Accurate prediction of dynamic characteristics is quite critical to understand the strength of layered structures.Nevertheless,the existing five-unknown higher-order theories encounter difficulties to forecast accurat...Accurate prediction of dynamic characteristics is quite critical to understand the strength of layered structures.Nevertheless,the existing five-unknown higher-order theories encounter difficulties to forecast accurately the dynamic response of sandwich structures.Therefore,a new five-unknown higher-order theory is developed for free vibration analysis of composite and sandwich plates,which possesses the same degree of freedom as those of other five-unknown higherorder theories.The developed model can meet beforehand interlaminar continuity conditions and the free-surface conditions of transverse shear stresses.To assess capability of the proposed model,analytical solution for such composite structures with simply-supported conditions has been presented by employing Hamilton’s principle,which is utilized for analysis of mechanical behaviors of composite and sandwich plates.Compared with the three-dimensional(3 D)elasticity solutions,3 D finite element results and the results obtained from the chosen five-unknown higher-order models,the proposed model can yield accurately natural frequencies of composite and sandwich plates.Even for the thick plates,the higher-order frequencies calculated from the proposed model are in good agreement with the 3 D finite element results.By studying effect of the thickness/length ratios on natural frequencies,it is found that the proposed model is adaptable to predicting natural frequencies of the sandwich plates with the thickness/length ratios between 1/4 and 1/100.In addition,some factors influencing accuracy of five-unknown higher-order models have been investigated in detail.Finally,by means of numerical analysis and discussion,some conclusions have been drawn as well,which can serve as a reference for other investigators.展开更多
Background Global climate change has resulted in precipitation regimes exhibiting an increasing trend in rainfall intensity but a reduction in frequency.In addition,nitrogen(N)deposition occurs simultaneously in arid ...Background Global climate change has resulted in precipitation regimes exhibiting an increasing trend in rainfall intensity but a reduction in frequency.In addition,nitrogen(N)deposition occurs simultaneously in arid and semi-arid regions.Microbial biomass,diversity,composition,and species interactions are key determinants of ecological functions.We examined the effects of changes in precipitation intensity and N addition on the soil bacterial and fungal communities in a semi-arid grassland in Inner Mongolia,China.Methods The microbial biomass(bacterial PLFAs and fungal PLFAs)was determined through phospholipid fatty acid(PLFA)analysis,and microbial diversity(Shannon index and evenness index)was determined with high-throughput sequencing(16S and ITS).Species interactions were determined using a molecular ecological network analysis.The relationships between microbial community(bacterial community and fungal community)and environmental variables were examined by Mantel tests.Results We found that N addition decreased fungal PLFA under moderate,high,and extreme precipitation intensity treatments and increased fungal community complexity under the high precipitation intensity treatment.Furthermore,N addition increased bacterial diversity under moderate and high precipitation intensity treatments.N addition caused greater environmental stress to the fungal community,which was dominated by deterministic processes.Conclusions The effects of N deposition on soil bacterial and fungal communities were altered by precipitation intensity.The changes in soil bacterial and fungal communities were different,implying that composition and functional traits adapt differently to projected global changes at a regional scale.展开更多
基金supported by SKLLIM1902 and the National Natural Sciences Foundation of China(No.11402152)。
文摘Accurate prediction of dynamic characteristics is quite critical to understand the strength of layered structures.Nevertheless,the existing five-unknown higher-order theories encounter difficulties to forecast accurately the dynamic response of sandwich structures.Therefore,a new five-unknown higher-order theory is developed for free vibration analysis of composite and sandwich plates,which possesses the same degree of freedom as those of other five-unknown higherorder theories.The developed model can meet beforehand interlaminar continuity conditions and the free-surface conditions of transverse shear stresses.To assess capability of the proposed model,analytical solution for such composite structures with simply-supported conditions has been presented by employing Hamilton’s principle,which is utilized for analysis of mechanical behaviors of composite and sandwich plates.Compared with the three-dimensional(3 D)elasticity solutions,3 D finite element results and the results obtained from the chosen five-unknown higher-order models,the proposed model can yield accurately natural frequencies of composite and sandwich plates.Even for the thick plates,the higher-order frequencies calculated from the proposed model are in good agreement with the 3 D finite element results.By studying effect of the thickness/length ratios on natural frequencies,it is found that the proposed model is adaptable to predicting natural frequencies of the sandwich plates with the thickness/length ratios between 1/4 and 1/100.In addition,some factors influencing accuracy of five-unknown higher-order models have been investigated in detail.Finally,by means of numerical analysis and discussion,some conclusions have been drawn as well,which can serve as a reference for other investigators.
基金supported by the National Natural Science Foundation of China(NSFC-31970410)Liaoning Revitalization Talents Program(XLYC2002083)+1 种基金Liaoning Province Science and Technology Plan Project(2018103004)Department of Science and Technology of Liaoning Province(2022JH5/10400111).
文摘Background Global climate change has resulted in precipitation regimes exhibiting an increasing trend in rainfall intensity but a reduction in frequency.In addition,nitrogen(N)deposition occurs simultaneously in arid and semi-arid regions.Microbial biomass,diversity,composition,and species interactions are key determinants of ecological functions.We examined the effects of changes in precipitation intensity and N addition on the soil bacterial and fungal communities in a semi-arid grassland in Inner Mongolia,China.Methods The microbial biomass(bacterial PLFAs and fungal PLFAs)was determined through phospholipid fatty acid(PLFA)analysis,and microbial diversity(Shannon index and evenness index)was determined with high-throughput sequencing(16S and ITS).Species interactions were determined using a molecular ecological network analysis.The relationships between microbial community(bacterial community and fungal community)and environmental variables were examined by Mantel tests.Results We found that N addition decreased fungal PLFA under moderate,high,and extreme precipitation intensity treatments and increased fungal community complexity under the high precipitation intensity treatment.Furthermore,N addition increased bacterial diversity under moderate and high precipitation intensity treatments.N addition caused greater environmental stress to the fungal community,which was dominated by deterministic processes.Conclusions The effects of N deposition on soil bacterial and fungal communities were altered by precipitation intensity.The changes in soil bacterial and fungal communities were different,implying that composition and functional traits adapt differently to projected global changes at a regional scale.
