材料特性对输送脉动流体的粘弹性轴向功能梯度管非线性动力行为的影响

The nonlinear dynamic behaviors of viscoelastic axially functionally graded material(AFG)pipes conveying pulsating internal flow are very complex.And the dynamic behavior will induce the failure of the pipes,and research of vibration and stability of pipes becomes a major concern.Considering that the elastic modulus,density,and coefficient of viscoelastic damping of the pipe material vary along the axial direction,the transverse vibration equation of the viscoelastic AFG pipe conveying pulsating fluid is established based on the Euler-Bernoulli beam theory.The generalized integral transform technique(GITT)is used to transform the governing fourth-order partial differential equation into a nonlinear system of fourth-order ordinary differential equations in time.The time domain diagram,phase portraits,Poincarémap and power spectra diagram at different dimensionless pulsation frequencies,are discussed in detail,showing the characteristics of chaotic,periodic,and quasi-periodic motion.The results show that the distributions of the elastic modulus,density,and coefficient of viscoelastic damping have significant effects on the nonlinear dynamic behavior of the viscoelastic AFG pipes.With the increase of the material property coefficient k,the transition between chaotic,periodic,and quasi-periodic motion occurs,especially in the high-frequency region of the flow pulsation.

Experimental characterization of guest molecular occupancy in clathrate hydrate cages: A review

Study on the microscopic structure of clathrate hydrate has made significant progress in the past decades.This review aims to summarize the state of the art of the experimental characterization of guest molecular occupancy in clathrate hydrate cages,which is an important area of the microscopic structures.The characterizing method and features of different guest molecular,such as hydrocarbon,carbon dioxide,hydrogen and inhibitor/promoter,in different hydrate cages have been extensively reviewed.A comprehensive use of advanced technologies such as X-ray diffraction,Raman spectroscopy and nuclear magnetic resonance may provide better understanding on the compositions and microscopic mechanisms of clathrate hydrate.

Methane hydrate crystal growth on shell substrate

Hydrate crystals growth on the surface of methane bubble(hydrate film)in pure water was studied by using a high-pressure visible microscope under the conditions of subcoolingΔT=5.44-13.72 K and methane concentration differenceΔC=2.92-8.19 mol·L^(-1).It was found the hydrate film is porous and the hydrate crystals grow towards the liquid phase on the film substrate.The crystal morphology and growth rate are affected byΔT andΔC.WhenΔT<8.82 K andΔC<4.12 mol·L^(-1),the hydrate grows into scattered columnar crystals,and the axial growth rate of the crystal gradually decreases.WhenΔT>8.82 K orΔC>4.12 mol·L^(-1),the hydrate crystals grow in dendritic shape,and the axial growth rate increases first and then decreases.The perimeter and area of the growing hydrate crystals were measured,and the fractal dimension of hydrate crystal under differentΔC andΔT was calculated.The results show that the fractal dimension of columnar hydrate crystal is greater than 3.When3.87 mol·L^(-1)<ΔC<4.20 mol·L^(-1) and 7.4 K<ΔT<8.8 K,the fractal dimension of columnar hydrate crystal is greater than 4;The fractal dimension of dendritic hydrate crystal is less than 3.WhenΔC>4.77 mol·L^(-1),ΔT<8.52 K,the fractal dimension of dendritic hydrate crystal is less than 2.

A prediction method of natural gas hydrate formation in deepwater gas well and its application

To prevent the deposition of natural gas hydrate in deepwater gas well,the hydrate formation area in wellbore must be predicted.Herein,by comparing four prediction methods of temperature in pipe with field data and comparing five prediction methods of hydrate formation with experiment data,a method based on OLGA&PVTsim for predicting the hydrate formation area in wellbore was proposed.Meanwhile,The hydrate formation under the conditions of steady production,throttling and shut-in was predicted by using this method based on a well data in the South China Sea.The results indicate that the hydrate formation area decreases with the increase of gas production,inhibitor concentrations and the thickness of insulation materials and increases with the increase of thermal conductivity of insulation materials and shutdown time.Throttling effect causes a plunge in temperature and pressure in wellbore,thus leading to an increase of hydrate formation area.

Distribution laws and effects analysis of casing external pressure taking elastic parameters matching into account

Distribution laws of casing external pressure,which are obtained by different scholars in different conditions,are not the same.Thus,a model to calculate the external pressure of casing is established with finite element method.In the model a contact is built between the outer wall of the casing and the inner wall of the cement sheath.The casing external pressure can be got through extracting contact force of results.The numerical results and analysis show that:The largest casing external pressure exists in the direction of minimum horizontal stress of formation rather than in the direction of the maximum horizontal stress.There exists such matching between the cement sheath elastic modulus and formation elastic modulus:When the elastic modulus of the cement sheath is small,reducing its value is conducive to reduce the casing external pressure and to prolong casing service life.When the elastic modulus of the cement sheath is large,increasing its value is conducive to reduce the casing external pressure and to prolong casing service life.The casing external pressure will become large with the increase of Poisson's ratio of cement sheath.With the increase of the degree of the formation stress unevenness,the maximum casing external pressure increases and the smallest external decreases.The increasing of the non-uniformity degree of formation stress makes the non-uniformity degree of casing external pressure and the risk of casing failure increase.The study can provide certain reference for drilling workers to take measures to prolong service life of casing.