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The stress state of joints is the key to the mechanical performance of the space structure. In this paper the constant amplitude fatigue performance of the pin in space structure was investigated. The fatigue numerical simulation of 32 theoretical models with 5 factors was carried out on the basis of similar numerical models and nCode Designlife analysis software. The S-N curve was obtained and the fatigue life calculation formula was established. The analysis results indicate that: Under the symmetrical cyclic loading (R=-1), the hot spot stress of the pin locates at the contact surface of the pin with the interface of the outer and inter ear plates, and the nominal allowable stress amplitude corresponding to 2×106 cycles is 94.42 MPa. The constant amplitude fatigue performance of the pin is negatively correlated with the three parameters, the pin hole clearance, the thickness of the ear plate, and the distance between the ear plates, while positively correlated with the pin diameter and the yield strength of the pin material. The ranking of the sensitivity of the factors affecting the constant amplitude fatigue performance of the pin is: the material of pin→the clearance of pin hole→the space between ear plates→the diameter of pin→the thickness of ear plate.

The ubiquitous power Internet of things encourages a large number of new power equipment, such as distributed power supply, energy storage and electric vehicles, to connect to the distribution network.With the increasing penetration of renewable energy in the distribution network and the gradual opening of the electricity market, the investment entities of the power grid tend to be diversified.The uncertainty of the access of renewable energy to the power grid and the coordination of the interests of various entities resources is increasingly prominent.Considering the profits of distributed energy resources (DER) investors in the regional distribution network, an optimal operation strategy based on the incentive mechanism in ubiquitous power Internet of things was proposed.This strategy could reduce the adverse effects of load fluctuations and reversed power flow on the power grid, while increasing profits for DER investors.The calculation example shows the effectiveness of the proposed method.

Large quantity of observational data from ground and sounding meteorological observation data, ocean station observation data, ERA reanalysis data are used to count the sea fog process that occurred during April to July in Rizhao City from 1988 to 2019 altogether 32 years in this paper. The synoptic characteristics of the sea fog and their formation mechanism are statistically analyzed, and furthermore the main meteorological elements affecting the formation of sea fog in Rizhao area and their combined effects are put forward. The results indicate that sea fog occur in Rizhao area is most likely under the control of several weather conditions, such as the west of transition high to sea, the Pacific subtropical high ridge or the front of low or trough of the eastern China in spring and summer. Under the control of these synoptic characteristics, the direction and speed of wind, dew-point temperature, atmospheric temperature, SST, stratification stability of these hydrometeorological elements play an important role in the formation of sea fog. On these basis, the method of discriminance analysis is used to establish of discriminant equation for sea fog forecast. Through the forecast testing, the statistical forecasting method of sea fog has a great application, the forecast accuracy is between 88% and 94%. It can be used for short-term forecast of sea fog characteristics in Rizhao City, providing services for industry, agriculture, fishery production, sea and land transportation.

An in-situ measurement device combining contact probe and capacitive displacement sensor is developed. An aspherical measurement and compensation machining software is also developed. The single point diamond ultra precision cutting experiments for C3604 brass spherical and aspherical surface are carried out. The in-situ measurement and compensation machining experiments are also carried out. After compensation machining, the spherical surface form accuracy PV reaches 231.4 nm, and the aspheric surface form accuracy PV reaches 206.3 nm. Compared with the off-line measurement results, the difference between the results is 3.0 nm, 7.0 nm respectively, the measuring accuracy of the in-situ measurement system and the validity of compensation machining are verified.

A visualization experimental method of foam flooding was developed by combining nuclear magnetic resonance (NMR) and traditional core flooding method. On this basis, a new method to evaluate the dynamic stability of foam in the core during displacement process was established. Using this method, the displacement characteristics and dynamic stability of foam of S-2 (the main component is sodium lauryl sulfate) and S-NP-2 (the main components are sodium lauryl sulfate and silica nanoparticles) in two different displacement modes, i.e. direct foam flooding and foam flooding after water flooding, were studied. The results show that the NMR images and the T2 (transverse relaxation time) spectrum reflected the displacement characteristics. The flooding efficiency of S-2 and S-NP-2 after water flooding was increased by 18.05% and 25.68% and reached 63.72% and 67.50% respectively at last, higher than direct foam flooding. The same foam system had better stability in foam flooding after water flooding than in direct foam flooding, and foam S-NP-2 is more stable than foam S-2 under the same displacement mode. Key words: foam flooding, flooding experiment, flooding efficiency, nuclear magnetic resonance (NMR), foam stability, evaluation method

The distribution and migration characteristics of weak gel in the core were observed by combining nuclear magnetic resonance (NMR) imaging technology with the core displacement experiment, and the oil displacement features of different polymer-weak gel combinations were examined with visualization experiments. Three combination patterns of polymer and weak gel were designed: waterflooding + polymer flooding (pattern 1), waterflooding + polymer flooding + weak gel flooding (pattern 2), and waterflooding + weak gel flooding + polymer flooding (pattern 3). The pressure variations, T2 spectra, nuclear magnetic resonance images, oil displacement efficiencies under the different patterns were analyzed. The results show that the nuclear magnetic images can not only provide the direct information of weak gel distribution and migration characteristics inside the core, but also reflect the distribution characteristics of remaining oil; the T2 spectrum characteristics indicate that both polymer and weak gel have the function of profile control and oil displacement, and the pattern 2 has the best profile control effect; of the three patterns, pattern 2 has the highest oil displacement efficiency of 78.84%, which is 18.33% higher than the displacement efficiency of water flooding in the initial stage. Key words: weak gel, polymer, nuclear magnetic resonance (NMR), visualization displacement experiment, oil displacement efficiency

A digital watermark method based on the bar-block-margin characteristics of PDF417 two-dimension code was presented.The proposed method prejudges the watermark information to choose the suitable embedding positions.According to the watermark,the information of the original PDF417 image was modified for embedding and extracting.The experimental results showed that,in comparison with the other methods in the spatial domain,the proposed method has a higher capacity and better watermarked image quality,as well as better robustness against JPEG compression,Gaussian noise and printing and scanning.

Aiming at the problem of spontaneous combustion prevention in the process of mining close distance coal seams in southern Sichuan Mining Area, this paper takes the first mining face of No. 8 coal seam in Xinwei Mine as an example, and analyzes spontaneous combustion risk factors during the recovery of 8102 working face. It is concluded that high residual coal and goaf residual coal are high risk areas of spontaneous combustion. The comprehensive fire prevention technical measures with spontaneous combustion prediction and forecasting as the lead, the plugging and controlling wind, the open area nitrogen injection and the high position grouting as the core are proposed, which fundamentally reduces the natural fire probability of the coal seam. During the recovery process, the CO concentration in the working face and the goaf is always kept below 20 ppm, which ensures the safe recovery of the working face.

In order to study damage deformation of low permeability and soft coal under pulsating water pressure, the experiment of different maximal pulsating water pressure acting on standard raw coal was done by using the RLW-2000M coal rheometer controlled by microcomputer. The results show that the strain curve can be characterized by three phases when the samples are damaged by pulsating pore-pressure. In the initial stage, that is compaction coupling phase, the strain curve will generate large deformation in the process of loading and unloading, so the hysteresis loop curve will not be formed. In the elastic coupling phase, the strain curve demonstrats a stable hysteresis loop curve. In the yield deformation phase, coal will generate fatigue failure after several large deformation. The deformation state of elastic coupling phase was determined by using energy dissipation, and the results show that the coal unit produces plastic deformation and damage after a cycle of pulsating water pressure. At last, on the basis of Logistic equation, the mathematical model of coal damage was established and the unknown parameters were calculated by fitting analysis. [ABSTRACT FROM AUTHOR]