Impulsive Pressure Loading Research Articles

Empirical formulations for prediction of permanent set evolution of steel plates due to repeated impulsive pressure loadings induced by slamming

While in service, marine structures can be damaged due to repeated impact pressures induced by slamming. This paper presents empirical formulations for prediction of permanent set evolution of steel plates used in marine applications under repeated impulsive pressure arising from slamming. The applied numerical computation methodology was developed using the nonlinear finite element commercial software package ABAQUS/Explicit. The numerical analysis model was substantiated against relevant experimental data in the open literature. Subsequently, a rigorous parametric study was performed on various fully clamped plates having actual scantlings of marine structures. The effects of the key design parameters on the damage extents of the plates under repeated impact pressure loadings were determined and are presented herein. Additionally, the effects of the boundary conditions (represented by the number of stiffeners) on the permanent set evolution were addressed. Finally, through regression analysis of the parametric study results, simple empirical formulations for prediction of permanent set evolution of plates against slamming loads were derived. The accuracy and reliability of these formulations were established by comparison with existing formulations and numerical simulations. The proposed formulae are expected to be usefully employed as a quick and effective tool for the reliable prediction of marine-structural damage extents incurred from slamming loads.

Development of simplified method for prediction of structural response of stiffened plates under explosion loads

During their lifetime, marine structures may be exposed to accidental loadings such as from collisions or explosions, as well as environmental loadings such as from slamming, sloshing and green water. Such loadings can cause damage to structures. Therefore, to minimize such damage, advanced and robust design guidelines should be formulated. Among those loads, in this study, explosions imparting an impulsive pressure loading containing a rapid increase in pressure and a short duration that can cause serious casualties, property losses, and marine pollution were considered. In this paper, a practical and robust method for damage assessment of marine structures exposed to explosion loads based on a single degree of freedom (SDOF) system and numerical simulations is proposed. The SDOF method was improved by introduction of new and better idealization resistance for the system and consideration of the effect of strain-rate, and subsequently was verified by a numerical method developed using the commercial ABAQUS software package. The numerical method was itself validated by comparison with relevant pulse pressure test data available in the open literature (good correlation was shown). Based on the validated numerical models, a rigorous parametric study of the structural response of stiffened plates having actual scantlings of offshore structures was performed. The numerically obtained maximum deformations were compared with the results from the improved SDOF method in a parametric study, and the variation of both methods was verified. Finally, simple yet accurate and reliable formulations for prediction of structural response were empirically derived. These formulations are expected to be usefully employed as a first-hand tool for prediction of damage extent of marine structures (including offshore structures) due to explosion loads.

Reactive astrocytes contribute to decreased blood-brain barrier integrity after impulsive pressure loading <i>in vitro</i>

Reactive astrocytes contribute to decreased blood-brain barrier integrity after impulsive pressure loading <i>in vitro</i>

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.

Permanent set evolution of aluminium-alloy plates due to repeated impulsive pressure loadings induced by slamming

This study investigates the response of marine aluminium-alloy plates to repeated impulsive pressure loadings due to slamming. The numerical simulations performed using the ABAQUS commercial software package were validated against relevant experimental data from the open literature. In the calculations, linear strain hardening was applied and no strain-rate hardening was considered owing to the insensitivity of the aluminium alloys to strain rate. The triangular pressure pulses with linear decay and isosceles are idealised for water-pressure impact profiles. A fully clamped unstiffened plate made of Al 5083-O with practical plate slenderness ratios is considered. The effect of the typical heat-affected zone is also numerically evaluated. Simple yet accurate closed-form equations for the prediction of the permanent set evolution of the plates due to repeated impulsive pressure loadings are derived based on the parametric study results. The results showed that the permanent set of plates was significantly increased for the first few repeated impulsive pressure loadings, while later, the total permanent set tended to have certain values regardless of the impulsive pressure and aspect ratio. Therefore, this indicates that the effect of the repetition of impulsive pressure loadings cannot be neglected in marine structural designs.

Experimental investigation of slamming impact acted on flat bottom bodies and cumulative damage

Most offshore structures including offshore wind turbines, ships, etc. suffer from the impulsive pressure loads due to slamming phenomena in rough waves. The effects of elasticity & plasticity on such slamming loads are investigated through wet free drop test results of several steel unstiffened flat bottom bodies in the rectangular water tank. Also, their cumulative deformations by consecutively repetitive free drops from 1000 mm to 2000 mm in height are measured.

Damage assessment of marine grade aluminium alloy-plated structures due to air blast and explosive loads

The objective of this paper is to investigate the response of fusion welded AA5083-H116 rectangular plates and orthogonally stiffened panels, typically found in high-speed vessels and topsides of offshore platforms, under impulsive pressure loading, such as air blast and explosions. Rigorous nonlinear finite element analyses are performed by using ABAQUS/Explicit to determine the deformation of these plated-structures under different impulses. Particular emphasis is given on the effect of the heat affected zone (HAZ), which is due to fusion welding. Based on the extensive numerical results, simple yet accurate formulae to predict the permanent set of the plates are derived as function of a non-dimensional impulse parameter. The derived equations are also compared with the existing analytical and empirical formulae in the literature.

On the Dynamic Collapse of Cylindrical Shells Under Impulsive Pressure Loadings

The dynamic collapse of submerged cylindrical shells subjected to lateral impulsive pressure loads caused by underwater explosions is studied via coupled experimental and numerical work. Two sets of experiments were performed. Initially, 50.8 mm outside diameter aluminum tubes with diameter-to-thickness ratio of 32.3 were tested inside a pressure vessel. Hydrostatic pressure was applied quasi-statically up to the onset of collapse in order to obtain the collapse pressure of the tubes tested. Subsequently, similar tubes were tested in a 5 m × 5 m × 1.6 m deep water tank under various explosive charges placed at different distances. Explosive charges and standoff distances were combined so as to eventually cause collapse of the specimens. Dynamic pressures were recorded using a fit-for-purpose data acquisition system with sampling rates of up to 1 mega samples/s/channel. In parallel, finite element models were developed using commercially available software to simulate underwater explosion, pressure wave propagation, its interaction with a cylindrical shell, and the subsequent onset of dynamic collapse. The surrounding fluid was modeled as an acoustic medium, the shells as J2 flow theory based materials with isotropic hardening, and proper fluid–structure interaction elements accounting for relatively small displacements of the boundary between fluid and structure were used. Subsequently, the physical explosion experiments were numerically reproduced with good correlation between results. Finally, a parametric study was carried out to examine the effect on the pipe under different impulsive pressure loads.

Non-linear Finite Element Analysis of Offshore Stainless Steel Blast Wall under High Impulsive Pressure Loads

Typical blast walls of offshore platform are stainless steel light-weight walls installed to contain the effect of an accidental explosion on the topside of an offshore installation. These walls are mostly designed using simplified analytical techniques like single degree of freedom (SDOF) method using global deformation or displacement as primary response parameter. Thin plate structures like stainless steel blast walls when subjected to high impulsive pressure loads, may damage severely in a particular region without experiencing a significant global deformation. This study presents realistic responses of offshore blast walls under various high impulsive pressure loads generated from accidental hydrocarbon explosions by using detailed non-linear finite element analysis (NFEA). The numerical models were verified against past experimental study on similar metal blast panels. An extensive parametric study was conducted using the verified finite element models to construct pressure-impulse (P-I) diagrams for different deformation levels. These P-I curves or iso-damage lines can be used as a quick assessment tool to determine possible level of damage of similar offshore blast walls due to different high impulsive pressure loading caused from different explosion scenarios.

Experimental and numerical studies of non-composite Steel–Concrete–Steel sandwich panels under impulsive loading

Abstract The performance of non-composite Steel–Concrete–Steel (SCS) sandwich panels under impact-induced impulsive loading was experimentally and numerically studied in this paper. Two SCS sandwich panels with different core depths were tested and the impulsive loading was applied in the laboratory by utilizing an inflated high pressure airbag to transfer the impact load from dropped projectile onto the panels. The deformation modes, applied pressures, displacement and strain responses of the panels were determined in the test. A combination of bending and shear deformation mode was observed in the SCS panel with thinner core while there was minimal visible deformation in the thicker panel. The maximum and permanent deformations of the panel with thicker panel were significantly reduced due to the increase in resistance and mass. Debonding between grout core and bottom plate was also noted in both panels during impact from the strain–time histories. Following the test, Finite Element (FE) models were constructed and verified against the test data to simulate the tests. It was shown in the FE analysis that the steel plates absorbed more energy due to its higher strength and ductility as compared to the grout core under the impact-induced impulsive pressure loading.

S0230103 衝撃圧力負荷による毛細血管様構造の崩壊と血管内皮透過性の亢進

Intracranial pressure changes during head impact cause brain injuries such as vasogenic edema and cerebral contusion. The purpose of this research is better understanding of the effect of impulsive pressure during head impact on the disruption of blood-brain barrier (BBB) that forms a physical barrier to filter blood-borne substances between the blood and the brain parenchyma. Firstly, changes in the capillary-like network formed by endothelial cells were observed using an inverted microscope. The capillary-like structure was broken down after 1 h following impulsive pressure, and the capillary network gradually disappeared until 24 h after loading. Then, following impulsive pressure loading, transendothelial electrical resistance (TEER) was measured using the in vitro BBB models consisting of cultured endothelial cells, pericytes and astrocytes from rat brain capillaries. Lower TEER indicates the disruption of endothelial integrity and the formation of intercellular gap. In the result, TEER decreased immediately after loading and the decrease in TEER was larger in the co-culture model with endothelial cells and astrocytes than in the endothelial monolayer model or the co-culture model with endothelial cells and pericytes. These results suggest that the impulsive pressure during head impact impair endothelial barrier function by the disruption of the integrity of endothelial cell-cell junctions, and the degree of increase in endothelial permeability depends on injured cells that compose BBB.

Long-Term, High-Throughput Operation of a Controlled Detonation Chamber Based on Shakedown Under Initial Overload in the Plastic Range

Hydrostatic or pneumatic overpressure testing prior to actual service provides a number of purposes related to structural integrity of pressure vessels, including some degree of confirmation of both the design and fabrication processes. For detonation chambers designed to control impulsive pressure loadings, preservice hydrostatic testing at impulses greater than those expected during normal operation can provide an added benefit—the ability to reduce cyclic fatigue damage caused by long-term, high-throughput operation, where the chamber may be use to control hundreds or even thousands of detonations without compromising structural integrity through excessive fatigue crack initiation and growth. This paper illustrates the favorable characteristics of controlled detonation chamber operation following an initial preservice impulsive over-testing program that demonstrates shakedown and satisfaction of strain ratcheting criteria, leading to favorable cyclic fatigue behavior during subsequent long-term, high-throughput operation.

FSI Research on the Noise Barrier of High-Speed Railway in the Composite Conditions

Based on the model, it firstly gets the fluid distribution of noise barrier of high-speed railway, which is under the action of train-induced impulsive wind pressure and natural wind load, then transfers the computed result as exported load to the structural analysis module through the coupling interface, by proceeding the transient dynamic analysis and modal analysis, it finally obtains the equivalent stress, total deformation and modal distribution of noise barrier. The results indicate that, compared with train-induced impulsive wind pressure, the natural wind load has a more obvious effect on the structural performance of noise barrier, and its natural frequency is much less than the external load’s, so there will be no resonate happen in practice.

Metallic sandwich panels subjected to multiple intense shocks

The mechanical response and fracture of metal sandwich panels subjected to multiple impulsive pressure loads (shocks) were investigated for panels with honeycomb and folded plate core constructions. The structural performance of panels with specific core configurations under multiple impulsive pressure loads is quantified by the maximum transverse deflection of the face sheets and the core crushing strain at mid-span of the panels. A limited set of simulations was carried out to find the optimum core density of a square honeycomb core sandwich panels under two shocks. The panels with a relative core density of 4%–5% are shown to have minimum face sheet deflection for the loading conditions considered here. This was consistent with the findings related to the sandwich panel response subjected to a single intense shock. Comparison of these results showed that optimized sandwich panels outperform solid plates under shock loading. An empirical method for prediction of the deflection and fracture of sandwich panels under two consecutive shocks – based on finding an effective peak over-pressure – was provided. Moreover, a limited number of simulations related to response and fracture of sandwich panels under multiple shocks with different material properties were performed to highlight the role of metal strength and ductility. In this set of simulations, square honeycomb sandwich panels made of four steels representing a relatively wide range of strength, strain hardening and ductility values were studied. For panels clamped at their edge, the observed failure mechanisms are core failure, top face failure and tearing at or close to the clamped edge. Failure diagrams for sandwich panels were constructed which reveal the fracture and failure mechanisms under various shock intensities for panels subjected to up to three consecutive shocks. The results complement previous studies on the behavior and fracture of these panels under high intensity dynamic loading and further highlights the potential of these panels for development of threat-resistant structural systems.

Overpressure generation and repetition of collapsing microbubbles induced by shock wave reflection in a narrow gap

This paper reports the summary of experiments performed to successive generate small-scale underwater shock waves by means of shock-induced collapse of microbubbles confined in a narrow gap. The project is motivated to develop a method for efficient inactivation of marine bacteria contained in ship ballast water by high impulsive pressure loading. The shock wave–air bubbles interaction was visualized by shadowgraph; the images were recorded by ImaCon200, and simultaneous pressure measurements were performed by using an optical fiber pressure transducer with higher temporal resolution. Attaching small air bubbles on a single nylon fiber and placing it in a confined space, we demonstrated sequential generation of impulsive high pressures at the successive collapses of small bubbles at incident and reflected shock loadings. The values of the very short impulsive pressures that occurred repeatedly for a relatively long term are found high enough to inactivate marine bacteria.

낙하실험에 의한 슬래밍 충격의 실험 연구

When ships are sailing with large motions in rough waves, the slamming phenomenon occurs and the ships suffer from impulsive pressure loadings. Recently, ships are becoming lager and faster than before and it becomes more possible that the ships experience larger impacts on their bows and sterns. Many researchers have been performing the investigations on slamming experimentally and theoretically for a long time. Most of the research reported in the open literature focused on how to accurately estimate the amplitude of the peak pressure of slamming. According to the results of a recently published work, not only the amplitude of peak pressure but also the width of the peak may play an important role in predicting the extents of damage of impacted structures. The uncertainty of impulsive pressure loadings due to slamming has been indicated by many researchers. However, probabilistic treatments of the impulsive pressure loadings are few. In this study, drop tests were conducted on wedges having dead-rise angles of <TEX>$0^{\circ}$</TEX> and <TEX>$10^{\circ}$</TEX>. Not only the amplitude of peak pressure but also the width of peak pressure were measured. Furthermore, the variations of those values are also provided for the probabilistic approach of the slamming problem.

Glass breakage by blasts: A prediction model and real-world validation.

The structural elements most sensitive to blast damage are usually windows. A classic paper by Hershey et al. [J. Acoust. Soc. Am. 55, 1009–1017 (1974)] developed a powerful statistical model for damage to windows from impulsive (sonic boom) pressure loads. The key part of the model depended on both the pressure load and failure stress having a log normal distribution; that is, the log of these variables was normally distributed. This basic concept, applied by the author in several studies on blast and sonic boom damage, is briefly reviewed here for application to blast damage to windows. Validation of the model is provided by data from an accidental explosion of an equivalent 20 lbs of TNT near a nearby nine-building apartment complex. 58 windows were broken, fortunately without any injuries. The predicted damage was augmented by results of a model study of diffraction around a cubical obstacle to approximate the changes in the net pressure loading on the apartment building windows located at various orientations to the blast wave front. The predicted window breakage rate, varying from 0.5% to 61% compared well with the observed values in the range of 0–64%. [Work supported by Wyle Labs.]

Laminated and sandwich panels subject to blast pulse loading

A recently developed optimisation technique is employed for relaxing the interlaminar stress concentration of laminated and sandwich flat panels undergoing impulsive pressure loading. We determine the through-the-thickness distribution of the core properties of sandwich panels and the in-plane distribution of the stiffness properties of their face sheets, as well as that of the constituent layers of laminates maximizing the energy absorbed through wanted modes (e.g., membrane and bending contributions) and minimizing the energy absorbed through unwanted modes (e.g., interlaminar shears). As a structural model, we employ a refined zigzag model with a piecewise high-order variation of in-plane and transverse displacements that fulfils a priori the interfacial stress and displacement contact conditions. The zigzag model, a characteristic feature of the method, is incorporated through a strain energy updating into a conventional shear deformable plate element, for the sake of reducing the computational effort required for accurately computing the stresses. The dynamic equations are solved using the Newmark implicit time integration scheme; various pulse pressure time histories are employed. Simple, suboptimal distributions of reinforcement fibres and core density compatible with current manufacturing processes are considered in the numerical applications. It appears that these distributions can effectively reduce the critical interlaminar stress concentration under impulsive loadings, with beneficial effects on the strength at the onset of damage, and improve the dynamic response properties as well

An inverse approach for pressure load identification

An inverse approach for the identification of pressure loading on a structure has been proposed and developed. In this approach, surface measurements of structural response (e.g. strain, displacement and velocity field measurements, such as can be measured with 3D digital image correlation) are utilized as input data and are combined with numerical simulations to identify the pressure load on a structure. The inverse approach has been verified by numerical benchmarks involving pressure identification under quasi-static as well as dynamic impulse loading conditions, and also been validated by an experiment involving a quasi-static pressure load. The results indicate that the proposed inverse method can identify not only the magnitude of the quasi-static pressure but also the impulsive pressure loading history. The developed inverse approach offers an opportunity to apply inverse analysis techniques to identify interactive pressure loads (such as those resulting from a blast wave) on structures in explosive events.

Numerical modeling of effect of polyurea on response of steel plates to impulsive loads in direct pressure-pulse experiments

Results of computational modeling and simulation of the response of monolithic DH-36 steel plates and bilayer steel-polyurea plates to impulsive loads in direct pressure-pulse experiments ( Amini et al., in press-b), are presented and discussed. The corresponding experiments and their results are presented in an accompanying paper ( Amini et al., 2010). The entire experimental setup is modeled using the finite-element code, LS-DYNA, in which a physics-based temperature- and strain rate-sensitive constitutive model for DH-36 steel, developed by Nemat-Nasser and Guo (2003b) and an experimentally supported temperature-, rate-, and pressure-sensitive constitutive model for polyurea, developed and incorporated into the computer code, LS-DYNA, by Amirkhizi et al. (2006), have been implemented. The transient response of the plates under impulsive pressure loads is studied, focusing on the effects of the relative position of polyurea with respect to the loading direction, the thickness of the polyurea layer, and the polyurea-steel interface bonding strength. The numerical simulations of the entire experiment support the experimentally observed results reported by Amini et al. (2010).