Three dimensional shape measurement in the microscopic range becomes increasingly important with the development of micro manufacturing technology. Microscopic fringe projection techniques offer a fast, robust, and full-field measurement for field sizes from approximately 1 mm2 to several cm2. However, the depth of field is very small due to the imaging of non-telecentric microscope, which is often not sufficient to measure the complete depth of a 3D-object. And the calibration of phase-to-depth conversion is complicated which need a precision translation stage and a reference plane. In this paper, we propose a novel telecentric phase-shifting projected fringe profilometry for small and thick objects. Telecentric imaging extends the depth of field approximately to millimeter order, which is much larger than that of microscopy. To avoid the complicated phase-to-depth conversion in microscopic fringe projection, we develop a new system calibration method of camera and projector based on telecentric imaging model. Based on these, a 3D reconstruction of telecentric imaging is presented with stereovision aided by fringe phase maps. Experiments demonstrated the feasibility and high measurement accuracy of the proposed system for thick object.
Taking the exact demands of chemical additive components added in oil products into account, it is necessary to prepare a drag reducer both with desirable functions and pure composition for oil products differing from that for crude oil. However, that is evidently difficult. This article presents the research and application of a newly-developed drag reducer for oil products, which is innocuous to oil products and easy to handle in its applications. The preparation of the drag reducer was based upon a series of integrative techniques involving adsorbent purification of monomers, implementation of bulk polymerization at low temperatures and ultramicro grinding of polyalphaolefins at normal temperatures. Simultaneously, the drag reducer can be manufactured in different scales by purpose-made equipment system with a little manual operation on safe, reliable, efficient and convenient base. The application test of the drag reducer was conducted successfully and has been commercially applied in Lanzhou-Chengdu-Chongqing Oil Products Pipeline. The application results for the pipeline showed that this drag reducer, as a feasible and available technical method, was not only positively helpful to increase the flow rate of Lanzhou-Chengdu-Chongqing Oil Products Pipeline, but also of great significance for other oil products pipelines in throughput increase and energy saving.
With high-precision DEM (Digital Elevation Model) and GMTI (Ground Moving Target Indicator) as the demand background, the influence of J 2 zonal harmonic term perturbation on the relative motion of the millimeter-level short-range leader-follower satellites in near-circular orbit is studied through the relative perturbation method. An equation of motion that can describe the motion of the leader-follower satellites under the influence of J 2 perturbation in near-circular orbit is derived, and the characteristics of the trajectory of in-plane periodic motion are analyzed. A study shows that under the influence of the relative perturbation of the J 2 term, the in-plane periodic motion of the leader-follower satellites in near-circular orbit is a symmetrical closed “drop-shaped” trajectory with a period of 2 π / n . By comparing with the results of numerical simulations, the correctness of the conclusions obtained in this paper is verified. According to the research results, it can be known that only using a thruster as the actuator to maintain the relative position can no longer meet the requirements of the long-term mm-level relative position maintenance. In the future, a new technical approach needs to be explored to achieve the long-term relative position maintenance with millimeter-level control accuracy.
The influence of the natural perturbation force will cause the eccentricity of the GEO satellite to produce a periodic motion with a period of years, and then cause the east–west station of the GEO satellite to oscillate. From the perspective of the best fuel-saving or the failure of the thruster used for station keeping, some scholars have proposed a method of slightly deflecting the thrust used for north–south station keeping (NSSK) to the east or west to achieve the integrated keeping of inclination and longitude. The disadvantage of this strategy is that the eccentricity cannot be maintained, and even causes the continuous divergence of the eccentricity. Based on the above problems, this paper proposes a low fuel consumption keeping method for eccentricity under the integrated maintenance of inclination and longitude. Assuming that the satellite is only equipped with a south (north) direction thruster for station keeping, on the premise of not affecting the satellite’s Earth observation, the satellite’s forward flight and backward flight are switched every year at the spring equinox and autumn equinox, which can prevent the eccentricity divergence when performing mean longitude keeping. When the accuracy of the east–west station keeping is not pursued, this method can not only effectively save the fuel consumption of the station keeping, but also greatly reduce the number of eccentricity maintenance interventions and the interference to the whole satellite due to the eccentricity keeping, which has a certain engineering application value.
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