Research has shown in recent years that acute and cumulative exposure to excessive ultraviolet radiation (UVR) can cause a range of degenerative ocular conditions such as pterygium, photokeratitis and pinguecula. The increase in natural solar UVR as a result of the depletion of the ozone layer has led to a greater awareness of the adverse effects of UVR on the anterior ocular surface tissues. The relevance of this lies in the fact that these tissues are not immune to photodamage and that there is selective absorption of UVR by conjunctival and corneal tissue in the anterior ocular surface. Therefore, there is a demand for more precise quantification and localisation of UVR incidence at the anterior ocular surface. A novel solar blind photodiode sensor array has been designed, constructed and tested for this purpose. The emphasis of the measurements made by this sensor system is the acquisition of real time, field based surveys of the ocular UVR light field in a broad range of insolation environments. These data will then provide a thorough database of UVR irradiances that can be related to induced damage of anterior ocular tissue. Results to date show the first measured, in-vivo, absolute UVR levels on the eye, the corresponding relative field across the eye and the presence of nasal-temporal biases that exist.
The series-hybrid bearing couples a fluid-film bearing with a rolling-element bearing such that the rolling-element bearing inner race runs at a fraction of shaft speed. A series-hybrid bearing was analyzed and experiments were run at thrust loads from 100 to 300 lb and speeds from 4000 to 30,000 rpm. Agreement between theoretical and experimental speed sharing was good. The lowest speed ratio (ratio of ball bearing inner-race speed to shaft speed) obtained was 0.67. This corresponds to an approximate reduction in DN value of 1/3. For a ball bearing in a 3 million DN application, fatigue life would theoretically be improved by a factor as great as 8.
A general method of analysis is presented for determining the developing velocity field and pressure drop for laminar flow in the entrance region of ducts having arbitrary cross sections. Application of the solution method is made to rectangular ducts and to triangular ducts. Available experimental data are compared with the analytical results and good agreement is found to prevail. Development characteristics for six ducts are brought together and compared, and various trends are identified.
Seals can exert large forces on rotors. As an example, in turbopump ring seals film stiffness as high as 90 MN/m (500,000 lb/in) have been calculated. This stiffness is comparable to the stiffness of rotor support bearings; thus seals can play an important part in supporting and stabilizing rotor systems. The work done to determine forces generated in ring seals is reviewed. Working formulas are presented for seal stiffness and damping, and geometries to maximize stiffness are discussed. An example is described where a change in seal design stabilized a previously unstable rotor.
This paper presents a description of a dual clearance squeeze film damper (SFD) test rig and a dynamic model of a single SFD. The purpose of a dual SFD is to provide protection at high levels of vibration, when conventional devices are no longer effective. An experimental facility was designed and built for tire study of SFD behavior within mechanically controlled orbits. It can be used for both single and dual squeeze film dampers. In Part 1 of this paper, measured and computed responses are presented while operating as a single squeeze film device. Numerical and experimental results for undamped cases are presented, i.e., when no oil film is present in the damper. Subsequently, the effects of the oil film are considered. Good agreement was obtained between experimental data and predictions.
A single-mass flexible-rotor analysis was used to optimize the stiffness and damping of a flexible support for a symmetric five-mass rotor. The flexible, damped support attenuates the amplitudes of motions and forces transmitted to the support bearings when the rotor operates through and above its first bending critical speed. An oil squeeze film damper was designed based on short bearing lubrication theory. The damper design was verified by an unbalance response computer program. Rotor amplitudes were reduced by a factor of 16 and loads reduced by a factor of 36 compared with the same rotor with rigid bearing supports.
NASA technical memorandum reviews state of technology of magnetic bearings, focusing mainly on attractive bearings rather than repulsive, eddy-current, or Lorentz bearings. Attractive bearings offer greater load capacities and preferred for aerospace machinery.
Radial stiffness of annular (ring-type) gas path seals is calculated for both constant-clearance designs and tapered designs for which the inlet clearance is larger than the outlet clearance. Under some conditions a constant-clearance seal can have a negative stiffness; this undesirable property can be completely eliminated by use of tapered seals. Leakage rates are only moderately higher in tapered seals
