Pressure Wave Propagation Research Articles

Dynamics study of shock wave intersection under high-frequency sine oscillation incoming flow

This paper numerically studies the dynamics of symmetrical wedge shock intersection under sinusoidal supersonic oscillation conditions. The 15° symmetrical wedges are used as the shock generator, and the sinusoidal oscillation is used as the inflow condition. Two forms are considered: (I) The fluctuation amplitude is kept constant (A = 1.4), and the influence of the fluctuation frequency from 4 kHz with a step of 2–10 kHz in the shock wave system is considered. (II) Keeping the frequency constant (f = 10 kHz), the effect of three amplitudes (A = 1.0, 1.4, 1.8) on shock waves is considered. A detailed analysis of unsteady flow features, including the Mach stem growth, the swing of slip lines, pressure evolution, and peculiar pressure wave phenomenon are presented with a focus on the bi-directional regular intersection (RI ↔ MI) Mach intersection transition process. The study found that: RI ↔ MI always occurs near the von Neumann solution, and there are premature transformation and hysteresis. The higher the frequency, the more noticeable the hysteresis and premature transformation are, the more obvious the swing of slip lines is. The lower the frequency, the longer the bi-directional transition time of the RI ↔ MI, the greater the maximum height of the Mach stem, the more frequent the triple points' pressure fluctuation. In addition, the oscillating flow will cause the propagation of pressure waves in the slip line channel and the transition from transverse waves to longitudinal waves. Under the condition of different amplitudes, the greater the amplitude is, the greater the height of the Mach stem is. When the amplitude is maximum, the Mach number of partial incoming flow is less than the minimum Mach number of the attached oblique shock wave. The evolution of the detached shock wave will lead to the complexity of the system. As the amplitude increases, the greater the pressure difference of the triple points, the greater the curvature of the incident shocks. The research of the unsteady shock wave intersection under the oscillating flow is useful to the study of supersonic flow, loss control, and heat and mass transfer of detonation engines and intake ducts.

Tracking the explosion characteristics of the hydrogen-air mixture near a concrete barrier wall using CESE IBM FSI solver in LS-DYNA incorporating the reduced chemical kinetic model

Barriers are introduced as an efficient method for the protection of infrastructures and people from overpressure effects owing to accidental gaseous explosions. Therefore, capturing the pressure wave propagation in front of and behind the barrier plays an important role in designing a protective wall and hazard analysis of pipeline explosion accidents. To this end and to track the explosion characteristics of the hydrogen-air mixture near a concrete barrier wall, a new numerical approach in the compressible CESE solver based on the immersed boundary method (IBM) was utilized and coupled with the LS-DYNA® structural FEM solver in which the finite-rate chemistry model was in touch with the fluid-structure interaction (FSI). For the wall, the Concrete Damage Model (MAT_72R3) was employed as the constitutive material model. Existing experimental results were utilized to verify the 3D numerical model. Furthermore, the obtained numerical simulation results were compared with the conventional numerical approach called the TNT equivalent method using the MMALE algorithm in the open literature to show its drawbacks in predicting the pressure wave propagation in front of and particularly behind the wall surface. The results showed that by incorporating the finite-rate chemistry model in the CESE IBM FSI solver, all the explosion characteristics related to the hydrogen-air mixture detonation in front of and behind the wall surface can be accurately predicted since it involves detonation wave/structure interaction, chemical reaction, fluid motion, and structural deformation. Therefore, it is strongly recommended to use the CESE IBM FSI solver in conjunction with appropriate chemical kinetics as an alternative method instead of the conventional method to accurately model the gaseous mixture explosion process in a relatively complex environment and solve more practical applications in explosion and safety industries.

Model of the Impact of Focused Ultrasound on Biological Tissues

To study tissue permeability under extracorporeal exposure to various types of radiation, it is necessary to use multiphysical and mathematical modeling of all stages of the technology being developed, taking into account the dielectric and acoustic properties of human body tissues. The technologies used in medicine with focused ultrasound often have a high level of artifacts in the visualization of diagnostic studies and complications during therapy. When modeling exposure to focused ultrasound, the applied solvers must take into account pressure wave propagation, density changes and jumps, non-linearity and diffusion losses that occur in human tissues, and offer simulation of acoustic propagation in inhomogeneous installations in near real time. The article presents the results of multiphysics and mathematical modeling in the Sim4Life for Science V7.0 package using a full-wave acoustic solver (P-ACOUSTICS) of modern computational acoustics.

Optical Wave Microphone Measurement and Visualization of Pressure Waves Generated From a Surface Dielectric Barrier Discharge Element Driven by a High-Voltage Pulse Power Supply

In this study, pressure waves generated by applying a pulsed high voltage (HV) to a surface dielectric barrier discharge element were measured using optical wave microphone. The authors conducted experiments by changing parameters, such as the magnitude, polarity, and repetition rate of the applied pulsed voltage, and the distance between the laser of the optical wave microphone and the electrode of the surface discharge element. In the measurements at different distances between the laser and the electrode, the propagation of pressure waves was observed, and the propagation speed could be estimated. Measurements taken within 4 mm from the HV electrode suggested the influence of shock waves due to significant intensity and propagation speed above the speed of sound in air. Furthermore, the sound field of the surface discharge driven by the pulsed HV was measured by using the optical wave microphone computer tomography (CT) scan technique, and the two-dimensional sound field distribution was made.

Contribution of initial bubble radius distribution to weakly nonlinear waves with a long wavelength in bubbly liquids

In this study, the weakly nonlinear propagation of plane progressive pressure waves in an initially quiescent liquid was theoretically investigated. This liquid contains several small uniformly distributed spherical polydisperse gas bubbles. The polydispersity considered here represents various types of initial bubble radii, and the liquid contains multiple bubbles, each with an initial radius. Using the method of multiple scales, we first derived the Korteweg–de Vries–Burgers (KdVB) equation with a correction term as a nonlinear wave equation. This equation describes the long-range wave propagation with weak nonlinearity, low frequency, and long wavelength in the polydisperse bubbly liquid using the basic equations in a two-fluid model. The utilization of the two-fluid model incorporates the dependence of an initial void fraction on each coefficient in the nonlinear, dissipation, and dispersion terms in the KdVB equation. Furthermore, unlike previous studies on waves in polydisperse bubbly liquids, we achieved the formulation without assuming an explicit form of the polydispersity function. Consequently, we discovered the contribution of polydispersity to the various effects of wave propagation, that is, the nonlinear, dissipation, and dispersion effects. In particular, the dispersion effect of the waves was found to be strongly influenced by polydispersity.

Consumption Change‐Induced Transients in a Water Distribution Network: Laboratory Tests in a Looped System

AbstractAt the Water Engineering Laboratory of the University of Perugia, Italy, a wide experimental program has been carried out in a polymeric pipe network with two 100 × 100 m square loops. The aim of this program is to analyze the dynamic response of the system to transients caused by a change in water consumption. To emphasize such a response, transients are generated by the complete and fast closure of an end‐user, located at the downstream end of a service line. During tests, the combined effect of simultaneous consumers, whose consumption is varied both deterministically and stochastically, has been analyzed. The tests allow examining the propagation of the generated pressure waves within the network for different water consumption variations and end‐user locations. The lessons learnt from the experimental results may help the water utility managers to identify the reasons for the higher frequency of occurrence and severity of faults in some specific portions of water distribution networks apparently “similar” to others where damages are less frequent and severe.

An analysis of the pressure wave propagation by the sodium-water reaction in the printed circuit steam generator using the SWAAM-II code

The Sodium-Water Reaction (SWR) is the biggest problem for the development of the steam generator (SG) of the Sodium-cooled Fast Reactor (SFR). The pressure wave generation by the SWR has effects on the structural integrity of the Intermediate Heat Transport System (IHTS). However, when the Printed Circuit Steam Generator (PCSG) is used, the safety of SFR is expected to be improved. Since the PCSG is composed of a millimeter size of flow channels, the SWR zone is limited to the small channel. Therefore, it is necessary to evaluate the pressure spike and propagation in the PCSG. In this study, the SWAAM-II is used to analyze the pressure wave transfer by the SWR when the PCSG is used. The pressure in the sodium channel suddenly increases when the SWR occurs and the high pressure wave is transferred towards the headers. The peak pressure in the sodium channel is 16 MPa which is 21 % of the allowable stress based on the design by rule. However, the pressure wave is attenuated in the header due to the large difference in the cross-section area between the sodium channel and header. When it is assumed that the SWR occurs in the header, the pressure in the IHTS is increased. However, the increase of pressure in the IHTS is much less than the case of in the shell and tube type SG.

A Rapid Solver for the Prediction of Flow-Field of High-Speed Vehicle Moving in a Tube

High-speed vehicles traveling in a tube with pressures similar to those experienced by aircraft at their maximum altitude are presented. Although the concept resembles Hyperloop, the pressure level investigated here is much higher and safer than that suggested by Hyperloop, and, therefore, the system design is markedly different. Calculating a vehicle’s aerodynamic performance in the initial design stages requires low-budget computational tools to enable iterative design processes. This study presents an algorithm for rapid flow-field prediction based on a one-dimensional Reimann solution, including viscosity and heat transfer effects. The flow-field is divided into near- and far-fields, where the near-field represents the solution directly around the vehicle. The far-field demonstrates the impact of the vehicle’s motion on the vehicle’s flow-field upstream and downstream. Two-dimensional URANS models are compared to the current numerical scheme. The developed algorithm analyzes the flow-field and the propagation of pressure waves along the tube to simulate the vehicle’s movement. The one-dimensional model shows the robustness and predictability of the near and far flow-fields. The results from the developed scheme provide good agreement, with less than a few percent deviations, compared to CFD simulations but with significantly lower computational resources.

Numerical simulation method of surge experiments on gas turbine engines

In order to obtain the surge margin of an aero-engine during its operation, an engine surge experiment is required. A multi-dimensional simulation method for an aero-engine is established in this paper. The simulation of a surge experiment using high-pressure air-injection is then carried out on a turbo-shaft engine to obtain the surge boundary using this method. More specifically, firstly, a body-force model is employed to calculate the compressor performance owing to its capability of capturing the main three-dimensional features of compressor surge and avoiding excessive simulation time required by the traditional fully-three-dimensional Reynolds Averaged Navier-Stokes (RANS) method. Then, a one-dimensional model combining a lumped-parameter plenum model is used for the combustor to account for the propagation of pressure waves and the heat-release process, and a zero-dimensional throttle model is used to mimic the choking effect at the turbine nozzle. Finally, the air-injection system is modeled by imposing an injection boundary condition, which can be used conveniently in changing injection parameters. Based on the established method, the influences of different test parameters, such as the air-injection location, the pressure, the orifice size, the number of injection orifices, and the injection time duration on the surge characteristics and boundary are further studied, which offer effective guidance to optimize an actual experimental design.

Pressure pattern for fault diagnosis in gas pipelines through graph tools

This paper deals with the detection and localization of damage in gas-filled pipelines by means of an oriented-signals graph. The purpose is to search for transient patterns in a faulty main conduit, when an external acoustic source excites the viscous fluid. The study assumes a linearized model of distributed parameters for the healthy sections of the pipe and two-port lumped models for leaks and blockages. Based on these models, the exact transcendental transfer function of an acoustic source at the upstream end P(0,s) to the pressure P(z0,s) at point z0 is derived and transformed through graph tools in an oriented-signals graph for one and two faults. Thus, one establishes the transient response patterns associated with the faults from the graph paths without numerical parameters. This shown that graph theory is another suitable tool to visualize pressure wave propagation in a damage conduit. To validate the responses for one and two leaks, one compares the features with the analytical solution and the digital simulated pressure.

Toward fully compressible numerical simulations of stellar magneto-convection with the RAMSES code

Context. Numerical simulations of magneto-convection have greatly expanded our understanding of stellar interiors and stellar magnetism. Recently, fully compressible hydrodynamical simulations of full-star models have demonstrated the feasibility of studying the excitation and propagation of pressure and internal gravity waves in stellar interiors, which would allow for a direct comparison with asteroseismological measurements. However, the impact of magnetic fields on such waves has not been taken into account yet in three-dimensional simulations. Aims. We conduct a proof of concept for the realization of three-dimensional, fully compressible, magneto-hydrodynamical numerical simulations of stellar interiors with the RAMSES code. Methods. We adapted the RAMSES code to deal with highly subsonic turbulence, typical of stellar convection, by implementing a well-balanced scheme in the numerical solver. We then ran and analyzed three-dimensional hydrodynamical and magneto-hydrodynamical simulations with different resolutions of a plane-parallel convective envelope on a Cartesian grid. Results. Both hydrodynamical and magneto-hydrodynamical simulations develop a quasi-steady, turbulent convection layer from random density perturbations introduced over the initial profiles. The convective flows are characterized by small-amplitude fluctuations around the hydrodynamical equilibrium of the stellar interior, which is preserved over the whole simulation time. Using our compressible well-balanced scheme, we were able to model flows with Mach numbers as low as ℳ ∼ 10−3, but even lower Mach number flows are possible in principle. In the magneto-hydrodynamical runs, we observe an exponential growth of magnetic energy consistent with the action of a small-scale dynamo. The weak seed magnetic fields are amplified to mean strengths of 37% relative to the kinetic equipartition value in the highest resolution simulation. Since we chose a compressible approach, we see imprints of pressure and internal gravity waves propagating in the stable regions above and beneath the convection zone. In the magneto-hydrodynamical case, we measured a deficit in acoustic and internal gravity wave power with respect to the purely hydrodynamical counterpart of 16% and 13%, respectively. Conclusions. The well-balanced scheme implemented in RAMSES allowed us to accurately simulate the small-amplitude, turbulent fluctuations of stellar (magneto-)convection. The qualitative properties of the convective flows, magnetic fields, and excited waves are in agreement with previous studies in the literature. The power spectra, profiles, and probability density functions of the main quantities converge with resolution. Therefore, we consider the proof of concept to be successful. The deficit of acoustic power in the magneto-hydrodynamical simulation shows that magnetic fields must be included in the study of pressure waves in stellar interiors. We conclude by discussing future developments.

A Multi-Parametric and Multi-Layer Study to Investigate the Largest 2022 Hunga Tonga–Hunga Ha’apai Eruptions

On 20 December 2021, after six quiet years, the Hunga Tonga–Hunga Ha’apai volcano erupted abruptly. Then, on 15 January 2022, the largest eruption produced a plume well registered from satellites and destroyed the volcanic cone previously formed in 2015, connecting the two islands. We applied a multi-parametric and multi-layer study to investigate all the possible pre-eruption signals and effects of this volcanic activity in the lithosphere, atmosphere, and ionosphere. We focused our attention on: (a) seismological features considering the eruption in terms of an earthquake with equivalent energy released in the lithosphere; (b) atmospheric parameters, such as skin and air temperature, outgoing longwave radiation (OLR), cloud cover, relative humidity from climatological datasets; (c) varying magnetic field and electron density observed by ground magnetometers and satellites, even if the event was in the recovery phase of an intense geomagnetic storm. We found different precursors of this unique event in the lithosphere, as well as the effects due to the propagation of acoustic gravity and pressure waves and magnetic and electromagnetic coupling in the form of signals detected by ground stations and satellite data. All these parameters and their detailed investigation confirm the lithosphere–atmosphere–ionosphere coupling (LAIC) models introduced for natural hazards such as volcano eruptions and earthquakes.

The effect of flow speed on the bubble dynamics: A numerical study

The Naiver-Stokes equations are utilized to investigate the bubble dynamics subjected to the flow speed in the vicinity of a rigid wall. The predictions are compared with the Gilmore method and available experimental results, and a reasonable agreement is obtained. The important flow properties, e.g., bubble morphology, collapse time, jet development, pressure wave propagation, and vorticity evolution are studied in detail. The results demonstrate that the combined effect of the flow speed and rigid wall results in the generation of oblique jet, which may contribute to the development of the fish-scale pits on the surface of the hydraulic machinery. Moreover, our results show that the impulse loads caused by the bubble collapse in moving water are lower than those in stationary water. Finally, it is indicated that the stretching term plays a major role in the vorticity both inside and outside the bubble, while the dilatation term mainly influences the vorticity inside the bubble.

Diagnosis of colonic dysmotility associated with autonomic dysfunction in patients with chronic refractory constipation

We report the first study assessing human colon manometric features and their correlations with changes in autonomic functioning in patients with refractory chronic constipation prior to consideration of surgical intervention. High-resolution colonic manometry (HRCM) with simultaneous heart rate variability (HRV) was performed in 14 patients, and the resulting features were compared to healthy subjects. Patients were categorized into three groups that had normal, weak, or no high amplitude propagating pressure waves (HAPWs) to any intervention. We found mild vagal pathway impairment presented as lower HAPW amplitude in the proximal colon in response to proximal colon balloon distention. Left colon dysmotility was observed in 71% of patients, with features of (1) less left colon HAPWs, (2) lower left colon HAPW amplitudes (69.8 vs 102.3 mmHg), (3) impaired coloanal coordination, (4) left colon hypertonicity in patients with coccyx injury. Patients showed the following autonomic dysfunction: (1) high sympathetic tone at baseline, (2) high sympathetic reactivity to active standing and meal, (3) correlation of low parasympathetic reactivity to the meal with absence of the coloanal reflex, (4) lower parasympathetic and higher sympathetic activity during occurrence of HAPWs. In conclusion, left colon dysmotility and high sympathetic tone and reactivity, more so than vagal pathway impairment, play important roles in refractory chronic constipation and suggests sacral neuromodulation as a possible treatment.

Numerical model of an ultrasonically induced cavitation reactor and application to heavy oil processing

This study describes a numerical approach to model ultrasonically induced cavitation (UIC) reactors. UIC forms vapour-filled cavities in a liquid medium due to an applied acoustic field and their eventual collapse. UIC reactors are characterized by the presence of a vibrating probe that generates pressure waves by high-frequency oscillations (>20 kHz), which control the formation, dynamics, and eventual collapse of the vapour cavities. Those vapour cavities eventually enhance mixing and favour the occurrence of gas-liquid reactions. The zones of high mixing and reactivity coincide with the presence of the bubble cloud, which depends on the shape of the vessel and sonotrode. The development of advanced computational fluid dynamics (CFD) models is crucial to optimizing UIC processes’ geometry and operation parameters. A new algorithm for modelling UIC has been implemented within the OpenFOAM framework in the present study. The volume-of-fluid (VoF) method employs a diffuse interface approach for the volume fraction transport equation. The bubble dynamics are solved with sub-grid models, and the coupling between the main flow field and the sub-grid scales is performed through source terms in the transport equations. The source terms are de-coupled from convective and diffusive components of the volume fraction equation. The history of the bubbles is considered to consist of nucleation, oscillations, and collapse. The oscillations are resolved via the Rayleigh–Plesset equation. The concluding part of the work demonstrates the application of the algorithm to simulate the operation of an UIC reactor, which was designed to desulfurize fuels using the oxidative (ODS) process.

Laboratory Rat Thrombi Lose One-Third of Their Stiffness When Exposed to Large Oscillating Shear Stress Amplitudes: Contrasting Behavior to Human Clots

Rats impress by their high platelet count resulting in hypercoagulability, which protects the animals from severe bleeding. However, platelets also import numerous stiff junction points into the fibrous system of a clot, also enhancing the pre-stress of the fibrin fibers, which lowers their deformability. Clot deformation is clinically important since large strains are present in the arterial tree (caused by the propagation of pressure and pulse waves), and a clot is considered “safe” when it can deform over a long range of strain amplitudes. We tested clot formation and the behavior of fully formed blood clots of laboratory rats at large sinusoidal shear stress amplitudes by rheometry and compared outcomes to human reference data. We found that fiber density (by scanning electron microscopy) and clot stiffness (by rheometry) was pronounced compared to humans and differed with sexual dimorphism and with rat strain. Using our large amplitude oscillation (LAOS) protocol, we detected that rat clots yielded with a frustrated attempt to stiffen instead of showing the macroscopic stiffening response that is typical for human clots. We attribute this behavior to the appearance of multiple microfractures until, finally, a few leading fibers uptake the load. Rat clots also failed to align fibers in shear direction to initiate affine deformation. The rat clot phenotype differs substantially from the human one, which must be considered in research and toxicological testing. If microfractures in the fiber meshwork are concentrated in vivo, parts of a clot may break off and be washed away. However, homogenously distributed microfractures may open pores and allow the penetration of plasminogen activators. What occurs in the rat vasculature depends on the on-site clot composition.

Study on the propagation characteristics of pressure wave generated by mechanical shock in leaking pipelines

This paper focuses on the characteristics of pressure wave generated by an active mechanical shock in leaking pipelines. A piston type pressure wave generator was designed and applied to the pipeline experimental system and a three-dimensional (3D) numerical simulation model was developed based on the k-ε turbulence model and dynamic mesh. The experimental results showed that the maximum amplitude of pressure wave was about 104.71 kPa, and the leakage intensified the attenuation of pressure wave in space and time through quantitative analysis. Based on the 3D simulations, the processes of the pressure wave generation and propagation were revealed. The amplitude of pressure wave increased linearly with the increase of the maximum velocity of mechanical shock, and the effects of leakage on the waveforms of pressure wave were observed under the dimensionless analysis. In addition, a shorter duration of mechanical shock can increase the amplitude of the pressure wave generated. The results presented in this paper will contribute to the development and application of the transient leak detection method for pipeline systems.

A deep learning model for mapping the perturbation in pressurised irrigation systems

Nowadays, the management of pressurised irrigation networks requires plenty of information to provide an efficient and reliable service to farmers. Perturbation is the propagation of pressure waves through the networks pipes which could expose the network to a serious risk that could cause components damaging. Several computational codes were developed to simulate such phenomenon. The most recent ones are efficient enough to provide a good image of the perturbation occurrence through different indicators, but they are time and computationally expensive. For real time decision making and more flexible management, there is a need for faster models to be developed. In this study the directly programmed models were used as big data generators to train a developed deep learning model. This approach was applied on a pressurised on-demand irrigation system located in south of Italy that consists of 19 hydrants (service outlets) and covers 57 ha. Two thousand configurations (operational scenarios) were simulated using a predeveloped directly programmed model and fed to train a deep learning model with the objective of forecasting the maximum pressure occurred due the perturbation at each section. The occurred pressure is represented as classes according to the case sensitivity and the required precision. In the present work, scenarios for 1, 2 and 3 bars steps were simulated. The model proved to be significantly time saving compared to previous approaches as the results are produced instantaneously with a forecasting accuracy of 85 %. Furthermore, from the called confusion matrix, the error committed by the model is of one class lower or higher that may be considered tolerable according to the system sensitivity. Thus, modelling the perturbation in the on-demand pressurised irrigation networks would add a significant contribution to provide practical recommendations for real-time decision-making processes.

Amplification of high-intensity pressure waves and cavitation in water using a multi-pulsed laser excitation and black-TiOx optoacoustic lens.

A method for amplification of high-intensity pressure waves generated with a multi-pulsed Nd:YAG laser coupled with a black-TiOx optoacoustic lens in the water is presented and characterized. The investigation was focused on determining how the multi-pulsed laser excitation with delays between 50 µs and 400 µs influences the dynamics of the bubbles formed by a laser-induced breakdown on the upper surface of the lens, the acoustic cavitation in the focal region of the lens, and the high-intensity pressure waves generation. A needle hydrophone and a high-speed camera were used to analyze the spatial distribution and time-dependent development of the above-mentioned phenomena. Our results show how different delays (td ) of the laser pulses influence optoacoustic dynamics. When td is equal to or greater than the bubble oscillation time, acoustic cavitation cloud size increases 10-fold after the fourth laser pulse, while the pressure amplitude increases by more than 75%. A quasi-deterministic creation of cavitation due to consecutive transient pressure waves is also discussed. This is relevant for localized ablative laser therapy.

New Dimensionless Number for the Transition from Viscous to Turbulent Flow

Within the framework of Classical Continuum Thermomechanics, we consider an unsteady isothermal flow of a simple isotropic linear viscous fluid in the liquid state to investigate the transient flow conditions. Despite the attention paid to this problem by several research works, it seems that the understanding of turbulence in these flow conditions is controversial. We propose a dimensionless procedure that highlights some aspects related to the transition from viscous to turbulent flow which occurs when a finite amplitude pressure wave travels through the fluid. This kind of transition is demonstrated to be described by a (first) dimensionless number, which involves the bulk viscosity. Furthermore, in the turbulent flow regime, we show the role played by a (second) dimensionless number, which involves the turbulent bulk viscosity, in entropy production. Within the frame of the 1D model, we test the performance of the dimensionless procedure using experimental data on the pressure waves propagation in a long pipe (water hammer phenomenon). The obtained numerical results show good agreement with the experimental data. The results’ inspection confirms the predominant role of the turbulent bulk viscosity on energy dissipation processes.