Experimental and numerical investigation of rectangular reinforced concrete columns under contact explosion effects
The response of reinforced concrete (RC) members subjected to contact explosion effects is more severe than the response to noncontact explosions due to local material failure. The shockwave reflection within the RC member causes severe local material damage. The resulting loss of concrete crosssection reduces the axial load and bending capacity of the RC member. It is hypothesized that the concrete loss from the sides can be prevented by increasing the aspect ratio of the crosssection. In a low aspect ratio RC column, the reflection is from three faces whereas in RC slabs and high aspect ratio columns the shockwave reflection from the backface only is significant. This study experimentally investigates the response of rectangular RC columns with varying widths of the crosssection, subjected to contact explosion effects. A range of aspect ratios was investigated to preclude the side face damage for a given depth of rectangular RC column. High fidelity numerical models were developed to predict the blastresponse and the residual axial capacity of the blastdamaged rectangular columns. The numerical models were validated, and the results show a good correlation with the experimental results. Using a rectangular RC column aspect ratio with a width that precludes the side face spall significantly improves the residual axial capacity of the blastdamaged columns. Furthermore, parametric analyses were performed to numerically investigate the influence of the width on the residual axial load carrying capacity of rectangular RC columns subjected to contact explosion effects of breachcharge mass required for the provided depth. An increase in the width of the column improved the damage resistance even though the rectangular column was breached around the point of detonation. Hence, increasing the width of the rectangular RC columns can be effectively used to mitigate contact explosion effects.
Real-time machine learning for operational safety of nonlinear processes via barrier-function based predictive control
This work proposes a real-time model predictive control (MPC) system using control Lyapunov–barrier functions (CLBF) and recurrent neural network (RNN) models to ensure simultaneous closed-loop stability and operational safety for a general class of nonlinear systems subject to time-varying disturbances. An RNN model is first developed for the nominal system (i.e., without disturbances) and incorporated in the designs of CLBF-based MPC and of CLBF-based economic MPC (EMPC) to provide state predictions for the optimization problems of MPCs. Subsequently, to improve the closed-loop performance in terms of operational safety and stability in the presence of disturbances, online learning of RNN models is incorporated within the real-time implementation of CLBF-MPC and of CLBF-EMPC to update the RNN models using the most recent process measurement data. The proposed adaptive machine-learning-based CLBF-MPC and CLBF-EMPC schemes are evaluated using a nonlinear chemical process example.
Coulomb explosion of CD 3 I induced by single photon deep inner-shell ionisation
L-shell ionisation and subsequent Coulomb explosion of fully deuterated methyl iodide, CD 3 I, irradiated with hard X-rays has been examined by a time-of-flight multi-ion coincidence technique. The core vacancies relax efficiently by Auger cascades, leading to charge states up to 16+. The dynamics of the Coulomb explosion process are investigated by calculating the ions’ flight times numerically based on a geometric model of the experimental apparatus, for comparison with the experimental data. A parametric model of the explosion, previously introduced for multi-photon induced Coulomb explosion, is applied in numerical simulations, giving good agreement with the experimental results for medium charge states. Deviations for higher charges suggest the need to include nuclear motion in a putatively more complete model. Detection efficiency corrections from the simulations are used to determine the true distributions of molecular charge states produced by initial L1, L2 and L3 ionisation.
Fly ash and zinc slag blended geopolymer: Immobilization of hazardous materials and development of paving blocks
The potential for practical application of fly ash, zinc slag and their blends for geopolymer synthesis at ambient temperature have been investigated in this paper. Fly ash is an alumino-silicate byproduct suitable for geopolymer reaction, but its low reactivity at ambient condition is the restriction of its bulk utilization. Above limitation can be overcome by blending with zinc slag (ZS). Additionally, ZS contains heavy and toxic metals (Pb, Zn, Cr, Cd, As), which can be stabilize in Al-Si based geopolymer network structure. Isothermal conduction calorimetry (ICC) is used to monitor the geopolymer reaction with time. Slag rich specimens are characterized with higher rate of reaction with augmented peak. The mineralogy and microstructure of the geopolymers have been examined through X-ray diffraction and scanning electron microscope. The detected chief reaction product is N-(C)-A-S-H and C-(N)-A-S-H¹1(where, N=Na₂O, C=CaO, A=Al₂O₃, S=SiO₂ and H=H₂O) type hydrated gel. Continual improvement of compressive strength of the geopolymers with increasing slag content is explained with higher degree of reaction, formation of more reaction products and development of compact microstructure. According to toxicity characteristic leaching procedure (TCLP), toxic metals leaching is within permissible limit. Paver blocks using 40−80 wt% ZS has been developed, which meets IS 15,658: 2006 standard and comply with US-EPA specification.
Gas transport across the low-permeability containment zone of an underground nuclear explosion
Understanding the nature of gas transport from an underground nuclear explosion (UNE) is required for evaluating the ability to detect and interpret either on-site or atmospheric signatures of noble gas radionuclides resulting from the event. We performed a pressure and chemical tracer monitoring experiment at the site of an underground nuclear test that occurred in a tunnel in Nevada to evaluate the possible modes of gas transport to the surface. The site represents a very well-contained, low gas-permeability end member for past UNEs at the Nevada National Security Site. However, there is very strong evidence that gases detected at the surface during a period of low atmospheric pressure resulted from fractures of extremely small aperture that are essentially invisible. Our analyses also suggest that gases would have easily migrated to the top of the high-permeability collapse zone following the detonation minimizing the final distance required for migration along these narrow fractures to the surface. This indicates that on-site detection of gases emanating from such low-permeability sites is feasible while standoff detection of atmospheric plumes may also be possible at local distances for sufficiently high fracture densities. Finally, our results show that gas leakage into the atmosphere also occurred directly from the tunnel portal and should be monitored in future tunnel gas sampling experiments for the purpose of better understanding relative contributions to detection of radioxenon releases via both fracture network and tunnel transport.
Suppression mechanism of Al dust explosion by melamine polyphosphate and melamine cyanurate
The suppression mechanism of melamine polyphosphate (MPP) and melamine cyanurate (MCA) for Al dust explosions is investigated experimentally and computationally. Results show that depending on the concentration of suppressants, the addition of MCA and MPP promotes or suppresses Al dust explosion. For high additive concentration, large agglomerated residues are generated, and condensed phase residues may contain Al particles, MCA or MPP. The chemical composition of condensed phase residues of Al/MCA mixture explosion is mainly Al 2 O 3 and the high boiling products of MEL decomposition (mainly C‒ and N‒containing species). The explosion residues of Al/MPP mixture are composed of Al 2 O 3 , high boiling products of MEL decomposition and condensed phosphates. To understand the reasons for pressure enhancement and explosion suppression, a kinetic model considering both gas and surface chemistry of Al particles combustion is developed. The simulations indicate that the high pressure rise is caused by the extra heat released from the exothermic reactions of suppressants and the increase of gas phase products. MPP and MCA can suppress surface reaction by decreasing Al(L) site fraction. Additionally, the vaporization rate of Al particles and the diffusion rate of oxidizers close to the droplet surface are reduced by MPP and MCA addition.
Effects of concentration and initial turbulence on the vented explosion characteristics of methane-air mixtures
The testing of vented explosion of methane-air mixtures was conducted in a custom-designed 4.5-m 3 steel chamber. Methane concentrations in the mixed gas varied between 7 and 13 vol% and the static hysteresis time was set as 0, 1, and 5 min to characterize strong, medium and weak turbulence levels. The effects of concentration and initial turbulence on pressure characteristics and flame development were investigated. It is found that the quasi-static pressure in the chamber during vented explosion can be divided into three stages: pressure release, Helmholtz oscillation, and acoustic oscillation. The Helmholtz oscillation at a frequency of about 20–40 Hz is produced after the peak pressure P 1 caused by the pressure release at all concentrations; however, the acoustic oscillation at a frequency of about 300 Hz only occurs after Helmholtz oscillation when the concentration is near the optimum. In the early stage of internal flame development, the cellular structure is generated due to hydrodynamic instability and diffusive-thermal instability, and the flame front is distorted owing to the instability caused by venting. Initial turbulence distorts the flame front, significantly increases the peak pressure, and stimulates the generation of acoustic oscillation at the upper and lower limits of concentration. Under the influence of initial high turbulence, the internal flame propagation distance has a power function relationship with time, and the turbulence acceleration factor and distance also show a power function relationship.
Experimental and numerical study of CFRP protective RC piers under contact explosion
In the wake of the event of September 2001, the increasing terrorist attacks have been a destabilizing threat around the world. Public infrastructures, such as tall buildings and traffic facilities, have become attractive bombing targets for terrorists. Crucial bridges subjected to great destruction from bomb attacks can contribute to casualties, property loss and interruption of the transportation system. Bridge piers are the main axial bearing components that are common in bridge construction, and it can readily suffer damage under blast loading. Therefore, it should be necessary to explore protective measures for reinforced concrete (RC) piers to resist blast loading. In this paper, carbon fibre reinforced polymer (CFRP) is chosen to protect RC piers under contact explosion. Five piers, consisting of two unprotected piers and three CFRP protective piers, were constructed and the explosion testing was conducted in the field. Additionally, finite element models of CFRP protective piers were built, considering the contact between concrete and CFRP as well as the anisotropy of CFRP composite material. The models were calculated using the Arbitrary Lagrange Euler (ALE) algorithm and validated by experimental acceleration as well as damage extent. Then, the damage development and CFRP protective effect for RC piers were further analysed. Finally, all specimens experienced local failure under contact explosion and the simulative models were proved accurate for depth analysis.
Risk assessment of gas explosion in coal mines based on fuzzy AHP and bayesian network
Gas explosion is one of the most deadly hazards in underground coal mining. Risk assessment has played an effective role in avoiding gas explosions and revising coal mine regulations. However, the traditional methods are deficient in quantitative evaluation, dynamic control and dealing with uncertainty. In this paper, a method of quantitative assessment the risk of gas explosion in underground coal mine using Bayesian network was proposed. A fuzzy analytic hierarchy process (FAHP) method based on subjective and objective information of experts was developed in the process of fuzzification. Through the Bayesian inference, the probability of occurrence of potential risk events and the probability distribution of risk factors can be calculated in real time according to on prior knowledge and evidence updating. Meanwhile, the most likely potential causes of accidents can be determined. A sensitivity analysis technique was utilized to investigate the contribution rate of each risk factor to a risk event, so as to determine the most critical risk factor. Taking Babao Coal Mine in China as the case, this study conducted a gas explosion risk assessment. The results show that the mothed of fuzzy AHP and Bayesian Network is feasible and applicable. It can be used as a decisionmaking tool to prevent coal mine gas explosions and provide decision makers with a technical guide for managing the coal mine gas explosion risk.
Minimum ignition temperature of carbonaceous dust clouds in air with CH4/H-2/CO below the gas lower explosion limit
GodbertGreenwald furnace was used to investigate the minimum ignition temperature of dust clouds (MITC) in air with the presence of flammable gas which is lower than its lower explosion limit (LEL). Three flammable gases (CH4, H2 and CO) and three carbonaceous dusts (anthracite coal, bituminous coal and sweet potato starch) were tested. Results showed that all flammable gases have distinct effects on the MITC of the dust samples and volatile matter content of dust plays an important role during the ignition process. Specifically, the MITC of anthracite coal dust decreased from 610 degrees C to 560 degrees C, 580 degrees C and 570 degrees C with 3% CH4, 3% CO and 2.5% H2, respectively. Moreover, a heterogeneous ignition mechanism model was proposed to verify the equally global ignition characteristic between hybrid anthracite coalCxHy mixture and bituminous coal. All three gases had an ignorable effect on the MITC of starch dust considering the experimental error. The presence of CO and H2 slightly promoted the ignition of bituminous coal dust, but the addition of CH4 showed a distinct concentration effect on the MITC of bituminous coal: the MITC decreased with 1% CH4 while increased with 2% and 3% CH4. This negativeeffect of flammable gases at such low concentrations on ignition temperature of bituminous coal dusts was found for the first time. Furthermore, the presence of the 2nd flammable gas had a smaller effect on the MITC of dust samples with a higher volatile content, resulted from the competition of heterogeneous and homogeneous ignition mechanisms.