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21.
Scanning Electron Microscopic (SEM) studies were carried out on the failure surface of syntactic foam material tested in a short beam three point bend test (SBT) by employing 21 × 15 × 3 mm3 dimension bearing specimens. The syntactic foams were fabricated using glass microballoons in epoxy binder. The failure of the tensile, compression, and shear dominated regions were studied by SEM at different magnifications. The tensile region had characteristic features, such as partial debonding of the microballoons from the matrix and cracking of glass microballoons, apart from matrix cracking and some river pattern features. The compression side was characterized by crushing and collapsing of microballoons, resulting in accumulation of debris with no apparent river pattern for matrix‐rich regions. The midway positions of the SBT failed surface comprised of deformation bands in the matrix and occasional debonding of microballoons. The morphology recorded in the tensile and compression regions corroborated well with the results obtained on these foam samples in those specimens that were subjected to pure uniaxial tension and compression, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 673–679, 2005 相似文献
22.
Surface reconstruction for incremental forming 总被引:1,自引:0,他引:1
A. Erman Tekkaya Ravi Shankar Gerd Sebastiani Werner Homberg Matthias Kleiner 《Production Engineering》2007,1(1):71-78
In spite of extensive efforts being made with regard to virtual process optimization technology, the production of prototype
parts is still a necessity. With respect to the production of sheet metal parts in low quantities, incremental sheet metal
forming (ISMF) is a highly interesting process. ISMF allows the production of complex parts with drastically reduced costs
in tooling and machinery compared to conventional processes like deep drawing. However, ISMF, with it’s incremental nature,
introduces the need for generating a tool path considering both final geometry and process-induced deviations or constraints.
Consequently, for the generation of the tool path a (tool path) surface, with an adequate offset, is necessary. That is why,
within the scope of extensive research work at the Institute of Forming Technology and Lightweight Construction (IUL), a special
correction module has been developed, determining this offset e.g. depending on the workpiece geometry. This paper presents
the algorithm, the application, and the effect on the produced parts. Furthermore, a concept for an extension regarding further
constraints like elastic workpiece behavior is presented. 相似文献
23.
This paper investigates the exponential observer design problem for one‐sided Lipschitz nonlinear systems. A unified framework for designing both full‐order and reduced‐order exponential state observers is proposed. The developed design approach requires neither scaling of the one‐sided Lipschitz constant nor the additional quadratically inner‐bounded condition. It is shown that the synthesis conditions established include some known existing results as special cases and can reduce the intrinsic conservatism. For design purposes, we also formulate the observer synthesis conditions in a tractable LMI form or a Riccati‐type inequality with equality constraints. Simulation results on a numerical example are given to illustrate the advantages and effectiveness of the proposed design scheme. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
24.
A Measurement‐Based Approach for Designing Fixed‐Order Controllers for Unknown Closed‐Loop Architecture 下载免费PDF全文
Sofiane Khadraoui Hazem N. Nounou Mohamed N. Nounou Aniruddha Datta Shankar P. Bhattacharyya 《Asian journal of control》2016,18(2):686-698
This paper presents a new technique to design fixed‐structure controllers for linear unknown systems using a set of measurements. In model‐based approaches, the measured data are used to identify a model of the plant for which a suitable controller can be designed. Due to the fact that real processes cannot be described perfectly by mathematical models, designing controllers using such models to guarantee some desired closed‐loop performance is a challenging task. Hence, a possible alternative to model‐based methods is to directly utilize the measured data in the design process. We propose an approach to designing structured controllers using a set of closed‐loop frequency‐domain data. The principle of such an approach is based on computing the parameters of a fixed‐order controller for which the closed‐loop frequency response fits a desired frequency response that describes some desired performance indices. This problem is formulated as an error minimization problem, which can be solved to find suitable values of the controller parameters. The main feature of the proposed control methodology is that it can be applied to stable and unstable plants. Additionally, the design process depends on a pre‐selected controller structure, which allows for the selection of low‐order controllers. An application of the proposed method to a DC servomotor system is presented to experimentally validate and demonstrate its efficacy. 相似文献
25.
Lesa Lorenzen Huber Kalpana Shankar Kelly Caine Kay Connelly L. Jean Camp Beth Ann Walker 《International journal of human-computer interaction》2013,29(7):441-455
In-home technologies can support older adults' activities of daily living, provide physical safety and security, and connect elders to family and friends. They facilitate aging in place while reducing caregiver burden. One of older adults' primary concerns about in-home technologies is their potential to reduce human contact, particularly from cherished caregivers. In this exploratory in situ study, we provided an ecosystem of networked monitoring technologies to six older adults and their caregivers. We analyzed the amount and content of communication between them. The amount of noncomputer-mediated communication did not decrease through the 6-week study. The content of communication coalesced into four themes: communication about the technologies, communication facilitated by technologies, intrusiveness of technologies, and fun and playfulness with the technologies. Results suggest that in-home technologies, designed with sensitivity to older adults' primary motivations, have the potential to shape and tailor important relationships in later life. 相似文献
26.
In this paper, an Adaptive Hierarchical Ant Colony Optimization (AHACO) has been proposed to resolve the traditional machine
loading problem in Flexible Manufacturing Systems (FMS). Machine loading is one of the most important issues that is interlinked
with the efficiency and utilization of FMS. The machine loading problem is formulated in order to minimize the system unbalance
and maximize the throughput, considering the job sequencing, optional machines and technological constraints. The performance
of proposed AHACO has been tested over a number of benchmark problems taken from the literature. Computational results indicate
that the proposed algorithm is more effective and produces promising results as compared to the existing solution methodologies
in the literature. The evaluation and comparison of system efficiency and system utilization justifies the supremacy of the
algorithm. Further, results obtained from the proposed algorithm have been compared with well known random search algorithm
viz. genetic algorithm, simulated annealing, artificial Immune system, simple ant colony optimization, tabu search etc. In
addition, the algorithm has been tested over a randomly generated problem set of varying complexities; the results validate
the robustness and scalability of the algorithm utilizing the concepts of ‘heuristic gap’ and ANOVA analysis. 相似文献
27.
Daewon Lee H. Jin Kim Shankar Sastry 《International Journal of Control, Automation and Systems》2009,7(3):419-428
This paper presents two types of nonlinear controllers for an autonomous quadrotor helicopter. One type, a feedback linearization
controller involves high-order derivative terms and turns out to be quite sensitive to sensor noise as well as modeling uncertainty.
The second type involves a new approach to an adaptive sliding mode controller using input augmentation in order to account
for the underactuated property of the helicopter, sensor noise, and uncertainty without using control inputs of large magnitude.
The sliding mode controller performs very well under noisy conditions, and adaptation can effectively estimate uncertainty
such as ground effects.
Recommended by Editorial Board member Hyo-Choong Bang under the direction of Editor Hyun Seok Yang. This work was supported
by the Korea Research Foundation Grant (MOEHRD) KRF-2005-204-D00002, the Korea Science and Engineering Foundation(KOSEF) grant
funded by the Korea government(MOST) R0A-2007-000-10017-0 and Engineering Research Institute at Seoul National University.
Daewon Lee received the B.S. degree in Mechanical and Aerospace Engineering from Seoul National University (SNU), Seoul, Korea, in 2005,
where he is currently working toward a Ph.D. degree in Mechanical and Aerospace Engineering. He has been a member of the UAV
research team at SNU since 2005. His research interests include applications of nonlinear control and vision-based control
of UAV.
H. Jin Kim received the B.S. degree from Korea Advanced Institute of Technology (KAIST) in 1995, and the M.S. and Ph.D. degrees in Mechanical
Engineering from University of California, Berkeley in 1999 and 2001, respectively. From 2002–2004, she was a Postdoctoral
Researcher and Lecturer in Electrical Engineering and Computer Science (EECS), University of California, Berkeley (UC Berkeley).
From 2004–2009, she was an Assistant Professor in the School of in Mechanical and Aerospace Engineering at Seoul National
University (SNU), Seoul, Korea, where she is currently an Associate Professor. Her research interests include applications
of nonlinear control theory and artificial intelligence for robotics, motion planning algorithms.
Shankar Sastry received the B.Tech. degree from the Indian Institute of Technology, Bombay, in 1977, and the M.S. degree in EECS, the M.A.
degree in mathematics, and the Ph.D. degree in EECS from UC Berkeley, in 1979, 1980, and 1981, respectively. He is currently
Dean of the College of Engineering at UC Berkeley. He was formerly the Director of the Center for Information Technology Research
in the Interest of Society (CITRIS). He served as Chair of the EECS Department from January, 2001 through June 2004. In 2000,
he served as Director of the Information Technology Office at DARPA. From 1996 to 1999, he was the Director of the Electronics
Research Laboratory at Berkeley (an organized research unit on the Berkeley campus conducting research in computer sciences
and all aspects of electrical engineering). He is the NEC Distinguished Professor of Electrical Engineering and Computer Sciences
and holds faculty appointments in the Departments of Bioengineering, EECS and Mechanical Engineering. Prior to joining the
EECS faculty in 1983 he was a Professor with the Massachusetts Institute of Technology (MIT), Cambridge. He is a member of
the National Academy of Engineering and Fellow of the IEEE. 相似文献
28.
Ravi Shankar 《International Journal of Communication Systems》2023,36(16):e5585
In this work, a deep learning (DL)-based massive multiple-input multiple-output (mMIMO) orthogonal frequency division multiplexing (OFDM) system is investigated over the tapped delay line type C (TDL-C) model with a Rayleigh fading distribution at frequencies ranging from 0.5 to 100 GHz. The proposed bi-directional long short-term memory (Bi-LSTM) channel state information (CSI) estimator uses online learning during training and offline learning during the practical implementation phase. The design of the estimator takes into account situations in which prior knowledge of channel statistics is limited and targets excellent performance, even with limited pilot symbols (PS). Three separate loss functions (mean square logarithmic error [MSLE], Huber, and Kullback–Leibler Distance [KLD]) are assessed in three classification layers. The symbol error rate (SER) and outage probability performance of the proposed estimator are evaluated using a number of optimization techniques, such as stochastic gradient descent (SGD), momentum, and the adaptive gradient (AdaGrad) algorithm. The Bi-LSTM-based CSI estimator is trained considering a specific number of PS. It can be readily seen that by incorporating a cyclic prefix (CP), the system becomes more resilient to channel impairments, resulting in a lower SER. Simulations show that the SGD optimization approach and Huber loss function-trained Bi-LSTM-based CSI estimator have the lowest SER and very high estimation accuracy. By using deep neural networks (DNNs), the Bi-LSTM method for CSI estimation achieves a superior channel capacity (in bps/Hz) at 10 dB than long short-term memory (LSTM) and other conventional CSI estimators, such as minimum mean square error (MMSE) and least squares (LS). The simulation results validate the analytical results in the study. 相似文献
29.
Ajay Kumar K. Abhishek M.R. Ghalib A. Shankar X. Cheng 《Digital Communications & Networks》2022,8(4):540-551
Internet of Things (IoT) security is the act of securing IoT devices and networks. IoT devices, including industrial machines, smart energy grids, and building automation, are extremely vulnerable. With the goal of shielding network systems from illegal access in cloud servers and IoT systems, Intrusion Detection Systems (IDSs) and Network-based Intrusion Prevention Systems (NBIPSs) are proposed in this study. An intrusion prevention system is proposed to realize NBIPS to safeguard top to bottom engineering. The proposed NBIPS inspects network activity streams to identify and counteract misuse instances. The NBIPS is usually located specifically behind a firewall, and it provides a reciprocal layer of investigation that adversely chooses unsafe substances. Network-based IPS sensors can be installed either in an inline or a passive model. An inline sensor is installed to monitor the traffic passing through it. The sensors are installed to stop attacks by blocking the traffic using an IoT signature-based protocol. 相似文献
30.
Kalita Kanak Ghadai Ranjan Kumar Chakraborty Shankar 《Engineering with Computers》2022,38(4):3549-3566
Engineering with Computers - Plate structures are the integral parts of any maritime engineering platform. With the recent focus on composite structures, the need for optimizing their design and... 相似文献