First-principles study of dissociation processes of O2 molecular on the Al (111) surface

Shiyang Sun,Pingping Xu,Yuan Ren,Xin Tan,Geyang Li 한국물리학회 2018 Current Applied Physics Vol.18 No.12

The trajectories of adsorption and dissociation process of O2 on the Al (111) surface were studied by the spinpolarized ab initio molecular dynamics method, and the adsorption activation energy was clarified by the NEB method with hybrid functionals. Three typical dissociation trajectories were found through simulation of O2 molecule at different initial positions. When vertically approaches to the Al surface, the O2 molecule tends to rotate, and the activation energy is 0.66eV. If O2 molecule does not rotate, the activation energy will increase to 1.43 eV, and it makes the O atom enter the Al sublayer eventually. When the O2 molecules parallel approach to the Al surface, there is no activation energy, due to the huge energy released during the adsorption process.

The Application of Built-in Beam Element Method in the Aqueduct Pile Foundation Analysis

Shiyang Pan,Tongchun Li,Xiao Qing Liu,Jian-qun Zhu,Zhen Cui,Zhengyi Wang 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.7

The solution using built-in beam element method to increase the calculation efficiency of aqueduct pile foundations is studied in this work. The formulations of built-in beam element method based on the normal generalized displacement method of beam element are introduced in this work. Then, the validity of the built-in beam element method is checked by a static problem of a simplified aqueduct model. Furthermore, the solution to increase calculation efficiency by built-in beam element method for aqueduct pile foundations is introduced by studying the features of built-in beam element method and normal generalized displacement method of beam element in models with different grid density and foundation stiffness. Finally, a static problem of an arch aqueduct is solved using the summed solution. The results show that it is feasible to improve efficiency with sufficient accuracy by reasonably selecting the built-in beam element method and normal generalized displacement method in the analysis of aqueduct pile foundation.

Effect of stacking conditions on performance of a centrifugal pump

Peng Yan,Shiyang Li,Shuai Yang,Peng Wu,Dazhuan Wu 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.2

In this study, the effect of stacking condition of centrifugal pump impeller was investigated by Computational fluid dynamics (CFD). The performance curves of impellers with three different stacking conditions were compared. The Local Euler head distributions (LEH distribution) at blade Leading edge (LE) and Trailing edge (TE) were obtained to evaluate the contribution of different spanwise location to the total work. The positive stacking characterised by the hub leading the shroud was considered inappropriate in centrifugal pump impellers as it deteriorated the performance of the pump in whole flow rate range. The negative stacking characterised by the shroud leading the hub could improve flow stability and efficiency in low flow rates, it was manufactured and tested. The test results showed good agreement with CFD calculations. A hump zone was observed in zero stacking impeller between 0.9Q d and Q d . It was closely related to the drastic change in pattern of LEH distribution at the two flow rates. The internal flow was analyzed to reveal the reasons responsible for the hump in head curve. It is found that the tremendous extension of low streamwise velocity region and its instant movement from the corner of shroud and blade suction surface to the midspan near blade suction surface when the flow rate decreases from Q dto 0.9Q d is the main reason for flow instability in zero stacking impeller.

Investigation of the impact of splitter blades on a low specific speed pump for fluid-induced vibration

Guitao Zeng,Qianqian Li,Peng Wu,Bo Qian,Bin Huang,Shiyang Li,Dazhuan Wu 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.7

Low specific speed centrifugal pumps are widely applied in the chemical industry and agricultural irrigation fields. The vibration characteristics are of great importance for centrifugal pumps. Apart from rotor installation, fluid-induced vibrations caused by internal flow also play an important role in the vibration performance, and special attention should be paid to low specific speed centrifugal pumps for long and narrow meridian flow channels where secondary flows are easy to generate. In this paper, splitter blades were studied for decreasing the pressure and radial force fluctuations of a low specific speed centrifugal pump at the design point, both numerically and experimentally. Numerical simulations based on the Reynolds averaged Navier–Stokes (RANS) turbulent model were performed for fluid-field analysis. The steady state and unsteady simulations were computed based on ANSYS Fluent. Here, the circumferential location, leading edge location, and the deflection angle of the splitter blades were considered to suppress the secondary flow and to reduce vibration. The experiments show the effectiveness of splitter blades for decreasing fluid-induced vibrations.

A Study on Construction and Simulation of Agricultural Machinery System Control Model

Wang Ying,Xu Shiyang,Liu Shiqiang,Li Xiaoxue,Ao Changlin 보안공학연구지원센터 2016 International Journal of u- and e- Service, Scienc Vol.9 No.8

In order to study the state-changing and running rules of agricultural machinery system, this paper establishes the control model of agricultural machinery system under the discrete-state space based on control theory, from the perspective of the complex systems and with reference to the actual conditions of agricultural production; conducts the qualitative analysis on the system model, builds the relevant simulation model of agricultural machinery system accordingly, and verifies the running of the simulation model. This control model can provide effective basis and reference for further quantitative studies on state evolution of agricultural machinery system.

Stator modification methods for diagonal flow fans to achieve noise reduction of rotor-stator interaction

Jieting Han,Yu Zhang,Shiyang Li,Bin Huang,Dazhuan Wu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.2

The effect of three noise reduction methods for rotor-stator interaction in diagonal flow fans was studied. The unsteady flow field and directivity of tonal noise were obtained by numerical simulation based on computational fluid dynamics (CFD) and the Ffowcs Williams and Hawkings (FW-H) method; the baseline model was tested in a semi-anechoic chamber. The generation mechanism and location of noise were investigated. In addition, the characteristics of tonal noise at blade-passing frequency (BPF) were studied, along with its harmonics. The results show that the tonal noise at 1 BPF dominates the overall sound pressure level. Proper rotor-stator spacing, a large forward-leaned angle, and a large backward-swept angle are beneficial to reduce tonal noise. Also, the noise reduction effect is related to the low amplitude and to the phase shift caused by the pressure response of the rotor wake impinging on stator surfaces, especially near the leading edge at 1 BPF.

A new transient CFD method for determining the dynamic coefficients of liquid annular seals

Dazhuan Wu,Xinkuo Jiang,Shiyang Li,Leqin Wang 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.8

Currently, the dynamic characteristics of annular seals are numerically investigated mainly by solving the bulk flow equations using perturbation method, or by simulating the perturbed flow field of annular seal using CFD method. The adopted disturbance way is generally the circular whirling motion of rotor around seal centre with constant speed. Relative to the transient CFD simulation, the quasisteady CFD simulation introducing Moving reference frame (MRF) has been widely used by researchers. Both the dynamic mesh problem and the time-consuming problem suppress the use of transient CFD simulation in annular seal research. In the paper, a new transient CFD method based on rotor’s variable-speed whirl is presented to improve the time-consuming problem and all the (total 20) dynamic coefficients of concentric liquid seal can be obtained by only two transient CFD simulations, one for the variable-speed cylindrical whirl and the other for the variable-speed conical whirl. The results are compared with those from the experiment, the quasi-steady CFD method and the traditional transient CFD method based on constant-speed whirl. The comparisons show that the new transient method can keep the good accuracy of traditional transient method and meantime largely save the computational time.