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Realistic Boundary Conditions (realistic + boundary_condition)

Distribution by Scientific Domains
Engineering50%

Selected Abstracts

Modelling poroelastic hollow cylinder experiments with realistic boundary conditions

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2004
S. Jourine
Abstract A general poroelastic solution for axisymmetrical plane strain problems with time dependent boundary conditions is developed in Laplace domain. Time-domain results are obtained using numerical inversion of the Laplace transform. Previously published solutions can be considered as special cases of the proposed solution. In particular, we could reproduce numerical results for solid and hollow poroelastic cylinders with suddenly applied load/pressure (Rice and Cleary, Rev. Geophys. Space Phys. 1976; 14:227; Schmitt, Tait and Spann, Int. J. Rock Mech. Min. Sci. 1993; 30:1057; Cui and Abousleiman, ASCE J. Eng. Mech. 2001; 127:391). The new solution is used to model laboratory tests on thick-walled hollow cylinders of Berea sandstone subjected to intensive pressure drawdown. In the experiments, pressure at the inner boundary of the hollow cylinder is observed to decline exponentially with a decay constant of 3,5 1/s. It is found that solutions with idealized step-function type inner boundary conditions overestimate the induced tensile radial stresses considerably. Although basic poroelastic phenomena can be modelled properly at long time following a stepwise change in pressure, realistic time varying boundary conditions predict actual rock behaviour better at early time. Experimentally observed axial stresses can be matched but appear to require different values for , and , than are measured at long time. The proposed solution can be used to calculate the stress and pore pressure distributions around boreholes under infinite/finite boundary conditions. Prospective applications include investigating the effect of gradually changing pore pressure, modelling open-hole cavity completions, and describing the phenomenon of wellbore collapse (bridging) during oil or gas blowouts. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Applications of patient-specific CFD in medicine and life sciences

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6-7 2003
Rainald Löhner
Abstract Recent advances in medical image segmentation, grid generation, flow solvers, realistic boundary conditions, fluid,structure interaction, data reduction and visualization arc reviewed with special emphasis on patient-specific flow prediction. At the same time, present shortcomings in each one of these areas are identified. Several examples are given that show that this methodology is maturing rapidly, and may soon find widespread use in medicine. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Altered T Wave Dynamics in a Contracting Cardiac Model

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 2003
NICOLAS P. SMITH Ph.D.
Introduction: The implications of mechanical deformation on calculated body surface potentials are investigated using a coupled biophysically based model. Methods and Results: A cellular model of cardiac excitation-contraction is embedded in an anatomically accurate two-dimensional transverse cross-section of the cardiac ventricles and human torso. Waves of activation and contraction are induced by the application of physiologically realistic boundary conditions and solving the bidomain and finite deformation equations. Body surface potentials are calculated from these activation profiles by solving Laplace's equation in the passive surrounding tissues. The effect of cardiac deformation on electrical activity, induced by contraction, is demonstrated in both single-cell and tissue models. Action potential duration is reduced by 7 msec when the single cell model is subjected to a 10% contraction ramp applied over 400 msec. In the coupled electromechanical tissue model, the T wave of the ECG is shown to occur 18 msec earlier compared to an uncoupled excitation model. To assess the relative effects of myocardial deformation on the ECG, the activation sequence and tissue deformation are separated. The coupled and uncoupled activation sequences are mapped onto the undeforming and deforming meshes, respectively. ECGs are calculated for both mappings. Conclusion: Adding mechanical contraction to a mathematical model of the heart has been shown to shift the T wave on the ECG to the left. Although deformation of the myocardium resulting from contraction reduces the T wave amplitude, cell stretch producing altered cell membrane kinetics is the major component of this temporal shift. (J Cardiovasc Electrophysiol, Vol. 14, pp. S203-S209, October 2003, Suppl.) [source]

Heat capacity measurement by flow calorimetry: An exact analysis

AICHE JOURNAL, Issue 1 2009
T. K. Hei
Abstract The principal unsolved problem in flow calorimetry for liquid heat capacity measurement accurate accounting for heat loss from the heater lead-in wires as a function of system properties is analyzed by exact procedures for a five-zone calorimeter model. Temperature distributions in the fluid, and bi-metal wire are obtained from solutions of the governing third-order ODE in the fluid temperature for realistic boundary conditions. Conductive heat losses at the fluid exit qHL/q, are large (up to 20% of energy input), and physical property and flow rate dependent. A new correlating equation for (qHL/q,) gives separately and explicitly, for the first time, its dependence on calorimeter characteristics, flow rates and fluid properties. Experiments on five pure liquids confirmed the predictions of the theoretical model and produced Cp values in close agreement with literature data. Fluid friction and small convection heat losses (UiAi (,T)lm) were accounted for experimentally. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source]