28,322 research outputs found
Fuzzy control and its application to a pH process
Full text linkIn the chemical industry, the control of pH is a well-known problem that presents
difficulties due to the large variations in its process dynamics and the static nonlinearity
between pH and concentration. pH control requires the application of advanced control
techniques such as linear or nonlinear adaptive control methods. Unfortunately, adaptive
controllers rely on a mathematical model of the process being controlled, the parameters
being determined or modified in real time. Because of its characteristics, the pH control
process is extremely difficult to model accurately.
Fuzzy logic, which is derived from Zadeh's theory of fuzzy sets and algorithms,
provides an effective means of capturing the approximate, inexact nature of the physical
world. It can be used to convert a linguistic control strategy based on expert knowledge,
into an automatic control strategy to control a system in the absence of an exact
mathematical model. The work described in this thesis sets out to investigate the
suitability of fuzzy techniques for the control of pH within a continuous flow titration
process.
Initially, a simple fuzzy development system was designed and used to produce an
experimental fuzzy control program. A detailed study was then performed on the
relationship between fuzzy decision table scaling factors and the control constants of a
digital PI controller. Equation derived from this study were then confirmed
experimentally using an analogue simulation of a first order plant. As a result of this
work a novel method of tuning a fuzzy controller by adjusting its scaling factors, was
derived. This technique was then used for the remainder of the work described in this
thesis.
The findings of the simulation studies were confirmed by an extensive series of
experiments using a pH process pilot plant. The performance of the tunable fuzzy
controller was compared with that of a conventional PI controller in response to step
change in the set-point, at a number of pH levels. The results showed not only that the
fuzzy controller could be easily adjusted to provided a wide range of operating characteristics, but also that the fuzzy controller was much better at controlling
the highly non-linear pH process, than a conventional digital PI controller. The fuzzy
controller achieved a shorter settling time, produced less over-shoot, and was less
affected by contamination than the digital PI controller.
One of the most important characteristics of the tunable fuzzy controller is its ability
to implement a wide variety of control mechanisms simply by modifying one or two
control variables. Thus the controller can be made to behave in a manner similar to that
of a conventional PI controller, or with different parameter values, can imitate other
forms of controller. One such mode of operation uses sliding mode control, with the
fuzzy decision table main diagonal being used as the variable structure system (VSS)
switching line. A theoretical explanation of this behavior, and its boundary conditions,
are given within the text.
While the work described within this thesis has concentrated on the use of fuzzy
techniques in the control of continuous flow pH plants, the flexibility of the fuzzy
control strategy described here, make it of interest in other areas. It is likely to be
particularly useful in situations where high degrees of non-linearity make more
conventional control methods ineffective
Effect of castration on hair re-growth in Pomeranians with hair cycle arrest (Alopecia X)
No full textDiabetic dogs with concurrent hyperadrenocorticism: a retrospective study of 11 cases during 1995-1999
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Overexpression of MUC15 Activates Extracellular Signal–Regulated Kinase 1/2 and Promotes the Oncogenic Potential of Human Colon Cancer Cells
No full textExtreme Food-Plant Specialisation in Megabombus Bumblebees as a Product of Long Tongues Combined with Short Nesting Seasons
No full text© 2015 Huang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. http://creativecommons.org/licenses/by/4.0/ The attached file is the published version of the article.NHM Repositor
A Maximizing-Discriminability-Based Self-Organizing Fuzzy Network for Classification Problems
No full text[[abstract]]A maximizing-discriminability-based self-organizing fuzzy network (MDSOFN) that can classify highly confusable patterns is proposed in this paper. The underlying notion of the proposed MDSOFN is to split the generation of fuzzy rules into linear discriminant analysis (LDA) and Gaussian mixture model (GMM). In LDA, the weights are updated by seeking directions that are efficient for discrimination. In GMM, parameter learning adopts the gradient-descent method to reduce the cost function. Since LDA-derived fuzzy rules increase the discriminative capability among different classes, the proposed MDSOFN can classify highly confusable patterns. The effectiveness of the proposed MDSOFN is demonstrated by two classification problems. A detailed comparative performance analysis for the fuzzy networks using LDA, principal component analysis (PCA), and the support vector machine (SVM), with various noise types, is presented. Experimental results and theoretical analysis indicate that the LDA-derived fuzzy network performs better than the PCA-based fuzzy network and the SVM-based fuzzy network.[[note]]SC
A Novel Entropy Based Image Watermarking in Wavelet Domain
No full text[[abstract]]In this paper, we proposed a novel entropy-based image watermarking method in wavelet domain. Unlike traditional entropy, we use the normalized energy instead of the probability which is called energy-based entropy (EBE). Based on EBE, the watermark can be embedded robustly and imperceptibly. In our proposed method. the wavelet-trees are grouped into super-trees. Then each super-tree is also divided into live subblocks. According to the watermark bit state. the EBE of each sub-block will be modified respectively. In an experiment. three images (Lenna, Goldhill and Peppers) are chosen for evaluating the performance. The PSNR of these watermarked images are 44.039. 43.51 and 43.67. Compared with Wang et al. [18]. it greatly increases the PSNR. by about 5.8. 4.8 and 3.9 dB respectively. For the consideration of the capacity for embedding. the maximum number of watermark, bits is also increased. The experimental results show that the proposed entropy-based watermarking method performs well in JPEG compression. filtering (Gaussian filter. median filter and sharpen) and geometrical attacks (pixel shift and rotation). In addition, it is also very robust to against the multiple watermark attack.[[note]]SC
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