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Quantitative characterization of seepage behavior in rough fracture considering hydromechanical coupling effect: an experimental study

Yu Xiang, Zhang Tong, Yang Ke, Yu Fei, Liu Yang, Tang Ming

Acta Geophysica

2023

Vol. 71, no. 5

2245--2264

To study the effect of fracture morphology and in situ stress on the seepage behavior of rough fractures, hydraulic–mechanical experiments with different confining stresses, pore pressures and fracture geometry were carried out. The dimensionless parameter non-Darcy coefficient factor K and K-based critical Reynolds number model (KCRN) was proposed to characterize the behavior of rough-wall fracture and fluid seepage. The results show that the seepage flow of rough-wall fracture can be well described by Forchheimer equation. As the confining pressure increases from 1 to 31 MPa, the two walls of the rough fracture are compressed, and the fluid flow capacity is weakened, resulting in an increase of 2–3 orders of magnitude in Forchheimer viscosity coefficient A. Also affected by the increase in the confining pressure, the contact area between the two walls of the rough fracture increases, which makes the fluid channel become curved, increases the dissipation of water pressure in the inertial process and causes the inertial term coefficient B to increase by 2–3 orders of magnitude in general. In the whole range of test confining pressure (1 MPa–31 MPa), the flow state of rough fracture fluid is divided into zones based on the critical Reynolds number. The average hydraulic aperture decreases with the increase in the confining pressure, which can be perfectly fitted by hyperbolic function. The calculated critical Reynolds number of six rough fracture samples varies from 0.0196 to 1.0424. According to the experimental data, the K-based critical Reynolds number model (KCRN) is validated, and the validation results prove the accuracy and reliability of the model.

Interception of a hypersonic vehicle by low-speed interceptors: novel perspectives and cost optimisation

Liu Shuangxi, Liu Shijun, Yan Binbin, Zhang Tong, Zhang Xu, Yan Jie

Bulletin of the Polish Academy of Sciences. Technical Sciences

2022

Vol. 70, nr 6

art. no. e143537

The conditions for accurately intercepting hypersonic vehicles by low-speed interceptors in the terminal guidance process are examined, considering the general form of a guidance scheme. First, based on the concept of the engagement geometry, three interception scenarios are established considering different manoeuvring configurations of the interceptors and hypersonic vehicle. Second, the boundary conditions for intercepting hypersonic vehicles (with speeds higher than those of the interceptors) are specified for the three scenarios, considering several factors: the speed, path angle, line-of-sight angle, and available overload of the interceptor; path angle and manoeuvrability of the hypersonic vehicle; and relative distance between the interceptor and vehicle. A series of simulations are performed to clarify the influence of each factor on the interception performance in the three interception scenarios. The challenges associated with accurately intercepting hypersonic vehicles by low-speed interceptors are summarised, and several recommendations for designing guidance laws are presented.

Numerical and experimental investigation on nonlinear dynamic characteristics of planetary gear train

Zhang Jianwu, Guo Han, Yu Haisheng, Zhang Tong

Journal of Theoretical and Applied Mechanics

2020

Vol. 58 nr 4

1009--1022

A deep hybrid electric vehicle (DHEV) equipped with a Ravigneaux compound planetary gear train (PGT) encounters severe gear whine noises during acceleration in the EV drive mode. For the analysis of vibro-acoustic sources, a 5DOF lumped-parameter vibration model for the PGT dynamic system is established as well as sound pressures radiated from the transmission on a test bench are measured for data processing and recognition. By comparison between numerical and experimental analyses, natural vibration modes of the PGT are examined and high frequency modal resonances in association with the planetary gears are observed only to cause narrow band whine noises. Furthermore, a 2DOF reduced dynamic model for the planetary gears with consideration of nonlinearities such as time-varying mesh stiffness and backlash is proposed, and numerical solutions to bifurcations and dynamic instabilities of the two sets of planetary gears are obtained. It is found that nonlinear vibration behaviour of the long and short planets are major causes of shock and vibration of the hybrid transmission. Severe vibro-acoustic noises excited dominantly by the planetary gears are alleviated after implementing micro-geometry modifications to the PGT.