2,342 research outputs found
Implementation of an intelligent control system
A laboratory testbed facility which was constructed at NASA LeRC for the development of an Intelligent Control System (ICS) for reusable rocket engines is described. The framework of the ICS consists of a hierarchy of various control and diagnostic functions. The traditional high speed, closed-loop controller resides at the lowest level of the ICS hierarchy. Above this level resides the diagnostic functions which identify engine faults. The ICS top level consists of the coordination function which manages the interaction between an expert system and a traditional control system. The purpose of the testbed is to demonstrate the feasibility of the OCS concept by implementing the ICS as the primary controller in a simulation of the Space Shuttle Main Engine (SSME). The functions of the ICS which are implemented in the testbed are as follows: an SSME dynamic simulation with selected fault mode models, a reconfigurable controller, a neural network for sensor validation, a model-based failure detection algorithm, a rule based failure detection algorithm, a diagnostic expert system, an intelligent coordinator, and a user interface which provides a graphical representation of the event occurring within the testbed. The diverse nature of the ICS has led to the development of a distributed architecture consisting of specialized hardware and software for the implementation of the various functions. This testbed is made up of five different computer systems. These individual computers are discussed along with the schemes used to implement the various ICS components. The communication between computers and the timing and synchronization between components are also addressed
Integrated health monitoring and controls for rocket engines
Current research in intelligent control systems at the Lewis Research Center is described in the context of a functional framework. The framework is applicable to a variety of reusable space propulsion systems for existing and future launch vehicles. It provides a 'road map' technology development to enable enhanced engine performance with increased reliability, durability, and maintainability. The framework hierarchy consists of a mission coordination level, a propulsion system coordination level, and an engine control level. Each level is described in the context of the Space Shuttle Main Engine. The concept of integrating diagnostics with control is discussed within the context of the functional framework. A distributed real time simulation testbed is used to realize and evaluate the functionalities in closed loop
Quasiharmonic elastic constants corrected for deviatoric thermal stresses
The quasiharmonic approximation (QHA), in its simplest form also called the
statically constrained (SC) QHA, has been shown to be a straightforward method
to compute thermoelastic properties of crystals. Recently we showed that for
non-cubic solids SC-QHA calculations develop deviatoric thermal stresses at
high temperatures. Relaxation of these stresses leads to a series of
corrections to the free energy that may be taken to any desired order, up to
self-consistency. Here we show how to correct the elastic constants obtained
using the SC-QHA. We exemplify the procedure by correcting to first order the
elastic constants of MgSiO-perovskite and MgSiO-post-perovskite, the
major phases of the Earth's lower mantle. We show that this first order
correction is quite satisfactory for obtaining the aggregated elastic averages
of these minerals and their velocities in the lower mantle. This type of
correction is also shown to be applicable to experimental measurements of
elastic constants in situations where deviatoric stresses can develop, such as
in diamond anvil cells.Comment: 4 figures, 1 table, submitted to Phys. Rev. B, July 200
Comparing March and May Calving Systems in the Nebraska Sandhills
Three production years for March and May calving, Red Angus- based cows and their off spring from the Gudmundsen Sandhills Laboratory (GSL), Whitman, NE, were evaluated. Steer progeny were evaluated through harvest and carcass data collected. Calf birth body weight (BW) and breeding BW were greater for May calves vs. March; however, adjusted weaning BW was greater for March calves. Pregnancy rates, weaning rates, calving interval, calving difficulty, and calf vigor were similar between calving systems. Udder score was greater for March cows. Compared with March calf- fed steers, May calf- fed steers had greater hot carcass weight (HCW), longissimus muscle area (LMA), marbling, and backfat. May yearlings had greater HCW, LMA, marbling, and backfat compared with March calf- feds. In the Sandhills, a May calving system can increase production while reducing total herd inputs when compared to a March calving system
A proposal of a UCN experiment to check an earthquake waves model
Elastic waves with transverse polarization inside incidence plane can create
longitudinal surface wave (LSW) after reflection from a free surface. At a
critical incidence angle this LSW accumulates energy density, which can be
orders of magnitude higher than energy density of the incident transverse wave.
A specially arranged vessel for storage of ultracold neutrons (UCN) can be used
to verify this effect.Comment: 8 pages 3 figures added a paragraph on vibrations along surface at
critical angl
Those wonderful elastic waves
We consider in a simple and general way elastic waves in isotropic and
anisotropic media, their polarization, speeds, reflection from interfaces with
mode conversion, and surface waves. Reflection of quasi transverse waves in
anisotropic media from a free surface is shown to be characterized by three
critical angles.Comment: 11 Figures 26 page
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