Gypsum Mud Rheological Behavior

Gypsum muds are considered as the most important ones used in oil well drilling due to their thermal stability in addition to the durability of their ingredients. The main aim of this work is to study the effect of the gypsum mud compositions on their rheological behavior under the conditions of high-pressure and high temperature. Eleven samples of gypsum mud were tested using Fann viscometer model 50-C. All the tested samples had the same trend of reduction in both plastic viscosity and yield point with increasing temperature. The results showed that with 5 ppb of Q Broxine thermal degradation is obtained at approximately 150 0 F; this is due to the over treatment with thinner which result in more soluble solids and higher rheological properties while the decrement in NaOH concentration from 0.7 ppb to 0.35 ppb results in an increase in both yield point and plastic viscosity; this is due to the loss of OH-1 ions. Six rheological models were adopted: Bingham, power law, modified power law, Robertson stiff, modified Robertson stiff and Casson. Both Robertson stiff model and Casson model showed more acceptable values that fit the experimental data accurately.

Investigation of Velocity Profile in Time Dependent Boundary Layer Flow of a Modified Power-Law Fluid of Fourth Grade

This paper deals with the investigation of time dependent boundary layer flow of a modified power-law fluid of fourth grade on a stretched surface with an injection or suction boundary condition. The fluid model is a mixture of fourth grade and power-law fluids in which the fluid may display shear thickening, shear thinning or normal stress textures. By using the scaling and translation transformations which is a type of Lie Group transformation, time dependent boundary layer equations are reduced into two alternative ordinary differential equations systems (ODEs) with boundary conditions. During this reduction, special Lie Group transformations are used for translation, scaling and combined transformation. Numerical solutions have been carried out for the ordinary differential equations for various fluids and boundary condition parameters. As a result of numerical analysis, it is observed that the boundary layer thickness decreases as the power-law index value increases. It was also observed that for the fourth-grade fluid parameter, as the parameter increases, the boundary layer thickness decreases while the velocity in the y direction increases.

Effective Correlation of Stress and Thermal Effects on Porosity and Permeability of Naturally Fractured Formations by a Modified Power Law

Summary Effective theory and methodology are proposed and validated for accurate correlation of stress–dependent petrophysical properties of naturally fractured or induced–fractured reservoir formations by means of a matrix/fracture dual–compressibility treatment. Inspection of various experimental data indicates a sudden change in trends at a certain critical net effective stress in the stress dependence of petrophysical properties of porous rocks as a result of a stress shock caused by the opening or closing of fractures. The variation of petrophysical properties in fractured–rock formations subjected to stress loading/unloading and thermally induced stress occurs mainly by deformation of the fractures below the critical effective stress and the deformation of the matrix above the critical effective stress. The alteration of petrophysical properties and a slope discontinuity might also be experienced when the stress exceeds the onset of other rock–alteration/damaging processes, such as pore collapsing and grain crushing. Proper formulations of the relevant processes and special correlation methods are presented in a manner to capture this nature of the petrophysical experimental data obtained by testing of cores extracted from naturally fractured or induced–fractured reservoir–rock formations. The dependency of porosity and permeability of fractured–rock samples under stress because of thermal, hydraulic, and mechanical effects is represented accurately by a modified–power–law equation derived from a kinetics model as confirmed by effective correlations of various experimental data. It is shown that this new model represents the thermal effect better than the frequently used Arrhenius (1889) equation and Vogel–Tammann–Fulcher (VTF) equation (Vogel 1921; Fulcher 1925; Tammann and Hesse 1926).

Thermo-Mechanical Vibration Analysis of Imperfect Inhomogeneous Beams Based on a Four-Variable Refined Shear Deformation Beam Theory Considering Neutral Surface Position

In this disquisition, an exact solution method is developed for analyzing the vibration characteristics of porous functionally graded (FG) beams by considering neutral surface position and different thermal loadings via a four-variable shear deformation refined beam theory. Four types of environmental conditions through the z-axis direction are supposed as: uniform (UTR), linear (LTR), nonlinear (NLTR) and sinusoidal (STR) temperature rises. Mechanical properties of porous FG beams are supposed to vary through the thickness direction and are modeled via the modified power-law. The modified power-law is formulated using the concept of even and uneven porosity distributions. Since the variation of pores along the thickness direction influences the mechanical properties, porosity plays a key role in the mechanical response of FG structures. The governing differential equations and related boundary conditions of porous FG beams are subjected to temperature field that is derived by Hamilton's principle based on a four-variable refined theory which verifies shear deformation regardless of any shear correction factor. The Navier-type solution procedure is used to achieve the natural frequencies of porous-FG beams supposed to various thermal loadings which satisfies the simply-simply boundary condition. A parametric study is led to carry out the effects of material graduation exponent, porosity volume fraction, different porosity distribution, and thermal effect on dimensionless frequencies of porous FG beams. It is concluded that these parameters play noticeable roles in the vibration behavior of imperfect FG beams. Presented numerical results can be applied as benchmarks for future designs of imperfect FG structures with porosity phases.

The haptic and perceptional characteristics of an anthropomorphic curved soft finger structure

In recent decades, modeling of soft fingertips has fascinated a superior momentum in research initiatives concerned with development of an anthropomorphic soft finger tip. In design and development of soft fingertips, analysis of contact a characteristic plays a vital role on dexterous manipulation. This research work presents the results of the experimental investigation in relation to the formulations of contact area for soft fingertips pressed against assorted target profiles. A dimensionless parameter, curve factor Y (r/R) is introduced to derive a parametric relationship among the key parameters. It also addresses the growth of contact area of fingertips for five different combinations. From experimental observations, a modified power law equation with conversion factor (X) is proposed to interpolate the magnitude of contact area for different profiles.

Stability of Audiometric Thresholds for Children with Hearing Aids Applying the American Academy of Audiology Pediatric Amplification Guideline: Implications for Safety

Background: Children who wear hearing aids may be at risk for further damage to their hearing from overamplification. Previous research on amplification-induced hearing loss has included children using linear amplification or simulations of predicted threshold shifts based on nonlinear amplification formulae. A relationship between threshold shifts and the use of nonlinear hearing aids in children has not been empirically verified. Purpose: The purpose of the study was to compare predicted threshold shifts from amplification to longitudinal behavioral thresholds in a large group of children who wear hearing aids to determine the likelihood of amplification-induced hearing loss. Research Design: An accelerated longitudinal design was used to collect behavioral threshold and amplification data prospectively. Study Sample: Two-hundred and thirteen children with mild-to-profound hearing loss who wore hearing aids were included in the analysis. Data Collection and Analysis: Behavioral audiometric thresholds, hearing aid outputs, and hearing aid use data were collected for each participant across four study visits. Individual ear- and frequency-specific safety limits were derived based on the Modified Power Law to determine the level at which increased amplification could result in permanent threshold shifts. Behavioral thresholds were used to estimate which children would be above the safety limit at 500, 1000, 2000, and 4000 Hz using thresholds in dB HL and then in dB SPL in the ear canal. Changes in thresholds across visits were compared for children who were above and below the safety limits. Results: Behavioral thresholds decreased across study visits for all children, regardless of whether their amplification was above the safety limits. The magnitude of threshold change across time corresponded with changes in ear canal acoustics as measured by the real-ear-to-coupler difference. Conclusions: Predictions of threshold changes due to amplification for children with hearing loss did not correspond with observed changes in threshold over across 2–4 yr of monitoring amplification. Use of dB HL thresholds and predictions of hearing aid output to set the safety limit resulted in a larger number of children being classified as above the safety limit than when safety limits were based on dB SPL thresholds and measured hearing aid output. Children above the safety limit for the dB SPL criteria tended to be fit above prescriptive targets. Additional research should seek to explain how the Modified Power Law predictions of threshold shift overestimated risk for children who wear hearing aids.