Peak Pressure Levels Research Articles

Marine compressed air source array acoustic field characterization from at-sea measurements: Long-range propagationa).

In 2007, the Littoral Acoustic Demonstration Center conducted a comprehensive experiment in the northern Gulf of Mexico to measure the three-dimensional acoustic field of a standard marine compressed-air source array used in seismic exploration. This study aims to enhance understanding of long-range acoustic propagation of the array signals, with focus on variations in received sound pressure levels and sound exposure levels (SELs) at various ranges from the source. These variations are influenced by factors, such as receiver depth, array orientation, and propagation conditions. The long-range measurements show that received peak pressure levels and SELs exhibit non-monotonic (oscillatory) behavior with range leading up to 10 dB increase in received levels at longer ranges. At ranges beyond 20 km, acoustic levels at the shallowest hydrophone consistently surpassed those at deeper ones by 3-10 dB, suggesting the impact of surface duct propagation effects. The results demonstrate that range-independent bathymetry leads to approximately 4 dB higher received acoustic levels than range-dependent propagation conditions. The measured long-range propagation acoustic metrics from controlled experiment provide a unique and critical dataset for validating both source and propagation model accuracy in predicting received sound pressure and SEL in the far-field of the source array.

Effect of tube bend angle on liquid propulsion system priming event pressures

Experimental work was performed to measure the priming event pressure transient levels in unrestricted liquid propulsion system tubing. An existing water hammer experimental setup was utilized, where system tubing diameter, length, and bend angle were examined. Experiments were performed under both atmospheric and low-pressure pre-test element conditions to understand any impact of tube bend angle on the mitigation of priming event pressure transients inside the liquid system. Experimental results showed pressure levels were influenced by a combination of tube diameter, length, and pre-test pressures; however, tube bend angle had minimal to no discernible change on the average peak pressure levels or rise times to peak pressure for all conditions examined.

Mitigation ofHearing Damage With Liraglutide Treatment inChinchillas After Repeated Blast Exposures at Mild-TBI.

Although hearing protection devices (HPDs) have been widely used during training and combat, over one million veterans experience service-connected hearing loss. Hearing damage has been reported to be associated with blast-induced mild traumatic brain injury (mTBI) and there is a lack of understanding and treatment. Liraglutide is a glucagon-like peptide-1 receptor agonist and a potential treatment for TBI-induced memory deficits. This study aims to investigate the function of the liraglutide to prevent damage and facilitate hearing restoration in chinchillas exposed to multiple high-intensity, mTBI-level blasts. Chinchillas were divided into three treatment groups: blast control, pre-blast drug treatment, and post-blast drug treatment. On day 1, the chinchilla ears were protected by HPDs and exposed to three blasts with peak pressure levels of 15-25 psi. The auditory brainstem response (ABR), distortion product otoacoustic emission (DPOAE), and middle latency response (MLR) were recorded pre- and post-blast on day 1 and on days 4, 7, 14, and 28. Substantial acute damage was observed and progressively recovered in chinchillas after the blast exposures. The pre-blast treatment group exhibited the lowest elevation of the ABR threshold and reduction of the wave I amplitude on day 1 after blasts. The liraglutide treatment insignificantly facilitated the recovery of the DPOAE levels and ABR thresholds on days 14 and 28. The pre-blast treatment chinchillas showed reduced MLR amplitudes on days 4 and 7. This study indicated that the pre-blast liraglutide administration provided damage protection against blasts in addition to the HPDs. Current evidence suggests that the effect of liraglutide is more prominent in the early phase of the experiment.

Plastic buckling of oil storage tanks under blast loads

This paper deals with the dynamic behavior of cylindrical shells under blast loads, with special reference to plasticity and plastic buckling. Interest in this problem focuses on the response of steel vertical oil storage tanks with a flat roof under a nearby explosion. The problem is modeled using a finite element discretization of the structure, in which the loads are represented by an impulsive pressure which is variable around the circumference. The results for tanks show that, at low pressure levels, there is an elastic shell behavior, and first yield occurs as the peak blast pressure is increased. For subsequent increases of peak pressure, the dimple extends in the area affected by the pressures, so that vertical stripes with plastic material behavior are formed from top to bottom of the shell. For even higher pressures, a global mode develops with large amplitude displacements. The total plastic energy is investigated under increasing peak pressure levels. It is found that a change in slope occurs in total plastic energy versus peak pressure when plasticity spreads in the shell, and this is associated to the development of a plastic buckling mode. Parametric studies show that the main variable affecting the change in behavior of the shell as identified through the total plastic energy depends on the shell thickness and is only marginally affected by the shell height and diameter. These conclusions are valid for squat shells, such as those used in the oil industry, and may not be accurate for taller shells.

Evaluation of Lateral Head Rotation on Eficacy of Face Mask Ventilation during Induction of Anesthesia in Children

Background: The head's position during mask ventilation on the time of anesthesia induction in children may improve the lung ventilation.
 Aim: Current study was designed to verify whether lateral head rotation improves face mask ventilation efficiency during anesthesia induction in children.
 Methods: Fifty-six patients aged 1-4 years, candidate for elective surgery, were randomly divided into two equal groups. During induction of general anesthesia, face mask lung ventilation of patients continued with pressure-controlled mode, at a peak pressure level of 10 cmH2O for children 13-24 months and 14cmH20 for children 24-48 month. In patients in the N group, the head position during ventilation was initially in the neutral position for one minute, then the head was axially rotated 45-degree to the right position for one minute and pulmonary ventilation continued in this position, then the head was rotated again to the neutral position and ventilation continued for one minute. In group R patients, mode and time of ventilation was the same, but the order of head placement was first in the lateral rotated to the right, then neutral and then lateral rotated to the right. The primary outcome was the measurement of expiratory tidal volume in each position.
 Results: Generally, the mean measured expiratory tidal volume did not change in the neutral position compared to laterally rotated head position, 256.6 vs. 233.5 ml: difference -23.1 [95% confidence interval: 10.8 to 39.4 ml]. Also, the change of head position from lateral to neutral position did not show a significant change in the mean expiratory tidal volume, 232.28 vs.247.86 ml: difference -15 .82 (p= 0.4).
 Conclusion: The rotation of the head to the lateral position during induction of anesthesia in apnoeic children 1-4 years old could not improve the efficiency of mask ventilation relative to the neutral head position.

Can Wideband Tympanometry Predict the Prognosis of Otitis Media With Effusion?

This study aims to evaluate the capacity of wideband tympanometry (WBT) in predicting the prognosis of otitis media with effusion (OME). Sixty-one ears with effusion and 30 healthy ears of children were enrolled. The patients were followed up monthly using WBT. After the completion of measurements, the ears were separated into four groups according to the duration of recovery; Group 1: Good prognosis (≤1-month, n=18), Group 2: Worse prognosis (>1-month, n=29), Group 3: Surgical (no recovery, n=14), and Group 4: Control (healthy ears, n=30). Tympanometric peak pressure (TPP), resonance frequency (RF), and absorbance levels were compared within and between the groups. The TPP and RF values of the study group were lower than those of the controls (p<0.001). The ears with OME had lower absorbance measures than the controls at all frequencies; the differences were significant at 250, 500, and 1,000 Hz (p<0.001). However, at 2,000 Hz, the absorbance levels of the ears with OME were similar with those of the control group only in the good prognosis group (p>0.05). The receiver-operating characteristic analysis revealed that absorbance measures over 0.237 and 0.311 at 1,000 Hz and 2,000 Hz, respectively, have sensitivities and specificities over 70% for prediction of good prognosis, and the calculated odd ratio for these measures were 6 (p<0.05). WBT measurement is promising in predicting the recovery of OME in children.

Peak sound pressure level decay from large C-4 detonations: Establishing a 140 dB threshold

Far-field acoustical characterization of blast wave propagation from explosives is often carried out using relatively small shot sizes (less than 1 kg). This paper describes a series of eleven C-4 detonations, with shot sizes varying from 13.6 kg to 54.4 kg (30 to 120 lbs) that were recently measured at the Big Explosives Experimental Facility (BEEF) at the Nevada National Security Site. Pressure waveform data were recorded at up to nine different stations, ranging from 23 m to 2.7 km from the blast origin, with some angular variation. As part of examining blast overpressure decay with distance and comparing with literature, the data were analyzed from the context of human safety regulations. To provide improved guidance for BEEF personnel working distances, an empirical model equation was developed for the distance, as a function of shot size, at which the peak pressure level drops below 140 dB. A preliminary investigation into peak level variability due to wind was also conducted. [Work supported by Los Alamos National Laboratory.]

Focused ultrasound stimulation of an ex-vivo Aplysia abdominal ganglion preparation

BackgroundA growing body of research demonstrates that focused ultrasound stimulates activity in human and other mammalian nervous systems. However, there is no consensus on which sonication parameters are optimal. Furthermore, the mechanism of action behind ultrasound neurostimulation remains poorly understood. An invertebrate model greatly reduces biological complexity, permitting a systematic evaluation of sonication parameters suitable for ultrasound neurostimulation. New MethodHere, we describe the use of focused ultrasound stimulation with an ex-vivo abdominal ganglion preparation of the California sea hare, Aplysia californica, a long-standing model system in neurobiology. We developed a system for stimulating an isolated ganglion preparation while obtaining extracellular recordings from nerves. The focused ultrasound stimulation uses one of two single-element transducers, enabling stimulation at four distinct carrier frequencies (0.515 MHz, 1.l MHz, 1.61 MHz, 3.41 MHz). ResultsUsing continuous wave ultrasound, we stimulated the ganglion at all four frequencies, and we present quantitative evaluation of elicited activation at four different sonication durations and three peak pressure levels, eliciting up to a 57-fold increase in spiking frequency. Comparison with Electrical StimulationWe demonstrated that ultrasound-induced activation is repeatable, and the response consistency is comparable to electrical stimulation. ConclusionsDue to the relative ease of long-term recordings for many hours, this ex-vivo ganglion preparation is suitable for investigating sonication parameters and the effects of focused ultrasound stimulation on neurons.

Improving the Therapeutic Effect of Ultrasound Combined With Microbubbles on Muscular Tumor Xenografts With Appropriate Acoustic Pressure.

Ultrasound combined with microbubbles (USMB) is a promising antitumor therapy because of its capability to selectively disrupt tumor perfusion. However, the antitumor effects of repeated USMB treatments have yet to be clarified. In this study, we established a VX2 muscular tumor xenograft model in rabbits, and performed USMB treatments at five different peak negative acoustic pressure levels (1.0, 2.0, 3.0, 4.0, or 5.0 MPa) to determine the appropriate acoustic pressure. To investigate whether repeated USMB treatments could improve the antitumor effects, a group of tumor-bearing rabbits was subjected to one USMB treatment per day for three consecutive days for comparison with the single-treatment group. Contrast-enhanced ultrasonic imaging and histological analyses showed that at an acoustic pressure of 4.0 MPa, USMB treatment contributed to substantial cessation of tumor perfusion, resulting in severe damage to the tumor cells and microvessels without causing significant effects on the normal tissue. Further, the percentages of damaged area and apoptotic cells in the tumor were significantly higher, and the tumor growth inhibition effect was more obvious in the multiple-treatment group than in the single USMB treatment group. These findings indicate that with an appropriate acoustic pressure, the USMB treatment can selectively destroy tumor vessels in muscular tumor xenograft models. Moreover, the repeated treatments strategy can significantly improve the antitumor effect. Therefore, our results provide a foundation for the clinical application of USMB to treat solid tumors using a novel therapeutic strategy.

Focused ultrasound for safe and effective release of brain tumor biomarkers into the peripheral circulation

The development of noninvasive approaches for brain tumor diagnosis and monitoring continues to be a major medical challenge. Although blood-based liquid biopsy has received considerable attention in various cancers, limited progress has been made for brain tumors, at least partly due to the hindrance of tumor biomarker release into the peripheral circulation by the blood-brain barrier. Focused ultrasound (FUS) combined with microbubbles induced BBB disruption has been established as a promising technique for noninvasive and localized brain drug delivery. Building on this established technique, we propose to develop FUS-enabled liquid biopsy technique (FUS-LBx) to enhance the release of brain tumor biomarkers (e.g., DNA, RNA, and proteins) into the circulation. The objective of this study was to demonstrate that FUS-LBx could sufficiently increase plasma levels of brain tumor biomarkers without causing hemorrhage in the brain. Mice with orthotopic implantation of enhanced green fluorescent protein (eGFP)-transfected murine glioma cells were treated using magnetic resonance (MR)-guided FUS system in the presence of systemically injected microbubbles at three peak negative pressure levels (0.59, 1.29, and 1.58 MPa). Plasma eGFP mRNA levels were quantified with the quantitative polymerase chain reaction (qPCR). Contrast-enhanced MR images were acquired before and after the FUS sonication. FUS at 0.59 MPa resulted in an increased plasma eGFP mRNA level, comparable to those at higher acoustic pressures (1.29 MPa and 1.58 MPa). Microhemorrhage density associated with FUS at 0.59 MPa was significantly lower than that at higher acoustic pressures and not significantly different from the control group. MRI analysis revealed that post-sonication intratumoral and peritumoral hyperenhancement had strong correlations with the level of FUS-induced biomarker release and the extent of hemorrhage. This study suggests that FUS-LBx could be a safe and effective brain-tumor biomarker release technique, and MRI could be used to develop image-guided FUS-LBx.

Mechanical ventilation as a surrogate for diagnosing the onset of abdominal compartment syndrome (ACS) in severely burned patients (TIRIFIC-study Part II)

Intra-abdominal compartment syndrome (ACS) is a devastating complication in burn patients with a high mortality. Apart from high-volume resuscitation as known risk factor, also mechanical ventilation seems to influence the development of ACS. The TIRIFIC trial is a retrospective, matched-pair analysis. Thirty-eight burn patients with ACS were matched for burned total body surface area (TBSA), age and mechanical ventilation (MV). In contrast to the already published part I addressing fluid resuscitation as a risk factor, the parameters analyzed in part II were maximum and average PEEP and peak pressure levels as well as serum lactate levels and prokinetic therapy. For subgroup-analysis the ACS-group was split up into an early-onset and late-onset ACS-group according to the median time between burn trauma and ACS. The groups were analyzed with a two-sided Mann-Whitney-U-test with significance set at p < 0.05. In the ACS-group all ventilation pressures (maximum and average PEEP and peak pressure levels) were significantly increased compared to control. The subgroup-analysis showed significantly increased maximum PEEP and peak pressure levels in early- and late-onset ACS-groups versus control. However, the average ventilation pressure levels were only increased in the early-onset ACS-group (average PEEP p = 0.0069; average peak pressure p = 0.05). The TIRIFIC trial showed significantly increased ventilation pressures in the ACS group in general as a surrogate parameter to support early diagnostics. Especially, maximum PEEP levels and peak pressures are significantly increased in both, early- and late-onset ACS. As an addition to the actual WSACS guidelines we suggest IAP measurement in mechanically ventilated burn patients if ventilating pressures are rising continuously without a clear pulmonary or otherwise identifiable reason.

Multi-band SWIFT enables quiet and artefact-free EEG-fMRI and awake fMRI studies in rat

Functional magnetic resonance imaging (fMRI) studies in animal models provide invaluable information regarding normal and abnormal brain function, especially when combined with complementary stimulation and recording techniques. The echo planar imaging (EPI) pulse sequence is the most common choice for fMRI investigations, but it has several shortcomings. EPI is one of the loudest sequences and very prone to movement and susceptibility-induced artefacts, making it suboptimal for awake imaging. Additionally, the fast gradient-switching of EPI induces disrupting currents in simultaneous electrophysiological recordings. Therefore, we investigated whether the unique features of Multi-Band SWeep Imaging with Fourier Transformation (MB-SWIFT) overcome these issues at a high 9.4 T magnetic field, making it a potential alternative to EPI. MB-SWIFT had 32-dB and 20-dB lower peak and average sound pressure levels, respectively, than EPI with typical fMRI parameters. Body movements had little to no effect on MB-SWIFT images or functional connectivity analyses, whereas they severely affected EPI data. The minimal gradient steps of MB-SWIFT induced significantly lower currents in simultaneous electrophysiological recordings than EPI, and there were no electrode-induced distortions in MB-SWIFT images. An independent component analysis of the awake rat functional connectivity data obtained with MB-SWIFT resulted in near whole-brain level functional parcellation, and simultaneous electrophysiological and fMRI measurements in isoflurane-anesthetized rats indicated that MB-SWIFT signal is tightly linked to neuronal resting-state activity. Therefore, we conclude that the MB-SWIFT sequence is a robust preclinical brain mapping tool that can overcome many of the drawbacks of conventional EPI fMRI at high magnetic fields.

Dynamic hazard evaluation of explosion severity for premixed hydrogen–air mixtures in a spherical pressure vessel

To evaluate dynamic explosion severity levels of premixed hydrogen–air mixtures, pressure sensors were used to test explosion pressure in a spherical pressure vessel (inner diameter: 0.34 m). ANSYS Fluent 19.0 three-dimensional software was used to simulate the explosion process. The results revealed that when the hydrogen volume fraction was 30 vol%, the explosion pressure and pressure rise rate reached maximum values at 1.0 atm. As the initial pressure increased, the explosion pressure, and pressure rise rate increased gradually. At initial pressures of 1.0, 1.2, 1.5, and 2.0 atm, the peak pressure levels were 0.85, 0.87, 0.92, and 0.99 MPa and the pressure rise rates were approximately 198, 241, 302, and 558 MPa/s, respectively. The initial pressure exerted greater effects on the pressure rise rate than did the explosion pressure. The simulation results were consistent with the experimental findings. Moreover, the simulation yielded multi-dimensional transient explosion parameters—such as turbulent kinetic energy distribution—that are difficult to obtain in experiments. The findings pertaining to the physical experiments, numerous simulations, and influence of initial pressure on the explosion reaction mechanism of premixed hydrogen–air mixtures were discussed.

Curettage adenoidectomy versus endoscopic microdebrider adenoidectomy in children: A randomized controlled trial

IntroductionAdenoidectomy is one of the most frequently performed surgical procedures with different techniques and technologies. Although curettage adenoidectomy (CA) has been practiced conventionally for many years, endoscopic microdebrider adenoidectomy (EMA) has emerged as an innovative surgical method. Comparing physiological effects, efficacy and safety of the endoscopic microdebrider adenoidectomy (EMA) and curettage adenoidectomy (CA) in pediatric population is aimed with this prospective, single-blind, randomized, controlled trial. MethodsSixty pediatric patients with type-A tympanogram according to Jerger classification in both ears before surgery were randomly assigned to receive the CA (n = 30) and the EMA (n = 30). Tympanometry evaluation for each ear was performed the day before surgery firstly and was repeated on days 1, 7 and 14 after surgery. Intraoperative time, complications during and after the operation were recorded. Postoperative pain was also evaluated for 10 days postoperatively. ResultsTympanometric evaluation revealed significantly reduced middle ear peak pressure levels with the EMA than with the CA for each ear on day 1 after surgery and for only left ear on day 7 after surgery (P < 0.05). In addition, statistically significant reduced pain scores in postoperative first 3 days were related to the EMA (P < 0.05). There was no significant difference between the methods in terms of duration of surgery and complications. ConclusionAccording to findings from this study, the EMA procedure may be as safe and rapid as the CA. Furthermore, the EMA may be more controlled and less invasive to the surrounding tissues. Further studies are advised to support these data.

The use of microperforations to attenuate the cavity pressure fluctuations induced by a low-speed flow

The paper describes experimental and numerical studies on the use of micro-perforated panels to reduce the flow cavity pressure fluctuations under a low-speed turbulent boundary layer. This passive strategy has been hardly studied in shallow cavities with length-to-depth ratios of the order of 10, for which flow reattachment might occur at the cavity floor. This implies the formation of a localized recirculation bubble upstream in the cavity, which is referred to as a closed cavity flow regime. An open flow regime takes place when the cavity is separated from the main flow by a shear layer over the full length. For a transitional case with a length-to-depth ratio of 10.6, micro-perforating the cavity floor reduces by up to 8 dB the dominant spectral peaks related to the bottom wall-pressure fluctuations in the first half of the cavity. For the closed regime with a length-to-depth ratio of 17.6, up to 6 dB reduction is found. The broadband fluctuations that are dominating in the downstream part of the cavity are not affected by the presence of the micro-perforations. Reduction of the peak pressure levels by the apertures is confirmed by two-dimensional Lattice Boltzmann simulations. Maximum dissipation occurs when outflow conditions are established within and at the inlet-outlet of the orifices. The impedance of the micro-perforated floor has been optimised and its effect on the bottom wall-pressures has been assessed.

S.12.02 - Ketamine restores changes in glutamate release, dendrite morphology and BDNF trafficking in the hippocampus of rats vulnerable to chronic mild stress

A growing body of research demonstrates that focused ultrasound stimulates activity in human and other mammalian nervous systems. However, there is no consensus on which sonication parameters are optimal. Furthermore, the mechanism of action behind ultrasound neurostimulation remains poorly understood. An invertebrate model greatly reduces biological complexity, permitting a systematic evaluation of sonication parameters suitable for ultrasound neurostimulation.Here, we describe the use of focused ultrasound stimulation with an ex-vivo abdominal ganglion preparation of the California sea hare, Aplysia californica, a long-standing model system in neurobiology. We developed a system for stimulating an isolated ganglion preparation while obtaining extracellular recordings from nerves. The focused ultrasound stimulation uses one of two single-element transducers, enabling stimulation at four distinct carrier frequencies (0.515 MHz, 1.l MHz, 1.61 MHz, 3.41 MHz).Using continuous wave ultrasound, we stimulated the ganglion at all four frequencies, and we present quantitative evaluation of elicited activation at four different sonication durations and three peak pressure levels, eliciting up to a 57-fold increase in spiking frequency.We demonstrated that ultrasound-induced activation is repeatable, and the response consistency is comparable to electrical stimulation.Due to the relative ease of long-term recordings for many hours, this ex-vivo ganglion preparation is suitable for investigating sonication parameters and the effects of focused ultrasound stimulation on neurons.

Dependence of Boiling Histotripsy Treatment Efficiency on HIFU Frequency and Focal Pressure Levels

Boiling histotripsy (BH) is a high-intensity focused ultrasound (HIFU)–based method of mechanical tissue fractionation that utilizes millisecond-long bursts of HIFU shock waves to cause boiling at the focus in milliseconds. The subsequent interaction of the incoming shocks with the vapor bubble mechanically lyses surrounding tissue and cells. The acoustic parameter space for BH has been investigated previously and an inverse dependence between the HIFU frequency and the dimensions of a BH lesion has been observed. The primary goal of the present study was to investigate in more detail the ablation rate and reliability of BH in the frequency range relevant to treatment of deep abdominal tissue targets (1–2 MHz). The second goal was to investigate the effect of focal peak pressure levels and shock amplitude on BH lesion formation, given a constant duty factor, a constant ratio of the pulse duration to the time to reach boiling and a constant number of BH pulses. A custom-built 12-element sector array HIFU transducer with F-number = 1.05 was used in all experiments. BH pulses at 5 different frequencies (1, 1.2, 1.5, 1.7 and 1.9 MHz) were delivered to optically transparent polyacrylamide gel phantoms and ex vivo bovine liver and myocardium tissue to observe cavitation and boiling bubble activity with high-speed photography and B-mode ultrasound imaging, correspondingly. In gel phantoms, a cavitation bubble cloud was shown to form prefocally and to shield the focus in all exposures at 1 and 1.2 MHz and in the highest amplitude exposures at 1.5–1.7 MHz; shielding was not observed at 1.9 MHz. In ex vivo tissue, this shielding effect was observed in 25% of exposures when peak negative in situ pressure exceeded 10.2 MPa at 1 MHz and 14.5 MPa at 1.5 MHz. When shielding occurred, the exposures resulted in mild tissue disruption in the prefocal region, but not liquefaction. The dimensions of liquefied lesions followed the inverse proportionality trend with frequency; consequently, the frequency range of 1.2–1.5 MHz appeared to be preferable for BH exposures in terms of the compromise between the ablation rate and reliability. The lesion size was independent of the duration of the BH pulses (or the total “HIFU on” time), provided that the number of pulses was constant and boiling was induced within each pulse. Thus, the use of shorter (1 ms vs. 10 ms), higher amplitude BH pulses allowed up to 10-fold reduction in treatment time for a given duty factor.

Evaluation of a novel therapeutic focused ultrasound transducer based on Fermat’s spiral

The purpose of this study was to evaluate a novel phased array transducer design rule for therapeutic focused ultrasound applications. This design rule uses the discretized Fermat’s spiral to determine the positioning of the transducer elements for a given number of elements and f-number. Using this principle, three variations of Fermat’s spiral were generated, aimed at (1) grating lobe minimization, (2) side lobe minimization, and (3) an optimized element packing efficiency. For each spiral, sparse layouts using identical circular elements and fully populated layouts based on additional Voronoi tessellation were evaluated numerically. Evaluation criteria included the element size distribution, beam steering capabilities, focal plane pressure distribution, prefocal pressure distribution, and practical considerations. Finally, one Voronoi-tessellated design with a focal length and aperture diameter of 16 cm and a natural frequency of 1.3 MHz was evaluated experimentally through hydrophone measurements. The numerical evaluation showed that while sparse arrays possess superior beam steering capabilities for a given number of elements, the focal point quality and prefocal pressure distribution is substantially more favorable when using the Voronoi-tessellated designs. Beam steering was shown to be feasible with the tessellated designs for lateral deflections up to 10 mm and axial deflections up to 20 mm. The experimental evaluation showed that such a transducer is capable of inducing 40.00 MPa rarefactional and 237.50 MPa compressional peak pressure levels at 800 W instantaneous acoustic output power under free-field conditions, making the system potentially relevant for thermal ablation therapy, histotripsy applications, and shockwave-enhanced heating.

Hydroacoustic measurements and modeling of pile driving operations in Ketchikan, Alaska

Underwater acoustic measurements of pile driving operations were made at the Ketchikan ferry terminal in July 2016. At the time of the measurements, marine mammal injury and disturbance criteria developed by the National Marine Fisheries Service (NMFS) were based on sound pressure level (SPL) thresholds. Shortly after the measurements, NMFS changed the injury thresholds to a dual criteria involving peak pressure and sound exposure levels specific to marine mammal functional hearing groups. This paper presents distances to both injury criteria and the (unchanged) SPL-based disturbance criteria for vibratory driving and impact hammering 30-inch diameter cylindrical piles. Threshold distances were obtained using empirical regressions of sound levels measured by seabed-mounted recorders at 10 and 1000 m nominal range. A finite-difference method pile driving source model was used with a parabolic equation propagation model to compare measurements with simulations and to estimate received levels at all ensonifi...

Fluctuations of the peak pressure level of man-made impulsive sound signals propagating in the ocean

The theory of wave propagation and fluctuations in random media has been broadly studied; however the works studying the influence of a changing underwater acoustic environment on the spatial decay and fluctuations of the peak pressure in broadband and impulsive signals are limited. Using a method based on the formulation developed by Dyer and Makris to estimate intensity fluctuations of sound signals in the ocean in conditions of saturated multipath propagation, this paper presents an approach to model peak pressure fluctuations of transient signals propagating underwater. In contrast to the formulation of Dyer and Makris, the approach presented in this work applies extreme value theory using the properties of the peak pressure as a maximum value taken from a Rayleigh distributed amplitude. The location and scale parameters obtained from the best fit to a Gumbel distribution are used to estimate the probability of the peak pressure level staying below a certain threshold. The theory was applied to measurements of signals from an airgun array and offshore impact pile driving, resulting in good agreement in both cases.