Establishment of a creep model is an important method to analyze the relationship between soil creep deformation and time,and the element model is widely used for studying soil creep.However,the element creep model is...Establishment of a creep model is an important method to analyze the relationship between soil creep deformation and time,and the element model is widely used for studying soil creep.However,the element creep model is employed for fitting saturated soil,and the mechanical element model is generally linear,which cannot well fit the nonlinear deformation of the soil with time in practice.The creep process of the soil is not only time-dependent,but also related to the deviatoric stress level.Therefore,the fractional calculus theory and a parameter n reflecting the effect of deviatoric stress level on the creep properties of the soil were introduced into the element model,and the fractional qBurgers creep model was established by using the fractional Koeller dashpot and Caputo fractional calculus.The proposed model was used to fit the triaxial test data of reticulated red clay under different net confining pressures and matric suctions by unsaturated triaxial apparatus.The proposed model can well describe the nonlinearity of unsaturated reticulated red clay,has memory and global correlation to the creep development process of unsaturated reticulated red clay,and has clear physical meaning.The functional relationships of the model parameters with the matric suction,net confining pressure and deviatoric stress level were deduced,so that the creep curves of unsaturated reticulated red clay can be obtained for any conditions,which is of great value for the study of unsaturated soils.展开更多
Single-layer reticulated dome structure are commonly high-profile building in the public and can be attractive targets for terrorist bombings,so the public can benefit from enhanced safety with a stronger understandin...Single-layer reticulated dome structure are commonly high-profile building in the public and can be attractive targets for terrorist bombings,so the public can benefit from enhanced safety with a stronger understanding of the behavior of single-layer reticulated dome structure under explosion.This paper investigates the fluid-structure interaction process and the dynamic response performance of the singlelayer reticulated dome under external blast load.Both experimental and numerical results shown that structural deformation is remarkably delayed compared with the velocity of blast wave,which advises the dynamic response of large-span reticulated dome structure has a negligible effect on the blast wave propagation under explosion.Four failure modes are identified by comparing the plastic development of each ring and the residual spatial geometric of the structure,i.e.,minor vibration,local depression,severe damage,and overall collapse.The plastic deformation energy and the displacement potential energy of the structure are the main consumers of the blast energy.In addition,the stress performance of the vertex member and the deep plastic ratio of the whole structure can serve as qualitative indicators to distinguish different failure modes.展开更多
The two waves period of the COVID-19 pandemic saw the use of hydro- alcoholic gel and the consumption of capsules containing improved traditional remedies. At one point, there was a stock-out and a price increase...The two waves period of the COVID-19 pandemic saw the use of hydro- alcoholic gel and the consumption of capsules containing improved traditional remedies. At one point, there was a stock-out and a price increase forthese products. Furthermore, in the food industry, the catering industry adopts gelatin in its current practice. Pig gelatin dominates the international market. And for some religious practices, pork is forbidden and yet these people consume them without taking notice. The production of gelatin from broiler feet seems economically viable because broiler feet are considered slaughterhouse waste that is sold at very low prices. The poultry industry has seen an increase in broiler farming over the last twenty years. However, the latter has all the characteristics required for the production of gelatin. It will therefore comply with the standards of use described in the international codex oenological for gelatins. Physical and chemical analyses such as, ash content, moisture content, and pH measurements were done for the extracted gelatins. Sensible elements are checked with ED XRF spectroscopy. All the results were good and showed without any doubt that broiler gelatin is edible.展开更多
The series Variantia Ching et S. H. Wu mainly occur in China and its members are highly variable in morphology. The denomination on this group of Asplenium is very confused in the herbaria. We hop e by means of a bios...The series Variantia Ching et S. H. Wu mainly occur in China and its members are highly variable in morphology. The denomination on this group of Asplenium is very confused in the herbaria. We hop e by means of a biosystematic study to find out their genetic relationships in the reticulate evolution, and to raise a suggestion on their taxonomic treatment. Evidence from cytology, allozyme, morphology, and palynology shows that three ancestor diploids have formed Asplenium sarelii complex comprising 13 members. A. sarelii Hook. should be typified as a diploid. The so-called tetraploid 'A. sarelii' before is an allotetraploid that comes from the doubled hybrid between diploid A. sarelii and A. tenuicaule Hayata, which should be treated as a new species A. wudangense Z. R. Wang et X. Hou. A. pekinense Hance is an autotetraploid that comes from the doubled diploid ancestor A. sarelii. A. lushanense C. Chr., a diploid species and the only ancestor of A. yunnariense group, should not been sunk as a synonym of tetraploid A. yunnariense Franch. Most probably, A. varians Wall. ex Hook. et Grev. is an autotetraploid of A. tenuicaule Hayata. Three new natural tetraploid hybrids and their origins have been found out: they are A. x longmenense ( = A. pekinense x varians), A. x jingyunense ( = A. pekinense x yunnanense) and A. x kidoi ( = A. pekinense x wudangense). Three other new natural triploid hybrids have been found and their origins have been inferred: they are A. X huawuense ( = A. sarelii X wudangense), A. x luyunense ( = A. lushanense x yunnanense) and A. x teniuvaians ( = A. tenuicaule x varians). The method of allozyme comparion combined with cytological observation is employed to reveal the complicated relationships among the members of Asplenium sarelii complex in reticulate evolution and proved to be a highly effective tool to investigate the origin of polyploid and hybrid.展开更多
To investigate the effects of initial geometric imperfection and material nonlinearity on the stability analysis of the suspen-dome, the steel roof of Jiangsu Culture Sports Center Gymnasium was utilized as a numerica...To investigate the effects of initial geometric imperfection and material nonlinearity on the stability analysis of the suspen-dome, the steel roof of Jiangsu Culture Sports Center Gymnasium was utilized as a numerical model, and modal analyses were performed. Then, linear buckling analysis,geometric nonlinear stability analysis, geometric nonlinear stability analysis with initial imperfection, and double nonlinear analysis considering material nonlinearity and geometric nonlinearity were discussed in detail to compare the stability performance of the ellipse-like suspen-dome and the single-layer reticulated shell. The results showthat the cable-strut system increases the integrity of the suspen-dome, and moderates the sensibility of the single-layer reticulated shell to initial geometric imperfection. However, it has little influence on integral rigidity, fundamental vibration frequencies, linear ultimate live loads, and geometric nonlinear ultimate live loads without initial imperfection. When considering the material nonlinearity and initial imperfection, a significant reduction occurs in the ultimate stability capacities of these two structures. In this case, the suspen-dome with a lowrise-span ratio is sensitive to the initial imperfection and material nonlinearity. In addition, the distribution pattern of live loads significantly influences the instability modes of the structure, and the uniform live load with full span is not always the most dangerous case.展开更多
At about 173 ka BP of the late period of mid-Pleistocene, the second terrace of the river had been formed as a result of uplift happening in Shangshan area because of the climate, sea level change and tectonic action....At about 173 ka BP of the late period of mid-Pleistocene, the second terrace of the river had been formed as a result of uplift happening in Shangshan area because of the climate, sea level change and tectonic action. Between 173-75 ka BP, aeolian deposited on the terrace, a layer of reticulate red clayey soil about 80-100 cm thick deposited and developed under the warmer and higher temperature. In the last glacial period, the drop of the temperature and the decrease of the precipitation induced the dust-storms increased, A layer of Xiashu loess about 1.0-1.5 m thick accumulated on Shangshan terrace in the last glacial, which has the reticulate red clayey soil buried. At the beginning of the Holocene （11500 a BP-）, temperature went higher gradually and precipitation got more, the pre-persons moved on the Shangshan terrace （11,400-8600 a BP）, which is one of the most important archaeological sites, and can connect the paleolithic culture with Neolithic culture. It could be assumed from the results that the lower reaches of the Yangtze River are the home of rice cultivation, too. The lower place to the west of the Shangshan site experienced the two cycles process of the fluvial facies and the lacustrine facies, indicating that the water source of the pre-historical Shangshan is the river water or lake water. Two AMS 14C age proved the water source disappeared more than 1000 years ago.展开更多
3D reticulated ceramics (3DRCs) with the composition containing SrFe12O19-SiC-TiO2 were prepared by a replication process with polyurethane sponges as the template in ceramic slurry. The electrical conductivity, diele...3D reticulated ceramics (3DRCs) with the composition containing SrFe12O19-SiC-TiO2 were prepared by a replication process with polyurethane sponges as the template in ceramic slurry. The electrical conductivity, dielectric and magnetic parameters of 3D reticulated ceramics (3DRCs) were measured with changes in cell size of the sponges, contents in the slurry and sintering temperature in this paper. Discussions about the influential factors of those parameters were focused on their electrical conductivity. The experimental results indicated that the electrical conductivity of 3DRCs raised with the increase of cell size, SiC/SrO 6Fe2O3 with weight ratio and sintering temperature. X-ray diffractions and SEM were used to investigate the relationship between electrical conductivity and sintering temperature. Deoxidizing reactions of SrO 6Fe2O3 caused the increasing electrical conductivity. The real part of permittivity (ε') and imaginary part of permeability (μ') raised with the increase of electrical conductivity (σ). The imaginary part of permittivity (ε') has a maximum at 10o S/cm with the increase of a, and the real part of permeability (μ') changes slightly with the increase of a. When a is at the range of 10-4 S/cm to 10o S/cm (a semi conductive state), both the imagine part of permittivity and permeability raises with increasing a, therefore, the 3DRCs present their high electromagnetic loss properties.展开更多
In this study,a method for control of reticulated shells is proposed and its practicality is demonstrated.The control is implemented by replacing selected bars of the shell with passive viscoelastic dampers.By applyin...In this study,a method for control of reticulated shells is proposed and its practicality is demonstrated.The control is implemented by replacing selected bars of the shell with passive viscoelastic dampers.By applying the eigenvalue perturbation technique and the earthquake spectrum concept,the sensitivities of various topologies of the shell are analyzed,and the optimal topology is determined by taking their symmetries into consideration.The results of this research show that common damper topologies are not effective for all types of responses and recorded earthquakes.The optimal topology identifi ed requires a minimal number of dampers for each type of earthquake record.The displacement control effect of the dynamic responses of the optimal topology is 10% – 20%; the acceleration control effect is also about 10% – 20%; and the axial force control effect is as much as 30% – 45%.Furthermore,the incremental dynamic analysis(IDA) method is used to investigate the stability of the controlled shell.The results show that the dynamic stability of the controlled shell is well preserved when it is vibrated under vibration and is better than the uncontrolled shell.The ultimate load increased by 10% and the elements entered into the plastic stage when the peak acceleration reached 580 Gal,which is 200 Gal larger than the uncontrolled shell.展开更多
The paper presents the theory of Hamilton variation principle which is the current method for impact problem, central difference method which is efficient solution of finite element (FE) method for impact problem and ...The paper presents the theory of Hamilton variation principle which is the current method for impact problem, central difference method which is efficient solution of finite element (FE) method for impact problem and adapts to solve non-linear dynamic problem. And it introduces the ANSYS/LS-DYNA which is the popular FE software for impact problem both at home and abroad. Then it gives solutions for one simple model by analytical method and ANSYS/LS-DYNA respec-tively to validate function of software, and they are consistent. Afterward, it gives model of single-layer Kiewitt reticulated dome with a span of 60 m, and the cylinder impactor, and introduces the contact interface arithmetic, especially the material model of steel (piecewise linear plasticity model) which takes stain rate into account and makes steel failure stress higher under impact loads. The vertical displacement, stress in main members, and the plastic deformation for dome under impact loads were obtained. Then four failure modes (no failure, moderate failure, global failure and slight failure) were summarized according to the rules of dynamic response. And the characteristics of dynamic response for each failure mode were shown.展开更多
Reticulated shell structures （RSSs） are characterized as cyclically periodic structures. Mistuning of RSSs will induce structural mode localization. Mode localization has the following two features： some modal vect...Reticulated shell structures （RSSs） are characterized as cyclically periodic structures. Mistuning of RSSs will induce structural mode localization. Mode localization has the following two features： some modal vectors of the structure change remarkably when the values of its physical parameters （mass or stiffness） have a slight change; and the vibration of some modes is mainly restricted in some local areas of the structure. In this paper, two quantitative assessment indexes are introduced that correspond to these two features. The first feature is studied through a numerical example of a RSS, and its induced causes are analyzed by using the perturbation theory. The analysis showed that internally, mode localization is closely related to structural frequencies and externally, slight changes of the physical parameters of the structure cause instability to the RSS. A scaled model experiment to examine mode localization was carried out on a Kiewit single-layer spherical RSS, and both features of mode localization are studied. Eight tests that measured the changes of the physical parameters were carried out in the experiment. Since many modes make their contribution in structural dynamic response, six strong vibration modes were tested at random in the experimental analysis. The change and localization of the six modes are analyzed for each test. The results show that slight changes to the physical parameters are likely to induce remarkable changes and localization of some modal vectors in the RSSs.展开更多
Cymbidium,which includes approximately 80 species,is one of the most ornamental and cultivated orchid genera.However,a lack of markers and sparse sampling have posed great challenges to resolving the phylogenetic rela...Cymbidium,which includes approximately 80 species,is one of the most ornamental and cultivated orchid genera.However,a lack of markers and sparse sampling have posed great challenges to resolving the phylogenetic relationships within the genus.In the present study,we reconstructed the phylogenetic relationships by utilizing one nuclear DNA(nrITS)and seven plastid genes(rbcL,trnS,trnG,matK,trnL,psbA,and atpI)from 70 species(varieties)in Cymbidium.We also examined the occurrence of phylogenetic conflict between nuclear(nrITS)and plastid loci and investigated how phylogenetic conflict bears on taxonomic classification within the genus.We found that phylogenetic conflict and low support values may be explained by hybridization and a lack of informative characteristics.Our results do not support previous classification of the subgenera and sections within Cymbidium.Discordance between gene trees and network analysis indicate that reticulate evolution occurred in the genus Cymbidium.Overall,our study indicates that Cymbidium has undergone a complex evolution.展开更多
No failure, moderate failure, severe failure, and slight failure are the four failure modes generalized observed in the dynamic response of the single-layer reticulated dome under vertical impact load on apex. TE (the...No failure, moderate failure, severe failure, and slight failure are the four failure modes generalized observed in the dynamic response of the single-layer reticulated dome under vertical impact load on apex. TE (the time that the end of impact force) and TF (the time that members are broken) are two key times in the failure process. Characteristics of dynamic responses at the two key times are shown in order to make the failure mechanism clear. Then three steps of energy transfer are summarized, i.e. energy applying, energy loss and energy transfer, energy consump-tion. Based on the three steps, energy transfer process for the failure reticulated dome under once impact is introduced. Energy transmissibility and local loss ratio are put forward firstly to obtain EL F(the energy left in the main reticulated dome) from the initial kinetic energy of impactor. More-over, the distribution of failure modes is decided by EL F which leads to the maximum dynamic re-sponse of the reticulated dome, but not by the initial impact kinetic energy of impactor.展开更多
基金supported by the National Science Fund for Distinguished Young Scholars (Grant No.52025085)the National Key Research and Development Program of China (Grant No.2021YFB2600900)the Open Fund of Key Laboratory of Special Environment Road Engineering of Hunan Province,China (Changsha University of Science and Technology) (Grant No.kfj230606).
文摘Establishment of a creep model is an important method to analyze the relationship between soil creep deformation and time,and the element model is widely used for studying soil creep.However,the element creep model is employed for fitting saturated soil,and the mechanical element model is generally linear,which cannot well fit the nonlinear deformation of the soil with time in practice.The creep process of the soil is not only time-dependent,but also related to the deviatoric stress level.Therefore,the fractional calculus theory and a parameter n reflecting the effect of deviatoric stress level on the creep properties of the soil were introduced into the element model,and the fractional qBurgers creep model was established by using the fractional Koeller dashpot and Caputo fractional calculus.The proposed model was used to fit the triaxial test data of reticulated red clay under different net confining pressures and matric suctions by unsaturated triaxial apparatus.The proposed model can well describe the nonlinearity of unsaturated reticulated red clay,has memory and global correlation to the creep development process of unsaturated reticulated red clay,and has clear physical meaning.The functional relationships of the model parameters with the matric suction,net confining pressure and deviatoric stress level were deduced,so that the creep curves of unsaturated reticulated red clay can be obtained for any conditions,which is of great value for the study of unsaturated soils.
基金financial support from the China Postdoctora Science Foundation(project No.2021M690406)financial supports from the National Natural Science Foundation of China(project No.51708521,51778183)。
文摘Single-layer reticulated dome structure are commonly high-profile building in the public and can be attractive targets for terrorist bombings,so the public can benefit from enhanced safety with a stronger understanding of the behavior of single-layer reticulated dome structure under explosion.This paper investigates the fluid-structure interaction process and the dynamic response performance of the singlelayer reticulated dome under external blast load.Both experimental and numerical results shown that structural deformation is remarkably delayed compared with the velocity of blast wave,which advises the dynamic response of large-span reticulated dome structure has a negligible effect on the blast wave propagation under explosion.Four failure modes are identified by comparing the plastic development of each ring and the residual spatial geometric of the structure,i.e.,minor vibration,local depression,severe damage,and overall collapse.The plastic deformation energy and the displacement potential energy of the structure are the main consumers of the blast energy.In addition,the stress performance of the vertex member and the deep plastic ratio of the whole structure can serve as qualitative indicators to distinguish different failure modes.
文摘The two waves period of the COVID-19 pandemic saw the use of hydro- alcoholic gel and the consumption of capsules containing improved traditional remedies. At one point, there was a stock-out and a price increase forthese products. Furthermore, in the food industry, the catering industry adopts gelatin in its current practice. Pig gelatin dominates the international market. And for some religious practices, pork is forbidden and yet these people consume them without taking notice. The production of gelatin from broiler feet seems economically viable because broiler feet are considered slaughterhouse waste that is sold at very low prices. The poultry industry has seen an increase in broiler farming over the last twenty years. However, the latter has all the characteristics required for the production of gelatin. It will therefore comply with the standards of use described in the international codex oenological for gelatins. Physical and chemical analyses such as, ash content, moisture content, and pH measurements were done for the extracted gelatins. Sensible elements are checked with ED XRF spectroscopy. All the results were good and showed without any doubt that broiler gelatin is edible.
文摘The series Variantia Ching et S. H. Wu mainly occur in China and its members are highly variable in morphology. The denomination on this group of Asplenium is very confused in the herbaria. We hop e by means of a biosystematic study to find out their genetic relationships in the reticulate evolution, and to raise a suggestion on their taxonomic treatment. Evidence from cytology, allozyme, morphology, and palynology shows that three ancestor diploids have formed Asplenium sarelii complex comprising 13 members. A. sarelii Hook. should be typified as a diploid. The so-called tetraploid 'A. sarelii' before is an allotetraploid that comes from the doubled hybrid between diploid A. sarelii and A. tenuicaule Hayata, which should be treated as a new species A. wudangense Z. R. Wang et X. Hou. A. pekinense Hance is an autotetraploid that comes from the doubled diploid ancestor A. sarelii. A. lushanense C. Chr., a diploid species and the only ancestor of A. yunnariense group, should not been sunk as a synonym of tetraploid A. yunnariense Franch. Most probably, A. varians Wall. ex Hook. et Grev. is an autotetraploid of A. tenuicaule Hayata. Three new natural tetraploid hybrids and their origins have been found out: they are A. x longmenense ( = A. pekinense x varians), A. x jingyunense ( = A. pekinense x yunnanense) and A. x kidoi ( = A. pekinense x wudangense). Three other new natural triploid hybrids have been found and their origins have been inferred: they are A. X huawuense ( = A. sarelii X wudangense), A. x luyunense ( = A. lushanense x yunnanense) and A. x teniuvaians ( = A. tenuicaule x varians). The method of allozyme comparion combined with cytological observation is employed to reveal the complicated relationships among the members of Asplenium sarelii complex in reticulate evolution and proved to be a highly effective tool to investigate the origin of polyploid and hybrid.
基金The National Key Technology R&D Program of China(No.2012BAJ03B06)the National Natural Science Foundation of China(No.51308105)+1 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the Fundamental Research Funds for the Southeast University(No.KYLX_0152,SJLX_0084,KYLX_0149)
文摘To investigate the effects of initial geometric imperfection and material nonlinearity on the stability analysis of the suspen-dome, the steel roof of Jiangsu Culture Sports Center Gymnasium was utilized as a numerical model, and modal analyses were performed. Then, linear buckling analysis,geometric nonlinear stability analysis, geometric nonlinear stability analysis with initial imperfection, and double nonlinear analysis considering material nonlinearity and geometric nonlinearity were discussed in detail to compare the stability performance of the ellipse-like suspen-dome and the single-layer reticulated shell. The results showthat the cable-strut system increases the integrity of the suspen-dome, and moderates the sensibility of the single-layer reticulated shell to initial geometric imperfection. However, it has little influence on integral rigidity, fundamental vibration frequencies, linear ultimate live loads, and geometric nonlinear ultimate live loads without initial imperfection. When considering the material nonlinearity and initial imperfection, a significant reduction occurs in the ultimate stability capacities of these two structures. In this case, the suspen-dome with a lowrise-span ratio is sensitive to the initial imperfection and material nonlinearity. In addition, the distribution pattern of live loads significantly influences the instability modes of the structure, and the uniform live load with full span is not always the most dangerous case.
基金National Science and Technology Support Program, No.2006BAK21B02 National Basic Research Program of China, No.2003CB415201 National Natural Science Foundation of China, No.40671016
文摘At about 173 ka BP of the late period of mid-Pleistocene, the second terrace of the river had been formed as a result of uplift happening in Shangshan area because of the climate, sea level change and tectonic action. Between 173-75 ka BP, aeolian deposited on the terrace, a layer of reticulate red clayey soil about 80-100 cm thick deposited and developed under the warmer and higher temperature. In the last glacial period, the drop of the temperature and the decrease of the precipitation induced the dust-storms increased, A layer of Xiashu loess about 1.0-1.5 m thick accumulated on Shangshan terrace in the last glacial, which has the reticulate red clayey soil buried. At the beginning of the Holocene （11500 a BP-）, temperature went higher gradually and precipitation got more, the pre-persons moved on the Shangshan terrace （11,400-8600 a BP）, which is one of the most important archaeological sites, and can connect the paleolithic culture with Neolithic culture. It could be assumed from the results that the lower reaches of the Yangtze River are the home of rice cultivation, too. The lower place to the west of the Shangshan site experienced the two cycles process of the fluvial facies and the lacustrine facies, indicating that the water source of the pre-historical Shangshan is the river water or lake water. Two AMS 14C age proved the water source disappeared more than 1000 years ago.
文摘3D reticulated ceramics (3DRCs) with the composition containing SrFe12O19-SiC-TiO2 were prepared by a replication process with polyurethane sponges as the template in ceramic slurry. The electrical conductivity, dielectric and magnetic parameters of 3D reticulated ceramics (3DRCs) were measured with changes in cell size of the sponges, contents in the slurry and sintering temperature in this paper. Discussions about the influential factors of those parameters were focused on their electrical conductivity. The experimental results indicated that the electrical conductivity of 3DRCs raised with the increase of cell size, SiC/SrO 6Fe2O3 with weight ratio and sintering temperature. X-ray diffractions and SEM were used to investigate the relationship between electrical conductivity and sintering temperature. Deoxidizing reactions of SrO 6Fe2O3 caused the increasing electrical conductivity. The real part of permittivity (ε') and imaginary part of permeability (μ') raised with the increase of electrical conductivity (σ). The imaginary part of permittivity (ε') has a maximum at 10o S/cm with the increase of a, and the real part of permeability (μ') changes slightly with the increase of a. When a is at the range of 10-4 S/cm to 10o S/cm (a semi conductive state), both the imagine part of permittivity and permeability raises with increasing a, therefore, the 3DRCs present their high electromagnetic loss properties.
基金Natural Science Foundation of China under Grant Nos.50908036&51261120376Natural Science Foundation of Liaoning Province No.201202040
文摘In this study,a method for control of reticulated shells is proposed and its practicality is demonstrated.The control is implemented by replacing selected bars of the shell with passive viscoelastic dampers.By applying the eigenvalue perturbation technique and the earthquake spectrum concept,the sensitivities of various topologies of the shell are analyzed,and the optimal topology is determined by taking their symmetries into consideration.The results of this research show that common damper topologies are not effective for all types of responses and recorded earthquakes.The optimal topology identifi ed requires a minimal number of dampers for each type of earthquake record.The displacement control effect of the dynamic responses of the optimal topology is 10% – 20%; the acceleration control effect is also about 10% – 20%; and the axial force control effect is as much as 30% – 45%.Furthermore,the incremental dynamic analysis(IDA) method is used to investigate the stability of the controlled shell.The results show that the dynamic stability of the controlled shell is well preserved when it is vibrated under vibration and is better than the uncontrolled shell.The ultimate load increased by 10% and the elements entered into the plastic stage when the peak acceleration reached 580 Gal,which is 200 Gal larger than the uncontrolled shell.
基金Supported by National Natural Science Foundation of China(No.90715034)
文摘The paper presents the theory of Hamilton variation principle which is the current method for impact problem, central difference method which is efficient solution of finite element (FE) method for impact problem and adapts to solve non-linear dynamic problem. And it introduces the ANSYS/LS-DYNA which is the popular FE software for impact problem both at home and abroad. Then it gives solutions for one simple model by analytical method and ANSYS/LS-DYNA respec-tively to validate function of software, and they are consistent. Afterward, it gives model of single-layer Kiewitt reticulated dome with a span of 60 m, and the cylinder impactor, and introduces the contact interface arithmetic, especially the material model of steel (piecewise linear plasticity model) which takes stain rate into account and makes steel failure stress higher under impact loads. The vertical displacement, stress in main members, and the plastic deformation for dome under impact loads were obtained. Then four failure modes (no failure, moderate failure, global failure and slight failure) were summarized according to the rules of dynamic response. And the characteristics of dynamic response for each failure mode were shown.
基金National Natural Science Foundation of China Under Grant No. 50878010
文摘Reticulated shell structures （RSSs） are characterized as cyclically periodic structures. Mistuning of RSSs will induce structural mode localization. Mode localization has the following two features： some modal vectors of the structure change remarkably when the values of its physical parameters （mass or stiffness） have a slight change; and the vibration of some modes is mainly restricted in some local areas of the structure. In this paper, two quantitative assessment indexes are introduced that correspond to these two features. The first feature is studied through a numerical example of a RSS, and its induced causes are analyzed by using the perturbation theory. The analysis showed that internally, mode localization is closely related to structural frequencies and externally, slight changes of the physical parameters of the structure cause instability to the RSS. A scaled model experiment to examine mode localization was carried out on a Kiewit single-layer spherical RSS, and both features of mode localization are studied. Eight tests that measured the changes of the physical parameters were carried out in the experiment. Since many modes make their contribution in structural dynamic response, six strong vibration modes were tested at random in the experimental analysis. The change and localization of the six modes are analyzed for each test. The results show that slight changes to the physical parameters are likely to induce remarkable changes and localization of some modal vectors in the RSSs.
基金funded by The National Key Research and Development Program of China(Nos.2018YFD1000401 and 2018YFD1000400)the Natural Science Foundation of Guangdong Province(No.2017A030312004)the Science and Technology Plan Project of Shenzhen(No.JCYJ20170817151501595).
文摘Cymbidium,which includes approximately 80 species,is one of the most ornamental and cultivated orchid genera.However,a lack of markers and sparse sampling have posed great challenges to resolving the phylogenetic relationships within the genus.In the present study,we reconstructed the phylogenetic relationships by utilizing one nuclear DNA(nrITS)and seven plastid genes(rbcL,trnS,trnG,matK,trnL,psbA,and atpI)from 70 species(varieties)in Cymbidium.We also examined the occurrence of phylogenetic conflict between nuclear(nrITS)and plastid loci and investigated how phylogenetic conflict bears on taxonomic classification within the genus.We found that phylogenetic conflict and low support values may be explained by hybridization and a lack of informative characteristics.Our results do not support previous classification of the subgenera and sections within Cymbidium.Discordance between gene trees and network analysis indicate that reticulate evolution occurred in the genus Cymbidium.Overall,our study indicates that Cymbidium has undergone a complex evolution.
基金Supported by National Natural Science Foundation of China(No.90715034)
文摘No failure, moderate failure, severe failure, and slight failure are the four failure modes generalized observed in the dynamic response of the single-layer reticulated dome under vertical impact load on apex. TE (the time that the end of impact force) and TF (the time that members are broken) are two key times in the failure process. Characteristics of dynamic responses at the two key times are shown in order to make the failure mechanism clear. Then three steps of energy transfer are summarized, i.e. energy applying, energy loss and energy transfer, energy consump-tion. Based on the three steps, energy transfer process for the failure reticulated dome under once impact is introduced. Energy transmissibility and local loss ratio are put forward firstly to obtain EL F(the energy left in the main reticulated dome) from the initial kinetic energy of impactor. More-over, the distribution of failure modes is decided by EL F which leads to the maximum dynamic re-sponse of the reticulated dome, but not by the initial impact kinetic energy of impactor.
