Applied Mechanics and Materials Vols. 568-570

Abstract: The mathematical model based on temperature formulation for describing freezing course of soil is presented and the explicit finite difference method is used to perform computer simulation of freezing time of soil in this paper. It seems to be satisfactory by comparing the numerical results by the method of TDMA with experimental data. It is significant for freezing process and freezing units, optimum design of practical engineering.

Abstract: This paper discussed the working principle of the LLL night vision(low-light level night vision)device and researched into the LLL night vision objective opjective optical system.An LLL night vision objective optical system with good image quality is finally got,which comes after debugging with the optical design software ZEMAX according to the theoretical calculation of the objective lens parameters specific to night vision system.

Abstract: To solve the problem that single stage booster pump has the problem of low oil pressure at low speed condition. Paper gave a design method for three stage combination vortex pump which uses radial series. The preliminary structural parameters of the vortex pump were designed by using the empirical coefficient method. Then Hex/Wedge grid is used to generate mesh for the established 3D model of the vortex pump. The final structure parameters were obtained by CFD numerical simulation optimization iterately. Finally, the flow field of combination vortex pump was analyzed. Simulation results show that: The combination vortex pump meet the design requirements.

Abstract: In order to meet the demand of hydraulic experiment teaching in universities, base on the analysis of the function of virtual hydraulic experimental system, the main research contents、 system scheme and key technology are determined. Three-dimensional model of the hydraulic components are established. Working principle of hydraulic component is displayed. The action process and the performance of the hydraulic circuit are simulated. A virtual hydraulic experimental system with its own characteristics is built. The virtual experiment system is not only suitable for classroom teaching but also suitable for the experimental teaching and learning activeness of students is enhanced by using the system.

Abstract: Cavitation is a common harmful phenomenon in hydraulic transmission systems. It not only damages flow continuity and reduces medium physical performance, but also induces vibration and noise. At the same time, the efficiency of a system is reduced due to cavitation, especially dynamic performance are deteriorated. Applying commercial CFD software FLUENT, the cavitation issuing from the orifice was numerically investigated, reducing the harm. The effect of liquid parameters (such as surface tension, gas content, and the temperature) on the oscillation of bubble is studied numerically. The modified Rayleigh-Plesset equations are presented to describe the oscillation of bubble in different liquids. Employing the finite difference calculus, the behavior of a cavitation bubble in liquids with different physics parameters are obtained. Meanwhile, the numerical results are compared with experiment results. It is observed that the viscous force decreases the growth and collapse of a bubble, making it expand or collapse less violently. And the surface-tension forces stave bubble growth progress and speed up bubble collapse process. On the other hand, both the maximum bubble radius and bubble lifetime increase with increasing temperature. These results can provide theory basis for understanding cavitation bubble dynamics in the hydraulic systems.

Abstract: A inducer and impeller combination aero fuel centrifugal pump design method was given. Based on empirical coefficient method the preliminary structural parameters of the combination Centrifugal pump were designed firstly. Then the Centrifugal pump Hybrid Grid model was built with muti-block structure and octree style.The final structure parameters were obtained by CFD numerical simulation optimization. Finally, the flow field of combination Centrifugal pump was analyzed and compared simulation datas with test datas by making the test samples.The relative error of the design point doesn’t exceed 5%, indicates that the inducer and impeller combination pump meet the design requirements.

Abstract: The construction of ultra-high voltage grid and the input of large generating units make the out-of-step protection become increasingly important. Traditional out-of-step protection device can only judge from local perspective, no consideration to the global situation. In order to solve this problem, a coordination control method of generator out-of-step protection based on WAMS transient stability prediction is proposed, the coordination between grid side out-of-step protection and the generator out-of-step protection is achieved. Using the self-memory trajectory to predict the stability of grid, calculate excess energy of system based on EEAC theory, and utilize convexity-concavity of phase diagram method which is not affected by the change of network structure to judge the stability of system. Utilize double forecast strategy to improve the stability of the system further.

Abstract: Based on load specification, the power supply model and requirement of well clusters is presented and established in gas gathering and transmission engineering, which is applied on type I and type II. The study considers both reliability and economy of all power supply proposals, and comparatively calculates and analyzes the numbers and types of main electrical equipments, capital expenses (CAPEX) and operating expenses (OPEX). Specially, for the problem of voltage drop, it illustrates the contrast and selection of power transformers with two ratings by the technical features of standard. Finally, the paper respectively puts forward the power supply schemes for well clusters type II and type II from different proposals based on the detailed results, which shows that the conclusions are feasible and reasonable in the practical engineering application.

Abstract: Specifying technical features of all kinds of distributed energy resources in operation control is the foundation of deploying active distribution network. This paper analyzes the technical characteristics of various distributed energy resources (DER) including micro-turbines, wind turbines, photovoltaic generations, distributed energy storage devices and flexible loads (FL), and discusses the demand response (DR) mechanisms and controllability of FL profoundly. Furthermore, on the basis of the economy and the reliability of the overall system, the in-depth study of active distribution network (ADN) typical integration modes which adapt to a low-carbon environment are carried out.

Abstract: Based on the comparative analysis of the fast Fourier transform (FFT), the short-time Fourier transform (STFT), the wavelet transform (WT) and other power quality detection algorithms, this paper puts forward to a new power quality detection algorithm which combines the Fourier transform with the wavelet transform. The transient as well as the steady state signals are separated on the basis that the wavelet transform is sensitive to the singular signals. The presented algorithm detects a variety of harmonic parameters of the gird after the separation of steady state signals is finished by fast Fourier transform. A new power quality detection system is then designed based on the core chip of S3C2440A, and the algorithm which is ARM-9 based is transplanted into the embedded Linux operating system to carry out the experiments. Analysis of the experimental data shows the detection algorithm is reliable by Fourier transform and wavelet transform.