This study analyzes and predicts the vibration characteristics of fiberreinforced composite sandwich(FRCS)cylindrical-spherical(CS)combined shells with hexagon honeycomb core(HHC)for the first time based on an analyti...This study analyzes and predicts the vibration characteristics of fiberreinforced composite sandwich(FRCS)cylindrical-spherical(CS)combined shells with hexagon honeycomb core(HHC)for the first time based on an analytical model developed,which makes good use of the advantage of the first-order shear deformation theory(FSDT),the multi-segment decomposition technique,the virtual spring technology,the Jacobi-Ritz approach,and the transfer function method.The equivalent material properties of HHC are firstly determined by the modified Gibson’s formula,and the related energy equations are derived for the HHC-FRCS-CS combined shells,from which the fundamental frequencies,the mode shapes,and the forced vibration responses are solved.The current model is verified through the discussion of convergence and comparative analysis with the associated published literature and finite element(FE)results.The effects of geometric parameters of HHC on the dynamic property of the structure are further investigated with the verified model.It reveals that the vibration suppression capability can be greatly enhanced by reducing the ratio of HHC thickness to total thickness and the ratio of wall thickness of honeycomb cell to overall radius,and by increasing the ratio of length of honeycomb cell to overall radius and honeycomb characteristic angle of HHC.展开更多
The conductivity of polymer-derived SiOCN ceramics exhibited an Arrhenius dependence on pyrolysis temperature, with the activation energy of ~3.95 eV. The formation and structure change of the free carbon phase were d...The conductivity of polymer-derived SiOCN ceramics exhibited an Arrhenius dependence on pyrolysis temperature, with the activation energy of ~3.95 eV. The formation and structure change of the free carbon phase were detected by means of electron spin resonance spectroscopy and X-ray photoelectron spectroscopy. It reveals that the number of dangling bonds on the free carbon is increased as pyrolysis temperature increases, with the activation energy of ~3.87 eV. So it is demonstrated that the pyrolysis-temperature induced increase in the conductivity is mainly attributed to the increase of dangling on the graphite-like carbon.展开更多
There exists a lot of research on the nonlinear vibration of the pipeline system with different boundary conditions.To the best of our knowledge,little research on the actual constraint of the clamp has been performed...There exists a lot of research on the nonlinear vibration of the pipeline system with different boundary conditions.To the best of our knowledge,little research on the actual constraint of the clamp has been performed.In this paper,according to hysteresis loops of the clamp obtained from experimental test,the simplified bilinear stiffness and damping model is proposed.Then the Finite Element(FE)model of L-type pipeline system with clamps is established using Timoshenko beam theory in combination with aforementioned stiffness-damping model.Both hammering and shaker tests verify the FE model via the comparisons of natural frequencies and vibration responses.The results show that the maximum errors of natural frequencies and vibration responses are about 8.31%and 17.6%,respectively.The proposed model can simulate the dynamic characteristics of the L-type pipeline system with clamps well,which is helpful to provide some guidance for the early design stage of pipeline in aero-engine.展开更多
Similitude design plays a vital role in the analysis of vibration and shock problems encountered in large engineering equipment. Similitude design, including dimensional analysis and governing equation method, is foun...Similitude design plays a vital role in the analysis of vibration and shock problems encountered in large engineering equipment. Similitude design, including dimensional analysis and governing equation method, is founded on the dynamic similitude theory. This study reviews the application of similitude design methods in engineering practice and summarizes the major achieve- ments of the dynamic similitude theory in structural vibration and shock problems in different fields, including marine structures, civil engineering structures, and large power equipment. This study also reviews the dynamic similitude design methods for thin-walled and composite material plates and shells, including the most recent work published by the authors. Structure sensitivity analysis is used to evaluate the scaling factors to attain accurate distorted scaling laws. Finally, this study discusses the existing problems and the potential of the dynamic similitude theory for the analysis of vibration and shock problems of structures.展开更多
A balancing method without trial weights based on the dynamic similitude scale model was proposed as a solution to the balancing problem of a large-scale rotor system. This method could be used to directly obtain the ...A balancing method without trial weights based on the dynamic similitude scale model was proposed as a solution to the balancing problem of a large-scale rotor system. This method could be used to directly obtain the required coefficients for the balancing problem of the prototype system through a similarity model test without a prototype test. Thus, the weight test process of the prototype system was effectively eliminated in the proposed balancing method. First, with the rotor system as the research object, the analytical expression of the influence coefficient was derived on the basis of rotor dynamics theory. Then, through calculation and dimen- sional analysis methods, the similitude relationships of the rotor system and the influence coefficient were deduced on the basis of dynamic similitude theory. The correctness of the proposed similitude relationships was verified through numerical simulation and experiment. The balancing method without trial weights was proposed based on the similitude relationship of the influence coefficient. The effect of the balancing method without trial weights was compared with that of the traditional influence coefficient method through numerical simulation, and the results verified the correctness and effectiveness of the proposed balancing method. The results of this study provide theoretical supplements for the balancing method and the similitude design of the rotor system.展开更多
Cell fate determination is a major unsolved problem in cell and developmental biology.The discovery of reprogramming by pluri-potent factors offers a rational system to investigate the molecular mechanisms associated ...Cell fate determination is a major unsolved problem in cell and developmental biology.The discovery of reprogramming by pluri-potent factors offers a rational system to investigate the molecular mechanisms associated with cell fate decisions.The idea that reprogramming of fibroblasts starts with a mesenchymal-epithelial transition(MET)suggests that the process is perhaps a reversal of epithelial to mesenchymal transition(EMT)found frequently during early embryogenesis.As such,we believe that investigations into MET-EMT may yield detailed molecular insights into cell fate decisions,not only for the switching between epithelial and mesenchymal cells,but also other cell types.展开更多
In this paper, a three-dimensional finite-element formulation for the multiferroic composite is developed and implemented into the commercial software ABAQUS for its transient analysis. First, a special three-dimensio...In this paper, a three-dimensional finite-element formulation for the multiferroic composite is developed and implemented into the commercial software ABAQUS for its transient analysis. First, a special three-dimensional eight-node solid element is designed to handle the multiferroic composite made of elastic, piezoelectric, and piezomagnetic materials. Second, a userdefined subroutine for this newly developed element is implemented into ABAQUS. Finally, the transient responses of a bi-layered multiferroic composite are calculated by using the direct time integration method. Two typical magnetic potential signals, Gauss and Ricker pulses, are applied to the composite with various time durations of excitation. The induced electric field shows that the transient response can be substantially influenced by the input signal, which could be tuned for the strongest electric output.展开更多
In response to the identification problem concerning multi-degree of freedom (MDOF) nonlinear systems, this study presents the extended forward orthogonal regression (EFOR) based on predicted residual sums of squa...In response to the identification problem concerning multi-degree of freedom (MDOF) nonlinear systems, this study presents the extended forward orthogonal regression (EFOR) based on predicted residual sums of squares (PRESS) to construct a nonlinear dynamic parametrical model. The proposed parametrical model is based on the non-linear autoregressive with exogenous inputs (NARX) model and aims to explicitly reveal the physical design parameters of the system. The PRESSbased EFOR algorithm is proposed to identify such a model for MDOF systems. By using the algorithm, we built a common-structured model based on the fundamental concept of evaluating its generalization capability through cross-validation. The resulting model aims to prevent over-fitting with poor generalization performance caused by the average error reduction ratio (AERR)-based EFOR algorithm. Then, a functional relationship is established between the coefficients of the terms and the design parameters of the unified model. Moreover, a 5- DOF nonlinear system is taken as a case to illustrate the modeling of the proposed algorithm. Finally, a dynamic parametrical model of a cantilever beam is constructed from experimental data. Results indicate that the dynamic parametrical model of nonlinear systems, which depends on the PRESS-based EFOR, can accurately predict the output response, thus providing a theoretical basis for the optimal design of modeling methods for MDOF nonlinear systems.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52175079 and 12072091)the Science Foundation of the National Key Laboratory of Science and Technology on Advanced Composites in Special Environments of China(No.6142905192512)+2 种基金the Fundamental Research Funds for the Central Universities of China(No.N2103026)the Major Projects of AeroEngines and Gas Turbines of China(No.J2019-I-0008-0008)the China Postdoctoral Science Foundation(No.2020M680990)。
文摘This study analyzes and predicts the vibration characteristics of fiberreinforced composite sandwich(FRCS)cylindrical-spherical(CS)combined shells with hexagon honeycomb core(HHC)for the first time based on an analytical model developed,which makes good use of the advantage of the first-order shear deformation theory(FSDT),the multi-segment decomposition technique,the virtual spring technology,the Jacobi-Ritz approach,and the transfer function method.The equivalent material properties of HHC are firstly determined by the modified Gibson’s formula,and the related energy equations are derived for the HHC-FRCS-CS combined shells,from which the fundamental frequencies,the mode shapes,and the forced vibration responses are solved.The current model is verified through the discussion of convergence and comparative analysis with the associated published literature and finite element(FE)results.The effects of geometric parameters of HHC on the dynamic property of the structure are further investigated with the verified model.It reveals that the vibration suppression capability can be greatly enhanced by reducing the ratio of HHC thickness to total thickness and the ratio of wall thickness of honeycomb cell to overall radius,and by increasing the ratio of length of honeycomb cell to overall radius and honeycomb characteristic angle of HHC.
文摘The conductivity of polymer-derived SiOCN ceramics exhibited an Arrhenius dependence on pyrolysis temperature, with the activation energy of ~3.95 eV. The formation and structure change of the free carbon phase were detected by means of electron spin resonance spectroscopy and X-ray photoelectron spectroscopy. It reveals that the number of dangling bonds on the free carbon is increased as pyrolysis temperature increases, with the activation energy of ~3.87 eV. So it is demonstrated that the pyrolysis-temperature induced increase in the conductivity is mainly attributed to the increase of dangling on the graphite-like carbon.
基金supported by National Natural Science Foundation of China(No.11772089)Fundamental Research Funds for the Central Universities(Nos.N170308028,N170306004 and N180708009)Program for the Innovative Talents of Higher Learning Institutions of Liaoning(LR2017035)。
文摘There exists a lot of research on the nonlinear vibration of the pipeline system with different boundary conditions.To the best of our knowledge,little research on the actual constraint of the clamp has been performed.In this paper,according to hysteresis loops of the clamp obtained from experimental test,the simplified bilinear stiffness and damping model is proposed.Then the Finite Element(FE)model of L-type pipeline system with clamps is established using Timoshenko beam theory in combination with aforementioned stiffness-damping model.Both hammering and shaker tests verify the FE model via the comparisons of natural frequencies and vibration responses.The results show that the maximum errors of natural frequencies and vibration responses are about 8.31%and 17.6%,respectively.The proposed model can simulate the dynamic characteristics of the L-type pipeline system with clamps well,which is helpful to provide some guidance for the early design stage of pipeline in aero-engine.
文摘Similitude design plays a vital role in the analysis of vibration and shock problems encountered in large engineering equipment. Similitude design, including dimensional analysis and governing equation method, is founded on the dynamic similitude theory. This study reviews the application of similitude design methods in engineering practice and summarizes the major achieve- ments of the dynamic similitude theory in structural vibration and shock problems in different fields, including marine structures, civil engineering structures, and large power equipment. This study also reviews the dynamic similitude design methods for thin-walled and composite material plates and shells, including the most recent work published by the authors. Structure sensitivity analysis is used to evaluate the scaling factors to attain accurate distorted scaling laws. Finally, this study discusses the existing problems and the potential of the dynamic similitude theory for the analysis of vibration and shock problems of structures.
基金Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant No. 11572082), the Excellent Talents Support Program in Institutions of Higher Learning in Liaoning Province of China (Grant No. LJQ2015038), and the Fundamental Research Funds for the Central Universities of China (Grant Nos. N160312001, N150304004, and N140301001).
文摘A balancing method without trial weights based on the dynamic similitude scale model was proposed as a solution to the balancing problem of a large-scale rotor system. This method could be used to directly obtain the required coefficients for the balancing problem of the prototype system through a similarity model test without a prototype test. Thus, the weight test process of the prototype system was effectively eliminated in the proposed balancing method. First, with the rotor system as the research object, the analytical expression of the influence coefficient was derived on the basis of rotor dynamics theory. Then, through calculation and dimen- sional analysis methods, the similitude relationships of the rotor system and the influence coefficient were deduced on the basis of dynamic similitude theory. The correctness of the proposed similitude relationships was verified through numerical simulation and experiment. The balancing method without trial weights was proposed based on the similitude relationship of the influence coefficient. The effect of the balancing method without trial weights was compared with that of the traditional influence coefficient method through numerical simulation, and the results verified the correctness and effectiveness of the proposed balancing method. The results of this study provide theoretical supplements for the balancing method and the similitude design of the rotor system.
基金funded in part by the grants from Ministry of Science and Technology 973 Program (2009CB941102,2011CB965200,and 2011CBA01106)‘Strategic Priority Research Program’of the Chinese Academy of Sciences (Grant No.XDA01020401,XDA01020106,XDA01020202,XDA01020404).
文摘Cell fate determination is a major unsolved problem in cell and developmental biology.The discovery of reprogramming by pluri-potent factors offers a rational system to investigate the molecular mechanisms associated with cell fate decisions.The idea that reprogramming of fibroblasts starts with a mesenchymal-epithelial transition(MET)suggests that the process is perhaps a reversal of epithelial to mesenchymal transition(EMT)found frequently during early embryogenesis.As such,we believe that investigations into MET-EMT may yield detailed molecular insights into cell fate decisions,not only for the switching between epithelial and mesenchymal cells,but also other cell types.
基金supported by the National Natural Science Foundation of China (No.50775028)
文摘In this paper, a three-dimensional finite-element formulation for the multiferroic composite is developed and implemented into the commercial software ABAQUS for its transient analysis. First, a special three-dimensional eight-node solid element is designed to handle the multiferroic composite made of elastic, piezoelectric, and piezomagnetic materials. Second, a userdefined subroutine for this newly developed element is implemented into ABAQUS. Finally, the transient responses of a bi-layered multiferroic composite are calculated by using the direct time integration method. Two typical magnetic potential signals, Gauss and Ricker pulses, are applied to the composite with various time durations of excitation. The induced electric field shows that the transient response can be substantially influenced by the input signal, which could be tuned for the strongest electric output.
基金Acknowledgements This work was supported by the National Science Foundation of China (Grant No. 11572082), the Excellent Talents Support Program in Institutions of Higher Learning in Liaoning Province, China (Grant No. LJQ2015038), the Fundamental Research Funds for the Central Universities of China (Grant Nos. N150304004 and N140301001), and the Key Laboratory for Precision and Non-traditional Machining of the Ministry of Education, Dalian University of Technology (Grant No. JMTZ201602).
文摘In response to the identification problem concerning multi-degree of freedom (MDOF) nonlinear systems, this study presents the extended forward orthogonal regression (EFOR) based on predicted residual sums of squares (PRESS) to construct a nonlinear dynamic parametrical model. The proposed parametrical model is based on the non-linear autoregressive with exogenous inputs (NARX) model and aims to explicitly reveal the physical design parameters of the system. The PRESSbased EFOR algorithm is proposed to identify such a model for MDOF systems. By using the algorithm, we built a common-structured model based on the fundamental concept of evaluating its generalization capability through cross-validation. The resulting model aims to prevent over-fitting with poor generalization performance caused by the average error reduction ratio (AERR)-based EFOR algorithm. Then, a functional relationship is established between the coefficients of the terms and the design parameters of the unified model. Moreover, a 5- DOF nonlinear system is taken as a case to illustrate the modeling of the proposed algorithm. Finally, a dynamic parametrical model of a cantilever beam is constructed from experimental data. Results indicate that the dynamic parametrical model of nonlinear systems, which depends on the PRESS-based EFOR, can accurately predict the output response, thus providing a theoretical basis for the optimal design of modeling methods for MDOF nonlinear systems.