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Viscoelastic Models (viscoelastic + models)
Selected AbstractsUSE OF NONLINEAR DIFFERENTIAL VISCOELASTIC MODELS TO PREDICT THE RHEOLOGICAL PROPERTIES OF GLUTEN DOUGHJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2001M. DHANASEKHARAN ABSTRACT Nonlinear viscoelastic models of the differential type, such as the Phan Thien Tanner model, White-Metzner model and Giesekus model were used to predict the steady shear, oscillatory shear and transient shear properties of gluten dough. The predictions were compared with new data and the experimental results of Wang and Kokini (1995b). The Phan-Thien Tanner model and the Giesekus model were used in eight modes to fit the relaxation modulus accurately. The White-Metzner model gave the best prediction for the steady shear properties as it used a Bird-Carreau dependence for the shear viscosity. The Phan-Thien Tanner model and the Giesekus model predicted the transient shear viscosity and the transient first normal stress coefficient better than the White-Metzner model. A consistent prediction of all the experimental data could not be obtained using a single model. [source] Post-seismic relaxation following the great 2004 Sumatra-Andaman earthquake on a compressible self-gravitating EarthGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2006Fred F. Pollitz SUMMARY The Mw, 9.0 2004 December 26 Sumatra-Andaman and Mw= 8.7 2005 March 28 Nias earthquakes, which collectively ruptured approximately 1800 km of the Andaman and Sunda subduction zones, are expected to be followed by vigorous viscoelastic relaxation involving both the upper and lower mantle. Because of these large spatial dimensions it is desirable to fully account for gravitational coupling effects in the relaxation process. We present a stable method of computing relaxation of a spherically-stratified, compressible and self-gravitating viscoelastic Earth following an impulsive moment release event. The solution is cast in terms of a spherical harmonic expansion of viscoelastic normal modes. For simple layered viscoelastic models, which include a low-viscosity oceanic asthenosphere, we predict substantial post-seismic effects over a region several 100s of km wide surrounding the eastern Indian Ocean. We compare observed GPS time-series from ten regional sites (mostly in Thailand and Indonesia), beginning in 2004 December, with synthetic time-series that include the coseismic and post-seismic effects of the 2004 December 26 and 2005 March 28 earthquakes. A viscosity structure involving a biviscous (Burgers body) rheology in the asthenosphere explains the pattern and amplitude of post-seismic offsets remarkably well. [source] AVO investigations of shallow marine sedimentsGEOPHYSICAL PROSPECTING, Issue 2 2001M. Riedel Amplitude-variation-with-offset (AVO) analysis is based on the Zoeppritz equations, which enable the computation of reflection and transmission coefficients as a function of offset or angle of incidence. High-frequency (up to 700 Hz) AVO studies, presented here, have been used to determine the physical properties of sediments in a shallow marine environment (20 m water depth). The properties that can be constrained are P- and S-wave velocities, bulk density and acoustic attenuation. The use of higher frequencies requires special analysis including careful geometry and source and receiver directivity corrections. In the past, marine sediments have been modelled as elastic materials. However, viscoelastic models which include absorption are more realistic. At angles of incidence greater than 40°, AVO functions derived from viscoelastic models differ from those with purely elastic properties in the absence of a critical angle of incidence. The influence of S-wave velocity on the reflection coefficient is small (especially for low S-wave velocities encountered at the sea-floor). Thus, it is difficult to extract the S-wave parameter from AVO trends. On the other hand, P-wave velocity and density show a considerably stronger effect. Attenuation (described by the quality factor Q) influences the reflection coefficient but could not be determined uniquely from the AVO functions. In order to measure the reflection coefficient in a seismogram, the amplitudes of the direct wave and the sea-floor reflection in a common-midpoint (CMP) gather are determined and corrected for spherical divergence as well as source and streamer directivity. At CMP locations showing the different AVO characteristics of a mud and a boulder clay, the sediment physical properties are determined by using a sequential-quadratic-programming (SQP) inversion technique. The inverted sediment physical properties for the mud are: P-wave velocity ,=1450±25 m/s, S-wave velocity ,=90±35 m/s, density ,=1220±45 kg/m3, quality factor for P-wave QP=15±200, quality factor for S-wave QS=10±30. The inverted sediment physical properties for the boulder clay are: ,=1620±45 m/s,,=360±200 m/s,,=1380±85 kg/m3,QP=790±660,QS=25±10. [source] USE OF NONLINEAR DIFFERENTIAL VISCOELASTIC MODELS TO PREDICT THE RHEOLOGICAL PROPERTIES OF GLUTEN DOUGHJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2001M. DHANASEKHARAN ABSTRACT Nonlinear viscoelastic models of the differential type, such as the Phan Thien Tanner model, White-Metzner model and Giesekus model were used to predict the steady shear, oscillatory shear and transient shear properties of gluten dough. The predictions were compared with new data and the experimental results of Wang and Kokini (1995b). The Phan-Thien Tanner model and the Giesekus model were used in eight modes to fit the relaxation modulus accurately. The White-Metzner model gave the best prediction for the steady shear properties as it used a Bird-Carreau dependence for the shear viscosity. The Phan-Thien Tanner model and the Giesekus model predicted the transient shear viscosity and the transient first normal stress coefficient better than the White-Metzner model. A consistent prediction of all the experimental data could not be obtained using a single model. [source] | ||||||||||