Measured Pressure Histories Research Articles

An offline coupling approach for efficient SPH simulations of long-distance tsunami events using wave source boundary condition

The entire procedure of tsunami events consists of wave generation and propagation toward the coastal structures encompassing the long-range system domain. Therefore, instead of an integrated continuous simulation, two or several consecutive simulations are preferred for numerical efficiency, where the hydrodynamic information within a particular domain from the preceding simulation can be utilized for the wave sources in the subsequent simulation. In this study, as an offline coupling approach, the wave source boundary condition is proposed based on the particle-based Lagrangian framework. This boundary condition is integrated with the solution algorithm of the smoothed particle hydrodynamics (SPH) in-house parallel code. In the dambreak simulation, it is validated that the wave source boundary condition can encompass both the forward and reverse flows, where the numerical results of the full and partial simulations show good agreement in terms of the wave profile, velocity distributions, and measured pressure histories. Thereafter, the full and partial simulations of a tsunami experiment are carried out. The numerical results in the partial simulation agree well with those obtained in the full simulation in terms of the particle distributions, physical quantities, and loading histories (e.g., pressure, acceleration) on the shoreline structure. It is demonstrated that the proposed offline coupling approach using the wave source boundary condition is compatibly utilized with the developed in-house SPH parallel solver, facilitating the detailed FSI simulations within a reduced domain of interest for long-distance tsunami-like phenomena.

Experimental Investigation of Column Separation Using Rapid Closure of an Upstream Valve

In this study, the phenomenon of column separation that occurs in the downstream pipeline of a rapid closure valve is experimentally investigated. Special attention is paid to the dynamic behavior of the formation, growth, and collapse processes of cavities, which are observed using a high-speed camera. Synchronized images of cavity patterns and measured pressure histories are analyzed to elucidate the process of water column separation, the mechanism of column separation events, and the influence of parameters on the transient flow. Experimental results indicate that during the collapse process of vapor cavities, a superposition phenomenon involving a positive pressure wave and collapse wave occurs, resulting in a nearly three times rise of Joukowsky pressure. In all test cases, the maximum pressure of the pipeline exceeded 150 times the reservoir static pressure. A new classification for a water hammer combined with cavitation (four types of pressure oscillation patterns) is proposed based on whether the duration of column separation decreases sequentially and the maximum pipeline pressure follows the first collapse of cavities at the valve. As the initial flow velocity increases, there is generally an increase in maximum pressure; however, this trend may be scattered under certain operation conditions.

On Sources of Damping in Water-Hammer

Various potential causes of damping of pressure waves in water-hammer-like flows are discussed, with special attention being paid to their qualitative influences on measured pressure histories. A particular purpose is to highlight complications encountered when attempting to interpret causes of unexpected behaviour in pipe systems. For clarity, each potential cause of damping is considered in isolation even though two or more could exist simultaneously in real systems and could even interact. The main phenomena considered herein are skin friction, visco-elasticity, bubbly flows and porous pipe linings. All of these cause dispersive behaviour that can lead to continual reductions in pressure amplitudes. However, not all are dissipative and, in such cases, the possibility of pressure amplification also exists. A similar issue is discussed in the context of fluid–structure interactions. Consideration is also given to wavefront superpositions that can have a strong influence on pressure histories, especially in relatively short pipes that are commonly necessary in laboratory experiments. For completeness, attention is drawn towards numerical damping in simulations and to a physical phenomenon that has previously been wrongly cited as a cause of significant damping.

Influence of cellophane diaphragm rupture processes on the shock wave formation in a shock tube

Diaphragm opening processes with a finite time affect the generated shock waves and shock tube flows. This effect is dominant in short and low-pressure shock tubes. In this research, a high-speed visualization of the opening process of a cellophane diaphragm, which is a suitable material for operation in a low-pressure shock tube, is conducted. The self-shaping opening morphology of cellophane diaphragms is observed at the initial stage with an approximate crack propagation speed of 807 m/s, which is greater than the speed of sound of the test gas. The initial opening motion of the petals, which are formed by cracks, is successfully modeled by the rotational equation of motion. Through analysis of the generation and coalescence of compression waves, whose characteristic velocities are calculated from the measured pressure histories, the shock formation distance is reasonably estimated. From the visualized diaphragm opening processes and analysis of coalescence of compression waves, we revealed that the initial stage of the diaphragm opening process plays a dominant role in shock wave formation rather than the entire process.

Explosion-induced ignition and combustion of acetylene clouds

We investigate the explosion-induced ignition and combustion of an acetylene cloud in a rectangular chamber ( $$10\,\hbox {cm}\times 10\,\hbox {cm} \times 39\,\hbox {cm}$$ ). In the experiments, a 0.2-g PETN charge was located at $$x = 9.7\,\hbox {cm}$$ and a soap bubble ( $$d = 5\,\hbox {cm}$$ ) filled with pure acetylene was located at $$x= 27\,\hbox {cm}$$ as measured relative to the end wall. Detonation of the charge created a blast wave that crushed the soap bubble—inducing mixing with the air. After 0.55 ms, the mixture ignited, forming at turbulent combustion cloud. The flow was modeled using the compressible Navier–Stokes equations assuming unity Lewis number. Arrhenius-based kinetics were used to model ignition. Adaptive mesh refinement was used to capture turbulent mixing on the grid (the MILES approach of J. Boris). Computed pressures were found to be in agreement with measured pressure histories. Finite-rate kinetics were required to capture the ignition processes over the duration of the experiment.

On the Interpretation and Correlation of High‐Temperature Ignition Delays in Reactors with Varying Thermodynamic Conditions

ABSTRACTIgnition delay time (IDT) is a useful global metric for fuel performance screening and a major target for kinetic modeling. Measurements of IDT are conceptually straightforward; however, interpretation could be complicated, especially for systems with changing temperature and pressure. Some experimental conditions in the high repetition rate miniature shock tube (HRRST) exhibit complex temperature and pressure state histories. To better interpret and correlate IDTs, especially those obtained in reactors with varying thermodynamic conditions, an inverse Livengood–Wu (L‐W) integral technique is applied to deconvolve the constant condition IDTs from measured IDTs in the HRRST using information on the varying state history. In this paper, the approximate problem is demonstrated using only the measured pressure history leading up to ignition, where the temperature history is estimated based on an isentropic assumption. The IDTs of several fuels were first measured in the HRRST including isooctane and acetone to represent those fuels without strong low‐temperature chemistry effects. Based on the measured pressure and approximated temperature history, measurements of IDTs in the HRRST compare very favorably with those measured using more conventional techniques, including conventionally sized shock tubes, via the inverse L‐W correlation with relaxed Newton iteration and genetic algorithm. This study demonstrates the feasibility of using a high throughput ignition testing facility, like the HRRST to extract the constant state IDT measured in regular shock tubes, assisted by the inverse L‐W correlation. It is expected with an independent temperature measurement available in the future, IDTs in a broader range of thermodynamic conditions and effects of heat loss could be better resolved.

A study on accumulated damage of steel wedges with dead-rise 10° due to slamming loads

This paper presents the results of experimental investigation on the elastic–plastic response of steel unstiffened wedges with dead-rise 10° subjected to repeated impulsive pressure loadings. Repeated drop tests were performed with both wedge thickness and drop height varied. The pressure and histories were recorded during the tests and the permanent deflections were measured after every drop. Using the recorded test result, the effects of flexibility of wedges and repetition have been investigated. From the pressure history obtained from the tests the characteristics of the impulses were identified. Numerical simulations of the tests were made using the measured pressure history and the permanent deflection predictions were compared with those of the experiments.

Experimental study and numerical simulation of the afterburning of TNT by underwater explosion method

We studied the afterburning of TNT in an open space, underwater test. A double-layer container (DLC) was used to enhance the afterburning effect of an underoxidized explosive. The explosive charge was in the inner container, and the outer container was filled with different gases (air, oxygen and nitrogen). After initiation, the DLC cracks and allows the detonation products to mix with the surrounding gas in the outer container. The afterburning energy was calculated from the data of a pressure transducer. Results show that pressure and impulse histories for tests with oxygen and air are greater than those recorded with nitrogen; the afterburning energy increases with higher concentration of oxygen, but does not reach the theoretically maximum value with an excess oxygen required to combust all the products. Finally, two-dimensional numerical simulations were performed using the Jones–Wilkins–Lee (JWL) equation of state (EOS) with a Miller extension. Computed pressure histories were in good agreement with measured pressure histories for all cases studied.

Physicochemical effects of varying fuel composition on knock characteristics of natural gas mixtures

The physicochemical origins of how changes in fuel composition affect autoignition of the end gas, leading to engine knock, are analyzed for a natural gas engine. Experiments in a lean-burn, high-speed medium-BMEP gas engine are performed using a reference natural gas with systematically varied fractions of admixed ethane, propane and hydrogen. Thermodynamic analysis of the measured non-knocking pressure histories shows that, in addition to the expected changes arising from changes in the heat capacity of the mixture, changes in the combustion duration relative to the compression cycle (the combustion “phasing”) caused by variations in burning velocity dominate the effects of fuel composition on the temperature (and pressure) of the end gas. Thus, despite the increase in the heat capacity of the fuel–air mixture with addition of ethane and propane, the change in combustion phasing is actually seen to increase the maximum end-gas temperature slightly for these fuel components. By the same token, the substantial change in combustion duration upon hydrogen addition strongly increases the end-gas temperature, beyond that caused by the decrease in mixture heat capacity. The impact of these variations in in-cylinder conditions on the knock tendency of the fuel have been assessed using autoignition delay times computed using SENKIN and a detailed chemical mechanism for the end gas under the conditions extant in the engine. The results show that the ignition-promoting effect of hydrogen is mainly the result of the increase in end-gas temperature and pressure, while addition of ethane and propane promotes ignition primarily by changing the chemical autoignition behavior of the fuel itself. Comparison of the computed end-gas autoignition delay time, based on the complete measured pressure history of each gas, with the measured Knock-Limited Spark Timing shows that the computed delay time accurately reflects the measured knock tendency of the fuels.

Numerical Analysis of Ignition Overpressure Effect on H-IIB Launch Vehicle

A numerical simulation was conducted to investigate the ignition overpressure mechanism generated by the Japanese H-IIB launch vehicle. A simplified benchmark problem and analysis of a free jet exhausted from a single solid booster were used to verify the present numerical method; the unsteady Reynolds-averaged Navier–Stokes simulation was found to be essential for determining the typical features of ignition overpressure, such as the shock wave generated in front of the plume and following starting vortex. Comparing with the measured pressure history at the launch complex, the numerical result agreed reasonably. The correlation between the wave pattern measured at the launch complex and the ignition overpressure mechanism was clarified. The effect of ignition overpressure on the launch vehicle can be reduced by shielding the inlet of the flame duct with a mobile launcher; however, severe impact on the launch complex is unavoidable. The numerical technique and knowledge obtained in this study are applicable in the preliminary design of a launch pad to mitigate the impact of ignition overpressure.

Shock initiation of explosives investigated with small partition experiment and numerical simulation

In order to investigate the shock ignition of high energy solid explosives by shock waves, we carry out Lagrangian experiments with 2-D Lagrangian technique which uses composite manganin-constantan (CMC). The effects of the shock sensitivity of pressed solid high explosives, TNT, and the effect of the lateral rarefaction wave were studied. Based on the measured pressure histories and the radial displacements, we formulate the Ignition and Growth reactive flow models for the pressed TNT. The shock initiation process simulated by Ignition and Growth model agreed well with experimental data. This pressed TNT model can be applied to shock initiation scenarios which are highly unpredictable and have not been or cannot be tested experimentally.

Experimental and Numerical Study on the Afterburning Effect of TNT

In order to investigate the afterburning effect of TNT in an open space, a double-layer container (DLC) which can be filled with different gases and enhance the afterburning effect of underoxidized explosives was designed. The charges were located in the inner container, and the outer container was filled with different gases (air, oxygen or nitrogen). The experiments were conducted under water. After initiation, the DLC cracks and provides gas for the detonation products. Underwater static pressure transducer was the main diagnostic. It is shown that pressure and impulse histories for explosions in oxygen and air are greater than those recorded for explosions in nitrogen. Moreover, the afterburning energy was calculated. Results show that the afterburning energy increases with the increase of the amount of oxygen, but cannot reach the theoretically maximum value even though there is excessive oxygen. Finally, two-dimensional numerical simulations were performed by the explicit finite element program ANSYS AUTODYN. The Miller energy release model was used to describe the afterburning process. Results demonstrate that computed pressure histories agreed with measured pressure histories well in terms of initial peak pressure, waveforms and total impulse.

Modeling and simulation of pressure waves generated by nano-thermite reactions

This paper reports the modeling of pressure waves from the explosive reaction of nano-thermites consisting of mixtures of nanosized aluminum and oxidizer granules. Such nanostructured thermites have higher energy density (up to 26 kJ/cm3) and can generate a transient pressure pulse four times larger than that from trinitrotoluene (TNT) based on volume equivalence. A plausible explanation for the high pressure generation is that the reaction times are much shorter than the time for a shock wave to propagate away from the reagents region so that all the reaction energy is dumped into the gaseous products almost instantaneously and thereby a strong shock wave is generated. The goal of the modeling is to characterize the gas dynamic behavior for thermite reactions in a cylindrical reaction chamber and to model the experimentally measured pressure histories. To simplify the details of the initial stage of the explosive reaction, it is assumed that the reaction generates a one dimensional shock wave into an air-filled cylinder and propagates down the tube in a self-similar mode. Experimental data for Al/Bi2O3 mixtures were used to validate the model with attention focused on the ratio of specific heats and the drag coefficient. Model predictions are in good agreement with the measured pressure histories.

Shock initiation of the pressed Trinitrotoluene (TNT) investigated with the 2-D Lagrange method

In order to investigate the characters of high energy solid explosives initiated by shock waves, the Lagrange analytical experiment equipment was designed. The effects on the shock sensitivity of pressed TNT were quantitatively measured. Ignition and growth reactive flow models for the pressed TNT were formulated based on the measured pressure histories. The initiation process was calculated near the critical point by 2-D Lagrangian analysis method. The lateral effects to the shock waves were investigated. Key words: Shock wave, solid explosive, Lagrangian analysis, state equation.

Gasdynamic model of turbulent combustion in TNT explosions

A model is proposed to simulate turbulent combustion in confined TNT explosions. It is based on: (i) the multi-component gasdynamic conservation laws, (ii) a fast-chemistry model for TNT–air combustion, (iii) a thermodynamic model for frozen reactants and equilibrium products, (iv) a high-order Godunov scheme providing a non-diffusive solution of the governing equations, and (v) an ILES approach whereby adaptive mesh refinement is used to capture the energy-bearing scales of the turbulence on the grid. Three-dimensional numerical simulations of explosion fields from 1.5-g PETN/TNT charges were performed. Explosions in six different chambers were studied: three calorimeters (volumes of 6.6-L, 21.2-L and 40.5-L with L/ D = 1), and three tunnels ( L/ D = 3.8, 4.65 and 12.5 with volumes of 6.3-L)—to investigate the influence of chamber volume and geometry on the combustion process. Predicted pressures histories were quite similar to measured pressure histories for all cases studied. Experimentally, mass-fraction of products, Y P exp , reached a peak value of 88% at an excess air ratio of twice stoichiometric, and then decayed with increasing air dilution; mass-fractions Y P calc computed from the numerical simulations followed similar trends. Based on this agreement, we conclude that the dominant effect that controls the rate of TNT combustion with air is the turbulent mixing rate; the ILES approach along with the fast-chemistry model used here adequately captures this effect.

<italic>In situ</italic> measurement of gas diffusion properties of polymeric seals used in MEMS packages by optical gas leak testing

A novel inverse approach is proposed for in situ measurement of gas diffusion properties of polymeric seals used in microelectromechanical systems (MEMS) packages. The cavity pressure evolution of a polymer-sealed MEMS package subjected to a constant bombing pressure is documented as a function of time using classical interferometry, and the diffusion properties of the polymeric seal are subsequently determined from the measured pressure history. A comprehensive numerical procedure for the inverse analysis is established considering three diffusion regimes that characterize the leak behavior through a polymeric seal. The method is implemented to determine the helium diffusivity and solubility of a polymeric seal.

Numerical and experimental comparisons of the self-pressurization behavior of an LH2 tank in normal gravity

In optimizing the design of cryogenic storage facilities for future in-orbit or on-surface applications the boil-off and the self-pressurization rates must be accurately predicted for different g-levels and for a variety of heat loads and distributions. In this paper, a two-phase CFD model is presented that describes the self-pressurization behavior of a flightweight partially full LH2 tank in normal gravity. Existing experimental data at different fill levels are used to assess the predictive capability of the model. The model’s predictions indicate favorable agreement with the experimentally measured pressure histories. Small deviations are observed for the median fill level cases where it is suggested that a non-uniform heat load may be the source of this discrepancy.

A Volcanic Reservoir: Integrated Facies Distribution Modeling and History Matching of a Complex Pressure System

Summary A Tcf-class gas field has been producing over several decades in Japan. The reservoir body comprises stacked rhyolite lava domes erupted in a submarine environment. A porous network developed in each dome and rapid chilling on contact with seawater caused hyaloclastite to be deposited over it. Although hyaloclastite is also porous in this field, its permeability has been reduced dramatically by the presence of clay minerals. Impermeable basaltic sheets and mudstone seams are also present. Each facies plays a specific role in the pressure system. Stratigraphic correlation originally identified multiple reservoirs. Gas has been produced almost exclusively from the largest one. However, following 10 to 20 years of production, the pressures within unexploited reservoirs were noticed to have declined at a variety of rates. Unusual localized behavior has also been observed. Because seismic data were not proved particularly informative, we decided to remodel the entire system by specifically using pressure data. We employed a combination of multipoint geostatistics and probability perturbation theories. This approach successfully captured the curved facies boundaries within stacked lava domes while accounting for pressure data by means of history matching to address nonstationarity in the real field. Building a suitable training image is commonly a difficult aspect of multipoint methods and poses particular problems for volcanic reservoirs. It was accomplished here by iteratively adjusting the prototype until satisfactory history matching was achieved with a reasonable number of perturbations. Ambiguous reservoir boundaries were represented stochastically by populating a predetermined model space with pay and nonpay pixels. The modeling results closely simulate measured pressure histories and appear realistic in terms of both facies distributions and reservoir boundaries. They suggest that uneven pressure declines between different units are caused by the tortuous flow channels that connect them. The results also account for the unusual smaller-scale pressure performances observed. The final training image obtained here indicates more intensive spatial variations in facies than previously appreciated. Original gas in place (OGIP) estimates made with 20 equiprobable realizations are scattered within ±15% of the mean value. Estimates of incremental recovery made by drilling a step-out well reveal greater variation than those made by installing a booster compressor, which quantifies a higher associated geological risk.

Particle image velocimetry investigation of a finite amplitude pressure wave

Particle image velocimetry is used to study the motion of gas within a duct subject to the passage of a finite amplitude pressure wave. The wave is representative of the pressure waves found in the exhaust systems of internal combustion engines. Gas particles are accelerated from stationary to 150 m/s and then back to stationary in 8 ms. It is demonstrated that gas particles at the head of the wave travel at the same velocity across the duct cross section at a given point in time. Towards the tail of the wave viscous effects are plainly evident causing the flow profile to tend towards parabolic. However, the instantaneous mean particle velocity across the section is shown to match well with the velocity calculated from a corresponding measured pressure history using 1D gas dynamic theory. The measured pressure history at a point in the duct was acquired using a high speed pressure transducer of the type typically used for engine research in intake and exhaust systems. It is demonstrated that these are unable to follow the rapid changes in pressure accurately and that they are prone to resonate under certain circumstances.

Vapor condensation study for HIF liquid chambers

This paper presents the experimental study of transient cooling and condensation of the prototypical material flibe under conditions relevant to Heavy Ion Fusion (HIF) power plants. Superheated vapor is generated by a high-current, pulsed electrical discharge over a pool of liquid flibe. The excited vapor expands inside a temperature-controlled chamber designed to scale the initial density of the generated vapor, the initial energy density and the surface area available for condensation, considering HYLIFE-II as the reference design. Clearing rates are evaluated from the measured pressure history. Mass spectroscopy is used to characterize the composition of the residual gases. SEM analysis of material deposited on witness plates is also presented, showing that interface phenomena during the initial expansion phase depend on the orientation of the condensation surface relative to the gas velocity. The results show that chamber clearing can be characterized by an exponential decay with a time constant of 6.58 ms. However, the equilibrium pressure is one order of magnitude higher than the desired HIF base pressure because of the presence of non-condensable impurities dissolved in the material available for the experiments. If the exponential decay is applied to the pressure range of the reference design, the resulting period for chamber clearing is 60 ms. The conclusion is that condensation rates of flibe vapor are sufficiently fast to allow HIF power plants repetition rates, and that the main issue for flibe vapor condensation lies in the control of the impurities dissolved in the salt.