Showing papers on "Dynamic pressure published in 2012"

Supermagnetosonic subsolar magnetosheath jets and their effects: from the solar wind to the ionospheric convection

Abstract: . It has recently been proposed that ripples inherent to the bow shock during radial interplanetary magnetic field (IMF) may produce local high speed flows in the magnetosheath. These jets can have a dynamic pressure much larger than the dynamic pressure of the solar wind. On 17 March 2007, several jets of this type were observed by the Cluster spacecraft. We study in detail these jets and their effects on the magnetopause, the magnetosphere, and the ionospheric convection. We find that (1) the jets could have a scale size of up to a few RE but less than ~6 RE transverse to the XGSE axis; (2) the jets caused significant local magnetopause perturbations due to their high dynamic pressure; (3) during the period when the jets were observed, irregular pulsations at the geostationary orbit and localised flow enhancements in the ionosphere were detected. We suggest that these inner magnetospheric phenomena were caused by the magnetosheath jets.

Magnetosheath pressure pulses: Generation downstream of the bow shock from solar wind discontinuities

Abstract: [1] We present multipoint Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations of transient dynamic pressure pulses in the magnetosheath 3–10 times the background in amplitude, due to enhancements in both the ion density and velocity. Their spatial dimensions are of the order of ∼1 RE parallel to the flow and ∼0.2–0.5 RE perpendicular to it, inferred from the difference in the amplitudes observed by the different spacecraft. For the first time, simultaneous observations of the solar wind and foreshock are also shown, proving no similar dynamic pressure enhancements exist upstream of the bow shock and that the majority of pulses are downstream of the quasi-parallel shock. By considering previously suggested mechanisms for their generation, we show that the pressure pulses cannot be caused by reconnection, hot flow anomalies, or short, large-amplitude magnetic structures and that at least some of the pressure pulses appear to be consistent with previous simulations of solar wind discontinuities interacting with the bow shock. These simulations predict large-amplitude pulses when the local geometry of the shock changes from quasi-perpendicular to quasi-parallel, while the opposite case should also produce notable pulses but typically of lower amplitude. Therefore, in a given region of the magnetosheath, some of the discontinuities in the solar wind should generate pressure pulses, whereas others are expected not to. There is also evidence that the pulses can impinge upon the magnetopause, causing its motion.

Parametric study of separation and transition characteristics over an airfoil at low Reynolds numbers

Abstract: Time-resolved surface pressure measurements are used to experimentally investigate characteristics of separation and transition over a NACA 0018 airfoil for the relatively wide range of chord Reynolds numbers from 50,000 to 250,000 and angles of attack from 0° to 21°. The results provide a comprehensive data set of characteristic parameters for separated shear layer development and reveal important dependencies of these quantities on flow conditions. Mean surface pressure measurements are used to explore the variation in separation bubble position, edge velocity in the separated shear layer, and lift coefficients with angle of attack and Reynolds number. Consistent with previous studies, the separation bubble is found to move upstream and decrease in length as the Reynolds number and angle of attack increase. Above a certain angle of attack, the proximity of the separation bubble to the location of the suction peak results in a reduced lift slope compared to that observed at lower angles. Simultaneous measurements of the time-varying component of surface pressure at various spatial locations on the model are used to estimate the frequency of shear layer instability, maximum root-mean-square (RMS) surface pressure, spatial amplification rates of RMS surface pressure, and convection speeds of the pressure fluctuations in the separation bubble. A power-law correlation between the shear layer instability frequency and Reynolds number is shown to provide an order of magnitude estimate of the central frequency of disturbance amplification for various airfoil geometries at low Reynolds numbers. Maximum RMS surface pressures are found to agree with values measured in separation bubbles over geometries other than airfoils, when normalized by the dynamic pressure based on edge velocity. Spatial amplification rates in the separation bubble increase with both Reynolds number and angle of attack, causing the accompanying decrease in separation bubble length. Values of the convection speed of pressure fluctuations in the separated shear layer are measured to be between 35 and 50% of the edge velocity, consistent with predictions of linear stability theory for separated shear layers.

Full two-dimensional rapid chute flows of simple viscoplastic granular materials with a pressure-dependent dynamic slip-velocity and their numerical simulations

Abstract: We present a fully two-dimensional, novel Coulomb-viscoplastic sliding model, which includes some basic features and observed phenomena in dense granular flows like the exhibition of a yield strength and a non-zero slip velocity. The interaction of the flow with the solid boundary is modelled by a pressure and rate-dependent Coulomb-viscoplastic sliding law. The bottom boundary velocity is required for a fully two-dimensional model, whereas in classical, depth-averaged models its explicit knowledge is not needed. It is observed in experiments and in the field that in rapid flow of frictional granular material down the slopes even the lowest particle layer in contact with the bottom boundary moves with a non-zero and non-trivial velocity. Therefore, the no-slip boundary condition, which is generally accepted for simulations of ideal fluid, e.g., water, is not applicable to granular flows. The numerical treatment of the Coulomb-viscoplastic sliding model requires the set up of a novel pressure equation, which defines the pressure independent of the bottom boundary velocities. These are dynamically and automatically defined by our Coulomb-viscoplastic sliding law for a given pressure. A simple viscoplastic granular flow down an inclined channel subject to slip or no-slip at the bottom boundary is studied numerically with the marker-and-cell method. The simulation results demonstrate the substantial influence of the chosen boundary condition. The Coulomb-viscoplastic sliding law reveals completely different flow dynamics and flow depth variations of the field quantities, mainly the velocity and full dynamic pressure, and also other derived quantities, such as the bottom shear-stress, and the mean shear-rate, compared to the commonly used no-slip boundary condition. We show that for Coulomb-viscoplastic sliding law observable shearing mainly takes place close to the sliding surface in agreement with observations but in contrast to the no-slip boundary condition.

Statistical analysis of phase space density buildups and dropouts

Abstract: [1] The dynamics of the radiation belt Phase Space Density (PSD) is analyzed using measurements from four spacecraft taken during two hundred days in 1990 and 1991. In situ measurements from CRRES, Akebono, GPS, and GEO and a realistic model of the magnetic field are used to infer values of PSD. The inferred values of PSD are assimilated into a radial diffusion model by means of Kalman filtering to produce a reanalysis of the relativistic electron PSD during this time interval. The statistical analysis shows that the plasmapause location is well correlated with the location of the peak of PSD. Positive innovation outside of the plasmasphere shows that local acceleration is present in the trough region. The peak of PSD and the local source, as inferred from the innovation, are displaced inward during times of increased geomagnetic activity. Analysis of non-adiabatic dropouts in PSD shows that the dropouts often coincide with sudden increases in the solar wind dynamic pressure. Approximately 73% of the dropouts can be associated with the simultaneous sudden jumps (>7 nPa over several hours) in the solar wind dynamic pressure, approximately 15% could be associated with small jumps or gradual increases in solar wind dynamic pressure, and the remaining 12%, which consists of only 3 events, occurred during relatively steady solar wind dynamic pressure.

Wall Pressure Unsteadiness and Side Loads in Overexpanded Rocket Nozzles

Abstract: Surveys of both the static and dynamic wall pressure signatures on the interior surface of a sub-scale, cold-flow and thrust optimized parabolic nozzle are conducted during fixed nozzle pressure ratios corresponding to FSS and RSS states. The motive is to develop a better understanding for the sources of off-axis loads during the transient start-up of overexpanded rocket nozzles. During FSS state, pressure spectra reveal frequency content resembling SWTBLI. Presumably, when the internal flow is in RSS state, separation bubbles are trapped by shocks and expansion waves; interactions between the separated flow regions and the waves produce asymmetric pressure distributions. An analysis of the azimuthal modes reveals how the breathing mode encompasses most of the resolved energy and that the side load inducing mode is coherent with the response moment measured by strain gauges mounted upstream of the nozzle on a flexible tube. Finally, the unsteady pressure is locally more energetic during RSS, albeit direct measurements of the response moments indicate higher side load activity when in FSS state. It is postulated that these discrepancies are attributed to cancellation effects between annular separation bubbles.

An ultra-fast fiber optic pressure sensor for blast event measurements

Abstract: Soldiers who are exposed to explosions are at risk of suffering traumatic brain injury (TBI). Since the causal relationship between a blast and TBI is poorly understood, it is critical to have sensors that can accurately quantify the blast dynamics and resulting wave propagation through a helmet and skull that are imparted onto and inside the brain. To help quantify the cause of TBI, it is important to record transient pressure data during a blast event. However, very few sensors feature the capabilities of tracking the dynamic pressure transients due to the rapid change of the pressure during blast events, while not interfering with the physical material layers or wave propagation. In order to measure the pressure transients efficiently, a pressure sensor should have a high resonant frequency and a high spatial resolution. This paper describes an ultra-fast fiber optic pressure sensor based on the Fabry–Perot principle for the application of measuring the rapid pressure changes in a blast event. A shock tube experiment performed in US Army Natick Soldier Research, Development and Engineering Center has demonstrated that the resonant frequency of the sensor is 4.12 MHz, which is relatively close to the designed theoretical value of 4.113 MHz. Moreover, the experiment illustrated that the sensor has a rise time of 120 ns, which demonstrates that the sensor is capable of observing the dynamics of the pressure transient during a blast event.

Correction of Static Pressure on a Research Aircraft in Accelerated Flight Using Differential Pressure Measurements

Abstract: . A method is described that estimates the error in the static pressure measurement on an aircraft from differential pressure measurements on the hemispherical surface of a Rosemount model 858AJ air velocity probe mounted on a boom ahead of the aircraft. The theoretical predictions for how the pressure should vary over the surface of the hemisphere, involving an unknown sensitivity parameter, leads to a set of equations that can be solved for the unknowns – angle of attack, angle of sideslip, dynamic pressure and the error in static pressure – if the sensitivity factor can be determined. The sensitivity factor was determined on the University of Wyoming King Air research aircraft by comparisons with the error measured with a carefully designed sonde towed on connecting tubing behind the aircraft – a trailing cone – and the result was shown to have a precision of about ±10 Pa over a wide range of conditions, including various altitudes, power settings, and gear and flap extensions. Under accelerated flight conditions, geometric altitude data from a combined Global Navigation Satellite System (GNSS) and inertial measurement unit (IMU) system are used to estimate acceleration effects on the error, and the algorithm is shown to predict corrections to a precision of better than ±20 Pa under those conditions. Some limiting factors affecting the precision of static pressure measurement on a research aircraft are discussed.

Blade Tip Pressure Measurements Using Pressure Sensitive Paint

Abstract: This paper discusses the application of pressure sensitive paint using laser-based excitation for measurement of the upper surface pressure distribution on the tips of rotor blades in hover and simulated forward flight. The testing was conducted in the Rotor Test Cell and the 14- by 22-ft Subsonic Tunnel at the NASA Langley Research Center on the General Rotor Model System (GRMS) test stand. The Mach-scaled rotor contained three chordwise rows of dynamic pressure transducers for comparison with PSP measurements. The rotor had an 11 ft 1 in. diameter, 5.45 in. main chord and a swept, tapered tip. Three thrust conditions were examined in hover, C(sub T) = 0.004, 0.006 and 0.008. In forward flight, an additional thrust condition, C(sub T) = 0.010 was also examined. All four thrust conditions in forward flight were conducted at an advance ratio of 0.35.

Large scale field testing of hillslope debris flows r esulting in the design of flexible protection barriers

Abstract: 2 and 13 m/s. The flow heights are of the same order of magnitude as the size of the obstacles. The impact coefficients obtained range between 0.3 and 1.2 with median values of 0.65 and 0.78 for the large and small pressure plate respectively. These values are used in the procedure for the barrier design which will be described in detail in the paper. In the abstract first calculation steps for two impacts (Test 8) are described and the results are compared to the forces measured in the support ropes. CALCULATION METHOD The maximum impact pressure values are measured in the flow front. The front velocities are computed from the front passing time at a laser sensor and from the front impacting time at the pressure plates No 1 and No 2 located 3 m downstream of the laser sensor. Dynamic pressure for the first release ranges between p1 = c·ρ·v 2 = 0.48·1840·8.7 2 = 66 kN/m 2 and p2 = c·ρ·v 2 = 0.43·1840·7.0 2 = 38 kN/m 2 with the material density ρ=1840 kg/m 3 . From the high speed camera recordings, we observe the maximum deformation of the flexible barrier 2 s after the front impact coinciding with the peak loads in the support ropes. The filling process lasts for about 5 s.

Analysis of Cavity Passive Flow Control using High Speed Shadowgraph Images

Abstract: An examination of a rectangular cavity with an L/D of 5.67 was tested at Mach 0.7 with a corresponding Reynolds number of 2x10 6 /ft. High speed shadowgraph movies were simultaneously sampled with dynamic pressure sensors at 75 kHz. Fourier analysis was performed on the high speed movies as well as the dynamic pressure data, which resulted in determining the locations of dominant cavity frequencies in the flow field. Five passive flow control devices were tested, three of which have historically preformed well, while two neither reduced the main acoustic tones nor reduced the broadband levels. From the high speed shadowgraph movies, observations are made in the changes in the cavity flow physics when the passive flow control devices are used, and will be discussed.

Influence of the rotor-stator interaction on the dynamic stresses of Francis runners

Abstract: Thanks to advances in computing capabilities and Computational Fluid Dynamics (CFD) techniques, it is now possible to calculate realistic unsteady pressure fields in Francis turbines. This paper will explain methods to calculate the structural loads and the dynamic behaviour in order to optimize the turbine design and maximize its reliability and lifetime. Depending on the operating conditions of a Francis turbine, different hydraulic phenomena may impact the mechanical behaviour of the structure. According to their nature, these highly variable phenomena should be treated differently and specifically in order to estimate the potential risks arising on submerged structures, in particular the runner. The operating condition studied thereafter is the point at maximum power with the maximum head. Under this condition, the runner is excited by only one dynamic phenomenon named the Rotor-Stator Interaction (RSI). The origin of the phenomenon is located on the radial gap of the turbine and is the source of pressure fluctuations. A fluid-structure analysis is performed to observe the influence of that dynamic pressure field on the runner behaviour. The first part of the paper deals with the unsteady fluid computation. The RSI phenomenon is totally unsteady so the fluid simulation must take into account the entire machine and its rotation movement, in order to obtain a dynamic pressure field. In the second part of the paper, a method suitable for the RSI study is developed. It is known that the fluctuating pressure in this gap can be described as a sum of spatial components. By evaluating these components in the CFD results and on the scale model, it is possible to assess the relevance of the numerical results on the whole runner. After this step, the numerical pressure field can be used as the dynamic load of the structure. The final part of the paper presentsthe mechanical finite element calculations. A modal analysis of the runner in water and a harmonic analysis of its dynamic behaviour using the CFD results are carried out. These calculations will show that the RSI on the medium head Francis runner does not create damage on the runner even if the natural frequencies are closed to the wicket gates passing frequency. The numerical results are reinforced by experimental observations done on runner prototypes showing that the wicket gates passing frequency does not have significant influence on low and medium head Francis runner behaviour.

Effects of groove on behavior of flow between hydro-viscous drive plates

Abstract: The flow between a grooved and a flat plate was presented to investigate the effects of groove on the behavior of hydro-viscous drive. The flow was solved by using computational fluid dynamics (CFD) code, Fluent. Parameters related to the flow, such as velocity, pressure, temperature, axial force and viscous torque, are obtained. The results show that pressure at the upstream notch is negative, pressure at the downstream notch is positive and pressure along the film thickness is almost the same. Dynamic pressure peak decreases as groove depth or groove number increases, but increases as output rotary speed increases. Consequently, the groove depth is suggested to be around 0.4 mm. Both the groove itself and groove parameters (i.e. groove depth, groove number) have little effect on the flow temperature. Circumferential pressure gradient induced by the groove weakens the viscous torque on the grooved plate (driven plate) greatly. It has little change as the groove depth increases. However, it decreases dramatically as the groove number increases. The experiment results show that the trend of experimental temperature and pressure are the same with numerical results. And the output rotary speed also has relationship with input flow rate and flow temperature.

Bottom pressure distribution due to wave scattering near a submerged obstacle

Abstract: The dynamic pressure distribution on the bottom of a wave flume, due to the interaction of water waves with a submerged structure, is investigated experimentally and analytically, for both first- and second-order gravity waves of finite amplitude. The dynamic pressure excess is found to be very important, even for incoming waves propagating in deep water conditions. In this depth condition, a high pressure zone, thirty times larger than the dynamic pressure excess expected in the absence of the obstacle, is found in its vicinity. On the other hand, a low pressure zone is observed in the vicinity of the submerged obstacle for incoming waves propagating in smaller depth conditions. In any case, pressure gradients remain important. The second-order disturbance is found to be larger than first order in deep water conditions, for some specific conditions and locations. This result is interpreted in terms of nonlinear coupling of first-order components, including local modes.

Frequency analysis of a step dynamic pressure calibrator.

Abstract: A dynamic high pressure standard is becoming more essential in the fields of mobile engines, space science, and especially the area of defense such as long-range missile development. However, a complication arises when a dynamic high pressure sensor is compared with a reference dynamic pressure gauge calibrated in static mode. Also, it is difficult to determine a reference dynamic pressure signal from the calibrator because a dynamic high pressure calibrator generates unnecessary oscillations in a positive-going pressure step method. A dynamic high pressure calibrator, using a quick-opening ball valve, generates a fast step pressure change within 1 ms; however, the calibrator also generates a big impulse force that can lead to a short life-time of the system and to oscillating characteristics in response to the dynamic sensor to be calibrated. In this paper, unnecessary additional resonant frequencies besides those of the step function are characterized using frequency analysis. Accordingly, the main sources of resonance are described. In order to remove unnecessary frequencies, the post processing results, obtained by a filter, are given; also, a method for the modification of the dynamic calibration system is proposed.

Centrifugal blood pump

Abstract: As a dynamic pressure groove of a radial dynamic pressure bearing of a centrifugal blood pump, an alternative to a conventional spiral groove can be easily cut or can be easily punched by injection molding, while reducing manufacturing cost and manufacturing time. An object of the present invention is to provide a dynamic pressure groove shape of a high precision radial dynamic pressure bearing. In a centrifugal blood pump including a casing provided with an inlet and an outlet, and an impeller for sending liquid from the inlet to the outlet by rotating in the casing, a fixed shaft of the casing inner cylinder; A radial dynamic pressure bearing that generates dynamic pressure between the inner periphery of the rotating blades, and the dynamic pressure groove formed on the outer peripheral surface of the fixed shaft has a multi-circular shape in the rotating surface, and the axial shape is a groove. The part is parallel to the axis of rotation. [Selection] Figure 1

Experimental Characterization of Isolator Shock Train Propagation

Abstract: Quasi-steady shock trains in a rectangular isolator of the aspect ratio 3 were characterized with Mach 2.5 upstream flow and under slowly varying backpressure conditions. A time-history schlieren technique, accompanied by simultaneous static and dynamic pressure measurements, was performed to better understand the transient aspect of shock-boundary layer interaction leading to inlet unstart. Both spanwise and centerline static pressure measurements were utilized to characterize the propagation of shock trains inside the isolator, while the dynamic pressure measurements were further analyzed in an effort to find any precursor of unstart. A database showing time-resolved schlieren images with corresponding axial pressure profile and pressure gradient profile was constructed. The preliminary results revealed a clear difference between visible shock train length and the extent of the pressure gradient in the isolator. Investigation on the shock train dynamics revealed a highly oscillatory nature of the propagating shock trains. Additional research is in progress to characterize the shock train motion and the dynamic behavior with the downstream pressure disturbance characteristics.

Energy Harvesting From Hydraulic Pressure Fluctuations

Abstract: State-of-the-art hydraulic hose and piping systems employ integral sensor nodes for structural health monitoring in order to avoid catastrophic failures. These systems lend themselves to energy harvesting for powering sensor nodes. The foremost reason is that the power intensity of hydraulic systems is orders of magnitude higher than typical energy harvesting sources considered to date, such as wind turbulence, water flow, or vibrations of civil structures. Hydraulic systems inherently have a high energy intensity associated with the mean pressure and flow. Accompanying the mean pressure is what is termed dynamic pressure ripple caused by the action of pumps and actuators. Pressure ripple is conducive to energy harvesting as it is a deterministic source with an almost periodic time domain behavior. Pressure ripple generally increases in magnitude with the mean pressure of the system, which in turn increases the power that can be harvested. The harvested energy in hydraulic systems could enable self-powered wireless sensor nodes for applications such as energy-autonomous structural health monitoring and prognosis. An energy harvester prototype was designed for generating low-power electricity from dynamic pressure ripples. The prototype employed an axially-poled off-the-shelf piezoelectric stack. A housing isolated the stack from the hydraulic fluid while maintaining mechanical coupling to the system to allow for dynamic pressure induced deflection of the stack. The system exhibits an attractive off-resonance energy harvesting problem since the fundamental resonance of the piezoelectric stack is much higher than the frequency content of ripple. Although the energy harvester is not excited at resonance, the high energy intensity of the ripple results in significant electrical power output. The prototype provided a maximum output of 1.2 mW at 120Ω. With these results, it is clear that the energy harvester provides non-negligible power output suitable for powering sensors and other low power components. This work also presents electromechanical model simulations for predicting the piezoelectric power output in terms of the force transmitted from the pressure ripple as well as experimental characterization of the power output as a function of the force from the ripple.Copyright © 2012 by ASME

Method for jointly and synchronously measuring velocity/pressure during pitching/rolling movement of model

Abstract: The invention relates to an experiment method for jointly and synchronously measuring model motion track, object plane pressure and space velocity field during pitching-rolling two-degree-of-freedom dynamic simulation motion control process. A pitching motion mechanism and a model support rod are simultaneously driven through an industrial personal computer to respectively drive the model to makepitching and rolling motion along preset tracks. When the model moves to a position requiring data acquisition, the industrial personal computer sends an instruction to pressure measuring equipment and PIV (Particle Image Velocimetry) equipment at multiple points, and the actual motion position, the object plane pressure and the space velocity field of the model are collected synchronously. Experiment results show that two-degree-of-freedom coupled simulation motion has high precision under the control of PID (Proportion Integration Differentiation) closed loop feedback, and the error of synchronous measurement can be reduced by transmitting an external trigger signal of synchronous measurement according to a partitioning method. The joint and synchronous experiment technology provides aneffective research means for the analysis of the large angle-of-attack unsteady flow mechanism.

Coal seam water infusion device with high ground pressure, low porosity and low permeability and using process thereof

Abstract: The invention relates to a coal seam water infusion device with high ground pressure, low porosity and low permeability, which comprises a static pressure water infusion device and a dynamic pressure water infusion device. The static pressure water infusion device comprises a static pressure water infusion supply pipe, a static pressure main pipeline stop valve, a first differential pressure typepenetrant continuous and quantitative adding pump, a static pressure flow divider, a static pressure branch pipeline, a static pressure branch pipeline stop valve and a static pressure flow meter. The dynamic pressure water infusion device comprises a dynamic pressure water infusion supply pipe, a water storage tank, a second differential pressure type penetrant continuous and quantitative addingpump, a water return pipe, a water infusion pump, a water quality filter, a pressure gauge, a dynamic pressure main pipeline stop valve, a dynamic pressure flow divider, a dynamic pressure branch pipeline, a dynamic pressure branch pipeline stop valve and a dynamic pressure flow meter.

Synchronous data acquisition system used in wind tunnel based on stable dynamic pressure control

Abstract: The invention discloses a synchronous data acquisition system used in a wind tunnel based on stable dynamic pressure control The data acquisition system comprises a pressure sensor, a pressure acquisition system, an aerodynamic force balance unit, an aerodynamic force acquisition system, a standard pressure source, an industrial personal computer (IPC), a stable dynamic pressure sensor, an accuracy control device, an aerodynamic parameter system and a motor fan, wherein, the pressure sensor measures the pressure in the low-speed wind tunnel and transmits the measured pressure value to the pressure acquisition system; the aerodynamic force balance unit measures aerodynamic force on an experimental model and outputs the measured aerodynamic force value to the aerodynamic force acquisition system; the standard pressure source respectively calibrates the pressure sensor, the pressure acquisition system and the stable dynamic pressure sensor so as to obtain calibration factors, the calibration factors are transmitted to the IPC so as to obtain a controlled process mathematical model for stable dynamic pressure control, and then the controlled process mathematical model is transmitted to the accuracy control device; the accuracy control device drives the pressure acquisition system, the aerodynamic parameter system and the aerodynamic force acquisition system to perform synchronousdata acquisition; the stable dynamic pressure sensor acquires variation of a flow field in the low-speed wind tunnel, and then the variation value is transmitted to the IPC; and the IPC controls the motor fan to rotate The data acquisition system disclosed by the invention has the advantages that manpower is saved, high-accuracy data can be obtained, the operating method is simple and practical,the cost is low and the application prospect is wide

Analytical Model for Deflection of the Runway Pavement at Touchdown Point Caused by an Aircraft during Landing

Abstract: An estimation of the runway pavement deflection during landing for design purposes has been a challenging problem for engineers. This paper presents a simple analytical model to predict dynamic deflection of a runway pavement at touchdown point caused by a landing gear load during aircraft landing. Three independent parameters, modulus of subgrade reaction (ks), contact pressure (p), and vertical component of aircraft velocity (vv), are required to estimate the deflection using this model. This model shows that the dynamic deflection increases with an increase in vertical velocity and contact pressure. These observations follow an expected trend and the field observations made during inspection of the runways. Likewise, the impact factor, which is defined as the ratio of the dynamic deflection to static deflection, also increases with an increase in vertical velocity for a given value of the contact pressure. Irrespective of contact pressure values, the impact factor for zero vertical velocity is ...

Global‐scale observations of ionospheric convection variation in response to sudden increases in the solar wind dynamic pressure

Abstract: [1] We have used a superposed epoch analysis to study 205 sudden commencement (SC) events detected with ground-based magnetometers between the years 2000 and 2007. The strength of the SC events was clearly correlated to the magnitude of the jump in the solar wind dynamic pressure, regardless of whether or not the SC events were followed by a magnetic storm. Data from the Super Dual Auroral Radar Network (SuperDARN) demonstrated that both the ionospheric plasma drift speed and the number of echoes increased in the noon sector in response to the increase in solar wind dynamic pressure. In contrast, the number of SuperDARN echoes in the midnight sector decreased as the solar wind dynamic pressure increased, even though the average drift speed in the midnight sector also increased. We also uncovered that the ionosphere and ring current evolve differently in response to the pressure pulses. The SYM-H index, which represents changes in both the magnetopause and ring currents, responded immediately and either rapidly returned to pre-SC values or progressed into the main phase of a geomagnetic storm. In contrast, the ionospheric convection data were affected for a much longer time. The implication is that the ring current reacts to a sudden compression of the magnetosphere on a time scale of 10 min, while the convection pattern itself is affected for as long as the increase in solar wind dynamic pressure is sustained, or until a geomagnetic storm was triggered, as is the case in the sudden storm commencement (SSC) subset of events.

Separation of hydrodynamic perturbations in acoustic liner insertion loss measurements at a fan rig

Abstract: The scope of this study is the separation of the hydrodynamic pressure perturbations beneath a turbulent boundary layer in acoustic measurements in annular ow ducts. The hydrodynamic pressure perturbations superpose with the acoustic perturbations and cannot be distinguished by a microphone. In ow ducts with acoustical treatment, the magnitude of the hydrodynamic signal fraction can exceed that of the broadband acoustic fraction and therefore bias insertion loss measurements. In order to improve the measurement quality approaches for the separation of the hydrodynamic and acoustic pressure perturbations were studied. The investigations were carried out for an axial array of 60 microphones mounted in the bypass duct of the AneCom Universal Fan Facility for Acoustics (UFFA). In the paper is shown that the dierent constituents could be separated by means of an axial wave number decomposition. In a subsequent step ltered power spectral densities were reconstructed from the decomposed data, which represented solely the downstream propagating acoustic modes. Thus the liner insertion loss could be determined with signicantly improved accuracy. In an accompanied study the suitability of semi-empirical models to predict the spectrum of hydrodynamic pressure uctuations was examined. For this purpose a parametric study was conducted at a specic DLR test rig. Outcome was that using the dynamic pressure as pressure scale and the boundary layer thickness together with the ow speed as time scale an existing model can be adapted to the UFFA fan rig data. Thus, by subtraction of the of the unwanted hydrodynamic contributions the quality of liner insertion loss measurements can be improved also in cases when not enough microphones are available for wave number decomposition.

Sensor for measuring pressure and/or force

Abstract: A sensor for measuring pressure and/or force comprises at least one measurement arrangement with at least one piezoelectric measurement element (2) which is subjected to a compression stress for dynamic pressure and/or force measurement, and a diaphragm (3) for introducing the pressure and/or the force to at least the piezoelectric measurement element In order to specify a further embodiment of a sensor for pressure or force measurement that permits improved capturing of static and dynamic effects, a further measurement arrangement (4, 7) for static pressure and/or force measurement based on another physical measurement principle is proposed for this sensor