The tubular column of drilling and screw pumps is subjected to both the axial pressure and torque loads in operations. Slow dynamic method is proposed to calculate the column buckling torque and pressure. Based on the idea of the transient dynamics method in solving the statics problem, the loading, and the strategies of choosing the damping factor and sub-steps are analyzed. The numerical results show that when the axial pressure and torque are acted alone or simultaneously, the finite element solution is in good agreement with the analytical solution. This paper also analyzes the influencing factors of the computational effciency of the slow dynamic method.
The studies on discrete Boltzmann modeling and simulation of phase separation are reviewed. According to the system component, the studies cover the single-component two-phase separation and the multi-component phase separation. According to the physical modeling, the studies cover the LBM (lattice Boltzmann method) simulations based on traditional hydrodynamic modeling and discrete kinetic modeling of the phase separation system. According to the main focus, the topic covers method/model studies and physical behavior investigations. The discrete kinetic modeling has brought some deeper insights into the phase separation process. The features of non-equilibriums obtained from discrete Boltzmann simulations can serve as some simple and effective physical criteria for dividing the two stages of phase separation, and can be used to discriminate and track various interfaces.
The prediction of high-frequency dynamic response of composite structures is one of key steps in the structural design of the aircraft and other vehicles. In order to make an accurate prediction, three methods are discussed. The energy finite element method is found to be suitable to obtain accurately the dynamic response of composite structures. In this paper, the energy finite element analysis and its applications for composite structures are reviewed. Some important issues for the further applications are suggested.
The common way of airing clothes has the disadvantages of low utilization ratio of space, poor adjustment capability and poor wind resistance. Based on the mechanical self locking principle, a new type of clothes airing device is designed. According to the hook self-locking mechanism and using the static equilibrium equation for the analysis of mechanical characteristics，the dangerous section, the optimal self locking angle and the tensile strength and the shear strength of the material are determined. The impact of the stability of the system and the material safety control factors are analyzed. A clothes airing device based on the hook locking mechanism is designed, with the hanger column angle adjustable, with an enhanced new mechanism of windbreak protection, and with arbitrary number of hangers. The space utilization is improved.
The trajectory tracking control of a space robot system with flexible joints in the joint space with uncontrolled base and uncertain parameters is discussed. From the conservations of the linear and angular momentum, the dynamic equations of the system are derived by the Lagrange method. A joint flexible compensation is used to reduce the system's joint flexibility in order to reduce the effect of the flexible joints on the system's control precision. As for the uncertain parameters, the singular perturbation method is used to design an adaptive back-stepping sliding mode control with the disturbance observation to track the desired trajectory in the joint space. With the proposed scheme, it is not required to linearly parameterize the dynamic equation of the system, and the controller is simple and achieves the accurate tracking control of the space robot joint movement. A planar space robot with two links is simulated to verity the feasibility of the proposed control scheme.
According to the complexity in the construction of shallow-buried bias multi-arch tunnel and the actual situation of Dazhongshan1# tunnel, setting testing component in typical cross-sections, the tunnel's surrounding rock and supporting structure force are duly monitored.comparing with the result about software MIDAS analyzed force of the mid-board can be drawn the characteristics of force and deformation when the tunnel under unsymmetrical pressure. the result concluded that toreduce unbalanced force make a important role anduse twoanalytical methods can precisely analysis the stability of structure and effciently guide construction.
In order to test the mechanical properties of the freeway guardrail's columns, including the old standard column, the new standard column and the updated column, an indoor static load test is designed. By comparing and analyzing the results of the test, the actual effect of the updating scheme is assessed. The single variable test on the parameters of the updating scheme is made, which shows the controlling factors of the column's force peak value in different stages. It is shown that the column updating scheme can improve the mechanical properties of the old columns, which would become even better than the new standard columns. To a certain extent, the mechanical properties of the old columns are controlled by the height of the concrete which is poured in the column. When the concrete height reaches the height of the ground, the updating influence of the concrete pouring height can be ignored.
The thermal cracking of the steam granite is studied under the condition of the non uniform stress state by using the developed convection heating in situ mining simulation test rig and the true three axis press. Under this experimental condition, the granite undergoes brittle fracture, the brittle fracture temperature of the granite is 483℃, and the steam pressure is 10.6MPa. At the same time, under the action of the high temperature and high pressure steam, the main crack of the granite is along the direction normal to the minimum principal stress direction, in addition, due to the thermal cracking, a certain number of randomly distributed secondary cracks in other directions appear. Because of the formation of cracks in different directions, the space crack network connected with each other is of practical significance. The long term experiment study helps to improve the effciency of the geothermal exploitation.
This paper studies the flow process of two stratified fluids in a cylinder, using the Planar Laser Induced Fluorescence and the High Speed Camera techniques, covering both miscible and immiscible stratified liquids. It is shown that the directions of the liquid density gradient and the viscosity gradient are the key factors for the interface instability between liquids. When the directions of the two gradients are the same, the violent mixing would not occur during the spin-up process, and the light fluid will impact the heavy fluid during the spin-down process. When the directions of the two gradients are not the same, the pumping action occurs during the spin-up process, the interface breaks up in the later period of the spin-up, and the heavy fluid will impact the light fluid during the spin-down process. Among the three stages of spinning-the spin-up, the rigid body rotation and the spin-down, the spin-down has a big effect on the mixing process, which means that no matter whether the directions of the two gradients are the same, the interface instability between liquids will occur.
The reinforced sandwich composite cantilever structure sees a wide application in the ship engineering. However, due to many design variables, it is diffcult to determine the bending stiffness at the design stage. Based on typical structure application background demands, a bending stiffness calculation model for the reinforced sandwich composite beam with variable cross-section is established. A model is made for stiffness tests, the result of which is compared with the calculation model. Finally, the influences of several factors on the stiffness are discussed, such as the material parameters of the main components, the hybrid fiber content of the panel, the allocation proportions of the panel and web sections, and the layer proportion of the web. The results can be used in designing reinforced sandwich composite cantilever structures.
Frame structures are mainly designed to prevent the progressive collapse through two resistance mechanisms under the condition of sudden destruction of vertical bearing components, including the beam mechanism under a small deformation condition and the catenary mechanism under a large deformation condition. The large planar stiffness of the composite slab can significantly improve the resistance of the progressive collapse of the structures. This paper simplifies a concrete floor-steel frame structure into a steel-concrete composite beam structure. The structure resistance curve obtained by previous researches is simplified. The mechanical characteristics in various stages during the progressive collapse are analyzed to obtain formulas of the resistance curve at every stages by using the energy method. Subsequently, the reliability of the proposed formulas is validated against a case study of an example by using the large-scale finite element analysis software ANSYS, and a good agreement is observed. It is shown that the slabs can greatly strengthen the progressive collapse resistance of the structures.