Horizontal SH Research Articles

On the Design of Two EAHE Assemblies with Four Ducts

This article applies the constructal design method to analyze how to improve the thermal performance of earth-air heat exchangers (EAHE) composed by four ducts. The paper evaluates two types of arrangements for which the centers of the ducts take the shape of rectangles and diamonds. Under volumetric constraints, the vertical Sv and horizontal Sh spacings between the ducts are left free to vary. The objective is to maximize the magnitude of the EAHE instantaneous thermal potential P which is an average of the differences between the temperatures at the ducts outlets and inlets at any instant of time. The temperature fields are computed through numerical simulations, adopting a verified and validated three-dimensional model. Among the results, this work shows how the design can raise by 11% the annual thermal efficiency of the EAHE.

Sensitivity analysis for Love mode acoustic gravimetric sensors

An approximate mass sensitivity formula for Love mode sensors is presented. The optimal thickness of the guiding layer, at which the sensitivity, Sfm is maximum for a given frequency or wavelength is obtained. The (Sfm)max can be expressed as −k0/ρ1λ1, where ρ1 is the density, λ1 is the wavelength of the surface transverse wave of the substrate, and k0 is a coefficient determined by the ratio of shear wave velocity and the ratio of density of the substrate to those of the overlayer. The (Sfm)max of the Love mode device can be 20 times higher than that of the shear horizontal SH–surface acoustic wave device fabricated on the same substrate and operating at the same frequency.

Measurement ofQ−1 forSwaves in mudstone at Chikura, Japan: Comparison of incident and reflected phases in borehole seismograms

AbstractSeismograms from small events in the southern Kanto region have been recorded by a seismometer installed in a 732-m-deep borehole at Chikura observatory, Japan, where mudstone of early Pliocene age is found from the ground surface to the bottom of the borehole. Strong phases occurring 1.5 ∼ 1.6 sec after the S-wave arrival were interpreted as reflections at the ground surface. Ray path directions of the incident S waves were determined from the minimum principal axis of the three-dimensional trajectory ellipsoid, which represents the particle motion for a head wave of S phase. Transverse horizontal SH components were used to estimate the Q−1 value for S waves. Assuming the free surface acted as an 100% reflector for the SH waves and the incident SH phase as an input and the reflected phase as an output, we calculated system functions. The Q−1 value was measured from the transfer characteristics between the incident and the reflected phases in a single seismogram, thus no corrections were necessary for source or site (including instrument) effects. If we applied a power law model, the following relationship was obtained from the regression analyses of 20 events: log 10 ( Q − 1 ) = ( − 0.52 ± 0.48 ) ⋅ log 10 ( f ) − ( 1.28 ± 0.22 ) ( 1.0 < f < 5.0 Hz ) , where f is frequency in Hz and error values are the 95% confidence levels of the regression coefficients.

Radiation patterns of a shear‐wave vibrator in near‐surface shale

Two shallow, surface‐to‐borehole field tests were conducted to investigate the radiation patterns of a shear‐wave vibrator in near‐surface shale. In the in‐line direction, for which baseplate motion is transverse to the source‐geophone raypath, the vibrator produces a broadband, high‐amplitude signal of the SH type and virtually no signal of the SV or P types. The amplitude of the SH radiation is approximately constant as a function of polar angle, but it falls off as the cosine of the azimuthal angle measured with respect to the in‐line direction. In the broadside direction, the vibrator produces a strong, uncontaminated signal of the SV type. The radiation pattern of the SV signature is lobate in the polar plane and peaks at an incident angle of 30 to 35 degrees. In the horizontal plane, the SV radiation varies as the sine of the azimuthal angle measured with respect to the in‐line direction. The field tests were conducted on a Permian shale in Oklahoma and an Eocene shale in East Texas. Comparison between SH and SV wave surfaces indicates that both shales behave approximately like transversely isotropic solids with a vertical axis of symmetry. Theoretical wave surfaces are fit to the observed data by using elastic moduli determined from the field measurements and by making the assumption that the near‐surface shale at each field site is a single, homogeneous, inherently transversely isotropic material. The analyses indicate that horizontal SH group velocity is about 30 percent greater than horizontal SV group velocity in the Permian shale and about 25 percent greater in the Eocene shale.

INVESTIGATION OF SHEAR WAVES

A series of measurements was made to investigate some of the fundamental properties of shear waves and to explore the possibility of using horizontally polarized (SH) shear waves for reflection prospecting. A special source was devised to produce a shearing motion which was detectable as far as 400 feet vertically and 1,000 feet horizontally. Direct, refracted, and reflected SH and SV (vertically polarized) shear waves were identified on a series of surface and subsurface recordings. A strong, highly dispersive surface wave, which satisfies the theoretical criteria of Love waves, was also observed. Certain anomalous features of the data which did not conform to the predictions of simple isotropic theory were readily explained by considering the stratified section under observation to be transversely isotropic. It was found that horizontal SH velocity exceeded vertical SH velocity by 100 percent whereas the corresponding compressional wave velocities differed by only 12 percent. SV anisotropy was manifested by a complex variation of velocity at intermediate directions of travel. Other theoretical predictions were confirmed in detail by the experimental data. An evaluation of SH reflection recording was made in four different areas. It was possible at one location, using multiple horizontal geophones and the shear source, to obtain an SH reflection from the base of a thick weathered layer. However, the results in general indicate that the method is not likely to have much practical importance.