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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 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.

The dynamics of unstart in a floor-mounted inlet-isolator model in a Mach 5 flow are investigated experimentally using particle image velocimetry and fast-response wall pressure measurements. The inlet compression is obtained with a 6-deg ramp and the isolator is a rectangular straight duct that is 25.4 mm high by 50.8 mm wide by 242.3 mm long. Unstart is initiated from the scram jet mode (fully supersonic in the isolator) by deflecting a motorized flap at the downstream end of the isolator. With the flap fully down, the particle image velocimetry data of the started flow capture the characteristics of the isolator boundary layers and the initial inlet reflected shock system. During unstart, the unstart shock system propagates upstream through the inlet-isolator. The particle image velocimetry data reveal a complex, three-dimensional flow structure that is strongly dependent on viscous mechanisms. Particularly, the unstart shock system propagates upstream and induces significant boundary-layer separation. Side-view particle image velocimetry data show that the locations of strongest separation during unstart correlate with the impingement locations of the initial inlet shock as it reflects down the isolator. For example, in the middle of unstart, the unstart shock system is associated with massive separation of the ceiling boundary layer that begins where the first inlet shock reflection impinges on the ceiling. The observation that separation increases at the inlet shock reflection impingement locations is likely due to the fact that the boundary layers in these locations are subject to larger adverse pressure gradients, thus making them more susceptible to separation. During the unstart process, large regions of separated flow form near the floor and ceiling with reverse flow velocities up to about 0.4[U.sub.[infinity]]. These regions of separated, subsonic flow appear to extend to the isolator exit, creating a path by which the isolator exit boundary condition can be communicated upstream. Plan-view particle image velocimetry data show the unstart process begins with separation of the isolator sidewall boundary layers. Overall, the unstart flow structure is highly three-dimensional. DOI: 10.2514/1.J050037

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.

Although uplift motion of flat-bottom cylindrical shell tanks has been considered to contribute toward various damages to the tanks, the mechanics were not fully understood. As well as uplift displacement of the tanks, fluid pressure accompanying the uplift motion of the tanks may play an important role in the cause of the damage. An accurate estimate of the fluid pressure induced by the uplift motion of the tanks is indispensable in protecting the tanks against destructive earthquakes. As a first step of a series of research, this study mathematically derives the fluid pressure on a rigid rectangular tank with a unit depth accompanying angular acceleration, which acts on a pivoting bottom edge. The rectangular tank employed herein is equivalent to a thin slice of the central vertical cross section of a rigid flat-bottom cylindrical shell tank. Assuming a perfect fluid and velocity potential, a continuity equation is given by the Laplace equation in Cartesian coordinates. The fluid velocities accompanying the motions of the walls and bottom plate constitute the boundary conditions. Since this problem is set as a parabolic partial differential equation of the Neumann problem, the velocity potential is solved with the Fourier-cosine expansion. The derivative of the velocity potential with respect to time gives the fluid pressure at an arbitrary point inside the tank. A mathematical solution for evaluating the fluid pressure accompanying the angular acceleration acting on the pivoting bottom edge of the tank is given by an explicit function of a dimensional variable of the tank, but with the Fourier series. The proposed mathematical solution well converges with a few first terms of the Fourier series. Values of the fluid pressure computed by the explicit finite element (FE) analysis well agrees with those by the proposed mathematical solution. For the designers' convenience, diagrams that depict the fluid pressures normalized by the maximum tangential acceleration given by the product of the angular acceleration and diagonals of the tank are also presented. Consequently, the mathematical solution given by the Fourier series converges easily and provides accurate evaluation of the fluid pressures on a rigid rectangular tank accompanying the angular acceleration acting on the pivoting bottom edge. Irregularity in the fluid pressure distribution increases as the tank becomes taller. [DOI: 10.1115/1.4000546] Keywords: flat-bottom cylindrical shell tank, fluid pressure, angular acceleration, uplift motion, Fourier-cosine expansion, velocity potential, normalized fluid pressure, rigid rectangular tank

To protect flat-bottom cylindrical tanks against severe damage from uplift motion, accurate evaluation of accompanying fluid pressures is indispensable. This paper presents a mathematical solution for evaluating the fluid pressure on a rigid flat-bottom cylindrical tank in the same manner as the procedure outlined and discussed previously by the authors (Taniguchi, T., and Ando, Y., 2010, 'Fluid Pressures on Unanchored Rigid Rectangular Tanks Under Action of Uplifting Acceleration,' ASME J. Pressure Vessel Technol., 132(1), p. 011801). With perfect fluid and velocity potential assumed, the Laplace equation in cylindrical coordinates gives a continuity equation, while fluid velocity imparted by the displacement (and its time derivatives) of the shell and bottom plate of the tank defines boundary conditions. The velocity potential is solved with the Fourier--Bessel expansion, and its derivative, with respect to time, gives the fluid pressure at an arbitrary point inside the tank. In practice, designers have to calculate the fluid pressure on the tank whose perimeter of the bottom plate lifts off the ground like a crescent in plan view. However, the asymmetric boundary condition given by the fluid velocity imparted by the deformation of the crescent-like uplift region at the bottom cannot be expressed properly in cylindrical coordinates. This paper examines applicability of a slice model which is a rigid rectangular tank with a unit depth vertically sliced out of a rigid flat-bottom cylindrical tank with a certain deviation from (in parallel to) the center line of the tank. A mathematical solution for evaluating the fluid pressure on a rigid flat-bottom cylindrical tank accompanying the angular acceleration acting on the pivoting bottom edge of the tank is given by an explicit function of a dimensional variable of the tank, but with Fourier series. It well converges with a few first terms of the Fourier series and accurately calculates the values of the fluid pressure on the tank. In addition, the slice model approximates well the values of the fluid pressure on the shell of a rigid flat-bottom cylindrical tank for any points deviated from the center line. For the designers' convenience, diagrams that depict the fluid pressures normalized by the maximum tangential acceleration given by the product of the angular acceleration and diagonals of the tank are also presented. The proposed mathematical and graphical methods are cost effective and aid in the design of the flat-bottom cylindrical tanks that allow the uplifting of the bottom plate. [DOI: 10.1115/1.4000374] Keywords: flat-bottom cylindrical tank, fluid pressure, uplift motion, Fourier--Bessel expansion, velocity potential pivoting edge, normalized fluid pressure, angular acceleration, slice model

This study assessed the effects of meal volume (MV) and calorie load (CL) on gastric function. MRI and a minimally invasive fiber-optic recording system (FORS) provided simultaneous measurement of gastric volume and pressure changes during gastric tilting and emptying of a liquid nutrient meal in physiological conditions. The gastric response to 12 iso-osmolar MV-CL combinations of a multinutrient drink (MV: 200, 400, 600, 800 ml; CL: 200, 300, 400 kcal) was tested in 16 healthy subjects according to a factorial design. Total gastric volume (TGV) and gastric content volume (GCV = MV + secretion) were measured by MRI during nasogastric meal infusion and gastric emptying over 60 min. Intragastric pressure was assessed at 1 Hz by FORS. The dynamic change in postprandial gastric volumes was described by a validated three-component linear exponential model. The stomach expanded with MV, but the ratio of GCV:MV at [t.sub.0] diminished with increasing MV (P < 0.01). Postprandial changes in TGV followed those of GCV. Intragastric pressure increased with MV, and this effect was augmented further by CL (P = 0.02); however, the absolute pressure rise was gastric accommodation; gastric emptying; intragastric pressure doi: 10.1152/ajpgi.00117.2009.

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

Experimental pitot pressure measurements in impulse facilities have typically had large-scale harmonic fluctuations associated with them. A combined experimental and numerical approach is used to investigate if a Helmholtz resonance is created from the shrouding that protects the pressure sensor from particle impact, rather than from disturbances being present in the freestream. To verify this experimentally, hydraulic oil was used to change the sound speed in the cavity. Numerical calculations of the pitot probe were used to show that both the steady and the expected transient inflow cause a Helmholtz resonance of similar period. However, a 5 % isothermal level of freestream noise was required to match the experimental fluctuation levels. Viscous effects were also shown to be significant during the initial transient response of the pressure measurement. A new pitot probe design was successfully tested and shown to be able to reduce the magnitude and period of the fluctuations. DOI: 10.2514/1.42543

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.

The burst pressure of cylinders with hillside nozzle is determined using both experimental and finite element analysis (FEA) approaches. Three full-scale test models with different angles of the hillside nozzle were designed and fabricated specifically for a hydrostatic test in which the cylinders were pressurized with water. 3D static nonlinear finite element simulations of the experimental models were performed to obtain the burst pressures. The burst pressure is defined as the internal pressure for which the structure approaches dimensional instability, i.e., unbounded strain for a small increment in pressure. Good agreement between the predicted and measured burst pressures shows that elastic-plastic finite element analysis is a viable option to estimate the burst pressure of the cylinders with hillside nozzles. The preliminary results also suggest that the failure location is near the longitudinal plane of the cylinder-nozzle intersection and that the burst pressure increases slightly with an increment in the angle of the hillside nozzle. [DOl: 10.1115/1.3147987] Keywords: burst pressure, hillside nozzle, cylinder-nozzle intersection, finite element analysis

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

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.

Byline: Valentin Becker (1), Roland M. Schmid (1), Andreas Umgelter (1) Keywords: Measurement; Intra-abdominal pressure; Intra-abdominal hypertension; CiMon monitoring device; Abdominal compartment syndrome Abstract: Objective To evaluate a new commercially available system for the intra-gastric measurement of intra-abdominal pressure (IAP). Design and setting Prospective interventional trial in an intensive care unit of a university hospital. Patients Ten patients with cirrhosis and tense ascites scheduled for paracentesis and instrumented with a ballon-tipped nasogastric tube. Intervention Intermittent paracentesis with repeat paired measurements of IAP. Measurements and results Intra-abdominal pressure was measured directly through the paracentesis catheter using a scaled measurement gauge. Simultaneously, intra-gastric measurements were performed with the CiMon device (Pulsion Medical Systems, Munich, Germany), by means of a ballon-tipped nasogastric tube connected to a pressure transducer. The range of IAP was 6.5--28 mmHg for direct measurements and 3.7--16 mmHg for measurements obtained with the CiMon device. The regression equation according to Passing and Bablok for the two methods had an intercept of 0.054 (95% CI--1.475--1.669) and a slope of 0.674 (95% CI 0.538--0.813). The cusum test showed a significant deviation from linearity (P < 0.05). In the Bland--Altman test bias and limits of agreement were -- 4.9 (+-6.8) mmHg or, expressed as percentage of the average, -44% (+-49%). Conclusion Intra-gastric measurments of IAP using the CiMon device were not reliable enough to be clinically useful in these ascitic patients. Author Affiliation: (1) II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universitat Munchen, Ismaningerstr. 22, 81675, Munich, Germany Article History: Registration Date: 11/02/2009 Received Date: 26/09/2008 Accepted Date: 05/02/2009 Online Date: 26/02/2009 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s00134-009-1451-2) contains supplementary material, which is available to authorized users.

Wall pressure and wall pressure fluctuations in turbulent flows are of interest in many engineering applications. This paper focuses on the design and fabrication of aero-micro-electromechanical system surface pressure sensor arrays and their application to wall pressure measurements on a wall-mounted cylinder. The sensor arrays have been developed to be highly sensitive and mounted flush with the measurement surface. Thus, dynamic properties of the sensors are not limited by tubing, and an accurate measurement of the wall pressure and its fluctuations becomes possible. The arrays introduced herein consist of a number of individual sensors, which feature a maximum sensitivity of 12 [micro]V/(VPa) and a pressure resolution of up to 0.5 Pa. Employing six arrays (three different types) consisting of up to 13 individual pressure sensors, wall pressure measurements have been conducted at the University of Rostock at a Reynolds number of 200,000. The results prove that the developed sensor arrays are a powerful measurement tool for experimental fluid mechanics. The wall pressure measurement data obtained are in good agreement with the results of the laser Doppler anemometry measurements and large-eddy simulations, which are also presented herein.

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 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 loss of the initial tightness during service is one of the major causes of failure of tube-to-tubesheet joints. The initial residual contact pressure and its variation during the lifetime of the joint are among the parameters to blame. A reliable assessment of the initial contact pressure value requires accurate and rigorous modeling of the elastoplastic behavior of the tube and the tubesheet during the expansion process. This paper deals with the development of a new analytical model used to accurately predict the residual contact pressure resulting from a hydraulic expansion process. The analytical model is based on the elastic perfectly plastic material behavior of the tube and the tubesheet and the interaction between these two elements of the expanded joint. The model results have been compared and validated with those of the more accurate finite element analysis models. Additional comparisons have been made with existing methods. [DOI: 10.1115/1.3027462]

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

The center of body mass (COM), center of foot pressure (COP), and body segment acceleration signals are commonly used to indicate movement performance and stability during standing activities and walking. For balance maintenance and restoration, the human brain is capable of estimating and predicting the COM even in the absence of visual or vestibular information. Thus, we hypothesized that the COM may be acquired through the processing of proprioceptive somatosensory information, represented by body segment accelerations, and an external spatial reference, the ground support, represented by the COP. To investigate this hypothesis, we modeled the relationships that exist between the COP and accelerometer data with the 3-D COM trajectory, during walking on firm and irregular surfaces. The models accounted for 99.85 [+ or -] 0.20% and 99.77 [+ or -] 0.39% of the resultant COM trajectory's variability for the firm and irregular surfaces, respectively. This corresponded to a percentage error between the estimated and actual resultant COM of 16.06 [+ or -] 11.11% for the firm surface and 21.41 [+ or -] 12.70% for the doweling surface. In turn, this translates into an absolute error between the true and actual resultant COM of 3.62 [+ or -] 2.69 cm and 4.74 [+ or -] 3.01 cm for the firm and doweling surfaces, respectively. The model is novel in that it does not require any calibration and provides a reasonably accurate estimation of the COM, which can be compared to the brain's balance performance. Hence, this model could be used instead of the cumbersome method of video motion analysis for COM calculation. Index Terms--Body acceleration, center of body mass (COM), center of foot pressure (COP), modeling, walking.

To investigate the mechanisms responsible for the neonatal increase in glomerular filtration rate (GFR), renal function studies (whole kidney and micropuncture) were carried out in anesthesized fetal sheep (133-140 days gestation; term = 150 days) and lambs (12-18 days). Fetuses were delivered and placed in a water bath (39.5[degrees]C), keeping the umbilical cord moist and intact. Lambs were studied on a thermostatically controlled heating pad. Animals were prepared for either blood flow studies or micropuncture measurements. Expected differences in blood composition and cardiovascular and renal function were observed between fetuses and lambs, and values obtained for most variables were similar to those measured in chronically catheterized unanesthetized animals. Fetal GFR was much lower than that of lambs (0.20 vs. 0.62 ml x [min.sup.-1] x g [kidney.sup.-1], P < 0.001). Free-flow, stop-flow, and net filtration pressures (NFP) were lower in the fetuses than the lambs (NFP 20.8 vs. 23.8 mmHg, P < 0.001), as was the calculated ultrafiltration coefficient (0.014 vs. 0.022 ml x [min.sup.-1] x [g.sup.-1] x mm[Hg.sup.-1], P < 0.001). Thus, we conclude that rises in both net filtration pressure and the ultrafiltration coefficient contribute to the large increase in GFR between fetal life and ~2 wk after birth. fetus; lamb; micropuncture; flee-flow pressure; stop-flow pressure

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

The paper presents the methodologies and results of an experimental study aimed at measuring the soil contact pressures which develop on a buried structure as it interacts with the surrounding soil under load. The study has been based on measurements made on model structures tested in a pressure chamber filled with a fine uniform sand. The buried model structure was a very rigid right cylinder designed such that it could be fitted with roofs of different thicknesses. The structure bottom and roof were instrumented with newly designed and constructed soil pressure cells based on the null response concept. The device is unaffected by the issues that affect the use of traditional soil pressure cells. The development of pressure on the structure was measured as uniform pressure was applied to the soil surface. The results illustrate the effect of roof stiffness on the development of pressure at the roof center. The midroof pressure was seen to increase with roof stiffness, however the development of pressure was also seen to be dependent upon the actual deflection. In the case of a flexible roof it was seen that the development of contact pressure is a nonlinear function of the pressure applied at the soil surface and is highly dependent upon stress history. In contrast, it was seen that pressure on a stiff roof develops as a linear function of pressure applied at the soil surface and is less dependent of stress history. The results of the model tests together with soil stiffness data supplied in the paper will be useful in the calibration and validation of numerical and analytical frameworks. CE Database subject headings: Soil pressure; Measurement; Underground structures; Validation.

The analysis of the dynamic response of a pressurized water pipeline system is important for the design and also the integrity monitoring of these systems. An efficient method for summarizing the behavior of a pipeline system is through the determination of their system response functions. These functions can be extracted by injecting a pressure signal with a wide bandwidth that persists over the length of a pipeline system. Unlike electrical and mechanical systems, generating such signals in pressurized water systems is difficult. Valves capable of generating a signal against the system back-pressure often lack the necessary maneuverability to ensure the signal is sharp (and hence with high-frequency content) and the generated transient is often large in amplitude, risking damage to the system. A method for generating a small amplitude transient signal with a wide band of frequencies is desirable. This paper presents the design for a side discharge valve for generating a pseudorandom binary sequence of pressure changes that are of a small magnitude in relation to the steady state head of the pipeline. The pseudorandom pressure sequence is used to provide an estimate of the system response function. The continuous form of the signal allows the amplitude of each individual pulse within the signal to be small while maintaining the same signal bandwidth. The valve has been tested experimentally and was found to provide a good match with the theoretical response of the pipeline. The method provides a practical alternative to frequency sweeping using sinusoidal signals or sharp valve closures for the extraction of the response functions. Once determined, the system response function can be utilized to detect system faults such as leaks and blockages. DOI: 10.1061/(ASCE)0733-9429(2008)134:6(858) CE Database subject headings: Pipes; Pressure measurement; Transfer functions; Transient flow; Water pipelines.

A simple model is developed here to predict the pressure drop and discharge coefficient for incompressible flow through orifices with length-to-diameter ratio greater than zero (orifice tubes) over wide ranges of Reynolds number The pressure drop for flow through orifice tubes is represented as two pressure drops in series; namely, a pressure drop for flow through a sharp-edged orifice in series with a pressure drop for developing flow in a straight length of tube. Both of these pressure drop terms are represented in the model using generally accepted correlations and experimental data for developing flows and sharp-edged orifice flow. We show agreement between this simple model and our numerical analysis of laminar orifice flow with length-to-diameter ratio up to 15 and for Reynolds number up to 150. Agreement is also shown between the series pressure drop representation and experimental data over wider ranges of Reynolds number. Not only is the present work useful as a design correlation for equipment relying on flow through orifice tubes but it helps to explain some of the difficulties that previous authors have encountered when comparing experimental observation and available theories.

A single-jet water meter was modeled and simulated within a wide measuring range that included flow rates in laminar, transitional, and turbulent flow regimes. The interaction between the turbine and the flow, on which the operating principle of this kind of meter is based, was studied in depth from the detailed information provided by simulations of the three dimensional flow within the meter. This interaction was resolved by means of a devised semi-implicit time-marching procedure in such a way that the speed and the position of the turbine were obtained as part of the solution. Results obtained regarding the turbine's mean rotation speed, measurement error, and pressure drop were validated through experimental measurements performed on a test rig. The role of mechanical friction on the performance of the meter at low flow rates was analyzed and interesting conclusions about its influence on the reduction of the turbine's rotation speed and on the related change in the measurement error were drawn. The mathematical model developed was capable of reproducing the performance of the meter throughout the majority of the measuring range, and thus was shown to be a very valuable tool for the analysis and improvement of the single-jet water meter studied. Keywords: single-jet water meter, CFD, fluid-structure interaction, measurement error, pressure drop, mechanical friction

An experimental investigation has been made on a turbulent boundary layer near the trailing edge on a long flat plate. The flow was controlled by an additional splitter plate fitted to the trailing edge along the wake centerline. The length of the splitter plate, l, was varied from a half, to five times the trailing edge thickness, h. Measurements of base pressure behind the trailing edge and of mean velocity and pressure distribution in the turbulent boundary layer on the flat plate were made under the freestream zero-pressure gradient. The absolute value of the base pressure coefficient of the long flat plate was considerably smaller than that of the short flat plate without the splitter plate. A significant increase in the base pressure coefficient was achieved with the splitter plate (l/h [greater than or equal to] 1), fitted to the long flat plate. Within an inner layer in the turbulent boundary layer near the trailing edge, the mean velocity increased more than that in the upstream position in the case without the splitter plate. With the splitter plate, however, the base pressure rise made the mean velocity distribution more closely approach that of a fully developed turbulent boundary layer. Keywords: flat plate, boundary layer, separation, splitter plate, base pressure

An analytical model to predict the primary stagnation pressure that starts an annular injection supersonic ejector is presented. If the length of the mixing chamber is longer than the critical length, the starting pressure increases proportionally to the mixing chamber length, which differs from conventional ejectors using central injection. To describe the dependency of the starting pressure on the mixing chamber length, we assume that the ejector starts when the exiting supersonic primary flow reaches the second throat. In the present model, we use a subsonic mixing model to calculate the secondary flow pressure in the mixing chamber. Applying the obtained pressure as a back pressure condition, the distance that the supersonic primary flow develops is calculated. Comparing the distance to the mixing chamber length, we derive a minimum pressure requirement diagram that accurately predicts the starting pressure and hysteresis for a given geometry.

Fundamental aspects of Common Rail (CR) fuel-injection-system dynamics were investigated, paying specific attention to the wave propagation induced pressure oscillations and to their relationships with the system control parameters and multiple-injection performance. A detailed experimental analysis of the pressure-wave propagation phenomena in a last-generation CR Multijet equipment of the solenoid type was carried out on a high performance new test-bench Moehwald-Bosch MEP2000-CA4000 under real engine simulated conditions. The experimental results include pressure time histories in the rail and at the injector inlet, as well as flow-rate patterns, for both single and multiple injection events. The measured volume of fuel injected at each injection pulse is also reported. The analysis of the system oscillating behavior was carried out with the support of a simple lumped parameter model. Such a model was shown to be capable of predicting the main frequencies of the hydraulic circuit and their dependence on the geometrical parameters. The good agreement between the outcome of this simple model and the experimental data also substantiated the reliable authors' interpretation of the primary cause and effect relations underlying the complex flow phenomena occurring in the system. A refined computational model was developed and validated in a parallel work, providing a hydrodynamic analysis tool that is complementary to experimentation and also a means of hydraulic-system layout design and optimization. Finally, the mutual fluid-dynamic interactions taking place between consecutive injection events by distinct injectors of the same system are investigated in addition to the difference in dynamics of valve covered orifice and Minisac-nozzle injectors. Cycle-to-cycle variations in system performance were also investigated. [DOI: 10.1115/1.2835353]