When dealing with the oscillations of fixed-base structures or machines induced by external forces,suppressing the vibrational impact on the adjacent structures and the environment helps to maintain the structural dur...When dealing with the oscillations of fixed-base structures or machines induced by external forces,suppressing the vibrational impact on the adjacent structures and the environment helps to maintain the structural durability and ensure the users′comfort level.This study proposed an inerter-based optimal solution to suppress the vibrational forces and energy transmitted to the supporting ground by utilizing the great potential of the inerter.For the external force,which contains various frequency bands,the stochastic response and an energy balance analysis are conducted to evaluate the force transmissibility,structural displacement,and vibration power flow.Given the benefits of the inerter,a transmitted-force-based optimal design framework is proposed for inerter systems,of which the effectiveness is validated by numerical examples.The obtained results show that inerter systems are capable of providing significant reductions in the structural displacement and the force transmitted to the supporting ground.Particularly,the closed-form power equation indicated that a grounded inerter can suppress the force transmission and vibrational energy,thus leading to a less negative impact on the ground and environment.Revealing the working mechanism and optimal design strategy of the inerter can help solve the force-transmission control problem experienced by some practical structures.展开更多
Shrapnel projectiles from low-velocity weapons often cause perforations and thereby result in multiple wounds. As shrapnel penetrates, its kinetic energy dissipates and generates forces that influence the extent of da...Shrapnel projectiles from low-velocity weapons often cause perforations and thereby result in multiple wounds. As shrapnel penetrates, its kinetic energy dissipates and generates forces that influence the extent of damage. However, quantifying these forces and understanding the mechanics of tissue damage remain challenging. To address this, there is a need to measure time-varying forces that will provide critical insights into the mechanics of damage initiation and progression. In this study, a new experimental methodology was developed using a custom-designed fixture integrated with a low-velocity gas gun to study shrapnel-induced damage in ballistic gelatin. The fixture was equipped with piezoelectric sensors to capture transmitted force(TF), while a high-speed camera recorded the damage morphology. The maximum TF response varied significantly, ranging from 45 to 225 N for chisel-nose shrapnel and 75–295 N for blunt-nose shrapnel, across incident velocities of 25–100 m/s. The damage mechanisms, characterized by the formation of temporary cavities, resulted in cavity sizes three to four times larger than the shrapnel diameter. The maximum energy absorbed by the ballistic gelatin was 14.81 J at 92.10 m/s for chisel-nose and 18.50 J at 98.35 m/s for blunt-nose shrapnel. A finite element(FE) model was developed and validated against experimental results with an error margin of less than 15% in the maximum value of TF. This methodology provides a platform for further studies on soft tissue damage by correlating dynamic force measurements with damage mechanisms. These insights can inform advancements in battlefield injury assessment, medical interventions strategies, and the design of protective materials to mitigate shrapnel injuries.展开更多
A reinterpretation of the well-known formula of the 'mass-velocity relation' is exactlyderived from a new viewpoint with new concepts, such as the finiteness of the transmitting velocityof force (TVF), effecti...A reinterpretation of the well-known formula of the 'mass-velocity relation' is exactlyderived from a new viewpoint with new concepts, such as the finiteness of the transmitting velocityof force (TVF), effective action, and the coupled effect of the TVF for two EM fields, etc. Then, atrue meaning hidden in the Lorentz factor is exploited : i.e., when a charged particle is moving at aspeed v under an EM field, the effective action exerted on it by the field varies inversely with thespeed ratio β= v / U, where U is the TVF, which probably is equal to the propagation velocity ofEM field. The actual reduction of the effective action gives a false impression of mass gain.Accordingly, it is a major mistake in orientation to ascribe the (genuine) electrodynamics of movingbodies to any observation, or to any motion of an observer, while disregarding the facts of mutualaction.展开更多
基金Scientific Research Fund of Institute of Engineering Mechanics,China Earthquake Administration under Grant Nos.2019EEVL03,2019D14 and 2020EEEVL0401National Natural Science Foundation of China under Grant No.51978525National Key R&D Program of China 2021YFE0112200。
文摘When dealing with the oscillations of fixed-base structures or machines induced by external forces,suppressing the vibrational impact on the adjacent structures and the environment helps to maintain the structural durability and ensure the users′comfort level.This study proposed an inerter-based optimal solution to suppress the vibrational forces and energy transmitted to the supporting ground by utilizing the great potential of the inerter.For the external force,which contains various frequency bands,the stochastic response and an energy balance analysis are conducted to evaluate the force transmissibility,structural displacement,and vibration power flow.Given the benefits of the inerter,a transmitted-force-based optimal design framework is proposed for inerter systems,of which the effectiveness is validated by numerical examples.The obtained results show that inerter systems are capable of providing significant reductions in the structural displacement and the force transmitted to the supporting ground.Particularly,the closed-form power equation indicated that a grounded inerter can suppress the force transmission and vibrational energy,thus leading to a less negative impact on the ground and environment.Revealing the working mechanism and optimal design strategy of the inerter can help solve the force-transmission control problem experienced by some practical structures.
基金financial support from DRDO Industry Academia Centre of Excellence IIT Delhi (Grant No.DFTM/ 03/3203/M/01/JATC)。
文摘Shrapnel projectiles from low-velocity weapons often cause perforations and thereby result in multiple wounds. As shrapnel penetrates, its kinetic energy dissipates and generates forces that influence the extent of damage. However, quantifying these forces and understanding the mechanics of tissue damage remain challenging. To address this, there is a need to measure time-varying forces that will provide critical insights into the mechanics of damage initiation and progression. In this study, a new experimental methodology was developed using a custom-designed fixture integrated with a low-velocity gas gun to study shrapnel-induced damage in ballistic gelatin. The fixture was equipped with piezoelectric sensors to capture transmitted force(TF), while a high-speed camera recorded the damage morphology. The maximum TF response varied significantly, ranging from 45 to 225 N for chisel-nose shrapnel and 75–295 N for blunt-nose shrapnel, across incident velocities of 25–100 m/s. The damage mechanisms, characterized by the formation of temporary cavities, resulted in cavity sizes three to four times larger than the shrapnel diameter. The maximum energy absorbed by the ballistic gelatin was 14.81 J at 92.10 m/s for chisel-nose and 18.50 J at 98.35 m/s for blunt-nose shrapnel. A finite element(FE) model was developed and validated against experimental results with an error margin of less than 15% in the maximum value of TF. This methodology provides a platform for further studies on soft tissue damage by correlating dynamic force measurements with damage mechanisms. These insights can inform advancements in battlefield injury assessment, medical interventions strategies, and the design of protective materials to mitigate shrapnel injuries.
文摘A reinterpretation of the well-known formula of the 'mass-velocity relation' is exactlyderived from a new viewpoint with new concepts, such as the finiteness of the transmitting velocityof force (TVF), effective action, and the coupled effect of the TVF for two EM fields, etc. Then, atrue meaning hidden in the Lorentz factor is exploited : i.e., when a charged particle is moving at aspeed v under an EM field, the effective action exerted on it by the field varies inversely with thespeed ratio β= v / U, where U is the TVF, which probably is equal to the propagation velocity ofEM field. The actual reduction of the effective action gives a false impression of mass gain.Accordingly, it is a major mistake in orientation to ascribe the (genuine) electrodynamics of movingbodies to any observation, or to any motion of an observer, while disregarding the facts of mutualaction.
