Mechanical vibration is an effective fruit harvesting method.To evaluate the dynamic characteristics of dwarf Chinese hickory(Carya cathayensis Sarg.)trees and the influence of the tree structure on transmission and a...Mechanical vibration is an effective fruit harvesting method.To evaluate the dynamic characteristics of dwarf Chinese hickory(Carya cathayensis Sarg.)trees and the influence of the tree structure on transmission and attenuation of dynamic response,a new method was proposed based on acceleration admittance measurement on dwarf Chinese hickory trees in orchard environment under impact excitation.The primary resonance frequencies of the tree can be determined based on the acceleration admittance measurement.The effect of the tree structure on the vibratory transmission was quantified using the attenuation ratio of the acceleration admittance.A 5-year-old dwarf Chinese hickory tree sample was tested.The responses at three resonance frequencies(5,9 and 12 Hz)were analyzed because they were identified as the most effective bands of excitation for the main part of the tree specimen.The results reveal that the variation of the dynamic response along the testing tree is greatly related to the Chinese hickory tree structure.The attenuation ratio of the acceleration admittance at the branch crotches indicates the leader top crotch may amplify the acceleration admittance no matter what the crotch angle and the branch diameter is.Unlike the crotches,the branch chain nodes generally have negative influence on the acceleration admittance along the branch chains which heavily depend on the branch chain configuration.The branch chains with a chain angle no less than 150°and a wood diameter ratio close to 1.0 could produce little influence on the vibration transmission.For those branches with chain angle less than 150°,the vibration was generally attenuated at their chain nodes at three resonance frequencies.To impose impact excitations on the tree,high mechanical harvesting efficiency could be achieved on those branch chains which are almost straight and uniform.展开更多
对CAARC(Commonwealth Advisory Aeronautical Research Council)标准矩形高层建筑开展同步测压风洞试验,获得建筑表面的风压分布,并建立其三维有限元模型,详细分析有、无设置黏滞阻尼器下的结构风致加速度响应的减振控制率。结果表明:...对CAARC(Commonwealth Advisory Aeronautical Research Council)标准矩形高层建筑开展同步测压风洞试验,获得建筑表面的风压分布,并建立其三维有限元模型,详细分析有、无设置黏滞阻尼器下的结构风致加速度响应的减振控制率。结果表明:结构顶层峰值加速度的减振控制率随着阻尼系数C的增大而增加、随着阻尼指数α的增大而减小;靠近结构上部楼层布置黏滞阻尼器的风振控制效果较好;随着阻尼器布置数量增加,结构的减振控制率逐渐增大,且顺风向的减振控制率都比横风向的大;隔层布置时的减振控制率比逐层布置时更好。展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.51475433,51175476)the Research Fund for the Doctoral Program of Higher Education of China(RFDP)(Grant No.20113318110001)+1 种基金the Program for Scientific Research Innovation Team of Zhejiang Sci-Tech University(Grant No.13020049-Y)the 521 Talent Plan of Zhejiang Sci-Tech University.
文摘Mechanical vibration is an effective fruit harvesting method.To evaluate the dynamic characteristics of dwarf Chinese hickory(Carya cathayensis Sarg.)trees and the influence of the tree structure on transmission and attenuation of dynamic response,a new method was proposed based on acceleration admittance measurement on dwarf Chinese hickory trees in orchard environment under impact excitation.The primary resonance frequencies of the tree can be determined based on the acceleration admittance measurement.The effect of the tree structure on the vibratory transmission was quantified using the attenuation ratio of the acceleration admittance.A 5-year-old dwarf Chinese hickory tree sample was tested.The responses at three resonance frequencies(5,9 and 12 Hz)were analyzed because they were identified as the most effective bands of excitation for the main part of the tree specimen.The results reveal that the variation of the dynamic response along the testing tree is greatly related to the Chinese hickory tree structure.The attenuation ratio of the acceleration admittance at the branch crotches indicates the leader top crotch may amplify the acceleration admittance no matter what the crotch angle and the branch diameter is.Unlike the crotches,the branch chain nodes generally have negative influence on the acceleration admittance along the branch chains which heavily depend on the branch chain configuration.The branch chains with a chain angle no less than 150°and a wood diameter ratio close to 1.0 could produce little influence on the vibration transmission.For those branches with chain angle less than 150°,the vibration was generally attenuated at their chain nodes at three resonance frequencies.To impose impact excitations on the tree,high mechanical harvesting efficiency could be achieved on those branch chains which are almost straight and uniform.
文摘对CAARC(Commonwealth Advisory Aeronautical Research Council)标准矩形高层建筑开展同步测压风洞试验,获得建筑表面的风压分布,并建立其三维有限元模型,详细分析有、无设置黏滞阻尼器下的结构风致加速度响应的减振控制率。结果表明:结构顶层峰值加速度的减振控制率随着阻尼系数C的增大而增加、随着阻尼指数α的增大而减小;靠近结构上部楼层布置黏滞阻尼器的风振控制效果较好;随着阻尼器布置数量增加,结构的减振控制率逐渐增大,且顺风向的减振控制率都比横风向的大;隔层布置时的减振控制率比逐层布置时更好。
