Juncture stress fields in multicellular shell structures. Volume I - Numerical methods of solving large matrices Final report

Numerical techniques for digital computer solution of algebraic simultaneous linear equations from finite difference approximation of partial differential equations of thin elastic shell

Enhancements to the STAGS computer code

The power of the STAGS family of programs was greatly enhanced. Members of the family include STAGS-C1 and RRSYS. As a result of improvements implemented, it is now possible to address the full collapse of a structural system, up to and beyond critical points where its resistance to the applied loads vanishes or suddenly changes. This also includes the important class of problems where a multiplicity of solutions exists at a given point (bifurcation), and where until now no solution could be obtained along any alternate (secondary) load path with any standard production finite element code

Global function approach in structural analysis: Basic approach, numerical results

The structural response to a given environment is described by the differential equations of motion of deformable bodies. Analytic solutions of such problems for a reasonably large class of structural configurations are not within the realm of the possible. Consequently, the mathematical problem is recast into a numerical problem for solution on the computer. New technology in the space and energy fields led to a growing demand for accurate analysis which at times cannot be met due to the limits set by available budgets for computer time. In response to this need for more efficient numerical analysis, the possibilities of reducing the number of freedoms in the system through a revival of the global function approach were explored

Investigation of juncture stress fields in multicellular shell structures

Discontinuity stress fields in thin elastic multicellular shell structures subject to inertial, pressure, and thermal loadin

Failure Analysis of Discrete Damaged Tailored Extension-Shear-Coupled Stiffened Composite Panels

The results of an analytical and experimental investigation of the failure of composite is tiffener panels with extension-shear coupling are presented. This tailored concept, when used in the cover skins of a tiltrotor aircraft wing has the potential for increasing the aeroelastic stability margins and improving the aircraft productivity. The extension-shear coupling is achieved by using unbalanced 45 plies in the skin. The failure analysis of two tailored panel configurations that have the center stringer and adjacent skin severed is presented. Finite element analysis of the damaged panels was conducted using STAGS (STructural Analysis of General Shells) general purpose finite element program that includes a progressive failure capability for laminated composite structures that is based on point-stress analysis, traditional failure criteria, and ply discounting for material degradation. The progressive failure predicted the path of the failure and maximum load capability. There is less than 12 percent difference between the predicted failure load and experimental failure load. There is a good match of the panel stiffness and strength between the progressive failure analysis and the experimental results. The results indicate that the tailored concept would be feasible to use in the wing skin of a tiltrotor aircraft

The Deepest Radio Study of the Pulsar Wind Nebula G21.5-0.9: Still No Evidence for the Supernova Shell

We report on sensitive new 1.4-GHz VLA radio observations of the pulsar wind nebula G21.5-0.9, powered by PSR J1833-1034, and its environs. Our observations were targeted at searching for the radio counterpart of the shell-like structure seen surrounding the pulsar wind nebula in X-rays. Some such radio emission might be expected as the ejecta from the <~ 1000 yr old supernova expand and interact with the surrounding medium. We find, however, no radio emission from the shell, and can place a conservative 3-sigma upper limit on its 1-GHz surface brightness of 7 x 10^-22 W/m^2/Hz/sr, comparable to the lowest limits obtained for radio emission from shells around other pulsar-wind nebulae. Our widefield radio image also shows the presence of two extended objects of low-surface brightness. We re-examine previous 327-MHz images, on which both the new objects are visible. We identify the first, G21.64-0.84, as a new shell-type supernova remnant, with a diameter of ~13' and an unusual double-shell structure. The second, G21.45-0.59, ~1' in diameter, is likely an HII region.Comment: 8 Pages, submitted to MNRA

The (Re-)Discovery of G350.1-0.3: A Young, Luminous Supernova Remnant and Its Neutron Star

We present an XMM-Newton observation of the long-overlooked radio source G350.1-0.3. The X-ray spectrum of G350.1-0.3 can be fit by a shocked plasma with two components: a high-temperature (1.5 keV) region with a low ionization time scale and enhanced abundances, plus a cooler (0.36 keV) component in ionization equilibrium and with solar abundances. The X-ray spectrum and the presence of non-thermal, polarized, radio emission together demonstrate that G350.1-0.3 is a young, luminous supernova remnant (SNR), for which archival HI and 12-CO data indicate a distance of 4.5 kpc. The diameter of the source then implies an age of only ~900 years. The SNR's distorted appearance, small size and the presence of 12-CO emission along the SNR's eastern edge all indicate that the source is interacting with a complicated distribution of dense ambient material. An unresolved X-ray source, XMMU J172054.5-372652, is detected a few arcminutes west of the brightest SNR emission. The thermal X-ray spectrum and lack of any multi-wavelength counterpart suggest that this source is a neutron star associated with G350.1-0.3, most likely a "central compact object", as seen coincident with other young SNRs such as Cassiopeia A.Comment: 6 pages, uses emulateapj. One B/W figure, one color figure. Minor text changes and update to Fig 2 following referee's report. ApJ Letters, in pres

Status of Identification of VHE gamma-ray sources

With the recent advances made by Cherenkov telescopes such as H.E.S.S., the field of very high-energy (VHE) gamma-ray astronomy has recently entered a new era in which for the first time populations of Galactic sources such as e.g. Pulsar wind nebulae (PWNe) or Supernova remnants (SNRs) can be studied. However, while some of the new sources can be associated by positional coincidence as well as by consistent multi-wavelength data to a known counterpart at other wavelengths, most of the sources remain not finally identified. In the following, the population of Galactic H.E.S.S. sources will be used to demonstrate the status of the identifications, to classify them into categories according to this status and to point out outstanding problems.Comment: To appear in Astrophysics and Space Science (Proceedings of "The multimessenger approach to unidentified gamma-ray sources