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Combined natural convection and radiation in a vertical annulus

HEAT AND MASS TRANSFER 1996年第6期31卷 371-379页

作者： Weng, LC Chu, HS NATL CHIAO TUNG UNIV DEPT ENGN MECHHSINCHU 30050TAIWAN

This paper presents a numerical study of the effects of thermal radiation on the heat transfer of steady natural convection in a participating fluid contained inside a cylindrical annulus. The fluid absorbs and emits radiation energy. Uniform temperature difference is imposed across the inner and outer cylinder walls. The radiation part of the problem is treated by using the two-dimensional P-l approximation. The numerical calculations were executed using the projection algorithm with a power law scheme. The analysis are performed for Rayleigh number ranging from 10(4) to 10(6), aspect ratio varying between 2 and 10, and the radius ratio ranging from 1.25 to 10 for N=0.1, 1, and infinity where N is the conduction-to-radiation parameter. The thermal radiation greatly influences the flow field and temperature distribution inside the enclosure for different aspect ratio and radius ratios. Those results are presented vividly by the streamlines and isotherms. Based on the results, the average Nusselt number is correlated by a relation of the form <(Nu)over bar = a+blnA> and <(Nu)over bar = c+d> exp(-eta/e). The coefficients for various N are tabulated.

关键词： radiation of heat Natural convection Rayleigh number isotherm Enclosures Temperature distribution nitrogen Radius ASPECT RATIO cylinder wall Heat transfer Power law flow field projection algorithms Nusselt number

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Rotational motion estimation for ISAR via triangle pose difference on two range-Doppler images

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IET RADAR SONAR AND NAVIGATION 2010年第4期4卷 528-536页

作者： Yeh, C. -M. Xu, J. Peng, Y. -N. Xia, X. -G. Wang, X. -T. Tsinghua Univ Dept Elect Engn Beijing 100084 Peoples R China Univ Delaware Dept Elect & Comp Engn Newark DE USA

Rotational motion estimation is essential for inverse synthetic aperture radar (ISAR) imaging and understanding. For an object rotating with a constant acceleration, a closed-form solution is proposed to jointly estimate the initial rotating velocity (IRV) and the rotating acceleration (RA) by exploiting the pose difference of a triangle on two range-Doppler (RD) images. Then, the RA can be compensated with interpolation processing and an equivalent uniformly rotating object may be obtained. After that, the estimated IRV can be used to re-scale the RD image into the homogeneous range-cross range domain, or to provide more satisfactory imaging result via elaborated algorithms such as polar format algorithm or convolution back-projection algorithm. Finally, experimental results with both simulated and real airplane data are provided to demonstrate the effectiveness of the proposed method.

关键词： Convolution Inverse synthetic aperture radar motion estimation constant acceleration projection algorithms REMEDIAL DESIGN Triangle

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Alternating projections and Douglas-Rachford for Sparse Affine Feasibility

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2014年第18期62卷 4868-4881页

作者： Hesse, Robert Luke, D. Russell Neumann, Patrick Univ Gottingen Inst Numer & Angew Math D-37083 Gottingen Germany

The problem of finding a vector with the fewest nonzero elements that satisfies an underdetermined system of linear equations is an NP-complete problem that is typically solved numerically via convex heuristics or nicely-behaved non-convex relaxations. In this work we consider elementary methods based on projections for solving a sparse feasibility problem without employing convex heuristics. It has been shown recently that, locally, the fundamental method of alternating projections must converge linearly to a solution to the sparse feasibility problem with an affine constraint. In this paper we apply different analytical tools that allow us to show global linear convergence of alternating projections under familiar constraint qualifications. These analytical tools can also be applied to other algorithms. This is demonstrated with the prominent Douglas-Rachford algorithm where we establish local linear convergence of this method applied to the sparse affine feasibility problem.

关键词： Compressed sensing iterative methods linear systems optimization projection algorithms sparse matrices

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Evaluation of the impact of finite-resolution effects on scintillation compensation using two deformable mirrors

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2001年第12期18卷 3098-3109页

作者： Barchers, JD USAF Res Lab Starfire Opt Range Directed Energy Directorate Kirtland AFB NM 87117 USA

The impact of finite-resolution deformable mirrors and wave-front sensors is evaluated as it applies to full-wave conjugation using two deformable mirrors. The first deformable mirror is fixed conjugate to the pupil, while the second deformable mirror is at a finite range. The control algorithm to determine the mirror commands for the two deformable mirrors is based on a modification of the sequential generalized projection algorithm. The modification of the algorithm allows the incorporation of Gaussian spatial filters into the optimization process to limit the spatial-frequency content applied to the two deformable mirrors. Simulation results are presented for imaging and energy projection scenarios that establish that the optimal spatial filter waist to be applied is equal to the subaperture side length in strong turbulence. The effect of varying the subaperture side length is examined, and it is found that to effect a significant degree of scintillation compensation, the subapertures, and corresponding spacing between actuators, must be much smaller than the coherence length of the input field. (C) 2001 Optical Society of America.

关键词： Optimization Procedure coherence length scintillations projection algorithms side length Pupil deformable mirrors Spatial filters

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Quantitative Analysis and Interpretation of Transient Electromagnetic Data via Principal Component Analysis

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IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 2012年第5期50卷 1910-1918页

作者： Kass, M. Andy Li, Yaoguo Colorado Sch Mines Ctr Grav Elect & Magnet Studies Golden CO 80401 USA

Transient electromagnetic (TEM) data in applied geophysics are invariably contaminated by random and coherent noise associated with acquisition, geology, and the environment. Advanced unexploded ordnance (UXO) detection and discrimination using TEM data require the suppression of the random noise and reliable separation of UXO signal from other coherent signals. The random noise is usually easier to remove, with coherent signal being more difficult to identify as well as separate. We have developed a method based on principal component analysis (PCA) to achieve both objectives. As a data-adaptive linear transformation, PCA is a fast and reliable method for the removal of random uncorrelated noise as well as for the separation of coherent undesired signals from those due to UXO and UXO-like anomalies. In this paper, we outline the PCA method, including the choice of data organization, construction of covariance matrices, and choice of principal components in reconstruction. We then show both synthetic and field data as examples of the efficacy of the method.

关键词： Classification algorithms electromagnetics geophysical signal processing principal component analysis (PCA) projection algorithms

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Fast and Accurate Amplitude Demodulation of Wideband Signals

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2021年 69卷 4039-4054页

作者： Gabrielaitis, Mantas IST Austria A-3400 Klosterneuburg Austria

Amplitude demodulation is a classical operation used in signal processing. For a long time, its effective applications in practice have been limited to narrowband signals. In this work, we generalize amplitude demodulation to wideband signals. We pose demodulation as a recovery problem of an oversampled corrupted signal and introduce special iterative schemes belonging to the family of alternating projection algorithms to solve it. Sensibly chosen structural assumptions on the demodulation outputs allow us to reveal the high inferential accuracy of the method over a rich set of relevant signals. This new approach surpasses current state-of-the-art demodulation techniques apt to wideband signals in computational efficiency by up to many orders of magnitude with no sacrifice in quality. Such performance opens the door for applications of the amplitude demodulation procedure in new contexts. In particular, the new method makes online and large-scale offline data processing feasible, including the calculation of modulator-carrier pairs in higher dimensions and poor sampling conditions, independent of the signal bandwidth. We illustrate the utility and specifics of applications of the new method in practice by using natural speech and synthetic signals.

关键词： Demodulation Modulation Wideband Task analysis Minimization projection algorithms Optimization Alternating projections amplitude demodulation convex programming fast algorithms multidimensional signals nonuniform sampling speech processing wideband signals

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ROBUST ADAPTIVE REGULATION WITHOUT PERSISTENT EXCITATION

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IEEE TRANSACTIONS ON AUTOMATIC CONTROL 1989年第12期34卷 1260-1267页

作者： LOZANOLEAL, R NASA LANGLEY RES CTRHAMPTONVA 23665

A globally convergent adaptive regulator for minimum or nonminimum phase systems subject to bounded disturbances is presented. The control strategy is designed for a particular input-output representation obtained from the state-space representation of the system. The leading coefficient of the novel representation is the product of the observability and controllability matrices of the system. The controller scheme uses a least-squares identification algorithm with a dead zone. The dead zone is chosen to obtain convergence properties on the estimates and on the covariance matrix as well. This allows the definition of modified estimates which secure well-conditioned matrices in the adaptive control law. Explicit bounds on the plant output are given.< >

关键词： Robustness Controllability Covariance matrix Convergence Adaptive control projection algorithms Delay estimation Stability Frequency Regulators

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Reconstruction of compact binary images from limited Fourier amplitude data

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2008年第10期25卷 2600-2607页

作者： Lo, V. L. Millane, R. P. Univ Canterbury Dept Elect & Comp Engn Computat Imaging Grp Christchurch 1 New Zealand

The problem of reconstructing a binary image from undersampled Fourier amplitude data is considered. This problem maps to an image reconstruction problem in x-ray crystallography. The binary constraint is sufficient to overcome the undersampling and enforce uniqueness, but is insufficient in the case of the additional loss of data that can occur in practice. An iterative projection algorithm is developed that uses binary, connectivity, and compactness constraints to solve the image reconstruction problem, Simulations show the utility of the reconstruction algorithm. (C) 2008 Optical Society of America

关键词： Undersampling Reconstructions Binary images image reconstruction projection algorithms additional loss Fourier amplitude Reconstructive Surgical Procedures Reconstruction algorithm

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Non-Linear Reconstruction of Delta-Sigma Modulated Signals: Randomized Surrogate Constraint Decoding Algorithm

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2013年第21期61卷 5361-5373页

作者： Marijan, Malisa Ignjatovic, Zeljko Univ Rochester Rochester NY 14627 USA

Delta-sigma (Delta Sigma) A/D conversion is a popular technique used to achieve high resolution data conversion for low to moderate bandwidth applications. It is commonly accepted that the digital circuitry of the Delta Sigma A/D converters should perform a linear time-invariant (LTI) filtering on the output of the Delta Sigma modulator in order to reconstruct the input signal. However, it has been shown that, when higher order Delta Sigma A/D converters are operated at higher oversampling ratios (OSRs), non-linear reconstruction algorithms extract more information about the input signal than LTI methods. Still, use of non-linear algorithms has been limited due to their complexity and stability issues. Two practical nonlinear methods presented in the literature are fast projection onto convex sets (POCS) and direct projection (DP). In this work, we show that the non-linear reconstruction process for Delta Sigma modulated sequences can be treated as a linear feasibility problem(LFP). We then show that if the reconstruction process is defined as an LFP, its implementation is less complex than in the case of the DP method. We further describe how the LFP can be well-conditioned and demonstrate the reconstruction process by using the surrogate constraint algorithm with random constraint selection. The described algorithm considers a small number of constraints at a time, which makes it suitable for serial implementation.

关键词： Delta-sigma modulation projection algorithms signal reconstruction

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Ultrasonic tomographic imaging of temperature and flow fields in gases using air-coupled capacitance transducers

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 1998年第6期104卷 3446-3455页

作者： Wright, WMD Schindel, DW Hutchins, DA Carpenter, PW Jansen, DP Univ Warwick Dept Engn Coventry CV4 7AL W Midlands England NRC Inst Aerosp Res Ottawa ON K1A 0R6 Canada Ontario Hydro Technol Toronto ON M8Z 5S4 Canada

A pair of air-coupled ultrasonic capacitance transducers with polished metal backplates have been used to image temperature and Bow fields in gases using ultrasonic tomography. Using a filtered back-projection algorithm and a difference technique, cross-sectional images of spatially variant changes in ultrasonic attenuation and slowness caused by the presence of temperature and Bow fields were reconstructed. Temperature fields were produced in air by a commercial soldering iron, and the subsequent images of slowness variations used to reconstruct the air temperature at various heights above the iron. When compared to measurements made with a thermocouple, the tomographically reconstructed temperatures were found to be accurate to within 5%. The technique was also able to resolve multiple heat sources within the scan area. Attenuation and Velocity images were likewise produced for flow fields created by an air-jet from a l-mm-diam nozzle, at both 90 and 45 degrees to the scanning plane. The fact that temperature and flow fields can be measured in a gas without the need to insert any measuring devices into the image region is an advantage that may have many useful applications. (C) 1998 Acoustical Society of America. [S0001-4966(98)00412-3].

关键词： air temperature Tomography Temperature fields projection algorithms flow field Ultrasonic attenuation air coupling Heat sources Temperature Gases region of an image Capacitive transducers measuring instruments Ultrasonic Tomography

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