Pressure-time Curve Research Articles

Research on recoil dynamic characteristics of a gatling gun automatic machine

This paper takes an aerogun automatic machine as the research object, and uses the classical internal ballistic theory to establish a mathematical model for calculating the bore resultant force. The fourth-order Runge-Kutta solution is used to calculate the average pressure-time curve in the internal ballistic and after-effect period. The automatic machine virtual prototype model is established by using the 3D model of the automatic machine and the calculation result of the bore resultant force, and the recoil displacement, recoil velocity and recoil force of the automatic machine are obtained, which provides a theoretical basis for the subsequent research and design of the automatic machine.

Accuracy of P0.1 measurements performed by ICU ventilators: a bench study

BackgroundOcclusion pressure at 100 ms (P0.1), defined as the negative pressure measured 100 ms after the initiation of an inspiratory effort performed against a closed respiratory circuit, has been shown to be well correlated with central respiratory drive and respiratory effort. Automated P0.1 measurement is available on modern ventilators. However, the reliability of this measurement has never been studied. This bench study aimed at assessing the accuracy of P0.1 measurements automatically performed by different ICU ventilators.MethodsFive ventilators set in pressure support mode were tested using a two-chamber test lung model simulating spontaneous breathing. P0.1 automatically displayed on the ventilator screen (P0.1vent) was recorded at three levels of simulated inspiratory effort corresponding to P0.1 of 2.5, 5 and 10 cm H2O measured directly at the test lung and considered as the reference values of P0.1 (P0.1ref). The pressure drop after 100 ms was measured offline on the airway pressure–time curves recorded during the automated P0.1 measurements (P0.1aw). P0.1vent was compared to P0.1ref and to P0.1aw. To assess the potential impact of the circuit length, P0.1 were also measured with circuits of different lengths (P0.1circuit).ResultsVariations of P0.1vent correlated well with variations of P0.1ref. Overall, P0.1vent underestimated P0.1ref except for the Löwenstein® ventilator at P0.1ref 2.5 cm H2O and for the Getinge group® ventilator at P0.1ref 10 cm H2O. The agreement between P0.1vent and P0.1ref assessed with the Bland–Altman method gave a mean bias of − 1.3 cm H2O (limits of agreement: 1 and − 3.7 cm H2O). Analysis of airway pressure–time and flow–time curves showed that all the tested ventilators except the Getinge group® ventilator performed an occlusion of at least 100 ms to measure P0.1. The agreement between P0.1vent and P0.1aw assessed with the Bland–Altman method gave a mean bias of 0.5 cm H2O (limits of agreement: 2.4 and − 1.4 cm H2O). The circuit’s length impacted P0.1 measurements’ values. A longer circuit was associated with lower P0.1circuit values.ConclusionP0.1vent relative changes are well correlated to P0.1ref changes in all the tested ventilators. Accuracy of absolute values of P0.1vent varies according to the ventilator model. Overall, P0.1vent underestimates P0.1ref. The length of the circuit may partially explain P0.1vent underestimation.

New insights on supercritical CO2fracturing coal mass: a staged analysis method

AbstractAs a water‐less fracturing mining technology, supercritical CO2fracturing has attracted increasing attention in the mining industry. Based on detailed analysis of CO2phase behavior in the whole process of supercritical CO2fracturing, the whole cycle of supercritical CO2fracturing was divided into the supercritical CO2fracturing stage and the CO2phase transition–induced fracturing stage, and according to the characteristics of each fracturing stage, the fracturing mechanism of supercritical CO2was analyzed in stages, and the roles of the two stages in the life cycle of the entire supercritical CO2fracturing process were obtained. Through the laboratory test of supercritical CO2fracturing coal mass, the pressure–time curves during the whole process of supercritical CO2fluid fracturing were analyzed, and the rationality and correctness of the supercritical CO2fracturing staged analysis method proposed in this paper were verified. Based on the energy conservation theory and the state function equation of classical thermodynamics, the burst energy of the CO2phase transition–induced fracturing stage was estimated. By comparing the trinitrotoluene equivalent of phase‐transition energy with the trinitrotoluene amount of explosive explosion, it was proved that the CO2phase transition–induced fracturing stage was not negligible. The research results of this paper are of considerable significance for the full understanding of the supercritical CO2fracturing mechanism. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Investigating Different Grounds Effects on Shock Wave Propagation Resulting from Near-Ground Explosion

A massive explosion of a liquid-propellant rocket in the course of an accident can lead to a truly catastrophic event, which would threaten the safety of personnel and facilities around the launch site. In order to study the propagation of near-ground shock wave and quantify the enhancement effect on the overpressure, models with different grounds have been established based on an explicit nonlinear dynamic ANSYS/LS-DYNA 970 program. Results show that the existence of the ground will change the propagation law and conform to the reflection law of the shock wave. Rigid ground absorbs no energy and reflects all of it, while concrete ground absorbs and reflects some of the energy, respectively. Ground may influence the pressure-time curve of the shock wave. When the gauge is close to the explosive, the pressure-time curve presents a bimodal feature, while when the gauge reaches a certain distance to the explosive, it presents a single-peak feature. For gauges at different heights, different grounds may have different effects on the peak overpressure. For gauges of height not greater than 4 m, the impact on the shock wave is obvious when the radial to the explosive is small. On the contrary, as for the gauges of height greater than 4 m, the impact on the shock wave is obvious when the radial to the explosive is big. Ground has the enhancement effect on peak overpressure, but different grounds have different ways. For rigid ground, the peak overpressure factor is about 2. However, for the concrete and soil ground, peak overpressure factor is from 1.43 to 2.1.

Physical Vein Models to Quantify the Flow Performance of Sclerosing Foams

Foam sclerotherapy is clinically employed to treat varicose veins. It involves intravenous injection of foamed surfactant agents causing endothelial wall damage and vessel shrinkage, leading to subsequent neovascularization. Foam production methods used clinically include manual techniques, such as the Double Syringe System (DSS) and Tessari (TSS) methods. Pre-clinical in-vitro studies are conducted to characterize the performance of sclerosing agents; however, the experimental models used often do not replicate physiologically relevant physical and biological conditions. In this study, physical vein models (PVMs) were developed and employed for the first time to characterize the flow behavior of sclerosing foams. PVMs were fabricated in polydimethylsiloxane (PDMS) by replica molding, and were designed to mimic qualitative geometrical characteristics of veins. Foam behavior was investigated as a function of different physical variables, namely (i) geometry of the vein model (i.e., physiological vs. varicose vein), (ii) foam production technique, and (iii) flow rate of a blood surrogate. The experimental set-up consisted of a PVM positioned on an inclined platform, a syringe pump to control the flow rate of a blood substitute, and a pressure transducer. The static pressure of the blood surrogate at the PVM inlet was measured upon foam administration. The recorded pressure-time curves were analyzed to quantify metrics of foam behavior, with a particular focus on foam expansion and degradation dynamics. Results showed that DSS and TSS foams had similar expansion rate in the physiological PVM, whilst DSS foam had lower expansion rate in the varicose PVM compared to TSS foam. The degradation rate of DSS foam was lower than TSS foam, in both model architectures. Moreover, the background flow rate had a significant effect on foam behavior, enhancing foam displacement rate in both types of PVM.

The influence of pipe length on explosion of flammable premixed gas in 90° bending pipe and dynamic response of the thin-walled pipe

An experimental platform of gas cloud deflagration is built in this study, and the propane–air premixed gas blasting experiment was carried out in curved pipes with different lengths. The effect of pipe length on combustible gas explosion and the influence of explosion shock wave on thin-walled pipe loading were also studied. The experimental device included photoelectric, pressure, and strain sensors which were used to evaluate the explosion parameters and stress of the thin-walled pipe. The result was that the longer the pipeline, the higher the wall overpressure and the bigger the maximum tube wall. The pressure time curve was consistent with the thin-walled strain time–history curve. The pipe bend accelerates the flame propagation to a certain extent, and the pipe length influenced the law of flame ignition and explosion in pipe integrally; the longer the pipe, the greater the pressure and the speed of the flame. The maximum explosion pressure appears at the end of the pipe, and the loading of the shock wave on pipe wall belongs to dynamic response.

Explosion Characteristics of Propanol Isomer–Air Mixtures

This paper describes a series of experiments performed to study the explosion characteristics of propanol isomer (1-propanol and 2-propanol)–air binary mixtures. The experiments were conducted in two different experimental arrangements—a 0.02 m3 oil-heated spherical vessel and a 1.00 m3 electro-heated spherical vessel—for different equivalence ratios between 0.3 and 1.7, and initial temperatures of 50, 100, and 150 °C. More than 150 pressure–time curves were recorded. The effects of temperature and test vessel volume on various explosion characteristics, such as the maximum explosion pressure, maximum rate of pressure rise, deflagration index, and the lower and upper explosion limits were investigated and the results were further compared with the results available in literature for other alcohols, namely methanol, ethanol, 1-butanol, and 1-pentanol. The most important results from evaluated experiments are the values of deflagration index 89–98 bar·m/s for 2-propanol and 105–108 bar·m/s for 1-propanol/2-propanol–air mixtures. These values are used to describe the effect of isomer blends on a deflagration process and to rate the effects of an explosion.

Pharmacokinetic, Cardiovascular and Locomotor Effects of alpha‐Pyrrolidinopentiophenone (alpha‐PVP) in Male Sprague Dawley Rats after Active Vaccination

Alpha‐pyrrolidinopentiophenone (alpha‐PVP) is a psychoactive synthetic cathinone that elicits pharmacological effects similar to methamphetamine and cocaine and at high doses can produce psychosis, cardiovascular toxicity, and death. The goal for these studies was to characterize the pharmacokinetics (PK) of alpha‐PVP and test an active vaccine for treating alpha‐PVP‐induced effects. The hapten‐protein conjugate vaccine was developed from an alpha‐PVP/MDPV‐like hapten structure capable of generating high affinity antibodies that significantly cross react with both alpha‐PVP and 3,4‐methylenedioxypyrovalerone (MDPV). Previous studies showed the bi‐specific vaccine could significantly reduce locomotor effects of MDPV. For the current studies, we hypothesized that treatment with this vaccine could stimulate production of high affinity antibodies against alpha‐PVP capable of altering the PK disposition and attenuating the cardiovascular and locomotor effects of alpha‐PVP. The hapten was conjugated to immunocyanin monomers of keyhole limpet hemocyanin, mixed with Sigma Adjuvant System, and used to immunize male Sprague Dawley rats (n=6/group) at 0, 3, and 9 weeks. Pharmacological testing occurred between 12–26 weeks from the start of immunizations. For the PK studies, three doses of alpha‐PVP (0.56, 1, and 3 mg/kg) were administered subcutaneously (sc) to control and vaccinated rats (n=6/group/dose); and tail vein blood samples were collected over time. PK values of alpha‐PVP showed linear PK with a half‐life of 1.7 h in controls and a significant (p<0.05) treatment‐dependent difference in the area under the alpha‐PVP concentration time curve between control and vaccinated rats. In a separate group of rats (n=5–6/group), cardiovascular parameters recorded by radiotelemetry showed a significantly lower area under the heart rate and blood pressure time curves after 0.56, 1 and 3 mg/kg alpha‐PVP in vaccinated rats compared to controls. Finally, locomotor studies of control and vaccinated rats (n=6/group) were conducted using a series of increasing doses of alpha‐PVP (0.3–5.6 mg/kg, sc, 2 days apart). The immunized rats displayed significantly lower alpha‐PVP‐induced locomotor activity and a significantly shorter duration of action compared to controls. In conclusion, alpha‐PVP has linear PK in control rats, and active vaccination with a bi‐specific conjugate vaccine significantly increased the binding of alpha‐PVP in the serum and reduced alpha‐PVP‐induced cardiovascular and locomotor effects compared to controls.Support or Funding InformationFunded by NIDA grants DA039195 and F31 DA046121, and T32 GM106999This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Staged numerical simulations of supercritical CO2 fracturing of coal seams based on the extended finite element method

As a water-less fracturing mining technology, supercritical CO2 (SC-CO2) fracturing has attracted increasing attention in the mining industry. In order to simulate the whole process of SC-CO2 fracturing and fully understand the fracturing mechanism of SC-CO2, the thermodynamic analysis method was used to analyze the phase transitions of CO2 in SC-CO2 fracturing, and the whole process of SC-CO2 fracturing was divided into the SC-CO2 fracturing stage and the CO2 phase-transition induced fracturing stage. Based on the extended finite element method, the fluid-solid coupling model at the SC-CO2 fracturing stage, the TNT equivalence of CO2 phase transition induced fracturing, pressure-time history curves of blast loads, and numerical model of CO2 phase transition induced fracturing stage were comprehensively analyzed, and the staged numerical simulation method of SC-CO2 fracturing was proposed. The simulation results showed that cracks in the coal seam were initiated and propagated at the SC-CO2 fracture stage, and the cracks broadened, and new cracks were generated during the CO2 phase-transition induced fracturing stage. At the same time, the injection rate of SC-CO2 fluid had a positive impact on its fracturing effect. The larger the injection rate of SC-CO2 fluid, the larger the length and width of crack propagation. This study is of great significance for enriching SC-CO2 fracturing theory.

Calculation of permeability coefficient of coal seam under rapid measurement conditions

In order to achieve rapid determination of coal seam permeability, the calculation method of coal seam permeability coefficient was studied. Based on the Darcy's law in the flow of gas in the coal seam, the relationship equation between the gas pressure of the borehole and the gas permeability coefficient of the coal seam is established under the radial unsteady flow state. The gas permeability coefficient of the coal seam is obtained by coordinate transformation and integral transformation. Solve the expression. The analysis and verification of the field measured data show that the expression of the analytical solution of the coal seam permeability coefficient is consistent with the variation of the borehole pressure-time curve, which can provide a theoretical basis for the rapid determination of coal seam permeability.

Approach to the Patient with Acute Respiratory Failure

Acute respiratory failure (ARF) is a common reason for admission to the intensive care unit (ICU), and is associated with significant morbidity and mortality. Failure of one or more components of the respiratory system can lead to hypoxemia, hypercabia, or both. Initial evaluation of patients with ARF should include physical examination, chest imaging, and arterial blood gases (ABG) sampling. As ARF is often a life-threatening emergency, a patient’s oxygenation and ventilation will need to be supported at the same time that diagnostic and therapeutic interventions are planned. The priorities for early treatment are essentially those of basic life support: airway and breathing. The first step is to assess a patient’s airway and ascertain that it is patent. This is followed by efforts to support both oxygenation and ventilation. This can include non-invasive or invasive mechanical ventilatory support. As with all interventions, there are risks inherent in the use of mechanical ventilation, which may be minimized by the use of lung protective ventilation (i.e., with low tidal volumes and airway pressures). Finally, due to the potential complications associated with mechanical ventilation, it is important to regularly assess whether a patient continues to require the assistance of the ventilator, and to liberate patients from mechanical ventilation at the earliest opportunity when clinically safe and feasible to do so. Figures depict pressure-time curve. Tables list the clinical causes of hypoxemic respiratory failure, oxygen delivery devices, indications for noninvasive positive pressure support, common causes of abnormal respiratory mechanics, and common causes of acute respiratory distress syndrome (ARDS). This review contains 2 highly rendered figures, 5 tables, and 86 references.

Stress Index Can Be Accurately and Reliably Assessed by Visually Inspecting Ventilator Waveforms.

Stress index provides a noninvasive approach to detect injurious ventilation patterns and to personalize ventilator settings. Obtaining the stress index (SI), however, requires quantitatively analyzing the shape of pressure-time curve with dedicated instruments or a specific ventilator, which may encumber its clinical implementation. We hypothesized that the SI could be qualitatively determined through a visual inspection of ventilator waveforms. Thirty-six adult subjects undergoing volume controlled ventilation without spontaneous breathing were enrolled. For each subject, 2 trained clinicians visually inspected the pressure-time curve directly from the ventilator screen. They then qualitatively categorized the shape of pressure-time curve as linear, a downward concavity, or an upward concavity at the bedside. We simultaneously recorded airway pressure and flow signals using a dedicated instrument. A quantitative off-line analysis was performed to calculate the SI using specific research software. This quantitative analysis of the SI served as the reference method for classifying the shape of the pressure-time curve (ie, linear, a downward concavity, or an upward concavity). We compared the SI categorized by visual inspection with that by the reference. We obtained 200 SI assessments of pressure-time curves, among which 125 (63%) were linear, 55 (27%) were a downward concavity, and 20 (10%) were an upward concavity as determined by the reference method. The overall accuracy of visual inspection and weighted kappa statistic (95% CI) was 93% (88-96%) and 0.88 (0.82-0.94), respectively. The sensitivity and specificity to distinguish a downward concavity from a linear shape were 91% and 98%, respectively. The respective sensitivity and specificity to distinguish an upward concavity from a linear shape were 95% and 95%. Visual inspection of the pressure-time curve on the ventilator screen is a simple and reliable approach to assess SI at the bedside. This simplification may facilitate the implementation of SI in clinical practice to personalize mechanical ventilation. (ClinicalTrials.gov registration NCT03096106.).

A pore structure based real gas transport model to determine gas permeability in nanoporous shale

Gas flows in the forms of multiple transport mechanisms in shale nanoporous media with complex pore structure and different pore types. Laboratory pressure pulse decay technique is often applied to measure gas permeability but the current gas permeability interpretation model is mostly based on the homogeneous macro scale model while the influence of pore structure on real gas transport is neglected. In this study, a novel pore structure based real gas transport model is proposed to determine gas permeability in nanoporous shale combining laboratory pressure pulse decay technique with pore network simulation. The laboratory pressure pulse decay process is simulated in a virtual system based on the similarity principle which contains upstream vessel, downstream vessel, and core sample. The core sample is constructed by a series of connected pore networks and the sizes of pores and throats in each location of the pore network are randomly assigned according to laboratory measured pore size distribution. Gas transport mechanisms inside the core sample consider viscous flow, Knudsen diffusion, surface diffusion and real gas effect. At each time step, the upstream vessel pressure decreases and the downstream vessel pressure increases until the upstream vessel pressure and downstream vessel pressure become equal. The simulated pressure drop versus time curve is obtained and is applied to fit the laboratory measured pressure drop data by repeating core sample construction and pressure pulse decay process. The proposed model is applied to measure gas permeability of Sichuan basin, Longmaxi formation shale core sample. The results indicate that the predicted value based on the proposed model matches well with the experimental measured pressure drop data. The proposed model is used to study the influences of test gas type and pore size on gas permeability. When the average organic pore radius is less than 20 nm, helium tested permeability overestimates at least 40% of the methane permeability.

Performance and applications of bedside visual inspection of airway pressure-time curve profiles for estimating stress index in patients with acute respiratory distress syndrome.

To determine the performance of bedside visual inspection of airway pressure-time (Paw-t) curve profiles(VI) for estimating stress index (SI) in patients with acute respiratory distress syndrome (ARDS). A prospective study in 30 subjects with ARDS receiving mechanical ventilation at two peak inspiratory flow (PIF) settings: 60 or 40L/min. For each study session, two physicians inspected real-time Paw-t waveforms from mechanical ventilator's monitoring screens at bedside for 30s and interpreted which of the three patterns (tidal recruitment, noninjurious ventilation or tidal overdistension) the Paw-t curve profile was compatible with. Subsequently, the study was repeated again at the second PIF setting. SI was derived from a standardized dedicated software program and categorized into three groups: SI < 0.9, or tidal recruitment; SI = 0.9-1.05, or noninjurious ventilation; and SI > 1.05, or tidal overdistension. The lower PIF setting increased the sensitivity of VI to correctly estimate SI (75% vs. 50%; p = 0.005). At PIF 40L/min, the likelihood ratio of a positive test was 3.6, 5.4 or 7 if the Paw-t curve profile was interpreted as noninjurious ventilation, tidal recruitment or tidal overdistension, respectively. The likelihood ratio of a negative test ranged from 0.55 for tidal recruitment to 0.32 and 0.19 for noninjurious ventilation and tidal overdistension, respectively. Experience in mechanical ventilation did not influence the accuracy. Bedside VI is moderately accurate for estimating SI and may be used to monitor injurious ventilation in patients with ARDS, in addition to plateau airway pressure.

Experiments and analysis on the influence of perforation mode on hydraulic fracture geometry in shale formation

Hydraulic fracture (HF) geometry is significant when evaluating simulated reservoir volume for shale gas reservoirs. The HF geometry is affected mainly by geological and engineering factors. The physical simulation experiment of hydraulic fracturing is an effective way to obtain the geometry and propagation criterion of HFs in a shale formation. However, the HF geometries created by the different perforation modes are not been well understood. To clarify this mechanism, several groups of true tri-axial hydraulic fracturing experiments were conducted on Longmaxi shale specimens to investigate the influence of perforation modes on the HF geometry. Results show that the HF geometry displays five basic patterns when intersecting with structural planes (SPs), namely, penetration/non-dilation, penetration/dilation, branching, derivation, and deflection. The diversities of HF geometries are the precondition for the formation of complex fractures. The HF geometries induced from oriented, helical, planar and combinatorial perforations show great differences, in which the combinatorial perforation fracturing has a certain promoting effect on the formation of complex fractures. The fluctuation degree of the pressure-time curve and the complexity of fractures show a positive correlation. Similar to previous studies, the HFs show a tendency for propagation beyond the natural fractures when there are higher stress differences. Higher cementing strength and roughness of SPs with weak points is favorable for forming the complex fracture network. The results provide some theoretical support and experimental basis for the optimization of fracturing parameters in the field.

Numerical analysis of tunnel in rock with basalt fiber reinforced concrete lining subjected to internal blast load

The present study focuses on the performance of basalt fiber reinforced concrete (BFRC) lining in tunnel situated in sandstone rock when subjected to internal blast loading. The blast analysis of the lined tunnel is carried out using the threedimensional (3-D) nonlinear finite element (FE) method. The stress-strain response of the sandstone rock is simulated using a crushable plasticity model which can simulate the brittle behavior of rock and that of BFRC lining is analyzed using a damaged plasticity model for concrete capturing damage response. The strain rate dependent material properties of BFRC are collected from the literature and that of rock are taken from the authors\' previous work using split Hopkinson pressure bar (SHPB). The constitutive model performance is validated through the FE simulation of SHPB test and the comparison of simulation results with the experimental data. Further, blast loading in the tunnel is simulated for 10 kg and 50 kg Trinitrotoluene (TNT) charge weights using the equivalent pressure-time curves obtained through hydrocode simulations. The analysis results are studied for the stress and displacement response of rock and tunnel lining. Blast performance of BFRC lining is compared with that of plain concrete (PC) and steel fiber reinforced concrete (SFRC) lining materials. It is observed that the BFRC lining exhibits almost 65% lesser displacement as compared to PC and 30% lesser displacement as compared to SFRC tunnel linings.

HYBRID OPTIMIZATION OF STAR GRAIN PERFORMANCE PREDICTION TOOL

ABSTRACTIn solid propellant rocket propulsion, the design of the propellant grain is a decisiveaspect. The grain design governs the entire motor performance and, hence, thewhole rocket mission. The ability to decide, during design phase, the proper graindesign that satisfies the predefined rocket mission with minimum losses is theultimate goal of solid propulsion experts. This study enables to predict the pressuretime curve of rocket motor with star grain configuration and also to optimize theperformance prediction tool through optimization methods to maximize its predictionefficiency. A hybrid optimization technique is used. Genetic Algorithm (GA) is firstimplemented to find the global optimum followed by Simulated Annealing (SA)optimization method to find the accurate local optimum. A program for predicting thepressure time curve of the rocket motor is created on MATLAB and then linked to GA- SA optimizers as an application on a case study. The purposed approach isvalidated against satisfying data. It is found that the developed optimized program iscapable of predicting rocket motor performance (including the effect of erosiveburning) with acceptable accuracy for preliminary design purposes.

Experimental study of gasoline vapor deflagration in a duct with an open end

An experimental investigation was conducted on gasoline vapor deflagration in a duct (100 × 100 mm, L/D = 4, 6, 10) with the ignition end closed and the other end open. The tests were focused on the flame behavior and the pressure generation inside and outside the duct. High-speed flame images, schlieren images, and the instantaneous pressure at different test points were recorded. The experimental results verified Bychkov's model [Combust. Flame 150 (2007) 263] in predicting the flame propagation at the early stages. Moreover, a new model was proposed to predict the axial flame moving distance when the flame front moved out of the tube. This model predicts the experimental data precisely when L/D = 4–10, and the deviation increases with larger L/D ratio. Effusive gas mixture gave rise to a vortex ring at the edge of the opening and leads to the formation of a mushroom-shaped gas cloud. A distortion of the flame skirt was observed several milliseconds after the flame ejection at about 10–40 mm away from the opening. The entire external flame was enveloped by the flammable gas cloud. Three peak pressures were obtained for each test point inside the vessel. The first peak was observed when the flame shirt touched the side walls. The second peak appeared when the flame front reached the opening. The third peak pressure was a result of the external explosion. For external test points, the pressure-time curves reached their peaks when the combustion reactions ended, and then dropped below zero due to the dissipation of energy and the low density of the burned gas.

Monitoring hydraulically-induced fractures in the laboratory using acoustic emissions and the fluorescent method

We investigated the relation between seismic events and fractures induced by hydraulic fracturing in laboratory experiments under uniaxial loading conditions using granite and shale blocks by monitoring acoustic emissions (AEs). We used a thermosetting acrylic resin mixed with a fluorescent compound as the fracturing fluid and fixed it within the blocks by heating immediately after fracturing. This allowed observation of fluid penetration regions and fracturing patterns on cross-sectional planes under ultraviolet light irradiation. The obtained AE hypocenters and resin penetration regions observed after the fracturing extended on both wings along the loading axis from the fracturing hole for all the samples. This was as expected theoretically, although the AEs were concentrated primarily on only one side for some samples. Patterns of wellbore pressurization histories, AE activities, and resin penetration regions were significantly different between the two rock types. In the experiments using granite samples, wellbore pressure increased linearly until 87.2–97.4% of the peak pressure, followed by a gradual decrease of the rate and sudden drop of pressure (breakdown). AEs started to occur at 49.6–93.2% of the peak pressure, significantly before the breakdown. Resin penetration regions have a width of 10–30 mm and such wide penetration regions resulted in indistinguishable main fractures. For the shale samples, both the nonlinearity of the wellbore pressure–time curve and the AE activity were initiated immediately before breakdown. The number of detected AEs was much smaller than for the granites. Resin in the rock samples showed thin traces with widths of < 1 mm, corresponding to the main fracture. Such dissimilarities between the two rock types likely resulted from differences in their permeability, grain size, and/or mineralogy. We also found aseismic regions that lacked AEs despite evidence of fluid penetration. Although such regions were affected by the fracturing operations, they cannot be revealed by the microseismic observations used in shale gas/oil fields and enhanced geothermal systems.

Preliminary analysis of underwater detonation performance of titanium fiber explosive

In this study we examined the changing tendency of the shock wave energy, bubble energy, total energy per unit mass and the total energy per unit volume by analysis of the pressure-time curves, and analyzed the chemical reaction process of the Ti fiber explosive through the total energy per unit mass. The results show that the peak pressure and the shock wave energy of the Ti fiber explosive per unit decreases as the Ti fiber content increases, the bubble energy per unit mass increases with the increase of the Ti fiber content, the total energy per unit mass and its energy density increase with the increase of the Ti fiber content. With the increase of the distance between the sensor and explosive, the rate of the Ti fiber explosive's peak pressure decay is slower than that of RDX, while the tendency of the shock wave energy and the bubble energy per unit mass with different contents of the Ti fiber explosive is basically in keeping with the increase of the distance. The chemical reaction process of the Ti fiber explosive was also obtained through the total energy per unit mass.