The drill string fatigue failure caused by drill string vibration is increasingly an issue related with the development of ultra-deep drilling operations. The research methods of drill string vibration can be classified into two types, the theoretical analysis or numerical simulation, and the the measurement technology. Owing to various complicated nonlinear mechanical problems, especially, the impact between moving drilling tools and hole wall, it is dificult to study the drill string vibration in many cases using the theoretical analysis or numerical simulation method, and therefore, the down hole vibration measurement technology becomes more and more important. This paper gives a comprehensive and systematic review of the status and progress of drill string vibration measurement technology, followed by a detailed discussion of the working mechanism, analytical approach and application technology for several overseas measurement tools which have been widely used around the world. The results would provide important supports to develop the down hole vibration measurement technology in our country.
Notched specimens are more and more widely used in fatigue studies. Since Neuber rule was proposed, the local stress-strain method has been used widely because of its simplicity. Conservative prediction results were usually obtained by this approach. The fatigue notch factor based on notched specimens has been used for the fatigue study instead of the stress concentration factor. However, the prediction precision has not been improved essentially. The stress gradient approach was proposed for the notched study with considerations of the stress gradient near the "hot point" and the concept of stress gradient was used in the stress field intensity approach. The dificult problem in the stress field intensity approach is how to decide the damage area accurately. The effective unification between the Neuber rule, the Peterson approach, and the stress field intensity approach can be achieved by the critical distance theory. The improvement of the finite element method supports the critical distance theory further. Now, better prediction results on high cycle fatigue were obtained by the critical distance theory, but this approach has not been much used for the predictions of low cycle fatigue.
The phase image in tapping mode of atomic force microscope indicates that the process of interaction and separation between the tip and the samples dissipates energy, which is primarily due to the liquid bridge in ambient air. This paper studies the dynamic process of the formation and rupture of liquid bridge in tapping mode of atomic force microscope in order to reveal the AFM working mechanism, and finally the dissipation energy in tapping mode of AFM is determined.
The nonlinear factor influence on the vibration isolation effect of damper was studied under the foundation on think about stiff nonlinear and damped nonlinear. The computational formula of motion responses and transmissibility of nonlinear system were obtained under at the same time to consider cube stiff nonlinear and oval damped nonlinear. The nonlinear factor influence on motion responses and transmissibility were discussed.
Based on Lattice Boltzmann method and constitutive equation for power-law fluid, a model for flow in a channel is proposed, and the fully development velocity of outflow obtained is in good agreement with the analytic solution. A simulation of power-law fluid past a cylinder is carried out, where the bounce-back boundary scheme is adopted for non-slip velocity at the circular cylinder surface. The drag coeficient is calculated by integrating the total stresses on the boundary of the circular cylinder, the effect of power-law index and Re on the drag coeficient is further analyzed. For elliptic cylinder, the influences of different shapes and power-law indexes on the pressure coeficient and viscosity coeficient are investigated. The model is validated by the good agreement between the simulation results and those obtained by other numerical simulation methods.
Due to the sudden shutdown of pump, the power off or the mechanical failure, the flow velocity in the lifting pipeline of a deep-sea mining system may be changed in short time, which can be accompanied with a sharp pressure change. This phenomenon, the water hammer, may cause a great damage to the mining system. Based on the principles of continuity and momentum theorems of solid-liquid two-phase flow, a formula of water hammer pressure is derived for the lifting pipeline with coarse solid. By using the parameters of the pilot system, the water hammer pressure is calculated and analyzed under the conditions of different flow velocities, solid volume concentrations and pipe diameters. The results show that the parameters are important factors to the water hammer pressure, including the flow velocity, the solid volume concentration and the pipe diameter, especially, for the flow velocity. The results can provide some references for deep-sea mining system designs and safety risk analysis.
A model of damage mechanics of fluid and solid near the wellbore is established, for the multi-fracture initiation near wellbore under complicated geological conditions, and the distribution of stress and damage of perforated wall is obtained by numerical analysis. Calculation shows that the smaller the crustal stress value is, the smaller the well perforation azimuth angle is, the lower the crack pressure will be. The crack stress increases with the increase of the perforation azimuth angle. When the near wellbore has inflexion cracks and an angle of 45° micro crack, the crack pressure increases. Based on this conclusion, the perforation azimuth angle is less than 30° for normal fault and smooth fault, when the spiral perforation angle is 30° or 45° and the thrust fault is 45°, multi-fracture initiation will be implemented effectively.
Focusing on the failure modes, 5T concrete beams with different anchorages, surface characters, materials of FRP bars, strengthened with near surface mounted FRP (fiber reinforced polymer) bars, are used in flexural experiment. It is shown that the bonding failure happens in the strengthened beams without anchorage, and those with plain GFRP bars and CFRP bars. The ultimate load is influenced by anchorage and surface characters of FRP bars; the yield load and the ultimate load are larger in beams strengthened with CFRP bars. The coeficient of utilization of FRP bar is larger for beams strengthened with ribbed FRP bars and anchorage. Therefore, it is most effective to strengthen beams with ribbed GFRP bars and anchorage.
In meso-scale, bituminous mixture consists of bituminous mortar, aggregate and voids. The mechanical parameters of bituminous mortar are important parts of meso-scale properties of bituminous mixture and they have very significant effect on the tensile strength. To this end, a loading fixture is designed. Tensile tests for 9 groups of specimens at different loading rate and temperatures are carried out, and the whole tensile curve for bituminous is obtained. From the curve, the maximum tensile stress σmax, the stiffness Knn, and the displacement of failure process U are determined. The parameters obtained are essential to simulate the cracking behavior of bituminous mixture using the cohesive constitutive model.
A mechanical model of casing cutting in deepwater is proposed based on the model of long pole milling. Through this model, the cutting torque of drill string and the maximum permitted pump stroke can be obtained. It is concluded that the relationship between the proportion of the cutting torque in the drive torque and the depth of water during operating provides some guidance for forming the judge index to determine whether the casing pipe is cut off completely in the deep water. Combined with the field data of two wells in the South China Sea, the model is verified. The results can be used for providing a theoretical reference for selecting the appropriate pump stroke and a technical guarantee for deepwater abandonment operations to improve the cutting speed and the time eficiency.
As a simple component, the beam is widely used in engineering. in the classical beam theory, a modification factor and an equilibrium of the internal forces are introduced to obtain the shear stress, which makes the process complicated. In this paper, a displacement function of Legendre polynomials is proposed to analyze the shear stress with consideration of the conditions of zero transverse shear stress at the top and the bottom. The excellent agreement between the theoretical results and those obtained by the finite element method shows that the theoretical model of Legendre polynomials is capable of determining the shear stress of the beam accurately. Therefore, the method may provide a new theoretical reference for the mechanics analysis of the beam.