593 research outputs found
The Influence of the Testing Machine on the Buckling of Cylindrical Shells Under Axial Compression
Testing machine influence on buckling of cylindrical shells under axial compressio
Experimental investigation of the effect of general imperfections on the buckling of cylindrical shells
Imperfection survey data on cylindrical shells before and during axial compression loading up to buckling loa
A Mechanical Model for Elastic Fiber Microbuckling
A two-dimensional mechanical model is presented to predict the compressive strength of unidirectional fiber composites using technical beam theory and classical elasticity. First, a single fiber resting on a matrix half-plane is considered. Next, a more elaborate analysis of a uniformly laminated, unidirectional fiber composite half-plane is presented. The model configuration incorporates a free edge which introduces a buckling mode that originates at the free edge and decays into the interior of the half-plane. It is demonstrated that for composites of low volume fraction (<0.3), this decay mode furnishes values of buckling strain that are below the values predicted by the Rosen (1965) model. At a higher volume fraction the buckling mode corresponds to a half wavelength that is in violation of the usual assumptions of beam theory. Causes for deviations of the model prediction from existing experimental results are discussed
Millstone Hill Thomson Scatter Results for 1973
During 1973, the vertically-directed incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure electron density, electron and ion temperature and vertical ion velocity in the F-region over periods of 24 hours one or two times per month. The observations spanned the height interval 200-900 km approximately, and achieved a time resolution of about 30 minutes. This report presents the results of these measurements in a set of contour diagrams.
For a number of the days, the results have been used to derive the diurnal variation of the temperature of the neutral atmosphere above 300 km (the exospheric temperature) as well as the speed of the neutral wind in the magnetic meridian plane at this altitude. These results were used to define a model for the pressure variation in the thermosphere over Millstone whose E-W variation is set by the observed temperature variation, and whose N-S variation was adjusted to reproduce the observed winds calculated by solving momentum equations for the neutral air. These results, together with similar results obtained using data gathered over the six-year period 1970-1975 have been used in a study of the seasonal and sunspot cycle variation of the mean meridional and zonal winds. Also reported are the results of a study of the effect of magnetic storms on the thermospheric winds observed over Millstone Hill
Thermal/structural analysis of a transpiration cooled nozzle
The 8-foot High Temperature Tunnel (HTT) at LaRC is a combustion driven, high enthalpy blow down wind tunnel. In Mar. 1991, during check out of the transpiration cooled nozzle, pieces of platelets were found in the tunnel test section. It was determined that incorrect tolerancing between the platelets and the housing was the primary cause of the platelet failure. An analysis was performed to determine the tolerance layout between the platelets and the housing to meet the structural and performance criteria under a range of thermal, pressure, and bolt preload conditions. Three recommendations resulted as a product of this analysis
Preliminary Reconnaissance Water Quality Survey of the Buffalo National River
In accordance with Contract No. CX 700030105, dated 12 February 1973, the University of Arkansas , Water Resources Resear ch Center is submitting a Preliminary Reconnaissance Water Quality Survey of the Buffalo National River. The Water Resources Research Center of Arkansas has supplied the necessary personnel and facil ities to perform a preliminary reconnaissance survey of the Buffalo National River of Arkansas with special emphasis placed on the establishment of both permanent and temporary benchmarks for water quality sampling. Preliminary water quality samples have been collected to make those chemical, physical, and biological analyses as defined by Mr . Roland H. Wauer and other Park Service personnel on 3 May 1973
Solar Polar Fields During Cycles 21 --- 23: Correlation with Meridional Flows
We have examined polar magnetic fields for the last three solar cycles,
{}, cycles 21, 22 and 23 using NSO Kitt Peak synoptic magnetograms.
In addition, we have used SoHO/MDI magnetograms to derive the polar fields
during cycle 23. Both Kitt Peak and MDI data at high latitudes
(78--90) in both solar hemispheres show a significant
drop in the absolute value of polar fields from the late declining phase of the
solar cycle 22 to the maximum of the solar cycle 23. We find that long term
changes in the absolute value of the polar field, in cycle 23, is well
correlated with changes in meridional flow speeds that have been reported
recently. We discuss the implication of this in influencing the extremely
prolonged minimum experienced at the start of the current cycle 24 and in
forecasting the behaviour of future solar cycles.Comment: 4 Figures 11 pages; Revised version under review in Solar Physic
Recommended from our members
Whole-arm obstacle avoidance system conceptual design
Whole-arm obstacle avoidance is needed for a variety of robotic applications in the Environmental Restoration and Waste Management (ER WM) Program. Typical industrial applications of robotics involve well-defined workspaces, allowing a predetermined knowledge of collision-free paths for manipulator motion. In the unstructured or poorly defined hazardous environments of the ER WM Program, the potential for significant problems resulting from collisions between manipulators and the environment in which they are utilized is great. The conceptual design for a sensing system that will provide protection against such collisions is described herein. The whole-arm obstacle avoidance system consists of a set of sensor bracelets,'' which cover the surface area of the manipulator links to the maximum extent practical, and a host processor. The host processor accepts commands from the robot control system, controls the operation of the sensors, manipulates data received from the bracelets, and makes the data available to the manipulator control system. The bracelets consist of a subset of the sensors, associated sensor interface electronics, and a bracelet interface. Redundant communications links between the host processor and the bracelets are provided, allowing single-point failure protection. The system allows reporting of 8-bit data from up to 1000 sensors at a minimum of 50 Hz. While the initial prototype implementation of the system utilizes capacitance proximity sensor, the system concept allows multiple types of sensors. These sensors are uniquely addressable, allowing remote calibration, thresholding at the bracelet, and correlation of a sensor measurement with the associated sensor and its location on the manipulator. Variable resolution allows high-speed, single-bit sensing as well as lower-speed higher-resolution sensing, which is necessary for sensor calibration and potentially useful in control
- …