Arc faults within the transformers can generate sudden pressure surges,constituting significant hazards that may precipitate oil tank explosions and severely compromise power system stability.Conventional power−freque...Arc faults within the transformers can generate sudden pressure surges,constituting significant hazards that may precipitate oil tank explosions and severely compromise power system stability.Conventional power−frequency arc discharge experiments encounter limitations in isolating pressure wave characteristics due to persistent gas generation and arc reignition.To circumvent these challenges,an oil-immersed impulse voltage discharge platform was conceived and engineered to investigate pressure wave propagation dynamics.A pressure numerical simulation model and theoretical model of oil−solid interface reflection and refraction were subsequently established to elucidate the pressure propagation mechanism.The experimental and simulation results show that the pressure wave generated by pulsed arc discharge in oil propagates radially in the form of spherical waves.Due to the viscous loss and wave front expansion of transformer oil,the peak pressure decays exponentially with distance,with a decay coefficientβ=1.15.When pressure waves encounter metal obstacles inside transformer oil,there are two propagation paths:direct transmission through and multiple reflections through,and a mode transformation of pressure waves occurs at the oil−solid interface,mainly propagating through obstacles in the form of transverse waves.This work quantitatively delineates the energy pressure wave coupling,propagation dynamics,and attenuation mechanisms,providing critical insights for assessing and mitigating arc fault-induced transformer explosion risks.展开更多
When gas invasion,especially overflow,occurs at the bottom hole in the process of managed pressure drilling(MPD),it is common to apply backpressure on the wellbore by adjusting the backpressure pump and throttle valve...When gas invasion,especially overflow,occurs at the bottom hole in the process of managed pressure drilling(MPD),it is common to apply backpressure on the wellbore by adjusting the backpressure pump and throttle valve,so as to rebuild bottom hole pressure balance.If it is still thought that the wellhead backpressure is loaded to the bottom hole instantaneously,there will be larger errors between the calculated wellbore parameters and the actual wellbore flow parameters,which will result in well control failure and even well blowout.In this paper,a pressure wave propagation equation suitable for the gaseliquid two-phase flow in the annulus was established based on the global averaged gaseliquid two-phase flow model to investigate the propagation velocity and time of backpressure wave in the wellbore.Then,gaseliquid interaction was introduced to carry out coupling solution on the equation set.It is shown that pressure wave velocity increases with the increase of drilling mud density,but decreases with the increase of void fraction and virtual mass force coefficient.It changes drastically at first,and then slows down.What's more,when the void fraction is greater than 0.1 or the virtual mass force coefficient exceeds 0.2,the momentum between gas phase and liquid phase is fully exchanged,and the pressure wave velocity decreases slowly,approaching a stable value.In Well Penglai 9 in the Sichuan Basin,for example,the average time of single pressure wave propagation is about 50 s,and the total propagation time of 4 rounds is about 200 s,which accounts for more than 67%of the total time of system control response.It is indicated that the propagation velocity and time of the pressure wave in the annulus calculated by this method can greatly improve the accuracy of managed pressure response time of MPD drilling system and the control precision of adaptive throttle valve.展开更多
Pressure waves induced by high-speed trains passing through a tunnel have adverse effects on train structures and passenger comfort. These adverse effects can be alleviated when the train passing through the tunnel wi...Pressure waves induced by high-speed trains passing through a tunnel have adverse effects on train structures and passenger comfort. These adverse effects can be alleviated when the train passing through the tunnel with a speed mode of deceleration. Thus, to investigate the effect of speed modes on pressure waves, three-dimensional compressible unsteady Reynolds-averaged Navier-Stokes simulations and the sliding mesh are used to simulate pressure waves on train surfaces and tunnel walls when trains passing through a tunnel with three different speed modes(a constant speed at350 km/h, a uniform deceleration from 350 to 300 km/h, and another uniform deceleration from 350 to 250 km/h).Compared with the constant speed, the peak-to-peak of the train surface pressure under the other two speed modes reaches a maximum difference of 11.0%. The maximum positive pressure difference of the tunnel wall under different speed modes is caused by the different attenuation of the friction effect when the train enters the tunnel, and the maximum difference is 12.8%. The difference of the maximum negative pressure on the tunnel wall is caused by the different speed and pressure wave intensity of the train arriving at the same measuring point in different speed modes,and the maximum difference is 15.8%. Hence, it can be concluded that a speed mode of deceleration for trains passing a tunnel can effectively alleviate the aerodynamic effect in the tunnel, especially for the pressure on the tunnel wall.展开更多
Pressure wave plays an important role in the occurrence of behind armor blunt trauma(BABT),and ballistic gelatin is widely used as a surrogate of biological tissue in the research of BABT.Comparison of pressure wave i...Pressure wave plays an important role in the occurrence of behind armor blunt trauma(BABT),and ballistic gelatin is widely used as a surrogate of biological tissue in the research of BABT.Comparison of pressure wave in the gelatin behind armor for different rifle bullets is lacking.The aim of this study was to observe dynamic changes in pressure wave induced by ballistic blunt impact on the armored gelatin block and to compare the effects of bullet type on the parameters of the transient pressure wave.The gelatin blocks protected with National Institute of Justice(NIJ) class III bulletproof armor were shot by three types of rifle bullet with the same level of impact energy.The transient pressure signals at five locations were recorded with pressure sensors and three parameters(maximum pressure,maximum pressure impulse,and the duration of the first positive phase) were determined and discussed.The results indicated that the waveform and the twin peak of transient pressure wave were not related to the bullet type.However,the values of pressure wave's parameters were significantly affected by bullet type.Additionally,the attenuation of pressure amplitude followed the similar law for the three ammunitions.These findings may be helpful to get some insight in the BABT and improve the structure design of bullet.展开更多
A wave rotor is suitable for compact and efficient pressure-exchange between gas flows.This work measured the circumferential pressure distribution of the rotor/stator interfaces and utilized a CFD method to simulate ...A wave rotor is suitable for compact and efficient pressure-exchange between gas flows.This work measured the circumferential pressure distribution of the rotor/stator interfaces and utilized a CFD method to simulate the unsteady pressure waves.The experimental and CFD results showed some slopes in the circumferential pressure distributions,and the slopes indicated the traces of specific unsteady pressure waves.Such traces varied regularly if the rotational speed varied within a range from-11%to+11%off the baseline value,but they were seriously disturbed if the rotational speed varied by-45%from the baseline value.It verified that a pressure wave in a wave rotor tended to keep its pressure ratio and propagation velocity unchanged if the rotational speed varied by a small extent,and that the pressure wave could not keep its propagation patterns if the rotational speed varied by a large extent.Because of the pressure wave behaviors,the wave rotor demonstrated specific regulations of the rotational speed effects on its operational states.展开更多
Considering the high-temperature distribution along a tunnel in a high-altitude area,the effects of high geotemperature and high altitude on the pressure wave of trains running in long tunnels were investigated using ...Considering the high-temperature distribution along a tunnel in a high-altitude area,the effects of high geotemperature and high altitude on the pressure wave of trains running in long tunnels were investigated using a 3D,compressible,unsteady turbulence model.To reduce the simulation cost and reflect the pressure wave characteristics in long tunnels,a representative tunnel length was first determined for simulation.The simulation results indicated that compared to the condition of a normal ambient-temperature tunnel,when trains go through a high geotemperature tunnel,the distribution of the minimum pressure(Pmin)along the tunnel moves to the tunnel entrance.The pressure amplitudes on the tunnel and train decrease integrally,with maximum reductions of 7.9%in the maximum pressure(Pmax)and 44%in Pmin on the tunnel,and 4.6%in P_(max)and 12%in Pmin on the train.When trains meet in high geotemperature tunnels,the distributions of P_(max)and Pmin along the tunnel change.The pressure amplitudes decrease integrally,with maximum reductions of 13.8%in P_(max)and 36.9%in Pmin on the tunnel,and 7.1%in P_(max)and 15.6%in Pmin on the train.The pressure difference between the two sides of the train during the intersection decreases by 15.9%.As the altitude rises,when trains cross and meet in tunnels,the waveforms of pressures on the tunnel and train and the pressure difference between the two sides of the train remain unchanged,and the peaks decrease linearly.展开更多
For the reduction of atmospheric effects,observed gravity has initially been corrected by using the computed barometric admittance k of the in situ measured pressure,expressed in nms-2/hPa units and estimated by least...For the reduction of atmospheric effects,observed gravity has initially been corrected by using the computed barometric admittance k of the in situ measured pressure,expressed in nms-2/hPa units and estimated by least squares method.However,the local pressure changes alone cannot account for the atmospheric mass attraction and loading when the coherent pressure field exceeds a specific size,i.e.,with increasing periodicities.To overcome this difficulty,it is necessary to compute the total atmospheric effect at each station using the global pressure field.However,the direct subtraction of the total gravity effect,provided by the models of pressure correction,is not yet satisfactory for S2 and other tidal components,such as K2 and P1,which include solar heating pressure tides.This paper identifies the origin of the problem and presents strategies to obtain a satisfactory solution.First,we set up a difference vector between the tidal factors of M2 and S2 after correction of the pressure and ocean tides effects.This vector,hereafter denoted as RES,presents the advantage of being practically insensitive to calibration errors.The minimum discrepancy between the tidal parameters of M2 and S2 corresponds to the minimum of the RES vector norm d.Secondly we adopt the hybrid pressure correction method,separating the local and the global pressure contribution of the models and replacing the local contribution by the pressure measured at the station multiplied by an admittance kATM.We tested this procedure on 8 stations from the IGETS superconducting gravimeters network(former GGP network).For stations at an altitude lower than 1000 m,the value of dopt is always smaller than0.0005.The discrepancy between the tidal parameters of the M2 and S2 waves is always lower than0.05% on the amplitude factors and 0.025° on the phases.For these stations,a correlation exists between the altitude and the value kopt.The results at the three Central European stations Conrad,Pecny and Vienna are in excellent agreement(0.05%) with the DDW99NH model for all the main tidal waves.展开更多
A study on the character of pressure wave propagation was proposed for the gas liquid oxygen two-phase flow in the pipe between pumps.According to the practical working conditions,the homogenous model based on the com...A study on the character of pressure wave propagation was proposed for the gas liquid oxygen two-phase flow in the pipe between pumps.According to the practical working conditions,the homogenous model based on the compressibility theory regarding a single bubble in an infinite liquid,and Redlich-Kwong gas equation was derived a model for the low temperature and high pressure case,especially considering the change of the ratio of density of gas to one of liquid.The numerical tests were conducted.The results not only show the agreement between numerical simulation for this model and experiment at the normal temperature and pressure is good,but also show that the modifications of the model for the low temperature and high pressure condition are necessary.The study is of reference to further study of oscillation restrain and relative pipe tests.展开更多
A non-invasive laser enhancing transdermal drug delivery technique has been investigated. The second harmonic wavelength of 532 nm of a Q-Switched Nd:YAG laser with pulse duration of 15 ns was used to irradiate on a b...A non-invasive laser enhancing transdermal drug delivery technique has been investigated. The second harmonic wavelength of 532 nm of a Q-Switched Nd:YAG laser with pulse duration of 15 ns was used to irradiate on a black polyethylene sheet covering on the surface of the drug solution, and hence produced pressure waves in the solution. Porcine skin and Rhodamine B were used as skin model and reagent respectively. Fluorescence microscope was employed to examine the mechanisms of drug delivery via the skin samples after laser treatment. The experiment revealed that the penetration depth of Rhodamine B under the illumination of laser increased with the energy density of the laser beam. After 20 laser shots at laser energy density of 70 mJ/cm2, the penetration depth reached 440 μm in 30 minutes, which was about three times as that without laser illumination. One possible explanation was that laser-induced pressure waves formed microchannels in the stratum corneum of the skin tissue. These microchannels provided much more effective paths for infiltration of Rhodamine B through the SC than follicular and intercellular paths. The drug solution diffused into the SC under the concentration gradient through the channels.展开更多
We conduct simulation study on the typical influencing factors for negative pressure wave in liquid pipeline leakage. We first analyse the liquid pipeline leakage detection based on negative pressure wave method and o...We conduct simulation study on the typical influencing factors for negative pressure wave in liquid pipeline leakage. We first analyse the liquid pipeline leakage detection based on negative pressure wave method and obtain the essential simulation parameters. Then based on the physical model of pipeline and by introducing leakage boundary condition, we simulate the variation of pressure and flow rate in pipeline after leakage, the influence of leakage scale and leakage position on the pressure and flow rate in the pipeline. The results show that the leakage scale mainly influences the amplitude of negative pressure wave, and that the leakage position inflnenees both the amplitude and the shape of the curves of negative pressure wave.展开更多
The arc faults inside oil-immersed power equipment can produce high-amplitude pres-sure waves inside tanks,which might cause ignition and explosion accidents.This kind of failure is one of the most severe faults for p...The arc faults inside oil-immersed power equipment can produce high-amplitude pres-sure waves inside tanks,which might cause ignition and explosion accidents.This kind of failure is one of the most severe faults for power equipment and has attracted consid-erable attention in recent years.However,due to the high risk of the experiments and the complex development of arc in oil,the characteristics of the pressure wave formed by the arc are still confusing.In this paper,the time-frequency characteristics of pressure waves are analysed using several experiments of 1-8 kA power-frequency arc inside a closed oil tank.The experimental results show that the pressure wave produced by the arc in oil contains three frequency bands,0-500 Hz,500 Hz-40 kHz,and above 40 kHz,which are related to the arc energy,the average current around arc ignition and the metal wire explosion respectively.This helps further understand the formation mechanism of the pressure wave caused by the arc in oil.This paper discusses the influences of ignition wire on arc-formed pressure waves.A wire diameter selection method for arc experiments is established to reduce the pressure differences between wire-ignited arcs and actual arc faults.展开更多
The prediction of the pressure wave amplitude produced when two trains pass each other in the tunnel is important to the train design for airtightness and tunnel conditions in China.In this paper,the key factors of th...The prediction of the pressure wave amplitude produced when two trains pass each other in the tunnel is important to the train design for airtightness and tunnel conditions in China.In this paper,the key factors of this problem were firstly stud-ied based on theoretical analysis.The equation of the worst tunnel length for the global maximum and minimum pressure values was derived.Then,the influence of tunnel length on global minimum pressure and the critical region in which the global minimum pressure varies rapidly were investigated.Finally,a numerical method based on two-dimensional Na-vier-Stokes equations was established.Typical conditions of two trains passing-by in tunnels of different lengths were simulated.The theoretical and computational results agree with each other closely.展开更多
We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai Volcano by synthesizing diverse preliminary seismic, volcanological, sound wave, and...We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai Volcano by synthesizing diverse preliminary seismic, volcanological, sound wave, and lightning data available within the first few weeks after the eruption occurred. The first hour of eruptive activity produced fast-propagating tsunami waves, long-period seismic waves, loud audible sound waves, infrasonic waves, exceptionally intense volcanic lightning and an unsteady volcanic plume that transiently reached-at 58km-the Earth’s mesosphere. Energetic seismic signals were recorded worldwide and the globally stacked seismogram showed episodic seismic events within the most intense periods of phreatoplinian activity, and they correlated well with the infrasound pressure waveform recorded in Fiji. Gravity wave signals were strong enough to be observed over the entire planet in just the first few hours, with some circling the Earth multiple times subsequently. These large-amplitude, long-wavelength atmospheric disturbances come from the Earth’s atmosphere being forced by the magmatic mixture of tephra, melt and gasses emitted by the unsteady but quasicontinuous eruption from 0402±1–1800 UTC on January 15, 2022. Atmospheric forcing lasted much longer than rupturing from large earthquakes recorded on modern instruments, producing a type of shock wave that originated from the interaction between compressed air and ambient(wavy) sea surface. This scenario differs from conventional ideas of earthquake slip, landslides, or caldera collapse-generated tsunami waves because of the enormous(~1000x) volumetric change due to the supercritical nature of volatiles associated with the hot,volatile-rich phreatoplinian plume. The time series of plume altitude can be translated to volumetric discharge and mass flow rate. For an eruption duration of ~12 h, the eruptive volume and mass are estimated at 1.9 km^(3) and~2 900 Tg, respectively, corresponding to a VEI of 5–6 for this event. The high frequency and intensity of lightning was enhanced by the production of fine ash due to magma-seawater interaction with concomitant high charge per unit mass and the high pre-eruptive concentration of dissolved volatiles. Analysis of lightning flash frequencies provides a rapid metric for plume activity and eruption magnitude. Many aspects of this eruption await further investigation by multidisciplinary teams. It represents a unique opportunity for fundamental research regarding the complex, non-linear behavior of high energetic volcanic eruptions and attendant phenomena, with critical implications for hazard mitigation, volcano forecasting, and first-response efforts in future disasters.展开更多
A new concept of bend-mode inkjet nozzle with double PZT (lead zirconate titanate) actuators has been designed and fabricated in the present study. Then the pressure wave and fluid velocity at the nozzle exit have bee...A new concept of bend-mode inkjet nozzle with double PZT (lead zirconate titanate) actuators has been designed and fabricated in the present study. Then the pressure wave and fluid velocity at the nozzle exit have been investigated. The complex pressure behavior inside the channel was solved numerically based on the narrow channel acoustic theory. The two PZTs attached to a rectangular channel were actuated sequentially by setting the waveforms of each PZT to be center-aligned with various pulse widths. As a result, the double PZT actuation is superior to the single PZT actuation in view of strong momentum force and fast dissipation of residual pressure. The maximum fluid velocity at the nozzle exit is observed when the respective pulse widths equal to their optimum pulse widths. The numerical results are supported by the experimental results with the fabricated inkjet device by measuring the speed of meniscus just out of the nozzle.展开更多
This paper presents a new model used to describe the propagation of pressure waves at the inlet systems of internal combustion engine. In the first part, an analogy is made between the compressible air in a pipe and a...This paper presents a new model used to describe the propagation of pressure waves at the inlet systems of internal combustion engine. In the first part, an analogy is made between the compressible air in a pipe and a mechanical ideal mass damper spring system. A new model is then presented and the parameters of this model are determined by the use of an experimental setup (shock tube test bench). With this model, a transfer function is defined in order to link directly the pressure and the air mass flow rate. In the second part, the model is included into an internal combustion engine simulation code. The results obtained with this code are compared to experimental ones which are measured on a one-cylinder engine test bench. This last one is driven by an electric motor in order to study only the effect of the pressure waves on the engine behavior. A good agreement is obtained between the experimental results and the numerical ones and the new approach is an alternative method for modeling the pressure wave phenomena in an internal combustion engine manifold.展开更多
The one dimensional (1 D) unsteady flow induced by a high speed train entering a tunnel is numerically studied by the method of characteristics. The tube area is dependent on time and distance. The energy equatio...The one dimensional (1 D) unsteady flow induced by a high speed train entering a tunnel is numerically studied by the method of characteristics. The tube area is dependent on time and distance. The energy equation used by Kage et al. is corrected to avoid the conflict with the isentropic assumption. The effect of the tunnel hood on the pressure wave is studied near the tunnel exit. Results show that the tunnel hood is useful in reducing the peak value and the time derivative of the pressure wave.展开更多
Water-rich cracks represent common tunnel defects.Intense pressure waves generated by trains traveling through tunnels may undergo enhancement within water-rich cracks.Using the re-normalization group(RNG)k-εturbulen...Water-rich cracks represent common tunnel defects.Intense pressure waves generated by trains traveling through tunnels may undergo enhancement within water-rich cracks.Using the re-normalization group(RNG)k-εturbulence model and volume of fluid(VOF)method,this study analyzes the spatiotemporal distribution,spectral features,and influencing factors of pressure wave propagation in water-rich cracks when two high-speed trains intersect in a tunnel.The flow mechanisms underlying the pressure enhancement within water-rich cracks are also revealed.The main conclusions are as follows:1)The positive and negative peak pressure coefficients in water-rich cracks are 1.34 and-2.36,with corresponding pressure gradient peaks of 31.41 kPa/s and-34.01 kPa/s.Compared to the tunnel wall,the peak pressure coefficients and gradients exhibit increases of 34.41%/44.63%and 31.61%/60.46%,respectively.2)The dominant frequency of the pressure wave power spectral density(PSD)at the crack tip is 26.97%higher than that in the tunnel.The PSD peak value continuously increases with depth and is the largest at the crack tip,representing an increase of 9.36%compared to the tunnel.3)An increase in crack width reduces the peaks of pressure waves,pressure gradients,and PSD,while increases in vertical and transverse depths amplify these peaks.Crack width has the most significant impact on pressure waves and pressure gradients,while transverse depth has the most significant effect on PSD peak values.4)Driven by inertia and pressure differences,the water body oscillates variably,enhancing pressure fluctuation amplitude at the crack tip.The higher the water body's movement velocity,the greater the pressure gradient at the crack tip.The above research results may provide a reference for crack harnessing in high-speed railway tunnels.展开更多
The pressure comfort of passengers and crew in high-speed trains faces significant challenges under alternating open-tunnel conditions.To better understand the mechanism of pressure transmission and control interior p...The pressure comfort of passengers and crew in high-speed trains faces significant challenges under alternating open-tunnel conditions.To better understand the mechanism of pressure transmission and control interior pressure fluctuations in high-altitude regions,this study develops an interior pressure fluctuation model.By establishing the frameworks of the non-ideal gas state equation and the polytropic process equation,gas heat transfer and mass transfer were expressed through the first law of thermodynamics and the continuity equation.Simulation results,evaluated by root mean square error,coefficient of determination,peak-to-peak error,and pressure change rate,show that the proposed model closely aligns with measured signals in both overall trends and local details.Data from various train types and tunnel scenarios further demonstrate the model's accuracy and practical applicability.This study provides a critical foundation for evaluating interior pressure comfort for high-speed trains in high-altitude regions.展开更多
Standing waves are formed due to the reflection when waves meet vertical wall, therefore strong structures are needed to keep the wall stability under the serious wave attack. For the improvement of the working condit...Standing waves are formed due to the reflection when waves meet vertical wall, therefore strong structures are needed to keep the wall stability under the serious wave attack. For the improvement of the working condition and increase of the stability of the wall, the lower reflecting breakwaters have attracted close attention Reports mostly from Japanese researchers are often concerned with the wall of caisson equipped with open windows. In this paper a kind of hollow-pipe perforated breakwater is examined which waves may partially perforate into the harbour basin. The wave in front of the wall can only form partial standing wave and wave force is reduced obviously. And the theoretical calculation of wave force and analysis of wave force spectrum are all derived. Comparison between the results from theoretical calculation and hydraulic modeling shows reasonable agreement.展开更多
Rocky landslides on river banks can result in the generation of ultra-high waves,which may destroy structures on the opposite bank.Existing methods to calculate the pressure on bank slopes under the effect of impulse ...Rocky landslides on river banks can result in the generation of ultra-high waves,which may destroy structures on the opposite bank.Existing methods to calculate the pressure on bank slopes under the effect of impulse waves generated by landslides are,however,few and of low precision.Therefore,in this study,a three-dimensional physical model test was conducted by taking into account factors such as landslide geometry parameters and the bank slope angle.The model test section was generalized on the basis of a certain section of the Three Gorges reservoir area as a prototype,after which the wave parameters and wave pressure acting on the bank slope were measured.Subsequently,the magnitude,acting point,and distribution of the pressure of the impulse waves generated by the rocky landslide upon the bank slope were determined.The distribution curve of the impact pressure was similar to that calculated using theСНиПⅡ57-75 formula,and the experimental pulsating pressure value was close to the value calculated using the Subgrade formula.Based on the test results,a power function of the relative pulsating pressure steepness with respect to the reciprocal of the wave steepness,relative water depth,and slope ratio was proposed.The acting point of the maximum pulsating pressure was found to be located near the still water level.Finally,an empirical formula for calculating the envelope of the maximum pulsating pressure distribution curve was proposed.These formulas can serve as a theoretical basis for the prediction of impulse wave pressure generated owing to landslides on bank slopes.展开更多
基金funded by the Science and Technology Program of State Grid Corporation of China(5500-202356358A-2-1-ZX).
文摘Arc faults within the transformers can generate sudden pressure surges,constituting significant hazards that may precipitate oil tank explosions and severely compromise power system stability.Conventional power−frequency arc discharge experiments encounter limitations in isolating pressure wave characteristics due to persistent gas generation and arc reignition.To circumvent these challenges,an oil-immersed impulse voltage discharge platform was conceived and engineered to investigate pressure wave propagation dynamics.A pressure numerical simulation model and theoretical model of oil−solid interface reflection and refraction were subsequently established to elucidate the pressure propagation mechanism.The experimental and simulation results show that the pressure wave generated by pulsed arc discharge in oil propagates radially in the form of spherical waves.Due to the viscous loss and wave front expansion of transformer oil,the peak pressure decays exponentially with distance,with a decay coefficientβ=1.15.When pressure waves encounter metal obstacles inside transformer oil,there are two propagation paths:direct transmission through and multiple reflections through,and a mode transformation of pressure waves occurs at the oil−solid interface,mainly propagating through obstacles in the form of transverse waves.This work quantitatively delineates the energy pressure wave coupling,propagation dynamics,and attenuation mechanisms,providing critical insights for assessing and mitigating arc fault-induced transformer explosion risks.
基金Project supported by General Program of National Natural Science Foundation of China“Wellbore Multi-phase Flow Coupling Mechanism Research-Formations Based on Precise Backpressure Control”(No.:51474073)“Research on Wellbore Temperature Field and Pressure Field Distribution Laws of Deep Unbalanced Drilling Based on Thermal-fluid Coupling”(No.:51374077).
文摘When gas invasion,especially overflow,occurs at the bottom hole in the process of managed pressure drilling(MPD),it is common to apply backpressure on the wellbore by adjusting the backpressure pump and throttle valve,so as to rebuild bottom hole pressure balance.If it is still thought that the wellhead backpressure is loaded to the bottom hole instantaneously,there will be larger errors between the calculated wellbore parameters and the actual wellbore flow parameters,which will result in well control failure and even well blowout.In this paper,a pressure wave propagation equation suitable for the gaseliquid two-phase flow in the annulus was established based on the global averaged gaseliquid two-phase flow model to investigate the propagation velocity and time of backpressure wave in the wellbore.Then,gaseliquid interaction was introduced to carry out coupling solution on the equation set.It is shown that pressure wave velocity increases with the increase of drilling mud density,but decreases with the increase of void fraction and virtual mass force coefficient.It changes drastically at first,and then slows down.What's more,when the void fraction is greater than 0.1 or the virtual mass force coefficient exceeds 0.2,the momentum between gas phase and liquid phase is fully exchanged,and the pressure wave velocity decreases slowly,approaching a stable value.In Well Penglai 9 in the Sichuan Basin,for example,the average time of single pressure wave propagation is about 50 s,and the total propagation time of 4 rounds is about 200 s,which accounts for more than 67%of the total time of system control response.It is indicated that the propagation velocity and time of the pressure wave in the annulus calculated by this method can greatly improve the accuracy of managed pressure response time of MPD drilling system and the control precision of adaptive throttle valve.
基金Project(2017J010-B)supported by the Technology Research and Development Program of China Railway CorporationProject(414010033)supported by the National Natural Science Foundation of China+1 种基金Project(CX20210232)supported by Hunan Provincial Innovation Foundation for Postgraduate,ChinaProjects(2021zzts0671,2021zzts0163)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Pressure waves induced by high-speed trains passing through a tunnel have adverse effects on train structures and passenger comfort. These adverse effects can be alleviated when the train passing through the tunnel with a speed mode of deceleration. Thus, to investigate the effect of speed modes on pressure waves, three-dimensional compressible unsteady Reynolds-averaged Navier-Stokes simulations and the sliding mesh are used to simulate pressure waves on train surfaces and tunnel walls when trains passing through a tunnel with three different speed modes(a constant speed at350 km/h, a uniform deceleration from 350 to 300 km/h, and another uniform deceleration from 350 to 250 km/h).Compared with the constant speed, the peak-to-peak of the train surface pressure under the other two speed modes reaches a maximum difference of 11.0%. The maximum positive pressure difference of the tunnel wall under different speed modes is caused by the different attenuation of the friction effect when the train enters the tunnel, and the maximum difference is 12.8%. The difference of the maximum negative pressure on the tunnel wall is caused by the different speed and pressure wave intensity of the train arriving at the same measuring point in different speed modes,and the maximum difference is 15.8%. Hence, it can be concluded that a speed mode of deceleration for trains passing a tunnel can effectively alleviate the aerodynamic effect in the tunnel, especially for the pressure on the tunnel wall.
基金supported by the National Basic Scientific Research Project(Grant NO.JCKYS2019209C001)National Key Research and Development Program of China(Grant NO.2017YFC0822301&Grant NO.2018YFC0807206)National Natural Science Foundation of China(Grant NO.11772303)。
文摘Pressure wave plays an important role in the occurrence of behind armor blunt trauma(BABT),and ballistic gelatin is widely used as a surrogate of biological tissue in the research of BABT.Comparison of pressure wave in the gelatin behind armor for different rifle bullets is lacking.The aim of this study was to observe dynamic changes in pressure wave induced by ballistic blunt impact on the armored gelatin block and to compare the effects of bullet type on the parameters of the transient pressure wave.The gelatin blocks protected with National Institute of Justice(NIJ) class III bulletproof armor were shot by three types of rifle bullet with the same level of impact energy.The transient pressure signals at five locations were recorded with pressure sensors and three parameters(maximum pressure,maximum pressure impulse,and the duration of the first positive phase) were determined and discussed.The results indicated that the waveform and the twin peak of transient pressure wave were not related to the bullet type.However,the values of pressure wave's parameters were significantly affected by bullet type.Additionally,the attenuation of pressure amplitude followed the similar law for the three ammunitions.These findings may be helpful to get some insight in the BABT and improve the structure design of bullet.
基金co-supported by the National Natural Science Foundation of China(No.51906007)the National Key Laboratory Foundation of China(No.6142702190204)。
文摘A wave rotor is suitable for compact and efficient pressure-exchange between gas flows.This work measured the circumferential pressure distribution of the rotor/stator interfaces and utilized a CFD method to simulate the unsteady pressure waves.The experimental and CFD results showed some slopes in the circumferential pressure distributions,and the slopes indicated the traces of specific unsteady pressure waves.Such traces varied regularly if the rotational speed varied within a range from-11%to+11%off the baseline value,but they were seriously disturbed if the rotational speed varied by-45%from the baseline value.It verified that a pressure wave in a wave rotor tended to keep its pressure ratio and propagation velocity unchanged if the rotational speed varied by a small extent,and that the pressure wave could not keep its propagation patterns if the rotational speed varied by a large extent.Because of the pressure wave behaviors,the wave rotor demonstrated specific regulations of the rotational speed effects on its operational states.
基金supported by the National Key Research and Development Program of China(No.2020YFA0710902)the National Natural Science Foundation of China(Nos.12122211 and 11772275).
文摘Considering the high-temperature distribution along a tunnel in a high-altitude area,the effects of high geotemperature and high altitude on the pressure wave of trains running in long tunnels were investigated using a 3D,compressible,unsteady turbulence model.To reduce the simulation cost and reflect the pressure wave characteristics in long tunnels,a representative tunnel length was first determined for simulation.The simulation results indicated that compared to the condition of a normal ambient-temperature tunnel,when trains go through a high geotemperature tunnel,the distribution of the minimum pressure(Pmin)along the tunnel moves to the tunnel entrance.The pressure amplitudes on the tunnel and train decrease integrally,with maximum reductions of 7.9%in the maximum pressure(Pmax)and 44%in Pmin on the tunnel,and 4.6%in P_(max)and 12%in Pmin on the train.When trains meet in high geotemperature tunnels,the distributions of P_(max)and Pmin along the tunnel change.The pressure amplitudes decrease integrally,with maximum reductions of 13.8%in P_(max)and 36.9%in Pmin on the tunnel,and 7.1%in P_(max)and 15.6%in Pmin on the train.The pressure difference between the two sides of the train during the intersection decreases by 15.9%.As the altitude rises,when trains cross and meet in tunnels,the waveforms of pressures on the tunnel and train and the pressure difference between the two sides of the train remain unchanged,and the peaks decrease linearly.
基金supported by Major Program of the National Natural Science Foundation of China (42192535)。
文摘For the reduction of atmospheric effects,observed gravity has initially been corrected by using the computed barometric admittance k of the in situ measured pressure,expressed in nms-2/hPa units and estimated by least squares method.However,the local pressure changes alone cannot account for the atmospheric mass attraction and loading when the coherent pressure field exceeds a specific size,i.e.,with increasing periodicities.To overcome this difficulty,it is necessary to compute the total atmospheric effect at each station using the global pressure field.However,the direct subtraction of the total gravity effect,provided by the models of pressure correction,is not yet satisfactory for S2 and other tidal components,such as K2 and P1,which include solar heating pressure tides.This paper identifies the origin of the problem and presents strategies to obtain a satisfactory solution.First,we set up a difference vector between the tidal factors of M2 and S2 after correction of the pressure and ocean tides effects.This vector,hereafter denoted as RES,presents the advantage of being practically insensitive to calibration errors.The minimum discrepancy between the tidal parameters of M2 and S2 corresponds to the minimum of the RES vector norm d.Secondly we adopt the hybrid pressure correction method,separating the local and the global pressure contribution of the models and replacing the local contribution by the pressure measured at the station multiplied by an admittance kATM.We tested this procedure on 8 stations from the IGETS superconducting gravimeters network(former GGP network).For stations at an altitude lower than 1000 m,the value of dopt is always smaller than0.0005.The discrepancy between the tidal parameters of the M2 and S2 waves is always lower than0.05% on the amplitude factors and 0.025° on the phases.For these stations,a correlation exists between the altitude and the value kopt.The results at the three Central European stations Conrad,Pecny and Vienna are in excellent agreement(0.05%) with the DDW99NH model for all the main tidal waves.
文摘A study on the character of pressure wave propagation was proposed for the gas liquid oxygen two-phase flow in the pipe between pumps.According to the practical working conditions,the homogenous model based on the compressibility theory regarding a single bubble in an infinite liquid,and Redlich-Kwong gas equation was derived a model for the low temperature and high pressure case,especially considering the change of the ratio of density of gas to one of liquid.The numerical tests were conducted.The results not only show the agreement between numerical simulation for this model and experiment at the normal temperature and pressure is good,but also show that the modifications of the model for the low temperature and high pressure condition are necessary.The study is of reference to further study of oscillation restrain and relative pipe tests.
基金SRIT program in Beijing Institute of Technology,Grant number:P0000043
文摘A non-invasive laser enhancing transdermal drug delivery technique has been investigated. The second harmonic wavelength of 532 nm of a Q-Switched Nd:YAG laser with pulse duration of 15 ns was used to irradiate on a black polyethylene sheet covering on the surface of the drug solution, and hence produced pressure waves in the solution. Porcine skin and Rhodamine B were used as skin model and reagent respectively. Fluorescence microscope was employed to examine the mechanisms of drug delivery via the skin samples after laser treatment. The experiment revealed that the penetration depth of Rhodamine B under the illumination of laser increased with the energy density of the laser beam. After 20 laser shots at laser energy density of 70 mJ/cm2, the penetration depth reached 440 μm in 30 minutes, which was about three times as that without laser illumination. One possible explanation was that laser-induced pressure waves formed microchannels in the stratum corneum of the skin tissue. These microchannels provided much more effective paths for infiltration of Rhodamine B through the SC than follicular and intercellular paths. The drug solution diffused into the SC under the concentration gradient through the channels.
文摘We conduct simulation study on the typical influencing factors for negative pressure wave in liquid pipeline leakage. We first analyse the liquid pipeline leakage detection based on negative pressure wave method and obtain the essential simulation parameters. Then based on the physical model of pipeline and by introducing leakage boundary condition, we simulate the variation of pressure and flow rate in pipeline after leakage, the influence of leakage scale and leakage position on the pressure and flow rate in the pipeline. The results show that the leakage scale mainly influences the amplitude of negative pressure wave, and that the leakage position inflnenees both the amplitude and the shape of the curves of negative pressure wave.
基金National Key Research and Development Program of China,Grant/Award Number:2023YFB2407001National Natural Science Foundation of China(Young Scientistic Program),Grant/Award Number:52007148。
文摘The arc faults inside oil-immersed power equipment can produce high-amplitude pres-sure waves inside tanks,which might cause ignition and explosion accidents.This kind of failure is one of the most severe faults for power equipment and has attracted consid-erable attention in recent years.However,due to the high risk of the experiments and the complex development of arc in oil,the characteristics of the pressure wave formed by the arc are still confusing.In this paper,the time-frequency characteristics of pressure waves are analysed using several experiments of 1-8 kA power-frequency arc inside a closed oil tank.The experimental results show that the pressure wave produced by the arc in oil contains three frequency bands,0-500 Hz,500 Hz-40 kHz,and above 40 kHz,which are related to the arc energy,the average current around arc ignition and the metal wire explosion respectively.This helps further understand the formation mechanism of the pressure wave caused by the arc in oil.This paper discusses the influences of ignition wire on arc-formed pressure waves.A wire diameter selection method for arc experiments is established to reduce the pressure differences between wire-ignited arcs and actual arc faults.
基金supported by the National Key Technology R&D Program,Aerodynamic Optimization Design and Safe Evaluation Techniques on Chinese High-Speed Trains(Grant No.2009BAG12A03)the National Basic Research Program of China("973" Project)(Grant No.2011CB71100)
文摘The prediction of the pressure wave amplitude produced when two trains pass each other in the tunnel is important to the train design for airtightness and tunnel conditions in China.In this paper,the key factors of this problem were firstly stud-ied based on theoretical analysis.The equation of the worst tunnel length for the global maximum and minimum pressure values was derived.Then,the influence of tunnel length on global minimum pressure and the critical region in which the global minimum pressure varies rapidly were investigated.Finally,a numerical method based on two-dimensional Na-vier-Stokes equations was established.Typical conditions of two trains passing-by in tunnels of different lengths were simulated.The theoretical and computational results agree with each other closely.
基金partially supported by US Department of Energy Grant DE-SC0019759National Science Foundation (NSF) Grants EAR-1918126, EAR-2027150, EAR-1925965, and OCE-1842989。
文摘We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai Volcano by synthesizing diverse preliminary seismic, volcanological, sound wave, and lightning data available within the first few weeks after the eruption occurred. The first hour of eruptive activity produced fast-propagating tsunami waves, long-period seismic waves, loud audible sound waves, infrasonic waves, exceptionally intense volcanic lightning and an unsteady volcanic plume that transiently reached-at 58km-the Earth’s mesosphere. Energetic seismic signals were recorded worldwide and the globally stacked seismogram showed episodic seismic events within the most intense periods of phreatoplinian activity, and they correlated well with the infrasound pressure waveform recorded in Fiji. Gravity wave signals were strong enough to be observed over the entire planet in just the first few hours, with some circling the Earth multiple times subsequently. These large-amplitude, long-wavelength atmospheric disturbances come from the Earth’s atmosphere being forced by the magmatic mixture of tephra, melt and gasses emitted by the unsteady but quasicontinuous eruption from 0402±1–1800 UTC on January 15, 2022. Atmospheric forcing lasted much longer than rupturing from large earthquakes recorded on modern instruments, producing a type of shock wave that originated from the interaction between compressed air and ambient(wavy) sea surface. This scenario differs from conventional ideas of earthquake slip, landslides, or caldera collapse-generated tsunami waves because of the enormous(~1000x) volumetric change due to the supercritical nature of volatiles associated with the hot,volatile-rich phreatoplinian plume. The time series of plume altitude can be translated to volumetric discharge and mass flow rate. For an eruption duration of ~12 h, the eruptive volume and mass are estimated at 1.9 km^(3) and~2 900 Tg, respectively, corresponding to a VEI of 5–6 for this event. The high frequency and intensity of lightning was enhanced by the production of fine ash due to magma-seawater interaction with concomitant high charge per unit mass and the high pre-eruptive concentration of dissolved volatiles. Analysis of lightning flash frequencies provides a rapid metric for plume activity and eruption magnitude. Many aspects of this eruption await further investigation by multidisciplinary teams. It represents a unique opportunity for fundamental research regarding the complex, non-linear behavior of high energetic volcanic eruptions and attendant phenomena, with critical implications for hazard mitigation, volcano forecasting, and first-response efforts in future disasters.
基金supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education,Science and Technology(2010-0009054)
文摘A new concept of bend-mode inkjet nozzle with double PZT (lead zirconate titanate) actuators has been designed and fabricated in the present study. Then the pressure wave and fluid velocity at the nozzle exit have been investigated. The complex pressure behavior inside the channel was solved numerically based on the narrow channel acoustic theory. The two PZTs attached to a rectangular channel were actuated sequentially by setting the waveforms of each PZT to be center-aligned with various pulse widths. As a result, the double PZT actuation is superior to the single PZT actuation in view of strong momentum force and fast dissipation of residual pressure. The maximum fluid velocity at the nozzle exit is observed when the respective pulse widths equal to their optimum pulse widths. The numerical results are supported by the experimental results with the fabricated inkjet device by measuring the speed of meniscus just out of the nozzle.
文摘This paper presents a new model used to describe the propagation of pressure waves at the inlet systems of internal combustion engine. In the first part, an analogy is made between the compressible air in a pipe and a mechanical ideal mass damper spring system. A new model is then presented and the parameters of this model are determined by the use of an experimental setup (shock tube test bench). With this model, a transfer function is defined in order to link directly the pressure and the air mass flow rate. In the second part, the model is included into an internal combustion engine simulation code. The results obtained with this code are compared to experimental ones which are measured on a one-cylinder engine test bench. This last one is driven by an electric motor in order to study only the effect of the pressure waves on the engine behavior. A good agreement is obtained between the experimental results and the numerical ones and the new approach is an alternative method for modeling the pressure wave phenomena in an internal combustion engine manifold.
文摘The one dimensional (1 D) unsteady flow induced by a high speed train entering a tunnel is numerically studied by the method of characteristics. The tube area is dependent on time and distance. The energy equation used by Kage et al. is corrected to avoid the conflict with the isentropic assumption. The effect of the tunnel hood on the pressure wave is studied near the tunnel exit. Results show that the tunnel hood is useful in reducing the peak value and the time derivative of the pressure wave.
基金Project(51978670)supported by the National Natural Science Foundation of ChinaProject(N2024G018)supported by the Science and Technology Research and Development Program Project of China Railway+1 种基金Projects(Major Project:2021-Major-01 and 2023-Major-12Major Special Project:2021-Special-04-2)supported by the Science and Technology Research and Development Program Project of China Railway Group Limited。
文摘Water-rich cracks represent common tunnel defects.Intense pressure waves generated by trains traveling through tunnels may undergo enhancement within water-rich cracks.Using the re-normalization group(RNG)k-εturbulence model and volume of fluid(VOF)method,this study analyzes the spatiotemporal distribution,spectral features,and influencing factors of pressure wave propagation in water-rich cracks when two high-speed trains intersect in a tunnel.The flow mechanisms underlying the pressure enhancement within water-rich cracks are also revealed.The main conclusions are as follows:1)The positive and negative peak pressure coefficients in water-rich cracks are 1.34 and-2.36,with corresponding pressure gradient peaks of 31.41 kPa/s and-34.01 kPa/s.Compared to the tunnel wall,the peak pressure coefficients and gradients exhibit increases of 34.41%/44.63%and 31.61%/60.46%,respectively.2)The dominant frequency of the pressure wave power spectral density(PSD)at the crack tip is 26.97%higher than that in the tunnel.The PSD peak value continuously increases with depth and is the largest at the crack tip,representing an increase of 9.36%compared to the tunnel.3)An increase in crack width reduces the peaks of pressure waves,pressure gradients,and PSD,while increases in vertical and transverse depths amplify these peaks.Crack width has the most significant impact on pressure waves and pressure gradients,while transverse depth has the most significant effect on PSD peak values.4)Driven by inertia and pressure differences,the water body oscillates variably,enhancing pressure fluctuation amplitude at the crack tip.The higher the water body's movement velocity,the greater the pressure gradient at the crack tip.The above research results may provide a reference for crack harnessing in high-speed railway tunnels.
基金Project(52372402)supported by the National Natural Science Foundation of China。
文摘The pressure comfort of passengers and crew in high-speed trains faces significant challenges under alternating open-tunnel conditions.To better understand the mechanism of pressure transmission and control interior pressure fluctuations in high-altitude regions,this study develops an interior pressure fluctuation model.By establishing the frameworks of the non-ideal gas state equation and the polytropic process equation,gas heat transfer and mass transfer were expressed through the first law of thermodynamics and the continuity equation.Simulation results,evaluated by root mean square error,coefficient of determination,peak-to-peak error,and pressure change rate,show that the proposed model closely aligns with measured signals in both overall trends and local details.Data from various train types and tunnel scenarios further demonstrate the model's accuracy and practical applicability.This study provides a critical foundation for evaluating interior pressure comfort for high-speed trains in high-altitude regions.
基金This work was financially supported by the State Key Coastal and Offshore Engineering Laboratory of Dalian University of Technology
文摘Standing waves are formed due to the reflection when waves meet vertical wall, therefore strong structures are needed to keep the wall stability under the serious wave attack. For the improvement of the working condition and increase of the stability of the wall, the lower reflecting breakwaters have attracted close attention Reports mostly from Japanese researchers are often concerned with the wall of caisson equipped with open windows. In this paper a kind of hollow-pipe perforated breakwater is examined which waves may partially perforate into the harbour basin. The wave in front of the wall can only form partial standing wave and wave force is reduced obviously. And the theoretical calculation of wave force and analysis of wave force spectrum are all derived. Comparison between the results from theoretical calculation and hydraulic modeling shows reasonable agreement.
基金financial support from the National Natural Science Foundation of China(Grant No.51479015)the Chongqing Research Program of Basic Research and Frontier Technology(Grant No.cstc2017 jcyj BX0070)+6 种基金the Chongqing Science and Technology Commission of China(Grant No.cstc2017jcyj A1642)the Technology innovation and application demonstration project in Chongqing(Grant No.cstc2018jscx-msyb0328)the Chongqing,the Chongqing Municipal Education Commission of China(Grant No.KJ1705123)the China Postdoctoral Science Foundation funded project(Grant No.2019M663890XB)Chongqing Postdoctoral Science Foundation funded project(Grant No.228512)Chongqing Municipal Education Commission Effects of Global Warming on Extreme Weather Events in Chongqing(Grant No.KJQN201800711)Chongqing Municipal Education Commission Project(Grant No.KJQN202000747)。
文摘Rocky landslides on river banks can result in the generation of ultra-high waves,which may destroy structures on the opposite bank.Existing methods to calculate the pressure on bank slopes under the effect of impulse waves generated by landslides are,however,few and of low precision.Therefore,in this study,a three-dimensional physical model test was conducted by taking into account factors such as landslide geometry parameters and the bank slope angle.The model test section was generalized on the basis of a certain section of the Three Gorges reservoir area as a prototype,after which the wave parameters and wave pressure acting on the bank slope were measured.Subsequently,the magnitude,acting point,and distribution of the pressure of the impulse waves generated by the rocky landslide upon the bank slope were determined.The distribution curve of the impact pressure was similar to that calculated using theСНиПⅡ57-75 formula,and the experimental pulsating pressure value was close to the value calculated using the Subgrade formula.Based on the test results,a power function of the relative pulsating pressure steepness with respect to the reciprocal of the wave steepness,relative water depth,and slope ratio was proposed.The acting point of the maximum pulsating pressure was found to be located near the still water level.Finally,an empirical formula for calculating the envelope of the maximum pulsating pressure distribution curve was proposed.These formulas can serve as a theoretical basis for the prediction of impulse wave pressure generated owing to landslides on bank slopes.
