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It is critical to discover the behavior of piston wind induced by a braking train in a tunnel, but there is little research on the theoretical derivation for piston wind behavior. Predicting piston wind behavior as an unsteady airflow by a theoretical formula is hard work due to the complexity of train running states and airflow fields. Herein, we develop a mathematical model to investigate the behavior of piston wind as an unsteady airflow, considering the variation of wind direction in the annular area. In general, the theoretical model is validated by experiments. However, experimental studies about piston wind are scarce. In this study, we simulated the emergent braking process of a train to validate the mathematical model by establishing a 1/50 scaled experimental configuration. The piston wind data tested in the experiment have good agreement with the results calculated by theoretical formulas. In addition, sensitivity analysis of the effect parameters of piston wind (i.e., tunnel length, train length, train speed and blockage ratio) was conducted. The theoretical formulas derived in this paper are applicable to similar train running conditions in railway tunnels or subway tunnels.

In the medical field and in biotechnology, a new type of micropump such as peristaltic micropump that can supply miero liquid flow has urgently been demanded. It is our purpose to develop a type of peristaltic micropump that has the characteristics of flexibility, driven by a low voltage, good response, safety and working at a kind of peristaltic mode. In this paper, we propose a new prototype model of a peristaltic micropump using SMA (Shape Memory Alloy) spring actuator as the servo actuator. This paper describes the new structure and the motion mechanism of the micropump and discusses the possibility of the micropump. This micropump consists of two diffusers (Inlet) as one-way valve, four pump chambers made of elastic tube, and extrusion poles. The overall size of this micropump prototype is 30mm in diameter and 14 mm in length. The flow characteristic of the micropump is measured. The experimental results indicate that the micropump has the satisfactory responses, and it is able to make a microflow and very useful for the biomedical applications.

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