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Air handling units (AHUs) with long distance flexible film air ducts are commonly adopted in modern large-scale greenhouses for temperature controlling. To study the performance of this type of AHU, theoretical analysis and numerical simulation methods were used to discover its air supply characteristics, and a full-scale experiment was carried out to verify the correctness of the calculation model. The calculation showed that the static pressure of different cross-sections in the thin film air duct sharply decreased to 0 at the small-hole opening, where the airflow velocity increased significantly. However, this influence only exists locally and had little effect on the pressure and gas velocity fields inside the wind duct. The velocity and velocity distribution of the gas flowing out from different openings on the same section of the wind duct are basically the same. Taking the wind speed of 2.45 m/s at the inlet end of the wind duct as an example, the maximum velocity of the airflow at the opening position of the wind duct wall at 60.06 m is 5.64 m/s, located at the center of the opening and flowing outward perpendicular to the opening plane. The velocity distribution is that the center has the highest velocity, and the closer to the edge of the hole, the lower the velocity. The volum of the airflow flowing out through the openings on the wall of the wind duct along the length direction shows that the air supply remains basically constant under different inlet wind speed conditions, and the uniformity coefficient is greater than 0.92. This indicates that this type of AHU can evenly distribute airflow along the length direction, and can evenly distribute heat or cold in the large space of the greenhouse, thus providing a guarantee for maintaining a uniform temperature field in modern large greenhouses. [ABSTRACT FROM AUTHOR]

Taking No.12302 roadway of Wangjialing Mine as the research background, the advance support technology was researched by means of field investigation, theoretical analysis and engineering practice. The main problems that should be solved of the advance support are analyzed by field investigation, and the advance support ideas of long-distance support and non-repeted support was proposed. The distance from the peak of the advance concentrated stress to the working face was 8.22 m, and the length of the area affected by the advance mining was 37.09 m through theoretical analysis. Combined with the actual monitoring results of the previous site, the length of the advance support was determined to be no less than 40 m. Considering the support effect of the bolt (cable) support system, the advance support strength was determined to be no less than 267.38 kPa. This way, the long-distance advance support concepts of “pre-active support, one-time bearing, cooperative operatation, and overall support” was proposed, the type of ZLQ3200/18/37 advance support and transportation equipment was developed, the main technical parameters of the support device were introduced, and the long-distance advance support scheme was determined combined with the actual mining geological conditions. Practice shows that the application of long-distance and non-repeated advance support technology is effective, the entry surrounding rock has been well maintained, which can meet the requirements of safety advance support for mining entry.

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The traditional triangle elevation method for ranging is affected by the error by vertical refraction of the atmosphere, distance measuring error and the error in measurement of the heights of the instrument and the targets, as a result, it is difficult to control the measurement accuracy and the working efficiency is low. To overcome these, this paper proposes a triangular elevation leveling method based on high and low prism method, that is, two high -precision total stations with automatic alignment functions are used to perform multiple measurement returns opposite observation in multiple periods of time on the self-designed high and low prism set. It is found after the cross-river measurement of the main body of Yanji Changjiang River Bridge in Hubei Province that, the maximum error of the height difference between measurement returns was 10.00 mm, and the maximum error of loop closure was 1.30 mm, and after adjustment, the accidental error per kilometer is only ±0.71 mm, the mean square error of elevation at the weakest point is ±0.20 mm, and the mean square error of elevation in the weakest survey section is ±0.20 mm, which all meet the limit requirements of the second-class leveling measurement. It has been proved that this method can meet the second-class leveling requirements for long-distance cross-river leveling of less than3500 m, and improve the working efficiency by 50% compared with the traditional ranging triangle elevation method, worth wide promotion and application. [ABSTRACT FROM AUTHOR]

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Water Conservancy Science & Techonlogy & Economy is the property of Water Conservancy Science & Technology & Economy Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aiming at the problem of target track offset that easily occurs in multi-radar multi-target detection and tracking when the target distance is close, this paper proposes a new type of multi-radar multi-target particle filter tracking before detection algorithm(NM-PF-TBD). The algorithm uses a two-layer particle filter structure. When tracking a target in the target tracking layer, the sensor detection information is recalculated based on other target points in the previous cycle. Secondly, the particle weight is calculated based on the corrected sensor detection information, and then. Based on the distribution of particles with different weights in the particle swarm, it deletes harmful particles, supplements beneficial particles, and avoids the shift of the center of the tracking particle swarm after re-sampling, so as to ensure that the target point trace does not shift. Simulation results show that, compared with other algorithms, the algorithm proposed in this paper can accurately correlate target traces and improve target accuracy when observing multiple closer targets at a long distance.

In order to realize the power line extraction of long distance linear airborne light detection and ranging (LiDAR), a power line extraction method of long-distance airborne LiDAR based on cloth simulation was proposed. On the basis of data preprocessing, the function between cloth and corresponding airborne LiDAR point cloud was analyzed by simulating the falling process of cloth. The position where cloth stayed after gravity faUing was determined as the power line point cloud with similar height, and then the straight line was fitted in the xOy plane. The distances from points to the fitting line were used to judge the number of power lines whether odd or even. And the power line point clouds were divided by the judgment of points on both sides of the line to achieve the extraction of a single power line. The experimental results show that the accuracy of the proposed method is 98.9%, with high degree of automation and not sensitive to the lack of local point cloud, which has good engineering application value for intelligent poweriine inspection and automatic analysis of transmission channel spatial structure. [ABSTRACT FROM AUTHOR]

At present, the virtual navigation aids mainly refers to the AIS virtual navigation mark. Because the signal coverage of the AIS base station is limited, it is only suitable for inland rivers and offshore waters. In view of the problem that the AIS virtual navigation aids is not suitable for deep sea and ocean setting use, the concept of virtual navigation aids based on VDE)SAT was proposed. The VDE-SAT module in VDES can communication with satellites without the distance limit of information transmission. The VDE-SAT module was used to broadcast virtual navigation aids. At the same time, the message format for long-distance virtual navigation aids information was designed and verified whether it is reasonable, which provides a reference for the realization of the long-distance virtual navigation aids. [ABSTRACT FROM AUTHOR]

In ultrasonic measuring distance technology, traditional signal processing algorithms are difficult to analyze signals with long distances and weak echoes, and it is also impossible to measure the distance of multiple obstacles at the same time. In order to solve this problem, an ultrasonic measurement distance method based on random forest is proposed in this paper. Firstly the time domain characteristics of the signal—the relative peak amplitude and frequency domain characteristics—the relative area of the spectrum are extracted to judge the number of obstacles in the detection area by random forest method, and then calculates distance of obstacles. After the experiment, the algorithm can effectively measure the distance of multiple obstacles within 10 meters, and the measurement error is within 3 cm, which satisfies the practical application and has high practical value and theoretical reference significance.

In order to explore the impact of long-distance overlapping mining and coal pillar remaining on the roof collapse and floor pressure relief effect in No.8 mine of Pingdingshan Coal Company Limited, the similar simulation experiment of mining along coal seam dip was carried out. The experimental results show that with group Ding or group Wu coal seam mining, the stress increasing or releasing effect of the floor under the goaf or isolated island coal pillar weakens with the increase of the buried depth. The pressure relief angles of the upper and lower sides are respectively 65° and 75°. Coal pillar pressurization zone affects the group Ji coal seam. The pressure relief angles of group Ding and group Wu coal seams overlapping mining of the upper and lower sides are respectively 75° and 65°. The pressure relief area and pressure boosting area affects the group Wu coal seam with stress increment range limited. The dynamic pressurization value and pressure relief value of group Wu coal seam are higher than the additional stress after mining. Mining of group Ding coal seam has little effect on pressure relief protection, but the coal pillar causes additional stress in the coal seam. With group Ding and group Wu coal seams overlapping mining, the staggered arrangement of coal pillar and goaf is beneficial to the mining of group Ji coal seam. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the popularity of mobile terminals in recent years，people expect more convenient and more efficient wireless networks. Today s wireless networks are committed to providing characteristics such as efficiency, fairness and quality of service. However，in the long distance wireless network environment, these requirements are difficult to meet. We propose an uplink transmission scheme of the control terminal，which can perform long distance transmission and short distance transmission at the same time to improve the bandwidth utilization o£ the base station. Our proposal mainly solves the following problems ： (1) how to get the distance of the terminal ； (2) how to schedule the transmission of each terminal to improve the bandwidth utilization rate. [ABSTRACT FROM AUTHOR]

The paper gave mechanical structure model of belt conveyor with long distance in coal mine, and established resistance model of the belt conveyor with different angle in different sections. In view of actual condition of belt conveyor driven by double rollers with 1 200 m long of Huangling Jianzhuang Coal Mine, it calculated dynamic resistance of load-bearing section and return section with dip angle of 0, 3, 15°, redirection roller at the tail, driving roller at the head, and made fault simulation, so as to obtain law of resistance of the belt conveyor influence on displacement. It provides basis for fault prediction of belt conveyor with long distance.