查看更多>>摘要：The coupled acoustic-structural analysis is an efficient and practical approach to underwater explosion (UNDEX) resistance evaluation of various underwater structures, including dams. It features its simple manner of implementing UNDEX shock loadings on structures in a direct way without in detail considering the detonation physics and shock wave propagation processes. The loading implementation is thus believed to be the most critical step in determining the reliability of coupled acoustic-structural analyses of structures in UNDEX events. The present paper aims to clarify two important loading issues frequently confronting the coupled acoustic-structural analysis of UNDEX responses of dams, i.e. the reservoir water thickness and the rise time in a typical UNDEX loading pulse. The ABAQUS code is used for the present numerical imple-mentation. The centrifuge-based physical UNDEX test on a gravity dam performed by Wang (2020) is numerically simulated with the coupled acoustic-structural analysis strategy. The simulation results are found to be in reasonable agreement with the corresponding test ones under the planar-wave assumption for the shock loading implementation. The water thickness is found to have little effect on the simulation results. This validates the reliability of the present simu-lation strategy and indicates the feasibility of using a relatively thin water domain with the planar-wave assumption in UNDEX analyses of gravity dams. However, it is indicated that the predicted response of the dam is significantly stronger than the measured one when the spherical -wave assumption is made with the total wave formulation. This is due to the insufficient water thickness modeled that leads to wave reflection at the fluid boundaries. After that, a parameter analysis is carried out concerning the rise time period in the loading pulse. The comparison results show that the effect of the rising duration on the UNDEX response of the dam is limited. It is thus suggested that a rise time period of around 30-50 mu s should be reasonable in most UNDEX resistance evaluation scenarios for general dams. The current findings should be of interest to practitioners who are engaged in the UNDEX resistance evaluation of dams.
查看更多>>摘要：Understanding historical accidents are essential for accident prevention. This study analysed industrial accidents' characteristics and the domino effect of 478 major industrial accidents in China from 2000 to 2020, including time, location, accident levels and types, hazardous sub-stances involved, working situations, and accident causes. Industrial accidents are mainly distributed in the eastern coastal industrial provinces, and concentrated in March, April, July and August, more likely to occur at 9:00-11:00 and 15:00-16:00. More than 80 % of industrial ac-cidents occurred during normal operations and maintenance & overhaul work. 41.6 % were explosions, and 32.4 % were fires. Industrial accidents mainly involved flammable liquids and gases, and 49 % were caused by violations or improper operation. The primary events of in-dustrial domino accidents were mainly explosions. The most frequent final domino sequences were explosion-* fire (23.7 %), fire-* explosion (15.3 %) and leakage-* explosion (15.3 %). The ratio between first-level and second-level domino effect sequences was 2.5.
查看更多>>摘要：The key components in combustion chamber of high power density diesel engines are apt to be damaged rapidly under abnormal combustion. To investigate the surface damage behavior and evolution mechanism of vermicular graphite cast iron in unsteady combustion, a self-developed plasma thermal shock test method was adopted. And the effect of the single-pulsing duration (0.2, 0.5, 5, and 50 s) of combustion on reciprocating thermal shock characteristics was mainly studied. Results showed that as the sample with the longest loading duration (50 s) exhibited the highest mass gain rate (0.05 mg/s), thickness growth rate (0.096 mu m/s), roughness (1.889 mu m), and hardness (515 HV). The cumulative thickening and spalling of the oxide layer during the plasma impact is the main cause of the changes in ablation rate and surface roughness. And the bainite phase transformation in the heat affected zone increased the hardness of the material.
Korkmaz, Hasan HusnuDere, YunusOzkilic, Yasin OnuralpBozkurt, Mehmet Bakir...
21页
查看更多>>摘要：In January 2017, collapses of the numerous roofs were reported due to excessive snowfall in many provinces of Turkey. In this study, the reasons behind the collapses of the steel roofs of 19 factory buildings were investigated. The steel roofs supported by the precast reinforced concrete columns indicated a similar collapse pattern to each other under the unexpected heavy snow loading. The failure mechanisms of the roofs under the snow loading were simulated numerically. Nonlinear finite element models of a typical industrial building were developed and analyzed under an incremental vertical loading that is identical to snow loading. As a result of the analysis, the vertical load carrying capacity of the roof system and the snow load level causing the collapse of roof were determined. The resulting snow load was compared with the snow load values provided by the code specifications. In addition, the collapse mechanism of the steel roof system was analytically determined and compared with the collapse modes observed in the field and the causes of the failure were evaluated. The failure mechanism and the buckling modes obtained from analyses were found very similar to those observed during the site inspections. The main reasons of the roof failures may be attributed to excessive amount of snow caused by climate change and discrepancy of designed project and as-built project due to lack of building inspection control during the construction of the buildings.
查看更多>>摘要：In this paper, an accurate prediction model, which screened from 8 machine learning-based models (LR, ANN, DT, SVC, RF, AdaBoost, GBDT, XGBoost), is established for identifying the failure mode of flat slabs. A database contains 610 experimental data is collected. The hyper -parameters are determined through grid search method with 10-fold cross validation, and pre-cision, recall, F1 score and accuracy are utilized for appraising the prediction of each model. After comparison with other 7 machine learning-based models and 3 empirical models, XGBoost is selected as the best model, in which the precision, recall, F1 score and accuracy of which are 97.30%, 94.74%, 96.00% and 99.02%, respectively. The prediction of XGBoost is explained by SHAP, the results including global and individual interpretations and the feature dependency relationship between input variables. According to these results, the relationship between failure mode of flat slabs and influence factors is exhibited through another perspective.
查看更多>>摘要：Type 316L stainless steel (SS) reveals its superior corrosion resistance against uniform and localized corrosion. But, it might be prone to intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC) due to detrimental Cr-rich carbides formed along the grain boundaries. The present investigation was aimed to study the sensitization behavior and Charpy impact property of type 316L SS experienced isothermally aging at 650, 750 and 850 degrees C for 2 h to compare with type 316 SS exposed to the actual service at temperature between 800 and 900 degrees C for nearly 20 years. The results indicated that the degree of sensitization (DOS) values of below 0.5 % were obtained for type 316L SS, whereas type 316 SS revealed its DOS value of around 48 %. The presence of sigma-phase transformed from delta-ferrite was a predominant factor to lower the Charpy impact energy of type 316L SS. The grain boundary Cr-rich carbide network played a key role in decreasing the Charpy impact energy of type 316 SS with indicating an intergranular fracture mode.
查看更多>>摘要：To predict variation of maximum localized penetration with exposure time, long-term localized corrosion was assessed in an emergency cooling water system composed of two carbon steel pipelines of 700 mm diameter transporting raw river water at flow velocities of 1 m/s and 0.1 m/ s.Field tests, visual inspection, ultrasonic testing, BART testing, SEM-EDS and metagenomic analyses were performed to assess the progress of long-term corrosion and determine the influ-ence of microbes in the corrosion process.High corrosion was linked to sulphate reducing bacteria and potentially to methanogenic archaea in the low-velocity pipeline, while moderate corrosion was linked to non-sulphate reducing bacteria in the higher velocity pipeline. Using historical and literature data available as well as our own test results, an empirical model was developed to predict Maximum Localized Penetration change over time to be applied in the ageing management of cooling water systems.Molecular Microbiological Methods in combination with traditional techniques are useful tools in the ageing management of pipelines. By applying the empirical model developed and the approach presented, unexpected through-wall leaking can be avoided, thus, saving costs and assets.
NSTL
Elsevier