As a novel structural damper, the unique structural characteristics of the integral squeeze film damper (ISFD) solve the nonlinear problem of the traditional squeeze film damper (SFD), and it has good linear damping characteristics. In this research, the experimental studies of ISFD vibration reduction performance are carried out for various working conditions of unbalanced rotors. Two ball bearing-rotor system test rigs are built based on ISFD: a rigid rotor test rig and a flexible rotor test rig. When the rotational speed of rigid rotor is 1500 rpm, ISFD can reduce the amplitude of the rotor by 41.79%. Under different unbalance conditions, ISFD can effectively improve the different degrees of unbalanced faults in the rotor system, reduce the amplitude by 43.21%, and reduce the sensitivity of the rotor to unbalance. Under different rotational speed conditions, ISFD can effectively suppress the unbalanced vibration of rigid rotor, and the amplitude can be reduced by 53.51%. In the experiment of the unbalanced response of the flexible rotor, it is found that ISFD can improve the damping of the rotor system, effectively suppress the resonance of the rotor at the critical speed, and the amplitude at the first-order critical speed can be reduced by 31.72%.
Abstract. Casing treatments are required for expanding the stall margin of multi-stage high-load turbofans designed with high blade-tip Mach numbers and high leakage flow. In the case of a low mass flow, the casing treatment effectively reduces the blockages caused by the leakage flow and enlarges the stall margin. However, in the case of a high mass flow, the casing treatment affects the overall flow capacity of the fan, the thrust when operating at the high speeds usually required by design-point specifications. Herein, we study a two-stage high-load fan with three-dimensional numerical simulations. We use the simulation results to propose a scheme that enlarges the stall margin of multistage high-load fans without sacrificing the flow capacity when operating with a large mass flow. Furthermore, a circumferential groove casing treatment is used and adjustments are made to the upstream stator angle to match the casing treatment. The stall margin is thus increased to 16.3%, with no reduction in the maximum mass flow rate or the design thrust performance.
The rock breaking efficiency of drill bit is deeply affected with the increase of drilling depth. The increase length of the drill string leads to torsional stiffness decrease, which may even result in the stick-slip phenomena. In order to improve the rock breaking efficiency and reduce the stick-slip, this paper proposed a longitudinal–torsional coupled impactor. The internal working mechanism was carried out by theoretical analysis and experimental test. Moreover, comparing the computation and test results, the following conclusions can be obtained and verified. This innovative design can provide appropriate longitudinal-torsional coupled impact to drill bit during drilling process, and the movement of the hammer and pendulum is periodic. With the increasing flow rate of drilling fluid, this tool can generate corresponding larger impact force, torque and higher impact frequency. The theoretical analysis results are consistent with the experimental test results, which verify the reliability of the innovative design and the accuracy of theoretical analysis. This paper can provide reference for the innovative design of downhole drilling tool, the development of drilling dynamics and the improvement of drilling efficiency especially in the conditions of complex and ultra-deep wells.
With the fast growth of renewable energy generation, the power system faces the challenge of low inertia. Lower system inertia makes it more challenging to keep the frequency stable, and the conventional frequency response mechanism is not capable of ensuring frequency within the limit. In this paper, a new frequency response mechanism is proposed to help to improve the frequency performance, where electric vehicles (EV) are used as energy storage, and they will cooperate with existing primary frequency response (PFR) to form an EV+X storage supporting power system frequency. This approach is proposed based on rigorous mathematical derivation, where the relationship between frequency and active power is quantitively analysed. To validate the new mechanism’s feasibility, simulation models are built to simulate the frequency behaviour after a big disturbance, and a series of tests are conducted. Both technical and economic benefits are investigated, considering the difference in EV control strategies and the proportion of EV responses. The result shows that EV+X storage can be a promising solution to the frequency stability problem.
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