Non-uniform Pressure Distribution Research Articles

Moment of momentum equation for curvilinear free-surface flow

The control volume approach in fluid mechanics relies upon the conservation of energy, momentum and angular momentum. However, open channel flows are typically related to only conservation of energy and momentum. Thus, for flows of non-uniform velocity and non-hydrostatic pressure distributions, the number of unknowns is larger than that of equations for depth-averaged models. This gap resulted in semi-empirical approaches either using momentum or using energy conservation. However, a more fundamental depth-averaged model may be developed by accounting for angular momentum balance. This basic approach was largely overlooked in hydraulic practice. The generalized form of the control volume conservation laws in curvilinear flow are presented herein, including the angular momentum balance. The development is used to prove that the classical Boussinesq-type solution does not satisfy the angular momentum balance. A more general Boussinesq approach is considered and applied to the 2D free overfall, indicating its ability to reproduce the salient flow features.

Analysis of Contact Pressure between Rolls under Non-Symmetrical Roll Bending of UCM Cold Rolling Mill

. For UCM cold rolling mill, the intermediate roll shifting can enhance the ability of mill for better flatness control, but it will increase the non-uniform distribution of pressure between rolls, as result of a reduced roll life. In order to improve the contact state among rolls in rolling processes and to slow down the roll wear, the distribution of pressure between rolls under different forms of roll bending control has been calculated and analyzed by the influence function method in this paper. For the purpose of obtaining comprehensive information, not only the distributions of pressure between rolls with traditional work roll symmetrical bending and intermediate roll symmetrical bending have been analyzed, but also the distributions of pressure between rolls with non-symmetrical roll bending have been analyzed. All the analyses show that the work roll non-symmetrical bending as well as the intermediate roll non-symmetrical bending can play an important role in the slowing down of roll wear.

Toward Deterministic Material Removal and Surface Figure During Fused Silica Pad Polishing

The material removal and surface figure after ceria pad polishing of fused silica glass have been measured and analyzed as a function of kinematics, loading conditions, and polishing time. Also, the friction at the workpiece/lap interface, the slope of the workpiece relative to the lap plane, and lap viscoelastic properties have been measured and correlated to material removal. The results show that the relative velocity between the workpiece and the lap (i.e., the kinematics) and the pressure distribution determine the spatial and temporal material removal, and hence the final surface figure of the workpiece. In cases where the applied loading and relative velocity distribution over the workpiece are spatially uniform, a significant nonuniformity in material removal, and thus surface figure, is observed. This is due to a nonuniform pressure distribution resulting from: (1) a moment caused by a pivot point and interface friction forces; (2) viscoelastic relaxation of the polyurethane lap; and (3) a physical workpiece/lap interface mismatch. Both the kinematics and these nonuniformities in the pressure distribution are quantitatively described, and have been combined to develop a spatial and temporal model, based on Preston's equation, called Surface Figure or SurF. The surface figure simulations are consistent with the experiment for a wide variety of polishing conditions. This study is an important step toward deterministic full‐aperture polishing, allowing optical glass fabrication to be performed in a more repeatable, less iterative, and hence more economical manner.

Drag reduction in Stokes flows over spheres with nanostructured superhydrophilic surfaces

Nanostructured surfaces offer opportunities to modify flow induced drag on solid objects. Measurements of the terminal velocity reveal that the drag associated with laminar Stokes flows can be reduced for spheres with nanostructured superhydrophilic as well as superhydrophobic surfaces. Numerical simulations suggest that the formation of recirculating or nearly stagnant flow zones leads to significant reduction in the friction drag. Such reduction, however, is offset by an increase in the form drag that arises from nonuniform pressure distributions. Our work motivates further studies to optimally balance the friction and form drag and control resistance to laminar flows over objects with nanostructured surfaces.

Contrast distortion correction for photoacoustic image based on compensation for pressure distribution of sound field

The nonuniform energy density distribution of laser pulses leads to nonuniform pressure distribution of sound field on photoacoustic effect, and photoacoustic image would be distorted at the edge of the absorbed optical energy deposit area. In this paper, a new method for compensating the sound field pressure and correcting the photoacoustic image is reported and testified. Distribution of the photoacoustic pressure was measured with a phase-controlled focus array transducer, and the theoretic function of the photoacoustic pressure was extracted by fitting the distribution curve. The compensation weight factor of the photoacoustic pressure defined as a reciprocal of the theoretic function. Photoacoustic images of a simulation sample and an in vivo mouse brain were reconstructed by correcting with the pressure compensation weight factor. The experimental results showed that this method can uniform the contrast distribution and correct the edge distortion of the PA image, suggesting the potential application in vascular imaging.

Engineering a Titanium and Polycaprolactone Construct for a Biocompatible Interface Between the Body and Artificial Limb

Intraosseous transcutaneous amputation prostheses may be able to overcome the problems that stem from the nonuniform distribution of pressure seen in the conventional stump-socket prosthetic replacement devices. Transcutaneous devices have had limited success in amputees. By optimizing the attachment of the skin to the prosthetic, intraosseous transcutaneous amputation prostheses may become clinically viable options. This report details studies evaluating the development of a modified titanium construct with a specially machined surface to increase the adherence of tissue as well as scaffold. A computer-aided biology tool was used to fabricate polycaprolactone (PCL) scaffolds with a specific three-dimensional architecture. To extrude the PCL, it was dissolved in acetic acid to produce a 70% PCL liquid. A scaffold with a porosity of >50% was fabricated to have a tensile strength similar to skin. The presence of a specially machined surface greatly increased the adhesion of the PCL scaffold to the titanium constructs. When the 70% PCL was properly neutralized by heating at 55 degrees C and washing in 90% ethanol (EtOH), there was only a decrease (10%) in the viability of cells seeded onto the PCL constructs when compared with the cells in culture. The antibacterial properties of titanium dioxide anatase, silver nanoparticles, and chlorhexidine diacetate mixed in either type I collagen or hyaluronic acid (HA) were assessed. The addition of 1% (w/w) chlorhexidine diacetate in HA resulted in a 71% decrease in bacteria seen in nontreated HA. These results show promise in developing a novel engineered titanium and PCL construct that promotes effective adhesion between the titanium-skin interface.

Lateral Pressure Profile and Curvature Frustration in Mechanosensitive Channel Gating

Experimental evidence of a link between the function and the lipid environment of a membrane protein is increasingly available. While some of the experimental data can be explained by specific lipid-protein interactions, others can only be understood through protein induced perturbations in the membrane shape [1].In the latter case, the free-energy of a protein state is connected to membrane thickness (hydrophobic mismatch), membrane elasticity and curvature energy [1]. Connection to membrane elasticity and curvature energy can also be formulated using the so-called lateral pressure profile. A conformational change of a membrane protein has to do work against a non-uniform pressure distribution, i.e lateral pressure profile, inside a membrane [2]. Previously it has been shown that this work might be significantly larger than thermal energy by assuming simple conformation changes [3].Here we analyze the work done against the lateral pressure profile in mechanosensitive channel gating using a recently developed method to calculate a full 3D pressure field from molecular dynamics simulations [4]. For this purpose we have simulated closed and open states of a Mechanosensitive channel of large conductance (MscL) embedded in a DOPC bilayer using the MARTINI force field [5]. To analyze the effect of curvature frustration we have also performed simulations with symmetric and asymmetric lipid distributions. The advantage compared to previous analyzes [3] is that instead of a simple cone model, we have a more realistic model for different states of a mechanosensitive channel.[1] R. Phillips et al., Nature 495, 379-385 (2009).[2] R. Cantor, J. Phys Chem. B 101, 1723-1725 (1997).[3] P. S. Niemela et al., PLoS Comput Biol 3, 304-312 (2007).[4] O. H. S. Ollila et al., PRL 102, 078101 (2009).[5] S. J. Marrink et al., J. Phys. Chem. B 111, 7812-7824 (2007).

Violation of The Steady-State Friction behaviour of A Precise Hydraulic Pair Due To Imbalanced Radial Hydrostatic Force

Violation of The Steady-State Friction behaviour of A Precise Hydraulic Pair Due To Imbalanced Radial Hydrostatic Force W hat has been presented in the paper is a question of violation of the steady-state friction behaviour of a sliding hydraulic pair due to imbalanced radial hydrostatic force that affects the pair. The origins of hydrostatic radial forces in a sliding pair and the effect of this imbalance have been discussed. Computations have been outlined to illustrate how radial hydrostatic forces affect the cylindrical slide. Reasons for the cylindrical slide getting wedged in the sleeve have also been shown. Qualitative assessment of radial forces on the cylindrical slide located in the sleeve has been carried out, and the amounts of imbalance - shown. The qualitative assessment of radial forces in the precise hydraulic pair included a few characteristic variants of a non-uniform distribution of pressure of the working liquid in the annular clearance between the slide and the sleeve. The ways of reducing the imbalance of radial forces from liquid's pressure that affect the cylindrical slide of the hydraulic pair.

Energy Separation in High Subsonic Turbine Cascade

Trailing edge vortex shedding from a turbine cascade was numerically simulated for an exit isentropic Mach number of 0.79 and a Reynolds number of 2.8×106. The objective of this study is to clarify the time evolution of the vortex shedding process from a turbine blade and the mechanism of energy separation appearing in the wake. Calculations used a locally developed numerical code, employing a second-order AUSM scheme for inviscid numerical fluxes, a second-order implicit dual time method for time integration, and Detached Eddy Simulation for turbulence. Calculated results confirmed a non-uniform pressure distribution along the trailing edge, which was observed experimentally and different from a uniform distribution at low subsonic Mach number. The energy separation where instantaneous total temperature splits into hot and cold spots in the wake is caused by convection and vortex rotation. In addition, the formation and dissipation phases of vortices affect the energy separation.

Predicting the pressure distribution during roll compaction from uniaxial compaction measurements

The accuracy of predicting the pressure distribution in a roll compaction process using confined uniaxial compaction was assessed using microcrystalline cellulose (MCC, Avicel-PH102) as a model pharmaceutical powder. This involved an instrumented roll press and a range of roll gaps and roll speeds. The measured pressure-displacement data were described using the Johanson equation and a comparison was made with data obtained from uniaxial compaction. In addition, an existing uniaxial compression relationship was adapted to describe the data with the advantage that it can be applied to the whole pressure range especially at the lower pressure range. It has been shown that the predicted maximum pressure values using uniaxial compaction data are generally less than those measured. This was attributed to the more complex powder flow field in roll compaction compared to uniaxial compaction, which leads to (1) a non-uniform pressure distribution across the roll width with the pressure in the centre of the roll width being greater than the mean value and (2) a shear component of the flow field, and even the formation of shear band when the roll gap is small. Despite the differences between the measured and predicted pressure distributions, it is believed that uniaxial compaction is a useful method for screening different formulations in terms of ranking their expected performance in roll compaction.

Classical hydraulic jump: basic flow features

The dynamics of free surface flow is characterised by the so-called Froude number F, whose value F = 1 separates subcritical (F < 1) and supercritical (F > 1) flows. The transition from F < 1 to F > 1 is smooth and continuous, as observed in weir flow. However, the reverse transition from F > 1 to F < 1 is abrupt and discontinuous. In the present research the simplest approximation is proposed to describe hydraulic jump flow. The 2D flow features of the classical hydraulic jump are properly described and favorably compared with experimental data. Based on one-dimensional results, the hydraulic jump flow is rationally related to the critical flow condition and it is proved that the specific energy of the main flow reaches a minimum value at F = 1, whereas the total energy head decreases due to energy dissipation. Further results relate to the effects of air, and the non-uniform pressure and velocity distributions.

Nonlinear acoustic wave propagation in inhomogeneous moving media.

Extensive theoretical analysis, numerical studies, and both large-scale and laboratory-scale experiments have been dedicated to the problem of shock wave propagation in air during recent years. The current interest is motivated by supersonic civil transport which is necessarily affected by problems of sonic boom propagation in the atmosphere. The high-amplitude shock wave generated by a supersonic aircraft propagates through the atmosphere toward the ground and generates an acoustic field with non-uniform pressure distribution. Temporal characteristics and spatial structure of the sonic boom are influenced by aircraft trajectory, nonlinear effects, and diffraction and scattering by inhomogeneities. We review recent results from various teams based on a generalized KZK-type equation that includes the effects of a moving inhomogeneous media. Statistical analysis of the numerical solutions is performed, and the results are compared to experimental data obtained in the controlled laboratory-scale experiments conducted in the Ecole Centrale de Lyon anechoic wind tunnel.

Time-Dependent Shape Factors for Uniform and Non-Uniform Pressure Boundary Conditions

Matrix–fracture transfer functions are the backbone of any dual-porosity or dual-permeability formulation. The chief feature within them is the accurate definition of shape factors. To date, there is no completely accepted formulation of a matrix–fracture transfer function. Many formulations of shape factors for instantly-filled fractures with uniform pressure distribution have been presented and used; however, they differ by up to five times in magnitude. Based on a recently presented transfer function, time-dependent shape factors for water imbibing from fracture to matrix under pressure driven flow are proposed. Also new matrix–fracture transfer pressure-based shape factors for instantly-filled fractures with non-uniform pressure distribution are presented in this article. These are the boundary conditions for a case for porous media with clusters of parallel and disconnected fractures, for instance. These new pressure-based shape factors were obtained by solving the pressure diffusivity equation for a single phase using non-uniform boundary conditions. This leads to time-dependent shape factors because of the transient part of the solution for pressure. However, approximating the solution with an exponential function, one obtains constant shape factors that can be easily implemented in current dual-porosity reservoir simulators. The approximate shape factors provide good results for systems where the transient behavior of pressure is short (a case commonly encountered in fractured reservoirs).

Attenuation anisotropy in the linear-slip model: Interpretation of physical modeling data

This study attempts to validate a mathematical formalism of introducing attenuation into Schoenberg’s linear slip model. This formalism is based on replacing the real-valued weaknesses by complex-valued ones. During an ultrasonic experiment, performed at a central frequency of [Formula: see text] on a plate-stack model with [Formula: see text]-thick Plexiglas™ plates, the velocity and attenuation (inverse of the quality factor [Formula: see text]) of P-, SH-, and SV-waves are measured in directions from 25° to 90° with the symmetry axis for dry and oil-saturated models and loading uniaxial pressures of 2 and [Formula: see text]. The velocity and attenuation data are fitted by the derived theoretical functions. The values of the real and imaginary parts of the complex-valued weaknesses are estimated. Thereal parts of the weaknesses, which have a clear physical meaning (they affect the weakening of the material), are three times larger for the dry model than for the oil-saturated one. The imaginary parts of the weaknesses are responsible for attenuation; their values are an order of magnitude smaller than the real parts. The derived expressions for angle-dependent velocities and attenuations can be used to distinguish between dry and oil-saturated fractures. In particular, the P-wave attenuation function in the symmetry-axis direction (normal to fracture planes) is different in dry and saturated media. The experiment shows that the plate-stack model is inhomogeneous because of the nonuniform pressure distribution, which degrades the experimental results and creates difficulties in the inversion for the complex-valued weaknesses — particularly in joint inversion of P- and S-wave data.

Dismantling the lining of an electrolyzer cathode unit for aluminum production using hydraulic press equipment and diamond cutting tools

Technology is considered for dismantling the lining of a aluminum electrolyzer cathode unit for major overhaul directly within the electrolyzer building. In order to accelerate breakdown of the lining and reduce the effect of impact and vibration loads during dismantling on the neighbourhood during repair of the electrolyzer, cathode dismantling is performed using hydraulic press equipment for impact-free breaking of materials using diamond tools for cutting and boring. Acceleration of dismantling is achieved as a result of the use of hydraulic equipment making it possible to create within the electrolyzer cathode lining material local nonuniform pressure distribution providing crack formation breaking the integrity of the lining.

Spectral characteristics of unstable flow in the mixing layer of supersonic underexpanded jet over its initial region

An experimental study of spectral characteristics of unstable flow in the mixing layer of supersonic axisymmetric underexpanded jets with Mach number Ma = 1 is reported. The destabilization of the flow is related to the formation, in the mixing layer of the jets, of disturbances in the form of streamwise vortical structures of the Taylor — Goertler type. As a result, in the mixing layer there forms an azimuthally non-uniform stationary distribution of total pressure. The Fourier transform of azimuthal sweeps of non-uniformity in pressure distributions was used to calculate the amplitude-wave spectra. An analysis of the spectral characteristics has allowed us to evaluate the longitudinal increment of amplitude growth of the disturbances and their dependence on the wavenumber and on the nozzle pressure ratio. The range of wavenumbers in which the streamwise vortical structures grow in amplitude is identified.

Pressure Mapping Using a Double Layer Dielectric System

Results of investigation of a double layer dielectric system applied for distribution determination is discussed in the paper. The system consists of elastic and rigid solid dielectric layers. The trybo-charge is generated on the contact between the rough surface of the elastic and dielectric layers when the system is subjected to an external stress. It was shown that the local effective surface charge density on the rigid dielectric layer depends on the local value. The generated charge produces a proportional voltage across the solid dielectric layer after removing the elastic one (foam). This way, the may be converted into a voltage signal, which is 'memorised by a solid dielectric layer. Finally, the pressure map converted into 'an electric potential map can be visualised by potential distribution determination. The potential distributions obtained in the system for different cases of non-uniform distributions and different elastic layers are presented in the paper.

Finite Element Analysis of Composite Hardened Walls Subjected to Blast Loads

Problem statement: There is currently no standard design guideline to determine the number of composites needed to retrofit masonry walls in order to withstand a given explosion. Past design approaches were mainly based on simplified single-degree-of-freedom analysis. A finite element analysis was conducted for concrete masonry walls hardened with composites and subjected to short duration blast loads. Approach: The analysis focused on displacement time history responses which form the basis for retrofit design guidelines against blast loadings. The blast was determined from 0.5 kg equivalent TNT explosive at 1.83 m stand-off distance to simulate small mailroom bombs. Two and four layered retrofitted walls were investigated. Uncertainties in the finite model analysis of walls such as pressure distributions, effect of mid height explosive bursts versus near the ground explosive bursts and variations in modulus of elasticity of the wall were presented. Results: Uniformly distributed blast loads over the retrofitted wall height produced a small difference in peak displacement results when compared to the non-uniform pressure distribution. Ground explosive burst was shown to produce a 62.7% increase in energy and a higher peak displacement response when compared to mid-height explosive burst. Conclusion: The parametric study on the variation of modulus of elasticity of concrete masonry showed no significant effect on peak displacement affirming the use of the resistance deflection contribution of the composite in retrofit designs.

Control of 3003-H18 Aluminum Ultrasonic Consolidation

Ultrasonic consolidation of 150 μm thick 3003-H18 aluminum foil to a 3003-H18 build plate has been investigated. The effects of the normal load, vibrational amplitude, and sonotrode velocity on consolidation quality as characterized by the total linear weld density (LWD) including both edge and edge defects were examined utilizing two sequential three-level full factorial design of experiments at a constant build plate temperature of 150°C. These showed that the normal load and the vibrational amplitude have a significant influence on LWD, while the sonotrode rotational velocity has only a marginal effect. The formation of edge defects at the foil-build plate interface has been attributed to the nonuniform strain state across the foil width, while the central defects were related to sonotrode-foil contact pressure variations following the sonotrode pattern. In addition, LWD variations in ±10–20% were attributed to a nonuniform sonotrode-foil contact pressure distribution. Finally, representation of the total LWD as a function of the control parameters indicates that high total linear weld densities can be achieved with a control space bounded by high normal loads and intermediate to high vibrational amplitudes. Consideration of only central defects expands this control space allowing utilization of lower normal loads and vibrational amplitudes to achieve similar linear weld densities.

Energy and momentum under critical flow conditions

The definitions of the critical flow condition in open channel hydraulics, based on the momentum and the energy equations, differ from each other if non-hydrostatic pressure and non-uniform velocity distributions are considered. The concept of minimum energy and minimum momentum yields two distinct critical flow conditions, both in terms of their magnitude and their position. Consequently, for a given discharge, there are two singular points in the water surface profile, derived from the momentum and the energy principles, respectively. Extended momentum and energy equations for non-uniform velocity and non-hydrostatic pressure distributions are presented and the critical flow condition is generalized in relation to those conservation laws.