The vibration control in the frequency domain is significant.Therefore,an active vibration control in frequency domain is studied in this paper.It is generally known that piezo-intelligent structures possess satisfact...The vibration control in the frequency domain is significant.Therefore,an active vibration control in frequency domain is studied in this paper.It is generally known that piezo-intelligent structures possess satisfactory performances in the area of vibration control,and macro-fiber composites(MFCs)with high sensitivity and deformability are widely applied in engineering.So,this paper uses the MFC patches and designs a control method based on the pole placement method,and the natural frequency of the beam can be artificially designed.MFC patches are bonded on the top and bottom surfaces of the beam structure to act as the actuators and sensors.Then,the finite element method(FEM)is used to formulate the equation of motion,and the pole placement based on the out-put feedback method is used to design the active controller.Finally,the effectiveness of the active control method is verified.展开更多
Thorium was discovered in 1828 by the Swedish chemist Jons J. Berzelius. Despite some advantages over uranium for use in nuclear reactors, its main use, in the almost two centuries since its discovery, thorium was res...Thorium was discovered in 1828 by the Swedish chemist Jons J. Berzelius. Despite some advantages over uranium for use in nuclear reactors, its main use, in the almost two centuries since its discovery, thorium was restricted to use for gas mantles, especially in the early 20th century. In the beginning of the nuclear era, many countries had interested on thorium, particularly during the 1950-1970 period. There are about 435 nuclear reactors in the world nowadays. They need more than 65,000 tons of uranium yearly. The future world energy needs will increase and, even if we assumed a conservative contribution of nuclear generation, there will be a significant increasing in the uranium prices occur, taking into account that uranium, as used in the present thermal reactors, is a finite resource. Thorium is nearly three times more abundant than uranium in the Earth＇s crust. Despite thorium is not a fissile material, ^232Th can be converted to ^233U （fissile） more efficiently than ^238U to ^239pu. Besides this, since it is possible to convert thorium waste into non-radioactive elements, thorium is an environment-friendly alternative energy source. Thorium fuel cycle is also inherently resistant to proliferation. Some papers evaluate the thorium resources in Brazil over 1,200,000 metric t. Then, the thorium alternative must be seriously considered in Brazil for strategic reasons. In this paper a brief history of thorium is presented, besides a review of the world thorium utilization and a discussion about advantages and restrictions of thorium use.展开更多
基金supported by the National Natural Science Foundation of China(Nos.11802069,11761131006)the China Postdoctoral Science Foundation(No.3236310534)+1 种基金the Heilongjiang Provincial Postdoctoral Science Foundation(Nos.002020830603,LBHTZ2008)the China Fundamental Research Funds for the Central Universities(No.GK2020260225).
文摘The vibration control in the frequency domain is significant.Therefore,an active vibration control in frequency domain is studied in this paper.It is generally known that piezo-intelligent structures possess satisfactory performances in the area of vibration control,and macro-fiber composites(MFCs)with high sensitivity and deformability are widely applied in engineering.So,this paper uses the MFC patches and designs a control method based on the pole placement method,and the natural frequency of the beam can be artificially designed.MFC patches are bonded on the top and bottom surfaces of the beam structure to act as the actuators and sensors.Then,the finite element method(FEM)is used to formulate the equation of motion,and the pole placement based on the out-put feedback method is used to design the active controller.Finally,the effectiveness of the active control method is verified.
文摘Thorium was discovered in 1828 by the Swedish chemist Jons J. Berzelius. Despite some advantages over uranium for use in nuclear reactors, its main use, in the almost two centuries since its discovery, thorium was restricted to use for gas mantles, especially in the early 20th century. In the beginning of the nuclear era, many countries had interested on thorium, particularly during the 1950-1970 period. There are about 435 nuclear reactors in the world nowadays. They need more than 65,000 tons of uranium yearly. The future world energy needs will increase and, even if we assumed a conservative contribution of nuclear generation, there will be a significant increasing in the uranium prices occur, taking into account that uranium, as used in the present thermal reactors, is a finite resource. Thorium is nearly three times more abundant than uranium in the Earth＇s crust. Despite thorium is not a fissile material, ^232Th can be converted to ^233U （fissile） more efficiently than ^238U to ^239pu. Besides this, since it is possible to convert thorium waste into non-radioactive elements, thorium is an environment-friendly alternative energy source. Thorium fuel cycle is also inherently resistant to proliferation. Some papers evaluate the thorium resources in Brazil over 1,200,000 metric t. Then, the thorium alternative must be seriously considered in Brazil for strategic reasons. In this paper a brief history of thorium is presented, besides a review of the world thorium utilization and a discussion about advantages and restrictions of thorium use.
