Dynamics similarity design and verification of rotor system

In order to study the dynamics similarity of original model similar to normal model, the similarity criteria and the similarity ratio of the normal and original models for the rotor system were derived by the dimension analysis method. ANSYS was used to numerically calculate the critical speeds, modal shapes and harmonic response of the original and normal models of rotor system. The analysis results show that, for the rotor system, the dynamic characteristics of the normal and original models satisfy the requirement of the similarity criteria perfectly. The dynamic characteristics of the original model can be predicted accurately by the corresponding normal model

Effect of Aspect Ratio on Field Emission Properties of ZnO Nanorod Arrays

ZnO nanorod arrays are prepared on a silicon wafer through a multi-step hydrothermal process. The aspect ratios and densities of the ZnO nanorod arrays are controlled by adjusting the reaction times and concentrations of solution. The investigation of field emission properties of ZnO nanorod arrays revealed a strong dependency on the aspect ratio and their density. The aspect ratio and spacing of ZnO nanorod arrays are 39 and 167 nm (sample C), respectively, to exhibit the best field emission properties. The turn-on field and threshold field of the nanorod arrays are 3.83 V/μm and 5.65 V/μm, respectively. Importantly, the sample C shows a highest enhancement of factorβ, which is 2612. The result shows that an optimum density and aspect ratio of ZnO nanorod arrays have high efficiency of field emission

Integration of Communication and Navigation Technologies toward LEO-Enabled 6G Networks: A Survey

As the number of wireless applications and devices grows, higher standards for the quality of service and navigation performance of mobile networks are required. Numerous critical applications, including unmanned aerial vehicles, internet of things, digital twin, and military systems, require reliable communication and accurate navigation services. To meet these requirements, the development of the sixth generation (6G) network is necessary. 6G networks provide seamless 3-dimensional coverage in space–air–ground–sea area, as well as deep coupling of communication, sensing, and computation. 6G networks will be combined with low Earth orbit (LEO) satellites to construct a universal and intelligent integrated system of communication, sensing, and computing by utilizing the benefits of LEO satellites, such as miniaturization, modularity, large bandwidth, low latency, and wide area coverage. One of the critical construction tasks in this system is the integration of communication and navigation (ICAN), which can break the limitations of the global navigation satellite system, provide high-precision, robust navigation capability, and enable high-quality communication services. In this article, a comprehensive survey is presented for ICAN technologies toward LEO-enabled 6G networks (LEO-ICAN), including the framework design, system implementation, and key technologies. We also highlight the challenges and opportunities ahead faced by the LEO-ICAN system. Finally, the prospect development and future research trends are discussed, and a few ideas for practical and effective LEO-ICAN solutions are provided. This survey provides a reference for the theoretical design, technological innovation, and system implementation of LEO-ICAN, which is capable of coping with the demand of massive access and global seamless coverage in the upcoming 6G network era

Measures for controlling large deformations of underground caverns under high in-situ stress condition – A case study of Jinping I hydropower station

The Jinping I hydropower station is a huge water conservancy project consisting of the highest concrete arch dam to date in the world and a highly complex and large underground powerhouse cavern. It is located on the right bank with extremely high in-situ stress and a few discontinuities observed in surrounding rock masses. The problems of rock mass deformation and failure result in considerable challenges related to project design and construction and have raised a wide range of concerns in the fields of rock mechanics and engineering. During the excavation of underground caverns, high in-situ stress and relatively low rock mass strength in combination with large excavation dimensions lead to large deformation of the surrounding rock mass and support. Existing experiences in excavation and support cannot deal with the large deformation of rock mass effectively, and further studies are needed. In this paper, the geological conditions, layout of caverns, and design of excavation and support are first introduced, and then detailed analyses of deformation and failure characteristics of rocks are presented. Based on this, the mechanisms of deformation and failure are discussed, and the support adjustments for controlling rock large deformation and subsequent excavation procedures are proposed. Finally, the effectiveness of support and excavation adjustments to maintain the stability of the rock mass is verified. The measures for controlling the large deformation of surrounding rocks enrich the practical experiences related to the design and construction of large underground openings, and the construction of caverns in the Jinping I hydropower station provides a good case study of large-scale excavation in highly stressed ground with complex geological structures, as well as a reference case for research on rock mechanics

Study on the Vibration Mitigation Characteristic of Dual Clearance Squeeze Film Damper

In this paper, a novel model of dual clearance squeeze film damper (DCSFD) was constructed considering convection effect and the vibration mitigation characteristic of DCSFD was researched. The DCSFD film force linearity rFSFD was proposed. The response characteristics of rigid rotor containing DCSFD were studied based on the DCSFD model. A response experiment of the DCSFD was arranged, and the model was verified. A good consistence was achieved between the simulation and experiment. The experiment and simulation result manifests that the unbalance response of DCSFD was smaller than that of SFD at every excitation frequency. The DCSFD could inhibit the nonlinear vibration such as the bistability and bifurcation due to big mass eccentricity, and nonlinear film force for the DCSFD film force linearity was bigger than that for SFD. The thickness ratio of inner and outer film, pressure loss coefficient, and inner film thickness were the important parameters that have great influence on DCSFD vibration mitigation characteristic