Concurrent multi-scale design optimization of composite frame structures using the Heaviside penalization of discrete material model

This paper deals with the concurrent multi-scale optimization design of frame structure composed of glass or carbon fiber reinforced polymer laminates. In the composite frame structure, the fiber winding angle at the micro-material scale and the geometrical parameter of components of the frame in the macro-structural scale are introduced as the independent variables on the two geometrical scales. Considering manufacturing requirements, discrete fiber winding angles are specified for the micro design variable. The improved Heaviside penalization discrete material optimization interpolation scheme has been applied to achieve the discrete optimization design of the fiber winding angle. An optimization model based on the minimum structural compliance and the specified fiber material volume constraint has been established. The sensitivity information about the two geometrical scales design variables are also deduced considering the characteristics of discrete fiber winding angles. The optimization results of the fiber winding angle or the macro structural topology on the two single geometrical scales, together with the concurrent two-scale optimization, is separately studied and compared in the paper. Numerical examples in the paper show that the concurrent multi-scale optimization can further explore the coupling effect between the macro-structure and micro-material of the composite to achieve an ultralight design of the composite frame structure. The novel two geometrical scales optimization model provides a new opportunity for the design of composite structure in aerospace and other industries.

Realization of an Optimal Dynamic Geodetic Reference Frame in China:Methodology and Applications

China Geodetic Coordinate System 2000(CGCS2000)has been used for several years as a formal published reference frame.The coordinates of all global navigation satellite system(GNSS)stations in China need to be corrected to align with the CGCS2000 frame.Different strategies can be adopted for the realization of an optimal reference frame.However,different strategies lead to different results,with differences as great as several decimeters when GNSS station coordinates are transformed into CGCS2000-defined coordinates.The two common methods for the coordinate correction of a GNSS station are quasi-stable adjustment under CGCS2000 and plate movement correction,and the differences between their results can be greater than 10 cm.In this study,a statistic method called"supervised clustering"is applied to the selection of GNSS reference stations;a new scheme named"partition spacing"for the grouping of all processed GNSS stations is proposed;and the plate movement correction method is used to correct the coordinates of all GNSS stations from the GNSS epoch to the CGCS2000 epoch.The results from the new partitioning method were found to be significantly better than those from the conventional station-blocking approach.When coordinates from the stations without grouping were used as the standard,the accuracy of all the three-dimensional coordinate components from the new partitioning method was better than 2 mm.The root mean squares(RMSs)of the velocities in the x,y,and z directions resulting from the supervised clustering method were 0.19,0.45,and 0.32 mm∙a1,respectively,which were much smaller than the values of 0.92,0.72,and 0.97 mm∙a1 that resulted from the conventional approach.In addition,singular spectrum analysis(SSA)was used to model and predict the position nonlinear movements.The modeling accuracies of SSA were better than 3,2,and 5 mm in the east(E),north(N),and up(U)directions,respectively;and its prediction accuracies were better than 5 mm and 1 cm for the horizontal and vertical domains,respectively.

Update China geodetic coordinate frame considering plate motion

China Geodetic Coordinate System 2000(CGCS2000),as the formal national coordinate reference frame,has been used for 20 years.The coordinates of all Global Navigation Satellite System(GNSS)stations in China need referring to this system.To this end,the first step is to align the coordinates of all stations,usually included in a regional GNSS network,with a given International Terrestrial Reference Frame(ITRF),then these coordinates are corrected to the CGCS2000 in consideration of plate movement.For a better alignment result,regional control stations are needed and their coordinates were estimated from the combination of constraint-free normal equation systems provided by several International GNSS Service(IGS)analysis centers.The effect in using these refined coordinates,which deter-mine a regional coordinate datum,on the alignment result should be evaluated by the coordinate corrections of the regional control stations to the regional coordinate datum,i.e.smaller corrections mean better alignments of the two associated frames.The test results show that the refined coordinates are more accurate than the ones calculated from the station’s velocity,and are well aligned with the ITRF2005.Moreover,for obtaining the coordinates of GNSS stations in an updated CGCS2000 frame,a gridded linear velocity field based on the estimated velocities at 1025 CGCS2000 stations was generated for China's Mainland using the optimal interpolation method,the inverse distance weighting,which is selected from five interpolation methods.The overall precisions of the constructed velocity field at all stations in the East(E)and,North(N)directions are 0.78 mm/a and 0.95 mm/a,respectively.For evaluating the accuracy of the updated CGCS2000 frame,monthly solutions for the coordinates of some CGCS2000 CORS stations in the ITRF2014 during the period from 2000.0 to 2018 were obtained and the Root Mean Square(RMS)of the differences between the coordinates corrected to the CGCS2000 and the known coordinates at these stations are about 2-3 cm.

Optimal Data Transmission in Backscatter Communication for Passive Sensing Systems

Computational Radio Frequency IDentification (CRFID) is a device that integrates passive sensing and computing applications,which is powered by electromagnetic waves and read by the off-the-shelf Ultra High Frequency Radio Frequency IDentification (UHF RFID) readers.Traditional RFID only identifies the ID of the tag,and CRFID is different from traditional RFID.CRFID needs to transmit a large amount of sensing and computing data in the mobile sensing scene.However,the current Electronic Product Code,Class-1 Generation-2 (EPC C1G2)protocol mainly aims at the transmission of multi-tag and minor data.When a large amount of data need to be fed back,a more reliable communication mechanism must be used to ensure the efficiency of data exchange.The main strategy of this paper is to adjust the data frame length of the CRFID response dynamically to improve the efficiency and reliability of CRFID backscattering communication according to energy acquisition and channel complexity.This is done by constructing a dynamic data frame length model and optimizing the command set of the interface protocol.Then,according to the actual situation of the uplink,a dynamic data validation method is designed,which reduces the data transmission delay and the probability of retransmitting,and improves the throughput.The simulation results show that the proposed scheme is superior to the existing methods.Under different energy harvesting and channel conditions,the dynamic data frame length and verification method can approach the theoretical optimum.