scholarly journals PHOTOACOUSTIC GENERATION OF FOCUSED QUASI-UNIPOLAR PRESSURE PULSES

2010 ◽  
Vol 03 (04) ◽  
pp. 247-253 ◽  
Author(s):  
KONSTANTIN MASLOV ◽  
HAO F. ZHANG ◽  
LIHONG V. WANG
Keyword(s):  
Energy Deposition ◽  
Acoustic Pressure ◽  
Pressure Pulse ◽  
Positive Pressure ◽  
Focal Region ◽  
Free Boundaries ◽  
Spatial Profile ◽  
Photoacoustic Effect ◽  
Temporal Profile ◽  
Pressure Pulses

The photoacoustic effect was employed to generate short-duration quasi-unipolar acoustic pressure pulses in both planar and spherically focused geometries. In the focal region, the temporal profile of a pressure pulse can be approximated by the first derivative of the temporal profile near the front transducer surface, with a time-averaged value equal to zero. This approximation agreed with experimental results acquired from photoacoustic transducers with both rigid and free boundaries. For a free boundary, the acoustic pressure in the focal region is equal to the sum of a positive pressure that follows the spatial profile of the optical energy deposition in the medium and a negative pressure that follows the temporal profile of the laser pulse.

Experimental Measurement of Pressure Pulses From a Pulp Screen Rotor

2010 ◽  
Author(s):  
Sean Delfel ◽  
James Olson ◽  
Carl Ollivier-Gooch ◽  
Phil Wallace
Keyword(s):  
Reynolds Number ◽  
Flow Velocity ◽  
Negative Pressure ◽  
Pressure Pulse ◽  
Pressure Coefficient ◽  
Positive Pressure ◽  
Single Element ◽  
Experimental Measurements ◽  
Main Function ◽  
Pressure Pulses

Pressure screens are the most industrially effective way to remove contaminants from a pulp stream, improving the strength, smoothness, and optical qualities of both new and recycled paper. Pressure screens are comprised of two main components: a screen cylinder with narrow slots or small holes and a rotor. The main function of the rotor is to prevent the narrow cylinder apertures from becoming plugged by pulp and debris. In this study, the pressure pulses generated by a novel multi-element foil (MEF) and a single-element foil rotor in a pressure screen were measured at various foil configurations, rotor speeds, and flow rates. The experimental measurements were compared to the results from a computational fluid dynamics model (CFD). Experimental measurements showed that increasing both the angle-of-attack and the flap angle of the MEF increases the magnitude of the negative pressure pulse and reduce the magnitude of the maximum pressure pulse generated by the rotor. At the optimum configurations, the MEF was shown to produce a 126% higher magnitude negative pressure pulse and a 39% lower magnitude positive pressure pulse. It was also found that at higher tip speeds the magnitude of the pressure pulse varies with tip speed squared and the non-dimensional pressure coefficient is Reynolds number independent. Similarly, at higher tip speeds increasing the velocity of the flow through the slots had no effect on the pressure pulse generated by the rotor. At lower rotor speeds, however, the dimensionless pressure was increasingly depending on Reynolds number as slot flow velocity was increased. This is likely due to the increase in slot flow velocity causing the onset of flow separation over the foil. Finally, the numerical model was shown to accurately predict the pressure pulses generated by the MEF at low angles-of-attack and flap angles. However, the model predicted that the foil would stall at lower angles than what was shown experimentally. This is probably because the CFD model used a solid wall boundary condition rather than modeling the slots in the cylinder, preventing low momentum fluid from re-entering the domain.

Numerical Simulation and Experimental Measurement of Pressure Pulses Produced by a Pulp Screen Foil Rotor

2004 ◽  
Vol 127 (2) ◽  
pp. 347-357 ◽  
Author(s):  
Mei Feng ◽  
Jaime Gonzalez ◽  
James A. Olson ◽  
Carl Ollivier-Gooch ◽  
Robert W. Gooding
Keyword(s):  
Negative Pressure ◽  
Pressure Pulse ◽  
Pressure Coefficient ◽  
Angle Of Attack ◽  
Tangential Velocity ◽  
Positive Pressure ◽  
Experimental Measurements ◽  
Wide Range ◽  
Pressure Pulses ◽  
Naca 0012

Pressure screening is an efficient means of removing various contaminants that degrade the appearance and strength of paper. A critical component of a screen is the rotor, which induces a tangential velocity to the suspension and produces pressure pulses to keep the screen apertures clear. To understand the effect of key design and operating variables for a NACA foil rotor, a computational fluid dynamic (CFD) simulation was developed using FLUENT, and the results were compared to experimental measurements. Comparing the pressure pulses obtained through CFD to experimental measurements over a wide range of foil tip speeds, clearances, angles of attack, and foil cambers, general trends of the pressure pulses were similar, but the overall computed values were 40% smaller than the measured values. The pressure pulse peak was found to increase linearly with the square of tip speed for all the angles of attack studied. The maximum magnitudes of negative pressure pulse occurred for the NACA 0012 and 4312 foils at a 5deg angle of attack and for the NACA 8312 foil at 0deg. The stall angle of attack was found to be ∼5deg for NACA 8312, ∼10deg for NACA 4312, and ∼15deg for NACA 0012. The positive pressure peak near the leading edge of the foil was eliminated for foils operating at a positive angle of attack. The magnitude of the negative pressure coefficient peak increased as clearance decreased. Increased camber increases both the magnitude and width of the negative pressure pulse.

High-Intensity Focused Ultrasound Scattering at Mammal Vertebrae

2020 ◽  
Author(s):  
David Sanford ◽  
Christoph Schaal
Keyword(s):  
High Intensity ◽  
Laboratory Experiments ◽  
Energy Deposition ◽  
Focused Ultrasound ◽  
Complex Geometry ◽  
Ex Vivo ◽  
Pulsed Laser ◽  
High Intensity Focused Ultrasound ◽  
Focal Region ◽  
Homogeneous Media

Abstract High-intensity focused ultrasound (HIFU) is used clinically to heat cells therapeutically or to destroy them through heat or cavitation. In homogeneous media, the highest wave amplitudes occur at a predictable focal region. However, HIFU is generally not used in the proximity of bones due to wave absorption and scattering. Ultrasound is passed through the skull in some clinical trials, but the complex geometry of the spine poses a greater targeting challenge and currently prohibits therapeutic ultrasound treatments near the vertebral column. This paper presents a comprehensive experimental study involving shadowgraphy and hydrophone measurements to determine the spatial distribution of pressure amplitudes from induced HIFU waves near vertebrae. First, a bone-like composite plate that is partially obstructing the induced waves is shown to break the conical HIFU form into two regions. Wave images are captured using pulsed laser shadowgraphy, and hydrophone measurements over the same region are compared to the shadowgraphy intensity plots to validate the procedure. Next, shadowgraphy is performed for an individual, clean, ex-vivo feline vertebra. The results indicate that shadowgraphy can be used to determine energy deposition patterns and to determine heating at a specific location. The latter is confirmed through additional temperature measurements. Overall, these laboratory experiments may help determine the efficacy of warming specific nerve cells within mammal vertebrae without causing damage to adjacent tissue.

Acoustic pressure pulse generator

1996 ◽  
Vol 100 (4) ◽  
pp. 1938
Author(s):  
F. Plisek ◽  
B. Hartinger
Keyword(s):  
Acoustic Pressure ◽  
Pressure Pulse ◽  
Pulse Generator

Midlatency respiratory-related somatosensory activity and perception of oral pressure pulses in normal humans

2001 ◽  
Vol 90 (6) ◽  
pp. 2048-2056 ◽  
Author(s):  
J. Andrew Daubenspeck ◽  
Harold L. Manning ◽  
John C. Baird
Keyword(s):  
Evoked Potentials ◽  
Pressure Pulse ◽  
Applied Pressure ◽  
Normal Subjects ◽  
Magnitude Production ◽  
Global Field Power ◽  
Oral Pressure ◽  
Pressure Pulses ◽  
Standard Pressure ◽  
The Right

A direct relationship exists within subjects between midlatency features (<100 ms poststimulus) of respiratory-related evoked potentials and the perceived magnitude of applied oral pressure pulse stimuli. We evaluated perception in 18 normal subjects using cross-modality matching of applied pressure pulses via grip force and estimated mechanoafferent activity in these subjects by computing the global field power (GFP) from respiratory-related evoked potentials recorded over the right side of the scalp. We compared across subjects 1) the predicted magnitude production for a standard pressure pulse and 2) the slope (β) and 3) the intercept (INT) of the Stevens power law to the summed GFP over 20–100 ms poststimulus. Both the magnitude production for a standard pressure pulse and the β showed an inverse relationship with the summed GFP over 20–100 ms poststimulus, although there was no relationship between INT and the summed GFP. This may partially reflect characteristics of the mechanosensors and surely includes aspects of cognitive judgment, because we found and corrected for a high correlation between, respectively, β (and INT) for pressure pulses and β (and INT) for estimation of line lengths, a nonrespiratory modality. The relatively shallow, even inverse GFP-to-perception relationship suggests that, despite marked differences in the magnitude of afferent traffic, normal subjects seem to perceive things similarly.

Response of Water-Filled Thin-Walled Pipes to Pressure Pulses: Experiments and Analysis

1980 ◽  
Vol 102 (1) ◽  
pp. 56-61 ◽  
Author(s):  
C. M. Romander ◽  
L. E. Schwer ◽  
D. J. Cagliostro
Keyword(s):  
Pressure Pulse ◽  
Fluid Structure Interaction ◽  
Two Dimensional ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Modeling Techniques ◽  
Pressure Pulses ◽  
Piping Systems ◽  
Dimensional Finite Element ◽  
Thin Walled

Experiments are performed to verify modeling techniques used in fluid-structure interaction codes that predict the response of liquid-filled piping systems to strong pressure pulses. Pressure pulses having a 150-μs rise time, a 2000-psi (13.8 MPa) magnitude, and a 3-ms duration are propagated into straight, water-filled Ni 200 pipes (3-in. (7.6-cm) O.D. 0.065-in. (0.165-cm) wall). Attenuation of the pressure pulse and the strain and deformation along the pipes are measured. The experiments are modeled in WHAM, a two-dimensional, finite-element, compressible fluid-structure interaction code. The experimental and analytical results are discussed in detail and are found to compare favorably.

On the Phenomenon of Pressure Pulses Reflecting Between Blades of Adjacent Blade Rows of Turbomachines

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Jerzy A. Owczarek
Keyword(s):  
Pressure Pulse ◽  
Physical Phenomenon ◽  
Research Work ◽  
Axial Compressor ◽  
Rotor Blades ◽  
Test Results ◽  
Lehigh University ◽  
Pressure Pulses ◽  
Excitation Frequencies ◽  
Asme Paper

The recently revived interest in “acoustic resonances,” whose details are still not well defined or understood, points to a realization that a new look at some previously unrecognized findings is needed to explain problems encountered in operation of compressors and turbines. The purpose of this paper is to call the attention of the turbomachinery community to an important physical phenomenon of pressure waves in form of pulses, which reflect between blades of adjacent blade rows of turbomachines discovered more than 40 years ago, about whose existence and consequences there is little awareness today. The turbine test results which led the author in 1957 to hypothesize the existence of the phenomenon of reflecting pressure pulses are described. Subsequently, his 1966 ASME paper is discussed. In it, the author reported on the photographed observations of pressure pulses reflecting between stationary nozzles and moving blades of a water-table turbine at Lehigh University, on the description of the various types of such waves, and on an explanation of some of the resonant blade excitation frequencies observed by National Advisory Committee for Aeronautics (NACA) in a turbine of turbojet engine. This is followed by a description of his 1984 ASME paper, in which more general formulae were derived for the blade excitation frequencies caused by the reflections of pressure pulses between the rotor blades, and both upstream and downstream stator vanes. These equations were subsequently used to explain the blade excitation frequencies measured in an axial compressor stage. Finally, his 1992 AIAA paper is discussed, in which additional formulae relating to the reflecting pressure pulses were derived, and the process of formation of a pressure pulse was explained. To put this work in perspective, the author provided, in mostly chronological order, excerpts from reports on operational problems encountered with turbomachines in service and brief descriptions, from selected publications, of pertinent research work.

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