Direct Blast Research Articles

Forward scattering detection of a submerged moving target based on adaptive filtering technique.

Forward scattered waves are always overwhelmed by severely intense direct blasts when a submerged target crosses the source-receiver line. A processing scheme called direct blast suppression based on adaptive filtering (DBS-AF) is proposed to suppress such blasts. A verification experiment was conducted in a lake with a vertical hydrophone array and 10 kHz CW impulses. Processing results show that the direct blast is suppressed in a single channel, and an intruding target is identified by the lobes in the detection curve. The detection performance is improved by adopting a time-delay beam-former on the array as a pre-processing technique.

Changes in Diffusion Kurtosis Imaging and Magnetic Resonance Spectroscopy in a Direct Cranial Blast Traumatic Brain Injury (dc-bTBI) Model.

Explosive blast-related injuries are one of the hallmark injuries of veterans returning from recent wars, but the effects of a blast overpressure on the brain are poorly understood. In this study, we used in vivo diffusion kurtosis imaging (DKI) and proton magnetic resonance spectroscopy (MRS) to investigate tissue microstructure and metabolic changes in a novel, direct cranial blast traumatic brain injury (dc-bTBI) rat model. Imaging was performed on rats before injury and 1, 7, 14 and 28 days after blast exposure (~517 kPa peak overpressure to the dorsum of the head). No brain parenchyma abnormalities were visible on conventional T2-weighted MRI, but microstructural and metabolic changes were observed with DKI and proton MRS, respectively. Increased mean kurtosis, which peaked at 21 days post injury, was observed in the hippocampus and the internal capsule. Concomitant increases in myo-Inositol (Ins) and Taurine (Tau) were also observed in the hippocampus, while early changes at 1 day in the Glutamine (Gln) were observed in the internal capsule, all indicating glial abnormality in these regions. Neurofunctional testing on a separate but similarly treated group of rats showed early disturbances in vestibulomotor functions (days 1–14), which were associated with imaging changes in the internal capsule. Delayed impairments in spatial memory and in rapid learning, as assessed by Morris Water Maze paradigms (days 14–19), were associated with delayed changes in the hippocampus. Significant microglial activation and neurodegeneration were observed at 28 days in the hippocampus. Overall, our findings indicate delayed neurofunctional and pathological abnormalities following dc-bTBI that are silent on conventional T2-weighted imaging, but are detectable using DKI and proton MRS.

Vulnerability of simple braced steel building under extreme load

This paper studies the behaviour of steel building under extreme load. A 10-storey steel building with a variety of lateral bracing system for a column loss is first investigated using conventional alternate path approach. The numerical study shows that the simple braced steel frames are susceptible to progressive collapse due to a column loss, due to weak column-to-beam joints compared to moment resisting frames, which have higher redundancy to redistribute the damaged column load to all other floor level. The alternate path approach, which is a threat-independent methodology, is commonly used as a design guide for minimising the potential for progressive collapse. This method may not be always conservative in assessing the robustness of the structure, especially for building subjected to heavy blast loads and thus nonlinear direct blast analysis is often needed to investigate the building response under such extreme load. The same 10-storey steel frame response is investigated for a surface blast using ...

Interference Mitigation for Multistatic Active Sonar

Two methods for detecting and classifying mutual interference between sources in multistatic active sonar systems are developed and compared for frequency-modulated transmissions. Both methods compare the output of matched-filtered time-series data using two different waveform replicas: the intended transmit replica and a hypothesized interferer replica. The first method compares the absolute magnitudes of the two outputs, whereas the second method compares the local shape of the magnitude of the outputs to idealized replica correlations using an ${L}_{5}$ -norm. Simulated examples indicate that the two methods are both effective, but with different tradeoffs. The magnitude-based method often performs better when the interference is relatively strong, and the shape-based method often performs better when the interference is weaker, and thereby harder to detect. It is also shown that excising the detected interfering direct blast at the beamformer output level effectively reduces clutter on displays and removes false contacts due to the interferer. The approach also shows potential for improving multistatic detection across platforms.

Impact of strong direct blast on active sonar systems

Pulsed active sonar (PAS) and continuous active sonar (CAS) in the presence of a strong direct blast are studied for the Doppler-tolerant linear frequency modulation waveform. A comparative analysis is done between PAS and CAS based on the range-Doppler and range-compression images obtained. Furthermore, a generalized likelihood ratio–based criterion is developed for moving target detection. CAS is further studied with a Doppler-sensitive SHAPE waveform, and weighted range-Doppler processing for CAS-SHAPE system is introduced.

Forward scattering detection of a submerged object by a vertical hydrophone array.

When an object crosses a source-receiver line, the resulting weak acoustic field aberration is often overwhelmed by a strong direct blast. In this study, a lake experiment with a vertical receiver array spanning the water column was designed and conducted with a 10 kHz pulse. The study aimed to detect the aberration caused by forward scattering from an intercepting submerged object. Although such aberration could be directly observed, it varies by only 3 dB, at most, around the direct blast. Hence, the vertical hydrophone array was subjected to time-delay beamforming, and a principal component analysis was conducted on the stable portion of the beam output. The second principal component was extracted from the horizontally directed beam output waveform at the vertical receiver array. The invariant direct blast component was reduced after analysis, and the field aberration caused by forward scattering of the submerged object was amplified by up to 10 dB above the background acoustic field.

Experimental and Numerical Investigation of the Mechanism of Blast Wave Transmission Through a Surrogate Head

This work is to develop an experiment-validated numerical model to elucidate the wave transmission mechanisms through a surrogate head under blast loading. Repeated shock tube tests were conducted on a surrogate head, i.e., water-filled polycarbonate shell. Surface strain on the skull simulant and pressure inside the brain simulant were recorded at multiple locations. A numerical model was developed to capture the shock wave propagation within the shock tube and the fluid-structure interaction between the shock wave and the surrogate head. The obtained numerical results were compared with the experimental measurements. The experiment-validated numerical model was then used to further understand the wave transmission mechanisms from the blast to the surrogate head, including the flow field around the head, structural response of the skull simulant, and pressure distributions inside the brain simulant. Results demonstrated that intracranial pressure in the anterior part of the brain simulant was dominated by the direct blast wave propagation, while in the posterior part it was attributed to both direct blast wave propagation and skull flexure, which took effect at a later time. This study served as an exploration of the physics of blast-surrogate interaction and a precursor to a realistic head model.

Numerical Simulation on the Overturn Process of Towering Reinforced Concrete Chimney during Directional Demolition Blasting

On the basis of plastic-elastic mechanics and finite element method, one selected 150m high reinforced concrete chimney was taken as the target in this paper to analyze the mechanical condition of directional demolition blasting, the capsizing time, the internal force of support abutment and constitutive relation of the chimney during directional blasting. A finite element model of the towering reinforced concrete chimney was established through separated modeling method by finite element analysis software LS-DYNA of ANSYS. Results show that the constitutive relation given by this paper conforms to reality. The finite element model of the towering reinforced concrete chimney established by separated modeling method is reasonable. The real overturn process, capsizing location and capsizing length of towering reinforced concrete chimney during directional demolition blasting are agree with that of numerical simulation.

Numerical Simulation on the Overturn Process of Towering Reinforced Concrete Chimney during Directional Demolition Blasting

On the basis of plastic-elastic mechanics and finite element method, one selected 150m high reinforced concrete chimney was taken as the target in this paper to analyze the mechanical condition of directional demolition blasting, the capsizing time, the internal force of support abutment and constitutive relation of the chimney during directional blasting. A finite element model of the towering reinforced concrete chimney was established through separated modeling method by finite element analysis software LS-DYNA of ANSYS. Results show that the constitutive relation given by this paper conforms to reality. The finite element model of the towering reinforced concrete chimney established by separated modeling method is reasonable. The real overturn process, capsizing location and capsizing length of towering reinforced concrete chimney during directional demolition blasting are agree with that of numerical simulation.

Mutation analysis and prenatal diagnosis of FBN1 gene mutations for four patients with Marfan syndrome

To screen for mutations of fibrillin-1 (FBN1) gene in 4 patients with Marfan syndrome in order to provide prenatal diagnosis and genetic counseling. Potential mutations of the FBN1 gene in the probands were detected with PCR and DNA sequencing. Subsequently, genomic DNA was extracted from amniotic fluid sampled between 18 to 20 weeks gestation. The mutations were confirmed with denaturing high-performance liquid chromatography - robust microsatellite instability (DHPLC-MSI) analysis with maternal DNA as reference. The products were further analyzed by direct sequencing and BLAST search of NCBI database. An IVS46+1G>A substitution was identified in patient A at +1 position of intron 46 of the FBN1 gene. Two novel missense mutations were respectively discovered at positions +4453 of intron 35 in patient B (Cys1485Gly) and position +2585 of intron 21 in patient C (Cys862Tyr). In patient D, a novel deletion (c.3536 delA) was found at position +3536 of intron 28. In all of the 4 cases, the same mutations have been identified in the fetuses. FBN1 gene analysis can provide accurate diagnosis of Marfan syndrome, which can facilitate both prenatal diagnosis and genetic counseling.

Model Test and Numerical Simulation for Directional Pressure Relief Blasting

To study directional pressure relief blasting, cement mortar model tests are carried out. Protecting borehole wall, free-face wall and bottom wall are tested of the dynamic strain. Three-dimensional numerical simulation and numerical calculation of the tests are conducted by using LS-DYNA3D. The pressure values and test results of the protecting borehole wall, free-face wall and bottom wall with the same distance from the explosives are compared. Development and distribution of pressure regularity are analyzed; blast hole pressure relief effect of protecting borehole wall materials and bottom interval air column are explicated. The present results indicate that there is an obvious stress concentration phenomenon on the free-face wall, with an average pressure decrease rate of 26% from the free-face wall to the protecting borehole wall with the same distance to the explosive center, while the isolation materialPVCU plays a good directional protection. The pressure effect of the blast hole bottom air column on the blast hole is apparent. The simulation results are consistent with the experimental dates.

Computational modeling of human head under blast in confined and open spaces: primary blast injury

In this paper, a computational modeling for biomechanical analysis of primary blast injuries is presented. The responses of the brain in terms of mechanical parameters under different blast spaces including open, semi-confined, and confined environments are studied. In the study, the effect of direct and indirect blast waves from the neighboring walls in the confined environments will be taken into consideration. A 50th percentile finite element head model is exposed to blast waves of different intensities. In the open space, the head experiences a sudden intracranial pressure (ICP) change, which vanishes in a matter of a few milliseconds. The situation is similar in semi-confined space, but in the confined space, the reflections from the walls will create a number of subsequent peaks in ICP with a longer duration. The analysis procedure is based on a simultaneous interaction simulation of the deformable head and its components with the blast wave propagations. It is concluded that compared with the open and semi-confined space settings, the walls in the confined space scenario enhance the risk of primary blast injuries considerably because of indirect blast waves transferring a larger amount of damaging energy to the head.

Measurement and relationship between critical tube diameter and critical energy for direct blast initiation of gaseous detonations

For the explosion safety assessment in industrial setting, detonation dynamic parameters provide important information on the sensitivity and conditions whereby detonations can be favorably occurred. In this study, new measurement of the critical tube diameter and the critical energy for direct initiation of a detonation is reported for a number of hydrocarbon–oxygen mixtures. The simultaneous experimental measurement carried out in this work allows the investigation of the direct scaling between these two dynamic parameter quantities of gaseous detonations. Using the new set of data, this paper also assesses the validity of an existing semi-empirical initiation model, namely, the surface energy model by Lee, and a simplified work done model. Both phenomenological models provide a general relationship between the two dynamic detonation parameters and comparison shows a good agreement between the theoretical results and the experimental measurement. The scaling of critical tube diameter with detonation cell size in this study also confirms the results in the previous literature.

Risk assessment of structures subjected to blast

Attacking city centers with pack portable bombs has become one of the regular terrorist attacks around the world. In these situations, life losses and injuries can be caused from various sources such as direct blast effects, structural collapse, debris impact, fire, and smoke. Casualties could increase when indirect effects are combined with closed exits or timely evacuation. So, calculating the annual risk of the structural collapses resulting from extreme loading conditions is subjected to many efforts. In this paper, the annual risk of blast-induced progressive structural collapse is calculated. The blast fragility is also calculated by a simulation procedure which generate possible blast configuration, and finally kinematic plastic limit analysis is used to verify the structural stability under gravity loading. As a case study, the blast fragility and the annual risk of collapse of a four-storey steel building are calculated.

Construction of Customized Sub-Databases from NCBI-nr Database for Rapid Annotation of Huge Metagenomic Datasets Using a Combined BLAST and MEGAN Approach

We developed a fast method to construct local sub-databases from the NCBI-nr database for the quick similarity search and annotation of huge metagenomic datasets based on BLAST-MEGAN approach. A three-step sub-database annotation pipeline (SAP) was further proposed to conduct the annotation in a much more time-efficient way which required far less computational capacity than the direct NCBI-nr database BLAST-MEGAN approach. The 1st BLAST of SAP was conducted using the original metagenomic dataset against the constructed sub-database for a quick screening of candidate target sequences. Then, the candidate target sequences identified in the 1st BLAST were subjected to the 2nd BLAST against the whole NCBI-nr database. The BLAST results were finally annotated using MEGAN to filter out those mistakenly selected sequences in the 1st BLAST to guarantee the accuracy of the results. Based on the tests conducted in this study, SAP achieved a speedup of ∼150–385 times at the BLAST e-value of 1e–5, compared to the direct BLAST against NCBI-nr database. The annotation results of SAP are exactly in agreement with those of the direct NCBI-nr database BLAST-MEGAN approach, which is very time-consuming and computationally intensive. Selecting rigorous thresholds (e.g. e-value of 1e–10) would further accelerate SAP process. The SAP pipeline may also be coupled with novel similarity search tools (e.g. RAPsearch) other than BLAST to achieve even faster annotation of huge metagenomic datasets. Above all, this sub-database construction method and SAP pipeline provides a new time-efficient and convenient annotation similarity search strategy for laboratories without access to high performance computing facilities. SAP also offers a solution to high performance computing facilities for the processing of more similarity search tasks.

On the effect of steel columns cross sectional properties on the behaviours when subjected to blast loading

For buildings subjected to blast loading, structural failure can be categorized into local failure (direct blast effects) and progressive collapse (consequential effects). In direct blast effects, the intensive blast pressures create localized failure of structural elements such as exterior columns and walls. Columns, and their behaviour, play a key role in these situations. Therefore investigating the behaviour of columns under blast loading is very important to estimate the strength, safety and reliability of the whole structure. When a building is subjected to blast loading, it experiences huge loading pressures and undergoes great displacement and plastic behaviour. In order to study the behaviour of an element under blast loading, in addition to elastic properties of materials, plastic and elastic-plastic properties of materials and sections are needed. In this paper, using analytical studies and nonlinear time-history analysis by Ansys software, the effects of shape of column sections and boundary conditions, on behaviour and local failure of steel columns under blast load are studied. This study identifies the importance of elastic-plastic properties of sections and proposes criteria for choosing the best section and boundary conditions for columns to resist blast loading.

Dynamic response and robustness of tall buildings under blast loading

Recently, extensive research has been focused on the progressive collapse analysis of the multi-storey buildings. However, most of the research is based on the alternative path method (APM) with sudden removal of the columns, ignoring the duration of the blast load working on the structures. In this paper, a 3-D numerical model with the direct simulation of blast load is proposed to study the real behavior of a 20 storey tall building under the blast loading. A typical package bomb charge of 15kg was detonated on the 12th floor. The corresponding dynamic response of structure was studied in detail. The robustness of the building under blast load was assessed. Comparison between the proposed method and the APM was also made. It is found that, due to the uplift and downward pressure working on the slab, the column force under the direct blast simulation method is smaller than that of the alternative path method. The method to enhance the robustness of the buildings is also recommended.

Blasting Demolition Technology and Vibration Testing of 210m Reinforced Concrete Chimney

This paper describes the successful experience of the directional control blasting of 210m-high reinforced concrete chimney of Nanchang Power Plant in Jiangxi Province called as “First height in Asia”. It emphatically describes the pretreatment measures, blasting cut shape and size, blasting parameters, electronic digital detonator detonating network and blasting safety technology. And the blasting vibration was tested and analyzed, and this paper presents the method for opening the arch overlarge oriented window and comprehensive protection method for anti-flyrock splash, vibration reduction and dustfall. Especially, the electronic digital detonator was first applied in the blasting demolition of 210m-high structures, it improves the delay precision and also has a good anti-stray current effect to ensure that the blasting can be safely implemented in the power plant, and it has a good application prospect in the future large-scale and high level complex engineering blasting.

Blasting Demolition Technology and Vibration Monitoring of Two 90m-High Cooling Towers in Complex Environment

This paper describes the successful experience of the directional control blasting of two 90m-high reinforced concrete cooling towers of Hefei Power Plant in Anhui Province. The blasting is in the complex environment. It emphatically describes the pretreatment measures, blasting cut shape and size, blasting parameters, detonator detonating network and blasting safety technology of the directional window, oriented window and load reducing slot, and the blasting vibration was tested and analyzed, and this paper provides the protection method for opening the special-shape load reducing slot and dense mesh safety net cross-multilayer coverage. Especially, the blast holes for opening the special-shape load reducing slot and the herringbone column are centralized at the bottom and top, which not only reduces the drilling workload, but also reduces the maximum detonating explosive amount of single section, and also reduces the safety protection workload. It can be a reference for similar projects.

Demolition of a Complex Brick-Structure Chimney with a Height of 56 Meters without Recoil by Demolitional Blasting

A complex brick-structure chimney with a height of 56 meters was successfully demolished without recoil through directional blasting in complicated environment. Some effective measures that helped control the direction of collapse and avoid recoil were taken in the demolition of brick chimney. The calculation principle and method of blasting cut is elaborated. The blasting is satisfactory.