Shape Of Pressure Pulse Research Articles

Finite-element study of residual stress distribution in Ti-6Al-4V alloy treated by laser shock peening with varying parameters

Laser shock peening (LSP) is used to enhance surface quality of the metallic structures by the generation of compressive residual stresses on it. This work studies the effect of the main LSP parameters on residual stress fields by the finite-element method. The specimen under investigation is a square plate with a thickness of 3 mm made of Ti-6Al-4V. The performed analysis enhances understanding of LSP application to structures manufactured from this material and this information can be useful for a choice of optimal peening parameters. The effect of the spot size and shape, the pulse energy, the number of peen layers, overlapping of spots and temporal variation of the mechanical pressure induced by plasma is considered and analyzed. A 3D finite-element model based on the Johnson-Cook constitutive relation is developed and verified by the results of residual stress measurements performed for the LSP-treated samples under different conditions. From the obtained results the following main conclusions can be drawn: pulse energy provides the more significant effect although the resulting residual stresses profile tends to some saturation curve; temporal pressure pulse shape and its total duration also substantially alter the residual stress field; the least significant parameter is the spot shape.

Experimental study on the propagation characteristics of the slamming pressures

The ship slamming pressure may exhibit a propagating feature and would have a significant influence on the local response of ship structure. This paper presents an experimental investigation on the characteristics of the slamming pressure, such as the slamming pressure coefficient, time duration, spatial pressure distribution and propagation speed. A series of experiments on the water entry of rigid and elastic wedges have been carried out for deadrise angles ranging from 0° to 45° and for drop heights ranging from 0.1 m to 1.0 m. Wedge plates with varying thicknesses are tested in the experiments to study the effect of structural elasticity on the propagating feature of the slamming pressure. Based on the experimental results, the spatial variation of the slamming pressure is analyzed. Besides, the effects of the water entry velocity, deadrise angle and wedge plate's structural elasticity on the propagating feature of the slamming pressure is studied. For the flat bottom slamming with a deadrise angle of 0°, the slamming pressure instantaneously acts on the structure, which shows no propagating feature and is close to the uniformly distributed pulse load. The propagation of slamming pressure is found to occur when the deadrise angle exceeds 0.2°. When the deadrise angle is between 4° and 45°, the pressure pulse shape is nearly unchanged during the propagation of the slamming pressure, and the ratio between the experimental speed of propagation and Wagner's theoretical speed is about 0.8. The effect of wedge plate flexibility on the slamming pressure is mainly observed in the cases with small deadrise angles. The wedge plate flexibility causes the duration of the slamming pressure to increase and the pressure coefficient to increase or decrease depending on the ratio between pressure duration and the structure's natural period.

Numerical parameter optimizations of the Ignition and Growth model for a HMX plastic bonded explosive

We present a novel method for optimizing parameters of the Ignition and Growth (I&G) reactive flow model for high explosives. The I&G model predicts the shock initiation response of explosives subjected to dynamic loading. However, calibrating the model is a time-consuming process because it has several parameters, typically requires multiple data sets, and there are no direct correlations between parameters and data. In this study, we couple a scalable optimization algorithm to simulations of shock initiation experiments in the multi-physics code ALE3D. We develop four I&G model parameter sets for the HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane)-based explosive LX-07 [90 wt. % HMX, 10 wt. % Viton A] based on minimizing the difference between calculations and measurements at the embedded pressure gauges in 1D gun shock experiments. Our study shows that a cost function based on both shock time of arrival and pressure pulse shape demonstrates the best agreement with experimental data.

Accuracy of some algorithms to determine the oscillometric mean arterial pressure

To compare different algorithms to determine the oscillometric mean arterial pressure. Using a computer-based model, the accuracy of five algorithms was studied: maximum amplitude algorithm, 33 and 40% formulas calculating the mean arterial pressure from oscillometrically measured systolic and diastolic pressures, and two oscillation shape-based algorithms. We examined to which extent the tested algorithms were influenced by variations in four affective factors: pulse pressure, arterial pressure pulse shape index, and two shape indices (symmetry and steepness) of the artery-cuff pressure/volume relationship. Different ranges of variation of affecting factors were applied. The accuracy of the oscillation shape-based algorithms was found to be higher than the accuracy of the oscillation amplitude-based algorithms. The oscillation mean shape index-based determination had an almost 2-3 times narrower error range compared with the maximum amplitude algorithm. Modeling showed that the mean arterial pressure changes resulting from the varying shape of the arterial pressure waveform cannot be measured using the oscillation amplitude-based algorithms, whereas these changes can be determined effectively using the oscillation shape-based algorithms. The maximum amplitude algorithm has a relatively low accuracy for the estimation of the mean arterial pressure. Its error range is even larger than that of estimates calculated by the 33 or 40% formulas from the oscillometrically measured systolic and diastolic blood pressures. A considerably higher accuracy can be achieved by applying the oscillation shape-based algorithms.

The influence of different factors on the shape of pressure pulse at the liquid-vapor contact

The process of formation and propagation of the depression wave at spontaneous contact of cold liquid and saturated vapor is investigated in a gas dynamics approach. Modeling of wave processes was performed using Godunov’s method based on solving the Riemann problem on arbitrary discontinuity decomposition. The influence of various factors, namely, the kinetics of condensation and intensification of heat-transfer processes, on the pressure pulse form is investigated. Results of the investigation are in good agreement with results of modeling based on numerical solving the Boltzmann kinetic equation.

Modeling and Parameter Design of a Laser Shock Peening Process

Laser shock peening (LSP) is a surface treatment technique that has been applied to improve fatigue and corrosion properties of metals. The ability to use a high energy laser pulse to generate shock waves, inducing a compressive residual stress field in metallic materials, has applications in multiple fields such as turbomachinery, airframe structures, and medical appliances. In the past, researchers have investigated the effect of LSP parameters experimentally [1, 2, 3, 4, 5] and performed a limited number of simulations on simple geometries [6, 7, 8, 9]. However, monitoring the dynamic, intricate relationship of peened material experimentally is expensive and challenging. With an increasing number of applications on complex geometries, these limited experimental and simulations capabilities are not sufficient for LSP process design. A computational mechanics procedure is required that can perform simulations of multiple treatments of LSP at the same location, sequential LSP at multiple locations, different overlapping configurations of LSP locations, and complex geometries. With increased computer speed as well as increased sophistication in non-linear finite element (FE) analysis software, it is now possible to develop a simulation-based design investigation approach for an effective LSP process design. In this paper, the process parameters are identified and a three-dimensional simulation is adopted and validated. This simulation is then used in sensitivity analysis of performance metrics of residual stress for variations in the LSP parameters such as pressure pulse magnitude and shape, spot shape and size, component thickness, number of shots, layout of shots, and multiple shot sequences.

A laser optoacoustic method of inducing high-energy states and the investigation of phase transitions in metals at high pressures

Results are given of investigations of high-energy states and phase transitions, using lead as an example, under the effect of nanosecond laser pulse in a wide range of intensities. The metal surface being irradiated is mechanically confined by a transparent dielectric plate in order to realize conditions of highly effective generation of pressure while maintaining local thermodynamic equilibrium. The dynamics of thermodynamic state of metal are analyzed by the shape and amplitude of pressure pulse propagating from the surface being heated and by the variation of reflectivity of the metal surface being irradiated. The measurements of pressure pulse make possible the recording of phase transitions in lead: melting on the sample surfaces being irradiated at a pressure up to P max ≈ 0.1 GPa. It is demonstrated that the pressure amplitude prior to melting is proportional to the intensity of laser radiation, and that upon passing the melting threshold — to the absorbed energy of laser pulse. The instant of time, at which the “deformation” of the leading edge of pressure pulse begins, corresponds to the beginning of melting. When high-energy states are realized in the thin surface layer of metal, the density decreases significantly; this results in a significant decrease in both reflectivity and electrical conductivity.

Measures of intraoral pressure pulse shape during stop consonants

To maintain voicing during a stop consonant, adult speakers typically perform articulatory actions that increase supraglottal volumes and slow the rate at which of intraoral pressure (Pio) rises. In an influential study, Müller and Brown [in Speech and Language: Advances in Basic Research and Practice 4, edited by N. Lass (Academic, New York, 1980), pp. 318–389] proposed a quantitative measure of Pio pulse shape, based on the difference between (a) the slope from pressure at closure to average pressure and (b) from average pressure to pressure at release. We recently applied these techniques to data from women and child speakers of English and observed some shortcomings in Müller and Brown’s measurement technique, such that the slope difference angle did not clearly reflect the actual pressure pulse shape. The purpose of this paper is to explore new methods of analyzing intraoral pressure contours, based on fitting a mathematical model to the pressure pulse shapes. It will report our progress and compare our results with the previous technique.

Coordination between ventilatory pressure oscillations and venous return in the cephalopod Sepia officinalis under control conditions, spontaneous exercise and recovery

Venous blood flow was measured for the first time in a cephalopod. Blood velocity was determined in the anterior vena cava (AVC) of cuttlefish S. officinalis with a Doppler, while simultaneously, ventilatory pressure oscillations were recorded in the mantle cavity. In addition, magnetic resonance imaging (MRI) was employed to investigate pulsatile flow in other major vessels. Blood pulses in the AVC are obligatorily coupled to ventilatory pressure pulses, both in frequency and phase. AVC peak blood velocity (v(AVC)) in animals of 232 (+/- 30 SD) g wet mass at 15 degrees C was found to be 14.2 (+/- 7.1) cm s(-1), AVC stroke volume (SV(AVC)) was 0.2 (+/- 0.1) ml stroke(-1), AVC minute volume (MV(AVC)) amounted to 5.5 (+/- 2.8) ml min(-1). Intense exercise bouts of 1-2 min resulted in 2.2-fold increases in MV(AVC), enabled by 1.6-fold increments in both, AVC pulse frequency (f (AVC)) and v(AVC). As increases in blood flow occurred delayed in time by 1.7 min with regard to exercise periods, we concluded that it is not direct mantle cavity pressure conveyance that drives venous return in this cephalopod blood vessel. However, during jetting at high pressure amplitude (> 1 kPa), AVC blood flow and mantle cavity pressure pulse shapes completely overlap, suggesting that under these conditions, blood transport must be driven passively by mantle cavity pressure. MRI measurements at 15 degrees C also revealed that under resting conditions, f (AVC )and ventilation frequency (f (V)) match at 31.6 (+/- 2.1) strokes min(-1). In addition, rates of pulsations in the cephalic artery and in afferent branchial vessels did not significantly differ from f (AVC) and f (V). It is suggested that these adaptations are beneficial for high rates of oxygen extraction observed in S. officinalis and the energy conserving mode of life of the cuttlefish ecotype in general.

Numerical analysis of plastic deformation of a circular sheet metal subjected to transverse impact loading

Based on the concept of Tensor Code a numerical method is presented for analysis of the plastic deformation process of circular sheet metals subjected to transverse impact loading. In the solution process, the equation of motion is solved explicitly with finite difference method in a series of small time steps over a Lagrangian mesh of zones. Using this method, a code has been developed and utilized for investigation of the deformation behavior of an explosively loaded circular sheet metal under various conditions. Deformation characteristics of a sheet under rectangular and triangular pressure distributions are discussed. It is shown that when these simple distributions are combined with each other, their individual effects on the deformation behavior are also combined in the deformation process. Effects of shape and duration of pressure pulse as well as boundary conditions have been explored. Moreover, results of the numerical simulation have been compared with those of theoretical solution and experiments reported by other researchers. Good agreements between them show the validity of the developed code.

The eccentric position of the heart in the mammalian body and optimal energy transfer in single tube models

Many phenomena cannot be explained by traditional haemodynamics models. For example, the hearts of all mammals are neither at one end of the circulatory system nor at the geometric centre. Based on a new circulation model, we report that if the heart is located at either of these two positions, the energy saving rule will be violated. We assume that the main arterial system is under a steady, distributed transverse vibration with the heart as the input power source. The equation of motion of the artery is governed by a new pressure wave equation with total energy. We analyse the effects of the heart position on the pressure pulse shape and the spectrum. By a simplifying T-tube model, we find that there are many harmonic oscillating modes for the overall arterial system. The position of the heart affects the weights of different modes. If the heart is at the midpoint or at one end of the body, none of the even harmonic modes can be excited. If the heart is at a third along the whole system, the third oscillation mode in the system is missing. Thus, from an efficiency point of view, this model gives a strong reason for all mammals' hearts being at an eccentric position. Tube simulations were carried out to confirm the theoretical prediction. A new standing wave model to analyse the variation of the pressure pulse shape along the artery is discussed. The interesting result indicates that our new pressure wave equation possesses a high problem solving potential. It provides a new tool for studying arterial dynamics.

DETERMINATION OF AORTIC PRESSURE-TIME PROFILE, ALONG WITH AORTIC STIFFNESS AND PERIPHERAL RESISTANCE

Aortic pressure measurement is of significant clinical importance. However, the techniques require invasive approach, such as cardiac catheterization. In this study, we are providing the analysis for the aortic pressure to be determined non-invasively, as well as indicating how it can be employed to determine cardiac contractility, compliance and peripheral resistance. We record systolic and diastolic pressure during the cardiac cycle using cuff method, assumed that the systolic phase of the supra-systolic cuff signal and the diastolic phase of the sub-diastolic cuff signal most closely approximate systolic and diastolic aortic pressure, respectively. The pressure curves for the systolic phase are derived from the aortic volume-time curve. In both Ayuredic-medicine and traditional Chinese-medicine, the pressure-pulse shape is felt to provide diagnosis information concerning diseases and disorders. In this regard, a precise evaluation of the aortic pressure-time profile and correlation of its shape parameters with diseases (using traditional Chinese and Ayuredic medical knowledge-base system) would constitute a significant contribution to medicine.

Design of compact piezoelectric transducers for shock wave applications

The application of focused intense sound pulses to treat several orthopedic diseases has gained in importance during the past years. Self-focusing piezoelectric transducers known from ESWL are not well suited for this purpose due to their size. Therefore compact transducers have to be designed. This implies an increase of the pressure pulse amplitude generated at the radiating surface. A stacked placement of two piezoelectric layers driven by two high-voltage pulses with an adjustable delay accomplishes this. Several designs are presented here representing transducers of different sizes. In principle piezoelectric transducers have the ability to vary the pressure pulse shape to a wider extent than other shock wave sources. Based on FEM simulations of the transducer the influence of some driving parameters, like a variation of the interpulse delay or shape of the driving voltage, on the resulting focal pressure signal is demonstrated. The results show the feasibility to control some parameters of the signal, for example the peak negative pressure amplitude. This possibility could provide new aspects in basic research as well as in clinical applications.

Direct-drive cryogenic target implosion performance on OMEGA

Layered and characterized cryogenic D2 capsules have been imploded using both low- and high-adiabat (α, the ratio of the electron pressure to the Fermi-degenerate pressure) pulse shapes on the 60-beam OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] at the Laboratory for Laser Energetics (LLE). These experiments measure the sensitivity of the direct-drive implosion performance to parameters such as the inner-ice-surface roughness, the adiabat of the cryogenic fuel during the implosion, the laser power balance, and the single-beam nonuniformity. The goal of the direct-drive program at LLE is to demonstrate a high neutron-averaged fuel ρR at a significant fraction of the predicted one-dimensional (1-D) neutron yield using an energy-scaled, low-adiabat (α∼3) ignition pulse shape driving a hydrodynamically scaled deuterium–tritium ignition capsule. New results are reported from implosions of ∼920-μm-diam, thin (∼5 μm) polymer shells containing 100 μm D2-ice layers with characterized inner-surface ice roughness of 3–12 μm rms. These capsules have been imploded using ∼17–23 kJ of 351 nm laser light with a beam-to-beam rms energy imbalance of less than 5% and full beam smoothing [1 THz bandwidth, two-dimensional (2-D) smoothing by spectral dispersion and polarization smoothing]. Near-1-D performance has been measured for a high-adiabat (α∼25) drive pulse, and the implosion performance with a low-adiabat (α∼4) pulse is in agreement with 2-D hydrocode predictions.

Beat-to-beat measurement of the finger arterial pressure pulse shape index at rest and during exercise.

Arterial pressure waveform can be characterized by the pulse shape index kpulse determined as kpulse = (Pmean - Pdiast) / (Psyst - Pdiast). For brachial artery, the shape index value of 0.33 is usually applied to approximate Pmean from the measured Psyst and Pdiast. Our purpose was to test whether this value can validly be applied to finger vascular beds under different experimental conditions. By using Finapres, we non-invasively estimated the beat-to-beat values of kpulse in the fingers of young healthy persons in supine position at rest and during a 4-min moderate exercise (rhythmical exercise with the quadricep muscles in combination with handgrip compression). To detect intensive peripheral vasoconstrictions, a laser-Doppler probe was attached to the thumb pulp of the same hand. Periods of 30 s without intensive vasoconstriction for rest, different stages of exercise and recovery were involved in the analysis in every subject. The results demonstrated that the group-averaged value of kpulse (median with a 95% confidence interval) in the fingers of 11 healthy volunteers aged from 20 to 24, equalled 0.33 (0.31- 0.34), 0.31 (0.28-0.34), 0.35 (0.33-0.39) and 0.38 (0.34-0.43) for rest, first and second stages of exercise and recovery, respectively. We conclude that in the fingers of young healthy persons in supine position formula Pmean = Pdiast + 1/3 (Psyst - Pdiast) gives an adequate approximation for rest and low intensity exercise (first stage), and slightly underestimates the actual finger mean blood pressure during moderate exercise (second stage) and recovery.

Modeling the pressure pulse shape of piezoelectric lithotripters

Piezoelectric focusing transducers are widely used in extracorporeal lithotripsy. To optimize the therapeutically relevant focal pressure pulse it is necessary to affect the generated pulse shape at the transducer surface. Therefore a modeling approach is required containing the acousto-mechanical properties of the transducer structure as well as the influence of the electrical drive. The procedure presented here uses three dimensional transient finite element simulations to calculate an electro-acoustical impulse response of the transducer structure and linear systems theory to model the influence of the driving circuit on the emitted acoustical signal. Applying a short electrical pulse an acoustical impulse response can be simulated under plane wave conditions, which is valid at sufficiently large distances from the transducer. Focal pressures are estimated rapidly by linear calculations or accurately by a nonlinear propagation model. The influence of electrical drive conditions on the emitted acoustical signal is investigated very efficiently by a convolution with the desired electrical input, avoiding FEM simulations for each case. Reverting this process the required driving voltage course for a given pressure signal is determined. Alterations of the pressure signal in terms of pulse width and tensile components are demonstrated theoretically, varying the design parameters of the transducer.

DRYNESS AND PHYSICAL PROPERTIES OF PAPER WEBS IN LABORATORY-SCALE IMPULSE PROCESSING

This investigation evaluates the changes in dryness and physical properties of impulse processed paper webs. A laboratory-scale platen press was used to process 60 g/m2 webs under a wide range of pressure impulses and temperatures (23–380°C). The heat transfer rate to the web was also varied by using two different platen materials (steel and copper). Both thermomechanical and bleached kraft pulps were tested, and the dryness, density, surface roughness, and Scott bond were measured for each trial. Results show that dewatering is enhanced with increased temperature, pressure, and nip residence time, while pressure pulse shape and platen material have little influence. An empirical correlation is given to relate sheet dryness to the key process variables. This correlation suggests that resulting dryness values are not unique; that is, different combinations of temperature, pressure, and nip residence time can be used to obtain a similar level of dryness. Physical reasoning was used to develop a second correlation that links the resulting dryness to the density of the completely dried web. Surface roughness decreased with increasing surface temperature, while Scott bond rose sharply under conditions of high temperature and long nip residence time.

Mathematical modelling of non-invasive oscillometric finger mean blood pressure measurement by maximum oscillation criterion

A mathematical study is performed to assess how the arterial pressure-volume (P-V) relationship, blood pressure pulse amplitude and shape affect the results of non-invasive oscillometric finger mean blood pressure estimation by the maximum oscillation criterion (MOC). The exponential models for a relaxed finger artery and for a partly contracted artery are studied. A new modification of the error equation is suggested. This equation and the results of simulation demonstrate that the value of pressure estimated by the MOC does not exactly agree with the value of the true mean blood pressure (the latter being defined as pressure corresponding to maximum arterial compliance). The error depends on the arterial pressure pulse amplitude, as well as on the difference between the arterial pressure pulse shape index and the arterial P-V curve shape index. In the case of contracted finger arteries, the MOC can give an overestimation of up to 19 mmHg, the pressure pulse shape index being 0.21 and the pulse amplitude 60 mmHg. In the case of relaxed arteries, the error is less evident.

Theoretical analysis of non-invasive oscillometric maximum amplitude algorithm for estimating mean blood pressure.

A theoretical analysis is performed to evaluate the effect of arterial mechanical and blood pressure pulse properties on the accuracy of non-invasive oscillometric maximum amplitude algorithm (MAA) estimates of the mean blood pressure obtained using air-filled occlusive cuffs. Invasively recorded blood pressure pulses, selected for their varied shapes, are scaled to simulate a wide range of blood pulse pressures (diastolic blood pressure minus systolic blood pressure). Each scaled blood pressure pulse is transformed through an exponential model of an artery to create a series of blood volume pulses from which a simulated oscillometric waveform is created and the corresponding MAA estimate of the mean blood pressure and error (mean blood pressure minus MAA estimate) are determined. The MAA estimates are found to depend on the arterial blood pressure. The errors are found to depend on the arterial mechanical properties, blood pressure pulse shape and blood pulse pressure. These results suggest that there is no direct relationship between the mean blood pressure and MAA estimate, and that multiple variables may affect the accuracy of MAA estimates of the mean blood pressure obtained using air-filled occlusive cuffs.

Dynamics of nonlinear blood pressure waves in large arteries

We present a nonlinear quasi-one-dimensional model which describes blood pressure propagation in large arteries. In the limit of an ideal fluid and for slowly varying arterial parameters a Boussinesq-type equation is obtained. Numerical simulations reveal the influence of changing the diameter and the Young modulus on the pressure pulse shape. Physiological features such as “peaking” and “steepening” show that the pulse can be seen as a wave whose shape evolves between a solitary and a shock wave.