5,626 research outputs found
Borehole effects on downhole seismic measurements
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994.Includes bibliographical references (p. 270-281).by Chengbin Peng.Ph.D
Acoustic Wave Propagation In And Around A Fluid-Filled Borehole Of Irregular Cross-Section
No full textBoreholes with 10% or more ellipticity are not uncommon. In this paper, we consider
the coupling of an incident elastic wave into a borehole of irregular cross-section and
investigate the cross-mode coupling phenomenon in sonic well logging in the presence
of borehole irregularity. The mode-matching method is used. Different from its original
formulation, we employ the Reichel et al. algorithm to obtain the discrete least square
approximation by trigonometric polynomials, a technique closely related to the fast
Fourier transform (FFT). Our method not only yields great accuracy but also gains
computational speed. Our study shows that the pressure in the borehole fluid is sensitive
to the irregularity of the borehole cross-section, it is larger if the incident wave is along the effective minor axis and smaller if the incident wave is along the effective major axis. In the frequency range of a typical borehole experiment, the solid displacement in the formation is much less affected by the borehole irregularity. In an elliptical borehole, a monopole source excites dipole wave trains that are characteristic of the tube waves, and a centered dipole source excites monopole wave trains that are characteristic of the flexural waves.Massachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu
Optimal Absorbing Boundary Conditions For Finite Difference Modeling Of Acoustic And Elastic Wave Propagation
No full textAn optimal absorbing boundary condition is designed to model acoustic and elastic wave
propagation in 2D and 3D media using the finite difference method. In our method,
extrapolation on the artificial boundaries of a finite difference domain is expressed as
a linear combination of wave fields at previous time steps and/or interior grids. The
acoustic and elastic reflection coefficients from the artificial boundaries are derived.
They are found to be identical with the transfer functions of two cascaded systems: one
is the inverse of a causal system and the other is an anticausal system. This method
makes use of the zeros and poles of reflection coefficients in a complex plane. The
optimal absorbing boundary condition designed in this paper yields about 10 dB smaller
in magnitude of reflection coefficients than Higdon's absorbing boundary condition, and
around 20 dB smaller than Reynolds' absorbing boundary condition. This conclusion is
supported by a simulation of elastic wave propagation in a 3D medium on an nCUBE
parallel computer.ERL/nCUBE Geophysical Center for Parallel Processin
Tube Wave Generation At A Layer Boundary For An Incident Compressional Plane Wave
No full textAn approximate theory for the scattering of an incident plane P wave into tube waves
in a fluid-filled borehole drilled through two homogeneous half-spaces is proposed in
this paper. This theory is in excellent agreement with the zero frequency formulation
(White, 1983) for frequencies below hundreds of Hertz (in the range of conventional
crosshole or VSP experiments) and finite difference simulation at high frequencies. At
low frequency the excited tube wave is found to be independent of the borehole radius
and shows stronger sensitivity to the formation shear velocity contrast across the layer
boundary. The sensitivity towards the compressional velocity perturbation is opposite
to that of the shear wave and density such that little tube wave can be generated if the
compressional and shear velocities are both increased or decreased accordingly. Unlike
the tube wave excited in the borehole when an incident plane wave hits a fracture,
the reflected and transmitted tube waves generated at a layer boundary show opposite
polarities.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumnCUBE (Graduate Student Fellowship
Borehole Effects On Downhole Seismic Measurements
No full textAn exact formulation for borehole coupling, which is valid for all frequencies and all
azimuthally symmetric and nonsymrnetric components, is given in this paper. The borehole
effects on downhole measurements are studied in detail as functions of frequency,
incidence angle and polarization of an incident wave as well as geophone orientation.
We found that correction of the borehole effect for downhole measurements should be
made for frequencies above 500 Hz in a hard formation. In a soft formation, if the
incidence angle is well away from the resonance angle for a SV incidence, no borehole
correction is needed for frequencies below 300 Hz; while for frequencies above 300 Hz,
the borehole can cause severe problems on downhole measurements. The borehole can
also significantly alter the particle motion direction such that horizontal components
rotation from data itself is unreliable for experiments with frequencies above 1 kHz in
the hard formation and around 500 Hz in the soft formation.ERL/nCUBE Geophysical Center for Parallel PrecessingMassachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu
Cased Borehole Effect On Downhole Seismic Measurements
No full textApproximate and exact formulations are presented for the interaction of an incident
wave with a cased borehole. In the approximate method, the borehole coupling theory
is used to compute pressure in the fluid at a low frequency. The results are simple
and explicit. They are useful in the study of cased borehole coupling and as well
as borehole radiation. In the exact method, elastic potentials in each annulus are
represented as a superposition of fundamental solutions to the Helmholtz equations.
Continuity of displacements and stresses across layer boundaries are used to determine
unknown coefficients. The global matrix method is employed to simultaneously compute
these coefficients in individual layers. This method is advantageous over the Thomson Haskell propagator matrix method in handling evanescent waves. Our results show that,
in a cased borehole, the borehole effects on downhole seismic measurements are more
significant than those in an open borehole, especially when the formation is soft and
the casing is steel. For hard formations and frequency below 1 kHz, cased borehole
influence on downhole geophone measurement is minimal, while at high frequencies,
large discrepancies occur, especially at grazing incidence. For soft formations, both
the pressure in the fluid and the solid displacement on the borehole wall show strong
dependence on frequency and incidence angle, even at very low frequencies. Strong
resonance occurs in the fluid for an SV incidence at angle δ = cos[superscript -1]β/C[subscript T] where CT is the tube wave velocity in a cased borehole. This resonance is prominent even at a very high frequency and large incidence angle because the tube wave velocity is raised well above the formation shear velocity by the steel pipe. This behavior is very different from that in an open borehole. At a particular angle of incidence of a plane P wave, the pressure in the fluid is near zero at low frequencies. This angle is dependent on the casing thickness and can be computed exactly. In general the casing behaves like a shield in such a way that the amplitude of both pressure in the fluid and solid motion on the borehole wall are reduced compared to those in an open borehole.ERL/nCUBE Geophysical Center for Parallel PrecessingMassachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu
Pressure in a fluid‐filled borehole caused by a seismic source in stratified media
No full textA method for numerically simulating hydrophone vertical seismic profiles (VSP) and crosswell data measured in a fluid-filled borehole (either open or cased) embedded in stratified media is presented. The method makes use of both the borehole coupling theory and the global matrix formulation for computing synthetic seismograms in a stratified medium. The global matrix formulation is used to calculate the stress field at the borehole location. Borehole coupling theory is then employed to obtain the pressure in the borehole fluid. Comparisons with exact solutions for an open borehole
in a homogeneous and unbounded formation show that this method is accurate for frequencies below 2 kHz. This method is used to model the Kent Cliffs hydrophone VSP data, where good agreement between the numerical simulations and the field measurements has been found, in both traveltimes and rms amplitudes of the direct P-wave. Examples show that this method is efficient and accurate, and can be applied to model VSP and crosswell experiments using an array of hydrophones.United States. Department of Energy (Grant No. DE-FG02-86ER1363)Reservoir Delineation ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory (nCUBE/ERL Geophysical Center for Parallel Processing
Comparison between a phenomenological approach and a morphoelasticity approach regarding the displacement of extracellular matrix
No full textPlastic (permanent) deformations were earlier, modeled by a phenomenological model in Peng and Vermolen (Biomech Model Mechanobiol 19(6):2525–2551, 2020). In this manusctipt, we consider a more physics-based formulation that is based on morphoelasticity. We firstly introduce the morphoelasticity approach and investigate the impact of various input variables on the output parameters by sensitivity analysis. A comparison of both model formulations shows that both models give similar computational results. Furthermore, we carry out Monte Carlo simulations of the skin contraction model containing the morphoelasticity approach. Most statistical correlations from the two models are similar, however, the impact of the collagen density on the severeness of contraction is larger for the morphoelasticity model than for the phenomenological model.Numerical Analysi
[[alternative]]The study of the ocean sport’s attraction, service quality and behavioral consequences in Peng-hu
No full text[[abstract]]The main purpose of this study were to explore the relations between the ocean sport’s attraction, service quality and behavioral consequences in Peng-hu. The researcher applied the questionnaire of “the ocean sport’s attraction, service quality and behavioral consequences in Peng-hu “ and I drew 500 visitors as the research samples who participated in ocean sports in Peng-hu during August and September in 2005. The data collected from valid questionnaires were analyzed by descriptive statistics, Pearson’s product moment correlation, stepwise multiple regression analysis and canonical correlation analysis. The results are as followed:
1. The ocean sports in Peng-hu attracted visitors to a certain degree and the whole service quality is comfortable to them.
2. The relationship between the ocean sport’s attraction and service quality in Peng-hu was positive to a certain degree, and the higher service quality is, the greater ocean sport’s attraction in Peng-hu is.
3. Within each factors of the ocean sport’s attraction and the service quality, “the specialty of designing activity “and “the comfort of the environment “ had the best prediction to the loyalty of behavioral consequences; “advertisement and spread of the main activity” and “personal requirement” explain “better than any other factors.
4. The canonical correlation analysis of the study was the ocean sport’s attraction and service quality in Peng-hu have a high and positive correlation with the loyalty of behavioral consequences; the ocean sport’s attraction in Peng-hu has a moderate and positive correlation with the tendency of complaint of behavioral consequences.
Based on the results, we suggest the related organizations should:（1）strengthen the diversity of activity and develop package route of travel;（2）enforce the communication of information and promote the quality of complementary service;（3）integrate the resources and set up conservation area to build the continuous managing mold of ocean sport’s tourism.
For further research in the future: incorporate the follow-up issue of ocean sport’s tourism with profound interview and pay equal attention to qualitative research and quantitative research. Extending the subjects to related organization administrators、managers and dealers、local people and foreign tourist etc. and proceeding a comprehensive research.
Haphsa sita Wang & Peng & Wei 2021, comb. n.
No full text4. Haphsa sita (Distant, 1881) comb. n. Cosmopsaltria sita Distant, 1881: 636. Khimbya sita Distant, 1906: 141. Changa sita Lee, 2016: 596. Haphsa stellata Lee, 2009b: 335; Lee, 2016: 596. Distribution. China (Guangxi), India, Vietnam. Remarks. This species was formerly attributed to Changa as the type species by Lee (2016), and the same author synonymized H. stellata Lee, 2009 with Changa sita (Distant, 1881) (Lee, 2016). In the present paper, we remove it to Haphsa based on morphological characterization and phylogenetic analysis (Fig. 4). Lee (2016) also transferred H. jsguillotsi (Boulard, 2005) to Changa, but we confirm it is a member of Haphsa (see below). Accordingly, Changa Lee, 2016 syn. n. is synonymized with Haphsa.Published as part of Wang, Siyue, Peng, Xiaodong & Wei, Cong, 2021, A review of the cicada genus Haphsa Distant, 1905 with the description of one new species from China (Hemiptera: Cicadidae) and a phylogenetic analysis of Haphsa and its allies, pp. 523-538 in Zootaxa 4991 (3) on page 530, DOI: 10.11646/zootaxa.4991.3.5, http://zenodo.org/record/504258
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