Study on Buffering Performance of Aluminum Foam during Water-entry Process

The structure will suffer a huge overload, when it enters into water. The buffer head cap can effectively reduce the overload, and the buffer material in the cap is the key to its load reduction performance. In order to study the buffering ability of aluminum foam, an effective numerical simulation method is established in this paper. The numerical simulation method can effectively observe the motion of the structure and the energy absorption process of aluminum foam. It is found that the aluminum foam has strong capacity of buffering and reducing load by comparing with the structure without buffer head cap under the same conditions. In the process of energy absorption deformation, it can effectively protect the projectile from buckling deformation.

Study on the Semiactive Control and Optimal Layout of a Hydropower House Based on Magnetorheological Dampers

With the continuous development of hydropower stations, the capacities and the heads of hydro generator units are increasing, and the plant vibration problem is becoming more and more serious. A numerical simulation method for the vibration reduction control of magnetorheological (MR) dampers suitable for large-scale complex structures was proposed. The method is simple and easy to implement, and the semiactive control of the MR damper could be achieved by adjusting the current switch and size. On the basis of a numerical simulation, a mathematical model for the optimal layout of an MR damper device was established. The objective function was the vertical velocity and the vertical acceleration response of the generator floor. The results showed that the proposed semiactive control numerical simulation method could be applied to the vibration control of the hydropower plant structure, and the vertical velocity and vertical acceleration were reduced by 10.96% and 12.90%, respectively, compared with those without structural vibration control. At the same time, the proposed optimized layout method was effective and feasible, and the damping effect of the MR damper could be effectively improved through the optimized layout.

Numerical calculation of transient electric field considering space charge in oil-paper insulation of converter transformers

Purpose The purpose of this paper is to develop a numerical simulation method based on the transient upstream finite element method (FEM) and Schottky emission theory to reveal the distribution characteristics of space charge in oil-paper insulation. Design/methodology/approach The main insulation medium of the converter transformer in high voltage direct current transmission is oil-paper insulation. However, the influence of space charge is difficult to be fully considered in the insulation design and simulation of converter transformers. To reveal the influence characteristics of the space charge, this paper proposes a numerical simulation method based on Schottky emission theory and the transient upstream FEM. This method considers the influence of factors, such as carrier mobility, carrier recombination coefficient, trap capture coefficient and diffusion coefficient on the basis of multi-physics field coupling calculation of the electric field and fluid field. Findings A numerical simulation method considering multiple charge states is proposed for the space charge problem in oil-paper insulation. Meanwhile, a space charge measurement platform based on the electrostatic capacitance probe method for oil-paper insulation structure is built, and the effectiveness and accuracy of the numerical simulation method is verified. Originality/value A variety of models are calculated and analyzed by the numerical simulation method in this paper, and the distribution characteristics of the space charge and total electric field in oil-paper insulation medium with single-layer, polarity reversal of plate voltage and double-layer are obtained. The research results of this paper have the guiding significance for the engineering application of oil-paper insulation and the optimal design of converter transformer insulation.

Numerical Simulation of The Response of An Underground Pipeline Connector With a Super-Large Section Under Complex Geological Conditions

Aiming at the low simulation accuracy of the numerical simulation method of the joint response of the super-large section underground comprehensive pipeline gallery under the current complicated geological conditions, a numerical simulation method of the joint response of the super-large section underground comprehensive pipe gallery joint response under the complicated geological conditions based on the finite element model was proposed. According to the analysis process for the super-large section underground comprehensive pipe gallery, the viscous boundary of the comprehensive pipe gallery is determined. Additionally, by analyzing soil and structural parameters, the optimal combined dynamic boundary is used as the model boundary. The HSS model is used to describe the constitutive structure of the soil, and by improving the Goodman element to describe the contact surface of the model, the finite element model of the joint response of the comprehensive pipe gallery is constructed. Furthermore, based on the internal force balance and deformation coordination conditions, considering the influence of the deformation shape of the joint joints and the elongation of the prestressed tendons on the finite element model, the response model of the integrated pipe gallery joint is optimized. Experimental results show that the proposed method has higher numerical simulation accuracy.