Measured Pressure Data Research Articles

Testing of global pressure/temperature (GPT) model and global mapping function (GMF) in GPS analyses

Several sources of a priori meteorological data have been compared for their effects on geodetic results from GPS precise point positioning (PPP). The new global pressure and temperature model (GPT), available at the IERS Conventions web site, provides pressure values that have been used to compute a priori hydrostatic (dry) zenith path delay z h estimates. Both the GPT-derived and a simple height-dependent a priori constant z h performed well for low- and mid-latitude stations. However, due to the actual variations not accounted for by the seasonal GPT model pressure values or the a priori constant z h, GPS height solution errors can sometimes exceed 10 mm, particularly in Polar Regions or with elevation cutoff angles less than 10 degrees. Such height errors are nearly perfectly correlated with local pressure variations so that for most stations they partly (and for solutions with 5-degree elevation angle cutoff almost fully) compensate for the atmospheric loading displacements. Consequently, unlike PPP solutions utilizing a numerical weather model (NWM) or locally measured pressure data for a priori z h, the GPT-based PPP height repeatabilities are better for most stations before rather than after correcting for atmospheric loading. At 5 of the 11 studied stations, for which measured local meteorological data were available, the PPP height errors caused by a priori z h interpolated from gridded Vienna Mapping Function-1 (VMF1) data (from a NWM) were less than 0.5 mm. Height errors due to the global mapping function (GMF) are even larger than those caused by the GPT a priori pressure errors. The GMF height errors are mainly due to the hydrostatic mapping and for the solutions with 10-degree elevation cutoff they are about 50% larger than the GPT a priori errors.

A method for direct impedance measurements in long range propagation of low-frequency sound.

A method for direct impedance measurements in long range propagation of sound, significantly below 200 Hz, is presented. The linear least‐squares fit to the measured pressure data, as a function of the sensor height, the so called “pressure derivative method,” was utilized to obtain the pressure derivatives. Several sensors were installed vertically on the array above the ground. The ground was a flat agricultural farm. The propagation distance of sound over the ground was 0.41 km. Sound sources included pulses and pure tones. The impedances for the pulses and tones showed good agreement. Overall, the imaginary components of the impedance were much larger than the corresponding real components in the frequency range studied.

Thermodynamic modeling of direct injection methanol fueled engines

In-cylinder pressure is an important parameter that is used to investigate the combustion process in internal combustion (IC) engines. In this paper, a thermodynamic model of IC engine combustion is presented and examined. A heat release function and an empirical conversion efficiency factor are introduced to solve the model. The pressure traces obtained by solving the thermodynamic model are compared with measured pressure data for a fully instrumented laboratory IC spark ignition (SI) engine. Derived scaling parameters for time to peak pressure, peak pressure, and maximum rate of pressure rise (among others) are developed and compared with the numerical simulations. The models examined here may serve as pedagogic tools and, when suitably refined, as preliminary design tools.

Evolution of a hydrodynamic field and its effect on hydrocarbon accumulation in the Biyang depression, Henan province

Abstract The hydro-geologic stages in the Biyang Depression, Henan Province, were defined and factors controlling the evolution of the hydrodynamic field in this area were analyzed. The evolution of the paleo-hydrodynamic field was studied by using the method of sedimentary-water-head and the changing patterns of the present hydrodynamic field as determined from measured pressure data. The results show that the evolution of the hydrodynamic field is one of inheritance and that it controls hydrocarbon accumulation. The deposition center in the southeast of the depression is always a high-value zone for water-head and a dynamic-source zone of the hydrodynamic field. The slope zone in the northwest of the depression is always a low-value zone for water-head and is the main discharge area for groundwater; this is the hydrocarbon accumulation zone. Hydrocarbon accumulation is controlled by the hydrodynamic field. The reservoir shows a ring-shaped horizontal pattern. Accumulation occurs in a pressure equilibrium zone at the frontal surface between sedimentary water and infiltrating water. The hydrocarbon accumulations occur in two vertically different discharge units, Eh31 and Eh32 under the action of overpressure.

Numerical and Experimental Studies of Oscillatory Airflows Induced by Rotation of a Grass-Cutting Blade

Three-dimensional oscillatory airflows induced by a rotating grass-cutting blade in a cylindrical chamber are studied experimentally and numerically in this paper. Experimental pressure results are obtained using a sound pressure transducer and a data acquisition system. The measured pressure data contain background noise and high-frequency sound signals due to the blade vibrations. The background noise is separately measured; its effect on the signal is determined from a spectral subtraction algorithm. A time-accurate finite volume numerical solution to the three-dimensional incompressible unsteady Navier–Stokes equations is also sought using the sliding frame technique and the unstructured tetrahedral mesh. Convergence studies are conducted using various combinations of mesh sizes and time increments to ensure the stability of the numerical scheme. The experimental and numerical pressure results are in good agreement.

Development of Local Gas Temperature Measurement Technique inside a Combustion Chamber Using Two-Wire Thermocouple

Thermocouples are widely used to measure the local gas temperature due to its accuracy and convenience. However, it is difficult to use thermocouples in a transient phenomenon such as reacting fields. In this study, the unsteady gas temperature inside a combustion chamber was measured by using an improved two-wire thermocouple technique. Based on previous two-wire methods, some modifications were examined. Firstly, numerical analysis of heat transfer between transient flow and thermocouple was performed to see what kind of modification was required. Secondly, a correction term was added to the basic equation, which was validated by experiments using a Rapid Compression and Expansion Machine. Finally, an improved two-wire thermocouple technique was evaluated by measuring the transient gas temperature inside a combustion chamber and compared to the estimated temperature using measured pressure data and assumptions of chemical equilibrium.

Development of an Efficient 3–D CFD Software to Simulate and Visualize the Scavenging of a Two-Stroke Engine

In this paper we want to describe in detail how the task of numerically solving the flow through a two-stroke engine with moving parts is solved in an efficient way. The mathematical model behind the scenes is illuminated and the used numerical schemes are specified. First, the computation of the convective flux function is carried out by the AUSMDV Riemann solver, which has been proven to be very efficient in comparison to other schemes. Then the introduction of the temperature dependency of the material properties of the fluid has augmented the realistic setting within the compression and expansion of the hot gas within the cylinder. This temperature dependency of the heat capacity causes a change in the equation of state. The gas is not polytropic any more but calorically imperfect. Thus, the use of a relaxation method is necessary in order to retain our Riemann solver. To account for the complex geometry, it was necessary to realize a special mesh treatment. The computational domain can be assembled by different meshes that are connected in a mass conservative way. Furthermore, the piston and crankshaft motion is obtained by very efficient algorithms. In order to speed up the computation of the numerical solution, different strategies have been followed. Adaptive local time-stepping has been implemented in a time consistent manner. Additionally, a dynamic local mesh adaption with hanging knots is used to reach a better resolution in critical areas. A further reduction in computational time has been obtained by the parallelization of the numerical scheme and the mesh routines. To handle this parallelization of the mesh treatment, an extended partitioning for the dynamic load balancing has been implemented. Finally, a simulation of flow through a real-world geometry of an existing two-stroke engine has been performed, the results have been validated with measured pressure data for this engine, and the flow has been qualitatively and quantitatively studied.

Development of Local Gas Temperature Measurement Technique Inside a Combustion Chamber Using Two-Wire Thermocouple

Thermocouples are widely used to measure the local gas temperature due to its accuracy and convenience. However, it is difficult to use thermocouples in a transient phenomenon such as reacting fields. In this study, the unsteady gas temperature inside a combustion chamber was measured by using an improved two-wire thermocouple technique. Based on previous two-wire methods, some modifications were examined. Firstly, numerical analysis of heat transfer between transient flow and thermocouple was performed to see what kind of modification was required. Secondly, a correction term was added to the basic equation, which was validated by experiments using a Rapid Compression and Expansion Machine. Finally, an improved two-wire thermocouple technique was evaluated by measuring the transient gas temperature inside a combustion chamber and compared to the estimated temperature using measured pressure data and assumptions of chemical equilibrium.

A microfluidic experimental platform with internal pressure measurements

Large inconsistencies in previous microchannel pressure drop data have motivated the development of a microchannel experimental platform that enables the measurement of pressures inside the microchannel. The system utilizes bulk etched silicon components that integrate pressure-sensing membranes with the microchannel test section. The deflection of the membranes is detected by an off-chip, optical-lever based system that allows the sensors to be calibrated for pressure measurement. The sensor sensitivity can be adjusted after microfabrication is complete, allowing for sensor optimization after fabrication. The sensor can be used in many applications where the fabrication of electrical contacts, piezoresistors and capacitors is problematic. Calibration uncertainties as low as 2% have been obtained during actual use of the system. The presented system resolves many of the issues associated with measuring pressures inside microchannels for the range of hydraulic diameters tested, 25–100 μm. The system has been used to study pressure drop in microchannels and a sample of the results is presented. It has been found that standard models with appropriate assumptions can accurately predict the measured pressure data.

Deformation induced design for economical shield tunnel lining

Conventional design method of shield tunnel is based on the principle that the segmental lining will bear entire pressure of earth and water to prevent from settling the ground surface. In order to strengthen the principle, practical efforts have been made in design and execution, such that closed face type shield tunnels have been extensively used, and execution efforts have been made to minimize the deformation by decreasing overbreaks, tail voids and time to bury tail voids by grouts. Hence the most of modern shield tunnels could avoid serious settlement problems, however in reality small deformations of the ground into the tunnel cavern exist and cause slight settlement on the surface. The NATM theory positively employs deformations of the ground and reduces support pressures as defined qualitatively by Fenner-Pacher curve. In order to integrate the design method between shield and NATM tunnel, NATM theory has been applied to the shield tunnel design. Key issue is a deformation, or can be explained by stress relief after excavation. Authors have developed simplified design procedures to unite both of shield and NATM tunnels by proposing the virtual segmental analysis. Deformation induced design could reduce the pressures on the segmental lining and was verified with the in-situ measured pressure data. The shield tunnel could obtain an innovative and slimmed-down design method by adapting the normal range of deformation in practice without causing serious settlement problems. Through defining the support pressures to the tunnel as being divided into the ground bearing pressures (GBP) and the mechanical support pressures (MSP), deformations could be related with mechanical support pressures to the segmental lining or ground bearing ratio (GBR) by using the virtual segmental analyses based on the elastic model of FEM. By setting the deformation to the tunnel as the design value through the empirical, practical and measured data, load pressures to the segmental lining can be obtained as MSP directly or through GBR. By comparing in-situ data of practical two shield tunnels with the load pressures calculated by FEM analysis, 22 and 34% of load pressures are recognized to be supported by the ground, and tunnel deformations were 2.0 and 3.8 cm respectively. By applying reduced load pressures to the segmental lining, slimmed down design can be carried out. In this sense, deformation induced design for shield tunnel can slim down the segmental lining. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Comparison of three different interface mass transfer models used in the experimental measurement of solvent diffusivity in heavy oil

Design and modeling of solvent-based heavy oil recovery processes require the knowledge of solvent diffusivity in heavy oil. The solvent diffusivity in heavy oil at constant temperature can be measured by using the so-called pressure decay method. In this method, the solvent diffusivity is determined by monitoring the decaying pressure of solvent phase while it is in contact with heavy oil in a closed high-pressure cell. This paper examines the effects of three different boundary conditions at the solvent–heavy oil interface on the determined diffusion coefficient. The so-called equilibrium, quasi-equilibrium and non-equilibrium boundary conditions are applied to represent three rather different interface mass transfer models. An analytical solution to the bulk diffusion equation subjected to each boundary condition is presented to determine the concentration distribution of solvent in the heavy oil. With the determined solvent concentration distribution in the heavy oil, pressure in the solvent phase is then predicted by utilizing the solvent mass conservation and the equation of state for a real gas. Therefore, an average solvent diffusivity, i.e., independent of solvent concentration, is determined by matching the numerically predicted pressures with the experimentally measured data. Experimental data for two different systems, CO 2-heavy oil and CH 4-heavy oil, are analyzed and the diffusion coefficients are compared with the previously published values. Based on the minimum discrepancy between the predicted and measured pressure data, it is found that the non-equilibrium BC is more applicable to CO 2-heavy oil system and that the equilibrium BC is most suitable for CH 4-heavy oil system. Thus it is concluded that the obtained solvent diffusivity is sensitive to the boundary condition applied at the solvent–heavy oil interface. Hence, a proper boundary condition for each solvent–heavy oil system should be used to determine the solvent diffusivity in heavy oil.

Reduction of Cooling Loss in Hydrogen Combustionby Direct Injection Stratified Charge

Reduction of cooling loss from burning gas to the wall is crucial for improving thermal efficiency in hydrogen combustion engines. The research proposes the direct injection stratified charge to reduce the cooling loss in hydrogen combustion and analyzes its characteristics. The stratified charge in this research adopts direct fuel injection into lean mixture and spark ignition. The stratification is controlled by a fraction of directly injected fuel to the totally supplied fuel. A lowered temperature of the burning gas around the combustion chamber wall due to the leaner mixture by the stratification is expected to effectively reduce the heat transfer. The characteristics are analyzed in a constant volume combustion vessel by using measured pressure data and combustion gas compositions. Flame propagation is also observed for some cases.

Development of empirically based burning rate sub-models for a natural gas engine

Computer models of engine processes are valuable tools for predicting and analyzing engine performance and allow exploration of many engine design alternatives in an inexpensive fashion. At the present work, experimentally based burning rate sub-models for flame initiation and propagation periods were developed for a natural gas engine. The sub-models do not require any knowledge of the flame shape and propagation speed to calculate the burning rate. The flame initiation sub-model determines where the flame propagation period starts so that experimental spark timing can be used for the calculations. The flame initiation and propagation sub-models were used along with a Zero Dimensional (Zero-D) model to calculate cylinder pressure traces for various engine operating conditions. The Zero-D model is able to match the measured pressure data with less than 8% error in magnitudes if the computations are started at the experimental spark timing. If the flame initiation sub-model is tuned for a specific engine operating condition, then the model is able to match the measured pressure with less than 1% error in magnitudes.

An investigation of dynamic stall onset on a pitching wing

AbstractThis paper presents an examination of dynamic stall onset on both a rectangular wing and a nominally two-dimensional aerofoil with the same cross-section. The intention is to determine the extent to which the onset of dynamic stall is changed in the three-dimensional case. To do this, three different criteria are applied to measured pressure data to identify both the onset of the stalling process and the formation of the dynamic stall vortex. It is shown that examination of the vorticity flux in the vicinity of the leading edge provides a means of determining vortex formation in the absence of strong three-dimensional effects. It is also shown that this technique is not applicable on outboard sections of the rectangular wing where the phasing of dynamic stall onset with respect to the leading edge response is altered by the three-dimensionality of the flow. It is concluded that the application of two-dimensional stall onset criteria is inappropriate under such conditions.

Estimating regional pore pressure distribution using 3D seismicvelocities in the Dutch Central North Sea Graben

The application of the empirical Eaton method to calibrated sonic well information and 3D seismic interval velocity data in the southeastern part of the Central North Sea Graben, using the Japsen (Glob. Planet. Change 24 (2000) 189) normal velocity-depth trend, resulted in the identification of an undercompacted and overpressured zone within the shaly Lower North Sea Group. Calculated overpressures near the bottom part of the group increase from east to west, from 3.5 to 5.5 MPa, that is in the direction of increasing sedimentary loading rates in Pliocene-Quaternary times. This ability of the application of sonic and 3D seismic velocity in empirical methods to assess the spatial distribution of overpressures in such shaly units is of importance because measured pressure data are usually not available for shaly sections.

Numerical Simulation of the Ram Accelerator Using a New Chemical Kinetics Mechanism

Computational fluid dynamics (CFD) solutions of the full Navier-Stokes equations, including finite-rate chemical kinetics, are used to numerically simulate the reacting in-bore flowfield for a 90-mm (bore diameter) ram-accelerator projectile propulsion system. In this system a gun tube is filled with a high-pressure gaseous mixture of hydrogen, oxygen, and nitrogen. An axisymmetric projectile is launched into this tube, and rails are attached to the tube wall to ensure projectile centering. The shock system that develops around the projectile, along with boundary layers on the projectile and tube surfaces, ignites the mixture on or near the projectile afterbody. The resulting pressure imbalance on the projectile generates thrust. Numerical predictions of this pressure field can be used to evaluate the thrust efficiency of the system, i.e., the projectile design combined with the chemical composition of the propellant gas. Comparison of the predicted pressure field and the measured pressure data is used to judge the accuracy of the CFD code. The choice of chemical kinetics mechanism used in the CFD code is of critical importance in achieving an accurate numerical simulation of the ram accelerator.

Probabilistic characteristics of pressure fluctuations in separated and reattaching flows for various free-stream turbulence

Abstract The statistical characteristics of the fluctuating pressures acting on bluff bodies in the region of flow separation are investigated in this paper. Probability density functions of the pressure fluctuations have shown a significant non-Gaussian behaviour. The lognormal density function is found to be in close agreement with the obtained experimental data. A probability distribution for the maximum magnitude of peak pressures expected during a period is proposed and the agreement between the experimental data and predicted results are good. The effects of free-stream turbulence intensity and integral scale on the statistical nature of pressure fluctuations are presented and discussed. The second part of this paper concerns the action of fluctuating wind pressure on building cladding. The effect of free-stream turbulence intensity and integral scale in model test on equivalent constant pressures for the purpose of cladding design is investigated, making use of direct integration of measured pressure data in the wind tunnels.

Oxidation Kinetics of North Sea Light Crude Oils at Reservoir Temperature

Air injection into deep, light oil reservoirs is a potential technique for large scale improved oil recovery. The feasibility of an air injection process relies on complete consumption of oxygen from the injected air to achieve a nitrogen flood. In this study, the oxidation kinetics of light crude oils was investigated at typical reservoir temperatures (90–140°C), and high pressures. The oxygen consumption rate was measured from the reduction in the oxygen partial pressure using a small batch reactor (SBR). Measured pressure data for different crude oils was used to establish a simple reaction rate model of acceptable accuracy for reservoir simulation. At the relatively low reservoir temperature of the experiments, the main gaseous product from the reaction was carbon dioxide. Additional experiments were performed in a high pressure oxidation tube (0.1 m diameter and 1.25 m long). The oxidation rate data obtained was used to validate the reaction rate model. The low temperature oxidation (LTO) scheme and its implications for the Air Injection LTO Process are discussed.

Prediction of wave pressures on smooth impermeable seawalls

Simple prediction methods are proposed to estimate the wave induced pressures on smooth impermeable seawalls. Based on the physics of the wave structure interaction, the sloped seawall is divided into a total of five zones (zones 1, 2 and 3 during run-up (corresponding pressures are called as positive pressures) and zones 4 and 5 during run-down (corresponding pressures are called negative pressures)) (Fig. 1 ). Zone 1 (0<z<d−Hi/2), where the wave pressure is governed by the partial reflection and phase shift; Zone 2 (d−Hi/2<z<d), where the effect of wave breaking and turbulence is significant; Zone 3 (d<z<Run-up height), where the pressure is induced by the run-up water; Zone 4 (Run-down<z<d), where the wave pressure is caused by the run-down effect and Zone 5 (0<z<d-Run down), where the negative wave pressures are due to partial reflection and phase shift effects. Here d is the water depth at the toe of the seawall, Hi is the incident wave height and z is the vertical elevation with toe of the seawall as origin and z is positive upward. For wave pressure prediction in zones 1 and 5, the empirical formula proposed by Ahrens et al. (1993)to estimate the wave reflection and Sutherland and Donoghue's recommendations (1998) for the estimation of phase shift of the waves caused by the sloped structures are used. Multiple regression analysis is carried out on the measured pressure data and empirical formulas are proposed for zones 2, 3 and 4. The recommendations of Van der Meer and Breteler (1990)and Schüttrumpf et al. (1994) for the prediction of wave run-down are used for pressure prediction at zone 4. Comparison of the proposed prediction formulas with the experimental results reveal that the prediction methods are good enough for practical purposes. The present study also shows a strong relation between wave reflection, wave run-up, wave run-down and phase shift of waves on wave pressures on the seawalls.

Dynamics of collapsing fluidized beds and its application in the simulation of pulsed fluidized beds

A new method to study collapsing process of fluidized bed was proposed. The method is based on the analysis of the pressure variation during collapse. A model is proposed to describe the pressure variation of any location of the bed during collapse. Three kind of particles were fluidized by air and the pressure variation after shutting down the gas supply was measured by pressure transducers and simulated by the proposed model. The simulated results were in good agreement with the experimental data. The parameters of the fluidized bed, such as bubble fraction α b, particle fraction in dense phase σ p, bubble velocity μ b and slip velocity of particle μ p, can be estimated from the measured pressure data by using the proposed model. The model was also used to calculate the pressure variation in pulsed fluidized beds with low frequency.