High viscosity linear polysiloxane magnetorheological fluid (HVLP MRF) was demonstrated with excellent suspension stability. Such material is suitable for application in the magnetorheological energy absorbers (MREAs) under axial impact loading conditions. On this basis, a new energy absorber incorporating a radial valve with high magnetic field utilization and a corrugated tube is proposed. In energy absorption applications where the MREA is rarely if ever used, our MREA takes the ultra-stable HVLP MRF as controlled medium in order for a long-term stability. For MREA performing at very high shear rates where the minor losses are important contributing factors to damping, a nonlinear analytical model, based on the Herschel-Bulkley flow model (HB model), is developed taking into account the effects of minor losses (called HBM model). The HB model parameters are determined by rheological experiments with a commercial shear rheometer. Then, continuity equation and governing differential equation of the HVLP MRF in radial flow are established. Based on the HB model, the expressions of radial velocity distribution are deduced. The influences of minor losses on pressure drop are analyzed with mean fluid velocities. Further, mechanical behavior of the corrugated tube is investigated via drop test. In order to verify the theoretical methodology, a MREA is fabricated and tested using a high-speed drop tower facility with a 600 kg mass at different drop heights and in various magnetic fields. The experiment results show that the HBM model is capable of well predicting the impact behavior of the proposed MREA.

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The quasi-static model, without considering the inertia effect, is usually used to design and evaluate magnetorheological energy absorbers (MREAs). Although the quasi-static model is generally acceptable to describe the behavior of MREA operated at low velocity and low frequency, it is not sufficient to predict that under high-speed impact conditions. For this situation, we develop an analytical model inclusive of fluid Inertia as well as Minor losses based on the Bingham-plastic model (called BPIM model). In particular, instead of using area-averaged acceleration (assuming fluid acceleration uniformly distributes over the flow cross-sectional area), we directly take the non-averaged acceleration to analyze fluid inertia. Then, the governing equation is obtained from Navier–Stokes equations and continuity equation, in which the time-related term representing inertia effect is no longer neglected. In addition, the expression of damping force is derived by solving the initial-value problems obtained from the governing equation, boundary conditions and initial conditions using the method of separation of variables. Further, the influence of inertia effect and minor losses on MREA force is quantitatively analyzed. Besides, the MREA coupled with disc springs as the storage element is presented, and the nonlinear model of disc spring is employed. To validate the theoretical model, two identical MREAs are fabricated, and a high-speed drop tower is set up to test the two MREAs placed in parallel. It is shown that the BPIM model is capable of well predicting the dynamic behavior of the MREA.

Object detection is a challenging task in the field of remote sensing applications due to the complex backgrounds and uncertain orientation of targets. Compared with the horizontal bounding box, the oriented bounding box can provide orientation information while retaining the true size. Most existing oriented object detection methods are based on Faster-RCNN and the other one-stage methods that can achieve real-time speed but have shortcomings in localization and detection accuracy. To further enhance the performance of one-stage methods, we propose an oriented object detection framework that is based on the single shot detector, namely, single shot anchor refinement network (S 2 ARN). The S 2 ARN obtains the accurate detection results by performing two consecutive regressions. More precisely, the multilevel features of the backbone are used to regress the coordinate offsets between the predefined rotated anchors and the ground-truth boxes to generate the refined anchors. The classification and regression subnetworks assigned to the output features are used to perform the second regression to determine the class labels and further adjust the location of the refined anchors. In addition, receptive field amplification modules (RFAMs) are inserted to enlarge the receptive field and extract more discriminative features. Furthermore, in the anchor matching step, angle-related Intersection over Union (ArIoU) is used to calculate the Intersection over Union (IoU) score instead of the traditional method. Benefiting from the multiple regressions and the insensitivity of the ArIoU score to the angle deviation, the angle sampling interval of the rotated anchor can be reduced. The experimental results for the two public datasets, HRSC2016 and UCAS-AOD, demonstrate the effectiveness of the proposed network. INDEX TERMS Convolutional neural network (CNN), remote sensing, oriented object detection, anchor refinement.

Magnetorheological energy absorbers (MREAs) have manifested their superiority as a controllable damper. An ideal feature for MREA is to remain a constant damping force within a certain impact displacement (referred to as plateau behavior) in the transient impact process. Realizing this plateau behavior by introducing the structure of drain hole is able to effectively reduce harmfulness from the overshoot to the buffered object. In this study, a radial flow mode MREA with a center drain hole configuration is proposed, in order to achieve an approximate plateau as well as to expand the dynamic range. The Power-Law model is employed to analyze the impact behaviors of the MREA due to its smooth shear stress-shear rate curve and simple mathematical form. Five parameters (i.e., plateau angle, radial flow velocity ratio, minor losses ratio, dynamic range ratio, and peak force ratio) are defined to characterize the effects of the drain hole quantitatively and comprehensively. The diameter of center drain hole is specially focused on because of its significant influences on the parameters. Two types of MREAs with/without drain holes are fabricated and tested using a drop tower facility with a 600 kg mass. The experimental results show that the plateau angle of MREA with drain hole is reduced by 56.1% compared to that without hole, and also demonstrate that the Power-Law based model is capable of well predicting the dynamic behavior of the MREA.

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High-viscosity linear polysiloxane-based magnetorheological fluid features its excellent suspension stability. Few reports could be found for magnetorheological energy absorbers using such highly viscous but highly stable magnetorheological fluids as the controlled medium. This study presents a design strategy for the high-viscosity linear polysiloxane-based magnetorheological fluid-based magnetorheological energy absorber with multi-stage radial flow mode. The design strategy is based on the Herschel-Bulkley flow model incorporating minor losses proposed in our prior work. The optimal geometrical parameters were obtained by gradually reducing the number of unknown variables. By analyzing the effect of thicknesses of baffle and outer cylinder and number of coil turns on magnetic circuit, the distribution of magnetic flux in the effective region of magnetorheological valve was optimized. Furthermore, a magnetorheological energy absorber was fabricated and tested using a high-speed drop tower facility with a 600 kg mass. The maximum nominal impact velocity was 4.2 m/s, and the applied current varied discretely from 0, 1, 2, to 3 A. Comparison of our Herschel-Bulkley flow model with measured data was conducted via analysis of peak force, dynamic range, and maximum displacement that indicate the performance of magnetorheological energy absorber. The results validated the effectiveness of the design strategy for the high-viscosity linear polysiloxane-based magnetorheological fluid-based magnetorheological energy absorber.