Repair of Severely Damaged Rotor as an Emergency Spare

Case StudyCase Study 10: When the subject compressor was opened for an unrelated reason, it was unexpectedly found to have severe cracking, including a missing piece, on the first stage impeller and foreign object damage to the remaining three impellers. To mitigate risk while the common spare was running and a new rotor was manufactured, the subject rotor was repaired for use as an emergency spare. This case study discusses the extensive repairs performed to bring the rotor to a usable state

Cepheid variables in the LMC cluster NGC 1866. I. New BVRI CCD photometry

We report BV(RI)c CCD photometric data for a group of seven Cepheid variables in the young, rich cluster NGC 1866 in the Large Magellanic Cloud. The photometry was obtained as part of a program to determine accurate distances to these Cepheids by means of the infrared surface brightness technique, and to improve the LMC Cepheid database for constructing Cepheid PL and PLC relations. Using the new data together with data from the literature, we have determined improved periods for all variables. For five fundamental mode pulsators, the light curves are now of excellent quality and will lead to accurate distance and radius determinations once complete infrared light curves and radial velocity curves for these variables become available.Comment: To appear in ApJ Supp., AASTeX, 24 pages, 8 tables, 8 figure

Fundamental differences between SPH and grid methods

We have carried out a hydrodynamical code comparison study of interacting multiphase fluids. The two commonly used techniques of grid and smoothed particle hydrodynamics (SPH) show striking differences in their ability to model processes that are fundamentally important across many areas of astrophysics. Whilst Eulerian grid based methods are able to resolve and treat important dynamical instabilities, such as Kelvin-Helmholtz or Rayleigh-Taylor, these processes are poorly or not at all resolved by existing SPH techniques. We show that the reason for this is that SPH, at least in its standard implementation, introduces spurious pressure forces on particles in regions where there are steep density gradients. This results in a boundary gap of the size of the SPH smoothing kernel over which information is not transferred.Comment: 15 pages, 13 figures, to be submitted to MNRAS. For high-resolution figures, please see http://www-theorie.physik.unizh.ch/~agertz

Preliminary Design and Kinematic Analysis of a Mobility Platform with Two Actuated Spoke Wheels

Active Spoke System) is a novel locomotion system concept that utilizes rimless wheels with individually actuated spokes to provide the ability to step over large obstacles like legs, adapt to uneven surfaces like tracks, yet retaining the speed and simplicity of wheels. Since it lacks the complexity of legs and has a large effective (wheel) diameter, this highly adaptive system can move over extreme terrain with ease while maintaining respectable travel speeds. This paper presents the concept, preliminary kinematic analyses and design of an IMPASS based robot with two actuated spoke wheels and an articulated tail. The actuated spoke wheel concept allows multiple modes of motion, which give it the ability to assume a stable stance using three contact points per wheel, walk with static stability with two contact points per wheel, or stride quickly using one contact point per wheel. Straight-line motion and considerations for turning are discussed for the one- and two-point contact schemes followed by the preliminary design and recommendations for future study. Index Terms – IMPASS, rimless wheel, actuated spoke wheel, mobility, locomotion