Measurements of a turbulent horseshoe vortex formed around a cylinder

An experimental investigation was conducted to characterize a symmetrical horseshoe vortex system in front of and around a single large-diameter right cylinder centered between the sidewalls of a wind tunnel. Surface flow visualization and surface static pressure measurements as well as extensive mean velocity and pressure measurements in and around the vortex system were acquired. The results lend new insight into the formation and development of the vortex system. Contrary to what has been assumed previously, a strong vortex was not identified in the streamwise plane of symmetry, but started a significant angular distance away from it. Rather than the multiple vortex systems reported by others, only a single primary vortex and saddle point were found. The scale of the separation process at the saddle point was much smaller than the scale of the approaching boundary layer thickness. Results of the present study not only shed light on such phenomena as the nonsymmetrical endwall flow in axial turbomachinery but can also be used as a test case for three-dimensional computational fluid mechanics computer codes

The February 9, 1971 San Fernando earthquake: A study of source finiteness in teleseismic body waves

Teleseismic P, SV, and SH waves recorded by the WWSS and Canadian networks from the 1971 San Fernando, California earthquake (ML = 6.6) are modeled in the time domain to determine detailed features of the source as a prelude to studying the near and local field strong-motion observations. Synthetic seismograms are computed from the model of a propagating finite dislocation line source embedded in layered elastic media. The effects of source geometry and directivity are shown to be important features of the long-period observations. The most dramatic feature of the model is the requirement that the fault, which initially ruptured at a depth of 13 km as determined from pP-P times, continuously propagated toward the free surface, first on a plane dipping 53°NE, then broke over to a 29°NE dipping fault segment. This effect is clearly shown in the azimuthal variation of both long period P- and SH-wave forms. Although attenuation and interference with radiation from the remainder of the fault are possible complications, comparison of long- and short-period P and short-period pP and P waves suggest that rupture was initially bilateral, or, possibly, strongly unilateral downward, propagating to about 15 km depth. The average rupture velocity of 1.8 km/sec is well constrained from the shape of the long-period wave forms. Total seismic moment is 0.86 × 10^(26) dyne-cm. Implications for near-field modeling are drawn from these results

Corvallis, Oregon, crustal and upper mantle receiver structure from teleseismic P and S waves

Structure under Corvallis, Oregon, was examined using long-period Ps and Sp conversions and P reverberations from teleseismic events as recorded at the WWSSN station COR. A distinct low-velocity zone in the uppermost mantle is inferred by modeling these phases in the time domain using a data set composed of six deep and intermediate-depth earthquakes. The lower boundary occurs at 45-km depth and has S and P velocity contrasts of 1.3 and 1.4 km/sec, respectively. The material comprising the low-velocity zone has a Poisson ratio of at least 0.33 and is constrained by the average P and S travel times determined from the converted phases. The top of the earth model conforms to previously published refraction results

A body wave inversion of the Koyna, India, earthquake of December 10, 1967, and some implications for body wave focal mechanisms

With a generalized inverse technique, WWSSN (World-Wide Standard Seismograph Network) long-period P and SH wave forms are analyzed from the Koyna earthquake. The effects of local plane-layered earth structure near an imbedded point dislocation source are put in by using a modified plane-wave ray theory which includes the standard reflection and transmission coefficients plus source corrections for radiation pattern and geometrical spreading. The generalized inverse compares synthetic seismograms to the observed ones in the time domain through the use of a correlation function. By using published crustal models of the Koyna region and primarily by modelling the crustal phases P, pP, and sP, the first 25 s of the long-period wave forms is synthesized for 17 stations, and a focal mechanism is obtained for the Koyna earthquake which is significantly different from previous mechanisms. The fault orientation is 67° dip to the east, −29° rake plunging to the northeast, and N16°E strike, all angles being ±6°. This is an eastward dipping, left lateral oblique slip fault which agrees favorably with the trend of fissures in the meizoseismal area. The source time duration is estimated to be 6.5±1.5 s from a triangular time pulse which has a rise time of 2.5 s, a tail-off of 3.9 s, source depth of 4.5±1.5 km, and seismic moment of 3.2±1.4×10^(25) dyn cm. Some short-period complexity in the time function is indicated by modelling shortperiod WWSSN records but is complicated by crustal phases. The long-period P wave forms exhibit complicated behavior due to intense crustal phase interference caused by the shallow source depth and radiation pattern effects. These structure effects can explain much of the apparent multiplicity of the Koyna source. An interpretation of the Koyna dam accelerograms has yielded an S-P time which can be used along with the IMD (Indian Meteorological Department) epicenter and present depth determination to place the epicenter directly on the meizoseismal area

Turbine endwall single cylinder program

Measurements of the flow field in front of a large-scale single cylinder, mounted in a wind tunnel are discussed. Static pressures on the endwall and cylinder surfaces, extensive five-hole probe pressures in front of and around the cylinder, and velocity fluctuations using a hot-wire probe where the flow is steady enough to yield meaningful results are included

The effect of planar dipping structure on source and receiver responses for constant ray parameter

A geometrical ray method is developed for wave calculations involving three-dimensional planar dipping interfaces. Justification for the method is based on analogy with first-motion approximations derived from generalized ray theory where frequency dependence in the reflection-transmission coefficients is related to changes in the complex ray parameter. The method is applied to finding the teleseismic response of an arbitrarily oriented dislocation source in dipping layered media and for receiver calculations which assume an impinging P or S wave beneath a stack of dipping layers. Source results indicate that wave forms from fast azimuthally varying sources, such as strike-slip faults, are significantly distorted from the plane layered case for simple structures. A simple dipping Moho for dips up to 10° does not significantly distort vertical and radial P waves for the receiver response. However, due to azimuth anomalies introduced by interface dip a significant tangential P component is produced. In addition, the S-wave response becomes a function of source mechanism due to the need for specifying the incident polarization angle. Polarization studies are suggested for finding dipping structure

Focal mechanism of the August 1, 1975 Oroville earthquake

Long-period teleseismic P and S waves from the WWSS and Canadian networks are modeled to determine the focal parameters for the main shock in the Oroville earthquake series. Using the techniques of P first motions, wave-form synthesis, and phase identification, the focal parameters are determined as follows: dip 65°; rake −70°; strike 180°; depth 5.5 ± 1.5km; moment 5.7 ± 2.0 × 10^(24) dyne-cm; and a symmetric triangular time function 3 sec in duration. This is a north-south striking, westward dipping, normal fault with a small component of left-lateral motion. The time separation between the small foreshock and mainshock appears to be 6.5 sec at teleseismic distances, rather than 8.1 sec as observed at short distances

The April 29, 1965, Puget Sound earthquake and the crustal and upper mantle structure of western Washington

Simultaneous modeling of source parameters and local layered earth structure for the April 29, 1965, Puget Sound earthquake was done using both ray and layer matrix formulations for point dislocations imbedded in layered media. The source parameters obtained are: dip 70° to the east, strike 344°, rake −75°, 63 km depth, average moment of 1.4 ± 0.6 × 10^(26) dyne-cm, and a triangular time function with a rise time of 0.5 sec and falloff of 2.5 sec. An upper mantle and crustal model for southern Puget Sound was determined from inferred reflections from interfaces above the source. The main features of the model include a distinct 15-km-thick low-velocity zone with a 2.5-km/sec P-wave-velocity contrast lower boundary situated at approximately 56-km depth. Ray calculations which allow for sources in dipping structure indicate that the inferred high contrast value can trade off significantly with interface dip provided the structure dips eastward. The effective crustal model is less than 15 km thick with a substantial sediment section near the surface. A stacking technique using the instantaneous amplitude of the analytic signal is developed for interpreting short-period teleseismic observations. The inferred reflection from the base of the low-velocity zone is recovered from short-period P and S waves. An apparent attenuation is also observed for pP from comparisons between the short- and long-period data sets. This correlates with the local surface structure of Puget Sound and yields an effective Q of approximately 65 for the crust and upper mantle