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During the operation of non-clogging pumps, the flexible long fiber is prone to clogging and winding during the flow process, which can result in damage to the non-clogging pump, so a numerical simulation method of a solid–liquid two-phase flow in a non-clogging pump with a flexible long fiber is proposed in this paper. The unsteady numerical simulation of the two-phase flow of a single flexible fiber with different densities, lengths and diameters in a double-blade non-clogging pump was carried out to study the influence of fiber parameters on fiber transport capability. The results show that at a density of 920 kg/m3, 300 kg/m3 and 732 kg/m3, the transport capability of flexible fibers decreases successively, and the transport time T0 is 0.32 s, 0.36 s and 0.48 s, respectively. The transport capability of flexible fibers with a length of 150 mm, 200 mm and 250 mm decreases successively, and the transport time T0 is 0.34 s, 0.48 s and 0.96 s, respectively. The transport time T0 is 0.48 s when the fiber diameter dp is 5 mm. When the fiber diameter dp is 7.5 mm, the transport time T0 is 0.51 s. When the fiber diameter dp is 10 mm, the fiber transport capability of the non-clogging pump decreased significantly, and the transport time T0 is 0.68 s. The fiber length has the most obvious effect on fiber transport capability, followed by the fiber diameter and fiber density. [ABSTRACT FROM AUTHOR]

It is still a great challenge to prepare high‐performance graphene/polymer nanocomposites by fully utilizing the large surface area, high tensile strength, and high thermal stability. Herein, a simple but efficient approach based on ball milling was developed to in situ exfoliate graphite into single‐layer graphene and simultaneously deposit them onto polyvinyl chloride (PVC) surface. Graphene/PVC nanocomposites were prepared via the plasticized molding and followed by hot pressing. Resulting from incorporation of highly exfoliated and evenly distributed graphene nanosheets, the obtained graphene/PVC nanocomposites displayed a significantly enhanced thermal stability. In contrast with neat PVC, the temperature of maximum weight loss (Tmax), glass transition temperature (Tg), and residual content of composite with 2.0 wt% graphene were increased by 10, 13°C, and 4.4%, respectively. Based on the deep analysis on heat releasing behavior and structure of residue, we proposed the related enhancing mechanism. Large‐area and highly exfoliated graphene sheets effectively inhibited the heat/mass transfer in composite system and prevented the degradation of PVC, as well as promoted the compact residue formation from polymer itself at high temperatures. In short, this work provided an environmentally friendly strategy to prepare high‐performance graphene/polymer nanocomposites with using low additive amount of single‐layer graphene. Highlights: A simple graphite exfoliation method based on ball milling was proposed.Strong shearing and compact force induce graphene exfoliation and deposition.Graphene/PVC nanocomposites with enhanced thermal stability was prepared. [ABSTRACT FROM AUTHOR]

Non-side-looking airborne radar provides important applications on account of its all-round multi-angle airspace coverage. However, it suffers clutter range dependence that makes the samples fail to satisfy the condition of being independent and identically distributed (IID), and it severely degrades traditional approaches to clutter suppression and target detection. In this paper, a novel reweighted extreme learning machine (ELM)-based clutter suppression and range compensation algorithm is proposed for non-side-looking airborne radar. The proposed method involves first designing the pre-processing stage, the special reweighted complex-valued activation function containing an unknown range compensation matrix, and two new objective outputs for constructing an initial reweighted ELM-based network with its training. Then, two other objective outputs, a new loss function, and a reverse feedback framework driven by the specifically designed objectives are proposed for the unknown range compensation matrix. Finally, aiming to estimate and reconstruct the unknown compensation matrix, special processes of the complex-valued structures and the theoretical derivations are designed and analyzed in detail. Consequently, with the updated and compensated samples, further processing including space–time adaptive processing (STAP) can be performed for clutter suppression and target detection. Compared with the classic relevant methods, the proposed algorithm achieves significantly superior performance with reasonable computation time. It provides an obviously higher detection probability and better improvement factor (IF). The simulation results verify that the proposed algorithm is effective and has many advantages. [ABSTRACT FROM AUTHOR]

The ground clutter of sidelooking Multiple-Input Multiple-Output (MIMO) bistatic radar has severe problems of range-dependence and clutter spectrum spreading. In this paper, the clutter characteristics of bistatic airborne radars are analyzed and a method of range-ambiguous clutter suppression is proposed. This method employs the range-dependent phase term in the traditional MIMO bistatic radar to provide extra degrees of freedom. The range information of the phase term enables clutter separation with different ranges and consequent suppression. Thus, a range-ambiguous clutter suppression for bistatic airborne early warning radars is achieved. The simulation results show the accuracy of the method. By a comparison with the existing Doppler Warping (DW) and clutter suppression method with the Improved Factor (IF) line, the results showed that the method has better performance, which proved the effectiveness of ambiguous clutter suppression in MIMO bistatic radars.

The carrier frequencies of array elements in a Frequency Diverse Array (FDA) radar are slightly distinguished, leading to a range-angle-time-dependent transmit beampattern. Thus, an FDA radar carries additional information in a certain range and provides more flexibility in signal processing and new technical issues. FDA is covered by scope of the general waveform diversity concept. This paper overviews the state-ofthe-art FDA technology and its radar applications. From the viewpoint of the general radar system theory, we mainly introduce the coherent FDA and orthogonal FDA frameworks. The orthogonal FDA is also referred to as Multiple-Input Multiple-Output (MIMO) radar using FDA or FDA-MIMO radar. Key applications in antijamming and issues related with range ambiguity are addressed. We also outline the challenges in FDA radar applications and several interesting research topics.