An easily stackable multi-layer quasi-zero-stiffness(ML-QZS)meta-structure is proposed to achieve highly efficient vibration isolation performance at low frequency.First,the distributed shape optimization method is us...An easily stackable multi-layer quasi-zero-stiffness(ML-QZS)meta-structure is proposed to achieve highly efficient vibration isolation performance at low frequency.First,the distributed shape optimization method is used to design the unit cel,i.e.,the single-layer QZS(SL-QZS)meta-structure.Second,the stiffness feature of the unit cell is investigated and verified through static experiments.Third,the unit cells are stacked one by one along the direction of vibration isolation,and thus the ML-QZS meta-structure is constructed.Fourth,the dynamic modeling of the ML-QZS vibration isolation metastructure is conducted,and the dynamic responses are obtained from the equations of motion,and verified by finite element(FE)simulations.Finally,a prototype of the ML-QZS vibration isolation meta-structure is fabricated by additive manufacturing,and the vibration isolation performance is evaluated experimentally.The results show that the vibration isolation performance substantially enhances when the number of unit cells increases.More importantly,the ML-QZS meta-structure can be easily extended in the direction of vibration isolation when the unit cells are properly stacked.Hence,the ML-FQZS vibration isolation meta-structure should be a fascinating solution for highly efficient vibration isolation performance at low frequency.展开更多
Due to the increasing burden on healthcare budgets of musculoskeletal system disease and injury, there is a growing need for safe, effective and simple therapies. Conditions such as osteoporosis severely impact onqual...Due to the increasing burden on healthcare budgets of musculoskeletal system disease and injury, there is a growing need for safe, effective and simple therapies. Conditions such as osteoporosis severely impact onquality of life and result in hundreds of hours of hospital time and resources. There is growing interest in the use of low magnitude, high frequency vibration(LMHFV) to improve bone structure and muscle performance in a variety of different patient groups. The technique has shown promise in a number of different diseases, but is poorly understood in terms of the mechanism of action. Scientific papers concerning both the in vivo and in vitro use of LMHFV are growing fast, but they cover a wide range of study types, outcomes measured and regimens tested. This paper aims to provide an overview of some effects of LMHFV found during in vivo studies. Furthermore we will review research concerning the effects of vibration on the cellular responses, in particular for cells within the musculoskeletal system. This includes both osteogenesis and adipogenesis, as well as the interaction between MSCs and other cell types within bone tissue.展开更多
In order to control the low frequency vibration of railway vehicles, a vertical two degrees of freedom(2DOF) low frequency dynamic vibration absorber(DVA) based on acceleration is proposed. Parameters of the dynamic v...In order to control the low frequency vibration of railway vehicles, a vertical two degrees of freedom(2DOF) low frequency dynamic vibration absorber(DVA) based on acceleration is proposed. Parameters of the dynamic vibration absorber are put forth to control the low frequency vibration of car body bouncing and pitching. Next, the acceleration power spectrum density(PSD)and ride quality of the car body are calculated based on the pseudo excitation method(PEM) and covariance algorithm,respectively. According to the requirement of 2DOF low frequency DVA, the isolators with high static low dynamic stiffness(HSLDS) are designed. A high-speed train dynamic model containing HSLDS isolators is established to validate the effects on the car body vibration. The results reveal that the 2D low frequency DVA can significantly reduce the vibration of the car body bouncing and pitching. Thus, the ride quality of the vehicle is increased, and passenger comfort is improved.展开更多
Three destructive mining shocks successively occurred nearby the seismic Station No.6 located in a shaft of the Fangshan Coal Mine of Beijing Mining Service in 4 minutes at 19 o′clock of May 15, 1993. The largest sho...Three destructive mining shocks successively occurred nearby the seismic Station No.6 located in a shaft of the Fangshan Coal Mine of Beijing Mining Service in 4 minutes at 19 o′clock of May 15, 1993. The largest shock is of M =2.3 ( M 0=1.5×10 11 N·m). Analysis of synthetic seismogram provides that the three shocks exhibited predominantly a dip slip movement mode, which is consistent with the collapse of coal mass from the coal bed at high dip angle, as observed by those who were present at the site. The near field records of the main shock and a series of events prior to it made at the Station No.6 are different from normal records, it had not only high frequency vibration, but also low frequency vibration. By using elastic wave theory and nucleation theory of seismic fracture during recent years, analysis of the data indicates that the low frequency vibration maybe long period wave as the subcritical extension is pushing forward. It is an unrecovered deformation. The high frequency vibration is just the mining shock event, exhibiting a wave field of brittle fracture radiation. From the dominant frequency of low frequency vibration in the records of M =2.3 event and the records of foreshocks at 5.4 s before it, it is inferred that the volume of dilatation zone at the termination of shock generating fracture has rapidly enlarged during the occurrence of the main shock. In 20 or more days before the main shock, the source process was of the following characteristics: the subcritical extension occurred for many times; during this period the volume of dilatation zone at the termination of shock generating fracture little changed. The subcritical extension not only exits long period waves, but also induced small events at the same time. The dominant orientation of subcritical extension is basically consistent with the direction of slip movement during main shock.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12122206 and 12272129)the Natural Science Foundation of Hunan Province of China(No.2024JJ4004)the Zhejiang Provincial Natural Science Foundation of China(No.LQ24A020006)。
文摘An easily stackable multi-layer quasi-zero-stiffness(ML-QZS)meta-structure is proposed to achieve highly efficient vibration isolation performance at low frequency.First,the distributed shape optimization method is used to design the unit cel,i.e.,the single-layer QZS(SL-QZS)meta-structure.Second,the stiffness feature of the unit cell is investigated and verified through static experiments.Third,the unit cells are stacked one by one along the direction of vibration isolation,and thus the ML-QZS meta-structure is constructed.Fourth,the dynamic modeling of the ML-QZS vibration isolation metastructure is conducted,and the dynamic responses are obtained from the equations of motion,and verified by finite element(FE)simulations.Finally,a prototype of the ML-QZS vibration isolation meta-structure is fabricated by additive manufacturing,and the vibration isolation performance is evaluated experimentally.The results show that the vibration isolation performance substantially enhances when the number of unit cells increases.More importantly,the ML-QZS meta-structure can be easily extended in the direction of vibration isolation when the unit cells are properly stacked.Hence,the ML-FQZS vibration isolation meta-structure should be a fascinating solution for highly efficient vibration isolation performance at low frequency.
基金Engineering and Physical Sciences Research Council
文摘Due to the increasing burden on healthcare budgets of musculoskeletal system disease and injury, there is a growing need for safe, effective and simple therapies. Conditions such as osteoporosis severely impact onquality of life and result in hundreds of hours of hospital time and resources. There is growing interest in the use of low magnitude, high frequency vibration(LMHFV) to improve bone structure and muscle performance in a variety of different patient groups. The technique has shown promise in a number of different diseases, but is poorly understood in terms of the mechanism of action. Scientific papers concerning both the in vivo and in vitro use of LMHFV are growing fast, but they cover a wide range of study types, outcomes measured and regimens tested. This paper aims to provide an overview of some effects of LMHFV found during in vivo studies. Furthermore we will review research concerning the effects of vibration on the cellular responses, in particular for cells within the musculoskeletal system. This includes both osteogenesis and adipogenesis, as well as the interaction between MSCs and other cell types within bone tissue.
基金supported by the National Natural Science Foundation of China(Grant No.51805373)
文摘In order to control the low frequency vibration of railway vehicles, a vertical two degrees of freedom(2DOF) low frequency dynamic vibration absorber(DVA) based on acceleration is proposed. Parameters of the dynamic vibration absorber are put forth to control the low frequency vibration of car body bouncing and pitching. Next, the acceleration power spectrum density(PSD)and ride quality of the car body are calculated based on the pseudo excitation method(PEM) and covariance algorithm,respectively. According to the requirement of 2DOF low frequency DVA, the isolators with high static low dynamic stiffness(HSLDS) are designed. A high-speed train dynamic model containing HSLDS isolators is established to validate the effects on the car body vibration. The results reveal that the 2D low frequency DVA can significantly reduce the vibration of the car body bouncing and pitching. Thus, the ride quality of the vehicle is increased, and passenger comfort is improved.
文摘Three destructive mining shocks successively occurred nearby the seismic Station No.6 located in a shaft of the Fangshan Coal Mine of Beijing Mining Service in 4 minutes at 19 o′clock of May 15, 1993. The largest shock is of M =2.3 ( M 0=1.5×10 11 N·m). Analysis of synthetic seismogram provides that the three shocks exhibited predominantly a dip slip movement mode, which is consistent with the collapse of coal mass from the coal bed at high dip angle, as observed by those who were present at the site. The near field records of the main shock and a series of events prior to it made at the Station No.6 are different from normal records, it had not only high frequency vibration, but also low frequency vibration. By using elastic wave theory and nucleation theory of seismic fracture during recent years, analysis of the data indicates that the low frequency vibration maybe long period wave as the subcritical extension is pushing forward. It is an unrecovered deformation. The high frequency vibration is just the mining shock event, exhibiting a wave field of brittle fracture radiation. From the dominant frequency of low frequency vibration in the records of M =2.3 event and the records of foreshocks at 5.4 s before it, it is inferred that the volume of dilatation zone at the termination of shock generating fracture has rapidly enlarged during the occurrence of the main shock. In 20 or more days before the main shock, the source process was of the following characteristics: the subcritical extension occurred for many times; during this period the volume of dilatation zone at the termination of shock generating fracture little changed. The subcritical extension not only exits long period waves, but also induced small events at the same time. The dominant orientation of subcritical extension is basically consistent with the direction of slip movement during main shock.
