In this paper a fully parametrized finite element simulation model of the stator bar end is created using the COMSOL Multiphysics.The model allows conducting the comparison of different corona protection structures’d...In this paper a fully parametrized finite element simulation model of the stator bar end is created using the COMSOL Multiphysics.The model allows conducting the comparison of different corona protection structures’design,various materials properties,and finally optimizing the corona protection system.Several samples of SiC based nonlinear conductivity materials for corona protection were fabricated in laboratory and then investigated.The conductivity dependencies on electric field(0.05 to 1 kV/mm)and temperature(20 to 155℃)were measured.By comparing the heat-resistant grades of the corona protection material and the insulating material,the maximum working temperature of the corona protection material corresponds to the heat-resistant grade F of the insulating material.As the temperature increases,the nonlinear characteristics of the corona protection material in the experiment decrease dramatically,reducing the heat-resistant grade of the corona protection material.The decrease in the nonlinear characteristics of the corona protection material at the maximum operating temperature causes the maximum electric field strength at the end of the HV rotating machines end corona protection(ECP)exceeding the corona discharge electric field strength,resulting in corona phenomenon.展开更多
The graded density impactor(GDI)dynamic loading technique is crucial for acquiring the dynamic physical property parameters of materials used in weapons.The accuracy and timeliness of GDI structural design are key to ...The graded density impactor(GDI)dynamic loading technique is crucial for acquiring the dynamic physical property parameters of materials used in weapons.The accuracy and timeliness of GDI structural design are key to achieving controllable stress-strain rate loading.In this study,we have,for the first time,combined one-dimensional fluid computational software with machine learning methods.We first elucidated the mechanisms by which GDI structures control stress and strain rates.Subsequently,we constructed a machine learning model to create a structure-property response surface.The results show that altering the loading velocity and interlayer thickness has a pronounced regulatory effect on stress and strain rates.In contrast,the impedance distribution index and target thickness have less significant effects on stress regulation,although there is a matching relationship between target thickness and interlayer thickness.Compared with traditional design methods,the machine learning approach offers a10^(4)—10^(5)times increase in efficiency and the potential to achieve a global optimum,holding promise for guiding the design of GDI.展开更多
The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have ...The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have been incorporated into the typical Al@AP composites through the spray drying technique.The thermal behavior,ignition and combustion characteristics were comprehensively evaluated and compared.The experimental results showed that with the varying inclusion of the graded Al,the heat of reaction exhibited a significant change,ranging from 9090 J·g^(-1) to 11036 J·g^(-1),which was strongly dependent on the particle size of Al.The combination of Al with diverse range of particle sizes in graded configuration serves to significantly enhance the decomposition of AP,resulting in the disappearance of the LTD stage and a conspicuous decrease of at least 11.7℃ in the peak temperature of the HTD.Furthermore,the maximum burning rate achieved by the Al-3@AP composite was 33.6 mm·s^(-1),which was exactly twice as high as that of the graded Al-1@AP composite with the lowest burning rate.Diffraction peaks corresponding to unburned Al were detected in the condensed combustion products of Al-1@AP,and the combustion images clearly indicated an incomplete combustion tendency for this sample.In contrast,a well-designed gradation of Al powders,such as a combination of fine Al powders with a particle size below 5μm,has proven to be the most conducive to enhancing the combustion efficiency of the composites.展开更多
Recent advancements in additive manufacturing(AM)have revolutionized the design and production of complex engineering microstructures.Despite these advancements,their mathematical modeling and computational analysis r...Recent advancements in additive manufacturing(AM)have revolutionized the design and production of complex engineering microstructures.Despite these advancements,their mathematical modeling and computational analysis remain significant challenges.This research aims to develop an effective computational method for analyzing the free vibration of functionally graded(FG)microplates under high temperatures while resting on a Pasternak foundation(PF).This formulation leverages a new thirdorder shear deformation theory(new TSDT)for improved accuracy without requiring shear correction factors.Additionally,the modified couple stress theory(MCST)is incorporated to account for sizedependent effects in microplates.The PF is characterized by two parameters including spring stiffness(k_(w))and shear layer stiffness(k_(s)).To validate the proposed method,the results obtained are compared with those of the existing literature.Furthermore,numerical examples explore the influence of various factors on the high-temperature free vibration of FG microplates.These factors include the length scale parameter(l),geometric dimensions,material properties,and the presence of the elastic foundation.The findings significantly enhance our comprehension of the free vibration of FG microplates in high thermal environments.In addition,the findings significantly enhance our comprehension of the free vibration of FG microplates in high thermal environments.In addition,the results of this research will have great potential in military and defense applications such as components of submarines,fighter aircraft,and missiles.展开更多
In this paper,the isogeometric analysis(IGA)method is employed to analyze the oscillation characteristics of functionally graded triply periodic minimal surface(FG-TPMS)curved-doubly shells integrated with magneto-ele...In this paper,the isogeometric analysis(IGA)method is employed to analyze the oscillation characteristics of functionally graded triply periodic minimal surface(FG-TPMS)curved-doubly shells integrated with magneto-electric surface layers(referred to as"FG-TPMS-MEE curved-doubly shells")subjected to low-velocity impact loads.This study presents low-velocity impact load model based on a single springmass(S-M)approach.The FG-TPMS-MEE curved-doubly shells are covered with two magneto-electric surface layers,while the core layer consists of three types:I-graph and Wrapped Package-graph(IWP),Gyroid(G),and Primitive(P),with various graded functions.These types are notable for their exceptional stiffness-to-weight ratios,enabling a wide range of potential applications.The Maxwell equations and electromagnetic boundary conditions are applied to compute the change in electric potentials and magnetic potentials.The equilibrium equations of the shell are derived from a refined higher-order shear deformation theory(HSDT),and the transient responses of the FG-TPMS-MEE curveddoubly shells are subsequently determined using Newmark's direct integration method.These results have applications in structural vibration control and the analysis of structures subjected to impact or explosive loads.Furthermore,this study provides a theoretical prediction of the low-velocity impact load and magneto-electric-elastic effects on the free vibration and transient response of FG-TPMS-MEE curved-doubly shells.展开更多
目的对中药治疗特发性肺纤维化系统评价/Meta分析进行再评价研究,以期为临床医师及研究者提供更科学的决策支持。方法检索中药治疗特发性肺纤维化系统评价/Meta分析的文献,筛选文献后提取资料,采用AMSTAR2(A Measurement Tool To Assess...目的对中药治疗特发性肺纤维化系统评价/Meta分析进行再评价研究,以期为临床医师及研究者提供更科学的决策支持。方法检索中药治疗特发性肺纤维化系统评价/Meta分析的文献,筛选文献后提取资料,采用AMSTAR2(A Measurement Tool To Assess Systematic Reviews 2)量表和GRADE(Grade of Recommendation,Assessment,Development,and Evaluation)系统工具进行评估。结果共纳入14篇文献,106次结局指标;AMSTAR2量表结果示3篇属于低质量,11篇属于极低质量;GRADE分级显示,10次结局指标证据质量等级中等,83次等级低,13次等级极低。结论中药治疗特发性肺纤维化系统评价/Meta分析的方法学质量为低、极低,结局指标的证据质量等级多为低,高质量、证据强度高级别的系统评价亟需开展,从而作为高级别证据来指导临床。展开更多
通过文献检索和筛选,选取了43个校园欺凌的干预研究,使用CMA3.0分析干预效果及影响因素,并使用GRADE系统对所有结局指标的证据质量进行评估。结果显示,针对欺凌者的干预项目具有中等效果量(g=0.57, p <0.05);针对欺凌受害者的干预项...通过文献检索和筛选,选取了43个校园欺凌的干预研究,使用CMA3.0分析干预效果及影响因素,并使用GRADE系统对所有结局指标的证据质量进行评估。结果显示,针对欺凌者的干预项目具有中等效果量(g=0.57, p <0.05);针对欺凌受害者的干预项目使得受害者的受欺凌行为减少(g=0.42, p <0.05),心理健康得到改善(g=0.40, p <0.01);针对所有学生的欺凌干预项目对其欺凌行为的效果g=0.17 (p <0.001),对其受欺凌行为效果g=0.19 (p <0.001),可能存在出版偏差;学生态度改变的效果g=0.40 (p <0.01)。除了态度改变的证据质量为中等,其他结局指标的证据都为低或者极低质量。对于所有学生干预项目,干预周期小于1学期的效果量大于干预周期大于1学期的效果量,教育干预项目效果量小于系统干预效果量,非随机研究效果量大于随机对照研究。直接针对欺凌者或者欺凌受害者的干预效果量中等,但是样本量少,需要进一步的研究证据支持。针对所有学生的欺凌干预项目虽然效果量低,但是仍具有实践意义,其效果量受到干预周期和干预特征的影响。展开更多
文摘In this paper a fully parametrized finite element simulation model of the stator bar end is created using the COMSOL Multiphysics.The model allows conducting the comparison of different corona protection structures’design,various materials properties,and finally optimizing the corona protection system.Several samples of SiC based nonlinear conductivity materials for corona protection were fabricated in laboratory and then investigated.The conductivity dependencies on electric field(0.05 to 1 kV/mm)and temperature(20 to 155℃)were measured.By comparing the heat-resistant grades of the corona protection material and the insulating material,the maximum working temperature of the corona protection material corresponds to the heat-resistant grade F of the insulating material.As the temperature increases,the nonlinear characteristics of the corona protection material in the experiment decrease dramatically,reducing the heat-resistant grade of the corona protection material.The decrease in the nonlinear characteristics of the corona protection material at the maximum operating temperature causes the maximum electric field strength at the end of the HV rotating machines end corona protection(ECP)exceeding the corona discharge electric field strength,resulting in corona phenomenon.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2021B0301030001)the National Key Research and Development Program of China(Grant No.2021YFB3802300)the Foundation of National Key Laboratory of Shock Wave and Detonation Physics(Grant No.JCKYS2022212004)。
文摘The graded density impactor(GDI)dynamic loading technique is crucial for acquiring the dynamic physical property parameters of materials used in weapons.The accuracy and timeliness of GDI structural design are key to achieving controllable stress-strain rate loading.In this study,we have,for the first time,combined one-dimensional fluid computational software with machine learning methods.We first elucidated the mechanisms by which GDI structures control stress and strain rates.Subsequently,we constructed a machine learning model to create a structure-property response surface.The results show that altering the loading velocity and interlayer thickness has a pronounced regulatory effect on stress and strain rates.In contrast,the impedance distribution index and target thickness have less significant effects on stress regulation,although there is a matching relationship between target thickness and interlayer thickness.Compared with traditional design methods,the machine learning approach offers a10^(4)—10^(5)times increase in efficiency and the potential to achieve a global optimum,holding promise for guiding the design of GDI.
文摘The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have been incorporated into the typical Al@AP composites through the spray drying technique.The thermal behavior,ignition and combustion characteristics were comprehensively evaluated and compared.The experimental results showed that with the varying inclusion of the graded Al,the heat of reaction exhibited a significant change,ranging from 9090 J·g^(-1) to 11036 J·g^(-1),which was strongly dependent on the particle size of Al.The combination of Al with diverse range of particle sizes in graded configuration serves to significantly enhance the decomposition of AP,resulting in the disappearance of the LTD stage and a conspicuous decrease of at least 11.7℃ in the peak temperature of the HTD.Furthermore,the maximum burning rate achieved by the Al-3@AP composite was 33.6 mm·s^(-1),which was exactly twice as high as that of the graded Al-1@AP composite with the lowest burning rate.Diffraction peaks corresponding to unburned Al were detected in the condensed combustion products of Al-1@AP,and the combustion images clearly indicated an incomplete combustion tendency for this sample.In contrast,a well-designed gradation of Al powders,such as a combination of fine Al powders with a particle size below 5μm,has proven to be the most conducive to enhancing the combustion efficiency of the composites.
文摘Recent advancements in additive manufacturing(AM)have revolutionized the design and production of complex engineering microstructures.Despite these advancements,their mathematical modeling and computational analysis remain significant challenges.This research aims to develop an effective computational method for analyzing the free vibration of functionally graded(FG)microplates under high temperatures while resting on a Pasternak foundation(PF).This formulation leverages a new thirdorder shear deformation theory(new TSDT)for improved accuracy without requiring shear correction factors.Additionally,the modified couple stress theory(MCST)is incorporated to account for sizedependent effects in microplates.The PF is characterized by two parameters including spring stiffness(k_(w))and shear layer stiffness(k_(s)).To validate the proposed method,the results obtained are compared with those of the existing literature.Furthermore,numerical examples explore the influence of various factors on the high-temperature free vibration of FG microplates.These factors include the length scale parameter(l),geometric dimensions,material properties,and the presence of the elastic foundation.The findings significantly enhance our comprehension of the free vibration of FG microplates in high thermal environments.In addition,the findings significantly enhance our comprehension of the free vibration of FG microplates in high thermal environments.In addition,the results of this research will have great potential in military and defense applications such as components of submarines,fighter aircraft,and missiles.
文摘In this paper,the isogeometric analysis(IGA)method is employed to analyze the oscillation characteristics of functionally graded triply periodic minimal surface(FG-TPMS)curved-doubly shells integrated with magneto-electric surface layers(referred to as"FG-TPMS-MEE curved-doubly shells")subjected to low-velocity impact loads.This study presents low-velocity impact load model based on a single springmass(S-M)approach.The FG-TPMS-MEE curved-doubly shells are covered with two magneto-electric surface layers,while the core layer consists of three types:I-graph and Wrapped Package-graph(IWP),Gyroid(G),and Primitive(P),with various graded functions.These types are notable for their exceptional stiffness-to-weight ratios,enabling a wide range of potential applications.The Maxwell equations and electromagnetic boundary conditions are applied to compute the change in electric potentials and magnetic potentials.The equilibrium equations of the shell are derived from a refined higher-order shear deformation theory(HSDT),and the transient responses of the FG-TPMS-MEE curveddoubly shells are subsequently determined using Newmark's direct integration method.These results have applications in structural vibration control and the analysis of structures subjected to impact or explosive loads.Furthermore,this study provides a theoretical prediction of the low-velocity impact load and magneto-electric-elastic effects on the free vibration and transient response of FG-TPMS-MEE curved-doubly shells.
文摘通过文献检索和筛选,选取了43个校园欺凌的干预研究,使用CMA3.0分析干预效果及影响因素,并使用GRADE系统对所有结局指标的证据质量进行评估。结果显示,针对欺凌者的干预项目具有中等效果量(g=0.57, p <0.05);针对欺凌受害者的干预项目使得受害者的受欺凌行为减少(g=0.42, p <0.05),心理健康得到改善(g=0.40, p <0.01);针对所有学生的欺凌干预项目对其欺凌行为的效果g=0.17 (p <0.001),对其受欺凌行为效果g=0.19 (p <0.001),可能存在出版偏差;学生态度改变的效果g=0.40 (p <0.01)。除了态度改变的证据质量为中等,其他结局指标的证据都为低或者极低质量。对于所有学生干预项目,干预周期小于1学期的效果量大于干预周期大于1学期的效果量,教育干预项目效果量小于系统干预效果量,非随机研究效果量大于随机对照研究。直接针对欺凌者或者欺凌受害者的干预效果量中等,但是样本量少,需要进一步的研究证据支持。针对所有学生的欺凌干预项目虽然效果量低,但是仍具有实践意义,其效果量受到干预周期和干预特征的影响。
