Experiments on dynamic stiffness and damping of tapered bore seals

Stiffness and damping were measured in tapered bore ring seals with air as the sealed fluid. Excitation was provided by a known unbalance in the shaft which rotated in the test seals. Results were obtained for various seal supply pressures, clearances, unbalance amounts, and shaft speeds. Stiffness and damping varied little with unbalance level, indicating linearity of the seal. Greater variation was observed with speed and particularly supply pressure. A one-dimensional analysis predicted stiffness fairly well, but considerably overestimated damping

Magnetic bearings-state of the art

Magnetic bearings have existed for many years, at least in theory. Earnshaw's theorem, formulated in 1842, concerns stability of magnetic suspensions, and states that not all axes of a bearing can be stable without some means of active control. In Beam's widely referenced experiments, a tiny (1/64 in diameter) rotor was rotated to the astonishing speed of 800,000 rps while it was suspended in a magnetic field. Despite a long history, magnetic bearings have only begun to see practical application since about 1980. The development that finally made magnetic bearings practical was solid state electronics, enabling power supplies and controls to be reduced in size to where they are now comparable in volume to the bearings themselves. An attempt is made to document the current (1991) state of the art of magnetic bearings. The referenced papers are large drawn from two conferences publications published in 1988 and 1990 respectively

Active vibration control for flexible rotor by optimal direct-output feedback control

Experimental research tests were performed to actively control the rotor vibrations of a flexible rotor mounted on flexible bearing supports. The active control method used in the tests is called optimal direct-output feedback control. This method uses four electrodynamic actuators to apply control forces directly to the bearing housings in order to achieve effective vibration control of the rotor. The force actuators are controlled by an analog controller that accepts rotor displacement as input. The controller is programmed with experimentally determined feedback coefficients; the output is a control signal to the force actuators. The tests showed that this active control method reduced the rotor resonance peaks due to unbalance from approximately 250 micrometers down to approximately 25 micrometers (essentially runout level). The tests were conducted over a speed range from 0 to 10,000 rpm; the rotor system had nine critical speeds within this speed range. The method was effective in significantly reducing the rotor vibration for all of the vibration modes and critical speeds

Quantification of the Environmental Solar Ultraviolet Radiation Field at the Human Eye and the Investigation of Peripherally Focused Rays.

The increase of terrestrial solar ultraviolet radiation (UVR) due to the reduction of the ozone layer has promoted a variety of research into establishing the impact of this elevated potential dose of UVR on biological tissues. Anterior ocular tissues such as the cornea have been found to be susceptible to damage by terrestrial solar UVR and diseases such as pterygium are commonly thought to be a direct result of absorbed UVR at the nasal limbus. There is a need for more accurate quantification and localisation of incident UVR at the anterior ocular surface. A novel solar blind photodiode sensor array system has been designed, constructed and tested for this purpose. The distribution of terrestrial solar UVR across the palpebral fissure for two test subjects has been quantified for a range of head orientations under different environmental conditions. The results herein outline the protection provided by different facial anatomies and the methodology has been proven through the repeatability of measurements over a range of cardinal point orientations. Added to the ambient terrestrial irradiance across the palpebral fissure, the phenomenon of Peripheral Light Focusing (PLF) has been investigated. Through the incorporation of modeling software and an anatomically based artificial eye, a novel fibre optic method has been developed to measure the corneal transmission in vivo

Vibration Transmission through Bearings with Application to Gearboxes

Cabin noise has become a major concern to manufacturers and users of helicopters. Gear noise is the largest part of this unwanted sound. The crucial noise path is generally considered to be from the gears through the gear-supporting shafts and bearings into the gearbox case, and from there either through the gearbox mounts or the surrounding air to the helicopter cabin. If the noise, that is, the gear and shaft vibration, can be prevented from traveling through the gearbox bearings, then the noise cannot make its way into the helicopter cabin. Thus the vibration-transmitting properties of bearings are of paramount importance. This paper surveys the literature concerning evaluation of properties for the types of bearings used in helicopter gearboxes. A simple model is proposed to evaluate vibration transmission, using measured or calculated bearing stiffness and damping. Less-commonly used types of gearbox bearings (e.g., fluid film) are evaluated for their potential in reducing vibration transmission

Software Developed for Analyzing High- Speed Rolling-Element Bearings

COBRA-AHS (Computer Optimized Ball & Roller Bearing Analysis--Advanced High Speed, J.V. Poplawski & Associates, Bethlehem, PA) is used for the design and analysis of rolling element bearings operating at high speeds under complex mechanical and thermal loading. The code estimates bearing fatigue life by calculating three-dimensional subsurface stress fields developed within the bearing raceways. It provides a state-of-the-art interactive design environment for bearing engineers within a single easy-to-use design-analysis package. The code analyzes flexible or rigid shaft systems containing up to five bearings acted upon by radial, thrust, and moment loads in 5 degrees of freedom. Bearing types include high-speed ball, cylindrical roller, and tapered roller bearings. COBRA-AHS is the first major upgrade in 30 years of such commercially available bearing software. The upgrade was developed under a Small Business Innovation Research contract from the NASA Glenn Research Center, and incorporates the results of 30 years of NASA and industry bearing research and technology

Rotordynamics on the PC: Further Capabilities of ARDS

Rotordynamics codes for personal computers are now becoming available. One of the most capable codes is Analysis of RotorDynamic Systems (ARDS) which uses the component mode synthesis method to analyze a system of up to 5 rotating shafts. ARDS was originally written for a mainframe computer but has been successfully ported to a PC; its basic capabilities for steady-state and transient analysis were reported in an earlier paper. Additional functions have now been added to the PC version of ARDS. These functions include: 1) Estimation of the peak response following blade loss without resorting to a full transient analysis; 2) Calculation of response sensitivity to input parameters; 3) Formulation of optimum rotor and damper designs to place critical speeds in desirable ranges or minimize bearing loads; 4) Production of Poincard plots so the presence of chaotic motion can be ascertained. ARDS produces printed and plotted output. The executable code uses the full array sizes of the mainframe version and fits on a high density floppy disc. Examples of all program capabilities are presented and discussed

STARRY: Analytic Occultation Light Curves

We derive analytic, closed form, numerically stable solutions for the total flux received from a spherical planet, moon or star during an occultation if the specific intensity map of the body is expressed as a sum of spherical harmonics. Our expressions are valid to arbitrary degree and may be computed recursively for speed. The formalism we develop here applies to the computation of stellar transit light curves, planetary secondary eclipse light curves, and planet-planet/planet-moon occultation light curves, as well as thermal (rotational) phase curves. In this paper we also introduce STARRY, an open-source package written in C++ and wrapped in Python that computes these light curves. The algorithm in STARRY is six orders of magnitude faster than direct numerical integration and several orders of magnitude more precise. STARRY also computes analytic derivatives of the light curves with respect to all input parameters for use in gradient-based optimization and inference, such as Hamiltonian Monte Carlo (HMC), allowing users to quickly and efficiently fit observed light curves to infer properties of a celestial body's surface map.Comment: 55 pages, 20 figures. Accepted to the Astronomical Journal. Check out the code at https://github.com/rodluger/starr

DETC2011-47414 DOUBLE NONLINEARITY -UNBALANCE RESPONSE OF ROTOR ON BALL BEARINGS WITH SQUEEZE FILM DAMPERS

ABSTRACT The nonlinear behavior of rolling-element bearings and squeeze-film dampers is well recognized; stiffness coefficients (and for dampers, damping coefficients also) increase as vibration amplitude increases. In the design of rotating systems using these elements, nonlinear aspects must be accounted for, and support properties chosen to handle the specific imbalance expected. Rolling-element bearings (e.g., ball bearings) are often used in combination with squeeze-film dampers (SFD). However, there seems to be no public information on the interaction of these two nonlinear elements. The purpose of this paper is to analytically document this interaction, and provide design guidance to optimize system performance for normal and extraordinary imbalance levels. Results show that a welldesigned SFD in conjunction with a ball bearing performs similar to an optimized linear support with linear bearing, but care must be taken to ensure that the SFD can handle the maximum load encountered. INTRODUCTION Rotordynamic response of all but very flexible rotors depends strongly on bearing and support properties. When bearings and supports are nonlinear, accurate rotor response cannot be obtained by use of average properties. Fluid film bearings are often reasonably linear for small deflections (although properties usually vary strongly with speed), but rolling-element bearings have a much less linear forcedisplacement relationship. Moreover, since rolling-element bearings have very low damping, rotors for many applications (e.g., gas turbines) are often supported in squeeze film dampers (SFD) in order to ensure low vibration response. Squeeze film dampers are themselves nonlinear. Damping coefficients are fairly constant for low vibration amplitudes, but stiffness increases directly with amplitude as well as with speed. Bot