National University of Defense Technology

About: National University of Defense Technology is a education organization based out in Changsha, China. It is known for research contribution in the topics: Computer science & Radar. The organization has 39430 authors who have published 40181 publications receiving 358979 citations. The organization is also known as: Guófáng Kēxuéjìshù Dàxué & NUDT.

Parametric effects on the combustion flow field of a typical strut-based scramjet combustor

Abstract: The flame-holding mechanism in hypersonic propulsion technology is the most important factor in prolonging the duration time of hypersonic vehicles. The two-dimensional coupled implicit Reynolds-averaged Navier-Stokes equations, the shear-stress transport k-ω turbulence model and the finite-rate/eddy-dissipation reaction models were used to simulate the combustion flow field of a typical strut-based scramjet combustor. We investigated the effects of the hydrogen-air reaction mechanism and fuel injection temperature and pressure on the parametric distributions in the combustor. The numerical results show qualitative agreement with the experimental data. The hydrogen-air reaction mechanism makes only a slight difference in parametric distributions along the walls of the combustor, and the expansion waves and shock waves exist in the combustor simultaneously. Furthermore, the expansion wave is formed ahead of the shock wave. A transition occurs from the shock wave to the normal shock wave when the injection pressure or temperature increases, and the reaction zone becomes broader. When the injection pressure and temperature both increase, the waves are pushed out of the combustor with subsonic flows. When the waves are generated ahead of the strut, the separation zone is formed in double near the walls of the combustor because of the interaction of the shock wave and the boundary layer. The separation zone becomes smaller and disappears with the disappearance of the shock wave. Because of the horizontal fuel injection, the vorticity is generated near the base face of the strut, and this region is the main origin for turbulent combustion.

New generation of synthetic jet actuators

Abstract: I N the last 20 years, much attention has been given to developing microfluidic systems [1]. Among them, synthetic-jet actuators (SJA) have been intensely studied recently [2]. Synthetic-jet actuators have many potential applications such as jet vectoring [3,4], boundary-layer control [5,6], combustion control [7], and micro-pumps [8], etc. A synthetic-jet actuator is a zero net mass flux device. Figure 1a shows a typical structure of an existing SJA, which is composed of an exit slot (or orifice) and a diaphragm (or double diaphragms [9]) mounted to enclose a volume of fluid in a cavity. Piezoelectric (PZT) diaphragms are used in most minior microSJAs because of their size, rapid time response, and relatively low power consumption. The PZT-driven SJA also fits within the microelectromechanical system (MEMS) discipline and can be coupled with MEMS sensors, control and logic electronics into a single very lightweight and compact device. Unfortunately, the pressure loading limits to obtain a small deflection of the PZTdiaphragm on the existing SJA requires a high power to drive the PZT-diaphragm when the pressure differential between the base flow (to be controlled by the SJA) and the environment is large. This limits applications of the SJA. In addition, the diaphragm of the existing SJA (as shown in Fig. 1a) has one surface exposed to the fluid drawn from the base flow and the other surface exposed to the environment, which indicates that half of the radiation energy of the vibrating diaphragm is wasted in the environment. Keeping the advantages of a PZT-driven SJA,while resolving themajor problems of pressure loading and energy inefficiency, is the main impetus for designing a new generation SJA. A newSJA prototype is schematically shown in Fig. 1b. It consists of two cavities, a PZT-diaphragm, two exit slots, and a slide block (SB). In the new SJA concept, two adjacent jets are established under the two exit slots and are driven by the motion of the same PZTdiaphragm. The slide block regulates the two jets (as shown in Figs. 1b–1d), and then two adjacent jets merge into a single, larger synthetic jet. In this Note, numerical simulations are conducted to study the new SJA. We include a discussion focused on the novelty and merits of the new SJA in comparison with the existing SJAs.

An Efficient Approach to Integrating Radius Information into Multiple Kernel Learning

Abstract: Integrating radius information has been demonstrated by recent work on multiple kernel learning (MKL) as a promising way to improve kernel learning performance. Directly integrating the radius of the minimum enclosing ball (MEB) into MKL as it is, however, not only incurs significant computational overhead but also possibly adversely affects the kernel learning performance due to the notorious sensitivity of this radius to outliers. Inspired by the relationship between the radius of the MEB and the trace of total data scattering matrix, this paper proposes to incorporate the latter into MKL to improve the situation. In particular, in order to well justify the incorporation of radius information, we strictly comply with the radius-margin bound of support vector machines (SVMs) and thus focus on the l2-norm soft-margin SVM classifier. Detailed theoretical analysis is conducted to show how the proposed approach effectively preserves the merits of incorporating the radius of the MEB and how the resulting optimization is efficiently solved. Moreover, the proposed approach achieves the following advantages over its counterparts: 1) more robust in the presence of outliers or noisy training samples; 2) more computationally efficient by avoiding the quadratic optimization for computing the radius at each iteration; and 3) readily solvable by the existing off-the-shelf MKL packages. Comprehensive experiments are conducted on University of California, Irvine, protein subcellular localization, and Caltech-101 data sets, and the results well demonstrate the effectiveness and efficiency of our approach.

Kinematic control of free rigid bodies using dual quaternions

Abstract: This paper proposes a new type of control laws for free rigid bodies. The start point is the dual quaternion and its characteristics. The logarithm of a dual quaternion is defined, based on which kinematic control laws can be developed. Global exponential convergence is achieved using logarithmic feedback via a generalized proportional control law, and an appropriate Lyapunov function is constructed to prove the stability. Both the regulation and tracking problems are tackled. Omnidirectional control is discussed as a case study. As the control laws can handle the interconnection between the rotation and translation of a rigid body, they are shown to be more applicable than the conventional method.

An Adaptive Contoured Window Filter for Interferometric Synthetic Aperture Radar

Abstract: An adaptive contoured window filter is proposed to filter off the noise from phase images of interferometric synthetic aperture radar (InSAR) in this letter. The contoured windows can best satisfy the requirement that constrains the phase signal constant inside windows on which low-pass filtering can remove the noise well while the fringe phases are well preserved. The contoured windows are determined by tracing along the local fringe orientation. An algorithm for determining window sizes adaptive to the fringe density is also proposed. The theoretical analysis and experiments prove that the proposed filter can greatly remove decorrelation noise while preserving the fringe phase well, even for those fringes with strong curvatures for InSAR processing