Foam Barrier Research Articles

Suppression effects of energy-absorbing materials on natural gas explosion in utility tunnels

The energy-absorbing material of metal foam have enormous potential in mitigating the consequences of natural gas explosion disaster in urban utility tunnels. When double-layer metal foam with different pore structures of first larger pores and then smaller pores (LP-SP model), the suppression efficiency of explosion overpressure can reach more than 60% and is 2–3 times that of first smaller pores and then larger pores (SP-LP model), and the error between that and that of the same thickness all with smaller pore structure is only 0.86%. Similarly, the metal foams with the LP-SP model can block the explosion flame propagation chain entirely, while reversing the combination order weakens the suppression effect on the explosion flame. Two suppression mechanisms of double-layer metal foam, including the Sudden Shrinkage Effect (SSE) of the LP-SP model and the Amplification Effect (AE) of the SP-LP model. The metal foam barrier device based on SSE is designed for utility tunnels, which can take effect within 0.1 s under electromagnetic force and gravity. This study can provide scientific theoretical support for designing gas explosion suppression measures in utility tunnels.

Cellulosic biocomposite foam papers impregnated by crosslinked starch/poly (vinyl alcohol) biopolymers

Bio-based materials offer tremendous contributions by replacing conventional fossil-based products for a more sustainable society. The aim of the current study was to study the effect of crosslinked starch (CST) and poly (vinyl alcohol) (PVA) on the properties of cellulose foam papers prepared by compression molding. Several experimental techniques were applied to characterize prepared foam materials, including SEM, contact angle, thermogravimetric, mechanical, and barrier analysis. The chemical structure of the foam papers were analyzed using FTIR and XRD spectroscopy. The crystallinity of the foam papers increased from 75.8% for cellulose foam papers to 79.3% for CST/PVA reinforced cellulose foam papers. The tensile test results indicated that the addition of CST/PVA improved the mechanical properties of the foam papers. The tensile strength increased from 0.9 MPa for neat cellulose foam to 9.9 MPa for the CST/PVA reinforced cellulose foam papers. Therefore, the materials developed in this work can be a viable ecological alternative to replace the non-biodegradable polystyrene foam trays used in single-used food packaging containers.

Neither Skin Sutures nor Foam Dressing Use Affect Tracheostomy Complication Rates

BackgroundTracheostomy is commonly used for managing the airway of trauma patients. Complications are common and result in increased length of stays and treatment cost. The aim of this study is to evaluate whether the utilization of skin sutures or foam barrier dressings affect tracheostomy complication rates. Materials and methodsThis is a single-center retrospective review of patients who underwent a tracheostomy by the trauma service between January 2014 and December 2017. Collected variables included demographics, patient history, treatment variables, complications, and outcomes. Univariate and multivariate analyses were constructed to identify significant predictors for the development of complications. ResultsA total of 268 patients were included. The median age was 43.5 y, 221 (82.5%) patients were men, and the median BMI was 28 (IQR 24.6, 32.2). Most (87.3%) of the procedures were performed in the operating room and 82.5% were open. Skin sutures were used in 46.3% and 53.4% had a foam barrier dressing placed. Current smoking [OR 8.1 (95% CI 1.5, 43.6)] and BMI [OR 1.1 (95% CI 1.03, 1.2)] significantly increased the risk of developing pressure necrosis. Use of sutures or foam dressings was not associated with pressure necrosis, bleeding, or surgical site infection. There were no unexpected tracheostomy decannulations regardless of the use of skin sutures. ConclusionsSuturing the tracheostomy or applying a foam barrier dressing was not associated with overall complications or decannulation rates. Based on our data, we suggest that skin sutures may be safely abandoned.

A full experimental and numerical modelling of the practicability of thin foam barrier as vibration reduction measure

This paper presents the performance of geofoam-filled trenches in mitigating of ground vibration transmissions by the means of a full experimental study. The results are interpreted in the frequency domain. Fully automated 2D and 3D numerical models are applied to evaluate the screening effectiveness of geofoam-filled trenches in the active and passive schemes. Experimental results are in good agreement with the prediction of numerical modelling. The validated model is used to investigate the influence of geometrical and dimensional features on the trench. In addition, three different systems including single, double and triangle wall obstacles are selected for analysis, and the results are compared for various situations. The parametric study is based on complete automation of the model through coupling finite element analysis software (Plaxis) and Python programming language to control input, change the parameters, as well as to produce output and calculate the efficiency of the barrier. The results show that the depth and the width of approximately 1λr and 0.2λr, respectively are enough to reach the acceptable amount of efficiency for the active isolation for all three systems. For the passive scheme, the role of depth can be ignored for the single and double wall barriers, while depth plays a significant role for the triangle wall system.

Shock Loading of Closed Cell Aluminum Foams in the Presence of an Air Cavity

It is important to protect assets located within cavities vulnerable to incident shock waves generated by explosions. The aim of the present work is to explore if closed cell aluminum foams can mediate and attenuate incident shocks experienced by cavities. A small cavity of 9 mm diameter and 2 mm length was created within the steel end-wall of a shock tube and exposed to shocks, directly or after isolating by aluminum foam liners. Shock waves with incident pressure of 9–10 bar travelling at a velocity of 1000–1050 m/s were generated in the shock tube. Compared to the no-foam condition, the pressure induced in the cavity was either equal or lower, depending on whether the foam density was low (0.28 g/cc) or high (0.31 to 0.49 g/cc), respectively. Moreover, the rate of pressure rise, which was very high without and with the low density foam barrier, reduced substantially with increasing foam density. Foams deformed plastically under shock loading, with the extent of deformation decreasing with increasing foam density. Some interesting responses such as perforation of cell walls in the front side and densification in the far side of the foam were observed by a combination of scanning electron microscopy and X-ray microscopy. The present work conclusively shows that shocks in cavities within rigid walls can be attenuated by using foam liners of sufficiently high densities, which resist densification and extrusion into the cavities. Even such relatively high-density foams would be much lighter than fully dense materials capable of protecting cavities from shocks.

Pressure Injuries of the Nose and Columella in Preterm Neonates Receiving Noninvasive Ventilation via a Specialized Nasal Cannula: A Retrospective Comparison Cohort Study.

The aims of this study were to measure the incidence and severity of nasal septum injury in premature infants receiving continuous positive airway pressure (CPAP) via a noninvasive thin-walled cannula, and to evaluate the effect of a polyvinyl chloride foam barrier dressing in reducing these injuries. Retrospective chart review, comparison cohort study. The sample comprised 235 neonates with a gestational age of 28 weeks or younger. Their mean gestational age was 26 weeks (range 22-28 weeks) and mean birth weight was 840 g (range 430-1320 g). The study setting was a level 4, regional neonatal intensive care unit housed in a 200-bed freestanding children's hospital located in the Northeastern United States. Data were collected during 3 periods. During all 3 data collection periods, we used a soft, thin-walled nasal cannula, with a relatively short, binasal prong interphase and small diameter tubing connected to a ventilator circuit capable of transmitting positive airway pressure in neonates. During data collection periods 1 and 3, we used a polyvinyl foam barrier dressing as a preventive intervention against nasal skin damage; specifically, we placed a precut barrier on the prongs to protect the nasal skin. One side of the barrier foam has an adhesive surface, which was placed against the prongs. Study period 2 differed; during this period neonates were treated with the nasal cannula without the foam barrier based on manufacturer experience suggesting the foam barrier is not needed for prevention of skin damage. Pressure injuries (PIs) that occurred during each study period were staged according to National Pressure Ulcer Advisory Panel definitions. Eighty neonates were evaluated during study period 1 (thin-walled nasal cannula plus foam barrier). We evaluated 27 neonates during period 2 (thin-walled nasal cannula and no foam barrier) and 128 were evaluated during study period 3 (thin-walled nasal cannula plus foam barrier). Six neonates (7%) developed PIs during period 1, and 2 (1.5%) developed during study period 3. All were stage 1 and 2 PIs, no full-thickness injuries, also referred to as columella necrosis developed during use of the thin-walled nasal cannula in combination with the foam barrier dressings. In contrast, 13 PIs (48%) of neonates managed during data collection period 2 (thin-walled nasal cannula with no foam barrier) developed PI, and 40% experienced stage 3 PI or columella necrosis. This difference reflects a 6-fold increase in nasal injury occurred when nasal continuous positive airway pressure (NCPAP) was administered without use of the protective barrier dressing. We found clinically relevant difference in the occurrences of nasal PI in neonates managed with NCPAP; occurrences of stage 3 PI were 6-fold higher when a thin-walled cannula was used without a protective foam barrier dressing.

Dynamics of a spherical explosion in aqueous foam taking into account heat-exchange and dissipative processes

Numerical study of the features of spherical explosion propagation process in a cylindrical pipe surrounded by an inner layer of aqueous foam with liquid volume fraction α10 = 0.2 has been carried out. The solution method is based on a two-phase model of gas-liquid mixture under conditions of single-pressure, two-temperature, two-velocity approximations and is implemented using the twoPhaseEulerFoam solver of the OpenFOAM software. In order to test the proposed model, a comparison was made of the calculations and experimental data on a spherical explosion in aqueous foam with liquid volume fraction α10 = 0.0083. When solving the main task, the efficiency of the considered foam barrier is shown in a comparative analysis with the solution obtained in the absence of a foam layer.

Wave dynamics and vortex formation under the impact of a spherical impulse on the boundary between gas and aqueous foam

The process of interaction of air shock-wave pulse and protective aqueous foam barrier in two-dimensional axisymmetric formulation using two-phase model of gas-liquid mixture including the laws of conservation of mass, momentum and energy for each phase is numerically investigated. The numerical implementation of the model is carried out using the twoPhaseEulerFoam solver of the OpenFOAM package. The results are presented in the form of spatial distributions of pressure fields, velocities and streamlines. The causes and dynamics of toroidal vortices formation in gas are investigated.

Shock waves dynamics and evolution of vortex formation during the interaction of spherical air pulse with aqueous foam layer

The numerical study of the powerful air spherical shock-wave pulse interaction with the protective aqueous foam barrier with the initial liquid volume fraction of 0.2 is carried out. The foam layer thickness is selected to satisfy the condition of the non-reflection of compression wave from the foam external boundary at the considered time intervals. In studying the wave flows dynamics, we used the assumption of the foam structure destruction into the microdrops suspension behind the strong shock wave front. The two-phase medium is described on the basis of the gas-droplet mixture model, which includes the laws of conservation of mass, momentum and energy for each phase in accordance with the single-pressure, two-speed, two-temperature approximations in a two-dimensional axisymmetric formulation. The Schiller–Naumann model is used for taking into account the interfacial drag forces. The contact heat transfer influence at the interface between the phases is taken into account by the Ranz–Marshall model. To describe the properties of air and water, the Peng–Robinson and perfect fluid equations of state are used. The numerical implementation of the model is carried out using the OpenFOAM open-source software with the two-step PIMPLE algorithm. The numerical study results are presented as spatial distributions of pressure fields, velocities and streamlines. The significant attenuation of the spherical shock wave intensity during its interaction with the aqueous foam layer has been established. The causes and dynamics of the toroidal vortices series formation in the gas region behind the shock front are investigated. The results reliability is confirmed by comparison with the solutions of the similar problem, found by another numerical method.

Modification of Vapor Phase Concentrations in MoS2 Growth Using a NiO Foam Barrier.

Single-layer molybdenum disulfide (MoS2) has attracted significant attention due to its electronic and physical properties, with much effort invested toward obtaining large-area high-quality monolayer MoS2 films. In this work, we demonstrate a reactive-barrier-based approach to achieve growth of highly homogeneous single-layer MoS2 on sapphire by the use of a nickel oxide foam barrier during chemical vapor deposition. Due to the reactivity of the NiO barrier with MoO3, the concentration of precursors reaching the substrate and thus nucleation density is effectively reduced, allowing grain sizes of up to 170 μm and continuous monolayers on the centimeter length scale being obtained. The quality of the monolayer is further revealed by angle-resolved photoemission spectroscopy measurement by observation of a very well resolved electronic band structure and spin-orbit splitting of the bands at room temperature with only two major domain orientations, indicating the successful growth of a highly crystalline and well-oriented MoS2 monolayer.

Mitigation of explosions of hydrogen–air mixtures using bulk materials and aqueous foam

The objective of this work is to determine experimentally the effectiveness of protective barriers under conditions when blast waves are generated during premixed hydrogen– air combustion in various regimes. Experiments are conducted in a vertical tube having a diameter of 54 mm and a length of up to 2 m. Blast loads are produced by acceleration of premixed hydrogen–air flames in the tube with ring obstacles. Comparative tests are performed between protection barriers made of bulk materials with different densities and aqueous foams with different expansion ratios. It is demonstrated that the degree of blast load attenuation by an aqueous foam barrier increases with decreasing molecular weight of the filling gas and increasing density (decreasing expansion ratio) of the foam. An Aerosil barrier three times thicker than a titanium-dioxide one is found to have a similar attenuating effect on blast action. However, the mass per unit area of an Aerosil barrier is lower than titanium dioxide by a factor of 6 and is comparable to foam. The observed dependence of blast load attenuation on parameters of bulk materials and aqueous foams must be taken into account in systems designed to mitigate the consequences of accidental hydrogen release and combustion.

Attenuation of strong external blast by foam barriers

The mitigation of externally generated strong blast waves by an aqueous foam barrier of varying configurations within fixed distance between the explosion origin and the object to be protected is investigated and quantified both experimentally and numerically. The blast waves of shock Mach number 4.8 at 190 mm from the explosion plane are generated using exploding wire technique. The initially cylindrical blast waves are transformed into a plane blast wave in a specially constructed test unit in which the experiments are performed. The shock waves emanating from the foam barrier are captured using shadowgraph technique. A simple numerical model treating the foam by a pseudo-gas approach is used in interpreting and re-constructing the experimental results. The additional contribution of the impedance mismatch factor is analysed with the aid of numerical simulation and exploited for achieving greater blast wave pressure reduction.

Mitigation of exploding-wire-generated blast-waves by aqueous foam

In this work, we implement an exploding wire technique to generate small-scale cylindrical blast waves in aqueous foam. The exploding wire system offers an easy to operate and effective tool for studying blast-wave/foam interaction related phenomena in real explosion scenarios. The mitigation of blast waves as a function of the thickness of the foam barrier is discussed and quantified. A fluid mixture pseudo-gas based numerical approach with the aid of the point explosion theory is used to separate the mitigation mechanisms into the near- and the far-field related groups and to analyze the contribution of each group to the overall losses of the blast wave energy.

Analysis of shock-wave propagation in aqueous foams using shock tube experiments

This paper reports experimental results of planar shock waves interacting with aqueous foams in a horizontal conventional shock tube. Four incident shock wave Mach numbers are considered, ranging from 1.07 to 1.8, with two different foam columns of one meter thickness and expansion ratios of 30 and 80. High-speed flow visualizations are used along with pressure measurements to analyse the main physical mechanisms that govern shock wave mitigation in foams. During the shock/foam interaction, a precursor leading pressure jump was identified as the trace of the liquid film destruction stage in the foam fragmentation process. The corresponding pressure threshold is found to be invariant for a given foam. Regarding the mitigation effect, the results show that the speed of the shock is drastically reduced and that wetter is the foam, slower are the transmitted waves. The presence of the foam barrier attenuates the induced pressure impulse behind the transmitted shock, while the driest foam appears to be more effective, as it limits the pressure induced by the reflected shock off the foam front. Finally, it was found that the pressure histories in the two-phase gas-liquid mixture are different from those previously obtained within a cloud of droplets. The observed behavior is attributed to the process of foam fragmentation and to the modification of the flow topology past the shock. These physical phenomena occurring during the shock/foam interaction should be properly accounted for when elaborating new physical models.

地铁运行时连续屏障隔振效果数值分析

选取武汉地铁2号线和4号线某区间四孔交叠隧道为研究对象，运用ANSYS 14.0有限元软件建立了土体–隧道–屏障的三维有限元模型，分析四孔交叠隧道地铁运行时连续屏障的隔振效果，以及连续屏障隔振效果与屏障宽度，屏障深度和屏障刚度的关系。分析结果表明：设置连续屏障时，屏障前存在一个振动放大区域；屏障宽度不同，隔振效果也不同，宽度增加，隔振效果增强；屏障深度增加，隔振效果越明显，但当屏障深度超过振源深度时，屏障深度增加，隔振效果不明显；空沟隔振效果最好，其次为泡沫阻隔板，混凝土地下连续墙。 3D finite element model of soil-tunnel-barrier was established by ANSYS 14.0 under the back-ground of certain four-holes overlapping multi-tunnels of Wuhan metro line 2 and line 4. The iso-lation effect of continuous barrier when subway operates; and the relationship between isolation effect and width of barrier, depth of barrier, as well as stiffness of barrier were analyzed. The results showed that an enlarged vibration region existed in front of barrier when continuous barrier was set; the barrier width was different, and the vibration isolation effect was also different; the isolation effect was enhanced if the width of barrier increased; the isolation effect was obvious if the depth of barrier increased, but the isolation effect was not obvious with increasing depth of barrier when barrier depth was deeper than vibration sources; the isolation effect of open trench was the best, the second was foam barrier plate, and the last was concrete underground continuous wall.

Thermal performance of concrete-based roofs in tropical climate

Abstract In this work, an analytical Complex Fast Fourier Transform (CFFT) method is used and modified to predict the transient roof temperature and transmitted heat flux through the multilayer roofs of naturally ventilated rooms. A field experiment is carried out on two full-scale roofs to validate the CFFT model. The mean bias error (MBE) and cumulative variation of root mean square error (CVRMBE) in the ceiling temperature prediction using CFFT model are found less than 4% during both sunny and rainy days. After validation, a parameter study is conducted to investigate the impacts of rooftop surface solar reflectivity (from 0.1 to 0.9) and thermal resistance (from 0.1 to 2.5 m 2 K/W) on the thermal performance of two types of concrete-based roofs, namely the unventilated and ventilated roofs. Compared to the roofs with solar reflectivity of 0.1, increasing the solar reflectivity by 0.1 reduces the daily heat gain by 11% in both the unventilated and ventilated roofs during a typical weather day in Singapore. Compared with the unventilated roofs, the individual uses of roof ventilation and 2.5-cm expanded polystyrene (EPS) foam insulation reduce the daily roof heat gain by 42% and 68% respectively, and the daily roof heat gain reductions increase to 73% and 84% in the ventilated roofs incorporated with 2.5-cm EPS foam and radiant barrier respectively.

Features of propagation of shock waves in aqueous foams with an inhomogeneous density

Numerical investigations and comparison with experimental data of the shock wave interaction with aqueous foam barrier are conducted, taking into account the change of the foamy veil density on time. The efficiency of damping properties of foam barriers depends on water content is evaluated.

Blast Wave Mitigation by a Particulate Foam Barrier

Blast waves mitigate in foam due to various mechanisms, whose contribution to the final result is not fully understood yet. Actually, blast waves can destroy the foam barrier that is usually prone to decay and thus subsides with time. Fortunately, different time scales allow separating between these processes. The foam shattering, for example, could be completed within several milliseconds, while the foam decay lasts minutes and even hours. Recently, an increasing interest in this area has emerged, because particle-laden foams are much more stable and thus, could be applied for blast wave protection. To explore the full advantage of these new foams, the relationship between the micro-properties of the foam structure and the blast wave mitigation has to be clarified. In order to specify this relationship, little has been done. Information available in the literature on this subject clearly shows that during the test, the foam structure could be changed in a wide range, which is not usually controlled. This complicates the analysis of the occurring processes and ensures that the new factor involved in the studied problem has to be tested one by one, after the result of the previous step is well understood. To follow this strategy, this study continues our previous investigation (Britan et al in Colloid Surf A Physicochem Eng Aspects 309:137–150, 2007; Colloid Surf A Physicochem Eng Aspects 344:15–23, 2009; 2011), while mainly focusing on a single new factor, namely blast-shaped profile. To separate out the effect of the foam decay, which was discussed elsewhere (Britan et al in 2011), a special effort has been spent to ensure that the tested foam is homogeneous over its height. To exclude the bubble shattering, preference was given to weak impact conditions (Mach number of the shock generated inside the shock tube was about MS = 1.05). Under these circumstances, the blast wave mitigation inside the tested foam barrier solely depended on the concentration of the solid additives.

Shock wave propagation through wet particulate foam

Among the materials, which are capable of dissipating or absorbing the blast energy, aqueous foams is a good solution, when the place and the time of the blast are known in advance. If the height and the density of foam barrier are sufficient, the blast energy transmitted to nearby objects and personnel could be reduced to harmless levels. Unfortunately, a relationship between these two parameters (height and density) and the optimal protection effect is not specified yet. The reason is that the mechanisms responsible for blast attenuation in foam are interrelated and the contribution of each mechanism is not clear. Actually blast waves can destroy the foam barrier, which in turn is unstable and sensitive to the pre-blast decay. Little has been done even to evaluate the conditions when these mechanisms become important or/and to estimate their consequences. Fortunately, since the foam shattering occurs within milliseconds, while the pre-blast decay occurs in the order of minutes and even hours, these two processes could be treated independently, assuming that the protective action depends on: (a) The shock wave conditions: intensity, profile and duration of the pressure pulse. (b) The foam conditions: formulation, preparation method and the aging time, Δ t, before the blast exposure. Following our strategy to simplify the problem we recently studied the mitigation of weak shock waves having a blast shaped pressure profile [5]. Low intensity and short duration of the impact as well as the freshly prepared foam samples that were used in this study precluded the bubble shattering and/or foam non-homogeneous caused by the decay. In the present study, which is a continuation of previous tests [3–5] we have focused on particles-related phenomena, which modify the foam stability and thus may cause indirect effect on the propagation history of the shock wave. To separate these factors, we initially have put our concern on the free decay of particulate foams and thereafter the shock wave mitigation. In both cases, as the main parameters controlling the problem, we changed the aging time before the impact, Δ t i , and the particles mass fraction or loading factor, n 0.

Mitigation of Ammonia and Hydrogen Sulfide Emissions by Stable Aqueous Foam-Microbial Media

Stable aqueous foam-microbial media consisting of protein-based foams and odor-degrading bacteria were developed to control the emissions of odorous compounds. The optimum foam formulation was determined based on foam characteristics including 50% drainage time, foam lifetime, and foam expansion ratio. When only the aqueous foam was applied onto the surface of a test odor source (i.e., swine manure), ammonia emission was completely suppressed for about 177, 225, 265, 297, and 471 min when the height of foam barrier was 2.5, 5, 10, 15, and 30 cm, respectively. According to the increasing foam height, ammonia emission rates after breakthrough points decreased to 0.16, 0.13, 0.09, 0.07, and 0.02 mg/m3/min, and thus volatilized ammonia concentrations decreased significantly after 600 min. Hydrogen sulfide was similarly suppressed. Ammonia emission was better controlled by incorporating odor-degrading bacteria into the aqueous foam. The odor suppression capacity of the 5-cm foam barrier with microbes was more than eight times greater than that of the barrier only and was similar to that of 30-cm foam barrier without microbes after 1440 min. A significant amount of dinitrogen gas was evolved by the foam-microbial media, indicating a successful biological transformation of ammonia.