Formation Of Pressure Waves Research Articles

Small Model Experiment on the Pressure Wave Formation by Entering the Tunnel of Conventional Limited Express with Diaphragmless Driver Acceleration Apparatus

Small Model Experiment on the Pressure Wave Formation by Entering the Tunnel of Conventional Limited Express with Diaphragmless Driver Acceleration Apparatus

Aortic Wave Dynamics and Its Influence on Left Ventricular Workload

The pumping mechanism of the heart is pulsatile, so the heart generates pulsatile flow that enters into the compliant aorta in the form of pressure and flow waves. We hypothesized that there exists a specific heart rate at which the external left ventricular (LV) power is minimized. To test this hypothesis, we used a computational model to explore the effects of heart rate (HR) and aortic rigidity on left ventricular (LV) power requirement. While both mean and pulsatile parts of the pressure play an important role in LV power requirement elevation, at higher rigidities the effect of pulsatility becomes more dominant. For any given aortic rigidity, there exists an optimum HR that minimizes the LV power requirement at a given cardiac output. The optimum HR shifts to higher values as the aorta becomes more rigid. To conclude, there is an optimum condition for aortic waves that minimizes the LV pulsatile load and consequently the total LV workload.

Investigation of the Stability of Melt Flow in Gating Systems

Melt flow in four different gating systems designed for the production of brake disks was analyzed experimentally and by numerical modeling. In the experiments, molds were fitted with glass fronts and melt flow was recorded on video. The video recordings were compared with the modeling of melt flow in the gating systems. Particular emphasis was on analyzing local pressure and formation of pressure waves in the gating system. It was possible to compare melt flow patterns in experiments directly with modeled flow patterns. Generally, there was good agreement between flow patterns and filling times. However, the description of free liquid surfaces proved to be incorrect in the numerical model. The modeled pressure fields served to explain how specific parts of the gating systems cause instability and are a good tool to describe the quality of a gating system. The results show clearly that sharp changes in the geometry of the gating system causes pressure waves to form that eventually lead to defective castings. It is clear that sharp corners and dead ends in gating systems should be avoided, and that more streamlined, organic, or naturally pressurized designs based on fluid dynamic principles will are necessary to design gating systems for the production of high-quality castings.

G201 収縮拡大流路に発生するキャビテーションクラウドの放出パターンに関する検討(GS-2 キャビテーション・マイクロバブル・数値計算1,一般セッション)

Cavitation cloud shows an unsteady periodic behavior and causes high impact. The periodicity of cavitation cloud shedding can be related to a reentrant motion and formation of pressure waves. A pattern of reentrant motion is dependent on re-circulating flow as well as pressure wave due to collapse of shedding clouds. In this study, we present some shedding patterns of cavitation cloud and the role of pressure wave accompanied with cloud collapse using an image analysis method.

Mathematical simulation of transient processes in a circular channel with granular layer under conditions of subcooled water boiling. Formation of pressure wave

The process of formation and growth of vapor bubbles until the instant of their merging into a vapor film is investigated in view of actual roughness of the surface and of the dependence of activation time of the respective nucleation sites on the surface temperature under conditions of pulsed heat release in the heater wall. A microlayer model is employed in view of formation of dry spot under the bubble. Also solved is the problem on the formation of a pressure wave in a circular channel as a result of explosive boiling of superheated microlayer under the bubbles. The obtained results enable one to describe a number of experimental data and investigate unsteady-state wave processes occurring under subcooled liquid boiling in the presence of a granular layer.

Coupled molecular dynamics-Monte Carlo model to study the role of chemical processes during laser ablation of polymeric materials

The coarse grained chemical reaction model is enhanced to build a molecular dynamics (MD) simulation framework with an embedded Monte Carlo (MC) based reaction scheme. The MC scheme utilizes predetermined reaction chemistry, energetics, and rate kinetics of materials to incorporate chemical reactions occurring in a substrate into the MD simulation. The kinetics information is utilized to set the probabilities for the types of reactions to perform based on radical survival times and reaction rates. Implementing a reaction involves changing the reactants species types which alters their interaction potentials and thus produces the required energy change. We discuss the application of this method to study the initiation of ultraviolet laser ablation in poly(methyl methacrylate). The use of this scheme enables the modeling of all possible photoexcitation pathways in the polymer. It also permits a direct study of the role of thermal, mechanical, and chemical processes that can set off ablation. We demonstrate that the role of laser induced heating, thermomechanical stresses, pressure wave formation and relaxation, and thermochemical decomposition of the polymer substrate can be investigated directly by suitably choosing the potential energy and chemical reaction energy landscape. The results highlight the usefulness of such a modeling approach by showing that various processes in polymer ablation are intricately linked leading to the transformation of the substrate and its ejection. The method, in principle, can be utilized to study systems where chemical reactions are expected to play a dominant role or interact strongly with other physical processes.

Reducing the flash hazard

Electrical workers are commonly exposed to three types of hazards: electrical shock, electrical burns resulting from contact and arc flash, and arc blast. Electrical burns that result from contact with energized parts occur due to current flow through the body. Burns as a result of arc flash occur due to radiant heat given off by an electrical arc. Lastly, arc blast is the result of the heating effects of an arc flash which produce tremendous pressures through the expansion of destroyed circuit materials. Of these three, electrical shock and electrical contact burns are the hazards of which most personnel are aware. An arc fault is the result of current flowing through air between conductors in phase-to-phase, single phase-to-ground, or multiple phase-to-ground configurations (i.e. a three-phase bolted fault). Arc faults can release large amounts of energy in an extremely short amount of time in the form of radiant heat, intense light, and high pressure waves. The radiant heat given off travels at the speed of light and can reach temperatures of 35,000degF. In recent years, the dangers and impact of arc flash have been studied and are now becoming better understood. However, the electrical industry is still in the process of studying the effects of arc blast and ways to mitigate its risks. This article is limited to the review of arc-flash hazards, their analysis, and corresponding ways to reduce incident energy in low-voltage systems.

Plasma Ignition in a 30-mm Cannon

Plasma ignition of conventional propelling charges has been studied in a 30-mm cannon using plasma generated in a capillary external to the charge. It is shown that the interaction distance for strong response from a propellant is limited even for this caliber, which may have implications for pressure wave formation during ignition. The use of confinement of a portion of the charge for enhanced ignition is shown to result in the most prompt ignition. However, with JA2 propellant, direct action of the plasma on the charge produces good results. The effect of plasma pulse length is explored; observations that enhanced radiation from high peak power that increases propellant response to plasma are discussed. A limited comparison of the response of JA2 and M30 propellants has been made

Inlet boundary conditions for the simulation of fluid dynamics in gas–solid fluidized beds

The interaction between a fluidized bed and the air-supply system is studied numerically in a cold circulating fluidized bed unit. The bed was operated with Group B solids and with an air-distributor pressure-drop similar to that often applied under industrial conditions. The simulations and experiments are compared through power spectral density distributions of pressure fluctuations in the bed and air plenum. This work focuses on the inlet boundary conditions of the numerical simulations, i.e., the purpose is to include a representation of fluctuations in pressure and flow in the air-supply system. The fluctuations are computed and coupled with the simulations of the flow field in the bed and the air plenum, based on an Eulerian approach. Parametric models are employed for spectral estimates as the time consumption for the three-dimensional simulation limits the length of the pressure time series. The simulations provide satisfactory agreement with experiments, and it is seen that, under certain conditions, there is a strong interaction between the fluidized bed and the air-supply system in the form of pressure waves, as well as pressure and flow pulsations from the air-supply system, which propagate through the entire system. It is demonstrated that for such a system, the assumption of a uniform inlet gas flow over the air distributor, assumed in most previous fluidized-bed studies, is not appropriate. This study demonstrates the importance of further development of numerical models for simulating the hydrodynamics of fluidized beds, in particular for industrially sized units.

Brachio-ankle pulse wave velocity and cardio-ankle vascular index (CAVI)

In order to diagnose arteriosclerosis in any part of the body, pulse wave velocity (PWV) measurement is a useful approach. However, it is considered that the technique of PWV measurement should be simplified. A new method for measuring PWV has therefore been proposed in Japan. The PWV of the brachial artery (ba) and the ankle was measured by applying air pressure with the aid of a volume plethysmograph. Comparisons between the baPWV measurement method and the conventional method are currently being performed. Since satisfactory results have been obtained to date, baPWV has gained popularity throughout Japan. Since this method measures PWV in the arm and foot, it may be said that aortic PWV is not reflected though a large amount of past PWV measurements. BaPWV is influenced by blood pressure. With the baPWV technique, blood pressure compensation is not carried out. Furthermore, the pulse pressure is measured by air pressure; therefore any stimulus that exerts pressure on an artery may influence these results. Due to these reasons, a cardio-ankle vascular index (CAVI) has been proposed in which the pressure wave form indicating the closing of the aortic valve appears in the form of an arterial pressure wave after a fixed delay time. This delay is the time difference between the actual closing of the aortic valve and the measuring point. Prior to the introduction of baPWV, PWV was measured in the carotid artery and foot. As in traditional PWV, baPWV uses the delay time, but between the brachial artery and the ankle artery. However, the carotid artery differs from the brachial artery, and the measured value differs depending on whether the arteriosclerosis is present in the carotid artery or the brachial artery. CAVI is calculated from the ECG, PCG, brachial artery waveform and ankle artery waveform using a special algorithm. This new method represents a breakthrough in the diagnosis of atherosclerosis.

Geometrical study of spark ignition in two dimensions

Spark ignition, as the first step during the combustion in Otto engines, has a profound impact on the further development of the flame kernel. Over the last ten years growing concern for environment protection, including low emission of pollutants has increased the interest in the numerical simulation of ignition phenomena to guarantee successful flame kernel development even for lean mixtures.However, the process of spark ignition in a combustible mixture is not yet fully understood. The use of detailed reaction mechanisms, combined with electrodynamical modelling of the spark, is necessary to optimize ignition of lean mixtures.This work presents simulations of the coupling of flow, chemical reactions and transport with discharge processes in order to investigate the development of a stable flame kernel initiated by an electrical spark. A two-dimensional code to simulate the early stages of flame kernel formation, shortly after the breakdown discharge, has been developed. The model includes Joule heating. The spark plasma channel formed as a consequence of the breakdown is incorporated into the initial conditions. The computations include the initial phase (1–5 µs), which is governed by pressure wave formation, but also the transition to flame propagation. A thorough study of the influence of the electrodes' geometry, i.e. shape and size, and gap width, has been performed for air and a lean H2–air mixture. Also a detailed methane-air mechanism was chosen as another example including combustion.Due to the fast expansion of the plasma channel, together with the geometrical complexity of the electrodes, a complicated flow field develops after the emission of a pressure wave by the expanding channel. Special numerical methods, including artificial viscosity, are required to resolve the complicated flow field during these first 1–5 µs. The heat release through chemical reactions and transport processes is almost negligible during this short phase. The second phase, i.e. the development of a propagating flame and the flame kernel expansion, can last up to several milliseconds and is dominated by diffusive processes and chemical reactions. It has been found that the geometry greatly influences the developing flame kernel and the flow field. As soon as chemical reactions begin to contribute significantly to the heat release, the effect becomes smaller.

Perspectives of coronary excimer laser angioplasty: Multiplexing, saline flushing, and acoustic ablation control

Background and Objective Bubble formation, pressure wave generation, and cavitations constitute major factors influencing the outcome of clinical Excimer laser angioplasty. Thus, the rationale of this study was to determine the extent of pressure waves occurring during excimer laser ablation and to discuss possibilities that allow a less traumatic plaque removal in the coronary circulation. Study Design/Materials and Methods Conventional and experimental Xenon-Chlorid-Excimer lasers emitting light at a wave-length of 308nm and a pulse duration of 115ns were used for testing of signals. Whereas the conventional excimer laser light source transmits light through all fibres of a 1.7 mm laser catheter simultaneously, the prototype excimer laser divides the laser beam into several areas of uniform energy fluence by scanning the beam from one section to the other using the intermission between two laser discharges. Hydrophones consisting of piezoelectric films detected the acoustic signals, which were obtained on normal arterial wall and atherosclerotic plaque. Results Multiplexing decreases maximum pressures for both normal arterial wall and calcified plaque significantly, whereas pressure rise time remains comparable. During ablation of pure blood, a linear increase of peak pressures of 1 MPa at 10 mJ/mm2 to 7.5 MPa at 50 mJ/mm2 is found. Contrast media intensifies the extent of pressure wave formation. At 20 mJ/mm2, 60% contrast media added to blood results in an increase of maximum pressures from 1.5 MPa up to 5 MPa. Dilution with saline solution is effective; however, high concentrations of > 90% are required to achieve a significant pressure wave reduction. Conclusion Peak pressures of several thousand kPa occur during excimer laser ablation of contrast media, blood, calcified plaque, and normal arterial wall in a decreasing order. Multiplexing and saline flushing are capable of reducing the intensity of the generated acoustic signals during tissue ablation. It has to be taken into consideration, however, that high concentrations of saline solution are necessary to achieve a significant reduction of peak pressures. Lasers Surg. Med. 21:72–78, 1997. © 1997 Wiley-Liss, Inc.

Perspectives of coronary excimer laser angioplasty: multiplexing, saline flushing, and acoustic ablation control.

Bubble formation, pressure wave generation, and cavitations constitute major factors influencing the outcome of clinical Excimer laser angioplasty. Thus, the rationale of this study was to determine the extent of pressure waves occurring during excimer laser ablation and to discuss possibilities that allow a less traumatic plaque removal in the coronary circulation. Conventional and experimental Xenon-Chlorid-Excimer lasers emitting light at a wave-length of 308 nm and a pulse duration of 115 ns were used for testing of signals. Whereas the conventional excimer laser light source transmits light through all fibers of a 1.7 mm laser catheter simultaneously, the prototype excimer laser divides the laser beam into several areas of uniform energy fluence by scanning the beam from one section to the other using the intermission between two laser discharges. Hydrophones consisting of piezoelectric films detected the acoustic signals, which were obtained on normal arterial wall and atherosclerotic plaque. Multiplexing decreases maximum pressures for both normal arterial wall and calcified plaque significantly, whereas pressure rise time remains comparable. During ablation of pure blood, a linear increase of peak pressures of 1 MPa at 10 mJ/mm2 to 7.5 MPa at 50 mJ/mm2 is found. Contrast media intensifies the extent of pressure wave formation. At 20 mJ/mm2, 60% contrast media added to blood results in an increase of maximum pressures from 1.5 MPa up to 5 MPa. Dilution with saline solution is effective; however, high concentrations of > 90% are required to achieve a significant pressure wave reduction. Peak pressures of several thousand kPa occur during excimer laser ablation of contrast media, blood, calcified plaque, and normal arterial wall in a decreasing order. Multiplexing and saline flushing are capable of reducing the intensity of the generated acoustic signals during tissue ablation. It has to be taken into consideration, however, that high concentrations of saline solution are necessary to achieve a significant reduction of peak pressures.

Magnetic and gas dynamic effects on arc motion in miniature circuit breakers

This paper presents new results on the magnetic and atmospheric environment in the arc chamber of a miniature circuit breaker under short circuit conditions. Finite element magnetic field calculations provide data on the flux density in the arc chamber and the effects of steel plates placed around the arc chamber. The magnetic calculations are used with a one-dimensional flow model to assess the influence of the magnetic environment on the arc dynamics. The results are compared with new experimental data on arc dynamics obtained using an an optical fiber imaging system in a production miniature circuit breaker. Additional information on the environment within the arc chamber is supplied by pressure and conductance measurements. Results show that the presence of steel in the sides of the arc chamber has a large effect on the magnetic field and the arc dynamics. Plasma jet and pressure wave formation have a significant effect on atmospheric conditions in the arc chamber.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Formation of pressure waves during in vitro excimer laser irradiation in whole blood and the effect of dilution with contrast media and saline

Pressure waves during excimer laser ablation of vascular tissue may be responsible for complications of coronary excimer laser angioplasty. In this experimental study, pressure waves were measured during excimer laser irradiation in blood and contrast media using a polyvinilidenefluoride hydrophone. At a distance of 4 mm lateral to the tip of a 1.7 mm multifiber laser catheter, excimer laser irradiation in blood resulted in a linear increase of peak pressures from 1,365 +/- 165 kPa at 30 mJ/mm2 to 2,866 +/- 404 kPa at 60 mJ/mm2. In contrast media, peak pressure increased from 3,172 +/- 573 kPa (30 mJ/mm2) to 5,763 +/- 467 kPa (60 mJ/mm2). Contrast media and saline were added to blood. At a concentration of 60% contrast in blood, a 3.4 fold increase of peak pressures was documented as compared to pure blood. Further increase of the concentration did not result in higher pressure waves. Concentrations of saline in blood of 90% and 96% reduced the peak pressures by 16% and > 50%, respectively, as compared to pure blood.

Spectral distortions of the microwave background radiation resulting from the damping of pressure waves

view Abstract Citations (108) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectral Distortions of the Microwave Background Radiation Resulting from the Damping of Pressure Waves Daly, R. A. Abstract Initial inhomogeneities of the energy density of the primeval radiation field which enter the horizon prior to recombination lead to the formation of pressure waves as they enter the horizon. On scales less than about 5 × 1016 M_s these waves will be damped prior to recombination by the processes of nonlinear dissipation and photon diffusion. The damping of these waves leaves its signature in spectral distortions of the microwave background radiation. The type of distortion depends upon the epoch of the damping. The magnitude of the distortion may be related to the amplitude of the waves which have been damped during a particular epoch. The amplitude of the perturbations of the energy density of the radiation field on a given scale may be related to those of the mass distribution on the same scale, in a manner which depends on whether the perturbations are of the isocurvature or adiabatic type. The limit on the amplitude of the initial perturbations of the mass distribution on the damping scale is used in conjunction with that on a much larger scale: the amplitude of the initial perturbations of the mass distribution needed to account for the observed variance of the number counts of galaxies at the current epoch, which depends on cosmological parameters. Combining these, an upper bound to the index of the initial power spectrum of the mass distribution is obtained. This bound depends on cosmological parameters, and on whether the initial perturbations are of the isocurvature or adiabatic type. The current and projected limits of the magnitude of the Compton y-parameter and of a chemical potential are used to constrain the index of the initial power spectrum of the mass distribution for several cosmological parameter sets for isocurvature and adiabatic perturbations. Publication: The Astrophysical Journal Pub Date: April 1991 DOI: 10.1086/169866 Bibcode: 1991ApJ...371...14D Keywords: Astronomical Spectroscopy; Damping; Elastic Waves; Microwaves; Relic Radiation; Universe; Computational Astrophysics; Mass Distribution; Perturbation Theory; Photons; Power Spectra; Radiation Distribution; Astrophysics; Damping; Relic Radiation; Power Spectra; Cosmic Background Radiation; Cosmology; Early Universe; Wave Motions full text sources ADS |

Direct optical pumping of high-pressure CO&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;and N&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;O lasers with a pulsed HF pump laser

Pulsed HF laser radiation has been used for direct optical excitation of CO 2 and N 2 O lasers at 10 and 5 atm gas pressures, respectively, which are the pressures required for continuous laser frequency tuning between the line centers in these gases. The maximum demonstrated quantum efficiency is about 14 percent, which seems to be limited by the formation of pressure waves in the gas, in addition to losses in the resonator optics. We find that quantum efficiencies close to unity are theoretically feasible with a low-loss resonator, and by using a sufficiently short pump pulse to avoid a serious influence from pressure waves. The excitation scheme can be used with any of the CO 2 and N 2 O laser isotopes.

Density waves in the solar nebula: Diffential Lindblad torque

The differential torque between a two-dimensional fluid disc and an embedded perturber due to waves launched at its resonances is calculated. For a non-self-gravitating disc, the disturbance is in the form of pressure waves which propagate away from co-rotation and asymptotically become trailing spirals. The torque calculation includes lowest order contributions from gradients in various disc properties. The orbital drift rate of the perturber is determined and the results applied to the motion of preplanetary material in the solar nebula.

The Microcomputer and Pipeline Transients

A number of concepts related to computer studies of transient flow in pipeline systems are addressed. The topics are directed to applications on microcomputers, but are not limited to that special purpose. The topics include organizational concepts for system data handling, and ideas to realize certain storage and computational efficiencies when using the method of characteristics as the computational procedure. Alternatives to the method of specified time intervals, namely a staggered grid and an algebraic treatment, are discussed. A simple improved modification in the friction term is also emphasized. Two common elements in hydraulic systems that influence the form of pressure waves, series connections and lossy elements, are focused upon with a view to providing an improved visualization of their response characteristics. Equations and graphs are presented for cases with and without initial through flow. Finally, an example of the failure of a physical system is presented to emphasize the importance of unsteady flow visualization in hydraulic system design.

Report on MWD Experimental Downhole Sensors

Summary Measurement while drilling (MWD) provides a means for monitoring drilling and formation parameters as drilling progresses. The technique, based on the use of advanced downhole sensor and telemetry technology, makes possible the real-time acquisition of data that was previously impossible without stopping the drilling previously impossible without stopping the drilling operation. Some downhole data, such as weight and torque on bit (WOB and TOB) can be obtained only while drilling. In Summer 1976, Teleco Oilfield Services began an experimental program to demonstrate the feasibility and usefulness of a multisensor MWD tool for real-time measurement of drilling mechanics, formation evaluation, and well-control parameters. A package incorporating six sensors was designed and implemented in a downhole tool capable of transmitting data to the surface by means of mud-pulse telemetry. In this paper we discuss the experimental 6-sensor tool and representative results obtained in a series of 12 field tests in various pails of the world, both onshore and offshore. Introduction The MWD tool was introduced in Aug. 1976 on a limited basis. It was designed to provide the directional-drilling industry with real-time measurements of hole deviation, azimuth, and tool facing. Full commercial directional service was made available in the Gulf of Mexico and the North Sea in Sept. 1978. In a parallel effort begun in 1976, an experimental system was built to demonstrate the broader potential of down hole MWD technology for enhancing the safety and efficiency of dulling while simultaneously obtaining formation-evaluation data. Two prototype MWD tools incorporating six downhole sensors and using mud-pulse telemetry were built. More than 1,200 hours of continuous mud-pulse data transmission were accumulated in the field test program. Telemetry System Mud-pulse telemetry is a wireless means of communicating data from downhole to the surface. Information in the form of binary bits is communicated through a sequence of pressure pulses generated in the mud column within the drill pipe by a valve located in a special sub near the bit. This information, in the form of pressure waves, propagates through the drilling mud and is detected and displayed at the surface. This technique imposes no restrictions on the drilling operation, is rugged, reliable, safe, and only marginally affected by mud composition or depth. So far, MWD technology has been applied primarily to directional surveying. Its use in other applications, such as formation evaluation and drilling efficiency, offers great promise to the oil and gas well drilling industry. In the balance of this paper, some of these applications are discussed on the basis of an extensive series of tests with the experimental six-sensor MWD tool. Additional discussions of MWD technology and applications are found in Refs. 1 through 4. The essential elements of the telemetry system consist of the transmitter and surface receiving equipment. JPT P. 899