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Numerical Study of High Gradient Thermobuoyant Flow in a Tilted Cavity Using a Novel Non-Boussinesq Algorithm

NUMERICAL HEAT TRANSFER PART A-APPLICATIONS 2010年第12期58卷 984-1003页

作者： Hosseinizadeh, S. F. Darbandi, M. Heidarnataj, M. Babol Univ Technol Babol Sar Mazandaran Iran Sharif Univ Technol Dept Aerosp Engn Ctr Excellence Aerosp Syst Tehran Iran Islamic Azad Univ Sama Org Babol Sar Iran

We study the natural convection heat transfer in a tilted square cavity with different tilt angles. The cavity is subject to a high gradient temperature resulting in high Rayleigh number flows. The fluid is air and is treated as an ideal gas. The flow is laminar. The fluid properties change with temperature variation using Sutherland's law. Because of imposing large temperature gradients to the two cavity opposite walls, there is substantial density variation in the domain. We use a novel non-Boussinesq algorithm to model the density variation fully. Therefore, the current results are considerably different from those obtained using the classical Boussinesq-based methods, which replace the density variation with the temperature changes. The differences become serious as the Rayleigh number increases. The outcome of this study emphasizes that the numerical heat transfer researchers should simulate high thermobuoyant flow domains via applying variable density-based algorithms instead of using the classical Boussinesq-based methods.

关键词： HEAT transfer HEAT -- Convection, Natural HIGH temperatures RAYLEIGH number computer algorithms BUOYANT convection SIMULATION methods & models

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A Novel Method Based on Oblique Projection Technology for Mixed Sources Estimation

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MATHEMATICAL PROBLEMS IN ENGINEERING 2014年第1期2014卷 1-12页

作者： Si, Weijian Li, Xiaolin Jiang, Yilin Wan, Liangtian Harbin Engn Univ Coll Informat & Commun Engn Harbin 150001 Peoples R China

Reducing the computational complexity of the near-field sources and far-field sources localization algorithms has been considered as a serious problem in the field of array signal processing. A novel algorithm caring for mixed sources location estimation based on oblique projection is proposed in this paper. The sources are estimated at two different stages and the sensor noise power is estimated and eliminated from the covariance which improve the accuracy of the estimation of mixed sources. Using the idea of compress, the range information of near-field sources is obtained by searching the partial area instead of the whole Fresnel area which can reduce the processing time. Compared with the traditional algorithms, the proposed algorithm has the lower computation complexity and has the ability to solve the two closed-spaced sources with high resolution and accuracy. The duplication of range estimation is also avoided. Finally, simulation results are provided to demonstrate the performance of the proposed method.

关键词： OBLIQUE projection ESTIMATION theory COMPUTATIONAL complexity NEAR-fields computer algorithms SIGNAL processing

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An adaptive semiactive control algorithm for magnetorheological suspension systems

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JOURNAL OF VIBRATION AND ACOUSTICS-TRANSACTIONS OF THE ASME 2005年第5期127卷 493-502页

作者： Song, XB Ahmadian, M Southward, S Miller, LR Eaton Corp Innovat Ctr Southfield MI 48076 USA Virginia Polytech Inst & State Univ Dept Engn Mech Adv Vehicle Dynam Lab Blacksburg VA 24060 USA Lord Corp Thomas Lord Res Ctr Cary NC 27511 USA

In this paper we will present a nonlinear-model-based adaptive semiactive control algorithm developed for magnetorheological (MR) suspension systems exposed to broadband nonstationary random vibration sources that are assumed to be unknown or not measurable. If there exist unknown and/or varying parameters of the dynamic system such as mass and stiffness, then the adaptive algorithm can include on-line system identification such as a recursive least-squares method. Based on a nonparametric MR damper model, the adaptive system stability is proved by converting the hysteresis inherent with MR dampers to a memoryless nonlinearity with sector conditions. The convergence of the adaptive system, however is investigated through a linearization approach including further numerical, illustration of specific cases. Finally the simulation results for a magnetorheological seat suspension system with the suggested adaptive control are presented. The results are compared with low-damping and high-damping cases, and such comparison further shows the effectiveness of the proposed nonlinear model-based adaptive control algorithm for damping timing.

关键词： Converge System identification DAMPER Dynamic systems Suspension System Sectoring computer algorithms Adaptive systems Self tuning adaptive control

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An Efficient Multiobjective Backtracking Search Algorithm for Single Machine Scheduling with Controllable Processing Times

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MATHEMATICAL PROBLEMS IN ENGINEERING 2017年第1期2017卷 1-24页

作者： Lu, Chao Gao, Liang Li, Xinyu Wang, Qi Liao, Wei Zhao, Qingyao Huazhong Univ Sci & Technol State Key Lab Digital Mfg Equipment & Technol Sch Mech Sci & Engn Wuhan Peoples R China

The scheduling problem with controllable processing times (CPT) is one of the most important research topics in the scheduling field due to its widespread application. Because of the complexity of this problem, a majority of research mainly addressed single-objective small scale problems. However, most practical problems are multiobjective and large scale issues. Multiobjective metaheuristics are very efficient in solving such problems. This paper studies a single machine scheduling problem with CPT for minimizing total tardiness and compression cost simultaneously. We aim to develop a new multiobjective discrete backtracking search algorithm(MODBSA) to solve this problem. To accommodate the characteristic of the problem, a solution representation is constructed by a permutation vector and an amount vector of compression processing times. Furthermore, two major improvement strategies named adaptive selection scheme and total cost reduction strategy are developed. The adaptive selection scheme is used to select a suitable population to enhance the search efficiency of MODBSA, and the total cost reduction strategy is developed to further improve the quality of solutions. For the assessment of MODBSA, MODBSA is compared with other algorithms including NSGA-II, SPEA2, and PAES. Experimental results demonstrate that the proposed MODBSA is a promising algorithm for such scheduling problem.

关键词： computer scheduling PROBLEM solving PERMUTATION groups computer algorithms COMPUTATIONAL complexity

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Basic Unit Layer Rate Control Algorithm for H.264 Based on Human Visual System

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MATHEMATICAL PROBLEMS IN ENGINEERING 2013年第1期2013卷 1-6页

作者： Chen, Xiao Liu, Haiying Nanjing Univ Informat Sci & Technol Jiangsu Key Lab Meteorol Observat & Informat Proc Nanjing 210044 Jiangsu Peoples R China Nanjing Univ Informat Sci & Technol Sch Elect & Informat Engn Nanjing 210044 Jiangsu Peoples R China

In the process of the video coding, special attention should be paid to the subjective quality of the image. In the JVT-G012 algorithm for H.264, the influence of the human visual characteristic in basic unit layer rate control was not taken into account. This paper takes the influence of the human visual characteristic into the full consideration and offers ways to improve the subjective quality of the image. The visual characteristic factor, which is constituted by the motion feature and edge feature, is used to reasonably allocate the target bits, and then its quantization parameter is adjusted by encoded frame information. The experimental results show that, in comparison to the original algorithm, the proposed algorithm can not only control the bit rate more accurately but also make the peak signal to noise ratio (PSNR) stable, so as to improve the stationarity of the video image. The subjective quality of the reconstructed video is more satisfying.

关键词： computer algorithms computer vision VIDEO coding (computer science) IMAGE quality analysis FEATURE extraction (Data processing) INFORMATION theory

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A high-order compact finite-difference scheme for large-eddy simulation of active flow control

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PROGRESS IN AEROSPACE SCIENCES 2008年第6期44卷 397-426页

作者： Rizzetta, Donald P. Visbal, Miguel R. Morgan, Philip E. USAF Res Lab Computat Sci Branch RBAC Wright Patterson AFB OH 45433 USA

The purpose of this article is to summarize a computational approach, which developed and matured over an extended period of time, and has been shown to be useful for performing large-eddy Simulation (LES) of flows with active control. Because of the nature of active flow control, simulation of this class of problems typically cannot be carried out accurately by methods less sophisticated than LES. Active control flowfields are highly unsteady, and can be characterized by small-scale fluid structures which are produced by the control process, but may also be inherent in the original uncontrolled situation. The numerical scheme is predicated upon an implicit time-marching algorithm, and utilizes a high-order compact finite-difference approximation to represent spatial derivatives. Robustness of the scheme is maintained by employing a low-pass Pade-type nondispersive spatial filter, which also accounts for the fine-scale turbulent dissipation that otherwise is traditionally provided by an explicitly added subgrid-scale (SGS) stress model. Geometrically complex applications are accommodated by an overset grid technique, where spatial accuracy is preserved through use of high-order interpolation. Utility of the method is illustrated by specific computational examples, including suppression of acoustic resonance in supersonic cavity flow, leading-edge vortex control of a delta wing, efficiency enhancement of a transitional highly loaded low-pressure turbine blade, and separation control of a wall-mounted hump model. Control techniques represented in these examples are comprised of both steady and pulsed mass injection or removal, as well as plasma-based actuation. For each case, features of the flowfield are elucidated and the solutions are compared to the baseline situation where no control was enforced. Where available, comparisons are also made with experimental data. Published by Elsevier Ltd.

关键词： FLUID dynamics FINITE differences FLUID-structure interaction MULTIPHASE flow computer algorithms SIMULATION methods & models

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Relativized codes

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THEORETICAL computer SCIENCE 2012年 429卷 54-64页

作者： Daley, Mark Juergensen, Helmut Kari, Lila Mahalingam, Kalpana Univ Western Ontario Dept Comp Sci London ON N6A 5B7 Canada IIT Madras Dept Math Madras 600036 Tamil Nadu India

A code C over an alphabet Sigma is a set of words such that every word in C+ has a unique factorization over C, that is, a unique C-decoding. When not all words in C+ appear as messages, a weaker notion of unique factorization can be used. Thus we consider codes C relative to a given set of messages L, such that each word in L has a unique C-decoding. We extend this idea of relativizing code concepts to restricted message spaces. In general terms, from a predicate P defining a class of codes, P-codes, we derive a relativized version of such codes, P-codes relative to a given language L. In essence, C subset of Sigma(+) is a P-code relative to L subset of Sigma(+) if P is true on its domain restricted to L. This systematic approach leads to the relativization of the definitions of many classes of codes, including prefix, suffix, bifix and solid codes. It can also be applied to certain classes of languages, like overlap-free languages, which are not codes, but which can be defined using a similar logical framework. In this paper, we explore the mechanism of this relativization and compare it to other existing methods for relativizing code properties to restricted message spaces. (C) 2011 Elsevier B.V. All rights reserved.

关键词： CODING theory FACTORIZATION (Mathematics) INFORMATION theory computer science computer software computer algorithms

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New Algorithm Based on Sign Decomposition to Verify the Robust Stability Property for a Class of Linear Time-Delay Systems

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MATHEMATICAL PROBLEMS IN ENGINEERING 2015年第1期2015卷 1-8页

作者： Diaz-Rodriguez, Ivan D. Romero, Gerardo Elizondo, Cesar Texas A&M Univ ECEN College Stn TX 77840 USA UAT UAM Reynosa Rodhe Reynosa 88779 Tamps Mexico Univ Autonoma Nuevo Leon FIME San Nicolas Del Los Garz 66450 Mexico

The main focus of this paper is to analyze the robust stability property for a class of time-delay systems when parametric polynomic uncertainty is considered. The analysis is made by replacing the time-delay part with an auxiliary equation and then using the sign definite decomposition to deal with the polynomic parametric uncertainty. Also, it is shown that it is possible to verify the robust stability property by first obtaining the Hurwitz matrix from the characteristic equation for this class of systems and then checking the leading principal minors positivity using the sign definite decomposition. Finally, an algorithm codified in MATLAB is used to evaluate and graphically show the robust stability property. This is shown by a series of points that were calculated using the sign definite decomposition.

关键词： computer algorithms DECOMPOSITION (Mathematics) ROBUST stability analysis LINEAR systems TIME delay systems PARAMETER estimation

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Decentralized sliding mode control of a building using MR dampers

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SMART MATERIALS AND STRUCTURES 2008年第5期17卷 55006-1-55006-15-0页

作者： Lu, Kung-Chun Loh, Chin-Hsiung Yang, J. N. Lin, Pei-Yang Natl Taiwan Univ Dept Civil Engn Taipei 10617 Taiwan Univ Calif Irvine Dept Civil & Environm Engn Irvine CA 92697 USA Natl Ctr Res Earthquake Engn Taipei Taiwan

This paper presents the structural control results of shaking table tests for a steel frame structure in order to evaluate the performance of a number of proposed semi-active control algorithms using multiple magnetorheological (MR) dampers. The test structure is a six-story steel frame equipped with MR dampers. Four different cases of damper arrangement in the structure are selected for the control study. In experimental tests, the El Centro earthquake and Kobe earthquake ground motion data are used as excitations. Further, several decentralized sliding mode control algorithms are developed in this paper specifically for applications of MR dampers in building structures. Various control algorithms are used for the semi-active control studies, including the proposed decentralized sliding mode control (DSMC), LQR control, and passive-on and passive-off control. Each control algorithm is formulated specifically for the use of MR dampers installed in building structures. Additionally, each algorithm uses measurements of the device velocity and device drift for the determination of the control action to ensure that the algorithm can be implemented in a physical structure. The performance of each algorithm is evaluated based on the results of shaking table tests, and the advantages of each algorithm are compared and discussed. The reduction of story drifts and floor accelerations throughout the structure is examined.

关键词： SEISMIC RESPONSE CONTROL UTILIZING SEMIACTIVE MR ACCELERATION FEEDBACK EXCITED BUILDINGS WIND algorithms SYSTEMS Variable structure systems Decentralized built structure DAMPER Shaking table test computer algorithms test structure Wind algorithms control action Buildings semi-active control steel frame construction

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An optimized reconfigurable power spectral density converter for real-time shrew DDoS attacks detection

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computerS & ELECTRICAL ENGINEERING 2013年第2期39卷 295-308页

作者： Chen, Hao Gaska, Thomas Chen, Yu Summerville, Douglas H. SUNY Binghamton Dept Elect & Comp Engn Binghamton NY 13902 USA

The shrew DDoS attacks are stealth low-rate TCP-targeted DDoS attacks, which conceal their malicious activities into normal traffic. Although the good pretense eludes them from being detected in time domain, the existent energy exposes them in frequency domain. Online Power Spectral Density (PSD) analysis necessitates real-time PSD data conversion is a must. In this paper, an optimized FPGA based real-time PSD converter is proposed, which is based on our innovative component-reusable Auto-Correlation (AC) algorithm and the adapted 2N-point real-valued Discrete Fourier Transform (DFT) algorithm. Further optimization is achieved through the exploration of algorithm characters and hardware parallelism for this case. The evaluation results from both simulation and synthesis are provided. The conversion of a 512-point data sequence can be finished in the time interval of sampling one data point;and the overall design could be easily fitted in a Xilinx Virtex2 Pro FGPA. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： DENIAL of service attacks MATHEMATICAL optimization REAL-time computing DEBUGGING in computer science DISCRETE Fourier transforms computer algorithms computer simulation

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