified to enable the calculation of bearing properties with modified groove patterns. The reduced order bearing model is coupled to a linear rigid body rotordynamic model for predicting the whirl speed map and the corresponding stability. By introducing a critical mass parameter as a measure for stability, a criterion for the instability onset is proposed. The optimum groove geometry is found by coupling the gas bearing supported rotor model with a multi-objective optimizer. By maximizing both the clearance to diameter ratio and the rotordynamic stability it is shown that with optimal groove geometry, which deviates from helicoids with constant pitch and cross-section, the critical mass parameter can be improved by more than one order of magnitude compared to traditional HGJB geometries. The clearance to diameter ratio can be increased by up to 80% while keeping the same stability margin, thus reducing both losses and manufacturing constraints. The optimum groove pattern distributions (width ratio, angle and depth) are summarized for a variety of L/D ratios and for different compressibility numbers in a first attempt to set up general design guidelines for enhanced gas lubricated HGJB.

Enhanced Groove Geometry for Herringbone Grooved Journal Bearings

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
J. Schiffmann
Keyword(s):  
Cross Section ◽  
Mass Parameter ◽  
Critical Mass ◽  
Stability Margin ◽  
Design Guidelines ◽  
Journal Bearings ◽  
Diameter Ratio ◽  
Width Ratio ◽  
Constant Pitch ◽  
Order Of Magnitude

Although gas-lubricated herringbone grooved journal bearings (HGJB) are known for high rotordynamic stability thresholds, small clearance to diameter ratios are required for stable rotor operation. Tight clearances not only increase bearing losses but also yield challenging manufacturing and assembly tolerances, which ultimately translate into cost. Traditionally, the grooves of HGJB are of helical nature with constant cross section and pitch. The current paper aims at increasing the clearance to diameter ratio and the stability threshold of grooved bearings by introducing enhanced groove geometries. The axial evolution of groove width, depth, and local pitch are described by individual third order polynomials with four interpolation points. The expression for the smooth pressure distribution resulting from the narrow groove theory is modified to enable the calculation of bearing properties with modified groove patterns. The reduced order bearing model is coupled to a linear rigid body rotordynamic model for predicting the whirl speed map and the corresponding stability. By introducing a critical mass parameter as a measure for stability, a criterion for the instability onset is proposed. The optimum groove geometry is found by coupling the gas bearing supported rotor model with a multiobjective optimizer. By maximizing both the clearance to diameter ratio and the rotordynamic stability it is shown that with optimal groove geometry, which deviates from helicoids with constant pitch and cross section, the critical mass parameter can be improved by more than one order of magnitude compared to traditional HGJB geometries. The clearance to diameter ratio can be increased by up to 80% while keeping the same stability margin, thus reducing both losses and manufacturing constraints. The optimum groove pattern distributions (width ratio, angle, and depth) are summarized for a variety of L/D ratios and for different compressibility numbers in a first attempt to set up general design guidelines for enhanced gas-lubricated HGJB.

scholarly journals Improving the usability of climate indicator visualizations through diagnostic design principles

2021 ◽  
Vol 166 (3-4) ◽  
Author(s):  
Michael D. Gerst ◽  
Melissa A. Kenney ◽  
Irina Feygina
Keyword(s):  
Design Guidelines ◽  
Party Affiliation ◽  
Abstract Concepts ◽  
Design Modification ◽  
Climate Indicators ◽  
Present Complex ◽  
Control Versus ◽  
Climate Indicator ◽  
Political Party Affiliation ◽  
The Impact

AbstractVisual climate indicators have become a popular way to communicate trends in important climate phenomena. Producing accessible visualizations for a general audience is challenging, especially when many are based on graphics designed for scientists, present complex and abstract concepts, and utilize suboptimal design choices. This study tests whether diagnostic visualization guidelines can be used to identify communication shortcomings for climate indicators and to specify effective design modifications. Design guidelines were used to diagnose problems in three hard-to-understand indicators, and to create three improved modifications per indicator. Using online surveys, the efficacy of the modifications was tested in a control versus treatment setup that measured the degree to which respondents understood, found accessible, liked, and trusted the graphics. Furthermore, we assessed whether respondents’ numeracy, climate attitudes, and political party affiliation affected the impact of design improvements. Results showed that simplifying modifications had a large positive effect on understanding, ease of understanding, and liking, but not trust. Better designs improved understanding similarly for people with different degrees of numerical capacity. Moreover, while climate skepticism was associated with less positive subjective responses and greater mistrust toward climate communication, design modification improved understanding equally for people across the climate attitude and ideological spectrum. These findings point to diagnostic design guidelines as a useful tool for creating more accessible, engaging climate graphics for the public.

scholarly journals Influence of the Spatial Pressure Distribution of Breaking Wave Loading on the Dynamic Response of Wolf Rock Lighthouse

2021 ◽  
Vol 9 (1) ◽  
pp. 55
Author(s):  
Darshana T. Dassanayake ◽  
Alessandro Antonini ◽  
Athanasios Pappas ◽  
Alison Raby ◽  
James Mark William Brownjohn ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Pressure Distribution ◽  
Distinct Element ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Wave Loading ◽  
Wave Impact ◽  
Pressure Distributions ◽  
Impact Area ◽  
The Impact

The survivability analysis of offshore rock lighthouses requires several assumptions of the pressure distribution due to the breaking wave loading (Raby et al. (2019), Antonini et al. (2019). Due to the peculiar bathymetries and topographies of rock pinnacles, there is no dedicated formula to properly quantify the loads induced by the breaking waves on offshore rock lighthouses. Wienke’s formula (Wienke and Oumeraci (2005) was used in this study to estimate the loads, even though it was not derived for breaking waves on offshore rock lighthouses, but rather for the breaking wave loading on offshore monopiles. However, a thorough sensitivity analysis of the effects of the assumed pressure distribution has never been performed. In this paper, by means of the Wolf Rock lighthouse distinct element model, we quantified the influence of the pressure distributions on the dynamic response of the lighthouse structure. Different pressure distributions were tested, while keeping the initial wave impact area and pressure integrated force unchanged, in order to quantify the effect of different pressure distribution patterns. The pressure distributions considered in this paper showed subtle differences in the overall dynamic structure responses; however, pressure distribution #3, based on published experimental data such as Tanimoto et al. (1986) and Zhou et al. (1991) gave the largest displacements. This scenario has a triangular pressure distribution with a peak at the centroid of the impact area, which then linearly decreases to zero at the top and bottom boundaries of the impact area. The azimuthal horizontal distribution was adopted from Wienke and Oumeraci’s work (2005). The main findings of this study will be of interest not only for the assessment of rock lighthouses but also for all the cylindrical structures built on rock pinnacles or rocky coastlines (with steep foreshore slopes) and exposed to harsh breaking wave loading.

Thermohydrodynamic Behavior of a Slider Pocket Bearing

2005 ◽  
Vol 128 (2) ◽  
pp. 312-318 ◽  
Author(s):  
Mihai B. Dobrica ◽  
Michel Fillon
Keyword(s):  
Pressure Distribution ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Convective Boundary ◽  
Inertia Effects ◽  
Good Convergence ◽  
Bearing Design ◽  
The One ◽  
Volume Method ◽  
Generalized Reynolds Equation

Pocket-pads or steps are often used in journal bearing design, allowing improvement of the latter’s dynamic behavior. Similar “discontinuous” geometries are used in designing thrust bearing pads. A literature review shows that, to date, only isoviscous and adiabatic studies of such geometries have been performed. The present paper addresses this gap, proposing a complete thermohydrodynamic (THD) steady model, adapted to three-dimensional (3D) discontinuous geometries. The model is applied to the well-known geometry of a slider pocket bearing, operating with an incompressible viscous lubricant. A model based on the generalized Reynolds equation, with concentrated inertia effects, is used to determine the 2D pressure distribution. On this basis, a 3D field of velocities is constructed which, in turn, allows the resolution of the 3D energy equation. Using a variable-size grid improves the accuracy in the discontinuity region, allowing an evaluation of the magnitude of error induced by Reynolds assumptions. The equations are solved using the finite volume method. This ensures good convergence even when a significant reverse flow is present. Heat evacuation through the pad is taken into account by solving the Laplace equation with convective boundary conditions that are realistic. The runner’s temperature, assumed constant, is determined by imposing a zero value for the global heat flux balance. The constructed model gives the pressure distribution and velocity fields in the fluid, as well as the temperature distribution across the fluid and solid pad. Results show important transversal temperature gradients in the fluid, especially in the areas of minimal film thickness. This further justifies the use of a complete THD model such as the one employed.

Australian Biotechnology: A 10-Year Study of Investor Performance

2021 ◽  
Vol 26 (4) ◽  
Author(s):  
Peter L. Molloy ◽  
Lester W. Johnson ◽  
Michael Gilding
Keyword(s):  
Drug Development ◽  
Global Financial Crisis ◽  
Critical Mass ◽  
Share Price ◽  
Annual Growth Rate ◽  
Compound Annual Growth Rate ◽  
Listed Firms ◽  
Investor Returns ◽  
The Global Financial Crisis ◽  
The Impact

A recent study assessed the investor performance of the Australian drug development biotech (DDB) sector over a 15-year period from 2003 to 2018. The current study builds on that research and extends the analysis to 2020, using a 10-year period starting 2010, to exclude the impact of the global financial crisis in 2008/09. Based on a value-weighted portfolio of all 41 DDB firms, the overall sector delivered a negative annualized return of -4.1%. Individual firm performance was also assessed using the compound annual growth rate (CAGR) in share price over the period as a measure of investor outcomes. On this basis 68% of firms produced negative CAGRs over the period, and of the 32% of firms that produced positive CAGRs, six firms produced CAGRs greater than 20% per annum and in three cases of recently-listed firms, the CAGR’s were greater than 50%. Overall however, the sector overall delivered very poor investor returns and despite a relatively large number of listed biotech firms, Australian biotechnology continues to be small and weak in terms of its contribution to global biotechnology industrialization. As such it lacks the critical mass to grow a robust bioeconomy based on drug development, which remains the standard-bearer of biotechnology industrialization.

scholarly journals The effect of national cultural differences of board members on integrated reporting

2018 ◽  
Vol 14 (1) ◽  
pp. 7-21 ◽  
Author(s):  
Simona Alfiero ◽  
Massimo Cane ◽  
Ruggiero Doronzo ◽  
Alfredo Esposito
Keyword(s):  
Cultural Differences ◽  
Critical Mass ◽  
Cultural Dimensions ◽  
Board Members ◽  
Cultural Dimension ◽  
Integrated Reporting ◽  
Independent Variables ◽  
The Impact ◽  
The Relationship ◽  
Positive Effect

This research, based on stakeholder theory and the national cultural dimensions, aims to test the influence of foreigners on board and its size on Integrated Reporting (IR) practices. The analysis is based on a sample of 1,058 European companies from 18 different countries, who adopted or not the IR for the year 2015, and it relies on a Logit. The dependent variable is a dummy (presenting or not the IR) and the independent variables are represented by the board characteristics (foreigners and size). The impact of the critical mass on the presence of foreigners and the cultural dimension on the basis of directors’ nationality was tested relying on the masculinity/femininity dimension of Hofstede. Besides, the directors’ country of origin was considered, namely if they belong to the major European countries presenting a wider IR diffusion. The relationship between foreigners on board and IR is found to be negative. This means that companies with at least one foreigner are less inclined to adopt IR. The results show that the boards with more of three foreign administrators have a major propensity to adopt the IR. The membership of the directors in countries with a feminist culture also has a positive effect.

Design guidelines for bump-type compliant conical foil bearing

2021 ◽  
pp. 095440622110127
Author(s):  
Hongyang Hu ◽  
Ming Feng
Keyword(s):  
Load Capacity ◽  
Design Guidelines ◽  
Foil Thickness ◽  
Axial Stiffness ◽  
Structural Stiffness ◽  
Foil Bearing ◽  
Stiffness Model ◽  
Opposite Position ◽  
Stiffness Distribution ◽  
Half Length

The integral bump foil strip cannot optimize the performance for the compliant conical foil bearing (CFB) as the uneven distribution of structural stiffness. To maximize the bearing characteristics, this paper proposed different bump foil schemes. Firstly, the anisotropy of CFB was studied based on the nonlinear bump stiffness model, and the circumferentially separated foil structure was proposed. Moreover, an axially separated bump foil structure with the variable bump length was introduced to make the axial stiffness distribution more compliant with the gas pressure. In addition, the effect of foil thickness was also discussed. The results show that CFB with integral bump foil exhibits obvious anisotropy, and the suggested installation angle for largest load capacity and best dynamic stability are in the opposite position. Fortunately, a circumferential separated bump foil can improve this defect. The characteristics of CFB with axial separated foil structure can be improved significantly, especially for that with more strips and the variable bump half-length design. The suitable bump and top foil thickness should be set considering the improved supporting performance and proper flexibility. The results can give some guidelines for the design of CFB.

THE IMPACT OF SELECTED PARAMETERS ON PRESSURE DISTRIBUTION IN THE FACE THROTTLE OF A CENTRIFUGAL PUMP AUTOMATIC BALANCING DEVICE

Tribologia ◽  
2021 ◽  
Vol 297 (3) ◽  
pp. 35-44
Author(s):  
Yuliia Tarasevych ◽  
Nataliia SOVENKO
Keyword(s):  
Fluid Flow ◽  
Pressure Distribution ◽  
Hydrodynamic Pressure ◽  
Centrifugal Pumps ◽  
Unsteady Fluid Flow ◽  
The Face ◽  
Unsteady Fluid ◽  
Angular Displacements ◽  
Automatic Balancing ◽  
The Impact

Face throttles are a necessary functional element of non-contact face seals and automatic balancing devices of centrifugal pumps of different constructions. To calculate the hydrodynamic forces and moments acting on the rotor and fluid flow through the automatic balancing device, it is necessary to know the pressure distribution in the cylindrical and face throttle when considering all important factors which predetermine fluid flow. The face throttle surfaces are moving, which leads to unsteady fluid flow. The movement of the walls of the face throttle causes an additional circumferential and radial flow, which subsequently leads to the additional hydrodynamic pressure components. The paper analyses viscous incompressible fluid flow in the face throttle of an automatic balancing device taking into account the axial and angular displacements of throttle’s surfaces and the inertia component of the fluid. The effect of local hydraulic losses as well as random changes in the coefficients of local hydraulic resistance at the inlet and outlet of the throttle is analysed.

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