Pressure Time Histories Research Articles

Hemodynamic alternations following stent deployment and post-dilation in a heavily calcified coronary artery: In silico and ex-vivo approaches

In this work, hemodynamic alterations in a patient-specific, heavily calcified coronary artery following stent deployment and post-dilations are quantified using in silico and ex-vivo approaches. Three-dimensional artery models were reconstructed from OCT images. Stent deployment and post-dilation with various inflation pressures were performed through both the finite element method (FEM) and ex vivo experiments. Results from FEM agreed very well with the ex-vivo measurements, interms of lumen areas, stent underexpansion, and strut malapposition. In addition, computational fluid dynamics (CFD) simulations were performed to delineate the hemodynamic alterations after stent deployment and post-dilations. A pressure time history at the inlet and a lumped parameter model (LPM) at the outlet were adopted to mimic the aortic pressure and the distal arterial tree, respectively. The pressure drop across the lesion, pertaining to the clinical measure of instantaneous wave-free flow ratio (iFR), was investigated. Results have shown that post-dilations are necessary for the lumen gain as well as the hemodynamic restoration towards hemostasis. Malapposed struts induced much higher shear rate, flow disturbances and lower time-averaged wall shear stress (TAWSS) around struts. Post-dilations mitigated the strut malapposition, and thus the shear rate. Moreover, stenting induced larger area of low TAWSS (<0.4 Pa) and lager volume of high shear rate (>2000 s−1), indicating higher risks of in-stent restenosis (ISR) and stent thrombosis (ST), respectively. Oscillatory shear index (OSI) and relative residence time (RRT) indicated the wall regions more prone to ISR are located near the malapposed stent struts.

통합보존식 해석과 HCIB 법을 이용한 슬로싱 탱크 내부 갇힌 공기에 의한 압력 진동 모사

The code developed using a pressure-based method for unified conservation laws of incompressible/compressible fluids is expanded to handle moving or deforming body boundaries using the hybrid Cartesian/immersed boundary method. An instantaneous pressure field is calculated from a pressure Poisson equation for the whole fluid domain, including the compressible gas region. The polytropic gas is assumed for the compressible fluid so that the energy equation is decoupled. Immersed boundary nodes are identified based on edges crossing body boundaries. The velocity vector is reconstructed at the immersed boundary node using an interpolation along the assigned local normal line. The developed code is validated by comparing the time histories of pressure and wave elevation for sloshing in a rectangular and a membrane-type tank. The validated code is applied to simulate air cushion effects in a rectangular tank under sway motion. Time variations of pressure fields are analyzed in detail as the air pocket pulsates. It is shown that the contraction and expansion of the air pocket dominate the pressure loads on the wall of the tank. The present results are in good agreement with other experimental and computational results for the amplitude and the decay of the pressure oscillations measured at the pressure gauges.

The research into the propagation law of the shock wave of a gas explosion inside a building

Based on the dissipation rate conservation equations of turbulent kinetic energy in the k-ε turbulence model, a complicated three-dimensional finite element model of a kitchen filled with gas mixture is developed by using the open source field operation and manipulation (OpenFOAM). Two representative kitchens were used to investigate the propagation law of the shock wave of a gas explosion inside a building by considering the key characteristics of the blast shock wave. The influence of some crucial parameters, such as initial conditions and kitchen parameters, on the properties of the blast shock wave is investigated. The basic steps to predict the peak pressure of the blast shock wave are given in consideration of the initial condition and the kitchen whilst the injury effect of the blast shock wave on the humans and animals is evaluated. The research results indicate that the pressure time history and the peak pressure space distribution are greatly influenced by the kitchen design layout. The coupled interaction between the initial temperature and gas volume concentration, especially at the upper and lower explosion limits of the gas, significantly affects the peak pressure. The peak pressure varies significantly with the opening and the buffer; however, it has little relation with the width, length, and height of the kitchen. The proposed method can accurately and effectively predict the peak pressure of the blast shock wave inside buildings. In terms of the peak pressure space distribution of the explosion shock wave, the peak pressure is much higher than the threshold of the killing pressure, which is unsafe for the humans and animals in the building.

Research on bubble jet of underwater explosion at the bottom of fixed square plate

<p indent=0mm>The water jet formed after the collapse of the bubble in the near-field underwater explosion can cause serious damage to the local structure of the ship, and the formation of the jet is asymmetric, which makes it difficult to measure its data in the experiment. At present, studies on the pressure time history curves of the bubble jet in the underwater explosion are still relatively rare. In order to study the characteristics of the jet, the underwater explosion test of <sc>2.5 g</sc> TNT explosive at the bottom of fixed square plate at different detonation distances was carried out. First, the accuracy of the test data was verified by the underwater pressure sensor. Second, the image of the whole process from the explosive initiation to the bubble jet generated by the action of the bubble and the steel plate was obtained by high-speed camera. Finally, the time-history curve of water jet pressure was measured by the wall pressure sensor in the center of the steel plate, and another group of wall pressure sensors was set <sc>15 cm</sc> away from the center of the steel plate as a control group to ensure that the measured jet data were not clutter. The test data recorded by the underwater sensor show that the error between the shock wave overpressure, the maximum bubble radius of the bubble pulse period and the empirical formula is within 10%. The results recorded by the high-speed camera and wall pressure sensor show that three jets can be observed when the burst distance is <sc>28 cm,</sc> but the pressure time history curve is not measured due to the long burst distance. When the burst distances are <sc>15,</sc><sc> 17.5</sc> and <sc>20 cm,</sc> three jet pressure time history curves are measured. However, due to the short burst distance and the presence of a large number of bubbles between the steel plate and the water surface under the action of the shock wave, it is difficult to observe the test phenomenon with high-speed cameras. The pressure time history curve shows that three jets are generated after the first bubble pulse peak, and the jet pressure can reach 1/4 of the shock wave. The jet appears 1–3 ms after the first bubble pulse peak, and the time interval of each jet is between <sc>0.9</sc> and <sc>2.4 ms.</sc> The duration of jet load is between 4–27 μs, and it is greatly reduced as the distance increases.

Experiments on duct-vented explosion of hydrogen–methane–air mixtures: Effects of equivalence ratio

In this study, experiments on the duct-vented deflagrations of hydrogen–methane–air mixtures were performed in a cylindrical vessel connected with a relief duct, at an initial pressure of 101 kPa and an initial temperature of 290 K, to investigate the effects of equivalence ratio (ϕ), in the range of 0.6–1.8, on flame evolution and pressure buildup within and outside the venting configuration. Experimental results reveal that secondary explosion in the relief duct occurred and a pressure peak with amplitude higher than the overpressure in the vented chamber formed, which resulted in the gases in the relief duct flowing reversely to the vented chamber (reverse flow). The secondary explosion in the relief duct reduced the venting efficiency in the vented chamber and created a pressure peak there, which dominated the pressure–time histories in the vented cylindrical vessel for ϕ ranging from 0.8 to 1.4. Acoustic oscillations of the overpressure in the cylindrical vessel could be easily distinguished forϕ ≤ 1.0, and the pressure peak owing to acoustic enhanced combustion was dominant atϕ = 0.6. The maximum overpressure in the cylindrical vessel first increased and thereafter decreased as ϕ was increased from 0.6 to 1.5 and was independent of ϕ for richer mixtures. A shock wave was visualized in the tests with ϕ in a range of 1.0–1.2 when the combustible cloud outside the venting configuration was ignited, which resulted in a pressure spike in the external pressure–time histories. The maximum overpressure outside the relief duct first increased and thereafter decreased as ϕ was increased.

Further Analysis of Non-Gaussian Wind Pressure Peak Factor Calculation

The wind pressure time history of high-rise building cladding is mostly non-Gaussian distribution, and there is a one-to-one correspondence between a specified guarantee rate and its corresponding peak factor. A stepwise search method for calculating the peak factor of non-Gaussian wind pressure and a gradual independent segmentation method for extracting independent peak values have been proposed to determine the relationship accurately in the previous study. Based on the given experiment and calculation results in the existing research results, more analysis can be given to enrich the study on this topic. In this paper, some characteristics of wind pressure coefficient time series in time and frequency domain are analysed. Based on the basic theory of fractal, the R/S analysis of wind pressure time series is made, and the fractal characteristics of wind pressure coefficient time series are explained. Based on the statistical theory, the relationship characteristics between high-order statistics and peak factors are studied. The correlation between the guarantee rate and the corresponding peak factor is analysed, and the guarantee rates calculated by the Davenport peak factor method are evaluated. The power spectrum characteristics of fluctuating wind pressure are analysed and the relationship between turbulence characteristic frequency and optimal observation time interval is discussed.

An Experimental Study on the Force Coefficient and the Discharge Coefficient of a Safety Valve in Air-water Mixture Flow

Due to the low number of experimental investigations on the sizing of safety valves in multiphase flow, a novel set of measurement data of an air-water mixture is reported. This paper presents an experimental study on three different geometries of safety valves, a poppet valve with jet angle θ = 120°, and two-disc valves with deflection angles θ = 0° and θ = 90°, respectively. Our test rig comprises a pipeline with 42.5 mm inner diameter, spray nozzles to supply the added water quality (water mass fraction) to the pressurized airflow up to 40 % mass fraction and an inlet pressure up to 6.6 bar(g). The time histories of force, valve lift, and pressures were recorded. We present correlation data for the force coefficient and the discharge coefficient. The widely used omega technique for the Homogenous Equilibrium Model (HEM) is employed to predict the theoretical mass flux. The results show that the poppet valve experiences less momentum force and lower mass flow rates compared to disc valves, while the disc valve with deflection angle θ = 90° presents the highest discharged flow rates among the tested geometries. Our most important finding is that up to 60 % relative valve lift and 40 % mass fraction, neither the force nor the discharge coefficient changes significantly compared to the pure-air case. Finally, we propose a new correlation with a single equation for the resultant force and the discharge coefficient as a function of the relative valve lift for all tested water mass fractions.

The effect of fire location and the reverse stack on fire smoke transport in high-rise buildings

In this paper, smoke transport in high-rise buildings through elevator shafts and stairwells is investigated for various fire location and stack effect conditions. For this purpose, a transient network model, Fire-STORM, is upgraded and used. The results are benchmarked by using a computational fluid dynamics (CFD) model. Six scenarios are tested, which are 1st floor, mid-floor, and top-most floor fires under normal stack (cold environment) and reverse stack (hot environment) conditions. For each scenario, the time history of pressures, temperatures, and soot mass fractions in the fire floors, elevator shafts, and stairwells and the average soot mass fraction in all stories of the building are presented. Overall, Fire-STORM has reasonably good accuracy compared to CFD with significantly faster computation times (90 s on a single core vs. 4 days on 32 cores in parallel). One of the intended uses of this fast low-order model is a data generation engine for neural network modeling of high-rise building fires. As such, one of the unique features of this work is the development of a realistic random heat release rate (HRR) modeling approach created using a Gaussian process.

An injected quantity estimation technique based on time–frequency analysis

An innovative injected quantity estimation method, based on time–frequency​ analysis, has been developed for passenger car Common-Rail (CR) injection systems. This method involves capturing the pressure time history from a transducer installed along the rail-to-injector pipe, and its overall accuracy has been found to be within 1.5 mg. The dependence of the injected mass on the fuel temperature has been investigated, and the correlation of the injected mass with the nominal rail pressure and the energizing time has been evaluated for different thermal regimes. It has been verified that if the duration of the hydraulic injection is considered instead of the energizing time, the influence of the temperature on the injected mass is implicitly taken into account. Thus, the corresponding correlations between the injected mass and the duration of the hydraulic injection have been obtained for different nominal rail pressures. The duration of the hydraulic injection has been measured through an effective time–frequency analysis technique, which has been used to realize a virtual sensor of the needle lift. The experimental campaign has been performed over a wide range of working conditions for single injections, and the accuracy of the innovative prediction methodology, which can be exploited to design a closed-loop control of the injected mass, has been assessed.

Experimental study on the vapor-liquid two-phase explosion of n-heptane under high-temperature source ignition

The combustion and explosion characteristics of vapor-liquid two-phase (aerosol) under high-temperature sources ignition are an essential subject in fuel utilization and prevention of chain explosion accidents. In this study, a series of experiments were carried out in a 20 L vessel to observe instantaneous concentration and droplet size distribution of n-heptane aerosol and analyze the energy characteristics of n-heptane aerosol explosion under high-temperature source ignition. Tests were conducted for n-hexane/air mixtures of mass concentrations from 50.19 g/m3 to 317.87 g/m3, the ignition temperature of 1373.15 K, and the initial temperature and pressure of 22 ℃ and 0.10 MPa, respectively. The influence of the instantaneous concentration and droplet size of n-heptane aerosol on the explosive characteristics under high-temperature source ignition was examined. The results show that the explosion pressure-time history of the n-heptane aerosol at the high-temperature ignition was found to have a “double peak” structure produced in the first and second explosion respectively. The second peak of the pressure in an explosion time history of the n-heptane aerosol ignited at the high-temperature source is 2–5 times the first. The liquid n-heptane was driven by pressure to form aerosol in the vessel. The aerosol flows from the nozzle on the vessel wall to the center of the vessel (high-temperature source). The first explosion formed when the mist contacts a high-temperature source will generate outward radiation pressure waves, which are opposite to the initial converging flow direction of the aerosol, forming a reverse flow, and then causing a transient negative pressure. When the high-temperature product of the first explosion swells and meets the droplets of unburned n-heptane, a second explosion occurs, forming the second explosion peak. Compared with premixed aerosol explosion under electric spark ignition, the explosion process under high-temperature source ignition is more complicated. The explosion is coupled with the flow, and the explosion energy output is significantly increased. The latter is about 1.6 times the former. At the moment when the first explosion was initiated by the high-temperature source, the concentration of 301.14 g/m3 at which the first explosion pressure reached maximum was greater than the stoichiometric concentration of 83.65 g/m3 due to energy consumption caused by heat absorption of the droplets.

Shaking-Induced Sublayer Vertical Strains of Saturated Sands Estimated from Partially Drained Dynamic Centrifuge Tests

Earthquake-induced free-field settlement of coarse-grained soils has historically been assessed using laboratory element tests under drained or undrained conditions. However, in saturated sands, dynamic centrifuge and 1g shaking table tests illustrate that excess porewater pressure generation/dissipation and settlement occur simultaneously during shaking under partially drained conditions. The average vertical strains computed from measured surface settlements in these tests neglect (1) the impact of effective stress on compressibility and (2) settlements that occur in denser and potentially nonliquefiable sands present in the centrifuge models. Here, the authors employ a simple procedure that uses measured porewater pressure and surface settlement time histories from partially drained centrifuge and 1g shaking table tests to properly distribute vertical strain throughout the coarse-grained soil profiles, thereby incorporating variations of effective stress and relative density on vertical strain. The vertical strains are resolved into a shaking-induced component and a post-shaking reconsolidation component, and the procedure yields computed surface settlement time histories that reasonably match the rate and magnitude of measured settlements both during and after shaking. Using this procedure, we interpreted 151 individual (sublayer) estimates of vertical strain from 34 shaking events applied in dynamic centrifuge and 1g shaking table tests. Combined with the sublayer shaking intensities, the 151 vertical strain values constitute a new database that can be used to develop shaking-induced settlement correlations for realistic partially drained conditions.

Comparison of two community noise models applied to a NASA urban air mobility concept vehicle

Predictions of community noise exposure from the NASA urban air mobility (UAM) concept vehicles have been conducted for representative operations using the FAA Aviation Environmental Design Tool (AEDT) in order to demonstrate modeling tool interoperability and assess applicability, capabilities and limitations of integrated noise modeling tools. To both quantify limitations and highlight other capabilities, a comparative analysis is performed using a time simulation method, in particular, using the Volpe Advanced Acoustic Model (AAM). Starting with the same source noise model, the 3D directivity of a UAM concept vehicle is predicted in terms of aeroacoustic pressure time histories at a sphere of observers near the vehicle. In addition to distilling those data to a set of noise-power-distance data for input to AEDT, the data are processed preserving directivity, into narrowband, one-twelfth and one-third octave bands for input to AAM. Results from AEDT and AAM modeling are provided for a variety of metrics to demonstrate the effect that source noise and propagation modeling fidelity have on predicted results at receptors over a study area.

Experimental investigation of cavity dynamics and pressure created by cumulative hydrodynamic ram

The impact of high-velocity projectile on fluid-filled containers can cause hydrodynamic ram (HRAM) events. When multiple projectiles impact, HRAM effect is superimposed. In this paper, we presented the experimental results of cavity dynamic, pressure-time histories, and impulse-time histories caused by single and double projectiles impacting water-filled containers.

Influence of water storage on deflagration characteristics of methane in confined space

Comparative experiments were conducted under different water level heights and methane concentration conditions using a self-designed explosion experiment pipeline. The results showed that, in comparison with the scenario without water storage, when the water level was 2 cm and methane concentration was 6.5–12.5%, there was a dual effect including a pressure decrease caused by the endothermic cooling of liquid water and a pressure increase caused by the expansion of water vapour. These effects caused the pressure time history curve to exhibit a double-peak or multi-peak structure, and the average decrease in the peak deflagration pressure was 23.76%. The heat of vaporisation absorbed by the stored water and barrier effect of water vapour on the transfer of the heat slowed down the increase in the deflagration temperature. The average decrease in the peak deflagration temperature of methane was 13.82%, and the time to reach the peak deflagration temperature was extended as a whole, with an average delay of 0.22 s. Water storage also changed the shape of the deflagration flame front, which exhibited ‘knife’, ‘V’, and ‘crescent’ structures. Moreover, the flame propagation speed was significantly reduced, with the peak and average flame propagation speeds decreased by 83.3% and 83.6%, respectively. The research results can provide a certain reference for preventing gas explosions in typical confined spaces, and also help to explore new anti-explosion methods, which can be applied to marine equipment such as ships.

Experimental investigation of viscoelastic turbulent fluid hammer in helical tubes, considering column-separation

The fluid hammer phenomenon is a devastating incident that can cause substantial damages to the hydraulic systems. If the fluid reaches the vapor pressure due to high pressure gradients, the phenomenon is called column separation. In this study, the overpressures and the column separation induced by the sudden closure of the valve are studied experimentally. To this end, an experimental apparatus consisting of copper and polyethylene tubes is built, and polyacrylamide (PAA) aqueous solution is used as the viscoelastic fluid. Experiments are carried out with water, fresh, and degraded PAA solutions at different concentrations of 100, 200, 300, and 400 ppm. Results indicated that the occurrence of the column separation in the copper tube is considerably impeded by implementing polymer additives. However, the influence is weakened significantly after degradation. On the other hand, this phenomenon in PE tubes is not as significant, because of the viscoelastic behavior of the pipe wall, which eliminates the abnormal pressure peaks, leading to a smoother pattern for the pressure wave. The overpressures are more remarkable in fresh polymer solutions at higher concentrations, and decreasing the concentration, as well as the degradation, mitigates them. Furthermore, the pressure wave rate of attenuation in the copper tube became 9.82% less substantial when the Deborah number increased from 6.59 to 9.21 (roughly 40%). Besides, this attenuation was 35.71, 62.00, 37.00, and 21.78% more severe in the degraded 100, 200, 300, and 400 ppm solutions than the corresponding fresh solutions, respectively. The pressure-time history in PE tubes with viscoelastic fluids followed a different trend. Also, the viscoelasticity has resulted in a decrease in acoustic wave speed as the wave speed in the 400 ppm solution is roughly 15.04% lower than water.

솔리드 모델링과 레벨셋 기법을 이용한 고체 로켓 추진기관 성능해석

The performance prediction and grain burn-back analysis of rocket motor are important steps in the designing of a solid propellant rocket motor. The grain burn-back analysis of the solid grain identifies the burning surface area at each burning step in order to predict pressure-time history of the rocket motor. In this study, the shape of propellant grains was conveniently designed based on a solid modeling program of conventional purpose and the internal ballistics analysis was performed using a Matlab code which was developed to analyze the grain burn-back for this shape model. Upon carrying several analyses for rocket motors, it was confirmed that the developed code is suitable and useful.

Provisions and comparison of Chinese wind load standard for roof components and cladding

This paper presents the main theoretical foundation and innovation of winad load provisions for wind loads on components and cladding in the newly-revised Standard for Wind Loads on Roof Structures (JGJ/T 481-2019). Generally, by introducing the concept of peak wind pressure coefficients, a more reasonable and convenient wind load determination for roof components and cladding can be obtained for structural designers. Moreover, based on extensive wind tunnel test data of external wind pressures on components and cladding of typical roofs, the corresponding peak external wind pressure coefficients are proposed, with more specific wind load zones. Regarding those large-span curved roofs, innovative external wind pressure coefficient values on detailed roof zones are firstly presented. In addition, according to comparisons, it is seen that the roof zones in the Chinese standard are similar to those in the Canada wind load code. The resulting peak external wind pressure coefficients in corner, edge and interior zones reach the international advanced level. Finally, optional three methods to determine peak wind pressure coefficient are also clearly specified, which are applicable to cases with different wind pressure time history lengths. All the development and improvement of the standard provide necessary supplement and reference for the international and Chinese wind-resisting design.

Effects of nitrogen addition on vented hydrogen–air deflagration in a vertical duct

In this paper, experiments were performed to investigate the coupling effects of venting and nitrogen addition ratio (χ) on flame behavior and pressure evolution during hydrogen–air deflagration within and outside a 1-m-high vertical duct with a vent on its top. Experimental results reveal that χ has significant effects on the pressure–time histories in the duct. Helmholtz oscillations of the internal overpressure were observed in all tests, and acoustic type oscillations appears in the tests only for χ = 25% and 30%. For a certain χ, the maximum overpressure (Pmax) increased with the distance to the vent, i.e., the highest overall explosion overpressure was attained near the duct bottom; however, the difference in Pmax between various measuring points decreases with an increase in χ. In all tests, a pressure peak in the duct was observed shortly after external explosion. The maximum internal and external overpressure decreased as χ was increased.

Experimental and Numerical Study of Ignition and Flame Propagation for Methane–Air Mixtures in Small Vessels

Methane is one of the most common gaseous fuels that also exist in nature as the main part of the natural gas, the flammable part of biogas or as part of the reaction products from biomass pyrolysis. In this respect, the biogas and biomass installations are always subjected to explosion hazards due to methane. Simple methods for evaluating the explosion hazards are of great importance, at least in the preliminary stage. The paper describes such a method based on an elementary analysis of the cubic law of pressure rise during the early stages of flame propagation in a symmetrical cylindrical vessel of small volume (0.17 L). The pressure–time curves for lean, stoichiometric and rich methane–air mixtures were recorded and analyzed. From the early stages of pressure–time history, when the pressure increase is equal to or less than the initial pressure, normal burning velocities were evaluated and discussed. Qualitative experiments were performed in the presence of a radioactive source of 60Co in order to highlight its influence over the explosivity parameters, such as minimum ignition energy, maximum rate of pressure rise, maximum explosion pressure and normal burning velocity. The results are in agreement with the literature data.

Effect of hydrogen enrichment of compressed natural gas on combustible limit and flame kernel evolution in a constant volume combustion chamber using laser ignition

Laser ignition of hydrogen-enriched compressed natural gas (HCNG) enables lean-burn combustion, a key technology for future emissions norms compliance for internal combustion (IC) engines. HCNG overcomes the limitations of low volumetric energy density and lowers the flame speed of CNG fueled spark ignition (SI) engine-powered vehicles. In this study, laser beam profile and beam quality (M2) of a Q-switched Nd: YAG laser at fundamental wavelength of 1064 nm, having 6–9 ns pulse duration, were characterized. During the Constant volume combustion chamber (CVCC) experiments, relative air-fuel ratio (λ) of different HCNG blends were varied to identify the lean-burn limits, and observe flame kernel evolution, pressure–time history, and detect the start of combustion (SoC). At 10 bar initial chamber filling pressure, lean flammability limit increased due to hydrogen (H2) enrichment of CNG. It was found to be λ = 1.6, 1.8, 1.9, 2.0, and 2.1 for CNG, 10HCNG (10% v/v hydrogen and balance CNG), 20HCNG, 30HCNG, and 40HCNG respectively. Flame kernel displacement (Early stages of flame initiation and its development in µs time-scale) was the highest for λ = 1.1 for all HCNG mixtures, irrespective of the test fuel composition. Knocking or two-stage combustion increased with lowering λ at 10 bar initial chamber filling pressure. SoC advanced and combustion duration (CD) decreased with increasing H2 enrichment of CNG. Increased H2 enrichment of CNG accelerated the flame kernel evolution and made it a predominantly a 3D combustion phenomenon (volumetric combustion). Lower λ and higher H2 enriched CNG mixtures were effective in reducing the CD.