Search

The polymer air-drawing model of polyethylene terephthalate spunbonding nonwovens and the air jet flow field model in wide slot positive pressure spunbonding process have been established. The influence of the density and the specific heat capacity of polymer melt at constant pressure changing with polymer temperature on the fiber diameter have been studied, which is solved by introducing the numerical computation results of the air jet flow field of attenuator. It is simulated by means of the finite difference method. The predicted fiber diameter agrees with the experimental data. The effects of the processing parameters on the fiber diameter with the help of the image analysis method have been investigated. A higher inlet pressure, smaller slot width, and smaller jet angle will all cause higher z-axis position of air velocity and air pressure, which are beneficial to the air drawing of the polymer melt and thus to reducing the fiber diameter. The experimental results show that the agreement between the results and experimental data is better, which verifies the reliability of these models. The results present great prospects for this research in the field of computer assisted design of spunbonding process, technology, and equipment., INTRODUCTION Spunbonding technology is used commercially as a single-step process for converting polymer resin into nonwoven web, which dates back to 1950s [1-4], in spunbonding process, a molten stream of [...]

Rubber compounds have highly viscoelastic properties. The viscoelastic behaviors that have been exhibited during die extrusion include die swell and vortices in regions of sudden contraction. In this study, the application of rheological models to the capillary die extrusion process is investigated. Experiments and simulations were conducted using a fluidity tester and finite element analysis, respectively. The velocity distributions, velocity profiles, pressure drops, and vortices at the capillary die entrance were analyzed through computer simulations for various viscoelastic models [i.e., Phan-Thien and Tanner (PTT), Giesekus, POMPOM, simplified viscoelastic, and generalized Newtonian models]. Different models exhibited different pressure drops and different velocity profiles in the capillary die. Only the full viscoelastic models (PTT, Giesekus, and POMPOM) predicted the vortex at the corner of the reservoir that is the capillary die entrance. However, the simplified viscoelastic and generalized Newtonian models did not predict the vortex. All the viscoelastic models studied in this article predicted the die swells in various ways, and these were compared with the experimental results. The PTT and simplified viscoelastic models exhibited good agreement with the experimental results of the die swells., INTRODUCTION Computer simulations are used widely in science and engineering to solve problems and understand physical behaviors. The accuracy of the simulation results depends on the numerical computations and theoretical [...]

The recent discovery of more than a thousand planets outside our Solar System (1,2), together with the significant push to achieve inertially confined fusion in the laboratory (3), has prompted a renewed interest in how dense matter behaves at millions to billions of atmospheres of pressure. The theoretical description of such electron-degenerate matter has matured since the early quantum statistical model of Thomas and Fermi (4-10), and now suggests that new complexities can emerge at pressures where core electrons (not only valence electrons) influence the structure and bonding of matter (11). Recent developments in shock-free dynamic (ramp) compression now allow laboratory access to this dense matter regime. Here we describe ramp-compression measurements for diamond, achieving 3.7-fold compression at a peak pressure of 5 terapascals (equivalent to 50 million atmospheres). These equation-of-state data can now be compared to first-principles density functional calculations (12) and theories long used to describe matter present in the interiors of giant planets, in stars, and in inertial-confinement fusion experiments. Our data also provide new constraints on mass-radius relationships for carbon-rich planets., Mass-radius data for extrasolar planets combined with equation-of-state (EOS) models for constituent materials reveal that matter at pressures of several terapascals is quite common throughout the Universe (1,2,13). At several [...]

Passive earth pressure is recorded in two different tests, using a 6.7-m long, 2.9-m wide soil container. In these tests, sand with 7% silt content is densely compacted behind a moveable test wall to a supported height of 1.68 m (5.5 ft). Lateral load is applied to the vertical reinforced concrete wall section, which displaces freely along with the adjacent backfill in the horizontal and vertical directions. The recorded passive resistance is found to increase until a peak is reached at a horizontal displacement of 2.7-3% of the supported backfill height, decreasing thereafter to a residual level. In this test configuration, a triangular failure wedge shape is observed, due to the low mobilized wall-soil friction. Backfill strength parameters are estimated based on this observed failure mechanism. From these estimates, along with triaxial and direct shear test data, theoretical predictions are compared with the measured passive resistance. Using the test data, a calibrated finite-element model is employed to produce additional load-displacement curves for a wider range of practical applications (e.g., potential bridge deck displacement during a strong earthquake). Hyperbolic model approximations of the load-displacement curves are also provided. DOI: 10.1061/(ASCE)GT.1943-5606.0000386 CE Database subject headings: Passive pressure; Earth pressure; Retaining walls; Full-scale tests; Soil-structure interactions; Load factors; Simulation; Displacement. Author keywords: Passive pressure; Retaining wall: Large-scale tests; Soil-structure interaction.

Full explanation for the pathogenesis of syringomyelia (SM), a neuropathology characterized by the formation of a cystic cavity (syrinx) in the spinal cord (SC), has not yet been provided. It has been hypothesized that abnormal cerebrospinal fluid (CSF) pressure, caused by subarachnoid space (SAS) flow blockage (stenosis), is an underlying cause of syrinx formation and subsequent pain in the patient. However, paucity in detailed in vivo pressure data has made theoretical explanations for the syrinx difficult to reconcile. In order to understand the complex pressure environment, four simplified in vitro models were constructed to have anatomical similarities with post-traumatic SM and Chiari malformation related SM. Experimental geometry and properties were based on in vivo data and incorporated pertinent elements such as a realistic CSF flow waveform, spinal stenosis, syrinx, fexible SC, and flexible spinal column. The presence of a spinal stenosis in the SAS caused peak-to-peak cerebrospinal fluid CSF pressure fluctuations to increase rostral to the stenosis. Pressure with both stenosis and syrinx present was complex. Overall, the interaction of the syrinx and stenosis resulted in a diastolic valve mechanism and rostral tensioning of the SC. In all experiments, the blockage was shown to increase and dissociate SAS pressure, while the axial pressure distribution in the syrinx remained uniform. These results highlight the importance of the properties of the SC and spinal SAS, such as compliance and permeability, and provide data for comparison with computational models. Further research examining the influence of stenosis size and location, and the importance of tissue properties, is warranted. [DOI: 10.1115/1.4000089] Keywords: cerebrospinal fluid hydrodynamics, syringomyelia, Chiari malformation, hydrocephalus, fluid-structure interaction, spinal cord, subarachnoid space stenosis, syrinx, intracranial and spinal pressures, in vitro model

The National Institute of Standards and Technology (NIST) has redefined its gas pressure scale, up to 17 MPa, based on two primary standard piston gauges. The primary standard piston gauges [...]

The statistics of pressure fluctuations above and within three types of porous granular beds such as in gravel bed streams, rivers, and man-made canals are investigated by data gained via laboratory flume experiments. The flow conditions examined include a diversity of hydrodynamic loads that increase up to the point where single grains are moving from time to time, without causing severe modification to the bed texture and the related positions of the pressure sensors. Analysis is performed by means of histograms and spectral techniques and vertical intensity profiles. Two simplified equations are found that describe the vertical decrease for the standard deviation of the measured fluctuations indicating drag and lift, respectively, nondimensionalized by the mean bed shear stress. The former fluctuation is described by a crude linear fit, whereas the latter clearly shows that the lift intensity decreases exponentially in the porous bed with a decay distance of one to two times the equivalent grain roughness. Within the subsurface layer the standard deviation reaches a nonzero constant, mainly dominated by long-wave pressure fields that are convected in the outer flow. These findings can be used in future sediment transport models that use force balance approaches to determine incipient motion conditions. DOI: 10.1061/(ASCE)HY.1943-7900.0000251 CE Database subject headings: Open channel flow; Gravel; Turbulence; Power spectral density; Laboratory tests; River beds. Author keywords: Open-channel flow; Gravel bed; Turbulence; Pressure fluctuation; Spectral density; Interstitial.

An infinite-line probe is commonly used to measure unsteady pressure in high-temperature environments while protecting the pressure transducer. In this study, an existing theoretical model is used to derive the response of a waveguide pressure measuring system. An ambient temperature centrifugal compressor rig acts as an experimental source of fluctuating pressure. The compressor is operated at different discrete rotational speeds, and the blade-passing frequencies are used to obtain frequency response data. In the experiments, pressure waves attenuated at a rate faster than that predicted by the theoretical model for a 0.322 m (12 in.) sensor offset. Furthermore, the decay in the magnitude of the pressure oscillations accelerated at blade-passing frequencies above 9 kHz. A unique contribution of this study is to show that whereas the experimentally observed overall attenuation is broadly consistent with the theoretical predictions, pressure oscillations corresponding to individual blade passages may be disproportionally attenuated. [DOI: 10.1115/1.3159387]

The hydrant pressure head in an on-demand water distribution system can be subject to high fluctuation depending on the discharge flowing inside the pipes, with consequent impacts on the performance of on-farm irrigation systems. In this work, an Italian water distribution system was analyzed using the AKLA model at upstream discharges of 1,200 and 600 L x [s.sup.-1] to estimate the range of hydrant pressure variation. A computer model was developed, calibrated, and used to evaluate the performance of a drip irrigation system by relating the on-farm network with the hydrant characteristic curve at a certain operating status. The flow regulator within the hydrant played an important role in stabilizing the performance of the network at hydrant pressures higher than 27 m. At lower hydrant pressures, to apply the same amount of water, irrigation time must be extended by 17 and 95% for pressure heads of 20 and 12 m, respectively. These approaches described have great utility to ensure adequate irrigation management when water is delivered by pressurized on-demand systems. DOI: 10.1061/(ASCE)IR.1943-4774.0000170 CE Database subject headings: Network analysis; Hydraulic networks; Hydraulic pressure; Trickle irrigation; Water flow; Water distribution systems. Author keywords: Network characteristic curve; Hydrant pressure variation; Irrigation performance; Network analysis; Flow regulator.

Author(s): Kresimir Kumericki [sup.1] Author Affiliations: (1) Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia ARISING FROM V. D. Burkert et al. Nature 10.1038/s41586-018-0060-z (2018) Understanding the [...]

This paper presents new results for numerical predictions of air flow and pressure distribution in two commonly used elbows: (1) 90[degrees] mitered duct elbows with turning vanes having 0.05 m radius, 0.038 m vane spacing and (2) 90[degrees] mitered duct elbows without turning vanes, in 0.2 x 0.2 m (8 in. X 8 in.) duct cross section using the STAR-CD computational fluid dynamics (CFD) code. A k-[epsilon] turbulence model for high Reynolds number and k-[epsilon] Chen model were used for that purpose for comparative purposes. The simulation used 13 different Reynolds numbers chosen between the range of 1 X [10.sup.5] and 2 x [10.sup.6]. To validate the CFD results, the results of two experimental papers using guided vanes were compared with simulated vane runs under the same condition. The first experimental study used a 0.6 x 0.6 m (24 in. X 24 in.) square elbow with 0.05 m radius, 0.038 m vane spacing and air velocities at 2.54 m/s (500 fpm) and 25.4 m/s (5,000 fpm), the second experiment used a 0.81 X 0.2 m (32 in. X 8 in.) rectangular elbow geometry with 0.05 m radius, 0.038 m vane spacing with air velocities from 10.16 m/s (2,000 fpm) to 13.97 m/s (2,750 fpm). For Reynolds numbers (1.00-2.00) x [10.sup.5] the pressure drop difference between vaned and unvaned elbows was found to be 35 Pa as compared to 145 Pa. The simulations also agreed reasonably well with published experimental results. For the 0.6X0.6 m (24 in. x 24 in.) square elbow and 0.81 X 0.2 m (32 in. X 8 in.) rectangular elbow with vanes, the difference in pressure drop was 3.9 and 4.1% respectively and indicates that CFD models can be used for predictive purposes in this important HVAC applications area. DOI: 10.1061/(ASCE)0733-9402(2009)135:4(119) CE Database subject headings: Flow simulation; Velocity profile; Predictions; Air flow.

A detailed review and analysis of the hydrodynamic characteristics of laminar developing and fully developed flows in noncircular ducts is presented. New models are proposed, which simplify the prediction of the friction factor--Reynolds product f Re for developing and fully developed flows in most noncircular duct geometries found in heat exchanger applications. By means of scaling analysis it is shown that complete problem may be easily analyzed by combining the asymptotic results for the short and long ducts. Through the introduction of a new characteristic length scale, the square root of cross-sectional area, the effect of duct shape has been minimized. The new model has an accuracy of [+ or -]10% or better for most common duct shapes when nominal aspect ratios are used, and [+ or -]3% or better when effective aspect ratios are used. Both singly and doubly connected ducts are considered. [DOI: 10.1115/1.4000377] Keywords: laminar flow, noncircular ducts, hydrodynamic entrance length, developing flow, modeling, pressure drop

This paper discussed the computational accuracy of roughsurface point-contact isothermal elastohydrodynamic lubrication (EHL) analysis by investigating the effects of differential scheme, viscosity-pressure, and shear-thinning models. An EHL experiment with multitransverse ridges was employed as simulated target. Four differential schemes, including the combined and the separate first-order and second-order backward schemes, were investigated. It is found that the separate second-order backward scheme offers the best results based on the comparison with the experimental data, with which two roughness derivatives may be fully or partially canceled each other; thus, the discretization error induced by roughness can be reduced. The consistency of differential schemes is an important issue for the separate schemes. The Yasutomi free-volume viscosity-pressure model and the Eyring rheological model are found to yield the numerical simulations the closest to experimental results. [DOI: 10.1115/1.2842245] Keywords: EHL, differential schemes, viscosity-pressure models, rheological models

Contours of surface texture of contact faces are not always parallel to the directions of the axis in solving Reynolds equations with finite difference method, and this often induces significant pressure saw-tooth effect, which results in an unignored analysis error. In this paper, pseudo-nine-point finite difference, as a new finite difference method, is introduced to solve the lubrication numerical problem of pressure saw-tooth. Also, application is carried out in gas lubrication of hard disk systems to verify the validity of the new method. In analysis, pressure distributions and gas floating forces are calculated for two different types of sliders, and the astringency and efficiency of the new method is discussed. Numerical results show that the pseudo-nine-point finite difference method can restrain pressure saw-tooth evidently, and presents better astringency and efficiency than the traditional five-point finite difference method. With the increase in mesh density, pressure distribution and gas floating force trend to steady. Also, numerical values of the floating force agree well with the experimental ones. [DOI: 10.1115/1.3195039] Keywords: pseudo-nine-point finite difference, pressure saw-tooth, gas lubrication

A real-time estimation of water distribution system state variables such as nodal pressures and chlorine concentrations can lead to savings in time and money and provide better customer service. While a good knowledge of nodal demands is prerequisite for pressure and water quality prediction, little effort has been placed in real-time demand estimation. This study presents a real-time demand estimation method using field measurement provided by supervisory control and data acquisition systems. For real-time demand estimation, a recursive state estimator based on weighted least-squares scheme and Kalman filter are applied. Furthermore, based on estimated demands, real-time nodal pressures and chlorine concentrations are predicted. The uncertainties in demand estimates and predicted state variables are quantified in terms of confidence limits. The approximate methods such as first-order second-moment analysis and Latin hypercube sampling are used for uncertainty quantification and verified by Monte Carlo simulation. Application to a real network with synthetically generated data gives good demand estimations and reliable predictions of nodal pressure and chlorine concentration. Alternative measurement data sets are compared to assess the value of measurement types for demand estimation. With the defined measurement error magnitudes, pipe flow data are significantly more important than pressure head measurements in estimating demands with a high degree of confidence. DOI: 10.1061/(ASCE)HY.1943-7900.0000086 CE Database subject headings: Estimation; Least squares method; Water distribution systems; Uncertainty principles; Limit analysis.

The performance of rigid surface structures such as concrete pavements and slabs-on-grade supported by a deteriorated subgrade and experiencing local contact loss is investigated experimentally and numerically in this study. A laboratory setup has been designed to facilitate the simulation of subsurface erosion and measure the changes in contact pressure at selected locations under a slab-on-grade supported on granular material. The presence of erosion voids under a slab-on-grade can lead to rapid increase in the contact pressure in the immediate vicinity of the void in addition to an increase in tensile stresses at the outermost fibers of the slab. This preliminary study suggests that efforts to detect and arrest the growth of erosion voids under slabs-on-grade should be made before the voids reach the size where significant loss of support develops and the tensile strength of the slab material is exceeded. DOI: 10.1061/(ASCE)GT.1943-5606.0000097 CE Database subject headings: Slabs; Soil erosion; Deterioration; Voids; Subgrades; Underground structures.

This paper presents the practical elastic settlement formulae for the eccentrically loaded surface footings resting upon an elastic mass. The presented closed-form solutions can be readily implemented into the practice allowing efficient and accurate prediction of elastic settlement under the rectangular footing which is subjected to the biaxial bending. The presented solutions are determined by evaluating the integration of strain expressions based on the Boussinesq stress equations. The common assumption of linear contact pressure in footing-soil interface is adopted for the solutions. The presented formulae are validated to be used for the settlement under any point of linear full-contact loading and their applicability to the current design process is demonstrated. The solutions are also developed for the theoretical cases where the location of incompressible soil layer is infinitely deep. The simplified influence factors are presented graphically and the numerical examples are provided for their practical use. In this respect, the paper represents a significant step forward in understanding of elastic settlement, rotation, and differential elastic settlement under eccentrically loaded footings. DOI: 10.1061/(ASCE)GT.1943-5606.0000113 CE Database subject headings: Settlement; Sand; Contact pressure; Footings; Eccentric loads.

A series of centrifuge model tests was conducted to investigate the behavior of pile groups of various sizes and configurations behind a retaining wall in very soft clay. With a 1.2-m excavation in front of the wall, which may simulate the initial stage of an excavation prior to strutting, the test results reveal that the induced bending moment on an individual pile in a free-head pile group is always smaller than that on a corresponding single pile located at the same distance behind the wall. This is attributed to the shadowing and reinforcing effects of other piles within the group. The degree of shadowing experienced by a pile depends on its relative position in the pile group. With a capped-head pile group, the individual piles are forced to interact in unison though subjected to different magnitudes of soil movement. Thus, despite being subjected to a larger soil movement, the induced bending moment on the front piles is moderated by the rear piles through the pile cap. A finite element program developed at the National University of Singapore is employed to back-analyze the centrifuge test data. The program gives a reasonably good prediction of the induced pile bending moments provided an appropriate modification factor is applied for the free-field soil movement and the amount of restraint provided by the pile cap is properly accounted for. The modification factor applied to the free-field soil movement accounts the reinforcing effect of the piles on the soil movement. DOI: 10.1061/(ASCE)GT.1943-5606.0000095 CE Database subject headings: Pile groups; Bending; Centrifuge models; Clays; Deflection; Excavation; Retaining walls; Soil pressure.

Pressure pulsations in the piping system of the reciprocating compressor produce excessive noise and even lead to damage in piping and machinery. Therefore, it is very important to predict precisely the pressure pulsation with large amplitude in the piping system. In this paper, the finite disturbance theory is used to solve the nonlinear partial differential equations that describe the unsteady one-dimensional compressible flow in the complex piping system. The solution is then compared with experimental results. The comparison shows that the finite theory fits the large pressure disturbance more precisely than the acoustic theory. [DOI: 10.111511.3085882] Keywords: pressure pulsation, piping system, reciprocating compressor, finite disturbance theory, acoustic theory

The effects of placing a slot through a two-dimensional Wortmann FX 63-137 airfoil in ground effect were examined using computational fluid dynamics. The geometric shape of the slot was varied in three different ways: the width of the slot (w/c = 0.02, 0.04, and 0.06), the angle of the slot with respect to the airfoil's chord line (d = 20, 30, and 40), and the position of the slot along the chord line, (x/c = O. 15, 0.20, and 0.25). In addition, the airfoil was tested at five different angles of attack: -3, 0, 5, 10, and 15 deg. The commercially available software Gambit 2.3.16 was used to create the computational grids. FLUENT 6.2.16 with the renormalized group k-e turbulence model was then used to simulate the flow. Pitch stability of the slotted airfoil was examined and results indicated that increasing the angle of attack of the slotted airfoil while in ground effect had a reduced increase in lift when compared with the lift generated by the baseline Wortmann FX 63-137 airfoil. Results also showed that the slot could be used to reduce center-of-pressure movement along the chord of the airfoil for the range of angles of attack investigated, thus improving the overall pitch stability of the airfoil. The slot geometry that produced a minimal center-of-pressure fluctuation was located at 20 % of the chord length from the leading edge with a width of 2 % and an angle of 20 deg between the slot and a line normal to the chord line. DOI: 10.2514/1.31246

This technical note describes the derivation of an analytical expression for the total active force on the retaining wall for c-[phi] soil backfill considering both the horizontal and vertical seismic coefficients. The results based on this expression are compared with those obtained from earlier analytical expressions for the active force for c-[phi] soil backfill under seismic conditions, and found to have a similar trend of variation. The parametric study shows that the inclination of the critical failure plane with the horizontal plane decreases with the increase in values of seismic coefficients; the decrease being more for their higher values. The total active force increases with the increase in value of horizontal seismic coefficient; while it decreases with the increase in value of vertical seismic coefficient except for a very high value of horizontal seismic coefficient. Design charts are presented for various combinations of horizontal and vertical seismic coefficients ([k.sub.h] and [k.sub.v]), and values of cohesion and angle of shearing resistance for estimating the total active force on the retaining wall for c-[phi] soil backfill for practical applications. DOI: 10.1061/(ASCE)GT.1943-5606.0000003 CE Database subject headings: Backfills; Earth pressure; Earthquakes; Retaining walls; Seismic loads.

The present work is a numerical investigation on waves generated by a pressure disturbance moving at constant speed in a channel with a variable cross-channel depth profile. The channel profile, which is uniform in the along-channel direction, has a deep trench located along the centerline of the channel, and shallow banks near the channel walls. Characteristic features upstream and downstream of the moving pressure disturbance are related to the parameters of the pressure disturbance and the cross-channel profile. Our numerical investigation is based on the COULWAVE long wave model. DOI: 10.1061/(ASCE)0733-950X(2009) 135:3(120) CE Database subject headings: Long waves; Solitary waves; Wave propagation; Shallow water; Channel flow; Topography; Cross sections; Pressure distribution.

Cyclic loading has been known to induce fluid flow and thus mechanotransduction in bones. In the past, four-point bending tests have been used exclusively in studying fluid flow in bones. In order to better understand the mechanism of deformation and fluid flow under loading, compression tests were done on trabecular bone specimens under drained and undrained conditions. In the drained tests, the volume change was observed, whereas in the undrained tests, excess pore fluid pressure was measured. Cyclic loading tests were conducted in addition to monotonic loading tests to observe the permanent volume change or excess pore fluid pressure with loading cycles. A fast loading rate gave a sharp rise in the excess fluid pressure compared to a slow loading rate. The strength and stiffness of the specimens appeared to deteriorate with an increased speed of loadings, but there was no appreciable difference between the results obtained from drained and undrained tests. The drained and undrained tests as described allowed a better understanding of bone behavior under loadings for a coupled stress-flow analysis. DOI: 10.1061/(ASCE)0733-9399(2009) 135:5(375) CE Database subject headings: Human factors; Biological properties; Mechanical properties; Deformation; Cyclic loads.

We here extend the theory of microporomechanics by Dormieux et al. to multiple pore spaces. As an application, we reveal, on the basis of a recently validated multiscale elastic model for bone tissues by Fritsch and Hellmich, the effects of multiple pore pressures in various, scale-separated pore spaces, on the overall behavior of the multiporous composite material. Thereby, our focus is on the lacunar pore space, and on its interplay with the pore spaces found further below: not only those between the mineral crystals (of some 10 nm characteristic pore size) but also those of the collagen molecules building up (micro-)fibrils (with a little more than 1 nm distance between these molecules). Our results clearly show that the interplay between pore pressure and skeleton deformation depends strongly on the loading direction and on the characteristic size of the pores--hence, we can conclude that the consideration of these strongly hierarchical and anisotropic effects in whole-organ simulations including fluid mass transport, would allow for valuable new insights into the ongoing discussion on poromechanobiology of bone. DOI: 10.1061/(ASCE)EM. 1943-7889.0000001 CE Database subject headings: Pore pressures; Elasticity; Foundations; Drainage; Material properties.

This paper describes experimental work performed at General Electric, Global Research Center to evaluate the performance and understand the risks of using dry low N[O.sub.x] (DLN) technologies in exhaust gas recirculation (EGR) conditions. Exhaust gas recirculation is viewed as an enabling technology for increasing the C[O.sub.2] concentration of the flue gas while decreasing the volume of the postcombustion separation plant and therefore allowing a significant reduction in C[O.sub.2] capture cost. A research combustor was developed for exploring the performance of nozzles operating in low [O.sub.2] environment at representative pressures and temperatures. A series of experiments in a visually accessible test rig have been performed at gas turbine pressures and temperatures, in which inert gases such as [N.sub.2]/C[O.sub.2] were used to vitiate the fresh air to the levels determined by cycle models. Moreover, the paper discusses experimental work performed using a DLN nozzle used in GE's F-class heavy-duty gas turbines. Experimental results using a research combustor operating in a partially premixed mode include the effect of EGR on operability, efficiency, and emission performance under conditions of up to 40% EGR. Experiments performed in a fully premixed mode using a DLN single nozzle combustor revealed that further reductions in N[O.sub.x] could be achieved while at the same time still complying with CO emissions. While most existing studies concentrate on limitations related to the minimum oxygen concentration (MOC) at the combustor exit, we report the importance of C[O.sub.2] levels in the oxidizer. This limitation is as important as the MOC, and it varies with the pressure and firing temperatures. [DOI: 10.1115/1.2982158]

An ex-vessel steam explosion may occur when, during a severe reactor accident, the reactor pressure vessel fails and the molten core pours into the water in the reactor cavity. A steam explosion is a fuel-coolant interaction process where the heat transfer from the melt to water is so intense and rapid that the timescale for heat transfer is shorter than the timescale for pressure relief This can lead to the formation of shock waves and production of missiles that may endanger surrounding structures. A strong enough steam explosion in a nuclear power plant could jeopardize the containment integrity and so lead to a direct release of radioactive material to the environment. In the article, different scenarios of ex-vessel steam explosions in a typical pressurized water reactor cavity are analyzed with the code MC3D, which is being developed for the simulation of fuel-coolant interactions. A comprehensive parametric study was performed by varying the location of the melt release (central and side melt pours), the cavity water subcooling, the primary system overpressure at vessel failure, and the triggering time for explosion calculations. The main purpose of the study was to determine the most challenging ex-vessel steam explosion cases in a typical pressurized water reactor and to estimate the expected pressure loadings on the cavity walls. Special attention was given to melt droplet freezing, which may significantly influence the outcome of the fuel-coolant interaction process. The performed analysis shows that for some ex-vessel steam explosion scenarios much higher pressure loads are predicted than obtained in the OECD program SERENA Phase 1. [DOI: 10.1115/1.3078789] Keywords: steam explosion, ex-vessel, reactor cavity, pressure load, severe accident

The paper will present an analytical model for the evaluation of the pressure and flow rate oscillations in a given axial inducer test facility. The proposed reduced order model is based on several simplifying assumptions and takes into account the facility design and the dynamic properties of the tested inducer. The model has been used for evaluating the dynamic performance of a prototype of the LE-7 engine liquid oxygen (LOX) inducer, in tests carried out under given external flow rate excitations. The main results of these calculations will be shown, including the expected oscillations under a wide range of operational conditions and the influence of facility design. Calculations showed that the only way to obtain the two linearly independent test conditions, necessary for evaluating the inducer transfer matrix, is by changing the facility suction line: Any other changes in the facility design would result ineffective. Some other important design indications provided by the analytical model will be presented in the paper. [DOI: 10.1115/1.3089535]

Recently, several studies on the dissipation of excess pore pressure in liquefied sandy grounds have been reported on evaluation of postliquefaction behavior of structures. To further contribute to the understanding of this complicated dynamic phenomenon, centrifuge tests were performed in this research to analyze the liquefaction behavior of level saturated sandy grounds. The test results showed that the excess pore pressure in the liquefied sand was dissipated by the combined process of the solidification of the sand grains and the consolidation of the solidified layer. Based on the test results, a nonlinear model for the solidified layer thickness versus time, i.e., the solidification velocity, was developed. A new dissipation model was also developed by combining the nonlinear solidification model with Scott's theory to improve the prediction for the time history of excess pore pressure. In addition, a method for evaluating the input parameters in the dissipation model was proposed by relating the parameters to the particle size and the relative density of soils. The proposed dissipation model properly estimated the dissipation of excess pore pressure with time observed in the centrifuge experiments. CE Database subject headings: Soil liquefaction; Soil consolidation; Solidification; Centrifuge models; Sand.

Bridge abutments typically contain a backwall element that is designed to break free of its base support when struck by a bridge deck during an earthquake event and push into the abutment backfill soils. Results are presented for a full-scale cyclic lateral load test of an abutment backwall configured to represent the dimensions (1.7 m height), boundary conditions, and backfill materials (compacted silty sand) that are typical of California bridge design practice. An innovative loading system was utilized that operates under displacement control and that assures horizontal wall displacement with minimal vertical displacement. The applied horizontal displacement ranged from null to approximately 11% of the wall height (0.11H). The maximum earth pressure occurred at a wall displacement of 0.03H and corresponded to a passive earth pressure coefficient of [K.sub.p]= 16.3. The measured force distribution applied to the wall from hydraulic actuators allowed the soil pressure distribution to be inferred as triangular in shape and the mobilized wall-soil interface friction to be evaluated as approximately one-third to one-half of the soil friction angle. Post-test trenching of the backfill showed a log-spiral principal failure surface at depth with several relatively minor shear surfaces further up in the passive wedge. The ultimate passive resistance is well estimated by the log-spiral method and a method of slices approach. The shape of the load-deflection relationship is well estimated by models that produce a hyperbolic curve shape. CE Database subject headings: Bridge abutments; Passive pressure; Seismic design; Lateral pressure; Backfills; Granular materials.

The present investigation focuses on assessing the predictive capabilities of state-of-the-art computational fluid dynamics for a generic fan-in-wing configuration by comparison with experimental data. The objective is to reproduce a short take off and landing or a transition-flight situation without ground effect. A rotating fan is placed in the wing plane, inside of the wing's rear part and close to the root section. The obtained experimental data include force measurements, surface pressure measurements, flowfield mapping using particle image velocimetry and wool-tufts visualization. A structured mesh of the entire configuration with minimum geometrical simplifications is used to perform unsteady Reynolds-averaged Navier-Stokes computations. The area surrounding the rotor blades is set up as sliding mesh to simulate the rotation. Because of the abrupt deflection of the flow by the fan, an unsteady recirculation area is generated above the rotor blades resulting in a highly distorted inflow. The blocking of the freestream by the jet exiting the fan's nozzle creates a back pressure affecting the internal aerodynamics. The jet rolls up in a counter-rotating vortex pair with considerable impact on the wing's aerodynamic performance. Time-averaged unsteady results over one fan revolution show a good agreement with the experimental data. The major turbulence phenomena are well predicted by the simulation.

The primary difficulty with obtaining high-fidelity pressure measurements is acoustical distortion within the various components of the pneumatic system. The method of Berg and Tijdeman is the de facto standard for the aerospace industry for calculating the frequency response of pressure-sensing systems. However, the model is complex, difficult to program, and inherently linked to the frequency domain. For many applications, a less complex time-domain model is desired, and considerable work has previously been performed on this topic. Unfortunately, existing low-order response models are not particularly accurate. These models are derived using simplifying assumptions that lose many of the salient features of the flow physics. This paper derives a second-order model directly from the Berg and Tijdeman solution and the model accurately describes the physical characteristics of the dominant response harmonic. The model is modified for application to both laminar and turbulent flow conditions. Frequency- and step-response comparisons are presented to demonstrate that the derived second-order model has superior response fidelity. Accuracies of model predictions are validated by a series of laboratory step-response experiments.

This paper describes the development of analytical models used to predict the response of bonded membrane retrofit concrete masonry walls subjected to out-of-plane impulse pressure loads. Full scale tests have shown significant improvement in the resistance of unreinforced concrete masonry walls retrofitted by membrane materials. The majority of the membrane retrofit concrete masonry wails survived compared to their unretrofitted counterparts that collapsed. Polymer membrane retrofit materials may be sprayed on, trowled on, or attached with adhesives to the tension face of the wall. Other membrane materials such as thin steel or aluminum sheets may be attached to the tension face of the wall using expansion screws or other structurally sound methods. Resistance functions previously presented by the writers for membrane retrofit concrete masonry walls are used in the development of the response. Single-degree-of-freedom equations are developed to predict the response of these walls to impulse pressure and the results of the analysis are compared with available full-scale tests. CE Database subject headings: Dynamic pressure; Membranes; Rehabilitation; Masonry; Walls; Concrete; Polymers.

This technical paper presents analytical expressions to estimate the probability function of head losses in any path of an on-demand branched irrigation network. They are developed for estimating the probability of pressure deficit of a given magnitude at any hydrant. They are also useful for examining the probability of a power deficit at a pumping station designed to guarantee service to a hydrant, as well as the head characteristic curve of the distribution system linked to a definite probability. All this quantified information is useful for decision making on network design and performance. The probabilities calculated with the developed expressions can be taken as complementary or alternative concepts to C1ement's classical design flow method, which is taken here as a benchmark for comparisons. Illustrative examples of network designs are presented to validate the proposed expressions. The least cost design solutions using C1ement's design flows are compared with design solutions here obtained to get the same probability of pressure deficit at the most unfavorable hydrants. The new solutions are less expensive because the flow constraint can be avoided. CE Database subject headings: Network analysis; Pipeline design; Pressure distribution; Probability distribution; Simulation models; Statistics; Water pipelines.

Tekscan pressure sensors are used in biomechanics research to measure joint contact loads. While the overall accuracy of these sensors has been reported previously, the effects of different calibration algorithms on sensor accuracy have not been compared. The objectives of this validation study were to determine the most appropriate calibration method supplied in the Tekscan program software and to compare its accuracy to the accuracy obtained with two user-defined calibration protocols. We evaluated the calibration accuracies for test loads within the low range, high range, and full range of the sensor. Our experimental setup used materials representing those found in standard prosthetic joints, i.e., metal against plastic. The Tekscan power calibration was the most accurate of the algorithms provided with the system software, with an overall rms error of 2.7% of the tested sensor range, whereas the linear calibrations resulted in an overall rms error of up to 24% of the tested range. The user-defined ten-point cubic calibration was almost five times more accurate, on average, than the power calibration over the full range, with an overall rms error of 0.6% of the tested range. The user-defined three-point quadratic calibration was almost twice as accurate as the Tekscan power calibration, but was sensitive to the calibration loads used. We recommend that investigators design their own calibration curves not only to improve accuracy but also to understand the range(s) of highest error and to choose the optimal points within the expected sensing range for calibration. Since output and sensor nonlinearity, depend on the experimental protocol (sensor type, interface shape and materials, sensor range in use, loading method, etc.), sensor behavior should be investigated for each different application. [DOI: 10.1115/1.3005165] Keywords: Tekscan, pressure sensor, calibration, accuracy, prosthetic joints

A finite strain micromorphic pressure-sensitive plasticity model is formulated starting with thermodynamically conjugate stresses and plastic deformation rates in the reduced dissipation inequality, written in the intermediate configuration. Isotropic linear elasticity and nonassociative Drucker--Prager plasticity with cohesion hardening/softening are assumed for the constitutive equations. The reduced dissipation inequality dictates three levels of plastic evolution: (1) evolution of [F.sup.p], the plastic part of the deformation gradient; (2) evolution of [[chi].sup.p], the plastic part of the microdeformation tensor; and (3) evolution of [bar.[nabla]][[chi].sup.p], the covariant derivative of [[chi].sup.p]. A semi-implicit time integration of the stress and plastic evolution equations is outlined after assuming small elastic deformations and Cartesian coordinates for the current configuration. CE Database subject headings: Plasticity; Strain; Pressure; Thermodynamics; Microstructure.

It has been recognized that the ductility demands on a superstructure might be reduced by allowing rocking behavior and mobilization of the ultimate capacity of shallow foundations during seismic loading. However, the absence of practical reliable foundation modeling techniques to accurately design foundations with the desired capacity and energy dissipation characteristics and concerns about permanent deformations have hindered the use of nonlinear soil-foundation-structure interaction as a designed mechanism for improving performance of structural systems. This paper presents a new 'contact interface model' that has been developed to provide nonlinear relations between cyclic loads and displacements of the footing-soil system during combined cyclic loading (vertical, shear, and moment). The rigid footing and the soil beneath the footing in the zone of influence, considered as a macroelement, ate modeled by keeping track of the geometry of the soil surface beneath the footing, along with the kinematics of the footing-soil system, interaction diagrams in vertical, shear, and moment space, and the introduction of a parameter, critical contact area ratio (A/[A.sub.c]); the ratio of footing area (A) to the footing contact area required to support vertical and shear loads ([A.sub.c]). Several contact interface model simulations were carried out and the model simulations are compared with centrifuge model test results. Using only six user-defined model input parameters, the contact interface model is capable of capturing the essential features (load capacities, stiffness degradation, energy dissipation, and deformations) of shallow foundations subjected to combined cyclic loading. CE Database subject headings: Shallow foundations; Ductility; Cyclic loads; Combined loads; Contact pressure.

The indicated mean effective pressure (IMEP) is typically used as an engine running quality metric. IMEP depends on cylinder pressure, which is costly to measure, therefore it is useful to estimate IMEP from currently measured crankshaft encoder data. In this paper, the difficulties in developing an optimal linear estimator from acceleration computed from crankshaft rotational speed and cylinder pressure data are discussed, and strategies are presented to reduce these difficulties. Estimating IMEP from crankshaft data requires the determination of which data to use in the estimator Without this step, the estimator can become unnecessarily complex due the inclusion of strongly correlated data points in the estimator. A strategy to determine the angular location of the acceleration points to use is presented and is shown to greatly reduce the estimator complexity without significantly affecting estimation error Additionally, while increasing the estimator order usually decreases the estimation error, it will be shown that increasing the estimator order can actually increase the estimation error. This effect is due to uncertainties in the gains of the estimator. These uncertainties in the gains can result from using limited training data to estimate the statistics necessary to compute the gains or when dealing with a nonstationary system. A method of reducing the effect of these uncertainties by optimizing the estimator order based on the number of available training data cycles is developed and demonstrated. [DOI: 10.1115/1.3023115]

The context of structural monitoring of concrete dams as part of hydropower assets management is described. A tool that fits well into this context is the control of the uplift pressure of concrete dams. A monitoring technique suitable for this purpose was developed based on an automated water-level measurement technique using time-domain reflectometry and standard air-dielectric coaxial cable sensors. The signal is interpreted automatically by applying a threshold method to determine the apparent water level, which is then used to calculate the uplift pressure. A field test at a concrete dam column displayed consistent results, which were used as input to a reliability-based stability safety analysis. The results show that this technique can be very useful for uplift pressure monitoring. The information determined can serve as input to the maintenance work as well as assist engineering decisions. CE Database subject headings: Dams, concrete; Uplift pressure; Structural reliability; Monitoring.

Between 2001 and 2002, a 6.4-m (21.0-ft) diameter corrugated steel pipe culvert was erected and buried under a 22.9-m (75.0-ft) highway embankment fill in Meigs County, Ohio. This steel pipe culvert was the first of its kind to be constructed in the southeastern region of Ohio. The culvert structure was selected by the Ohio Department of Transportation over an alternative of a 5 million conventional bridge structure, because it would cost about $3.4 million less. The field performance of the culvert was monitored by measuring the pressure distribution around the pipe, as well as the deflections of the pipe culvert during and after construction. The culvert study also included comparing measured field performance with numerical predictions given by the finite-element computer program CANDE-89. CANDE-89 with the slotted joint option had a limited ability to simulate the actual field behavior of the large-diameter multiplate culvert structure, especially in the earlier stages of construction. CE Database subject headings: Culverts; Steel pipes; Deflection; Soil pressure; Simulation; Computer analysis; Ohio; Measurement.

An experimental investigation was conducted to study the effects of increased ambient pressure (up to 6.89 MPa) and increased nozzle pressure drop (up to 2.8 MPa) on the cone angles for sprays produced by pressure-swirl atomizers having varying amounts of initial swirl. This study extends the classical results of DeCorso and Kemeny, (1957, 'Effect of Ambient and Fuel Pressure on Nozzle Spray Angle,' ASME Transactions, 79(3), pp. 607-615). Shadow photography was used to measure cone angles at x/[D.sub.0] = 10, 20, 40, and 60. Our lower pressure results for atomizer swirl numbers of 0.50 and 0.25 are consistent with those of DeCorso and Kemeny, who observed a decrease in cone angle with an increase in nozzle pressure drop, [DELTA]P, and ambient density, [[rho].sub.air] until a minimum cone angle was reached when [DELTA]P[[rho].sub.air.sup.1.6] ~100 MPa[(kg/[m.sup.3]).sup.1.6] (equivalent to 200 psi[(lbm/[ft.sup.3]).sup.1.6]). Results for atomizers having higher initial swirl do not match the DeCorso and Kemeny results as well, suggesting that their correlation be used with caution. Another key finding is that an increase in [DELTA]P[[rho].sub.air.sup.1.6] to a value of 600 MPa[(kg/[m.sup.3]).sup.1.6] leads to continued decrease in cone angle, but that a subsequent increase to 2000 MPa[(kg/[m.sup.3]).sup.1.6] has little effect on cone angle. Finally, there was little effect of nozzle pressure drop on cone angle, in contrast to findings of previous workers. These effects are hypothesized to be due to gas entrainment. [DOI: 10.1115/1.2939004] Keywords: pressure swirl, cone angle, nozzle pressure drop, ambient pressure, entrainment

Metallization of pure solid hydrogen is of great interest, not least because it could lead to high-temperature superconductivity, but it continues to be an elusive goal because of great experimental challenges. Hydrogen-rich materials, in particular, C[H.sub.4], Si[H.sub.4], and Ge[H.sub.4], provide an opportunity to study related phenomena at experimentally achievable pressures, and they too ate expected to be high-temperature superconductors. Recently, the emergence of a metallic phase has been observed in silane for pressures just above 60 GPa. However, some uncertainty exists about the crystal structure of the discovered metallic phase. Here, we show by way of elimination, that a single structure that possesses all of the required characteristics of the experimentally observed metallic phase of silane from a pool of plausible candidates can be identified. Our density functional theory and GW calculations show that a structure with space group P4/nbm is metallic at pressures >60 GPa. Based on phonon calculations, we furthermore demonstrate that the P4/nbm structure is dynamically stable at >43 GPa and becomes the ground state at 97 GPa when zero-point energy contributions are considered. These findings could lead the way for further theoretical analysis of metallic phases of hydrogen-rich materials and stimulate experimental studies. hydrogen-rich | metallization

Pressure drop through anisotropic porous mediumlike cylinder bundles is experimentally examined in turbulent flow regime. Three porosities, [epsilon] = 0.66, 0.82, and 0.90, are considered. The flow blockage by the cylinder bundles is varied, with the yaw angle ([alpha]) used as an anisotropic measure. When the yaw angle is fixed while the porosity is varied, the pressure drop behaves as predicted by the force balance model, consistent with the classic observation: The pressure drop is proportional to the square of the flow velocity with the empirical proportionality as a function of (1 - [[epsilon].sup.1/2])[[epsilon].sup.2] obtained from the force balance model compared to that of (1 - [epsilon])/[[epsilon].sup.3] from the hydraulic radius theory. On the other hand, for a given porosity, topological anisotropy of the cylinder bundles causes the sinusoidal response of the pressure drop to the variation of yaw angle. At [alpha] = 0 deg with a 60 deg period, the lowest pressure drop occurs from the most open configuration of the cylinder bundle whereas the largest flow blockage at [alpha] = 30 deg causes the highest pressure drop. This variation appears to result from an increase in the drag coefficient of each cylinder element in a harmonic manner.

Soil nailing has been widely used in many places in the world in the last two decades because of its technical and economical advantages. The nail--soil interface shear strength is an important parameter in soil nail design. This parameter is governed by a number of factors, among which the influence of the overburden pressure (or soil depth) is the most controversial. There are differing views concerning the effect of overburden on the nail--soil interface shear strength. In order to examine the influence of the overburden pressure, a series of laboratory pullout tests on soil nails installed in compacted completely decomposed granite fill have been conducted using two pullout boxes. Numerical simulations have also been carried out and the results are compared with the pullout test data. The procedures of the pullout tests and new features of the pullout boxes used are briefly described. Changes of the vertical stress in soil close to the nail throughout the course of soil nail installation and pullout are presented and discussed in detail. It is observed from the results of this study that the installation process of soil nail induced significant vertical stress changes in soil around the soil nails, and that the soil nail pullout shear resistance is independent of the overburden pressure (or soil depth). CE Database subject headings: Soil nailing; Shear resistance; Fills; Soil compaction; Shear strength; Soil pressure.

The development of expansion injection molding as new technology for producing thin plastic parts has raised questions about polymer melt behavior in the process of rapid high pressure compression and expansion. To investigate those phenomena, the new in-line injection molding machine mounted measurement system has been developed. Measuring nozzle equipped with hydraulically driven closing bolts and contact fast response pressure and infrared temperature sensors enabled us to measure the compression and expansion of polymer melts at different starting conditions. Results presented for high impact polystyrene and polyamide show that polymer melt temperature rise is linearly dependent on compression pressure as well as it is dependent on compression speed. Comparable effect of temperature fall has been recorded during the polymer expansion, resulting in no noticeable loss of dissipation energy during this reversible process. Measurements have been compared with modified 2-domain Tait equation of state. Curve fitting analysis to manufacturer's material data show that measurements fit well with the model, even at very high compression speeds. POLYM. ENG. SCI., 48:1815-1823, 2008. [C] 2008 Society of Plastics Engineers, INTRODUCTION Plastic products are indispensable in our everyday life. They are made out of different kind of polymeric materials, most commonly out of thermoplastic polymeric materials. Thermoplastic polymeric materials consist [...]

A normalized P-V curve is proposed for quantitative comparisons of quasistatic P-V curves from different sources, including data from different investigators, airway pressure-volume curves versus transpulmonary pressure-volume curves, normal versus injured respiratory system, and animal tests versus clinical data. Similarities and differences among five different data groups we analyzed are shown to be quantified through the nondimensional pressure range of an individual data set, combined with the magnitudes of two nondimensional parameters of the inflation limb, derived from a respiratory system model previously reported. [DOI: 10.1115/1.2913345] Keywords: pulmonary pressure-volume curve, respiratory system model, alveolar recruitment, lung injury, ARDS, similitude

Experimental studies on the hydraulics of flow through and over gabion-stepped weirs are presented. Two flow components were observed, i.e., base flow through the void between filled stones and overflow on the gabions. The energy loss ratios in the gabion-stepped weirs are greater than those in the corresponding horizontal stepped weirs by approximately 7, 10, and 14% for weir slopes of 30, 45, and 60[degrees], respectively. As a result, the velocity at the outlet is lower. Stone size and shape have little influence on the energy loss and flow velocity as compared to the increasing effect of the weir slope. The pressure acting on the step face for the gabion-stepped weirs is less than that of the horizontal steps owing to the cushioning effect generated by filled stones. To reduce pressure on a step face at a fixed discharge for different weir slopes, the void ratio of the filled stones should be low to allow a small amount of base flow. The pressure distribution pattern on the horizontal face of a step is provided. DOI: 10.1061/(ASCE)0733-9429(2008) 134:8(1147) CE Database subject headings: Weirs; Hydraulic structures; Overflow; Energy; Pressure measurement.

Numerical analysis of flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer (thereafter, heat exchanger), which will be used for hydrogen production, wherein the sulfur iodine thermochemical cycle is performed. To validate the numerical model, experimental investigation of the heat exchanger is accomplished. The study of the flow distribution in the base line design heat exchanger shows that the design has large-flow maldistribution and the reverse flow may occur at poor inlet and outlet manifold configurations. To enhance uniformity of the flow rate distribution among the heat exchanger internal channels, several improved designs of the heat exchanger manifolds and supply channels are proposed. The proposed designs have a sufficiently uniform flow rate distribution among the internal channels, with an appropriate pressure drop. [DOI: 10.1115/1.2911680] Keywords: CFD, pressure drop, fluid flow distribution, channel flow, gross flow maldistribution

A respiratory system model (RSM) is developed for the deflation process of a quasistatic pressure-volume (P-V) curve, following the model for the inflation process reported earlier. In the RSM of both the inflation and the deflation limb, a respiratory system consists of a large population of basic alveolar elements, each consisting of a piston-spring-cylinder subsystem. A normal distribution of the basic elements is derived from Boltzmann statistical model with the alveolar closing (opening) pressure as the distribution parameter for the deflation (inflation) process. An error minimization by the method of least squares applied to existing P-V loop data from two different data sources confirms that a simultaneous inflation-deflation analysis is required for an accurate determination of RSM parameters. Commonly used terms such as lower inflection point, upper inflection point, and compliance are examined based on the P-V equations, on the distribution function, as well as on the geometric and physical properties of the basic alveolar element. Keywords: pulmonary pressure-volume curve, respiratory system model, alveolar recruitment, lung injury, ARDS