Negative stiffness(NS)structures leverage multi-stable mechanisms to demonstrate energy-absorbing capabilities.Nonetheless,existing implementations are impeded by material and manufacturing,which constrain load-bearin...Negative stiffness(NS)structures leverage multi-stable mechanisms to demonstrate energy-absorbing capabilities.Nonetheless,existing implementations are impeded by material and manufacturing,which constrain load-bearing capacity,reusability,and energy absorption efficiency.The observed flexural bounce behavior in beam structures offers a promising avenue for achieving multi-stability and reusability.Consequently,we utilize continuous carbon fiber reinforced thermoplastic polymers(CCFRTP)and three-dimensional(3D)printing to fabricate NS structures featuring cosine beam cells,aiming to elucidate the mechanisms through which CCFRTP modulates their multi-stability.Prior to this,a wet twisted method for continuous carbon fiber(CCF)was employed to augment the mechanical properties and elucidate the failure behaviors and interfacial adhesion mechanisms.Building upon this,a one-stroke path planning model was utilized to delve into the bistability principles and energy absorption mechanisms of the CCFRTP cosine beam structure.The displacement-controlled loading and unloading experiments were conducted to assess the energy absorption characteristics of the structure in both energy-locked and repetitive energy absorption modes.Furthermore,a dual-unit assembly structure was fabricated to investigate its overall deformation and energy absorption properties,thereby validating the feasibility of the negative stiffness honeycomb structure.This approach holds promise for aerospace and naval applications requiring efficient energy absorption under large deformation and high loading.展开更多
A model of grade transition is presented for a commercialized fluidized bed gas-phase polyethylene production process. The quantity of off-specification product and the time of grade transition can be minimized by the...A model of grade transition is presented for a commercialized fluidized bed gas-phase polyethylene production process. The quantity of off-specification product and the time of grade transition can be minimized by the optimization of operating variables, such as polymerization temperature, the ratio of hydrogen to ethylene, the ratio of co-monomer to ethylene, feed rate of catalyst, and bed level. A new performance index, the ratio of melt flow (MFR), is included in the objective function, for restraining the sharp adjustment of operation variables and narrowing the distribution of molecular weight of the resin. It is recommended that catalyst feed rate and bed level are decreased in order to reduce the grade transition time and the quantity of off-specification product. This optimization problem is solved by an algorithm of sequential quadratic programming (SQP) in MATLAB. There is considerable difference between the forward transition and reverse transition of grade with regard to the operating variables due to the non-linearity of the system. The grade transition model is extended to a high space time yield (STY) process with the so-called condensed model operation. In the end, an optimization strategy for multi-product transition is proposed with two-level optimization of the objective function J(x,u) on the basis of the optimal grade transition model. A sequential transition of six commercial polyethylene grades is illustrated for an optimal multi-product operation.展开更多
基金financially supported by the Ministry of Science and Technology of the People’s Republic of Chinathe China National Key Research and Development Program(2021YFB1715600)+1 种基金the Shanxi Provincial Science and Technology Department Common Technology Research and Development Project(2021GXJS-06)the Key Research and Development Program(2023-YBGY-363)。
文摘Negative stiffness(NS)structures leverage multi-stable mechanisms to demonstrate energy-absorbing capabilities.Nonetheless,existing implementations are impeded by material and manufacturing,which constrain load-bearing capacity,reusability,and energy absorption efficiency.The observed flexural bounce behavior in beam structures offers a promising avenue for achieving multi-stability and reusability.Consequently,we utilize continuous carbon fiber reinforced thermoplastic polymers(CCFRTP)and three-dimensional(3D)printing to fabricate NS structures featuring cosine beam cells,aiming to elucidate the mechanisms through which CCFRTP modulates their multi-stability.Prior to this,a wet twisted method for continuous carbon fiber(CCF)was employed to augment the mechanical properties and elucidate the failure behaviors and interfacial adhesion mechanisms.Building upon this,a one-stroke path planning model was utilized to delve into the bistability principles and energy absorption mechanisms of the CCFRTP cosine beam structure.The displacement-controlled loading and unloading experiments were conducted to assess the energy absorption characteristics of the structure in both energy-locked and repetitive energy absorption modes.Furthermore,a dual-unit assembly structure was fabricated to investigate its overall deformation and energy absorption properties,thereby validating the feasibility of the negative stiffness honeycomb structure.This approach holds promise for aerospace and naval applications requiring efficient energy absorption under large deformation and high loading.
文摘A model of grade transition is presented for a commercialized fluidized bed gas-phase polyethylene production process. The quantity of off-specification product and the time of grade transition can be minimized by the optimization of operating variables, such as polymerization temperature, the ratio of hydrogen to ethylene, the ratio of co-monomer to ethylene, feed rate of catalyst, and bed level. A new performance index, the ratio of melt flow (MFR), is included in the objective function, for restraining the sharp adjustment of operation variables and narrowing the distribution of molecular weight of the resin. It is recommended that catalyst feed rate and bed level are decreased in order to reduce the grade transition time and the quantity of off-specification product. This optimization problem is solved by an algorithm of sequential quadratic programming (SQP) in MATLAB. There is considerable difference between the forward transition and reverse transition of grade with regard to the operating variables due to the non-linearity of the system. The grade transition model is extended to a high space time yield (STY) process with the so-called condensed model operation. In the end, an optimization strategy for multi-product transition is proposed with two-level optimization of the objective function J(x,u) on the basis of the optimal grade transition model. A sequential transition of six commercial polyethylene grades is illustrated for an optimal multi-product operation.
