Structural Design Study of Air-Dropped Unmanned Maritime Mobile Search and Rescue Platforms

In order to improve the efficiency and safety of search and rescue(SAR)at sea,this paper proposes a kind of emergency rapid rescue unmanned craft(air-dropped unmanned maritime motorized search and rescue platform)that can be delivered by a large transport aircraft.This paper studies the structural design scheme of the platform,and the main scale of the platform,the choice of power system and the impact resistance performance are considered in the design process to ensure its rapid response and effective rescue capability under complex sea conditions.Simulation results show that the platform can withstand the impact of air injection into the water and the shipboard equipment can operate normally under the impact load,thus verifying the feasibility and safety of the design.This study serves to improve the maritime search and rescue system and enhance the oceanic emergency response capability.

Influence of soil——structure interaction on seismic collapse resistance of super-tall buildings

Numerous field tests indicate that the soilestructure interaction （SSI） has a significant impact on thedynamic characteristics of super-tall buildings, which may lead to unexpected structural seismic responsesand/or failure. Taking the Shanghai Tower with a total height of 632 m as the research object, thesubstructure approach is used to simulate the SSI effect on the seismic responses of Shanghai Tower. Therefined finite element （FE） model of the superstructure of Shanghai Tower and the simplified analyticalmodel of the foundation and adjacent soil are established. Subsequently, the collapse process of ShanghaiTower taking into account the SSI is predicted, as well as its final collapse mechanism. The influences ofthe SSI on the collapse resistance capacity and failure sequences are discussed. The results indicate that,when considering the SSI, the fundamental period of Shanghai Tower has been extended significantly,and the collapse margin ratio has been improved, with a corresponding decrease of the seismic demand.In addition, the SSI has some impact on the failure sequences of Shanghai Tower subjected to extremeearthquakes, but a negligible impact on the final failure modes. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Density Dependence of Tunnel Fire Resistance for Aerogel-Cement Mortar Coatings

Five kinds of mortars with density grades of 500, 600, 700, 800, and 900 kg/m3 were prepared. Their thermal conductivity and compressive strength were measured, and the morphological changes before and after simulated tunnel fire were observed. To investigate the fire resistance, the interfacial temperature of a 30 mm thick aerogel-cement mortar and self-compacting concrete (SCC) in a simulated tunnel fire with the maximum temperature of 1100 ℃ for 2.5 h was tested and recorded. The results showed that as the density decreased, both compressive strength and thermal conductivity of the aerogel-cement mortar exhibited an exponential decrease. The effective fire resistance time of the mortar with 500, 600, 700, 800, and 900 kg/m^3 for protecting SCC from tunnel fire were 97 min, 114 min, 144 min, > 150 min, 136 min, respectively. 700 - 800 kg/m3 was the optimum density for engineering application of tunnel concrete fireproof coating.

Numerical simulation study on the relationship between mining heights and shield resistance in longwall panel

A numerical model based on a Continuum-based Distinct Element Method(CDEM) was used to carry out a dynamic simulation of the interaction between shield and rock strata movement in longwall mining. In Northern China, the Ordos coal field geological conditions and operational characteristics were used as a case example. The CDEM was constructed on Ordos coal field shield's operation characteristics and geological conditions. Numerical modelling was carried out to investigate the effects of different mining heights on the caving process, movement characteristics, equilibrium and stability conditions of overburden as the interaction between shield and surrounding rocks. With the numerical model, the internal factors for changes in shield resistance under different mining heights was found. The quantitative relationship between mining heights and shield resistance was also obtained by the numerical simulation.

Investigation of image segmentation effect on the accuracy of reconstructed digital core models of coquina carbonate

Digital core models reconstructed using X-ray tomography(X-CT)enable the quantitative characterization of the pore structure in three dimensions(3D)and the numerical simulation of petrophysics.When the X-CT images accurately reflect the micro structures of core samples,the greyscale threshold in the image segmentation determines the accuracy of digital cores and the simulated petrophysical properties.Therefore,it is vital to investigate the comparison parameter for determining the key greyscale threshold and the criterion to describe the accuracy of the segmentation.Representative coquina digital core models from X-CT are used in this work to study the impact of grayscale threshold on the porosity,pore percolation,connectivity and electrical resistivity of the pore scale model and these simulations are calculated by Minkowski functions,component labeling and fi nite element method,respectively,to quantify the pore structure and simulate electrical resistivity.Results showed that the simulated physical properties of the digital cores,varied with the gradual increase of the greyscale threshold.Among the four parameters related to the threshold,the porosity was most sensitive and chose as the comparison parameter to judge the accuracy of the greyscale threshold.The variations of the threshold change the micro pore structures,and then the electrical resistivity.When the porosity of the digital core model is close to the experimental porosity,the simulated porosity exponent matches the experimental porosity exponents well.The good agreement proved that the porosity is the critical comparison parameter to describe the accuracy of image segmentation.The criterion is that the porosity of the digital core after segmentation should be close to the experimental porosity.

Water abundance of mine floor limestone by simulation experiment

The water abundance of mine floor limestone needs to be solved urgently as the average depth of coal mining in China has increased gradually. A method is presented to discuss water abundance with the numerical and physical layered geoelectrical model being established in the half-space, full-space and full-space with tunnel, respectively. The parameters of water abundance are changed in this study, which includes water quantity, water content and volume of abnormity of water-containing abnormity. Results indicate that the different work fields have different macroscopic influences on the apparent resistivity,and the water abundance parameters of water-containing abnormity have quantitative relationship with the apparent resistivity mean in abnormal regions(three-dimensional space region). The quantitative relationships are shown as following: firstly, the amount of water injection has negative linear correlation with the apparent resistivity mean; secondly, when abnormity is unsaturated, there is a negative power function relationship between water content and apparent resistivity mean; thirdly, the volume of abnormity and apparent resistivity mean behave as a decreasing power function law.

Hydration Process and Crack Tendency of Concrete Based on Resistivity and Restrained Shrinkage Crack

Hydration process, crack potential and setting time of concrete grade C30, C40 and C50 were monitored by using a non-contact electrical resistivity apparatus, a novel plastic ring mould and penetration resistance methods, respectively. The results show the highest resistivity of C30 at the early stage until a point when C50 accelerated and overtook the others. It has been experimentally confirmed that the crossing point of C30 and C50 corresponds to the final setting time of C50. From resistivity derivative curve, four different stages were observed upon which the hydration process is classified; these are dissolution, induction, acceleration and deceleration periods. Consequently, restrained shrinkage crack and setting time results demonstrated that C50 set and cracked the earliest. The cracking time of all the samples occurred within a reasonable experimental period thus the novel plastic ring is a convenient method for predicting concrete＇s crack potential. The highest inflection time（t_i） obtained from resistivity curve and the final setting time（t_f） were used with crack time（t_c） in coming up with mathematical models for the prediction of concrete＇s cracking age for the range of concrete grade considered. Finally, an ANSYS numerical simulation supports the experimental findings in terms of the earliest crack age of C50 and the crack location.

High-temperature performance study of chromium-containing stuffing sand for ladles

High-temperature performance tests of chromium-containing stuffing sand for a steel ladle w ith different ratios w ere performed. A high-temperature simulation test furnace w as used to analyze the influence of the composition ratio of ladle filler sand and sintering time on the high-temperature compression resistance of chromium-containing stuffing sand in the temperature range of 1 500- 1 600 ℃. The results show that the refractoriness of ladle filler sand w as the low est（ only 1 610 ℃） w hen the composition ratio of chromite sand and silica sand w as 6∶ 4. M oreover,the high-temperature compression resistance w as high w hen the content of chromite sand w as at 70%; the resistance increased w ith increasing sintering time. When the sintering time w as extended at a temperature of 1 600 ℃,the high-temperature compression resistance of ladle filler sand first increased and then decreased after being overburnt.