Seismic modeling using the frozen Gaussian approximation

We adopt the frozen Gaussian approximation (FGA) for modeling seismic waves. The method belongs to the category of ray-based beam methods. It decomposes seismic wavefield into a set of Gaussian functions and propagates these Gaussian functions along appropriate ray paths. As opposed to the classic Gaussian-beam method, FGA keeps the Gaussians frozen (at a fixed width) during the propagation process and adjusts their amplitudes to produce an accurate approximation after summation. We perform the initial decomposition of seismic data using a fast version of the Fourier-Bros-Iagolnitzer (FBI) transform and propagate the frozen Gaussian beams numerically using ray tracing. A test using a smoothed Marmousi model confirms the validity of FGA for accurate modeling of seismic wavefields.Comment: 5 pages, 8 figure

Bemessungskonzepte fuer Stabilitaetsfaelle imperfektionssensitiver Schalenstrukturen

In der vorliegenden Arbeit werden neue Bemessungsformeln und Diagramme fuer den Beulsicherheitsnachweis von Schalenstrukturen entwickelt. Im speziellen wird fuer sphaerische Schalen unter Aussendruck sowie fuer torikonische und torisphaerische Schalen unter Aussen- oder Innendruck eine einfache Stabilitaetsbemessung moeglich. Hierzu werden umfangreiche numerische Untersuchungen perfekter und imperfekter Schalen mit elastischen oder elastisch-plastischen Werkstoffkennlinien durchgefuehrt, die eine fundierte Basis fuer den Entwurf der neuen Richtlinien darstellen. Die Bemessungsvorschlaege werden zusaetzlich durch bereits vorhandene theoretische und numerische Ergebnisse sowie experimentelle Studien ueberprueft. (orig.)In this report new design formulas and diagrams are developed to guarantee the stability of shell structures. Particularly, a simple design concept of spherical shells under external pressure as well as toriconical and torispherical shells under external or internal pressure will be possible. In this context extensive numerical investigations of perfect and imperfect shells with elastic or elastic-plastic material behaviour are carried out to give a solid basis of the draft of new recommendations. Additionally, the proposals of design rules are examined by existing theoretical and numerical data as well as experimental studies. (orig.)Available from TIB Hannover: RR 275(2000,7) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman