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백형민,Adam W. Mix,A. Jeffrey Giacomin 한국유변학회 2014 Korea-Australia rheology journal Vol.26 No.2
For highly viscous fluids that slip in parallel sliding plate rheometers, we want to use a slightly convergingflow to suppress this wall slip. In this work, we first attack the steady shear flow of a highly viscousNewtonian fluid between two gently converging plates with no slip boundaries using the equationof motion in cylindrical coordinates, which yields no analytical solution. Then we treat the same problemusing the lubrication approximation in Cartesian coordinates to yield exact, explicit solutions for dimensionlessvelocity, pressure and shear stress. This work deepens our understanding of a drag flow througha gently converging slit of arbitrary convergence angle. We also employ the corotational Maxwell modelto explore the role of viscoelasticity in this converging shear flow. We then compare these analytical solutionsto finite element calculations for both Newtonian and corotational Maxwell cases. A worked examplefor determining the Newtonian viscosity using a converging shear rheometer is also included. Withthis work, we provide the framework for exploring other constitutive equations or other boundary conditionsin future work. Our results can also be used to design the linear bearings used for the parallel slidingplate rheometer (SPR). This work can also be used to evaluate the error in the shear stress that iscaused by bearing misalignment and specify the parallelism tolerance for the linear bearings incorporatedinto a SPR.
Baek, Hyung M.,Mix, Adam W.,Giacomin, A. Jeffrey 한국유변학회 2014 Korea-Australia rheology journal Vol.26 No.2
For highly viscous fluids that slip in parallel sliding plate rheometers, we want to use a slightly converging flow to suppress this wall slip. In this work, we first attack the steady shear flow of a highly viscous Newtonian fluid between two gently converging plates with no slip boundaries using the equation of motion in cylindrical coordinates, which yields no analytical solution. Then we treat the same problem using the lubrication approximation in Cartesian coordinates to yield exact, explicit solutions for dimensionless velocity, pressure and shear stress. This work deepens our understanding of a drag flow through a gently converging slit of arbitrary convergence angle. We also employ the corotational Maxwell model to explore the role of viscoelasticity in this converging shear flow. We then compare these analytical solutions to finite element calculations for both Newtonian and corotational Maxwell cases. A worked example for determining the Newtonian viscosity using a converging shear rheometer is also included. With this work, we provide the framework for exploring other constitutive equations or other boundary conditions in future work. Our results can also be used to design the linear bearings used for the parallel sliding plate rheometer (SPR). This work can also be used to evaluate the error in the shear stress that is caused by bearing misalignment and specify the parallelism tolerance for the linear bearings incorporated into a SPR.
Bauska, Thomas K.,Joos, Fortunat,Mix, Alan C.,Roth, Raphael,Ahn, Jinho,Brook, Edward J. Nature Publishing Group, a division of Macmillan P 2015 Nature geoscience Vol.8 No.5
The stability of terrestrial carbon reservoirs is thought to be closely linked to variations in climate, but the magnitude of carbon–climate feedbacks has proved difficult to constrain for both modern and millennial timescales. Reconstructions of atmospheric CO<SUB>2</SUB> concentrations for the past thousand years have shown fluctuations on multidecadal to centennial timescales, but the causes of these fluctuations are unclear. Here we report high-resolution carbon isotope measurements of CO<SUB>2</SUB> trapped within the ice of the West Antarctic Ice Sheet Divide ice core for the past 1,000 years. We use a deconvolution approach to show that changes in terrestrial organic carbon stores best explain the observed multidecadal variations in the δ<SUP>13</SUP>C of CO<SUB>2</SUB> and in CO<SUB>2</SUB> concentrations from 755 to 1850 CE. If significant long-term carbon emissions came from pre-industrial anthropogenic land-use changes over this interval, the emissions must have been offset by a natural terrestrial sink for <SUP>13</SUP>C-depleted carbon, such as peatlands. We find that on multidecadal timescales, carbon cycle changes seem to vary with reconstructed regional climate changes. We conclude that climate variability could be an important control of fluctuations in land carbon storage on these timescales.