Automatic and high quality hexahedral meshing of complex solid models is still a challenging task. To guarantee the quality of the generated mesh, current commercial software normally requires users to manually decompose a complex solid model into a set of simple geometry like swept volume whose high quality hexahedral mesh can be easily generated. The manual decomposition is a time-consuming process, and its effect heavily depends on the user's experience. Therefore, to automate the solid model decomposition for hexahedral meshing is of significance. However, the efficiency of the existing algorithms are still far from expected. In this paper, an automatic swept volume decomposition approach based on sweep directions extraction is presented. The approach first extracts all the potential local sweep directions (PLSDs) of a given solid model using heuristic rules, then generates a relevant face set (RFS) for each PLSD, and incrementally determines all the swept volumes including heavily interacting ones based on PLSDs. Furthermore, to make the decomposition good for high quality hexahedral meshing, the approach constructs reasonable cutting face sets (CFSs) to split the interacting swept volumes. Experimental results show the effectiveness of our approach.
Compared with the traditional multiple-input multiple-output (MIMO) systems, the large number of the transmit antennas of massive MIMO makes it more dependent on the limited feedback in practical systems. In this paper, we study the problem of precoding design for a massive MIMO system with limited feedback via minimizing mean square error (MSE). The feedback from mobile users to the base station (BS) is firstly considered; the BS can obtain the quantized information regarding the direction of the channels. Then, the precoding is designed by considering the effect of both noise term and quantization error under transmit power constraint. Simulation results show that the proposed scheme is robust to the channel uncertainties caused by quantization errors.
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