Nicholas S. Samaras

Optimized trajectory tracking control of multistage dynamic metal-cooling processes

Tracking a trajectory of multistage dynamic processes optimally is a challenging problem and spans a wide spectrum of interesting applications. Run-out table (ROT) cooling of hot strip is a supreme example of a thermal multistage process and entails special control considerations. In this paper, we formulate an optimized trajectory-tracking controller, to track the temperature throughout the multistage cooling process. It is based on optimal solutions with respect to a defined performance objective, subject to specified dynamic constraints. ROT cooling is chosen as the benchmark application for qualitative and quantitative evaluation of the proposed control structure. Optimization and optimal control play a central role in obtaining meaningful and tractable problem formulations and determining the necessary and sufficient conditions, which lead to optimal and efficient solutions.

Two-point boundary temperature control of hot strip via water cooling

Abstract This paper presents a two-point boundary temperature control system approach, for Run Out Table (ROT) cooling, used in hot strip mills. The system relies on a linearized model for describing heat radiated to the environment and heat transferred to cooling water. A basic feedforward control design to control the temperature at the second boundary point, the only measurable controlled parameter, is first presented. A modified control scheme, which minimizes the temperature error via Dynamic Programming, is then discussed in detail. System performance analysis via simulation is presented for both control schemes. Simulation results show that temperature error minimization by Dynamic Programming improves system performance.

A New Strategy for Optimal Control of Continuous Tandem Cold Metal Rolling

The control of continuous tandem cold rolling of metal strip is similar to the control of stand-alone tandem cold rolling except that additional challenges occur during the passage of the weld, which generally is done at reduced speed. The more significant issues that must be considered are the following: 1) reducing the length of strip near the weld that has excessive excursions in thickness; 2) reducing the excursions in tension and roll force as the weld goes through a stand; and 3) maintaining the mass flow balance in the mill. This paper presents the results of an investigation of the application of the state-dependent Riccati equation (SDRE) technique developed for improvement in the control of stand-alone tandem cold rolling, to continuous tandem cold rolling, particularly during passage of the weld. Two methods of control during this regime of operation are evaluated and a preferred method is selected. Using the preferred method, it was determined by simulation that the SDRE technique has the capability for successfully controlling the mill during weld passage, so that this novel approach offers a strong potential for improvement in the control of both the stand-alone and continuous tandem cold rolling processes.

A Novel Approach for Optimal Control of Continuous Tandem Cold Metal Rolling

The control of continuous tandem cold rolling of metal strip is similar to the control of stand-alone tandem cold rolling except that additional challenges occur during the passage of the weld, which generally is done at reduced speed. The more significant issues that must be considered are: (1) reducing the length of strip near the weld that has excessive excursions in thickness, (2) reducing the excursions in tension and roll force as the weld goes through a stand, and (3) maintaining the mass flow balance in the mill. This paper presents the results of an investigation of the application of the state-dependent Riccati equation (SDRE) technique developed for improvement in the control of stand-alone tandem cold rolling, to continuous tandem cold rolling, particularly during passage of the weld. Two methods of control during this regime of operation are evaluated and a preferred method is selected. Using the preferred method it was determined by simulation that the SDRE technique has the capability for successfully controlling the mill during weld passage, so that this novel approach offers a strong potential for improvement in the control of both the stand-alone and continuous tandem cold rolling processes.

An Integrated Modeling Framework for Routing of Hazardous Materials

We deal with the problem of vehicle routing optimization in the case of transportation of Hazardous Materials (HazMats). This paper introduces a collaborative approach for the HazMat Vehicle Routing Problem (HVRP) by integrating the element of transportation frequencies (as a macro variable) in order to create routing schemes that minimize the overall Cost and Risk factors. This work incorporates several risk and cost models into an innovative software framework which can simulate various decision making scenarios for dynamically formed road networks and can be used by the competent authorities. We include in the objective function under optimization the variance of road usage as an additional parameter to be minimized and we argue on its importance to accommodate traffic balancing on the networks under study. Experimental results verify that our approach outperforms well known methodologies for the case of risk optimization and equally competes for the case of cost optimization.

A simple rolling mill model with linear quadratic optimal controller

The tandem rolling of metal is a complex engineering process whose optimization represents a challenging control problem. The current technology relies on complex nonlinear models that are used to develop control strategies to address the various control problems encountered. Such models however, necessitate extensive computational requirements for simulation. Also, in various instances, access to the detailed models may be unavailable, or computational capability may be limited, yet it is desired to obtain some rough indication of performance of specific control systems when coupled to the mill. Thus the need arises for a simplified model (which can be easily implemented on a PC) for testing of control concepts. This paper fulfills such a need by providing a simple linearized model of the mill. An example of the usefulness of the model is presented by coupling to a linear quadratic optimal controller with a simple method to mitigate disturbances in incoming metal thickness. Satisfactory results are demonstrated by a simulation.

Optimized trajectory tracking control of dynamic multistage metal-cooling processes with nonlinear disturbances

This paper investigates how a control structure tracks a trajectory of multistage dynamic processes optimally in the presence of exogenous linear or nonlinear unknown system disturbances. In accordance with our previous work, run out table (ROT) temperature control for hot strip cooling (a prime model of metal-cooling multistage process) serves as the basic system. We study optimal solutions in terms of disturbance attenuation of various characteristics with minimal degradation on the performance of the system. Optimal control using dynamic programming is instrumental in obtaining meaningful and tractable problem formulations and in determining the necessary and sufficient conditions, which lead to optimal and efficient solutions in relation to the presence of the disturbance. The effectiveness of this development is presented in terms of robust system performance and verified by way of simulation.

Optimized trajectory tracking control with disturbance attenuation of dynamic multistage metal-cooling Processes

This paper investigates how a control structure tracks a trajectory of multistage dynamic processes optimally in the presence of exogenous linear or nonlinear unknown system disturbances. In accordance with previous work, run-out table temperature control for hot strip cooling (a prime model of metal-cooling multistage process) serves as the basis system. We study optimal solutions in terms of disturbance attenuation of various characteristics with minimal degradation on the performance of the system. Optimization and dynamic programming are instrumental in obtaining meaningful and tractable problem formulations and determining the necessary and sufficient conditions, which lead to optimal and efficient solutions in relation to the presence of the disturbance. The effectiveness of this development is presented in terms of robust system performance and verified by way of simulation.

On Direct Diffusion Routing for Wireless Sensor Networks

Energy efficiency is an important issue in the design of communication protocols in Wireless Sensor Network (WSN) architecture. Direct Diffusion (DD) is a routing protocol, which enables communication between sink and source nodes in random and mesh topology networks. This routing protocol is based on a data-centric approach, where intermediate nodes can aggregate data and send it to a sink node. Researchers have successfully applied DD utilizing Passive Clustering (PC), in order to improve the energy efficiency. In such approach, the network is divided into small clusters and the DD protocol is implemented at the application layer, ensuring reduced energy cost, improved delay and data delivery rate. This paper presents the results of an investigation of Direct Diffusion Routing Algorithm (DDRA) for WSNs. This routing algorithm involves DD using PC and a clustering selection scheme, considering network topology and energy level of nodes. The main objective is to create clusters that would improve energy efficiency and reduce delay. It was determined by simulation that the DDRA structure has the capability of improving delay and delivery rate in a fixed size scenario, therefore this approach can be a useful simulation tool for such environments and potentially lead to improved network performance.

A Collaborative Approach to Enviromental Modeling

Integrated Environmental Modeling Systems, (IEMS) are multidisciplinary systems which focus on complex environmental problems, decisions and policies. They are characterized by formulating dynamic and interdependent environmental, hydrological, climatological and sometimes socio-economical models under a unified framework that seeks to bridge the modeling, the monitoring and the decision making processes. The main concern of such systems is how to resolve various data and computational outcome inconsistencies emanated from the high computational burden, the lack of model interoperability and the model conceptualization characteristics. In this paper, we introduce an integrated modeling system that evaluates the hydrological, environmental ecosystem and socio-economic dynamics in lakes or wetland watersheds. Apart from the architectural design paradigm and the case study for the Lake Karla in Thessaly, Greece provided here, we also illustrate a roadmap for methodological planning, implementing, monitoring and managing such systems. Finally we provide the necessary steps of an environmentally related assessment process for such systems, however future research is needed to evaluate computational performance of this loosely coupled approach.