Analytical study of local damage on concrete slab subjected to a contact explosion

Local damage on concrete slab subjected to a contact explosion includes explosive cratering on the front face and spalling or perforating on the back face. It is a subject that has been studied by many investigators for many years for many purposes. However, computational methods on explosive spallation or perforation are rare while they are significant for the design of warhead, the protective structure and engineering blasting. In this paper, the dynamic behavior of material was described by rigid-plastic model, and the material resistance of concrete slab subjected to contact explosions was derived by utilizing limit equilibrium theory. Combined with the initial and boundary conditions, the formulae of the threshold thickness have been derived, which can predict the categories of local damage on concrete slab under contact explosion loads. Besides, a non-dimensional impact factor was derived, which reflects the integrated nature of explosive sources and material resistance. Finally, analysis study of the results of numerical simulation and the derived equations proved the rationality of the proposed calculation methods

Rainfall Erosion Damage of Residual Soil Slope in Intermittently Frozen Area Based on Discrete Element Method

This study developed a discrete element simulation model based on the 2D particle flow code (PFC2D), of which the mesoscopic parameters were calibrated by the indoor experiments, to investigate the rainfall erosion damage of residual soil slope in the intermittently frozen area. It is to be noted that the runoff scouring action was simulated according to the equivalent rainfall method, the soil particles on the slope were given initial velocity, and the water absorption was considered by increasing the unit weight. The results indicated that the scouring action only caused superficial erosion with the main damage region at the foot, regardless of the FT effect. A splitting phenomenon was observed in the lower part of the steeper slope under the FT effect. Moreover, regardless of the FT effect, the gentler slope tended to incur spalling rather than a splitting phenomenon, where the soil particles slid along the structural plane with strong anti-scouring ability. Besides, the gentler slope maintained higher stability and shorter scouring time. Finally, the scouring velocity increased the erosion damage to a large extent

Seizure and Myelin Oligodendrocyte Glycoprotein Antibody-Associated Encephalomyelitis in a Retrospective Cohort of Chinese Patients

Background: Myelin oligodendrocyte glycoprotein (MOG) antibody associated encephalomyelitis is increasingly being considered a distinct disease entity, with seizures and encephalopathy commonly reported. We investigated the clinical features of MOG-IgG positive patients presenting with seizures and/or encephalopathy in a single cohort.Methods: Consecutive patients with suspected idiopathic inflammatory demyelinating diseases were recruited from a tertiary University hospital in Guangdong province, China. Subjects with MOG-IgG seropositivity were analyzed according to whether they presented with or without seizure and/or encephalopathy.Results: Overall, 58 subjects seropositive for MOG-IgG were analyzed, including 23 (40%) subjects presenting with seizures and/or encephalopathy. Meningeal irritation (P = 0.030), fever (P = 0.001), headache (P = 0.001), nausea, and vomiting (P = 0.004) were more commonly found in subjects who had seizures and/or encephalopathy, either at presentation or during the disease course. Nonetheless, there was less optic nerve (4/23, 17.4%, P = 0.003) and spinal cord (6/16, 37.5%, P = 0.037) involvement as compared to subjects without seizures or encephalopathy. Most MOG encephalomyelitis subjects had cortical/subcortical lesions: 65.2% (15/23) in the seizures and/or encephalopathy group and 50.0% (13/26) in the without seizures or encephalopathy group. Cerebrospinal fluid (CSF) leukocytes were elevated in both groups. Subgroup analysis showed that 30% (7/23) MOG-IgG positive subjects with seizures and/or encephalopathy had been misdiagnosed for central nervous system infection on the basis of meningoencephalitis symptoms and elevated CSF leukocytes (P = 0.002).Conclusions: Seizures and encephalopathy are not rare in MOG encephalomyelitis, and are commonly associated with cortical and subcortical brain lesions. MOG-encephalomyelitis often presents with clinical meningoencephalitis symptoms and abnormal CSF findings mimicking central nervous system infection in pediatric and young adult patients

Sodium Metasilicate Cemented Analogue Material and Its Mechanical Properties

Analogue material with appropriate properties is of great importance to the reliability of geomechanical model test, which is one of the mostly used approaches in field of geotechnical research. In this paper, a new type of analogue material is developed, which is composed of coarse aggregate (quartz sand and/or barite sand), fine aggregate (barite powder), and cementitious material (anhydrous sodium silicate). The components of each raw material are the key influencing factors, which significantly affect the physical and mechanical parameters of analogue materials. In order to establish the relationship between parameters and factors, the material properties including density, Young’s modulus, uniaxial compressive strength, and tensile strength were investigated by a series of orthogonal experiments with hundreds of samples. By orthogonal regression analysis, the regression equations of each parameter were obtained based on experimental data, which can predict the properties of the developed analogue materials according to proportions. The experiments and applications indicate that sodium metasilicate cemented analogue material is a type of low-strength and low-modulus material with designable density, which is insensitive to humidity and temperature and satisfies mechanical scaling criteria for weak rock or soft geological materials. Moreover, the developed material can be easily cast into structures with complex geometry shapes and simulate the deformation and failure processes of prototype rocks

Experimental and Numerical Investigation of Internal Explosion in an Earth-Covered Magazine

Earth-covered magazine has some characteristics that are safer than the above-ground magazine and are more economical than underground magazine. To investigate the pressure distribution and the structural failure under the internal explosion, the scaled tests of the earth-covered magazine were conducted under a 0.5 kg TNT explosive charge. The overpressure in the 0°, 90°, and 180° directions outside the structure and the debris distribution were obtained. The numerical simulations were constructed in LS-DYNA software to analyze the test results. The results show that the external overpressure has a directional characteristic that the maximum and minimum overpressure appear in 0° and 180° directions, respectively. In the double logarithmic coordinate system, the overpressure peaks in three directions are linearly related to the scaled distance. Most of the fragments in the 0° direction hit the ground within the front range of ±60°, and the further fragments (40 m or more) were confined to a limited sector within the front range of ±30°. The internal explosion numerical simulation shows that the concrete cracks first appeared at the roof and the ground, and then the damage occurred at the intersection of the walls, and then the damage occurred at each surface. The maximum debris velocity of the side and rear walls is lower than that of the front wall due to the limitation of the soil. The motion equations of the debris combined with numerical simulation can be adopted to predict the projection distance of fragments

Experimental and Numerical Investigation of Internal Explosion in an Earth-Covered Magazine

Earth-covered magazine has some characteristics that are safer than the above-ground magazine and are more economical than underground magazine. To investigate the pressure distribution and the structural failure under the internal explosion, the scaled tests of the earth-covered magazine were conducted under a 0.5 kg TNT explosive charge. The overpressure in the 0°, 90°, and 180° directions outside the structure and the debris distribution were obtained. The numerical simulations were constructed in LS-DYNA software to analyze the test results. The results show that the external overpressure has a directional characteristic that the maximum and minimum overpressure appear in 0° and 180° directions, respectively. In the double logarithmic coordinate system, the overpressure peaks in three directions are linearly related to the scaled distance. Most of the fragments in the 0° direction hit the ground within the front range of ±60°, and the further fragments (40 m or more) were confined to a limited sector within the front range of ±30°. The internal explosion numerical simulation shows that the concrete cracks first appeared at the roof and the ground, and then the damage occurred at the intersection of the walls, and then the damage occurred at each surface. The maximum debris velocity of the side and rear walls is lower than that of the front wall due to the limitation of the soil. The motion equations of the debris combined with numerical simulation can be adopted to predict the projection distance of fragments

Analysis of Traction and Unfolding Dynamics of Space-Symmetric Flexible Webs for UAV Interception and Capture

A new type of flexible web with a spatial symmetry structure is proposed to address the interception and acquisition of UAVs. It is different from the existing flexible web structure. According to the mechanical characteristics of the flexible web, the dynamic analysis model of the flexible web is established through theoretical deduction. Through finite element simulation calculation, the flexible webs of three different spatial symmetric structures are compared and analyzed. The internal force and air attitude of the three flexible webs are discussed. Among them, the new flexible web has a lag time of 0.162 s and a flight height of 11.624 m. The above simulation parameters are better than those of the other two symmetrical structures. It was proved that the new spatial symmetric flexible web has good traction and deployment performance. In addition, a ground verification test is designed and carried out. The web attitude and flight altitude parameters are compared with the simulation and test results. It is found that the simulation and experimental process of the new symmetric structure web are in good agreement, the synchronization of attitude change is good, and the flight altitude error of the two is controlled at about 5%. The feasibility and effectiveness of this method are proven and it can provide a reference for the research of flexible interception and acquisition of UAVs

Analysis of Traction and Unfolding Dynamics of Space-Symmetric Flexible Webs for UAV Interception and Capture

A new type of flexible web with a spatial symmetry structure is proposed to address the interception and acquisition of UAVs. It is different from the existing flexible web structure. According to the mechanical characteristics of the flexible web, the dynamic analysis model of the flexible web is established through theoretical deduction. Through finite element simulation calculation, the flexible webs of three different spatial symmetric structures are compared and analyzed. The internal force and air attitude of the three flexible webs are discussed. Among them, the new flexible web has a lag time of 0.162 s and a flight height of 11.624 m. The above simulation parameters are better than those of the other two symmetrical structures. It was proved that the new spatial symmetric flexible web has good traction and deployment performance. In addition, a ground verification test is designed and carried out. The web attitude and flight altitude parameters are compared with the simulation and test results. It is found that the simulation and experimental process of the new symmetric structure web are in good agreement, the synchronization of attitude change is good, and the flight altitude error of the two is controlled at about 5%. The feasibility and effectiveness of this method are proven and it can provide a reference for the research of flexible interception and acquisition of UAVs