The slant range of a radar maneuvering target is usually modeled as a multivariate function in terms of its illumination time and multiple motion parameters. This multivariate range function includes the modulations on both the envelope and the phase of an echo of the coherent radar target and provides the foundation for radar target motion estimation. In this paper, the maximum likelihood estimators (MLE) are derived for motion estimation of a maneuvering target based on joint envelope and phase measurement, phase-only measurement and envelope-only measurement in case of high signal-to-noise ratio (SNR), respectively. It is shown that the proposed MLEs are to search the maximums of the outputs of the proposed generalized Radon-Fourier transform (GRFT), generalized Radon transform (GRT) and generalized Fourier transform (GFT), respectively. Furthermore, by approximating the slant range function by a high-order polynomial, the inherent accuracy limitations, i.e., the Cramer-Rao low bounds (CRLB), and some analysis are given for high order motion parameter estimations in different scenarios. Finally, some numerical experimental results are provided to demonstrate the effectiveness of the proposed methods.
The parameters obtained in the study of single layer of laser cladding forming are not suitable for the forming of actual structures. The cooling condition varies with the height of clad layers, which result in instability and then failure of cladding. Therefore, the stability of laser cladding forming is of significance. In this paper, melt pool depth is used as a criteria for stability. And the effect of processing parameters such as laser power and laser velocity on melt pool depth, are investigated by numerical simulation method. The results unveil that there is a transition zone from the beginning to stable stage during laser cladding forming. In the transition zone, laser power should be decreased or laser velocity should be increased to maintain the constant melt pool depth and to ensure the former clad layer would not be remelt. The optimized processing parameters are obtained for stable processing for a thin flat wall and a cylindrical wall, which successfully guide the manufacturing of the real structures.
Pulse integration technology is widely used to enhance signal-noise-ratio (SNR) for moving ground target detection in Synthetic Aperture Radar and other radars systems. In this paper, the performance of pulse integration of moving targets accounting for target motion errors is analyzed. For the long dwell time condition, the effects of time-variant motion of targets are analytically discussed. The analytical estimation of biased and unbiased compensation residual errors for targets motion is derived. The estimated results show that the biased and unbiased residual errors can lead to significant performance degradation as the dwell time increases.
Statistical multiple-input multiple-output (MIMO) radar may improve the fluctuated target detection by utilizing the multiple separate transmitting and receiving elements. Nevertheless, the transmitting power of single element is reciprocal to the transmitting element number, and the ultimate detection performance of MIMO radar may be inversely deteriorated with the increase of the transmitting elements. In this letter, the optimal transmitting diversity DOF, i.e., the optimal separate transmitting elements, is defined based on the proposed likelihood ratio test (LRT) detectors. Furthermore, with the given false alarm probability and detection probability, the closed-form optimal DOF approximations are derived for the two sub-forms of statistical MIMO radar, i.e., distributed MIMO radar and multiple-input single-output (MISO) radar, respectively. It is shown that a small transmitting diversity DOF, as well as the small number of orthogonal transmitting waveforms, may be needed for optimizing the statistical MIMO radar spatial diversity performance. Finally, numerical experiments are also provided to demonstrate the effectiveness of the proposed methods.
Ultrasonic treatment is a hot research topic in the treatment of the melt of metals. Numerical simulation is a useful method to unveil the principles of ultrasonic treatment. In this paper, the Novier-Stoke equations and the cavitation model are coupled to simulate the cavitation during ultrasonic treatment by using Fluent. It is found that as the nucleation site volume fraction increases to a certain degree, there will be a bubble layer surrounding the amplitude transformer, which insulates the effect of ultrasound beyond the bubble blanket. Experiment was carried out, and the simulated results were validated. And the effect of nucleation site volume fraction in water is investigated. The nucleation site volume fraction should be controlled into a certain range to realize uniform cavitation.
Abstract This paper is a work in progress. Complex problem-solving has been considered as one of the core competencies in current engineering education. Research has presented different perspectives to realize the evaluation of complex problem-solving competency, for instance the decomposing skills and learning goals; the scientific scope of the problem and the size of the project; the decision-making process of domain professionals; and the psychometric viewpoint. In general, there has been multiple methods based on different conceptual frameworks and informative inputs from professional engineers; but there is a lack of investigation on how engineering teachers understand and practice this concept in classroom. The importance of complex problem-solving has not been widely recognised in engineering education practitioners. In this paper, we briefly review current research; and introduce a bottom-up exploration based on engineering teachers. Using semi-structured interviews, we focus specifically on the learning procedures and goals related to the solving of complex engineering problems in teachers' mind, and then present a conceptual framework. We pay close attention to the cognitive consensus and divergence between practicing teachers and current research. The implications on engineering teaching, educational reform, and future research are discussed.
Now, with China's power reform and the gradual formation of the electricity market, how to reduce the power losses and how to implement the economic operation are the responses to the electricity market bidding problem without delay. This study aimed to reduce transformer loss of power companies. This paper studies how the power system analysis and control operating of the Connecting Transformer (CT), the application of advanced control methods to adjust the output power of power plants to reduce contact the transformer active power and reactive power losses. Studying and learning from the idea of rapid decomposition, research will be divided into two steps to implement control strategies, namely, the first node to adjust active power generator, used to adjust the contact of the active power transformer, thereby reducing contact the transformer power loss; followed by adjustment of generator terminal voltage or reactive power, used to adjust the voltage across the contact transformer reactive power flow in order to reduce losses. At the same time with the actual operation data of the Northeast power grid, computer simulation studies, simulation results verify the effectiveness of the proposed control law.
The dynamic crushing behavior of cellular metals is closely related to their microstructure. Two types of random defects by randomly thickening/removing cell walls are investigated in this paper. Their influences on the deformation modes and plateau stresses of honeycombs are studied by finite element simulation using ABAQUS/Explicit code. Three deformation modes, i.e. the Homogeneous Mode, the Transitional Mode and the Shock Mode, are used to distinguish the deformation patterns of honeycombs under different impact velocities. The critical impact velocity for mode transition between the Homogeneous and Transitional modes is quantitatively determined by evaluating a stress uniformity index, defined as the ratio between the plateau stresses on the support and impact surfaces. It is found that the critical impact velocity decreases with increasing thickening ratio but increases with increasing removing ratio. The plateau stress on the impact surface heavily depends on the impact velocity due to the inertia effect. The random defects lead to a weakening effect on the plateau stress. For the honeycombs with randomly removing cell walls, the weakening effect is especially obvious at a moderate impact velocity. For the honeycombs with randomly thickening cell walls, the weakening effect is particularly severe at a low impact velocity, but this effect almost disappears when the impact velocity is high enough.
A varying cell-size method based on Voronoi technique is extended to construct 3D graded cellular models. The dynamic behaviors of graded cellular structures with different density gradients are then investigated with finite element code ABAQUS/Explicit. Results show that graded cellular materials have better performance as energy absorbers. Graded cellular structures with large density near the distal end can protect strikers, and those with low density near the distal end can protect structures at the distal end. It is concluded that graded cellular materials with suitable design may have excellent performance in crashworthiness.
Dynamic behavior of a semi-infinite elastic beam to a moving single sinusoidal pulse was theoretical investigated. An analytical model was developed based on the Bernoulli-Euler beam theory. The solutions of the deflection and stress of beam were obtained by using the superposition principle and applying the techniques of Fourier transform. It is found that when the moving pulse reaches a critical velocity for a given moving pulse duration, the maximal absolute value of stress in beam attains its maximum value.
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