Identification of Bearing Stiffness and Damping Coefficients Using Phase-Plane Diagrams

2012 ◽  
Author(s):  
Juan C. Jáuregui ◽  
Luis San Andrés ◽  
Oscar De Santiago
Keyword(s):  
Phase Diagram ◽  
Reference Model ◽  
Measurement Data ◽  
Point Of View ◽  
Dynamic Parameters ◽  
Force Coefficients ◽  
On Line ◽  
Bearing Stiffness ◽  
Spring System ◽  
Stiffness And Damping

The reliable identification of dynamic parameters in mechanical systems remains a big challenge, in particular for nonlinear systems. There is not a single mathematical model encompassing the universe of most systems. From a practical point of view, the identification of system parameters depends on the measurement data as well as on the reference model. This paper presents a novel method for identifying the dynamic parameters of a gas bearing, whose force coefficients are strong functions of frequency. The method is based on the analysis of the phase diagram with the model assuming a mass-damper-spring system with time-dependent force coefficients. The phase diagram could be implemented electronically for on line monitoring and ready fault detection.

Estimation of the Rotordynamic Coefficients of a Compressor Mounted on Gas Bearings Using the Phase Diagram and the Unbalance Response

2015 ◽  
Author(s):  
Claudia Aide González ◽  
Juan Carlos Jáuregui ◽  
Oscar De Santiago ◽  
Víctor Solórzano
Keyword(s):  
Phase Diagram ◽  
Three Dimensional ◽  
Dynamic Parameters ◽  
Gas Bearings ◽  
Force Coefficients ◽  
Rotordynamic Coefficients ◽  
Dynamic Coefficients ◽  
Unidentified Source ◽  
Spring System ◽  
Gas Bearing

This paper presents a novel method for identifying the dynamic parameters of a gas bearing, whose force coefficients are strong functions of frequency. The method is based on the analysis of the phase diagram with the model assuming a mass-damper-spring system with time-dependent force coefficients. Usually, it is necessary a controlled mechanism to find the transfer function, this condition limits the application of the method. On the other hand, estimation of the damping and stiffness parameters under real loading is very cumbersome and requires a special care on identifying the excitation forces. One of the main difficulties is the isolation of noise and those vibration signals with an unidentified source. In this work, the excitation force was taken from the unbalance loading of a rotor test. Therefore, there is no need for a special test rig. The dynamic parameters can be estimated analyzing data from the actual rotor mounted on the gas bearings. Identifying the parameters that cause gas bearing instabilities is a big challenge. The gas properties are very sensitive to temperature and pressure changes, and, as a consequence the bearing rotor-dynamic coefficients change drastically and the rotor behaves chaotically, which means that the dynamic parameters are nonlinear. In this research a methodology based on the phase diagram construction to identify nonlinear instabilities of gas bearings is presented. The results show the method capability to estimate the dynamic coefficients by the analysis of the energy variation. Among nonparametric methods, the phase diagram or phase space is in use to identify nonlinearities in dynamic systems. The identification is conducted through the analysis of the energy variations. The energy variations can be represented as a three dimensional function E(x,v,t). In this way the phase diagram can be related to the frequency and the dynamic parameters of the system. According to Taken’s theorem, a dynamic system can be obtained by reconstructing the phase diagram. Then, using this method, the damping and stiffness coefficients are estimated.

scholarly journals Optimal Controller Design for Ultra-Precision Fast-Actuation Cutting Systems

Micromachines ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 33
Author(s):  
Fei Ding ◽  
Xichun Luo ◽  
Duo Li ◽  
Zheng Qiao ◽  
Bo Wang
Keyword(s):  
Controller Design ◽  
Structural Parameters ◽  
Point Of View ◽  
Design Stage ◽  
Controller Tuning ◽  
Positioning Errors ◽  
Ultra Precision ◽  
Bearing Stiffness ◽  
Stiffness And Damping Coefficient ◽  
Stiffness And Damping

Fast-actuation cutting systems are in high demand for machining of freeform optical parts. Design of such motion systems requires good balance between structural hardware and controller design. However, the controller tuning process is mostly based on human experience, and it is not feasible to predict positioning performance during the design stage. In this paper, a deterministic controller design approach is adopted to preclude the uncertainty associated with controller tuning, which results in a control law minimizing positioning errors based on plant and disturbance models. Then, the influences of mechanical parameters such as mass, damping, and stiffness are revealed within the closed-loop framework. The positioning error was reduced from 1.19 nm RMS to 0.68 nm RMS with the new controller. Under the measured disturbance conditions, the optimal bearing stiffness and damping coefficient are 1.1×105 N/m and 237.7 N/(m·s−1), respectively. We also found that greater moving inertia helps to reduce all disturbances at high frequencies, in agreement with the positioning experiments. A quantitative understanding of how plant structural parameters affect positioning stability is thus shown in this paper. This is helpful for the understanding of how to reduce error sources from the design point of view.

Confidentiality of Statistical Records: A Threat-Monitoring Scheme for On Line Dialogue

1976 ◽  
Vol 15 (01) ◽  
pp. 36-42 ◽  
Author(s):  
J. Schlörer
Keyword(s):  
Statistical Data ◽  
Cost Benefit ◽  
Data Bank ◽  
High Ratio ◽  
Point Of View ◽  
Data Sets ◽  
Monitoring Scheme ◽  
Access Controls ◽  
On Line ◽  
Bona Fide

From a statistical data bank containing only anonymous records, the records sometimes may be identified and then retrieved, as personal records, by on line dialogue. The risk mainly applies to statistical data sets representing populations, or samples with a high ratio n/N. On the other hand, access controls are unsatisfactory as a general means of protection for statistical data banks, which should be open to large user communities. A threat monitoring scheme is proposed, which will largely block the techniques for retrieval of complete records. If combined with additional measures (e.g., slight modifications of output), it may be expected to render, from a cost-benefit point of view, intrusion attempts by dialogue valueless, if not absolutely impossible. The bona fide user has to pay by some loss of information, but considerable flexibility in evaluation is retained. The proposal of controlled classification included in the scheme may also be useful for off line dialogue systems.

scholarly journals New system of employment forecasting in Poland

2014 ◽  
Vol 15 (2) ◽  
pp. 75-90
Author(s):  
Łukasz Arendt
Keyword(s):  
Labour Market ◽  
Econometric Models ◽  
Point Of View ◽  
Labour Market Policy ◽  
Market Policy ◽  
On Line ◽  
New System

Abstract The goal of the paper was to describe the system of employment forecasting in Poland and to present forecasts results. The paper described the main assumptions and elements of the system of employment forecasting (the structure of econometric models and on-line forecasting tool). It also elaborated on employment forecasts at national, regional and occupational levels. The analysis of forecasts enabled drawing some conclusions, important from the point of view of the perspectives of the Polish labour market and the labour market policy.

scholarly journals Monitoring of Grid Scientific Workflows

2008 ◽  
Vol 16 (2-3) ◽  
pp. 205-216
Author(s):  
Bartosz Balis ◽  
Marian Bubak ◽  
Bartłomiej Łabno
Keyword(s):  
Real Life ◽  
Scientific Workflow ◽  
Point Of View ◽  
Scientific Workflows ◽  
Monitoring Data ◽  
Monitoring Point ◽  
Loosely Coupled ◽  
Provenance Data ◽  
On Line ◽  
Monitoring Architecture

Scientific workflows are a means of conducting in silico experiments in modern computing infrastructures for e-Science, often built on top of Grids. Monitoring of Grid scientific workflows is essential not only for performance analysis but also to collect provenance data and gather feedback useful in future decisions, e.g., related to optimization of resource usage. In this paper, basic problems related to monitoring of Grid scientific workflows are discussed. Being highly distributed, loosely coupled in space and time, heterogeneous, and heavily using legacy codes, workflows are exceptionally challenging from the monitoring point of view. We propose a Grid monitoring architecture for scientific workflows. Monitoring data correlation problem is described and an algorithm for on-line distributed collection of monitoring data is proposed. We demonstrate a prototype implementation of the proposed workflow monitoring architecture, the GEMINI monitoring system, and its use for monitoring of a real-life scientific workflow.

Study on the Truck Scale Cheating Automatic Monitoring System Based on the GPRS

2013 ◽  
Vol 703 ◽  
pp. 240-243 ◽  
Author(s):  
Yan Jun Zhao ◽  
Shou Guang Cheng ◽  
Bin Qu
Keyword(s):  
Monitoring System ◽  
Measurement Data ◽  
Experimental System ◽  
Automatic Monitoring ◽  
Experimental Results ◽  
Pneumatic Conveying ◽  
Automatic Monitoring System ◽  
On Line ◽  
Conveying System

The truck scale is more and more applied on the weighing system. To seek illegal profits, many kinds of truck scale cheating method is found in the weighing system. To monitoring the truck scale cheating method, the truck scale cheating automatic monitoring system based on the GPRS is brought out in this paper. The truck scale cheating automatic monitoring system is designed. The monitoring system includes three parts: the monitoring terminal, the GPRS transmission module and the upper monitoring system. The truck scale measurement data of the sensors are collected by the monitoring terminal and sent to the upper monitoring system through the GPRS module. The experimental system is established on the pneumatic conveying system and the experiment is carried out. The experimental results show that the automatic monitoring system can on-line monitor the truck scale cheating method and improves the security of the truck scale weighing system.

Performance Analysis of Gas-Expanded Lubricants in a Hybrid Bearing Using Computational Fluid Dynamics

2015 ◽  
Author(s):  
Brian K. Weaver ◽  
Gen Fu ◽  
Andres F. Clarens ◽  
Alexandrina Untaroiu
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Phase Behavior ◽  
Ambient Pressure ◽  
Operating Conditions ◽  
Full Potential ◽  
Dissolved Carbon ◽  
Bearing Stiffness ◽  
Multi Phase ◽  
Stiffness And Damping

Gas-expanded lubricants (GELs), tunable mixtures of synthetic oil and dissolved carbon dioxide, have been previously shown to potentially increase bearing efficiency, rotordynamic control, and long-term reliability in flooded journal bearings by controlling the properties of the lubricant in real time. Previous experimental work has established the properties of these mixtures and multiple numerical studies have predicted that GELs stand to increase the performance of flooded bearings by reducing bearing power losses and operating temperatures while also providing control over bearing stiffness and damping properties. However, to date all previous analytical studies have utilized Reynolds equation-based approaches while assuming a single-phase mixture under high-ambient pressure conditions. The potential implications of multi-phase behavior could be significant to bearing performance, therefore a more detailed study of alternative operating conditions that may include multi-phase behavior is necessary to better understanding the full potential of GELs and their effects on bearing performance. In this work, the performance of GELs in a fixed geometry journal bearing were evaluated to examine the effects of these lubricants on the fluid and bearing dynamics of the system under varying operating conditions. The bearing considered for this study was a hybrid hydrodynamic-hydrostatic bearing to allow for the study of various lubricant supply and operating conditions. A computational fluid dynamics (CFD)-based approach allowed for a detailed evaluation of the lubricant injection pathway, the flow of fluid throughout the bearing geometry, thermal behavior, and the collection of the lubricant as it exits the bearing. This also allowed for the study of the effects of the lubricant behavior on overall bearing performance.

Extended Finite Element Analysis of Journal Bearing Dynamic Forced Performance to Include Fluid Inertia Force Coefficients

2012 ◽  
Author(s):  
Luis San Andrés
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Small Amplitude ◽  
Forced Response ◽  
Inertia Force ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Force Coefficients ◽  
Reaction Forces ◽  
Bearing Stiffness

Reynolds equation governs the generation of hydrodynamic pressure in oil lubricated fluid film bearings. The static and dynamic forced response of a bearing is obtained from integration of the film pressure on the bearing surface. For small amplitude journal motions, a linear analysis represents the fluid film bearing reaction forces as proportional to the journal center displacements and velocity components through four stiffness and four damping coefficients. These force coefficients are integrated into rotor-bearing system structural analysis for prediction of the system stability and the synchronous response to imbalance. Fluid inertia force coefficients, those relating reaction forces to journal center accelerations, are routinely ignored because most oil lubricated bearings operate at relatively low Reynolds numbers, i.e., under slow flow conditions. Modern rotating machinery operates at ever increasing surface speeds to deliver more power in smaller size units. Under these operating conditions fluid inertia effects need to be accounted for in the forced response of oil lubricated bearings, as recent experimental test data also reveal. The paper presents a finite element formulation to predict added mass coefficients in oil lubricated bearings by extending a basic formulation that already calculates the bearing stiffness and damping force coefficients. That is, a small amplitude perturbation analysis of the lubrication flow equations keeps the temporal fluid inertia effects and develops a set of equations to obtain the bearing stiffness, damping and inertia force coefficients. The method does not impose on the cost of the original formulation which makes it very attractive for ready implementation in existing software. Predictions of the computational model are benchmarked against archival test data for an oil-lubricated pressure dam bearing supporting large compressors. The comparisons show fluid inertia effects cannot be ignored for operation at high rotor speeds and with small static loads.

It's YOUR Point of View…on Social Media

2010 ◽  
Vol 18 (4) ◽  
pp. 44-46
Author(s):  
Barbara Foster
Keyword(s):  
Social Media ◽  
New Technology ◽  
Point Of View ◽  
Emerging Trends ◽  
On Line ◽  
Trade Shows

For 20 years, Microscopy/Microscopy Education (MME) has been conducting market surveys for the industry, identifying emerging trends and, even more importantly, giving you, the practicing microscopist and spectroscopist, a chance to impact the direction of instrumentation via your input on our surveys. (Many of you remember us for the M&Ms we used to hand out in exchange for your input at key trade shows). The results of 20 years of your valued participation have been profound: new technology that fits your needs, coming on line faster and more economically.

Sign in / Sign up

Export Citation Format

Share Document