Mesoscopic fluid flow is the major cause of wave attenuation and velocity dispersion at seismic frequencies in porous rocks. The Johnson model provides solutions for the frequency-dependent quality factor and phase ve...Mesoscopic fluid flow is the major cause of wave attenuation and velocity dispersion at seismic frequencies in porous rocks. The Johnson model provides solutions for the frequency-dependent quality factor and phase velocity in partially saturated porous media with pore patches of arbitrary shapes. We use the Johnson model to derive approximations for the quality factor Q at the high and low frequency limit, and obtain the approximate equation for Qmin based on geophysical and geometric parameters. A more accurate equation for Qmin is obtained after correcting for the linear errors between the exact and approximate Q values. The complexity of the pore patch shape affects the maximum attenuation of Qmin and the transition frequency ftr; furthermore, the effect on ftr is stronger than that on Qmin. Numerical solutions to Biot’s equation are computationally intensive; thus, we build an equivalent viscoelastic model on the basis of the Zener model, which well approximates the wave attenuation and dispersion in porous rocks in the seismic band.展开更多
An implicit solvent coarse-grained （CG） lipid model using three beads to reflect the basically molecular structure of two-tailed lipid is developed. In this model, the nonbonded interaction employs a variant MIE pot...An implicit solvent coarse-grained （CG） lipid model using three beads to reflect the basically molecular structure of two-tailed lipid is developed. In this model, the nonbonded interaction employs a variant MIE potential and the bonded interaction utilizes a Harmonic potential form. The CG force field parameters are achieved by matching the structural and mechan-ical properties of dipalmitoylphosphatidylcholine （DPPC） bilayers. The model successfully reproduces the formation of lipid bilayer from a random initial state and the spontaneous vesiculation of lipid bilayer from a disk-like structure. After that, the model is used to sys-tematically study the vesiculation processes of spherical and cylindrical lipid droplets. The results show that the present CG model can effectively simulate the formation and evolution of mesoscale complex vesicles.展开更多
Segregation results in worse mechanical and durability performance of concrete.Therefore,an accurate modelling of segregation is required for reliable mesoscale modelling.In this context,this paper presents a method t...Segregation results in worse mechanical and durability performance of concrete.Therefore,an accurate modelling of segregation is required for reliable mesoscale modelling.In this context,this paper presents a method to develop the geometric mesoscale modelling of concrete taking into account segregation.In this method,coarse aggregate particles are generated as ellipsoids of random geometry and are randomly placed within concrete.The specimen is stratified in different numbers of layers(NoL)that represent different segregation conditions.The geometric models of four concrete mix designs are generated and the relevant key parameters,e.g.aggregate distribution are analysed and validated.In addition,the segregation level of generated models is classified based on the volumetric index and the correspondence between segregation level and the value of NoL is presented.The results show that 1)The generated geometric models with NoL ranging from 1 to 10 align well with real segregation in concrete and can accurately represent the majority of segregation cases resulting from various experimental factors;2)The NoL reflects the segregation level:more layers indicate a more heterogeneous mesostructure;3)The larger aggregates of the generated models tend to settle at the bottom,while smaller aggregates rise toward the top,leading to uneven vertical distribution,especially as the NoL increases;4)the mix 1 with low aggregate content can represent the construction material with large segregation,while the mix 2 is inverse.展开更多
基金sponsored by the National Science and Technology Major Project(Grant No.2011ZX05025-001-07)
文摘Mesoscopic fluid flow is the major cause of wave attenuation and velocity dispersion at seismic frequencies in porous rocks. The Johnson model provides solutions for the frequency-dependent quality factor and phase velocity in partially saturated porous media with pore patches of arbitrary shapes. We use the Johnson model to derive approximations for the quality factor Q at the high and low frequency limit, and obtain the approximate equation for Qmin based on geophysical and geometric parameters. A more accurate equation for Qmin is obtained after correcting for the linear errors between the exact and approximate Q values. The complexity of the pore patch shape affects the maximum attenuation of Qmin and the transition frequency ftr; furthermore, the effect on ftr is stronger than that on Qmin. Numerical solutions to Biot’s equation are computationally intensive; thus, we build an equivalent viscoelastic model on the basis of the Zener model, which well approximates the wave attenuation and dispersion in porous rocks in the seismic band.
基金We thank Professor Dr. Markus Deserno （Department of Physics, Carnegie Mellon University）, Jemal Guven （Institute of Nuclear Science, Universidad Nacional Autonoma de Mexico）, and Zhan-chun Tu （Department of Physics, Beijing Normal University） for their valuable advice. This work is supported by the National Natural Science Foundation of China （No.20974078, No.21274107, and No.91127046）. The computation and simulation are partly carried out in High Performance Computing Center of Tianjin University.
文摘An implicit solvent coarse-grained （CG） lipid model using three beads to reflect the basically molecular structure of two-tailed lipid is developed. In this model, the nonbonded interaction employs a variant MIE potential and the bonded interaction utilizes a Harmonic potential form. The CG force field parameters are achieved by matching the structural and mechan-ical properties of dipalmitoylphosphatidylcholine （DPPC） bilayers. The model successfully reproduces the formation of lipid bilayer from a random initial state and the spontaneous vesiculation of lipid bilayer from a disk-like structure. After that, the model is used to sys-tematically study the vesiculation processes of spherical and cylindrical lipid droplets. The results show that the present CG model can effectively simulate the formation and evolution of mesoscale complex vesicles.
基金supported by the Project of the Ministry of Science and Technology High-end Foreign Experts of China(No.G2023014042L)the China Scholarship Council(No.201906370013)the Portuguese Foundation for Science and Technology(UIDB/04625/2020).
文摘Segregation results in worse mechanical and durability performance of concrete.Therefore,an accurate modelling of segregation is required for reliable mesoscale modelling.In this context,this paper presents a method to develop the geometric mesoscale modelling of concrete taking into account segregation.In this method,coarse aggregate particles are generated as ellipsoids of random geometry and are randomly placed within concrete.The specimen is stratified in different numbers of layers(NoL)that represent different segregation conditions.The geometric models of four concrete mix designs are generated and the relevant key parameters,e.g.aggregate distribution are analysed and validated.In addition,the segregation level of generated models is classified based on the volumetric index and the correspondence between segregation level and the value of NoL is presented.The results show that 1)The generated geometric models with NoL ranging from 1 to 10 align well with real segregation in concrete and can accurately represent the majority of segregation cases resulting from various experimental factors;2)The NoL reflects the segregation level:more layers indicate a more heterogeneous mesostructure;3)The larger aggregates of the generated models tend to settle at the bottom,while smaller aggregates rise toward the top,leading to uneven vertical distribution,especially as the NoL increases;4)the mix 1 with low aggregate content can represent the construction material with large segregation,while the mix 2 is inverse.
