A new simple thixotropy model was proposed in the present paper to characterize the thixotropy-loop experiments and the start-up experiment of an LDPE （PE-FSB23D0221Q200） melt. The thixotropy model is a combination ...A new simple thixotropy model was proposed in the present paper to characterize the thixotropy-loop experiments and the start-up experiment of an LDPE （PE-FSB23D0221Q200） melt. The thixotropy model is a combination of a viscoelastic-component and a postulated kinetics process of structure change, which is constituted in terms of the indirect microstructural approach usually adopted in the characterization of thixotropy. The descriptions of the thixotropy model on both the thixotropy-loop tests and the startup test show good agreement with the experimental values, indicating the good capability of the model in characterizing the time-dependent nonlinear viscoelastic. The stress overshoot phenomenon and the stress relaxation after cessation of the thixotropy loop test can be described well by the model, whereas both of the typical viscoelastic phenomena could not be described in our previous work with a variant Huang model.展开更多
The quasi-geostrophic atmospheric and oceanic equations of momentum and thermodynamics with dissipation factors are used to create a simple coupled ocean-atmosphere model describing the large-scale shallow-water motio...The quasi-geostrophic atmospheric and oceanic equations of momentum and thermodynamics with dissipation factors are used to create a simple coupled ocean-atmosphere model describing the large-scale shallow-water motion. We discuss the ocean-atmosphere coupling effect in mid-high and low latitudes separately and analyze characteristics of which the oscillatory periods of coupled low-frequency modes (ocean mode) vary with the coupling frequency and latitudinal number. This can interpret the correlation between low-frequency oscillation and ocean-atmosphere interaction. Then from the dispersion curves of atmosphere and ocean, we reveal effect of the coupling strength on the propagation of Rossby waves. The convection mechanism between the two modes is also discussed in view of the slowly varying wave train.The results show that Newtonian cooling and Rayleigh friction play a stable rule in oceanic Rossby waves, the period of coupled low-frequency mode grows with the increment of the coupling frequency. The larger the latitudinal number is, the more rapidly it grows. When the coupling frequency tends to critical value, the oceanic Rossby waves become static. When the ocean-atmosphere coupling strength grows to some degree, the propagation of oceanic Rossby waves will become opposite to its original direction. One part of the oceanic Rossby waves is converted into atmospheric Rossby waves, the energy conversion coefficient is also solved out.展开更多
A quantitative description of the processes taking place among the atmosphere, vegetation and soil is needed for studying air-land interaction and interrelation between the geosphere and the biosphere. In this paper, ...A quantitative description of the processes taking place among the atmosphere, vegetation and soil is needed for studying air-land interaction and interrelation between the geosphere and the biosphere. In this paper, a simple land surface process model is proposed. Through transfers and exchanges of heat and water, the therrnal and moisture states of the atmosphere, vegetation and soil are linked in a coupled system, in which vegetation is considered as a horizontally uniform layer, soil is divided into three layers and the horizontal differences of variables in the system are neglected. The preliminary results of the experiment indicate that the model is capable of predicting the thermal and moisture conditions of the land surface and suitable to climate study.展开更多
In this paper,by simplifying the governing equation in low latitudes a nonlinear model which takes into consideration the equatorial β-plane approximation and describes the natural oscillation of the atmosphere has b...In this paper,by simplifying the governing equation in low latitudes a nonlinear model which takes into consideration the equatorial β-plane approximation and describes the natural oscillation of the atmosphere has been set up.By applying this model the following results are shown: (1)There exists the pure inertial oscillation only in u_0>0(westerly current),the angular frequency of linear oscillation of y is ω_0~*=(β_0u_0~*)^(1/2),the corresponding oscillatory period is 1—2 weeks.There are two kinds of angular frequencies under the nonlinear condition,the one is ω_0=(β_0u_0)^(1/2)the other is ω_1= 1/2 β_0y_0.When a soliton oscillator occurs(ω_1=ω_0),the oscillatory period increases rapidly,and T→∞. (2)When the pressure field is considered,the oscillation exists not only in u_0>0(westerly current) but also in u_0<0(weak easterly current).However this weak pressure field has slight effect on the oscillatory period. (3)The stability of inertial oscillation depends on the linear inertial parameter μ.As the parameter μ changes sign from negative to positive,the supercritical bifurcation takes place in b<0.展开更多
基金The project supported by the National Natural Science Foundation of China(10402024)the Experiment Foundation for Precise Instrument of Shanghai Jiao Tong University(200207)
文摘A new simple thixotropy model was proposed in the present paper to characterize the thixotropy-loop experiments and the start-up experiment of an LDPE （PE-FSB23D0221Q200） melt. The thixotropy model is a combination of a viscoelastic-component and a postulated kinetics process of structure change, which is constituted in terms of the indirect microstructural approach usually adopted in the characterization of thixotropy. The descriptions of the thixotropy model on both the thixotropy-loop tests and the startup test show good agreement with the experimental values, indicating the good capability of the model in characterizing the time-dependent nonlinear viscoelastic. The stress overshoot phenomenon and the stress relaxation after cessation of the thixotropy loop test can be described well by the model, whereas both of the typical viscoelastic phenomena could not be described in our previous work with a variant Huang model.
基金This work is supported by the Laboratory of Numerical Modelling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Academia Sinica.
文摘The quasi-geostrophic atmospheric and oceanic equations of momentum and thermodynamics with dissipation factors are used to create a simple coupled ocean-atmosphere model describing the large-scale shallow-water motion. We discuss the ocean-atmosphere coupling effect in mid-high and low latitudes separately and analyze characteristics of which the oscillatory periods of coupled low-frequency modes (ocean mode) vary with the coupling frequency and latitudinal number. This can interpret the correlation between low-frequency oscillation and ocean-atmosphere interaction. Then from the dispersion curves of atmosphere and ocean, we reveal effect of the coupling strength on the propagation of Rossby waves. The convection mechanism between the two modes is also discussed in view of the slowly varying wave train.The results show that Newtonian cooling and Rayleigh friction play a stable rule in oceanic Rossby waves, the period of coupled low-frequency mode grows with the increment of the coupling frequency. The larger the latitudinal number is, the more rapidly it grows. When the coupling frequency tends to critical value, the oceanic Rossby waves become static. When the ocean-atmosphere coupling strength grows to some degree, the propagation of oceanic Rossby waves will become opposite to its original direction. One part of the oceanic Rossby waves is converted into atmospheric Rossby waves, the energy conversion coefficient is also solved out.
文摘A quantitative description of the processes taking place among the atmosphere, vegetation and soil is needed for studying air-land interaction and interrelation between the geosphere and the biosphere. In this paper, a simple land surface process model is proposed. Through transfers and exchanges of heat and water, the therrnal and moisture states of the atmosphere, vegetation and soil are linked in a coupled system, in which vegetation is considered as a horizontally uniform layer, soil is divided into three layers and the horizontal differences of variables in the system are neglected. The preliminary results of the experiment indicate that the model is capable of predicting the thermal and moisture conditions of the land surface and suitable to climate study.
文摘In this paper,by simplifying the governing equation in low latitudes a nonlinear model which takes into consideration the equatorial β-plane approximation and describes the natural oscillation of the atmosphere has been set up.By applying this model the following results are shown: (1)There exists the pure inertial oscillation only in u_0>0(westerly current),the angular frequency of linear oscillation of y is ω_0~*=(β_0u_0~*)^(1/2),the corresponding oscillatory period is 1—2 weeks.There are two kinds of angular frequencies under the nonlinear condition,the one is ω_0=(β_0u_0)^(1/2)the other is ω_1= 1/2 β_0y_0.When a soliton oscillator occurs(ω_1=ω_0),the oscillatory period increases rapidly,and T→∞. (2)When the pressure field is considered,the oscillation exists not only in u_0>0(westerly current) but also in u_0<0(weak easterly current).However this weak pressure field has slight effect on the oscillatory period. (3)The stability of inertial oscillation depends on the linear inertial parameter μ.As the parameter μ changes sign from negative to positive,the supercritical bifurcation takes place in b<0.
