The combination of edge computing (EC) and the Internet of Things is a hot research topic. And security is one of the most important problems to be solved. The trust measurement of devices is an effective way to solve the security problem, and the lack of a unified trust measurement model makes the untrusted devices destroy the quality of service. Establishing a reliable trust relationship between devices can effectively improve the security of the system. A decentralized trust measurement model for devices is proposed. First, a decentralized trust measurement framework is proposed, which combines EC with blockchain technology to establish a decentralized hierarchical structure; second, the credibility of devices is measured from multilevel and multi-attribute; finally, a feedback trust filtering mechanism is designed to filter reliable feedback information, and then the trust between devices and the comprehensive trust of devices are calculated. Experiments and analysis show that the proposed decentralized trust measurement model can effectively measure the trust degree of devices and resist various malicious feedback attacks. K E Y W O R D Sblockchain, edge computing, Internet of Things, trust measurement INTRODUCTIONWith the development of Internet of Things (IoT) technology, IoT has been widely used in all walks of life, such as smart city, 1 smart home, 2 intelligent logistics, 3 environmental monitoring 4 and so on. At the same time, the requirements for IoT and its related infrastructure are also improved, including system security, ultra-low latency, low power consumption, and data reliability. 5 In addition, the combination of artificial intelligence [6][7][8] intelligent optimization algorithm 9-11 and other technologies with the IoT is more and more, which further increases the demand of terminal equipment for computing, storage and other performance. The traditional cloud computing paradigm 12,13 is far from the edge of the network and the resources are relatively concentrated. The existing cloud based IoT model is difficult to meet the above new application requirements. The scheduling mode 14,15 based on cloud computing is also difficult to be used for a large number of IoT devices. The development of mobile edge computing (MEC) technology provides a reliable solution for these application requirements. 16,17 MEC technology is to deploy the basic implementation of mobile cloud computing to the edge of the network, to process data at the edge of the network, reduce the response time of service requests, reduce the energy consumption of mobile devices, reduce the network bandwidth, and provide a new idea for data security and network security.At present, the edge computing enabled IoT is a research hotspot in the academic and industrial circles, which has attracted extensive attention from scholars.The devices of the IoT sensing layer are usually deployed in complex scenes, such as sensors and cameras for monitoring purposes. Limited by the ability of storage, computing, energy consumption and other a...

This paper aims to find out the most vulnerable position and the suitable clearance ratio of the floating sleeve between the inside and outside floating sleeve of the tricone bit. In this paper, the mechanical analysis model of the drill bit is established to get the simulated working condition of the tri-cone bit, and then the stress condition of the floating bearing is simulated. Finally, the multi-factor variable orthogonal test method is used to optimize the clearance ratio of the floating sleeve. The results show that the simulation results are consistent with the wear position of the floating sleeve: during the operation of the floating sleeve, the most vulnerable position is the edge position, the largest deformation is the opening position, the recommended internal clearance of the floating sleeve is 0.06–0.07 mm, the recommended external clearance is 0.02–0.04 mm, and the recommended internal clearance ratio is 2.0–2.4.