CIVL 7610 STRUCTURAL DYNAMICS I (3) LEC. 3. Pr. CIVL 6670 or CIVL 6676. Single-degree-of-freedom systems, numerical solution techniques, response spectrum, multi-degree-of-freedom systems, eigenproblem solution, mode superposition analysis.
CIVL 7660 FINITE ELEMENT METHODS IN STRUCTURAL MECHANICS (3) LEC. 3. Pr. CIVL 6670 or CIVL 6676. Departmental approval. Introduction to finite element analysis; variational principles. 1D, 2D and 3D element formulation; nonlinear (geometric and constitutive) formulations and solutions; eigenvalue problems.
Preliminary Analysis of IGS Reprocessed Orbit and Polar Motion Estimates Jim Ray (Jim.Ray@noaa.gov) Jake Griffiths (Jake.Griffiths@noaa.gov) The Analysis Centers (ACs) of the International GNSS Service (IGS) are reanalyzing the history of global network GPS data collected since 1994 in a consistent way using the latest models and methodology. This is the first reprocessing by the IGS, but it is expected to be repeated in the future as further analysis and reference frame changes occur. All eight final-product ACs are participating, together with three other related groups. First partial results consisting of IGS combined weekly SINEX TRF and EOP combinations have been submitted to the IERS for ITRF2008. A snapshot of the available AC weekly SINEX files was used covering the reprocessed years 2000 through 2007 plus the IGS regular operational solutions for 2008 (from week 1460 onward). Meanwhile, the full reprocessing campaign will continue to completion by about the end of 2009 and will cover the period 1994 to present with long-term consistent, combined SINEX, orbit, and clock products. We have examined the reprocessed AC orbit and polar motion (PM) estimates from the 1024 days (or 1025 for differences) of results till the end of 2007. These parameters are linked since PM is sensed in the GPS modeling as a global diurnal sinusoidal motion of the terrestrial frame relative to the satellite frame. Any similar type errors in the orbital frame can bias the PM and PM rate estimates. For the orbits, each daily AC satellite ephemeris for each pair of consecutive days has been fit to the extended CODE orbit model, extrapolated to the mid-point epoch between the days, and the geocentric satellite position differences computed to give time series of orbit repeatabilities. Occasional data gaps have been filled by linear interpolation, FFT power spectra computed, and the spectra stacked over the full GPS constellation and lightly smoothed. Our analysis reveals considerable diversity among AC orbits. Several show broad semi-annual (probably related mostly to eclipsing) and fortnightly spectral peaks, as well as even harmonics of the GPS draconitic year (1.040 cpy) with varying amplitudes. High-frequency white noise floors can be detected in most AC orbit spectra, with an average sigma of 14 mm and larger. AC PM spectra mostly follow a power law with slope -4 for periods shorter than about 20 d, as expected, except in the few cases when ACs have applied tight day-to-day continuity constraints. Indications of high-frequency white noise are seen in some AC series. Day-boundary discontinuities computed using the AC PM rate estimates can provide a sensitive probe of the quality of the AC modeling, especially for the satellite orbit dynamics. Like the orbit discontinuities, we find the PM discontinuities vary greatly among the ACs. But most spectra of the PM discontinuities show peaks at the annual (broad) and the O1 tidal alias period of 14.19 d (narrow), in addition to odd (rather than even) harmonics of 1.040 cpy. Previously both even and odd harmonics of 1.040 cpy have been found in the spectra of station position time series.
High accuracy Global Navigation Satellite System (GNSS) positioning is a specialized skill involving expertise and fraught with accuracy-compromising nuance. With the goal of providing a robust and high accuracy positioning tool and convenient access to the United States' National Spatial Reference System (NSRS), the nation's fundamental positioning infrastructure, NOAA's National Geodetic Survey (NGS) developed the Online Positioning User Service (OPUS). OPUS is a free web utility for processing user-submitted GNSS observations and producing geodetic coordinates referenced to both NSRS and a global reference frame. Relying on NGS' national network of GNSS Continuously Operating Reference Stations (CORS), OPUS is a powerful and user-friendly tool for production and scientific research; it is widely used in geomatics professions.OPUS became operational in 2002 as a single point processing tool for multi-hour GPS occupations (OPUS-Static). It's capability has since evolved, adding the ability to process short (15 minutes) sessions (OPUS-RapidStatic) and to provide a solution sharing option. All OPUS variations have proven to be popular, with typical monthly submissions now numbering 40,000.In 2014, NGS released a network version of OPUS - OPUS-Projects, which offers rigorous geodetic network analysis and processing capability by assembling and processing GNSS observations collected over time and at multiple locations. Least squares geodetic network adjustment of all included observations results in an optimal set of station coordinates, including their uncertainties and graphical statistical plots, derived from user-submitted observation data, CORS observation data and corrdinates, satellite ephemerides, and models. Users have the ability to configure the processing, including tropospheric modeling, definition of observation sessions, network design, adjustment constraints, station descriptive information, and integration with passive geodetic control. 2b1af7f3a8