Journal of Zhejiang University - Science A

Tong, Zhe-ming; Miao, Jia-zhi; Li, Yuan-song; Tong, Shui-guang; Zhang, Qian; Tan, Gui-rong

doi: 10.1631/jzus.a2100006pmid: N/A

The issues of energy shortage and environmental pollution have accelerated the electrification of construction machinery (CM) industry globally. In China, the amount of electric construction machinery (ECM) has been growing across the industry. The sales of ECM are estimated to reach 600 000 vehicles by the end of 2025, while the total demand for battery power will reach 60 GWh. However, the development of ECM still faces critical challenges including reliable power supply and energy distribution among various components. In this review, we primarily focus on important technological breakthroughs and the difficulties faced by the CM industry in China. An overview of ECM including classification and characteristics is given at the beginning. Next, the selection of key components such as the electric motor and the energy storage units, and the control strategy in the pure electric drive system are discussed. The characteristics of the hybrid electric drive system such as structure design and power matching are analyzed in detail. The battery management system (BMS) is critical to ensure appropriate battery health for reliable power supply. Here, we extensively review technical developments in various BMSs. In addition, we roughly estimate the national total of CM emissions and the potential environmental benefits of employing ECMs in China. Finally, we set out future research directions and industrial development of ECM.

Qian, Jin-yuan; Mu, Juan; Hou, Cong-wei; Jin, Zhi-jiang

doi: 10.1631/jzus.a2000582pmid: N/A

In this paper, the piston type valve core and the unbalanced moment on its bottom are studied. To decrease the influence of non-common geometrical factors, a simplified model of the piston type globe valve is proposed in this study. Based on the computational fluid dynamics (CFD) method, the effects of different geometrical parameters on the unbalanced moment existing on the bottom of the valve core, which include the bending radius of the inlet flow channel, the diameter of the special-shaped pipe, and the height of the valve core, are studied. Finally, the effects of geometrical parameters on the unbalanced moment on the bottom of the valve core are clarified by correction and variation classification and provide a basis for further optimizing the structure of the piston type valve. The results show that the unbalanced moment decreases with the increase of the bending radius of the inlet flow channel, but increases with the increase of the diameter of the special-shaped pipe and the height of the valve core. Moreover, the relation between the unbalanced moment and flow rate is proposed.

Bian, Xue-cheng; Fu, Lei; Zhao, Chuang; Chen, Yun-min

doi: 10.1631/jzus.a2000235pmid: N/A

Long-pile groups of railway foundation undergo excessive settlements after groundwater reductions, which may exceed the settlement limit and threaten the safe operation of high-speed trains. However, the effect of groundwater reduction on a long-pile group (greater than 20 m in length) has not been fully understood, especially in respect of repeated reductions. In this study, a centrifuge test was conducted to investigate the responses of pile groups in silty soils subjected to repeated falls in the water table. The behavior of the piles was discussed based both on the test and on 3D numerical analyses. With the derived coefficient β for the axial force evaluation of the pile, the effect of lowering the water table on the railway pile foundation could be seen. Results of the tests and numerical analyses indicated that the water table decline significantly increased the down-drag and axial force of the pile, causing significant settlement. A longer pile presented a larger axial force at the neutral point. Nevertheless, the incremental percentage of the axial force decreased with increasing pile length with the same water table reduction. Because of group effect, the displacement of soil next to the center pile was smaller than that near the corner piles and showed a similar trend as the axial force of the pile. As the water table fell, the static load ratio affecting the progress of pile settlement increased disadvantageously, possibly inducing excessive pile settlement. A design method for railway pile foundations taking account of lowering groundwater was proposed with an example application, which provided a reference for similar projects.

Li, Shao-hua; Zhang, Ming-ju; Li, Peng-fei

doi: 10.1631/jzus.a2000120pmid: N/A

This paper focuses on the ground settlement induced by the construction of a curved shield tunnel. Ground loss and construction loadings are the two factors causing ground settlement, and two corresponding analytical models were developed. First, the ground settlement due to ground loss was analyzed based on 3D image theory. The “integrative gap at shield tail” (IGST) and overcutting gap of a curved tunnel were considered. Second, the ground settlement due to construction loadings was analyzed by modifying Mindlin’s solutions. The additional thrust, frictional force, and grouting pressure were considered. Subsequently, a case study and a parameter analysis were conducted. Finally, the obtained solutions were compared with a classical analytical solution, numerical simulations, and monitored results. The proposed model could effectively predict the ground settlement induced during curved shield tunneling.

Zhang, Jin-cheng; Sun, Ming-bo; Wang, Zhen-guo; Wang, Hong-bo; Liu, Chao-yang

doi: 10.1631/jzus.a2000087pmid: N/A

Flame stabilization is the key to extending scramjets to hypersonic speeds; accordingly, this topic has attracted much attention in theoretical research and engineering design. This study performed large eddy simulations (LESs) of lifted hydrogen jet combustion in a stepped-wall combustor, focusing on the flame stabilization mechanisms, especially for the autoignition effect. An assumed probability density function (PDF) approach was used to close the subgrid chemical reaction source. The reliability of the solver was confirmed by comparing the LES results with experimental data and published simulated results. The hydrogen jet and the incoming stream were first mixed by entraining large-scale vortices in the shear layer, and stable combustion in the near-wall region was achieved downstream of the flame induction region. The autoignition cascade is a transition of fuel-rich flame to stoichiometric ratio flame that plays a role in forming the flame base, which subsequently causes downstream flame stabilization. Three cases with different jet total temperatures are compared, and the results show that the increase in the total temperature reduces the lift-off distance of the flame. In the highest total temperature case, an excessively large scalar dissipation rate inhibits the autoignition cascade, resulting in a fuel-rich low-temperature flame.