Superposition Of Pressure Research Articles

Stress sensitivity of sandstones and 4D applications

Variation of reservoir properties over production time frames is a complex superposition of pore pressure and saturation changes. For this reason, time-lapse (4D) seismic projects to monitor reservoir changes are always subject to the nonuniqueness of interpretation, even if the quality of the 4D signal is good and the magnitude of stress/saturation change is strong. While saturation variations can be adequately handled by Gassmann's theory, stress changes due to pore-pressure depletion within the reservoir are less well understood and multiple conceptual models exist to account for this effect on seismic rock properties.

The discontinuous enrichment method for elastic wave propagation in the medium‐frequency regime

AbstractThe discontinuous enrichment method (DEM) is specified and developed for the solution of two‐dimensional elastic wave propagation problems in the frequency domain. The classical finite element polynomial approximation of the displacement field is enriched by the superposition of discontinuous pressure and shear wave functions. The continuity of the solution across the element interfaces is weakly enforced by suitable Lagrange multipliers. Higher‐order rectangular DEM elements are constructed and benchmarked against the standard higher‐order polynomial Galerkin elements for two‐dimensional problems in the medium frequency regime. In general, it is found that for such applications, DEM can achieve the same accuracy as the p finite element method using a similar computational complexity but with about 10 times fewer degrees of freedom. This highlights the potential of this hybrid method for problems where the scale of vibrations is very small compared to the characteristic dimension of the physical medium. Copyright © 2006 John Wiley & Sons, Ltd.

Effects of hydrostatic pressure on the flow and fracture of a bulk amorphous metal

Abstract The flow and fracture behaviour of a Zr-Ti-Ni-Cu-Be bulk amorphous metal have been determined in tension and compression at room temperature with levels of superimposed hydrostatic pressure ranging from 0.1 to 700 MPa. Metallographically polished cylindrical specimens tested in uniaxial tension and compression were utilized in the high pressure tests, while polished cylindrical torsion specimens were tested at 0.1 MPa (i.e. atmospheric pressure) in order to approach conditions of pure shear. All the tension and torsion tests, regardless of the level of superimposed pressure, exhibited linear elastic failure, as did the compression tests conducted with low levels (e.g. less than 450 MPa) of pressure. At the highest pressures (i.e. 450 MPa or higher), the compression tests exhibited elastic-perfectly plastic behaviour and an increase in the compressive elongation to fracture. The flow stress and fracture stress were not significantly affected by the superposition of pressure as failure occurred in ...

Performance evaluation of nanofiltration membranes for treatment of effluents containing reactive dye and salt

The main purpose of this work is to investigate the preliminary performance of nanofiltration membranes for treatment of effluents containing salt and reactive dye. The membranes, designated as ES20, NTR-729HF, and LES90, were kindly supplied by the Nitto Denko Corporation. ES20 and LES90 are negatively charged membranes. NTR-729HF, a substituted poly(vinyl alcohol) membrane, is neutral. Regardless of the feeds, LES90 provided the highest permeate fluxes, while ES20 gave the lowest flux. ES20 and LES90 membranes achieved the higher salt rejection than NTR-729HF. LES90, however, suffered a great loss in the salt rejection as the concentration of NaCl increased. The dye rejections of ES20 and LES90 are sufficient for the reuse of the permeate. The neutral NTR-729HF membrane exhibited lower dye retention than the charged membranes. For the feed containing salt and dye, the superposition of trans-membrane osmotic pressure and concentration polarization resulted in substantial flux decline. Nevertheless, with the presence of dye in the feed, the charged membranes were able to retain more salt. It was likely that a highly concentrated layer formed by the accumulation of dye near the membrane surface attributed to the higher salt rejection. An increase in the feed temperature contributed to a slight increase in the LES90 flux while the salt and dye rejections remained almost unchanged.

The Effect of Surface Contamination on Adhesive Forces as Measured by Contact Mechanics

ABSTRACTThe contact adhesive forces between two surfaces, one being a soft hemisphere and the other being a hard plate, can readily be determined by applying an external compressive load to mate the two surfaces and subsequently applying a tensile load to peel the surfaces apart. The contact region is assumed the superposition of elastic Hertzian pressure and of the attractive surface forces that act only over the contact area. What are the effects of the degree of surface contamination on adhesive forces? Clean aluminum surfaces were coated with hexadecane as a controlled contaminant. The force required to pull an elastomeric hemisphere from a surface was determined by contact mechanics, via the JKR model, using a model siloxane network for the elastomeric contact sphere. Due to the dispersive nature of the elastomer surface, larger forces were required to pull the sphere from a contaminated surface than a clean aluminum oxide surface.

A Theoretical Analysis of Mixed Lubrication by Macro Micro Approach: Part I—Results in a Gear Surface Contact

Mixed lubrication is a key to bring the performance analysis to the failure analysis in most tribological components. A macro-micro approach to mixed lubrication has been developed in the present model. The relation between the average contact pressure and the average gap for a typical rough contact patch is first determined numerically in micro scale. Using this relation, the average gap, average oil-film pressure, and average contact pressure in a mixed-lubricated elastohydrodynamic contact can be solved simultaneously in macro scale by treating the contact to be smooth. The total pressure is assumed a superposition of average asperity contact pressure and lubricant pressure. The new approach is simple, efficient and robust, and covers entire range of the load ratio, from unity (dry contact) to zero (full-film EHL). In addition, it can be used for a wide range of operating conditions and on a much larger contact area with a much less computing time than deterministic simulation of mixed lubrication. Implementation of the Fast Fourier Transform (FFT) allows for a rapid calculation of the elastic deformation and asperity con/act pressure. As a demonstration to this new approach, a parametric study of dimensionless speed, load and contact shape on the load ratio and gap ratio was conducted for a gear rough surface of the load ratio, from unity (dry contact) to zero (full-film EHL). In addition, it can be used for a wide range of operating conditions and on a much larger contact area with a much less computing time than deterministic simulation of mixed lubrication. Impletmentation of the Fast Fourier Transform (FFT) allows for a rapid calculation of the elastic deformation and asperity contact pressure. As a demonstration to this new approach, a parametric study of dimensionless speed, load and contact shape on the load ratio and gap ratio was conducted for a gear rough surface Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

Nonlinear Model of Vibrations in a Rotor-Bearings System

This article presents a theoretical model for the nonlinear description of vibrations occurring in the rotor-bearings-supports system. A new approach to the determination of viscous-elastic properties of the oil film that does not draw on the commonly used principle of superposition of pressure or hydrodynamic forces in the bearing is put forward. The dynamic features of the oil film are determined by means of nonlinear coefficients of stiffness and damping calculated by using a fast and modified perturbation method. The method applied to describe the oil filin properties enables us to take advantage of the equations of motion of the entire system derived on the basis of the finite element method. The theoretical model takes also into account the effect of heat transfer within the bearing. With regard to kinetostatic problems, the temperature distribution in the film is calculated on the basis of a sophisticated so-called diathermal model of the bearing that permits the determination of a mean dynamic viscosity of the oil, further applied to the problems of the system dynamics. A general calculation algorithm and a computer program consisting of two clearly separated parts, kinetostatic and dynamic, is described. This article also gives examples of experimental verification of the model at a special large-size test rig and presents the analysis of nonlinear vibrations of a real large turbo-set carried out with the help of the developed theoretical method and computer program.

A New Interpretation Model for Fracture-Callbration Treatments

Summary This paper introduces an interpretation model for fracture-calibration tests conducted in both low- and high-permeability reservoirs. The model is based on a detailed description of fluid flow into the porous medium with considerations of variable filtercake, non-Newtonian invasion effects, and superposition of fracture pressure. The leakoff rate is determined by the pressure profile instead of presumption of leakoff mode. This work, incorporating mass balance with principles of fluid and solid mechanics, provides a straight-line technique for determining formation permeability and fracture filtercake resistance. The determined pressure drops from the fracture face into the reservoir allow the separate computation of the compressibility-controlled component of leakoff and the combined filtercake and non-Newtonian invasion components. Leakoff is pressure-dependent. Case studies of actual treatments are provided to demonstrate the new model and its interpretation. Comparisons are made to elucidate the similarities and differences between the traditional method and the new method. The new method accounts for fluid leakoff more accurately, allows for better fracturing design, and is particularly attractive for the tip screenout fracturing (frac-pack) treatments conducted in medium-to-high permeability formations.

Estimate of the stress field in Kilauea's South Flank, Hawaii

SUMMARY We estimated stress and seismic strain tensors for the Kilauea volcano's south flank. The stress orientation inversion and the seismic strain calculation were performed using fault-plane solutions. The principal stress and seismic strain directions are approximately uniformly distributed in space and time during the interval covered by the data. However, the 01,03 plane is approximately orthogonal to the plane. Therefore, a weak layer may exist beneath the south flank. o1 has a plunge of 59 and an azimuth of 152, with a 10 95 per cent confidence range. We also developed a stress magnitude inversion to estimate magnitudes of boundary and interior stresses. In this inversion, the principal stress directions were taken as constraints in the seismic volume, and surface geodetic observations were used as data. The maximum magmatic pressure in Kilauea's rift zone is about 160 MPa. The direction of o1 can be interpreted as the superposition of hydrostatic stress (pgh) and magmatic pressure. Without the constraint imposed by the direction of ol, the estimated pressure is only 60 MPa. The distribution of magmatic pressure may be similar to that of pgh. In contrast, the upper rift zone may be in tension. The shear stress in the rift zone is about one order of magnitude smaller than the maximum compressive stress, supporting the interpretation of magmatic flow as fluid in dikes or channels. The combination of stress orientation inversion, seismic strain calculation, and stress magnitude inversion performed in this study provides a means by which to estimate the stress state in seismic areas.

Experiments and calculations on crack opening and leak rate of a pipe branch within the HDR-Program

Abstract In this paper experiments and calculations on crack opening and leak rates of a pipe branch are presented. The pipe branch has an artificial through-crack located in the weldment between nozzle and the larger pipe. A superposition of internal pressure and bending load is considered. The experiment was part of a series of experiments on straight pipes, branches and elbows, which were performed at the HDR-facility at Karlstein/Germany. For the pipe branch under consideration experimental and numerical results and comparisons between both are presented.

Fracture Toughness and the Effects of Stress State on Fracture of Nickel Aluminides

AbstractThe effects of stress state on the fracture behavior of Ni3Al, Ni3Al + B, and NiAl were determined using either notched, or fatigue-precracked bend bars tested to failure at room temperature, in addition to testing specimens in tension under superposed hydrostatic pressure. Although Ni3AI is observed to fail in a macroscopically brittle intergranular manner in tension tests conducted at room temperature, the fracture toughnesses (i.e. K IC presently obtained on Ni3Al exceeded 20 MPa1m and R-curve behavior was exhibited. In-situ monitoring of the fracture experiments was utilized to aid in interpreting the source(s) of the high toughness in Ni3Al, while SEM fractography was utilized to determine the operative fracture modes. The superposition of hydrostatic pressure during tensile testing of NiAl specimens was observed to produce increased ductility without changing the fracture mode.

Friction and Heat Transfer Characteristics of Helical Turbulent Air Flow in Annuli

Friction and Nusselt number data have been measured and semi-empirically evaluated for twisted tape generated helical flow in annuli. Results have been obtained for radius ratios of 0.41 and 0.61 and twist ratios of ∞, 5.302, 5.038, and 2.659. The increase in pressure drop and heat transfer rates obtained are comparable to those reported for twisted tape generated swirl flow in tubes. Also, for the same heat transfer rates the pumping power requirements compare favorably with those for empty annuli. The analytical predictions based on the principle of superposition of pressure drops and analogy between heat and momentum transfer have yielded excellent predictions for y = ∞ and 5.302 but somewhat poor agreement at y = 2.659.

Elemental Powder Approaches to Ni3Al-Matrix Composites

Reactive sintering and hot isostatic compaction of mixed elemental powders have been combined to fabricate full density NiAl intermetallic-matrix composites. This process involves the formation of the matrix compound from its elemental constituents through an exothermic reaction. Dispersed ceramic phases inhibit direct consolidation, necessitating superposition of external pressure via hot isostatic compaction to obtain full density. The latter process is termed reactive hot isostatic pressing (RHIP). Because of its flexibility and low cost, this fabrication process merits attention as a means of preparing monolithic compounds and intermetallic-matrix composites.

On crack paths

Crack paths are discussed from several different points of view. The remarkable reproducibility of crack paths, especially the frequent occurrence of straight cracks, is considered. The general dominance of mode I growth at mixed mode loading (via kinking or tilting of the crack edge) is examined, and it is shown that mode I growth can be suppressed by superposition of a high pressure. Mode I growth is scarcely combineable with mode II or III, because of different micromechanisms, whereas a mixture of modes II and III growth appears to be possible. Directional stability of straight crack paths is also analysed with special reference to the importance of a meaningful definition of the concept itself. Finally crack branching is briefly discussed.

Temperature- and wind-induced air flow patterns in a staircase. Computer modelling and experimental verification

The typical infiltration load for a residential building has been found to range from one-third to one-half of the total space conditioning load. However, most infiltration measurements have been made on single-family houses. Information about the role of infiltration in the energy consumption of large buildings is limited. Furthermore, the prediction of infiltration rates in high-rise buildings is a complex problem. The forces that drive this flow result from the superposition of wind pressure on the faces of the building and the stack effect across the height of the building. Infiltration models have shown the latter effect to be significant in single-family residences, particular in colder climates and, consequently, the stack effect is even greater in high-rise buildings. For this work, we performed tracer gas and fan pressurization measurements on a 30 m tall University of California dormitory in order to determine the importance of both wind and stack effect upon infiltration. Measured pressure and tracer gas distributions were compared with those from a predictive infiltration computer model for high-rise buildings. To study the influence of the air flow pattern around the building, this model uses various wind velocity profiles characteristic of urban areas and different sets of surface pressure coefficients derived from wind tunnel experiments.

The influence of hydrostatic pressure on the flow stress and ductility of a spherodized 1045 steel

The flow stress of a spheroidized 1045 steel was found to increase linearly with superimposed hydrostatic pressure in accord with published results on other iron-based materials. The nucleation and growth of voids at carbide particles was severely retarded by the superposition of pressure. In tests conducted under constant pressure, the final fracture strain was observed to increase linearly with pressure and the dimple size on the fracture surface to decrease linearly with pressure. Metallographic studies have been performed to determine the influence of pressure on damage accumulation. In interrupted tests where pressure was applied after a prestrain of 0.9 without pressure, the ductility was increased to values similar to those achieved in specimens deformed continuously under pressure.

Creep of organic glass under shear with superposition of hydrostatic pressure

Creep of organic glass under shear with superposition of hydrostatic pressure

The pressure and temperature effects on brittle-to-ductile transition in PS and PMMA

Abstract : Tensile experiments in polystyrene (PS) and poly(methyl methacrylate) (PMMA) conducted at constant strain rate over a wide range of pressure and temperature have shown that a brittle to ductile transition is induced in these amorphous polymers by the superposition of hydrostatic pressure as well as by the raise of the experimental temperature. A detailed stress-strain analysis permits explanation of the mechanism for the brittle to ductile transition in terms of interaction between two competing processes of plastic yielding -- crazing and shear banding phenomena. The crazing and shear banding processes respond quite differently to changes of pressure or temperature. The evidence that the brittle to ductile transition pressure becomes lower with increasing temperature refutes a previously suggested concept that the transition relates primarily to mechanical relaxation phenomena.

Piezo-remanent magnetization of lunar rocks

Characteristics of the piezo-remanent magnetization (PRM) of lunar rocks are particularly interesting in comparison with the PRM of terrestrial rocks, because ferromagnetic constituents in lunar materials are metallic iron grains whose average magnetostriction coefficient\((\bar \lambda )\) is negative. Experimentally observed characteristics of the PRM of lunar rocks are substantially the same as those of the PRM of terrestrial rocks and magnetites, in which\(\bar \lambda \) is positive. These experimental results indicate that the acquisition mechanism of PRM is due to a non-linear superposition of the magnetoelastic pressure upon the magnetostatic pressure on both sides of the 90° domain walls in ferromagnetic particles, as suggested by Nagata and Carleton.