Distributed Web caching allows multiple clients to quickly access a pool of popular Web pages. Conventional distributed Web caching schemes, e.g., the Internet cache protocol and hash routing, require the sending of m...
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Distributed Web caching allows multiple clients to quickly access a pool of popular Web pages. Conventional distributed Web caching schemes, e.g., the Internet cache protocol and hash routing, require the sending of many query messages among cache servers and/or impose a large load on the cache servers when they are widely dispersed. To overcome these problems, we propose a hash-based query caching method using both a hash function and a query caching method. This method can find cached objects among several cache servers by using only one query message. Compared to conventional methods, this method reduces cache server overhead, object retrieval latency and loads to the network.
In this paper we describe an admission control and load balancing scheme for multicomputer World Wide Web servers. The scheme consists of a Frontend admission control function which regulates requests sent to Backend ...
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In this paper we describe an admission control and load balancing scheme for multicomputer World Wide Web servers. The scheme consists of a Frontend admission control function which regulates requests sent to Backend web server using periodic load measurements passed from the Backends to the Frontends. The aims of scheme are two-fold: to ensure that traffic offered to Backends can be serviced promptly, and to make full use of the Backend capacity. We describe simulation results and an Erlang based implementation of the scheme. It is shown that the algorithm is trivial to implement, has negligible computational complexity, and provides effective load balancing and control. The scheme has now been implemented in the Eddie Open Source project, an Ericsson sponsored effort aimed at delivering commercial grade, quality of service driven web server solutions.
The paper demonstrates the utility of a model-based recurrent neural network (MBRNN) in fault diagnosis. The MBRNN can be formatted according to a state-space model. Therefore, it can use model-based fault detection a...
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The paper demonstrates the utility of a model-based recurrent neural network (MBRNN) in fault diagnosis. The MBRNN can be formatted according to a state-space model. Therefore, it can use model-based fault detection and isolation (FDI) solutions as a starting point, and improve them via training by adapting them to plant nonlinearities. In this paper, the application of MBRNN to the IFAC Benchmark Problem is explored and its performance is compared with `black box' neural network solutions. For this problem, the MBRNN is formulated according to the Eigen-Structure Assignment (ESA) residual generator. The results indicate that the MBRNN provides better results than `black box' neural networks, and that with training it improves the results from the ESA residual generator.
This paper describes the robust controldesign of a gas generator engine. A non-linear model of the engine has been developed within Simulink (1) from details previously presented in reference (2). State space H∞ con...
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This paper describes the robust controldesign of a gas generator engine. A non-linear model of the engine has been developed within Simulink (1) from details previously presented in reference (2). State space H∞ controldesigns are performed using a linearized model to represent the key components in the single loop control configuration. The performance criteria are specified in terms of stability margins, bandwidth and desired response of the engine to large step input. The engine is subject to constraints on its manipulated variable (i.e. the throttle valve angle) which cause integral wind up. The H∞ design is simplified to a classical Proportional-Integral (PI) controller. To take a full advantage of the design a technique so-called Utilize Saturation Feedback is used to reduce the effect of the integral windup. The results show that the PI control produces results similar to H∞ at low speeds but that H∞ gives better robustness and performance at higher speeds. Nonlinear simulations with parameter changes support the conclusion that the design is robust.
We describe an innovative hybrid controller that uses neural networks and Multivariable Predictive control (MPC) to handle abnormal events in process applications. The controller detects abnormal situations, such as g...
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We describe an innovative hybrid controller that uses neural networks and Multivariable Predictive control (MPC) to handle abnormal events in process applications. The controller detects abnormal situations, such as grinding mill spills or mill power excursions in mineral processing, or incipient flooding in separation columns and then reconfigures the multivariable controller to stabilize the operations. Neural networks are typically used to detect and classify the abnormal situation and knowledge of process dynamics and interactions is used to reconfigure the multivariable predictive controller parameters to stabilize the operations. Thus the MPC can be configured and tuned to provide good control around the `normal' operating range, and when an upset occurs and is detected a new set of tuning parameters are used.
Reactive distillation integrates reaction and separation into one apparatus and offers the possibility to overcome restrictions given by chemical and phase equilibria. The batch and semibatch modes permit a more flexi...
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Reactive distillation integrates reaction and separation into one apparatus and offers the possibility to overcome restrictions given by chemical and phase equilibria. The batch and semibatch modes permit a more flexible operation compared to the continuous case especially for multi product plants. Here the heterogeneously catalyzed esterification of methanol and acetic acid in a reactive distillation column which is operated in semibatch mode is investigated. The solution of a minimum batch time problem defines the optimal trajectory of the process. The task of feedback control is to track this trajectory in the presence of disturbances and model uncertainties. Due to the nonlinear plant behaviour, robustness properties have to be taken into consideration in the design. The nonlinearity of the system is considered as an uncertainty of the linear nominal model in the optimal operating region. A robust controller is designed using a combination of a loop shaping procedure and frequency response approximation. The linear closed-loop system is stable for the nominal model as well as for the models containing uncertainties. The controller also shows good tracking performance when used with the nonlinear model.
The design of suspension is very important for ride-comfort on automobiles. A lot of active and semi-active suspensions have been studied. In recent years, the car with active or semi-active suspension has been put in...
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The design of suspension is very important for ride-comfort on automobiles. A lot of active and semi-active suspensions have been studied. In recent years, the car with active or semi-active suspension has been put into practice. Since the active suspension needs large power and space, a semi-active suspension have recently received attention. In this study, the bilinear disturbance accommodating control theory is established and it is applied to the semi-active control of suspension for automobiles. In this study, a 1/2 body model with 4-DOF is used. By applying the proposed bilinear disturbance accommodating optimal control to the semi-active suspension, its performance is investigated in the simulation. As a result, it showed better performance than the passive control with respect to the vertical acceleration and the pitch angular acceleration of ear body which give influence on ride-comfort for automobiles.
In the head positioning control of hard disk drives, a digital control is widely used. Therefore, if a small sampling period could be used, the performance obtained by the digital controller is not so deteriorated com...
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In the head positioning control of hard disk drives, a digital control is widely used. Therefore, if a small sampling period could be used, the performance obtained by the digital controller is not so deteriorated compared with the one obtained by the analog controller. However, in hard disk systems, the sampling period cannot be chosen arbitrary. Because it is determined by the other factor which is nothing to do with control requirements in almost cases. In this paper, we apply the sampled-data H∞ control synthesis to the head positioning control of the hard disk drive. This method enable us to design a desirable digital controller directly by taking into account of intersampling behaviors. Experimental results show that good following performances can be achieved by the long sampling period.
In this paper a nonlinear controller is designed for a 6dof model of an unmanned underwater vehicle (UUV) which includes both the kinematics and the dynamics. It is shown how the use of a Lyapunov function consisting ...
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In this paper a nonlinear controller is designed for a 6dof model of an unmanned underwater vehicle (UUV) which includes both the kinematics and the dynamics. It is shown how the use of a Lyapunov function consisting of a quadratic term in the velocity (both linear and angular), a quadratic term in the position and a logarithmic term in the attitude leads to a design of a control law that achieves global asymptotic stabilization to an arbitrary set point in position/attitude. The control law is made linearly bounded by avoiding cancellation of some of the quadratic nonlinearities in the model. No information about the inertia matrix, the damping, and the Coriolis/centripetal parameters is used in the controller, endowing it with a certain amount of parametric robustness. The control law is given in terms of the Modified Rodrigues parameters. An extensive simulation study shows that the proposed control law achieves excellent tracking for slowly changing trajectories, even though it is designed only for set point regulation. The nonlinear controller dramatically outperforms a linear controller.
This paper deals with special-Purpose Devices Using Techniques of Discontinuous control and Setting Adjustment (DC&SA) in control Applications. DC&SA are result of a synthesis of two independent concepts of co...
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This paper deals with special-Purpose Devices Using Techniques of Discontinuous control and Setting Adjustment (DC&SA) in control Applications. DC&SA are result of a synthesis of two independent concepts of control: the Sliding Mode and Optimal Rating. This paper is aimed not only at stating and developing the results obtained in the sphere of discontinuous systemdesign, but also at presenting these results in close correlation with the basic concepts, problems and methods of theoretical aspects of present-day control theory. The discontinuity of control results in a discontinuity part of the differential equations describing the system motions. If such discontinuities are deliberately introduced on certain surfaces in the system state space, then motions in a sliding mode may occur in the system. To improve efficiency of practical implementation, long-period fiber Bragg Gratings, used as sensors, are regarded as electronic elements having a discontinuity-switching mode where the sliding modes are the basic motions. Implementation of this approach implies the knowledge of the conditions of the occurrence of sliding mode, for which purpose a sliding mode indicator has been developed. The state vector of the system is unknown. In this connection we designed spatial observer who uses measurements as basic data, and it will help to identificate the state vector of the system.
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