Showing papers on "Dynamic pressure published in 1998"

A Volume-Tracking Method for Incompressible Multifluid Flows with Large Density Variations

Abstract: A numerical technique (FGVT) for solving the time-dependent incompressible Navier-Stokes equations in fluid flows with large density variations is presented for staggered grids. Mass conservation is based on a volume tracking method and incorporates a piecewise-linear interface reconstruction on a grid twice as fine as the velocity pressure grid. It also uses a special flux-corrected transport algorithm for momentum advection, a multigrid algorithm for solving a pressure-correction equation and a surface tension algorithm that is robust and stable. In principle, the method conserves both mass and momentum exactly, and maintains extremely sharp fluid interfaces. Applications of the numerical method to prediction of two-dimensional bubble rise in an inclined channel and a bubble bursting through an interface are presented

Central plasma sheet ion properties as inferred from ionospheric observations

Abstract: A method of inferring central plasma sheet (CPS) temperature, density, and pressure from ionospheric observations is developed. The advantage of this method over in situ measurements is that the CPS can be studied in its entirely, rather than only in fragments. As a result, for the first time, comprehensive two-dimensional equatorial maps of CPS pressure, density, and temperature within the isotropic plasma sheet are produced. These particle properties are calculated from data taken by the Special Sensor for Precipitating Particles, version 4 (SSJ4) particle instruments onboard DMSP F8, F9, F10, and F11 satellites during the entire year of 1992. Ion spectra occurring in conjunction with electron acceleration events are specifically excluded. Because of the variability of magnetotail stretching, the mapping to the plasma sheet is done using a modified Tsyganenko [1989] magnetic field model (T89) adjusted to agree with the actual magnetotail stretch at observation time. The latter is inferred with a high degree of accuracy (correlation coefficient -0.9) from the latitude of the DMSP b2i boundary (equivalent to the ion isotropy boundary). The results show that temperature, pressure, and density all exhibit dawn-dusk asymmetries unresolved with previous measurements. The ion temperature peaks near the midnight meridian. This peak, which has been associated with bursty bulk flow events, widens in the Y direction with increased activity. The temperature is higher at dusk than at dawn, and this asymmetry increases with decreasing distance from the Earth. In contrast, the density is higher at dawn than at dusk, and there appears to be a density enhancement in the low-latitude boundary layer regions which increases with decreasing magnetic activity. In the near-Earth regions, the pressure is higher at dusk than at dawn, but this asymmetry weakens with increasing distance from the Earth and may even reverse so that at distances X less than approx. 10 to -12 R(sub E), depending on magnetic activity, the dawn sector has slightly higher pressure. The temperature and density asymmetries in the near-Earth region are consistent with the ion westward gradient/curvature drift as the ions ExB convect earthward. When the solar wind dynamic pressure increases, CPS density and pressure appear to increase, but the temperature remains relatively constant. Comparison with previously published work indicates good agreement between the inferred pressure, temperature, and density and those obtained from in situ data. This new method should provide a continuous mechanism to monitor the pressure, temperature, and density in the magnetotail with unprecedented comprehensiveness.

The structure of wall-pressure fluctuations in turbulent boundary layers with adverse pressure gradient and separation

Abstract: Space–time correlations and frequency spectra of wall-pressure fluctuations, obtained from direct numerical simulation, are examined to reveal the effects of pressure gradient and separation on the characteristics of wall-pressure fluctuations. In the attached boundary layer subjected to adverse pressure gradient, contours of constant two-point spatial correlation of wall-pressure fluctuations are more elongated in the spanwise direction. Convection velocities of wall-pressure fluctuations as a function of spatial and temporal separations are reduced by the adverse pressure gradient. In the separated turbulent boundary layer, wall-pressure fluctuations are reduced inside the separation bubble, and enhanced downstream of the reattachment region where maximum Reynolds stresses occur. Inside the separation bubble, the frequency spectra of wall-pressure fluctuations normalized by the local maximum Reynolds shear stress correlate well compared to those normalized by free-stream dynamic pressure, indicating that local Reynolds shear stress has more direct influence on the wall-pressure spectra. Contour plots of two-point correlation of wall-pressure fluctuations are highly elongated in the spanwise direction inside the separation bubble, implying the presence of large two-dimensional roller-type structures. The convection velocity determined from the space–time correlation of wall-pressure fluctuations is as low as 0.33U0 (U0 is the maximum inlet velocity) in the separated zone, and increases downstream of reattachment.

An Empirical Model of the Magnetopause for Broad Ranges of Solar Wind Pressure and BZ IMF

Abstract: A dayside magnetopause model is presented as an alternative to the well-known Roelof and Sibeck model. Model parameters are the same: solar wind dynamic pressure and B Z-component of the interplanetary magnetic field. The main differences and features of the model are the larger statistics and wider effective range of model parameters and the different method of the data treatment. The first is due to geosynchronous satellite magnetopause crossings added to the basic data on highapogee crossing. The second is based on a physical approach to the analysis of the data. An asymmetric dayside magnetopause shape during disturbed solar wind condition and the pressure balance change manner during strong negative B Z were derived from geosynhronous data analysis.

Multispacecraft observations of sudden impulses in the magnetotail caused by solar wind pressure discontinuities: Wind and IMP 8

Abstract: Two upstream solar wind pressure discontinuities that were associated with storm sudden commencements have been examined to determine their effect on the geomagnetic tail lobe field. During the two events, occurring on March 9, 1995, and August 17, 1995, the Wind spacecraft was located in the upstream region monitoring the solar wind, and the IMP 8 spacecraft was in the geomagnetic tail lobe observing the tail response. The two events occurred during periods with northward or weak southward interplanetary magnetic field. In each case, the data suggest that the magnetic field in the tail lobe increased in magnitude directly in response to the external solar wind pressure increase. It is shown that a simple model in which a uniform magnetic field is compressed by a step function constriction accurately predicts characteristic timescales, which are of the order of a couple minutes, and the magnetic field profiles. The inferred flaring angles are consistent with model predictions, and the changes in the flaring angle across the discontinuities correspond to expectations based on changes in the subsolar magnetopause position and tail width. Overall, the results of this study indicate that the magnetotail maintains an approximate MHD equilibrium even as it responds rapidly to interplanetary pressure discontinuities.

Constant Dynamic Pressure Trajectory Simulation in POST

Abstract: NOMENCLATURE Future space transportation vehicles may well rely on high speed airbreathing propulsion (ramjets and scramjets) to supply much of their motive power. Because of the tradeoff relationship between engine thrust and vehicle airframe weight, ascent trajectories are typically simulated using a constant dynamic pressure phase during airbreathing acceleration. That is, dynamic pressure is increased to benefit vehicle thrust up to some fixed limit imposed by the vehicle structure. The constant dynamic pressure portion of the trajectory typically begins around Mach 2 or 3 and continues to the maximum airbreathing Mach number or until some convective aeroheating limit is reached. This paper summarizes comparative research on three candidate guidance methods suitable for simulating constant dynamic pressure trajectories. These are generalized acceleration steering, linear feedback control, and cubic polynomial control. All methods were implemented in POST (Program to Optimize Simulated Trajectories) — an industry standard trajectory simulation code. Both quantitative and qualitative comparisons of these methods (i.e. in terms of computer processing time, number of required iterations for convergence, sensitivity to quality of initial values, accuracy and program robustness) are presented. Of the three methods, the linear feedback control approach is found to be the most efficient and robust, with good accuracy. * Assistant Professor, School of Aerospace Engineering, Senior member AIAA. ' Palace Knight Fellow, School of Aerospace Engineering, Student member AIAA. Copyright © 1998 by John R. Olds and Irene A. Budianto. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. max upper limit for an inequality constraint Cj additional trajectory constraints Ce optimization indicator CPU central processing unit GAS generalized acceleration steering ISP specific impulse (sec.) Kdg displacement gain in linear feedback guidance equation Krg rate gain in linear feedback guidance equation q dynamic pressure (psf) q time derivative of dynamic pressure (psf/s) LFC linear feedback control steering LH2 liquid hydrogen LOX liquid oxygen P2 weighted constraint error from POST POST Program to Optimize Simulated Trajectories RBCC rocket-based combined-cycle propulsion Sref reference surface area (ft) T/W vehicle thrust-to-weight ratio tf final time, constant dynamic pressure phase tj initial time, constant dynamic pressure phase a angle of attack (deg.) j8n angle of attack polynomial coefficients (n = 0, 1,2,3)

Gas-dynamic pressure wave machine

Abstract: The gas-dynamic pressure wave machine, which is destined for the charge air supply of an internal combustion engine, comprises a rotor (6, 40) with cells (18, 41), a low pressure fresh air inlet channel (14, 38), a high pressure charge air channel (10, 32) leading to the internal combustion engine (1, 33), a high pressure exhaust channel (3, 31) coming from the internal combustion engine, and a low pressure exhaust channel (4, 35), the low pressure exhaust channel (4, 35) and the high pressure exhaust channel (3, 31) being enclosed in a gas housing (5, 34) and the low pressure fresh air inlet channel (14, 38) and the high pressure charge air channel (10, 32) being enclosed in an air housing (15, 39), and each one of all four channels communicating with the rotor through sector-shaped openings (36A, 37A; 54A, 55A) in the gas housing resp. the air housing. The sector-shaped openings (36A, 37A) of the high pressure charge air channels are adjustably arranged in order to allow an adjustment of the process over the entire performance field of the internal combustion engine (33). For a further, even better adjustment of the process, the ratio of the total opening width of the high pressure channels (31, 32) to the total opening width of the low pressure channels (35, 38) is equal to or less than 1:3.25 while the total opening width of the high pressure channels amounts to 45° at the most. A further improvement is obtained by the fact that the air housing (39) and/or the rotor casing (42) are provided with a water cooling system (44, 45).

Investigation of the Circumferential Static Pressure Non-Uniformity Caused by a Centrifugal Compressor Discharge Volute

Abstract: The paper describes experimental and computational fluid dynamics analyses of the non-uniform static pressure distortion caused by the discharge volute in a high pressure, centrifugal compressor. The experiments described in this paper were done using a heavily instrumented gas re-injection compressor operating at over 6000 psia discharge. Instrumentation was installed to measure static, total, and dynamic pressure as well as impeller strain and mechanical vibrations. A brief description of the compressor and instrumentation are provided. Concurrent with the experimental work, CFD runs were completed to study the reasons for the pressure nonuniformity. The CFD pressure profile trends agreed well with the experimental results and provided analytical corroboration for the conclusions drawn from the test data. Conclusions are drawn regarding: a) the response of the non-uniformity to changing flow rates; b) the extent to which the non-uniformity can be detected upstream of the impeller; and c) the mechanical influences of the nonuniformity on the impellers.

Investigation of dynamic pressure behavior in a pultrusion die

Abstract: The fluid resin pressure rise in a pultrusion die inlet can have a significant effect on the quality of the pultruded product. An appreciable pressure rise is required to suppress void formation and promote good fiber "wet out." Most of the pressure rise in the die occurs in the short, tapered die entrance region. In this study a finite element model is developed to predict this pressure rise as a function of various process parameters for a given die entrance geometry. The fiber resin system was modeled based on the assumptions of Darcy's law for flow in porous media. The momentum equations were combined with the continuity equation to save computational time and memory. The resulting equation was solved using a Galerkin weighted residual based finite element method. This model predicts the pressure rise in the tapered entrance region of the pultrusion die as well as along the straight portion of the die. Variations in pressure rise in the die inlet as a result of changes in the pull speed, resin viscosi...

Three‐dimensional MHD simulations of interplanetary rotational discontinuities impacting the Earth's bow shock and magnetosheath

Abstract: The first ever fully three-dimensional magnetohydrodynamic (MHD) simulations of the detailed effects of MHD discontinuities on the magnetosheath have been performed. The simulation results predict that the interaction between a rotational discontinuity (RD) and the bow shock produces an MHD wave pulse that propagates downstream from the bow shock to the magnetopause. The main components of this pulse are two slow shocks sandwiched between two time-dependent intermediate shocks; in perfectly ideal MHD, these shocks would presumably resolve into slow shocks sandwiched between two RDs. Inside the pulse, the plasma density, thermal pressure, dynamic pressure (ρυ2), and total pressure all increase, while the magnetic field magnitude decreases. The pulse convects with the downstream flow through the magnetosheath at a speed that is markedly slower than that of the original RD. It comes to rest on the magnetopause, where it raises the total pressure by as much as 75% in some locations. The pulse eventually disappears, as it is convected away by the solar wind flow around the magnetopause. The pulse remains in the magnetosheath for a few Alfven times (i.e., solar wind Alfven velocity divided by the Earth's radius, perhaps 1–3 min depending on the actual solar wind parameters) after the initial RD has propagated downstream past the magnetopause. Comparisons are made with previous one-dimensional and two-dimensional studies of this problem. We conclude that the pulses seen in these simulations are possible causes of magnetic impulse events observed in the ionosphere and slow mode structures observed in the inner subsolar magnetosheath.

Dynamic pressure sensing with a fiber-optic polarimetric pressure transducer with two-wavelength passive quadrature readout

Abstract: We describe the combination of a polarimetric pressure sensor with a two-wavelength passive quadrature demodulation system allowing for dynamic pressure sensing in the 10-MPa range with unambiguous fringe counting. Furthermore, continuous phase measurement with the arctan method applied to the quadrature interference signals after automatic offset subtraction is demonstrated for the first time, to our knowledge. A single low-coherent superluminescent diode is used as a light source, and a polarizing beam splitter in combination with two adjustable interference filters of slightly different central wavelengths serves for the creation of the quadrature signals. Results of initial experiments with 60-ms pressure relaxation-time constants with the fringe-counting technique demonstrate the performance that was predicted theoretically. The measured pressure sensitivity exhibits excellent agreement with the previous research of Bock and Urbanczyk [IEEE Trans. Instrum. Meas.44, 694–697 (1995)] using a polarimetric readout. The fringe-contrast variation and the measurement range obtained experimentally show the fiber dispersion to influence dephasing (deviation from quadrature) and visibility decrease significantly with increasing pressure.

Banked flight stall warning device and method

Abstract: A flight warning system comprises an outside temperature probe for sensing outside temperature, a gyroscope for sensing aircraft bank angle, a static transducer for sensing static pressure, and a dynamic pressure sensor for receiving total pressure from a pitot tube. A computer is responsive to the gyroscope, static transducer, outside temperature probe and dynamic pressure sensor calculates whether the aircraft is entering a stall condition by comparing the aircraft's bank angle with the stall bank angle. The computer can also calculate whether sufficient altitude exists for the aircraft to safely return to a field after a power failure. An output device can also be provided for indicating the existence of said sufficient altitude, and a stall indicator can be provided for indicating whether the aircraft is entering a stall condition. A method for determining the existence of a stall condition with the aircraft is also disclosed.

Dynamic pressure bearing made of porous material

Abstract: The invention provides a dynamic pressure bearing capable of generating enough dynamic pressure even with the use of a porous material. Dynamic pressure grooves at an inner circumferential surface of a sleeve made of porous material are formed by rolling process. Voids of the porous material at a surface of the dynamic pressure grooves are crushed by this rolling process, making the dynamic pressure grooves airtight. Further, the inner circumferential surface at which the dynamic pressure grooves are formed is subject to a sizing process, by which a bearing surface of the sleeve is crushed so that substantially no voids are present.

Fluid dynamic pressure bearing

Abstract: PROBLEM TO BE SOLVED: To prevent seizure by reduction in lubricating fluid by preventing or reducing the leakage of the lubricating fluid to a bearing outside in the fluid dynamic pressure bearing SOLUTION: This fluid dynamic pressure bearing having a shaft member and a radial fluid dynamic pressure bearing means interposed toward a sleeve member ralatively ratatable to the shaft member is provided with a migration prevention means preventing the migration of the lubricating fluid promoted by a centrifugal force in the end released to the atmosphere of the radial fluid dynamic pressure bearing means

Three-dimensional magnetospheric response to variations in the solar wind dynamic pressure

Abstract: Several thousand magnetic measurements at distances from 3 to 10 RE from the database of Fairfield et al. [1994] have been used for studying the magnetic field response to variations of the hourly-averaged values of the solar wind dynamic pressure. The response differs from that predicted by the Mead [1964] model. Increase in the dynamic pressure compresses the magnetospheric field in the dayside sector mainly. In the most part of the nightside a depression dominates. The depression is connected with the growth of the cross-tail current.

Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers: Part 1 — Discrete-Passage Diffuser

Abstract: This is Part 1 of a two-part paper considering the performance of radial diffusers for use in a high performance centrifugal compressor. Part 1 reports on discrete-passage diffusers (shown in Fig. 1) while Part 2 describes a test of a straight-channel diffuser designed for equivalent duty. Two builds of discrete-passage diffuser were tested, with 30 and 38 separate passages. Both the 30 and 38 passage diffusers investigated showed comparable range of unstalled operation and similar level of overall diffuser pressure recovery.The paper concentrates on the influence of inlet flow conditions on the pressure recovery and operating range of radial diffusers for centrifugal compressor stages. The flow conditions examined include diffuser inlet Mach number, flow angle, blockage, and axial flow non-uniformity. The investigation was carried out in a specially built test facility, designed to provide a controlled inlet flow field to the test diffusers. The facility can provide a wide range of diffuser inlet velocity profile distortion and skew with Mach numbers up to unity and flow angles of 63° to 75° from the radial direction.The consequences of different averaging methods for the inlet total pressure distributions, which are needed in the definition of diffuser pressure recovery coefficient for non-uniform diffuser inlet conditions were also assessed. The overall diffuser pressure recovery coefficient, based on suitably averaged inlet total pressure, was found to correlate well with the momentum-averaged flow angle into the diffuser. Furthermore the pressure recovery coefficient was found to be essentially independent of the axial distortion at diffuser inlet, and the Mach number, over the wide flow range (from maximum flow to the beginning of flow instabilities) investigated. It is thus shown that the generally accepted sensitivity of diffuser pressure recovery performance to inlet flow distortion and boundary layer blockage can be largely attributed to inappropriate quantification of the average dynamic pressure at diffuser inlet. Use of an inlet dynamic pressure based on availability or mass-averaging in combination with definition of inlet flow angle based on mass average of the radial and tangential velocity at diffuser inlet removes this sensitivity.© 1998 ASME

Shape of the heliospheric termination shock: Effects of latitude variations of solar wind dynamic pressure

Abstract: We investigate the consequences of internal solar wind latitude variations on the heliospheric termination shock and the flow of the gas beyond the shock. We have developed a simple gasdynamic model, assuming the solar wind to be a steady, axially symmetric radial outflow of gas that passes through a termination shock and flows incompressibly beyond the shock. We ignore any latitude variations external to the heliosphere (i.e., due to the local interstellar medium) by requiring that the stagnation pressure infinitely far away must be spherically symmetric. Analysis of the model leads to three broad conclusions: (1) The shape of the heliospheric shock is qualitatively similar to what one would predict using the “naive” assumption that the heliocentric distance of the shock is proportional to the square root of the scaled solar wind dynamic pressure ρvr2. (2) However, the existence of an internal latitude dependence of the scaled dynamic pressure requires that the shock must be oblique at some latitudes, and this obliquity produces an outward “bulge” in the shape of the termination shock; this conclusion is completely general, and in particular is true for the case of an oblate shock. (3) For a prolate termination shock the far-down-stream flow is deflected toward the equator, and solar wind originating in the poleward half of (say) the northern hemisphere would fill more than half of the volume of the same hemisphere beyond the termination shock; the deflection would be in the opposite sense (poleward) for an oblate termination shock.

Gas dynamic pressure bearing apparatus

Abstract: A gas dynamic pressure bearing apparatus comprises a fixed shaft, a bearing member which is positioned opposite from the fixed shaft and at least a radial gas dynamic pressure bearing portion and a thrust gas dynamic pressure bearing portion which are positioned in a space between the fixed shaft and the bearing member. Dynamic pressure generating means are included for pressurizing gas in the radial gas dynamic pressure bearing portion and the thrust gas dynamic pressure bearing portion such that dynamic pressure action is generated. The bearing member is rotatably supported in relation to the fixed shaft by means of the pressurizing action such that rotational driving is performed by a predetermined motor. The radial gas dynamic pressure bearing portion and the thrust gas dynamic pressure bearing portion are structured such that gas is sealed from the space around the motor by a space sealing means and that gas flows from one side to other. The flowing gas is circulated between the radial gas dynamic pressure bearing portion and the thrust gas dynamic pressure bearing portion through a gas circulation path. A gas passage is formed on the fixed shaft such that the gas circulation path is connected to the outer end of the fixed shaft. Dust collecting means is formed in one of the gas circulation and the gas passage.

Vascular assist device

Abstract: The present invention is directed to a vascular assist device (21) which maintains a static graduated pressure as the minimum pressure at all times during use. The present invention incorporates at least two inflatable chambers (48, 50) which wrap around selected portions of a limb. The inflatable chambers (48, 50) apply elevated pressure to selected portions of a limb to disgorge blood therefrom. The inflatable chambers (48, 50) also apply static pressure which is graduated from distal to proximal along selected portions of a limb. A desired pressure level is generated and maintained in a pressure accumulator (22), and a pressure regulator (34) and regulator valve (36a, 36b, 36c) control the pressure in the inflatable chambers (48, 50) of the inflatable chambers (48, 50). The inflatable chambers (48, 50) are inflated to a predetermined and uniform dynamic pressure which is maintained in the inflatable chambers (48, 50) for a predetermined amount of time. The pressure is then decreased to a static pressure level which is graduated in pressure from the most distal inflatable chamber (48, 50) to the most proximal inflatable chamber (48, 50). The cycle is repeated after maintaining graduated static pressure for about forty five seconds.

Flush air data system calibration using numerical simulation

Abstract: The use of computational fluid dynamics simulations for calibrating a flush air data system is described, In particular, the flush air data system of the HYFLEX hypersonic vehicle is used as a case study. The HYFLEX air data system consists of nine pressure ports located flush with the vehicle nose surface, connected to onboard pressure transducers, After appropriate processing, surface pressure measurements can he converted into useful air data parameters. The processing algorithm requires an accurate pressure model, which relates air data parameters to the measured pressures. In the past, such pressure models have been calibrated using combinations of flight data, ground-based experimental results, and numerical simulation. We perform a calibration of the HYFLEX flush air data system using computational fluid dynamics simulations exclusively, The simulations are used to build an empirical pressure model that accurately describes the HYFLEX nose pressure distribution ol cr a range of flight conditions. We believe that computational fluid dynamics provides a quick and inexpensive way to calibrate the air data system and is applicable to a broad range of flight conditions, When tested with HYFLEX flight data, the calibrated system is found to work well. It predicts vehicle angle of attack and angle of sideslip to accuracy levels that generally satisfy flight control requirements. Dynamic pressure is predicted to within the resolution of the onboard inertial measurement unit. We find that wind-tunnel experiments and flight data are not necessary to accurately calibrate the HYFLEX flush air data system for hypersonic flight.

Dynamic simulation of the oscillating flow with porous media in a pulse tube cryocooler

Abstract: An improved numerical model has been developed for simulating the oscillating flow and detailed dynamic performance of a pulse tube cryocooler. The governing equations that include the pressure gradient, inertia, viscous, and convection terms are based on the conservation of mass, energy, and momentum for compressible oscillating flow. Good agreement has been found between the predicted results and the experimental data. Detailed time-dependent axial wall temperature distribution, transient gas temperature, mass flow rate, and dynamic pressure variations in the oscillation pulse tube cryocooler have been obtained. The effects of the orifice and double-inlet tubes on the dynamic parameters and refrigeration performance of the pulse tube cryocooler are also presented.

Pressure measuring sensor and apparatus having a seal between a housing having spring-elastic properties and a pressure measuring cell

Abstract: Pressure or force measurement device for static or dynamic pressure measurement, in particular for high pressures or forces, having a housing including a pressure or force measuring cell, e.g., a piezoresistive or capacitive measuring cell. In such devices, service life and chemical resistance are problematic. The pressure measurement device includes the housing, a seal between the pressure medium and an inner chamber of the housing, a pressure measuring cell having a main face exposed to the pressure medium and which pressure measuring cell having a deflection when pressure loaded, which deflection leads to a relative movement between the pressure measuring cell and the housing in a region of the seal. In a region of the seal, the housing has spring-elastic properties. The pressure measurement device further includes a flange with an elastic sealing rib forming a through opening. The housing may be rotationally symmetrical with respect to the flange.

Dynamic Differential Pressure Effects on Drilling of Permeable Formations

Abstract: In the mathematical modeling of bit penetration rate for tri-cone roller bits in permeable formations, virtually all of the current techniques assume that the differential pressure between the bottom-hole wellbore pressure and the formation is a “static” value. This work shows that the appropriate differential pressure is a dynamic quantity, because for overbalanced drilling, fluid filtrate from the wellbore requires a finite time to flow into the formation, producing a changing pressure gradient ahead of the bit. Moreover, this dynamic gradient is directly dependent upon the rate of drill bit penetration, which is in turn dependent upon the dynamic gradient itself. Accordingly, coupled penetration rate and dynamic gradient equations must be solved, which frequently result in the prediction of higher drilling penetration rates than when the static gradient is used. The appropriate dynamic differential pressure equations are developed and applied to an example drilling situation. It is shown that with water-based drilling fluids, for rock with permeability greater than a few microdarcies at virtually all penetration rates, and for penetration rates less than 3 m/h (9.84 ft/h) at permeabilities greater than 1 μd (microdarcy), the dynamic differential pressure is significantly less than the static differential pressure. Accordingly, using the conventional static differential pressure results in the prediction of penetration rates that are much too low. Moreover, using measured penetration rates from the field, the conventional approach yields predicted in-situ rock strength that is much too high.

Head slider and recording and reproducing device using the slider

Abstract: PROBLEM TO BE SOLVED: To suppress a floating amt. or fluctuation of contact force without utilizing dependence upon a yaw angle by providing at least two dynamic pressure generating parts on the head slider along the rotating direction of a disk and setting a shape of the forward dynamic pressure generating part without causing a change in pitching of the backward dynamic pressure generating part in the inner and outer circumferences of the disk. SOLUTION: This head slider 203a possesses the two dynamic pressure generating parts 2a and 2b across a deep groove 3, having their shapes on the surface opposite to the disk, formed with a length along the direction approximately orthogonal to the rotating direction of the disk longer than a length along the rotating direction respectively. The forward dynamic pressure generating part 2a is provided with a land part 5 formed with a 1st step 4 in the direction orthogonal to the rotating direction of the disk and extension land parts 60a and 60b extended in the vicinity of the side end parts of this land part 5. Consequently, since a side part of the step 4 is surrounded by extended steps 61a and 61b, a lateral leakage of an airflow is reduced, and a possitive pressure is efficiently generated, so that pitching fluctuation is prevented, and also a rolling preventing function by means of the steps 6a and 6b is properly adjusted.

Application of Pressure Sensitive Paint to Confined Flow at Mach Number 2.5

Abstract: Pressure sensitive paint (PSP) is a novel technology that is being used frequently in external aerodynamics. For internal flows in narrow channels, and applications at elevated nonuniform temperatures, however, there are still unresolved problems that complicate the procedures for calibrating PSP signals. To address some of these problems, investigations were carried out in a narrow channel with supersonic flows of Mach 2.5. The first set of tests focused on the distribution of the wall pressure in the diverging section of the test channel downstream of the nozzle throat. The second set dealt with the distribution of wall static pressure due to the shock/wall interaction caused by a 25 deg. wedge in the constant Mach number part of the test section. In addition, the total temperature of the flow was varied to assess the effects of temperature on the PSP signal. Finally, contamination of the pressure field data, caused by internal reflection of the PSP signal in a narrow channel, was demonstrated. The local wall pressures were measured with static taps, and the wall pressure distributions were acquired by using PSP. The PSP results gave excellent qualitative impressions of the pressure field investigated. However, the quantitative results, specifically the accuracy of the PSP data in narrow channels, show that improvements need to be made in the calibration procedures, particularly for heated flows. In the cases investigated, the experimental error had a standard deviation of +/- 8.0% for the unheated flow, and +/- 16.0% for the heated flow, at an average pressure of 11 kpa.

The calibration problem

Abstract: When measuring gas pressure changes in a container, for example an engine cylinder or a gun, by means of a piezoelectric pressure transducer, highly relatively accurate values must be made available in order to obtain the specified absolute accuracy. For this, special measuring and calibrating techniques are necessary, which allow the quantitative determination of the dynamic measuring properties of the transducer. The output from the transducer is in electric voltage. Therefore we must perform the calibration of the transducer so as to finally get the pressure. This is not difficult when we are working with a static pressure. The design of the equipment which enables well defined dynamic pressure measurement is much more complicated. This problem was solved by different authors by using a hydraulic pressure chamber, see [3]. For such a system we developed in our recent research project an experimental method for the dynamic pressure calibration. The essential problem connected with this method consists in the development of a physical model which allows a mathematical description of the hydraulic pressure pulses. This model enables us to calibrate a dynamic pulse pressure transducer in absolute pressure units. The schema of the experimental method is given in Figure 13.1. In the next chapter we will define a physical model using the results contained in [1].