The thermal vibration is the inherent vibration of nanostructures, which plays an important role in the dynamics of nanostructures. The quantum effects, the boundary effects and the van der Waals interaction have a significant influence on the thermal vibration of nanostructures. The carbon nanotubes and the graphene were extensively studied for their novel electronic properties and superior mechanical strength. This paper reviews some research methods for the thermal vibration of nanostructures, the thermal vibration of the carbon nanotube and the graphene in low temperatures and the nonlinear thermal vibration of the carbon nanotube.
The early-age concrete under the condition of restrained shrinkage is easy to crack, which would affect safety and durability of the structure, as well as the applicability. So it is very important to provide a simple and effective method to assess the crack resistance of the early-age concrete. In view of providing certain rigidity and the convenience of laboratory constraints, the restrained shrinkage ring test is widely used to evaluate the crack resistance of the concrete under restrained shrinkage conditions. This paper discusses the development of the restrained shrinkage ring test, the failure mechanism and the impact of three factors. The restrained shrinkage ring test is recommended as a standard test method by the American Association of State Highway and Transportation Officials (AASHTO) and the American Society for Testing and Materials (ASTM), and the test is conducted for different purposes, including the failure mechanism based on the maximum tensile stress fracture mechanics theory and the fracture energy to predict the concrete cracking. The annular test specimen geometry, the boundary conditions, the performance of the concrete materials and the pre-crack are considered as influencing factors. A test method of elliptical ring is adopted, which can effectively assess the crack resistance of the concrete under conditions of high degree of restraint.
During the seepage of the shale gas, its effect is due to the large Knudson number, which makes the gas molecules slip from the solid surface. Based on the REV (representative elementary volume) scale lattice Boltzmann method, the flow of the shale gas is simulated with consideration of the slippage effect. With the scanning electron microscope image, a physical model with organic rock, nonorganic rock and natural fractures is taken, and then the shale gas flow in the model is simulated. The simulated results indicate that the shale gas mainly flows in the natural fractures. However, the shale gas also flows slowly in the organic and nonorganic rocks, and the velocity in the organic rocks is larger than that in the nonorganic rocks. The influence of the reservoir pressure on the shale gas seepage is also studied by varying the reservoir pressure. It is indicated that with the decrease of the reservoir pressure, the Knudson number increases and the slippage effect intensifies, thus the velocity and the permeability of the whole fluid field increase.
The flow of the proppant-laden fluid in fractures is a two phase flow. The migration of the proppant laden fluid and the transportation and the arrangement of the proppant in the fracture are the key to keep the flow conductivity in the fracture. Based on the FLUENT software for the fluid mechanics, the two-fluid model is adopted, and the solid phase and the liquid phase are regarded as the pseudo-fluid and the newtonian fluid, respectively. The effects of the proppant volume fraction, the Ar number, the Re number, and the inlet boundary on the flow are investigated. It is shown that four different zones are developed with different volumetric fractions, including the sand bank zone, the sand tumble zone, the sand suspension zone, and the sand free zone. The thickness of the settled proppants increases with the increase of the proppant concentration and the Ar number, while it decreases with the increase of the Re number. Under the condition of the mesh type boundary, the accumulation of the proppants occurs at the inlet due to the sudden increase of the flow area.
A two way fluid-structure interaction method is employed to simulate the aerodynamic performance and the structural response of NACA0012 airfoils, with three flexible structures on a portion of the upper surface extending from 5% to 95% of the chord from the leading edge. The impact of the elastic modulus is analyzed. It is indicated that at a large angle of attack the deformation of the flexible surface affects the unsteady flow field around the airfoil, delays the stall and improves the lift coefficient. Even when the stall occurs, the lift coefficient of the flexible airfoil decreases more slowly with the increase of the angle of attack than that of a rigid airfoil. The flexible airfoil with smaller elastic modulus has better aerodynamic performance. But too small elastic modulus is not conducive to the enhancement of the aerodynamic performance and the flexible surfaces will experience a large amplitude vibration.
The wellbore trajectory control tool is a sort of guiding drilling tool to achieve the orientation function while drilling. Under complex conditions, the spindle is under the actions of the bit pressure, the torque, the force of biasing mechanism and so on. This paper studies the mechanical behavior of the prototype spindle. A spindle mechanical model is established. With the model, the influences of the housing stiffness and the position of the eccentric mechanism of the spindle on the mechanical behavior and the deflecting capacity are analyzed. The data analysis shows that the deflection angle of the lower end of the principal axis, the force of the biasing mechanism and the maximum bending moment will increase linearly with the eccentric displacement of the eccentric ring. With the increase of the housing stiffness and the axial bearing distance from the mounting position of the biasing mechanism, the tool deflecting capacity will be enhanced and the maximum bending moment of the spindle will increase. It is shown that, we have selected the most suitable house stiffness and the mounting position of the biasing mechanism, which would serve as a reference for the spindle design and the improvement of the deflecting capacity of the wellbore trajectory control tool.
With the wide applications of the logging technologies of the ultra-deep well, the horizontal well, the directional well, the extended-reach well and the highly-deviated well in the petroleum drilling engineering, the premature failure of the drill pipe joint caused by underground complex working conditions becomes increasingly a prominent issue, and it results in the increase of the drilling period and the drilling cost, as well as the reduction of the drilling efficiency. In recent years, the drill pipe joint was extensively studied, mainly focusing on the 2D axisymmetric model, with a few on the 3D mechanical model, but without consideration of the influence of the angle of thread and the bending of the hole at the same time. The ultimate bearing capacity of the drill pipe joint was not well studied. In this paper, a 3D numerical simulation model of the drill pipe joint and a model to convert the borehole curvature to the loading moment are established based on the principle of the virtual work, the von Mises yield criterion and the nonlinear contact theory, taking account of the influence of the angle of thread and the bending of the hole at the same time. The make-up property of the drill pipe joint is studied, as well as the influences of the borehole curvature on the connection strength and the sealing property of the drill pipe joint, and the ultimate working pull and the ultimate working torque of the drill pipe joint are calculated with consideration of the preload, the bending load and the dynamic load safety factor. It is shown that the make-up torque can provide a certain initial contact pressure to ensure the connection strength and the sealing property of the drill pipe joint in the process of the downhole operation. The borehole curvature has a great influence on the connection strength and the sealing property of the drill pipe joint in the process of the downhole operation. The connection strength and the sealing property of the drill pipe joint will be much affected under some common operating conditions. In consideration of the random vibration and the shock of service, the drill pipe joint used for the common ultra-deep well, the horizontal well, the directional well, the extended-reach well and the highly deviated well should be designed and selected with due consideration of the influence of the borehole curvature. For each kind of drill pipe joint to be designed, the accurate numerical calculation of the ultimate working pull and the ultimate working torque should be conducted for the corresponding borehole curvature and the axial tensile load to ensure safety.
The aeolian sandy soil is widely distributed in the desert zone. It is vulnerable to the wind erosion and serves as the dust source of the sandstorm due to its fine particles and the non-cohesion property between particles. The microbial induced calcite precipitation (MICP) is one of the bio-geotechnical technology. This paper examines the MICP-treated aeolian sandy soil through a self-designed preparation method and process. The strength properties and their influence factors, the concentration of the bacterium, the porosity and grain distributions, are discussed. Testing results indicate that the suitable curing time for obtaining enough strength with good efficiency is 7 d for the MICP-treated sandy soil samples in this study. It is found that the MICPtreated aeolian sandy soil can have an average unconfined compress strength of 0.66MPa and an average inner friction angle of 36ffi in this reasonable range of OD600 0.5~0.8. The feasibility of the MICP-treated aeolian sandy soil is verified in the application of bio-crusts in desert engineering. The pore space and the porosity of the soil matrix play an important role in the MICP process. When the soil matrix with high porosity is well-graded, the MICP-treated sandy soil samples may have a high strength. Furthermore, the pore features are tested through the nuclear magnetic resonance (NMR) technology before and after the mineralization. The results indicate that the pores are well developed after the mineralization. The radius of most pores is in the range of 30 μm to 50 μm, and the pore with radius of 100 μm offers most of pore volume. The porosity is decreased by about 15% after the mineralization as compared with the unmineralized for the same sample.
As an important relation of the proportion in the history of mathematics, the golden section relation plays an important role in aesthetics, architecture, and even engineering. This paper studies the gold segmentation effect for a class of vibration system of two degrees of freedom. The free vibration characteristics, and the resonance mechanism of the forced vibration under harmonic loading are analyzed. It is shown that, the ratios of the structure circular frequency to the layer stiffness and mass, and that of the structural amplitudes at two points conform well with the golden section ratio. The structure shows the beauty of harmony in vibration.
This paper presents the optimal design of a tunable nonlinear absorber. A nonlinear dynamic model is established based on the Hamilton principle of the minimum potential energy. The response equation of the two-DOF (degree of freedom) tunable nonlinear absorber is solved by the average method and the stability of the system is analyzed., It is shown that with the optimized parameters, the amplitude of the vibration is reduced.
Two methods for the construction of a Lagrangian in the theory of inverse problem, the Santilli' method and the first Engels'method, are discussed. (1) It is pointed out that the theoretical significance of the Santilli' method is in the fact that by a direct construction of Lagrangian one may prove that the self-adjoint differential equations can be derived by the variational principle, that is, represented in terms of the Lagrange's equations. (2) It is manifested that what constructed by the Santilli' method is not a unique Lagrangian, but a family of gauge equivalent Lagrangians, and the Santilli' method is modified. (3) The defects of the Santilli' method in practical applications are pointed out, especially for some mechanical systems, because the definite integral depending on a parameter is divergent, so the Lagrangian can not be constructed. (4) The significance and advantages of the first Engels' method are discussed, and the defects of this method are also pointed out. (5) Two examples are given to illustrate the application of the result.