Induced Pressure Variations Research Articles

Effect of gravity on phase transition for liquid–gas simulations

Direct simulations of phase-change and phase-ordering phenomena are becoming more common. Recently, qualitative simulations of boiling phenomena have been undertaken by a large number of research groups. One seldom discussed limitation is that large values of gravitational forcing are required to simulate the detachment and rise of bubbles formed at the bottom surface. The forces are typically so large that neglecting the effects of varying pressure in the system becomes questionable. In this paper, we examine the effect of large pressure variations induced by gravity using pseudopotential lattice Boltzmann simulations. These pressure variations lead to height dependent conditions for phase coexistence and nucleation of either gas or liquid domains. Because these effects have not previously been studied in the context of these simulation methods, we focus here on the phase stability in a one-dimensional system, rather than the additional complexity of bubble or droplet dynamics. Even in this simple case, we find that the different forms of gravitational forces employed in the literature lead to qualitatively different phenomena, leading to the conclusion that the effects of gravity induced pressure variations on phase-change phenomena should be very carefully considered when trying to advance boiling and cavitation as well as liquefaction simulations to become quantitative tools.

Wind Induced Pressure Variation on High-rise Geometrically Modified Building having Interference through CFD Simulation

The wind different forms i.e. cyclones, hurricanes, storms, tornados, etc., loads various structures which come in their way. To minimize the wind effects, different techniques have been used and geometrical modification is one of them. In this study, the pressure variation on a geometrically modified high-rise corner-cut building having interference has been evaluated. The study is carried out using ANSYS FLUENT in which CFD simulation is carried out for the different models at different wind incidence angles viz. 0°, 45°, and 90°. Two building models are used in this study, one is high rise Corner-cut building, which is called the principal or primary building. The other is a high-rise rectangular building, which is called interfering or secondary building. The results obtained in case of interference are then compared to that of an isolated corner-cut building. In general, from the present investigation, it is noticed that the suction effect increases due to the interference effect. When wind strikes obliquely the effect of interference is relatively lower.

Time-Dependent Electroosmotic Flow with Variable Slips along Microchannel

The micromixing effect due to hydrophobic slip effects along a microchannel is studied numerically. The flow enhancement and mixing are analyzed with different slips with the variation of the electric double layer (EDL) thickness and the solution strengths. Flow advection effects due to external electric fields are clearly observed along the flow direction. A parametric estimation is provided between solution strength and volume flow rate to obtain the effectiveness factor responsible for the flow dominance. Also, the overlapped EDL regions are considered to predict the flow nature and the induced pressure variation. The main aspect of this article is to analyze the mixing efficiency as a function of slip varying parameters with the electric field and molarity of the solution. A time scale analysis is made and an analytical estimation is achieved and compared with the existing experimental results at different time levels.

Acoustic Analog Front End for Proton Range Detection in Hadron Therapy

Clinical ions beams for cancer treatment provide maximum energy deposition (Bragg peak (BP)) at the end of their range and practically no dose behind. This enables a more efficient therapeutic option comparing with classical photon-based radiotherapy where maximum energy is deposited at the body interface. Obviously, minimum-error BP detection is, thus, a key aspect of this treatment. This paper investigates a promising detection technique, based on the so-called ionoacoustic effect. The BP energy deposition causes a small (millikelvin) heating of the surrounding volume that in turn induces a pressure variation. This generates a sound signal that can be detected by an acoustic sensor placed at a certain distance from the BP point. Thus, the sound time-of-flight measure aims, with sound speed, to detect the BP position with very high accuracy (<1mm). This paper presents the results of a complete cross-domain model that starting from proton beam energy provides the induced pressure variation in water, emulates the propagation of sound waves in the medium, and finally, returns a voltage signal whose time evolution determines BP position with an average deviation from effective position of 1% accuracy.

Integrated-fin gasket for palm cubic-anvil high pressure apparatus.

We described an integrated-fin gasket technique for the palm cubic-anvil apparatus specialized for the high-pressure and low-temperature measurements. By using such a gasket made from the semi-sintered MgO ceramics and the tungsten-carbide anvils of 2.5 mm square top, we successfully generate pressures over 16 GPa at both room and cryogenic temperatures down to 0.5 K. We observed a pressure self-increment for this specific configuration and further characterized the thermally induced pressure variation by monitoring the antiferromagnetic transition temperature of chromium up to 12 GPa. In addition to enlarge the pressure capacity, such a modified gasket also improves greatly the surviving rate of electrical leads hanging the sample inside a Teflon capsule filled with the liquid pressure-transmitting medium. These improvements should be attributed to the reduced extrusion of gasket materials during the initial compression.

Sea surface shape derivation above the seismic streamer

ABSTRACTThe rough sea surface causes perturbations in the seismic data that can be significant for time‐lapse studies. The perturbations arise because the reflection response of the non‐flat sea perturbs the seismic wavelet. In order to remove these perturbations from the received seismic data, special deconvolution methods can be used, but these methods require, as input, the time varying wave elevation above each hydrophone in the streamer. In addition, the vertical displacement of the streamer itself must also be known at the position of each hydrophone and at all times. This information is not available in conventional seismic acquisition. However, it can be obtained from the hydrophone measurements provided that the hydrophones are recorded individually (not grouped), that the recording bandwidth is extended down to 0.05 Hz and that data are recorded without gaps between the shot records.The sea surface elevation, and also the wave‐induced vertical displacement of the streamer, can be determined from the time‐varying pressure that the sea waves cause in the hydrophone measurements. When this was done experimentally, using a single sensor seismic streamer without a conventional low cut filter, the wave induced pressure variations were easily detected. The inversion of these experimental data gives results for the sea surface elevation that are consistent with the weather and sea state at the time of acquisition. A high tension approximation allows a simplified solution of the equations that does not demand a knowledge of the streamer tension. However, best results at the tail end of the streamer are obtained using the general equation.

Implications of carbon flux from the Cascadia accretionary prism: results from long-term, in situ measurements at ODP Site 892B

A 403-day in situ field experiment at Ocean Drilling Program Site 892B sought to quantify the flux of methane along a fluid-active fault and to experimentally determine rates of methane hydrate and authigenic carbonate deposition associated with fluid expulsion from the borehole. An instrument package was deployed that osmotically sampled fluid, measured borehole pressure and flow rates, and contained reaction chambers in which deposition of gas hydrates and carbonates was anticipated, and from which microbial communities might be extracted. Flow is highly variable in the three-phase water–methane system that exists at Site 892B. Flow rates fluctuate over two orders of magnitude in response to tidally induced pressure variations and gas hydrate formation and dissociation. Hydrate formation began 45 days into the experiment and reduced the initial flow (∼2 l/day) to 20 ml/day. Unexpectedly, the hydrate destabilized after about 125 days. Tidally induced flow reversals are common (∼25% of time) in this setting characterized by ‘overpressured’ pore waters. These reversals pump sulfate-rich bottom water into near-surface sediments where Archaea anaerobically oxidize CH 4 and induce carbonate precipitation. At the sediment–water interface, authigenic carbonates are undergoing dissolution. Methanotrophs dominated the microbial community where fluid is discharged to ambient seawater. All expelled methane is apparently oxidized in the water column.

Reducing gravity at the superfluid transition in helium-4

There are two intrinsic experimental limitations in measurements near Tλ for traditional ground based experiments: the gravitationally induced pressure variations present in any macroscopic helium sample limit how closely the transition can be approached, and the onset of convection in a sample with T>Tλ limits the range of heat values that can be used. To overcome these limitations, we have built a low gravity simulator consisting of a superconducting magnet with a magnetic field profile shaped to provide a magnetic force opposite that of gravity. Preliminary measurements have shown a decrease in the range of reduced temperatures across a sample but not the expected suppression of the onset of convection.

Induced transglottal pressure variations during voicing

The response of the vibratory pattern of the vocal folds to externally induced changes of supraglottal pressure was measured. Tracings of the variation of F 0 after a step change in pressure indicated that a pressure variation similar to a single bipolar cycle of an 8–10 Hz sinusoid is fast enough to vary the average transglottal and/or intraglottal pressure without stimulating compensatory action during the induced pressure pulse and slow enough to allow the vocal fold oscillatory behavior to respond to the change in pressure during each half of the pulse. An example is presented of the shape of the glottal airflow pulse during a continuous 10Hz sinusoidal induced pressure variation, as derived by inverse filtering oral airflow.

Effect of thoracic and abdominal pressure waves on blood flow in cardiopulmonary resuscitation

Based on the assumption that externally induced pressure variations inside the chest cavity generate life saving blood flow during cardiopulmonary resuscitation (CPR) in cardiac arrest, mathematical models of increased complexities were developed to describe the flow phenomena in the cardiovascular system. The lumped parameter representation of the cardiovascular system describes the flow phenomena during CPR, and is used to optimize the present CPR technique as well as to suggest a new CPR procedure. Clinical experimental studies (dogs) confirm the prediction that a sequential phased abdomino-thoracic compression (PCCPR) yields blood flows which are twice the values obtained in the classical CPR mode of manual chest compression. The newly suggested PCCPR technique greatly improves vital organs' blood flow in CPR and opens a new direction in the field of emergency medicine.

Low-temperature pressure variations in a self-clamping pressure cell

A simple method is described that permits a consistent determination of thermally induced pressure variations in a piston-cylinder, self-clamping pressure cell at temperatures less than ambient. Significant pressure changes are found to be present even for T&amp;lt;75 K. It is also shown that the pressure coefficient of resistance of a manganin-wire gauge is, to within experimental uncertainty, independent of temperature over the range 0&amp;lt;T≤300 K.

Effect of sampling lines on measured DOP aerosol concentration.

The effects of three types of sampling lines of various bore diameters and lengths on measured DOP aerosol concentration were studied under a variety of experimental conditions. Measurement errors, which were significant with long lines having small bore diameters, were independent of line material and aerosol concentration, but were well correlated with line induced pressure variations in the measurement instrument. Actual loss of aerosol in the lines appears to occur only at very low sampling rates.