Pressure Impulse Research Articles

Hydrodynamic ram analysis in high-speed projectile penetrating into water-filled vessels

Hydrodynamic ram (HRAM) is a phenomenon that occurs when a high-speed projectile penetrates a fluid-filled tank, where the energy transferred to the liquid could result in a catastrophic failure and excessive structural damage. It is essential to take physical comprehension of the hydrodynamic effects that occur during an HRAM event in the civilian domain as well as for the military aircraft design, which would in fact contribute to design better structures with respect to this particular threat. For this present work, the HRAM due to cavity evolution in confined vessels under ballistic impact by projectiles was investigated through theoretical analysis combined with experimental results. Taking the confinement effects due to the limited size of the fluid-filled vessel and corresponding structure deformation into account, a model is proposed to describe the pressure between the liquid and vessel wall along the penetration trajectory based on cavity dynamics analysis. By studying relevant parameters, changes of wall pressure, non-dimensional disturbance range and energy of two extreme containers, (namely, non-pressure resistance containers and rigid containers without deformation) were examined. The results show that the cavitation pressure has less intense peak but much greater temporal extent compared with the pressure generated during the shock stage, thereby the cavity pressure impulse induced by cavity evolution is a non-negligible factor affecting the deformation and failure of a fluid-filled vessel. The aim of the present work is to reveal the mechanism of the pressure acting on the container wall caused by cavity evolution rather than the initial shock wave in an HRAM event, which will help to study the nature of hydrodynamic ram and understand the role of the cavitation pressure in the damage or deformation of liquid-filled vessels under projectile impact.

Numerical derivation of P-I diagrams for shallow buried RC box structures

To perform quick damage assessment and preliminary blast resistant design, the present study develops Pressure-Impulse (P-I) diagrams for the shallow-buried box structures based on high fidelity numerical modelling. Shock wave propagation in the soil and its interaction with the roof slab and vertical wall are considered in the blast load modelling, both flexure and shear damage of the roof slab under surface blast loads are considered in the P-I diagram. Parametric studies are carried out to investigate the effects of roof span, wall thickness, concrete strength, flexure and shear reinforcement ratio on the P-I diagram. Based on the numerical results, analytical formulae to predict the P-I diagrams for buried box structures are derived. The applicability of the improved P-I diagrams approaches in practical evaluation is illustrated through case studies.

An experimental study on steam explosion of a small melt jet falling into a water pool

To address the mechanisms and influential factors of steam explosions which may occur during severe accidents in a nuclear power plant (NPP), the VULCAN apparatus is designed and built to investigate the characteristics of a steam explosion when molten material falls into a water pool. The test facility is composed of a high-speed measurement system and an induction furnace which enables preparation and delivery a small melt jet at temperature up to 1500 ℃. In the first campaign of tests, tin is employed as the simulant of melt material, and the steam explosion process and pressure signals of a small molten tin jet falling into a deep water pool are recorded by a high-speed camera and a high-frequency pressure sensor, respectively. Debris particles from part test are collected and sieved for analysis of morphology and size distribution of the particles. Multiple occurrences of steam explosion are observed during the traveling of the melt jet into the water pool, with several cycles of expansion–contraction in each occurrence of steam explosion. The time interval between two occurrences is around 80 ms and between two cycles is around 4 ms. For the melt mass ranging from 20 to 140 g in the present study, it is found that the number of steam explosion occurrences increases with the melt mass. Both the pressure impulse and the conversion ratio of steam explosion increase with melt mass. However, the pressure impulse and conversion ratio do not have a monotonic relation with melt superheat, and the conversion ratio increase with melt superheat when it is below a threshold (370℃), but decrease above the threshold.

The physical properties of organic aircraft deicers under low temperature

Ethylene glycol (EG) deicer and propylene glycol (PG) deicer were frequently used as the aircraft de-icing fluids in cold region. In this paper, the icing pressure (Ip), icing volume expansion rate (ΔVP), freezing point (T0) and under-cooling (△T) of aircraft deicers with different concentrations were investigated, and the above indicators of aircraft deicers were also compared with that of water and NaCl deicers. The results showed that the icing volume expansion of deicers was the direct cause of icing pressure. During the cooling process, values of Ip and ΔVP firstly increased sharply, then slowly, and finally became stable. The stabilized values of Ip and ΔVP decreased with concentration. The stabilized Ip value of EG deicer was slightly higher than that of 3.5% NaCl deicer and far greater than 3.5% PG deicer. Of all the tested deicers, the stabilized ΔVP value of NaCl deicer was the highest and that value of EG deicer was close to that of PG deicer. The results further confirmed the feasibility of using impulse of icing pressure as the indicator to evaluate the freeze-thaw deterioration to concrete.

Simultaneous High-Speed Observation in Two Directions and Impulsive Pressure Measurement for Bubble Collapse near a Rigid Wall

Simultaneous high-speed observations in two-directions and pressure measurements using a Fiber Optic Probe Hydrophone (FOPH) are conducted to investigate the collapse of a laser-induced bubble near a rigid wall and the corresponding impulsive pressure distribution. It is shown that the measured pressure distributions next to the wall and the observations of top and side views reveal a strong correlation with the pitting damage due to the bubble collapse by Philipp and Lauterborn (1998). The results also show that asymmetric bubble collapse is observed at the second collapse.

Impulse Pressure Transducers: Applicability Criteria

Impulse Pressure Transducers: Applicability Criteria

The concept of improvement high-strength aluminum alloys FSW joint properties via post-weld explosive treatment

The study describes the theoretical background and technological aspects of the post-weld explosive treatment of high-strength aluminum alloy FSW joints. Although FSW allows to effective join high-strength aluminum alloys, the heat generated during the process causes undesirable changes in the strengthening phase, giving a joint efficiency of about 80%. The load-carrying capabilities of these joints can be increased via post-weld treatment (e.g. shot peening, laser shock peening). The new, potential post-weld treatment that is presented in this paper is based on the affection of the welded joint by a shock wave generated during the detonation of explosive material. Such post-weld explosive treatment would result in the hardening of the low-hardness zone, which often determines the mechanical properties of precipitation-hardened aluminum alloy FSW joints. Studies show that explosive welding of annealed aluminum alloys increases their microhardness by about 25% as the result of a high-velocity collision. If a similar effect can be achieved in explosive hardening, the microhardness of the low-hardness zone will increase entailing an improvement of entire joint mechanical properties. The variety of explosives materials used in metalworking (covering the values of detonation velocity from about 2000 m/s to 8000 m/s) and different systems for shock-wave affection gives many technological possibilities. In this work are discussed two different explosive hardening systems: with direct placement of explosive material on a treated welded plate and with an additional driven plate, which provides a higher pressure impulse. Considering that affecting of high amplitude shock wave introduces defects into the structure and decreases residual stresses in the welded joints, the application of an appropriate technological system creates a potential for improving the load-carrying capacities of discussed joints, especially in a condition of cyclic loading.

Influence of grain size on dynamic characterizations of laser-driven grain ejection

When intense laser pulse irradiates a target surface, the energetic processes of generation and expansion of laser-induced plasma will affect a localized pressure impulse around the irradiation zone. As a result, pulsed laser ablating granular target can drive a physical phenomenon of grain ejection. In this work, taking dry glass beads with different grain sizes as an example of granular targets and using high-speed video camera, we experimentally investigate the grain-size dependent dynamics of grain ejection driven by nanosecond laser pulses. The measured video sequences clearly exhibit that the laser-driven grain ejection process can be separated into two regimes: early-stage fast ejecting process and later-stage slow ejecting process. We find that there exists an obvious grain size effect on the kinetic energy of grains in the early-stage ejecting process. In addition, the temporal evolution of transient ejection of a curtain diameter <inline-formula><tex-math id="M6">\begin{document}$ D\left(t\right) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M6.png"/></alternatives></inline-formula> corresponding to the later-stage ejecting process obeys the well-known “point source” law, <inline-formula><tex-math id="M7">\begin{document}$ {D\left(t\right)=\alpha t}^{\beta } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M7.png"/></alternatives></inline-formula>, where both parameters <inline-formula><tex-math id="M8">\begin{document}$ \alpha $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M8.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M9">\begin{document}$ \beta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M9.png"/></alternatives></inline-formula> depend on grain size. The observations mentioned above can be reasonably explained by considering the grain size dependent efficiency of impulse coupling between grain and plasma flow and plasma features generated by interaction of laser pulse with granular targets. These experimental results improve the understanding of the mechanism of laser-driven grain ejection.

A sharp interface multiphase flow model for two-dimensional water impact of a symmetric and asymmetric wedge

A Cartesian grid based sharp interface (SI) multiphase flow model is developed to investigate the symmetric and asymmetric impact of a wedge with sharp phase changes. A level set based ghost fluid method (GFM) with formal second-order accuracy is incorporated to maintain the jump properties across the two-phase interface with transient phase change. The arbitrary moving boundaries and free surfaces are handled by a radial basis function ghost cell method (RBFGCM) and a gradient augmented level set (GALS) method, respectively. The water impact of a symmetric wedge is simulated to demonstrate the accuracy and capability of the present SI method by comparing the present peak pressures with the experimental data. Also, satisfactory convergences of the grid size and the time step are obtained. Then, the symmetric and asymmetric water impact with different deadrise and inclination angles is investigated by the present SI model and the diffused interface (DI) model. The present SI model is demonstrated to perform well for various deadrise and inclination angles, except the nearly flat plate slamming. By contrast, the diffuse interface (DI) model can obtain reasonable solution for the relative impact angle no less than 15o. However, the peak pressure is considerably underestimated and its occurring moment lags behind the experimental data for a smaller impact angle, which is severer for a smaller impact angle. In addition, we analyzed the variation rules of the impulsive pressure, the motion response, the pressure distribution, and the free surface motion with respect to the relative impact angle. The maximum fluid force grows acceleratingly as the relative impact angle decreases, while the duration is shortened. Also, some typical impact phenomena are observed such as flow separation, jet flow, and ventilation for a small impact angle.

HYDROSTATIC GENERATOR OF NON-PERIODIC PRESSURE IMPULSES FOR TESTING TECHNICAL PRODUCTS

The article reviews the possibility of using the hydrostatic generators of oscillators with nonlinear power elements (elastic shells) as part of the structures of various test benches in the field of mechanical tests for vibration strength and vibration resistance, as well as when testing with external and internal pressure. The hydrostatic generator of non-periodic pressure impulses for engineering products testing is a new patented technical solution in the field of testing machines. The ratios of the angular velocities of the shafts, which provides the movement of the operating fluid into the actuator of the test bench in the form of a non-periodic function and with impulses varying in amplitude in a random manner were obtained. It makes a continuous and non-repetitive sequence of pressure impulses and corresponds to the operation of the tested objects in real conditions. The random nature of the amplitudes settings is provided by signals controlled from electric generators through controlled hydraulic valves. The development of a hydrostatic generator with a power element in the form of an elastic shell is represented by a hydromechanical diagram of a generator of non-periodic pressure impulses with corresponding kinematic and dynamic dependencies. In addition, there were developed three hydro-mechanical systems with the use of a new hydrostatic generator for engineering products testing both for mechanical random vibration and for testing the external and internal pressure of engineering objects that operate in such conditions. The result of the research is the expansion of the range of systems and methods for the test processes implementation under random non-periodic force effects on various engineering objects.

A FE model to evaluate the resisting capacity of RC beams and columns under blast loading based on P-I diagram

An improved numerical model to evaluate the resisting capacity of RC beams and columns subjected to blast loading is proposed in this paper. To describe the bending behavior of a structure, the moment-curvature relation of a RC section is employed with the definition of a dynamic increase factor (DIF) as a function of the curvature rate. The direct shear failure is also considered through adoption of the dynamic shear stress-slip relation proposed by Krauthammer et al. Upon verification of the validity of the proposed numerical model through a comparison between the obtained numerical results and the experimental data, additional parametric studies are performed for the pressure-impulse (P-I) diagrams to demonstrate that the SDOF method, which has been popularly used in constructing the P-I diagrams, has a limitation in determining the blast resisting capacity of RC members, especially in describing the shear failure mode. Since the direct three-dimensional (3-D) nonlinear blast analysis of structural members is time-consuming and costly, the direct use of the 3-D analysis appears to be extremely difficult whereas the use of the proposed numerical model will provide an alternative in construction the P-I diagrams.

Strength analysis of warship hull’s bottom loaded by the pressure wave from a non-contact explosion of sea mine explosion of sea mine

The study was based on the analysis of stamina of steel flat bottom section of transport warships, burdened by the spherical pressure wave from the non-contact explosion of TNT at a distance of 20 m under the keel. This study aims to determine the TNT mass required to break the hull. The task was solved by finite element method (FEM) explicite using CAE program [1], in which the hull’s bottom was modelled as thin shell space. The hull’s burden with pressure wave was modelled as a pressure impulse specified by the formula introduced by T.L. Geers, K.S. Hunter and R.S. Price [2]. To describe the material properties, considering high-speed strain, the Johnson-Cook model was used [3]. Therefore, the main goal of the hereby paper is to present how to correctly model the impact of large, concentrated masses of the ship’s equipment on its hull. The study presents the results of the calculated stress and strain states of the analysed section of the construction of the hull.

Dynamics of an acoustically driven cavitation bubble cluster in the vicinity of a solid surface

The dynamics of a cavitation bubble cluster under the influence of an acoustic field is a complex multiphase system that can be observed in acoustic cavitation. In the present study, a three-dimensional computational technique based on the multiphase lattice Boltzmann method (LBM) with multiple relaxation time (MRT) is adopted to investigate the acoustically driven cavitation bubble cluster dynamics near a solid wall at different wetting conditions. Herein, the Peng–Robinson–Stryjek–Vera equation of state with an acentric factor is incorporated in the LBM to accurately impose the physical properties of actual fluids. The validity and capability of the adopted MRT-LBM are confirmed by the excellent agreement of the present results compared to the computed data based on the Rayleigh–Plesset equation for a heterogeneous cavitation phenomenon. The obtained results for the acoustically driven cavitation bubble cluster dynamics demonstrate that the shielding effect of top bubbles prevents the pressure pulse from reaching the lower bubbles. Therefore, the cluster core and the bubbles near the solid surface are more affected by the destruction of the upper layer bubbles than the acoustic field. Also, it is found that the wettability of the solid wall significantly affects the irradiated impulsive pressure waves around the cluster. To justify this result from the physical point of view, the magnitude of the primary and secondary Bjerknes forces is measured and, accordingly, the growth and collapse of bubbles in the cluster under the influence of the acoustic field are discussed in detail.

On the structure dynamic response of a coastal structure subject to the dam break induced surge impact pressure

ABSTRACT Detailed laboratory datasets of the dam break-induced surge impact pressures measured by Lobovský et al. are analyzed, upon which the dynamic amplification factors (DAF) of the single degree of freedom structures with different natural periods are calculated to quantify the dynamic responses of the measured total pressure series, the decomposed impulsive and quasi-steady pressure series based on the Hilbert-Huang transform algorithm. The maximum DAFs of the measured total and decomposed impulsive pressure series increase with the decrease of structure natural periods, while those of the decomposed quasi-steady pressure series show no relation with structure natural periods. The impulsive pressure is more influential to structures with small natural periods, whereas the quasi-steady pressure plays a predominant role regarding structures with large natural periods. Due to the resonance effect, the oscillatory pressure can significantly increase the maximum DAFs and delay its occurrence time of the measured total pressure series for structures with small natural periods. Nevertheless, the damping effect can generally decrease the DAFs of structures and therefore the resonance effect. Considering the damping coefficient varies from 0 to 0.1 in reality, increase of the maximum DAF induced by resonance is non-negligible for structures with small damping and short natural period.

Study on failure mechanism of concrete subjected to freeze-thaw condition in airport deicers

The rapid freeze–thaw test about ordinary Portland cement concrete (PCC) was performed in the deicers of water, 3.5% ethylene glycol, 3.5% NaCl and 3.5% calcium magnesium acetate (CMA). The ice pressure (Ip) of deicer was tested, and the concept of the ice pressure impulse (IPI) was proposed. A crack density model was employed to describe the freeze–thaw damage process of concrete. Results indicated that the freeze–thaw damage of PCC in CMA deicer was the mildest. The Ip value of water was the highest but its IPI value was the lowest. The freeze–thaw microcracks inside concrete was induced by the Ip of deicer restrained in concrete pores. The freeze–thaw crack density decreased with the relative depth of specimen. The value of superficial critical crack density was 0.85 ∼ 0.88, when the exterior mortar of concrete began spalling. The value of central critical crack density was 0.32 ∼ 0.34, when the interior freeze–thaw failure of concrete occurred.

How Does Coastal Gravel Get Sorted Under Stormy Longshore Transport?

AbstractStorm waves transport and sort coarse gravel along coasts. This fundamental process is important under changing sea‐levels and increased storm frequency and intensity. However, limited information on intra‐storm clast motion restricts theory development for coastal gravel sorting and coastal management of longshore transport. Here, we use smart boulders equipped with loggers recording underwater, real‐time, intra‐storm clast motion, and measured longshore displacement of varied‐mass marked boulders during storms. We utilize the unique setting of the Dead Sea shores where rapidly falling water levels allow isolating boulder transport during individual storms. Guided by these observations, we develop a new model quantifying the critical wave height for a certain clast mass mobilization. Then, we obtain an expression for the longshore clast displacement under the fluid‐induced pressure impulse of a given wave. Finally, we formulate the sorting enforced by wave‐height distributions during a storm, demonstrating how sorting is a direct manifestation of regional hydroclimatology.

Phenomenological Studies for Optimizing Subsonic Underwater Discharges

Powerful subsonic underwater discharges are used as a tool in various industrial applications. The aim of this article is to find the essential design parameters required for a pulsed-power system to efficiently drive such discharges. Using different capacitor banks and electrode geometries, a large number of studies were conducted in an effort to better understand the phenomenology of the discharge. Without developing a numerical model for the underwater plasma discharge, the phenomenological studies clearly demonstrated that the maximum pressure that can be generated depends on the discharge current, the distance between the electrodes, and the characteristic time of the discharge. The results of this work will allow the design of efficient pulsed-power-driven strong pressure impulse systems.

Air entrapment and its effect on pressure impulses in the slamming of a flat disc on water

The presence of ambient air in liquid-slamming events plays a crucial role in influencing the shape of the liquid surface prior to the impact, and the distribution of loads created upon impact. We study the effect of trapped air on impact loads in a simplified geometry, by slamming a horizontal flat disc onto a stationary water bath at a well-controlled velocity. We show how air trapping influences pressure peaks at different radial locations on the disc, how the pressure impulses are affected and how local pressure impulses differ from those obtained from area-integrated (force) impulses at impact. More specifically, we find that the air layer causes a gradual buildup of the load before the peak value is reached, and show that this buildup follows inertial scaling. Further, the same localised pressure impulse at the disc centre is found to be lower than the corresponding (area-integrated) force impulse on the entire disc. While the (area-integrated) force impulses are close to the classical result of Batchelor (An Introduction to Fluid Dynamics, Cambridge University Press, 1967, § 6.10) and Glasheen & McMahon (Phys. Fluids, vol. 8, issue 8, 1996, pp. 2078–2083), the localised pressure impulses at the disc centre, where the trapped air layer is at its thickest, lie closer to the theoretical estimation by Peterset al.(J. Fluid Mech., vol. 724, 2013, pp. 553–580) for an air-cushioned impact.

Shock wave characteristics in a conical water explosion shock tube under cylindrical charge condition

A conical shock tube is a kind of underwater explosive devices which uses small conical explosive charge to form high intensity shock pressure. Theoretically, the shock wave pressure in the conical shock tube is the same as that generated by a virtual spherical explosive charge in free field water. However, considering the effect of practical factors, the characteristics of shock wave in the actual device and the theoretical device are different to some extent. In order to investigate the shock wave characteristics in the conical water explosion shock tube under a cylindrical charge condition, and to obtain the variation rules of the peak pressure value, the specific impulse and the energy flux density, a series of numerical calculations with different cone angles and different quality of cylindrical charges were conducted. The reliability of the simulation methods was verified by comparing with the published experimental data. Through the analysis of the pressure data obtained by the validated simulation method, it is found that the shock wave in the tube follows the same scaling law as it is in the free field underwater explosion. The constants k and n of the empirical expressions for peak pressure, the impulse and the energy flux density for the shock wave in shock tube are obtained by data fitting. Furthermore, the relationships among the coefficient k, index n and cone angle α were deduced, and the result shows that the coefficients k have well linear relationship with constructed angle coefficient β, and the indexes n can be quantitatively expressed by cone angle α. Regarding the free field as a special case with a cone angle of 360°, it’s constants k and n also conform to the obtained relationships. It is also found that the secondary pulsation pressure period shows an anomalous change rule with explosive mass, which can be well explained by the significant increasement of the equivalent hydrostatic pressure depth. The ratio between the secondary impulse pressure peak and initial pressure peak is bigger than that in free field while the ratio between the secondary impulse pressure’s impulse to the initial pressure impulse is almost the same. These results can provide support for the application of conical shock tubes.

Contribution of higher modes in the dynamic response of reinforced concrete member subjected to blast

Response of reinforced concrete structures subjected to blast load of high intensity and short duration is difficult to analyze. P-I (pressure-impulse) curves are one of the approaches for describing structural response against blast load. Design codes also suggest preparing P-I curves based on SDOF for obtaining structural response subjected to blast. Blast load excites higher modes of vibrations. The SDOF analysis does not cover the higher modes effect.The structural dynamic response of RC flexure members under a varying range of explosion scenarios was predicted by carrying out investigations. The linear elastic beam with variable boundary conditions was analyzed using the Modal superposition method based upon Euler-Bernoulli, Rayleigh, Shear, and Timoshenko theories. For various ranges of the blast, Iso-damage (P-I) curves, including the effect of higher modes, were generated, and the types of failure were established. These iso-damage curves differ significantly from those obtained using the SDOF concept for the case of blast in the dynamic and impulsive regime. In the case of near blast, understandably higher modes (both flexure and shear) play a significant role. The present study suggests that the Timoshenko formulation yields an accurate response irrespective of the Flexibility of the structure.